Parametric Studies on Solar air Heater with Naca Profile Ribs In Different v-Orientations

Abstract

The major limitation of solar air heaters is low convective heat transfer coefficient due to formation of a laminar sub layer between the absorber plate and air. It can be overcome by breaking this laminar sub layer with the use of artificial roughness (rib) on the absorber plate. The provision of artificial ruggedness will increase the heat transfer coefficient but simultaneously it also increases the pressure drop; hence, the ribs shall be provided in such a manner that it improves the overall thermal-hydraulic performance of the solar air heater. The objective of the study is to analyse the effects of NACA 0040 profile ribs in transverse and V-orientations and also to optimize the various parameters of V-orientation. In the first phase, numerical simulations were carried out with smooth and NACA 0040 profile ribs with transverse orientation. In the second phase, numerical investigations were carried out with V- orientation and optimized the attack angle (α) of V-orientation. The parametric studies were done with attack angle in the range of 60° to 90° with a constant value of relative roughness P/e of 5 and e/D of 0.065. From the numerical investigations, V-orientation with α is 90° led to the maximum THPP of 1.87. In order to validate the numerical results, an absorber plate was developed with NACA 0040 profile ribs with V-orientation having α is 90°, P/e is 5 mm and e/D is 0.065. It was found that the V-orientation (90°) led to 40.07 - 202.26% increase in the Nusselt number and 20.35 –45.82% increase in the friction factor in comparison with the smooth duct. Moreover, it resulted in 5.39 - 53.0% rise in Nu and 8.54 - 58.41% improvement in THPP in in the Reynolds number range of 14000 to 18000 in comparison with the transverse orientation.