Effects of particle radius, fluid viscosity and relative velocity on the surface heat transfer coefficient of spherical particles at low Reynolds numbers

The temperature profile in spherical alginate particles during heating in fluids was monitored. The surface heat transfer coefficient (h(fp)) at the interface between fluid and particles was then evaluated analytically. The results show that h(fp)s in this system range from 165 W m(-3) degrees C-1 to 2376 W m(-2) degrees C-1 when the radius of particles is between 0.0025 m and 0.0088 m, the viscosity of the fluid is between 0.00033 poise and 0.038 poise, and the relative velocity is set below 0.0025 m s(-1). These results correspond to Nusselt numbers (Nu) in the range between 2.01 and 55.10, particle Reynolds numbers (Re) smaller than 106.1, Prandtl numbers (Pr) in the range between 2.27 and 260.7, and Grashof numbers (Gr) in the range between 1.54 x 10(3) and 1.82 x 10(8). Data analysis shows that the relations between dimensionless parameters follow the linear regression equation: In(Nu Re-2) = 2.1396 ln(Re(-1)Pr(0.55)Gr(0.45)) -11.4282. The results also reveal the importance of free convection in liquid/solid hear transfer at low Re. (C) 1997 Elsevier Science Limited.