Analysis Of Thermoelectric And Mechanical Performance Of Thermoelectric Materials And Devices

Thermoelectric material is an environment-friendly function material,which can convert energy between heat and electricity directly.Thermoelectric material holds extensive application potentiality in power generation and refrigeration.However,the large-scale application of thermoelectric devices is limited due to the low conversion efficiency of thermoelectric materials.It has become a key problem in the field of thermoelectric that how to improve the performance of thermoelectric materials and ensure the mechanical reliability of materials at high temperature.Firstly,a three dimensional finite element model is built to assess the thermoelectric performance and mechanical performance of thermoelectric materials and devices.In terms of thermoelectric performance,based on the heat-electricity coupling calculation,the relationship between electric current and output power as well as conversion efficiency is explored.The influence of size and cross-sectional area of thermoelectric legs on the performance of output power and conversion efficiency with temperature-dependent material properties of the thermoelectric devices are studied.The optimum height and cross-sectional area of the thermoelectric legs are obtained by means of constantly adjusting the structure size of thermoelectric legs and the thermoelectric conversion efficiency is improved finally.In terms of mechanical performance,based on the heat-electricity coupling calculation,the stress characteristics of thermoelectric generator are analyzed.The influence of size,cross-sectional area and different boundary restraints of thermoelectric legs on the stress are mainly studied;the optimization method of reducing material stress is put forward.The results show that the mechanical reliability of materials should be taken into account when maximize thermoelectric performance.Optimum size and shape designs exist for specific conditions.Secondly,since the thermoelectric generator will have convection and radiation heat transfer with the environment in the actual use process,part of the heat will inevitably be dissipated to the environment,which will affect the thermoelectric performance and mechanical performance of the thermoelectric generator.For these phenomena,a novel collinear-type thermoelectric generator model is proposed considering the heat dissipation in the side surface.Then,based on the finite element method,performance of collinear thermoelectric generator considering the heat dissipation in the side surface is simulated;the temperature field,electric potential field and stress field in the thermoelectric generator are obtained.The influence of various convective heat transfer coefficient on thermoelectric performance and mechanical performance of the thermoelectric generator is investigated.The results demonstrate that thermal convection can decrease the energy conversion efficiency of the thermoelectric generator.Though heat loss from the side surface is increased due to heat convection,thermal stress is reduced.Finally,based on the theory of elasticity and mechanics of composite materials,a three-dimensional finite element model of functionally graded thermoelectric materials is built.The temperature distribution,thermoelectric performance and stress under thermal-electric-mechanical coupling in the thermoelectric generator are obtained by means of numerical simulation.The performance of graded materials in different forms is studied systematically by changing the gradient factor of gradient materials and the optimal design scheme is given.The results show that the functionally graded thermoelectric materials have better thermoelectric and mechanical performance than the conventional homogeneous segmented materials.