1. Experimental apparatus The experimental devices used in this study were the condensing weighing steam flow metering standard device, the negative pressure sonic nozzle gas flow metering standard device, and the quality water metering standard device. The condensing weighing steam flow metering standard device is the only flow standard device using steam flow calibration in China, with an extended uncertainty of 0.1% (k=2) and a certified flow range of 0.01 to 10, t/h. The principle is shown in Fig. 2. Superheated steam is used as the verification medium. The principle of condensing and weighing steam through the steam flow meter is used to carry out real-time calibration of the steam flow meter. The gas device is a negative pressure sonic nozzle gas flow metering standard device with an extended uncertainty of 0.25% (k=2) and a certified flow range of 2.5 to 10,000 m3/h. The water device is a standard device for mass flow metering, with an expanded uncertainty of 0.05% (k=2), and a certified flow range of 0.05 to 200 m3/h.
2. Experimental scheme Steam meters of different manufacturers, models and sizes are tested according to the requirements of steam flow meter national verification procedures [12]. They are installed on steam equipment, air equipment and water equipment, respectively. The temperature of the steam equipment is Tested at about 150°C and pressure at 0.35MPa, and the flow rate was verified from 20%, 40%, 60%, 80%, and 100% of the minimum flow rate to the maximum flow rate. The total flow rate was 6 flow points. Repeat the test 3 times. At present, nearly 100 steam flow meter test experiments have been conducted, and unqualified steam flow meters have been removed. The results of these steam flow meter experiments have been summarized. The deviations of the meter coefficients are basically similar in direction and the deviations are of different sizes within a certain range. . In this article, only the representative DN50 and DN100 steam flowmeter experimental data are analyzed to compare the variation of the meter coefficient at different flow points under different fluid conditions.
3 experimental data through 3 sets of experimental tests under different fluid media, 3 devices under the meter coefficient, meter coefficient deviation and calculated by the calculation of the coefficient deviation of the meter E ', E'a, E'a, E'e, As shown in Table 5, the relationship between meter factor and flow rate is shown in Figure 3 and Figure 4.
From the experimental data, it can be seen that the meter coefficient of the steam flow meter under the conditions of air, water, and steam flow decreases in turn, and the meter coefficients of the air and steam fluid media increase with the flow rate, which is consistent with theoretical calculation and analysis. According to the accumulated experimental data, the K value measured by the ratio of air to water as the fluid medium is larger by 0.2% to 1.0%, which is larger by 1.5% to 3.0% than the K measured by the steam as the fluid medium. The value of the meter coefficient deviation is due to the instrument. Manufacturers and specifications vary, but the positive and negative trends of deviations are basically the same.

(1) In the measurement of high temperature steam, it is necessary to consider the influence of temperature-induced linear expansion, otherwise it will cause the meter coefficient to be large. The measurement error caused can be compensated according to the formula derived from the article.
(2) The effect of gas compressibility on the meter coefficient of a steam flow meter is affected by the medium flow velocity u, pressure p, density ρ, and isentropic index κ and other related parameters, and is proportional to the flow velocity u and to 11p / ρ Inversely, the gas isentropic index κ does not cause a one-way change in the meter coefficient.
(3) The compressibility of different media will affect the meter coefficient of the steam flow meter. The meter coefficient under the air medium is the largest, the water time is the lowest, and the steam is the smallest. At the same flow velocity, the influence of the steam medium on the meter coefficient is smaller than that of the air. , The specific difference size can be obtained according to the analysis and calculation under operating conditions.
(4) According to the experimental data, the meter coefficient of the steam flow meter measured under different media is consistent with the theoretical calculation and analysis, but there are certain deviations in the two results, which may be due to the impact of other media properties on the meter coefficient. It also needs in-depth theoretical analysis, in actual use as far as possible using real-flow calibration to obtain the instrument coefficient.

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