CONVECTIVE HEAT TRANSFER IN LOUVERED SOLAR COLLECTORS
Abstract
A family of air-heating solar collectors having a louvered absorber-convector has been analyzed experimentally and theoretically for normal ranges of design and operating conditions. The first theoretical model is based on an algebraic formulation of the conversion equations. It accounts for conduction, convection, and thermal and solar band radiation exchange. The second theoretical model is a differential formulation and numerical solution of the two-dimensional conservation equations. The analysis includes variable properties, buoyancy, and radiative transfer between surfaces. The multiply-connected computational region lies between the lower cover plate and the backplate and contains the absorber, which is made of overlapping, opaque louvers. The experimental and differential models are used to determine the convective heat transfer coefficient along the louver surfaces. The thermal efficiency of the louvered collector is determined from the experimental results and from the algebraic model. Parametric studies are performed to determine the effects that collector and louver geometry and several operating parameters have on the louver Nusselt number and the collector thermal efficiency. The local Nusselt number along the louver is shown to be proportional to the inlet temperature. The collector tilt is shown to have little influence on the Nusselt number; however, the buoyancy forces do cause greater mass flow rate between the louvers near the entrance than between louvers near the exit. Increasing the overlap length did not appreciably increase the heat transfer but it did improve the uniformity of the flow distribution through the vent regions between louvers. Finally, the collector design containing ten 12 cm louvers per meter of collector length will retain the high convective heat transfer rate inherent in the louver design. For this design, the thermal efficiency of the louvered solar collector was found to be at least 20% greater than that of a comparable flat-plate collector because of the improved heat transfer in the louvered design.
Degree
Ph.D.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.