Back absorbing parallel plate polymer absorbers in solar collector design

Abstract

Serious efforts are currently devoted towards making solar water heating technology economically competitive. Among them, the development of large, all plastic, innovative design, low cost collector modules suitable for mass production is one of the most promising, which will eventually lead to a drastic reduction of the solar collector subsystem cost. Although appreciable development work was earlier devoted towards production of all plastic solar collectors, the polymer absorber still remains the most crucial part of the polymer collector design, since severe limitations are imposed by the low thermal conductivity of polymers. To overcome these restrictions, a suitable design should be implemented, allowing extended wetted surfaces of the absorbers, something which leads to the familiar extruded parallel polymer plate absorber design. Recent investigations have been directed toward definition of the limitations and development of design criteria for the top absorbing parallel polymer plate absorber. In the present work, a subsequent analysis is developed for evaluation of the back absorbing polymer plate design, which allows the absorption of radiation at the water stream and the back plate. The results of the current analysis, which are presented comparatively to those obtained for the top absorbing plate design, show a remarkable improvement of the collector efficiency factor and a corresponding reduction of the collector loss coefficient, something which leads to a significant improvement of the instantaneous heat collection efficiency of collectors using a back absorbing plate absorber design.