Experimental and numerical simulation-based investigation for thermal characteristic of frustum roughened solar air heater

Abstract

ABSTRACT This research paper aims to investigate the effect of frustum shape roughness geometry on the thermal characteristic (Nusselt no. and friction factor) of solar air heaters (SAH). The study includes experimental and numerical investigation of a solar air heater equipped with frustum roughened absorber plate under varying operating conditions. Frustum shape roughness element produced more disturbances and greater mixing of primary and secondary flow that resulted in greater augmentation in thermal characteristics of SAH. The investigation was conducted in varying Reynolds number range of 2500 -12,500. Dimensionless parameter for Frustrum shaped roughness is varied as relative frustum height (e/Dh) 0.013–0.054, relative frustum pitch (p/e) 8–14, Relative frustum height to base diameter (e/d1) 0.37–0.75 and relative frustum diametral ratio (d1/d2) 1–3. To save time and resources a three-dimensional numerical simulation was also performed. This simulation helped to visualize flow field behavior with the help of streamline, temperature, turbulence kinetic energy and pressure contours. Maximum performance for roughened system was obtained at optimum value of flow and geometric configuration within the range of investigated parameters. The geometric orientation of proposed roughness geometry produced tremendous rise in Nusselt number (Nu) with an acceptable rise in friction (f). Maximum enhancement in Nu for varying p/e, e/Dh, e/d1, and d1/d2 was, 4.58, 5.21, 6.62 and 6.09 times and that of friction was 5.59, 4.69, 4.92 and 4.66 times respectively over conventional smooth SAH.