Effect of thermal conductivity on performance of thermoelectric systems based on Effective Medium Theory

Currently thermoelectric (TE) systems have very low efficiency due to unfavorable TE properties (e.g., high thermal conductivity and low power factor). Figure of merit (ZT = α2σT/k) is a measure of TE material's performance which suggests that relatively lower thermal conductivity of TE materials can improve the performance (e.g., efficiency and coefficient of performance) of TE systems. A bulk composite TE material can have low thermal conductivity which can be made-up of TE micro/nano particles and base TE materials. There are various models reported in the literature based on Effective Medium Theory (EMT) which can predict thermal conductivity of composites. In this paper, three different models based on EMT are applied to investigate the performance of thermoelectric generator (TEG) and thermoelectric cooler (TEC). These models are Maxwell model, Hasselman-Johnson model, and Minnich-Chen model. Analytical modeling and numerical simulations have been performed to evaluate TE systems' performance (e.g., COP and thermal efficiency). Thermal efficiency of thermoelectric generator (TEG) increases from 2.06% to 5.59% which is 170% rise when composite thermal conductivity decreases from 1.1 W m−1 K−1 to 0.11 W m−1 K−1 based on Minnich-Chen model with particle size of 100 nm. An increase in thermal efficiency/COP can be attributed to reduction in Fourier heat conduction contribution to total heat input which leads to increase in total heat input. Results also show that performance of TE systems significantly depends on size and volume fraction of particles.