An Improved Method to Estimate Temperatures and Lethality During the Cooling Stage of Sterilized Cylindrical Cans

The apparent position numerical solution (APNS) method, which is based on the solution of the heat transfer equation for a spherical geometry, is commonly used in thermal treatment calculations to accurately predict the temperature history of products in containers of arbitrary shapes. This is accomplished by finding the 'apparent position' within a sphere that represents the actual temperature profile at the slowest heating and cooling points of a canned food container of arbitrary geometry. The APNS method provides a good temperature prediction during the late heating sterilization stage of processes that have approximately constant heating temperatures or those that have heating temperatures experiencing small deviations. However, the agreement between the temperature predicted by the APNS method and the actual temperature of the product at a given location is not good in the initial stage of the process cooling phase. An equation able to calculate differences between the temperature at any location of a cylindrical container and that predicted by the APNS method was derived from the heat transfer equations governing the thermal process. By incorporating the calculated temperature differences into the APNS method, during the cooling phase, a better agreement between the actual and predicted temperatures was obtained for several process conditions.