CFD ANALYSIS OF HEAT TRANSFER AND FRICTION CHARACTERISTICS OF SAH DUCT USING BROKEN ‘S’ SHAPED RIBS ROUGHNESS

Mechanical Engineering

In this paper, results of CFD analysis on heat transfer and friction in rectangular ducts with ‘S’ shape with gap roughness has been presented. The rib roughness has relative roughness pitch was varied from 8 to 11, arc angle of 30° and relative roughness height of 0.043. The relative gap width of 1.0. The effects of relative roughness pitch on Nusselt number, friction factor and thermo-hydraulic performance parameter have been discussed and results compared with smooth duct under similar conditions. The rough ribs were efficient enough to transfer the desired heat, but they are not economical and are very complex in design and construction. Whereas, roughness 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 ‘S’ shaped rib with different relative roughness pitch, when compared with the smooth plate, it was concluded that the related Nusselt Number and friction factor for ‘S’ shaped rib with different relative roughness pitch was more efficient. The smooth plate 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 roughness pitch 10 at a Reynolds number of 16000.

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