The Estimation of Convective Heat Transfer Coefficients between a Spherical Particle and Fluid at Lower Reynolds Number

Abstract

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, Ranz & 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°C initially for solid-water system and at 30°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 Ranz & 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 Ranz & Marshall's equation. Although Reynolds number measured in solid-air system was small, heat transfer coefficient was as large large as ones calculated with following empirical equation.
Nu=2.0+0.6Pr^1/3Re_p^1/2+0.43(PrGr)^1/4