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

A computerized mathematical model was developed to examine theoretical ly the applicability of a continuous point heat source method for simu ltaneous determination of thermal conductivity (k) and thermal diffusi vity (alpha) of foods by developing proper data reduction methods. A p robe of composite structure as well as an overall finite contact condu ctance coefficient between the probe and the food was assumed. Glycero l and agar gel were used as reference materials to obtain a mean effec tive distance 'r' from the point heat source to the temperature sensor location that is needed in the determination. Estimated k for 15 diff erent foods was in good agreement with values obtained from the litera ture (2.5% maximum deviation), whereas the agreement for alpha was rea sonably good only for foods with large alpha values. A small overall t hermal contact conductance coefficient introduced an error of 46% in k and 35% in alpha determination. The minimum food size for accurate de termination of thermal transport properties was 22 mm height x 8 mm ra dius, but was further reduced to 17 mm x 5 mm when the heater dimensio ns were decreased by a factor of four.