How many hours can a freeze dryer freeze dry things? Generally, the freeze drying time ranges from more than ten hours to more than forty hours, and the freeze drying time varies for different products. Because the freeze drying process is actually a process in which heat transfer and mass transfer (water vapor) are carried out simultaneously, the heat and mass transfer rates jointly affect the drying rate, thereby affecting the entire freeze drying cycle. All factors that affect heat and mass transfer will affect the drying rate. A simple analysis is as follows:
1. Material form and components
According to the form of freeze-dried materials, they are usually divided into solids and liquids. The form of solids and the concentration of liquids have a greater impact on the freeze drying rate.
2. Pre-freezing rate
The size of the 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: quick freezing produces smaller ice crystals, and slow freezing produces larger ice crystals. 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 leads to fast sublimation rate and slow desorption rate.
3. Loading volume
When the material is freeze-dried, there is a certain ratio of surface area to material thickness after it is divided into containers, that is, freeze-drying is related to loading volume. Small surface area and thickness are conducive to water sublimation, easy freeze-drying and ideal quality. During drying, the wet weight load per unit area of the material tray is an important factor in determining the drying time. Generally, the thinner the thickness of the material stack, the faster the heat and mass transfer speed, and the shorter the drying time. However, if the material thickness is thin, less material is dried per batch per unit freeze-drying area, which is not conducive to increasing the output per unit freeze-drying area and per unit time.
