mixed gas

Gases with more than two components exceeding the specification

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Gas mixture refers to a gas mixture containing two or more effective components, or a non effective component whose content exceeds the specified limit Gas 。

Chinese name: mixed gas
Foreign name: gas mixture
Interpretation: Gases with more than two components exceeding the specification

Purpose: Working medium commonly used in engineering
Research law: Dalton's law of partial pressure
Component classification: volume component quality component mole component

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one definition
two component
three testing
four case

definition

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The mixture of several gases is a common working medium in engineering. The gas mixture is usually treated as ideal gas Research.^[1]

Dalton's law of partial pressure The total pressure p of the gas mixture is equal to the gas composition Partial pressure The sum of. The partial pressure of each component gas is the pressure that the component gas has when it occupies the total volume of the gas mixture alone at the temperature of the gas mixture. The mathematical expression of this law is

p=p one +p two +…=∑p i

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The nature of the gas mixture depends on the type and composition of the constituent gases. The composition of mixed gas can be expressed in three ways.

① volume Composition: ratio of partial volume of component gas to total volume of mixed gas, expressed in ri

The so-called partial volume refers to the volume of the component gas under the temperature and total pressure of the mixed gas.

② Mass composition: the ratio of the mass of the constituent gas to the total mass of the mixed gas, expressed in wi

③ mole Composition: Molar is Amount of substance Company. If a system contains Basic unit (It can be atoms, molecules, ions, electrons or other particles) number is equal to the number of 0.012 kg carbon-12 atoms, then the amount of material in the system is 1 mole. Molar number of composition gas and total of mixed gas Mole ratio , denoted by xi

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When the mixed gas is regarded as a pure substance, the equivalent molar mass μ and Equivalent gas constant R The density of the gas mixture is equal to the sum of the product of the density of each component gas under the total pressure and temperature of the gas mixture and its volume composition, that is^[2]

There are many different methods to detect the gas concentration, and some widely used methods are as follows:

(1) Electrochemical method: the electrical parameters such as the resistance or conductivity of the material change with the gas concentration Gas sensor 。 Insert the cathode and anode into the electrolyte at the same time, and transfer the electrons through the reaction, thus generating current changes and information about the reaction concentration.

(2) Solid gas method: use a heater to prepare beads or flakes metallic oxide When heating, oxygen accumulates on their surfaces, changing the resistance value and the reaction concentration information.

(3) Catalytic combustible gas: the resistance value changes with the temperature on the screw ring, which reacts with the relevant concentration information, destroys the balance of the bridge, and is expressed in the form of electrical signals.

(4) Infrared absorption method: lambert-beer law Based on, the concentration related information is expressed through the gas characteristic absorption mode.

Infrared mixed gas detection has been widely used in many fields, including atmospheric chemical analysis, industrial process control, agricultural production management, urban environmental quality detection, life science research, etc.

In the mixed gas detection based on infrared spectrum technology, optical multiplexing structure is the core part of the detection system. It is not only the medium for infrared light propagation, but also the main place for gas to absorb infrared light energy. According to the difference of light energy conversion process, infrared spectrum detection technology can be divided into two types: direct detection and indirect detection. In NDIR spectroscopy, a broadband light source is used. By selecting filter elements with different central wavelengths and bandwidths, approximately monochromatic light matching the gas absorption characteristics is obtained, and then it is directly detected by the detector.

The detector usually integrates a filter element, including an action channel and a reference channel. The output signal of the action channel and the reference signal are calculated to eliminate the influence of light source, detector instability, external interference and other factors. The selection and control of light source, the selection of filter parameters and the matching degree of light source and detector are all worthy of in-depth study in NDIR spectroscopy technology. Danilova et al. have proved in the experiment that the drive current should be properly reduced Pulse duty ratio It can improve the luminous efficiency of the light source. The reasonable selection of filter elements is conducive to determining the optimal parameters of gas absorption. In order to avoid 1/f noise caused by infrared thermal light source at low modulation frequency (less than 10Hz), selecting LED light source with high modulation frequency and detector with low time constant can improve the detection speed of the whole system and reduce noise.

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Common mixed gas^[3]

Dry air: a mixture of 21% oxygen and 79% nitrogen

CO2 mixture: 2.5% carbon dioxide +27.5% nitrogen+70% helium

excimer laser Mixed gas: 0.103% Fluorine gas + argon + neon +Helium gas mixture

Welding gas mixture: 70% helium+30% argon gas mixture

High efficiency energy-saving bulb filled with mixed gas: 50% Krypton +50% argon gas mixture

Mixed gas for labor analgesia: 50% nitrous oxide+50% oxygen

Blood analysis gas mixture: 5% carbon dioxide+20% oxygen+75% nitrogen gas mixture

S/N	Dilution gas	Name of component gas	Main purpose
one	ethylene	Methane, ethane, propane, cyclopropane, isobutane, n-butane, propylene, acetylene, trans butene, isobutene, maleic butene, isopentane, n-pentane, 1,3-butadiene, propane, pentene, with the content of 100-1000 μ mol/mol	Scientific research, ethylene product quality control standard
two	propylene	Methane, ethane, propane, cyclopropane, isobutane, n-butane, propylene, acetylene, trans butene, n-butene, isobutene, maleic butene, isopentane, n-pentane, 1,3-butadiene, propane, pentene, with the content of 100~1000 μ mol/mol	Scientific research, propylene product quality control standard
three	nitrogen	Methane, ethane, propane, cyclopropane, isobutane, n-butane, propylene, acetylene, trans butene, n-butene, isobutene, maleic butene, isopentane, n-pentane, 1,3-butadiene, propane, pentene, with the content of 10~1000 μ mol/mol	Scientific research, quality control standards for ethylene and propylene products
four	methane	Oxygen, nitrogen, helium, ethane, propane, isobutane, n-butane, isopentane, n-pentane, neopentane, n-hexane (binary and multivariate standards Mixture Body)	Natural gas analysis standard and scientific research
five	nitrogen	Toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, (binary and multi-component standard gas mixtures)	Polyethylene, monomer analysis standard, environmental detection control standard
six	nitrogen	Methyl mercaptan, ethyl mercaptan, n-propyl mercaptan, isopropyl mercaptan, sec butyl mercaptan, diethyl mercaptan (binary and multi-component standard mixed gas)	Standard for quality analysis of petrochemical products
seven	hydrogen	Oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane, propane, isobutane, n-butane, isopentane, n-pentane, 1,3-butadiene, propadiene, and propane (binary and multi-component standard gas mixtures)	Standard for quality analysis of petrochemical products
eight	nitrogen	Hydrogen sulfide, carbon oxysulfide, sulfur dioxide, carbon disulfide (binary and multi-component standard gas mixtures)	Analytical standard for sulfide in natural gas, liquefied petroleum gas and food carbon dioxide
nine	nitrogen	Oxygen, hydrogen, methane, carbon dioxide (binary and multi-component standard gases)	Petrochemical industry, scientific research, coal mining sector
ten	nitrogen	Carbon monoxide, carbon dioxide, methane	Petrochemical industry, coal mining sector
eleven	Synthetic air	carbon monoxide	Environmental detection Pollution source detection Labor health inspection
twelve	Synthetic air	carbon dioxide
thirteen	Synthetic air	Carbon monoxide, carbon dioxide
fourteen	nitrogen	carbon monoxide
fifteen	nitrogen	carbon dioxide
sixteen	nitrogen	formaldehyde
seventeen	nitrogen	ethanol
eighteen	nitrogen	hydrogen sulfide
nineteen	nitrogen	Hydrogen, carbon monoxide, carbon dioxide, methane, ethylene, acetylene, ethane, oxygen, propane, propylene	Analysis of Dissolved Gas in Transformer Oil
twenty	nitrogen	carbon dioxide	Hematometry
twenty-one	nitrogen	Carbon dioxide, oxygen	Hematometry
twenty-two	nitrogen	Carbon monoxide, helium, oxygen	Pulmonary function test
twenty-three	Synthetic air	Carbon monoxide, helium	Pulmonary function test
twenty-four	nitrogen	Carbon monoxide, methane, acetylene, oxygen	Pulmonary function test
twenty-five	Synthetic air	carbon dioxide	Pulmonary function test

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