Ph.D Research Topic and Brief

PhD Research Topic and Brief

“Optimal Thermohydraulic Performance In Three Sides Artificially Roughened Solar Air Heater”

Flat plate solar air heaters are usually applied in space heating and drying processes of agricultural products, herbal medicines, clothing etc. This system occupies an important place among solar thermal systems because of minimal use of materials. A solar air heater has low heat transfer coefficient between absorber plate and the flowing air that results in higher heat losses to the environment which ultimately leads to low thermal efficiency of such thermal systems. In order to improve the heat transfer rate several methods for enhancement of thermal performance have been proposed and investigated by researchers. Provision of small diameter wires of varying diameter on the underside of the absorber plate of a solar air heater at varying pitch induces turbulences thereby resulting in enhanced value of heat transfer resulting in enhanced heat transfer coefficient between flowing air and absorber plate. However, there is also an increase of friction factor leading to higher pumping power. The roughness and flow parameters together play an important role for the thermo hydraulic performance of the artificially roughened solar air heaters. Analysis (Prasad and Saini, 1991), shows that an optimization parameter known to be the roughness Reynolds number and written as , which gives the combined effect of roughness and flow parameters, could always attain the optimal thermo hydraulic performance at a given value. The value of this optimization parameter for the optimal thermo hydraulic performance of only top side roughened and glass covered solar air heater was found to be .

The present work is aimed towards the analysis of optimal thermo hydraulic performance of three sides roughened and glass covered solar air heater duct with large aspect ratio and its experimental verification. The present analysis deals with optimization of thermo hydraulic performance in three sides artificially roughened and glass covered solar air heaters, and arrives at the conclusion that the equation given by , always corresponds to the optimal thermo hydraulic performance, when every set of the values of the roughness and flow parameters p/e, e/D and Re, separately or combined, results in the optimal thermo hydraulic performance, which needed to be experimentally verified. As such, experiment has been conducted on such solar air heater and the present work further deals with the experimental results obtained with respect to heat transfer, Stanton number, friction factor, thermal performance and finally thermo hydraulic performance to validate that, , corresponds to the optimal thermo hydraulic performance condition in three sides roughened and glass covered solar air heaters. On the basis of experimental study, correlations of heat transfer, friction factor and thermo hydraulic efficiency for three sides artificially roughened (rectangular with three sides wire) and glass covered has been developed.