Fluid-to-particle Heat Transfer Coefficients for Continuous Flow of Suspensions in Coiled Tube and Straight Tube with Bends

Abstract

Fluid-to-particle heat transfer coefficient (h fp ) for spherical particles in continuously flowing food suspensions (0–30% v/v green peas in 1.5% sodium carboxymethylcellulose solution) in the holding section of an aseptic processing system was determined. The effects of hold tube geometry, temperature, flow rate, and particle concentration were investigated. The h fp values ranged from 538 to 1450 W/m 2·°C in the coiled tube and from 204 to 1220 W/m 2·°C in the straight tube. Significantly, higher h fp value was observed for particles in the coiled tube as compared to that in the straight tube. The h fp value increased with temperature, flow rate, and particle concentration. Dimensionless correlations relating the Nusselt number to Reynolds and Prandtl numbers were developed. Estimation of h fp values based on the particle resistance temperature device (RTD) data and dimensionless correlations indicated a reduction in the degree of overprocessing of average particles when a coiled tube was used instead of a straight tube for the holding section.