PARTICLE MOTION AND HEAT TRANSFER IN CANS DURING END-OVER-END ROTATION: INFLUENCE OF PHYSICAL PROPERTIES AND ROTATIONAL SPEED

Abstract

The effect of particle density and fluid viscosity on particle motion and fluid-to-particle heat transfer coefficient, hfp, was investigated experimentally, at different rotational speeds (0 to 20 rpm) during end-over-end rotation of cans. Cans filled with water or oil, and fitted with a spherical particle (diameter = 19 mm) suspended using a flexible fine-wire thermocouple were processed in a water immersion rotary retort (Stock PR-900) at 120C. Temperatures at the center of the particle and the surrounding fluid were measured during end-over-end rotation. The hfp was evaluated by matching the accumulated lethalities computed from experimental time-temperature data with those obtained by solving the governing partial differential equations of conduction heat transfer in spherical geometry with appropriate initial and boundary conditions, using a finite difference computer program. Overall heat transfer coefficient, U, was calculated from thermal energy balance. U values varied from 118 to 800 W/m2. K and hfp values varied from 34 to 825 W/m2. K depending on the operating conditions. U values increased with decreasing fluid viscosity and increasing rotational speed and the results were comparable to those reported in the literature. The hfp values were also affected in a similar fashion increasing with rotational speed and particle density and decreasing with fluid viscosity. The effect of particle density on hfp was more significant than those of fluid viscosity and rotational speed. The particle motion video taped under simulated end-over-end rotation was used to explain the variations in heat transfer between the different runs.