SIMULTANEOUS DETERMINATION OF THERMAL-CONDUCTIVITY AND DIFFUSIVITY OF FOODS USING A POINT HEAT-SOURCE PROBE - A THEORETICAL-ANALYSIS

A computerized mathematical model was developed to examine theoretically the applicability of a continuous point heat source method for simultaneous determination of thermal conductivity (k) and thermal diffusivity (alpha) of foods by developing proper data reduction methods. A probe of composite structure as well as an overall finite contact conductance coefficient between the probe and the food was assumed. Glycerol and agar gel were used as reference materials to obtain a mean effective distance 'r' from the point heat source to the temperature sensor location that is needed in the determination. Estimated k for 15 different foods was in good agreement with values obtained from the literature (2.5% maximum deviation), whereas the agreement for alpha was reasonably good only for foods with large alpha values. A small overall thermal contact conductance coefficient introduced an error of 46% in k and 35% in alpha determination. The minimum food size for accurate determination of thermal transport properties was 22 mm height x 8 mm radius, but was further reduced to 17 mm x 5 mm when the heater dimensions were decreased by a factor of four.