Calculation of food freezing times and heat transfer coefficients

The freezing of food is one of the most significant applications of refrigeration. In order for freezing operations to be cost-effective, it is necessary to optimally design the refrigeration equipment. This requires estimation of the freezing times of foods and the corresponding refrigeration loads. These estimates, in turn, depend upon the surface heat transfer coefficient for the freezing operation. Therefore, ASHRAE research project 1123-RP was initiated to determine surface heat transfer coefficients for a wide variety of food items. This paper describes the procedures used in ASHRAE research project 1123-RP to resolve deficiencies in heat transfer coefficient data for food freezing processes. Members of the food refrigeration industry were contacted to collect cooling curves and surface heat transfer data. A unique iterative algorithm was developed to estimate the surface heat transfer coefficients of foods based upon their cooling curves. Making use of this algorithm, heat transfer coefficients for various food items were calculated from the cooling curves collected during the industrial survey. The accuracy of the calculated heat transfer coefficients was found to be within ±30%. These heat transfer coefficients will be tabulated in the ASHRAE Hand-book - Refrigeration.