Performance analysis of two-stage TECs (thermoelectric coolers) using a three-dimensional heat-electricity coupled model

This work for the first time uses a three-dimensional multi-physics model to optimize the performance of three kinds of two-stage TECs, connected electrically in series, in parallel, and separated, respectively. The optimizations are performed for the two-stage TEC with 30 thermoelectric elements. The number ratio and current ratio are searched to reach the optimal cooling capacity, COP, and maximum temperature difference, respectively. A marked three-dimensional temperature distribution is observed for the two-stage TEC with number ratio larger or smaller 1.00. In addition, temperature-dependent material properties are proven to be extremely important for predicting the two-stage TEC performance. Therefore, thermal resistance models extensively adopted in the previous two-stage TEC studies can not predict the two-stage TEC performance accurately because they assume the one-dimensional temperature distribution and constant material properties. The results also show that the thermoelectric element number on the hot stage should be larger than that on the cold stage for improving the cooling capacity and COP, and the optimal number ratio is found to be about 1.73-2.33 for the series configuration. The performance can be further improved by supplying a higher current to the hot stage, and the optimal current ratio ranges from 1.50 to 2.00.