Impact of multi-staggered rib parameters of the ‘W’ shaped roughness on the performance of a solar air heater channel

Abstract

ABSTRACT 8The collection efficiency of a solar air heater can be enhanced by employing artificial roughness as one of the modus operandi to create turbulence which helps in breaking the laminar sub-layer. The present investigation takes into account the impact of multi-staggered rib parameters of the W-rib roughness on the performance of the solar air heater channel. The chosen geometry in the current investigation is novel in a way that no such combination of roughness in the form of ribs has ever been tried earlier. The dimensionless factors for investigation were varied to study the effect of staggered ribs in the form of relative staggered pitch (p/P) 0.45–0.75 and relative staggered rib length (w/e) 1.5–6.0 for Reynolds number in the workable range of solar air heater channel as 4000–14000. Other parameters/factors were kept constant by selecting the optimal values from available works as relative roughness pitch (P/e) 12, relative roughness height (e/Dh) 0.0423, angle of attack (α) 60°, relative gap width (g/e) 1, number of gaps (n) 2. The augmentation in Nusselt number ratio has emerged in the range of 2.3–4.1, optimum values of p/P and w/e correspond to 0.65 and 4.5, respectively. A comparison with geometries under the analogous flow and thermal conditions has also been carried out.