Energy and exergy analyses and optimizations for two-stage TEC driven by two-stage TEG with Thomson effect

Based on the non-equilibrium thermodynamics and energy and exergy analyses, a thermodynamic model of two-stage thermoelectric (TE) cooler (TTEC) driven by two-stage TE generator (TTEG) (TTEG-TTEC) combined TE device is established with involving Thomson effect by fitting method of variable physical parameters of TE materials. Taking total number of TE elements as constraint, influences of number distributions of TE elements on three device performance indictors, that is, cooling load, maximum COP and maximum exergetic efficiency, are analyzed. Three number distributions of TE elements are optimized with three maximum performance indictors as the objectives, respectively. Influences of hot-junction temperature of TTEG and cold-junction temperature of TTEC on optimization results are analyzed, and difference between optimization results corresponding to three performance indicators are studied. Optimal performance intervals and optimal variable intervals are provided. Influences of Thomson effect on three general performance indicators, three optimal performance indicators and optimal variables are comparatively discussed. Thomson effect reduces three general performance indicators and three optimal performance indicators of device. When hot- and cold-junction temperatures of TTEG and TTEC are 450, 305, 325 and 295 K, respectively, Thomson effect reduced maximum cooling load, maximum COP and maximum exergetic efficiency from 9.528 W, 9.043×10 −2 and 2.552% to 6.651 W, 6.286×10 −2 and 1.752%, respectively.