| Two-percent agar gel was treated as a model food to study the temperature distribution (TD) during continuous and pulsed microwave heating. Microwave power, derived from Maxwell's equations and/or the Lambert's law, was applied to a heat transfer model which was solved numerically to predict the TD within 3.5-cm and 4-cm radius agar gel samples. The sample temperatures were measured and compared to the numerical predictions. The TDs predicted based on the Maxwell's equations were more accurate than those predicted based on the Lambert's law, especially around the sample edges. This is because, unlike the Lambert's law, the power solution based on Maxwell's equations accounts for the standing wave effect. The predicted and measured TDs were more uniform under pulsed than continuous microwave heating.; When microwave energy is applied to a food material, the TD within the material depends on the heating duration, pulsing ratio (ratio of total microwave heating time to power-on time under pulsed mode), sample size, and power level. These effects were examined using a 3 x 2 x 2 factorial experimental design. The pulsed and continuous microwave applications were maintained at the same average power based on the oven settings. Analysis of variance indicated that all variables affect the sample TD significantly. The interactions among the experimental parameters were also determined. The results show that pulsed microwave heating is preferred when temperature uniformity is a major concern.; Pulsed microwave heating was applied to mashed potato cylinders to determine an optimal set of operating parameters. The effects of sample radius, power level, processing duration and temperature constraints during the microwave application were evaluated. The sample radius and temperature constraints were critical. Depending on the dielectric properties of the sample, the pulsed microwave heating is best suited only over a certain range of sample sizes (about one to two times the penetration depth of microwaves in the sample). The simulation model presented in this thesis is suitable for evaluating optimal pulsed microwave heating of other solid foods. |
