Thesis (MScEng) -- Stellenbosch University , 2001. / ENGLISH ABSTRACT: In an effort to improve the fuel efficiency and to reduce emission levels of automobiles, the development of Hybrid Electrical Vehicles (HEVs) has been a major focus area of the automotive industry. The Centre of Automotive Engineering (CAE) at the University of Stellenbosch in conjunction with the Electric and Industrial Engineering Departments are currently developing an HEV. For this thesis, however, the focus is limited to the utilization of Pulsating Heat Pipes (PHPs) for the purpose of the thermal management and control of HEV components. As part of the study of PHPs a theoretical model is developed to simulate the heat transfer rate of PHPs. Several experiments were devised to assist in the understanding of the operating principles of PHPs. An experiment was conducted to determine the average thickness of the liquid film deposited at the trailing end of a liquid plug as it moves down a vertically orientated glass capillary tube under gravity. It was found that the average liquid film thickness varied between 100 and 200 |im for water. The movement of a liquid plug in a vertically orientated U-shaped capillary tube due to gravity and heat transfer was experimentally investigated. It was possible to observe the deposition and the evaporation of a liquid film at the trailing end of the liquid plug with the naked eye. The movement of the liquid plug was then theoretically determined and compared to the experimental results. The theoretical model did not predict the exact movement of the liquid plug but the final steady state values was predicted within 7.39%. The movement of a liquid plug in a horizontally orientated straight capillary tube was experimentally investigated. It was noticed that the plug exhibited a wide variety of movement ranging from irregular oscillations with amplitudes of ~ 50 mm to more steady oscillations with amplitudes of ~ 1 mm. Again it was possible to observe the deposition and evaporation of a liquid film at the trailing end of the liquid plug with the naked eye. A PHP was manufactured using glass and filled with pentane as the working fluid. This made it possible to visually observe the fluid motion inside the PHP. It was found that the liquid plugs moved in an irregular oscillatory manner. It was also observed that two plugs Stellenbosch University http://scholar.sun.ac.za/ sometimes coalesce to form a single plug and that a plug can split up to form two separate plugs. The heat transfer rate was determined for a stainless steel closed end PHP and an aluminium closed loop PHP for different working fluids, power inputs, filling ratios and inclination angles. It was found that the overall heat transfer coefficient varied between 100 and 500 W/m K for the stainless steel closed end PHP using water. The overall heat transfer coefficient varied between 0 and 400 W/m2K for the aluminium closed loop PHP using water. It was found that the stainless steel closed end PHP with ammonia as working fluid was not able to transfer heat in the top heat mode. The inside diameter of the tube (3.34 mm) exceeds the required diameter of 2.96 mm which prevents liquid plugs and vapour bubbles to form causing the PHP to operate similarly to a thermosyphon. The overall heat transfer coefficient varied between 170 and 3000 W/m2K. It is concluded that the experimentally determined heat transfer coefficients can be used to design similar PHPs in the future. The theoretical model was used to predict the heat transfer rate of the stainless steel closed end PHP. The experimental heat transfer rate in the top heat mode was 61 W compared to 60 W predicted by the theoretical model. In the bottom heat mode the experimental heat transfer rate was 63 W compared to the predicted value of 90 W. The theoretical model currently only caters for closed end PHPs. It is recommended that the model be extended to include closed loop PHPs. The internal diameter of the PHPs is too great for ammonia to be used as working fluid. It is recommended that a PHP be constructed with dt < 2.5 mm to allow for ammonia to be used as working fluid. Concepts were generated for the thermal management of selected HEV components. A concept was developed for the thermal management of the HEV batteries. It was found that a Stereo-type heat lane can provide promising solutions for the thermal management of Insulated Gate Bipolar Transistors (IGBTs). / AFRIKAANSE OPSOMMING: In ‘n poging om voertuie se brandstof-benuttingsgraad te verbeter en die vlakke van uitlaatgasse te verminder word daar deur die motorvoertuigindustrie gefokus op die ontwikkeling van ‘n Hibriede Elektriese Voertuig (HEV). Die Centre of Automotive Engineering (CAE) aan die Universiteit van Stellenbosch in samewerking met die Elektriese - en Bedryfsingenieurswese Departemente is tans besig met die ontwikkeling van ‘n HEV. Die fokus van hierdie tesis is egter beperk tot die gebruik van Pulserende Hittepype (PHPe) vir die doel van die termiese beheer van HEV komponente. As deel van die studie van PHPe is ‘n teoretiese model ontwikkel waarmee die warmte oordragstempo van PHPe simuleer kan word. Verskeie eksperimente is prakseer om die beginsels waarvolgens PHPe werk, beter te verstaan. ‘n Eksperiment was uitgevoer om die gemiddelde dikte van die vloeistof-film wat gedeponeer word by die agterkant van ‘n vloeistofprop wat in ‘n vertikaal georienteerde kapillere pypie onderworpe aan gravitasie, beweeg. Dit was gevind gewees dat die gemiddelde dikte van die vloeistof-film het gewissel tussen 100 en 200 (im vir water. Die beweging van ‘n vloeistofprop in ‘n vertikaal georienteerde U-vormige kapillere pyp as gevolg van gravitasie en warmte-oordrag was eksperimenteel ondersoek. Dit was moontlik gewees om die deponering en verdamping van ‘n vloeistof-film by die agterkant van die vloeistofprop met die oog te sien. Die beweging van die vloeistofprop was teoreties bepaal en vergelyk met die eksperimentele resultate. Die teoretiese resultate het nie die presiese beweging van die vloeistofprop voorspel nie maar die finale gestadigde posisie was voorspel binne 7.39%. Die beweging van ‘n vloeistofprop in ‘n horisontaal georienteerde reguit kapillere pyp was eksperimenteel bestudeer. ‘n Wye verskeidenheid van beweging van die vloeistofprop was waargeneem wat wissel van onreelmatige ossilasies met amplitudes van ~ 50 mm tot meer reelmatige ossilasies met amplitudes van ~ 1 mm. Die deponering en verdamping van die vloeistof-film by die agterkant van die vloeistofprop was weereens met die oog waargeneem. ‘n PHP was van glas vervaardig en met pentaan gevul as die vloeier. Dit het dit moontlik gemaak om die vloeistofbeweging binne die PHP visueel waar te neem. Dit was gevind gewees dat die vloeistofproppe in ‘n onreelmatige ossilerende wyse beweeg. Dit was ook waargeneem dat twee vloeistofproppe somtyds saamsmelt om een vloeistofprop te vorm en dat ‘n vloeistrofprop kan opbreek om twee aparte vloeistofproppe te vorm. Die warmte oordragstempo was bepaal van ‘n vlekvrye-staal geslote ent PHP en van ‘n aluminium geslote lus PHP vir verskillende vloeiers, drywing insette, vulverhoudings en inklinasie hoeke. Die algehele warmte oordragskoeffisient was tussen 100 en 500 W/m2K vir die vlekvrye-staal geslote end PHP gevul met water en tussen 0 en 400 W/m2K vir die geslote lus aluminium PHP gevul met water. Dit was gevind gewees dat die vlekvrye-staal geslote ent PHP gevul met ammoniak nie in staat was om warmte oor te dra in die boonste verhittingsmodus nie. Die binnediamter van die pyp (3.34 mm) is groter as die vereiste diameter van 2.96 mm wat verhoed dat vloeistofproppe en gasborrels gevorm word wat veroordaak dat die PHP soortgelyk aan ‘n termoheuwel werk. Die algehele warmte oordragskoeffisient was tussen 170 en 3000 W/m2K. Die eksperimentele bepaalde waardes vir die warmte oordragskoeffisiente kan gebruik word vir ontwerpdoeleindes van soortgelyke PHPe in die toekoms. Die toeretiese model was aangewend om die warmte oordragstempo van die vlekvrye staal geslote end PHP te bepaal. Die eksperimentele warmte oordragstempo in die boonste verhittingsmodus was 61 W in vergeleke met die teoretiese waarde van 60 W. In die onderste verhittingsmodus was die eksperimentele warmte oordragstempo 63 W in vergeleke met die voorspelde waarde van 90 W. Die teoretiese model kan huidiglik slegs geslote ent PHPe simuleer. Dit word aanbeveel dat die model uitgebrei word sodat dit geslote lus PHPe ook kan simuleer. Die binne diameter van die PHPe is te groot om ammoniak te gebruik as vloeier. Dit word aanbeveel dat ‘n PHP vervaardig word met d, < 2.5 mm sodat ammoniak ook gebruik kan word as vloeier. Verskeie konsepte was gegenereer vir die termiese beheer van geselekteerde HEV komponente. ‘n Konsep was ontwikkel vir die termiese beheer van die HEV batterye. Dit was gevind gewees dat ‘n Stereo-type heat lane belowende oplossings kan bied vir die termiese beheer van Insulated Gate Bipolar Transistors (IGBTs).

The design of a fabric composite heat pipe has been completed. It is composed of two end caps, between which a fluid containment liner composed of metal foil and an outer structural layer composed of a ceramic fabric is stretched. The interior of the heat pipe is layered with a ceramic fabric wick. This heat pipe is being constructed currently at Oregon State University. The heat pipe test facility has been designed and built. Final assembly of the various components is now under way. This test facility consists of a vacuum chamber with a coolant jacket on the outside. Inside this chamber a test stand is placed which is composed of radiation shields and a supporting stand for the heat pipe and the heaters. Experimental work has been performed to ensure material compatibility of the metal foils used as a fluid containment liner. Specific materials tested include copper, aluminum, titanium, FEP teflon and three ceramic fabrics. These materials have been exposed to a variety of working fluids for up to 5000 hours at various sub-boiling temperatures. The best combinations of materials include aluminum or copper and acetone, or titanium and water. The least compatible combinations included aluminum or copper and water. An experimental apparatus to measure the wettability of candidate ceramic fabric wicks was designed and built. This apparatus included a pressure chamber to allow measurements to be taken at elevated pressures and temperatures. The liquid front velocity in one meter lengths of unwetted samples of ceramic fabrics was measured. A computer was used to determine liquid front position at 30 finite points along the fabric sample. Analysis of the data allowed calculation of a constant composed of two wicking parameters to be measured. Analysis of various analytical methods for predicting these parameters was performed. / Graduation date: 1993

Conventional stainless steel - water and ceramic fabric composite water heat pipes have been built and tested. The tests have been conducted to compare the performance characteristics between conventional and fabric composite heat pipe radiators for space nuclear power heat rejection systems. The fabric composite concept combines a strong ceramic fabric with a thin metal liner to form a very lightweight heat pipe. The heat pipes tested have used identical, homogeneous fabric wicks and water as the working fluid. One fabric composite heat pipe has been constructed by fitting a braided aluminoborosilicate fabric tube over the outside of the conventional stainless steel heat pipe. A more advanced fabric composite design combines the woven fabric with a 0.25 mm (10 mil) stainless steel tube as the liner, and reduces the mass of the heat pipe by a factor of three. A heat pipe testing facility was designed and built for the purpose of testing various conventional and fabric composite heat pipes. This facility allows the testing of heat pipes in a vacuum, at low temperatures, and can accommodate a variety of heat pipe designs. Instrumentation and computer interfacing provide for continuous monitoring and evaluation of heat pipe performance. Tests show that heat pipe radiator capacity can be significantly enhanced by using the fabric composite design. Tests comparing a conventional heat pipe with fabric composite heat pipes achieved a 100% increase in the emissivity and heat rejection capacity of the radiator. Since the ceramic fabric is strong enough to withstand the internal pressure of the heat pipe, a very thin metal foil can be used to contain the working fluid. The increase in heat rejection capacity, combined with the significant reduction in the heat pipe mass, translates into a substantial savings for space power systems employing fabric composite heat pipe radiators. / Graduation date: 1993

No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 17, 2009) Includes bibliographical references.

Thesis (M. App. Sc.)--Carleton University, 2003. / Includes bibliographical references (p. R1-R3). Also available in electronic format on the Internet.

Thesis(M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 21, 2009). Thesis advisor: Dr. Hongbin Ma. Includes bibliographical references.

<p> An existing transient network model for wicked heat pipes was extended to incorporate the effects of axial heat transfer along the wall and wick, heat transfer in the surrounding media, and non-condensable gases in the vapour region. The thermal resistance of the different components was broken down into a larger number of smaller resistances in both axial and radial directions to account for the axial conduction and to handle non-uniform boundary conditions. Two sets of experiments were performed on copper-water wicked heat pipes to evaluate the effect of non-condensable gases, axial conduction, surrounding media and non-uniform boundary conditions. In the first set of experiments, the heat pipes were electrically heated at one end and cooled on the other end using a water jacket. This set of experiments was used to investigate the effect of non-condensable gases, axial conduction and surrounding media on the steady state and transient performance. The effect of the surrounding media was investigated by heating the heat pipe through two different sized aluminum blocks mounted around then heat pipe evaporator section. In the second set of experiments, the effect of using a finned condenser on the steady state performance of the heat pipes were tested in a wind tunnel. The condenser section of the heat pipes in this case was mounted in the test section of the wind tunnel and cooled at different air velocities. Three fin densities were tested along with a heat pipe with no fins. The model predictions of the steady and transient response of the vapour and wall temperature of the heat pipes were in good agreement with the experimental results. </p> <p> The presence of non-condensable gases inside the heat pipe increased the overall thermal resistance of the heat pipe. While the non-condensable gases did not notably affect the transient response during the heat-up phase, it significantly slows down the cool-down phase. The axial conduction through the pipe wall and the wick structure decreases the overall thermal resistance of the heat pipe. The axial conduction did not have a great influence on the time response during the heat-up phase, but was very important in the cooldown phase, especially with the presence of non-condensable gases. The wick structure was found to be the most dominant component in the transient performance of the heat pipe. The evaporator block was the dominant capacitance in the overall conjugate system, and significantly affects the transient response. The experimental results from the finned condenser study showed that the internal resistance increased slightly with the fin density. There was some nonuniformity in the condenser surface temperature at the locations of the fins. However, this non-uniformity did not propagate to other parts of the heat pipe. </p> / Thesis / Master of Applied Science (MASc)

The Loop Heat Pipe (LHP) is a passive, two-phase heat transfer device used, most commonly, for thermal management of aerospace and aeronautical electronic equipment. A unique feature is a porous wick which generates the necessary capillary action required to maintain circulation between the heat source and the heat exchanger. What differentiates LHP devices from traditional heat pipes, which also work through the use of a wick structure, is the constrained locality of the wick, placed solely in the evaporator, which leaves the remainder of the piping throughout the device as hollow. This provides the LHP with a number of advantages, such as the ability to transport heat over long distances, operate in adverse gravitational positions and to tolerate numerous bends in the transport lines. It is also self-priming due to the use of a compensation chamber which passively provides the wick with constant liquid access. These advantages make LHPs popular in aerospace and aeronautical applications, but there is growing interest in their deployment for terrestrial thermal management systems. This research had two aims. Firstly, to create and validate a robust mathematical model of the steady-state operation of an LHP for terrestrial high heat flux electronics. Secondly, to construct an experimental LHP, including a sintered porous wick, which could be used to validate the model and demonstrate the aforementioned heat exchange and gravity resistant characteristics. The porous wick was sintered with properties of 60% porosity, 6.77x10-13 m2 permeability and an average pore radius of 1μm. Ammonia was the chosen working fluid and the LHP functioned as expected during horizontal testing, albeit at higher temperatures than anticipated. For safety reasons the experimental LHP could not be operated past 18 bar, which translated into a maximum saturated vapour temperature of 45°C. The heat load range extended to 60 W, 50 W and 110 W for horizontal, gravity-adverse and gravity-assisted operation respectively. Because of certain simplifying assumptions in the model, the experimental results deviated somewhat from predicted values at low heat loads. Model accuracy improved as the heat load increased. The experimental LHP behaved as expected for 5° and 10° gravity-assisted and gravity-adverse conditions, as well as for transport line variation, in which performance was assessed while the total tubing length was increased from 2.5 m to 4 m. Overall, the construction of the LHP, particularly of the porous wick, its operation and the modeling of the constant conductance mode of operation proved to be successful. The variable conductance mode of operation was not accurately modeled, nor was expected behaviour in the elevation testing encountered, although the reasons for these results are suggested. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.