Concepts, principles and devices related to refrigeration equipment

Refrigeration: The process of using the low temperature source generated by refrigeration to cool the product from room temperature and then freeze it.

Refrigeration: The process of using the cold effect generated by the change in the physical state of the refrigerant to obtain a low temperature source. Types of refrigeration equipment: cold source production (refrigeration), freezing and cooling of materials.

Refrigeration methods: piston, screw, centrifugal refrigeration compressor units, absorption refrigeration units, steam jet refrigeration units and liquid nitrogen.

Freezing methods: air cooling, immersion and devices in which the refrigerant contacts the metal pipe, wall and material to transfer heat and cool down.

Refrigeration capacity: The amount of heat removed from the frozen object by the refrigerant per unit time under certain operating conditions (i.e., a certain refrigerant evaporation temperature, condensation temperature, and supercooling temperature). It is also called the refrigeration capacity of the refrigerant. Under the same conditions, the refrigeration capacity of the same refrigerant is related to the size, speed and efficiency of the compressor.

Direct refrigeration: In the refrigeration cycle, if the evaporator that absorbs heat from the refrigerant directly exchanges heat with the object to be cooled or the surrounding environment of the object to be cooled. Generally used in single refrigeration equipment that requires industrial cooling, such as ice cream freezers, small cold storage and household refrigerators.

Refrigerant: The working substance that circulates continuously in the refrigeration device to achieve refrigeration. The vapor compression refrigeration device realizes heat transfer through the change of the physical state of the refrigerant. Refrigerant is an indispensable substance for realizing artificial refrigeration.

Indirect refrigeration: Use cheap substances as medium carriers to realize heat exchange between the refrigeration device and the cold-consuming place or machine.

Coolant: The cold generated in the evaporator of the refrigeration device refrigerant is transferred to the refrigeration device where the heat absorbed by the cooled object is transferred to the refrigerant, and then to the refrigerant, and it is cooled and recycled.

Indirect refrigeration principle: After the coolant absorbs cold from the refrigerant in the evaporator, it enters the cold storage through the brine pump, exchanges heat with the medium of the cooled object or workplace to absorb heat, returns to the evaporator, and transfers the absorbed heat to the refrigerant, and it is cooled and recycled.

Common coolants: air, water, brine and organic aqueous solution.

Main devices of refrigeration equipment

Compression function: used to compress the refrigerant to obtain energy, and after condensation and expansion, form a cold source that can absorb heat.

Condenser function: heat exchanger, which cools the superheated steam of the refrigerant and condenses it into liquid. There are horizontal shell and tube type, vertical shell and tube type, water spray type, evaporation type, and air cooling type.

Expansion valve function: reduce the pressure of the refrigerant and control the flow of the refrigerant. When the high-pressure liquid refrigerant passes through the expansion valve, the condensation pressure drops sharply to the evaporation pressure. At the same time, the liquid refrigerant boils and absorbs heat, and its own temperature decreases.

Evaporator function: the refrigerant absorbs the heat of the cooled medium and is divided into three categories according to the properties of the cooling medium. ■ Evaporator for cooling liquid refrigerant; ■ Evaporator for cooling air; ■ Contact evaporator for cooling frozen materials;

Refrigeration cycle principle: When the refrigerant is in a low-temperature and low-pressure liquid state, it absorbs heat and reaches the boiling point, then evaporates to become a low-temperature and low-pressure steam. The refrigerant that evaporates into gas becomes a high-temperature and high-pressure gas under the action of the compressor. This high-temperature and high-pressure condenses into a high-pressure liquid. The high-pressure liquid passes through the expansion valve and becomes a low-pressure and low-temperature liquid. It absorbs heat and evaporates again to form the refrigeration cycle of the refrigerator.

Vertical cooling pipe: The refrigerant is easy to discharge after vaporization, and the heat transfer effect is good. However, when the pipe is high, the evaporation temperature of the lower refrigerant is higher due to the static pressure of the liquid column.

Single-row coil wall pipe: The amount of refrigerant is small, about 50% of the pipe volume, but the refrigerant will not be discharged from the pipe quickly after vaporization, which reduces the heat transfer effect.

Warp-fin pipe: Large heat dissipation area.

Function of oil separator: Used to separate the lubricating oil carried in the compressed liquid and gas to prevent the lubricating oil from entering the condenser and deteriorating the heat transfer conditions.

The function of the oil collector is to collect the refrigerant and oil mixture separated from the oil separator, condenser and other devices of the refrigeration system, and then separate the oil from the mixed refrigerant under low pressure, and then release them separately, so as to ensure the safety of oil discharge and reduce the loss of refrigerant.

The function of the liquid storage tank is to store and regulate the liquid refrigerant supplied to various parts of the refrigeration system to meet the safe operation of the equipment. The liquid storage tank is divided into high pressure, low pressure, drainage tank and circulating liquid storage tank.

The function of the gas-liquid separator is to separate the refrigerant from the evaporator to prevent the refrigerant liquid from entering the compressor and causing cylinder knocking; to separate the invalid steam carried by the low-pressure ammonia liquid after throttling to improve the heat transfer effect of the evaporator.

The function of the air separator is to separate the non-condensable gas in the discharge system to ensure the normal operation of the refrigeration system.

Function of the intercooler: Installed in a two-stage (or multi-stage) compression refrigeration system, it is used to cool the superheated gas discharged from the low-pressure stage for inter-stage cooling to ensure the normal operation of the high-pressure stage compressor; separate the lubricating oil carried in the low-pressure stage exhaust gas, and cool the refrigerant to obtain a larger degree of subcooling.