DIMENSIONLESS ANALYSIS OF FLUID-TO-PARTICLE HEAT-TRANSFER COEFFICIENTS

Average fluid-to-particle heat transfer coefficients were experimental ly determined for spherical aluminium particles heated in carboxymethy lcellulose solutions. Two situations were considered: a still particle immersed in a moving fluid, and a particle rotating in an otherwise s tagnant fluid. Fluid flow rate, rotating particle velocity, particle d iameter and fluid rheological properties were varied, covering a large range of the generalized Reynolds (0 to 801) and Prandtl (69 to 5358) numbers. Average heat transfer coefficients ranged between 56 and 261 2 W/m(2)K. The results were compared with values predicted by publishe d dimensionless correlations, showing that correlations based on a Fro szling-type equation were more adequate. It was found that the contrib ution due to natural convection should be considered for proper correl ation of the results at low Reynolds numbers. The results also show th e importance of the fluid velocity profile. (C) 1997 Elsevier Science Limited.