CFD Analysis of Solar Air Heater Having Broken Double Arc Rib Roughness in Absorber Plate

In this thesis, results of CFD analysis on heat transfer and friction in rectangular ducts roughened with Broken double arc rib roughness has been presented. The rib roughness has relative gap position of 0.65, relative roughness pitch of 10, arc angle of 30° and relative roughness height of 0.043. The relative gap width was varied from 0.5 to 2.5. The effects of relative gap width on Nusselt number, friction factor and thermo-hydraulic performance parameter have been discussed and results compared with smooth duct and continuous arc rib roughened duct under similar conditions and also compare with previous experimental results. The rough ribs were enough efficient to transfer the desired heat, but they are not economical and are very complex in design and construction. Whereas, the broken double arc ribs with different relative gap width gives more area of contact. So, there is enough time to transfer the heat from the ribs to the passing air which touches the ribs and the heat transfer takes place efficiently. Thus, the broken double arc ribs with different relative gap width, when compared with the smooth and continuous arc ribs with symmetrical gaps, it was concluded that the related Nusselt Number and friction factor for broken double arc ribs with different relative gap width was more efficient as well as economical, than that of smooth and rough ribs with symmetrical gaps for flow Reynolds Number. The smooth ribs could not transfer the desired heat due to absence of friction; so, they are not preferred practically. One of the most important techniques used are passive heat transfer technique. These techniques when adopted in heat transfer surfaces proved that the overall thermal performance improved significantly. Rib roughness on the underside of the top wall of a duct has been found to substantially enhance the heat transfer coefficient. Surface roughness disturbs the laminar sub-layer in the turbulent flow and promotes local wall turbulence that, in turn, increases the heat transfer from the surfaces. The augmentation in heat transfer accompanies a higher pressure drop penalty of the fluid flow. In this work the maximum value is found to be relative gap width 1.0. Solar energy is one of the environmentally compatible sources of renewable energy. It is most recognized as one of the promises that can conserve the Earth to survive in a reasonable shape. Solar energy is virtually unlimited. The Sun is the primary source of renewable energy and it harvest more abundant than any other type of energy. A conventional solar air heater generally consists of an absorber plate with a parallel plate below forming a passage of high aspect ratio through which the air to be heated flows. As in the case of the liquid flat-plate collector, a transparent cover system is provided above the absorber plate, while a sheet metal container filled with insulation is provided on the bottom and sides.