Design and performance analysis of the thermoelectric power generation device for the heat recovery of electric heating dryer

Electric heating drying system has been widely used for structural drying, sanitizing with heat, and space heating at present. The metal steel plate can often be the main material of the heating box and air duct of the dryer in the mechanical arrangement. Nevertheless, a large heat transfer coefficient can make it easy to lose heat, when converting the electric current to the heat in the system. The insulation material can normally be laid on the outer layer of the steel plate. However, the traditional configuration cannot recover the heat, although the heat loss can be prevented in this case. Alternatively, thermoelectric power generation has attracted extensive attention in the field of heat recovery, because it can directly convert temperature differences into electricity. In this study, an energy-saving mode was proposed to recover the heat of the dryer using a Thermoelectric Generator (TEG). A thermoelectric power generation system was designed and developed for the dryer to directly recover the heat. In addition to recovering the heat of the metal wall of the dryer, the thermoelectric cell was also used to recover the part of the heat of the hot air, resulting in a decrease in the hot air temperature. Therefore, the Fluent software was firstly used to simulate the temperature field of the dryer before and after the installation of TEG. The measured parameters were combined to evaluate the impact of TEG installation on the dryer. Secondly, the output electric energy was controlled to obtain stable electricity in the thermoelectric power generation device. The reason was that the cold end, hot end, and power generation performance of TEG fluctuated dynamically, due to the heating power. The STM32F334 was used as the controller to realize the DC-DC conversion function. The test was also carried out to verify the performance of raising and lowering the voltage of the controller. As such, the battery was charged to fully meet the requirements of the TEG for the heat recovery of the dryer. Finally, the test platform of TEG was built for the heat recovery of the dryer. A systematic evaluation was made of the hot air temperature of the dryer before and after the installation of TEG, as well as the parameter characteristics of the power generation system. The test results showed that the installation of TEG presented no outstanding impact on the dryer. The better performance of the dryer was achieved under different operating conditions of thermoelectric power generation. Specifically, the power regulator and frequency converter were utilized to control the heating power and the wind speed of the centrifuge. There was a significant variation in the output power of thermoelectric power generation, the consumption power of the water pump, and the net output power with the cooling water flow. Among them, the water pump was controlled by the DC power supply. Consequently, there was optimal water flow to maximize the net output power under the different working conditions. An optimal parameter combination was achieved, where the optimal water flow rate was 22.3 L/min, the pump power consumption was 6.4 W, the system output power was 31.8 W, the maximum net output power was 25.40 W, and the thermoelectric conversion efficiency was 3.90%, particularly when the heating power was 3.0 kW and the wind speed was 12 m/s. Anyway, the experiment verified the feasibility of the developed device. The finding can also provide a new idea for drying energy-saving technology. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.