Thermal management of hybrid electrical vehicles using heat pipes

Swanepoel, Gerhardus (2001-12)

Thesis (MScEng) -- Stellenbosch University , 2001.

Thesis

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).

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