ENHANCEMENT OF RATE OF HEAT TRANSFER USING VORTEX GENERATORS IN AIR HEATER

Abstract

There are many applications in engineering industry that require heat addition or removal and a wide variety of heat exchange devices are used for different applications. Performance of improving coefficient of heat trsnsfer and pressure drop reducing becomes essential in all applications. Most of thermal devices like high temperature gas turbines , heat exchangers, electronic equipment, convective heat transfer plays an major role in most of the engineering applications. There are many methods to enhance rate of heat transfer. Delta wing vortex generators or promoters of turbulence are often used to calculate the flow field and they can give a worth full effect on the performance of thermal device. Many researchers have been studied extensively the applications of heat transfer which involves internal flow and mixed convection in ducts and non-circular ducts such as, rectangular, square, triangular. To attain higher coefficient of heat transfer, it is necessary that the surface of heat transfer flow is to be made turbulent. However, energy for producing such turbulence has to come from the blower or fan and the maximum turbulence leads to excessive power requirement to make the air flow through the duct. Therefore maximum turbulence must be produced in the region which is very near to surface of heat transfer i.e. in the laminar sub-layer only Excessive friction losses can be avoided by making flow should be not unduly disturbed and it is done by making the height of the roughness element to be small as compared with the dimensions of duct. The roughness element height (e) and pitch (P) are the most important parameters to characterize the roughness shape and arrangement. All these parameters namely , angle of attack (β), relative roughness pitch (P/e), relative roughness height (e/D) are usually specified as dimensionless parameters.