Behavior of the effective heat transfer coefficient and global thermal resistance in freezing of fruit juice model solutions in cylindrical packages

Abstract

In this study the effect of packing on freezing time, effective heat transfer coefficient and global thermal resistance were evaluated during the freezing of fruit juice model solution in an air blast freezer. Two configurations were arranged with 40 buckets and 15 kg of solution in each, totaling 600 kg. Thermocouples were installed to monitor the temperature profiles within the solution and at the packaging and cooling air surface. The temperature data were used to calculate the effective heat transfer coefficients and the resistances throughout the freezing process. The use of metal buckets represented reductions of up to 19.60% in the freezing times. Also, the temperature curve plateau, characterizing solidification (phase change period), was reduced. The main result of this paper was the possibility of calculating the effective heat transfer coefficients and global thermal resistances during the complete process of freezing. These properties assumed different values, not having a constant distribution throughout the freezing process.