Dependence of Seebeck coefficient on a load resistance and energy conversion efficiency in a thermoelectric composite

Abstract

The thermo-emf Δ V and current Δ I generated by imposing the alternating temperature gradients (ATG) at a period of T and the steady temperature gradient (STG) on a thermoelectric (TE) composite were measured as a function of t, where t is the lapsed time and T was varied from 60 to or ∞ s. The STG and ATG were produced by imposing steadily and alternatively a source voltage V in the range from 1.0 to 4.0 V on two Peltier modules sandwiching a composite. Δ T, Δ V, Δ I and V P oscillate at a period T and their waveforms vary significantly with a change of T, where Δ V and V P are the voltage drops in a load resistance R L and in resistance R P of two modules. The resultant Seebeck coefficient | α| = |Δ V|/Δ T of a composite under the STG was found to be expressed as | α| = | α 0|(1 − R comp/ R T), where R T is the total resistance of a circuit for measuring the output signals and R comp is the resistance of a composite. The effective generating power Δ W eff has a local maximum at T = 960 s for the p-type composite and at T = 480 s for the n-type one. The maximum energy conversion efficiency η of the p- and n-type composites under the ATG produced by imposing a voltage of 4.0 V at an optimum period were 0.22 and 0.23% at Δ T eff = 50 K, respectively, which are 42 and 43% higher than those at Δ T = 42 K under the STG. These maximum η for a TE composite sandwiched between two Peltier modules, were found to be expressed theoretically in terms of R P, R T, R L, α P and α, where α P and α are the resultant Seebeck coefficients of Peltier modules and a TE composite.