Freeze-Drying of Spheres and Cylinders

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Abstract
A quasi-steady analysis is presented for freeze-drying spheres and cylinders of beef, taking into account the diffusional and bulk flow of a binary gas mixture inside the food product. A variation in the interface temperature is accounted for by solving the mass-transfer equations with property data from previous investigations. This analysis involves the solution of the coupled equations of continuity, momentum, energy, and specie concentration. The effects of controllable freeze-drying parameters are considered. Drying times for the two models are compared. The interface position and temperature are calculated. Drying time is predicted as a function of chamber condition and particle size. Typical temperature profiles in the product are given. The diffusional contribution to the total flow is determined. Results indicate that drying time increases with chamber pressure and chamber water concentration, and with the square of the diameter of the particle. The interface temperature increases nonlinearly during drying. More than half the total flow is found to be diffusional under some chamber conditions.

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