Thermal rectification and thermal resistive phase cross over in exponential mass graded materials

Abstract

Concept of the functional graded materials (FGMs) has been explored by considering exponential mass variation along the chain of anharmonic oscillators in the study of heat transport at low dimensions. This exponential distribution of mass along the space invokes the diffusion of phonons transport which results to temperature gradient, asymmetric heat flow, thermal rectification and cross over between positive differential thermal resistance (PDTR) and negative differential thermal resistance (NDTR) in one-dimensional (1D) exponential mass graded chain. The temperature dependence thermal rectification achieved is 4−74% and also predicted that the thermal rectification can be controlled by tuning the higher and lower average temperature limits of two thermal reservoirs. It is also seen that in FGMs, the thermal conductivity does not change drastically against the average temperature of two heat baths. The cross over between PDTR and NDTR can be tuned either by mass ratio of one dimensional (1D) exponential mass graded anharmonic chain and/or by temperature difference between two heat baths. The figure of merit of the 1D structure can also be tuned by mass gradient, the higher mass gradient material will work as the potential candidate for better thermoelectric material.