Experimental And Theoretical Study About The Influence Of Peltier Effect On The Performance Of Thermoelectric Generator

Waste heat energy is widely contained in waste liquid and waste gas produced by industry,transportation and other fields.Recycling this part of low grade energy can optimize the existing energy structure and be conducive to achieve the goal of carbon peak and carbon neutrality.Thermoelectric Generator(TEG)has been used in different grade waste heat recovery of many industries due to its unique advantages such as no chemical pollution and direct conversion from thermal energy to electricity.However,the low energy conversion efficiency limits its large-scale commercial use.Aiming at the energy loss caused by the Peltier effect during the operation of TEG,this paper explores the mechanism of performance loss caused by the Peltier effect by combining experimental and theoretical analysis,and proposes method to reduce the Peltier effect from the aspects of TEG thermal resistance structure and hybrid system.Main research contents are as follows:(1)The TEG-thermal silicone grease experimental system was established and the influence of the Peltier effect on the temperature loss distribution difference at both sides of TEG and performance loss was investigated by using the analytical model.During the pre-experiment,the optimal parameters of thermal silicone grease layer were determined to temporarily isolate the influence of cold and hot source on the Peltier effect.Firstly,the optimal cooling water flow rate was determined according to the cooling effect and energy-saving principle.Then,the actual temperature of TEG surface with Peltier effect was obtained through the experiment.Combined with the analytical model,the difference between the influence of the Peltier effect on the temperature loss of the cold and the hot side of TEG was studied.Finally,the overall performance loss of TEG caused by the Paltier effect was analyzed.The optimal cooling water flow in this experiment is 3.5 L/min;The temperature loss at the hot side of TEG is greater than that at the cold side,and the ratio of total temperature loss to temperature difference is up to21.7%.It is more effective to reduce the thermal resistance at the hot side of TEG.The power loss has a linear relationship with the product of temperature difference and temperature loss.The maximum power loss,energy efficiency loss and exergic efficiency loss occur at the load corresponding to the maximum of power,energy efficiency and exergic efficiency.(2)The TEG-external ceramic substrate experimental system was established to study the variation of output performance with different thermal resistance at both sides of TEG and to verify the optimization strategy that reducing thermal resistance is more effective.In the experiment,the ceramic substrate with different thermal conductivity and thickness was used to simulate the different thermal resistance at the cold and hot side of TEG.The results show that when the thermal resistance at both sides of TEG is same,the temperature difference and open-circuit voltage firstly increase and then decrease with the increase of thermal conductivity of the ceramic substrate,and also increase with the decrease of the thickness of the ceramic substrate.Based on the TEG with the same thermal resistance at both sides,the ceramic substrate with the smaller thermal resistance at the hot side is more beneficial to improve TEG performance,and the improvement effect is more obvious near the maximum power point.The open-circuit voltage,maximum output power and effective temperature difference increase by 0.64 V,0.87 W and 24.5℃,respectively.(3)Thermoelectric cooler(TEC)-TEG experimental system was established and exergic analysis was adopted to study the influence of Peltier effect produced by TEG on itself,TEC and system.In the system,TEC can be used for refrigeration and its heat dissipation is used as the heat input of TEG.The results show that the Peltier effect generated by TEG can bring gain to TEC in the system,and the loss caused by TEG can be offset under some conditions.Exergy efficiency of the hybrid system with TEG operation is higher than that without TEG operation,but lower than that of the single TEC system.Therefore,system heat dissipation needs to be further optimized.