Numerical analysis of the lethality and processing uniformity in a double-pipe helical heat exchanger

A numerical study of a double-pipe helical heat exchanger was performed to ascertain the residence time, temperature, and processing uniformity for food processing applications. A range of laminar flow rates were used, with both parallel flow and counterflow configurations. Both heating and cooling in the inner tube were studied. Heating/cooling uniformity was estimated by using a first-order kinetics model for sterilization. Process uniformity is important in the quest for high quality product and this report is a first study for the uniformity in double-pipe helical heat exchangers. Residence time distributions became more uniform with increased flow rates in both the inner tube and in the annulus. Temperature uniformity in the inner tube increased with increasing flow rate. However, it was shown that changing the flow rate in the annulus, for a constant flow rate in the inner tube, affected the uniformity. Similar results were found for the annulus. Heating uniformity in the inner tube tended to increase with increased flow rates. It was also shown that the cooling process was more uniform than the heating process. The findings in this study are important to the design of helical heat exchangers for the processing of liquid foods. (C) 2010 Elsevier B.V. All rights reserved.