A Three-Step Approach to Working Principle
The initial stage preceding the freezing process. The material exhibits rapid freezing at low temperatures, resulting in the formation of a uniform ice crystal structure. It is imperative that the cooling rate is meticulously regulated in order to circumvent the formation of substantial ice crystals, which, if left unchecked, can result in the rupture of the cells. The precise design of the temperature control curve facilitates the formation of a fine, uniform ice crystal network, which in turn provides a greater surface area for subsequent sublimation and thus enhances the drying efficiency.
Subsequent to this initial stage, the material is subjected to a process of sublimation drying. In the absence of atmospheric pressure, ice crystals undergo direct sublimation to form water vapour. The vacuum system functions to maintain low pressure in the chamber (typically ranging from 10 to 100 Pa). Concurrently, the refrigeration system operates to ensure a consistent decrease in the temperature of the cold trap, ranging from -50°C to -80°C. This results in the condensation of water vapour on the surface of the cold trap. It is imperative that this stage is meticulously calibrated to ensure equilibrium between the temperature of the heating plate and the vacuum level. This is to avert the potential for overheating of the material or sublimation rate that is inadequate.
The resolution drying stage is the process by which the substance undergoes a transformation from a liquid to a solid state. Following sublimation, approximately 10% of the combined water is retained within the material. It is imperative to gradually elevate the temperature of the heating plate in order to disband the intermolecular bonds that bind water molecules and material molecules, thereby facilitating the process of deep drying. In this stage, the temperature gradient must be meticulously regulated to avert the collapse of the material structure or the degradation of the active ingredients.
Freeze-drying technology can maximise the retention of biological activity, nutrients and structural integrity of materials, and is especially suitable for drying heat-sensitive substances. For example, in the field of biomedicine, freeze-drying technology can be used for the long-term preservation of biological products such as vaccines, antibodies, enzyme preparations, etc., to maintain their activity and facilitate transport and storage. In the field of food processing, freeze-drying technology can be applied to fruits and vegetables, coffee, milk powder and other foodstuffs to retain the nutrients and fresh taste.