Views: 43 Author: Site Editor Publish Time: 2021-12-23 Origin: Site
Since the development of laboratory freeze dryers, its types have gradually increased. According to its functions, it can be divided into: ordinary freeze dryer, capping freeze dryer, multi-manifold common freeze dryer, multi-manifold capping freeze dryer, T-frame freeze dryer, in-situ type freeze dryer.
The freeze-drying process includes pre-cooling, primary drying, secondary drying and storage stages, which are all very complicated heat and mass transfer processes; and these processes are closely related to the thermophysical properties of medicines, foods, excipients, and cryoprotectants .
Therefore, it is necessary to clarify the factors that affect the heat and mass transfer of the drying process, and to determine the thermophysical properties of the relevant materials, in order to formulate a reliable procedure, adopt an optimized freeze-drying process, and produce high-quality medicines and foods; and can achieve shortening The purpose of production time, energy saving, and cost reduction.
The freeze-drying of the product needs to be carried out in a certain device, which is called a vacuum freeze dryer, or freeze dryer for short. According to the system, the freeze dryer is composed of four main parts: the refrigeration system, the vacuum system, the heating system, and the control system. According to the structure, it is composed of a freeze-drying box or drying box, a condenser or a water vapor condenser, a refrigerator, a vacuum pump and valves, and electrical control components.
The freeze-drying process is actually the material change and transfer process of water. The freeze-drying process has two exothermic processes and two absorption processes: the liquid biological product releases heat and solidifies into a solid biological product, and the solid biological product absorbs heat under vacuum and sublimates into water vapor. The water vapor releases heat in the condenser to condense into frost, and after freeze-drying, the frost absorbs heat in the condenser and melts into water.
The heat mass transfer phenomenon takes place during the entire freeze-drying process. The heat transfer runs through the whole process of freeze-drying. The pre-freezing stage, the drying stage, the second stage and the defrosting stage are all carrying out heat transfer; the mass transfer is only carried out in the drying stage, and the water vapor generated in the dry box products is condensed into frost in the condenser. The process is actually the process of mass transfer. Only when mass transfer occurs, the product can be dried. In the drying stage, heat transfer is to promote mass transfer, and improving heat transfer can also improve mass transfer.
