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

THERMAL ENGINEERING

The solar air heater has an important place among solar heat collectors. It can be used as sub-systems in many systems meant for the utilization of solar energy. Possible applications of solar air heaters are drying or curing of agricultural products, space heating for comfort regeneration of dehumidifying agents, seasoning of timber, curing of industrial products such as plastics. When air at high temperature is required the design of a heater becomes complicated and very costly. As far as the ultimate application for heating air to maintain a comfortable environment is concerned, the solar air heater is the most logical choice. In general solar heaters are quite suitable for low and moderate temperatures application as their design is simple. These solar air heaters have low heat transfer efficiency which can be improved using geometrical modifications like optimizing duct geometry or adding artificial roughness. The use of artificial roughness on the underside of the absorber plate is an effective and economic way to improve the thermal performance of a solar air heater. Several experimental investigations, involving different types of roughness elements, have been carried out to improve the heat transfer from the absorber plate to air flowing in solar air heaters. In this paper the CFD analysis on heat transfer and friction in rectangular ducts roughened with broken ‘S’ shaped ribs has been presented. The relative gap width (g/e) is 1.0 and relative gap position(d/W) varied from 0.30 to 0.60 and other parameter are constant. The effects of relative gap position (d/W) on Nusselt number, friction factor and thermo-hydraulic performance parameter have been discussed and results compared with smooth duct under similar conditions. It is found that the maximum heat transfer and friction characteristic at a relative gap position of 0.50.

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