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1
Behbahani, Reza M. "Heat transfer and heat transfer fouling in phosphoric acid evaporators". Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/842710/.
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The primary problem in concentrating phosphoric acid is due to fouling on the tube-side of the heat exchangers of the evaporators. Scaling on the heat transfer surfaces occurs because of high supersaturation of phosphoric acid liquor with respect to calcium sulfate. A review of the existing literature reveals that no information is available on heat transfer and on crystallisation fouling of phosphoric acid solutions. Solubility of calcium sulfate is very important with regards to the scaling problems in phosphoric acid concentration plants. Hence, the solubility of different calcium sulfate types in phosphoric acid solution was studied and their dependency on acid concentration and temperature were investigated. A large number of measurements of heat transfer coefficient for water and phosphoric acid solutions under forced convective, subcooled flow boiling and pool boiling conditions at different temperatures, flow velocities, heat fluxes and concentrations were performed. The results show that the modified Gnielinski and Petukhov and Popov con-elations fit the experimental results for forced convective heat transfer to phosphoric acid solutions better than the other correlations. The Chen model and associated correlations were found suitable for the prediction of subcooled flow boiling heat transfer coefficients for phosphoric acid solutions. Applying the actual temperature driving force (Tw-Ti) instead of (Tw-Tb), a theoretical model was proposed, which permits the prediction of pool boiling heat transfer coefficients of phosphoric acid solutions with good accuracy. A large number of fouling experiments were carried out at different flow velocities, surface temperatures and concentrations to determine the mechanisms, which control deposition process. After clarification of the effect of operational parameters on the deposition process, a mathematical model was developed for prediction of fouling resistance. The activation energy evaluated for the surface reaction of the deposit formation was found to be 56,829 J/mol. The predicted fouling resistances were compared with the experimental data. Quantitative and qualitative agreement for measured and predicted fouling rates, is good. Also, a kinetic model for crystallization fouling was developed, using the field data. The predictions of the suggested model are in good agreement with the plant operating data. Finally, a numerical model was developed for computer simulation of shell and tube heat exchangers. The agreement between the field data and the prediction of the model was very satisfactory.
2
Macbeth, Tyler James. "Conjugate Heat Transfer and Average Versus Variable Heat Transfer Coefficients". BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5801.
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An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.
3
Roth, Eric. "Transient heat transfer". PDXScholar, 1991. https://pdxscholar.library.pdx.edu/open_access_etds/4264.
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With the advent of the new high Tc superconductors, liquid nitrogen will be one of the preferred cryogens used to cool these materials. Consequently, a more thorough understanding of the heat transfer characteristics of liquid nitrogen is required. In our investigations we examine the transient heating characteristics of liquid nitrogen to states of nucleate and film boiling under different liquid flow conditions. Using a platinum hot wire technique, it is verified that there is a premature transition to film boiling in the transient case at power levels significantly lower than under steady state nucleate boiling conditions. It is also shown that the premature transition can be reduced or eliminated depending on the flow velocity.
4
Webber, Helen. "Compact heat exchanger heat transfer coefficient enhancement". Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540881.
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Riegler, Robert L. "Heat transfer optimization of grooved heat pipes /". free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1422959.
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Wahlberg, Tobias. "Modeling of Heat Transfer". Thesis, Mälardalens högskola, Akademin för hållbar samhälls- och teknikutveckling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-12217.
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Modeling of heat transfer using Dymola. In this report a evaporator, economizer and superheater where modeled. The report describes how the models where modeled and what input was most suitable for a accurate model.
7
Jones, Alastair Stephen. "Convection heat transfer problems". Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267356.
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Najibi, Seyed Hesam. "Heat transfer and heat transfer fouling during subcooled flow boiling for electrolyte solutions". Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/773/.
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Holzaepfel, Gregory M. "Convective Heat Transfer in Parallel Plate Heat Sinks". Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1292521397.
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Wang, Yufei. "Heat exchanger network retrofit through heat transfer enhancement". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/heat-exchanger-network-retrofit-through-heat-transfer-enhancement(c504dc06-f261-4968-8c58-4f4de153c694).html.
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Heat exchanger network retrofit plays an important role in energy saving in process industry. Many design methods for the retrofit of heat exchanger networks have been proposed during the last three decades. Conventional retrofit methods rely heavily on topology modifications which often results in a long retrofit duration and high initial costs. Moreover, the addition of extra surface area to the heat exchanger can prove difficult due to topology, safety and downtime constraints. These problems can be avoided through the use of heat transfer enhancement in heat exchanger network retrofit. This thesis develops a heuristic methodology and an optimization methodology to consider heat transfer enhancement in heat exchanger network retrofit. The heuristic methodology is to identify the most appropriate heat exchangers requiring heat transfer enhancements in the heat exchanger network. From analysis in the heuristic roles, some great physical insights are presented. The optimisation method is based on simulated annealing. It has been developed to find the appropriate heat exchangers to be enhanced and to calculate the level of enhancement required. The new methodology allows several possible retrofit strategies using different retrofit methods be determined. Comparison of these retrofit strategies demonstrates that retrofit modification duration and pay-back time are reduced significantly when only heat transfer enhancement is utilised. Heat transfer enhancement may increase pressure drop in a heat exchanger. The fouling performance in a heat exchanger will also be affected when heat transfer enhancement is used. Therefore, the implications of pressure drop and fouling are assessed in the proposed methodology predicated on heat transfer enhancement. Methods to reduce pressure drop and mitigate fouling are developed to promote the application of heat transfer enhancement in heat exchanger network retrofit. In optimization methodology considering fouling, the dynamic nature of fouling is simulated by using temperature intervals. It can predict fouling performance when heat transfer enhancement is considered in the network. Some models for both heat exchanger and heat transfer enhancement are used to predict the pressure drop performance in heat exchanger network retrofit. Reducing pressure by modifying heat exchanger structure is proposed in this thesis. From case study, the pressure drop increased by heat transfer enhancement can be eliminated by modifying heat exchanger structure.
11
Bartuli, Erik. "Optimization of Heat Transfer Surfaces of Heat Exchangers". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401602.
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Disertační práce je zaměřena na kovové a polymerní výměníky tepla. Hlavním předmětem zkoumání je optimalizace teplosměnných ploch za účelem zvýšení účinnosti výměníku tepla. Tyto cíle byly dosaženy experimentálně a numericky pomocí modelování v ANSYS. Na základě dosažených výsledků byla rozpracována technologie křížového navíjení polymerních výměníků z dutých vláken. Experimentální zařízení původně určené pro navíjení tlakových nádrží bylo modifikované pro automatizovanou výrobu polymerních výměníků z dutých vláken, ježto může být použita při jejich masové výrobě. Tato práce se také zabývala výměníky tepla pro klimatizační systémy. Byly zkoumány možnosti využití polymerních výměníků z dutých vláken v těchto systémech. Mimo jiné byla provedena studie vlivu cyklického tepelného zatížení standardního kovového žebrovaného tepelného výměníku.
12
Dellorusso, Paul Robert. "Electrohydrodynamic heat transfer enhancement for a latent heat storage heat exchanger". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0027/MQ31562.pdf.
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Souccar, Adham. "Heat transfer and mass transfer with heat generation in drops at high peclet number /". Connect to Online Resource-OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177603981.
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Dissertation (Ph.D.)--University of Toledo, 2007.Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy degree in Engineering." Bibliography: leaves 65-74.
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Lee, Jeongik. "Gas heat transfer in a heated vertical channel under deteriorated turbulent heat transfer regime". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41296.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (p. 283-289).
Passive cooling via natural circulation of gas after a loss of coolant (LOCA) accident is one of the major goals of the Gas-cooled Fast Reactor (GFR). Due to its high surface heat flux and low coolant velocities under natural circulation in post-LOCA scenarios, the capability of turbulent gas flow to remove heat from the GFR core can be impaired by either a buoyancy effect or an acceleration effect. These phenomena lead to a Deteriorated Turbulent Heat Transfer (DTHT) regime. To predict accurately the cladding temperature at the hot spot, reliable heat transfer correlations that account correctly for these effects are needed. This work addresses this need by experimentally obtaining heat transfer data and developing new heat transfer correlations that can be used in system analysis codes, such as RELAP5-3D, to reduce uncertainties of predictions in these DTHT regimes. An experimental facility was designed and built using similitude analysis to match key experimental loop parameters to the GFRs' Decay Heat Removal (DHR) system operating conditions to the largest extent possible. Through a thorough literature survey two non-dimensional numbers namely (1) the buoyancy parameter (Bo*) and (2) the acceleration parameter (K,) were identified as important indicators of the DTHT regime. The experimental data was collected for a range of (1) inlet Reynolds number from 1800 to 42,700, (2) inlet Bo* up to 1X10-5 (3) and inlet Kv up to 5x10-6. The data showed significantly higher reduction of the Nusselt number (up to by 70%) than previously reported (up to 50%). Also, the threshold at which DTHT regime occurs was found to be at smaller non-dimensional numbers than previously reported. A new phenomenon "re-turbulization", where the laminarized heat transfer recovers back to turbulent flow along the channel, was observed in the experiment.
(cont.) A new single phase gas flow heat transfer map is proposed based on the non-dimensional heat flux and the Reynolds number in our data, and is shown to compare well with data in the literature. Three sets of new correlations were developed, which reflect both the buoyancy and acceleration effects and have better accuracy as well as ease of numerical implementation than the existing correlations. The correlations are based on the Gnielinski correlation and replace the Reynolds number subtracting constant by a functional form that accounts for the buoyancy and acceleration effects separately, or in the combined form through a newly introduced non-dimensional "DTHT" number. The three correlation types have different complexity level, with the first being the most complex and the third being the most simple and easy to apply without any need for iterations. Additional runs with natural circulation showed that the friction factor in the DTHT regime could be significantly higher than predicted by conventional friction factor correlations, although more experiments will be needed to develop reliable correlations for pressure drop in these regimes. Overall, it is concluded that due to the low heat transfer coefficient and increased friction factor in the DTHT regime, the GFR DHR system should be ideally designed to operate outside the DTHT regime to (1) avoid reduction of heat transfer capability, (2) avoid increase of pressure drop, and (3) reduce uncertainties in predictions of the cladding temperature.
by Jeongik Lee.
Ph.D.
15
Souccar, Adham W. "Heat Transfer and Mass Transfer with Heat Generation in Drops at High Peclet Number". University of Toledo / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177603981.
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Parker, Gregory K. "Heat transfer parametric system identification". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA268525.
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Douglas, Zachary W. "Acoustically Enhanced Boiling Heat Transfer". Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16325.
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An acoustic field is used to increase the critical heat flux of a copper boiling heat transfer surface. The increase is a result of the acoustic effects on the vapor bubbles. Experiments are being performed to explore the effects of an acoustic field on vapor bubbles in the vicinity of a rigid heated wall. Work includes the construction of a novel heater used to produce a single vapor bubble of a prescribed size and at a prescribed location on a flat boiling surface for better study of an individual vapor bubble s reaction to the acoustic field. Work also includes application of the results from the single bubble heater to a calibrated copper heater used for quantifying the improvements in critical heat flux.
18
Ozerinc, Sezer. "Heat Transfer Enhancement With Nanofluids". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611862/index.pdf.
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A nanofluid is the suspension of nanoparticles in a base fluid. Nanofluids are promising for heat transfer enhancement due to their high thermal conductivity. Presently, discrepancy exists in nanofluid thermal conductivity data in the literature, and enhancement mechanisms have not been fully understood yet. In the first part of this study, a literature review of nanofluid thermal conductivity is performed. Experimental studies are discussed through the effects of some parameters such as particle volume fraction, particle size, and temperature on conductivity. Enhancement mechanisms of conductivity are summarized, theoretical models are explained, model predictions are compared with experimental data, and discrepancies are indicated.
Nanofluid forced convection research is important for practical application of nanofluids. Recent experiments showed that nanofluid heat transfer enhancement exceeds the associated thermal conductivity enhancement, which might be explained by thermal dispersion, which occurs due to random motion of nanoparticles. In the second part of the study, to examine the validity of a thermal dispersion model, hydrodynamically developed, thermally developing laminar Al2O3/water nanofluid flow inside a circular tube under constant wall temperature and heat flux boundary conditions is analyzed by using finite difference method with Alternating Direction Implicit Scheme. Numerical results are compared with experimental and numerical data in the literature and good agreement is observed especially with experimental data, which indicates the validity of the thermal dispersion model for explaining nanofluid heat transfer. Additionally, a theoretical analysis is performed, which shows that usage of classical correlations for heat transfer analysis of nanofluids is not valid.
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Ströder, Simon. "Convective Heat Transfer with Nanofluids". Thesis, KTH, Tillämpad termodynamik och kylteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48216.
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The present Master thesis is concerned with forced convection heat transfer in laminar and turbulent flowwith nanofluids. Nanofluids are defined as a colloidal suspension of particles in a base fluid, where theparticles have a characteristic length of less than 100 nm. Experiments were conducted to determine thequalification of nanofluids for laminar and turbulent flow forced convection heat transfer. Theexperiments were conducted in two different devices: Firstly, a stainless steel pipe with an inner diameterof 3.7 mm, heated directly by a DC current in the pipe wall, and secondly, a tubular heat exchanger, whichthe fluid was cooled down in. The tested nanofluids were not only assessed considering Nu/Re, as it hasbeen found to be common in a short literature review, but also by taking into account the pressure drop indifferent ways. A way of considering pressure drop in non-dimensional quantities was introduced that hadnot been seen in literature. In some cases, an opposite assessment for the fluid could be found fromcomparing Nu/Re of base fluid and nanofluid and comparing h/Δp. Difficulties during validation of thetest rig had called for system improvement; an extensive error investigation was conducted on the test rigand the calculation. The error investigation resulted in changes concerning the calculation and the test rig.
20
Ekundayo, C. O. "Heat Transfer In Enclosures: Ovens". Thesis, Cranfield University, 1994. http://hdl.handle.net/1826/3995.
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The use of natural convection to effect heat transfers in enclosures is limited
principally because of its low heat transfer coefficients. This study aimed to
establish a better understanding of the heat transfers occurring in
enclosures which are heated by cylindrical heat sources and to identify
preferred heating arrangements for improving the rates of natural convection
heat transfers.
Experimental investigations including interferometric observations were
carried out on a square-sectioned enclosure containing a rectangularsectioned,
isothermal inner body and cylindrical, sheathed electrical heating
elements. The locations of the heaters were varied and the effects on
natural convection heat transfers established. The findings conformed to
intuitive expectations, concluding that the maximum position for natural
convection heat transfer was with the heaters located in the lower half of the
sidewalls.
The flow patterns and heat transfer characteristics of a single horizontal
cylindrical (9.5mm dia) heater in a square-sectioned enclosure were studied
by traversing the heater both horizontally and vertically across the enclosure
at distinct Rayleigh numbers (7.5x104 and 1.1x105). Optimal positions for
maximum and minimum Nusselt numbers were established with respect to
heater diameter and vertical height, and horizontal offset from a vertical wall.
Flow and Interferometric observations were also carried out on an enclosed
single tubular 55mm dia. heater, and two 55mm dia. heaters. Improved
arrangements for enhanced heat losses by natural convection from
horizontal tubular arrays were deduced, applicable to arrays either totally
enclosed or In the proximity of a vertical wall.
A square-sectioned (35Ox35Oxl7OOmmtu)n nel oven was designed which
would withstand operations under vacuum. Within this enclosure, the heating
arrangements were located and varied essentially in the lower half of the
enclosure, flow and thermal profiles obtained, a multi-surface radiation
model developed and the convective heat transfers validated by evacuating
the enclosure. At oven temperatures, over 40% of the heat input was
achieved by natural convection.
21
Mealey, Liam Robert. "Heat Transfer in Porous Media". Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494108.
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Illingworth, Justin Barrett. "Fluid-solid heat transfer coupling". Thesis, University of Sussex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430954.
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This thesis documents the application of a computer code developed by the author which makes possible the coupling of heat transfer between fluid and solid thermal models. The code was written using FORTRAN and couples the commercial computational fluid dynamics (CFD) software FLUENT with the Rolls-Royce finite element analysis program, SC03. The thermal modelling of a solid domain bounded by a fluid typically uses heat transfer correlations to define the heat flux at those boundaries. Considerable engineering judgement is required to appropriately select and apply these correlations, so that they accurately model the flow and geometry being considered. The objective of the coupling code is to replace the correlations with a CFD model of the fluid. The coupling is achieved by extracting metal temperatures determined from the finite element solver, using them to define CFD boundary conditions, and passing heat fluxes from the resulting CFD solution back to the finite element model. The finite element model then solves the newly defined problem and the process is repeated until a converged solution is obtained. The coupling code was evaluated through its application to two test cases. The first was an axisymmetric representation of a compressor stator well rig, the experimental apparatus or which comprised a two stage axial compressor, driven by a single stage axial turbine. The coupling code was used to model a temperature transient generated in the rig by injecting liquid nitrogen into the mainstream annulus, upstream of the compressor stages. For the second test case, an industrial application was chosen with real engine geometry. Using an axisymmetric finite element whole engine model of the Rolls-Royce Trent 500 aero-engine the code was employed to couple both axisymmetric and three dimensional representations of the fluid domain surrounding the pre-swirl system. Following the successful completion of these two test cases, the coupling code (now known as SC89) was production released by Rolls-Royce in July 2004 and is now available to their engineering community, as a design tool worldwide.
23
Reddy, M. A. "Single phase heat transfer enhancement". Thesis, University of Manchester, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616903.
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This thesis presents investigations into the enhancement of heat transfer inside tubes using HiTRAN® tube inserts manufactured by Cal Gavin Ltd. The applicability of heat transfer enhancement in vertical thermo syphon reboilers was investigated using a computer simulation. In vacuum operation, reboilers can have a significant subcooled length (as high as 60 % of the tube length). Heat transfer coefficients in this region are lower than in the two-phase region. Using tube inserts, an increase is made in the heat transfer rate occurring in the sub-cooled region and, a corresponding increase in the length of the tube subjected to two-phase heat transfer and improvement of heat transfer performance results. Geometric variables of the tube insert were investigated experimentally, to study their influence on heat transfer and pressure drop performance. Loop density, loop wire diameter, core wire diameter, loop material and uniformity of loop density were investigated. Two experimental facilities were designed, commissioned and constructed to measure the heat transfer and pressure drop performance of these tube inserts. The new rig at UMIST is located in a flameproof location and was constructed with the intention of investigating a wide range of other processes in the future. Two tube inserts were tested over a Reynolds number range of 200 to 200000 using water as the working fluid. Adiabatic, cooling and heating tests were performed using an inside tube diameter of28.25 mm. At the Cal Gavin Ltd. facility, the rig was redesigned to extend the operating range of data collection. It was enhanced by the provision of automatic data collection, improved accuracy of temperature measurement and new equipment to allow cooling experiments. Tube inserts were tested between a Reynolds number of 100 to 2000 using a viscous oil as the working fluid. Again adiabatic, cooling and heating tests were performed. An inside tube diameter of 21.18 mm was used in the maj ority of the tests, but some preliminary results using a tube diameter of 28.45 mm are also reported. Using the results of the experimental work, pressure drop performance was correlated using an approach similar to that used for packed beds. It was found that 90 % of the data were correlated between ± 15 % of the prediction using specific insert dimensions and inside tube diameter. Further investigations into the prediction of heat transfer coefficients were made. However no general correlation could be developed from a fundamental basis, to predict heat transfer across the full range of Reynolds numbers investigated in this study. A recommendation is made for a suitable correlation. The influence of the insert geometry was associated with the fundamental pressure drop and heat transfer performance of the tube insert, leading to recommendations for the optimisation of tube insert design.
24
Schraudner, Steven. "Convective Heat Transfer in Nanofluids". Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5487.
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In recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we study the effects of radiation on the heat and mass transfer characteristics of nanofluid flows over solid surfaces. In Chapter 2, an investigation is made into the effects of radiation on mixed convection over a wedge embedded in a saturated porous medium with nanofluids, while in Chapter 3 results are presented for the effects of radiation on convection heat transfer about a cone embedded in a saturated porous medium with nanofluids. The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results in the literature, and the results are found to be in very good agreement. The numerical results for the velocity, temperature, volume fraction, the local Nusselt number and the Sherwood number are presented graphically. The salient features of the results are analyzed and discussed for several sets of values of the pertinent parameters. Also, the effects of the Rosseland diffusion and the Brownian motion are discussed.ID: 031001347; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Kuppalapalle Vajravelu.; Title from PDF title page (viewed April 18, 2013).; Thesis (M.S.)--University of Central Florida, 2012.; Includes bibliographical references (p. 32-34).
M.S.
Masters
Mathematics
Sciences
Mathematical Science; Industrial Mathematics
25
Khalifa, Abdul-Jabbar N. "Heat transfer processes in buildings". Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254459.
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Cooke, Adam. "Turbomachinery disc heat transfer uncertainty". Thesis, University of Sussex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442442.
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Govatzidakis, George John. "Heat transfer in rotating passages". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/49954.
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Siu, Billy Chin Pang. "Condensation heat transfer in microchannel /". View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?MECH%202004%20SIU.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 43-46). Also available in electronic version. Access restricted to campus users.
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Williams, Winifred Elizabeth. "HEAT TRANSFER IN THE MICROCIRCULATION". Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275277.
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Rahimi, Rahbar. "Heat transfer in bubble columns". Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380868.
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Nguyen, Clayton Ma. "Heat transfer coefficients of particulate in tubular heat exchangers". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53960.
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This experimental study explores the heat transfer from heated bare and finned tubular surfaces to particulates in packed bed cross flow. The results from this experiment will be used to help select the type of particulates that will be used. Additionally, these results will assist in estimating heat transfer in prototype and commercial particle to fluid heat exchangers (PFHX).
This research is part of larger effort in the use of particulates in concentrating solar power technology. These solid particles are heated by concentrated sunlight to very high temperatures at which they are a suitable heat source for various thermal power and thermochemical cycles. Furthermore, one of the advantages of this concept is the ability to store thermal energy in the solid particles at relatively low cost. However, an important feature of any Particle Heat Receiver (PHR) system is the PFHX, which is the interface between the solar energy system and the thermal power or chemical system. In order to create this system material data is needed for the design and optimization of this PFHX.
The paper focuses on the heat transfer properties of particulates to solid surfaces under plug flow conditions. The particulates will be evaluated for three grain sizes of sand and two grain sizes of proppants. These two materials will be tested at one, five and ten millimeters per second in order to see how the various flow rates, which will be required for different loads, will affect the heat transfer coefficient. Finally the heat transfer coefficient will also be evaluated for both finned and non-finned heat exchangers to see the effect that changes in the surface geometry and surface area have on the heat transfer coefficient. The heat transfer coefficient will help determine the appropriate material that will be used in the PHR system.
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Lee, Man. "Forced convection heat transfer in integrated microchannel heat sinks /". View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20LEE.
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Adams, Juan Carlos. "Advanced heat transfer surfaces for gas turbine heat exchangers". Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534221.
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McClean, A. "Heat transfer in a diver's respiratory gas heat exchanger". Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381650.
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Staats, Wayne Lawrence. "Active heat transfer enhancement in integrated fan heat sinks". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78179.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 205-211).
Modern computer processors require significant cooling to achieve their full performance. The "efficiency" of heat sinks is also becoming more important: cooling of electronics consumes 1% of worldwide electricity use by some estimates. Unfortunately, current cooling technologies often focus on improving heat transfer at the expense of efficiency. The present work focuses on a unique, compact, and efficient air cooled heat sink which addresses these shortcomings. While conventional air cooled heat sinks typically use a separate fan to force air flow over heated fins, the new design incorporates centrifugal fans directly into the body of a loop heat pipe with multiple planar condensers. These "integrated fans" rotate between the planar condensers, in close proximity to the hot surfaces, establishing a radially outward flow of cooling air. The proximity of the rotating impellers to the condenser surfaces results in a marked enhancement in the convective heat transfer coefficient without a large increase in input power. To develop an understanding of the heat transfer in integrated fan heat sinks, a series of experiments was performed to simultaneously characterize the fan performance and average heat transfer coefficients. These characterizations were performed for 15 different impeller profiles with various impeller-to-gap thickness ratios. The local heat transfer coefficient was also measured using a new heated-thin-film infrared thermography technique capable of applying various thermal boundary conditions. The heat transfer was found to be a function of the flow and rotational Reynolds numbers, and the results suggest that turbulent flow structures introduced by the fans govern the transport of thermal energy in the air. The insensitivity of the heat transfer to the impeller profile decouples the fan design from the convection enhancement problem, greatly simplifying the heat sink design process. Based on the experimental results, heat transfer and fan performance correlations were developed (most notably, a two-parameter correlation that predicts the dimensionless heat transfer coefficients across 98% of the experimental work to within 20% relative RMS error). Finally, models were developed to describe the scaling of the heat transfer and mechanical power consumption in multi-fan heat sinks. These models were assessed against experimental results from two prototypes, and suggest that future integrated fan heat sink designs can achieve a 4x reduction in thermal resistance and 3x increase in coefficient of performance compared to current state-of-the-art air cooled heat sinks.
by Wayne L. Staats, Jr.
Ph.D.
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Grosu, Vicentiu. "Heat transfer analysis of nanosecond laser-induced forward transfer". Ann Arbor, Mich. : ProQuest, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3208002.
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Thesis (Ph.D. in Mechanical Engineering)--S.M.U.Title from PDF title page (viewed July 6, 2007). Source: Dissertation Abstracts International, Volume: 67-02, Section: B, page: 1106. Adviser: David A. Willis. Includes bibliographical references.
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Grundén, Emma, i Max Grischek. "Testing the Heat Transfer of a Drain Water Heat Recovery Heat Exchanger". Thesis, KTH, Energiteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-190188.
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This study investigates the change in thermal resistance due to fouling in drain water pipes. As insulation of houses and energy efficiency of appliances improve, the importance of Drain Water Heat Recovery (DWHR) is growing steadily. In older houses, the relative heat loss through drain water is smaller than in newly built houses, but should still be considered. For example, 17 % of the total heat loss in Swedish multi-family houses built before 1940 was transported with the drain water (Ekelin et al., 2006). The average temperature of drain blackwater is between 23 °C and 26 °C (Seybold & Brunk, 2013), and a part of its heat can be recovered in DWHR systems. This allows cold incoming water to houses and buildings to be pre-heated by drain water before it is heated in the heat pump. Depending on the system, 30 % to 75 % of the heat from drain water can be recovered (Zaloum et al., 2007b). A threat to heat exchanger performance is that additional materials, so called fouling, accumulate on the surfaces of the heat exchangers and increases its thermal resistance. This resistance can be described by a fouling resistance and can be very costly due to losses in heat transfer and required cleaning. To quantify the fouling resistance, experiments were conducted in a climate chamber on Brinellvägen 66, using a pipe that had been installed for 3 years in the sewage system from the men’s toilet on Brinellvägen 64B. The installed pipe was compared with a pipe from the same manufacturer with the same dimensions. The pipes were sealed and filled with water at about 20 °C. Thermocouples were used to measure the decrease in water temperature over time in both pipes. Based on these measurements, the difference in thermal resistance was found, using curve fitting and the Lumped Capacitance Method. The fouling resistance was quantified by comparing the thermal resistances of the test pipe with and without fouling. The main findings were firstly that fouling significantly increases the thermal resistance of aluminium pipes. Secondly, corrosion causes a significant decrease in the pipes’ thermal resistance. The combination of these effects led to a decrease of 14 % in thermal resistance in the examined system after three years compared to the time of installation. The decrease in thermal resistance due to corrosion in the test pipe was 44 % compared to the time of installation. Furthermore, the thermal resistance of the test pipe decreased by 51 % when it was cleaned from the fouling. The fouling resistance of the 0.81 mm fouling layer was found to be 0.03068 m2K/W.Denna studie undersöker den ökade termiska resistansen i avloppsrör på grund av beläggningar. Idag lägg stor vikt vid bra isolering och energieffektiv utrustning i nybyggda hus, vilket även sätter press på värmeåtervinning av avloppsvatten. Värmeåtervinningen av avloppsvatten är mindre viktig i äldre hus, då den relativa värmeförlusten av avloppsvatten är lägre än i nybyggda hus, men bör likväl tas i akt vid utvärderingen av värmeanvändning. I ett svenskt flerfamiljshus byggt före 1940 stod värmeförlusten på grund av varmt avloppsvatten för 17 % av den totala värmeförlusten (Ekelin et al., 2006). Den genomsnittliga temperaturen för svartvatten ligger på 23 °C till 26 °C (Seybold & Brunk, 2013), varav delar av värmen kan återvinnas i värmeväxlare. Detta bidrar till att det kalla ingående vattnet till värmepumpen förvärms av värmen från avloppsvattnet. Beroende på system och material kan 30 % till 75 % av värmen från avloppsvatten återvinnas (Zaloum et al., 2007b). Ett hot mot prestandan av värmeväxlare är att beläggning formas på de värmeöverförande ytorna i värmeväxlaren. Detta bidrar till en ökad termisk resistans och kan vara mycket kostsam på grund av minskning av värmeöverföring och nödvändig rengöring av anordningen. För att undersöka omfattningen av den ökade termiska resistansen utfördes en rad experiment i en klimatkammare på Brinellvägen 66. En jämförande metod användes där ett aluminiumrör, som tidigare installerats i avloppssystemet från herrarnas toalett i korridoren på Brinellvägen 64B, jämfördes med ett identiskt rör av samma tillverkare. Rören var tätade och fyllda med 20-gradigt kranvatten. Termoelement användes för att, över tid, mäta minskningen av vattentemperaturen i rören. Temperaturskillnaden användes för att beskriva skillnaden i termisk resistans genom att utföra kurvanpassning och tillämpa Lumped Capacitance Method. Skillnaden i termisk resistans mellan de båda rören antogs vara lika med beläggningens motstånd för värmeöverföring. Två huvudsakliga resultat kom av studien. Det första var att beläggning bidrar till ökad termisk resistans av aluminiumrör. Den andra var att korrosion tillsammans med andra externa faktorer orsakar en märkbar minskning av rörens termiska resistans. Totalt sett orsakade beläggningen tillsammans med korrosion en minskning av 14 % av den termiska resistansen i provröret, jämfört med den termiska resistansen vid installationstillfället. Vidare låg minskningen i termisk resistans på grund av korrosion i teströret på 44 % jämfört med den termiska resistansen vid installationstillfället och den genomsnittliga termiska resistansen av det rengjorda teströret låg på 51 % lägre än den genomsnittliga resistansen av teströret innan rengöring. Den beräknade resistansen för ett 0.81 mm tjockt lager av beläggning var 0.03068 m2K/W.
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Wangdhamkoom, Panitan. "Characteristics of multimode heat transfer in a differentially-heated horizontal rectangular duct". Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/1007.
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This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.
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Haji, Aghaee Khiabani Reza. "Heat transfer in nano/micro multi-component and complex fluids with applications to heat transfer enhancement". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41154.
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Thermal properties of complex suspension flows are investigated using numerical computations. The objective is to develop an efficient and accurate computational method to investigate heat transport in suspension flows. The method presented here is based on solving the lattice Boltzmann equation for the fluid phase, as it is coupled to the Newtonian dynamics equations to model the movement of particles and the energy equation to find the thermal properties. This is a direct numerical simulation that models the free movement of the solid particles suspended in the flow and its effect on the temperature distribution. Parallel implementations are done using MPI (message passing interface) method. Convective heat transfer in internal suspension flow (low solid volume fraction, φ<10%), heat transfer in hot pressing of fiber suspensions and thermal performance of particle filled thermal interface materials (high solid volume fraction, φ>40%) are investigated. The effects of flow disturbance due to movement of suspended particles, thermo-physical properties of suspensions and the particle micro structures are discussed.
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Gupta, Jatin. "Application Of Conjugate Heat Transfer (Cht) Methodology For Computation Of Heat Transfer On A Turbine Blade". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230064860.
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Da, Riva Enrico. "Two-phase Heat Transfer in Minichannel Heat Exchangers: Heat Pump Applications, Design, Modelling". Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426130.
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Refrigerant charge minimization is one of the most important targets for heating and air conditioning applications when using natural refrigerants like hydrocarbons or ammonia to cope with the new environmental challenges.
Some applications of minichannels for charge minimization in heat pumps are presented and discussed in this thesis.
The design of an innovative condenser, an evaporator and an internal heat exchanger is presented. These devices are shell-and-tube heat exchangers using 2 mm i.d. minichannels and realized for the use with propane. Computational procedures based on empirical correlations available in the literature and a simplified model of the heat transfer and pressure drop processes have been developed and used for the design. Experimental performance data of the heat exchangers when using R22 and propane is reported and compared against the predictions given by the computational procedures.
The shell-and-tube minichannel heat exchangers have been installed in a 100 kW heat pump using propane as the refrigerant. The unit has been designed for laboratory tests and the minichannel shell-and-tube heat exchangers have been installed in the facility together with a conventional plate condenser and an evaporator. Different configurations have been tested in order to quantify the advantages of operating the heat pump using the low charge heat exchangers, with regard to both energy performance and propane charge. In particular, the experimental performance when using the minichannel condenser is compared to the one obtained when using the plate condenser, and the influence of the internal heat exchanger on the performance of the equipment is measured and discussed. Experimental data about the efficiency with propane of the semihermetic compressor installed in the heat pump is also reported.
Besides empirical correlations to predict the global thermal performance, a more complete understanding of the two-phase flow and heat transfer in minichannels is needed for the design and optimization of heat exchangers.
Some CFD simulations are presented in this thesis using the innovative Volume Of Fluid (VOF) method, which is able to directly compute multiphase flows without using any empirical closure law to model the interaction between the phases.
In order to assess the capability of the method to compute the motion of the gas-liquid interface, which is crucial for two-phase flow and heat transfer, simulations of the adiabatic churn flow regime of air-water mixture at different pipe diameters and liquid and gas superficial velocities have been initially performed. A comparison of the numerical results with experimental visualizations is reported and a simplified theoretical model of the wave levitation process has been developed and used to explain the numerical results. The VOF simulations were then extended to the study of condensation of R134a inside a minichannel with 1 mm internal diameter. Computational results about the evolution of the vapour-liquid interface and the heat transfer coefficient along the channel are reported.La riduzione della carica di refrigerante nelle applicazioni di condizionamento e riscaldamento è uno dei vincoli di progetto principali quando vengono utilizzati, per motivi di carattere ambientale, refrigeranti naturali come idrocarburi ed ammoniaca. Alcune applicazioni dei minicanali per la minimizzazione della carica nelle pompe di calore vengono presentate e discusse nella presente tesi. Viene presentato il progetto di un condensatore, un evaporatore ed uno scambiatore di calore rigenerativo innovativi. Questi componenti sono degli scambiatori di calore a fascio tubiero utilizzanti minicali del diametro di 2 mm e progettati per l’uso con propano. Delle procedure di calcolo basate su di correlazioni disponibili in letteratura ed un modello semplificato del processo di scambio termico sono state utilizzate per il progetto. Le prestazioni sperimentali degli scambiatori con R22 e propano vengono riportate e confrontate con le stime fornite dalle procedure di calcolo. Gli scambiatori di calore sono stati installati in una pompa di calore della capacità termica di 100 kW utilizzante propano come fluido frigorigeno. Nell’impianto della pompa di calore, destinata a test di laboratorio, sono stati installati anche un condensatore ed un evaporatore a piastre convenzionali. In questo modo è stato possibile confrontare diverse configurazioni al fine di quantificare in via sperimentale i vantaggi apportati dall’utilizzo degli scambiatori a minicanali, in termini sia di prestazioni energetiche, sia di carica di propano richiesta. In particolare, le prestazioni delle configurazioni utilizzanti il condensatore a minicanali vengono confrontate con quelle delle configurazioni utilizzanti lo scambiatore a piastre, e l’influenza sulle prestazioni energetiche dello scambiatore rigenerativo viene misurata e discussa. Vengono inoltre riportati dati sperimentali relativi all’efficienza con propano del compressore semiermetico installato nella pompa di calore. Oltre a correlazioni empiriche in grado di stimare le prestazioni termiche globali, il progetto e l’ottimizzazione di scambiatori di calore richiede una più approfondita conoscenza del deflusso e dello scambio termico all’interno di minicanali. Vengono presentate in questa tesi delle simulazioni di termofluidodinamica computazionale tramite l’innovativo metodo VOF (Volume Of Fluid) in grado di simulare direttamente deflussi multifase senza la necessità di utilizzare correlazioni empiriche per la modellazione dell’interazione tra le fasi. Al fine di validare l’efficacia di questo metodo nel calcolare il moto dell’interfaccia gas-liquido, il quale è un aspetto cruciale nello scambio termico bifase, sono state in un primo momento eseguite delle simulazioni del regime di deflusso ”churn flow” per una miscela aria-acqua nel caso di un tubo liscio verticale adiabatico, a differenti valori di diametro del tubo e di velocità superficiale delle due fasi. I risultati sono stati confrontati con visualizzazioni sperimentali ed un modello teorico semplificato del processo di levitazione delle onde è stato sviluppato ed utilizzato per commentare i risultati numerici. Le simulazioni con il metodo VOF sono state in un secondo momento estese allo studio della condensazione di R134a all’interno di un minicanale del diametro di 1 mm. Vengono riportati risultati computazionali relativi all’evoluzione dell’interfaccia vapore-liquido e dei coefficienti di scambio termico lungo il minicanale.
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Cooper, Paul. "Electrically enhanced heat transfer in the shell/tube heat exchanger". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37978.
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Mori, Hiromi. "Enhancement of heat transfer for ground source heat pump systems". Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11483/.
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Uptake of geothermal heat pump (GSHP) systems has been slow in some parts of the world due to the unpredictable operational performance, large installation space requirement and high installation costs. Therefore, design modification was searched in order to improve the feasibility. With regard to relatively small impact of the construction costs, efficient thermal energy collection was targeted in horizontal ground-loop systems with shallow underground construction. The research started with a sensitivity analysis of the underground heat collection system using computational fluid dynamics (CFD). The results indicated essential design parameters to enhance the performance. Strategies to improve one of the parameters, thermal conductivity of soil surrounding the heat exchanger, were investigated through lab experiments. Subsequently, further design optimisation with the CFD intended to select the most competitive modified design against the existing design. It was discovered that an indication to achieve economic and practical modifications for efficient heat collection was to increase the moisture content of sub-soil up to the optimum moisture content (OMC). Annual operation analysis with the CFD disclosed that additional costs for even simple design modifications could easily worsen the payback period. Consequently, solutions to improve the performance of the GSHP within reasonable payback period were proposed.
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Rolston, R. M. "The transfer of heat to a ground-source heat pump". Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373542.
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Gardner, David Alan. "Numerical analysis of conjugate heat transfer from heat exchange surfaces". Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329229.
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Sivanantharaja, G. (Geethanchali). "Effect of surface roughness on heat transfer in heat exchanger". Bachelor's thesis, University of Oulu, 2017. http://urn.fi/URN:NBN:fi:oulu-201712143310.
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The heat exchanger is a device that transfers heat from one fluid to another or between fluid and the environment. Over the last few decades, the role of heat exchangers has increased in the process of heat recovery and introduction of new energy sources. Surface roughness of heat exchanger wall plays a vital role in the efficiency of heat transfer. Therefore, significance of surface roughness is examined by many researchers applying different shapes of roughness. Roughness is the variation in the height of a surface. It could be either a part of the geometry or due to deposition of undesired materials (which decreases the thermal function of the heat exchanger, increases the pressure drop and could cause corrosion). Dimensionless heat transfer correlations such as Nusselt number provides a clear view about the effect of heat transfer by surface roughness. This thesis combines different Nusselt correlations for distinct shapes of surface roughness and investigates the suitability of them on a test experiment by comparing the values gotten. From this investigation it was clear that the value of Nunner correlation delivers the most reasonable results for a fouled layer formed by means of crystallization. Also the Nusselt correlation by Saini et al. could be more suitable for artificial surface roughness than for a fouled surfaceLämmönvaihdin on laite, joka siirtää lämpöä fluidista toiseen tai fluidin ja ympäristön välillä. Viimeisimpien vuosikymmenten aikana lämmönvaihtimien rooli on kasvanut lämmön talteenottoprosesseissa ja uusien energialähteiden käyttöönotossa. Lämmönvaihtimien pinnankarheudella, jolla tarkoitetaan seinämän pintakuvion korkeuden muutosta verrattuna tasaiseen pintaan, on merkittävä rooli lämmönvaihtimen tehokkuudessa. Pinnankarheuden vaikutusta lämmönsiirtoon onkin tarkasteltu useissa tutkimuksissa. Pinnankarheus voi olla osa lämmönvaihdinrakennetta tai johtua ei haluttujen materiaalien kerrostumisesta pinnalle. Tällöin puhutaan likaantumisesta, joka heikentää lämmönvaihtimen lämmönsiirtoa, lisää painehäviötä ja voi aiheuttaa korroosiota. Dimensiottomat korrelaatiot, kuten Nusseltin luku antavat tietoa pinnankarheuden aiheuttamasta vaikutuksen lämmönsiirtoon. Tässä kandidaatintyössä on tarkasteltu kirjallisuudessa esitettyjä Nusseltin luvun korrelaatioita ja niiden soveltuvuutta eri pinnankarheuden muotoihin sekä tutkittu niiden soveltuvuutta todellisen lämmönvaihtimen tapauksessa. Tästä tutkimuksessa tarkastelluista korrelaatioista Nunnerin korrelaatio soveltui parhaiten likaantuneen lämmönvaihtimen lämmönsiirron tarkasteluun. Sainin ym. korrelaatio arvioitiin soveltuvan paremmin keinotekoisen pinnankarheuden kuin likaantuneen pinnan lämmönsiirron tarkasteluun
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Mulford, Rydge Blue. "Dynamic Radiation Heat Transfer Control Through Geometric Manipulation". BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8134.
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The surface area and radiative properties of an object influence the rate of radiative emission from the object's surface and the rate of radiative absorption into the surface. Control of these variables would allow for the radiative heat transfer behavior of the surface to be manipulated in real time. Origami tessellations, being a repeated pattern of linked, dynamic surfaces, provide a framework by which dynamic control of apparent radiative properties and surface area is possible. The panels within a tessellation form cavities whose aspect ratio varies as the device actuates. The cavity effect suggests that the apparent radiative properties of the cavity openings will vary as a function of aspect ratio. The apparent absorptivity of an accordion tessellation formed from folded shim stock is shown experimentally to increase by 10x as the tessellation actuates from fully extended to within 10\% of a completely-folded state. Analytical models and Monte Carlo ray tracing are used to quantify the apparent radiative properties of an infinite V-groove for a variety of conditions, including specular or diffuse reflection and diffuse or collimated incident irradiation. For a diffuse V-groove, apparent radiative properties increase with increasing V-groove aspect ratio but do not approach unity. Highly reflective surfaces exhibit the largest relative increase in apparent radiative properties with actuation. Closed-form correlations achieve an average relative error of 2.0\% or less. For a specular V-groove, apparent radiative properties approach unity as the V-groove collapses towards an infinite aspect ratio. The apparent absorptivity for a V-groove exposed to collimated irradiation shows significant variations over small actuation distances, increasing by 5x over a small actuation range. For certain conditions the apparent absorptivity of a V-groove subject to collimated irradiation decreases as the aspect ratio increases.For an isothermal accordion tessellation the net radiative heat exchange continuously decreases as the surface is collapsed for most conditions, indicating that the reduction in apparent surface area generally dominates the increase in apparent radiative properties. Net radiative heat transfer values decrease by 7x for collimated irradiation and specular reflection over small actuation distances. Specular V-grooves subject to collimated irradiation occasionally show an increase in net radiative heat transfer as the device collapses. A non-isothermal dynamic radiative fin achieves a 3x reduction in heat transfer as the fin collapses; this value can be increased with the use of highly conductive materials and by increasing the length of the fin. The fin efficiency of a collapsible fin increases as the fin collapses. An experimental prototype of a collapsible fin is developed and tested in a vacuum environment, achieving a 1.32x reduction in heat transfer for a limited actuation range, where a numerical model suggests this prototype may achieve a 2.23x reduction in heat transfer over the full actuation range.
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Baird, James Robert. "Phase change heat transfer in narrow passages". Thesis, Graduate School of Engineering, 2001. http://hdl.handle.net/2123/5130.
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Colomer, Rey Guillem. "Numerical methods for radiative heat transfer". Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6691.
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L'objectiu principal d'aquesta tesi es l'estudi de la transferència d'energia per radiació. Per aquest motiu, s'ha estudiat la fenomenologia bàsica de la transferencia de calor per radiació. Tenint en compte el tipus d'equació que descriu aquesta transferència d'energia, aquesta tesi esta encarada als metodes numèrics que ens permetran incorporar la radiació en els nostres càlculs. Donat que aquest és el primer treball d'aquestes característiques en el grup de recerca CTTC ("Centre Tecnològic de Transferència de Calor"), està limitat a geometries senzilles, cartesianes i cilíndriques. En el capítol 1 s'exposa una breu introducció a la transferència d'energia per radiació, i una explicació de les equacions que la governen. Es tracta de l'equació del transport radiatiu, formulada en termes dels coeficients d'absorció i de dispersió, i l'equació de l'energia. També s'indica quan cal tenir en compte aquest fenòmen, i a més a més, es defineixen totes les magnituds i conceptes que s'han utilitzat en aquesta tesi. També es dóna una breu descripció d'algunes simplificacions que es poden fer a les equacions governants.
El mètode de les radiositats s'explica en el capítol 2. També s'hi descriu un procediment numèric que permet calcular els factors de vista en geometries amb simetria cilíndrica, i es presenten resultats obtinguts amb el mètode descrit. Tot i que aquest capítol està una mica deslligat de la resta de la tesi, l'algoritme ideat per tractar geometries tridimensionals amb un temps computacional molt proper al de geometries bidimensionals, sense un increment de memòria apreciable, dóna uns resultats prou bons com per formar part de la tesi.
El mètode de les ordenades discretes (DOM) es detalla en el capítol 3. L'aspecte més important d'aquest mètode es l'elecció del conjunt d'ordenades per integrar l'equació del transport radiatiu. S'enumeren quines propietats han d'acomplir aquests conjunts. S'hi explica amb detall la discretització de la equació del transport radiatiu, tant en coordenades cartesianes com en cilíndriques. Es presenten també alguns resultats ilustratius obtinguts amb aquest mètode.
En el moment en que es vol resoldre un problema real, cal tenir present que el coeficients d'absorció pot dependre bruscament de la longitud d'ona de la radiació. En aquesta tesi s'ha considerat aquesta dependència amb especial interés, en el capítol 4. Aquest interès ha motivat una recerca bibliogràfica sobre la modelització aquesta forta dependència espectral del coeficient d'absorció. Aquesta recerca s'ha dirigit també a l'estudi dels diferents models numèrics existents capaços d'abordar-la, i de resoldre la equació del transport radiatiu en aquestes condicions. Es descriuen diversos mètodes, i, d'aquests, se n'han implementat dos: el mètode de la suma ponderada de gasos grisos (WSGG), i el mètode de la suma de gasos grisos ponderada per línies espectrals (SLW). S'hi presenten també resultats ilustratius.
S'han realitzat multitud de proves en el codi numèric resultant de l'elaboració d'aquesta tesi. Tenint en compte els resultats obtinguts, es pot dir que els objectius proposats a l'inici de la tesi s'han acomplert. Com a demostració de la utilitat del codi resultant, aquest ha estat integrat en un codi de proposit general (DPC), resultat del treball de molts investigadors en els darrers anys.
Aquesta esmentada integració permet la resolució de problemes combinats de transferència de calor, analitzats en els capítols 5 i 6, on la radiació s'acobla amb la transferència de calor per convecció. La influència de la radiació en la transferència total de calor s'estudia en el capítol 5, publicat a la International Journal of Heat and Mass Transfer, volum 47 (núm. 2), pàg. 257-269, 2004. En el capítol 6, s'analitza l'efecte d'alguns paràmetres del mètode SLW en un problema combinat de transferència de calor. Aquest capítol s'ha enviat a la revista Journal of Quantitative Spectroscopy and Radiative Transfer, per què en consideri la publicació.
The main objective of the present thesis is to study the energy transfer by means of radiation. Therefore, the basic phenomenology of radiative heat transfer has been studied. However, considering the nature of the equation that describes such energy transfer, this work is focussed on the numerical methods which will allow us to take radiation into account, for both transparent and participating media. Being this the first effort within the CTTC ("Centre Tecnològic de Transferència de Calor") research group on this subject, it is limited to simple cartesian and cylindrical geometries.
For this purpose, chapter 1 contains an introduction to radiative energy transfer and the basic equations that govern radiative transfer are discussed. These are the radiative transfer equation, formulated in terms of the absorption and scattering coefficients, and the energy equation. It is also given a discussion on when this mode of energy transfer should be considered. In this chapter are also defined all of the magnitudes and concepts used throughout this work. It ends with a brief description of some approximate methods to take radiation into account.
The Radiosity Irradiosity Method is introduced in chapter 2. In this chapter it is also described a numerical method to calculate the view factors for axial symmetric geometries. The main results obtained in such geometries are also presented. Although a little disconnected from the rest of the present thesis, the algorithm used to handle "de facto"' three dimensional geometries with computation time just a little longer than two dimensional cases, with no additional memory consumption, is considered worthy enough to be included in this work.
In chapter 3, the Discrete Ordinates Method (DOM) is detailed. The fundamental aspect of this method is the choice of an ordinate set to integrate the radiative transfer equation. The characterization of such valuable ordinate sets is laid out properly. The discretization of the radiative transfer equation is explained in etail. The direct solution procedure is also outlined. Finally, illustrative results obtained with the DOM under several conditions are presented.
In the moment we wish to solve real problems, we face the fact that the absorption and scattering coefficients depend strongly on radiation wavelength. In the present thesis, special emphasis has been placed on studying the radiative properties of real gases in chapter 4. This interest resulted on a bibliographical research on how the wavenumber dependence of the absorption coefficient is modeled and estimated. Furthermore, this bibliographical research was focussed also on numerical models able to handle such wavenumber dependence. Several methods are discussed, and two of them, namely the Weighted Sum of Gray Gases (WSGG) and the Spectral Line Weighted sum of gray gases (SLW), have been implemented to perform non gray calculations. Some significant results are shown.
Plenty of tests have been performed to the numerical code that resulted from the elaboration of this thesis. According to the results obtained, the objectives proposed in this thesis have been satisfied. As a demonstration of the usefulness of the implemented code, it has been succesfully integrated to a general purpose computational fluid dynamics code (DPC), fruit of the effort of many researchers during many years.
Results of the above integration lead to the resolution of combined heat transfer problems, that are analyzed in chapters 5 and 6, where radiative heat transfer is coupled to convection heat transfer. The effect of radiation on the total heat transfer is studied in chapter 5, which has been published as International Journal of Heat and Mass Transfer, volume 47 (issue 2), pages 257--269, year 2004. In chapter 6, the impact of some parameters of the SLW model on a combined heat transfer problem is analyzed. This chapter has been submitted for publication at the Journal of Quantitative Spectroscopy and Radiative Transfer.
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Logan, Stephen Alister. "Respiratory heat transfer devices for divers". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46414.
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