Views: 11 Author: Site Editor Publish Time: 2022-01-05 Origin: Site
The vacuum freeze dryer is an excellent drying method. The dried product can be stored for a long time at room temperature without any additives under the sealed condition. The structure of freeze-dried items is porous and crisp, and the rehydration is fast when used. The color, fragrance, taste, shape and activity of the items are basically unchanged after rehydration. The vacuum freeze dryer is especially suitable for the food, health, health, and pharmaceutical industries. . The vacuum freeze dryer is to freeze the wet material or solution into a solid state at a lower temperature (-10℃～-50℃), and then make the water in it sublimate directly into a gaseous state under a vacuum (1.3～13 Pa). , Drying technology to dehydrate materials.
The working principle of the vacuum freeze dryer is to first freeze the dried items to below the triple point temperature, and then directly sublime the solid water (ice) in the items into water vapor under vacuum conditions, and remove them from the items. , Make the item dry. After pre-processing, the materials are first quick-frozen, then vacuum dried, sublimated and dehydrated, and then packaged in the post-processing workshop. The heating system of the vacuum freeze dryer provides sublimation latent heat to the material, and the refrigeration system provides the required cold energy to the water trap and the drying bin. The quality requirements for freeze-dried products are: unchanged biological activity, uniform appearance and color, full shape, firm structure, solid, fast dissolving speed, and low residual moisture. To obtain high-quality products, you should have a more comprehensive understanding of the theory and technology of freeze-drying. The freeze-drying process of the vacuum freeze dryer includes three stages: pre-freezing, sublimation and re-freezing. The vacuum freeze dryer is reasonable and effective. Shortening the cycle of freeze-drying has obvious economic value in industrial production.
In the process of freeze-drying, the temperature of the liquid products needs to be controlled within a certain range required by the process during the cooling and pre-freezing of the liquid products and the subsequent sublimation of the moisture in the solid products. This requires the vacuum freeze dryer to have a certain accuracy. Temperature adjustment function. The temperature adjustment problem of the vacuum freeze dryer is better solved without setting the temperature adjustment unit. The specific plan is as follows:
1. Under the premise of surplus refrigeration compressor refrigeration, a refrigeration branch that can provide appropriate refrigeration capacity is added next to the refrigeration system pipeline that provides cooling to the front box of the vacuum freeze dryer. Amount needed;
2. At the same time, when the temperature is adjusted, the refrigeration compressor is cooling two evaporators with different evaporating temperatures. The difference in working conditions may have a greater impact on the refrigeration compressor due to the lag of the expansion valve control, and it may be severe. It will cause the liquid shock of the refrigeration compressor to cause failure, which requires a good grasp of the control of the return steam pressure. The current technicians have added an electromagnetic valve to the return steam pipeline of the front box evaporator, and the pressure controller is used to control the return steam pressure. The pressure difference between the front and back of the solenoid valve is monitored to control the opening or closing of the valve to reduce the load impact during temperature adjustment, and to ensure the smooth operation of the vacuum freeze dryer compressor;
3. In order to prevent the pressure increase in the front box evaporator caused by the closing of the electromagnetic valve, and the temperature adjustment effect cannot be guaranteed, the vacuum freeze dryer technicians will return in front of the electromagnetic valve. A return steam branch pipe is added to the steam pipeline, which is connected to the second-stage compressed suction pipe of the refrigeration compressor. Through practice on multiple vacuum freeze dryers, the results have proved that this treatment scheme is feasible, and it can avoid . It avoids the increase in the cost of adding a temperature control unit, and solves the temperature control effect caused by the commonly used capillary temperature control. The result is not ideal and the load impact on the compressor.