FLOW FIELD ANALYSIS ON ARTIFICIALLY ROUGHENED RIB WITH GROOVES OF A SOLAR AIR HEATER

Abstract

The thermal performance of conventional solar air heater is generally poor because of low convective heat transfer coefficient between air and the absorber plate. The heat transfer coefficient of the absorber plate can be substantially increased by enhancing turbulence near the absorber plate. The use of artificial roughness in a solar air heater duct has been proposed to be an excellent option to enhance the heat transfer from absorber plate to the air. However, the artificial roughness results in higher frictional losses leading to excessive power requirement for the fluid to flow through the duct. It is therefore desirable that turbulence must be created only in a region very close to the heat-transferring surface to break the viscous sub-layer for augmenting the heat transfer. In this report, a detailed analysis of the flow structure of flow over rib roughened surface has been carried out using 2-D particle Image velocimetry (PTV). The two types of the roughened surfaces are used for the investigation, first is the rib-groove structure and other is square rib structure. For both the structure, the relative roughness pitch and relative roughness pitch has been kept as 7.5 and 0.0325 respectively. The Reynolds number has been varied between 10000 to 15000. Graphs of the velocity component, velocity magnitude, vorticity, streamlines, Reynolds stresses and turbulence intensity are plotted in xy plane. It has been observed that, as the turbulence increases with increase in the Reynolds number. Reattachment line is clearly visible and is in 5 times of the rib height away from the rib. In the vorticity counter, the maximum magnitude of the vorticity is along the shear layer of the flow. The CFD analysis of the present problem is also done and the result is same as experimental result.