CFD ANALYSIS OF HEAT TRANSFER AND FRICTION CHARACTERISTICS OF SOLAR AIR HEATER DUCT USING BROKEN MULTI ARC SHAPED RIBS ROUGHNESS

THERMAL ENGINEERING

In this paper results of CFD analysis on heat transfer and friction in rectangular ducts roughened with broken multi arc-rib roughness has been presented. The rib roughness has relative roughness pitch of 10, relative , 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 under similar conditions.Thus, the broken multi arc shaped with different relative gap width, when compared with the smooth and rough ribs with symmetrical gaps, it was concluded that the related Nusselt Number and friction factor for broken multi arc shaped 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 is 1.0.

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