Complete production line of food freeze dryer

Complete production line of food freeze dryerFreeze drying machines have become a must-have equipment for air compressor purification in various industries due to their reliable operation, convenient management, and low operating costs. The reason why a freeze dryer affects the freezing cycle is that heat and mass transfer (water vapor) occur simultaneously, and the rate of heat and mass transfer jointly affects the drying rate.

1. Form and composition of materials

Freeze dried materials are usually divided into solid and liquid forms. The solid form and liquid concentration have a significant impact on the freeze-drying rate.

2. Pre freezing rate

The size of crystals formed during freezing greatly affects the drying rate and the dissolution rate of the dried product. The quick freezing and slow freezing processes have the following differences: the ice crystals produced by quick freezing are smaller, while those produced by slow freezing are larger. Large ice crystals are conducive to sublimation, while small ice crystals are not conducive to sublimation. Rapid freezing leads to low sublimation rate and fast desorption rate; Slow freezing results in fast sublimation rate and slow resolution rate.

3. Packing quantity

When materials are freeze-dried, there is a certain ratio of surface area to material thickness after being packaged into containers, which is related to the amount of freeze-drying and packaging. Small surface area and thickness are conducive to moisture sublimation, easy to freeze dry, and have ideal quality. During drying, the wet weight load per unit area of the material tray is an important factor determining the drying time. Generally, the thinner the thickness of the material accumulation, the faster the heat and mass transfer rates, and the shorter the drying time. However, if the material thickness is thin, the amount of material dried per batch per unit freeze-drying area will be less, which is not conducive to improving the unit freeze-drying area and unit time yield.

4. Dry indoor pressure

The pressure inside the drying chamber affects the rate of heat and mass transfer. In terms of mass transfer, the lower the pressure, the better, while for heat transfer, the higher the pressure, the better. The magnitude of mass transfer rate is mainly determined by the temperature and pressure of the sublimation interface and the surface of the drying layer. To increase the escape rate of water vapor in the drying layer, one is to increase the temperature of the sublimation interface to increase the interface water vapor pressure; The second is to increase the vacuum degree of the drying chamber and reduce the vapor pressure on the surface of the drying layer.

5. Heat transfer method

According to traditional classification, it can be divided into conduction, convection, thermal radiation, and medium heating (microwave heating). Due to the fact that the process of sublimation drying involves the transfer of heat and mass (water vapor), the most effective heat transfer method to transfer heat to the material has a significant impact on the drying rate.