Dissertations / Theses on the topic 'Particle Heat Transfer'
To see the other types of publications on this topic, follow the link: Particle Heat Transfer.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Particle Heat Transfer.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Siebert, Annegret Waltraud. "Heat transfer characteristics of mechanically mobilised particle beds." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323829.
Full text
2
Black, Jennifer May. "Particle motion and heat transfer in rotary drums." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/11987.
Full text
3
Kelly, Barry P. "Liquid-particle heat transfer in two phase flow systems." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286853.
Full text
4
Lints, Michael C. "Particle-to-wall heat transfer in circulating fluidized beds." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/13065.
Full text
5
Balasubramaniam, V. M. "Liquid-to-particle convective heat transfer in aseptic processing systems." Connect to resource, 1993. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1145452388.
Full text
6
Sistern, M. I. "An investigation into fluid to particle heat transfer and particle mixing in air and water fluidised beds." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381700.
Full text
7
Malhotra, Karun. "Particle flow and contact heat transfer characeristics of stirred granular beds." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74233.
Full textAbstract:
Particle flow features and wall-to-bed contact heat transfer characteristics of beds of granular solids stirred by flat blades (paddle-type) in horizontal cylindrical troughs are presented and discussed. Variables examined include: bed-to-blade height ratio (2-10), agitator speed (0-60 rev/min), wall-to-blade clearance (2.3-80 mm), vessel diameter (250 and 500 mm), solids flowability (0.07-0.25), air flow rate (0-0.5 m/s), particle moisture content (0-0.85 kg water/kg dry particles), particle surface stickiness (0-1.3 $ times$ 10$ sp{-3}$ kg glycerine/kg dry particles) and blade configuration (perforated and non-perforated). Glass beads, rice, millet and linseed were used as model particles.Overall mixing maps showing regimes of good and poor solids mixing are presented. Granular solids flowability was found to influence particle flow characteristics substantially within the bulk as well as the wall-to-blade clearance region of the bed. Bulk solids flowability in stirred vessels was characterized by a novel procedure which incorporated the combined effects of particle shape, surface roughness, moisture/stickiness and deformability. The torque required to stir the particulate bed is influenced strongly by the solids flowability and blade configuration.
A physical model for the wall-to-bed contact heat transfer coefficient based on particle renewal rates at the heated surface is proposed. The particle renewal rates and particle-surface contact times are evaluated exclusively from the particle flow information in the clearance region with no empirical parameters. The effects of particle shape and bed porosity at the contacting surface on the surface-to-particle thermal contact resistance were evaluated. Experimental results showing the effects of agitator speed, wall-to-blade clearance, solids flowability and air flow rate on the wall-to-bed average heat transfer rate are presented and discussed. The contact heat transfer model was found to predict the experimentally measured results reasonably well.
8
He, Long. "Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/91400.
Full textAbstract:
Gas-solid flow is fundamental to many industrial processes. Extensive experimental and numerical studies have been devoted to understand the interphase momentum and heat transfer in these systems. Most of the studies have focused on spherical particle shapes, however, in most natural and industrial processes, the particle shape is seldom spherical. In fact, particle shape is one of the important parameters that can have a significant impact on momentum, heat and mass transfer, which are fundamental to all processes. In this study particle-resolved simulations are performed to study momentum and heat transfer in flow through a fixed random assembly of ellipsoidal particles with sphericity of 0.887. The incompressible Navier-Stokes equations are solved using the Immersed Boundary Method (IBM). A Framework for generating particle assembly is developed using physics engine PhysX. High-order boundary conditions are developed for immersed boundary method to resolve the heat transfer in the vicinity of fluid/particle boundary with better accuracy. A complete framework using particle-resolved simulation study assembly of particles with any shape is developed. The drag force of spherical particles and ellipsoid particles are investigated. Available correlations are evaluated based on simulation results and recommendations are made regarding the best combinations. The heat transfer in assembly of ellipsoidal particle is investigated, and a correlation is proposed for the particle shape studied. The lift force, lateral force and torque of ellipsoid particles in assembly and their variations are quantitatively presented and it is shown that under certain conditions these forces and torques cannot be neglected as is done in the larger literature.Ph. D.
9
English, Justin. "HEAT TRANSFER CHARACTERISTICS IN WILDLAND FUELBEDS." UKnowledge, 2014. http://uknowledge.uky.edu/me_etds/52.
Full textAbstract:
The fundamental physics governing wildland fire spread are still largely misunderstood. This thesis was motivated by the need to better understand the role of radiative and convective heat transfer in the ignition and spread of wildland fires. The focus of this work incorporated the use of infrared thermographic imaging techniques to investigate fuel particle response from three different heating sources: convective dominated heating from an air torch, radiative dominated heating from a crib fire, and an advancing flame front in a laboratory wind tunnel test. The series of experiments demonstrated the uniqueness and valuable characteristics of infrared thermography to reveal the hidden nature of heat transfer and combustion aspects which are taking place in the condensed phase of wildland fuelbeds. In addition, infrared thermal image-based temperature history and ignition behavior of engineered cardboard fuel elements subjected to convective and radiative heating supported experimental findings that millimeter diameter pine needles cannot be ignited by radiation alone even under long duration fire generated radiant heating. Finally, fuel characterization using infrared thermography provided a better understanding of the condensed phase fuel pyrolysis and heat transfer mechanisms governing the response of wildland fuel particles to an advancing flame front.
10
Al-Rjoub, Marwan Faisal. "Enhanced Heat Transfer in Micro-Scale Heat Exchangers Using Nano-Particle Laden Electro-osmotic Flow (EOF)." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439305691.
Full text
11
Jia, Wenhan Jia. "Simulation of Heat Transfer with Gas-liquid Coexistence Using Dissipative Particle Dynammics." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471346931.
Full text
12
Leising, Guillaume M. "Radial heat transfer studies in low tube to particle diameter ratio fixed bed reactors." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050205-154724/.
Full text
13
Mitchell, William James. "Transport phenomena in viscous flow and particle motion in fluidized beds /." Title page, table of contents and abstract only, 1988. http://web4.library.adelaide.edu.au/theses/09ENS/09ensm682.pdf.
Full text
14
Zareifard, Mohammad Reza. "Evaluation of fluid-to-particle heat transfer coefficient under tube-flow conditions involving particle motion with relevance to aseptic processing." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ55397.pdf.
Full text
15
Noymer, Peter Daniel. "Heat transfer by particle convection at the wall of a circulating fluidized-bed." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10435.
Full text
16
Mort, P. E. "The deposition of sub-micrometer particles from hot turbulent gas to a cold rough surface." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385217.
Full text
17
Venkataraman, Manoj. "THE EFFECT OF COLLOIDAL STABILITY ON THE HEAT TRANSFER CHARACTERISTICS OF NANOSILICA DISPERSED FLUIDS." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3656.
Full textAbstract:
Addition of nano particles to cooling fluids has shown marked improvement in the heat transfer capabilities. Nanofluids, liquids that contain dispersed nanoparticles, are an emerging class of fluids that have great potential in many applications. There is a need to understand the fundamental behavior of nano dispersed particles with respect to their agglomeration characteristics and how it relates to the heat transfer capability. Such an understanding is important for the development and commercialization of nanofluids. In this work, the stability of nano particles was studied by measuring the zeta potential of colloidal particles, particle concentration and size. Two different sizes of silica nano particles, 10 nm and 20 nm are used in this investigation at 0.2 vol. % and 0.5 vol. % concentrations. The measurements were made in deionized (DI) water, buffer solutions at various pH, DI water plus HCl acid solution (acidic pH) and DI water plus NaOH solution (basic pH). The stability or instability of silica dispersions in these solutions was related to the zeta potential of colloidal particles and confirmed by particle sizing measurements and independently by TEM observations. Low zeta potentials resulted in agglomeration as expected and the measured particle size was greater. The heat transfer characteristics of stable or unstable silica dispersions using the above solutions were experimentally determined by measuring heat flux as a function of temperature differential between a nichrome wire and the surrounding fluid. These experiments allowed the determination of the critical heat flux (CHF), which was then related to the dispersion characteristics of the nanosilica in various fluids described above. The thickness of the diffuse layer on nano particles was computed and experimentally confirmed in selected conditions for which there was no agglomeration. As the thickness of the diffuse layer decreased due to the increase in salt content or the ionic content, the electrostatic force of repulsion cease to exist and Van der Waal's force of agglomeration prevailed causing the particles to agglomerate affecting the CHF. The 10nm size silica particle dispersions showed better heat transfer characteristics compared to 20nm dispersion. It was also observed that at low zeta potential values, where agglomeration prevailed in the dispersion, the silica nano particles had a tendency to deposit on the nickel chromium wire used in CHF experiments. The thickness of the deposition was measured and the results show that with a very high deposition, CHF is enhanced due to the porosity on the wire. The 10nm size silica particles show higher CHF compared to 20nm silica particles. In addition, for both 10nm and 20nm silica particles, 0.5 vol. % concentration yielded higher heat transfer compared to 0.2 vol. % concentration. It is believed that although CHF is significantly increased with nano silica containing fluids compared to pure fluids, formation of particle clusters in unstable slurries will lead to detrimental long time performance, compared to that with stable silica dispersions.M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
18
Amritkar, Amit Ravindra. "Parallel implementation and application of particle scale heat transfer in the Discrete Element Method." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/51192.
Full textAbstract:
Dense fluid-particulate systems are widely encountered in the pharmaceutical, energy, environmental and chemical processing industries. Prediction of the heat transfer characteristics of these systems is challenging. Use of a high fidelity Discrete Element Method (DEM) for particle scale simulations coupled to Computational Fluid Dynamics (CFD) requires large simulation times and limits application to small particulate systems. The overall goal of this research is to develop and implement parallelization techniques which can be applied to large systems with O(105- 106) particles to investigate particle scale heat transfer in rotary kiln and fluidized bed environments.
The strongly coupled CFD and DEM calculations are parallelized using the OpenMP paradigm which provides the flexibility needed for the multimodal parallelism encountered in fluid-particulate systems. The fluid calculation is parallelized using domain decomposition, whereas N-body decomposition is used for DEM. It is shown that OpenMP-CFD with the first touch policy, appropriate thread affinity and careful tuning scales as well as MPI up to 256 processors on a shared memory SGI Altix. To implement DEM in the OpenMP framework, ghost particle transfers between grid blocks, which consume a substantial amount of time in DEM, are eliminated by a suitable global mapping of the multi-block data structure. The global mapping together with enforcing perfect particle load balance across OpenMP threads results in computational times between 2-5 times faster than an equivalent MPI implementation.
Heat transfer studies are conducted in a rotary kiln as well as in a fluidized bed equipped with a single horizontal tube heat exchanger. Two cases, one with mono-disperse 2 mm particles rotating at 20 RPM and another with a poly-disperse distribution ranging from 1-2.8 mm and rotating at 1 RPM are investigated. It is shown that heat transfer to the mono-disperse 2 mm particles is dominated by convective heat transfer from the thermal boundary layer that forms on the heated surface of the kiln. In the second case, during the first 24 seconds, the heat transfer to the particles is dominated by conduction to the larger particles that settle at the bottom of the kiln. The results compare reasonably well with experiments. In the fluidized bed, the highly energetic transitional flow and thermal field in the vicinity of the tube surface and the limits placed on the grid size by the volume-averaged nature of the governing equations result in gross under prediction of the heat transfer coefficient at the tube surface. It is shown that the inclusion of a subgrid stress model and the application of a LES wall function (WMLES) at the tube surface improves the prediction to within ± 20% of the experimental measurements.Ph. D.
19
Gomez, Ramirez David. "Heat Transfer and Flow Measurements in an Atmospheric Lean Pre-Mixed Combustor." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71812.
Full textAbstract:
Energy conservation, efficiency, and environmental responsibility are priorities for modern energy technologies. The ever increasing demands for lower pollutants and higher performance have driven the development of low-emission gas turbine engines, operating at lean equivalence ratios and at increasingly higher turbine inlet temperatures. This has placed new constraints on gas turbine combustor design, particularly in regards to the cooling technologies available for the combustor liner walls. To optimize combustor thermal management, and in turn optimize overall engine performance, detailed measurements of the flame side heat transfer are required. However, given the challenging environment at which gas turbine combustors operate, there are currently only limited studies that quantify flame side combustor heat transfer; in particular at reacting conditions.
The objective of the present work was to develop methodologies to measure heat transfer within a reacting gas turbine combustor. To accomplish this, an optically accessible research combustor system was designed and constructed at Virginia Tech, capable of operating at 650 K inlet temperature, maximum air mass flow rates of 1.3 kg/s, and flame temperatures over 1800 K. Flow and heat transfer measurements at non-reacting and reacting conditions were carried out for Reynolds numbers (Re) with respect to the combustor diameter ranging from ~11 500 to ~140 000 (depending on the condition). Particle Image Velocimetry (PIV) was used to measure the non-reacting flow field within the burner, leading to the identification of coherent structures in the flow that accounted for over 30% of the flow fluctuation kinetic energy along the swirling jet shear layers. The capability of infrared (IR) thermography to image surface temperatures through a fused silica (quartz) glass was demonstrated at non-reacting conditions. IR thermography was then used to measure the non-reacting steady state heat transfer along the combustor liner. A peak in heat transfer was identified at ~1 nozzle diameter downstream of the combustor dome plate. The peak Nusselt number along the liner was over 18 times higher than that predicted from fully developed turbulent pipe flow correlations, which have traditionally been used to estimate flame side combustor heat transfer.
For the reacting measurements, a novel time-dependent heat transfer methodology was developed that allowed for the investigation of transient heat loads, including those occurring during engine ignition and shutdown. The methodology was validated at non-reacting conditions, by comparing results from an experiment with changing flow temperature, to the results obtained at steady state. The difference between the time-dependent and the steady state measurements were between 3% and 17.3% for different mass flow conditions. The time-dependent methodology was applied to reacting conditions for combustor Reynolds numbers of ~12 000 and ~24 000. At an equivalence ratio of ~0.5 and a combustor Reynolds number of ~12 000, the peak heat load location in reaction was shifted downstream by 0.2 nozzle diameters compared to the non-reacting cases. At higher equivalence ratios, and more visibly at a Reynolds number of ~24 000, the heat transfer distribution along the combustor liner exhibited two peaks, upstream and downstream of the impingement location (X/DN=0.8-1.0 and X/DN=2.5). Reacting PIV was performed at Re=12 000 showing the presence of a strong corner recirculation, which could potentially convect reactants upstream of the impingement point, leading to the double peak structure observed.
The methodologies developed have provided insight into heat transfer within gas turbine combustors. The methods can be used to explore additional conditions and expand the dataset beyond what is presented, to fully characterize reacting combustor heat transfer.Ph. D.
20
Langrish, Timothy Alan Granville. "The mathematical modelling of cascading rotary dryers." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330063.
Full text
21
Nijemeisland, Michiel. "Influences of catalyst particle geometry on fixed bed reactor near-wall heat transfer using CFD." Digital WPI, 2003. https://digitalcommons.wpi.edu/etd-dissertations/445.
Full textAbstract:
Fixed bed reactors are an essential part of the chemical industry as they are used in a wide variety of chemical processes. To better model these systems a more fundamental understanding of the processes taking place in a fixed bed is required. Fixed bed models are traditionally based on high tube-to particle diameter ratio (N) beds, where temperature and flow profile gradients are mild and can be averaged. Low-N beds are used in extremely exo- and endothermic processes on the tube side of tube and shell type reactors. In these beds, heat transfer is one of the most important aspects. The importance of accurate modeling of heat transfer and its dependence on accurate modeling of the flow features leads to the need for studying the phenomena in these low-N beds in detail. In this work a comparative study is made of the influence of spherical and cylindrical packing particle shapes, positions and orientations on the rates of heat transfer in the near-wall region in a steam reforming application. Computational Fluid Dynamics (CFD) is used as a tool for obtaining the detailed flow and temperature information in a low-N fixed bed. CFD simulation geometries of discrete particle packed beds are designed and methods for data extraction and analysis are developed. After conceptual and quantitative analysis of the simulation data it is found that few clear relations between the complex phenomena of flow and heat transfer can be easily identified. Investigated features are the orientations of the particle in the flow, and many design parameters, such as the number and size of longitudinal holes in the particle and external features on the particle. We find that many of the investigated features are related and their individual influences could not be isolated in this study. Some of the related features are, for example, the number of holes in the particle design and the particle orientation in the flow. Some general conclusions could be drawn. External features on the particles enhance the overall heat transfer properties by better mixing of the flow field. When holes are present in the cylindrical particle design, heat transfer effectiveness can be improved with fewer larger holes. After identifying the packing-related features influencing the near-wall heat transfer under steam reforming conditions, an attempt was made to incorporate the steam reforming reaction in the simulation. In the initial attempts the reaction was modeled as an energy flux at the catalyst particle surfaces. This approach was based on the abilities of the CFD code, but turned out not accurate enough. Elimination of the effects of local reactant depletion and the lack of solid energy conduction in the catalyst particles resulted in an unphysical temperature field. Several suggestions, based on the results of this study, are made for additional aspects of particle design to be investigated. Additionally, suggestions are made on how to incorporate the modeling of a reaction in fixed bed heat transfer simulations.
22
Ebert, Todd Alan. "An experimental investigation of particle and gas convection heat transfer in a circulating fluidized bed." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13833.
Full text
23
Hubble, David Owen. "An experimental investigation of the mechanism of heat transfer augmentation by coherent structures." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26784.
Full textAbstract:
The mechanism by which convective heat transfer is augmented by freestream turbulence in the stagnation region was studied experimentally. Previous work has suggested that the primary mechanism for the observed augmentation is the amplification of vorticity into strong vortices which dominate the flow field near the surface. Therefore, two separate experimental investigations were performed to further study this phenomenon. In the first, the spatiotemporal convection from a heated surface was measured during the normal collision of a vortex ring. The convection was observed to increase dramatically in areas where vortices forced outer fluid through the natural convection boundary layer to the surface. Regions where fluid was swept along the surface experienced much smaller increases in convection. These observations led to the development of a mechanistic model which predicted the heat transfer based on the amount of time that fluid remained within the thermal boundary layer prior to reaching the surface. In subsequent testing, the model was able to accurately predict the time-resolved convection based solely on the transient properties of the vortex present. In the second investigation, the model was applied to the vortices which form in a stagnating turbulent flow. Three turbulence conditions were tested which changed the properties of the vortices produced. Again, the model was successful in predicting the time-resolved convection over much of the experimental measurement time.
The work of designing and calibrating the heat flux sensor used is also reported. A new sensor was developed specifically for the convection research performed herein as no existing sensor possessed the required spatiotemporal resolution and underwater capabilities. Utilizing spot-welded foils of thermoelectric alloys resulted in a very robust and sensitive sensing array which was thoroughly analyzed and calibrated. In the final section, the hybrid heat flux (HHF) method is presented which significantly increases the performance of existing heat flux sensors. It is shown (both numerically and experimentally) that by combining the spatial and temporal temperature measurements from a standard sensor, the time response increases by up to a factor of 28. Also, this method causes the sensor to be insensitive to the material to which it is mounted.Ph. D.
24
Alhamdan, Abdullah M. "Particle Residence Time Distribution and Bulk Heat Transfer Coefficients of Two-Phase Flow in Scraped Surface Heat Exchanger and Holding Tubes /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487929230742153.
Full text
25
Laurent, Bruno Francois Claude. "Powder flow patterns in a horizontal mixer using positron emission particle tracking." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343274.
Full text
26
Takeyama, Mao. "Convective heat transfer of saturation nucleate boiling induced by single and multi-bubble dynamics." Kyoto University, 2021. http://hdl.handle.net/2433/261621.
Full text
27
Gifford, Andrew R. "The Physical Mechanism of Heat Transfer Augmentation in Stagnating Flows Subject to Freestream Turbulence and Related Studies." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26097.
Full textAbstract:
The mechanism of heat transfer augmentation due to freestream turbulence in
classic Hiemenz stagnation flow was studied experimentally for the first time using time-resolved digital particle image velocimetry (TRDPIV) and a new thin film
heat flux sensor called the Heat Flux Array (HFA). Unique measurements of simultaneous, time-resolved velocity and surface heat flux data were obtained along the
stagnation line on a simple, rectangular flat plate model mounted in a water tunnel
facility. Identification and tracking of coherent structures in the stagnation region
lends support to the theory that coherent structures experience stretching and amplification of vorticity by the mean flow strain rate upon approaching the stagnation
surface. The resulting flow field in the near-wall region is comprised primarily of high
strength, counter-rotating vortex pairs with decreased integral length scale relative to
the imposed freestream turbulence. It is hypothesized that the primary mechanism
of heat transfer augmentation is the movement of cooler freestream fluid into the
heated near-wall region by these coherent structures. Furthermore, the level of heat
transfer augmentation is dictated by the integral length scale, circulation strength,
and core-to-surface distance of the coherent structures. To test this hypothesis, these
properties were incorporated into a mechanistic model for predicting the transient,
turbulent heat transfer coefficient. The model was successful in predicting the shape
and magnitude of the measured heat transfer coe±cient over much of the experimental
measurement time.
In a separate yet related set of studies, heat flux sensors and calibration methods
were examined. The High Temperature Heat Flux Sensor (HTHFS) was designed
and developed to become one of the most durable heat flux sensors ever devised for
long duration use in high temperature, extreme environments. Extensive calibrations
in both conduction and convection were performed to validate the performance of the
sensor near room temperature. The measured sensitivities in conduction and convection were both very close to the predicted sensitivity using a thermal resistance model
of the HTHFS. The sensor performance was unaffected by repeated thermal cycling
using kiln and torch firing. Finally, the performance of Schmidt-Boelter heat flux
sensors were examined in both shear and stagnation flow using two custom designed
convection calibration facilities. Calibration results were evaluated using an analytical sensitivity model based on an overall sensor thermal resistance from the sensor
to the heat sink or mounting surface. In the case of convection the model included
a term for surface temperature differences along the boundary layer. In stagnation
flow the apparent sensitivity of the Schmidt-Boelter sensors decreased non-linearly
with increasing heat transfer coefficient. Estimations of the sensor's internal thermal
resistance were obtained by fitting the model to the stagnation calibration data. This
resistance was then used with the model to evaluate the effects of non-uniform surface
temperature on the shear flow sensitivity. A more pronounced non-linear sensitivity
dependence on heat transfer coefficient was observed. In both cases the main result
is that convection sensitivity varies a great deal from standard radiation calibrations.Ph. D.
28
Park, Suhyeon. "Experimental Investigation of Flow and Wall Heat Transfer in an Optical Combustor for Reacting Swirl Flows." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82349.
Full textAbstract:
The study of flow fields and heat transfer characteristics inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers because of the harsh environment at high temperatures. Design improvements of gas turbine combustors for higher efficiency, reduced pollutant emissions, safety and durability require better understanding of combustion in swirl flows and thermal energy transfer from the turbulent reacting flows to solid surfaces. Therefore, accurate measurement and prediction of the flows and heat loads are indispensable.
This dissertation presents flow details and wall heat flux measurements for reacting flow conditions in a model gas turbine combustor. The objective is to experimentally investigate the effects of combustor operating conditions on the reacting swirl flows and heat transfer on the liner wall. The results shows the behavior of swirling flows inside a combustor generated by an industrial lean pre-mixed, axial swirl fuel nozzle and associated heat loads.
Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Experiments were conducted with various air flow rates, equivalence ratios, pilot fuel split ratios, and inlet air temperatures. Methane and propane were used as fuel. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a main part of the investigation. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows. Comparison between reacting and non-reacting flows yielded very striking differences. Self-similarity of the flow were observed at different operating conditions.
Flow temperature measurements with a thermocouple scanning probe setup revealed the temperature distribution and flow structure. Features of premixed swirl flame were observed in the measurement. Non-uniformity of flow temperature near liner wall was observed ranging from 1000 K to 1400 K. The results provide insights on the driving mechanism of convection heat transfer.
As a novel non-intrusive measurement technique for reacting flows, flame infrared radiation was measured with a thermographic camera. Features of the flame and swirl flow were observed from reconstructed map of measured IR radiation projection using Abel transformation. Flow structures in the infrared measurement agreed with observations of flame luminosity images and the temperature map. The effect of equivalence ratio on the IR radiation was observed.
Liner wall temperature and heat transfer were measured with infrared thermographic camera. The combustor was operated under reacting condition to test realistic heat load inside the industrial combustors. Using quartz glass liner and KG2 filter glass, the IR camera could measure inner wall surface temperature through the glass at high temperature. Time resolved axial distributions of inner/outer wall temperature were obtained, and hot side heat flux distribution was also calculated from time accurate solution of finite difference method.
The information about flows and wall heat transfer found in this work are beneficial for numerical simulations for optimized combustor cooling design. Measurement data of flow temperature, velocity field, infrared radiation, and heat transfer can be used as validation purpose or for direct inputs as boundary conditions. Time-independent location of peak location of liner wall temperature was found from time resolved wall temperature measurements and PIV flow measurements. This indicates the location where the cooling design should be able to compensate for the temperature increase in lean premixed swirl combustors.
The characteristics on the swirl flows found in this study points out that the reacting changes the flow structure significantly, while the operating conditions has minor effect on the structure. The limitation of non-reacting testing must be well considered for experimental combustor studies. However, reacting testing can be performed cost-effectively for reduced number of conditions, utilizing self-similar characteristics of the flows found in this study.Ph. D.
29
Roberts, Graham Trevor. "Shock tube studies of convective heat transfer (a) in non-equilibrium flow (b) in particle-laden flow." Thesis, University of Southampton, 1985. https://eprints.soton.ac.uk/52304/.
Full text
30
Varela, Ballesta Sylvana Verónica. "Computational and experimental modeling of fluid flow and heat transfer processes in complex geometries." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/80717.
Full textAbstract:
El objetivo principal de este trabajo es el estudio numérico (caffa3d.MB) y experimental (PIV) de los campos de velocidad y de temperatura en dominios complejos como los encontrados en las computadoras u otros sistemas electrónicos refrigerados que contengan circuitos impresos (PCB, Printed Circuit Board). La refrigeración es uno de los principales desafíos que estos dispositivos se deben tratar. La disipación del calor de los dispositivos de circuitos electrónicos se ha convertido en una cuestión importante a tener en cuenta durante su diseño. Los PCB son circuitos electrónicos que generan calor por efecto Joule y necesitan ser enfriados. Son cada vez más pequeños y por lo tanto los problemas del calentamiento disminuyen su eficiencia y vida útil. El estudio de la velocidad y los campos de temperatura está estrechamente relacionada con el análisis de la evolución espacial y temporal de las estructuras de flujo que se encuentran en las cavidades cerradas que contiene PCB y con el entendimiento de la influencia de la geometría, la velocidad de entrada de fluido y temperatura de la placa en el proceso de enfriamiento del PCB.The main objective of this work is the numerical (caffa3d.MB) and experimental (PIV) study of the velocity and temperature fields in complex domains like those encountered in computers or other electronic refrigerated systems with printed circuit board (PCB). Cooling is one of the main challenges these devices have to deal with. Heat removal from the electronic circuit devices has become an important issue to take into account during their design. PCB's are electronic circuits that generate heat by Joule effect and need to be cooled down. They are becoming smaller and therefore some warming problems appear that lowers their efficiency and lifespan. The study of the velocity and temperature fields is closely connected with the analysis of the spatial and temporal evolution of the flow structures found in PCB enclosed cavities and with the understanding of the influence of the geometry, the inlet fluid velocity and plate temperature in the cooling process of the PCB.
31
Jensen, Colby Bruce. "Bridging the Nano- and Macro-Worlds: Thermal Property Measurement Using Thermal Microscopy and Photothermal Radiometry – Application to Particle-Irradiation Damage Profile in Zirconium Carbide." DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/3105.
Full textAbstract:
Multiscaled experimental investigations of heat transfer from nanoscales to macroscales are requisite to progress in energy technologies. In nuclear applications, material properties can undergo significant alteration due to destructive interaction with irradiating particles at microstructural levels that affect bulk properties. Correlating material microstructure to bulk material properties remains a crucial hurdle for obtaining first-principles-based, full-scale material property predictive capability. Ion-irradiated material studies provide valuable insight into material behavior under irradiation conditions that can be correlated to neutron irradiation effects. Through such studies, the need of costly (money and time) studies of neutron interaction with materials can be mitigated significantly. One of the challenges associated with studies of ion-irradiated materials is that the affected layer, or penetration depth, is typically very thin (~0.1-100μm for laboratory accelerators). Few investigations have been reported of ion-irradiation effects on thermal transport properties, in part, due to the challenge associated with measurements at the spatial scales of the zones of interest.
This study expands the current knowledge base regarding thermal transport in ion-irradiated materials through the use of a multiscaled experimental approach using thermal wave methods. In a manner not previously explored, four thermal wave methods are used to characterize the proton-irradiated layer in ZrC including scanning thermal microscopy, spatial-scanning front-detection photothermal radiometry (PTR), lock-in IR thermography (lock-in IRT), and tomographic, frequency-based PTR. For the first time, the in-depth thermal conductivity profile of an ion-irradiated sample is measured directly. The profiles obtained by each of the spatial scanning methods are compared to each other and the numerical prediction of the ion-damage profile. The complementary nature of the various techniques validates the measured profile and the measured degradation of thermal conductivity in the ZrC sample showing the viability of such complementary studies.
32
Calderón, Díaz Alejandro. "Study of solid particle materials as high temperature Thermal Energy Storage and Heat Transfer Fluid for Concentrating Solar Power." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667863.
Full textAbstract:
Renewable energies have a major role in today’s energy systems development, energy security and climate change fight. Thermal Concentrating Solar Power (CSP) has the potential to get up to 11.3% of world’s electricity production with the adequate support. This type of renewable energy has proved to be price competitive and to have the advantage of integrating Thermal Energy Storage (TES). This adds the generation flexibility that other renewable energies, like wind or photovoltaics, does not have integrated.
In order to continue developing this technology, solid particle CSP has been proposed. This design uses granular solid materials as Heat Transfer Fluid (HTF) and TES material in solar towers in order to be able to achieve higher operation temperatures, than current commercial CSP. Higher temperature means more efficiency in heat-to-electricity conversion, due to the use of better power generation cycles.
The main objective of this thesis is to enhance relevance and provide theoretical and experimental background for solid particles to be used as TES material and HTF for CSP tower power plants, from the materials perspective, by using existent or new methodologies.
During this dissertation, current scientific output and relevance were studied in two separate contributions, one for CSP and the other for TES, both by using bibliometric methods. For the CSP study, additional analyses were carried out according to the harvesting technologies (parabolic trough, solar tower, Stirling dish and linear Fresnel). For the TES study, the additional analyses were performed according to the different ways to store thermal energy (sensible, latent and thermochemical). For both analyses, most productive countries, regions, authors, journals and research communities were identified. Moreover, funding impact and cooperation between countries and authors were analyzed. For developing these bibliometric analyses, a specific methodology was implemented following Bibliometrics principles. For these purposes, two existing software programs were used for a part of the analysis, while for performing the rest of the analysis a special software was developed ad-hoc for this study.
For providing background, two state-of-the-art analyses were performed in order to get current development status of solid particle CSP. The first one was oriented to the plant design itself. Several solar receivers were analyzed, as well as TES, Heat Exchanger (HEX) and conveyance systems. During the second state-of-the-art, a material driven study was carried out in order to understand the behavior expected by the particle media and to identify some of the materials proposed by the most relevant researchers in this field.
Next step of this dissertation was focused on establishing the design criteria for solid particle CSP technology, from the materials science perspective. This was achieved by finding the most relevant objectives that a power plant of this kind must comply, as well as the influence of the particle media properties and parameters.
Last part of this dissertation is related with two studies regarding the durability of some of the most promising solid particle materials from high temperature exposure effect perspective. The first study was focused on analyzing the effect of long term high temperature (900 °C) in the optical, mechanical, thermal and chemical properties and parameters of the solid particle material. The second study was focused in the effect of long term thermal cycling, in which is considered that the materials should resist several thousand charge-discharge cycles remaining with acceptable operational conditions. For achieving an accelerated thermal cycling test with realistic thermal conditions, a novel device was developed to perform the thousands of thermal cycles required. Electronic, software and hardware design was developed and implemented. Current device has performed more than 20 thousand cycles for different kind of materials, analyzing the same properties and parameters as the first study.Para continuar desarrollando la energía solar de concentración (CSP), se ha propuesto el uso de sólidos particulados. En este nuevo tipo de planta CSP de torre, se utilizan materiales sólidos granulados como Fluido de Transferencia de Calor (HTF) y material para el almacenamiento de energía térmica (TES). El objetivo principal de esta tesis es establecer la relevancia y proporcionar antecedentes, tanto teóricos como experimentales, sobre el uso de sólidos particulados para esta nueva tecnología. Durante este trabajo, la producción científica actual y la relevancia científica fueron estudiados mediante dos estudios bibliométricos, una para CSP y otra para TES. Para ambos análisis, se identificaron los países, regiones, autores, revistas, comunidades de investigación más productivos, el impacto del financiamiento y la cooperación entre países y autores. Para este fin, se utilizaron tres programas informáticos, de los cuales uno tuvo que se desarrollado a la medida. Se realizaron dos análisis del estado del arte para obtener el estado actual de desarrollo de las plantas CSP con uso de sólidos particulados. En el primero, se analizaron varios receptores solares, así como sistemas TES, intercambiadores de calor (HEX) y sistemas de transporte del material granulado. En el segundo, se llevó a cabo un estudio basado en los sólidos particulados, comprendiendo el comportamiento de estos materiales, así como recopilar los materiales potenciales. Se establecieron los criterios de diseño desde la perspectiva de los materiales, logrando encontrar los objetivos relevantes, y la influencia de las propiedades y parámetros de estos materiales. Se realizaron dos estudios sobre la durabilidad en cuanto a la exposición a altas temperaturas. El primero, se centró en analizar el efecto de la temperatura a largo plazo y su efecto en las propiedades ópticas, mecánicas, térmicas y químicas. El segundo, se centró en el efecto de los miles de ciclos térmicos esperados. Se desarrolló un nuevo dispositivo capaz de realizar los ciclos térmicos requeridos en las condiciones requeridas. Se desarrolló e implementó el diseño electrónico, de software y de hardware. Se caracterizaron las mismas propiedades analizadas en el primer estudio.
33
Farkas, Jon. "An Experimental Study of Formation of Circulation Patterns in Laminar Unsteady Driven Cavity Flows Using Particle Image Velocimeter (PIV) Techniques." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1359.
Full textAbstract:
Abstract
An experimental study is conducted to determine the velocity fields, from development to steady state, in a square enclosure due to movement of a constant velocity lid using Particle Image Velocitmetry (PIV). Experiments were conducted with water, seeded with hollow glass sphere particles 10 microns in diameter, at three different lid velocities leading to Reynolds numbers in the high laminar to transitional range. Driven Cavity Flow is a classic fluid dynamics case often used for benchmarking of computational codes. Previous work has primarily focused on improving computational codes, experimental work is lacking and focused on obtaining steady state readings. The test cavity is 1 inch (25.4mm) high by 1 inch (25.4 mm) wide leading to an aspect ratio of 1.0. The depth is taken to be 5 (127mm) inches to reduce the three dimensional effects. Readings are taken from development to steady state allowing for a full spectrum of flow characteristics. PIV technique is successful in capturing the development of driven cavity flow. Circulation is shown to increase strength with time and Reynolds number. PIV capture and processing settings are determined.
Keywords: Driven Cavity Flow, Particle Image Velocimeter (PIV)
34
Rozati, Ali. "Large Eddy Simulation of Leading Edge Film Cooling: Flow Physics, Heat Transfer, and Syngas Ash Deposition." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30127.
Full textAbstract:
The work presented in this dissertation is the first numerical investigation conducted to study leading edge film cooling with Large Eddy Simulation (LES). A cylindrical leading edge with a flat after-body represents the leading edge, where coolant is injected with a 30Ë compound angle. Three blowing ratios of 0.4, 0.8, and 1.2 are studied. Free-stream Reynolds number is 100,000 and coolant-to-mainstream density ratio is unity. At blowing ratio of 0.4, the effect of coolant inlet condition is investigated. Results show that the fully-turbulent coolant jet increases mixing with the mainstream in the outer shear layer but does not influence the flow dynamics in the turbulent boundary layer at the surface. As a result, the turbulent jet decreases adiabatic effectiveness but does not have a substantial effect on the heat transfer coefficient. At B.R.=0.4, three types of coherent structures are identified which consist of a primary entrainment vortex at the leeward aft-side of the coolant hole, vortex tubes at the windward side of the coolant hole, and hairpin vortices typical of turbulent boundary layers produced by the turbulent interaction of the coolant and mainstream downstream of injection. At B.R. = 0.8 and 1.2, coherent vortex tubes are no longer discernable, whereas the primary vortex structure gains in strength. In all cases, the bulk of the mixing occurs by entrainment which takes place at the leeward aft-side of the coolant jet. This region is characterized by a low pressure core and the primary entrainment vortex. Turbulent shear interaction between coolant jet and mainstream increases substantially with blowing ratio and contributes to the dilution of the coolant jet. As a result of the increased mixing in the shear layer and primary structure, adiabatic effectiveness decreases and heat transfer coefficient increases with increase in blowing ratio.
The dissertation also investigates the deposition and erosion of Syngas ash particles in the film cooled leading edge region. Three ash particle sizes of 1, 5, and 10 microns are investigated at all blowing ratios using Lagrangian dynamics. The 1 micron particles with momentum Stokes number St = 0.03 (based on approach velocity and cylinder diameter), show negligible deposition/erosion. The 10 micron particles, on the other hand with a high momentum Stokes number, St = 3, directly impinge and deposit on the surface, with blowing ratio having a minimal effect. The 5 micron particles with St=0.8, show the largest receptivity to coolant flow and blowing ratio. On a mass basis, 90% of deposited mass is from 10 micron particles, with 5 micron particles contributing the other 10%. Overall there is a slight decrease in deposited mass with increase in blowing ratio. About 0.03% of the total incoming particle energy can potentially be transferred as erosive energy to the surface and coolant hole, with contribution coming from only 5 micron particles at B.R.=0.4 and 0.8, and both 5 and 10 micron particles at B.R.=1.2.Ph. D.
35
Palaniappan, Sevugan. "Ohmic heating of foods : studies on microbicidal effect of electricity, electrical conductivity of foods, and heat transfer in liquid- particle mixtures /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487757723995203.
Full text
36
Raymond, Alexander William. "Investigation of microparticle to system level phenomena in thermally activated adsorption heat pumps." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34682.
Full textAbstract:
Heat actuated adsorption heat pumps offer the opportunity to improve overall energy efficiency in waste heat applications by eliminating shaft work requirements accompanying vapor compression cycles. The coefficient of performance (COP) in adsorption heat pumps is generally low. The objective of this thesis is to model the adsorption system to gain critical insight into how its performance can be improved. Because adsorption heat pumps are intermittent devices, which induce cooling by adsorbing refrigerant in a sorption bed heat/mass exchanger, transient models must be used to predict performance. In this thesis, such models are developed at the adsorbent particle level, heat/mass exchanger component level and system level.
Adsorption heat pump modeling is a coupled heat and mass transfer problem. Intra-particle mass transfer resistance and sorption bed heat transfer resistance are shown to be significant, but for very fine particle sizes, inter-particle resistance may also be important. The diameter of the adsorbent particle in a packed bed is optimized to balance inter- and intra-particle resistances and improve sorption rate. In the literature, the linear driving force (LDF) approximation for intra-particle mass transfer is commonly used in place of the Fickian diffusion equation to reduce computation time; however, it is shown that the error in uptake prediction associated with the LDF depends on the working pair, half-cycle time, adsorbent particle radius, and operating temperatures at hand.
Different methods for enhancing sorption bed heat/mass transfer have been proposed in the literature including the use of binders, adsorbent compacting, and complex extended surface geometries. To maintain high reliability, the simple, robust annular-finned-tube geometry with packed adsorbent is specified in this work. The effects of tube diameter, fin pitch and fin height on thermal conductance, metal/adsorbent mass ratio and COP are studied. As one might expect, many closely spaced fins, or high fin density, yields high thermal conductance; however, it is found that the increased inert metal mass associated with the high fin density diminishes COP. It is also found that thin adsorbent layers with low effective conduction resistance lead to high thermal conductance. As adsorbent layer thickness decreases, the relative importance of tube-side convective resistance rises, so mini-channel sized tubes are used. After selecting the proper tube geometry, an overall thermal conductance is calculated for use in a lumped-parameter sorption bed simulation. To evaluate the accuracy of the lumped-parameter approach, a distributed parameter sorption bed simulation is developed for comparison. Using the finite difference method, the distributed parameter model is used to track temperature and refrigerant distributions in the finned tube and adsorbent layer. The distributed-parameter tube model is shown to be in agreement with the lumped-parameter model, thus independently verifying the overall UA calculation and the lumped-parameter sorption bed model.
After evaluating the accuracy of the lumped-parameter model, it is used to develop a system-level heat pump simulation. This simulation is used to investigate a non-recuperative two-bed heat pump containing activated carbon fiber-ethanol and silica gel-water working pairs. The two-bed configuration is investigated because it yields a desirable compromise between the number of components (heat exchangers, pumps, valves, etc.) and steady cooling rate. For non-recuperative two-bed adsorption heat pumps, the average COP prediction in the literature is 0.39 for experiments and 0.44 for models. It is important to improve the COP in mobile waste heat applications because without high COP, the available waste heat during startup or idle may be insufficient to deliver the desired cooling duty. In this thesis, a COP of 0.53 is predicted for the non-recuperative, silica gel-water chiller. If thermal energy recovery is incorporated into the cycle, a COP as high as 0.64 is predicted for a 90, 35 and 7.0°C source, ambient and average evaporator temperature, respectively. The improvement in COP over heat pumps appearing in the literature is attributed to the adsorbent particle size optimization and careful selection of sorption bed heat exchanger geometry.
37
Mo, Jingwen. "Numerical and Experimental Study of Anisotropic Effective Thermal Conductivity of Particle Beds under Uniaxial Compression." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1288.
Full textAbstract:
Measurements of in situ planetary thermal conductivity are typically made using long needle-like probes inserted in a planet's surface, which measure effective thermal conductivity (ETC) in radial direction (parallel to surface). The desired vertical (perpendicular to surface) ETC is assumed to be the same as the horizontal. However, ETC of particle beds in vertical and horizontal directions is known to be an anisotropic property under low compressive pressures. This study further examines the anisotropy of bed ETC under low and high compressive pressures in both vacuum and air environments. The ratio of vertical to horizontal stress, K0, is measured for the particles used in these experiments. A resistance network heat transfer model has been developed in predicting the vertical and the horizontal ETC as a function of applied compressive pressure. The model predicts vertical ETC by using only macro-contact thermal resistances for both high and low applied compressive pressure regimes. It is proposed that the vertical and horizontal ETC of particle beds under uniaxial compression is related by compressive pressures in each direction. The horizontal compressive pressure, which is perpendicular to the applied compressive pressure, can be calculated with the use of at-rest pressure coefficient and subsequently used in macro-contact thermal resistance to predict the horizontal ETC. The vertical ETC is obtained using the same model by substituting vertical compressive pressure into macro-contact thermal resistance. A two-dimensional axisymmetric finite element model in the COMSOL Multiphysics software package has been developed to simulate heat transfer coupled with structural deformation of spheres under compressive pressures in a simple cubic (SC) packing arrangement. The numerical model is used as a tool to predict the lower limit of bed ETC as well as validating thermal contact resistance used in the theoretical model. The predictions from the numerical model can be extended to particle beds with different packing arrangements.
38
Westhoff, Andreas. "Spatial Scaling of Large-Scale Circulations and Heat Transport in Turbulent Mixed Convection." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-FD19-2.
Full text
39
Chadil, Mohamed-Amine. "Penalty methods for the simulation of fluid-solid interactions with various assemblies of resolved scale particles." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0205/document.
Full textAbstract:
Les simulations des écoulements diphasiques à l’échelle réelle de l’application nécessitent des modèles pour les termes non fermés des équations macroscopiques. Des simulations numériques directes à particule résolue utilisant la méthode de pénalisation visqueuse ont été réalisées afin de mesurer les interactions entre des particules de différentes formes (sphérique et ellipsoïdale) et le fluide porteur à différents régimes d'écoulement (de stokes à l'inertiel). Deux méthodes ont été développées durant cette thèse afin d'extraire les forces hydrodynamiques ainsi que le transfert de chaleur sur les frontières immergées représentant les particules. Plusieurs validations ont été conduites pour différentes configurations de particules : de la simulation d’une particule isolée à un réseau aléatoire de sphères en passant par réseau cubique face centrée de sphères. Une corrélation du nombre de Nusselt est proposée pour un sphéroïde allongé plongé dans un écoulement uniformeThe simulations of multiphase flows at real application scale need models for unclosed terms in macroscopic equations. Particle-Resolved Direct Numerical Simulations using Viscous Penalty Method have been carried out to quantify the interactions between particles of different shapes (spheres, ellipsoids) and the carrier fluid at different regimes (from Stokes to inertial). Two methods have been developed to extract hydrodynamic forcesand heat transfers on immersed boundaries representing the particles. Validations have been conducted for various configuration of particles: from an isolated sphere and spheroid to Face-Centered Cubic to a random arrangement of spheres. A correlation of the Nusselt number for an isolated prolate spheroid past by a uniform flow is proposed
40
Euzenat, Florian. "Simulation numérique directe et analyse des transferts de chaleur dans les lits de particules fixes et mobiles." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/21358/1/EUZENAT_Florian.pdf.
Full textAbstract:
Ces travaux de recherche s'intéressent à la caractérisation des transferts thermiques dans les milieux fluide-particules, et en particulier, les lits fluidisés au sein desquels un solide divisé est mis en suspension par un fluide. La grande diversité d'échelles spatiales et temporelles dans ces procédés nécessite d'étudier les interactions hydrodynamiques, thermiques et/ou chimiques entre les particules et le fluide à l'aide d'une approche multi-échelles. Une étude des transferts thermiques dans des lits fixes puis fluidisés, est réalisée à deux échelles : locale (Particle Resolved Simulation) et moyennée (Discrete Element Method-Computional Fluids Dynamics). L'étude PRS permet de caractériser les couplages locaux des transferts thermiques entre particules ainsi que la dynamique de ces transferts dans les configurations fluidisées. Une étude comparative entre les échelles met en évidence les limites du modèle DEM-CFD à capter les fluctuations des transferts thermiques observées dans les simulations PRS. Dans un dernier temps, les fermetures du modèle DEM-CFD sont améliorées de manière à réintroduire les fluctuations perdues par le changement d'échelles.
41
Dunand, Pierre. "Étude de l'impact de goutte sur une paroi chaude en régime de Leidenfrost." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0166/document.
Full textAbstract:
Les impacts de gouttes sur paroi chaude sont présents dans de multiples domaines, tels que l'injection de diesel sous forme de spray dans des moteurs à combustions internes, ou le traitement thermiques de l'acier dans le domaine de la sidérurgie. L'étude de l'interactions goutte/paroi permet de mieux comprendre les phénomènes thermiques mis en jeu, et ainsi d'aboutir à des économies d'énergies et d'eau. De nombreux travaux portent sur cette thématique, mais ils présentent des résultats divergents et uniquement basés sur l'étude de la paroi chaude. Cette thèse a pour but d'apporter des mesures expérimentales sur les caractéristiques inconnues en étudiant les gouttes. Pour cela, un dispositif expérimental a été mis au point afin de mener à bien l'ensemble des mesures souhaitées. Les diverses techniques de mesures de température utilisées sont présentées, et une attention plus particulière a été portée sur le développement de la technique de fluorescence induite par plan laser qui permet d'accéder au champ de température des gouttes durant leur impact. Cette méthode, combinée à une technique de thermographie par caméra infrarouge couplée à un modèle de conduction inverse, permet d'extraire les paramètres concernant l'aspect thermique, et de déterminer de nouvelles caractéristiques inédites, telles que l'échauffement des gouttes, l'évaporation relative de celles-ci ou encore l'efficacité de refroidissement. Les parts respectives jouées par la chaleur sensible et l'évaporation des gouttes sont tirées de cette dernière. Enfin, l'aspect dynamique est également abordé aboutissant au développement d'une technique d'ombroscopie rapide. Cette dernière a permis, grâce à la combinaison de mesures de diamètres précises et d'une fréquence d'acquisition élevée, d'extraire les paramètres dynamiques de l'impact tels que la vitesse et taille des gouttes, ou d'autres paramètres relatif au type d'impact rencontrés à l'aide d'un algorithme de suivi de particules développé durant la thèseThe droplet impact onto a heated wall interaction can be found in mutiples fields, such as internal combustion engines or the steel industry, specially in the thermal treatment of the steel where high energy dissipation rate is required. The study of this interaction should grant a better understanding of this phenomena, and thus, allow the enhancement of these processes and reduce the energy and water consumption. Several studies have already been carried out on this subjet but a great majority of them, whose results present great divergence, only consider the heated wall, neglecting the outgoing of the droplet. This thesis put the emphasis on the liquid phase where currently no data exist to our knowledge, with the help of multiples experimental technics that have been developped. A general experimental setup has been made in order to make all the wanted measurements. The measurement techniques used in this study are first presented, to begin with the planar laser induced fluorescence, which allow us to know the droplet temperature during the impact. Used with an infrared thermography technique coupled with an inverse conduction model, it is possible to extract some important parameter regarding the thermal aspect, such as the droplet heating, the relative evaporation ratio or the cooling efficiency. This latter can be written as the sum of the two major contributions of the cooling: the sensible heat and the evaporation of the droplet. Finally, a high speed shadow imagery technique is presented. It has been developped in order to study the dynamic aspect of the droplet impact. This technique can determine several dynamic parameters such as the droplet speed and diameter, or other parameter regarding the type of impact encountered
42
Kestel, Matthias. "Numerical modeling of moving carbonaceous particle conversion in hot environments." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-204732.
Full textAbstract:
The design and optimization of entrained flow gasifiers is conducted more and more via computational fluid dynamics (CFD). A detailed resolution of single coal particles within such simulations is nowadays not possible due to computational limitations. Therefore the coal particle conversion is often represented by simple 0-D models. For an optimization of such 0-D models a precise understanding of the physical processes at the boundary layer and within the particle is necessary.
In real gasifiers the particles experience Reynolds numbers up to 10000. However in the literature the conversion of coal particles is mainly regarded under quiescent conditions. Therefore an analysis of the conversion of single particles is needed. Thereto the computational fluid dynamics can be used.
For the detailed analysis of single reacting particles under flow conditions a CFD model is presented. Practice-oriented parameters as well as features of the CFD model result from CFD simulations of a Siemens 200MWentrained flow gasifier. The CFD model is validated against an analytical model as well as two experimental data-sets taken from the literature. In all cases good agreement between the CFD and the analytics/experiments is shown.
The numerical model is used to study single moving solid particles under combustion conditions. The analyzed parameters are namely the Reynolds number, the ambient temperature, the particle size, the operating pressure, the particle shape, the coal type and the composition of the gas. It is shown that for a wide range of the analyzed parameter range no complete flame exists around moving particles. This is in contrast to observations made by other authors for particles in quiescent atmospheres. For high operating pressures, low Reynolds numbers, large particle diameters and high ambient temperatures a flame exists in the wake of the particle. The impact of such a flame on the conversion of the particle is low. For high steam concentrations in the gas a flame appears, which interacts with the particle and influences its conversion.
Furthermore the impact of the Stefan-flow on the boundary layer of the particle is studied. It is demonstrated that the Stefan-flow can reduce the drag coefficient and the Nusselt number for several orders of magnitude. On basis of the CFD results two new correlations are presented for the drag coefficient and the Nusselt number. The comparison between the correlations and the CFD shows a significant improvement of the new correlations in comparison to archived correlations.
The CFD-model is further used to study moving single porous particles under gasifying conditions. Therefore a 2-D axis-symmetric system of non-touching tori as well as a complex 3-D geometry based on the an inverted settlement of monodisperse spheres is utilized. With these geometries the influence of the Reynolds number, the ambient temperature, the porosity, the intrinsic surface and the size of the radiating surface is analyzed. The studies show, that the influence of the flow on the particle conversion is moderate. In particular the impact of the flow on the intrinsic transport and conversion processes is mainly negligible. The size of the radiating surface has a similar impact on the conversion as the flow in the regarded parameter range.
On basis of the CFD calculations two 0-D models for the combustion and gasification of moving particles are presented. These models can reproduce the results predicted by the CFD sufficiently for a wide parameter range.
43
Oschmann, Tobias Sebastian [Verfasser], Harald [Akademischer Betreuer] Kruggel-Emden, Harald [Gutachter] Kruggel-Emden, and Viktor [Gutachter] Scherer. "Extension and improvement of the coupled CFD-DEM approach to describe multidimensional heat transfer and non-spherical particle shape for fluidized systems / Tobias Sebastian Oschmann ; Gutachter: Harald Kruggel-Emden, Viktor Scherer ; Betreuer: Harald Kruggel-Emden." Berlin : Technische Universität Berlin, 2019. http://d-nb.info/1184983836/34.
Full text
44
Dowd, Cody Stewart. "A Study of Centrifugal Buoyancy and Particulate Deposition in a Two Pass Ribbed Duct for the Internal Cooling Passages of a Turbine Blade." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81181.
Full textAbstract:
In this thesis, the ribbed ducts of the internal cooling passage in turbine blading are investigated to demonstrate the effects of high speed rotation. Rotation coupled with high temperature operating conditions alters the mean flow, turbulence, and heat transfer augmentation due to Coriolis and centrifugal buoyancy forces that arises from density stratification in the domain. Gas turbine engines operate in particle laden environments (sand, volcanic ash), and particulate matter ingested by the engine can make their way into the blade internal cooling passages over thousands of operating hours. These particulates can deposit on the walls of these cooling passages and degrade performance of the turbine blade. Large-Eddy Simulations (LES) with temperature dependent properties is used for turbulent flow and heat transfer in the ribbed cooling passages and Lagrangian tracking is used to calculate the particle trajectories together with a wall deposition model. The conditions used are Re=100,000, Rotation number, Ro = 0.0 and 0.2, and centrifugal Buoyancy parameters of Bo=0, 0.5, and 1.0.
First, the independent effects of Coriolis and centrifugal buoyancy forces are investigated, with a focus on the additional augmentation obtained in heat transfer with the addition of centrifugal buoyancy. Coriolis forces are known to augment heat transfer at the trailing wall and attenuate the same at the leading wall. Phenomenological arguments stated that centrifugal buoyancy augments the effects of Coriolis forces in outward flow in the first pass while opposing the effect of Coriolis forces during inward flow in the second pass. In this study, it was found that in the first pass, centrifugal buoyancy had a greater effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On the contrary, it aided heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. Also, contrary to phenomenological arguments, inclusion of centrifugal buoyancy augmented heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.
Sand ingestion is then investigated, by injecting 200,000 particles in the size range of 0.5-175μm with 65% of the particles below 10 μm. Three duct wall temperatures are investigated, 950, 1000 and 1050 °C with an inlet temperature of flow and particles at 527 °C . The impingement, deposition levels, and impact characteristics are recorded as the particles move through the domain. It was found that the Coriolis force greatly increases deposition. This was made prevalent in the first pass, as 84% of the deposits in the domain occurred in the first pass for the rotating case, whereas only 27% of deposits occurred in the first pass for the stationary case with the majority of deposits occurring in the bend region. This was due to an increased interaction with the trailing wall in the rotating case whereas particles in the stationary case were allowed to remain in the mean flow and gain momentum, making rebounding from a wall during collision more likely than deposition. In contrast, the variation of wall temperatures caused little to no change in deposition levels. This was concluded to be a result of the high Reynolds number used in the flow. At high Reynolds numbers, the particles have a short residence times in the internal cooling circuit not allowing the flow and particles to heat up to the wall temperature. Overall, 87% of the injected particles deposited in the rotating duct whereas 58% deposited in the stationary duct.Master of Science
45
Alhamdan, Abdullah M. "Experimental studies on natural and forced convection around spherical and mushroom shaped particles." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1145369315.
Full text
46
Rubenstein, Samuel. "Cold Flow Heat Transfer of Group D Particles in a Fluidized Bed." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1592717365378709.
Full text
47
Krishnamurthy, Nagendra. "A Study of Heat and Mass Transfer in Porous Sorbent Particles." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64412.
Full textAbstract:
This dissertation presents a detailed account of the study undertaken on the subject of heat and mass transfer phenomena in porous media. The current work specifically targets the general reaction-diffusion systems arising in separation processes using porous sorbent particles. These particles are comprised of pore channels spanning length scales over almost three orders of magnitude while involving a variety of physical processes such as mass diffusion, heat transfer and surface adsorption-desorption. A novel methodology is proposed in this work that combines models that account for the multi-scale and multi-physics phenomena involved. Pore-resolving DNS calculations using an immersed boundary method (IBM) framework are used to simulate the macro-scale physics while the phenomena at smaller scales are modeled using a sub-pore modeling technique.
The IBM scheme developed as part of this work is applicable to complex geometries on curvilinear grids, while also being very efficient, consuming less than 1% of the total simulation time per time-step. A new method of implementing the conjugate heat transfer (CHT) boundary condition is proposed which is a direct extension of the method used for other boundary conditions and does not involve any complex interpolations like previous CHT implementations using IBM. Detailed code verification and validation studies are carried out to demonstrate the accuracy of the developed method.
The developed IBM scheme is used in conjunction with a stochastic reconstruction procedure based on simulated annealing. The developed framework is tested in a two-dimensional channel with two types of porous sections - one created using a random assembly of square blocks and another using the stochastic reconstruction procedure. Numerous simulations are performed to demonstrate the capability of the developed framework. The computed pressure drops across the porous section are compared with predictions from the Darcy-Forchheimer equation for media composed of different structure sizes. The developed methodology is also applied to CO2 diffusion studies in porous spherical particles of varying porosities.
For the pore channels that are unresolved by the IBM framework, a sub-pore modeling methodology developed as part of this work which solves a one-dimensional unsteady diffusion equation in a hierarchy of scales represented by a fractal-type geometry. The model includes surface adsorption-desorption, and heat generation and absorption. It is established that the current framework is useful and necessary for reaction-diffusion problems in which the adsorption time scales are very small (diffusion-limited) or comparable to the diffusion time scales. Lastly, parametric studies are conducted for a set of diffusion-limited problems to showcase the powerful capability of the developed methodology.Ph. D.
48
Oliveira, Filho Ulisses Corr?a de. "Desenvolvimento de um secador spray para obten??o de p?s finos de precursores de ni?bio." Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15874.
Full textAbstract:
Made available in DSpace on 2014-12-17T15:01:44Z (GMT). No. of bitstreams: 1
UlissesCOF.pdf: 4000133 bytes, checksum: 2f1689ba64508ae157f48710d758ba50 (MD5)
Previous issue date: 2007-11-01This work presents a spray-dryer designed to oxalate-niobate precursors and suitable for the production of Niobium Carbide. The dryer was intended to produce powders of controlled particle size. First, the precursor is dissolved in water to produce a solution of known concentration and then it is atomized on the spray-dryer to produce the powder. This equipment consists of a 304 stainless steel chamber, 0.48 m x 1.9 m (diameter x length), with a conical shape at the lower portion, which is assembled on a vertical platform. The chamber is heated by three 4 kW electrical resistances. In this process, drying air is heated as it flows inside a serpentine surrounding the chamber, in contrary to more traditional processes in which the hot drying air is used to heat the component. The air enters the chamber at the same temperature of the chamber, thus avoiding adherence of particles on the internal surface. The low speed flow is concurrent, directed from the top to the bottom portion of the chamber. Powders are deposited on a 0.4 m diameter tray, which separates the cylindrical portion from the conical portion of the chamber. The humid air is discharged though a plug placed underneath the collecting tray. A factorial experimental planning was prepared to study the influence of five parameters (concentration, input flow, operation temperature, drying air flow and spray air flow) on the characteristics of the powders produced. Particle size distribution and shape were measured by laser granulometry and scanning electronic microscopy. Then, the powders are submitted to reaction in a CH4 / H2 atmosphere to compare the characteristics of spray-dried powders with powders synthetizided by conventional methods
O presente trabalho consiste em projetar e construir um secador spray com a finalidade de secar precursores do tipo oxalato-niobato de am?nia para obten??o de p?s com granulometria controlada e adequados ? produ??o de carbetos de Ni?bio policristalino. Este precursor ? atualmente obtido com granulometria dispersa, e morfologia n?o uniforme. A secagem em spray pode uniformizar as propriedades de materiais que s?o dissolvidos em ?gua, gerando uma solu??o de concentra??o conhecida que ? ent?o, atomizada no secador spray visando ? obten??o do material na forma de p?. O secador ? constitu?do por uma c?mara de secagem em a?o inox 304 medindo 0,48 m de di?metro por 1,90 m de comprimento, montado em uma plataforma vertical e com formato tronco c?nico na sua parte inferior. A c?mara ? aquecida por tr?s cintas de resist?ncias eletricas com pot?ncia total de 4 kW e o ar ? aquecido ao passar por serpentinas constru?das ao redor da c?mara de secagem. O sistema foi projetado de maneira n?o convencional tendo como objetivo principal a produ??o de p?s de precursores com granulometria fina e com uma boa distribui??o do tamanho das part?culas. Foi realizado um planejamento fatorial experimental visando ? an?lise da influ?ncia de cinco par?metros (concentra??o, vaz?o da alimenta??o, temperatura de opera??o, vaz?o do ar de secagem e vaz?o do ar do atomizador) sobre as caracter?sticas dos p?s obtidos usando-se solu??es de bicarbonato de s?dio. As Caracter?sticas f?sicas foram avaliadas a partir de an?lise de ?rea superficial, DRX, tamanho e forma das part?culas, granulometria a laser e microscopia eletr?nica de varredura. Em seguida foi realizada a secagem do precursor e, os p?s obtidos foram submetidos a rea??es com CH4 / H2 com o objetivo de comparar as caracter?sticas dos p?s oriundos do secador spray e aqueles que n?o tiveram esse tratamento. Os resultados mostraram que o equipamento produziu part?culas de bicarbonato de s?dio com di?metros m?dios de 2,4 a 52,4 μm, conforme as temperatura e vaz?es de alimenta??o, e se mostrou capaz de secar precursores do tipo oxalato-niobato de am?nia sem perda de suas caracter?sticas
49
Benoit, Hadrien. "Récepteur solaire tubulaire à suspension dense de particules en écoulement ascendant." Thesis, Perpignan, 2015. http://www.theses.fr/2015PERP0045/document.
Full textAbstract:
Cette thèse, financée dans le cadre du projet européen CSP2, porte sur l'étude d'un nouveau type de récepteur solaire thermique à concentration utilisant comme fluide caloporteur une suspension dense de fines particules en circulation ascendante dans des tubes verticaux. Ladite suspension est obtenue par fluidisation de particules de classe A. Le principe consiste à créer un écoulement ascendant de la suspension dans un tube vertical exposé au rayonnement solaire concentré qui chauffe la paroi du tube, qui transmet ensuite cette chaleur aux particules, qui la transportent jusqu'à un cycle de conversion d'énergie pour la production d'électricité. Au contraire des fluides solaires classiques, les particules peuvent atteindre les hautes températures (> 700 °C) permettant l'utilisation de cycles à haut rendement de conversion (Brayton, cycles combinés), tout en permettant un stockage direct de la pour une production continue. Au cours de la thèse, un récepteur à un tube a été testé avec succès au grand four solaire du laboratoire PROMES-CNRS à Odeillo, les particules en sortie atteignant 750 °C, ce qui a prouvé la faisabilité du concept et permis la détermination des premières valeurs de coefficient d'échange de chaleur tube-suspension. L'hydrodynamique de l'écoulement et les mécanismes d'échange de chaleur ont été observés grâce à des simulations numériques 3D. Un récepteur de 150 kWth à 16 tubes a ensuite été testé et modélisé, validant l'utilisation du procédé à plus grande échelleThis thesis, financed in the frame of the CSP2 European project, concerns the study of a new kind of thermal concentrating solar receiver using a dense suspension of solid particles circulating upward in vertical tubes. The suspension is obtained by fluidizing Geldart A-type particles. The principle consists in creating an upward flow of the suspension in a vertical tube exposed to the concentrated solar radiation that heats the tube wall. The heat is then transmitted to the particles circulating inside that transport it to a conversion cycle for electricity production. Contrarily to usual solar heat transfer fluids, particles can reach high temperatures (> 700 °C) that permit to power high efficiency thermodynamic cycles such as Brayton or combined cycles. Moreover they can be used as a direct heat storage medium for continuous electricity production. During this thesis, a one-tube solar receiver was successfully tested at the PROMES-CNRS solar furnace in Odeillo, with particle outlet temperatures of 750 °C reached. The first values of wall-to-suspension heat transfer coefficient were calculated and a Nusselt correlation was determined. A specific flow pattern with a particle downward flux close to the wall and upward flux in the tube center was underlined. The flow hydrodynamics and the heat transfer mechanisms were studied thanks to 3D numerical simulations. A 16-tube 150 kWth receiver was finally tested and modeled, proving the process applicability at larger scale
50
Zitoun, Khaled Bechir. "Convective heat transfer coefficients between fluid and cubic particles in continuous tube flow." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1300992767.
Full text