TEACHING HEAT TRANSFER … 2

Radiation Problems. A great deal of lecture time in this subject must be devoted to radiation configuration factors. As the integral for these quantities is usually exceedingly complex, analogue apparatus for obtaining easy solutions is essential. Figure 9 indicates two areas dA1 and A2 and it can be shown that the projected area S divided by the base circle gives the geometric factor. Figure 10 shows a simple piece of apparatus made at this College for obtaining the geometric factor. When using it and evaluating results, students are forced to think of the equation and its interpretation. Certain rectangular shapes are checked against graphical presentations in textbooks and unusual cases can be dealt with. For instance, to find the geometric factor for a standing person may increase a student's awareness of the variety of uses that exist. Another possible experiment, drawn from the research literature, is the study of furnace geometric factors using light as a heat analogue. A skeleton framework is constructed to the dimensions of the furnace and the furnace is represented by a number of lights behind diffusing sheets of frosted glass. The experiment is carried out in a darkroom — absorbing walls are left free and partially absorbing walls can be simulated by various shades of grey paint. The light incident on a wall is measured by a calibrated photo‐electric cell. In the original paper, cosine law corrections were made to the results, but it has been stated that the results are better without such corrections, and this means that a simpler and more effective demonstration can be made.