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A. Sarkar and R. P. SINGH. Dept. of Biological & Agricultural Engineering, Univ. of California, Davis, 1 Shields Ave., 2030 Bainer Hall, Davis, CA 95616-5294 Application of air impingement systems to food freezing requires optimization of a number of design parameters. Due to complex interaction among these parameters, an ideal optimization approach is to numerically simulate the air impingement freezing process and use the simulation model for optimization. The objective of the present research was to develop a numerical method to simulate air impingement freezing and to validate it through experiments. A numerical model was developed for boundary layer flow, heat transfer and internal freezing in a product subjected to impingement. External flow was simulated using a commercial computational package. Flow and heat transfer in the boundary layer surrounding the product and internal freezing in the product were simulated using a numerical algorithm consisting of falker-skan transformed equations for boundary layer, discretized using finite differences and solved using a recursion technique. Internal freezing was solved using an enthalpy-time step technique. The model was validated in a slot jet apparatus with tylose as a model food material. In general the simulations showed good agreement to the numerical simulations (deviations of +-1°C at most locations). Overall freezing time predictions from 0°C to -18°C predicted by the simulation model were within 5% of experimentally determined freezing times. Limitations of the simulation model were noted for regions where super cooling was considerable and in regions of separated flow (accuracy limited to +-3°C). The results indicated considerable time dependence of surface convective heat transfer coefficients in air impingement. Heat transfer coefficients varied from 200 W/m²K to 100W/m²K at certain locations on the surface during freezing in a time frame of 60-80 min. Significance: The results show the need of time dependent simulations for air impingement processes. The simulation model can be used for optimization of air impingement freezing processes.
Session 111, Food Engineering: Modeling heat transfer and microbial inactivation
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