1. What is air? What is normal air?
A: The atmosphere around the earth is customarily called air.
The air under the specified pressure of 0.1 Mpa, temperature of 20 ℃ and relative humidity of 36% is normal air. Normal air and standard air are different from temperature and contain water. When there is moisture in the air, once the moisture is separated, the gas volume will be reduced.

2. What is the standard state definition of air?
The definition of standard state is that the air state when the air suction pressure is 0.1MPa and the temperature is 15.6 ℃ (defined by the domestic industry as 0 ℃) is called the standard state of air.
Under the standard state, the air density is 1.185kg/m ³ (The capacity of air compressor, dryer, filter and other post-treatment equipment is marked by the flow rate under the standard air condition, and the unit is Nm ³/ min)。
3. What is saturated air and unsaturated air?
At a certain temperature and pressure, the content of water vapor in the wet air (i.e., the density of water vapor) is limited; When the amount of water vapor at a certain temperature reaches the maximum possible content, the wet air is called saturated air. When the water vapor does not reach the maximum possible content, the wet air is called unsaturated air.
4. Under what conditions does unsaturated air become saturated air? What is condensation?
Liquid droplets will condense out of the wet air, which is called condensation. The exposure phenomenon is common. For example, the air humidity is very high in summer, and it is easy to form water droplets on the surface of the water pipe. In winter morning, water droplets will appear on the windows of the residents. These are all the results of the condensation of wet air when it is cooled to the dew point temperature under constant pressure.
5. What is atmospheric pressure, absolute pressure and gauge pressure? What are the common units of stress?
The pressure caused by a thick layer of atmosphere surrounding the earth's surface on the earth's surface or surface objects is called atmospheric pressure, and the symbol is Pb; The pressure directly acting on the surface of the container or object is called absolute pressure; The absolute pressure value takes the absolute vacuum as the starting point, and the symbol is Pa; The pressure measured by pressure gauge, vacuum gauge, U-shaped tube and other instruments is called gauge pressure. The gauge pressure is based on atmospheric pressure and the symbol is Pg. The relationship between the three is
Pa=Pb+Pg
Pressure refers to the force per unit area. The unit of pressure is N/square, which is recorded as Pa and called Pascal. Commonly used in engineering (Mpa)
1Mpa=10 cubic Pa
1 Standard atmospheric pressure=0.1013Mpa
1kPa=1000Pa=0.01kgf/m2
1Mpa=10 to the sixth power Pa=10.2kgf/square
In the old system of units, pressure is usually expressed in kgf/cm2 (kg/cm2).
6. What is temperature? What are the common temperature units?
Temperature is the statistical average of the thermal motion of material molecules.
Absolute temperature: the temperature starting from the lowest limit temperature when the gas molecule stops moving, recorded as T. The unit is Kelvin, and the unit symbol is K.
Celsius temperature: the temperature starting from the melting point of ice, with the unit of Celsius and the unit symbol of Celsius.
In addition, Fahrenheit temperature is often used in British and American countries, and the unit symbol is F.
The conversion relationship between the three temperature units is
T(K)=t (℃)+273.16
t(F)=32+1.8t(℃)
7. What is the water vapor pressure in wet air?
Wet air is a mixture of water vapor and dry air. In a certain volume of wet air, the proportion of water vapor (by mass) is usually much less than that of dry air, but it occupies the same volume as dry air and has the same temperature. The pressure of wet air is the sum of the partial pressures of the constituent gases (i.e. dry air and water vapor). The pressure of water vapor in wet air is called the partial pressure of water vapor and is recorded as Pso. The value reflects the water vapor content in the wet air. The higher the water vapor content, the higher the water vapor partial pressure. The partial pressure of water vapor in saturated air is called the partial pressure of water vapor saturation, which is recorded as Pab.
8. What is air humidity? How many kinds of humidity are there?
The physical quantity indicating the degree of dryness and wetness of the air is called humidity. Common humidity expressions include absolute humidity and relative humidity.
Under standard conditions, the mass of wet air containing water vapor in 1 cubic volume is called the absolute humidity of wet air, with the unit of g/m3. The absolute humidity only indicates how much water vapor is contained in the unit volume of wet air, but not the ability of wet air to absorb water vapor, that is, the humidity degree of wet air. Absolute humidity is the density of water vapor in wet air.
The ratio of the actual water vapor content in the wet air to the maximum possible water vapor content at the same temperature is called relative humidity, which is commonly used φ To express. relative humidity φ Between 0-100%. Φ The smaller the value, the drier the air and the stronger the water absorption capacity; φ The higher the value, the wetter the air and the weaker the water absorption capacity. The hygroscopic capacity of wet air is also related to its temperature. When the temperature of wet air increases, the saturation pressure increases accordingly. When the content of water vapor remains unchanged, the relative humidity of wet air φ It will decrease, that is to say, the hygroscopic capacity of wet air will increase. Therefore, during the installation of the air compressor room, attention should be paid to maintaining ventilation, reducing temperature, and avoiding indoor drainage and ponding to reduce the moisture in the air.
9. What is moisture content? How to calculate the moisture content?
In wet air, the mass of 1kg dry air containing water vapor is called the moisture content of wet air, usually expressed as d. The moisture content d is almost proportional to the partial pressure of water vapor Pso, and inversely proportional to the total air pressure P. D exactly reflects the amount of water vapor contained in the air. If the atmospheric pressure is constant, when the temperature of wet air is constant, Pso is also constant. At this time, the relative humidity increases, its moisture content increases, and its hygroscopic capacity decreases.
10. What does the density of water vapor in saturated air depend on?
There is a limit to the amount of water vapor in the air (water vapor density). Within the range of pneumatic pressure (2Mpa), it can be considered that the density of water vapor in saturated air depends only on the temperature and has nothing to do with the air pressure. The higher the temperature, the greater the density of saturated water vapor. For example, at 40 ℃, 1 cubic meter of air, whether its pressure is 0.1Mpa or 1.0Mpa, its saturated water vapor density is the same.