Flows In Small Diameter Pipe Research Articles

Modeling of transition boundary from stratified to non-stratified liquid-liquid flows in small diameter pipe

Modeling the instability of the interfacial wave in stratified liquid-liquid flows is a popular topic and attracts the interest of scholars. In this study, an experimental study is implemented in horizontal and +5° inclined pipes with an inner diameter of 20 mm. A planar laser-induced fluorescence-60 (PLIF-60) system is utilized to visualize the flow structures at the pipe radial section, such as the curved interface and the droplet entrainment. Image processing is used to correct the PLIF-60 flow images and reconstruct quasi-3D flow structures. Flow pattern maps for horizontal and inclined flows are drawn to indicate the transition boundary between stratified and non-stratified flows. Young-Laplace equation with dynamic contact angle is developed to predict the interface configuration. The predicted interface configuration shows a good agreement with that detected by the PLIF-60 system. In view of the fact that the interface configuration is partly associated with the stratified/non-stratified flow transition, a modified model for the transition boundary is established based on Kelvin-Helmholtz (KH) stability. Comparisons of the proposed transitional criteria with experimental data and available data in liquid-liquid systems show reasonable agreement in small diameter pipes. Additionally, the proposed model with the consideration of interface configuration is basically not dependent on the wave parameters, such as wave amplitude and wavelength, providing a new way for predicting the transition boundary from stratified to non-stratified liquid-liquid flows in small diameter pipe.

Water Holdup Measurement of Gas-Liquid Flows Using Distributed Differential Pressure Sensors

In order to reduce the measurement error caused by non-uniform distribution of dispersed phase, distributed differential pressure sensors are used to measure the pressure drop of gas-liquid flows in small diameter pipe. Water holdup in vertical upward pipe is predicted by the distributed differential pressure sensors, based on the correlations of mixture friction coefficient ${f}_{\textit {tp}}$ under different flow patterns. The water holdup measured by the rotating electric field conductivity sensor is used as the reference value based on the improved Maxwell equations. The dynamic experiments prove that the water holdup prediction accuracy of Ansari model is higher than that of Zhang model, and it can achieve a satisfactory prediction result for water holdup of gas-liquid two-phase flow in small diameter pipe. The average absolute deviation (AAD) of the predicted water holdup relative to the reference water holdup is 0.026, and the average absolute percentage deviation (AAPD) is 5.52%.

Prediction of pressure drop for segregated oil-water flows in small diameter pipe using modified two-fluid model

Horizontal segregated oil-water two-phase flows are widely encountered in oil wells. The pressure drop is an important parameter to evaluate the productivity of the horizontal oil well. In this study, through introducing dynamic contact angle, we calculate the oil-water interface shape by solving Young-Laplace equation. The oil-water interface shapes and the wave characteristics are considered to modify the closure relations of the two-fluid model (TFM), and consequently the pressure drop of horizontal oil-water flows is predicted using the modified TFM. In addition, we predict the pressure drop of horizontal oil-water flows using the TFM with flat interface. Through comparing the prediction results of the pressure drop, it is found that the TFM modified with dynamic contact angle allows for higher accuracy in pressure drop prediction, and it is not dependent on the flow pattern discrimination.

Interfacial area transport due to shear collision of bubbly flow in small-diameter pipes

In view of the practical importance of the interfacial area transport equation in flow analysis based on the two-fluid model, especially for flow analysis in a reactor core which has a relatively small channel configuration, the dominant mechanism in the interfacial area transport in small diameter pipes was firstly identified by evaluating the experimental data obtained for pressurized bubbly flows under microgravity, where the source and sink terms of the interfacial area concentration due to bubble expansion and wake entrainment collision are negligible. The sink term of the interfacial area concentration of bubbly flow in small diameter pipe was modeled in terms of the shear collision mechanism. The one-dimensional interfacial area transport equation with the developed sink term was evaluated by using 74 datasets obtained for adiabatic gas-liquid bubbly flows, including upward flows and microgravity flows in pipes with inside diameters of 9.0, 5.0 and 3.0mm. A detailed discussion was provided on the interfacial area transport mechanism in small-diameter pipe. The overall standard deviation of the absolute error between predicted and measured interfacial area concentrations was 11.8%. The present model will reproduce the interfacial area transport of bubbly two-phase flows in small-diameter pipes with inside diameters of 3.0–9.0mm, at superficial liquid and gas velocities over the ranges 〈jf〉=0.073–0.949m/s, and 〈jg〉=0.00434–0.0500m/s, and also over a wide range of axial distances, z/D=5–188.

Pipeline transport of heavy crudes as stable foamy oil

A new idea was proposed to transport heavy crudes as foamy oil at normal temperature. The effects of foaming agent type and concentration, foam stabilizer type and concentration, oil–water volume ratio and temperature on the formation and stability of foamy oil were evaluated. The foamy oil properties and drag characteristics of foamy oil flow in small diameter pipes were investigated. The results indicate that the prepared stable foamy oil could be characterized as non-Newtonian power law fluid. The predicted pressure drops were in good agreement with the measured ones. The significant dynamic viscosity reduction rates were obtained.

Multi-scale cross-correlation characteristics of void fraction wave propagation for gas-liquid two-phase flows in small diameter pipe

The void fraction wave is a special physical phenomenon in a gas-liquid two-phase flow system. Understanding the propagation of the void fraction wave is of great significance for uncovering the physical mechanisms in both flow pattern transition and the fluid velocity measurement. In this study, detrended cross-correlation analysis (DCCA) is used to investigate the multi-scale cross-correlation characteristics of the coupled ARFIMA processes. It is found that the DCCA can effectively reveal the multi-scale cross-correlation dynamical behaviors of complex system. Then, we carry out the experimental test in a vertical gas-liquid two-phase flow pipe with small inner diameter. The DCCA is used to detect the cross-correlation characteristics of the void fraction wave on multiple time scales, and the growth rate of the cross-correlation level for the void fraction wave is observed on low time scales. Additionally, the spatial attenuation factor (SAF) of the void fraction wave is calculated to investigate the instability of the wave propagation. The SAF is close to zero under the transitional flow patterns, which means that the void fraction wave is in a stable propagating state. For bubble flows, the void fraction wave presents the attenuation characteristics, whilst the void fraction wave shows the amplification characteristics under the slug and churn flow patterns. Interestingly, the instability behaviors of the void fraction wave are always associated with its multi-scale cross-correlation characteristics. Specifically, the increasing rate of the wave cross-correlation level on low scales is much higher for transitional flow patterns, which is corresponding to the stable propagating characteristic of the void fraction wave. However, when the void fraction wave exhibits attenuation or amplification characteristics under other flow patterns, the increasing rate of the wave cross-correlation level on low scales is much lower.

Flow pattern and water holdup measurements of vertical upward oil–water two-phase flow in small diameter pipes

We experimentally investigate vertical upward oil–water two-phase flow in a 20mm inner diameter pipe. We first using vertical multiple electrode array conductance sensor measure the water holdup, and using mini-conductance probes define five observed flow patterns, i.e., very fine dispersed oil-in-water (VFD O/W) flow, dispersed oil-in-water (D O/W) flow, oil-in-water slug (D OS/W) flow, water-in-oil (D W/O) and transition flow (TF). Then we present an experimental flow pattern map with oil and water superficial velocity ranging from 0.258m/s to 3.684m/s and 0.184m/s to 1.474m/s, respectively. In addition, we obtain the flow pattern transition boundaries in terms of water holdup. Finally, we propose an effective quadric time–frequency representation, i.e., the adaptive optimal kernel time–frequency representation (AOK TFR) to investigate the complex behavior underlying vertical upward oil–water flow. In particular, we extract total energy and time–frequency entropy to characterize the evolutions of flow patterns. The results suggest that AOK TFR based method could potentially be a powerful tool for characterizing the dynamical characteristics of different vertical upward water-dominant oil–water flow patterns.

The split of vertical two-phase flow at a small diameter T-junction

Measurements and observations of the phase split occurring at a small diameter vertical T-junction are reported. Time varying, void fraction data obtained using ring-type conductance probes have been analysed to yield valuable information regarding the effect of the junction on flow behaviour. It is shown through comparisons with the work of Stacey et al. [2000. The split of annular two-phase flow at a small diameter T-junction. International Journal of Multiphase Flow 26, 845–856] in a horizontal T-junction of a similar size that the orientation of the junction has no influence on the flow split. This behaviour is attributed to the absence of flooding and is corroborated by our high-speed images. Subsequently, better prediction of the phase split is obtained when the model of Azzopardi [1988. Measurements and observations of the split of annular flow at a vertical T-junction. International Journal of Multiphase Flow 14, 701–710] is modified to account for the absence of flooding. Regarding flow transitions, the methods by Barnea et al. [1983. Flow pattern in horizontal and vertical two-phase flow in small diameter pipes. The Canadian Journal of Chemical Engineering 61, 617–620] and Omebere-Iyari et al. [2005. Flow patterns for gas/liquid flow in small diameter tubes. Ninth UK National Heat Transfer Conference, Manchester, UK, 5–6 September] are found to give good predictions of the exit flow patterns in the horizontal side arm and vertical run arm, respectively.

Steady and Dynamic Models of Fuel and Air Flow in Carburetors for Small Engines

This work presents the mathematical model of a complex flow network containing short metering orifices, compressible flow, and two-phase flow in small diameter pipes. It has been developed to study the steady and dynamic flows in a carburetor for small engines. It extends the previously published models by incorporating a detailed review of two-phase flow pressure drop, the effect of the fuel well on the control of air-bleed flow, and dynamic flow. The homogeneous two-phase flow model, which is commonly used in previous models, was compared to an empirical correlation derived from experiments in small pipes and found to be in poor agreement. In order to assess dynamic flow conditions, the model was extended by solving instantaneous one-dimensional Navier-Stokes equations in single-phase pipes. This strategy proved successful in explaining the mixture enrichment seen under pulsating flow conditions. The model was also used to derive a sensitivity analysis of geometries and physical properties of air and fuel.

Slug flow in small diameter pipes and T-junctions

To date, the majority of all experiments investigating phase split at T-junctions have been conducted using air–water at near atmospheric pressures in pipes greater than about 10 mm in diameter. The research reported here has studied the split of air–water flows using a 0.005 m T-junction with all pipes in the horizontal plane. Analysis of the phase split has been confined to the slug flow regime for four gas superficial velocities, 1.14, 1.82, 2.28, 4.56 m/s, and three liquid superficial velocities, 0.093, 0.166, 0.313 m/s. For each experimental run the pressure at the T-junction was maintained at 148 kPa. This compliments previous research conducted on the same rig when the flow pattern was annular or stratified. Qualitative and quantitative results of the slug flow under the differing gas and liquid inlet superficial velocities were obtained using a high-speed video. Footage was recorded of both the fully developed slug flow and how this flow divided at the T-junction. Measured properties of the slug flow were compared with previously published methods for predicting slug flow variables.

Two‐Phase Bubbly Flow Structure in Large‐Diameter Vertical Pipes

AbstractThe two‐phase flow structure of an air‐water, bubbly, upward flow in a 20 cm diameter pipe is presented with particular emphasis on the local interfacial area concentration. The radial distribution of void fraction, bubble velocity, bubble size, bubble frequency, and interfacial area concentration were measured using a local dual‐optical probe. The experimental results showed that the saddle‐type distribution of void fraction and interfacial area concentration, which are common for bubbly flow in small diameter pipes, only appeared in the present experiments under conditions of very low area‐averaged void fraction (<ϵ> < 0.04). The values for the interfacial area concentration were higher in large diameter pipes when compared with data obtained under the same flow conditions in small pipes. The area‐averaged void fraction data were correlated using the drift‐flux model.

New Interfacial Drag Force Model Including Effect of Bubble Wake, (I) Model Development for Steam-Water Bubbly Flow in Large-Diameter Pipes

Several experimental results show that bubbles can easily be captured in the wake formed by leading bubbles when multiple bubbles are rising in a liquid. It is suggested from this experimental result that the effect of bubble wake should be included in the constitutive relationships representing the interfacial drag force. In the present study, steam-water bubbly flow experiments were performed to develop a new interfacial drag force model including the effect of bubble wake. Since the validity of the existing constitutive equations have been tested mainly for two-phase flow in small-diameter pipes, our study focused on two-phase flow in a large-diameter pipe. Using a one-dimensional two-fluid model, the applicability of the new interfacial drag force model to our experimental conditions was investigated. As a result, it was shown that the present model markedly improves the accuracy of the predicted results. It was therefore demonstrated that the present bubble wake model is effective at least for the conditions which were used for model development. Its applicability to different conditions will be discussed in a subsequent study.

Film thickness in horizontal annular flow

AbstractFilm thickness in horizontal annular flow in small diameter pipes (8‐12 mm) was measured as a function of circumferential position. In addition a simple analytical model for the prediction of the film thickness at the top and bottom of the pipe is proposed.

Flow pattern in horizontal and vertical two phase flow in small diameter pipes

AbstractNew data on flow pattern transition for gas liquid flow in small diameter tubes (4 to 12 mm) is presented. The experimental results are compared with previously published models for horizontal and vertical flows considered to be valid for medium and large diameter pipes. The effect of surface tension which might be expected to be important in small diameter pipe flow has been found to affect only the stratified‐slug transition in horizontal flow. A modification to the model to include this effect is proposed.

Rheological Properties of High-Viscosity Solutions of Long Molecules

UNDER the above heading, we presented a note in Nature1 in which we directed attention to certain peculiar phenomena observed with concentrated solutions of rubber or of aluminium soaps in hydrocarbons and gave an explanation. These phenomena concerned secondary flows, high inlet losses for flow in pipes, existence of retardation layers with flow in small-diameter pipes and an increase in the surface energies of these systems when they are strained. It was noticed that the free energy of these systems increased on straining. Due to absence of experimental data, this increase in free energy was ascribed to a decrease in entropy, in analogy with the kinetic theory of rubber elasticity.