Experimental study on performances of flat-plate pulsating heat pipes without and with thermoelectric generators for low-grade waste heat recovery

Abstract

Low-grade waste heat recovery has significant importance to energy saving and emission reduction. Due to the lack of cost-effective heat recovery technology, a lot of low-grade heat is wasted. In this paper, performances of 3D-printed flat-plate PHPs and computerized numerical control (CNC) machined flat-plate PHPs without and with thermoelectric generators (TEGs) under four recycling modes were studied. The effects of the type and number of flat-plate PHPs, condenser section length, recycling mode, flow arrangement, velocity and temperature of hot/cold air, the number and layer number of TEGs on the performances of the waste heat recovery system were studied to maximize its performance. Results indicate that the performance of the heat recovery system with CNC machined flat-plate PHP is generally better than that with 3D-printed flat-plate PHP, and their maximum effective thermal conductivities can reach 585 and 541 W/(m·K), respectively. Performances of flat-plate PHPs based waste heat recovery system can be improved by using slotted fins, increasing the condenser section length and flat-plate PHPs number. For the air-to-air heat recovery system with three flat-plate PHPs, the maximum heat transfer rate and heat recovery rate can be up to 303 W and 85.3%, respectively. As for heat-to-power waste heat recovery under Mode 3, flat-plate PHP coupled with three TEGs can achieve its maximum open-circuit voltage of 7.6 V and output power of 1.98 W. Preliminary economic analysis proves that flat-plate PHPs based waste heat recovery system displays good economic benefits. These results may be helpful in designing a cost-effective flat-plate PHPs based low-grade waste heat recovery system.