Six Common Refrigeration Methods

01 Principle of Vapor Compression Refrigeration: In the vapor compression refrigeration cycle system, the compressor sucks in the low-temperature and low-pressure refrigerant vapor from the evaporator. After adiabatic compression by the compressor, it becomes high-temperature and high-pressure superheated vapor, which is then pressed into the condenser for constant-pressure cooling. Heat is released to the cooling medium, and then it is cooled into a subcooled liquid refrigerant. The liquid refrigerant undergoes adiabatic throttling through the expansion valve (or capillary tube) to become a low-pressure liquid refrigerant. It evaporates in the evaporator and absorbs the heat in the air conditioning circulating water (air), thus cooling the air conditioning circulating water (air) to achieve the purpose of refrigeration. The low-pressure refrigerant flowing out is sucked into the compressor, and the cycle repeats.
Function of the Compressor:
It compresses the refrigerant vapor from a low-pressure state to a high-pressure state, creating the conditions for the refrigerant to liquefy at room temperature in the condenser. It is called the "heart" of the entire device.
Function of the Condenser:
It cools the superheated vapor of the refrigerant discharged by the compressor and condenses it into a 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:
It is convenient to use and install, does not require cooling water, and the heat is carried into the atmosphere by the fan. However, it also has a low heat transfer coefficient, is relatively heavier than other types. Dust will accumulate on the surface of the fins, reducing the heat dissipation capacity, and it must be cleaned in a timely manner.
Function of the Evaporator:
It is a heat exchange device that relies on the evaporation of the refrigerant liquid to absorb the heat of the cooling medium. Its task in the refrigeration system is to output cooling capacity externally.
Classification: Full liquid (immersion) evaporator, dry evaporator. Dry evaporator: Immersed serpentine tube, shell and tube type, plate type, spray type, etc.
Function of the Throttling Device:
Throttling 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.
Controlling the Refrigerant Flow Rate: The expansion valve senses the change in the superheat degree of the refrigerant at the outlet of the evaporator through the temperature sensing bulb to control the opening degree of the valve, adjusting the refrigerant flow rate entering the evaporator to match the flow rate with the heat load of the evaporator.
Controlling the Superheat Degree: The expansion valve has the function of controlling the superheat degree of the refrigerant at the outlet of the evaporator, that is, maintaining the full utilization of the heat transfer area of the evaporator and preventing the occurrence of compressor cylinder-punching accidents.
Classification: Manual throttle valve, thermal expansion valve, capillary tube, electronic expansion valve, float plate, fixed orifice plate, variable orifice plate.
02 Vapor Absorption Refrigeration uses a refrigerant-absorbent as the working fluid, which is called the absorbent working fluid pair. Commonly used working fluid pairs: Lithium bromide-water (the refrigerant is water), ammonia-water (the refrigerant is ammonia) - the low-boiling-point working fluid is the refrigerant.
Device: The absorption refrigeration device is composed of components such as a generator, condenser, evaporator, absorber, circulation pump, and throttle valve. The working media include the refrigerant for producing cooling capacity and the absorbent for absorbing and desorbing the refrigerant, and the two form a working fluid pair.
Advantages:
In all-weather air conditioning areas where cooling is required in summer and heating is required in winter, the absorption system is most suitable. It operates quietly, minimizing wear (except for the operation of the liquid pump), has fewer failures, and is simple to maintain. It does not rely on electricity. Capacity control is easy, and only the heat source of the generator needs to be controlled. The system has high safety and no risk of explosion. The system has the same effect under full load and light load. When the load changes, only the heat source of the generator and the water circulation volume 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.
Disadvantages:
When water is used as the refrigerant, a low temperature cannot be obtained (the freezing point of water is 0°C). When operated improperly, lithium bromide is prone to crystallization.
03 Principle of Vapor Jet Refrigeration: The relatively high-pressure water vapor (called working steam) supplied by the boiler enters the main ejector. It undergoes adiabatic expansion in the Laval nozzle. Using this high-speed steam flow, it continuously extracts steam from the evaporator, maintaining a relatively high vacuum, that is, a relatively low evaporation pressure. The cold water from the refrigeration device enters the evaporator after throttling and pressure reduction. Part of it evaporates and absorbs the heat of the remaining water, reducing its temperature. The cooled cold water is output by the pump and reused after supplying the cooling capacity.
04 Principle of Adsorption Refrigeration: A certain solid adsorbent has an adsorption effect on a certain refrigerant gas, and the adsorption capacity varies with the change of the adsorbent temperature. By periodically cooling and heating the adsorbent, it alternately adsorbs and desorbs. During desorption, the refrigerant gas is released and condensed into a liquid; during adsorption, the refrigerant liquid evaporates, producing a refrigeration effect.
Classification According to the Adsorption Mechanism: Physical adsorption refrigeration, chemical adsorption refrigeration.
Principle: The basic structure of adsorption refrigeration consists of five modules: a solar collector, a condenser, a liquid receiver, an evaporator, and a valve. The operation mechanism of the adsorption refrigeration system is as follows: During the day, the temperature of the collector rises with the increase in the air temperature. The refrigerant evaporates, and the pressure in the collector rises. The gas enters the condenser and is condensed into a liquid; at night, the temperature drops, the adsorbent will absorb the refrigerant vapor, the pressure in the evaporator decreases, and more liquid will vaporize, absorbing heat during evaporation and reducing the temperature.
05 Thermoelectric Refrigeration: Thermoelectric refrigeration is a refrigeration method using 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 a temperature difference. It means that when the electrons in a heated object move from the high-temperature region to the low-temperature region along the temperature gradient, a current phenomenon occurs. Conversely, when direct current is passed through, materials with thermoelectric energy conversion characteristics can produce a refrigeration function, which is called thermoelectric refrigeration.
06 Magnetic Refrigeration and Acoustic Refrigeration: Magnetic Refrigeration: Based on the "magnetocaloric effect" (MCE), magnetic refrigeration is a promising alternative to traditional vapor cycle refrigeration technology. In materials with this effect, the alignment and randomization of magnetic moments when an external magnetic field is applied and removed cause a change in the temperature of the material, and this change can be transferred to the ambient air.
Acoustic Refrigeration: Based on the so-called thermoacoustic effect, the mechanism of the thermoacoustic effect can be simply described as adding heat when the sound wave is dense and discharging heat when the sound wave is sparse, then the sound wave is strengthened; conversely, discharging heat when the sound wave is dense and inhaling heat when the sound wave is sparse, then the sound wave is weakened. 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;
Halocarbons: Freon;
Hydrocarbons: Methane, ethane, propane;
Blended Refrigerants: Azeotropic and non-azeotropic;
Other Hydrocarbons: Ethylene, propylene.
Refrigeration Capacity: It refers to the total amount of heat removed per unit time from a closed space, room, or area when the refrigeration equipment is operating for refrigeration.
Ozone Depletion Potential (ODP): It indicates the degree of damage of a substance to the atmospheric ozone layer. The smaller the better. When ODP = 0, it is harmless to the atmospheric ozone layer.
Global Warming Potential (GWP): It indicates the degree of influence of a substance on the greenhouse effect. The smaller the better. When GWP = 0, it will not cause global warming.
Energy Efficiency Rating: It is a classification method indicating the difference in the energy efficiency of household electrical appliances. According to the relevant national standards, the energy efficiency label in China previously divided the energy efficiency into five grades. Now it is divided into three grades.
Watt: Symbol: W, the power unit of the International System of Units. The definition of a watt is 1 joule per second (1J/s), that is, the rate of energy (measured in joules) converted, used, or dissipated per second.
BTU: 1Btu is the amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. 1BTU is approximately equal to 251.9958 calories/1.055 kilojoules.
Refrigeration Ton: The refrigeration capacity required to freeze 1 ton of saturated water at 0°C into ice at 0°C within 24 hours. 1 US refrigeration ton = 3024 kcal/hour = 3.517 kilowatts. 1 Japanese refrigeration ton = 3320 kcal/hour = 3.861 kilowatts.

Dry-bulb Temperature: It is the temperature measured by a thermometer in ordinary air, that is, the air temperature often mentioned in general weather forecasts.
Wet-bulb Temperature: It refers to the air temperature when the water vapor in the air reaches saturation under the condition of the same enthalpy value. On the psychrometric chart, it is the dry-bulb temperature corresponding to the point obtained by moving down along the constant enthalpy line from the air state point to the 100% relative humidity line.

Harm of Air: It may cause the refrigeration oil to oxidize and turn black, generating oil stains, and reacting with the refrigerant to precipitate water and acid, corroding the refrigeration system. Air will also increase the condensation pressure, temperature, and pressure, reduce the refrigeration capacity, and decrease the refrigeration efficiency.
Harm of Moisture: During operation, due to the decrease in temperature at the throttling device, moisture condenses, causing ice blockage, and the system cannot operate. Moisture will also react with the refrigerant, causing adverse effects.
Harm of Impurities: Impurities include dust, metals, and metal oxides, etc. These impurities can lead to dirt blockage and mechanical and electrical circuit failures. At the same time, oxides can promote the decomposition of Freon.
In conclusion: By improving the vacuum degree of the refrigeration system, the above problems can be reduced to a certain extent, enabling the refrigeration system to operate according to the design requirements.