In hot summer days, we enjoy the coolness brought by air conditioners; in cold winter days, we rely on air conditioners to keep our homes warm as spring. Behind all this, it is inseparable from the silent efforts of refrigeration technology. Refrigeration technology, an indispensable part of modern life, not only makes our lives more comfortable and convenient, but is also widely used in many fields such as industry, agriculture, commerce, and scientific research.

I- Definition and Classification of Refrigeration Technology

Refrigeration refers to the process of using artificial methods to cool an object or fluid within a certain time and space so that its temperature drops below the ambient temperature and maintains this low temperature.

Refrigeration technology can be divided into multiple application fields according to the low temperature range obtained by refrigeration, such as household refrigeration, industrial refrigeration, low-temperature refrigeration and cryogenic refrigeration.

II- Basic Principles of Refrigeration Technology

The basic principle of refrigeration technology is to use the state change of a certain working fluid (refrigerant) to absorb a certain amount of heat from a lower-temperature heat source, and release it to a higher-temperature heat source through a compensation process that consumes work (mechanical energy or electrical energy). heat to achieve refrigeration.

1. Refrigerant Selection

Refrigerant is a key substance in refrigeration technology, and its type and properties have an important impact on the refrigeration effect. Common refrigerants include inorganic compounds (such as water, ammonia, carbon dioxide, etc.), Freons (such as R12, R22, R134a, etc.) and hydrocarbons (such as R600, R600a, etc.).

In addition, there are mixed refrigerants, which are composed of two or more types of Freon. The selection of refrigerant needs to consider its thermodynamic properties (such as boiling point, evaporation pressure, condensation pressure, etc.) and physical and chemical properties (such as thermal conductivity, heat transfer coefficient, viscosity, density, chemical stability, etc.).

2. Composition of Refrigeration System

Refrigeration systems usually include four basic components: compressor, condenser, throttling device (such as expansion valve or capillary tube) and evaporator, which are connected by pipes to form a closed cycle system.

1) Compressor:

The compressor is the "heart" of the refrigeration system, responsible for sucking in low-pressure refrigerant vapor from the evaporator and compressing it into high-temperature and high-pressure gas. During this process, the temperature and pressure of the refrigerant increase, providing conditions for the subsequent condensation process.

2) Condenser:

After the high-temperature and high-pressure refrigerant gas enters the condenser, it is cooled by the normal-temperature cooling water or air, and gradually condenses into a high-pressure liquid. During the condensation process, the refrigerant releases a large amount of heat, which is taken away by the cooling water or air, thereby lowering the temperature of the refrigerant.

3) Throttle device:

When the high-pressure liquid refrigerant flows through the throttling device, the pressure drops rapidly, and the temperature also drops accordingly, turning into a low-pressure and low-temperature gas-liquid two-phase mixture. During this process, part of the liquid refrigerant evaporates and absorbs heat from the surrounding environment.

4) Evaporator:

After the gas-liquid two-phase mixture enters the evaporator, it continues to evaporate in a low-pressure environment and absorbs the heat of the object being cooled, thereby achieving the refrigeration effect. During the evaporation process, the temperature and pressure of the refrigerant remain unchanged, but the state of the refrigerant changes from liquid to gas. After evaporation is completed, the low-pressure gaseous refrigerant is sucked into the compressor again to start a new cycle.

III- Specific Methods of Refrigeration Technology

There are many methods of refrigeration technology, each with its own unique characteristics and application scenarios. Here are a few common refrigeration methods:

1. Vapor Compression Refrigeration

Vapor compression refrigeration is currently the most widely used refrigeration technology. It uses a compressor to compress the refrigerant gas into a high-temperature and high-pressure gas, and then dissipates heat through the condenser to condense the refrigerant gas into a liquid. Then, the refrigerant liquid passes through the throttling device to reduce the pressure and temperature, and turns into a low-pressure and low-temperature gas-liquid two-phase mixture, and enters the evaporator for evaporation and refrigeration. Finally, the low-pressure gas refrigerant is sucked into the compressor again to start a new cycle. Vapor compression refrigeration has the advantages of high refrigeration efficiency, mature technology, and simple equipment.

2. Absorption Refrigeration

Absorption refrigeration uses the absorption and release of refrigerant gas by the absorbent to realize the refrigeration cycle. This refrigeration technology does not require a compressor, so it operates smoothly and quietly. However, its disadvantages are that the refrigeration efficiency is relatively low, the equipment is complex, and the cost is high. The absorption refrigeration system consists of two circuits: a refrigerant circuit and a solution circuit. In the refrigerant circuit, the high-pressure refrigerant gas condenses into liquid in the condenser, and then enters the evaporator for evaporation and refrigeration after throttling. In the solution loop, the absorbent absorbs the low-pressure refrigerant vapor from the evaporator to form a refrigerant-rich solution. The solution is heated and releases the refrigerant gas, which re-enters the refrigerant circuit.

3. Adsorption Refrigeration

Adsorption refrigeration utilizes the adsorption and desorption of refrigerant gas by solid adsorbents to achieve the refrigeration cycle. This refrigeration technology has the advantages of simple structure and reliable operation, but its refrigeration efficiency is also relatively low and the adsorbent needs to be replaced regularly. The working medium of adsorption refrigeration is an adsorbent-refrigerant pair. During the adsorption process, the solid adsorbent is heated and desorbs the refrigerant gas; during the cooling process, the adsorbent adsorbs the refrigerant vapor to achieve the refrigeration effect.

4. Thermoelectric Refrigeration

Thermoelectric refrigeration, also known as thermoelectric refrigeration or semiconductor refrigeration, is a refrigeration method that utilizes the thermoelectric effect (ie, Peltier effect). When the DC power supply is turned on, a temperature difference effect will occur at the joint of the thermocouple, that is, the cold end absorbs heat and the hot end releases heat. By adjusting the direction and size of the current, the cooling effect can be controlled. Thermoelectric refrigeration has the advantages of small size, light weight, and no noise, but its cooling efficiency is low and it consumes more electrical energy.

5. Magnetic Refrigeration

Magnetic refrigeration is a new type of refrigeration technology based on the "magnetocaloric effect". It uses the magnetization effect of the magnetic field on the magnetic material to cause the temperature of the magnetic material to change when the magnetic field changes, thereby achieving the cooling effect. Magnetic refrigeration has the advantages of environmental protection and high efficiency, but it is still in the research and development stage and has not yet been commercialized on a large scale.

IV- Application and Development of Refrigeration Technology

Refrigeration technology plays a pivotal role in modern life. It is not only used in household appliances such as home air conditioners and refrigerators, but is also widely used in industrial cooling, food processing, medical refrigeration, aerospace and other fields. With the advancement of science and technology and the improvement of environmental awareness, refrigeration technology is also constantly developing and innovating.

1. Development of Environmentally Friendly Refrigerants

Traditional Freon refrigerants have a destructive effect on the atmospheric ozone layer. Therefore, the development of environmentally friendly refrigerants has become an important direction for the development of refrigeration technology. At present, a variety of environmentally friendly refrigerants have been developed, such as R134a, R600a, etc., which have less damaging effects on the atmospheric ozone layer and have good cooling effects.

2. Refrigeration System Optimization

By optimizing the design and operating parameters of the refrigeration system, refrigeration efficiency can be improved and energy consumption reduced. For example, use efficient compressors, condensers and evaporators; optimize the design of throttling devices; adopt intelligent control systems, etc.

3. Research on New Refrigeration Technology

In addition to traditional vapor compression refrigeration, absorption refrigeration, adsorption refrigeration and thermoelectric refrigeration, new refrigeration technologies are constantly being researched and developed. Such as magnetic refrigeration, laser refrigeration, ultrasonic refrigeration, etc. These new refrigeration technologies have the advantages of high efficiency, environmental protection, and energy saving, and are expected to be widely used in the future.

4. Intelligence and Automation of Refrigeration Technology

With the continuous development of artificial intelligence, Internet of Things and other technologies, refrigeration technology will also become more intelligent and automated. Through the intelligent control system, the operating status and energy consumption of the refrigeration system can be monitored in real time; the cooling capacity can be automatically adjusted according to changes in ambient temperature and load; and functions such as remote monitoring and fault diagnosis can be realized. This will greatly improve the operating efficiency and reliability of the refrigeration system and reduce energy consumption and operation and maintenance costs.

V- Conclusion

As an important part of modern life, refrigeration technology not only makes our lives more comfortable and convenient, but is also widely used in various fields. With the advancement of science and technology and the improvement of environmental awareness, refrigeration technology is also constantly developing and innovating. In the future, we will usher in more efficient, environmentally friendly, and energy-saving refrigeration technologies, which will bring more convenience and contribution to our lives and social development. Let us look forward to the bright future of refrigeration technology!