A study on heat transfer enhancement for solar air heaters with ripple surface

Abstract Flat-Plate solar air heater (SAH) is utilized widely to relieve the fossil energy crisis nowadays. With the aim to improve the efficiency of the devices, heat transfer and flow characteristic in a solar air heater with novel inclined groove ripple surfaces were investigated in this work. The effect of three different parameters, such as groove amplitude, attack angle, and array number, on the overall performance of air heater was analyzed in the range of Reynolds number from 12000 to 24000. The inclined grooves on the ripple surface have a significant impact on the working fluid for generating longitudinal swirl flow in the duct of air heater, which mixes the air to enhance heat transfer, Nu/Nu0 = 1.21–3.38, and leads to a moderate increase of pressure drop in the same time, f/f0 = 1.54–6.96. The solar air heater composed with ripple surface is of excellent overall thermo-hydraulic performance, Nusselt numbers are 1.04–1.94 times higher than the smooth duct at same blowing energy consumption.