Performance Assessment of Double Pass Solar Air Heater with Inclined Discrete Ribs on Absorber Plate

Abstract

In double pass solar air heater thermal performance can be obtained by augment the rate of heat transfer and minimizes the top losses and bottom losses.Efficiency of solar air heater is low because of low value of heat transfer coefficient between absorber plate and flowing air. This is due to the presence of laminar sub layer that need to be broken to increase heat transfer. Therefore for enhancement of heat transfer turbulence is created by providing inclined discrete ribs on absorber plate. This paper presents an experimental investigation carried out to study the effect Inclined continues rib roughness on heat transfer coefficient and friction factor in an artificially roughened solar air heater duct. The experiment encompassed Reynolds number (Re) from 3000 to 15,000. Relative roughness height (e/D) values 0.027, relative roughness pitch (P/e) range of 6–12, angle of attack (α) - 600.Extensive experimentation has been conducted to collect data on heat transfer and fluid flow characteristics of a rectangular duct roughened with inclined discrete ribs. Using these experimental data, correlations for Nusselt number and friction factor in terms of roughness geometry and flow parameters have been developed. The roughened wall has roughness with pitch (P), ranging from 9-18 mm, height of the rib of 1.5 mm and duct aspect ratio of 6.67. The air flow rate corresponds to Reynolds number between 3000–15000. The heat transfer results have been compared with those for smooth ducts under similar flow and thermal boundary condition to determine the thermal efficiency of solar air heater.