Effect of pulsating flow on the heat transfer performance of slit-like perforated solar air collector

Slit-like perforated solar air collector can use free solar energy to effectively preheat the fresh air, thus greatly reducing the building heat load. In order to further improve its thermal performance, this paper introduces pulsating flow, and experimentally and simulatively studies the heat transfer characteristics of the collector combined with plane jet. A new pulsating flow generator with ESP32 MCU as the control core has been developed, and the effects of pulsating amplitude (0.2-1.0), pulsating waveform (sinusoidal regime, square regime), pulsating frequency (0.01 Hz-200 Hz) and pulsating flow rate (40 m3/h-80 m3/h) have been discussed. The results show that the pulsating flow would further promote the heat transfer of the absorbing plate, due to the accelerated air mixing of the near-wall region and the main flow zone along with the rapid generation and diffusion of vortex. Thermal efficiency can reach up to 60.87 %, 5.85 % higher than that of the steady flow. The enhanced heat transfer effect is more significant at larger pulsation amplitude and lower airflow rate. However, the influence of pulsation frequency is more complicated. When the pulsation frequency is up to 200hz, the effect of promoting heat transfer will no longer be increased due to limited vortex structure. The sudden change of velocity can help to keep the turbulent kinetic energy at a relatively high level, and thus the thermal efficiency of the square pulsation can be increased by 2.06 %, compared to that of the sinusoidal pulsation.