Rotary vacuum pump this pump product must be familiar to everyone, but for the real understanding of the vacuum pump is in a few, the function of the vacuum pump has a lot of, in the fruit and vegetable fresh keeping and cooked food processing on the vacuum pump in this aspect is also quite extensive.
Vacuum cooling is an ideal fast cooling method which can meet the following requirements
1. The fruits and vegetables after harvest are still living individuals. Obtain necessary material and energy through respiration. On the one hand, respiration maintains individual life, on the other hand, it consumes stored substances. As a result, fruits and vegetables began to age. The purpose of keeping fresh is to delay aging, so it is necessary to control respiration, and the most closely related factor to respiration is temperature. Respiration not only releases energy, but also causes the rise of product temperature. In turn, it promotes respiration and accelerates the aging of fruits and vegetables. Obviously, if we can reduce the temperature of fruits and vegetables, we can effectively control respiration and delay aging. Therefore, the fruits and vegetables must be pre cooled after picking to remove the field heat as soon as possible and reduce the respiratory heat. It creates conditions for prolonging the preservation period. At present, the natural cooling method is generally used, which covers a large area and takes a long time. It is not only difficult to meet the requirements of rapid precooling, but also not suitable for industrial production. Some of them are directly put into the cold storage for cooling, which is neither reasonable nor economical, and they can not be cooled quickly and evenly.
2. Cooked food must be cooled before packaging after processing. Traditional cooling methods include indoor cooling, natural cooling, forced ventilation cooling, air conditioning room cooling, cold storage cooling, etc. These cooling methods not only have a long cooling time (several to more than ten hours), slow turnover, large land occupation, but also uneven cooling, large temperature difference between the surface and the center, and more importantly, affect food safety and health. In the cooling process, the bacteria in the air will inevitably touch the food, resulting in “secondary pollution” of the food, especially between 50-25, which is the high-speed breeding area of bacteria. Through this temperature range quickly, the generation of bacteria can be greatly reduced, and the amount of original bacteria can be easily controlled, which is conducive to improving the safety of food and extending the shelf life.
Various vacuum obtaining techniques and corresponding vacuum cooling equipment
1. Rotary vane vacuum pump, water catcher combined system and fruit and vegetable vacuum precooler:
Rotary vane vacuum pump is one of the most basic vacuum equipment in vacuum technology. This is a kind of oil sealed mechanical vacuum pump with large pumping speed, small volume, high limit vacuum and low working noise. In this kind of vacuum pump, oil plays an important role. It has three functions of sealing, lubrication and cooling.
The principle of vacuum cooling is to make use of the heat absorption when the water vaporizes to cause the self cooling. Therefore, water vapor will be produced in the cooling process. If water vapor enters the vane pump directly, it will cause the emulsification of pump oil, not only affect the performance of the pump, but also damage the pump itself. The solution is to add a water catcher in front of the pump, which uses low temperature to condense water vapor into water and drain it. Therefore, the refrigeration system must be configured again, and the air with water vapor removed shall be discharged through the vacuum pump.
The vacuum precooler for fruits and vegetables is generally designed and manufactured according to the above principles. Its basic components are vacuum box, water catcher, refrigerating unit and rotary vane vacuum pump.
2. Hydraulic jet vacuum technology and normal temperature vacuum quick cooling machine
The cooling of cooked food is different from the precooling of fruits and vegetables. The initial temperature is very high, generally above 90, and a large amount of water vapor will escape during the cooling process. Therefore, if the combined system of rotary vacuum pump and water catcher is still used, the water catcher and refrigeration unit must be equipped with a large amount of water, not only the unit is huge, but also the energy consumption is very high, which is extremely uneconomical. For example, the rapid cooling effect of water jet vacuum technology applied to cooked food is very good.
The technology integrates three functions of vacuum pumping, condensation and drainage. It uses a certain pressure of water flow to spray out at a high speed through a nozzle symmetrically and evenly distributed with a certain side slope, which converges on a focus, thus forming a negative pressure around, making the vacuum box connected with it generate a vacuum. In addition, because of the direct contact between the steam and the jet water, heat exchange, most of the steam condenses into water, which is eliminated through the diffuser, greatly reducing the volume, thus further forming a higher vacuum.