EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER CHARACTERISTICS OF RECTANGULAR AIR DUCT HEATED FROM BOTTOM SURFACE

Abstract

Experimental investigation of solar air heaters has been, in forefront of heat transfer analysis in last few decades. Renewed interest in the field of renewable energy in view of depleting and limited fossil fuel reserves has been the guiding force behind study of solar air heaters. These solar air heaters can be simulated with that of an air flowing in rectangular duct whose three sides are insulated and one side top/bottom is heated at a constant heat flux. The heat transfer coefficient is generally poor for smooth heated flat plate and hence enhancement of heat transfer coefficient between the plate and the air is of paramount importance. An experimental set up has been fabricated to investigate heat transfer characteristics of a rectangular air duct. The three sides of this rectangular duct are smooth and well insulated to have a resemblance with that of solar air -heater. The top surface of this rectangular duct is made up of a glass plate. The heat is supplied through the bottom surface which is a sheet of stainless steel (SS-304) of 0.1 mm thickness. Two cases have been investigated in the present work. In first case, the bottom surface of the rectangular duct is in the form of plain sheet. In the second case it was replaced with a corrugated sheet of V shaped corrugation and made up of 0.1 mm thick stainless steel (SS-304). The effect of different parameters such as heat flux, air mass flux, gap between heated plate and glass cover on heat transfer coefficient has been studied. It is found that the heat transfer coefficient of bottom surface increases with an increase of mass flux and also with an increase of heat flux. Heat transfer coefficient in case of corrugated plate has been found to be higher as compared with the flat plate.