A Numerical Study on Effect of Rectangular Shaped Ribs Arranged In Different Patterns on Thermal Performance of a Solar Air Heater Duct

Solar air heater is a useful device that can be utilized to increase the temperature of air by extracting heat from solar energy. This thesis is concerned with a two-dimensional numerical study done to predict the influence of transverse rectangular cross-sectioned ribs on a solar air heater’s convective heat transfer properties. Solar air heater is a rectangular duct consisting of an absorber plate on its top and heat falls only on the top of absorber plate. When Different shape and orientation of ribs/baffles are introduced just beneath the absorber plate, there is a considerable alteration in the thermal performance of air flowing through the rectangular duct. A comparison was taken between the results of thin (high aspect ratio) and square ribs arranged in three patterns, namely, single wall arrangement, staggered arrangement and in-line arrangement on two opposite walls. The variation between Nusselt number and Reynolds number range 4000-25000 was checked at a fixed rib pitch (p) and height (e) values. Computational fluid dynamics (CFD) simulations were performed using commercially available software ANSYS FLUENT v15.0. This result was compared with the existing (Previous) experimental ones while performing simulations under same conditions. Only Two methods were used to find the average Nusselt number in which one method extracted the local Nusselt number at many points and on averaging these, gave the average Nusselt number and the second method resembled the one used in the existing experimental work. The results was evident that as compared with smooth duct, the introduction of ribs led to a considerable augmentation in heat transfer. Good agreement was found between the existing numerical output and experimental results, Out of the three arrangements, the best thermal performance was given by thin inline ribs whose convective heat transfer coefficient was 1.93 times smooth duct’s convective heat transfer coefficient.