Thermal management of hybrid electrical vehicles using heat pipes

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/