Heat Transfer Analysis On Heat Pipe Cooling System For Power Battery Pack

Battery thermal management system has crucial effect on power performance of new energy vehicles, effective cooling technology can improve power batteries’ working condition and working performance, which will ensure electric vehicles’ driving security and reliability. A large amount of research on cooling technology and thermal management of power batteries has been developed by domestic and foreign researchers, the main attention has been focused on the research and optimization of those kind of cooling technologies, such as forced air cooling, water cooling, phase change material cooling and heat pipe cooling. Currently, the forced air cooling and water cooling technologies are widely used in the practical engineering application, but considering that phase change cooling has its great advantages in promoting temperature field uniformity of power battery pack, phase change material cooling and heat pipe cooling are also expected to be a new generation battery thermal management technology.Based on theoretical research, simulation analysis and experiment confirmation, the lithium-ion battery electrochemical-thermal coupling model is built, and furthermore, the fundamental heat transfer problems within heat pipe cooling system were studied, the cooling effect and temperature field uniformity of heat pipe cooling system for power battery pack are researched through simulation analysis and experiment study in this paper. Through the research on common problems, lay the foundation for heat pipe cooling system applied to power battery thermal management system. The main research contents of this paper are listed as following:(1) The lithium-ion battery electrochemical-thermal coupling model is built through solving the simultaneous governing equations, and the basic characteristics are studied, which contain battery capacity, charger and discharger character in different C-rate, battery cell’s temperature characteristic.(2) The fundamental heat transfer problems within heat pipe cooling system are studied, containing phase change heat transfer, external force convection heat transfer coefficient while fluid horizontally flowing tube bundle and the contact thermal resistance within heat conduction of multi-layer solids. The structure and mechanism of heat pipe cooling system is introduced. The problem that two-phase flow couples with phase change heat transfer is simplified as equivalent thermal conduction model. The external force convection heat transfer coefficient while fluid horizontally flowing tube bundle is solved through experimental correlation formula. The fractal parameters of rough-surface contact model are determined using power spectrum method, furthermore, rough-surface profile was described with Monte Carlo random number simulation method, and based on that, the contact thermal resistance between rough contact surface is obtained.(3) Based on COMSOL simulation software, the heat pipe cooling system simulation model of power battery pack containing 12 battery cells is built, battery cell’s temperature rise characteristics, the temperature filed uniformity and the factors affect this are researched, besides Compared with natural convection, heat pipe cooling battery pack’s temperature rise characteristics, cooling characteristics in high temperature environment and heating characteristics in cold environment are studied.(4) The experiment system of heat pipe cooling is built, the cooling performance and temperature field uniformity during different cooling ways and different C-rates are analyzed compared heat pipe-forced air cooling with natural convection cooling, and further, the experiment results are compared with simulation results. Those results lay the foundation for heat pipe cooling system applied to power battery thermal management system.