Дисертації з теми "Insulation (Heat) Thermal properties"

This master thesis project was performed in collaboration with Scania CV AB, Engine Materials group. The purpose with the project was to investigate different ceramic TBC (Thermal Barrier Coating) thermal insulation properties inside the combustion chamber. Experimental testing was performed with a Single-Cylinder engine with TBC deposited on selected components. A dummy-valve was developed and manufactured specifically for this test in order to enable a water cooling system and to ease the testing procedure. The dummy-valve consists of a headlock, socket, valve poppet and valve shaft. Additionally, a copper ring is mounted between the cylinder head and the valve poppet to seal the system from combustion gases. Thermocouples attached to the modified valve poppet and valve shaft measured the temperature during engine test to calculate the heat flux. The TBCs consisted of three different materials: 7-8% yttrium-stabilized zirconia (8YSZ), gadolinium zirconia and lanthanum zirconia. The 8YSZ TBC was tested as standard, but also with microstructural modifications. Modifications such as pre-induced segmented cracks, nanostructured zones and sealed porosity were used. The results indicated that the heat flux of 8YSZ-standard, 8YSZ-nano and 8YSZ-segmented cracks was in level with the steel reference. In the case of 8YSZ-sealed porosity the heat flux was measured higher than the steel reference. Since 8YSZ-standard and 8YSZ-sealed porosity are deposited with the same powder it is believed that the high heat flux is caused by radiative heat transfer. The remaining samples have had some microstructural changes during engine testing. 8YSZ-nano had undergone sintering and its nanostructured zones became fewer and almost gone after engine testing leading to less heat barrier in the top coat of the TBC. However, for 8YSZ-segmented cracks and gadolinium zirconia lower heat flux was measured due to the appearance of horizontal cracks. These cracks are believed to act as internal barriers as they are orientated perpendicular to the heat flow. During long-time (5 hour) engine tests the 8YSZ-standard exhibited the same phenomena: a decrease in heat flux due to propagation of horizontal cracks. One-dimensional heat flux was not achieved and the main reason for that was caused by heating and cooling of the shafts outer surface. However, the dummy-valve system has proven to be a quick, easy and stable to perform tests with a Single-Cylinder engine. Both water-cooling and long-time engine tests were conducted with minor issues. The dummy-valve has been further developed for future tests. Changes to the valve shaft are the most remarkable: smaller diameter to reduce heat transfer and smaller pockets to ensure better thermocouple positioning. Another issue was gas leakage from the combustion chamber through the copper ring and valve poppet joint. The copper ring will be designed with a 1 mm thick track to improve sealing, hence better attachment to the valve poppet.

Material thermal properties are highly sought after to better understand the performance of a material under particular conditions. As new materials are created, their physical properties will determine their performance for various applications. These properties have been estimated using many techniques including experimental testing, numerical modeling, and a combination of both. Existing methods can be time consuming, thus, a time-efficient and precise method to estimate these thermal properties was desired. A one-dimensional finite difference numerical model was developed to replicate the heat transfer through an experimental apparatus. A combination of this numerical model and the Continuous Genetic Algorithm optimization technique was used to estimate material thermal properties of fibrous insulation from test data. The focus of this work was to predict these material thermal properties for an Alumina Paper that is commonly used in aerospace applications. The background, methodology, and results are discussed.

Presented work deals with the study progressive heat-reflecting foil thermal insulating materials and defines their thermal insulation properties. The work describes a transport mechanism of thermal energy in the structure of heat-reflecting materials, their physical properties, especially heat resistance, compared to the conventional thermal insulating materials available on Czech market. The main applications ways and installation methods of these materials (especially in low-energy and passive buildings) are also shown. The practical part is focused on asembling the measuring device HOT BOX in accordance with the valid standards, to determine the heat resistance of heat-reflecting materials. In next step the measurement of reflection of aluminum foils (an integral part of the structural arrangement heat-reflecting foil insulations) was performed.

Le caractère fortement hydrophile des isolants thermiques bio-sourcés, a montré que les modèles classiques de transfert thermique ne sont pas suffisamment adaptés pour leur caractérisation thermique. Ce travail de thèse vise à répondre à cette problématique par des approches expérimentale et théorique des transferts couplés chaleur-humidité. Dans l’approche expérimentale, un isolant thermique en feutre de fibres de lin (FFL) a été développé puis caractérisé, dans différents états hygrométriques, au moyen d’un dispositif Plan Chaud asymétrique. Des isothermes d’adsorption de l’humidité corrélés aux modèles théoriques GAB, GDW et Park permettent une caractérisation hydrique de cet isolant. Dans l’approche théorique, un modèle physique, de transfert couplé chaleur-humidité au sein de l’isolant FFL humide, est proposé. Il est résolu numériquement, en configuration 3D transitoire, par la méthode de éléments finis sous COMSOL Multiphysics et par la méthode des différences finies, en configuration 1D transitoire, sous MATLAB. La méthode de Levenberg-Marquardt couplée avec le modèle direct 1D transitoire et les températures mesurées a permis d’estimer la conductivité thermique apparente de l'échantillon étudié avec une erreur relative inférieure à 6% par rapport aux mesures expérimentales, validant ainsi les modèles théoriques
The conventional heat transfer models are not sufficiently suitable for thermal characterization of bio-sourced thermal insulating materials due to their strongly hydrophilic nature. The proposed work in this PhD thesis aims to answer this problem with experimental and theoretical approaches of coupled heat-moisture transfers. In the experimental approach, a thermal insulating material based on Flax Fiber Felt (FFF) is developed and then characterized at different hygrometric conditions with an asymmetric hot plate device. The humidity diffusion characterization of the samples is done using the GAB, GDW and Park theoretical moisture adsorption isotherm models. In the theoretical approach, a physical model of heat and mass transfer is proposed. It is solved numerically, in transient 3D configuration, by the finite element method under COMSOL Multiphysics and, in transient 1D configuration, by the finite difference method under MATLAB. The Levenberg-Marquardt method coupled with the 1D transient direct model and the measured temperatures made it possible to estimate the apparent thermal conductivity of the studied sample with a relative error of less than 6% compared to the experimental measurements, thus validating the theoretical models

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 74-76).
Buildings consume too much energy. For example, 16.6% of all the energy used in the United States goes towards just the heating and cooling of buildings. Many governments, organizations, and companies are setting very ambitious goals to reduce their energy use over the next few years. Because the time periods for these goals are much less than the average lifetime of a building, existing buildings will need to be retrofitted. There are two different types of retrofitting: shallow and deep. Shallow retrofits involve the quickest and least expensive improvements often including reducing infiltration around windows, under doors, etc and blowing more insulation into the attic. Deep retrofits are those that involve costly renovation and typically include adding insulation to the walls and replacing windows. A new, easily installable, inexpensive, and thin insulation would move insulating the walls from the deep retrofit category to the shallow retrofit category and thus would revolutionize the process of retrofitting homes to make them more energy efficient. This thesis provides an overview of a concept for a new, easily installable, inexpensive, thin aerogel-based insulation and goes into detail on how the thermal properties of the aerogel were measured and validated. The transient hot-wire method for measuring the thermal conductivity of very low thermal conductivity silica aerogel (1 0mW/m K at 1 atm) along with a correction for end effects was validated with the NIST (National Institute of Standards and Technology) Standard Reference Material 1459, fumed silica board to within 1 mW/mK. Despite the translucence of the aerogel at certain wavelengths, radiation is not an issue through the aerogel during the hot-wire test but may be an issue in actual use as an insulation. The monolithic aerogel thermal conductivity drops significantly with slightly reduced pressure (3.2 mW/m K at 0.1atm). For the final composite insulation, the new silica aerogel formula is a great choice and it is recommended to reduce the pressure around the aerogel to 1 / 1 0 th. In the future, a prototype of an insulation panel combining a 3-D truss structure, monolithic or granular silica aerogel, and reduced pressure will be constructed and tested.
by Ellann Cohen.
S.M.

Multilayer insulation (MLI) has been shown to be the best performing cryogenic insulation system at high vacuum (less than 10[super]-3 torr), and is widely used on spaceflight vehicles. Over the past 50 years, many numerous investigations of MLI have yielded a general understanding of the many variables associated with MLI. MLI has been shown to be a function of variables such as warm boundary temperature, the number of reflector layers, and the spacer material in between reflectors, the interstitial gas pressure and the interstitial gas. Because conduction between reflectors increases with the thickness of the spacer material, and yet the radiation heat transfer is inversely proportional to the number of layers, it stands to reason that the thermal performance of MLI is a function of the number of layers per thickness, or layer density. Empirical equations that were derived based on some of the early tests showed that the conduction term was proportional to the layer density to a powe
ID: 029050581; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.A.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 79-85).
M.S.A.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Aerospace Engineering

This thesis is concerned with developing porous materials from tyre shred residue and polyurethane binder for acoustic absorption and thermal insulation applications. The resultant materials contains a high proportion of open, interconnected cells that are able to absorb incident sound waves through viscous friction, inertia effects and thermal energy exchanges. The materials developed are also able to insulate against heat by suppressing the convection of heat and reduced conductivity of the fluid locked in the large proportion of close-cell pores. The acoustic absorption performance of a porous media is controlled by the number of open cells and pore size distribution. Therefore, this work also investigates the use of catalysts and surfactants to modify the pore structure and studies the influence of the various components in the chemical formulations used to produce these porous materials. An optimum type and amounts of catalyst are selected to obtain a high chemical conversion and a short expanding time for the bubble growth phase. The surfactant is used to reduce the surface tension and achieve a homogenous mixing between the solid particulates tyre shred residue, the water, the catalyst and the binder. It is found that all of the components significantly affect the resultant materials structure and its morphology. The results show that the catalyst has a particularly strong effect on the pore structure and the ensuing thermal and acoustical properties. In this research, the properties of the porous materials developed are characterized using standard experimental techniques and the acoustic and thermal insulation performance underpinned using theoretical models. The important observation from this research is that a new class of recycled materials with pore stratification has been developed. It is shown that the pore stratification can have a positive effect on the acoustic absorption in a broadband frequency range. The control of reaction time in the foaming process is a key function that leads to a gradual change in the pore size distribution, porosity, flow resistivity and tortuosity which vary as a function of sample depth. It is shown that the Pade approximation is a suitable model to study the acoustic behaviour of these materials. A good agreement between the measured data and the model was attained.

Thesis: S.M. in Building Technology, Massachusetts Institute of Technology, Department of Architecture, 2013.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 65-67).
Based on mounting evidence in support of anthropogenic global climate change, there is an urgency for developments in high-performance building techniques and technologies. New construction projects provide substantial opportunities for energy efficiency measures, but they represent only a small portion of the building stock. Conversely, while existing buildings are plentiful, they typically have a much narrower range of feasible energy efficiency options. Therefore, there will continue to be a need for the development of new and improved energy efficiency measures for new building construction and even more so for deep retrofits of existing buildings. This thesis provides an overview of the research performed into the on-going development at MIT of a high-performance panelized insulation system based on silica aerogel. Two test methods were used for measuring the thermal conductivity of the granules: the transient hot-wire technique and the guarded hot-plate system. Utilizing the hot-wire set-up, it was demonstrated that compressing a bed of granules will decrease the thermal conductivity of the system until a minimum point is reached around the monolithic density of the aerogel. For the Cabot granules, this was seen at 13 mW/m-K and about 150 kg/m3. The MIT granules showed equal performance to the Cabot granules at bed densities 20-30 kg/m3 lower. The hot-plate testing was able to experimentally evaluate previous analytical predictions regarding the conductivity impact of the internal panel truss and the under-prediction of radiant heat transfer in the hot-wire method. Hot-wire testing was also done in a vacuum chamber to quantify potential performance improvements at reduced air pressures. Since a vacuum would require the incorporation of a barrier film into the panel system, some analyses were done into the thermal bridging potential and gas diffusion requirements of such a film. Additionally, physical prototyping was done to explore how the film would be incorporated into the existing panel design. The aerogel-based insulation panel being developed at MIT continues to show promise, though there are still plenty of opportunities remaining in the development cycle.
by Adam Neugebauer.
S.M. in Building Technology

Vacuum insulation panels (VIPs) represent a high performance thermal insulation material solution offering an alternative to thick wall sections and large amounts of traditional insulation in modern buildings. Thermalperformance over time is one of the most important properties of VIPs to be addressed, and thus the ageing effectson the thermal properties have been explored in this work. Laboratory studies of ageing effects are conducted over a relatively limited time frame. To be able to effectivelyevaluate ageing effects on thermal conductivity, accelerated ageing experiments are necessary. As of today, nocomplete standardized methods for accelerated ageing of VIPs exist. By studying the theoretical relationshipsbetween VIP properties and external environmental exposures, various possible factors for accelerated ageing areproposed. The factors that are found theoretically to contribute most to ageing of VIPs are elevated temperature,moisture and pressure. By varying these factors it is assumed that a substantial accelerated ageing of VIPs can beachieved.Four different accelerated ageing experiments have been performed to study whether the theoretical relationshipmay be replicated in practice. To evaluate the thermal performance of VIPs, thermal conductivity measurementshave been applied.The different experiments gave a varying degree of ageing effects. Generally the changes in thermal performancewere small. Results indicated that the acceleration effect was within what could be expected from theoreticalrelationships, but any definite conclusion is difficult to draw due to the small changes. Some physical changes wereobserved on the VIPs, i.e. swelling and curving. This might be an effect of the severe conditions experienced by theVIPs during testing, and too much emphasis on these should be avoided.
Vakuumisolasjonspaneler (VIP) er en høyisolerende materialløsning som kan være et alternativ til tradisjonell bygningsisolasjon. På grunn av god isolasjonsevne kan man ved bruk av VIP redusere veggtykkelsen og fortsatt tilfredsstille energikravene som stilles til moderne bygninger. En av de viktigste egenskapene for VIP er evnen til å bevare høy termisk ytelse over tid. I den sammenheng har aldringseffekter for VIP blitt undersøkt. Siden laboratoriestudier av aldringseffekter gjøres i løpet av et relativt kort tidsrom, er akselerert aldring nødvendig for å få evaluert termiske egenskaper over tid. Det finnes pr. i dag ingen standardisert metode for akselerert aldring av VIP. Det finnes likevel flere studier av sammenheng mellom klimaforhold og VIP egenskaper. Spesielt er gass og fuktdiffusjon inn i panelet behandlet grundig i litteraturen. Basert på dette er det foreslått flere mulige faktorer for aldring av VIP. De faktorene som er funnet å bidra mest til aldring av VIP er temperatur, fuktinnhold i lufta og utvendig lufttrykk. Ved å variere disse faktorene er fire forskjellige aldringsforsøk beskrevet og gjennomført.Konduktivitetsmålinger er blitt brukt som et mål på de termiske egenskapene til de testede VIPene. De forskjellige forsøkene viste forskjellig grad av aldringseffekt. Generelt var endringen i konduktivitetsverdier liten. Resultatene indikerer at akselerasjonseffekten var innenfor hva som kan forutsies fra de teoretiske sammenhengene. Likevel er det vanskelig å trekke noen definitive konklusjoner, både siden endringen var så liten, og fordi få paneler ble brukt i forsøkene. Noen fysiske endringer ble observert under forsøkene. Blant annet este et av panelene noe ut, mens et annet bøyde seg permanent. Man burde likevel ikke legge for mye vekt på disse effektene, siden de kan skyldes de relativt ekstreme testforholdene.

Buildings consume more than 30 percent of the primary energy worldwide with 65 percent of this attributed to heating ventilation and cooling. To help address this, stratified concrete panels (SCP) have been developed to provide insulation without compromising the thermal mass of concrete. SCP is created by vibrating a single concrete mix containing heavy and lightweight aggregates. Vibration causes the heavy aggregates drop to the bottom so that two distinct strata are formed; an internal structural/heavyweight layer providing thermal mass and an external lightweight layer for insulation. SCP incorporates waste products, for both financial and environmental gains, from which technical benefits also result. Stratified concrete panels have been made and tested during past research projects with results suggesting that SCP could be a competitive product in the residential construction industry, an area in which precast concrete systems have not been favoured in New Zealand. Consideration has been given to the specific rheological requirements of the concrete mix design and the hardened properties of the finished panels. This research considers the commercial viability of SCP using an industrial setting. For practicality of the setting, some materials were altered from past laboratory work to materials that are more easily sourced and better understood but with similar properties as those used previously. Several panels were cast at Stahlton precast yard in an effort to optimise the production process. Consistent results were not achieved and a range of stratification levels were produced. This showed that some capital investment is required to commercialise SCP to provide more energy for vibration such that sufficient stratification can be reliably attained. Two panels were then stood up in an exposed area with the exterior facing north to test for warping effects in a practical setting. No measurable warping occurred over this time which concurred with past work and long term readings that were taken of four year old panels. Structural, thermal and durability tests were carried out on panels with a range of stratification levels to assess the sensitivity of these properties to the level of stratification. From this it was found that the panels with better stratification had significantly better thermal properties than those with moderate to poor stratification. Generally the thermal targets for this project were not met with the total thermal resistance (R-values) not meeting current code requirements. In some cases structural properties were improved with better stratification as the structural layer was stronger through better consolidation. Delamination potential increased with stratification and with age. This requires further research to minimise this effect using fibres across the layer boundary. Porosity was increased in the structural layer in the poorly to moderately stratified panels as the structural layer was not consolidated enough due to lightweight aggregate contamination. As with any new innovation, market acceptance is largely governed by public perception. With appropriate marketing as a sustainable energy saving product, SCP has the potential to be competitive in the residential construction market with some capital investment.

Dans les turbines à gaz aéronautiques, les matériaux employés dans les parties les plus chaudes sont soumis à des environnements chimiques extrêmes, sous fortes pressions et températures. Ainsi, des systèmes de revêtement « barrière thermique, BT » sont appliqués sur les substrats en superalliage à base nickel. Ces systèmes multicouches (zircone stabilisée à l’yttrine (YSZ) /couche de liaison en MCrAl ou NiPtAl/substrat refroidi) permettent d’abaisser la température à la surface des pièces, conduisant à un comportement thermomécanique adéquat et à une diminution des vitesses d’oxydation/corrosion. Cependant, l’augmentation nécessaire de la température des gaz d’entrée de turbine (augmentation du rendement moteur) entraîne de nouveaux phénomènes de dégradation (CMAS) et une perte d’efficacité des revêtements BT actuels. Par ailleurs, l’évaluation de la durée de vie des revêtements BT s’avère cruciale pour déterminer celle des moteurs. Comprendre l’évolution du pouvoir isolant des revêtements BT en environnement agressif constitue donc un enjeu essentiel du point de vue scientifique et technologique. A partir des revêtements couramment employés (YSZ) déposés par projection plasma (PS) ou en phase vapeur (EB-PVD), la présente étude a visé à mieux comprendre l’effet de l’évolution des propriétés microstructurales et chimiques des revêtements sur leur pouvoir isolant, dans le but de développer des outils nécessaires à la mise au point des revêtements du futur. De plus, une partie des travaux menés a porté sur une solution alternative plus économique et écologique d’élaboration de revêtements BT, fondée sur un procédé par voie barbotine, permettant in fine d’obtenir une barrière constituée de microsphères creuses d’alumine. Ce travail a permis de montrer que l’évolution par frittage des phases céramiques en YSZ, les changements de phase cristalline, les réactions avec les CMAS et la croissance d’oxydes thermiques modifient la diffusivité thermique. En revanche, celle-ci évolue moins avec la température puisque les revêtements en alumine issus de barbotines se sont avérés plus stables et ce, notamment, lorsque leur élaboration a été réalisée sous atmosphères hybrides (mélanges Ar/air)
In aeronautical gas turbine engines, the metallic materials employed in the hottest sections are subject to very harsh chemical environments at high pressures and temperatures. Therefore, thermal barrier coating systems (TBCs) are applied onto nickel-based superalloy substrates. These multi-layered systems (ceramic yttria-stabilized zirconia (YSZ) / MCrAl or NiPtAl bond coats / cooled substrate) lower the temperature at the components surface, which ensures an adequate thermomechanical behaviour and reduces the oxidation/corrosion rates. However, the increase of the turbine inlet temperature (increased engine performance) brings about new degradation phenomena (e.g. CMAS) and loss of efficiency of the current TBCs. Therefore, understanding the evolution of the insulation ability of TBCs in such harsh environments is key from both the scientific and technological perspectives to estimate the lifetime of these coatings, hence that of the engines. Based on current plasma-sprayed (PS) and electron-beam physical vapour deposited (EB-PVD) YSZ coatings, this thesis seeks to provide a better comprehension on the relationships between the intrinsic properties of the current TBCs and their thermal insulation capacity as a basis for the development of future coatings. Also, this work studies an alternative solution to create a TBC made of hollow alumina microspheres by the slurry route. We will show that the sintering of the YSZ, the evolution of crystal phases, the reactions between YSZ and CMAS and the growth of thermal oxides alter the thermal diffusivity to different extents. In contrast, the evolution of the thermal diffusivity with temperature is less marked with the slurry alumina coatings, which appear more stable when hybrid Ar/air annealing atmospheres are employed upon their synthesis

The main objective of the thesis is to study the thermal properties of Si-based polymer derived ceramics (PDCs) at elevated temperatures and to classify the main factors affecting the thermal transport through these ceramics. The polymer derived ceramics with the chemistry Si- O-C-N were prepared starting from commercial polycarbosilane, polysiloxane, and polysilazane precursors. These precursors are cross-linked at room temperature to obtain the preceramic, followed by controlled pyrolysis (at different temperatures ranging from 1200 oC to 1800 oC in argon, nitrogen or carbon-di-oxide atmospheres), to get the final ceramic. The first part of the thesis discusses on development and studies of dense polymer derived thin disks having a basic chemistry, Si-C, Si-O- C, and, Si-C-N-O, developed via a casting technique followed by specific pyrolysis cycles. Having a thickness in the range of 100 μm- 300 μm, these ceramic disks were studied to be nanocrystalline/amorphous at least up to a temperature of 1400 oC and were found to have a significant amount of Cfree phase existing in them along with the intended chemistry. The high-temperature thermal properties were primarily investigated on ceramics prepared at a pyrolysis temperature of 1200 oC (ceramic still in nanocrystalline/amorphous glassy phase). The disks were found to have very low expansion coefficients (CTE) measured up to ~900 oC and the thermal diffusivity (k) and thermal conductivity (l) of these disks were also measured. An attempt to understand the influence of the different phases in a SiOC ceramic (mainly the Cfree phase, studied by enriching the carbon percentages using DVB) in determining the final thermal properties was also conducted. The influence of carbon enrichment on the mechanical properties of these disks is also studied as a sub-part of this work. The second part of the work deals with testing the possibility to use these ceramics for high-temperature insulation applications. ‘Reticulated’ ceramic foams of relatively same chemistries as that of the disks were prepared by a template replica approach, using polyurethane (PU) foams (more open-celled to more closed-celled types of PU foams were used in the study) as the template. Porous structures having densities ranging from as low as 0.02 g.cm-3 to 0.56 g.cm-3 and with a porosity ~ 80 % to ~99% were prepared and tested. The developed foams showed excellent thermal stability up to a temperature of 1400 oC and possessed very low thermal expansion. The thermal conductivity measured on them at RT gave values in the range 0.03 W.m-1.K-1- 0.25 W.m-1.K-1. A Gibson-Ashby modeling approach to explain the thermal conductivity of the porous ceramics was also attempted. The developed foams were also found to be mechanically rigid. In a nutshell, the thesis work studies the thermal properties of Si-O-C- N ceramics in detail and probes into the possibility to develop these class of Si-O-C-N ceramics into promising high-temperature insulation material.

This study involves the modification of a bio-based aggregate, hemp shiv, using functionalised silica-based coatings. This is the first time sol-gel technology is used in the treatment of hemp shiv to develop sustainable thermal insulation building materials with enhanced hygrothermal properties. Bio-based materials such as hemp shiv have a tendency to absorb large amounts of water due to their hydrophilic nature and highly porous structure. In contrast, the high porosity of hemp shiv provides excellent moisture buffering and thermal insulating properties. In this work, the hydrophilicity of the hemp shiv was reduced without compromising its moisture buffering ability. A detailed investigation into the physical and chemical properties, surface roughness, porosity and microstructure of hemp shiv is presented. Application of coatings on hemp shiv was found to alter the properties of hemp shiv. The focus of this work was to particularly enhance the water-resistance of hemp shiv without significantly altering the morphology and microstructure of hemp shiv. The coatings were formulated by the cohydrolysis and polycondensation of tetraethoxyorthosilicate (TEOS). The effect of methytriethoxysilane (MTES) and hexadecyltrimethoxysilane (HDTMS) as functionalising agents in the coating was evaluated. The impact of precursors and their concentration in the coating formulation showed varying results on the hydrophobicity and roughness of hemp shiv. Furthermore, the porosity of hemp shiv was affected by the number of coating layers thereby blocking the pores responsible for the moisture buffering behaviour of hemp shiv. The selected coating formulation was found to increase the hydrophobicity of hemp shiv providing water contact angles up to 118° and reducing the water absorption rates by 250% without showing a significant reduction in the moisture absorption capacity. Novel thermal insulation building composites were developed using the coated hemp shiv in both a silica and a starch-based matrix. The composites were characterised for their hygrothermal, physical and mechanical properties where it was found that the sol-gel coating reduced water absorption capacity without affecting the moisture buffering ability of the composites. The newly designed light weight high performance composites have potential as sustainable thermal insulators and can establish innovative concepts for global application.

Poly(vinyl chloride)(PVC) wire and cable insulation has poor thermal stability, causing the plasticizer to separate from the PVC chain and produce an oily residue, lowering the tensile elongation at break and thus increasing brittleness. We have added 4 wt.% of three different types of cross-linking agents and antioxidants, as well as mixtures of both, to improve the thermal stability of the plasticizer and tensile properties of PVC after thermal exposure. We performed tensile tests, tribological tests, profilometry, scanning electron microscopy(SEM) and water absorption determination before and after thermal exposure at 136 ℃ for 1 week. After adding the agents, elongation at break increased by 10 to 20 % while the wear rate and water absorption were lower than for the control sample. Less voids are seen in the SEM images after adding these two kinds of agents. The thermal resistance of the PVC cable insulation is best enhanced by combinations of cross-linking agents and antioxidants.

In-cylinder thermal barrier materials have been thoroughly investigated for their potential improvements in thermal efficiency in reciprocating internal combustion engines. These materials show improvements both directly in indicated work and indirectly through reduced demand on the cooling system. Many experimental and analytical sources have shown reductions in heat losses to the combustion chamber walls, but converting the additional thermal energy to indicated work has proven more difficult. Gains in indicated work over the expansion stroke could be made, but these were negated by increased compression work and reduced volumetric efficiency due to charge heating. Typically, the only improvements in brake work would come from the pumping loop in turbocharged engines, or from additional exhaust energy extraction through turbine-compounding devices. The concept of inter-cycle wall-temperature-swing holds promise to reap the benefits of insulation during combustion and expansion, while not suffering the penalties incurred with hotter walls during intake and compression. The combination of low volumetric heat capacity and low thermal conductivity would allow the combustion chamber surface temperature to quickly respond to the gas temperature throughout combustion. Surface temperatures are capable of rising in response to the spike in heat flux, thereby minimizing the temperature difference between the gas and wall early in the expansion stroke when the greatest conversion of thermal energy to mechanical work is possible. The combination of low heat capacity and thermal conductivity is essential in allowing this temperature increase during combustion, and in enabling the surface to cool during expansion and exhaust to avoid harmfully affecting engine volumetric efficiency during the intake stroke and minimizing compression work performed on the next stroke. In this thesis, thermal and thermodynamic models are constructed in an attempt to predict the effects of material properties in the walls, and to characterize the effects of heat transfer at different portions of the cycle on indicated work, volumetric efficiency, exhaust energy and gas temperatures of a reciprocating internal combustion engine. The expected impact on combustion knock in spark-ignited engines was also considered, as this combustion mode was the basis for the experimental engine testing performed. Conventional insulating materials were evaluated to benchmark the current state-of-the-art, and to gain experience in the analysis of materials with temperature-swing capability. Unfortunately, the effects of permeable porosity within the conventional coating on heat losses, fuel absorption and compression ratio tended to mask the effects of temperature swing. The individual impact of each of these loss mechanisms on engine performance was analyzed, and the experience helped to further refine the necessary traits of a successful temperature-swing material Finally, from the learnings of this analysis phase, a novel material was created and applied to the piston surface, intake valve faces, and exhaust valve faces. Engine data was taken with these coated components and compared to an un-coated baseline. While some of the test pieces physically survived the testing, analysis of the data suggests that they were not fully sealed and suffered from the same permeability losses that affected the conventional insulation. Further development is necessary to arrive at a robust, effective solution for minimizing heat transfer through wall temperature swing in reciprocating internal combustion engines. The success of temperature-swing thermal barrier materials requires very low thermal conductivity, heat capacity, and appropriate insulation thickness, as well as resilient sealing of any porous volume within the coating to avoid additional heat and fuel energy losses throughout the cycle.
Los materiales aislantes han sido investigados a fondo por sus posibles mejoras en la eficiencia térmica de los motores de combustión interna alternativos. Estas mejoras se ven reflejadas tanto directamente en el trabajo indicado como indirectamente a través de la reducción del sistema de refrigeración del propio motor. Diferentes estudios, tanto experimentales como analíticos, han mostrado la reducción en la transferencia de calor a través de las paredes de la cámara de combustión mediante la utilización de estos materiales. Sin embargo, demostrar la conversión de la energía térmica adicional en trabajo indicado ha resultado más difícil. En ciertos estudios se pudieron obtener mejoras en el trabajo indicado durante la carrera de expansión, pero éstas fueron reducidas debido a un menor rendimiento volumétrico debido al calentamiento de la carga durante el proceso de admisión y un mayor trabajo en la carrera de compresión. Típicamente, las únicas mejoras en el trabajo al freno provendrían de la reducción de pérdidas por bombeo en los motores turboalimentados, o de la extracción de la energía adicional de los gases de escape a través de turbinas. El concepto de los materiales con oscilación de la temperatura durante el ciclo motor intenta aprovechar los beneficios del aislamiento durante los procesos de combustión y expansión, mitigando las perdidas por el incremento de la temperatura de las paredes durante la admisión y la compresión. La combinación de baja capacidad calorífica y baja conductividad térmica permitiría que la temperatura de la superficie de la cámara de combustión respondiera rápidamente a la temperatura del gas durante el proceso de combustión. Las temperaturas de la superficie son capaces de aumentar en respuesta al pico de flujo de calor, minimizando así la diferencia de temperatura entre el gas y la pared en la carrera de expansión cuando es posible la mayor conversión de energía térmica en trabajo mecánico. La combinación de baja capacidad calorífica y conductividad térmica es también esencial para permitir este aumento de temperatura durante la combustión y para permitir que la superficie se enfríe durante la expansión y el escape para no perjudicar así el rendimiento volumétrico del motor durante la carrera de admisión y minimizar el trabajo de compresión realizado en el siguiente ciclo. En esta tesis se han desarrollado modelos térmicos y termodinámicos para predecir los efectos de las propiedades de los materiales en las paredes y caracterizar los efectos de la transferencia de calor en diferentes partes del ciclo sobre el trabajo indicado, el rendimiento volumétrico, la energía en los gases de escape y las temperaturas del gas para un motor de combustión interna alternativo. También se ha evaluado el impacto del uso de estos materiales en el knock en motores de combustión de encendido provocado, ya que los estudios experimentales de esta tesis se realizaron en un motor de estas características. Durante la investigación se evaluaron materiales aislantes convencionales para comprender el estado actual de esta técnica y para adquirir también experiencia en el análisis de materiales aislantes con oscilación de temperatura. Desafortunadamente, los efectos de la permeabilidad a través de la porosidad del material en los recubrimientos convencionales, la absorción de combustible y la relación de compresión tendieron a ocultar los efectos de la oscilación de la temperatura y la reducción de la transferencia de calor a través de las paredes. Así pues, se analizó el impacto individual de cada uno de estos mecanismos y su influencia en el rendimiento del motor para así definir un nuevo material con las características necesarias que mejorasen el aislante con de oscilación de temperatura. Finalmente, a partir de los estudios de esta fase de análisis, se creó un nuevo material y se aplicó a la superficie del pistón y a la supe
Els materials aïllants han estat investigats a fons per les seves possibles millores en l'eficiència tèrmica en el motors de combustió interna alternatius. Aquestes millores es veuen reflectides tant directament en el treball indicat com indirectament a través de la reducció del sistema de refrigeració del propi motor. Diferents estudis, tant experimentals com analítics, han mostrat la reducció en la transferència de calor a través de les parets de la cambra de combustió mitjançant la utilització d'aquests materials. No obstant això, demostrar la conversió de l'energia tèrmica addicional en treball indicat ha resultat més difícil. En certs estudis es van poder obtenir millores en el treball indicat durant la carrera d'expansió, però aquestes van ser reduïdes a causa d'un menor rendiment volumètric causat de l'escalfament de la càrrega durant el procés d'admissió i un major treball en la carrera de compressió. Típicament, les úniques millores en el treball al fre provindrien de la reducció de pèrdues per bombeig en els motors turbo alimentats, o de l'extracció addicional de l'energia dels gasos d'escapament a través de turbines. El concepte dels materials amb oscil·lació de la temperatura durant el cicle motor intenta aprofitar els beneficis de l'aïllament durant els processos de combustió i expansió, mitigant les perdudes per l'increment de la temperatura de les parets durant l'admissió i la compressió. La combinació de baixa capacitat calorífica i baixa conductivitat tèrmica permetria que la temperatura de la superfície de la cambra de combustió respongués ràpidament a la temperatura del gas durant el procés de combustió. Les temperatures de la superfície són capaços d'augmentar en resposta al flux de calor, minimitzant així la diferència de temperatura entre el gas i la paret en la carrera d'expansió quan és possible la major conversió d'energia tèrmica en treball mecànic. La combinació de baixa capacitat calorífica i conductivitat tèrmica és també essencial per permetre aquest augment de temperatura durant la combustió i el refredament de la superfície durant l'expansió i l'escapament per no perjudicar així el rendiment volumètric del motor durant la carrera d'admissió i minimitzar el treball de compressió realitzat en el següent cicle. En aquesta tesi s'han desenvolupat models tèrmics i termodinàmics per predir els efectes de les propietats dels materials en les parets i caracteritzar els efectes de la transferència de calor en diferents parts del cicle sobre el treball indicat, el rendiment volumètric, l'energia en els gasos d'escapament i les temperatures del gas per un motor de combustió interna alternatiu. També s'ha avaluat l'impacte d'aquests materials en el knock en motors de combustió d'encesa provocada, ja que les proves experimentals d'aquesta tesi es van realitzar en un motor d'aquestes característiques. Durant la investigació es van avaluar materials aïllants convencionals per comprendre l'estat actual d'aquesta tècnica i per adquirir també experiència en l'anàlisi de materials aïllants amb oscil·lació de temperatura. Desafortunadament, els efectes de la permeabilitat a través de la porositat del material en el recobriment convencional, l'absorció de combustible i la relació de compressió van tendir a ocultar els efectes de l'oscil·lació de la temperatura i la reducció de la transferència de calor a través de les parets. Així doncs, es va analitzar l'impacte individual de cada un d'aquests mecanismes i la seva influència en el rendiment del motor per així definir un nou material amb les característiques necessàries que milloressin el aïllant d'oscil·lació de temperatura. Finalment, a partir dels estudis d'aquesta fase d'anàlisi, es va crear un nou material i es va aplicar a la superfície del pistó i a la superfície interna de les vàlvules d'admissió i d'escapament. Les dades de motor es van prendre a
Andruskiewicz, PP. (2017). ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF TEMPERATURE-SWING INSULATION ON ENGINE PERFORMANCE [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90467
TESIS

The problem solved in this thesis is one of transient linear heat conduction in a two layer, three-dimensional slab subjected to an arbitrary heat flux on one surface, where each layer is thermally orthotropic. The sides and bottom of the slab are either insulated (Bi = 0) or held at a constant temperature (Bi = infinity). The Biot number of the top surface varies from zero to infinity. The solution is developed by decomposing the problem into a number of simpler problems, each of which is solved using eigenfunction expansions. In the vertical direction, the eigenvalue problem is solved using the Krawczyk algorithm, and an orthogonality relationship is found by Vodicka's method.

Thesis (MScEng)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: The focus of this thesis is on South Africa's first micro space satellite SUNSAT, and the thermal modelling thereof. Background theory with relevance to thermal management and control of satellite systems and subsystems is presented. The mission profile and subsystem makeup of SUNSAT is also briefly discussed, with emphasis placed on the physical structure, possible orbit paths, internal heat generation, and the environmental heating. The environmental heating on the satellite surfaces from the direct and reflected earth solar radiation, as well as the earth emitted infrared radiation, is determined from the developed computer program ORBIT-FLUX. This program was used in tandem with numerical programs (developed in house), as well as an outsourced program TAS (Thermal Analysis Systems) to model SUNSAT for two possible orbit paths. The resistance-capacitance formulation method was used to develop the numerical programs, which served initially to establish the validity ofTAS. The first approximated thermal model of SUNSA T's batteries was the 7 lumped-mass model that focused on the batteries since their overheating is the suspected reason for SUNSA T'S failure to complete its mission. A numerical program as well as a similar TAS model was developed, and the results showed correlation to within 3°C. A lumped-mass model of SUNSAT was also developed, both numerically and using TAS. The models were tested and the results showed that the temperatures of the models were sensitive to changes in internal heating as well as varying emissivity and absorptivity. The numerical and TAS lumped-mass model results did not correlate well, possibly due to the higher number of control volumes used in the TAS lumped-mass model. The TAS SUNSAT 2 model was developed as advancement on the lumped-mass model. The higher number of control volumes and the effect of adding solar panels gave a more realistic model of SUNSA T. The results did not show good correlation with actual SUNSA T temperature data possibly due to the fact that the solar panels were not mounted on the model body as they were on SUNSA T; but the TAS SUNSA T 2 model did set the platform for the more advanced TAS SUNSAT 3 model. This thermal model included the effects of the solar panel mountings, and had a higher number of control volumes, which gave a better physical representation of the SUNSAT subsystems. The model was tested for possible orbit paths of SUNSA T. The results showed excellent correlation to actual SUNSA T data. For the comparison of the TAS SUNSA T 3 model results with data from SUNSAT for July 1999 showed that the SUNSA T battery temperature was modelled to within 8°C. And for June 2000, this same comparison was to within 1°C. A thermal management and control case study was done on a simple system (which included a cubic box and an internal solid block with heat generation) to illustrate the effects of using various passive and active thermal control hardware to regulate temperatures. The results showed that internal surfaces painted black provide for maximum heat sharing, and lowest block temperatures. The block temperatures were found to be very sensitive to changes in the cube external optical surface properties. A slight increase in emissivity lowered the block temperature, while a slight increase in absorptivity increased the block temperature. Heat pipes were also found to lower the temperatures of the block and immediate subsystems by providing a path of low thermal resistance to the flow of heat from the block directly to the radiator. The effect of thermal insulation was also investigated. For the two materials (rubber and plastic) that were tested, it was noticed that although insulation material does give more thermal control and predictability over a subsystem by thermally isolating it from its environment, it can cause a subsystem that has heat generation to become too hot. Recommendations were made relating to future micro satellite thermal management and control with regard to; thermal modelling techniques, acquisition of tried software, positioning of temperature sensors for optimisation of thermal data, and the verification of optical surface properties by physical measurement.
AFRIKAANSE OPSOMMING: Hierdie tesis fokus op Suid-Afrika se eerste mikro ruimte satelliet, SUNSAT, en die termiese ontwikkeling daarvan. Agtergrond teorie met betrekking tot die termiese bestuur en kontrole van die satelliet-sisteme en subsisteme word aangebied. Die missie-profiel en die samestelling van die subsisteme word ook kortliks bespreek met die klem op die fisiese strukture, moontlike wentelbane, interne hitte-opwekking, en die omgewingsverhitting. Die omgewingsverhitting op die oppervlaktes van die satelliet, veroorsaak deur direkte en weerkaatste aardlson bestraling, sowel as deur infrarooi bestraling afkomstig van die aarde, word bepaal deur die ontwikkelde rekenaarprogram ORBIT-FLUX. Hierdie program word gebruik in tandem met numeriese programme (intern ontwikkel), so weI as 'n uitgekontrakteerde program TAS (Termiese Analiese Sisteme) om SUNS AT vir twee moontlike wentelbane te modelleer. Die weerstandskapasitansie formuleringsmetode is gebruik om die numeriese programme te ontwikkel. Hierdie programme is oorspronklik gebruik om die validiteit van TAS vas te stel. Die eerste benaderde termiese model van SUNSAT se batterye was die 7 gekonsentreerdemassa model wat gefokus het op die batterye aangesien daar vermoed is dat oorverhitting van die batterye die rede is waarom SUNSAT nie sy missie voltooi het nie. 'n Numeriese program so weI as 'n gelyksoortige TAS model is ontwikkel en die resultate korreleer tot binne 3°C. 'n Gekonsentreerde-massa model van SUNSA T is ook ontwikkel, numeries en met gebruik van TAS. Die modelle is getoets en die resultate toon dat die temperature van die modelle gevoelig is vir veranderinge in interne hitte sowel as vir wissellende uitstralingsvermoe en absorpsievermoe, Die numeriese- en die TAS gekonsentreerde-massa model resultate het nie goed met mekaar korrelleer nie, moontlik weens die hoe aantal kontrole volumes wat in die TAS gekonsentreerde-massa model gebruik is. Die TAS SUNSA T 2 model is 'n verdere ontwikkeling van die gekonsentreerde-massa model. Die hoer aantal kontrole volumes en die byvoeging van solarpanele het tot gevolg gehad dat hierdie 'n meer realistiese model van SUNSA T is. Die resultate het nie goed gekorrelleer met die temperatuurdata van die werklike SUNSAT nie, moontlik weens die feit dat die solarpanele nie op die bakwerk monteer is, soos in die geval van SUNSA T nie. Nietemin het het die TAS SUNSAT 2 model gelei tot die meer gevorderde TAS SUNSAT 3 model. Hierdie termiese model het die solarpaneel montuur ingesluit en het 'n hoer aantal kontrole volumes gehad, wat 'n beter fisiese weergawe van die SUNSAT subsisteme tot gevolg gehad het. Die model is getoets vir moontlike wentelbane van SUNSAT. Die resultate het 'n hoe korrellasie getoon met die data van die werklike SUNSAT. 'n Vergelyking van die TAS SUNSAT 3 model resultate met data van SUNSAT vir Julie 1999 wys dat die SUNSAT battery temperatuur dieselfde is tot binne 8°C. Vergelyk met die resultate vir Junie 2000 was dit binne 1°C. 'n Termiese bestuurs- en kontrolestudie is gedoen op 'n eenvoudige sisteem (insluitende 'n kubieke boks en 'n interne soliede blok met hitte opwekking) om die uitwerking van die gebruik van passiewe en aktiewe termiese kontrole hardeware wat temperature reguleer, te illustreer. Die resultate toon dat interne oppervlaktes wat swart geverf is, lei tot die maksimum hitte-deling, en die laagste bloktemperature. Daar is gevind dat bloktemperature baie gevoelig is vir veranderinge in die eienskappe van die kubus se eksterne optiese oppervlaktes. 'n Effense vermedering van uitstralingsvermoe verlaag die bloktemperatuur, terwyl 'n effense vermedering van absorpsievermoe die bloktemperatuur verhoog. Daar is ook gevind dat hittepype die temperatuur van die blok en onmiddelike subsisteme verlaag deur om 'n pad van lae termiese weerstand teen die vloei van hitte vanaf die blok, direk na die verkoeler te verskaf. Die uitwerking van termiese isolasie is ook ondersoek. In die geval van die twee materiale (rubber en plastiek) wat getoets is, is daar opgemerk dat, alhoewel isolasie materiaal meer termiese beheer oor die subsisteem en voorspelbaarheid tot gevolg gehad het deurdat die subsisteem termies van die omgewing isoleer is, kan dit veroorsaak dat die subsisteem te warm word. Aanbevelings is gemaak met betrekking tot toekomstige mikro satelliet bestuur en kontrole en wel in verband met die volgende: termiese modelleringstegnieke, die aanskaffing van getoetste sagteware, die plasing van temperatuut sensors vir die beste termiese data, en die verifikasie van die eienskappe van optiese oppervlaktes deur fisiese meting.

In previous studies, evidence of thermal wave behavior was found in heterogeneous materials. Thus, the overall goal of this study was to experimentally verify those results, and develop a parameter estimation scheme to estimate the thermal properties of various heterogeneous materials. Two types of experiments (Experiments 1 and 2) were conducted to verify the existence or non-existence of thermal wave behavior in heterogeneous materials. In Experiment 1 sand, ion exchanger, and sodium bicarbonate were used as test materials, while processed meat (bologna) was used in Experiment 2. The measured temperature profiles of the samples were compared with the parabolic and hyperbolic heat conduction model results. The values of thermal diffusivity and thermal conductivity were obtained using the Box-Kanemasu parameter estimation method which is based on the comparison between temperature measurements and the solutions of the theoretical model. Overall, no clear experimental evidence was found to justify the use of hyperbolic heat conduction models rather than parabolic for the materials tested. Further comprehensive experimentation using different heating rates is warranted to definitely identify the accurate type of heat conduction process associated with such materials, and to describe the physical mechanisms which produce wave-like heat conduction in heterogeneous materials.
Master of Science

A thin-film heat flux sensor was used in two transient conduction applications. First it was used in a device for simultaneously determining the thermal conductivity, κ, and the thermal diffusivity, α, of solid materials. The device was heated and then touched to metal samples at room temperature. The thermal properties were characterized based on the heat flux response of the gage, and the change in temperature of the metal surface at a specified distance away from the gage. A finite difference program was developed and used to model the system response. The effect of α was most evident by the time delay in the temperature response on the metal surface. The effect of κ was most evident in the heat flux response after the first few seconds of contact. In the second application, the gage was used in a probe that was cooled and then touched to biological materials. A numerical model was used to demonstrate the effect of tissue blood perfusion on the surface heat flux. Experimental tests were performed on live dogs. Both the numerical model and the experiments showed that increases in blood perfusion could be detected from the transient heat flux measurements. In both applications, this research forms the basis for instrumentation which will be able to measure κ, α, and blood perfusion.
Master of Science

Over two decades of extensive research on nanofluids have established them as a better cooling media than traditional fluids such as ethylene glycol (EG) and water. Recently, hybrid nanofluids have emerged as advanced thermal transport media with improved thermal and fluid properties relative to nanofluids. Experimentally, limited studies have been carried out on the thermo- and thermomagnetic convection heat transfer of nanofluids in cavities. However, there is a dearth of documentation on the thermo- and thermomagnetic convection of hybrid nanofluids in cavities in the public domain. In this study, the thermo-convection heat transfer (Qav) performance of three magnetic hybrid nanofluids (MHNFs) contained in a rectangular cavity was experimentally investigated with and without magnetic stimuli. Aqueous MWCNT-ferrofluid (AMF) [MWCNT-Fe2O3/deionised water (DIW)], aqueous Al2O3-ferrofluid (AAF) [Al2O3-Fe2O3/DIW] and bi-aqueous Al2O3-ferrofluid (BAAF) [Al2O3-Fe2O3/EG-DIW] were formulated for volume concentrations (𝜑) of 0.05 to 0.40 vol.%. Key nanofluid formulation parameters of dispersion fraction, sonication time and amplitude were optimised to improve stability of the MHNFs. Stability, characterisation and thermal properties (μ and κ at 20-40 °C) of the MHNFs were carried out using standard instruments. AMF, BAAF, AAF, DIW and EG-DIW were charged into a rectangular cavity subjected to differential heating of the opposite vertical walls under varying ΔT of 20 to 35 °C. Samples of AMF, BAAF and AAF with the highest heat transfer were thereafter charged into the cavity where the walls (bottom, top and side) were exposed to magnetic stimuli (4.89 – 21.95 mT). Stable MHNFs were formulated according to the optimised parameters as verified using an ultraviolet visible spectrophotometer and visible inspection techniques. The images of the transmission electron microscope for the MHNFs showed an even suspension of the nanoparticles into DIW and EG-DIW. An increase in temperature and 𝜑 was observed to enhance κeff of AMF, BAAF and AAF by 3.83% to 14.17%, 2.14% to 12.56% and 2.21% to 10.51% respectively. Temperature rise detracted μeff and 𝜑 enhanced it for AMF, BAAF and AAF with augmentation of 11.83% to 28.79%, 1.66% to 13.33% and 4.55% to 20.43% respectively. With the MHNFs, higher κeff and lower μeff were recorded in comparison with the monoparticle nanofluids of Fe2O3, which made the MHNFs beneficial for convective heat transfer studies. Additionally, models were developed for predicting the κeff and μeff of AMF, BAAF and AAF from the obtained experimental data. Without magnetic stimuli, the Qav of AMF, BAAF and AAF was enhanced at 𝜑 ≤ 0.20 vol.% and attenuation was the case beyond 𝜑 = 0.20 vol.%. Optimum Qav enhancements of 11.2%, 10.09% and 10.79% were achieved for AMF (at 0.05 vol.%), BAAF (at 0.05 vol.%) and AAF (at 0.10 vol.%) respectively. Models were proposed for estimating the Nuav of AMF, BAAF and AAF. The vertical imposition of the magnetic stimuli on the sidewall of the cavity led to maximum enhancements of Qav by 4.48%, 4.02% and 4.31% for the AMF, BAAF and AAF samples respectively. These values were recorded for magnetic stimuli of 21.95 mT for AMF and AAF, and 11.84 mT for AAF. The MHNFs were observed to yield higher Qav than monoparticle nanofluids of Fe2O3 with and without magnetic stimuli. Conclusively, the κeff, μeff and Qav of AMF, BAAF and AAF were found to be better than those of the monoparticle nanofluids of Fe2O3, which revealed the benefit of NP hybridisation for engineering application, especially in thermo- and thermomagnetic convection studies.
Thesis (PhD)--University of Pretoria, 2019.
Mechanical and Aeronautical Engineering
PhD
Unrestricted

With the advent of the new" high Tc superconductors as well as the increasing use of cryo-cooled conventional electronics, liquid nitrogen will be one of the preferred cryogens used to cool these materials. Consequently, a more thorough understanding of the heat transfer characteristics of liquid nitrogen is required. In these investigations the transient heating characteristics of liquid nitrogen to states of nucleate and film boiling under different liquid flow conditions are examined. Using a metal hot wire/plate technique, it is verified that there is a premature transition to film boiling in the transient case at power levels as much as 30 percent lower than under steady state nucleate boiling conditions. It is also shown that the premature transition can be reduced or eliminated depending on the flow velocity The second part of this research analyses the nucleation (boiling) process from a dynamical systems point of view. By observing how the boiling system variables evolve and fluctuate over time, it is hoped that physical insight and predictive information can be gained. One goal is to discover some indicator or signature in the data that anticipates the transition from nucleate boiling to film/boiling. Some of the important variables that make up the boiling system are the temperature of the heater and the heat flux through the heater surface into the liquid nitrogen. Results, gained by plotting the system’s trajectory in the heat flux-temperature plane, are that on average the system follows a counterclockwise trajectory. A physical model is constructed that explains this behavior. Also, as the applied heater power approaches levels at which the transition to film is known to occur, the area per unit time swept out in the heat flux-temperature plane is seen to reach a maximum. This could be of practical interest as the threshold to film boiling can be anticipated and possibly prevented.

An important criteria for optimising hydraulic systems is their size. Especially for tanks and heat exchangers oil parameters as heat capacity and thermal conductivity have a big influence on the size. Additionally, various oils differ in their parameters. Accordingly, the heat capacity and thermal conductivity need to be known. However, little research has been done. Data-sheets usually do not provide any thermal data. In this paper, the thermal conductivity is measured for varying types of hydraulic oils. The thermal conductivity is determined by a newly designed test-rig measuring the radial temperature difference in a tube at a quasi-static state using a constant heat flux. Thus, an overview over the thermal conductivity of different oils is achieved. Based on the results, a comparison between different types of fluid is made.

Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above. In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools. First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal diffusivity measurement system is used to measure the thermal diffusivitiy and heat capacity of bulk materials at high temperatures. With regards to the specific experiments, I examine the thermal conductivity and interface thermal conductance of two different types of nanocrystalline metallic alloys of nickel-iron and cobalt-phosphorus. I find that the thermal conductivity of the nanocrystalline alloys is reduced by a factor of approximately two from the thermal conductivity measured on metallic alloys with larger grain sizes. With subsequent molecular dynamics simulations performed by a collaborator, and my own electrical conductivity measurements, we determine that this strong reduction in thermal conductivity is the result of increased electron scattering at the grain boundaries, and that the phonon component of the thermal conductivity is largely unchanged by the grain boundaries. We also examine four complex bulk metallic glass (BMG) materials with compositions of Zr₅₀Cu₄₀Al₁₀, Cu_46.25Zr_44.25Al_7.5Er₂, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂, and Ti_41.5Zr_2.5Hf₅Cu_42.5Ni_7.5Si₁. From these measurements, I find that the addition of even a small percentage of heavy atoms (i.e. Hf and Er) into complex disordered BMG structures can create a significant reduction in the phonon thermal conductivity of these materials. This work also indicates that the addition of these heavy atoms does not disrupt electron transport to the degree with which thermal transport is reduced.
Ph. D.

Graphite foams have high bulk thermal conductivity and low density, making them an excellent material for heat exchanger applications. This research focused on the characterization of graphite foams under various processing conditions (different foaming pressures and particle additions), specifically studying the effects of porosity on the thermal properties. The characterization of the foams included measuring cell sizes, percent open porosity, number of cells per square inch, bulk density, Archimedes density, compression strength, thermal conductivity, thermal resistance, and permeability. Several relationships between the structure and properties were established, and a recommendation for the processing conditions of graphite foams for the use in heat exchangers was determined.
Master of Science

The simultaneous estimation of multi-mode heat transfer properties, conductive and radiative, is investigated for materials that include significant heat transfer by radiation. The focus is on insulative type materials with a relatively large optical thickness. Two basic models were developed for the combined conduction and radiation heat transfer: a diffusion solution and a more exact absorbing and isotropically scattering solution. Both solutions were written for one-dimensional heat transfer in gray, isotropically scattering materials. Different experimental setups were compared through a sensitivity analysis of the parameters to determine the best experiment for estimating the properties. An experiment was performed to collect real data to verify estimation procedures. The material used for the experiment was Styrofoam and the experiment consisted of a heat flux supplied by a thin film heater on one boundary and a constant temperature on the other boundary. The thermal capacitance of the heater proved to have an effect on the temperature measurements at the heated surface and had to be incorporated into the model. The estimation procedure involved the use of two methods, the modified Box Kanemasu algorithm and a genetic algorithm. Difficulties were encountered in simultaneously estimating all the properties due to correlation between the thermal conductivity and the radiation parameters, as well as some correlation between the heat capacity of the Styrofoam and the heat capacity of the heater. However, the genetic algorithm did provide fairly narrow and well-defined property ranges and confirmed that radiation transfer was significant in the Styrofoam.
Ph. D.

Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in numerous industrial sectors. Recently submicron and high aspect ratio particles (nanoparticles and nanotubes) were introduced into the heat transfer fluids to enhance the thermal conductivity of the resulting nanofluids. The aim of this project was to investigate the physico-chemical properties of nanofluids synthesized using submicron and high aspect ratio particles suspended in heat transfer fluids .

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Wilkinson, Angus; Committee Member: Barefield, E. Kent; Committee Member: Snyder, Robert; Committee Member: Soper, Jake; Committee Member: Zhang, Z. John. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for further building energy savings by reducing the HVAC loadings. During the phase change process between the solid and liquid states, heat is being absorbed or released by PCMs depending on the surrounding temperature. This research explores the benefits of a polyurethane (PU)-PCM composite insulation material through infiltrating paraffin wax as PCM into PU open cell foam. The new PU-PCM composite provides extra shielding from the exterior hot temperatures for buildings. Through this study, it was demonstrated that PU-PCM composite insulation could potentially help building energy savings through reducing the loads on the HVAC systems based on the building energy modeling using EnergyPlus. The Zero Energy Lab (ZØE) at the University of North Texas was modeled and studied in the EnergyPlus. It is a detached building with all wall facades exposed to the ambient. It was determined that the new PU-PCM insulation material could provide 14% total energy saving per year and reduce the electricity use due to cooling only by around 30%.

In the year 2006, the energy performance directive 2002/91/EG was passed by the European Union, according to this directive the Swedish building code was supplemented by a key measure of energy use intensity (EUI). The implemented EUI equals some energy use within a building divided by its floor area and must be calculated in new housing estate and shown when renting or selling housing property. In order to improve the EUI, energy efficiency refurbishments could be implemented. Building energy simulation tools enables a virtual view a building model and can estimate the energy use before implementing any refurbishments. They are a powerful resource when determine the impact of the refurbishment measure. In order to obtain a correct model which corresponds to the actual energy use, some adjustments of the model are often needed. This process refers to as calibration. The used EUI has been criticized and thus, the first objective in this work was to suggest an alternative key measure of a buildings performance. The results showed that the currently used EUI is disfavoring some districts in Sweden. New housing estate in the far north must take more refined actions in order to fulfill the regulation demand, given that the users are behaving identical regardless where the house is located. Further, the suggested measure is less sensitive to the users’ behavior than the presently used EUI. It also has a significance meaning in building design as it relating the building shape and thermal properties and stating that extreme building shapes must undergo a stricter thermal construction rather than buildings that are more compact. Thus, the suggested key measure also creates a communication link between architects and the consultant constructors. The second objective of this thesis has been to investigate a concept of calibration using the data normally provided by energy bills, i.e. some monthly aggregated data. A case study serves to answer this objective, by using the building energy simulation tool IDA ICE 4.7 and a building located in Umeå, Sweden. The findings showed that the used calibration approach yielded a model considered as calibrated in eleven of twelve months. Furthermore, the method gives a closer agreement to the actual heat demand rather than using templates and standardized values. The major explanation of the deviation was influence of the users, but also that the case study building burden with large heat losses by domestic hot water circulation and thus, more buildings should be subjected to this calibration approach.

Söderberg electrodes take part in the production of ferroalloys, copper, nickel, platinum, and calcium carbide. They are involved in a continuous and with low costs operation. The study of such electrodes is essential, since research and new findings will provide us with vital information regarding the operation of such furnaces leading to a more efficient production. Therefore, the study of Söderberg electrodes materials characteristics is of great importance. The current work refers to the thermal properties of Söderberg electrode paste by focusing on the thermal conductivity coefficient from room temperature up to 800 °C with the Transient Plane Source (TPS) method applied to an electrode paste material with softening point at 65°C. Another electrode paste with higher softening point at 90 °C and an already baked material are studied to some extent. The study gives significant results for the thermal conductivity coefficient for all the investigated cases. Results indicate variation of coefficients regarding the phase evolved during heating at different temperatures. In principle, thermal conductivity of the green paste with low softening point decreases until 400°C and increases after the baking point which is found in between 400-500°C. A few measurements for the green paste with higher softening point indicate the same trend. For the case of the fully baked electrode, thermal conductivity seems to keep an increasing trend according to temperature increase. On the two last mentioned materials, more experimental work will be conducted in future.
Söderberg-elektroder används till produktionen av ferrolegeringar, koppar, nickel, platina och kalciumkarbider. De är involverade i kontinuerliga och lågkostnadsoperationer. Studien av sådana elektroder är väsentlig eftersom forskning och nya fynd kommer att ge oss viktig information om driften av sådana ugnar vilket leder till en effektivare produktion. Därför är studien av Söderberg-elektrodens materialegenskaper av stor betydelse. Det nuvarande arbetet refererar till de termiska egenskaperna hos Söderberg-elektrodpastan genom att fokusera på den termiska konduktivitetskoefficienten från rumstemperatur upp till 800°C med den TPS-metoden (Transient Plane Source) tillämpad på ett elektrodpasta-material med en mjukningspunkt vid 65°C. En annan elektrodpasta med en högre mjukningspunkt vid 90°C samt ett redan bakat material studeras även till viss del. Studien ger signifikanta resultat för värmeledningsförmågan för alla undersökta fall. Resultaten indikerar på variationer av koefficienterna gällande fasen som utvecklas under uppvärmning vid olika temperaturer. I stort sett minskar värmeledningsförmågan hos den gröna pastan med låg mjukningspunkt upp till 400°C och ökar efter bakningspunkten som finns mellan 400-500°C. Några mätningar för den gröna pastan med en högre mjukningspunkt visar samma trend. När det gäller den helt bakade elektroden verkar värmdeledningsförmågan hålla en ökande trend beroende på temeperaturökningen. På de två sistnämnda materialen kommer mer experimentellt arbete att genomföras i framtiden.

This thesis presents two different works. The first part introduces a thermal multimeter which measures heat capacity, thermal conductivity and density. The instrument gives continuous measurement data within a temperature range. With some exceptions this also holds for the prototype of a thermal multimeter which is built and tested. The measuring method is constant heating of one side of a slab. The slab is insulated on all other sides. After some time there will be equilibrium where there is a constant temperature difference over the slab. The thermal conductivity can be calculated from this temperature difference. The heat capacity can be calculated from how fast the temperature rises. Measurements of the slab thickness give density as function of temperature.

The second part discusses a practical method for measuring the heat transfer coefficient (α). The method is based on shell freezing of clear jelly which has the same shape as the product of interest. Transparent jelly is transparent before it freezes and white when frozen. If the sample is removed from the freezer and cut through before it is completely frozen thefreezing front is distinct and the thickness of the frozen layer can be measured. By measuring time the jelly sample was in the freezer and thicknessof the frozen layer the heat transfer coefficient can be calculated by using Plank's equation. The method is suitable for measuring local α because it can be shown that tangential heat flow can be neglected when the frozen layer is thin.

Computer simulations, automated data acquisition and data processing are a considerable part of this thesis, even though it is not obvious from the results presented. There are more lines in the data code written to obtain the results presented here then the number of lines in this thesis. The size of selected simulation results and processed data from the measurements are 6.3 GB.

Attachments can be downloaded from http://www.ub.ntnu.no/dravh/Brennvall_attachment.zip (1,33 GB)

All substances above zero kelvin temperature emit fluctuating electromagnetic waves due to the random motions of charge carriers. Controlling the spectral and directional radiative properties of surfaces has wide applications in energy harvesting and thermal management. Artificial metamaterials have attracted much attention in the last decade due to their unprecedented optical and thermal properties beyond those existing in nature. This dissertation aims at tailoring radiative properties at infrared regime and enhancing the near-field radiative heat transfer by employing metamaterials. A comprehensive study is performed to investigate the extraordinary transmission, negative refraction, and tunable perfect absorption of infrared light. A polarizer is designed with an extremely high extinction ratio based on the extraordinary transmission through perforated metallic films. The extraordinary transmission of metallic gratings can be enhanced and tuned if a single layer of graphene is covered on top. Metallic metamaterials are not the unique candidate supporting exotic optical properties. Thin films of doped silicon nanowires can support negative refraction of infrared light due to the presence of hyperbolic dispersion. Long doped-silicon nanowires are found to exhibit broadband tunable perfect absorption. Besides the unique far-field properties, near-field radiative heat transfer can be mediated by metamaterials. Bringing objects with different temperatures close can enhance the radiative heat flux by orders of magnitude beyond the limit set by the Stefan-Boltzmann law. Metamaterials provide ways to make the energy transport more efficient. Very high radiative heat fluxes are shown based on carbon nanotubes, nanowires, and nanoholes using effective medium theory (EMT). The quantitative application condition of EMT is presented for metallodielectric metamaterials. Exact formulations including the scattering theory and Green’s function method are employed to investigate one- and two-dimensional gratings as well as metasurfaces when the period is not sufficiently small. New routes for enhancing near-field radiative energy transport are opened based on proposed hybridization of graphene plasmons with hyperbolic modes, hybridization of graphene plasmons with surface phonon modes, or hyperbolic graphene plasmons with open surface plasmon dispersion relation. Noncontact solid-state refrigeration is theoretically demonstrated to be feasible based on near-field thermal radiation. In addition, the investigation of near-field momentum exchange (Casimir force) between metamaterials is also conducted. Simultaneous enhancement of the near-field energy transport and suppress of the momentum exchange is theoretically achieved. A design based on repulsive Casimir force is proposed to achieve tunable stable levitation. The dissertation helps to understand the fundamental radiative energy transport and momentum exchange of metamaterials, and has significant impacts on practical applications such as design of nanoscale thermal and optical devices, local thermal management, thermal imaging beyond the diffraction limit, and thermophotovoltaic energy harvesting.

Today’s buildings are responsible for 40% of the world’s energy use and also a substantial share of the Global Warming Potential (GWP). In Sweden, about 21% of the energy use can be related to the heat losses through the climatic envelope. The “Million Program” (Swedish: Miljonprogrammet) is a common name for about one million housing units, erected between 1965 and 1974 and many of these buildings suffer from poor energy performance. An important aim of this study was to access the possibilities of using Vacuum Insulation Panels (VIPs) in buildings with emphasis on the use of VIPs for improving the thermal efficiency of the “Million Program” buildings. The VIPs have a thermal resistance of about 8-10 times better than conventional insulations and offer unique opportunities to reduce the thickness of the thermal insulation. This thesis is divided into three main subjects. The first subject aims to investigate new alternative VIP cores that may reduce the market price of VIPs. Three newly developed nanoporous silica were tested using different steady-state and transient methods. A new self-designed device, connected to a Transient Plane Source (TPS) instrument was used to determine the thermal conductivity of granular powders at different gaseous pressure combined with different mechanical loads. The conclusion was that the TPS technique is less suitable for conducting thermal conductivity measurements on low-density nanoporous silica powders. However, deviations in the results are minimal for densities above a limit at which the pure conduction becomes dominant compared to heat transfer by radiation. The second subject of this work was to propose a new and robust VIP mounting system, with minimized thermal bridges, for improving the thermal efficiency of the “Million Program” buildings. On the basis of the parametric analysis and dynamic simulations, a new VIP mounting system was proposed and evaluated through full scale measurements in a climatic chamber. The in situ measurements showed that the suggested new VIP technical solution, consisting of 20mm thick VIPs, can improve the thermal transmittance of the wall, up to a level of 56%. An improved thermal transmittance of the wall at centre-of-panel coordinate of 0.118 to 0.132 W m-2K-1 and a measured centre-of-panel thermal conductivity (λcentre-of-panel) of 7 mW m-1K-1 were reached. Furthermore, this thesis includes a new approach to measure the thermal bridge impacts due to the VIP joints and laminates, through conducting infrared thermography investigations. An effective thermal conductivity of 10.9 mW m-1K-1 was measured. The higher measured centre-of-panel and effective thermal conductivities than the published centre-of-panel thermal conductivity of 4.2 mW m-1K-1 from the VIP manufacturer, suggest that the real thermal performance of VIPs, when are mounted in construction, is comparatively worse than of the measured performance in the laboratory. An effective thermal conductivity of 10.9 mW m-1K-1 will, however, provide an excellent thermal performance to the construction. The third subject of this thesis aims to assess the environmental impacts of production and operation of VIP-insulated buildings, since there is a lack of life cycle analysis of whole buildings with vacuum panels. It was concluded that VIPs have a greater environmental impact than conventional insulation, in all categories except Ozone Depilation Potential. The VIPs have a measurable influence on the total Global Warming Potential and Primary Energy use of the buildings when both production and operation are taken into account. However, the environmental effect of using VIPs is positive when compared to the GWP of a standard building (a reduction of 6%) while the PE is increased by 20%. It was concluded that further promotion of VIPs will benefit from reduced energy use or alternative energy sources in the production of VIP cores while the use of alternative cores and recycling of VIP cores may also help reduce the environmental impact. Also, a sensitivity analysis of this study showed that the choice of VIPs has a significant effect on the environmental impacts, allowing for a reduction of the total PE of a building by 12% and the GWP can be reduced as much as 11% when considering both production and operation of 50 yes. Finally, it’s possible to conclude that the VIPs are very competitive alternative for insulating buildings from the Swedish “Million Program”. Nevertheless, further investigations require for minimizing the measurable environmental impacts that acquired in this LCA study for the VIP-insulated buildings.
Dagens byggnader ansvarar för omkring 40% av världens energianvändning och  står också för en väsentlig del av utsläppen av växthusgaser. I Sverige kan ca 21 % av energianvändningen relateras till förluster genom klimatskalet. Miljonprogrammet är ett namn för omkring en miljon bostäder som byggdes mellan 1965 och 1974, och många av dessa byggnader har en dålig energiprestanda efter dagens mått. Huvudsyftet med denna studie har varit att utforska möjligheterna att använda vakuumisoleringspaneler (VIP:ar) i byggnader med viss fokus på tillämpning i Miljonprogrammets byggnader. Med en värmeledningsförmåga som är ca 8 - 10 gånger bättre än för traditionell isolering erbjuder VIP:arna unika möjligheter till förbättrad termisk prestanda med minimal isolerings tjocklek. Denna avhandling hade tre huvudsyften. Det första var att undersöka nya alternativ för kärnmaterial som bland annat kan reducera kostnaden vid produktion av VIP:ar. Tre nyutvecklade nanoporösa kiselpulver har testats med olika stationära och transienta metoder. En inom projektet utvecklad testbädd som kan anslutas till TPS instrument (Transient Plane Source sensor), har använts för att mäta värmeledningsförmågan hos kärnmaterial för VIP:ar, vid varierande gastryck och olika mekaniska laster. Slutsatsen blev att transienta metoder är mindre lämpliga för utföra mätningar av värmeledningsförmåga för nanoporösa kiselpulver låg densitet. Avvikelsen i resultaten är dock minimal för densiteter ovan en gräns då värmeledningen genom fasta material blir dominerande jämfört med värmeöverföring genom strålning. Det andra syftet har varit att föreslå ett nytt monteringssystem för VIP:ar som kan användas för att förbättra energieffektiviteten i byggnader som är typiska för Miljonprogrammet. Genom parametrisk analys och dynamiska simuleringar har vi kommit fram till ett förslag på ett nytt monteringssystem för VIP:ar som har utvärderats genom fullskaleförsök i klimatkammare. Resultaten från fullskaleförsöken visar att den nya tekniska lösningen förbättrar väggens U-värde med upp till 56 %. En förbättrad värmegenomgångskoefficienten för väggen i mitten av en VIP blev mellan 0.118 till 0,132 W m-2K-1 och värmeledningstalet centre-av-panel 7 mW m-1K-1 uppnåddes. Detta arbete innehåller dessutom en ny metod för att mäta köldbryggor i anslutningar med hjälp av infraröd termografi. En effektiv värmeledningsförmåga för 10.9 mW m-1K-1 uppnåddes. Resultaten tyder även på att den verkliga termiska prestandan av VIP:ar i konstruktioner är något sämre än mätvärden för paneler i laboratorium. En effektiv värmeledningsförmåga av 10.9 mW m-1K-1 ger dock väggkonstruktionen en utmärkt termisk prestanda. Det tredje syftet har varit att bedöma miljöpåverkan av en VIP-isolerad byggnad, från produktion till drift, eftersom en livscykelanalys av hela byggnader som är isolerade med vakuumisoleringspaneler inte har gjorts tidigare. Slutsatsen var att VIP:ar har en större miljöpåverkan än traditionell isolering, i alla kategorier förutom ozonnedbrytande potential. VIP:ar har en mätbar påverkan på de totala utsläppen av växthusgaser och primärenergianvändningen i byggnader när både produktion och drift beaktas. Miljöpåverkan av de använda VIP:arna är dock positiv jämfört med GWP av en standardbyggnad (en minskning med 6 %) medan primärenergianvändningen ökade med 20 %. Slutsatsen var att ytterligare användning av VIP:ar gynnas av reducerad energiförbrukning och alternativa energikällor i produktionen av nanoporösa kiselpulver medan användningen av alternativa kärnmaterial och återvinning av VIP kärnor kan hjälpa till att minska miljöpåverkan. En känslighetsanalys visade att valet av VIP:ar har en betydande inverkan på miljöpåverkan, vilket ger möjlighet att reducera den totala användningen av primärenergi i en byggnad med 12 % och utsläppen av växthusgaser kan vara minska, så mycket som 11 % när det gäller både produktion och drift under 50 år. Avslutningsvis är det möjligt att dra slutsatsen att VIP:ar är ett mycket konkurrenskraftigt alternativ för att isolera byggnader som är typiska för Miljonprogrammet. Dock krävs ytterligare undersökningar för att minimera de mätbara miljöeffekter som förvärvats i denna LCA-studie för VIP-isolerade byggnader.

QC 20151109

Simulations of heat and moisture conditions in a retrofit wall construction with Vacuum Insulation Panels
Textural and thermal conductivity properties of a low density mesoporous silica material
A study of the thermal conductivity of granular silica materials for VIPs at different levels of gaseous pressure and external loads
Evaluation of the thermal conductivity of a new nanoporous silica material for VIPs – trends of thermal conductivity versus density
A comparative study of the environmental impact of Swedish residential buildings with vacuum insulation panels
ETICS with VIPs for improving buildings from the Swedish million unit program “Miljonprogrammet”

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.