Freeze drying ejectors

Probably some of tbe foods you eat have been freeze-dried. In this process, foods are frozen and the ice is removed from the food by sublimation at low pressures in a vacuum chamber. Then, the water vapor produced by sublimation is removed from the chamber by pumps or water-vapor ejectors. 

Tray dryers may be operated under vacuum, often with indirect heating. The trays may rest on hollow metal plates supplied with steam or hot water or may themselves contain spaces for a heating fluid. Vapor from the solid is removed by an ejector or vacuum pump. Freeze-drying is the sublimation of water from ice under high vacuum temperatures below O C. This is done in special vacuum tray dryers for drying vitamins and other heat-sensitive products. 

Certain foodstuffs, pharmaceuticals, and biological materials, which may not be heated even to moderate temperatures in ordinary drying, may be freeze-dried. The substance to be dried is usually frozen by exposure to very cold air. In freeze drying the water is removed as a vapor by sublimation from the frozen material in a.-vacuum chamber. After the moisture sublimes to a vapor, it is removed by mechanical iSuum pumps or steam jet ejectors. 

Freeze drying (sublimation drying) Substances which cannot be heated even to moderate temperatures, such as foodstuffs and certain pharmaceuticals, can be dried by this method [27]. The substance to be dried is customarily frozen by exposure to very cold air and placed in a vacuum chamber, where the moisture sublimes and is pumped off by steam-jet ejectors or mechanical vacuum pumps. An alternative method of freezing is by flash vaporization of part of the moisture under vacuum, although foodstuffs which are not rigid in the unfrozen state may be damaged by this procedure. Some foods, e.g., beef, evidently... 

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