A Simplified Model for Freezing Time Calculations in Foods

A model is proposed for freezing time calculations which combines Plank's equation with the unsteady heat transfer solutions for the cooling of a slab of constant properties through the addition of pre-cooling, change of phase and tempering periods. The change of thermal properties with the ice content is taken into account by proposing average values for the different periods. No adjustable parameters are used in developing the model. Results are compared for the case of beef freezing with those obtained numerically by using a heat transfer model with simultaneous change of phase and with experimental measurements showing good agreement.     

Determination of Heat Transfer Coefficients for Continuous Belt Freezers

Air-product heat-transfer coefficients for belt freezers were determined experimentally. Measurements were performed for foods (beef hamburgers) and a model substance (copper disk) using a prototype tunnel. Air flow parallel, as well as perpendicular, to the belt, was employed; in the latter case moving upwards or downwards through the belt. From the measured temperatures, heat-transfer coefficients were calculated using appropriate mathematical methods. Values obtained for both types of materials were compared, and the usefulness of the test substance was discussed. From these data, simple and precise regressions were obtained, useful to predict the coefficient for the above mentioned types of air flow and valid over a wide range of operating conditions in belt freezers.