Study of heating characteristics for a continuous 915 MHz pilot scale microwave thawing system
2019
Zhang, Roujia | Wang, Yifen | Wang, Xichang | Luan, Donglei
Heating uniformity is the critical control point on quality and safety during microwave thawing process. The objective of this study was to investigate heating characteristics of a continuous 915 MHz pilot scale microwave thawing system with a numerical simulation model and experiments. The microwave frequency and physical properties of frozen surimi were measured to provide essential information for the numerical simulation model. To validate the developed model, infrared camera and fiber optic sensors were utilized to capture the heating pattern and record the time-temperature profiles of the processed surimi. Volume percentages of the obtained temperature data for both simulated and experimental results were calculated and plotted into curves to intuitively show the heating characteristics. Results showed that the operating frequency of the thawing system was changing with time and affected by presence of load. Simulation results showed that the overall heating pattern was not sensitive to frequency settings. However, different frequency settings brought big difference of local temperature which implied varying microwave energy concentration at different frequencies. Experimental results showed good repeatability and agreed well to simulation results in heating pattern but not in temperature profiles due to varying frequencies. Simulation models with combined frequencies were recommended to improve temperature accuracy. Sample distance and size for continuously moving surimi slabs were studied using developed simulation model. It illustrated that smaller sample distance reduced the edge heating in moving direction. And a larger size of food in moving direction brought better heating uniformity.
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