Effect of relative roughness pitch on heat transfer and flow characteristics in a solar air heater with inversed semi-circular ribs

چکیده مقاله

Fluid flow and heat transfer inside a solar air heater (SAH) equipped with inversed semi-circular ribs on the absorber plate considering three different arrangements are studied analytically and numerically. The semicircular ribs are positioned in a transverse manner to the flow. The numerical simulation of governing equations is applied considering a two-dimensional configuration employing the finite volume solver using ANSYSFluent 19. A daily uniform and constant heat flux of 21.6 MJ/m2 is evaluated by Metonorm V.8.0.3 and is supplied to the SAH. The effects of various parameters as relative roughness height (0.042), relative roughness pitch (from 7.14 to 17.86), and Reynolds number (from 2000 to 18,000) on the SAH flow field and heat transfer are studied. As a result, velocity, pressure, and temperature contours are evaluated to better presenting the flow physics inside the SAH. The results of present investigation shows that the SAH having inversed semi-circular ribs with a relative roughness pitch of 10.71 has the maximum Nusselt number enhancement factor of 3.23 and the maximum thermal enhancement ratio equal to 2.99 that take place at Reynolds number of 8000. Minimum friction factor increment is take place with roughness pitch of 10.71 and Reynolds number of 18,000 and was equal to 1.13. In addition, a correlation for the friction factor and Nusselt number are evaluated employing a regression study.