Automobile Waste Heat Thermoelectric Generator Flow Analysis And Optimization Based On Computational Fluid Dynamics

The auto industry has developed for more than a century, boosting world’s economic development while consuming terrific amount of oil resources, the consumption of oil produces much pollutants as Green-House Gas, NOX and Particulate Matter(PM). Engine thermal efficiency has been very low Due to the limitations of engine material and combustion cycle, up to40%of fuel energy is drained away by waste gas, whereas thermoelectric technology provides an effective way to recover waste heat, and has received extensive attention, studies and researches are conducted across the world. Primary Heat Exchanger(PHX) is one of the key components within the thermoelectric generator(TEG), conducting the heat energy absorbed from waste gas to thermoelectric modules(TEM). Temperature uniformity, TEM topology and PHX efficiency as well, are of great importance to the output of thermoelectric generator(TEG).In this study, concentrations are made on the waste heat recovery and studies of PHX.Computational Fluid Dynamics(CFD) theory is illustrated briefly at the beginning of the study. Two commonly used wall heat conducting models are then studied,the model to be used in the following simulation of PHX is determined through comparison of the two models. The computational model of current PHX is established within platform ANSYS Workbench to conduct conjugate heat transfer The boundary conditions are obtained from GT-Suite, The simulations are carried out with Commercial CFD Program FLUENT, Bench Tests are also conducted to gather data and validate the simulations. Local sensitivity analysis is conducted to determine the influence of boundary conditions to PHX backpressure and total heat transfer within the simulations results, the conception of temperature uniformity coefficient is proposed through the study of PHX surface temperature uniformity.Simulations results under certain boundary conditions indicates that increasing inlet gas velocity and temperature could increase the PHX surface average temperature effectively, and analysis also shows the flaws of current PHX, the improper layout of fins at the inlet contributes to the relatively low surface temperature at the inlet part. Local sensitivity analysis indicates that the velocity of waste gas has a greater contribution to backpressure of PHX in comparison with temperature of waste gas, while the temperature of waste gas has a greater contribution to total heat transfer. The study of temperature uniformity shows that the fins inside the PHX could not only improves the heat transfer but also improve the temperature uniformity coefficient. Besides, further simulations indicates that the temperature uniformity coefficient is less sensitive to inlet gas velocity than temperature, Increasing temperature could low the coefficient.Certain optimization models are proposed through comprehensive analysis, the models are established and simulation results under the same boundary conditions are obtained with FLUENT. The final option is made through the comparison of parameters as backpressure, PHX surface average temperature and temperature uniformity coefficient. Comparison results indicate that the ideal optimization model for the study has a low backpressure, the highest temperature uniformity coefficient and a relatively high surface average temperature.