MEASUREMENT OF THE THERMAL-CONDUCTIVITY OF UNFROZEN AND FROZEN FOOD MATERIALS BY A STEADY-STATE METHOD WITH COAXIAL DUAL-CYLINDER APPARATUS

Coaxial dual-cylinder apparatus was used to measure the effective ther mal conductivity of aqueous solutions of glucose, sucrose, gelatin and egg albumin over a temperature range from -20-degrees to 20-degrees-C by the steady state method. The accuracy of the apparatus was confirm ed by testing with water and ice. The effective thermal conductivity d ecreased with an increase in the total solid content in both the froze n and unfrozen states. In the unfrozen state, the effective thermal co nductivity was slightly dependent on temperature. In the frozen state, however, the effective thermal conductivity was strongly dependent on temperature; lower temperatures gave higher effective thermal conduct ivity, reflecting the increase in the ice fration. For the unfrozen sa mples, the intrinsic thermal conductivity of each solid component was calculated by heat transfer models. All the models tested, series, par allel and Maxwell-Eucken, were equally applicable to describe the heat conduction in the unfrozen state. In the frozen state, however, the s trong temperature dependency of the effective thermal conductivity sug gests that the effect of the temperature dependency of the ice fractio n should be incorporated into theoretical models.