Thermal-Electro-Mechanical Performances Analysis And Structural Optimization Design Of Several Types Of Thermoelectric Devices

Thermoelectric devices can realize the direct mutual conversion of heat energy and electric energy,which can not only use heat energy to produce electric energy,but also use current to realize the function of temperature control and heat pump.Due to their advantages of small size,high reliability and no pollution,thermoelectric devices are widely used in space exploration,medical treatment,military and daily life.According to the actual application background of thermoelectric devices,it is a key problem in the field of thermoelectric technology to maximize the performance of thermoelectric materials,improve thermoelectric conversion efficiency,and meet the core requirements of device structure and service characteristics.Thermoelectric devices always work in a temperature difference environment.The existing experiments show that a large temperature difference environment will lead to the damage of devices due to thermal mismatch between components.In addition,flexible thermoelectric devices can be damaged by mechanical loads such as bending.Therefore,while paying attention to the thermoelectric performances of thermoelectric devices,ensuring that they meet the requirements of mechanical strength has become the core problem in thermoelectric field.In view of this,a systematic numerical study on thermal-electro-mechanical performances of several types of thermoelectric devices in different application backgrounds is carried out in this paper.The influence of structural parameters and operating environment on their thermoelectric performances and mechanical reliability is revealed.The structure size of thermoelectric devices with high thermoelectric performances is obtained and the mechanical strength is satisfied.The following research results are presented:Firstly,for the annular thermoelectric generators used in waste heat recovery,the three-dimensional numerical models of bismuth telluride based and segmented annular thermoelectric generators were established.The thermoelectric performances and mechanical reliability of the devices were studied.For bismuth telluride based annular thermoelectric generators,the effects of structural parameters and number of thermocouples on the thermoelectric performances and stress state of the devices were investigated.It is shown that changing the Angle ratio of thermoelectric legs can not only improve the thermoelectric performances of the devices significantly,but also reduce the stress level in the thermoelectric legs.Furthermore,the optimum geometry of the annular thermoelectric generator with high thermoelectric and mechanical properties is given in this paper.For the segmented annular thermoelectric generators,the influence of structural parameters on the performance of segmented annular thermoelectric generators is discussed.It is found that with the increase of the proportion of hot segment material,the optimal value of output power and stress level of the segmented annular thermoelectric generator appears,and the optimal structural parameters of the segmented annular thermoelectric generator are obtained.Compared with bismuth telluride based annular thermoelectric generator,the output power of the optimized segmental annular thermoelectric generator is increased by 30.9%,and the stress level in bismuth telluride material is reduced by 40%,ensuring that it meets the mechanical strength requirements.On this basis,the thermoelectric and mechanical performances of segmented annular thermoelectric generators operating in sinusoidal heat sources are further studied.Secondly,based on the nonlinear thermoelectric coupling constitutive model,material deformation and Money-Rivlin three-parameter hyperelastic constitutive model,the three-dimensional finite element model of flexible thermoelectric generator encapsulated by PDMS material was established.The thermoelectric and mechanical performances of flexible thermoelectric devices under bending loads were studied.The influences of the the filling factor,the shape and height of the thermoelectric leg on the thermoelectric and mechanical performances of the flexible thermoelectric generator are revealed,and the optimal size of the flexible thermoelectric generator is obtained.It is found that increasing the number of thermocouples can improve both the thermoelectric performance and mechanical reliability of flexible thermoelectric devices under bending loads.The output power of the optimised device is 3.8 times higher than that before the optimisation,and the bending radius is not less than24.93 mm to meet the mechanical strength requirements.Thirdly,In order to optimize the cooling and mechanical performances of thermoelectric coolers,a three-dimensional numerical model of thermoelectric coolers was established,and the influence of structural parameters on their cooling performance and mechanical reliability is discussed.The steady-state thermoelectric performance of commercial thermoelectric coolers is tested experimentally and the experimental results are in good agreement with the numerical results.The results show that the cooling load does not affect the optimal input current of thermoelectric coolers.Under optimal current conditions,the minimum temperature of the cold end of thermoelectric coolers can be obtained by changing the height and width of thermoelectric legs.In this paper,the optimal structural parameters of thermoelectric coolers with good cooling performance were given and the mechanical strength requirements are satisfied.The influence of the period,amplitude and form of pulse current on the thermoelectric and mechanical performances of thermoelectric coolers is further studied.Finally,even if thermoelectric devices meet the mechanical strength requirements,they will still be damaged by cyclic thermal loading.In view of this,based on the interaction integral method and extended finite element method,the influence of operating temperature difference on the fracture parameters and fatigue life of the annular thermoelectric device with central crack in the thermoelectric leg is studied.The results show that the increase of temperature difference will increase the stress intensity factor of crack tip and decrease the service life of annular thermoelectric devices.In conclusion,in this paper,the thermoelectric performance,mechanical strength and reliability of several types of thermoelectric devices are systematically studied under different application backgrounds,and gives the optimized characteristic size to meet the application core requirements.Finally,the fatigue life of annular thermoelectric devices with a crack is predicted,and the important factors and influence law on their fatigue life is given.Relevant research provides theoretical suggestions and references for the optimal design and practical application of thermoelectric devices.