17G-19 |
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R. CHEMMINIAN, G. Kaletunç, and H. Keener. Dept. of Food, Agricultural & Biological Engineering, Ohio State Univ., 590 Woody Hayes Dr., 210 Agricultural Engineering Bldg., Columbus, OH 43210-1058 Thermal conductivity (k) is an important engineering parameter in design of food processing equipment and optimum conditions. Low moisture content, brittle structure, and the high air volume in the structural matrix make thermal conductivity measurements of porous foods challenging. The objective of this study was to examine the suitability and limitations of the Fitch apparatus and a thermal conductivity probe in measuring the thermal conductivity of porous food materials. A Fitch apparatus and a thermal conductivity probe were used to measure thermal conductivity of extruded snacks, bread, and pretzel. Agar gel (99 % water) was used as a standard. Temperature versus time data were obtained under unsteady-state conditions. Experimental data were fitted to an equation derived for unsteady-state conduction heat transfer in one direction to determine the effective thermal conductivity. k values appeared to be dependent on the sample radius in Fitch method. The k values for agar gels were 0.64 for a 5 mm radius sample and 0.445 W/mK for a 10 mm radius sample using the Fitch method. Measured k value of 0.62 W/m K using the probe method was similar to the reported literature value of 0.626 W/m K. The Fitch method gave significantly high k value (0.21 W/m K) for extruded corn samples with 93% air volume in comparison with the k value (0.03 W/m K) using probe method. The k value for extrudate with 83% air volume was 0.06 W/m K for the probe method and 0.22 W/m K for the Fitch method. The results demonstrated that the probe method gives more consistent results for measuring the thermal conductivity of porous materials in comparison with the Fitch method. In Fitch method, heat transfer in air surrounding the sample and contact resistance between the sample and the rod caused significant deviations in measured k values for porous food materials.
Session 17G, Food Engineering: Physical, chemical and electrical properties
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