29E-10 |
Impingement thawing model for foods |
B. A. ANDERSON and R. P. Singh. Dept. of Biological & Agricultural Engineering, Univ. of California, Davis, 1 Shields Ave., 2030 Bainer Hall, Davis, CA 95616-5294 Use of frozen foods is increasing both in retail and food service. In fact, frozen foods account for one-third of total food service sales. A USDA-ARS study reported that cooking thawed versus frozen hamburger patties improved the final product. Therefore, there is a need to develop faster thawing methods, especially since current methods can be undesirably slow (still air) or are very expensive and cause uneven thawing (microwave). One possible method to speed thawing is impingement. This is the utilization of high velocity jets of air directed at the product surface. A computer model was developed to study the feasibility of using impingement to improve thawing rates. A finite difference code was created in Matlab, utilizing the enthalpy method. Heat and mass transfer during thawing of Tylose (Karlshruhe Test Material), a meat analog, were compared between impingement and still air. The convective heat transfer coefficients used in the model were measured in the laboratory. The thawing times predicted by the model were verified through experiments. The heat transfer coefficient during impingement thawing was found to range from 75 to 145 W/m2K. The model was used to predict thawing times from -20°C to 0°C, using air at 5°C. Thawing in a refrigerator (still air) took more than 23 hours, almost four times longer than thawing under a single impingement jet. The model also demonstrated that the thawing time could be reduced to less than three hours by impinging with air at 20°C for two hours, followed by air at 5°C for the remaining time. Small differences between the model and experiments are attributed to uncertainty in mass transfer. This computer model demonstrated that the use of air impingement technology could significantly shorten thawing times. This model can be utilized to improve experimental design and set-up of future impingement thawing studies.
Session 29E, Food Engineering: Transport processes and kinetics
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