Performance evaluation and optimization of solar assisted air heater with discrete multiple arc shaped ribs

Abstract

Abstract Solar air heater is widely used for heating and drying applications. Many techniques have been used to improve the performance of a solar air heater but the most common technique is surface roughness in which ribs are provided over the absorber plate. In the present article, multiple-arc shaped (three arcs) rib roughness is provided on the underside of absorber plate. The impacts of different roughness elements i.e. number of gaps (ranged from 1 to 3), relative gap width (0.5 to 1.5) and relative gap position (0.3 to 0.9) are examined for fixed range of flow parameter on the performance of a single glazed duct solar air heater. To investigate the optimized thermal performance of solar air heater, response surface methodology was used for the design of experiments using analysis of variance. Remarkable improvement in thermal performance of solar air heater is observed by varying roughness parameters but it leads to increase in pumping power of solar air heater. Additionally, a generalized quadratic correlation for Nusselt number and friction factor is also developed based on the analysis of variance which show percentage deviation of ± 6.15% and ± 5.74% in comparison to experimentally estimated value of Nusselt number and friction factor respectively. The optimum thermo hydraulic performance calculated is 3.85 at relative gap width, relative gap position and number of gaps of 1, 0.6, and 3, respectively.