Performance analysis for two-stage TEC system driven by two-stage TEG obeying Newton’s heat transfer law

A combined device model of two-stage thermoelectric cooler (TEC) driven by two-stage thermoelectric generator (TEG) with external heat transfer, Joulean heat inside the thermoelectric device, and the heat leakage through the thermoelectric couple leg is proposed in this paper. The heat transfer between the reservoirs and hot or cold junctions of the combined device is assumed to obey Newton’s heat transfer law. Several design variables are defined, based on which the performances of the combined device model are analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. For a fixed total thermal conductance of four heat exchangers, the allocations of the thermal conductance among the four heat exchangers are optimized for maximizing the cooling capacity and the coefficient of performance (COP) of the combined thermoelectric device. For the fixed total number of thermoelectric thermocouples of the combined device, the allocations of the number of thermoelectric thermocouples among the two thermoelectric generators and the two thermoelectric coolers are also optimized for maximizing cooling capacity and COP, respectively. The numerical calculations show that the external heat transfers affect the performance of combined thermoelectric device strongly. There are optimum allocations of the number of thermocouples and optimum allocations of thermal conductance of heat exchangers corresponding to the maximum cooling capacity and the maximum COP, respectively. When the total thermal conductance of heat exchangers extends to infinity, the results of this paper approach the non-equilibrium thermodynamic results obtained.