Thermal design of uniformly heated inclined channels in natural convectionwith and without radiative effects

Dimensional charts for the design of inclined single channels in air natura l convection with symmetrical and asymmetrical uniform wall heat flux are p roposed on the basis of correlations between the significant dimensionless process parameters derived from previous articles. The radiative contributi on to heat transfer is taken into account. The design charts are obtained f or two values of surface emissivity, 0.05 and 0.8, and the thermophysical p roperties 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 Nusse lt and Rayleigh numbers cis functions of the angle. The estimated values of optimal spacing for vertical single channels correspond well with the resu lts obtained by Bar-Cohen and Rohsenow [14]. A simple estimation procedure is proposed to evaluate the error in the rele vant geometric and thermal parameters due to a different value of the refer ence temperature. The estimated error, however, is less than the uncertaint y of the experimental data employed. Worked examples are carried nut in order to show how simple and quick it is to use the proposed graphical procedure.