Non-compact Contact Heat Loss Analysis And Performance Optimization Of Flexible Thermoelectric Devices

With the popularity of smart wearable devices,traditional battery power has become the main obstacle to their development.Flexible thermoelectric devices,due to their advantages of being clean,highly stable,and requiring no frequent replacement,can directly convert human body heat into electrical energy,and are considered the most promising power supply for smart wearable devices.The main application scenario of flexible thermoelectric devices is on curved surfaces,but there are problems such as low output power and insufficient flexibility.Therefore,it is necessary to conduct research on the thermal loss and output performance of flexible thermoelectric devices under bending conditions.In this thesis,numerical simulation methods were used to study the basic performance,non-dense contact thermal loss,and performance enhancement of flexible thermoelectric devices.Firstly,a three-dimensional numerical model of a bismuth telluride-based thermoelectric device with flexible packaging was established for application to curve heat sources,and its basic performance under bending conditions was investigated.The effects of boundary conditions,curvature radius,and filling factor on the output performance of the device were discussed.The results show that reducing the curvature radius under convective conditions improve the output performance of the device.Secondly,this thesis analyzed the potential non-dense contact conditions of flexible thermoelectric devices under bending conditions.The effects of pore structure and position,as well as the heat transfer mode inside the pore,on the performance of flexible thermoelectric devices were revealed.The results show that pores cause a temperature gradient of 10-12K,resulting in a performance loss of up to 50.1%.Compared with the location of the pore under the thermoelectric leg and the length of the pore,the location of the pore under the filling and the height of the pore have a smaller effect on the output performance of the device.The study also find that using thermal interface materials,enhancing heat convection and radiation inside the pore reduce thermal loss caused by the pore.Among them,the use of thermal interface materials has the best results,followed by heat convection.Finally,the influences of flexible materials and cold-side heat sink on the device performance was examined.The results show that using a flexible packaging material made of porous PDMS with a lower thermal conductivity can improve the device output by up to 6.9%.Using a thinner and higher thermal conductivity flexible substrate can reduce the internal thermal resistance of the device and enhance its output performance.The use of a cold-side heat sink can significantly reduce the cold-side thermal resistance and increase the actual temperature difference between the hot and cold sides.Among the different heat sink structures tested,the foam copper with phase change material heat sink provided the best enhancement effect,and the enhancement effect was more significant with a larger temperature difference between the hot and cold sides.The radiative cooling film can significantly improve the device output performance at small temperature differences.The heat sink structure and the geometry of the thermoelectric legs were optimized to maximize the device’s output performance.The newly designed heat sink structure can improve the device output by up to 14.1%compared to the conventional structure.