Six common refrigeration methods

May 31, 2024

Six common refrigeration methods



01 Steam compression refrigeration


Principle: In a steam compression refrigeration cycle system, the compressor sucks in low-temperature and low-pressure refrigerant steam from the evaporator, which is adiabatic and compressed by the compressor to become high-temperature and high-pressure superheated steam. It is then compressed into the condenser for constant pressure cooling and releases heat to the cooling medium. It is then cooled into a subcooled liquid refrigerant. The liquid refrigerant is adiabatic and throttled by an expansion valve (or capillary) to become a low-pressure liquid refrigerant, which evaporates and absorbs heat from the air conditioning circulating water (air) in the evaporator, thereby cooling the air conditioning circulating water (air) to achieve the purpose of refrigeration. The low-pressure refrigerant that flows out is sucked into the compressor, and thus the cycle works.


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Compressor function:


Compressing refrigerant vapor from low pressure to high pressure creates conditions for refrigerant to liquefy at room temperature in the condenser. Known as the "heart" of the entire device.


Condenser function:


Cool the refrigerant discharged by the compressor with overheated vapor and condense it into refrigerant liquid. The heat of the refrigerant in the condenser is discharged to the cooling medium.


Classification: water-cooled condenser, air-cooled condenser, evaporative condenser.


Air cooled condenser:


Easy to use and install, no need for cooling water, heat is carried into the atmosphere by the unit. However, if the heat transfer coefficient is also low and the weight is relatively large compared to other types, the surface of the fins will accumulate dust, which will reduce the heat dissipation capacity. It is necessary to clean it in a timely manner.


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Evaporator function:


The heat exchange equipment that relies on the evaporation of refrigerant liquid to absorb the heat of the cooling medium, and its task in the refrigeration system is to output cold energy to the outside.


Classification: Full liquid (immersion) evaporator, dry evaporator. Dry evaporator: Immersive coil, shell and tube, plate, spray type, etc.


Throttling device function:


Shutoff and pressure reduction: After the high-pressure and normal temperature refrigerant flows through the expansion valve, it becomes a low-pressure and low-temperature refrigerant liquid.


Control refrigerant flow: The expansion valve controls the opening of the valve by sensing the change in superheat of the refrigerant at the outlet of the evaporator through the temperature sensor, adjusting the refrigerant flow entering the evaporator to match its heat load.


Control of superheat: The expansion valve has the function of controlling the superheat of the refrigerant at the outlet of the evaporator, which maintains the full utilization of the heat transfer area of the evaporator and prevents the occurrence of compressor cylinder flushing accidents.


Classification: Manual throttle valve, thermal expansion valve, capillary, electronic expansion valve, float plate, fixed orifice plate, variable orifice plate.


02 Steam absorption refrigeration


Using refrigerant absorbent as the working fluid is called the absorption working fluid pair. Common working fluid pairs: lithium bromide water (refrigerant is water), ammonia water (refrigerant is ammonia) - low boiling point working fluid is refrigerant.


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The absorption refrigeration device consists of components such as a generator, condenser, evaporator, absorber, circulation pump, throttle valve, etc. The working medium includes refrigerant for producing cooling capacity and absorbent for absorbing and desorbing refrigerant, and the two form a working fluid pair.




Areas with year-round air conditioning that require air conditioning in summer and heating in winter are most suitable for using absorption systems. Quiet operation can minimize wear and tear (except for liquid pump operation), with fewer malfunctions and simple maintenance. Not relying on electricity. Capacity control is easy, only the heat source of the generator needs to be controlled. The system has high security and no explosion. The full load and light load effects of the system are the same. When the load changes, only the generator heat source and water circulation need to be adjusted. When the evaporation temperature and pressure decrease, the absorption capacity only decreases to a limited extent, and the operation is stable.




When using water as the refrigerant, it is not possible to achieve low temperature (water freezing point is 0 ℃). Improper operation can lead to crystallization of lithium bromide.


03 Steam jet refrigeration


Principle: High pressure steam (called working steam) supplied by the boiler enters the main injector and adiabatic expands in the Laval nozzle. This high-speed steam flow is used to continuously extract steam from the evaporator, maintaining a high vacuum, i.e. a low evaporation pressure. The cold water from the refrigeration device enters the evaporator after throttling and depressurization, and a part of it evaporates and absorbs the heat of the remaining water, causing its temperature to decrease. The cooled cold water is pumped out and supplied with cooling capacity for repeated use.



04 Adsorption refrigeration


Principle: A certain solid adsorbent has an adsorption effect on a certain refrigerant gas, and the adsorption capacity varies with the temperature of the adsorbent. By periodically cooling and heating the adsorbent, it is alternately adsorbed and desorbed. During desorption, release refrigerant gas and condense it into a liquid; During adsorption, the refrigerant liquid evaporates, producing a cooling effect.


Classified by adsorption mechanism: physical adsorption refrigeration, chemical adsorption refrigeration.



The basic structure of adsorption refrigeration consists of five modules: solar collector, condenser, liquid storage, evaporator, and valve. The operating mechanism of adsorption refrigeration system is as follows: during the day, the temperature of the collector increases with the increase of temperature, the pressure in the refrigerant evaporation collector increases, and the gas enters the condenser and condenses to form a liquid; At night, as the temperature decreases, the adsorbent will absorb refrigerant vapor, causing a decrease in pressure in the evaporator. As a result, more liquid will vaporize, absorbing heat and cooling during evaporation.
05 Thermoelectric refrigeration
Thermoelectric refrigeration is a refrigeration method that utilizes the thermoelectric effect (i.e. the Peltier effect), also known as thermoelectric refrigeration or semiconductor refrigeration. Principle: Thermoelectric refrigeration is a direct conversion of voltage generated by temperature difference, which refers to the phenomenon of current generation when electrons in the heated object move from the high temperature zone to the low temperature zone with the temperature gradient, and vice versa. When direct current is used, materials with thermoelectric energy conversion characteristics can produce cooling function, which is called thermoelectric refrigeration.
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06 Magnetic refrigeration and acoustic refrigeration


Magnetic refrigeration:


Magnetic refrigeration based on the magnetocaloric effect (MCE) is a promising alternative to traditional steam cycle refrigeration technology. In materials with this effect, the arrangement and randomization of magnetic momentum when an external magnetic field is applied and removed cause temperature changes in the material, which can be transmitted to the ambient air.


Sound refrigeration: Based on the so-called thermoacoustic effect, the mechanism of the thermoacoustic effect can be simply described as adding heat when the sound waves are dense, and discharging heat when the sound waves are sparse, resulting in the enhancement of the sound waves; On the contrary, when sound waves are dense, heat is emitted, and when sound waves are sparse, heat is absorbed, resulting in weakened sound waves. Of course, the actual thermoacoustic theory is much more complex than this.


07 Other refrigeration related knowledge Refrigerant classification:


Inorganic compounds: water, ammonia, carbon dioxide;

Halogenated hydrocarbons: Freons;

Hydrocarbons: methane, ethane, propane;

Mixed refrigerants: azeotropic and non azeotropic;

Other hydrocarbons: ethylene, propylene.

Refrigeration capacity: refers to the total amount of heat removed by a refrigeration equipment from a confined space, room, or area per unit time during the refrigeration operation of the refrigeration machine.


Ozone Decay Index (ODP): Refers to the degree of damage that substances cause to the atmospheric ozone layer. The smaller the value, the better. If ODP=0, it is harmless to the atmospheric ozone layer.


Greenhouse Effect Index (GWP): Refers to the degree of impact of substances on the greenhouse effect. The smaller the value, the better. If GWP=0, it will not cause atmospheric warming.


Energy efficiency level: It is a classification method that represents the difference in energy efficiency between household appliances. According to relevant national standards, China's energy efficiency labeling previously divided energy efficiency into five levels. It is now divided into three levels.


Watt: Symbol: W, the unit of power in the International System of Units. The definition of watt is 1 joule per second (1J/s), which is the rate at which energy is converted, used, or dissipated (measured in joules) per second.


BTU: 1Btu is the amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. 1 BTU is approximately 251.9958 calories/1.055 kilojoules.


Cold ton: The cooling capacity required to freeze 1 ton of 0 ℃ saturated water to 0 ℃ ice within 24 hours. 1 US cold ton=3024 kcal/hour=3.517 kilowatts. 1 Japanese cold ton=3320 kcal/hour=3.861 kilowatts.


Dry bulb temperature: refers to the temperature measured by a thermometer in ordinary air, which is commonly referred to as temperature in weather forecasts.


Wet bulb temperature: refers to the air temperature at which water vapor in the air reaches saturation under the same enthalpy value of air. On the air enthalpy humidity chart, it is the dry bulb temperature at the corresponding point, which decreases from the air state point along the isoenthalpy line to the 100% relative humidity line.


Harm of air: It may be due to the oxidation and blackening of the refrigeration oil, which generates oil stains and reacts with the refrigerant, precipitating water and acid, and corroding the refrigeration system. Air can also increase the condensation pressure, temperature, and pressure, leading to a decrease in refrigeration capacity and a decrease in refrigeration efficiency.


Harm of moisture: During operation, due to the decrease in outlet temperature of the throttling device, water condenses, causing ice blockage and preventing the system from working. Moisture can also react with refrigerants, causing adverse effects.


Harm of impurities: Impurities include dust, metals, and metal oxides, which can cause dirt blockage and mechanical circuit failures. At the same time, oxides can promote the decomposition of Freon.


In summary, by increasing the vacuum degree of the refrigeration system, the above parts will be reduced to a certain extent, making the refrigeration system work according to the design requirements.





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