Search

For the sonic nozzles, the discharge coefficient ($C_{d}$) is an essential parameter of flow characteristics, which is obviously influenced by the thermal effect determined by the nozzle body temperature distribution. In this study, two types of thermocouple arrays for temperature acquisition of the nozzle body were designed to investigate the thermal effect. The temperature isothermal maps of the nozzle body were reconstructed by improved successive over-relaxation (SOR) method combining the simple Kriging interpolation method and particle swarm optimization (SKIM-PSO), which can effectively eliminate the phenomenon of bull’s eye and nonsmoothness of the SKIM. And then, the accuracy of the new algorithm was checked by cross validation with test sets of $d = 5.25$ -mm nozzles with different structures. It is found that the maximum error $\Delta e_{\mathrm {max}}$ of the new algorithm is less than 0.2 °C. The thermal effect on discharge coefficient was analyzed with the above-reconstructed temperature distribution, which is classified into two aspects, the thermal boundary layer correction factor $C_{\mathrm{ T}}$ and the constrained thermal deformation correction factor $C_{\mathrm{ a}}$ related to the throat area. The $C_{\mathrm{ T}}$ is $1- 3.845\text {Re}_{\mathrm{ t}}^{-0.5}\,\,\Delta T/T$ from a similar solution to the boundary layer. Unlike the free expansion, the slopes of the $C_{\mathrm{ a}}$ of constrained expansion for three AISI304 nozzles with $d = 2.00$ , 5.25, and 7.45 mm are $- 1.24 \times 10^{-5}$ , $+ 1.98 \times 10^{-5}$ , and $+ 2.49 \times 10^{-5}$ , respectively. With the correction of $C_{\mathrm{ T}}$ and $C_{\mathrm{ a}}$ , the prediction error of discharge coefficient is reduced from 0.14%–0.15% to 0.08%–0.1% for $d = 2.00$ - and 7.45-mm two nozzles. [ABSTRACT FROM AUTHOR]

The sonic nozzle is commonly used in flow measurement. However, the nonequilibrium condensation phenomenon of moist air in the nozzle has a negative effect on the measuring accuracy. To investigate this complex phenomenon, the experiments on the oscillating condensation flow of moist air were conducted by an adjustable humidification apparatus with different relative humidities (0%–100%), temperatures (30–50°C), and carrier gas pressures (1–6 bar), where the microsize pressure measuring system was designed by Bergh–Tijdeman (B–T) model. The accurate mathematical model of nonequilibrium condensation was also built and validated by the experimental data of time-averaged pressure distribution. Then, the frequency and intensity of pressure fluctuation of oscillating flow at a wide range of operation condition were obtained combining experimental data and physical simulation model. Importantly, a new semiempirical relation of dimensionless frequency deduced from dimensionless analysis was identified accurately by experimental data. Finally, the signal nonstationarity was also observed using the continuous wavelet transform (CWT). The instantaneous frequency saltation and the energy attenuation of pressure signals were observed in the condensation flow. [ABSTRACT FROM AUTHOR]

In this article, an accurate online measurement of gas flowrate in wet gas was developed by modeling the frequency and amplitude characteristics of a vortex flowmeter in annular mist flow. The low-frequency modulation behaviors of the vortex signals were analyzed by the ridge method based on continuous wavelet transform (CWT). It indicates that the instability of frequency and amplitude of the signals both enhance with the increase of liquid loading; and therefore, a feature extraction method based on ridge-averaged was proposed and validated by the tests. A film extraction device was developed to measure the flowrate of the liquid film and further obtain the droplet mass loading. Then, a uniform linear equation for the overreading was obtained experimentally on the basis of the scaling parameter analysis in particle-laden flow. A uniform exponential equation for the dimensionless signal amplitude of the sensor output was developed with droplet mass loading. Finally, a wet gas measurement model with the simultaneous equations from these two correlations was established and the iterative solution algorithm was given. In the present cases, the percentage errors (PEs) of the gas flowrate predicted by the modeling are within ±1.5% and the mean absolute PE is 0.37%. The method proposed in this article can achieve accurate measurement of gas flowrate by using only one vortex flowmeter and, hence, creates a simple inexpensive metering system for wet gas flow. [ABSTRACT FROM AUTHOR]

The amplitude–frequency characteristics of self-excited oscillating pressure in nozzle condensation dominate the actual flow field and mass flow rate, which affect the measurement accuracy of the sonic nozzle for the moist gas. In order to estimate this effect and improve the measurement accuracy, the complex supersonic vapor nozzle condensation with different nozzle geometries was investigated. First, the raw signals of the time-averaged and transient oscillating pressure during the condensation occurs in the nozzle were acquired, by using a multiparameter adjustable humidification apparatus, two nozzle sensors with distributed pressure probes and a 10th order low-pass hardware filter. Then, these raw signals were decomposed and reconstructed to further improve the filtering result, by using discrete wavelet transforms with the Db5 wavelet bases. Finally, the accurate amplitude–frequency characteristics of the transient pressure signals were extracted and analyzed by fast Fourier transform and the ratio correction method. It found that the experimental frequencies are mainly dependent on the curvature of nozzle wall and mass fraction of water vapor, which is also compared with a semiempirical formula derived from the experiments of 2-D symmetric rectangular nozzle. The results showed that this formula has a significant deviation from the experimental results of 3-D toroidal nozzles, which needs to be investigated further. All the research is contributed to further analyze the effect of condensation on the actual mass flow of the sonic nozzle. [ABSTRACT FROM AUTHOR]

High-precision thermal resistances are very often used in the sonic nozzle airflow standard facilities. In order to obtain the true transient temperature and minimize temperature effects on flow uncertainty, a thermodynamic model for flow temperature phenomena was presented and compared with experimental measurements. Numerical simulations using the software of FLUENT were carried out to analyze the difference between the experimental measurements and the model results. The analysis showed that such difference came from the temperature distribution in the stagnation tank. In addition, such difference could be ignored. In order to reduce the measurement uncertainty, a dynamic temperature compensation, which solved the actual model of thermal resistances and parameters of inverse model by least squares estimation method and wavelet filtering algorithm, had been presented. Comparing the output of the compensator with the true transient temperature obtained by the thermodynamic model, it proved the accuracy and the effectiveness of this compensation method. [ABSTRACT FROM AUTHOR]