混合工质成分对自复叠冷冻干燥装置降温速率的影响

首次对以精馏型自复叠制冷系统为冷源的冷冻干燥装置降温过程进行了准稳态数值模拟,发现在混合工质成分和循环压比给定时,循环单位容积制冷量随压力位变化有峰值存在,具有与纯工质循环不同的特征.通过定成分和变成分下循环制冷量的优化,深入分析了混合工质成分对降温过程中各温度位循环制冷量的影响规律,从而可以为各种不同降温速率要求的冻结工艺设计混合工质的成分,为冻结工艺所要求的降温速率控制提供便利.借助于总单位温降时间和单位温降时间两个新概念,对物品热容量与搁板蒸发器热容量相比很小时的特例进行了深入分析.设计和制作了一台以精馏型自复叠制冷系统为冷源的冷冻干燥装置,实现了-60～-80℃温区的稳定运行,实验结果初步验证了理论分析所得到的结论.

Influence of Mixture Composition on Cooling Rate of a Freeze-Dryer with an Auto-Cascade Refrigerating System

A quasi-steady state simulation was conducted on the cooling process of a freeze-dryer with an auto-cascade refrigerating system using a rectification column. It is found that, unlike the system with a pure refrigerant, a peak value of the volumetric refrigerating capacity occurs as the cycle pressure level varies at a specified mixture composition and a pressure ratio. Optimization of the cycle refrigerating capacity was also performed at the different mixture compositions and the influence of the mixture composition on the cycle refrigerating capacity at different temperature levels in the cooling process was analyzed. The two new concepts, total unit cooling time and unit cooling time, were applied for the detailed analysis on a special case in which the heat capacity of a freeze-drying sample was much smaller than that of the shelf evaporator. An experimental freeze-dryer with an auto-cascade refrigerating system using a rectification column was designed and it operated steadily from -60℃ to -80℃. The simulation results are in consistency with the experimental data.