制冷与空调专业英语第2版 林慧珠 主编 5-3新.pptVIP

Unit Five Lesson 17 Evaporative Air Cooling Lesson 18 Room Air Conditioners Lesson 19 Methods of Food Freezing Lesson 20 All-Air Systems Lesson 19 Methods of Food Freezing Lesson 19 Lesson 19 Text There are three basic freezing methods in commercial use: these are freezing in air, freezing by indirect contact with the refrigerant, and freezing by direct immersion in a refrigerating medium. These three basic methods can be further subdivided in various ways; one division is indicated in table1. Text: Text: Thus cold air may be used with various degrees of velocity progressing from still-air “sharp’’ freezing to the high velocity blast freezer tunnel1 .The velocity of air also may be used to subdivide and move particles of materials to be frozen , as in the case of fluidized-bed freezing.2 Text: Indirect contact freezing includes those methods in which the food or the food package is in contact with a surface which in turn is cooled by a refrigerant , but the food or food package does not contact the refrigerant directly . In the case of solid foods or foods in containers this most commonly involves providing a flat surface or nearly flat surface in contact with refrigerated plates , which may contact 1or 2 surfaces of the food or package .In the case of liquid foods and purees, the food is pumped through a cold wall heat exchanger and frozen to the slush condition . Text: Immersion freezing implies direct contact of the food or package with the refrigerant either by submerging the food in the cold liquid or spraying the cold liquid onto the food or package surface.3 With the exception of still-air “sharp” freezing, all of the methods may be engineered for batch, semicontinuous, or continuous operation. Also with the exception of still-air “sharp” freezing, all of the other methods generally are referred to as fast freezing methods. Text: “Freon” Freezing. ---The newe