NUMERICAL ANALYSIS OF ASEPTIC PROCESSING OF A NON-NEWTONIAN LIQUID FOOD IN A TUBULAR HEAT EXCHANGER

The aseptic processing of a non-Newtonian fluid in a tubular heat exchanger with no holding section was simulated numerically. Two tube diameters (1·270 × 10^-2 m and 1·905 × 10^-2 m), two process temperatures (410 K and 422 K) and three flow rates (1·0, 1·5 and 2·0L/min) were included in the analysis. A model liquid food with temperature dependent and shear thinning viscosity was used. For each case, the length of heating section needed to provide a required lethality (F₀) of approximately 6·0 min on the center line for low-acid foods was calculated. The lethalities for Clostridium botulinum and other microorganisms of interest were calculated using the modified General Method. Increasing the temperature from 410 K to 422 K decreased the required length of the heating section by about 20 to 30% for the same average velocity. Thiaminc retention was also calculated for each case and was found to be higher for a smaller diameter tube and lower temperature. The liquid traveling near the wall was predicted to be highly overprocessed and retained less than 10% thiamine