14A-44

K. S. PANNU, Consultant, 7852 109-A Street, Delta, BC V4C 4G6, Canada

Information on product thermal diffusivity and the heat transfer coefficient (h-value) are required to calculate (predict) the cook time of food products. Several methods are listed in literature to obtain thermal property data. However, obtaining such data from the heating of two particles of similar shape but different size was not investigated.

To develop a method that can be used to estimate the product thermal diffusivity by “comparing” temperature data from two food pieces of different size but similar shape.

Time-temperature data obtained from the heating of potato and carrot cubes (and infinite slabs) of.different sizes in steam was used to test the hypothesis. Assumption made was that during steam heating the h-value was not size dependent (similar). Thus, the two pieces will have different Biot numbers (Bi) and different values for the 1st root of the characteristic non-steady state heat transfer equation. Data for the heating rate index (f-value) was obtained under similar processing conditions. The f-value data and the product size were used to solve a set of equations and calculate the product thermal diffusivity and Bi.

Thermal diffusivity values of 1.61 and 1.69 (x10-7) m2/s were obtained for the potato and the carrot cubes, respectively (at T>100C). Infinite slabs provided diffusivity values of 1.64 and 1.73 for potato and carrot, respectively. These values are comparable to those available in literature. The method does not provide good data for products heated in liquid mediums under forced convection.

A simple method was developed to obtain product thermal diffusivity data. Additional work is needed to validate and refine the procedure.