Multi-Parameter Numerical Modeling And Optimization Of Thermoelectric Generators Used For Waste Heat Recovery Of Engine

Both energy-saving and environment-protecting are critical issues that humans are facing with in the 21 st century.Development of new energy and taking full advantage of low-grade heat energy are of great significance.About 30% of energy generated by internal combustion engine(ICE)is lost in the exhaust process,which causes substantial waste of resources and more serious environmental problems.Thermoelectric technology can directly convert thermal energy into electric energy by using thermoelectric materials.This technology has a simple structure and is environment-friendly,which can be easily arranged on automobiles and has enormous potentiality in waste heat recovery,being favored in the field of waste heat recovery of ICE.Considering some defects in modeling of thermoelectric generator(TEG)in previous works,this thesis developed a multi-parameter,three-dimensional numerical model based on the laws of thermodynamics and basic theory of FLUENT UDF.The main works are as follows:Firstly,the multi-parameter,three-dimensional numerical model of thermoelectric unicouple was built,which took a large number of parameters into account,such as temperature-dependent material properties,dimension,external temperature and flow parameters,as well as reversible and irreversible parameters.The reversible parameters mainly refer to Seebeck effect and Peltier effect,and the irreversible parameters mainly include Fourier and Joule effects,Thomson effect,heat loss of air gap,contact thermal and electric resistance.Secondly,evolutions of performance of the thermoelectric unicouple with electric current were analyzed at different temperatures of hot side and with different convective heat transfer coefficients.This section focused on the effects of variable material properties,Thomson effect and heat loss of air gap on the model,and accuracy of the numerical model built in this thesis was demonstrated.The results show that the variation tendency of output power and conversion efficiency is consistent with previous results.However,the maximum efficiency resistance not equal internal resistance but there is a certain drift;The influence of physical parameters on the numerical model is the largest,can't be ignored.Considering Thomson effect can improve the accuracy of the model.Air gap heat loss only affects thermoelectric conversion efficiency,and the impact on the output power can be ignored.Then,based on the above mentioned model,this section made optimal design for structure of the thermoelectric unicouple from two aspects,which are length and cross-sectional area of thermoelectric generator unicouple.The results show that there is an optimal length so that the output power and conversion efficiency are optimal value;the maximum output power increases with the cross-sectional area,but the conversion efficiency decreases with the cross-sectional area.Finally,the numerical model of thermoelectric unicouple was expended to the entire module level.The extended model is capable of simulation analysis and optimal design for TEG module with heat exchanger,which can provide evidence for exhaust heat recovery of engine.The results show that it can increase the output power,when a reasonable arrangement of different materials thermoelectric power generation module according to the surface temperature of the heat exchanger.