Surface Heat Transfer Distribution in a Weir Type Pressurized Water Retort for Processing Foods in Flexible Retort Pouches

Abstract

A method for measuring water surface (film) heat transfer coefficients in a retort for processing foods in flexible retort pouches was developed. The retort which was studied employs horizontally flowing water between stacked trays which contain the food pouches during the thermal sterilization cycle. The method was used to measure the distribution of the surface heat transfer coefficients throughout the retort during the heating and cooling cycles. Film coefficient values obtained at various temperatures were found to vary considerably according to test location, and processing phase (whether heating or cooling). The average values observed at 120°C varied between 1100 and 2400 W/(m2· °C) for heating and between 1800 and 4100 W/(m2·C°) for cooling. These values were found to be much smaller than film coefficient values for steam-air mixtures obtained by others under laboratory test conditions. The measured surface coefficient values were used in a computer simulation to determine the transient heat transfer response of beef and potato in pouches subjected to thermal processes of various process times. This study revealed that the observed variation in the film coefficient produces large relative variations in total integrated centre point lethality.