Structural Optimization Of Thermoelectric Generator For Gas Waste Heat Recovery

Semiconductor thermoelectric power generation technology is a green,environmentally friendly and energy-saving way to directly convert heat energy into electricity through temperature difference based on Seebeck effect of semiconductor materials.Due to the high price of thermoelectric materials,low efficiency of thermoelectric conversion and low heat transfer efficiency combined with waste heat energy utilization,it cannot be widely used.Therefore,to improve the thermoelectric performance of thermoelectric generator is very important.In this paper,the main objective is to improve the thermoelectric performance of the generator with the temperature difference between tail gas and wet gas,and a series of optimization studies are carried out from the thermal boundary conditions,circuit connection modes,fluid physical properties and heat transfer characteristics.Firstly,four different thermal boundary condition models were established using COMSOL Multiphysics simulation software.With maximal area power density as the target,the influence of different thermal boundary conditions on thermoelectric performance and structure optimization was analyzed.The influence of temperature dependence of thermoelectric materials under different thermal boundary condition models was also compared.In addition,based on the appropriate thermal boundary condition model,the thermoelectric arm of the thermoelectric module is optimized with multiple parameters and multiple objectives at different thermal end temperatures.The results show that considering the boundary conditions of air convection heat transfer and heat radiation has little effect on the thermoelectric properties,and the obtained results are more realistic.When the maximal area power density is taken as the optimization objective,the optimal height and the optimal side length of the thermoelectric arm have no change with the increase of the hot end temperature and PN pair number.With efficiency as the optimization objective,the thermoelectric conversion efficiency is maximized by the existence of higher thermoelectric arm height,higher hot end temperature and fewer PN pair number.When the temperature of the hot end is lower than 250℃,the constant physical properties calculation method can be used instead of the variable physical properties to simplify the model calculation,and the error is less than 2%.Further,based on the theoretical heat transfer formula,the optimal length analysis solution of the full series circuit of the thermal apparatus is derived,and the existence of the optimal structure size value is proved from the theoretical formula.The models of thermoelectric generators with different circuit connection modes are established by using Fortran program.The differences between full series circuit and multi-segment series circuit are compared from the perspectives of internal temperature,current,electromotive force and output power performance.With the maximum output total power and net power as optimization objectives,the length structure optimization and deviation of different circuit connection modes are analyzed,and the structure optimization of full series circuit and multisegment series circuit is explored.The results show that there are significant differences in the distribution of internal thermoelectric characteristics between the full series circuit and the multi-segment series circuit.The more the number of segments in the series circuit,the greater the output power.The optimal total length of thermoelectric module is greater than that of thermoelectric module when the maximum total output power is taken as the optimization goal.However,although the optimal total length of different circuit connections varies greatly,the actual power varies little when the optimal total length is near.Therefore,the optimal total length value of the full series circuit connection can be used as a reference for the optimal total length of the multi-segment series circuit connection,which can achieve a small power deviation.The total length,total width and height of the heat exchange channel of the multi-stage series circuit and the full series circuit have their own optimal length and total width under different hot fluid flow and temperature.Finally,the influence of the physical properties of hot fluid on the optimal structure of thermoelectric generator under different circuit connection modes is explored.The hot fluid physical properties of thermoelectric generator with and without phase change are compared under fixed cold and hot fluid temperature,heat exchange channel height and total width of thermoelectric module,and the overall structure of thermoelectric generator is optimized.The results show that when the temperature and mass flow of hot fluid are low,it is recommended to use the full series circuit connection.When the temperature and mass flow of the hot fluid are high,the multi-stage series circuit connection has better output power,and the optimal structure size should be selected according to the mass flow of the hot fluid and the temperature of the hot fluid.The multi-stage series current will complicate the circuit connection,but it will also reduce the risk of circuit damage caused by the full series circuit.For large-scale temperature difference power generation system,it is strongly recommended to use the multi-stage circuit connection method to improve the power.When the temperature of the cold and hot fluid is fixed,the total width of the thermoelectric module and the height of the heat exchange channel are fixed,the output power of the wet flue gas thermoelectric generator is higher than that of the dry flue gas thermoelectric generator because it contains water vapor.For the structure optimization of the wet flue gas temperature difference power generation system,it is not recommended to consider the total length and total width,using the area to optimize can get better results,using different circuit connection methods can also improve the output power of the system.