What Is a Refrigeration Technician?

Freezing means lowering the temperature to freeze and freeze objects. It is also called "refrigeration", which is a method of applying low temperature by artificial thermodynamics. Refrigerators and air conditioners use the principle of refrigeration. From a chemical point of view, a gas with a high critical point is generally used to liquefy under pressure, and then it is vaporized to absorb heat. This process is repeated. The liquefaction is exothermic elsewhere, and the required range is absorbed during vaporization. .
Synonymous refrigeration generally refers to freezing (Chinese words)

Chinese name: freezing
Foreign name: freeze

Pinyin: lngdòng
Zhuyin
nickname: Refrigeration

Frozen words concept

Freezing Basic Information

Word : frozen

Pinyin : lng dòng

Phonetic :

English : freeze ^[1]

Frozen citation explanation

1. It's still cold.

Zhao Shuli's "Li Youcai Banhua" II: "In freezing weather, talent is like a fire-as soon as he gets home, people who make fun of him come to talk in his earthen kiln."

2. Used to describe disappointment.

Kang Yun's "Three Mirrors": "After that, he lost cadres again, and lost courage and embarrassment on his body, and his heart was frozen and cold, but he has never done anything sorry for the new society! "

3. Reduce the temperature to freeze and freeze the object. Freezing can inhibit the reproduction of microorganisms, prevent the organism from spoiling, and facilitate storage and handling. ^[1]

Freezing other related

Frozen chemical

The essence of the freezing operation is to continuously extract heat from the low-temperature object (the object to be frozen) and transfer it to the high-temperature substance (water or air) to reduce the temperature of the frozen material. The transfer of heat from low-temperature objects to high-temperature objects is achieved by means of refrigerants. Generally speaking, the degree of freezing is related to the technology of freezing operation. Those freezing in the range of -100 ° C are referred to as freezing; and temperatures in the range of -100 to -210 ° C or lower are referred to as deep freezing or deep freezing for short.

Refrigerant

Basic parts composition: Generally used compression refrigerators are composed of four basic parts: compressor, condenser, evaporator and expansion valve.

In the past, ammonia was generally used as the refrigerant. Ammonia was the easiest gas to liquefy. However, ammonia leaked was toxic. Therefore, it was later changed to non-toxic and odorless chlorofluorocarbons. The culprit, which has led to climate change and an increase in human skin cancer, is now being investigated worldwide for fluorine-free refrigerators and air conditioners looking for alternatives to HCFCs.

There is also a non-chemical semiconductor refrigeration method. Passing current at the junction of two different metals will generate cold and hot poles at both ends. Refrigerators manufactured using this principle have appeared, but due to their low power and complex manufacturing, currently Can only be used in small refrigerators on cars.

Freezing in frozen food

Freezing concept

Freezing refers to the process of freezing liquid water in food such as fish and meat into a solid state by a low temperature method. This is a safe and healthy preservation method, which can effectively inhibit the growth and reproduction of microorganisms in food, prevent food from spoiling, and also easily restore the original state. However, the freezing method is not suitable for eggs, lettuce, canned foods, and some sauces. At the same time, it should be noted that not all harmful microorganisms will die during the freezing process, and it may be sub-death ^[2] .

Freezing principle

The freezing speed varies with food and equipment. Generally, the faster the freezing speed, the better. For example, fish meat myosin mutates most quickly between 3 and 2 ° C. Therefore, it is necessary to pass this temperature section as soon as possible when freezing. In a certain temperature range (-5 to -1 ° C), most of the water in the food is frozen, forming a large number of ice crystals. This temperature region is called the maximum ice crystal generation zone. Within this temperature range, the water state inside the food changes drastically, and the quality of the food also changes significantly. The faster the speed of passing the maximum ice crystal zone, the more favorable the quality of the food ^[2] .

The principle is that during the freezing process, the extracellular solution first generates ice crystals. Under the action of vapor pressure, the water in the cells flows to the ice crystals outside the cells. At this time, larger ice crystals are formed and the distribution is uneven. Due to protein denaturation, the cell membrane is more susceptible to water loss, which further increases the volume of ice crystals. Large ice crystals can damage the cell wall, cause cytoplasmic outflow, and cause degradation of food quality. In addition, when the food is frozen, the freezing speed decreases from the surface to the center, and the uneven distribution of the freezing speed also easily causes the food quality to decrease. Freeze for a long time, not only the large ice crystals will damage the tissue structure, and the cells cannot return to their original state after thawing, and the cell fluid is lost, which affects the flavor and quality of the food, and even inedible ^[2] .

Freezing Development

Freezing technology is an ancient food preservation technology. As early as 1000 BC, China already knew how to use ice cellars to freeze food; Greeks and Romans put crushed snow in the cellars to freeze food. The commercialization of frozen food in China began in the 1970s; in the 1980s, with the popularity of household refrigerators, freezers and freezers, the development of frozen foods was promoted; in the 1990s, China's cold chain was initially formed, and the variety continued to increase. Production The number of enterprises has increased significantly ^[2] .

Frozen packaging

Frozen food packaging should be able to withstand low temperatures below 0 ° C and be moisture-proof. Frozen food can use plastic containers, freezer bags, or vacuum packaging bags, where vacuum packaging separates food from air, which can effectively prevent food frostbite ^[2] .