Convective heat transfer in louvered solar collectors

A family of air-heating solar collectors having a louvered absorber-convector was 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.