Dissertations / Theses: 'Heat flows'

1

Takamura, S., M. Y. Ye, T. Kuwabara, and N. Ohno. "Heat flows through plasma sheaths." American Institute of Physics, 1998. http://hdl.handle.net/2237/6995.

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Astin, P. "Heat transfer in jet assimilation flows." Thesis, Keele University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292751.

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Amin, Norsarahaida. "Oscillation-induced mean flows and heat transfer." Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329339.

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Shu, Jian-Jun. "Heat characteristics of some thin film flows." Thesis, Keele University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314615.

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Li, Jintang. "Heat transfer in gas-solids flows through pipes." Thesis, Glasgow Caledonian University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313180.

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Mankad, Sunil. "Heat transfer in two phase solid-liquid flows." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307988.

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Tait, Nicole Lynn. "Recovery factors in zero-mean internal oscillatory flows." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306233.

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Thesis (M.S. in Mechanical Engineering and M.S. in Astronautical Engineering) Naval Postgraduate School, December 1995.
"December 1995." Thesis advisor(s): Ashok Gopinath, Oscar Biblarz. Bibliography: p. 61. Also available online.

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Moore, Bryce Kirk. "Gas-liquid flows in adsorbent microchannels." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47519.

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A study of two the sequential displacement of gas and liquid phases in microchannels for eventual application in temperature swing adsorption (TSA) methane purification systems was performed. A model for bulk fluid displacement in 200 m channels was developed and validated using data from an air-water flow visualization study performed on glass microchannel test sections with a hydraulic diameter of 203 m. High-speed video recording was used to observe displacement samples at two separate channel locations for both the displacement of gas by liquid and liquid by gas, and for driving pressure gradients ranging from 19 to 450 kPa m-1. Interface velocities, void fractions, and film thicknesses were determined using image analysis software for each of the 63 sample videos obtained. Coupled 2-D heat and mass transfer models were developed to simulate a TSA gas separation process in which impurities in the gas supply were removed through adsorption into adsorbent coated microchannel walls. These models were used to evaluate the impact of residual liquid films on system mass transfer during the adsorption process. It was determined that for a TSA methane purification system to be effective, it is necessary to purge liquid from the adsorbent channel. This intermediate purge phase will benefit the mass transfer performance of the adsorption system by removing significant amounts of residual liquid from the channel and by causing the onset of rivulet flow in the channel. The existence of the remaining dry wall area, which is characteristic of the rivulet flow regime, improves system mass transfer performance in the presence of residual liquid. The commercial viability of microchannel TSA gas separation systems depends strongly on the ability to mitigate the presence and effects of residual liquid in the adsorbent channels. While the use of liquid heat transfer fluids in the microchannel structure provides rapid heating and cooling of the adsorbent mass, the management of residual liquid remains a significant hurdle. In addition, such systems will require reliable prevention of interaction between the adsorbent and the liquid heat transfer fluid, whether through the development and fabrication of highly selective polymer matrix materials or the use of non-interacting large-molecule liquid heat transfer fluids. If these hurdles can be successfully addressed, microchannel TSA systems may have the potential to become a competitive technology in large-scale gas separation.

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Seyedein, Seyed Hossein. "Simulation of fluid flow and heat transfer in impingement flows of various configurations." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69587.

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Results of numerical simulation of two-dimensional flow field and heat transfer impingement due to laminar and turbulent single as well as multiple slot jets discharging normally into a confined channel are presented. Both low-Reynolds and high-Reynolds number versions of $k - epsilon$ models were used to model the turbulent jet flow. A control volume-based finite difference method was employed to solve the governing mass, momentum, turbulent kinetic energy, turbulent kinetic energy dissipation rate and energy equations in the turbulent impinging jet cases. A separate program was written based on a body-fitted coordinate system to predict the transport characteristics of multiple laminar jets impinging on a plate surface with an inclined upper confinement surface. The parameters studied include: the jet Reynolds number, nozzle-to-impingement surface spacing and for the inclined confinement surface cases, the angle of inclination of the upper surface. From the low-Reynolds number model studied it was found that models presented by Lam-Bremhorst and Launder-Sharma to be applicable to single turbulent jet impingement heat transfer predictions. Inclination of the confined surface so as to accelerate the exhaust flow was found to level the Nusselt number distribution on the impingement surface.

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Huang, Tao. "REGULARITY AND UNIQUENESS OF SOME GEOMETRIC HEAT FLOWS AND IT'S APPLICATIONS." UKnowledge, 2013. http://uknowledge.uky.edu/math_etds/10.

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This manuscript demonstrates the regularity and uniqueness of some geometric heat flows with critical nonlinearity. First, under the assumption of smallness of renormalized energy, several issues of the regularity and uniqueness of heat flow of harmonic maps into a unit sphere or a compact Riemannian homogeneous manifold without boundary are established. For a class of heat flow of harmonic maps to any compact Riemannian manifold without boundary, satisfying the Serrin's condition, the regularity and uniqueness is also established. As an application, the hydrodynamic flow of nematic liquid crystals in Serrin's class is proved to be regular and unique. The natural extension of all the results to the heat flow of biharmonic maps is also presented in this manuscript.

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Mahmood, T. "Heat transfer in convective boundary layer and channel flows." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233794.

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Yao, Guang-Fa. "Numerical modeling of condensing two-phase channel flows." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17678.

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Oakes, Brian K. "Reduction of convective heat transfer from reacting flows by application of electric fields." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-08042009-040424/.

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Yap, C. R. "Turbulent heat and momentum transfer in recirculating and impinging flows." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384178.

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Lamoureux, Alexandre. "Oscillatory flows in periodically interrupted rectangular passages in heat exchangers." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99415.

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Computational and experimental studies of fluid flow and heat transfer phenomena in interrupted-surface passages are presented. The computational investigation was focused on developing and fully-developed (spatially and temporally) laminar flow and heat transfer in essentially two-dimensional regions of the following passages: (1) a straight rectangular duct with spatially periodic in-line plate inserts; and (2) staggered-plate arrays. A second-order finite-volume method was developed, validated, and used to solve these problems. Time-mean modular friction factors and Colburn factors were obtained from the domain inlet to the spatially-periodic fully-developed region for a Reynolds number range of 100 to 600, thus exploring the laminar steady and unsteady regimes. Additionally, various cyclic domains were investigated. In the experimental investigation, single hot-wire measurements were used to obtain ensemble-averaged power spectrums and Strouhal numbers in the fully-developed region of the rectangular duct with spatially periodic in-line plate inserts, for Reynolds numbers ranging from 2000 to 30000.

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Shi, Yong. "Lattice Boltzmann models for microscale fluid flows and heat transfer /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20SHI.

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Kopfer, Eva [Verfasser]. "Heat flows on time-dependent metric measure spaces / Eva Kopfer." Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1160594120/34.

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Taheri, Shahnaz. "Nonconvex variational problems, heat flows and forward-backward diffusion equations." Thesis, University of Sussex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441611.

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Tham, K. M. "Flow and heat transfer in a H.P. compressor drive cone cavity." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270356.

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Howell, Christopher John. "Heat transfer in inundation and drainage flows associated with power condensers." Thesis, Keele University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334245.

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Lin, Xiang Wen. "Numerical study of unsteady heat transfer and fluid flow over a bluff body." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341453.

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22

Momeni, Parham. "Modelling the Effect of Pulsation on Flow and Heat Transfer in Turbulent Separated and Reattaching Flows." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492875.

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The focus of this thesis is on the response of separated turbulent flows to imposed unsteadiness in the form of pulsation. There are substantial modelling challenges in imputing flows exhibiting even steady separation and reattachment. Furthermore, to minimise computing times - particularly important in unsteady flows, given the requirement to perform a large number of time steps - there is a desire to use relatively simple RANS models of turbulence. However, simple linear eddy-viscosity models are known to perform badly in separated flows, hi this study refinements are introduced to both a non-linear eddy-viscosity (Craft et al; 2005) scheme and a DSM model (lacovides and Raisee; 1999) and these are shown to perform quite successfully in predicting the steady state flow and heat transfer through a sudden pipe-expansion. The main aim of current study is to then asses the performance of these models in computing three types of forced unsteady separated flows.

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23

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.

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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.

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Huval, Danny J. "Heat transfer in variable density, low mach number, stagnating turbulent flows." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/12394.

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Aktas, Murat K. Farouk Bakhtier. "Thermoacoustically induced and acoustically driven flows and heat transfer in enclosures /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/313.

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26

Ebadi, Alireza. "Transport of heat and momentum in non-equilibrium wall-bounded flows." Thesis, University of New Hampshire, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10241615.

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Transport of momentum and heat in non-equilibrium wall-bounded flows is studied analytically and experimentally to better understand the underlying physics, transition dynamics, and appropriate flow scaling in non-equilibrium flows. Non-equilibrium flows, in which the mean flow time scales are comparable to turbulent flow time scales, do not exhibit universal behaviors and cannot be characterized only in terms of local parameters. Pressure gradients, fast transients and complex geometries are among the sources that can perturb a flow from an equilibrium state to a non-equilibrium state. Since all or some of these perturbation sources are present in many engineering application relevant flow systems and geophysical flows, understanding and predicting the non-equilibrium flow dynamics is essential to reliably analyze and control such flows.

Reynolds-averaged Navier-Stokes (RANS) simulations are extensively used to model and predict fluid transport across a wide range of disciplines. The shortcoming is that most turbulence models used in RANS simulations use almost exclusively wall-models based on equilibrium boundary layer behaviors, despite the fact that many basic assumptions required of equilibrium boundary layers are not satisfied in the majority of the flow systems in which RANS simulations are used. In particular, pressure gradients, dynamic walls, roughness, and large-scale flow obstacles produce boundary layers that are strongly non-equilibrium in nature. Often the prediction of RANS simulations in complex engineering systems (with perturbations that induce non-equilibrium flow behaviors) fail spectacularly primarily owing to the fact that the turbulence models do not incorporate the correct physics to accurately capture the transport behaviors in non-equilibrium boundary layers. These failures result in over-engineered and hence, less efficient designs. This lack of efficiency manifests in higher economic and environmental costs. The broad objective of this dissertation work is to develop analytical and experimental tools needed to better understand the underlying transport physics in non-equilibrium boundary layers.

The key scaling parameter in wall-bounded flows is the wall flux of momentum and heat. It follows that an accurate determination of the wall fluxes is essential to study the dynamics of non-equilibrium wall-bounded flows. As part of this dissertation research, an integral method to evaluate wall heat flux suitable for experimental data is developed. The method is exact and does not require any streamwise gradient measurements. The integral method is validated using simulation and experimental data. Complications owing to experimental limitations and measurement error in determining wall heat flux from the method are presented, and mitigating strategies are described. In addition to the ability to evaluate the wall heat flux, the method provides a means to connect transport properties at the wall to the mean flow dynamics.

The integral method is further developed to formulate a novel and robust validation technique of Reynolds-averaged Navier-Stokes (RANS) turbulence models. Validation of the turbulence models employed in RANS simulations is a critical part of model development and application. The integral based validation technique is used to evaluate the performance of two low-Reynolds-number and two high-Reynolds number RANS turbulence models of reciprocating channel flow, and results are compared to the so-called standard validation technique. While the standard validation technique indicates that the low-Reynolds-number models predict the wall heat flux well, the integral validation technique shows that the models do not accurately capture the correct physics of thermal transport in reciprocating channel flow. Moreover, it shows that the correct prediction of the wall heat flux by the models is owed to the serendipitous cancellation of model errors.

One of the identified failures of the RANS simulations of reciprocating channel flow is the inability to accurately predict the flow dynamics during the laminar-turbulence transition. The development of improved RANS turbulence models, therefore requires an improved understanding of the underlying laminar-turbulent transition mechanisms. As part of this dissertation work, the balance of the leading order terms in the phase-averaged mean momentum equation are used to study the transition mechanism in a reciprocating channel flow. It is concluded that the emergence of an internal layer in the late acceleration phase of the cycle triggers the flow to transition from a self-sustaining transitional regime to an intermittently turbulent regime. In the absence of this internal layer, the flow remains transitional throughout the cycle.

Lastly, since experimental studies of heat transfer in non-equilibrium wall-bounded flows are very limited, a unique experimental facility was developed to study non-equilibrium boundary layers with heat transfer. The facility consists of boundary layer wind tunnel that nominally measures 303×135 mm cross-section and 2.7m in length. A freestream heater and a thermal wall-plate are used to maintain the desired outer and inner thermal boundary conditions, respectively. A rotor-stator assembly is fabricated to generate a periodic pressure gradient used to produce pulsatile boundary layer flow. (Abstract shortened by ProQuest.)

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27

Barozzi, Giovanni Sebastiano. "Combined convection and other effects in heat transfer in horizontal flows." Thesis, City, University of London, 1993. http://openaccess.city.ac.uk/16971/.

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For many internal flow situations the effect of buoyancy is to cause significant modifications of the internal flow field and heat transfer rate. The present study focuses on combined forced and free convection under laminar flow conditions in horizontal cylindrical ducts. There, the superposition of secondary, buoyancy induced circulations to the basic forced flow, and the presence of peripheral and axial conduction in the duct wall, give rise to a three-dimensional conjugate heat transfer problem. Such a combined convection feature had not been investigated previously. A novel parallel predictive and experimental study of combined convection for laminar flow in cylindrical ducts is carried out here. The finite volume code FLOW3D from Harwell is used to treat the fully elliptic three-dimensional thermal-flow problem. The choice derives from a complete and detailed survey of the numerical techniques used in the context of combined convection. The predictive work relates specifically to a new experimental study, which has the object of obtaining fresh data for combined convection in horizontal duct flow. A 3 m long, 16 mm I.D. copper pipe is used, with uniform peripheral electrical heating. Wall temperature measurements are taken at twelve axial positions. The experiment covers the range of stable mixed convection and strictly laminar flow conditions, with the Reynolds number ranging from 500 to 1000, and the modified Rayleigh number, Raq, from 1x10⁵ to 5x10⁶. The scope of the experiment is to provide data for comparison with numerical predictions. These, in turn, are designed to model the experimental conditions very accurately, including, in particular, the effects of peripheral and axial wall conduction. The study is complemented with various analyses intended to understanding properly both pure forced and natural convection modes. These are investigated separately in the first part of the work. Overall, this work provides fresh experimental and predictive evidence on various features relevant to the onset and the development of buoyancy induced secondary flows in round ducts under heating conditions. More specifically, the effects, of conduction in the duct wall are highlighted, and demonstrated to have a definite influence on wall temperature, and Nusselt number distributions, even in the case of long, thin-walled ducts.

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Yusuf, Mary E. "Heat transfer and mass transport studies in gas-particulate solids flows." Thesis, Glasgow Caledonian University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.688301.

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29

Pohner, John A. "Analysis of separated, non-parallel, axisymmetric, annular two-phase flows." Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/15838.

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30

Pouransari, Zeinab. "Numerical studies of turbulent flames in wall-jet flows." Doctoral thesis, KTH, Turbulens, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160609.

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The present thesis deals with the fundamental aspects of turbulent mixing and non-premixed combustion in the wall-jet flow, which has a close resemblance to many industrial applications. Direct numerical simulations (DNS) of turbulent wall-jets with isothermal and exothermic reactions are performed. In the computational domain, fuel and oxidizer enter separately in a nonpremixed manner and the flow is compressible, fully turbulent and subsonic. The triple “turbulence-chemistry-wall” interactions in the wall-jet flow have been addressed first by focusing on turbulent flow effects on the isothermal reaction, and then, by concentrating on heat-release effects on both turbulence and flame characteristics in the exothermic reaction. In the former, the mixing characteristics of the flow, the key statistics for combustion and the near-wall effects in the absence of thermal effects are isolated and studied. In the latter, the main target was to identify the heat-release effects on the different mixing scales of turbulence. Key statistics such as the scalar dissipation rates, time scale ratios, two-point correlations, one and two-dimensional premultiplied spectra are used to illustrate the heat release induced modifications. Finer small mixing scales were observed in the isothermal simulations and larger vortical structures formed after adding significant amounts of heat-release. A deeper insight into the heat release effects on three-dimensional mixing and reaction characteristics of the turbulent wall-jet flow has been gained by digging in different scales of DNS datasets. In particular, attention has been paid to the anisotropy levels and intermittency of the flow by investigating the probability density functions, higher order moments of velocities and reacting scalars and anisotropy invariant maps for different reacting cases. To evaluate and isolate the Damkohler number effects on the reaction zone structure from those of the heat release a comparison between two DNS cases with different Damkohler numbers but a comparable temperature rise is performed. Furthermore, the wall effects on the flame and flow characteristics, for instance, the wall heat transfer; the near-wall combustion effects on the skin-friction, the isothermal wall cooling effects on the average burning rates and the possibility of formation of the premixed mode within the non-premixed flame are addressed. The DNS datasets are also used for a priori analysis, focused on the heat release effects on the subgrid-scale (SGS) statistics. The findings regarding the turbulence small-scale characteristics, gained through the statistical analysis of the flow have many phenomenological parallels with those concerning the SGS statistics. Finally, a DNS of turbulent reacting wall-jet at a substantially higher Reynolds number is performed in order to extend the applicability range for the conclusions of the present study and figuring out the possible differences.

QC 20150225

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Khaleque, Tania Sharmin. "Strongly variable viscosity flows in mantle convection." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:851f7069-8164-4499-8afa-5a06141c5911.

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Convection in the Earth's mantle is a complicated phenomenon that causes various tectonic activities and affects mantle evolution on geologic time scales (billions of years). It is a subject as yet not fully understood. The early success of the high Rayleigh number constant viscosity theory was later tempered by the absence of plate motion when the viscosity is more realistically strongly temperature dependent. A similar problem arises if the equally strong pressure dependence of viscosity is considered, since the classical isothermal core convection theory would then imply a strongly variable mantle viscosity, which is inconsistent with results from postglacial rebound studies. We consider a mathematical model for Rayleigh-Bénard convection in a basally heated layer of a fluid whose viscosity depends strongly on both temperature and pressure, defined in an Arrhenius form. The model is solved numerically for extremely large viscosity variations across a unit aspect ratio cell, and steady solutions are obtained. To improve the efficiency of numerical computation, we introduce a modified viscosity law with a low temperature cut-off. We demonstrate that this simplification results in markedly improved numerical convergence without compromising accuracy. Continued numerical experiments suggest that narrow cells are preferred at extreme viscosity contrasts. We are then able to determine the asymptotic structure of the solution, and it agrees well with the numerical results. Beneath a stagnant lid, there is a vigorous convection in the upper part of the cell, and a more sluggish, higher viscosity flow in the lower part of the cell. We then offer some comments on the meaning and interpretation of these results for planetary mantle convection.

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Davies, A. Michael. "Computational and experimental three-dimensional conductive heat flows in and around buildings." Thesis, University of Westminster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238946.

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Tziranis, Alexander Konstantinos 1968. "Temperature, heat flux, and velocity measurements in oscillating flows with pressure variations." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12790.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1992.
Vita.
Includes bibliographical references (leaves 99-101).
by Alexander Konstantinos Tziranis.
M.S.

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Vujisić, Ljubomir B. (Ljubomir Branislav). "Heat transfer at transition to turbulence in channel flows with eddy promoters." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36499.

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35

Simonetti, Marco. "Study of convective heat transfer phenomena for turbulent pulsating flows in pipes." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2057/document.

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Dans le but de réduire la consommation en carburant et les émissions de CO2 des moteurs à combustion interne, un des leviers, qui a intéressé diffèrent acteurs dans le secteur automobile, est la récupération de l’énergie thermique disponible dans les gaz d’échappement. Malgré différents technologie ont été investigués dans le passé; les transferts de chaleur qui apparient dans les gaz d’échappement n’ont pas encore étés suffisamment étudiés. Le fait que les échanges de la chaleur apparent dans des conditions pulsatives, notamment due aux conditions de fonctionnement moteur, rende les connaissances acquis jusqu’à présent limités et ne pas exploitables. A l’état actuel on n’est pas capable de pouvoir prédire le transfert thermique convectif des écoulements pulsé. Les travaux de cette thèse s’instaurent dans la continuité de ce besoin, l’objectif principal est donc l’étude expérimentale du transfert thermique convectif des écoulements turbulent pulsés dans un conduit cylindrique. La première partie de ce travail a été consacrée à le dimensionnement d’un moyen d’essais permettant la création d’un écoulement pulsé type moteur; en suite différents méthodes de mesures ont étés développes afin de connaitre les variations instantanés de vitesse et température de l’écoulement. Plusieurs essais ont été reproduits afin de caractériser l’impact de la pulsation sur le transfert de la chaleur. Les résultats expérimentaux ont été analysés avec deux approches différentes: dans un premier temps une approche analytique 1D a permis de mettre en évidence le mécanisme principal responsable de l’amélioration du transfert thermique convectif,ainsi, il a fourni des éléments supplémentaires pour le futur développement de modèles mathématiques plus adaptés à la prédiction des transferts d’énergie. En suite une approche 2D, supporté d’une phase de modélisation numérique, a permis de caractériser le mécanisme de transport radial d’énergie thermique
Waste Energy Recovery represents a promising way to go further in fuel saving and greenhouse emissions control for Internal Combustion Engine applications. Although several technologies have been investigated in the past few years, the convective heat transfers, playing an important role in the energy exchanges at the engine exhaust, has not receive enough attention. Heat transfers, in such applications, occur in pulsating conditions because of the engine operating conditions, making thus the actual knowledge of the heat transfer phenomena limited and not exploitable. Nowadays there is not any model capable to predict convective heat transfers for pulsating flows. In this context, the present thesis addresses the purpose to study the convective heat transfer phenomena, by an experimental approach, occurring for turbulent pulsating flows in pipes. In the first part of this work, an experimental apparatus has been designed to reproduce an exhaust type pulsating flow in fully managed conditions, as well as, several measurement techniques have been developed to know the instantaneous profiles of air temperature and velocity. Many experiments have been performed in order to characterize the impact of the flow pulsation on the convective heat transfers. In the second part of this work, the experimental results have been analyzed with two different approaches: firstly, with a 1D assumption the time-average convective heat transfers has been computed, and the major mechanism responsible of the heat transfer enhancement has been pointed out. Furthermore, it has been possible to highlight the mathematical term representative of such mechanism, which should be accounted in future to define a more adapted numerical model for the heat transfer prediction. In a second phase with a 2D assumption, and, with an energy and a fluid-mechanic computational phase, the radial transport of thermal energy has been characterized for a pulsating flow

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Rajamani, Vignesh. "Heat transfer in continuum and non-continuum plasma flows in material processing applications." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1130076192.

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Birken, Philipp [Verfasser]. "Numerical Simulation of Flows at Low Mach Numbers with Heat Sources / Philipp Birken." Aachen : Shaker, 2006. http://d-nb.info/117052916X/34.

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Kang, Seongwon. "An improved immersed boundary method for computation of turbulent flows with heat transfer /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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Kamsanam, Wasan. "Development of experimental techniques to investigate the heat transfer processes in oscillatory flows." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/29067.

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Heat exchangers are important components of thermoacoustic devices. In oscillatory flow conditions, the flow and temperature fields around the heat exchangers can be quite complex, and may significantly affect heat transfer behaviour. As a result, one cannot directly apply the heat transfer correlations for steady flows to the design of heat exchangers for oscillatory flows. The fundamental knowledge of heat transfer in oscillatory flows, however, is still not well-established. The aim of the current work is to investigate the influence of certain geometric parameters of heat exchangers, and of operating conditions in oscillatory flow on heat transfer performance. The heat transferred between two heat exchangers forming a couple was measured over a range of testing conditions. Three couples of finned-tube heat exchangers with different fin spacing were selected for the experiment. The main parameters considered were fin spacing, fin length, thermal penetration depth and gas displacement amplitude. Their effects on the heat exchanger performance were studied. The results are summarised and analysed in terms of heat transfer rate, Nusselt number and heat transfer effectiveness; the latter defined by the ratio of the actual heat transfer rate to the maximum possible heat transfer rate. The measurement results are compared with results from models widely used in the design of thermoacoustic heat exchangers: Time-Average Steady-Flow Equivalent (TASFE), Root Mean Square Reynolds Number (RMSRe), boundary layer conduction model and selected correlations developed by different authors. Based on the experimental data, a new correlation is established aimed at improving the reliability of oscillatory flow heat transfer predictions. The correlation is proposed for the relationship between heat transfer effectiveness, and the normalized displacement amplitude and the normalized fin spacing (the ratio of fin spacing to thermal penetration depth). The uncertainties associated with the measurement of heat transfer rate are also considered.

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Hachem, Elie. "Stabilized finite element method for heat transfer and turbulent flows inside industrial furnaces." Paris, ENMP, 2009. http://pastel.paristech.org/5656/01/EH-These.pdf.

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La connaissance du comportement thermique des fours et des pièces est un problème difficile et cependant essentiel dans les thématiques de recherche industrielles actuelles. L'industrie cherche à se doter de moyens numériques de plus en plus efficaces tout en réduisant sans cesse le temps de calcul afin de modéliser des pièces et des assemblages de plus en plus réalistes. Les cinétiques de chauffe ainsi que la distribution de la température dans l'enceinte et dans les pièces traitées doivent également être maîtrisées, afin d'améliorer la qualité des produits chauffées en terme de résistance et dureté. Le travail présenté dans cette thèse porte donc sur le développement de méthodes de résolution numérique pour la simulation du transfert thermique. Ces méthodes permettent le calcul couplé de la température des pièces avec l'environnement du four afin d'optimiser la géométrie de ces pièces, leur position dans le four mais également les conditions initiales de chauffe. Le calcul de dynamique des fluides (CFD) peut être considéré comme un puissant outil technique de prédiction de l'écoulement des fluides et du transfert thermique dans des cas industriels réalistes. La première partie de la thèse porte sur l'étude de schémas numériques avancés relatifs aux méthodes éléments finis stabilisés. Ces méthodes de calculs efficaces ont étaient utilisées pour simuler des écoulements instationnaires et des transferts thermiques conjugués. Par la suite, deux modèles de turbulence (modèle k-epsilon et modèle Large Eddy Simulation) sont introduits et utilisés pour prendre en compte les écoulements complexes et turbulents dans l'enceinte du four. Le transfert radiatif est assuré par la résolution du modèle P1 tout en calculant un terme source volumique qui sera intégré dans l'équation de la chaleur. La deuxième partie de cette thèse se consacre à la mise en place d'une méthodologie de discrétisation robuste qui permet aux utilisateurs de générer de façon entièrement automatique un seul maillage. Ce maillage contient à la fois des domaines axés sur la résolution d'un problème fluide (air, eau, …) mais également solides spécifiques aux structures, et ce quel que soit le niveau de détail et donc de complexité du cas étudié. Cette approche, connue sous le nom d' « immersion de volume », garantit un maillage anisotrope précis aux interfaces fluide-solide afin de capturer plus précisément les gradients thermiques et la forte discontinuité des propriétés physiques. Cette méthode offre donc une grande flexibilité dans la mise en données du problème mixte fluide-structure et aussi dans la prise en compte de plusieurs géométries (four, pièces, supports) et elle est également bien adaptée aux solveurs thermomécaniques développés
The development of efficient methods to understand and simulate conjugate heat transfer for multi-components systems appears in numerous engineering applications and still a need for industrials, especially in the case of the heat treatment of high-alloy steel by a continuously heating process inside industrial furnaces. The thermal history of the load and the temperature distribution in the furnace are critical for the final microstructure and the mechanical properties of the treated workpieces and can directly determined their final quality in terms of hardness, toughness and resistance. The main objectives of this thesis is then to understand and better model the heat treatment process at the same time in the furnace chamber and within the workpieces under specified furnace geometry, thermal schedule, parts loading design, initial operation conditions, and performance requirements. The Computational Fluid Dynamics (CFD) simulation provides a useful tool to predict the temperature evolution and such processes. In the first part of this work, various stabilized finite element methods required for computing the conjugate heat transfer and the incompressible flows are proposed and analyzed. Two turbulence models, the k-epsilon and the Large Eddy Simulations (LES) models were introduced and used to simulate and take into account the complex turbulent flows inside the furnace chamber. The effect of thermal radiation was appropriately accounted for by means of a volumetric model known as the P1-model. In the latter part of this work, a multidomain approach referred as the immersed volume method (IVM) is introduced and applied to treat the fluid-solid interactions. It is based on the use of an adaptive anisotropic local grid refinement by means of the level-set function to well capture the sharp discontinuities of the fluid-solid interface. The proposed method showed that it is well suited to treat simultaneously the three modes, convective, conductive and radiative heat transfer that may interfere in both the fluid part and the solid part using anisotropic finite element meshes

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RAJAMANI, VIGNESH. "HEAT TRANSFER IN CONTINUUM AND NON-CONTINUUM PLASMA FLOWS IN MATERIALS PROCESSING APPLICATIONS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1130076192.

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Pond, Ian. "Toward an Understanding of the Breakdown of Heat Transfer Modeling in Reciprocating Flows." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/477.

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Reynolds average Navier-Stokes (RANS) modeling has established itself as a critical design tool in many engineering applications, thanks to its superior computational efficiency. The drawbacks of RANS models are well known, but not necessarily well understood: poor prediction of transition, non-equilibrium flows, mixing and heat transfer, to name the ones relevant to our study. In the present study, we use a direct numerical simulation (DNS) of a reciprocating channel flow driven by an oscillating pressure gradient to test several low- and high-Reynolds' RANS models. Temperature is introduced as a passive scalar to study heat transfer modeling. Low-Reynolds' models manage to capture the overall physics of wall shear and heat flux well, yet with some phase discrepancies, whereas high-Reynolds' models fail. We have derived an integral method for wall shear and wall heat flux analysis, which reveals the contributing terms for both metrics. This method shows that the qualitative agreement appears more serendipitous than driven by the ability of the models to capture the correct physics. The integral method is shown to be more insightful in the benchmarking of RANS models than the typical comparisons of statistical quantities. This method enables the identification of the sources of discrepancies in energy budget equations. For instance, in the wall heat flux, one model is shown to have an out of phase dynamic behavior when compared to the benchmark results, demonstrating a significant issue in the physics predicted by this model. Our study demonstrates that the integral method applied to RANS modeling yields information not previously available that should guide the derivation of physically more accurate models.

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Garicano, Mena Jesus. "On the computation of heat flux in hypersonic flows using residual distribution schemes." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209174.

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In this dissertation the heat flux prediction capabilities of Residual Distribution (RD) schemes for hypersonic flow fields are investigated. Two canonical configurations are considered: the flat plate and the blunt body (cylinder) problems, with a preference for the last one. Both simple perfect gas and more complex thermo-chemical non-equilibrium (TCNEQ) thermodynamic models have been considered.

The unexpected results identified early in the investigation lead to a thorough analysis to identify the causes of the unphysical hypersonic heating.

The first step taken is the assessment of the quality of flow field and heat transfer predictions obtained with RD methods for subsonic configurations. The result is positive, both for flat plate and cylinder configurations, as RD schemes produce accurate flow solutions and heat flux predictions whenever no shock waves are present, irrespective of the gas model employed.

Subsonic results prove that hypersonic heating anomalies are a consequence of the presence of a shock wave in the domain and/or the way it is handled numerically.

Regarding hypersonic flows, the carbuncle instability is discarded first as the cause of the erroneous stagnation heating. The anomalies are shown next to be insensitive to the kind and level of dissipation introduced via the (quasi-)positive contribution P to blended B schemes. Additionally, insufficient mesh resolution locally over the region where the shock wave is captured numerically is found to be irrelevant.

Capturing the bow shock in a manner that total enthalpy is preserved immediately before and after the numerical shock wave is, on the contrary, important for correct heating prediction.

However, a carefully conceived shock capturing term is, by itself, not sufficient to guarantee correct heating predictions, since the LP scheme employed (be it stand-alone in a shock fitting context or combined into a blended scheme for a shock capturing computation) needs to be immune to spurious recirculations in the stagnation point.

Once the causes inducing the heating anomalies identified, hypersonic shocked flows in TCNEQ conditions are studied.

In order to alleviate the computational effort necessary to handle many species non-equilibrium (NEQ) models, the extension of an entropic (or symmetrizing) variables formulation RD to the nS species, two temperature TCNEQ model is accomplished, and the savings in computational time it allows are demonstrated.

The multi-dimensional generalization of Roe-like linearizations for the TCNEQ model is addressed next: a study on the existence conditions of the linearized state guaranteeing discrete conservation is conducted.

Finally, the new dissipative terms derived for perfect gas are adapted to work under TCNEQ conditions; the resulting numerical schemes are free of the temperature undershoot and Mach number overshoot problem afflicting standard CRD schemes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Bressloff, N. W. "CFD prediction of coupled radiation heat transfer and soot production in turbulent flames." Thesis, Cranfield University, 1996. http://hdl.handle.net/1826/3622.

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The mechanisms governing the formation and destruction of soot in turbulent combustion are intimately coupled to thermal radiation due to the strong dependence of sooting processes and radiative loss on temperature. Detailed computational fluid dynamics (CFD) predictions of the radiative and soot output from turbulent non-premixed flames are normally performed by parabolic algorithms. However, the modelling of combustion systems, such as furnaces and unwanted enclosure fires, often require a fully elliptic description of the flow field and its related physical phenomena. Thus, this thesis investigates the intimate coupling between radiative energy exchange and the mechanisms governing soot formation and destruction within a three-dimensional, general curvilinear CFD code. Thermal radiation is modelled by the discrete transfer radiation model (DTRM). Special emphasis is given to approximate solutions to the radiative transfer equation encompassing various models for the radiative properties of gases and soot. A new algorithm is presented, entitled the differential total absorptivity (DTA) solution, which, unlike alternative solutions, incorporates the source temperature dependence of absorption. Additionally, a weighted sum of gray gases (WSGG) solution is described which includes the treatment of gray boundaries. Whilst the DTA solution is particularly recommended for systems comprising large temperature differences, the WSGG solution is deemed most appropriate for numerical simulation of lower temperature diffusion flames, due to its significant time advantage. The coupling between radiative loss and soot concentration is investigated via a multiple laminar flamelet concept applied within the CFD simulation of confined turbulent diffusion flames burning methane in air at 1 and 3 atm. Flamelet families are employed relating individual sooting mechanisms to the level of radiative loss, which is evaluated by the DTRM formulated for emitting-absorbing mixtures of soot, C02 and H20. Combustion heat release is described by an eddy break-up concept linked to the k-c turbulence model, whilst temperature is evaluated from the solved enthalpy field. Detailed comparisons between prediction and experiment for the critical properties of mixture fraction, temperature and soot volume fraction demonstrate the effectiveness of this novel, coupled strategy within an elliptic flow field calculation.

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Bapat, Akhilesh V. "Experimental and numerical evaluation of single phase adiabatic flows in plain and enhanced microchannels /." Online version of thesis, 2007. http://hdl.handle.net/1850/5536.

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Chick, Eric. "Problems in forced and free convection." Thesis, Keele University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241449.

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Wiberg, Roland. "A study of heat transfer from cylinders in turbulent flows by using thermochromic liquid crystals." Licentiate thesis, KTH, Mechanics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1695.

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In gas quenching, metal parts are rapidly cooled from hightemperatures, and the convection heat transfer coefficientdistributions are of importance for the hardness and thedistortion (the shape nonuniformities) of the quenched parts.Thermochromic liquid crystals (TLC) and a thin foil techniques,were investi- gated and used for studies of a circular cylinderin axial flows, affected and not affected by upstream owmodifying inserts. Quadratic prisms in cross ows were alsostudied, a single prism, two prisms arranged in-line, and forfour prisms arranged in a square pattern. In this study,particle image velocime- try (PIV) was used for visualizationof the flow, giving physical insight to the convection heattransfer data. Further, relations of the typeNu=CReewere established. The TLC and thin foil techniques werealso used to indicate the dimensions of separated flowregions.

Descriptors:Fluid mechanics, wind-tunnel, turbulence,gas quenching, con- vection heat transfer, thermochromic liquidcrystals, calibration, temperature measurement errors, thinfoils, particle image velocimetry, cylinder in axial flow, flowmodifying inserts, quadratic prisms in cross flow

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Keinath, Brendon Louis. "Void fraction, pressure drop, and heat transfer in high pressure condensing flows through microchannels." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45806.

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Flow mechanisms affect transport processes during condensation. Most studies on two-phase flow regimes are qualitative in nature, typically providing only information to guide the identification of the respective regimes and the transitions between them. These studies have, however, not yielded quantitative information to assist the development of pressure drop and heat transfer models. Such qualitative studies have also yielded results with considerable variability between investigators. A comprehensive investigation of flow mechanisms, void fraction, pressure drop and heat transfer during condensation of R404A in microchannels was conducted. In contrast to all prior investigations, high-speed video recordings and image analyses were used to directly measure void fraction, slug frequencies, vapor bubble velocity, vapor bubble dimensions and liquid film thicknesses in tube diameters ranging from 0.508 to 3.00 mm. Experiments were conducted at reduced pressures and mass fluxes ranging from 0.38 to 0.77 and 200 to 800 kg m-2 s-1, respectively, to document their influences on the condensation process at local vapor qualities ranging from 0 to 1. This information was used to develop a model for the void fraction in condensing flows. A complementing set of heat transfer and pressure drop measurements were conducted on the same geometries at similar conditions, and the void fraction model was used in conjunction with these measurements to develop improved heat transfer and pressure drop models. This comprehensive set of experiments and analyses yields a self-consistent and accurate treatment of high-pressure condensation in small hydraulic diameter geometries. Furthermore, the heat transfer model was found to agree well with condensing ammonia and carbon dioxide data that were obtained at significantly different conditions in different tube diameters. The added physical understanding of the condensation process and the models developed will serve as important building blocks for the design of microscale condensers and thermal systems.

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Ciofalo, Michele. "Large-eddy simulation of turbulent flows with heat transfer in simple and complex geometries." Thesis, University of London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262005.

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Etaig, Saleh. "Investigation of the enhancement of convective heat transfer for wall-bounded flows utilizing nanofluids." Thesis, Northumbria University, 2017. http://nrl.northumbria.ac.uk/36146/.

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Heat transfer is one of the main phenomena in many industrial processes and applications such as heat exchangers and power generation. For many years, liquids such as water, oil and ethylene glycol had been used as the heat transfer fluids. These fluids have a poor inherent thermal conductivity. Thus, innovation in developing another generation of heat transfer fluids is required for better efficiency. Nanofluids represent a class of pioneering engineering heat transfer fluids. These fluids are made by dispersing metallic or non-metallic particles with nanometer size in various base fluids. With their predominant thermophysical properties, nanofluids are promising medium for heat transfer enhancement of next generation heat dissipation in many industrial applications. This research is focused on studying the enhancement of heat transfer in wall-bounded flows using nanofluids. The enhancement was investigated numerically by modelling nanofluids using CFD technique. Several configurations were tested with different flow types namely, natural convection in a square cavity, forced convection in a backward facing step and flow in micro-channels. The effect of Brownian motion on the heat transfer performance and fluid flow characteristic was investigated for natural convection flow using various nanofluids with different volume fractions for a range of Raleigh numbers. The results showed that the increase in the volume fraction deteriorates the heat transfer. On the other hand, the increase in Ra number promotes the heat transfer rate. For backward facing step, the effect of the inclination angle of the face step using nanofluid was investigated thoroughly. The increase in the facing step angle was found not preferable from a heat transfer perspective, the results showed that the Nu number decreased by up to 3% when 90o inclination angle is tested compared to 125o inclination angle and this information may be valuable for designing industrial equipment. An empirical effective viscosity model is proposed as part of the study. The model is based on available experimental, numerical and theoretical data. The sensitivity of the model has been rigorously scrutinized for different volume fractions and wide range of temperatures. The results showed that the proposed model is reliable and can be employed for various flow configurations. The proposed model has also been used to predict flow through microchannels of various cross-sectional shapes and area. The effect on friction factor for such channels as well as the heat transfer performance has been thoroughly investigated. It was found from this investigation that most of the heat transfer occurred in the U-bend microchannel took place at the downstream flow and it was higher by up to 40.5% compared to the upstream when 6% volume fraction was tested. Finally, a general purpose test rig was designed and built in the lab to conduct some experimental investigation for a double pipe heat exchanger with nanofluids as a coolant. Four different nanoparticles were purchased and are ready for synthesising the nanofluid using ultrasound bath and magnetic stirrer. The rig is ready for the run and several test runs were conducted using water as the base fluid. Unfortunately, due to certain technical extenuating circumstances, experiments using nanofluids could not be conducted within the time span of the project.

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Dissertations / Theses on the topic 'Heat flows'

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