Thermal Design of Uniformly Heated Inclined Channels in Natural Convection with and without Radiative Effects

Abstract

Dimensional charts for the design of inclined single channels in air natural convection with symmetrical and asymmetrical uniform wall heat flux are proposed on the basis of correlations between the significant dimensionless process parameters derived from previous articles. The radiative contribution to heat transfer is taken into account. The design charts are obtained for two values of surface emissivity, 0.05 and 0.8, and the thermophysical properties are evaluated at the reference temperature equal to 40 ° C. The optimal spacing value for inclined single channels, in terms of thermal performance, is obtained from composite correlations between average Nusselt and Rayleigh numbers as functions of the angle. The estimated values of optimal spacing for vertical single channels correspond well with the results obtained by Bar-Cohen and Rohsenow [14]. A simple estimation procedure is proposed to evaluate the error in the relevant geometric and thermal parameters due to a different value of the reference temperature. The estimated error, however, is less than the uncertainty of the experimental data employed. Worked examples are carried out in order to show how simple and quick it is to use the proposed graphical procedure.