Abstract
Multiphase flow in annular channels is complex, particularly in the region where the flow direction abruptly changes between the inner pipe and the outer pipe, as the cases in horizontal drilling and pneumatic conveying. Simplified models and experience are still the main sources of information. First, to understand the process more deeply, Computational Fluid Dynamics (CFD) package Fluent is used to simulate the gas-solid flow in the horizontal and the inclined section of an annular pipe. Discrete Phase Model (DPM) is adopted to calculate the trajectories of solid particles of different sizes at different air velocities. Also, the Two-Fluid model is used to simulate the sand flow in the inclined section for the case of air flow stoppage, for which an experiment is also conducted to verify the CFD simulation. Simulation results reveal the behaviour of the solid particles showing the dispersed spatial distribution of small particles near the entrance. On the other hand, larger particles manifest a distinct sedimented flow pattern along the bottom of the pipe. The density distribution of the particles over a pipe cross section is demonstrated at a variety of air velocities. The results also show that the large airspeed tends to generate swirls near the outlet of the inner pipe. In addition, Electrical Capacitance Tomography (ECT) technology is used to reconstruct the spatial distribution of particles, and the cross-correlation algorithm to detect velocity. Both the distribution and the velocity measurement by electric sensors agree reasonably well with the CFD predictions. The details revealed by CFD simulation and the mutual-verification between CFD simulation and the ECT method of this study could be valuable for the industry in drilling process control and equipment development.
Highlights
Gas-solid two-phase flow is common in industrial applications
Horizontal drilling includes a horizontal section and an inclined section. This can be modelled by an annulus structure with an inner pipe supplying air as the carrier fluid to bring out the debris in the annular space
Attached at the end of the inner pipe is the drill where air exits the inner pipe and flows into the annulus space. This is the place where bit, the enter particles the space are and carried away bythe air;annulus it can regarded ascan the inlet boundary for where airannulus exitsenter the inner pipe flows space. This is it the place where solid the and annulus space andinto are carried away bybeair; be regarded as the the our numerical simulation to be introduced in the subsequent sections
Summary
Gas-solid two-phase flow is common in industrial applications. While the majority of studies are focused on the flows in circular pipes, flow in annular pipes has much to be investigated due to its frequent appearances in the oil industry, such as in horizontal drilling. Numerical simulation is becoming the main tool for gas-solid flows in the oil industry. Sedrez [8] studied the erosion modeling for gas-solids flow in cyclones via experiments and simulation. Andriyanto Setyawan [14] studied circumferential liquid film distribution in annular two-phase flow, he used the conductance probe detected thickness distribution in an air-water horizontal annular two-phase flow. Xie [15] studied droplet impact on a flowing liquid film in annular two-phase flow via simulation. In this study, we intend to describe the flow characteristics of the solids in the annulus section to a certain degree of detail This is to be carried out by both CFD simulations and Electrical Capacitance Tomography (ECT) measurement. We wish to verify the simulation methods and results by ECT measurement, which could establish a certain degree of guide or experience for future design of the trilling process and equipment development
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