Measurement of Bubbly Flow in a Vertical Pipe Using Ultrasonic Doppler Method

Application of ultrasonic doppler method for bubbly flow measurement using two ultrasonic frequencies

On the modelling of bubbly flow in vertical pipes

Correlation of heat transfer coefficient for two-component two-phase slug flow in a vertical pipe

Summary In oil and gas production, mainly during the development of offshore hydrocarbon fields, the extraction, gathering and transportation of oil and gas are often associated with gravitational, vertical upward and downward flows. Thus, such flows are common during the extraction of well product and movement of multiphase mixtures from seabed to the platform and vice versa through the vertical submarine oil and gas pipelines connecting offshore platforms. Predicting, modeling and analyzing two-phase flows is one of the challenging issues in the oil and gas industry. Thus, due to phase fluctuations, drifts and interactions, combined chaotic and dissipative flows, the study becomes difficult and requires special sensitivity. Therefore, Wire-mesh Sensor (UMS) is used in the study of horizontal gas-liquid two-phase flows. [1] During the gravitational movement of multiphase flows in vertical pipes, different flow patterns are formed and their physicochemical and rheological properties vary significantly along the flow. The diameter of the pipe, the physical properties of the flowing fluid, the flow rate all together create the structure of the flow patterns. There are two types of flow here, bubble and mist. At low values of velocity and gas-liquid ratio, bubble flow occurs, and at high values, mist flow occurs. Liquid-gas ratios also divide phases into two forms: continuous and dispersed. The dispersed phase is characterized by a low value of the ratio, and the continuous phase is characterized by a high ratio of liquid-gas mixture. [5] In the paper is given a study on change of the density of a multiphase mixture depending on the phase slippage in the form of a bubble (dispersed) flow. How the density of the gas-liquid mixture changes during the vertical upward movement of the gas-liquid mixture, taking into account the sliding effect has been studied, a monotonous increase in the density of the mixture depending on the relative velocity of the gas relative to the liquid for different values of gas volumetric flow rate in vertical pipes has been determined. In the paper, it is also shown that the dispersion of the gas varies depending on the size of the bubbles distributed in the liquid as a result of changes in the mode of motion of the gas-liquid mixture during its movement in a vertical pipe. As the gas bubbles agglomerate together with the pressure decreases, they also change the flow pattern. It is no coincidence that in many cases, in long vertical pipes, the bubble flow regime is transformed into a slug and then into a churn flow. As the hydrostatic pressure increases due to the aggravation of the multiphase mixture as a result of phase slippage, the total pressure loss during upward multiphase flow also increases. In the paper the use of a relatively small diameter vertical pipe to increase the fluid flow rate in order to reduce the slippage effect is also suggested or to form several streams by creating vortices along the length of the pipe during the flow. In this case, the importance of special calculations related to losses and justification of the diameter was noted.

CFD simulation of bubbly two-phase flow in horizontal pipes

Modeling of bubble flows in vertical pipes with the N-phase compressible algebraic slip model

Formulas are proposed for an analysis of the local and mean heat exchange on the initial thermal section for stabilized turbulent air flow in circular pipes and rectangular channels on the basis of an extension of test results.

Modeling of void fraction covariance and relative velocity covariance for upward boiling flow in vertical pipe

On the numerical study of isothermal vertical bubbly flow using two population balance approaches

Image processing techniques for the measurement of two-phase bubbly pipe flows using particle image and tracking velocimetry (PIV/PTV)

The effect of swirl on transition from churn flow to annular flow in an intermediate diameter pipe

The characteristics of two-phase flow in a vertical pipe are investigated to gain a better understanding of vibration excitation mechanisms. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.

Based on the large eddy simulation method, this study performed the three-dimensional transient numerical analysis of the near-wall flow field of the spiral flow in a circular pipe and applied the sub-grid model of the kinetic energy transport. The low-speed bands, streamwise vortices and hairpin vortices of the spiral flow in the near-wall region of the circular pipe are determined using the Q criterion. The ejection and sweeping of coherent structures are identified using the velocity vector of the near-wall region; moreover, the two methods of creating the hairpin vortices are established by the image time series. The results demonstrate that the development directions of the near-wall bands, streamwise vortices and hairpin vortices of the spiral flow in the circular pipe develop along the path of the spiral line. The average spanwise period of the low-speed bands in the near-wall region is approximately 120 wall units, the length is more than 900 wall units and the height is not more than 40 wall units. The separation distance of the streamwise vortices is about 119 wall units. It has a certain angle with the wall (approximately 22°). The average burst period of a hairpin vortices is less than 0.015 s.

Based on ultrasonic sound pressure attenuation, the ultrasonic pulse transmission method is proposed for measuring gas holdup in gas-liquid two-phase bubbly flows. Two ultrasonic transducers are positioned on opposite sides of a vertical upward pipe with an inner diameter of 20 mm. To obtain the relationship between ultrasonic attenuation and gas holdup, the mean value of the first pulse sequence of ultrasonic signals is first extracted as the measured signal. We used the quick closing valve method to obtain the gas holdup as the set value. Second, the relationship between the gas holdup and measured ultrasonic signals was established. The experiment result shows that the ultrasonic attenuation rate is significantly different at low and high gas holdups, as indicated by the bubble size images with a high-speed camera. We also investigated the ultrasonic field distribution using numerical simulation. The bubble size has an important effect on the ultrasonic attenuation coefficient, which provides a further physical explanation and reference for the experimental phenomena.

A model to calculate the velocity of single coarse particles in upward water flows in vertical pipes has been proposed in this paper. The model is based on the well-known drift flux model. In order to obtain both the correlations of the distribution parameter and the mean relative velocity required in the model, radial passage and velocity profiles of a single particle in upward water flow in a vertical pipe, 40 mm i. d., have been studied experimentally. In the experiment, six test particles of different size (2 to 10 mm), density (2540 to 7850 kg/m3) and shape (sphere, cube and cylinder) were used. The mean water velocity was varied up to 2.0m/s. The proposed model has been tested against the data of Toda et al., together with the present data, for different particle-pipe diameter combinations. Good agreement is obtained between the data and the calculations.