Combined effect of solar intensity and air mass flow rate on inline spherical dimple based solar air heater during summer season

Abstract

Experimental investigation was done in this study to compare the effectiveness of flat and inline spherical dimple engraved absorber plates solar air heater (SAH). During the summer, a SAH with a single glass cover, one pass, and two different types of absorber plates was evaluated on alternating days by taking readings from 9.30 a.m to 2.00p.m at an interval of 30 min. In order to conduct the investigation, the air mass flow rate (Ma) was raised from 0.0098 kg/s to 0.0520 kg/s (corresponding Re: 1861–10218) while solar intensities varied throughout the days. By increasing the Ma, various parameters were measured and different thermal characteristics were examined, such as the convective heat transfer coefficient, the blower’s power consumption, extracted power, effective power, efficiency, the heat gain factor, the heat loss factor, the SAH-efficiency factor, the averaged Nusselt number (Nu), and the averaged friction factor (f). The investigation reveals that with an increase in Ma, both flat and dimpled roughened SAH exhibit an increase in convective heat transfer coefficient, extracted power, instantaneous efficiency, heat gain factor, heat loss factor, and SAH-efficiency factor. However, the enhancement rate of inline dimple plate-solar air heater (IDP-SAH) due to engraved dimples is always higher than the flat plate-solar air heater (FP-SAH). Up to a particular Ma, both types of SAH have higher effective efficiencies. Thereafter effective efficiency decreases due to a significant increase in required pumping power. Comparing IDP-SAH to FP-SAH, the averaged Nu and the averaged f of IDP-SAH is 83.42% and 176.51% greater, respectively. In addition, the effective efficiency of IDP-SAH is 31.24% higher than the FP-SAH. The friction factor (f) starts to decline as the Ma increases. Even though the IDP-SAH and FP-SAH performance analyses were conducted on different days during the summer, IDP-SAH outperformed FP-SAH. The indentation of dimple on absorber plate helps in increasing surface area as well as helps in changing flow structure which is responsible for augmentation of heat transfer rate.