Conductance Measurement of Water Vapor by the Time-Ratio Method

doi:10.12068/j.issn.1005-3026.2024.05.013

Abstract

Abstract:

There are currently few methods available to measure the conductance of water vapor through an orifice. The feasibility of the pressure rising method to measure the conductance of water vapor is analyzed by combining theory with experiment， indicating that the measurement error of this method increases with the decrease of intake volume， which is due to the strong adsorption characteristic of water vapor. To accurately obtain the relationship between the conductance of water vapor and the inlet pressure， a new method called the time-ratio method is proposed. This method calculates conductance by measuring the time of pressure change， reducing the effect of water vapor adsorption on the measurement effectively. Based on this method， a device is developed to provide a flow rate in the range of 3.7×10^-9~1.5×10^-5 Pa·m³·s^-1. The measurement and theoretical values of conductance have good consistency， and the relative standard uncertainty of this time?ratio method is 3.3%.

Key words: water vapor, conductance, uncertainty, measurement

CLC Number:

TB 753

Jian GENG, Xiao-dong WANG, Mei-ru GUO, Zheng-yi REN. Conductance Measurement of Water Vapor by the Time-Ratio Method[J]. Journal of Northeastern University(Natural Science), 2024, 45(5): 707-712.

Figures/Tables 10

Fig.1 Orifice conductance measurement device

Table 1 Uncertainty of the time?ratio method

$u r V 2$	$u r C 0$	$u r p 1$	$u r p 2$	$u r C 0'$
0.1	3.2	1.1	3.0	3.3

Table 1 Uncertainty of the time?ratio method

$u r V 2$	$u r C 0$	$u r p 1$	$u r p 2$	$u r C 0'$
0.1	3.2	1.1	3.0	3.3

Fig.2 Ratio of capacitance diaphragm gauge and spinning rotor gauge

Fig.3 Orifice which is made by laser drilling

Table 2 Volume measurement results of the test dome and pipeline by the expansion method

容积/mL	初始压力/Pa	平衡压力/Pa	容积/mL
679	5 058	1 146	2 317.8
679	1 036	234.8	2 316.9
679	315	71.4	2 616.6

Fig.4 Measurement results of water vapor conductance by the pressure rising method

Table 3 Five results of the time ratio method

次数	压力/Pa	时间/s	流导/（Pa·m³·s^-1）
1	3023	174.22	5.34E-9
2	3023	174.35	5.34E-9
3	3023	174.30	5.34E-9
4	3023	174.39	5.34E-9
5	3023	173.92	5.35E-9
平均值	3023	174.24	5.34E-9
实验标准偏差	—	—	6.65E-12
相对实验标准偏差	—	—	0.125%

Fig.5 Relationship between water vapor conductance and inlet pressure

Fig.6 Measurement results of H2O, N2 and Ar

Table 4 Conductance ratio under the molecular flow conditions

气体	流导测量结果	与氮气流导的理论比值	与氮气流导的测量比值
气体	m³·s^-1	与氮气流导的理论比值	与氮气流导的测量比值
水蒸气	3.7×10^-9	0.80	0.79
氩气	2.5×10^-9	1.19	1.18
氮气	2.9×10^-9	—	—

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