Absorption refrigeration

Absorption refrigeration is a form of liquid gasification. Like vapor compression refrigeration, it uses gas refrigerant to vaporize at low temperature and low pressure to achieve refrigeration. The difference is that vapor compression refrigeration relies on the consumption of mechanical work (or electrical energy) to transfer heat from low-temperature objects to high-temperature objects, while absorption refrigeration relies on the consumption of heat to complete this non-spontaneous process.

Principle of refrigeration

Figure 2.4 shows that the absorption chiller consists mainly of four exchange devices, namely the generator, condenser, evaporator and absorber, which form two loops: refrigerant cycle and absorber cycle. The left half is the refrigerant cycle, which is a reverse cycle and consists of a condenser, a throttling device and an evaporator. The high-pressure gaseous refrigerant is condensed into a liquid state in the condenser after being released to the cooling medium, and then decompressed by a throttling device to enter the evaporator; in the evaporator, the liquid is vaporized into a low-pressure gas state, and at the same time, the cooled medium is sucked. Heat produces a cooling effect. These processes are identical to vapor compression refrigeration. The right half is the absorbent cycle (the dotted line part in the figure), which is a positive cycle, mainly composed of an absorber, a generator and a solution pump, which is equivalent to a compressor for vapor compression refrigeration. In the absorber, the liquid absorbent is continuously absorbed by the liquid absorbent to achieve the purpose of maintaining the low pressure in the evaporator; the refrigerant-absorbent solution formed by the absorption of the refrigerant vapor by the absorbent is pumped up by the solution. After pressing, the generator enters the generator; in the generator, the solution is heated and boiled, wherein the refrigerant having a low boiling point is vaporized to form a high-pressure gaseous refrigerant, which is liquefied into the condenser, and the remaining absorbent solution is returned to the absorber to absorb the low pressure again. Gaseous refrigerant.

Absorbent

The absorbent in the absorption refrigerating machine is usually not a single substance, but participates in the circulation in the form of a binary solution. The difference between the absorbent solution and the refrigerant-absorbent solution is only the lower refrigerant ratio of the former. The latter is less, or the concentration of the refrigerant contained in the former is lower than the latter. The binary solution usually has an aqueous lithium bromide solution, an aqueous ammonia solution, or the like.

The choice of central air conditioning refrigeration system should be determined according to various objective conditions such as load size, energy supply mode and convenience. Among them, piston refrigeration compressors are mostly medium (standard cooling capacity 60~600KW) and small (less than 60KW), but due to their high noise, low efficiency and easy failure, there are not many used at present; scroll refrigeration compressor At present, it is mainly used in small refrigeration systems, and is widely used in small systems such as household air conditioners and commercial VRVs. The screw machine has a series of unique advantages such as simple structure, high reliability, convenient operation and maintenance, and mature technology, and has been widely used in air conditioners. The centrifugal compressor has simple and compact structure, less moving parts, reliable operation, low operating cost and low operating cost. It is generally applicable to refrigeration systems larger than 500RT, and can realize stepless adjustment, so that the load of the unit is in the range of 30%~100%. Working inside. In general, electric refrigeration is used, and in areas where gas or coal-rich resources are abundant, absorption refrigeration can be used.

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