Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Experimental investigations on a cross ﬂow solar air heater having perforated circular absorber plate for thermal performance augmentation Shreyas P. Shetty, Akhil Paineni, Madhav Kande, N. Madhwesh, N. Yagnesh Sharma, K. Vasudeva Karanth ⁎ Department of Mechanical and Manufacturing Engineering, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal 576 104, Karnataka, India ARTICLE INFO Keywords: Solar air heater Perforated absorber plate Thermo-hydraulic eﬃciency Cross ﬂow heat conﬁguration ABSTRACT Conventional solar air heaters are associated with low thermal and thermohydraulic eﬃciencies due to the formation of laminar sub-layer created in the region where the ﬂowing air comes in contact with the absorber plate. Hence there is a need to break this laminar sub-layer to improve the convective heat transfer capability of the collector. In this study, a solar air heater with perforated circular absorber plate is adopted with cross-ﬂow conﬁguration. The thermal performance is investigated for 5, 8 and 10 mm perforation vent diameters as well as 24, 36 and 54 number of vents. The conﬁguration with perforated absorber plate provides a better convective heat transfer and thereby leads to better thermal and thermohydraulic eﬃciencies. This is compared with the base model in the absence of perforated absorber plate for a wide operating range of Reynolds numbers from 3000 to 21000. It is found from the study that when there is an increase in the number of perforations, there is a signiﬁcant increase in thermohydraulic eﬃciency, even though there is a marginal drop in thermal eﬃciency. Also, with an increase in diameter of the perforated vents there is a remarkable improvement in the thermo- hydraulic eﬃciency though there is a marginal drop in the thermal eﬃciency. The best operating range of Reynolds number for the perforated solar collector is found to be between 9,000 to 15,000 having 54 vent perforations corresponding to 8 mm diameter and oﬀers an eﬃciency of 75.55%. 1. Introduction Dwindling natural resources and increase in global temperatures has forced the mankind to transition to alternate forms of energy. Solar energy can share with a big percentage in solving in the environmental pollution and energy crisis (Gouda et al., 2019). Solar air heaters are one of the applications of solar energy which have been proactively used to harness abundant supply of solar radiation for domestic, agri- cultural and industrial purposes. The conventional solar air heater consists of ﬂat, rectangular collector which captures both direct and diﬀuse radiations. The ﬂat absorber plate leads to more thermal losses which results in poor thermal characteristics of such solar air heaters. The laminar sub-layer formed on the interface of the absorber plate and air leads to reduction in thermal eﬃciency. Hence the main objective of various designs is to break the laminar sub-layer in order to maximize the thermal performance of solar air heaters. Several studies on using novel geometries to increase the thermal performance of the air heaters have been conducted. Singh et al. (Singh and Singh, 2018) conducted a numerical study on curved plate solar air heater and observed an increment of 3–7% in thermal eﬃciency cor- responding to a range of heat ﬂuxes from 800 to 1100 W/m 2 compared to conventional air heater. The best thermal performance was seen in V- corrugated conﬁguration when compared to smooth curved plate air heater. The pumping power required in case of corrugated conﬁgura- tion was however signiﬁcantly more than the smooth conﬁguration. Kumar et al. (Kumar et al., 2017) calculated thermal characteristics of a triangular duct solar air heater. Out of the three conﬁgurations (sharp cornered, rounded cornered and roughened collector) the one with rounded corners and roughness on the absorber plate exhibited en- hanced ﬂuid interaction and greater thermal performance. It was ob- served that the smooth triangular passage has signiﬁcantly lower thermal performance compared to the roughened conﬁgurations due to the formation of laminar sub-layer. Singh et al. (Singh and Dhiman, 2016) performed an experimental study of semi-circular absorber plate with rectangular ﬁns. The model was analyzed for varied passage of air. The conﬁguration with double glass recycled air exhibited a maximum thermal eﬃciency of 87%. It was observed that at most optimum con- ditions, a temperature rise of 15–18 degreesC was obtained. Heydari https://doi.org/10.1016/j.solener.2020.01.005 Received 17 August 2019; Received in revised form 1 January 2020; Accepted 3 January 2020 ⁎ Corresponding author. E-mail address: kv.karanth@manipal.edu (K. Vasudeva Karanth). Solar Energy 197 (2020) 254–265 0038-092X/ © 2020 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T