The estimation of convective heat transfer coefficients between a spherical particle and fluid at lower Reynolds number

Convective heat transfer coefficients between a spherical particle and fluid for two flow systems (solid-liquid, -gas) were measured and were calculated with computer simulation at relatively low Reynolds numbers, and the applicabilities of empirical equation, for example, Rant & Marshall's equation, to the estimations of convective heat transfer coefficients of these systems were investigated. An aluminum sphere, 32 mm in diameter, which was kept at about 60 degrees C initially for solid-water system and at 30 degrees C for solid-air system, was dipped into each fluid flow and the relationships between the Nusselt number, Nu, and the Reynolds number, Re-p, were obtained. Convective heat transfer coefficients were calculated with computer simulation and were compared with experimental results. For solid-water systems, convective heat transfer coefficient was as large as the value estimated by Rant & Marshall's equation for the range 300 < Re-p, but for lower Reynolds number region, heat transfer coefficients were slightly larger than the value calculated by Rant & Marshall's equation. Although Reynolds number measured in solid-air system was small, heat transfer coefficient was as large as ones calculated with following empirical equation. Nu = 2.0 + 0.6 (PrRep1/2)-Re-1/3 + 0.43(PrGr)(1/4)