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 x 10^-2m and 1.905 x 10~²m), 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 (/^) 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. Thiamine 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 nredicted to be hiehlv ovemrocessed and retained less than 10% thiamine.