Heat transfer coefficients during thermal processing of model particulate mixtures in non-Newtonian fluids undergoing reciprocation agitation as affected by process variables

Abstract

Overall (U) and fluid-to-particle heat-transfer coefficients (hfp) in canned particulates (Nylon spheres) suspended in non-Newtonian fluid (CMC dispersions) undergoing reciprocation agitation thermal processing was evaluated in a pilot-scale reciprocating retort. Five influencing process variables affecting U and hfp were selected. A CCRD and a 3 × 3 × 2 full-factorial design of experiments were used to relate the coefficients U and hfp to the various process variables viz. reciprocation frequency; reciprocation amplitude; temperature; liquid viscosity and headspace.U and hfp varied in the range 524–1124 W/m2oC and 549–1610 W/m2oC respectively. Analysis of variance showed frequency, amplitude, liquid viscosity, headspace and temperature to be significant factors for hfp, and frequency, amplitude and liquid viscosity for U (p < 0.001). Increasing the reciprocation frequency from 1 to 4 Hz almost doubled the value of both the heat transfer coefficients. Similarly increasing the reciprocation amplitude from 5 to 25 cm, resulted in 30–35% increase in the values of heat transfer coefficients. Overall with increase in temperature, frequency, amplitude, and headspace, associated hfp and U values also increased, but with increasing liquid viscosity, both hfp and U showed a decrease. Finally, optimization of processing conditions was carried out to minimize quality losses due to particle motion (agitation intensity) and thermal damage (severity of thermal processing).