Mass, volume, specific volume Mass is the weight of gas, often expressed in milligrams (mg), grams (g), kilograms (kg), and tons (t). Volume refers to the volume of the container in which the gas is located. It is often expressed in cubic millimeters (mm3), cubic centimeters (cm3), and cubic meters (m3). The specific volume is the volume occupied by the substance per unit weight, which is represented by the symbol V, the specific volume of gas is represented by m?/kg, and the specific volume of liquid is represented by l/kg. Pressure, pressure, atmospheric pressure, absolute pressure, relative pressure The force generated by the impact of gas molecules on the container wall when they are in motion is called pressure. The pressure generated per unit area of ​​the container is called pressure. The unit of pressure is customarily used millimeter mercury (mmHg)/square centimeter (cm2), internationally accepted (legal measurement) Pa (Pa), kilopascal (kPa), megapascal (MPa). After conversion, 1mmHg=133.3Pa=0.1333kPa, 1MPa=1000kPa=1000000Pao1ATA=0. 1MPao. The pressure caused by the thick atmosphere surrounding the surface of the earth on the surface of the earth or surface objects is called "atmospheric pressure", symbol B; the pressure directly acting on the surface of the container or object is called "absolute pressure", absolute pressure value Take absolute vacuum as the starting point, and the symbol is PABS. The pressure measured by pressure gauges, vacuum gauges, U-tubes and other instruments is called "gauge pressure" (also called relative pressure). The "gauge pressure" starts from atmospheric pressure and the symbol is Pg. The relationship between the three is: PABS==B+Pg. Temperature, absolute temperature, relative temperature, critical temperature, and critical pressure temperature are the statistical averages of the thermal motion of the material molecules. The temperature of a gas is caused by the thermal movement of gas molecules. The unit of gas temperature is usually expressed in Celsius (°C), and the temperature at which water freezes is 0°C. Absolute temperature is often used in physics, represented by "K". The absolute temperature is -273°C as zero. The relationship between Celsius and absolute temperature is T=t+273. In addition, British scientists often use "Fahrenheit temperature" with the symbol ?F. Because any gas can be liquefied at a certain temperature and pressure, the higher the temperature, the higher the pressure required for liquefaction, but when the temperature exceeds a certain value, the pressure cannot be liquefied even if the pressure is increased. This temperature is called the critical temperature , The lowest pressure at this temperature is called the critical pressure. Dew point, vaporization, and condensation refer to the temperature at which the water in the gas turns from unsaturated water vapor to saturated water vapor. When unsaturated water vapor becomes saturated water vapor, very fine dewdrops appear. The temperature at which dewdrops appear is called "Dew Point". The dew point is related to the pressure, so there are also the atmospheric pressure dew point (normal pressure dew point) and the dew point under pressure. Atmospheric dew point refers to the condensation temperature of moisture under atmospheric pressure, and dew point under pressure refers to the condensation temperature of moisture under that pressure. There is a conversion relationship between the two (check the conversion table). For example, the pressure dew point is 5 when the pressure is 0.7Mpa. ℃, the corresponding atmospheric pressure (0.101Mpa) dew point is -20℃. In the gas industry, unless otherwise specified, the dew point referred to is the atmospheric pressure dew point. Vaporization refers to the process of changing a substance from a liquid to a gas, which includes evaporation and boiling. Condensation refers to the process by which a gas becomes a liquid. Purity Purity is an important technical parameter of gas. Take nitrogen as an example. According to the national standard nitrogen purity is divided into three levels: industrial nitrogen, pure nitrogen and high-purity nitrogen. Their purity is 99.5% (O2 less than or equal to 0.5%), 99.99% (O2 less than or equal to 0.01%) and 99.99% (O2 is less than or equal to 0. 001%). Flow rate, volume flow rate, and mass flow rate The flow rate refers to the amount of gas that passes through any cross section in a unit time during the gas flow. There are two ways to express flow, namely volume flow and mass flow. The former refers to the volume of gas passing through any section of the pipeline, and the latter refers to the quality of the gas passing. In the gas industry, the volume flow is generally measured in m?/h (or L/H). Because the gas volume is related to temperature, pressure and humidity, in order to facilitate comparison, the volume flow rate usually refers to the standard state (temperature is 20℃, pressure is 0.101Mpa, relative humidity is 65%), and the flow rate at this time is in Nm ?/h is the unit, "N" means the standard state. Compressed air Air is compressible. The air that has been reduced in volume and increased in pressure by the mechanical work of the air compressor is called compressed air. Compressed air contains many impurities: 1. Water, including water mist, water vapor, and condensed water; 2. Oil: including oil stains and oil vapor; 3. Various solid substances such as rust mud, metal powder, rubber powder, and tar particles And filter materials, fines of sealing materials, etc.; in addition, there are a variety of harmful chemical odor substances, etc. Compressed air can be pressurized, cooled, adsorbed and other methods to remove water vapor. Liquid water can be removed by heating, filtering, mechanical separation and other methods. Adsorption and membrane permeation adsorption are the selective concentration of one or more components in the gas on the surface of the porous solid. The adsorbed component is called the adsorption medium, and the porous solid is called the adsorbent. The connection force between the adsorbent and the adsorption medium is a chemical bond, and the analysis of the adsorption medium depends on increasing the temperature or reducing the partial pressure of the component in the atmospheric pressure. Another situation is when the adsorbed component and the solid adsorbent dechemically react, it is called chemical adsorption, and chemical adsorption cannot be regenerated under normal circumstances. Membrane permeation refers to the separation of gas from polymer in the gas purification process based on the selective permeation of one or more gas components from one side of the membrane to the other. The component dissolves on the surface of the polymer film and travels along the film to form a concentration difference. The concentration difference is maintained because the partial pressure of the component on one side of the membrane is higher than the partial pressure of the component on the other side of the membrane. Various solid substances such as: rust mud, metal powder, rubber powder, tar particles and filter materials, fines of sealing materials, etc.; in addition, there are a variety of harmful chemical odor substances. Compressed air can be pressurized, cooled, adsorbed and other methods to remove water vapor. Liquid water can be removed by heating, filtering, mechanical separation and other methods. Adsorption and membrane permeation adsorption are the selective concentration of one or more components in the gas on the surface of the porous solid. The adsorbed component is called the adsorption medium, and the porous solid is called the adsorbent. The connection force between the adsorbent and the adsorption medium is a chemical bond, and the analysis of the adsorption medium depends on increasing the temperature or reducing the partial pressure of the component in the atmospheric pressure. Another situation is when the adsorbed component and the solid adsorbent dechemically react, it is called chemical adsorption, and chemical adsorption cannot be regenerated under normal circumstances. Membrane permeation refers to the separation of gas from polymer in the gas purification process based on the selective permeation of one or more gas components from one side of the membrane to the other. The component dissolves on the surface of the polymer film and travels along the film to form a concentration difference. The concentration difference is maintained because the partial pressure of the component on one side of the membrane is higher than the partial pressure of the component on the other side of the membrane. Various solid substances such as: rust mud, metal powder, rubber powder, tar particles and filter materials, fines of sealing materials, etc.; in addition, there are a variety of harmful chemical odor substances. Compressed air can be pressurized, cooled, adsorbed and other methods to remove water vapor. Liquid water can be removed by heating, filtering, mechanical separation and other methods. Adsorption and membrane permeation adsorption are the selective concentration of one or more components in the gas on the surface of the porous solid. The adsorbed component is called the adsorption medium, and the porous solid is called the adsorbent. The connection force between the adsorbent and the adsorption medium is a chemical bond, and the analysis of the adsorption medium depends on increasing the temperature or reducing the partial pressure of the component in the atmospheric pressure. Another situation is when the adsorbed component and the solid adsorbent dechemically react, it is called chemical adsorption, and chemical adsorption cannot be regenerated under normal circumstances. Membrane permeation refers to the separation of gas from polymer in the gas purification process based on the selective permeation of one or more gas components from one side of the membrane to the other. The component dissolves on the surface of the polymer film and travels along the film to form a concentration difference. The concentration difference is maintained because the partial pressure of the component on one side of the membrane is higher than the partial pressure of the component on the other side of the membrane.