Effects of Axial Conduction and Internal Radiation on Thermodynamic Optimization of a Tubular Space Radiator

Traditionally, the analysis of space radiators is loaded towards mass optimization. However, space radiators ought to be thermodynamically optimized for usage on extra-terrestrial bases, where energy resources are at a premium. Hence, a tubular space radiator is presently considered for thermodynamic optimization. The mathematical model of tubular space radiator, accounting for the axial conduction and internal radiation inside the tube, using radiosity-irradiation method has been developed. Using a finite difference scheme and Gauss-Seidel method, the temperature profiles of tube and working fluid, and the rate of entropy generation due to heat transfer as well as fluid flow are calculated. The effects of thermal conductivity of tube, internal surface emissivity and thickness of tube on total entropy generation are investigated through a parametric study. It is found that, when the outside surface emissivity is low, the total entropy generation increases by 19.6 % with variation of inside surface emissivity. The total entropy generation changes, as high as 80 %, with the variation of thermal conductivity of tube. It is also found that there exists an optimum diameter of radiator tube for which the entropy generation is a minimum, and a correlation is developed for the same. Owing to internal radiation and axial conduction in the tube, the optimum nondimensional diameter would change as high as 27 %, when compared to a case where both effects are absent. Hence, the effects of internal radiation and axial conduction in the tube cannot be ignored for a tubular space radiator.