15D-27 |
Effect of power level and sample size on temperature distribution during continuous and pulsed microwave heating |
H. W. YANG and S. Gunasekaran. Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, 460 Henry Mall, Madison, WI 53705 Typical microwave heating of foods often results in nonuniform temperature distribution and scorching. The temperature distribution in foods heated by microwave radiation depends largely on the dielectric properties, power level, and dimensions of the material being heated. These variables may be controlled to obtain a uniform temperature distribution. Objective of this work was to examine the effect of power level, sample size, and heating duration on temperature distribution during continuous and pulsed microwave heating. Two-percent agar gel cylinders (7 cm in height) were used as test samples. The experiments were performed in a Labotron 500 microwave oven. A 2-by-2-by-3 factorial experimental protocol was used to investigate the effect of different experimental variables: (A) sample radii (3.5 and 4 cm); (B) microwave application (250-W continuous and 500-W pulsed, 30-s on and 30-s off); and (C) heating time (1, 2, and 3 min). The pulsed application was controlled appropriately to have the same heating times as in continuous heating. During heating, temperatures were measured every minute at different radial locations within the samples using thermocouples. Analysis of variance indicated significant effect of all variables on sample temperature distribution. Sample temperature was also determined based on energy balance of absorbed power. Overall, for the same total microwave power output, the pulsed treatment resulted in a more uniform temperature distribution. The interaction effects of the variables were also observed. The results show that pulsed microwave heating should be preferred, for applications where sample temperature uniformity is critical, to the traditional continuous microwave heating.
Session 15D, Food Engineering: Processing Technologies
|