At present, most of the vacuum pumps used in vacuum precooling devices are rotary vane vacuum pumps. Although the vane vacuum pump with gas ballast device can pump out the mixed gas containing a small part of water vapor and a large amount of permanent gas, in the process of vacuum precooling, due to the evaporation of water inside the vegetables, a large amount of water vapor will be pumped into the vane pump, and the water vapor will condense in the pump cavity. This will lead to emulsification and deterioration of the lubricating oil of vacuum pump, seriously affect the limit pressure that vacuum pump can reach, reduce the lubricating performance, increase the wear, and fail to work normally, and even cause serious corrosion of pump body and rotor and other parts, resulting in the scrapping of the whole machine. Therefore, the application of Roots vacuum pump in vacuum precooling device is recommended.
Precooling after harvesting is an effective method to keep vegetables fresh and delay their aging. For different vegetables, four methods can be adopted respectively: cold air precooling, differential pressure precooling, vacuum precooling and water precooling. Roots vacuum pump vacuum cooling has been widely used in the field of food industry. Compared with traditional cooling methods such as blowing and soaking, vacuum precooling can greatly shorten the cooling time and make the internal temperature field of food more uniform. Obviously, from the perspective of fresh-keeping, vacuum precooling device is the most ideal cooling and refrigeration equipment for vegetables at present.
The vacuum cooling system includes a vacuum chamber, a bracket and a vacuum pump, wherein the vacuum pump is a Roots vacuum pump. During the operation of roots pump, attention shall be paid to:
① Ensure that the water temperature of the vacuum pump is as close to the design operation condition as possible and the water quantity is sufficient.
② Ensure the cooling water circulation of vacuum pump, otherwise the unit will be shut down due to the overheating protection of Roots vacuum pump when it is running for about 1H.
Roots vacuum pump Features:
1. Motor diversity
The motors of each roots vacuum pump can be air-cooled or water-cooled to ensure the normal use of customers
The whole pump is made of aluminum alloy or cast iron to realize the advantages of fast heat dissipation and strong corrosion resistance
2. Simple structure and convenient maintenance
The rotor profile makes the pump design more compact by elaborately designing the circular arc rotor
The pumping effect is more outstanding, and the pumping speed is greatly improved compared with other manufacturers of the same level
The maintenance is very convenient, and the maintenance cost is very low
3. High definition clean vacuum
There is no medium that can react with air in the cavity of roots pump
Ensure that the extracted gas is free from secondary pollution and achieve a high clean vacuum
4. Universal pump booster pump
Roots vacuum pump, also known as booster pump, can be combined with screw vacuum pump, rotary vane vacuum pump, water ring vacuum pump, slide valve vacuum pump, molecular pump and other pumps to form a pump group, greatly improving the pumping rate and vacuum degree, which can be more than 10 times higher under normal conditions!
It can be seen from the above contents that, compared with the rotary vane vacuum pump, the pressure in the vacuum chamber is basically reduced to the specified value in the same time, and the effect of the two is basically the same. However, in the experiment of a small number of vegetables, because roots vacuum pump can bear certain water vapor, there is no problem of lubricating oil emulsification, and it will not affect the operating condition of the vacuum pump, so it can be free of adding refrigeration system. The application of Roots vacuum pump in the vacuum precooling device not only extends the service life of the vacuum pump, but also saves the cost.