SOLAR HEATING OF A FLUID THROUGH A SEMI-TRANSPARENT PLATE - THEORY AND EXPERIMENT

A theoretical and experimental study of solar radiation passing through a thin semi-transparent slab to heat a fluid is presented. The system of differential equations describing the temperature of the slab and the fluid as a function of time is derived and solved; the theoretical curves generated by the solution for the fluid temperature are compared with experimental readings obtained using water as the fluid and acrylic plastic (methylmethacrylate) as the semi-transparent material. The theoretical solution assumes that the solid absorbs radiation according to Beer's law and that the fluid completely absorbs the transmitted radiation. The transient theoretical fluid temperature curves for heating oil through plastic and through an opaque (copper) plate are compared; a general criterion for steady-state has been derived, showing that, for the same parameters of solar intensity, convection coefficients, ambient temperature and container dimensions, the fluid temperatures attained by using semi-transparent materials are considerably higher than those obtained with opaque plates. © 1969.