Composite correlations for air natural convection in tilted channels

Design and thermal control of tilted channels in air natural convection req uires knowledge of relations between process parameters. Composite correlat ions of average Nusselt number in terms of channel Rayleigh number (10 less than or equal to Ra less than or equal to 9.0 x 10(4)) are proposed for in clined channels,vith uniform symmetric or asymmetric heat flux. The thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers. The surface emissivities considered are 0.05 and 0.8. Experimental data employed to obtain the proposed correlations are in good agreement wi th the correlations for a vertical channel from published literature. Compo site correlations between Nu and Ra cos theta valid in the whole range 0-85 degrees of the inclination angle are given. Moreover; a general composite correlation is proposed for all heating modes, in which the inclination ang le is in the range 0-85 degrees and for surface emissivity nor greater than 0.8. Recommendations for the thermal design of single or multiple channels are given.