Vacuum pumps should ensure that water vapor and dry air are removed within a certain period of time to maintain the vacuum required for food moisture sublimation and desorption in the drying box. Therefore, the main performance indicators of the vacuum system should be: A. vapor extraction capacity; B. drying box vacuum limit is low enough; C. effective pumping speed at the outlet of drying box meets the requirements.
At present, in food freeze-drying, the water vapor can be directly pumped out, and the performance index B and C can be met. The only vacuum pumps used in food freeze-drying are steam jet pumps. Other vacuum pumps, such as water ring pumps and water jet pumps, can not meet the requirements of the above performance index B and c, or do not have the ability to extract water vapor (oil-sealed mechanical pumps). Vacuum pumps without performance index B and C can not be used in food freeze-drying system at present. Vacuum pumps without performance index a are widely used with cold traps. Therefore, there are two kinds of vacuum systems in food freeze dryer, one is the steam ejector pump vacuum system without cold trap, the other is the oil-sealed mechanical vacuum pump system with cold trap.
没有评论:
发表评论