CFD analysis for thermal performance augmentation of solar air heater using deflector ribs

Abstract

This paper presents the effect of deflector ribs on the thermal performance of flat plate solar air heater using Computational Fluid Dynamics (CFD) methodology. The analysis is carried out using two-dimensional computational domain for the Reynolds number range of 6000-18000. RNG k-є turbulence model is used to capture the turbulence characteristics of the flow. The deflector rib has a cross-section of isosceles triangle and is placed transversely with respect to the flow. The distance between consecutive ribs is varied as 40mm, 80mm, 160mm and 320mm while the air gap height is varied as 2mm, 3mm, 5mm and 10mm. The numerical model is validated against the well-known correlation of Dittus-Boelter for smooth duct. The simulation results reveal that the presence of deflector ribs provide augmented heat transfer through flow acceleration and enhanced turbulence levels. With reference to smooth duct, the maximum achieved heat transfer improvement is about 1.39 times for the inter-rib distance of 40mm and an air gap height of 3mm while the maximum fiction factor achieved was about 3.82 times for pitch value of 40mm and air gap height of 3mm. The highest thermal enhancement factor is achieved for the pitch value of 320mm and an air gap height of 3mm at Re=6000. The air gap height value of 10mm exhibits thermal enhancement factor values lesser than 1.0 and hence is not recommended for use as heat transfer enhancement device for the entire Reynolds number range used in the analysis. The pitch value of 320 mm exhibits thermal enhancement factor greater than 1.0 for almost all the Reynolds number range used in the analysis and varies between 0.93 and 1.07.