STUDY OF SYSTEM AND WORKING PARAMETER FOR PERFORMANCE ENHANCEMENT OF ARTIFICIALLY ROUGHENED SOLAR AIR HEATER

Abstract

Solar air heaters being among the cheapest and most widely used collection devices have found applications in heating of building and crop drying and many other low temperature applications. Solar air heaters generally have poor thermal efficiency because of their inherently low heat transfer rates from the absorber plates to-the air in the ducts. Due to the low heat transfer rate the losses from the absorber plate increases. In order to increase the applicability of the solar air heater ,heat transfer coefficient between absorber plates and air required to be increased. There are several methods to increase the thermal efficiency of a solar air heater. Providing artificial roughness at under side of the absorbing plate is one of the most effective method to improve the thermal performance of solar air heaters. Artificial roughness can be produced in many forms, such as sand grain roughness, rib roughness wire roughness etc. Providing dimples on the absorbing plate as artificial roughness could be an attractive heat transfer augmentation process because it generally require uncomplicated manufacturing procedures, particularly if the dimple shape is a spherical indentation. Because of this characteristic, dimples do not add extra weight 'onto a component; especially if surface material is removed to form the dimples. On thinner materials, an indentation-producing device can be used to form the dimples, which then gives protrusions on the opposite side. This then leads to another advantage because substantial heat transfer augmentations are also provided by the array of protrusions. It has been planned to investigate the heat transfer and fluid flow characteristics of solar air heater ducts having dimple shape geometry on the underside of absorber plate.