HEAT TRANSFER TO CANNED PARTICULATES IN HIGH‐VISCOSITY NEWTONIAN FLUIDS DURING AGITATION PROCESSING

Heat transfer to canned particulate‐laden Newtonian high‐viscous fluids (Nylon particles suspended in aqueous glycerin solution [40, 60, 80, 90 and 100%, v/v] and motor oil [85W140]) during end‐over‐end rotation was studied in a pilot‐scale, full water‐immersion single‐cage rotary retort. Computations of conventional fluid‐to‐particle heat transfer coefficient ( h fp ) and overall heat transfer coefficient ( U ) were successful with multiple particles for an entire range of viscosity, but the predicted particle lethality was underestimated. With a single particle in the can, h fp and U calculations were successful only for low‐viscosity fluids (40 and 60% glycerin solutions), but again resulted in underestimation of particle lethality. Apparent heat transfer coefficients ( h ap ) between retort and particle surface and apparent overall heat transfer coefficient ( U a ) were also evaluated, and this methodology worked well for all cases. Further, the particle lethality predicted using h ap better matched the measured values. With a single particle in the can, the associated h ap was significantly ( P <  0.05) influenced by rotation speed, retort temperature, liquid viscosity, particle material and can size. U a was significantly ( P <  0.05) influenced by rotation speed and liquid viscosity. The effects of headspace, radius of rotation and particle size were not significant ( P >  0.05) on h ap and U a values.