Factors affecting the drying speed of vacuum dryers
1. The moisture content, density, viscosity and other properties of the material itself. Generally, if the material particles are fine and uniform, the pile is loose, and the thickness is thin, the internal moisture is easy to diffuse. If the initial temperature of the material is increased, the pre-treatment by vacuum filtration, and the moisture content of the material is reduced, the vacuum drying speed can be increased.
2. The higher the vacuum degree of the vacuum dryer, the more conducive to the vaporization of moisture at a lower temperature, but too high a vacuum is not good for heat conduction and will affect the heating effect of the material.
Vacuum dryer drying process
(1) The first heating is the preheating stage of heating the material to make it rise. In this stage, the amount of water vaporized in the material is very small;
(2) The first constant temperature is the constant-rate drying stage, during which a large amount of free water, surface water and capillary water of the material vaporize. Therefore, the temperature and vacuum are in a constant state, and the degree of vacuum is approximately equal to the saturated vapor pressure of water at the drying temperature;
(3) The second temperature increase is the process of heating the material to migrate the internal moisture to the surface of the material. Because the vaporized water is very small, the temperature of the material rises and the degree of authenticity also increases;
(4) The second constant temperature is the stage where the vaporized material is wrapped in water and part of the crystal water. The dry water mobility is determined by the vaporization rate, so the temperature and vacuum are in a stable state;
(5) At the beginning of the cooling stage, turn off the heating steam, and pass cooling water to the jacket of the cylinder to cool the cylinder to lower the temperature of the internal materials in order to discharge the dried products.