Heat transfer enhancement research of dynamical vortex generator in a solar air heater by using the piezoelectric fan array

摘要

Most of the vortex generators are static and used in fin-and-tube heat exchangers, whereas this paper presents experimental and numerical research on the effects of piezoelectric fan array in single pass solar air heater having one side heated and the other three sides insulated. The average Nusselt number of the rectangular channel is compared in detail with different Reynolds number of the air. Two different flow direction configurations including counter flow and downstream flow has been tested. The results show that the piezoelectric fan as a vortex generator can increase the local and average Nusselt number effectively. The average Nusselt number is increased by 40 similar to 100%, whereas the pressure drop is increased by no more than 30%. The counter flow has higher local and average Nusselt number compared to the downstream flow, while higher pressure drop in the counter flow setup can be found compared to the downstream flow setup. According to the numerical simulation results, this is because the most longitude vortices are concentrated in the middle of the absorber plate and attached or reflowed to the plate in the counter flow setup. However, most of the vortices are concentrated in the back end of the plate or out of the plate in downstream flow. All of these, result from the different velocity gradient distribution at the near-wall of the heated surface. The existences of the PE fan bracket decreases the pressure drop in the downstream flow setup.