Modelling Heat Transfer in Steam/Air Processing of Thin Profile Packages

Abstract

Heat transfer studies were carried out in two pilot scale batch- type steam/air retorts to evaluate the heating rate indices (f) and lag factors (j) for thin profile test bricks of silicone rubber and nylon. Using measured surface heat transfer coefficients for the steam/air mixtures along with thermal properties and dimensions of these test bricks, corresponding f and j values were predicted by theoretical calculations. The predicted f values were within ± 6% of experimental values; however, predicted lag factors were considerably higher than experimental values when evaluated at the commonly used come-up time effectiveness factor of 42%. A relationship was established for predicting the come-up period effectiveness which showed that, during steam/air processing of thin profile packages, the effectiveness value could be over 80%. A concept identifying a “limiting surface or overall heat transfer coefficient” below which heat transfer rates could be potentially retarded was detailed.