Refrigeration is not just for food preservation. There are 5 specialized companies in the United States specializing in keeping the remains of the deceased at -200 C. Many people have a hope before life, that is, they can revive one day with the help of some kind of medicine. James Bedford, a psychologist who chose to sleep in liquid nitrogen, was killed by cancer in 1967 when he was 73 years old. Since then dozens of people have followed his example, and thousands of others have signed a contract for "refrigeration" after death. These bodies are headed down in storage, so that once the automatic control system fails, the head will become the last thawing part.
Unlike the average person, the refrigerator is not a machine for making cold air, but a device for absorbing heat in food. It uses the liquid called "refrigerant" to extract the heat from food and transfer it to the outside of the refrigerator. Refrigerants flow through a series of refrigerators, including 3 basic components: compressors, condensers and evaporators, and repeat the same cycle of refrigeration (similar to the Kano cycle).
In addition to a few environmentally-friendly fridges, most refrigerators used in household refrigerators are mostly Freon (mainly two chloro two fluormethane), which is stored in special containers for refrigerators. When the refrigerator starts running, the motor drives the compressor to start working, and inhales the Freon vapor at low pressure and normal temperature, and compresses it into high temperature and high pressure steam (about 10 atmospheres).
The Freon vapor at high temperature and high pressure is sent to the condenser after leaving the compressor. Condenser is a tube that has been bent many times. It is called "serpentine tube", which is usually installed behind the fridge. Because the temperature of Freon vapor entering the condenser is higher than that at room temperature, the heat is emitted outward through the wall of the serpentine tube, so that the temperature of the Freon vapor decreases and condenses from the gaseous liquid to the liquid, then it flows away from the condenser to the evaporator. The evaporator is composed of another serpentine tube, which is in contact with the refrigerator. This serpentine tube is thinner than the serpentine tube of the condenser, so the flow rate of Freon is quickened, followed by a sudden drop in pressure. This is consistent with the so called Bernoulli principle.
As the pressure drops sharply in the evaporator, freon evaporates vigorously and changes from liquid to gaseous state, which is accompanied by a reduction in temperature. As the heat is always transferred from the hotter object to the colder object, the hotter food in the refrigerator transfers heat to the serpentine tube which runs on the freon gas, so as to achieve the purpose of refrigeration.
After the above process is completed, the refrigerant freon gas is ready to be re absorbed by the compressor, thus starting the next cycle.
Because Freon will destroy the ozone layer, it has been phased out and switched to other refrigerants, but they have the same refrigeration principle.
There are two main types of refrigerators. One is a vertical refrigerator like a household refrigerator, the other is a refrigerator refrigerator commonly used by a store. The cabinet refrigerator is not very convenient to use, but it is more efficient than the previous one. In fact, every time the door of a household refrigerator is opened, a large amount of cold air will flow downward and be replaced by hot air because of the cold air ratio. But this phenomenon will not happen on the cabinet refrigerator, and the advantage of the cabinet refrigerator is that it has very little need for defrosting.
The above is a schematic diagram of the refrigerating process of the refrigerator.
The refrigerant from the compression is in the high-pressure gas state. When it enters the condenser, it releases heat, and becomes liquid and enters the storage. The refrigerant then flows into a thinner tube and the pressure drops. This low pressure liquid becomes cold, and when it enters the serpentine tube that is in contact with the air around the food, the refrigerant becomes a gas again and absorbs the heat of the food. After absorbing the heat, the refrigerant enters the compressor and starts the next cycle.
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