第八章 干燥 Chapter 8 Chapter 8 第一节 基本概念 Basic Concepts Basic Concepts
第八章 干燥 Chapter 8 Chapter 8 第一节 基本概念 Basic Concepts Basic Concepts
8—1 Importance and 1 Importance and Purpose of drying Purpose of drying （重要性和目的） • Significance of Drying Process as an Unit Operation – It is widely used in every walk of life. E.g. Food stuff, wood processing, plastics industry, paper making etc. • It is one of the oldest methods of preserving food. – Primitive societies practiced the drying of meat and fish in the sun long before recorded history. – Today the drying of foods is still important as a method of preservation. Dried foods can be stored for long periods without deterioration occurring. • The principal reasons for this are that The microorganisms which cause food spoilage and decay are unable to grow and multiply in the absence of sufficient water . Many of the enzymes which promote undesired changes in the chemical composition of the food cannot function without water. (Without moisture or water, the enzyme activity is inactivated)
8—1 Importance and 1 Importance and Purpose of drying Purpose of drying （重要性和目的） • Significance of Drying Process as an Unit Operation – It is widely used in every walk of life. E.g. Food stuff, wood processing, plastics industry, paper making etc. • It is one of the oldest methods of preserving food. – Primitive societies practiced the drying of meat and fish in the sun long before recorded history. – Today the drying of foods is still important as a method of preservation. Dried foods can be stored for long periods without deterioration occurring. • The principal reasons for this are that The microorganisms which cause food spoilage and decay are unable to grow and multiply in the absence of sufficient water . Many of the enzymes which promote undesired changes in the chemical composition of the food cannot function without water. (Without moisture or water, the enzyme activity is inactivated)
The Purpose of Drying The Purpose of Drying • Easy for preservation or store Easy for preservation or store – Drying makes food or raw food materials have long Drying makes food or raw food materials have long shelf life. ( in terms of microorganism and enzyme shelf life. ( in terms of microorganism and enzyme action). action). – Need small space of storehouse Need small space of storehouse • Convenient for transportation Convenient for transportation – Weight and volume are greatly reduced,improves Weight and volume are greatly reduced,improves significantly the efficiency of transportation In terms significantly the efficiency of transportation In terms of loading and unloading of loading and unloading • Convenient for consumer use Convenient for consumer use – E.g. milk powder,dried vegetables etc. E.g. milk powder,dried vegetables etc
The Purpose of Drying The Purpose of Drying • Easy for preservation or store Easy for preservation or store – Drying makes food or raw food materials have long Drying makes food or raw food materials have long shelf life. ( in terms of microorganism and enzyme shelf life. ( in terms of microorganism and enzyme action). action). – Need small space of storehouse Need small space of storehouse • Convenient for transportation Convenient for transportation – Weight and volume are greatly reduced,improves Weight and volume are greatly reduced,improves significantly the efficiency of transportation In terms significantly the efficiency of transportation In terms of loading and unloading of loading and unloading • Convenient for consumer use Convenient for consumer use – E.g. milk powder,dried vegetables etc. E.g. milk powder,dried vegetables etc
8—2 Classification, Definition and 2 Classification, Definition and Contained Processes for Drying Contained Processes for Drying 8.2.1 Dehydration and Drying 8.2.1 Dehydration and Drying Dehydration By Mechanical Method Dehydration By Physical-Chemical Method Dehydration By Heating Method （Removing Solvent from solids by heating is called drying—The definition of drying）
8—2 Classification, Definition and 2 Classification, Definition and Contained Processes for Drying Contained Processes for Drying 8.2.1 Dehydration and Drying 8.2.1 Dehydration and Drying Dehydration By Mechanical Method Dehydration By Physical-Chemical Method Dehydration By Heating Method （Removing Solvent from solids by heating is called drying—The definition of drying）
Dehydration by Dehydration by Mechanical Method Mechanical Method • The moisture is removed by filtration , The moisture is removed by filtration , Express, Suction, and Centrifugation. Express, Suction, and Centrifugation. These methods are used only in the These methods are used only in the case that the moisture dose not need case that the moisture dose not need to be totally removed. to be totally removed. • 即通过过滤、压榨、抽吸 即通过过滤、压榨、抽吸 和离心分离等方法除 离心分离等方法除 去湿分，这些方法应用于溶剂无需完全除尽 去湿分，这些方法应用于溶剂无需完全除尽 的 情况，已在前面讲述。 情况，已在前面讲述
Dehydration by Dehydration by Mechanical Method Mechanical Method • The moisture is removed by filtration , The moisture is removed by filtration , Express, Suction, and Centrifugation. Express, Suction, and Centrifugation. These methods are used only in the These methods are used only in the case that the moisture dose not need case that the moisture dose not need to be totally removed. to be totally removed. • 即通过过滤、压榨、抽吸 即通过过滤、压榨、抽吸 和离心分离等方法除 离心分离等方法除 去湿分，这些方法应用于溶剂无需完全除尽 去湿分，这些方法应用于溶剂无需完全除尽 的 情况，已在前面讲述。 情况，已在前面讲述