Dissertations / Theses: 'Phase-change materials, thermal properties'

1

Hong, Yan. "Encapsulated nanostructured phase change materials for thermal management." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4929.

Full text

Abstract:

A major challenge of developing faster and smaller microelectronic devices is that high flux of heat needs to be removed efficiently to prevent overheating of devices. The conventional way of heat removal using liquid reaches a limit due to low thermal conductivity and limited heat capacity of fluids. Adding solid nanoparticles into fluids has been proposed as a way to enhance thermal conductivity of fluids, but recent results show inconclusive anomalous enhancements in thermal conductivity. A possible way to improve heat transfer is to increase the heat capacity of liquid by adding phase change nanoparticles with large latent heat of fusion into the liquid. Such nanoparticles absorb heat during solid to liquid phase change. However, the colloidal suspension of bare phase change nanoparticles has limited use due to aggregation of molten nanoparticles, irreversible sticking on fluid channels, and dielectric property loss. This dissertation describes a new method to enhance the heat transfer property of a liquid by adding encapsulated phase change nanoparticles (nano-PCMs), which will absorb thermal energy during solid-liquid phase change and release heat during freeze. Specifically, silica encapsulated indium nanoparticles, and polymer encapsulated paraffin (wax) nanoparticles have been prepared using colloidal method, and dispersed into poly-alpha]-olefin (PAO) and water for high temperature and low temperature applications, respectively. The shell, with a higher melting point than the core, can prevent leakage or agglomeration of molten cores, and preserve the dielectric properties of the base fluids. Compared to single phase fluids, heat transfer of nanoparticle-containing fluids have been significantly enhanced due to enhanced heat capacities. The structural integrity of encapsulation allows repeated uses of nanoparticles for many cycles.; By forming porous semi crystalline silica shells obtained from water glass, supercooling has been greatly reduced due to low energy barrier of heterogeneous nucleation. Encapsulated phase change nanoparticles have also been added into exothermic reaction systems such as catalytic and polymerization reactions to effectively quench local hot spots, prevent thermal runaway, and change product distribution. Specifically, silica-encapsulated indium nanoparticles, and silica encapsulated paraffin (wax) nanoparticles have been used to absorb heat released in catalytic reaction, and to mitigate the gel effect during polymerization, respectively. The reaction rates do not raise significantly owing to thermal buffering using phase change nanoparticles at initial stage of thermal runaway. The effect of thermal buffering depends on latent heats of fusion of nanoparticles, and heat releasing kinetics of catalytic reactions and polymerizations. Micro/nanoparticles of phase change materials will open a new dimension for thermal management of exothermic reactions. ID: 029809237; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 164-191). Ph.D. Doctorate Mechanical Materials and Aerospace Engineering Engineering and Computer Science

APA, Harvard, Vancouver, ISO, and other styles

2

CAMPI, DAVIDE. "Atomistic simulations of thermal transport and vibrational properties in phase-change materials." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2016. http://hdl.handle.net/10281/101863.

Full text

Abstract:

Phase change materials are a class of compounds employed for data storage applications such as rewritable optical disks (DVD-RW, Blue-Ray disks) and more recently for non-volatile electronic memories of new generation, named phase change memories (PCM)[1]. These applications rely on a fast (50 ns) and reversible transition between a crystalline and the amorphous phases upon heating. The strong optical and electronic contrast between the crystal and the amorphous allows discriminating between the two phases that correspond to the two states of the memory, i.e. the 0 and 1 bits. In this work I have studied, by means of first principle and classical calculations, the structural, vibrational and thermal properties of some of the most promising and widely used phase-change materials such as GeTe, Ge2Sb2Te5 (GST), GeTe-Sb2Te3 superlattices and InSbTe (IST) alloys. The first part of the thesis is focused on the calculation of bulk thermal conductivity and thermal boundary resistances(TBR) between the active media and the surrounding dielectrics and metallic electrodes. Since in PCMs the phase changes corresponding to the memory writing/erasing processes are induced by Joule heating, heat dissipation and transport are key factors that greatly affect the power consumption and the switching speed of the memory cell. Moreover these quantities also influence the thermal cross-talks among the different bits in a memory array which can rise serious reliability issues, especially in ultrascaled devices. Bulk thermal has been computed on the basis density functional calculations [2] for crystalline GeTe, Sb2Te3 and GST. These calculations allowed to identify the origin of the large variability in experimental measurement for GeTe and the origin of the glass-like thermal conductivity in GST. An estimate of IST thermal conductivity was also obtained based on the minimal thermal conductivity model and ab-initio phonons. Thermal boundary resistance at different interface of crystalline GST, IST and GeTe with dielectrics and metals have been estimated from ab-initio phonons and the Diffuse Mismatch Model. The calculations revealed that an important contribution to the TBR comes from the electron-phonon coupling within GST and GeTe. For the GeTe amorphous/crystalline interface, which is also present in the device, we used an interatomic potential generated with a Neural Network (NN) method [3] and non-equilibrium molecular dynamics simulations. In the second part of the thesis we calculated the vibrational Raman spectra GeTe multilayers and of different GeTe-Sb2Te3 superlattices and intermixed compounds which are proposed to be the basis of the so called interfacial phase-change memories, a new type of device with very low power consumption[4]. The comparison between theoretical and experimental spectra allowed the identification of the growth mechanism of GeTe thin films on silicon and could allow the identification of the structures in the superlattices. In the last part we studied the nanowires of Sb2Te3 and GeTe. In particular we studied the energetic of Sb2Te3 surfaces by mean of ab initio calculations in order to explain the observation of a new Sb2Te3 crystal structure in nanowires that turned out to be stabilized by the low dimensionality. Finally we extended the bulk NN potential for GeTe previously developed in our group, enabling the possibility to study the properties of GeTe surfaces and nanowires. [1] M. Wuttig and N. Yamada, Nature Materials 6, 824 (2007). [2] L. Paulatto et al., Phys. Rev. B 87, 214303 (2013). [3] G.C. Sosso et al., Phys. Rev. B 86, 104301 (2012). [4] R.E.Simpson et al., Nature Nanotechnology 6, 501 (2011).

APA, Harvard, Vancouver, ISO, and other styles

3

Campbell, Kevin Ryan. "Phase Change Materials as a Thermal Storage Device for Passive Houses." PDXScholar, 2011. http://pdxscholar.library.pdx.edu/open_access_etds/201.

Full text

Abstract:

This study describes a simulation-based approach for informing the incorporation of Phase Change Materials (PCMs) in buildings designed to the "Passive House" standard. PCMs provide a minimally invasive method of adding thermal mass to a building, thus mitigating overheating events. Phase change transition temperature, quantity, and location of PCM were all considered while incrementally adding PCM to Passive House simulation models in multiple climate zones across the United States. Whole building energy simulations were performed using EnergyPlus from the US Department of Energy. A prototypical Passive House with a 1500 Watt electric heater and no mechanical cooling was modeled. The effectiveness of the PCM was determined by comparing the zone-hours and zone-degree-hours outside the ASHRAE defined comfort zone for all PCM cases against a control simulation without PCM. Results show that adding PCM to Passive Houses can significantly increase thermal comfort so long as the house is in a dry or marine climate. The addition of PCM in moist climates will not significantly increase occupant comfort because the majority of discomfort in these climates arises due to latent load. For dry or marine climates, PCM has the most significant impact in climates with lower cooling degree-days, reducing by 93% the number of zone-hours outside of thermal comfort and by 98% the number of zone-degree-hours uncomfortable in Portland, Oregon. However, the application of PCM is not as well suited for very hot climates because the PCM becomes overcharged. Only single digit reductions in discomfort were realized when modeling PCM in a Passive House in Phoenix, Arizona. It was found that regardless of the climate PCM should be placed in the top floor, focusing on zones with large southern glazing areas. Also, selecting PCM with a melt temperature of 25°C resulted in the most significant increases in thermal comfort for the majority of climates studied.

APA, Harvard, Vancouver, ISO, and other styles

4

Li, Chuan. "Thermal energy storage using carbonate-salt-based composite phase change materials : linking materials properties to device performance." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7242/.

Full text

Abstract:

Thermal energy storage (TES) has a crucial role to play in conserving and efficiently utilising energy, dealing with mismatch between demand and supply, and enhancing the performance and reliability of our current energy systems. This thesis concerns TES materials and devices with an aim to establish a relationship between TES device level performance to materials properties. This is a multiscale problem. The work focuses on the use of carbonate-salt-based composite phase change materials (CPCMs) for medium and high temperature applications. A CPCM consists of a carbonate salt based phase change material (PCM), a thermal conductivity enhancement material (TCEM, graphite flake in this work) and a ceramic skeleton material (CSM, MgO in this work). Both mathematical modelling and experiments were carried out to address the multiscale problem. The wettability of carbonate salt and MgO system is first studied, followed by exploring the CPCMs microstructure characteristics and formation mechanism, and then the effective thermal conductivity of the CPCMs is carried out based on the developed microstructures. At the last part, heat transfer behaviour of CPCMs based TES at component and device levels is investigated.

APA, Harvard, Vancouver, ISO, and other styles

5

Min, Kyung-Eun. "A Study of Thermal Energy Storage of Phase Change Materials: Thermophysical Properties and Numerical Simulations." PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/4835.

Full text

Abstract:

A Thermal Energy Storage (TES) system is meant for holding thermal energy in the form of hot or cold materials for later utilization. A TES system is an important technological system in providing energy savings as well as efficient and optimum energy use. The main types of a TES system are sensible heat and latent heat. A latent heat storage is a very efficient method for storing or releasing thermal energy due to its high energy storage density at constant temperatures, and a latent heat storage material can store 5-14 times more heat per unit volume than a sensible heat storage material can. Phase Change Materials (PCMs) are called latent heat storage materials. PCMs can save thermal energy, and use energy efficiently because PCMs can absorb thermal energy in the solid state, and the thermal energy can be released in the liquid state. Therefore, PCMs as new materials for saving energy can be applied into building applications. PCMs have been widely researched, but the current issues are lack of accurate and detailed information about thermophysical properties of PCMs to apply to buildings and inaccurate materials properties measured by existing methodology. The objective of this study is to develop a methodology and procedure to accurately determine the thermophysical properties of PCMs based on salt hydrates. TES systems of PCMs are measured and analyzed by various methods, such as DSC method and heat flow method. In addition, this study demonstrates to design a building roof with PCMs to save energy using Finite Element Analysis (FEA). The developed methodology is designed based on ASTM C1784-14, Standard Test Method for Using a Heat Flow Meter Apparatus for Measuring Thermal Storage Properties of Phase Change Materials and Products, for measuring the thermal energy storage properties of PCMs. The thermophysical properties and thermal stabilities are evaluated by using a Differential Scanning Calorimetry (DSC), which is made with DSC Q 200 equipment from TA Instruments and DSC STA 8000 equipment from Perkin Elmer Company. The thermal conductivities are assessed by heat flow meter, which is FOX 314 equipment from TA Instruments, and the enthalpy changes of the PCMs are determined by DSC method and heat flow method. Numerical FEA to evaluate potential energy savings is conducted using ABAQUS software. Four types of Phase Change Materials (PCMs), which have phase changes at 21ºC, 23ºC, 26ºC, and 30ºC, respectively, are used for measuring the thermophysical properties. The onset/peak temperature, the enthalpy, the heat flow, and the heat capacity of the PCMs are measured to assess the thermal energy storage system under the dynamic DSC mode. The results obtained using DSC equipment have a higher melting temperature than their own temperatures, which are known theoretically. The freezing temperatures of the PCMs are decreased by about 30ºC ~ 40ºC compare to their theoretical freezing temperatures. It is speculated that supercooling happens during the solidification. The enthalpy change curves as a function of temperature, which are determined by DSC method and heat flow method, are indicated to assess thermal energy storage system of the PCMs. During the phase change, the energy is increased. This is the reason why the energy is utilized to loosen or break apart the molecular or atomic bond structures of the PCMs by the latent heat. Moreover, the enthalpy change curves determined by heat flow method show more precise results than the curves by DSC method, because various factors lead to a temperature gradient in the PCM and the heat flux signal peak being shifted toward high temperatures. Regarding the thermal conductivities results of the PCMs, the thermal conductivities of the PCMs in the solid state are higher than those of the PCMs in the liquid state. This phenomenon happens due to the effect of the microstructure changing from the orderly solid structure in the solid state to the disorderly liquid structure in the liquid state. The numerical Finite Element Analysis (FEA) is conducted to evaluate potential energy savings of a roof. The results, such as the temperature variations from the outdoor to indoor measured under step 1 (the daytime) condition, show that the outdoor temperatures are higher than the indoor temperatures. This is due to the low thermal conductivity of the PCM in the liquid state. The low thermal conductivity of the PCM reduces the heat transmission to the indoor that in turn increases the outdoor temperature. This study shows the developed methodology and procedure, the accurate material information for the newly developed PCM, and the numerical FEA to analyze the TES systems with much more precision in the area of the PCMs.

APA, Harvard, Vancouver, ISO, and other styles

6

Zhang, Guanhua. "Fabrication, characterization and thermo-physical properties of micro- and nano- scaled phase change materials for thermal energy storage." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/57041/.

Full text

Abstract:

Latent heat storage is one of the most efficient ways of storing thermal energy. Organic phase change materials are latent heat storage materials and they have been widely used as suitable materials for thermal energy storage applications due to their high latent heat and small temperature difference between storing and releasing heat. In this thesis, micro- and nano- scaled phase change materials were fabricated for thermal energy storage. A novel microencapsulated phase change material slurry (MPCS) was introduced by dispersing microencapsulated phase change materials (MEPCMs) into water with an amount of surfactants and its thermal and rheological properties were also investigated. The results showed that MPCS fabricated in the current research are suitable for potential application as heat transfer media in the thermal energy storage. A new methodology was proposed to investigate the heat transfer characteristics of MPCSs. Experiments were carried out in laminar, transition and turbulent flow for MPCSs in a circular tube under constant heat flux, respectively. The experimental results demonstrated that in comparison to water as a heat transfer fluid at the same flow rate, the heat transfer of 10 wt. % MPCS could be enhanced by 10 % in transition flow condition while the PCM particles were in solid/liquid state, and the heat transfer of 5 wt. % MPCS could be enhanced by 21.9 % and 19.2 % in turbulent flow condition while the PCMs are in solid and solid/liquid states, respectively. Nevertheless, the heat transfer enhancement depends on the combination factors, including concentration of the slurry and flow rate of the slurry. A novel heat transfer fluid containing microencapsulated phase change material and multi-walled carbon nanotubes was prepared. The results showed that addition of MWCNTs to microencapsulated phase change material slurry can effectively improve the thermal conductivity of suspensions and it is also found that a blend of 10 wt. % MEPCM and 1 wt. % MWCNTs suspension can achieve the best thermal performance and stability among other blends in the experiment. A novel nanocapsule containing n-octadecane with an average 50 nm thick shell of poly (ethyl methacrylate) (PEMA), and with a core/shell weight ratio of 80/20 was synthesized by direct miniemulsion method. The results showed that PEMA/octadecane nanocapsule had good thermo-physical properties and had much higher encapsulation ratio (89.5%) and encapsulation efficiency (88.9%). For the first time, a novel PCM nanoparticle suspension (nano-PCS) was synthesized by direct miniemulsion method for thermal energy system application. It was found that the nano-PCSs had good thermo-physical properties and durability. All nano-PCSs presented narrow size distribution and stable particles. In comparison to the convectional PCM emulsion and MPCS, the nano-PCS tends to be more stable and is much easier and cheaper to fabricate in terms of the method and materials used, however, the heat transfer characteristics of the nano-PCS require further experimental investigation

APA, Harvard, Vancouver, ISO, and other styles

7

Pitié, Frédéric. "High temperature thermal energy storage : encapsulated phase change material particles : determination of thermal and mechanical properties." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/57108/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Barhemmati, Rajab Nastaran. "Thermal Transport Properties Enhancement of Phase Change Material by Using Boron Nitride Nanomaterials for Efficient Thermal Management." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1752408/.

Full text

Abstract:

In this research thermal properties enhancement of phase change material (PCM) using boron nitride nanomaterials such as nanoparticles and nanotubes is studied through experimental measurements, finite element method (FEM) through COMSOL 5.3 package and molecular dynamics simulations via equilibrium molecular dynamics simulation (EMD) with the Materials and Process Simulations (MAPS 4.3). This study includes two sections: thermal properties enhancement of inorganic salt hydrate (CaCl2∙6H2O) as the phase change material by mixing boron nitride nanoparticles (BNNPs), and thermal properties enhancement of organic phase change material (paraffin wax) as the phase change material via encapsulation into boron nitride nanotubes (BNNTs). The results of the proposed research will contribute to enhance the thermal transport properties of inorganic and organic phase change material applying nanotechnology for increasing energy efficiency of systems including electronic devices, vehicles in cold areas to overcome the cold start problem, thermal interface materials for efficient heat conduction and spacecraft in planetary missions for efficient thermal managements.

APA, Harvard, Vancouver, ISO, and other styles

9

Ferrer, Muñoz Gerard. "Characterization, equation formulation and enhancement of phase change materials (PCM) for thermal energy storage (TES)." Doctoral thesis, Universitat de Lleida, 2016. http://hdl.handle.net/10803/399901.

Full text

Abstract:

L’edificació, la indústria i el transport són els tres principals sectors consumidors d’energia, representant el 96 % de l’energia final consumida a la Unió Europea, i essent responsable de gairebé la totalitat de les emissions de CO2. El programa Horizon 2020 de la Comissió Europea expressa la necessitat de reduir el consum d’energia i les emissions d’efecte hivernacle en un 20 % per l’any 2020. L’emmagatzematge d’energia és un dels principals camps considerats i desenvolupats per reduir les emissions, doncs permet emparellar la demanda i el subministrament d’energia amb sistemes simples i eficients. Els sistemes d’emmagatzematge d’energia tèrmica (TES) permeten emmagatzemar densitats d’energia elevades per poder variar la demanda d’energia i facilitat l’ús d’energia renovables. Aquesta tesi està principalment enfocada en l’emmagatzematge de calor latent, una tecnologia què, tot i que ha estat àmpliament estudiada, encara necessita millores i presenta buits importants. La edificación, la industria i el transporte son los tres principales sectores consumidores de energía, representando el 96 % de la energía total consumida en la Unión Europea, y siendo responsables de casi la totalidad de las emisiones de CO2. El programa Horizon 2020 de la Comisión Europea expresa la necesidad de reducir el consuma de energía i las emisiones de efecto invernadero en un 20 % para el año 2020. El almacenaje de energía es uno de los principales campos considerados y desarrollados para reducir las emisiones, pues permite emparejar la demanda y el subministro de energía con sistemas simples y eficientes.Los sistemas de almacenaje de energía térmica (TES) permiten almacenar densidades de energía elevadas para poder variar la demanda de energía y facilitar el uso de energías renovables. Esta tesis está principalmente enfocada en el almacenaje de calor latente, una tecnología que, aunque ha sido ampliamente estudiada, aún necesita mejoras y presenta vacíos importantes. Buildings, industry and transport are the three main energy consuming sectors, representing the 96 % of the final energy consumption in the European Union, and being responsible of almost the totality of the CO2 emissions. The horizon 2020 program of the European Commission expresses the need to reduce by 20 % the energy consumption and greenhouse emissions by the year 2020Energy storage is one of the main fields considered and developed to reduce emissions, allowing to match energy demand and supply with simple and efficient systems.Thermal energy storage (TES) systems allow the storage of high energy densities in order to shift the energy demand and ease the use of renewable energies. This thesis is mainly focused in latent energy storage, a technology that despite having been widely studied, still requires improvements and presents important gaps.

APA, Harvard, Vancouver, ISO, and other styles

10

Siegert, Karl Simon [Verfasser], Matthias [Akademischer Betreuer] Wuttig, and Raphaël P. [Akademischer Betreuer] Hermann. "Thermal Properties of Phase-Change Materials From Lattice Dynamics to Thermoelectricity / Karl Simon Siegert ; Matthias Wuttig, Raphaël P. Hermann." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1129365255/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Liang, Xin. "Structure and Thermoelectric Properties of ZnO Based Materials." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11191.

Full text

Abstract:

The present dissertation investigates the relationship between the structure and thermoelectric properties of ZnO based materials, with a focus on trivalent element doping on engineering the microstructure and altering the electrical and thermal transport properties. Within the solubility range, the addition of trivalent elements, such as In3+, Fe3+ and Ga3+, is observed to increase the electrical conductivity of ZnO and decrease the thermal conductivity. Engineering and Applied Sciences

APA, Harvard, Vancouver, ISO, and other styles

12

Bohnenstiehl, Scot D. "Thermal Analysis, Phase Equilibria, and Superconducting Properties in MgB2 and Carbon Doped MgB2." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330017829.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Boatright, David L. "Kinetic and mechanistic studies of the thermal decomposition of glycolate and N-Nitrosoiminodiacetic acid in aqueous basic salt solutions : II Phase transfer catalysis in supercritical fluids." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/29885.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Xu, Wenyue. "Towards numerical modeling of two-phase flow in seafloor hydrothermal systems." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/26014.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Однодворець, Лариса Валентинівна, Лариса Валентиновна Однодворец, Larysa Valentynivna Odnodvorets, et al. "Electrophysical, Magnetoresistivity and Magneto-optical Properties of Multilayer Materials Based on Nanocrystalline and Amorphous Films." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35009.

Full text

Abstract:

In work is presented to the results of complex investigate of phase formation, thermal resistivite, magnetoresistive and magneto-optical properties of multilayers based Fe and Pd, Ag or Ge, which obtained by sequential condensation of the layers with following thermal annealing. Investigation of phase formation processes of thin film systems and established of correlation between this processes and above-mention physical properties. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35009

APA, Harvard, Vancouver, ISO, and other styles

16

Lloyd, Hayleigh Jayne. "Co-crystallisation of energetic materials : a step-change in the control of properties and performance of munitions." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28860.

Full text

Abstract:

The research described in this thesis seeks to explore a concept that has the potential to make a step-change for the control of the properties of energetic materials (sensitivity, long-term storage, processability, performance, etc.), resulting in safer munitions with enhanced performance. This concept is co-crystallisation and involves crystallisation of the energetic material with one or more molecular components in order to modify the properties of the composition. The concept has been demonstrated in the pharmaceutical sector as a successful means of altering the physical properties of active pharmaceutical ingredients, e.g. solubility, bioavailability, stability to humidity. This project therefore aims to exploit the concepts of crystal engineering and co-crystallisation as applied to selected energetic materials in order to achieve the following objectives: (i) develop an enhanced understanding of how structure influences key properties such as sensitivity, (ii) control the sensitivity of existing, approved energetic materials, and (iii) identify new energetic materials with enhanced properties, e.g. reduced sensitivity, higher performance, and increased thermal stability. The compound 3,5-nitrotriazolone (NTO) was crystallised with a selection of co-formers to produce salts and co-crystals. The structure properties of these materials were explored using single-crystal and powder X-ray diffraction, and structural features were correlated with properties such as crystal density, difference in pKa of co-formers, thermal properties, and sensitivity to impact. Detonation velocities of the co-crystals were calculated based on densities, chemical composition, and heats of formation. Co-former molecules included a series of substituted anilines, substituted pyridines (including 4,4’-bipyridine, 2-pyridone), and substituted triazoles. A co-crystal was formed between NTO and 4,4’-bipyridine on crystallisation from ethanol, whilst a salt was formed when crystallised from water. Upon heating the salt to 50ºC, the co-crystal was formed. Structural differences between the salts formed by NTO with 3,5-DAT and 3,4- DAT were correlated with structural features. 3,5-DAT.NTO is substantially less impact sensitive than 3,4-DAT.NTO, and this is attributed to the layered structure of 3,5-DAT.NTO. An investigation into triazole-based NTO salts under high pressure was conducted. A new polymorph of 3,5-DAT.NTO was discovered upon increasing the pressure to 2.89 GPa. The high-pressure phase appears to retain the layered structure and remains in this phase up to 5.33 GPa, although it was not recoverable upon decompression to atmospheric pressure. The compression behaviour of the unit cell volume for phase I of 3,5-DAT.NTO has been fitted to a 3rd-order Birch- Murnaghan equation of state (EoS) with V0 = 957.7 Å3, B0 = 8.2 GPa and B’0 = 14.7. The unit cell was found to be most compressible in the a and c directions. Under high pressure 3,4-DAT.NTO does not give any indication of a phase change occurring up to 6.08 GPa. The coefficients of the 3rd-order Birch-Murnaghan EoS have been determined to be V0 = 915.9 Å3, B0 = 12.6 GPa and B’0 = 6.5.

APA, Harvard, Vancouver, ISO, and other styles

17

Mathevon, Alexandre. "Characterization and modelling of microstructural evolutions and mechanical properties during the thermal treatments of Dual-Phase steels." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI120.

Full text

Abstract:

L'objectif de cette thèse était de contribuer au développement et à la compréhension des phénomènes physiques pilotant les évolutions microstructurales et les propriétés mécaniques des aciers Dual-Phase. Dans un souci d'utilisation sur les lignes de production industrielle, le développement d'outils numériques à champ moyen a été retenu, utilisables pour une large gamme de compositions chimiques et de cycle thermique. Une calibration des modèles sur des aciers ternaires provenant de coulées de laboratoire a été effectuée avant leur validation sur deux nuances industrielles. Un modèle de prédiction de la cinétique de recristallisation (MiReX) a été développé à partir de la composition chimique, du taux de réduction par laminage à froid et de leur état de précipitation prévu en utilisant un couplage avec un logiciel de prédiction de la cinétique de précipitation (Preciso). Un modèle pour la transformation de phase entre la ferrite et l'austénite, basé sur la minimisation de l'énergie du système global (GEM), a été proposé pour les traitements isothermes et anisothermes. Il reproduit la cinétique de la formation de l'austénite sur un cycle thermique industriel comprenant une rampe de chauffage et un maintien pour les systèmes quaternaires en tenant compte de la dissolution de la cémentite. Un modèle permettant de prédire la température du début de la transformation martensitique a également été développé pour les aciers bi-phasés, en tenant compte de la taille des grains austénitiques et de l'enrichissement en carbone et en manganèse à l'interface. Enfin, une nouvelle loi d'interaction basée sur les observations lors d'un essai de traction ex-situ a permis d'améliorer une prédiction modèle des propriétés mécaniques des aciers DP. La considération de l'étape de revenu de la martensite sur les propriétés des aciers DP a été proposée après l'analyse des mécanismes métallurgiques impliqués dans le revenu par des mesures de pouvoir thermoélectrique et de dureté The aim of this thesis was to contribute to the development and understanding of the physical phenomena driving the microstructural evolutions and the mechanical properties of Dual-Phase steels. In a concern of use on industrial production lines, the development of physics-based mean-field numerical tools was retained, usable for a wide range of chemical composition and thermal cycle parameters. A calibration of the models on ternary steels from laboratory castings was carried out before their validation on two industrial grades. A model for predicting recrystallization kinetics (MiReX) was developed based on the chemical composition, the reduction ratio by cold rolling and their predicted precipitation state using a coupling with a software for predicting precipitation kinetics (Preciso). A model for the phase transformation between ferrite and austenite, based on the minimization of the global system energy (GEM), has been proposed for isothermal and anisothermal treatments. It reproduces the kinetics of austenite formation on an industrial thermal cycle including a heating ramp and holding for quaternary systems taking into account the dissolution of the cementite. A model for predicting the temperature of the beginning of martensitic transformation has also been developed for two-phase steels, taking into account austenitic grain size and carbon and manganese enrichment at the interface. Finally, a new interaction law based on observations during an ex-situ tensile test has allowed the improvement of a prediction model of the mechanical properties of DP steels. A consideration of the tempering step of martensite on the mechanical properties of DP steels has been proposed after the analysis of metallurgical mechanisms involved in tempering bythermoelectric power and hardness measurements

APA, Harvard, Vancouver, ISO, and other styles

18

Šebek, Jan. "Studium pasivní stabilizace teploty kompozitních stavebních materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-216639.

Full text

Abstract:

The topic of presented master’s thesis was study of passive stabilization of building materials temperature. The main goal of this thesis was measuring and characterization of the thermal properties of building materials, which are used to PCM technology. PCM technology is based on utilization of latent heat of phase change. At the beginning of this thesis it was needed to define physical principle of phase change, then the most usable PCM chemicals (e.g. paraffin, Glauber’s salt, hexahydrate calcium chloride) and their basic physical properties (especially thermo-physical), background research of building materials with PCM and also the methods of thermo-physical properties measurement. It was also needed to characterize measured building materials and define theirs thermal parameters; because the values of thermal parameters of measured samples were compared to these values. In the experimental part of my thesis are measurements of material thermal analysis, which are methods, where the properties of materials are studied as they change with temperature. I had used to differential scanning calorimetry, transient pulse method and other methods, which are usable for thermo-physical properties measuring and characterization. I have been much interested in properties of measured material, which were specific heat capacity, temperature diffusivity, heat conductivity and phase change temperature (the melting point of PCM). At the end of my thesis the findings of all methods were finally summarized, compared and commented.

APA, Harvard, Vancouver, ISO, and other styles

19

SILVA, MAVIAEL J. da. "Desenvolvimento de selantes vitrocerâmicos para uso em SOFC pertencentes ao sistema BAS (BaO-Alsub(2)0sub(3)-SiOsub(2)) modificados com Bsub(2)Osub(3)." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23655.

Full text

Abstract:

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-04-10T16:38:07Z No. of bitstreams: 0 Made available in DSpace on 2015-04-10T16:38:07Z (GMT). No. of bitstreams: 0 Tese (Doutorado em Tecnologia Nuclear) IPEN/T Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

APA, Harvard, Vancouver, ISO, and other styles

20

Bellander, Rickard. "Testing large samples of PCM in water calorimeter and PCM used in room applications by night-air cooling." Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-495.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Sathyanarayana, Aravind. "Pool and flow boiling of novel heat transfer fluids from nanostructured surfaces." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50299.

Full text

Abstract:

Steadily increasing heat dissipation in electronic devices has generated renewed interest in direct immersion cooling. The ideal heat transfer fluid for direct immersion cooling applications should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by poor thermal properties. These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. Computer Aided Molecular Design (CAMD) approach was used in this work to systematically design novel heat transfer fluids that exhibit significantly better properties than those of current high performance electronic coolants. The candidate fluids generated by CAMD were constrained by limiting their boiling points, latent heat of vaporization and thermal conductivity. The selected candidates were further screened using a figure of merit (FOM) analysis. Some of the fluids/additives that have been identified after the FOM analysis include C₄H₅F₃O, C₄H₄F₆O, C₆H₁₁F₃, C₄ H₁₂O₂Si, methanol, and ethoxybutane. The heat transfer performance of these new fluids/fluid mixtures was analyzed through pool boiling and flow boiling experiments. All the fluid mixtures tested showed an improvement in the critical heat flux (CHF) when compared to the base fluid (HFE 7200). A pool boiling model was developed using the phase field method available in COMSOL. Although these simulations are computationally expensive, they provide an alternate solution to evaluate several candidate fluids generated using the CAMD approach.

APA, Harvard, Vancouver, ISO, and other styles

22

Kulkarni, Ambarish J. "Atomistic Characterization and Continuum Modeling of Novel Thermomechanical Behaviors of Zinc Oxide Nanostructures." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19761.

Full text

Abstract:

ZnO nanowires and nanorods are a new class of one-dimensional nanomaterials with a wide range of applications in NEMS. The motivation for this work stems from the lack of understanding and characterization of their thermomechanical behaviors essential for their incorporation in nanosystems. The overall goal of this work is to develop a fundamental understanding of the mechanisms controlling the responses of these nanostructures with focus on: (1) development of a molecular dynamics based framework for analyzing thermomechanical behaviors, (2) characterization of the thermal and mechanical behaviors in ZnO nanowires and (3) development of models for pseudoelasticity and thermal conductivity. The thermal response analyses show that the values of thermal conductivity are one order of magnitude lower than that for bulk ZnO due to surface scattering of phonons. A modified equation for phonon radiative transport incorporating the effects of surface scattering is used to model the thermal conductivity as a function of wire size and temperature. Quasistatic tensile loading of wires show that the elastic moduli values are 68.2-27.8% higher than that for bulk ZnO. Previously unknown phase transformations from the initial wurtzite (WZ) structure to graphitic (HX) and body-centered-tetragonal (BCT-4) phases are discovered in nanowires which lead to a more complete understanding of the extent of polymorphism in ZnO and its dependence on load triaxiality. The reversibility of the WZ-to-HX transform gives rise to a novel pseudoelastic behavior with recoverable strains up to 16%. A micromechanical continuum model is developed to capture the major characteristics of the pseudoelastic behavior accounting for size and temperature effects. The effect of the phase transformations on the thermal properties is characterized. Results obtained show that the WZ→HX phase transformation causes a novel transition in thermal response with the conductivity of HX wires being 20.5-28.5% higher than that of the initial WZ-structured wires. The results obtained here can provide guidance and criteria for the design and fabrication of a range of new building blocks for nanometer-scale devices that rely on thermomechanical responses.

APA, Harvard, Vancouver, ISO, and other styles

23

Bugaje, Idris M. "Thermal energy storage in phase change materials." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335920.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Oliver, David Elliot. "Phase-change materials for thermal energy storage." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/17910.

Full text

Abstract:

There is a current requirement for technologies that store heat for both domestic and industrial applications. Phase-change materials (PCMs) represent an important class of materials that offer potential for heat storage. Heat-storage systems are required to undergo multiple melt/freeze cycles without any change in melting-crystallisation point and heat output. Salt hydrates are attractive candidates on account of their high energy densities, but there are issues associated with potential crystallisation of lower-hydrates, long-term stability, and reliable nucleation. An extensive review of the PCMs in the literature, combined with an evaluation of commercially available PCMs led to the conclusion that many of the reported PCMs, lack at least one of the key requirements required for use as a heat-storage medium. The focus of this research was therefore to identify and characterise new PCM compositions with tailored properties. New PCM compositions based of sodium acetate trihydrate were developed, which showed improved properties through the use of selective polymers that retard the nucleation of undesirable anhydrous sodium acetate. Furthermore, the mechanism of nucleation of sodium acetate trihydrate by heterogeneous additives has been investigated using variable-temperature powder X-ray diffraction. This study showed that when anhydrous Na2HPO4 was introduced to molten sodium acetate trihydrate at 58°C the hydrogenphosphate salt is present as the dihydrate. On heating to temperatures in the range 75-90°C the dihydrate was observed to dehydrate to form anhydrous Na₂HPO4. This result explains the prior observation that the nucleator is deactivated on heating. The depression of melting point of sodium acetate trihydrate caused by the addition of lithium acetate dihydrate has also been investigated using differential scanning calorimetry and powder X-ray diffraction. It has been possible to tune the melting point of sodium acetate trihydrate thereby modifying its thermal properties. Studies of the nucleation of sodium thiosulfate pentahydrate, a potential PCM, led to the structural characterisation of six new hydrates using single crystal Xray diffraction. All of these hydrates can exist in samples with the pentahydrate composition at temperatures ranging from 20°C to 45°C. These hydrates are: α-Na₂S₂O₃·2H₂O, which formed during the melting of α-Na₂S₂O₃·5H₂O; two new pentahydrates, β-Na₂S₂O₃·5H₂O and γ-Na₂S₂O₃·5H₂O; Na₂S₂O₃·1.33 H₂O, β-Na₂S₂O₃·2H₂O and Na₂S₂O₃·3.67 H₂O, which formed during the melting of β- Na₂S₂O₃·5H₂O. Furthermore, new PCMs in the 75-90°C range were identified. The commercial impact and route to market of several of the PCMs are discussed in the final chapter.

APA, Harvard, Vancouver, ISO, and other styles

25

Kasali, Suraju Olawale. "Thermal diodes based on phase-change materials." Thesis, Poitiers, 2021. http://www.theses.fr/2021POIT2254.

Full text

Abstract:

Nous étudions dans cette thèse la rectification thermique de diodes thermiques radiatives ou conductive constituées de matériaux à changement de phase.Cette thèse est divisée en trois parties. Dans les premières parties, nous modélisons comparativement les performances d’une diode thermique conductive sphérique et cylindrique constitués de VO2 présentant un transition de phase et des matériaux n’en présentant pas. Des expressions analytiques aux bornes des diodes sont dérivées. Des flux thermiques, des facteurs de rectifications ainsi que les profils de température à l’intérieur de la diode sont obtenus. Nos résul-tats montrent que les différentes géométries de diodes ont un impact significatif sur les profils de température et les flux thermiques, mais moins un sur les facteurs de rectification. Dans ce travail, nous avons obtenu des facteurs de rectification maximaux allant jusqu’à 20.8% et 20.7%, qui sont supérieurs à celui prédit pour une diode plane constituée de VO2. Nous montrons également que des facteurs de rectification similaires à ceux obtenus avec le VO2 dans les géométries sphériques et cylindriques peuvent être atteints avec des matériaux à changement de phase dont le contraste de conductivité est plus important que dans le cas du VO2. Dans la deuxième partie, nous étudions la rectification de diodes thermiques constituées de deux matériaux à changement de phase. Avec, l’idée de générer un facteur de redressement plus élevé que dans le cas d’une diode thermique conductive ne comprenant qu’un matériau à changement de phase unique. Là encore, le travail a conduit à l’établissement d’expressions explicites pour les profils de température, les flux thermiques et le facteur de rectification. Nous avons obtenu un facteur de rectification optimal de 60% avec une variation de température de 250 K couvrant les transitions métal-isolant des deux matériaux. Dans la troisième partie de notre travail, nous avons modélisé et optimisé la rectification thermique de diodes thermiques planes, cylindriques et sphériques radiatives à base de deux matériaux à changement de phase. Nous savons calculer et analyser les facteurs de rectification de ces trois diodes et obtenu les facteurs de rectification optimaux respectifs pour les trois géométries 82%, 86% et 90.5%. Nos résultats montrent que la géométrie sphérique est la meilleure pour optimiser la rectification des courants thermiques radiatifs. De plus, des facteurs de rectification potentiellement supérieurs à ceux prédits ici peuvent être réalisés en utilisant deux matériaux à changement de phase avec des contrastes d’émissivités plus élevés que ceux proposés ici. Ces résultats analytiques et graphiques fournissent un guide utile pour optimiser les facteurs de rectification des diodes thermiques conductives et radiatifs basées sur des matériaux à changement de phase de géométries différentes The thermal rectification of conductive and radiative thermal diodes based on phase-change materials, whose thermal conductivities and effective emissivities significant change within a narrow range of temperatures, is theoretically studied and optimized in different geometries. This thesis is divided into three parts. In the first part, we comparatively model the performance of a spherical and cylindrical conductive thermal diodes operating with vanadium dioxide (VO2) and non-phase-change materials, and derive analytical expressions for the heat flows, temperature profiles and optimal rectification factors for both diodes. Our results show that different diode geometries have a significant impact on the temperature profiles and heat flows, but less one on the rectification factors. We obtain maximum rectification factors of up to 20.8% and 20.7%, which are higher than the one predicted for a plane diode based on VO2. In addition, it is shown that higher rectification factors could be generated by using materials whose thermal conductivity contrast is higher than that of VO2. In the second part, on the other hand, we theoretically study the thermal rectification of a conductive thermal diode based on the combined effect of two phase-change materials. Herein, the idea is to generate rectification factors higher than that of a conductive thermal diode operating with a single phase-change material. This is achieved by deriving explicit expressions for the temperature profiles, heat fluxes and rectification factor. We obtain an optimal rectification factor of 60% with a temperature variation of 250 K spanning the metal-insulator transitions of VO2 and polyethylene. This enhancement of the rectification factor leads us to the third part of our work, where we model and optimize the thermal rectification of a plane, cylindrical and spherical radiative thermal diodes based on the utilization of two phase-change materials. We analyze the rectification factors of these three diodes and obtain the following optimal rectification factors of 82%, 86% and 90.5%, respectively. The spherical geometry is thus the best shape to optimize the rectification of radiative heat currents. In addition, potential rectification factors greater than the one predicted here can be realized by utilizing two phase-change materials with higher emissivities contrasts than the one proposed here. Our analytical and graphical results provide a useful guide for optimizing the rectification factors of conductive and radiative thermal diodes based on phase-change materials with different geometries

APA, Harvard, Vancouver, ISO, and other styles

26

Bahrar, Myriam. "Contribution au développement et à l’analyse d’une enveloppe de bâtiment multifonctionnelle dans le cadre de l’optimisation du confort dans l’habitat." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEE001/document.

Full text

Abstract:

Le secteur du bâtiment recèle un fort potentiel d’amélioration de l'efficacité énergétique et de réduction de l’empreinte écologique. Dans cette optique, l’enveloppe du bâtiment joue un rôle important pour relever le défi de la transition énergétique. En effet, une bonne conception de l’enveloppe contribue efficacement à réduire la consommation d’énergie tout en réduisant les émissions de CO2 associés. Cela s’accompagne notamment d’une démarche de développement de nouveaux matériaux et principes constructifs. Ce projet de thèse s’inscrit dans ce cadre en proposant un nouveau matériau composite, qui porte sur l’association de deux matériaux innovant : composite textile mortier (TRC) et matériaux à changement de phase (MCPs). L’objectif de cette combinaison est de contribuer au développement d’éléments de façades multifonctionnelles permettant d’allier performances énergétiques, mécaniques et environnementales. Le but de notre étude est de caractériser en premier lieu, les propriétés mécaniques et thermiques de ces composites puis, d’évaluer l’impact des MCPs sur le confort thermique intérieur pour différentes configurations. Pour atteindre ces objectifs, nous avons adopté une démarche expérimentale et numérique multi échelle. Une campagne expérimentale à l’échelle du laboratoire et in-situ a été menée. En parallèle, nous avons développé un modèle numérique de paroi multicouche, couplé à un modèle de bâtiment. Enfin, nous avons exploité ce couplage pour réaliser une optimisation multicritère à base d’algorithmes génétiques The building sector has a great potential to improve energy efficiency and reduce the greenhouse gas emissions. Improvements to the building envelope and Innovations in building materials have the potential to achieve sustainability within the built environment. This PhD thesis focuses on the development of multifunctional façade elements in order to optimize the building energy consumption while maintaining an optimal indoor human thermal comfort. The proposed solution consist of using passive storage by means of phase change materials associated with alternative construction materials such as textile reinforced concrete (TRC). The aim of the study is to characterize mechanical and thermal properties of TRC composites and to evaluate the effect of PCMs on indoor thermal comfort. To meet these objectives, experimental devices have been set up for the characterization (at the component scale and in situ) of the mechanical and thermal behaviour of different TRC panels. In parallel, we have developed a numerical model for the prediction of wall temperature profiles. Finally, a multi-objective optimization of the façade elements is carried out using genetic algorithms to determine the better combinations able to combine the energy performance with the mechanical performance

APA, Harvard, Vancouver, ISO, and other styles

27

Wang, Yu. "Mechanical properties and microstructure of laser sintered and starch consolidated iron-based powders." Doctoral thesis, Karlstad : Faculty of Technology and Science, Materials Engineering, Karlstads universitet, 2008. http://www.diva-portal.org/kau/abstract.xsql?dbid=1593.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Kotze, Johannes Paulus. "Thermal energy storage in metallic phase change materials." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96049.

Full text

Abstract:

Thesis (PhD) -- Stellenbosch University, 2014. ENGLISH ABSTRACT: Currently the reduction of the levelised cost of electricity (LCOE) is the main goal of concentrating solar power (CSP) research. Central to a cost reduction strategy proposed by the American Department of Energy is the use of advanced power cycles like supercritical steam Rankine cycles to increase the efficiency of the CSP plant. A supercritical steam cycle requires source temperatures in excess of 620°C, which is above the maximum storage temperature of the current two-tank molten nitrate salt storage, which stores thermal energy at 565°C. Metallic phase change materials (PCM) can store thermal energy at higher temperatures, and do not have the drawbacks of salt based PCMs. A thermal energy storage (TES) concept is developed that uses both metallic PCMs and liquid metal heat transfer fluids (HTF). The concept was proposed in two iterations, one where steam is generated directly from the PCM – direct steam generation (DSG), and another where a separate liquid metal/water heat exchanger is used – indirect steam generation, (ISG). Eutectic aluminium-silicon alloy (AlSi12) was selected as the ideal metallic PCM for research, and eutectic sodium-potassium alloy (NaK) as the most suitable heat transfer fluid. Thermal energy storage in PCMs results in moving boundary heat transfer problems, which has design implications. The heat transfer analysis of the heat transfer surfaces is significantly simplified if quasi-steady state heat transfer analysis can be assumed, and this is true if the Stefan condition is met. To validate the simplifying assumptions and to prove the concept, a prototype heat storage unit was built. During testing, it was shown that the simplifying assumptions are valid, and that the prototype worked, validating the concept. Unfortunately unexpected corrosion issues limited the experimental work, but highlighted an important aspect of metallic PCM TES. Liquid aluminium based alloys are highly corrosive to most materials and this is a topic for future investigation. To demonstrate the practicality of the concept and to come to terms with the control strategy of both proposed concepts, a storage unit was designed for a 100 MW power plant with 15 hours of thermal storage. Only AlSi12 was used in the design, limiting the power cycle to a subcritical power block. This demonstrated some practicalities about the concept and shed some light on control issues regarding the DSG concept. A techno-economic evaluation of metallic PCM storage concluded that metallic PCMs can be used in conjunction with liquid metal heat transfer fluids to achieve high temperature storage and it should be economically viable if the corrosion issues of aluminium alloys can be resolved. The use of advanced power cycles, metallic PCM storage and liquid metal heat transfer is only merited if significant reduction in LCOE in the whole plant is achieved and only forms part of the solution. Cascading of multiple PCMs across a range of temperatures is required to minimize entropy generation. Two-tank molten salt storage can also be used in conjunction with cascaded metallic PCM storage to minimize cost, but this also needs further investigation. AFRIKAANSE OPSOMMING: Tans is die minimering van die gemiddelde leeftydkoste van elektrisiteit (GLVE) die hoofdoel van gekonsentreerde son-energie navorsing. In die kosteverminderingsplan wat voorgestel is deur die Amerikaanse Departement van Energie, word die gebruik van gevorderde kragsiklusse aanbeveel. 'n Superkritiese stoom-siklus vereis bron temperature hoër as 620 °C, wat bo die 565 °C maksimum stoor temperatuur van die huidige twee-tenk gesmelte nitraatsout termiese energiestoor (TES) is. Metaal fase veranderingsmateriale (FVMe) kan termiese energie stoor by hoër temperature, en het nie die nadele van soutgebaseerde FVMe nie. ŉ TES konsep word ontwikkel wat gebruik maak van metaal FVM en vloeibare metaal warmteoordrag vloeistof. Die konsep is voorgestel in twee iterasies; een waar stoom direk gegenereer word uit die FVM (direkte stoomopwekking (DSO)), en 'n ander waar 'n afsonderlike vloeibare metaal/water warmteruiler gebruik word (indirekte stoomopwekking (ISO)). Eutektiese aluminium-silikon allooi (AlSi12) is gekies as die mees geskikte metaal FVM vir navorsingsdoeleindes, en eutektiese natrium – kalium allooi (NaK) as die mees geskikte warmteoordrag vloeistof. Termiese energie stoor in FVMe lei tot bewegende grens warmteoordrag berekeninge, wat ontwerps-implikasies het. Die warmteoordrag ontleding van die warmteruilers word aansienlik vereenvoudig indien kwasi-bestendige toestand warmteoordrag ontledings gebruik kan word en dit is geldig indien daar aan die Stefan toestand voldoen word. Om vereenvoudigende aannames te bevestig en om die konsep te bewys is 'n prototipe warmte stoor eenheid gebou. Gedurende toetse is daar bewys dat die vereenvoudigende aannames geldig is, dat die prototipe werk en dien as ŉ bevestiging van die konsep. Ongelukkig het onverwagte korrosie die eksperimentele werk kortgeknip, maar dit het klem op 'n belangrike aspek van metaal FVM TES geplaas. Vloeibare aluminium allooie is hoogs korrosief en dit is 'n onderwerp vir toekomstige navorsing. Om die praktiese uitvoerbaarheid van die konsep te demonstreer en om die beheerstrategie van beide voorgestelde konsepte te bevestig is 'n stoor-eenheid ontwerp vir 'n 100 MW kragstasie met 15 uur van 'n TES. Slegs AlSi12 is gebruik in die ontwerp, wat die kragsiklus beperk het tot 'n subkritiese stoomsiklus. Dit het praktiese aspekte van die konsep onderteken, en beheerkwessies rakende die DSO konsep in die kollig geplaas. In 'n tegno-ekonomiese analise van metaal FVM TES word die gevolgtrekking gemaak dat metaal FVMe gebruik kan word in samewerking met 'n vloeibare metaal warmteoordrag vloeistof om hoë temperatuur stoor moontlik te maak en dat dit ekonomies lewensvatbaar is indien die korrosie kwessies van aluminium allooi opgelos kan word. Die gebruik van gevorderde kragsiklusse, metaal FVM stoor en vloeibare metaal warmteoordrag word net geregverdig indien beduidende vermindering in GLVE van die hele kragsentrale bereik is, en dit vorm slegs 'n deel van die oplossing. ŉ Kaskade van verskeie FVMe oor 'n reeks van temperature word vereis om entropie generasie te minimeer. Twee-tenk gesmelte soutstoor kan ook gebruik word in samewerking met kaskade metaal FVM stoor om koste te verminder, maar dit moet ook verder ondersoek word.

APA, Harvard, Vancouver, ISO, and other styles

29

Guzzo, Talita Zanon. "Aplicação da espectroscopia fotoacústica na determinação da temperatura de transição vítrea de polímeros." Universidade do Estado do Rio de Janeiro, 2010. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=1377.

Full text

Abstract:

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro A espectroscopia fotoacústica (PAS) é uma técnica não destrutiva e muito utilizada na caracterização óptica e térmica de materiais. Ela é baseada no efeito fotoacústico que consiste, basicamente, na absorção de onda eletromagnética modulada e na geração de calor no interior do material em estudo (amostra), via processo de desexcitação não-radiativa. Dentre as muitas aplicações relacionadas à caracterização de materiais, recentemente, a técnica PAS vem sendo desenvolvida para estudos de transição de fase de segunda ordem. Entretanto, poucos trabalhos são encontrados na literatura com relação à aplicação da técnica PAS ao estudo da transição vítrea. Neste contexto, o objetivo deste trabalho é o de aplicar a técnica PAS na determinação da temperatura de transição vítrea de materiais poliméricos, de uma maneira inovadora com relação à célula fotoacústica e ao sistema de aquecimento. Para isso foi projetada e construída uma célula fotoacústica que possibilita a variação de temperatura da amostra, sem afetar a curva de resposta do microfone. Foi desenvolvido um sistema de aquecimento baseado no efeito Peltier, possibilitando fazer rampas de subida de temperatura, com várias velocidades, da temperatura ambiente até 130 C, de forma linear. Todo o aparato experimental foi testado e aplicado em várias amostras poliméricas: poliamida 6.0 (Nylon); poliestireno (PS-n1921 e PS-n2380); e poli(tereftalato de etileno) (PET). Os resultados obtidos foram: para o Nylon, ; para o PS-n1921, ; para o PS-n2380, ; e para o PET, . Estes resultados estão de acordo com os respectivos valores da temperatura de transição vítrea encontrados na literatura e mostram a potencialidade da técnica PAS ao estudo da transição vítrea de materiais poliméricos. Photoacoustic spectroscopy (PAS) is a non-destructive technique and it has been largely applied to the thermal and optical characterization of materials. PAS technique is based on the photoacoustic effect which consist, basically, absorption of a modulated electromagnetic radiation and generation of heat inside of the material studied (sample), by a nonradiative deexcitation processes. Nowadays, among many PAS applications, effort are carried out to apply PAS technique for second-order phase transitions. However, only a few works can be found in the literature about glass transition studies with PAS technique. In this context, the main goal of this work is to apply PAS technique to determine glass transition temperature of the polymeric materials, based on the new photoacoustic cell configuration and on the new heating system. In this way, a photoacoustic cell was builted up for monitoring temperature variation of the sample, where the performance of the microphone was not affected. A heating system was developed based on the Peltier effect, in such way that it is possible to scan the temperature from the environment one up to 130 C, linearly at several speeds. The experimental apparatus was tested and applied to some polymeric materials: polyamide 6.0 (Nylon); polystyrene (PS-n1921 e PS-n2380); and poli(tereftalato de etileno) (PET). The results obtained were: Nylon, ; PS-n1921, ; PS-n2380, ; and PET, . These results are in a good agreement with the respective values of glass transition temperature found in the literature and show the PAS technique potentiality for glass transition studies in polymeric materials.

APA, Harvard, Vancouver, ISO, and other styles

30

Pendyala, Swetha. "Macroencapsulation of Phase Change Materials for Thermal Energy Storage." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4200.

Full text

Abstract:

The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy. Latent heat storage enables high-energy storage density which reduces the footprint of the system and the cost. However, PCMs have very low thermal conductivities making them unsuitable for large-scale use without enhancing the effective thermal conductivity. In order to address, the low thermal conductivity of the PCMs, macroencapsulation of PCMs has been adopted as an effective technique. The macroencapsulation not only provides a self-supporting structure of PCM and separates the PCM from thermal fluids but also enhances the heat transfer rate. The current work involves study of various concepts of encapsulation of low cost inorganic PCMs. Sodium nitrate (NaNO3), a low cost PCM, was selected for thermal storage in a temperature range of 300 - 500˚C. Various techniques like electroless coatings, coatings using silicates, coatings with metal oxide (SiO2) and sand encapsulation are discussed. A novel technique of metal oxide coating was developed where firstly a high temperature polymer, such as, polymer (stable > 500˚C) was coated over PCM pellets, and cured, so that the pellet becomes insoluble in water as well as several organic solvents and later the metal oxide is coated over the pellet using self-assembly, hydrolysis, and simultaneous chemical oxidation at various temperatures. The coated PCM pellets were characterized.

APA, Harvard, Vancouver, ISO, and other styles

31

Neto, Mário Anselmo Pereira. "Desenvolvimento de um sistema de detecção fotoacústico utilizando dois microfones: aplicações em medidas de difusividade térmica." Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=3355.

Full text

Abstract:

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Neste trabalho, desenvolveu-se um sistema de detecção fotoacústico para medidas simultâneas e independentes dos sinais fotoacústicos dianteiro e traseiro, utilizando dois microfones e um único feixe de excitação. Utiliza-se a diferença de fase entre estes sinais para a determinação da difusividade térmica de materiais, com base na abordagem teórica da técnica da Diferença de Fase dos Dois Feixes (T2F). Na metodologia apresentada não há a necessidade de se alternar o feixe de excitação entre as faces da amostra. Esta característica torna mais rápido o procedimento de medida e simplifica o monitoramento automatizado de processos dinâmicos que afetam a difusividade térmica do material, como a cura de resinas poliméricas. É apresentado o procedimento utilizado para determinar a diferença entre as fases intrínsecas dos microfones e o método empregado para compensar tal diferença e, assim, obter a defasagem entre os sinais fotoacústicos dianteiro e traseiro. O sistema de detecção desenvolvido é avaliado em medidas de difusividade térmica de amostras metálicas (aço inoxidável AISI 304 e aço SAE 1020) e poliméricas (polipropileno e polietileno de baixa densidade). Os resultados obtidos concordam de forma satisfatória com dados disponíveis na literatura. Finalmente, a aplicação do sistema proposto ao monitoramento de cura de amostras de resina epóxi indicou sua potencialidade de acompanhar, em tempo real, este tipo de processo dinâmico. In this work, a photoacoustic detection system was developed for simultaneous and independent measurements of both front and rear photoacoustic signals, using two microphones and a single beam illumination mode. The phase-lag between these signals is used in the determination of thermal diffusivity of materials, based on the theoretical approach of the Two-Beam Phase-Lag technique. In the experimental setup presented in this work there is no need to alternate the light beam between the sample surfaces. This feature provides faster measurements and simplify the automated monitoring of dynamic processes that affect the material thermal diffusivity, as crosslinking processes. The procedure to determine the difference between the intrinsic phases of the microphones is presented, as well as the method to compensate this difference and to obtain the phase-lag between front and rear photoacoustic signals. The developed detection system is tested in thermal diffusivity measurements of metallic (AISI 304 stainless steel and SAE 1020 steel) and polymeric (polypropylene and low-density polyethylene) samples. The results are in good agreement with the available literature values. Finally, the system here proposed is applied in studies of epoxy resin curing, which shows its potentiality for real-time monitoring of dynamic process.

APA, Harvard, Vancouver, ISO, and other styles

32

Guichard, Stéphane. "Contribution à l'étude des parois complexes intégrant des matériaux à changements de phase : modélisation, expérimentation, et évaluation de la performance énergétique globale." Thesis, La Réunion, 2013. http://www.theses.fr/2013LARE0008/document.

Full text

Abstract:

Cette thèse s'inscrit dans une démarche de maîtrise de l'énergie dans le secteur du bâtiment. Elle a pour but d'utiliser des solutions passives pour atteindre de hautes performances énergétiques. Une des solutions proposée, est l'utilisation de Matériaux à Changements de Phase (MCP) dans les parois. Les matériaux à formes stabilisée solide-liquide, sont utilisés pour stocker l'énergie thermique sous forme de chaleur latente. Le but de l'étude est de mettre en évidence l'impact réel des MCP en terme de complément d'isolation thermique et de proposer un modèle thermique pour prédire son impact sur le champ de température et par conséquent, sur le confort thermique. Une séquence expérimentale en environnement naturel et à grande échelle a été menée à l'île de La Réunion, où le climat est tropical et humide, avec un fort taux d'ensoleillement. Le rayonnement solaire étant important, il est nécessaire de minimiser les sollicitations solaires sur l'ensemble du bâtiment et en particulier la toiture, qui constitue la surface la plus exposée. La présence de lames d'airs au niveau de la toiture, qualifie celle-ci de complexe. Il est alors nécessaire de proposer une modélisation adaptée. Le modèle est couplé à un code de simulation thermique du bâtiment (ISOLAB) et permet de prédire d'une part, les profils de températures de chacune des surfaces constituant l'enveloppe du bâtiment, et d'autre part, d'évaluer l'impact des MCP sur le confort thermique pour différentes configurations. Selon une méthodologie, alliant Modélisation, Expérimentation et Validation (MEV), la démarche a permis de valider l'expérimentation dédiée et d'évaluer la capacité du modèle à prédire l'ensemble des données issues de l'expérimentation This Ph.D thesis focusses on energy control in buildings in order to reach high energetic performances by the use of passive means. One of the proposed solution is based on the use of Phase Change Materials (PCMs). Located into walls, PCMs allow to stock thermal energy into latent heat. The aim of the study is thus to put in evidence PCMs actual impacts on the thermal field of a building and its role as thermal insulation. For these considerations, a thermal model has been developed and validated. An experimental device has been set-up for the collection of data in field environment and for a human scale. The measurement sequence has been conducted at Reunion Island, for a hot and humid tropical climate. For the determination of the thermal behaviour of a commplex wall included PCMs, we proposed a generic model, able to predict many configurations. The model has been implemented in a multizone building simulation code (ISOLAB), for the prediction of wall temperature profiles and PCMs impact on the thermal comfort. Following a combined metholodogy, including modelling and experimentation for validation, we were able to validate the model for actual conditions and to evaluate the model's prediction accuracy

APA, Harvard, Vancouver, ISO, and other styles

33

Graham, M. J. "Encapsulated salt hydrate phase change materials for thermal energy storage." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3012709/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Al-Maghalseh, Maher. "Compact solar thermal energy storage systems using phase change materials." Thesis, Northumbria University, 2014. http://nrl.northumbria.ac.uk/23579/.

Full text

Abstract:

The present research explores numerically and experimentally the process of melting and solidification of Phase Change Materials (PCM) in a latent heat thermal energy storage system (LHTESS). Further, the study will investigate various methods of intensification of heat transfer in such materials by means of metallic fins, filling particles or nanoparticles and by choosing the optimal system geometry for a rapid development of free convection flows during the melting process. The study includes three main parts. First, 3D CFD modelling was performed for the melting performance of a shell-and-tube thermal storage system with n-Octadecane as a PCM. The predicted model was in very good agreement with experimental data published in open literature. A series of numerical calculations were then undertaken to investigate the effect of nanoparticles on the heat transfer process. Dimensionless heat transfer correlations were derived for the system with Pure PCM and PCM mixed with nano-particles. In the second part of this study the experimental studies were carried out in order to investigate the performance of the laboratory thermal storage system with paraffin as the PCM. The thermal storage system was connected to evacuated tube solar collectors and its performance was evaluated in various conditions. 3D CFD model of the system was developed and numerical simulations were run for constant heat source conditions. Computational results were compared with experimental data obtained on the test rig at Northumbria University. Comparison revealed that the developed CFD model is capable to describe process of heat transfer in the system with high accuracy and therefore can be used with high confidence for modelling further cases. Finally, 3D CFD model was developed to predict the transient behaviour of a latent heat thermal energy storage system (LHTESS) in the form of a rectangular container with a central horizontal pipe surrounded by paraffin as PCM (melting temperature is 60 oC). Water was used as a heat transfer fluid (HTF). The enhancement of heat transfer in specific geometries by using external longitudinal fins on the tube and metallic porous matrix were numerically investigated. The influence of the number of fins and porosity of the matrix on the temperature distribution, melting process, melting time and natural convection phenomena were studied. Dimensionless heat transfer correlations were derived for calculation of the Nusselt number as function of Fourier, Stefan and Rayleigh numbers. These correlations to be used in the further designing process of similar thermal storage units at Northumbria University.

APA, Harvard, Vancouver, ISO, and other styles

35

Ozdenefe, Murat. "Phase change materials and thermal performance of buildings in Cyprus." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/phase-change-materials-and-thermal-performance-of-buildings-in-cyprus(a7b37f53-22de-47d4-ad19-2596ee75a558).html.

Full text

Abstract:

This work investigates the thermal performance of buildings in Cyprus and application of a particular passive technology; Phase Change Materials (PCMs) for the ultimate aim of reducing indoor air temperatures and energy supplied for the cooling season.PCMs for passive building applications are emerging technology and have not been tested for the buildings of Cyprus neither by computer simulations nor by practical applications. In this work, particular PCM end product; wallboard, having phase change temperature of 26 oC is employed together with various construction materials and simulated for buildings of Cyprus. Description of the current state in Cyprus has been carried out in terms of low energy building studies, widely used building fabric and building statistics. There is a huge gap in Cyprus in the field of energy performance and thermal comfort of buildings, which creates big room for research. Climatic design of buildings has been abandoned resulting in poor thermal comfort and increased energy consumption. There is still no regulation in place regarding the thermal performance of buildings in North Cyprus.Recent weather data of different Cyprus locations has been investigated and compared with the simulation weather data files that are employed in this work. The author has demonstrated that Finkelstein-Schafer statistics between recent weather data of Cyprus and simulation weather data files are close enough to obtain accurate results.Dynamic thermal simulations has been carried out by using Energy Plus, which is a strong and validated thermal simulation program that can model PCMs. Simulations are done for two different building geometry; “simple building” and “typical building” by employing different construction materials. Simple building is a small size box shaped building and typical building is a real existing building and selected by investigation of the building statistics.Simulation results showed that with this particular PCM product, indoor air temperatures and cooling energies supplied to simple building is reduced up to 1.2 oC and 18.64 % when heavier construction materials are used and up to 1.6 oC and 44.12 % when lighter construction materials are used. These values for typical building are found to be 0.7 oC, 3.24 % when heavier construction materials are used and 1.2 oC, 3.64 % when lighter construction materials are used. It is also found that, if thinner walls and slabs are used in the buildings the effectiveness of the PCM lining increases in significant amount.

APA, Harvard, Vancouver, ISO, and other styles

36

Apreutesei, Mihai. "Temperature impact on thermal evolution of advanced PVD ceramic and metallic glass thin films : Physico-chemical and microstructural analysis." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0009/document.

Full text

Abstract:

Ces dernières années, les exigences de l'industrie dans le développement de nouveaux matériaux fonctionnels en mesure de résister aux conditions difficiles pendant l'opération d'usinage sont en constante augmentation. Les chercheurs doivent donc trouver de nouvelles solutions pour répondre aux besoins industriels de plus en plus sévères. L’utilisation de revêtement protecteur à la surface de l’outil de coupe est une solution très efficace. Des nouveaux matériaux architecturés sont étudiés pour leurs propriétés mécaniques, physiques et chimiques uniques assurant une résistance aux dégradations de surface dues à la corrosion, l'usure, le frottement; en particulier lorsque ces outils sont utilisés dans des environnements hostiles. Dans le cadre de cette thèse de doctorat, l'influence de la température sur la stabilité structurale de deux types de films minces déposés par PVD a été étudiée. Des films céramiques et de verre métallique ont été envisagés. Afin de préparer et optimiser ces films, le projet s’est axé sur l'étude de l'influence des conditions de dépôt sur les caractéristiques de croissance du film: composition chimique, structure, morphologie, puis sur les changements ultérieurs des principales propriétés des films minces, à savoir la résistance à l’oxydation et à la cristallisation lors de leur utilisation à hautes températures. Une démarche multi-échelle a été développée pour caractériser au mieux les couches. La première partie du travail est liée aux revêtements céramiques à base de CrN pour donner de nouvelles fonctionnalités et améliorer la surface des outils de coupe dans le but essentiel d'accroître leur durée de vie. La seconde partie du manuscrit est dédiée aux films minces de verres métalliques de Zr-Cu préparés par un procédé de co-pulvérisation magnétron PVD. Le but de cette partie consiste en l’étude de la relation entre la structure amorphe de ces films et leurs propriétés mécaniques. La conservation du caractère amorphe de ces films en température présente également un caractère essentiel. Les verres métalliques ont récemment attiré un fort intérêt car ils présentent des propriétés mécaniques intéressantes à température ambiante. Ils présentent, de ce fait, un grand potentiel pour des applications d'ingénierie en raison de leurs caractéristiques mécaniques et physico-chimiques uniques (haute limite élastique, résistance à la corrosion ...). Pour relier les propriétés mécaniques des couches à l’évolution de leurs microstructures, une partie importante de ce travail a porté sur l’observation de l’évolution de la couche au cours du chauffage au moyen de techniques de caractérisation in situ. Les films minces proposés au cours de ce travail peuvent être envisagées pour un large gamme d’application dans l’ingénierie de surface pour protéger les surfaces et améliorer la durée de vie des matériaux In the recent years the industrial requirements to develop new functional materials able to overcome the severe conditions during machining operation are continuously increasing. Researchers then must find novel solutions to respond to their severe industrial requirements. To coat the tool surface with advanced coatings is the most efficient solution. New nanostructured materials may nowadays exhibit unique mechanical, physical and chemical properties ensuring notable degradation resistance where the surface protection of materials against corrosion, wear, friction or oxidation is a key issue, particularly when operating in hostile environments. Within the scope of this Ph.D. thesis the influence of the temperature on the structural stability of two different PVD ceramic and metallic glass thin films is proposed. The main goal consists in the development of two distinct classes of thin films, with a wide range of properties. In order to prepare these films, the project will be focused on the study on the influence of PVD deposition conditions in the particular film’s growth characteristics: chemical composition, structure, morphology and the subsequent changes in the main properties of the thin films, namely oxidation and crystallization resistance, especially. For that purpose we adopted the multiscale approach. The first part is related to the ceramic CrN-based coatings to give new functionalities and improve the tools’ surface with the primary aim to increase their lifetime. Secondly, new protective materials able to better protect the exposed surfaces against high temperature oxidation have been proposed, namely CrAlN and CrAlYN coatings as will be evidenced in this manuscript. The second part of the manuscript is dedicated to the innovative Zr-Cu thin films metallic glasses prepared by a PVD magnetron co-sputtering method with the objective to investigate the amorphization ability and their structural properties. Their excellent properties at room temperature have recently attracted attention as a new class of materials with great potential for engineering applications due to unique mechanical and physico-chemical characteristics (high elastic strain limit, corrosion resistance…). Finally, an important approach during the course of this thesis was the real time observation of the structure and surface modifications during heating by means of in situ methods. The thin films proposed during the course of the work could be straightforward used as surface engineering solutions to protect and extend the lifetime of the materials and components

APA, Harvard, Vancouver, ISO, and other styles

37

Gracia, Álvaro de. "Thermal analysis of a ventilated facade with phase change materials (PCM)." Doctoral thesis, Universitat de Lleida, 2013. http://hdl.handle.net/10803/117144.

Full text

Abstract:

L’objectiu d’aquesta tesis és el de analitzar el comportament tèrmic d’una façana ventilada amb material de canvi de fase macro encapsulat en el seu canal d’aire. L’ús de materials de canvi de fase incrementa la capacitat d’emmagatzematge d’energia tèrmica en la solució constructiva proposada, i intensifica l’emmagatzematge i l’operació de la façana ventilada a un rang de temperatures desitjat. El rendiment energètic d’aquest nou tipus de façana ventilada s’estudia de forma experimental per veure el seu potencial en reduir els consums energètics tant de calefacció com de refrigeració. Posteriorment, s’estudia mitjançant l’anàlisi de cicle de vida, quin és l’impacte mediambiental que suposa la manufactura i operació d’aquest sistema. Finalment, es desenvolupa un model numèric per optimitzar el funcionament i disseny d’aquesta façana. Aquest model numèric utilitza una nova correlació empírica de nombre de Nusselt, per al càlcul dels coeficients de transferència de calor entre el material de canvi de fase i el flux d’aire circulant per la cambra. El objetivo de esta tesis es el de analizar el comportamiento térmico de una fachada ventilada con material de cambio de fase macro encapsulado en su canal de aire. El uso de materiales de cambio de fase aumenta la capacidad de almacenamiento de energía térmica en la solución constructiva propuesta, e intensifica el almacenamiento y la operación de la fachada ventilada a un rango de temperaturas deseado. El rendimiento energético de este nuevo tipo de fachada ventilada se estudia experimentalmente para ver su potencial en reducir los consumos energéticos tanto de calefacción como de refrigeración. Posteriormente, se estudia mediante el análisis de ciclo de vida, el impacto medioambiental que supone la manufactura y operación de este sistema. Finalmente, se desarrolla un modelo numérico que optimiza el funcionamiento y diseño de esta fachada. Este modelo numérico utiliza una nueva correlación empírica de número de Nusselt, para el cálculo de los coeficientes de transferencia de calor entre el material de cambio de fase y el flujo de aire circulando por la cámara. The objective of this thesis is to analyse the thermal behaviour of a ventilated façade with macro-encapsulated phase change material in its air channel. The use of phase change materials increases the ability of thermal energy storage in the proposed constructive system, and enhances the storage and operation of the ventilated facade to a desired temperature range. The energy efficiency of this new type of ventilated facade is experimentally studied to determine its potential in reducing the energy consumption both for heating and cooling. Hereafter, the environmental impact of the manufacture and operation of this system is studied by a life cycle analysis. Finally, a numerical model is developed to optimize the operation and design of this facade. This numerical model uses a new empirical correlation for the Nusselt number to calculate the convective heat transfer coefficients between the phase change material and the air flow circulating in the chamber.

APA, Harvard, Vancouver, ISO, and other styles

38

Nath, Rupa. "Encapsulation of High Temperature Phase Change Materials for Thermal Energy Storage." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4180.

Full text

Abstract:

Thermal energy storage is a major contributor to bridge the gap between energy demand (consumption) and energy production (supply) by concentrating solar power. The utilization of high latent heat storage capability of phase change materials is one of the keys to an efficient way to store thermal energy. However, some of the limitations of the existing technology are the high volumetric expansion and low thermal conductivity of phase change materials (PCMs), low energy density, low operation temperatures and high cost. The present work deals with encapsulated PCM system, which operates at temperatures above 500°C and takes advantage of the heat transfer modes at such high temperatures to overcome the aforementioned limitations of PCMs. Encapsulation with sodium silicate coating on preformed PCM pellets were investigated. A low cost, high temperature metal, carbon steel has been used as a capsule for PCMs with a melting point above 500° C. Sodium silicate and high temperature paints were used for oxidation protection of steel at high temperatures. The emissivity of the coatings to enhance heat transfer was investigated.

APA, Harvard, Vancouver, ISO, and other styles

39

Alam, Tanvir E. "Experimental Investigation of Encapsulated Phase Change Materials for Thermal Energy Storage." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5632.

Full text

Abstract:

Thermal energy storage (TES) is one of the most attractive and cost effective solutions to the intermittent generation systems like solar, wind and other renewable sources, compared to alternatives. It creates a bridge between the power supply and demand during peak hours or at times of emergency to ensure the continuous supply of energy. Among all the TES systems, latent heat thermal energy storage (LHTES) draws lots of interests as it has high energy density and can store or retrieve energy isothermally. Two major technical challenges associated with the LHTES are low thermal conductivity of the phase change materials (PCMs), and corrosion tendency of the containment vessel with the PCMs. Macro-encapsulation of the PCM is one of the techniques to encounter the low thermal conductivity issue as it will maximize the heat transfer area for the given volume of the PCM and restrict the PCMs to get in contact with the containment vessel. However, finding a suitable encapsulation technique that can address the volumetric expansion problem and compatible shell material are significant barriers of this approach. In the present work, an innovative technique to encapsulate PCMs that melt in the 100-350 oC temperature range was developed for industrial and private applications. This technique did not require a sacrificial layer to accommodate the volumetric expansion of the PCMs on melting. The encapsulation consisted of coating a non-reactive polymer over the PCM pellet followed by deposition of a metal layer by a novel non-vacuum metal deposition technique. The fabricated spherical capsules were tested in different heat transfer fluid (HTF) environments like air, oil and molten salt (solar salt). Thermophysical properties of the PCMs were investigated by DSC/TGA, IR and weight change analysis before and after the thermal cycling. Also, the constrained melting and solidification of sodium nitrate PCM inside the spherical capsules of different sizes were compared to explore the charging and discharging time. To accomplish this, three thermocouples were installed vertically inside the capsule at three equidistant positions. Low-density graphene was dispersed in the PCM to increase its conductivity and compared with pure PCM capsules. A laboratory scale packed-bed LHTES system was designed and built to investigate the performance of the capsules. Sodium nitrate (m.p. 306oC) was used as the PCM and air was used as the heat transfer fluid (HTF). The storage system was operated between 286oC and 326oC and the volumetric flow rate of the HTF was varied from 110 m3/h to 151 m3/h. The temperature distribution along the bed (radially and axially) and inside the capsules was monitored continuously during charging and discharging of the system. The effect of the HTF mass flow rate on the charging and discharging time and on the pressure drop across the bed was evaluated. Also, the energy and exergy efficiencies were calculated for three different flow rates. Finally, a step-by-step trial manufacturing process was proposed to produce large number of spherical capsules.

APA, Harvard, Vancouver, ISO, and other styles

40

Elsanusi, Omer. "THERMAL ENERGY STORAGE WITH MULTIPLE FAMILIES OF PHASE CHANGE MATERIALS (PCM)." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1852.

Full text

Abstract:

The world is facing a major challenge when it comes to proper energy utilization. The increasing energy demand, the depleting fossil fuel resources and the growing environmental and ecological concerns are factors that drive the need for creative solutions. Renewable energy resources such as solar sit in the center of these solutions. Due to their intermittent nature, development of energy storage systems is crucial. This dissertation focused on the latent thermal energy storage systems that incorporate phase change materials (PCM). The main goal was to enhance the heat transfer rates in these systems to address the low melting (energy storage stage) and solidification (recovery stage) rates that are caused by the PCMs’ low thermal conductivity values. The application of multiple PCMs (m-PCMs) with varying melting temperatures in several arrangements was investigated. The effects of applying m-PCMs on the conduction heat transfer and on the natural convection heat transfer in both horizontally and vertically oriented heat exchangers were studied. This was followed by an optimization study of the PCMs’ melting temperatures and the working fluid flow rate. Further heat transfer enhancement using metal fins was also investigated. Numerical models were developed and validated. Results are reported and discussed. Significant enhancement in both complete melting time and energy storage capacity was obtained by the m-PCMs in series arrangement. This enhancement is more pronounced in the vertically oriented system. The working fluid flow rate was found to have a limited effect during the melting stage. However, it seems to be crucial in the solidification stage.

APA, Harvard, Vancouver, ISO, and other styles

41

Caleiro, Luis Carlos Ferreira. "Dynamic simulation of strategies for thermal comfort using phase change materials." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14382.

Full text

Abstract:

Mestrado em Engenharia Civil Nowadays, as global warming becomes one of the most urgent problems in the world, there is a need to find better ways to utilize energy: not only in the field of energy production, transmission, distribution, and consumption, but also in the area of energy storage. With energy storage technologies, it is possible to overcome the contradiction between the energy production and consumption, alleviate the tense production load of power plants at peak hours, and reduce consumers’ electricity costs by avoiding higher peak hour tariffs. Thermal energy storage, or heat and cold storage, allows the storage of heat or cold to be used later. This method needs to be reversible so it allows for multiple cycles. The technology that was studied for this effect was Phase Change Materials or PCMs. With that in mind, and with the help of dynamic building simulation software, EnergyPlus, several scenarios of an existing build that has PCM incorporated were studied in order to ascertain the real effect the technology is having on the case study, including thermal comfort. Hoje em dia, com o aquecimento global a tornar-se um dos problemas mais urgentes da Terra, há necessidade de encontrar melhores maneiras de utilizar energia: não apenas no campo da produção de energia, transmissão, distribuição e consumo, mas também na área de armazenamento de energia. Com tecnologias de armazenamento de energia, é possível de ultrapassar a contradição entre a produção e consumo, aliviar a tensão que existe na produção nas estações de energia nas horas de pico e reduzir o custo de electricidade aos utentes ao evitar as tarifas nas horas de pico. A armazenagem de energia calorífica, do calor e frio, permite o armazenamento de calor ou frio para ser usado mais tarde. Este método precisa de ser reversível para permitir vários ciclos deste processo. A tecnologia estudada para este efeito foi os materiais que mudam de fase, ou PCMs (Phase Change Materials). Com isto em mente, e com a ajuda de software de simulação dinâmica, EnergyPlus, vários cenários de um edifício existente que tem PCM incorporado foram estudados em ordem de poder concluir o verdadeiro efeito que a tecnologia está a ter no caso estudo, incluindo o conforto térmico.

APA, Harvard, Vancouver, ISO, and other styles

42

Johansson, Elin, and Filip Norrman. "Life cycle analysis on phase change materials for thermal energy storage." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264526.

Full text

Abstract:

Sustainable energy sources and utilization is a large area of interest and the developments are moving fast. Recently, thermal energy storage in the form of phase change materials other than water have caught more interest and a need of analysis for the entire life cycle of the materials have appeared. Previous work in the area shows that health and safety aspects of the products’ life cycle have been neglected and comparisons between different phase change materials other than water are sparsely researched. The objectives for this report are to compare three different phase change material intended for thermal energy storage in a life cycle analysis point of view with both environmental and health and safety aspects. A screening process of materials was subsequently performed in order to find suited materials given the objective (Octadecane, Xylitol and Manganese Nitrate Hexahydrate), taking into consideration the relevance in the scientific community amongst other criteria. The life cycle is in this work bounded from cradle to grave without recycling and for a thermal energy storage heating system operating in Scandinavian climates assuming 52 cycles per year. The results indicate that Octadecane are preferable in terms of global warming potential over 100 years (ca 4.5 kg CO2/kg Octadecane produced) and Xylitol more preferable in terms of cumulative energy demand (ca 21.5 MJ per kg Xylitol produced) and energy payback time (1.17 years). The health and safety aspects are difficult to evaluate in terms of working conditions and ecotoxicity but a simple scale have been put to use to give an overview of the health risk associated with each material. In the health and safety aspects Xylitol also show the most promise but further development of a methodology for evaluating these terms are recommended. Hållbar energiteknik är ett omtalat och snabbt utvecklande område där fasomvandlandematerial för termisk energiförvaring har dragit till sig uppmärksamhet. På grund av denna uppmärksamhet har behovet för en fullständig livscykelanalys för de relevanta materialen uppkommit. Föregående rapporter och journaler om ämnet har visat brister i fokus på hälso- och säkerhetsaspekter och i jämförelse med andra fasomvandlandematerial än paraffiner och vatten. Målet med denna rapport är att utföra och jämföra livscykelanalyser för tre olika fasomvandlandematerial med både miljöaspekter och hälso- och säkerhetsaspekter. En urvalsprocess av intressanta material har därmed genomförts för att hitta lämpliga kandidater att undersöka (Oktadekan, Xylitol och Mangan nitrat hexahydrat), med avseende på bl.a. hur mycket materialen studerats inom termisk energiförvaring. Livscykeln inom denna rapport är bunden från Cradle-to-grave utan återvinning av material och opererar under skandinaviska förhållanden med 52 värmecykler per år. Resultaten indikerar att Oktadekan är mest lämpad för globaluppvärmnings potential över 100 år (ca 4,5 kg CO2/kg Oktadekan producerad) och Xylitol mest lämpad för kumulativt energikrav (ca 21,5 MJ per kg Xylitol producerad) samt återbetalningstid för energi (1,17 år). De hälso- och säkerhetsaspekterna är svåra att definiera inom arbetsförhållanden och ekotoxicitet men en enkel skala baserad på ’GHS hazard statements’ har etablerats för att få en överblick över materialens hälsorisk. Även här visade Xylitol vara mest lämpad men fortsatt utveckling av en metodik för att analysera dessa aspekter rekommenderas.

APA, Harvard, Vancouver, ISO, and other styles

43

Gunasekara, Saman Nimali. "Phase Equilibrium-aided Design of Phase Change Materials from Blends : For Thermal Energy Storage." Doctoral thesis, KTH, Kraft- och värmeteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-212440.

Full text

Abstract:

Climate change is no longer imminent but eminent. To combat climate change, effective, efficient and smart energy use is imperative. Thermal energy storage (TES) with phase change materials (PCMs) is one attractive choice to realize this. Besides suitable phase change temperatures and enthalpies, the PCMs should also be robust, non-toxic, environmental-friendly and cost-effective. Cost-effective PCMs can be realized in bulk blends. Blends however do not have robust phase change unless chosen articulately. This thesis links bulk blends and robust, cost-effective PCMs via the systematic design of blends as PCMs involving phase equilibrium evaluations. The key fundamental phase equilibrium knowledge vital to accurately select robust PCMs within blends is established here. A congruent melting composition is the most PCM-ideal among blends. Eutectics are nearly ideal if supercooling is absent. Any incongruent melting composition, including peritectics, are unsuitable as PCMs. A comprehensive state-of-the-art evaluation of the phase equilibrium-based PCM design exposed the underinvestigated categories: congruent melting compositions, metal alloys, polyols and fats. Here the methods and conditions essential for a comprehensive and transparent phase equilibrium assessment for designing PCMs in blends are specified. The phase diagrams of the systems erythritol-xylitol and dodecane-tridecane with PCM potential are comprehensively evaluated. The erythritol-xylitol system contains a eutectic in a partially isomorphous system unlike in a non-isomorphous system as previous literature proposed. The dodecane-tridecane system forms a probable congruent minimum-melting solid solution, but not a maximum-melting liquidus or a eutectic as was previously proposed. The sustainability aspects of a PCM-based TES system are also investigated. Erythritol becomes cost-effective if produced using glycerol from bio-diesel production. Olive oil is cost-effective and has potential PCM compositions for cold storage. A critical need exists in the standardization of methods and transparent results reporting of the phase equilibrium investigations in the PCM-context. This can be achieved e.g. through international TES collaboration platforms. Energi är en integrerad del av samhället men energiprocesser leder till miljöbelastning, och klimatförändringar. Därför är effektiv energianvändning, ökad energieffektivitet och smart energihantering nödvändigt. Värmeenergilagring (TES) är ett attraktivt val för att bemöta detta behov, där ett lagringsalternativ med hög densitet är s.k. fasomvandlingsmaterial (PCM). Ett exempel på ett billigt, vanligt förekommande PCM är systemet vatten-is, vilket har använts av människor i tusentals år. För att tillgodose de många värme- och kylbehov som idag uppstår inom ett brett temperaturintervall, är det viktigt med innovativ design av PCM. Förutom lämplig fasförändringstemperaturer, entalpi och andra termofysikaliska egenskaper, bör PCM också ha robust fasändring, vara miljövänlig och kostnadseffektiv. För att förverkliga storskaliga TES system med PCM, är måste kostnadseffektivitet och robust funktion under många cykler bland de viktigaste utmaningarna. Kostnadseffektiva PCM kan bäst erhållas från naturliga eller industriella material i bulkskala, vilket i huvudsak leder till materialblandningar, snarare än rena ämnen. Blandningar uppvisar dock komplexa fasförändringsförlopp, underkylning och/eller inkongruent smältprocess som leder till fasseparation. Denna doktorsavhandling ger ny kunskap som möjliggör att bulkblandningar kan bli kostnadseffektiva och robusta PCM-material, med hjälp av den systematiskutvärdering av fasjämvikt och fasdiagram. Arbetet visar att detta kräver förståelse av relevanta grundläggande fasjämviktsteorier, omfattande termiska och fysikalisk-kemiska karakteriseringar, och allmänt tillämpliga teoretiska utvärderingar. Denna avhandling specificerar befintlig fasjämviktsteori för PCM-sammanhang, men sikte på att kunna välja robusta PCM blandningar med specifika egenskaper, beroende på tillämpning. Analysen visar att blandningar med en sammansättning som leder till kongruent smältande, där faser i jämvikt har samma sammansättning, är ideala bland PCM-blandningar. Kongruent smältande fasta faser som utgör föreningar eller fasta lösningar av ingående komponenter är därför ideala. Eutektiska blandningar är nästan lika bra som PCM, så länge underkylning inte förekommer. Därmed finns en stor potential för att finna och karakterisera PCM-ideala blandningar som bildar kongruent smältande föreningar eller fasta lösningar. Därigenom kan blandningar med en skarp, reversibel fasändring och utan fasseparation erhållas – egenskaper som liknar rena materialens fasändringsprocess. Vidare kan man, via fasdiagram, påvisa de blandningar som är inkongruent smältande, inklusive peritektiska blandningar, som är direkt olämpliga som PCM. Denna avhandling ger grundläggande kunskap som är en förutsättning för att designa PCM i blandningar. Genom en omfattande state-of-the-art utvärdering av fas-jämviktsbaserad PCM-design lyfter arbetet de PCM-idealiska blandningarna som hittills inte fått någon uppmärksamhet, såsom kongruenta smältande blandningar, och materialkategorierna metallegeringar, polyoler och fetter. Resultatet av arbetet visar dessutom att vissa PCM-material som ibland föreslås är direkt olämpliga då fasdiagram undersöks, bl a pga underkylning och även peritektiska system med fasseparation och degradering av kapaciteten (t ex Glauber-salt och natriumacetat-trihydrat). Denna avhandling specificerar och upprättar grundläggande teori samt tekniker, tillvägagångssätt och förhållanden som är nödvändiga för en omfattande och genomsynlig fasjämviktsbedömning, för utformning av PCM från blandningar för energilagering. Med detta som bas har följande fasdiagramtagits fram fullständigt: för erytritol-xylitol och för dodekan-tridekan, med PCM-potential för låg temperaturuppvärmning (60-120 °C) respektive frysning (-10 °C till -20 °C) utvärderas fullständigt. Erytritol-xylitol systemet har funnits vara eutektiskt i ett delvis isomorft system, snarare än ett icke-isomorft system vilket har föreslagits tidigare litteratur. Dodekan-tridekan systemet bildar ett system med kongruent smältande fast lösning (idealisk som en PCM) vid en minimumtemperatur, till skillnad från tidigare litteratur som föreslagt en maximumtemperatur, eller ett eutektiskt system. Teoretisk modellering av fasjämvikt har också genomförts för att komplettera det experimentella fasdiagrammet för systemet erytritol-xylitol. Efter granskning av de metoder som använts tidigare i PCM-litteraturen har här valts ett generiskt tillvägagångssätt (CALPHAD-metoden). Denna generiska metod kan bedöma vilken typ av material och fasändring som helst, till skillnad från en tidigare använda metoder som är specifika för materialtyper eller kemiska egenskaper. Denna teoretiska studie bekräftar termodynamiskt solvus, solidus, eutektisk punkt och erytritol-xylitol fasdiagrammet i sin helhet. Vad gäller hållbarhetsaspekter med PCM-baserad TES, lyfter denna avhandling fokus på förnybara och kostnadseffektiva material (t.ex. polyoler och fetter) som PCM. Som exempel har här undersökts erytritol och olivolja, med förnybart ursprung. Erytritol skulle kunna bli ett kostnadseffektivt PCM (163 USD/kWh), om det produceras av glycerol vilket är en biprodukt från biodiesel/bioetanolframställning. Olivolja är ännu ett kostnadseffektivt material (144 USD/kWh), och som här har påvisats innehålla potentiella PCM sammansättningar med lämpliga fasändringsegenskaper för kylatillämpningar. En övergripande slutsats från denna avhandling är att det finns ett behov av att standardisera tekniker, metoder och transparent resultatrapportering när det gäller undersökningar av fasjämvikt och fasdiagram i PCM-sammanhang. Internationella samarbetsplattformar för TES är en väg att koordinera arbetet. QC 20170830

APA, Harvard, Vancouver, ISO, and other styles

44

Oró, Prim Eduard. "Thermal energy storage (TES) using phase change materials (PCM) for cold applications." Doctoral thesis, Universitat de Lleida, 2013. http://hdl.handle.net/10803/110542.

Full text

Abstract:

L’objectiu d’aquesta tesis doctoral és el desenvolupament d’un sistema d’emmagatzematge d’energia tèrmica (TES) mitjançant la utilització de materials de canvi de fase (PCM) per aplicacions a baixa temperatura, en particular, per a congeladors comercials. Es provarà tant experimental com numèricament la millora de les condicions de l’emmagatzematge i també la millora de la qualitat dels aliments emmagatzemats/transportats. També inclou la investigació de nous PCMs, estudiant la modificació de la temperatura de canvi de fase i analitzant velocitats de degradació i corrosió amb els materials recipients. Els resultats obtinguts a les diferents aplicacions estudiades demostren el clarament el benefici de la utilització de PCM, reduint les fluctuacions i les caigudes de temperatura tant al interior dels sistemes com del producte, i per tant millorant la qualitat d’aquests. El objetivo de esta tesis doctoral es el desarrollo de un sistema de almacenamiento de energía térmica (TES) mediante la utilización de materiales de cambio de fase (PCM) para aplicaciones a baja temperatura, en particular, para los congeladores comerciales. Se probará experimental y numéricamente la mejora de las condiciones de almacenamiento, y también la mejora de la calidad de los alimentos almacenados/transportados. También incluye la investigación de nuevos PCM, estudiando la modificación de la temperatura de cambio de fase y analizando velocidades de degradación y corrosión con los materiales contenedores. Los resultados obtenidos en las diferentes aplicaciones demuestran el beneficio de usar PCM, reduciendo las fluctuaciones y las caídas de temperatura tanto del interior de los sistemas como del producto almacenado y por tanto la mejoría de la calidad de éstos. The aim of this PhD thesis is to develop a thermal energy storage (TES) system using phase change materials (PCM) for cold temperature applications in particular for commercial freezers testing experimentally and numerically the improvement of its thermal performance and the food quality stored. This thesis also includes the research on PCM with attractive properties for low temperature applications such as controllable phase change temperature and low corrosion and degradation rate. The results obtained in the proposed applications have proved the benefit of using PCM in the proposed cold applications based on reduction of the interior/product temperature fluctuations and

APA, Harvard, Vancouver, ISO, and other styles

45

Yang, Jia. "Melting and solidification models and thermal characteristics of microencapsulated phase change materials." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58140/.

Full text

Abstract:

Microencapsulated phase change material (MPCM) as a new thermal energy storage material and a heat transfer medium have attracted considerable attention in the thermal energy storage field. Solidification and melting models of a single PCM particle are constructed in this thesis. An effective numerical method for the problem of a spherical particle with a moving boundary was developed and validated by an iterative analytical series solution. A new liquid-solid interface model was proposed for modelling the effect of binary phase composition on the solidification of an alloy and a mixture PCM particle based on solid fraction. A full two-phase melting model of differentlysized micro/nano particles was also built. The initial melting point of particles is defined and depends on the minimum melting temperature of particles measured by DSC, the particle size and the Gibbs-Thomson equation. The model can predict the melting time of micro-particles flowing in a heat transfer channel, which agrees with the group melting behaviour of MPCM as observed by experiments. A test rig was built to explore the melting heat transfer behaviour of microcapsule phase change slurry (MPCS) flowing through a circular tube for a given constant heat flux. DPNT06-0182 slurries were investigated on the test rig. The experimental results indicate that the flow rate is a key factor in determining heat transfer coefficients of slurries. For the same energy efficiency, and in the situation of low flow rate and phase change, the pressure drop and local heat transfer coefficients of 10% DPNT slurry are lower compared with water, but the most heat energy is stored during the passage through the heated test section. However, in the case of high flow rates and no phase change, the local heat transfer coefficients of 10% DPNT slurry are higher with comparison to water under turbulent flows.

APA, Harvard, Vancouver, ISO, and other styles

46

Viry, Cédric. "Silica micro-encapsulation of organic phase-change materials for thermal energy storage." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122084.

Full text

Abstract:

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019 Cataloged from student-submitted PDF version of thesis. Includes bibliographical references (pages 99-107). Renewable energy production and storage are our main levers to fight climate change. As the battery industry struggles to manufacture cheap, cyclable and safe systems, thermal energy storage recently became a more active area of research, promising cheap and cyclable storage materials. In the U.S., nearly 70% of the energy input ends up as thermal losses. More than a third of these losses are generated at electricity production plants and another third in the transportation sector. Combined, these two sectors waste nearly 50% of the total U.S. energy feed. Thermal energy storage can help take advantage of this opportunity by allowing to revalorize waste heat. High-temperature thermal energy storage can be used to generate electricity but requires large and expensive systems that can only be charged with high-grade energy sources (usually electricity or solar energy). This study focuses on organic Phase-Change Materials for use with low-grade heat sources for domestic heating applications. Engineering organic phase-change material energy storage systems is complicated because of their very low thermal conductivity, the leakage of the liquid phase and the thermal expansion that comes with phase-change. Micro-encapsulation is an elegant solution to all of these problems. Polymer micro-encapsulation of these phase-change materials has been achieved with success but other classes of shell materials such as metals and ceramics can offer more desirable thermal properties. In this study, we use the sol-gel process of tetraethyl orthosilicate to synthesize silica microcapsules containing a variety of organic phase-change materials. We characterize these capsules to compare their thermal and protective properties to the bulk phase-change material in order to assess their viability as a heat storage medium. Our results show that it is possible to synthesize microcapsules containing several types of phase-change materials with this process. The synthesis leads to porous microcapsules which would require additional processing to achieve all of the micro-encapsulation goals. However, we also show that the main thermal properties are conserved and that for some materials such as sugar alcohols, some thermal properties can even be enhanced. by Cédric Viry. S.M. S.M. Massachusetts Institute of Technology, Department of Materials Science and Engineering

APA, Harvard, Vancouver, ISO, and other styles

47

Sharma, Shivangi. "Performance enhancement of building-integrated concentrator photovoltaic system using phase change materials." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/33859.

Full text

Abstract:

Building-integrated Concentrator Photovoltaic (BICPV) technology produces noiseless and pollution free electricity at the point of use. With a potential to contribute immensely to the increasing global need for a sustainable and low carbon energy, the primary challenges such as thermal management of the panels are overwhelming. Although significant progress has been made in the solar cell efficiency increase, the concentrator photovoltaic industry has still to go a long way before it becomes competitive and economically viable. Experiencing great losses in their electrical efficiencies at high temperatures that may eventually lead to permanent degradation over time, affects the market potential severely. With a global PV installed capacity of 303 GW, a nominal 10 °C decrease in their average temperatures could theoretically lead to a 5 % electricity efficiency improvement resulting in 15 GW increase in electricity production worldwide. However, due to a gap in the research knowledge concerning the effectiveness of the available passive thermal regulation techniques both individually and working in tandem, this lucrative potential is yet to be realised. The work presented in this thesis has been focussed on incremental performance improvement of BICPV by developing innovative solutions for passive cooling of the low concentrator based BICPV. Passive cooling approaches are selected as they are generally simpler, more cost-effective and considered more reliable than active cooling. Phase Change Materials (PCM) have been considered as the primary means to achieve this. The design, fabrication and the characterisation of four different types of BIPCV-PCM assemblies are described. The experimental investigations were conducted indoors under the standard test conditions. In general, for all the fabricated and assembled BICPV-PCM systems, the electrical power output showed an increase of 2 %-17 % with the use of PCM depending on the PCM type and irradiance. The occurrence of hot spots due to thermal disequilibrium in the PV has been a cause of high degradation rates for the modules. With the use of PCM, a more uniform temperature within the module could be realised, which has the potential to extend the lifetime of the BICPV in the long-term. Consequentially, this may minimise the intensive energy required for the production of the PV cells and mitigate the associated environmental impacts. Following a parallel secondary approach to the challenge, the design of a micro-finned back plate integrated with a PCM containment has been proposed. This containment was 3D printed to save manufacturing costs and time and for reducing the PCM leakage. An organic PCM dispersed with high thermal conductivity nanomaterial was successfully tested. The cost-benefit analysis indicated that the cost per degree temperature reduction (£/°C) with the sole use of micro-fins was the highest at 1.54, followed by micro-fins + PCM at 0.23 and micro-fins + n-PCM at 0.19. The proposed use of PCM and application of micro-finned surfaces for BICPV heat dissipation in combination with PCM and n-PCM is one the novelties reported in this thesis. In addition, an analytical model for the design of BICPV-PCM system has been presented which is the only existing model to date. The results from the assessment of thermal regulation benefits achieved by introducing micro-finning, PCM and n-PCM into BICPV will provide vital information about their applicability in the future. It may also influence the prospects for how low concentration BICPV systems will be manufactured in the future.

APA, Harvard, Vancouver, ISO, and other styles

48

Gowreesunker, Baboo Lesh Singh. "Phase change thermal enery storage for the thermal control of large thermally lightweight indoor spaces." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7649.

Full text

Abstract:

Energy storage using Phase Change Materials (PCMs) offers the advantage of higher heat capacity at specific temperature ranges, compared to single phase storage. Incorporating PCMs in lightweight buildings can therefore improve the thermal mass, and reduce indoor temperature fluctuations and energy demand. Large atrium buildings, such as Airport terminal spaces, are typically thermally lightweight structures, with large open indoor spaces, large glazed envelopes, high ceilings and non-uniform internal heat gains. The Heating, Ventilation and Air-Conditioning (HVAC) systems constitute a major portion of the overall energy demand of such buildings. This study presented a case study of the energy saving potential of three different PCM systems (PCM floor tiles, PCM glazed envelope and a retrofitted PCM-HX system) in an airport terminal space. A quasi-dynamic coupled TRNSYS®-FLUENT® simulation approach was used to evaluate the energy performance of each PCM system in the space. FLUENT® simulated the indoor air-flow and PCM, whilst TRNSYS® simulated the HVAC system. Two novel PCM models were developed in FLUENT® as part of this study. The first model improved the phase change conduction model by accounting for hysteresis and non-linear enthalpy-temperature relationships, and was developed using data from Differential Scanning Calorimetry tests. This model was validated with data obtained in a custom-built test cell with different ambient and internal conditions. The second model analysed the impact of radiation on the phase change behaviour. It was developed using data from spectrophotometry tests, and was validated with data from a custom-built PCM-glazed unit. These developed phase change models were found to improve the prediction errors with respect to conventional models, and together with the enthalpy-porosity model, they were used to simulate the performance of the PCM systems in the airport terminal for different operating conditions. This study generally portrayed the benefits and flexibility of using the coupled simulation approach in evaluating the building performance with PCMs, and showed that employing PCMs in large, open and thermally lightweight spaces can be beneficial, depending on the configuration and mode of operation of the PCM system. The simulation results showed that the relative energy performance of the PCM systems relies mainly on the type and control of the system, the night recharge strategy, the latent heat capacity of the system, and the internal heat gain schedules. Semi-active systems provide more control flexibility and better energy performance than passive systems, and for the case of the airport terminal, the annual energy demands can be reduced when night ventilation of the PCM systems is not employed. The semi-active PCM-HX-8mm configuration without night ventilation, produced the highest annual energy and CO2 emissions savings of 38% and 23%, respectively, relative to a displacement conditioning (DC) system without PCM systems.

APA, Harvard, Vancouver, ISO, and other styles

49

Mu, Mulan. "Development of shape stable phase change materials with improved thermophysical properties." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680062.

Full text

Abstract:

Shape stable phase change materials (SSPCMs) based on paraffin wax (PW) and high density polyethylene (HDPE) can be used as energy storage materials for utilization of renewable energy in buildings. An SSPCM could be formed by selecting a suitable wax in terms of melting temperature (T m) and a HDPE in terms of viscosity. However, the impact of waxes with different T m and HDPEs with different viscosities on the manufacture of SSPCMs and their thermo-physical properties has not been studied thoroughly. Therefore, the aim of the research reported in this thesis is to understand the effect of different waxes and HDPEs on the processing of SSPCMs typically used in buildings and the quantification of their thermal and mechanical propelties. SSPCMs based on a higher (H-PW, Tm = 56-58°C) and a lower (L-PW, Tm = 18-23 0c) Tm wax with a higher (hv-HDPE, MFI = 0.18) and a lower (lv-HDPE, MFI = 25) melt viscosity HDPE were prepared by an extrusion method and their thermal and mechanical properties investigated. The effect of addition of thermally conducting multi-walled carbon nanotubes (MWCNTs) to enhance thermal conductivity and other properties of these SSPCMs was also studied. Such understanding would thus help to assess and inform the design of SSPCMs as wall panels suitable for domestic applications.

APA, Harvard, Vancouver, ISO, and other styles

50

Wang, Guangyao. "An Investigation of Phase Change Material (PCM)-Based Ocean Thermal Energy Harvesting." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100989.

Full text

Abstract:

Phase change material (PCM)-based ocean thermal energy harvesting is a relatively new method, which extracts the thermal energy from the temperature gradient in the ocean thermocline. Its basic idea is to utilize the temperature variation along the ocean water depth to cyclically freeze and melt a specific kind of PCM. The volume expansion, which happens in the melting process, is used to do useful work (e.g., drive a turbine generator), thereby converting a fraction of the absorbed thermal energy into mechanical energy or electrical energy. Compared to other ocean energy technologies (e.g., wave energy converters, tidal current turbines, and ocean thermal energy conversion), the proposed PCM-based approach can be easily implemented at a small scale with a relatively simple structural system, which makes it a promising method to extend the range and service life of battery-powered devices, e.g, autonomous underwater vehicles (AUVs). This dissertation presents a combined theoretical and experimental study of the PCM-based ocean thermal energy harvesting approach, which aims at demonstrating the feasibility of the proposed approach and investigating possible methods to improve the overall performance of prototypical systems. First, a solid/liquid phase change thermodynamic model is developed, based on which a specific upperbound of the thermal efficiency is derived for the PCM-based approach. Next, a prototypical PCM-based ocean thermal energy harvesting system is designed, fabricated, and tested. To predict the performance of specific systems, a thermo-mechanical model, which couples the thermodynamic behaviors of the fluid materials and the elastic behavior of the structural system, is developed and validated based on the comparison with the experimental measurement. For the purpose of design optimization, the validated thermo-mechanical model is employed to conduct a parametric study. Based on the results of the parametric study, a new scalable and portable PCM-based ocean thermal energy harvesting system is developed and tested. In addition, the thermo-mechanical model is modified to account for the design changes. However, a combined analysis of the results from both the prototypical system and the model reveals that achieving a good performance requires maintaining a high internal pressure, which will complicate the structural design. To mitigate this issue, the idea of using a hydraulic accumulator to regulate the internal pressure is proposed, and experimentally and theoretically examined. Finally, a spatial-varying Robin transmission condition for fluid-structure coupled problems with strong added-mass effect is proposed and investigated using fluid structure interaction (FSI) model problems. This can be a potential method for the future research on the fluid-structure coupled numerical analysis of AUVs, which are integrated with and powered by the PCM-based thermal energy harvesting devices. Doctor of Philosophy

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Phase-change materials, thermal properties'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles