Three-dimensional study of combined conduction, radiation, and natural convection from discrete heat sources in a horizontal narrow-aspect-ratio enclosure

Three-dimensional natural convention flow and heat transfer were numericall y studied for a three-by-three array of discrete protruding heat sources on a horizontal substrate in an air-filled, rectangular, narrow-aspect-ratio enclosure with length, width, and height ratio of 6:6:1. The governing equa tions for natural convection in air, coupled with conjugate conduction and radiation within the enclosure were solved using a finite volume method. Th e study examines the complex thermal interactions between the heat sources, substrate, and enclosure walls as affected by the thermal conductance of t he walls and substrate with the intent of determining which physical effect s and level of detail are necessary to accurately predict thermal behavior of discretely heated enclosures. The influence of radiation on the overall heat transfer is given particular attention. The three dimensionality of th e problem was evident in the overall flow characteristics and in the convec tive heat transfer edge effects on the heat source surfaces. Excellent agre ement between temperature predictions on the hear sources and substrate and experimental measurements was obtained for modified Rayleigh numbers in th e range of 9.7 X 10(5) to 1.6 x 10(7).