1. Compressed media
Why use air as the compression medium? Because the air is compressible, clear and transparent, and it is convenient to transport (non-condensing), harmless, safe and inexhaustible. Inert gas is a kind of gas that has no chemical effect on the environment. Standard compressors can compress inert gas as well. Both dry nitrogen and carbon dioxide are inert gases.
Nature of air: Dry air Composition: Nitrogen (N2) 78.08% Oxygen (O2) 20.93% Carbon dioxide (CO2) 0.03% Density: At 0 ° C, 760mmHg column, R0 = 1.293kg / m3
Second, "level" and "paragraph"
In the positive displacement compressor, after each compression of the working chamber, the gas enters the cooler for cooling, which becomes a "stage". In power compressors, the compressor usually enters the cooler for cooling after two or more impeller compressions. The several compression "stages" for each cooling are collectively called a "section".
In Japan, the "stage" of the positive displacement compressor is called "segment". Affected by this in some regions and individual documents in our country, the "stage" is also called "segment".
The pressure in the compressor industry refers to the pressure (P)
The force acting on 1N on the area is 1Pa, that is, 1Pa = 1N / ㎡, Pa is the basic unit of pressure. When the pressure value is large, kPa (1kPa = 1000Pa) and MPa (1MPa = 1000000Pa) are available.
Ⅰ Standard atmospheric pressure (atm)
ⅡGage pressure and absolute pressure
①The pressure measured with a pressure gauge is the gauge pressure, which is the difference between the pressure in the container and the local atmospheric pressure, and is the pressure measured at the zero point of atmospheric pressure, expressed as P (G).
②The pressure with absolute vacuum as the zero point is called absolute pressure, which is the sum of the pressure in the container and the local atmospheric pressure, and is expressed by P (A). The relationship between gauge pressure and absolute pressure: gauge pressure + atmospheric pressure = absolute pressure
The discharge pressure usually given on the compressor nameplate is the gauge pressure.
Suction and discharge pressure refers to the pressure of suction and discharge of air compressor
The gas pressure measured at the intake flange of the first-stage cylinder working chamber of the compressor and the exhaust flange of the last-stage cylinder working chamber is called the compressor suction and discharge pressure.
In some cases, the discharge pressure of the compressor is also called "back pressure". The suction and discharge pressure of the screw air compressor refers to the suction and discharge pressure of the entire air compressor. Generally speaking, the working pressure of the air compressor refers to Is the exhaust pressure.
Ⅵ Commonly used pressure unit conversion for air compressor
1MPa (Mpa) = 1000kPa (kPa) = 1000000Pa (Pascal)
1bar (bar) = 0.1MPa
1atm (standard atmospheric pressure) = 0.1013MPa = 1.013bar = 760mmHg = 10.33mH2O
1kgf / cm2 (engineering kilogram force) = 0.981bar = 0.0981Mpa
1psi (Lb / in2) = 0.07031kgf / cm2 = 0.06893 bar = 6.893kpa
1MPa = 145psi
Psi (lb / in2) pounds per square inch, commonly used in product parameters of countries in English-speaking countries such as Europe and the United States, usually said "kg" in the air compressor industry refers to "bar".
ⅠIsothermal compression: A compression method in which the temperature is always kept constant when the gas is compressed.
II adiabatic compression: a compression method in an adiabatic state that neither heats nor removes heat from the outside.
Ⅲ Multilateral curve compression (actually used compression method): It is a compression method that dissipates part of the generated heat, has heat exchange with the outside, and is different from isothermal compression and adiabatic compression.
Five, compression ratio (pressure ratio, pressure ratio)
ⅠInternal compression ratio (ie internal pressure ratio)
The ratio of the final pressure (absolute pressure) of the gas after internal compression to the initial pressure (absolute pressure).
ⅡExternal compression ratio (ie external pressure ratio)
The ratio of the compressor's outlet discharge pressure (absolute pressure) to the inlet suction pressure (absolute pressure). For screw air compressors, the internal compression ratio refers to the pressure ratio (absolute pressure) of the suction and exhaust ports of the screw host, and the external compression ratio refers to the pressure ratio (absolute pressure) of the air compressor suction and exhaust ports. .
Generally speaking, the compression ratio of an air compressor refers to the external compression ratio, the suction pressure refers to the local atmospheric pressure, and the exhaust pressure refers to the rated working pressure of the air compressor. For example, the air compressor has an exhaust pressure of 8 bar, then The compression ratio is 9.
For multi-stage compressors, the pressure ratio is also called the total pressure ratio, which refers to the ratio of the exhaust pressure measured at the last-stage exhaust pipe connection to the intake pressure measured at the first-stage intake pipe connection. The ratio of the nominal suction and discharge pressures of the corresponding levels is called the pressure ratio of the levels.
Six, volume flow
Volumetric flow is also called exhaust volume or nameplate flow in China. Generally speaking, under the required exhaust pressure, the volume of gas discharged by the air compressor per unit time is converted to the intake state, that is, the suction pressure at the first stage intake nozzle and the suction temperature and humidity Volume value. That is the volume of inhalation. According to the national standard, the actual displacement of the air compressor is ± 5% of the nominal flow rate.
If the speed does not change, the pressure change does not affect the displacement in theory, specifically, it affects the volumetric flow rate and does not affect the mass flow rate. Because we generally refer to the exhaust volume as the intake air flow, there is no change.
Seven, gas oil content
Ⅰ. The mass of oil (including oil droplets, suspended particles, oil vapor) contained in the unit volume of compressed air is converted to the value under atmospheric conditions of pressure 0.1MPa, temperature 20 ℃ and relative humidity 65%. Unit: mg / m3
Ⅱ, PPM A symbol indicating the content of trace substances in a mixture, referring to parts per million or parts per million (parts weight ratio PPMw and volume ratio PPMv). (Refer to the ratio) Usually we call PPM by weight. (Parts per million of 1kg are milligrams) 1PPMw = 1.2mg / m3 (PA = 0.1MPa, t = 20 ℃, φ = 65%) The oil content of exhaust gas of the general oil-injected screw air compressor is below 5PPM, but The exhaust gas of the centrifuge and oil-free machine is oil-free. Taking into account the oil particles originally contained in the air, it is absolutely impossible to achieve 100%.
8. Dew point unit ℃ (degree Celsius)
Humid air is cooled under equal pressure, so that the unsaturated water vapor originally contained in the air becomes the temperature of the saturated water vapor, or when the temperature of the air decreases to a certain temperature, the unsaturated water vapor originally contained in the air becomes The saturation state is reached (that is, the water vapor starts to liquefy and liquid condenses out), and this temperature is the dew point temperature of the gas.
Pressure dew point means that a gas with a certain pressure is cooled to a certain temperature, and the unsaturated steam contained in it becomes saturated water vapor. This temperature is the pressure dew point of the gas.
Atmospheric dew point refers to the temperature at which the gas is cooled to the temperature at which the contained unsaturated water vapor becomes saturated water vapor at standard atmospheric pressure. In the air compressor industry, the dew point indicates the dryness of the gas.
Ⅰ, temperature. Temperature refers to a method of measuring the energy level of a substance at a certain time. (Or more simply, how hot or cold a thing is). The temperature range is based on the freezing point and boiling point of water.
On the Celsius thermometer, the freezing point of water is zero degrees and the boiling point is 100 degrees. On a Fahrenheit thermometer, the freezing point of water is 32 degrees and the boiling point is 212 degrees.
Is measured vertically upwards from sea level, and altitude is simply the height above sea level. Elevation is an important factor in compressor engineering, because the higher the altitude, the thinner the air becomes, and the lower the absolute pressure becomes.
Since the air at high altitude is relatively thin, the cooling effect of the motor is relatively poor, which makes the standard motor only limited to a certain altitude.
11. Working conditions.
The state parameters of the inlet and exhaust pressure and inlet temperature where the compressor is running are called the "operating conditions" of the compressor, and the parameter conditions marked on the nameplate of the compressor are called "rated operating conditions" and deviate from the "rated operating conditions". It is called "variable operating conditions".
Twelve, specific power
Refers to the power consumed by the compressor per unit volume flow. It is an important indicator for evaluating the energy efficiency of compressors. (Compress the same gas at the same discharge pressure)
Thirteen, protection level
Is a value indicating the degree of sealing of electrical equipment such as dustproof, anti-foreign body, waterproof, etc., expressed by IPxx (xx is two Arabic numerals):
14. Explosion-proof grade
When explosive gas, steam, liquid, flammable dust, etc. may cause fire or explosion hazards, the explosion-proof requirements must be set for the actuator, and the explosion-proof form and category should be selected according to different application areas. The explosion-proof grade can be indicated by the explosion-proof mark EX and explosion-proof content. The contents of the explosion-proof mark include: explosion-proof type + equipment category + (gas group) + temperature group.
Fifteen, electrical and other terms
Ⅰ 、 Power
Ⅱ 、 Current
Ⅲ 、 Voltage
Ⅳ 、 Phase
Ⅵ, frequency conversion. That is, change the frequency. In the application of air compressors, the frequency of the motor is changed by changing the frequency of the power supply, so as to achieve the purpose of adjusting the flow rate. Since the flow rate can be adjusted to 0.1 bar by frequency conversion, the useless power is greatly reduced to achieve the purpose of energy saving. The frequency converter is to achieve the purpose of energy saving through this principle.
Ⅷ, direct connection. Direct coupling, in the air compressor industry, refers to coupling with a coupling.
Ⅸ, load / unload. The working state of the air compressor generally refers to the complete suction and exhaust process of the air compressor is the loading state, otherwise the unloading state
Ⅹ. Air cooling / water cooling refers to the cooling method
Ⅺ, noise; unit: dB (A) (decibels)