58-8 |
Measurement of surface mass transfer coefficient during hot air jet impingement |
D. KOCER, N. Nitin, and M. V. Karwe. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Jet impingement ovens represent a special class of forced convection ovens in which high velocity (up to 50 m/s or ~100 mph) jets of hot air impinge on a food product. Jet impingement ovens are used for faster baking and toasting of food materials. The rate of surface moisture removal is higher under hot air jet impingement, which results in quick crust formation. Since the crust has lower moisture diffusivity, the product retains more moisture inside. Higher moisture retention can enhance the perceived quality of the baked food. Our objective was to find surface mass transfer coefficient for potato slices during hot air jet impingement. Jetzone Rotary dryer (Wolverine Corporation) was used in the baking experiments. The experimental conditions for hot air temperature (93, 101, 121, 140, 148 °C) and velocity (13.50, 17.50, 21.25, 24.50, 25.50 m/s) were selected based on a central composite design. 4 mm-thick and 25 mm-diameter potato slices were used in the baking experiments. Temperature and weight of the potato slices were recorded as a function of time. Mass transfer coefficients were calculated from weight loss data. The results showed that surface mass transfer coefficient values varied between 4.60E-05 m/s and 6.41E-05 m/s. It was strong function of temperature. Effect of velocity on the surface mass transfer coefficient was significant at lower temperatures. Correlation for Sherwood number as a function of jet Reynolds number and Schmidt number was developed. The results can be used in the numerical simulation of a baking process during jet impingement. If the surface heat and mass transfer coefficients are known the numerical simulation can be simplified.
Session 58, Food Engineering: Transport processes and kinetics
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