Effect of experimental parameters on temperature distribution during continuous and pulsed microwave heating

Temperature distribution (TD) in 2% agar gel cylinders heated by same average microwave power level was evaluated. The same average power level based on oven settings (OSP) and absorbed power (AP) were applied to agar gel samples. A 3 × 2 × 2 factorial design was used to evaluate the effect of different experimental variables: heating time (1, 2 and 3 min); microwave application (continuous vs. pulsed); and sample size (3.5 cm and 4 cm radius). Analysis of variance under the same average OSP condition indicates that all variables affected TD significantly. Overall, pulsed microwave treatment resulted in a more uniform TD than continuous microwave treatment under the same average OSP condition. Interactions among variables under the same average OSP condition were also observed. The results indicate that pulsed microwave heating should be preferred over continuous microwave heating when sample temperature uniformity is critical. When same average absorbed microwave power was delivered into the samples of same dimensions, pulsed application resulted in relatively more uniform TD compared to continuous application.