Vacuum drying is to place the materials to be dried in a closed space, and use vacuum equipment to lower the air pressure in the closed space to an atmospheric pressure, while continuously heating the materials, so that the water molecules in the materials gradually diffuse to the surface of the materials due to the effect of pressure difference and concentration difference, and after the material surface obtains enough kinetic energy, gradually overcome the bondage of intermolecular attraction and escape to the low pressure vacuum chamber, and then discharged to the atmosphere through the vacuum pump.
Vacuum drying goes through three main processes.
First, the heat transfer process, where the material absorbs heat through the heat source, warms up and vaporizes the internal wet content.
Secondly, the process of liquid mass transfer of the internal moisture of the material, the internal moisture of the material moves to the surface in the form of liquid, and then completes vaporization on the surface.
Finally, the gaseous transfer process of the wet part on the surface of the material, the vaporized water vapor on the surface of the material gradually escapes to the inside of the vacuum chamber and flows to the outside through the vacuum chamber.
To complete the above heat and mass transfer process, temperature, pressure and concentration are the key control factors.
Temperature: the temperature of the heat source should be significantly greater than the temperature of the material, to meet its own temperature rise and the energy required for the vaporization of wet parts, the higher the temperature, the faster the drying.
Concentration: the so-called concentration, refers to the concentration of the wet inside the material, the internal concentration of the material should be higher than the concentration of the material surface, in the capillary force and concentration difference, to the surface migration, and eventually the concentration of the wet continuously reduced.
Pressure: The vapor pressure on the surface of the material should be higher than the partial pressure of the vapor in the drying oven, which is the core theory of vacuum drying.
For lithium-ion battery cells baking process principle and the main process are as follows.
Heating under atmospheric pressure for a period of time, so that the overall temperature of the material rises to the set temperature, while the vaporization of water in the material.
Reduce the vaporization temperature of water by evacuating, accelerate the drying, after the moisture evaporates to a certain degree, break the vacuum by filling nitrogen, discharge the moisture, keep the drying environment heated for a certain time, evacuate again, so on and so forth until the drying is completed.