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冷冻干澡机涉及到冷冻、加热、气化等过程，即包含了传热、传质等多种过程。从传热角度看，冷冻干燥机、加热互为可逆过程，提高推动力(温度差)或降低热阻，都有利于传 热过程的进行。在工业生产中，多采用减小热阻来强化传热过程。传热的阻力主要来自物料内部和外部，如减小物料层厚度、增大导热性能等，都可提高冻干速率，从传质角度看，湿分由固相升华为气相后分离除去的过程包括:气相由物料内部向表面扩散过程，气相由物料表面向冷凝器表面迁移固化除去的过程，提高传质推动力、降低传质阻力都可提高冻干速率。 影响冷冻干燥速率的因素很多，物料的性质不同、干燥操作条件不同、干燥设备结构形式不同，使得干燥速率差别很大。
物料在固化冻结过程中，其结构发生变化(由液态逐渐变成固态)。该过程从温度上是无法测量到的，但是随着物质结构的改变，会同时发生导电性能的改变。在预冻结操作中，当温度降低时，电阻将会增大。当达到共熔点温度时，全部液体变成固体。这时电阻会发生突然增大的现象。反之，当冻结物料开始熔化时，电阻会突然减小。在冻干操作中，常利用温度测量和电阻测量手段，控制预冻结过程使其达到完全冻结，检侧升华干燥过程，以防止物料熔化，从而保证产品质量。
Frozen dry bath involves freezing, heating, gasification and other processes, that is, including heat transfer, mass transfer and other processes. From the point of view of heat transfer, freezing and heating are reversible processes, raising the driving force(temperature difference) or lowering the thermal resistance, which are conducive to heat transfer. In industrial production, heat transfer process is strengthened by reducing thermal resistance. Frozen dry bath involves the freezing, heating, gasification and other processes, that is, the removal of heat transfer, condensing mass and other processes. From the heat transfer point of view, the freezing and heating are reversible processes, which increase the driving force(temperature difference) or reduce the heat resistance. The transfer of heat from the surface to the solid material is facilitated by the transfer of heat. In industrial production, the heat transfer rate is enhanced by the reduction of the heat phase. The heat transfer resistance mainly comes from the internal and external materials, such as the reduction of the dry material thickness and the heat transfer. The freeze-drying rate can be increased by increasing the mass transfer force and reducing the mass transfer resistance. There are many factors affecting the freeze-drying rate. Different properties of materials, different operating conditions and different structure of drying equipment make the drying rate different. Material solidifying freeze |
