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1. The changing process and principle of the refrigeration system cycle such as ice machine
After the compressor of the ice maker completes the compression process, the high-temperature and high-pressure refrigerant vapor is discharged into the condenser. The heat in the condenser is absorbed by the outside air and exchanges heat with the air to complete the "heat release" process, that is, release high-pressure vapor In the heat. The condensed high-temperature and high-pressure steam gradually condenses into a high-pressure liquid, thereby completing the condensation process.
The high-pressure liquid refrigerant accumulated at the bottom of the condenser and in the filter drier flows into the capillary tube after being dried and filtered by the filter drier, and passes through the small channel of the capillary tube to achieve the purpose of throttling. After the high-pressure liquid gradually reduces the pressure and flow rate in the capillary tube Entering the evaporator (the cooling part in the freezer box of the refrigerator), the high-pressure liquid refrigerant is transformed into a low-pressure liquid state, thereby completing the throttling process.
The low-pressure liquid after throttling exchanges heat with the heat in the box in the evaporator to complete the "heat absorption" process. When the low-pressure refrigerant liquid undergoes heat exchange in the evaporator, boiling occurs, and vapor is formed when boiling, so that the low-pressure liquid refrigerant is transformed into low-pressure vapor, completing the evaporation process.
The evaporated (boiling) low-temperature and low-pressure refrigerant gas (vapor) is sucked in by the compressor and compressed in the compressor to convert the low-pressure and low-temperature vapor into high-pressure and high-temperature refrigerant vapor, thus completing the compression process.
Compression, condensation, throttling, and evaporation are the four major processes to form a complete refrigeration system. This cycle is repeated so as to continuously reduce the temperature in the cold storage and achieve the purpose of refrigeration. This is the change process of the refrigerant in the refrigeration system in the cycle. principle.
2. "Supercooling" and "Superheating"
The so-called "supercooling" is to pass the condensed saturated liquid through a certain device (such as a subcooler) and method (or measure) to recool it so that its temperature is lower than the saturation temperature under the condensing pressure, which is called supercooling . Compare the temperature of the liquid before the subcooling with the temperature after the subcooling, and the difference is the "degree of subcooling".
Subcooling is to reduce the flash gas generated during the throttling of the refrigerant liquid before throttling, reduce the specific volume occupied by the flash gas, and increase the unit refrigeration capacity; at the same time, it also increases the superheat of the return gas. There are certain benefits to protecting the compressor from wet stroke operation.
In larger ice machine refrigeration systems, in order to reduce the temperature of the refrigerant liquid entering the throttle valve, reduce the flash gas generated during or after throttling, and appropriately improve the refrigeration efficiency, the process design is in the storage After the liquid container (the system that uses the throttle valve for throttling must have a liquid reservoir), a special device for supercooling-a supercooler is installed. Its structure type is casing type, spray type, etc. The principle is to use cooling water whose temperature is lower than that of the saturated liquid after condensation to cool again (such as deep well water). Generally, the temperature can be lowered by 3 to 5 degrees than before cooling ( That is, the degree of subcooling is 3~5 degrees). There are also some small fluorine refrigeration systems, such as small cold storage. Although there is no special subcooler, the liquid supply pipe and the return air pipe are wrapped together for insulation, and the low temperature of the return air pipe is used to reduce the liquid temperature in the liquid supply pipe. A section of liquid supply pipe and expansion valve are directly installed in the warehouse to pass through, and achieve the purpose of subcooling after recooling, thereby improving the refrigeration efficiency. At the same time, the temperature of the return air pipe is heated to prevent the compressor from inhaling excessive moisture vapor and possible liquid hammer.
The capillary throttling system. The capillary tube and the return pipe (suction pipe) are combined and run together. Some are welded together, are sleeved with a hot glue sleeve, pass through the return pipe, and are wound around the return pipe. Some of them pass the capillary tube or the liquid supply tube directly in the box. The capillary tube exchanges heat with the return air pipe, so that the liquid refrigerant before throttling and the low-temperature refrigerant vapor in the return air pipeline are heat exchanged and cooled to obtain subcooling, which can reduce the liquid impact compressor that may be entrained in the return air pipeline. At the same time, it can achieve the purpose of subcooling the liquid refrigerant before throttling. If the condenser is deliberately enlarged, it is also feasible to leave room for cooling again and subcooling. However, this is not done in a standardized design. The consideration is to minimize the overall volume and weight and reduce manufacturing costs. For small or micro capillary throttling systems, no special subcooler will be added.
The steam whose temperature is higher than the saturation temperature under a certain pressure is called superheated steam. The steam temperature at the exhaust pipe of the refrigeration compressor is generally higher than the saturation temperature, so it belongs to superheated steam, which is called "exhaust superheat".
Due to the length and degree of heat insulation of the air return pipe (suction pipe), the steam in the pipe is transferred to the outside and heated. This phenomenon is called "inhalation overheating" or "pipe overheating". This kind of overheating will increase the suction temperature of the compressor and increase the specific volume of the suction steam, resulting in a decrease in the refrigeration capacity per unit volume and a decrease in the refrigeration capacity of the compressor, which is detrimental to the refrigeration cycle. "Harmful overheating." Therefore, it is required that the suction pipe must be well insulated, and the length of the suction pipe should be shortened as much as possible to reduce this harmful overheating.
In a fluorine refrigeration system using an expansion valve, the degree of superheat is used to adjust the degree of opening of the thermal expansion valve. This phenomenon is called "beneficial overheating". Similarly, the superheat generated by the fluorine vapor after reheating is also a beneficial superheat.
The difference between the saturation temperature before overheating and the saturation temperature after overheating is called the degree of superheat.