The thermal conductivity of fresh lamb meat, offals and fat was measured over the temperature range -40°C to + 30°C using a guarded hot plate apparatus. Simple empirical equations wcrc prcscntcd for the conductivity of high-moisture (65 to 80%) meat and offals. With indepcndcntly obtained values of physical parameters, scvcral thcoretical models were tested to set if thermal conductivity could bc calculated from composition and tcmpcraturc. Over a wide range of compositions and temperatures, best predictions (in terms of mean, standard deviation and range of errors) were obtained with Levy's modification to the Maxwell-Eucken equation. Its accuracy was not unduly sensitive to the uncertaintics in the values of the physical parameters, the prediction errors remaining in the range 2 10% for all reasonable values of the latter.
Simple equations were developed to describe the rate of desiccation of unprotected foodstuffs during frozen storage and to describe how the desiccated surface layer of these products affects desiccation rate. These equations indicate that this layer's thermal properties have little effect on the rate of desiccation. Experimental measurements of the resistance of frozen lamb to desiccation were used with these equations to predict desiccation of this product in different environmental conditions. Calculated results agree with measurements from previous surveys and diffusivity measurements. Air velocity should have little effect on desiccation rate once velocity exceeds about 0.1 m/s, whereas radiative heat transfer could have a major effect.
Existing food freezing time prediction methods yield widely differing results at high Biot numbers (internal resistance controlling), a situation that could not be previously resolved due to lack of data. Freezing tests were carried out on slabs of Tylose gel in a plate freezer to obtain more data, which alone and in combination with previous data, were used to test the methods of Cleland and Earle, Hung and Thompson, Pham, and finite differences. Good agreement was obtained with Pham's methods and with finite differences. Biot number, freezing rate and supercooling had negligible effect on the accuracy of these methods. The accuracy of the finite difference method has been significantly improved by our new thermal property data for Tylose gel.
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