What are the cooling methods you know Let's all talk!
1.Vapor compression refrigeration
Principle: In the vapor compression refrigeration cycle system, the compressor sucks in low-temperature and low-pressure refrigerant vapor from the evaporator, is adiabaticly compressed by the compressor to become high-temperature and high-pressure superheated vapor, then presses it into the condenser for constant pressure cooling, and releases it to the cooling medium The heat is then cooled into a supercooled liquid refrigerant. The liquid refrigerant is adiabatically throttled by an expansion valve (or capillary) to become a low-pressure liquid refrigerant, which evaporates in the evaporator and absorbs the heat in the air conditioning circulating water (air), thereby cooling the air conditioning cycle The water (air) achieves the purpose of refrigeration, and the low-pressure refrigerant flowing out is sucked into the compressor and works in this way.
Compressor function:
The refrigerant vapor is compressed from a low pressure state to a high pressure state, creating conditions for the refrigerant to liquefy at room temperature in the condenser. It is called the "heart" of the entire device.
Condenser function:
The superheated vapor of the refrigerant discharged from the compressor is cooled and condensed 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 cooling water or heat is needed to bring it into the atmosphere by the extension. However, the heat transfer coefficient is also low, and the weight is relatively large compared to other types. The surface of the fin will accumulate dust and the heat dissipation capacity will be reduced, so it must be cleaned in time.
Evaporator function:
The heat exchange equipment 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 cold energy to the outside.
Classification: flooded (immersed) evaporator, dry evaporator. Dry evaporator: immersed coil, shell and tube, plate, spray, etc.
Throttle device function:
Cut-off and pressure reduction: After the high-pressure and normal-temperature refrigerant flows through the expansion valve, it becomes a low-pressure, low-temperature refrigerant liquid.
Control refrigerant flow: The expansion valve controls the opening of the valve by sensing the change of refrigerant superheat at the outlet of the evaporator through the temperature sensing bulb, and adjusts the refrigerant flow into the evaporator to match the flow with the heat load of the evaporator.
Control the degree of superheat: The expansion valve has the function of controlling the degree of superheat of the refrigerant at the outlet of the evaporator, that is, to keep the heat transfer area of the evaporator fully utilized, and to prevent the occurrence of accidents of compressor flushing.
Classification: manual throttle valve, thermal expansion valve, capillary tube, electronic expansion valve, floating ball plate, fixed orifice plate, variable orifice plate.
2. Steam absorption refrigeration
The refrigerant-absorbent is used as the working fluid, which is called the absorption working fluid pair.
Common working fluid pair: lithium bromide-water (refrigerant is water), ammonia-water (refrigerant is ammonia)-low boiling point working fluid is refrigerant.
Device: The absorption refrigeration device is composed of generators, condensers, evaporators, absorbers, circulating pumps, throttle valves and other components. The working medium includes the refrigerant for producing cold capacity and the absorbent for absorbing and desorbing the refrigerant. The person constitutes a working fluid pair.
advantages:
In the year-round air-conditioning area where air conditioning is required in summer and heating is required in winter, absorption systems are most suitable.
Quiet operation, can reduce wear to a minimum (except for liquid pump operation), fewer failures, and simple maintenance. Does not rely on electricity. The capacity is easy to control, only the heat source of the generator needs to be controlled. The system has high security and no explosion. The effect of full load and light load of the system is the same. When the load changes, only the heat source and water circulation of the generator need to be adjusted. When the evaporation temperature and pressure decrease, the absorption capacity is only reduced to a limited extent, and the operation is stable.
Disadvantages:
When water is used as the refrigerant, low temperature cannot be obtained (water freezing point is 0°C). Improper operation can easily crystallize lithium bromide.
Three, steam jet refrigeration
Principle: The higher-pressure water vapor (called working steam) supplied by the boiler enters the main ejector and expands adiabaticly in the Laval nozzle. This high-speed steam flow is used to continuously extract steam from the evaporator and keep it relatively high. High vacuum means lower evaporation pressure. The cold water from the refrigeration device enters the evaporator after being throttled and decompressed. A part of it evaporates and absorbs the heat of the remaining water to lower its temperature. The cooled cold
Four, 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, the refrigerant gas is released and condensed into liquid; during adsorption, the refrigerant liquid evaporates to produce refrigeration.
Classified by adsorption mechanism: physical adsorption refrigeration, chemical adsorption refrigeration.
Principle: The basic structure of adsorption refrigeration is composed of five modules: solar collector, condenser, accumulator, evaporator and valve. The operation mechanism of the adsorption refrigeration system is: in the daytime, the temperature of the collector rises with the increase in air temperature, the pressure in the refrigerant evaporation collector rises, and the gas enters the condenser and condenses into a liquid; at night , The temperature decreases, the adsorbent will absorb the refrigerant vapor, the pressure in the evaporator will decrease, so more liquid will vaporize, and the heat will be absorbed during evaporation to cool down.
5. Thermoelectric cooling
Thermoelectric refrigeration is a refrigeration method that uses the thermoelectric effect (ie Peltier effect)-also known as thermoelectric refrigeration and semiconductor refrigeration.
Principle: Thermoelectric refrigeration is a direct conversion of voltage generated by temperature difference. It means that when the electrons in the heated object move from the high temperature area to the low temperature area with the temperature gradient, a current phenomenon is generated, and vice versa. When passing direct current, Materials with thermoelectric energy conversion properties can produce refrigeration function, which is called thermoelectric refrigeration.
Six, magnetic refrigeration, acoustic refrigeration
Magnetic refrigeration: Magnetic refrigeration based on the "magnetocaloric effect" (MCE) is a promising alternative to the traditional vapor cycle refrigeration technology. In materials with this effect, the arrangement and randomization of the magnetic momentum when an external magnetic field is applied and removed causes a temperature change in the material, which can be transmitted to the ambient air.
Acoustic cooling: 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 dissipating heat when the sound wave is sparse, then the sound wave is strengthened; conversely, the heat is discharged when the sound wave is dense, and inhaled when the sound wave is sparse Heat, the sound waves are weakened. Of course, the actual thermoacoustic theory is much more complicated than this.
Seven, other refrigeration related knowledge
Refrigerant classification:
Inorganic compounds: water, ammonia, carbon dioxide;
Halogenated hydrocarbon: Freon;
Hydrocarbons: methane, ethane, propane;
Mixed refrigerants: public boiling and non-azeotropic;
Other hydrocarbons: ethylene, propylene.
Refrigeration capacity: refers to the total amount of heat removed from a confined space, room or area per unit time when the refrigeration equipment is in refrigeration operation.
Ozone Attenuation Index ODP: Indicates the degree of destruction of the atmospheric ozone layer by a substance. The smaller the better, ODP=0 is harmless to the atmospheric ozone layer.
Greenhouse Effect Index GWP: indicates the degree of influence of a substance on the greenhouse effect. The smaller the better, GWP=0 will not cause atmospheric warming.
Energy efficiency rating: It means that the energy efficiency rating is a classification method that indicates the difference in energy efficiency of household appliances. According to the relevant regulations of national standards, the energy efficiency label in my country previously divided energy efficiency into five levels. There are now three levels.
Watt: Symbol: W, the power unit of the International System of Units. Watt is defined as 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 heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. 1 BTU is approximately equal to 251.9958 calories/1.055 kJ.
cold ton: the cooling capacity required for 1 ton of saturated water at 0°C to be frozen to ice at 0°C in 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: It is the temperature measured by a thermometer in ordinary air, that is, the temperature we often say in general weather forecasts.
Wet bulb temperature: refers to the air temperature when the water vapor in the air reaches saturation under the same enthalpy value. On the air enthalpy and humidity chart, the air state point drops along the isenthalpy line to the 100% relative humidity line, corresponding to the point Dry bulb temperature.
Air hazards: it may be that the refrigerating machine oil is oxidized and blackened, generating oil stains, and reacting with the refrigerant, separating out water and acid, and corroding the refrigeration system. Air will also increase the temperature and pressure of the condensing pressure, decrease the cooling capacity, and reduce the cooling efficiency
Moisture hazard: During operation, the temperature of the throttling device is reduced, which will cause moisture to condense and cause ice blockage, making the system unable to work. Moisture can also react with the refrigerant and cause adverse effects.
The hazards of impurities: Impurities include dust, metals and metal oxides, etc. These impurities can cause dirty blockage and mechanical circuit failure. At the same time, the oxide can promote the decomposition of freon.
To sum up, by increasing the vacuum of the refrigeration system, the above parts will be reduced to a certain extent, so that the refrigeration system can work according to the design requirements
