Thermodynamic investigation on solar air heater having roughness as multiple broken arc and circular protrusion

Abstract

This study looked at the effectiveness of a solar air heater for heating air that has multiple ribs (broken arc shaped) and an arc-shaped circular protrusion on the rear side of the solar air heater absorber plate. Simulations were done on the commercial code FLUENT (v14.0) using the RNG k-ξ model at a uniform heat flux of 1000 W/m2. The relative roughness pitch of the rib are ranging from 10 to 30, broken arc rib has height of 1 mm, the gap between the broken arc and circular protrusion is 2.5 mm, the distance between two broken arc ribs has been kept as 20 mm, and circular protrusion has diameter of 0.8 mm In present study the maximum hydraulic thermal performance (THP = 3.31) was observed at Re = 20,000 where g/e = 0.8, protrusion diameter d = 0.6 mm, distance between the roughness p = 30. To better understand fluid flow physics, velocity pathlines, temperature contours and turbulent kinetic energy contours have been plotted. The post-CFD result shows the design of roughness is beneficial in achieving desired performance of solar air heater. The presence of gaps and protrusions creates the required turbulence in the duct that improve the thermal performance of solar air heater with minimum penalty of frictional pressure drop.