Overall and Fluid-to-particle Heat Transfer Coefficients associated with Canned Particulate non-Newtonian Fluids during Free Bi-axial Rotary Thermal Processing

Heat transfer to canned particulates in non-Newtonian fluids (Nylon particles suspended in aqueous carboxymethyl cellulose - CMC - solution) during fixed and free bi-axial rotation was studied in a pilot-scale, full water-immersion single-cage rotary retort. A response surface methodology was used in order to study the effect of different process parameters, including rotational speed (7-23 rpm), CMC concentration (0.0-1.0%) and retort temperature (110-130C), at five levels of each, on overall heat transfer coefficient (U) and fluid to particle heat transfer coefficient (hfp) in both rotation modes. The analysis of variance showed that the rotational speed, CMC concentration and retort temperature were significant (p < 0.05) factors for hfp in the following order: rotation speed > CMC concentration > retort temperature; however, only rotational speed and CMC concentration were significant (p < 0.05) factors for U. With an increase in rotational speed and retort temperature, there was an increase in the associated U and hfp values; however, increasing the CMC concentration resulted in the opposite. Using the numerical optimization of the Design Expert software, optimum heat transfer was found at a rotational speed of 20 rpm, CMC concentration of 0.6% and retort temperature of 126C. T-test revealed that both U and hfp were significantly (p <0.05) higher in the free bi-axial mode as compared to the fixed axial mode of rotation.