Flow characteristics of V-Cone flowmeter in wet steam
Wet steam is a common two-phase flow whose mass flow-rate can be measured by V-Cone flowmeter. The mass flow coefficient CD of V-Cone is no longer approximately constant which affects the measuring accuracy subject to the complex flow characteristics of wet steam and discrete droplets. Firstly, five main impact factors for CD of V-Cone were obtained by dimensional analysis, namely, vapor Reynolds number, liquid-vapor density ratio, mass loading ratio, potential to kinetic energy ratio and dimensionless droplet diameter respectively. Then CFD simulation was carried out to study the influence of these parameters. Eulerian multiphase model and SST k-ω turbulence model were adopted for steady simulation. The simulation results coincided well with the experimental results. The results indicate that CD is almost not affected by vapor Reynolds number and potential to kinetic energy ratio; it increases with the liquid-vapor density ratio, mass loading ratio and dimensionless droplet diameter, among which mass loading ratio is the main factor.
Two-phase mass flow coefficient of V-Cone throttle device
The V-Cone throttle device has been paid more and more attentions on the measurement of the wet gas flow in recent years. However, it tends to over-read the gas flow rate when directly used to measure the wet gas. How to correct this over-reading and obtain an accurate yet simple wet gas correlation is still one of the challenges in the investigation on the V-Cone throttle device. In this paper, the two-phase mass flow coefficient of the V-Cone throttle device was proposed to correct the deviation of the readings produced by the device. The parameters affecting the coefficient were determined and discussed experimentally. Two V-Cone throttle devices with the respective equivalent diameter ratios of 0.65 and 0.75 were investigated under the condition of the wet gas flow. The test fluid was air and tap water. The gas-to-liquid density ratio ranged from 0.002445 to 0.006083, and the gas densiometric Froude number ranged from 0.3 to 2.0. The influencing parameters including the Lockhart–Martinelli parameter, the gas-to-liquid density ratio, the gas densiometric Froude number and the equivalent diameter ratio were studied. Then the correlations of the two-phase mass flow coefficient and the influencing parameters were proposed for the two V-Cone throttle devices and evaluated experimentally. The results show that the relative deviations of the correlations are less than ±5.0% and the average deviations of the correlations are 2.06% and 2.22% for the V-Cone throttle devices with the equivalent diameter ratio of 0.65 and 0.75, respectively. It can be concluded that the two-phase mass flow coefficient of the V-Cone throttle device is crucial for the development of the wet gas correlation.
A Kalman estimation based oil–water two-phase flow measurement with CRCC ☆
Abstract Measuring the individual phase flow rates of oil–water two-phase flow is an important issue in process industries. A Conductance Ring Coupled Cone (CRCC) meter is presented for this task, and conductance ring array (CRA) was installed in front of CRCC for results comparison. A CRCC provides multiple outputs regarding the flow rate and water holdup by implementing a pair of conductance rings in an annular flow channel formed by a long-waist cone and pipe wall. Three outputs, contracting differential pressure Δ p tp , overall differential pressure δ p tp and dimensionless conductance V a ∗ , are fused by a Kalman filter to estimate individual flow rate of oil ( W o ) and water ( W w ) simultaneously. A transition model with state vector [ W o , W w ] T is established based on the random walk assumption of two-phase flow, and an observation model is established with Δ p tp and δ p tp based on the separated flow assumption. The parameters of these two models are optimized with the Expectation–Maximization (EM) algorithm under each experimental condition. The present method treats the two-phase flow a dynamic process with a dynamic state estimation method. The estimation results demonstrate a dynamic response of CRCC to the change of flow conditions. The overall accuracy of the oil flow rate estimation is 2.3 % and for the water flow rate is 4.8 % . The comparison of the proposed method with CRCC model based dynamic/static estimation, as well as the CRA model based estimation, indicates that the proposed sensor structure improved the estimation accuracy by measuring the water holdup in annular channel. The dynamic estimation can also improve the estimate accuracy by incorporating dynamic fluctuation and unknown correlations with inferential parameters through optimizations. More accurate and reliable estimates can be obtained by optimizing the transition and observation models with profound multiphase physical flow models.