| The automotive thermoelectric generation system(TEG)can convert the heat from the exhaust gas into available electricity,which is beneficial for improving the fuel efficiency of the vehicle.However,the conversion efficiency of TEG system is still too low to make it use widespread.Based on the integration of TEG and muffler,porous material is applied in this thesis to improve the system performance of power generation and sound reduction.Based on the basic theory of heat transfer and computational fluid dynamic,the multi-field coupling numerical model of flow,temperature and pressure is established.The fluid analysis software FLUENT is used to calculate the influence characteristics of porous material on TEG system through iterative calculation,and the porous media model is adopted to simulate the flow in porous material.The acoustic analysis software LMS Virtual.lab and acoustic finite element method is applied to calculate the transmission loss of TEG,the Johnson-Champoux-Allard equivalent fluid model is used to describe the acoustic properties of porous material,and the influence of porous material on the sound reduction performance is summarized.First of all,based on the analysis of the integrated structure of TEG and muffler,considering the distribution of flow and acoustic field,four porous material arrangement plans are carried out.In case 1,the porous material is laid along the wall of heat exchanger;in case 2,the porous material is arranged around the perforating tube;in case 3,the porous material is covered the perforating plate;in case 4,the porous material is set at the end of the first tube.The CFD and sound performance of TEG in four cases are calculated and compared respectively,and the result shows that the porous material arrangement in case 1 can improve the wall temperature the most,and the effect on improving the temperature uniformity of case 4 is the best.Case 2 and case 3 show great effect in improving the sound reduction performance of low frequency,while case 1 and case 2 are better at reducing sound in high frequency.And the heat exchanger in case 4 has the great impacts on the pressure loss of TEG system.In view of the porous material of porosity,pore density and thickness,the TEGmodel employed case 1 and case 4 is built based on the research of porous material arrangement,to analyze the influence of this three parameters on TEG heat and fluid distribution.And the result show that the porous material with low porosity,high pore density and suitable thickness can lead to the optimal temperature distribution and output power.The influence of three parameters of porosity,pore density and material thickness on TEG acoustic properties is analyzed by using the model of case 2 and case 3.It comes to the conclusion that the transmission loss is improved by enhancing the three parameters.In order to deeply analyze the relation and influence between porous material parameters and TEG performance,the analytic hierarchy process is applied to evaluate the comprehensive performance of TEG.The power generation performance,acoustic performance and the impacts on engine performance are set as the research target,the three parameters of porous material which are porosity,pore density and thickness are set as solution layer.The research result shows that the weight of the three parameters from high to low is material thickness,porosity,pore density in turn.In this thesis,the innovative method of improving thermoelectric power generator performance by employing porous material is proposed,which provides a theoretic basis for the design and optimization of thermoelectric generator. |
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