17H-20 |
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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 With the continual growth in the use of frozen foods both in retail and in food service, there is a need to develop improved thawing methods. Current methods are often undesirably slow (still air) or are very expensive and cause uneven thawing (microwave). Air impingement technology is one possible method to improve the thawing of frozen foods. The objective of this research was to obtain a better understanding of the heat and mass transfer that occurs when air impingement technology is applied towards thawing of frozen foods. Frozen products were thawed using a laboratory impingement system with a single impingement jet. Both a simulated meat product (Tylose gel) and packages of frozen bratwursts were used as test materials. Heat transfer coefficients were evaluated using inverse heat transfer analysis for a nylon disk at thawing temperatures. A finite difference model was written in Matlab v.6.0 to predict heat and mass transfer during impingement thawing, and results were compared with experiments. Thawing of the Tylose disk in a refrigerator (still air) took more than 23 hours, while thawing under a single impingement jet took less than 5 hours, over four times faster. Thawing of frozen packages of bratwursts required over three times longer in still air than using an impingement jet. The degree of improvement in thawing rates for the air impingement system was influenced by the product thickness. Heat transfer coefficients ranged from 60 to 185 W/m2K and varied with position and time. Results from the finite difference model gave good agreement with experimental data. This research demonstrated that the use of air impingement technology has the potential of significantly shortening thawing times for frozen foods. The results could be used to improve the design for impingement thawing systems.
Session 17H, Food Engineering: Thermal processes
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