The heating system provides the necessary heat for the sublimation drying process. Under vacuum, ice crystals in the material absorb heat to sublime. The heating system transfers heat to the material, enabling the ice crystals to continuously sublime into water vapor.
The heating system provides the necessary heat for the sublimation drying process. Under vacuum, ice crystals in the material absorb heat to sublime. The heating system transfers heat to the material, enabling the ice crystals to continuously sublime into water vapor. Appropriate heating temperature and rate have a significant impact on freeze-drying efficiency and product quality. If the heating temperature is too low, the sublimation rate is slow, and drying time is prolonged. If the heating temperature is too high, the material temperature may exceed the maximum allowable temperature, causing material deterioration and inactivation, affecting product quality. The heating system can also perform desorption drying on the material in the later stages of drying, removing any remaining bound water and further improving the dryness of the product.
A common heating method is resistance heating. Resistance wires are installed in locations such as the shelf. When energized, the wires heat up and transfer heat to the material. This heating method is simple and easy to control, but temperature uniformity may be relatively poor. Thermal oil heating also uses thermal oil as a heat transfer medium. The heated oil then transfers the heat to the shelves, further heating the material. Thermal oil heating offers excellent temperature uniformity, suitable for freeze-drying processes requiring high temperature uniformity. Steam heating is also an alternative method, utilizing the latent heat of steam to heat the material. This method is generally suitable for applications where steam is readily available and offers high heating efficiency. Infrared heating also exists, using infrared radiation to absorb heat from the material. However, this method can result in uneven heating and is relatively uncommon in practice.
