Refrigeration principle of air conditioning system and structure diagram of each part?

Before talking about the principle of refrigeration, let's take a look at some common phenomena related to refrigeration in life:

Alcohol rubbing on the skin will be cool, indicating that it can be cooled by evaporation. Putting water on the skin is also cool, not as obvious as alcohol. Because alcohol evaporates more easily and faster than water, which means that the faster the evaporation, the better the refrigeration. Washing clothes in summer is easier to dry than in winter, because the temperature is high and evaporation is fast in summer. It shows that the higher the temperature, the faster the evaporation. Water is boiled on the Qinghai-Tibet Plateau and evaporated at 90 degrees. Because the Qinghai-Tibet Plateau has high terrain and low air pressure. The lower the pressure, the faster the evaporation. Influence of temperature and pressure on evaporation and condensation. The refrigeration cycle system consists of four basic components: compressor, condenser, evaporator and expansion valve. We use a diagram to show the change of their refrigerant state: we can roughly summarize it as: two controls and two conversions. 1, compressor: suck the steam in the evaporator to maintain its low temperature and low pressure; High pressure and high temperature steam is compressed. Why compress it? Because the refrigerant should be recycled. If it is not compressed, it will be directly discharged into the condenser. Normal temperature is higher than the boiling point of refrigerant, so it cannot be cooled and condensed into liquid. [The higher the pressure, the higher the boiling point; The lower the pressure, the lower the boiling point]. Only by increasing the pressure of the refrigerant and making the condensation point (boiling point) of the refrigerant higher than the outdoor temperature can the refrigerant dissipate heat to the outside, and the temperature is reduced, and the refrigerant condenses into liquid. 2. Condenser: cooling the high-temperature and high-pressure steam discharged from the compressor into liquid; The released heat is taken away by water or air. It is divided into three types: water cooling, air cooling and water-gas mixed cooling. Most air-conditioning condensers adopt fin-and-coil structure. In order to improve the heat exchange efficiency, aluminum alloy fins are often pressed into various shapes to increase the heat exchange area. 3. Throttle device: When the refrigerant fluid passes through a small hole, part of the static pressure becomes dynamic pressure, the flow rate increases sharply and becomes turbulent, the fluid is disturbed, the friction resistance increases and the static pressure decreases. The main functions of throttle valve: throttling and decompression; Adjust the flow rate to decompress the fluid and adjust the flow rate. 3. 1, capillary features: no moving parts, simple structure; There is no accumulator, so the refrigerant charge is small; After shutdown, the high and low pressure are basically the same, and it is easy to start; The accuracy of work is poor; Small air conditioner or refrigerator. Disadvantages: the liquid supply cannot be adjusted with the change of working conditions. Thermal expansion valve structure 3.2, thermal expansion valve features: also known as temperature-sensitive expansion valve, connected to the inlet of the evaporator, the temperature-sensitive package of the device is close to the outlet pipe of the evaporator. Another function of the expansion valve is to maintain a certain degree of superheat to prevent liquid hammer and abnormal overheating. Thermal expansion valves are divided into internal balance thermal expansion valves and external balance thermal expansion valves. Let's look at the structural differences between them. Structural difference: the internal balance thermal expansion valve transfers the evaporation pressure to the diaphragm. External balance thermal expansion valve: under the diaphragm, feel the outlet pressure of evaporator. ? Let's take a closer look at the internal structure and system connection: the use of internal structure expansion valve is different from that of refrigeration system. If the pressure drop of evaporator is high, an expansion valve with external balance should be used. The external balanced thermal expansion valve accurately controls the superheat of the evaporator outlet, makes full use of the heat exchange area of the evaporator and improves the energy efficiency of the unit. 3. Electronic expansion valve: It is a new control element, and its throttling device is controlled by microprocessor. It is used in variable frequency air conditioning refrigeration system to meet the needs of accurate, high-speed and wide-range load regulation. Of course, there are also many electronic expansion valves for refrigeration and refrigeration. Electronic expansion valve The electronic expansion valve is used to adjust the refrigerant heat at the evaporator outlet. Overheating signal can be collected by temperature sensor and pressure sensor installed at evaporator outlet, and the opening of expansion valve can be controlled by feedback adjustment. Feedforward and feedback compound adjustment can also be used to eliminate the lag of superheat control caused by the heat capacity of evaporator tube wall and sensor, improve the adjustment quality of the system, and control the superheat within the target range in a wide evaporation temperature range. Advantages of electronic expansion valve: large flow adjustment range; High control precision; The energy efficiency ratio is improved in high frequency and low frequency operation; The reliability of the compressor is improved, and the situation that the oil return, liquid return and exhaust temperature are too high is improved. Electronic expansion valves can be divided into electromagnetic type and electric type. 3. Evaporator: Evaporate liquid into gas; Absorb heat. Condensed water will be continuously generated between the fins of the evaporator, which will hinder the air flow. Therefore, the distance between the fins of the evaporator is greater than that of the condenser. In addition, the fin surface of evaporator needs hydrophilic treatment (hydrophilic aluminum foil) to reduce the surface tension of condensed water and increase the cross-sectional area of air circulation. 5. Four-way valve: used for heat pump air conditioning. When air conditioning heats in winter, the indoor heat exchanger works as a condenser and the outdoor heat exchanger works as an evaporator. Contrary to air conditioning refrigeration in summer, the refrigerant needs to flow in the opposite direction. The reverse flow of refrigerant and capillary tube are combined into a special channel to adapt to different operating conditions in winter and summer. The four-way reversing valve consists of a pilot valve, a main valve and an electromagnetic coil.

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