Principle of precooling and freeze-drying in microwave vacuum equipment

　　Vacuum cooling is the vacuum chamber in fruits and vegetables in the insulation, vacuum on indoor vacuum pump. When the vacuum degree reaches and the temperature corresponding to the saturated steam pressure, the surface water in the fruit and vegetable fiber gap began to evaporate, evaporation will take the latent heat of evaporation, increase and decrease of temperature, further pressure, until the fruits and vegetables cooled to the required temperature.

　　Water at an atmospheric pressure, boiling at 100 degrees, but the pressure drops, and its boiling point also decreased, which can be reduced from the phenomenon of boiling point of water in the mountains, while the water in order to evaporate, must absorb heat

　　The vegetables, fruits are placed in sealed containers (vacuum tank), using vacuum pump to tank air pressure drops, vegetables, fruits, such as the original temperature is 30 DEG C, when the pressure drops to 32Torr, the boiling point of water is reduced to 30 DEG C, while vegetables, fruit water boiling, intense evaporation. In vacuum condition, the moisture transport of fruits and vegetables from the center to the table, at the same time. Low temperature boiling liquid phase into water vapor process required for sensible heat latent heat of vaporization is released by vegetable service itself, so that the fruits and vegetables rapid and uniform cooling. Further pumping the pressure drop, with boiling down fruits and vegetables, the temperature dropped, when the pressure drops to 6Torr, fruits and vegetables can be reduced to 0~ temperature of 5 degrees Celsius.

　　Characteristics of vacuum precooling:

　　(1) the cooling speed is fast. It is only 20~30 minutes to cool the fruit and vegetables from room temperature to about 0 DEG C

　　(2) uniform cooling. The temperature difference between the center and the surface of the fruit and vegetable is very small

　　(3) the quality is good. After cooling, the fruits, vegetables, proteins, carbohydrates, lipids, vitamins and so on have not been damaged

　　(4) clean. For pre cooling of fruits and vegetables in the vacuum environment can, vacuum environment sterilization or preparation bacteria. (5) dry consumption. Vacuum pre cooling by controlling the vacuum evaporation, moisture control in fruits and vegetables, or in the pre cooling prior to spraying the amount of fruits and vegetables water. Dry fruits and vegetables consumption can be controlled within 2~3%. While the average consumption of dry cooling in more than 10%.

　　(6) without the restriction of packaging, there is no difference between the vacuum cooling rate of the fruits and vegetables, such as cartons and plastic bags

　　(7) compared with the pre cooling of fruits and vegetables, more suitable for the long distance trade and the rise of domestic city supermarket clean pollution-free vegetables, pollution-free vegetables, wild vegetables, fresh flowers and processing edible fungus, has broad prospects.

　　In practice, it is proved that the vegetables which are vacuum pre cooled, the surface is dry, fresh and green, and there are obvious differences compared with the vegetables directly into the cold air

　　The utility model is especially suitable for the use of vacuum pre cooling method for vegetables with small body / surface ratio, such as Chinese cabbage, spinach, leek, etc.:

　　Vacuum cooling equipment is designed to prevent fruits, vegetables, and flowers and other agricultural products in the process of storage and transportation of fresh and quality decline. It is the fruit vegetable and flower placed in a vacuum processing tank, under low pressure water evaporation from the surface of fruits and vegetables flowers, water use method of latent heat of evaporation from fruits and vegetables and flowers the surface, and achieve a cooling effect.

　　The refrigeration system of vacuum pre cooling equipment is mainly composed of a vacuum chamber, vacuum system and control system. The refrigeration system is used to provide cooling capacity for water vapor traps, cooling coil in the vacuum chamber and the evaporation of water vapor in the trap water vapor condensation, and the condensed water is discharged without being sucked into the vacuum pump, pump pumping performance.