Analysis of CFD heat transfer of vacuum freeze-drying shelf

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The vacuum freeze-drying technology is extensively used in biochemical technology industry, especially applicable to materials that are sensitive to temperature, easily deteriorate, and need to remain the original taste. The main defect of this process is long process time. This study used commercial computational fluid dynamics (CFD) software Fluent to research the impact of the shelf inside the vacuum freezedrying machine on the heat transfer performance of the object being dried in the course of heating, and used different shelving arrangements and inlet velocities for numerical simulation of flow field and heat transfer properties. The fluid flowing inside the shelf was 50% glycol water, the inlet velocity was 5m/s, 9.4m/s and 20m/s, and the shelf were stainless steel. Assuming that the shelf surface was a low temperature material layer 233K, and the shelf and materials were in a vacuum and heat insulated environment, the results showed that the temperature difference between the inlet and outlet reached was the smallest when the shelf inlet velocity was 20m/s, and was the highest when the shelf inlet velocity was 5m/s. Although the heat exchange between the fluid and the low temperature layer was better when the inlet velocity was low, the large shelf surface temperature difference was likely to cause unstable material quality. The inlet velocity could be set as 9.4m/s in consideration of saving the energy of pumps.