Investigations for efficient design of a new counter flow double-pass curved solar air heater

Abstract

The aim of this paper is to numerically investigate a new curved design of a counter flow double-pass solar air heater with arched baffles placed in the second duct. Due to high inertia of the flow and curved nature of design, fluid in second channel tend to move away from the absorber plate and thus, reduces the thermal efficiency significantly. In order to overcome this deficiency, new design parameters are introduced in the second duct in terms of arched baffles and their design is optimized for various geometric parameters such as angle of attack, variable pitch ratio etc. for best thermo-hydraulic performance. It was observed that arched baffles accelerate the flow near the absorber and facilitate the formation of large secondary vortices that enables multiple attachment zones at the absorber plate. Enhancement in thermal and hydraulic performances are discussed in terms of flow visualization, local Nusselt number, thermal effectiveness and friction factor ratio. Maximum enhancement of Nu in roughened curve counter double-pass solar air heater with baffle angles α/90 = 0.5 at P/d = 6 are found in the range of 20–28%, higher than without baffles. Moreover, two new regression correlations are developed for prediction of thermo-hydraulic performance in terms of geometrical and flow parameters.