Simulation and Analysis of Output Performance of Thermoelectric Devices Based on SiGe Material
Radioisotope thermoelectric generators(RTG)are widely used in the field of power supply for deep space exploration equipment,mainly using PbTe and SiGe as thermoelectric conversion materials.SiGe thermoelectric devices are favored by scientific researchers around the world due to their high mass specific power and service stability.In recent years,the preparation process of SiGe alloy has been continuously optimized,and its dimensionless figure of merit has been gradually improved.As a material for ther-moelectric power generation devices,it has great application value in future space exploration tasks.At home and abroad,the main fo-cus is on the performance control of thermoelectric materials,and the research on thermoelectric devices is relatively scarce.SiGe ther-moelectric devices have been used in space exploration tasks for many times,but the actual conversion efficiency of thermoelectric de-vices is relatively low,about 7％.Improving the conversion efficiency of thermoelectric devices is currently an urgent problem to be solved.The structure design and performance optimization of the device are mainly based on numerical simulation.Based on the latest development of SiGe alloy,on the basis of considering contact resistance and thermal resistance,a simulation model of planar SiGe thermoelectric device was constructed using ANSYS software.The accuracy of the model was first verified,and then the effect of the electrode thickness,the thermolelectric leg spacing,the structure of the thermolelectric leg,the heat loss and the temperature change of the hot side on the output performance of the thermoelectric device were studied.The calculation results showed that the open circuit voltage and maximum output power simulation results of the thermoelectric device were 0.315 V and 0.56 W,respectively,and the ex-perimental measurement results were 0.30 V and 0.54 W,respectively.The error was less than 5％.With the increase of electrode thickness from 1 to 9 mm,the output power of the device decreased from 0.85 to 0.27 W,and the conversion efficiency decreased from 6.80％to 4.50％.The output power of the device decreased from 0.78 to 0.47 W and the conversion efficiency decreased from 5.90％to 5.10％with the increase of the thermolelectric leg spacing from 1 to 5 mm.Reducing the thickness of the hot-side SiMo electrode and the distance between the thermolelectric legs could effectively improve the output performance of the device.When the electrode thick-ness of the device was 1 mm and the distance between the thermolelectric legs was 3 mm,the output power and conversion efficiency were increased to 0.85 W and 6.80％.The design of the thermolelectric leg structure found that when the ratio of the cross-sectional ar-ea of n-type to p-type thermolelectric leg was 0.90,the output power achieved the maximum value,and when the ratio of the cross-sec-tional area was 1.10,the conversion efficiency achieved the maximum value.As the ratio of the height of the thermolelectric leg to the sum of the cross-sectional area of the thermolelectric leg continued to increase,the maximum output power gradually decreased and the maximum conversion efficiency continued to increase,which could be seen that the structural design corresponding to the maxi-mum output power and the conversion efficiency was reversed.The practical applications needed to meet different requirements through the multi-parameter optimization design of the device.The research on the effect of heat loss on the output performance of thermoelec-tric devices found that when the heat transfer coefficient between the device and the environment was 0 or 100 W·m-2·K-1,the maxi-mum output power and the corresponding conversion efficiency were 0.57 W,6.33％and 0.58 W,5.66％,respectively,which showed that with the increase of the heat transfer coefficient,the maximum output power had increased by 1.75％,but the conversion efficien-cy had decreased by 10.58％.The good thermal protection measures should be adopted to reduce the heat loss of the device to the envi-ronment and improve the conversion efficiency of the device.The step or linear change of the hot-end temperature would influence the output performance of the device,and the output performance change had a hysteresis relative to the temperature change.The recovery time required for the device to reach a steady state after a step change in temperature was 0.048 s.The recovery time required for the device to reach a steady state after a linear change in temperature was 0.022 s,which took longer to return to steady state after a step change.During the operation of the device,the heat generation stability of the high-temperature heat source should be ensured as much as possible to maintain the steady-state operation of the thermoelectric device.The research results provided theoretical guidance for the subsequent fabrication of SiGe thermoelectric devices.
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