Thermal management of hybrid electrical vehicles using heat pipes

[摘要] ENGLISH ABSTRACT:In an effort to improve the fuel efficiency and to reduce emission levels of automobiles, thedevelopment of Hybrid Electrical Vehicles (HEVs) has been a major focus area of theautomotive industry. The Centre of Automotive Engineering (CAE) at the University ofStellenbosch in conjunction with the Electric and Industrial Engineering Departments arecurrently developing an HEV. For this thesis, however, the focus is limited to the utilizationof Pulsating Heat Pipes (PHPs) for the purpose of the thermal management and control ofHEV components.As part of the study of PHPs a theoretical model is developed to simulate the heat transferrate of PHPs. Several experiments were devised to assist in the understanding of theoperating principles of PHPs.An experiment was conducted to determine the average thickness of the liquid film depositedat the trailing end of a liquid plug as it moves down a vertically orientated glass capillary tubeunder gravity. It was found that the average liquid film thickness varied between 100 and200 |im for water.The movement of a liquid plug in a vertically orientated U-shaped capillary tube due togravity and heat transfer was experimentally investigated. It was possible to observe thedeposition and the evaporation of a liquid film at the trailing end of the liquid plug with thenaked eye. The movement of the liquid plug was then theoretically determined andcompared to the experimental results. The theoretical model did not predict the exactmovement 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 wasexperimentally investigated. It was noticed that the plug exhibited a wide variety ofmovement ranging from irregular oscillations with amplitudes of ~ 50 mm to more steadyoscillations with amplitudes of ~ 1 mm. Again it was possible to observe the deposition andevaporation 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. Thismade it possible to visually observe the fluid motion inside the PHP. It was found that theliquid plugs moved in an irregular oscillatory manner. It was also observed that two plugsStellenbosch University http://scholar.sun.ac.za/sometimes coalesce to form a single plug and that a plug can split up to form two separateplugs.The heat transfer rate was determined for a stainless steel closed end PHP and an aluminiumclosed loop PHP for different working fluids, power inputs, filling ratios and inclinationangles. It was found that the overall heat transfer coefficient varied between 100 and 500W/m K for the stainless steel closed end PHP using water. The overall heat transfercoefficient varied between 0 and 400 W/m2K for the aluminium closed loop PHP usingwater. It was found that the stainless steel closed end PHP with ammonia as working fluidwas 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 toform causing the PHP to operate similarly to a thermosyphon. The overall heat transfercoefficient varied between 170 and 3000 W/m2K. It is concluded that the experimentallydetermined 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 closedend PHP. The experimental heat transfer rate in the top heat mode was 61 W compared to 60W predicted by the theoretical model. In the bottom heat mode the experimental heat transferrate 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 themodel 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 isrecommended that a PHP be constructed with dt < 2.5 mm to allow for ammonia to be used asworking fluid.Concepts were generated for the thermal management of selected HEV components. Aconcept was developed for the thermal management of the HEV batteries. It was found that aStereo-type heat lane can provide promising solutions for the thermal management ofInsulated Gate Bipolar Transistors (IGBTs).

[发布机构] Stellenbosch University