GB/T 5832.2-1986 Determination of trace moisture in gases - Dew point method
Some standard content:
1 Scope of application
National Standard of the People's Republic of China
Determlnatio of trace water in the gasesDew polint method
UDC 661.91/.99:546
.212:543.06
GB5832.2-86
This standard is applicable to the determination of trace water dew point in gases such as oxygen, nitrogen, hydrogen, fluorine ...
The measured gas is made to flow at a constant pressure through the polished metal mirror in the chamber of the dew point meter at a certain flow rate. The temperature of the mirror can be artificially reduced and accurately measured. When the water vapor in the gas reaches saturation as the mirror temperature gradually decreases, the mirror begins to appear. The measured mirror temperature at this time is the dew point. (The trace moisture content in the gas can be obtained by the conversion formula or table between dew point and moisture content in the gas.)
3.1 Overview
The instrument can be designed in different ways. The main differences are the properties of the metal mirror, the method used to cool the mirror, how to control the temperature of the mirror, the method of measuring the temperature and the method of detecting dew. The mirror and its accessories are usually placed in the chamber through which the gas sample flows.
General requirements of the instrument
Any dew point meter that meets the basic requirements provided the following equipment is available can be used. .2.1 When the instrument temperature is at least 2 degrees higher than the dew point of the moisture in the gas, the flow rate of the gas in and out of the instrument can be controlled. . 2.2 Cool the flowing sample gas to a sufficiently low temperature so that the water vapor can condense. The cooling rate can be controlled. 3.2. The appearance of dew can be observed and the dew point can be accurately measured. 3.2.4 The dead volume of the gas system is small and the airtightness is good. The air pressure in the dew point room should be close to the atmospheric pressure. 3.2.5 Use standard samples to measure whether the instrument meets the requirements. According to G4471-84 "Determination of repeatability and reproducibility of inter-laboratory tests for chemical product test methods", Section 4.3. 8. Visual and photoelectric dew point meters
Simple dew point meters manually adjust the cooling capacity and control the cooling rate of the mirror surface, and use the visual method to observe the generation of dew. This method is based on experience and has large human error. The photoelectric dew point meter that uses a photoelectric system to determine the generation of dew has a fairly high accuracy and precision: users can choose according to their needs and possibilities.
Things. 4 Observation of dew
Visual dew point meters use the naked eye to observe the appearance of dew. The photoelectric group point instrument uses a light source installed in the measuring room to illuminate the mirror surface. The light source and the photocell National Standard Bureau issued on January 27, 1986
1966-11-01 implementation
GB 5432, 2-- 86
can be arranged in various ways. When the mirror surface is not condensed, no scattering occurs, and there is no light on the silicon photocell. After condensation on the mirror surface, the incident light is scattered on the mirror surface, and part of the light is irradiated on the silicon photocell to generate a photoelectric voltage and give a dew signal. ,5 Mirror cooling method
Use the following methods to reduce and adjust the mirror humidity. Among them, the methods introduced in 3.5.1 and 3.5.2 require the operator to pay attention and are not suitable for automatic devices. For automatic devices, two methods are used for cooling: liquefied gas cooling and thermoelectric effect cooling introduced in 3.5.3 and 3.5.4.
3.5.1. Solvent evaporation refrigeration
Use a volatile liquid in contact with the back of the mirror, and use low-pressure air or other compressed gas to bubble to vaporize the liquid.
3.5.2 Adiabatic expansion refrigeration
Let a gas flow through the back of the mirror through a nozzle, and the mirror surface will be cooled due to the expansion of the gas. This gas can be compressed carbon dioxide in a cylinder, or compressed air and compressed nitrogen can be used. This method can reduce the temperature of the mirror surface by at least 40°C. Refrigeration of liquefied gas
Currently, liquefied gas is widely used as a coolant. If liquid is used, a temperature of 80°C or lower can be obtained. When liquefied gas is used for refrigeration, the copper tumbler in contact with the back of the mirror can be directly contacted with the liquefied gas, or the liquefied gas can be vaporized by electric heating to refrigerate, or the compressed gas can be cooled by passing through a coil filled with liquid ammonia. .5.4 Refrigeration using the thermoelectric (Pelvis) effect This method is also known as semiconductor refrigeration, which uses multiple stages in series to obtain different low temperatures. Book. Temperature measurement
The temperature of the mirror surface during fermentation should be measured as accurately as possible. In order to avoid temperature differences on the mirror surface, a mirror with high thermal conductivity should be used, generally gold, copper, stainless steel and alloy. To measure the dew point temperature, use a precision mercury thermometer, thermocouple, thermistor or platinum resistance temperature sensing element. At present, high-precision measurements all use platinum resistance temperature sensing elements.
4 Preparation before analysis
4.1 Leak test
All joints of the test system should be free of leaks, otherwise the measurement results will be biased high due to the infiltration of moisture in the air. A simple leak test method is as follows:
Connect a U-shaped pressure gauge filled with water to the gas outlet of the instrument, adjust the gas line pressure so that the pressure difference in the U-shaped tube is 1000mmH, 0, turn off the gas source, and the water column drops no more than 5mm after 5 minutes, indicating that the system is airtight. When necessary, the pressure should be increased to test for leaks. If a system leak is found, it should be checked and solved in sections. 4.2 Sampling equipment
4.2.1 Sampling valve: Use a regulating valve with a small dead volume, such as a needle valve. 4.2.2 Sampling tube: In principle, use a small-diameter tube as short as possible. Generally, a stainless steel tube with a length of no more than 2m and an inner diameter of no more than 4mm or a polytetrafluoroethylene tube with a wall thickness of no less than 1mm should be used. Wash it before use, and then blow dry or dry it. Rubber hoses are not allowed. 4.2. Flushing of the sampling valve
Open the sampling valve slightly, and close it immediately after opening the top valve of the cylinder. Open the sampling valve until the released air flow becomes smaller, then close the sampling valve, and then open the top of the cylinder and close it immediately. Repeat this three times before measuring. 4.2.4 Calibration of the flow meter
The test flow of the sample gas should be calibrated with a soap film flow meter for different gas samples. 5~-General operation steps
6.1 Use gas to purge the pipeline and measurement chamber. For the instrument that has just been put into use, when the moisture dew point of the measured gas is about -60℃, it should be purged for 2 hours before measurement.
..com5.2 Adjust the sample gas flow rate to within the specified range. GB 5882.286
5.8 Start cooling. When the mirror temperature is about 5℃ away from the dew point, the rate of decrease should not exceed 5℃/min. For the sample gas whose dew point range is unknown, a rough measurement can be carried out first.
5.4 After shutdown, tighten the sealing nuts on the inlet and outlet of the sample gas. 6 Precautions
.6.1 Interfering substances
6.1.1 Overview
When solid particles or dust enter the instrument and adhere to the mirror surface, the dew point value measured by the photoelectric method will deviate. Other vapors besides water vapor may also condense on the mirror surface, making the observed dew point different from the required point of the corresponding water vapor content. .1.2 Solid impurities and oil stains
If solid impurities absolutely do not fall into the water, they will not change the dew point, but will hinder the observation of dew. In the automatic device, if no compensation device is used for solid impurities, sometimes the measured required point value will be higher when measuring low dew points due to solid impurities attached to the mirror surface. At this time, the mirror surface should be cleaned with anhydrous ethanol or tetrafluoroethylene on cotton wool. In order to prevent interference from solid impurities, a filter should be set at the inlet of the instrument, and the filter should not adsorb moisture in the gas. If there is oil stain in the measured gas, it should be removed before the gas enters the measurement chamber. 6.1.3 Impurities in the form of vapor
Hydrocarbons can condense on the mirror surface. If the dew point of hydrocarbons is lower than the dew point of water vapor, it will not affect the measurement. In the opposite case, they will condense before the water vapor, so the condensate of hydrocarbons must be separated before the water vapor condenses. If the measured gas contains methanol, it will condense on the mirror surface together with water, and the common dew point of methanol and water is obtained at this time. 8.2 Cold wall effect
Except for the mirror, the temperature of the rest of the instrument and the pipeline should be at least 2°C higher than the dew point of water in the gas, otherwise, water vapor will condense at the coldest point, changing the moisture content in the gas sample. Ref.*Cooling speed
If the water content in the gas sample is low, the mirror should be cooled as slowly as possible. Because the crystallization process of ice is relatively slow at this time, if the temperature is cooled at an inappropriate speed, before the ice layer grows and reaches stability, dew has not been observed, and the temperature has greatly exceeded the dew point. This is the phenomenon of supercooling.
Usually, the dew that can be observed by the naked eye is about 10-m/cm'. A sensitive photoelectric dew point meter can detect very low water content. When using a visual dew point meter to measure low water content, the following measures should be taken: When approaching the dew point, the mirror should be cooled as slowly as possible. b. Use a magnifying glass to observe the appearance of dew.
C. When the mirror temperature is slowly reduced, the average of the temperature measured when the dew just appears and the temperature measured when the dew disappears while the temperature slowly rises is taken as the dew point.
7 Result processing
7.1 The arithmetic mean of the two dew point measurement results is the curtain point value, and the difference between the two dew point measurement results should be less than the repeatability requirements in Chapter 8.
T.2 Dew point is converted to PPM (V/V) according to A.1 in Appendix A (Supplement) or by looking up the table. 7.3 Dew point is converted to absolute humidity g/m (20℃, 101.3kPa) according to A.2 in Appendix A (Supplement) or by looking up the table. . Precision
Precision of the method when the dew point is lower than -42: Repeatability r = -0.93 + 0.041m
Reproducibility R = 3.87 + 0.019m
Where: -- average value of the measurement results. GB 5832.2-86
The application of repeatability and reproducibility shall be carried out in accordance with the relevant provisions of Chapter 4 of GB4471-84. Report
The report shall include the following:
Information. Analysis date, room temperature, atmospheric pressure, b, sampling location, number, pressure in the container C. Sample name,
Analysis results: Concentration of water in the sample gas; any abnormal phenomena observed during the measurement; other names of analysts selected by the operator if not included in this standard.
GB B8 Information 2.2-8 Clinical
Appendix A
(Supplement)
This appendix gives the formulas and results for the conversion of dew point-ppm (V/V) and dew point-absolute humidity (g/m\) in gas. A.1 Dew point is converted to ppm by the following formula, p
where P—saturated vapor pressure of ice at dew temperature*, Pa. The calculation results are shown in Table A1.
A.2 Dew point is converted to g/m (20°C, 101.3 kPa) by the following formula: P
Where P-
The saturated vapor pressure of ice at dew point", Pa.
The calculation results are shown in Table A2.
Dew point-ppm conversion table
o++(A2)
The saturated vapor pressure of ice in the conversion formula is quoted from A. Wexler, Vapor Preasure Farmulation for Ice, J, Res. NBS-A. Phys. and Chem. Val, 81A, No.l, 17-18 (1977)
GB 5882.2—86
Continued Table A1
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6811'01 The arithmetic mean of the two dew point measurement results is the curtain point value. The difference between the two required point measurement results should be less than the repeatability requirements in Chapter 8.
T.2 Dew point is converted to PPM (V/V) according to A.1 in Appendix A (Supplement) or by looking up the table. 7.3 Dew point is converted to absolute humidity g/m (20℃, 101.3kPa) according to A.2 in Appendix A (Supplement) or by looking up the table. . Precision
When the dew point is lower than -42, the precision of the method is: Repeatability r = -0.93 + 0.041m
Reproducibility R = 3.87 + 0.019m
Where: -- the average value of the measurement results. GB 5832.2-86
The application of repeatability and reproducibility shall be carried out in accordance with the relevant provisions of Chapter 4 of GB4471-84. Report
The report should include the following:
Information. Analysis date, room temperature, atmospheric pressure, b, sampling location, number, pressure in the container C. Sample name,
Analysis results: Concentration of water in the sample gas; any abnormal phenomena observed during the measurement; the name of other operating analysts selected by yourself if not included in this standard.
GB B8 Information 2.2-8 Clinical
Appendix A
(Supplement)
This appendix gives the formula and results for the conversion of dew point-ppm (V/V) and dew point-absolute humidity (g/m\) in gas. A.1 Dew point is converted to ppm by the following formula, p
Where P—saturated vapor pressure of ice at dew temperature*, Pa. The calculation results are shown in Table A1.
A.2 Dew point is converted to g/m (20°C, 101.3 kPa) by the following formula: P
Where P-
The saturated vapor pressure of ice at dew point", Pa.
The calculation results are shown in Table A2.
Dew point-ppm conversion table
o++(A2)
The saturated vapor pressure of ice in the conversion formula is quoted from A. Wexler, Vapor Preasure Farmulation for Ice, J, Res. NBS-A. Phys. and Chem. Val, 81A, No.l, 17-18 (1977)
GB 5882.2—86
Continued Table A1
447, 4
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0. 05 908
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Continued Table A1
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6811'01 The arithmetic mean of the two dew point measurement results is the curtain point value. The difference between the two required point measurement results should be less than the repeatability requirements in Chapter 8.
T.2 Dew point is converted to PPM (V/V) according to A.1 in Appendix A (Supplement) or by looking up the table. 7.3 Dew point is converted to absolute humidity g/m (20℃, 101.3kPa) according to A.2 in Appendix A (Supplement) or by looking up the table. . Precision
When the dew point is lower than -42, the precision of the method is: Repeatability r = -0.93 + 0.041m
Reproducibility R = 3.87 + 0.019m
Where: -- the average value of the measurement results. GB 5832.2-86
The application of repeatability and reproducibility shall be carried out in accordance with the relevant provisions of Chapter 4 of GB4471-84. Report
The report should include the following:
Information. Analysis date, room temperature, atmospheric pressure, b, sampling location, number, pressure in the container C. Sample name,
Analysis results: Concentration of water in the sample gas; any abnormal phenomena observed during the measurement; the name of other operating analysts selected by yourself if not included in this standard.
GB B8 Information 2.2-8 Clinical
Appendix A
(Supplement)
This appendix gives the formula and results for the conversion of dew point-ppm (V/V) and dew point-absolute humidity (g/m\) in gas. A.1 Dew point is converted to ppm by the following formula, p
Where P—saturated vapor pressure of ice at dew temperature*, Pa. The calculation results are shown in Table A1.
A.2 Dew point is converted to g/m (20°C, 101.3 kPa) by the following formula: P
Where P-
The saturated vapor pressure of ice at dew point", Pa.
The calculation results are shown in Table A2.
Dew point-ppm conversion table
o++(A2)
The saturated vapor pressure of ice in the conversion formula is quoted from A. Wexler, Vapor Preasure Farmulation for Ice, J, Res. NBS-A. Phys. and Chem. Val, 81A, No.l, 17-18 (1977)
GB 5882.2—86
Continued Table A1
447, 4
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GB 0. 06 134
0. 05 908
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Continued Table A1
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6811'02—8 Temporary
Appendix A
(Supplement)
This appendix gives the formulas and results for the conversion of dew point-ppm (V/V) and dew point-absolute humidity (g/m\) in gas. A.1 Dew point is converted to ppm by the following formula, p
where. P—saturated vapor pressure of ice at dew temperature*, Pa. The calculation results are shown in Table A1.
A.2 Dew point is converted to g/m (20°C, 101.3 kPa) by the following formula: P
Where P-
The saturated vapor pressure of ice at dew point", Pa.
The calculation results are shown in Table A2.
Dew point-ppm conversion table
o++(A2)
The saturated vapor pressure of ice in the conversion formula is quoted from A. Wexler, Vapor Preasure Farmulation for Ice, J, Res. NBS-A. Phys. and Chem. Val, 81A, No.l, 17-18 (1977)
GB 5882.2—86
Continued Table A1
447, 4
.69.49
GB 0. 06 134
0. 05 908
心049
GB 682.2-86
Continued Table A1
0, 0388
0.02687 0.02635
0.015360.015050.014750.01450.014160.01599
5882.2—88
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699100
F82TO*0
920200
678200
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890 91'0
209600
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20810*0
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0 20 60 *0
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909200
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982500
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BFII'O||t t||ZI210*0
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605200
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602500
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6811'02—8 Temporary
Appendix A
(Supplement)
This appendix gives the formulas and results for the conversion of dew point-ppm (V/V) and dew point-absolute humidity (g/m\) in gas. A.1 Dew point is converted to ppm by the following formula, p
where. P—saturated vapor pressure of ice at dew temperature*, Pa. The calculation results are shown in Table A1.
A.2 Dew point is converted to g/m (20°C, 101.3 kPa) by the following formula: P
Where P-
The saturated vapor pressure of ice at dew point", Pa.
The calculation results are shown in Table A2.
Dew point-ppm conversion table
o++(A2)
The saturated vapor pressure of ice in the conversion formula is quoted from A. Wexler, Vapor Preasure Farmulation for Ice, J, Res. NBS-A. Phys. and Chem. Val, 81A, No.l, 17-18 (1977)
GB 5882.2—86
Continued Table A1
447, 4
.69.49
GB 0. 06 134
0. 05 908
心049
GB 682.2-86
Continued Table A1
0, 0388
0.02687 0.02635
0.015360.015050.014750.01450.014160.01599
5882.2—88
0958'0
.01 60
B8 F8\0
88S5\0
689°8
1986*0
99 06*0
2966\0
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0# 87'0
92 2*0
2021'0
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29 620
69 8*0
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6691 *0
z10g*0
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290s*0
PB 59 *0
0-089*0
No. 691 0
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699100
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920200
678200
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890 91'0
209600
689100
20810*0
889200
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129 80 *0
2801*0
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128 20 *0
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29 90*0
28820*0
B2 O *0
BEOT *0
682to0
9 2820*0
529800
99990*0
99b 20 *0
88860*0
19210\0
L6T7O~0
E6650*0
S99 200
16F60*0
6811'00
29 620
69 8*0
9521*0
60tt *0
1669~0
s0 99\0
8961~0
9T68*0
FEPI\O
6691 *0
z10g*0
OFT9\0
989心
290s*0
PB 59 *0
0-089*0
No. 6910
1629*0
GB 5832.2—88
699100
F82TO*0
920200
678200
16690\0
890 91'0
209600
689100
20810*0
889200
186200
SEI900
129 80 *0
2801*0
08T0'0
820200
298200
858600
902 90 *0
22650*0
128 20 *0
128600
292100
r98 t0*0
906900
FoFo\0
016200
12880~0
T99 10*0
828 100
260200
1OS 800
156800
15950'0
P5890*0
900800
+#6 80*0
soot*0
162100
2910*0
106TO*0
98180*0
T80S0*0
2 90*0
#60 80*0
0 20 60 *0
$ 69 To '0
981200
909200
28960*0
982500
0E20:0
061800
BFII'O||t t||ZI210*0
196T0*0
812200
605200
2600*0
602500
F9850*0
29 90*0
28820*0
B2 O *0
BEOT *0
682to0
9 2820*0
529800
99990*0
99b 20 *0
88860*0
19210\0
L6T7O~0
E6650*0
S99 200
16F60*0
6811'00
29 620
69 8*0
9521*0
60tt *0
1669~0
s0 99\0
8961~0
9T68*0
FEPI\O
6691 *0
z10g*0
OFT9\0
989心
290s*0
PB 59 *0
0-089*0
No. 6910
1629*0
GB 5832.2—88
699100
F82TO*0
920200
678200
16690\0
890 91'0
209600
689100
20810*0
889200
186200
SEI900
129 80 *0
2801*0
08T0'0
820200
298200
858600
902 90 *0
22650*0
128 20 *0
128600
292100
r98 t0*0
906900
FoFo\0
016200
12880~0
T99 10*0
828 100
260200
1OS 800
156800
15950'0
P5890*0
900800
+#6 80*0
soot*0
162100
2910*0
106TO*0
98180*0
T80S0*0
2 90*0
#60 80*0
0 20 60 *0
$ 69 To '0
981200
909200
28960*0
982500
0E20:0
061800
BFII'O||t t||ZI210*0
196T0*0
812200
605200
2600*0
602500
F9850*0
29 90*0
28820*0
B2 O *0
BEOT *0
682to0
9 2820*0
529800
99990*0
99b 20 *0
88860*0
19210\0
L6T7O~0
E6650*0
S99 200
16F60*0
6811'0
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