14A-47

C. M. SABLIOV¹, D. B. E. Farkas, D. K. M. Keener, and D. P. A. Curtis. (1) Food Science/Biological & Agricultural Engineering, North Carolina State University, 39 Schaub Hall, Raleigh, NC 27695-7624

On August 27, 1999, FSIS made effective a new regulation requiring shell eggs packed for consumers to be stored and transported under refrigeration at an ambient air temperature not to exceed 45°F. As an alternative to conventional cooling of eggs in still air, cryogenic cooling offers exceptional heat transfer rates and thus short cooling times.

The objectives of the research were 1) to characterize the dynamics of cryogenic CO2 cooling of shell eggs using numerical methods and 2) to validate the numerical model by comparing the temperature profiles with experimental data.

Heat transfer during cryogenic cooling was simulated by the finite element method. The following assumptions were made: 1) unsteady-state, two dimensional heat transfer, 2) egg of elliptical shape, composed of shell, albumen, yolk and air. A mesh of 4300 elements and 4111 nodes was created. Initial and boundary conditions and the egg properties were defined. Experimental temperature data was obtained in eight different locations in an egg using K-type thermocouples connected to a datalogger. A laboratory scale cryogenic cooler was used.

Cryogenic CO2 egg cooling was characterized by two stages: rapid cooling, and equilibration. During rapid cooling, egg components close to the shell quickly reached 0°C and an ice layer formed at the interface of the shell and albumen. The temperature in the center of the egg dropped 7°C to 18°C at the end of the cooling process. During equilibration, the ice-layer thawed and the temperature of the internal components decreased to an equilibrium temperature of 45°F. The simulation results compared favorably with results from laboratory testing.

Heat transfer during the two phases of cryogenic CO2 cooling was simulated by the finite element method. The simulated temperatures agreed well with experimental data. The numerical model can be used to improve the cooling process of eggs before distribution to consumers.