DIMENSIONLESS CORRELATIONS FOR MIXED AND FORCED CONVECTION HEAT TRANSFER TO SPHERICAL AND FINITE CYLINDRICAL PARTICLES IN AN ASEPTIC PROCESSING HOLDING TUBE SIMULATOR

摘要

Dimensionless correlations for estimating heat transfer coefficients for spherical and finite cylinders under mixed and forced convection heat transfer regimes were individually investigated using multiple regression of statistically significant dimensionless groups. Food and model particles were subjected to heat treatments in an aseptic processing holding tube simulator (carrier fluid: 0, 0.5, and 1.0%, carboxymethyl cellulose solutions, w/w basis; temperature: 90 to 110C; flow rate 1.0 to 1.9 X 10~4 m~3/s). The type of test material was found to have a significant effect on the Nusselt number, and hence developed correlations. Introducing a diffusivity ratio defined as the ratio of particle-to-fluid thermal diffusivities was found to consistently improve developed models. Excellent correlations (R~2 ≥ 0.97) were obtained between the Nusselt number and dimensionless groups for all models. Natural convection in heat transfer correlations in situations where forced convection is expected to be the dominant mechanism was accommodated.