Thermal Conductivity of Frozen Foods in Freezing and Defrosting Processes

The knowledge of thermo-physical properties of foods is essential in the design of equipment or in the evaluation of the process time for operations related to their storage and preservation: cooking, sterilization, refrigeration, drying, etc. The purpose of this investigation is to improve a theoretical model for the prediction of the thermal conductivity of frozen foods below the freezing point. The theoretical prediction of the thermal conductivity is carried out with the solution of the heat conduction equation under the assumption of a prescribed temperature or heat flux distribution. Thermal conductivity is predicted on the base of two thermal hypotheses, i.e. parallel isotherms or parallel heat flux lines, in order to confine the real solution within these two extremes. In each hypothesis two thermal conductivities have been obtained in defrosting and freezing. The foods below the freezing point are composed of three phases: fibre or solid, ice and water. In the freezing process the thermal conductivity increases as the temperature decreases, because the thermal conductivity of ice is higher than the unfrozen water one. A comparison between experimental data and theoretical predictions has been carried out for frozen meats with a fairly good agreement.