There are many refrigeration methods, and the following are commonly used:
1. Liquid vaporization refrigeration
2. Gas expansion and refrigeration
3. Vortex tube refrigeration
4. Thermoelectric cooling
Among them, liquid vaporization refrigeration is the most widely used. It uses the heat absorption effect of liquid vaporization to achieve refrigeration. Vapor compression, absorption, vapor injection and adsorption refrigeration are all liquid vaporization refrigeration.
Vapor compression refrigeration belongs to phase change refrigeration, which uses the heat absorption effect when the refrigerant changes from liquid to gas to obtain cold energy. It is composed of four parts: compressor, condenser, throttling mechanism and evaporator. They are connected in turn by pipes to form a closed system.
Main refrigeration components and accessories
1.Compressor
Compressors are divided into three structures: open type, semi-open type, and closed type. The function of the compressor is to suck low-temperature refrigerant from the evaporator side, and compress it into high-pressure, high-temperature refrigerant vapor and send it to the condenser.
2.Condenser
The condenser is a heat exchange device that transfers the refrigeration capacity of the evaporator in the refrigeration system together with the compression indication work of the compressor to the environmental medium (cooling water or air). According to the cooling method, the condenser can be divided into air-cooled, water-cooled and evaporative. The condenser is a heat exchange device that transfers the refrigeration capacity of the evaporator in the refrigeration system together with the compression indication work of the compressor to the environmental medium (cooling water or air). According to the cooling method, the condenser can be divided into air-cooled, water-cooled and evaporative.
3. Evaporator
The evaporator means that the refrigerant liquid boils and absorbs the heat of the cooled medium (air or water) at a lower temperature to achieve the purpose of refrigeration.
4. Solenoid valve
Solenoid valve is a kind of shut-off valve that is automatically opened under electrical control. It is usually installed on the system pipeline to automatically switch on and off the actuator of the two-position regulator of the refrigeration system pipeline. The solenoid valve is usually installed between the expansion valve and the condenser. The location should be as close as possible to the expansion valve, because the expansion valve is just a throttling element and cannot be closed by itself, so a solenoid valve must be used to cut off the liquid supply pipeline.
5.Thermal expansion valve
Refrigeration devices often use thermal expansion valves to adjust refrigerant flow. It is not only the regulating valve that controls the liquid supply of the evaporator, but also the throttle valve of the refrigeration device. The thermal expansion valve uses the change in the superheat of the refrigerant at the outlet of the evaporator to adjust the liquid supply. The thermal expansion valve is connected to the liquid inlet pipe of the evaporator, and the temperature sensing bulb is laid on the evaporator outlet (outlet) pipe. It is usually divided into different structures according to the structure of the thermal expansion valve:
(1) Internally balanced thermal expansion valve;
(2) Externally balanced thermal expansion valve.
Internally balanced thermal expansion valve: It is composed of temperature sensing bulb, capillary tube, valve seat, diaphragm, ejector rod, valve needle and adjusting mechanism. Internally balanced thermal expansion valves are generally used in small evaporators.
Externally balanced thermal expansion valve: Externally balanced thermal expansion valve For evaporators with long pipelines or greater resistance, externally balanced thermal expansion valves are often used. For the evaporator of the same size, an internally balanced expansion valve can be used when used in a high-temperature storage, while an externally balanced expansion valve may be used when used in a low-temperature storage. For the evaporator of the same size, an internally balanced expansion valve can be used when used in a high-temperature storage, while an externally balanced expansion valve may be used when used in a low-temperature storage.
6. Oil separator
An oil separator is usually installed between the compressor and the condenser to separate the refrigerating machine oil entrained in the refrigerant vapor. The oil return device is used to return the refrigerating machine oil to the crankcase of the compressor; the commonly used structure of the oil separator has two types: centrifugal type and filter type.
7. Gas-liquid separator
Separate the gaseous refrigerant from the liquid refrigerant to prevent the compressor from liquid hammer; store the refrigerant liquid in the refrigeration cycle, and adjust the liquid supply according to the load change.
8. Reservoir
By setting the accumulator, the liquid storage capacity of the accumulator can be used to balance and stabilize the refrigerant circulation in the system, so that the refrigeration device is in normal operation. The accumulator is generally set between the condenser and the throttling element. In order for the liquid refrigerant in the condenser to enter the accumulator smoothly, the position of the accumulator should be lower than the condenser.
9. Dryer
In order to ensure the normal circulation of refrigerant, the refrigeration system must be kept clean and dry. The filter drier is usually installed before the throttling element. When the liquid refrigerant first passes through the filter drier, it can effectively prevent clogging in the throttling element.
10. Sight glass
It is mainly used to indicate the condition of the refrigerant in the liquid pipeline of the refrigeration device and the water content in the refrigerant. Usually, different colors are marked on the case of the sight glass to indicate the water content of the refrigerant in the system.
11. High and low voltage relay
If the compressor discharge pressure is too high, it will automatically disconnect, stop the compressor and eliminate the cause of the high pressure, and then manually reset to start the compressor (fault + alarm); when the suction pressure drops to the lower limit, it will automatically disconnect. Stop the compressor, and energize the compressor again when the suction pressure rises to the upper limit.
12. Differential oil pressure relay
The electrical switch that uses the pressure difference between the suction and discharge of the lubricating oil pump as the control signal, when the pressure difference is less than the set value, stops the compressor to protect it.
13. Temperature relay
Use temperature as a control signal to control the temperature of the cold storage. The start and stop of the compressor can be directly controlled by controlling the on and off of the liquid supply solenoid valve; when one machine has multiple banks, the temperature relays of each bank can be connected in parallel to control the automatic start and stop of the compressor.
14. Refrigerant
Refrigerants, also known as refrigerants and refrigerants, are media materials used in various heat engines to complete energy conversion. These substances usually use reversible phase transitions (such as gas-liquid phase transitions) to increase power.
15. Refrigeration oil
The function of refrigerating machine oil is mainly to lubricate, seal, cool and filter. In multi-cylinder compressors, lubricating oil can also be used to control the unloading mechanism.
Post time: Nov-15-2021