Particle heat transfer coefficients under various retort operating conditions with end-over-end rotation

Abstract

Forced convection heat transfer in cans was studied experimentally during end-over-end sterilization in a full-immersion, hot-water rotary sterilizer. A polypropylene spherical particle (diameter = 19 mm) was suspended in a high temperature bath oil (Newtonian liquid) using a flexible fine-wire thermocouple attached to the can wall providing uninhibited heat transfer conditions. The overall heat transfer coefficient, U, was determined using a lumped capacity heat balance approach and the fluid-to-particle heat transfer coefficient, h was determined from transient temperature data at the center of the particle using a finite difference computer simulation. The effects of retort temperature (110 to 130C), rotational speed (0 to 20 rpm), radius of rotation (0 to 27 cm) and can headspace (6.4 and 10 mm) were examined on the associated heat transfer coefficients. Higher heat transfer coefficients were obtained with increasing values of all four variables, and the effects of rotational speed and headspace were more significant than those of retort temperature and radius of rotation. U values ranged from 120 to 187 W/m2.K and h values ranged from 23 to 145 W/m2.K depending on the operating conditions.