Radiative and convective heat exchange inside a test box with solar gain

Abstract

Measurements on a laboratory model permit the verification of the heat flow balance on the internal wall of a cubic test box. The extensive measurement evaluation and complex data analysis are carried out with a microcomputer. As a result of the analysis, the parameters are set for a mathematical model which excellently reflects the measurement results. The net heat flow of an internal wall surface can now be defined in terms of the proportion of solar, infrared and convective components under known boundary conditions. In general, the amount of convective flow is smaller than that of the IR or solar flow. Multiple IR reflections must be accounted for. The customary linearized models used in building physics for external wall surfaces will have to be modified for internal walls accordingly. Convection can be described by means of the Nu(Ra) relation usually used for turbulence, and the influence of the temperature field on the flow pattern, is recorded by means of two different-sized parameters Nu/(Ra 1 3 ) . From dimensional analysis, scaling rules are worked out in order to interpret data obtained from experiments on laboratory models for full-sized conditions in nature and vice versa.