29E-11 |
Predictive approaches to simulate cooling of strawberries |
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 Strawberries are packaged and cooled in polymeric clamshell packages that are stacked in corrugated trays. Mathematical modeling of the flow and heat transfer is an ideal approach to improve the cooling efficiency of the package. Modeling by solving the turbulent Navier-Stokes equation is constrained by computation time. Modeling by using porous media assumptions may be restricted by the validity of the porous media assumption itself. The objective of this research was to compare the two possible modeling approaches for cooling of strawberries in clamshell packages: appropriate porous media model and the k-e turbulence model. Using the k-e turbulence model, individual clamshells were modeled for various pressure gradients across the packages and the results were added in parallel and series configurations to model trays. Modeling of the entire tray was also done using Darcy-Forchheimer-Brinkman (DFB) theory of airflow through porous media. The results of the simulations were compared to experimental data for cooling of strawberries collected from lab-scale experiments and field trials. Simulations using the turbulence model showed agreement within 10 % for experiments with individual clamshells. But when added together for the entire tray the agreement was less than 20 %. Porosity of the stacked strawberries was determined to be 0.44. Using the porosity data and assuming strawberries as ellipsoids, the DFB model gave simulation results which agreed to the order of 15 % for the entire tray. The DFB model was less accurate in predicting spatial variations of temperature and pressure compared to the k-e model. Computation times were significantly shorter for the DFB model. The results indicated that turbulence models are more accurate in predicting flows inside clamshells. However, they are time consuming and difficult to apply for the entire trays as compared to models using porous media approach.
Session 29E, Food Engineering: Transport processes and kinetics
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