PARTICLE HEAT-TRANSFER COEFFICIENTS UNDER VARIOUS RETORT OPERATING-CONDITIONS WITH END-OVER-END ROTATION

Forced convection heat transfer in cans was studied experimentally dur ing end-over-end sterilization in a full-immersion, hot-water rotary s terilizer. A polypropylene spherical particle (diameter = 19 mm) was s uspended in a high temperature bath oil (Newtonian liquid) using a fle xible fine-wire thermocouple attached to the can wall providing uninhi bited heat transfer conditions. The overall heat transfer coefficient, U, was determined using a lumped capacity heat balance approach and t he fluid-to-particle heat transfer coefficient, h(fp), was determined from transient temperature data at the center of the particle using a finite difference computer simulation. The effects of retort temperatu re (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 ass ociated heat transfer coefficients. Higher heat transfer coefficients were obtained with increasing values of all four variables, and the ef fects of rotational speed and headspace were more significant than tho se of retort temperature and radius of rotation. U values ranged from 120 to 187 W/m(2).K and h(fp) values ranged from 23 to 145 W/m(2).K de pending on the operating conditions.