Aseptic processing of particulate foods: Computational models and experimental studies

The overall goal of this research is to achieve enhanced and more uniform heat transfer in aseptic processing of particulate foods using a helically coiled tube instead of a conventional straight hold tube assembly. Rheological properties of suspensions (0–30% v/v green peas in 1.5% CMC solution) in aseptic processing temperature range (85°C–135°C) were determined using tube viscometry. The rheological behavior was represented by a power law model. The consistency coefficient increased with particle concentration and decreased with temperature whereas opposite trends were found for the flow behavior index. Exponential equations described well the effects of temperature on the power law parameters of carrier fluid. The information on the rheological properties of the carrier fluid and the suspensions was used for analyses of particle residence time distribution and fluid-to-particle heat transfer coefficient (hfp) in tube flow. The particle residence time distributions in coiled and straight hold tubes were investigated. Significantly smaller mean normalized residence times in coiled tube, compared to those in straight tube, indicated smaller time lags between particles and the average product when a coiled tube was used. The fluid temperature and the interaction between hold tube geometry and particle concentration significantly influenced the minimum normalized residence time (MNNRT). In the coiled tube, the MNNRT increased with particle concentration whereas the standard deviation of normalized residence time decreased as particle concentration increased. The hfp values for spherical particles in continuously flowing food suspensions (0–30% v/v green peas in 1.5% CMC solution) in the coiled hold tube and straight hold tube assembly was determined. Using coiled tube instead of straight tube significantly increased the hfp. At 96°C, the hfp value increased 102% to 229%. At higher temperatures (110°C and 124°C), the increase in the hfp was within 45% and in most cases; it was between 10% and 25%. The hfp value significantly increased with temperature, flow rate, and particle concentration. The estimation of the hfp values using RTD data and empirical correlations relating the hfp to dimensionless parameters indicated a more uniform fluid-to-particle heat transfer when coiled hold tube was used instead of straight hold tube