(2017) Numerical investigation of the effect of viscosity in a multistage electric submersible pump, Engineering Applications of Computational Fluid Mechanics, 11:1, 258-272, DOI: 10.1080/19942060.2017 ABSTRACTElectric submersible pump (ESP) systems are commonly used as an artificial lift technique by the petroleum industry. Operations of ESPs in oil wells are subjected to performance degradation due to the effect of oil viscosity. To understand this effect a numerical study to simulate the flow in three stages of a multistage mixed-flow type ESP operating with a wide range of fluid viscosities, flow rates, and rotational speeds was conducted. The problem was solved by using a commercial computational fluid dynamics (CFD) software. The numerical model was validated with experimental head curves from the literature at different viscosities and rotational speeds available for the same ESP model used in this study, and good agreement was found. Performance degradation was evaluated by analyzing the effect of viscosity on head and flow rate. In addition, a flow field analysis to compare the flow behavior when the pump operates at different viscosities was carried out. The interaction between stages was also analyzed, and the influence of a previous stage on the upstream flow was evidenced. The flow field was analyzed at a curved surface that follows the complex mixed-flow geometry of the stages. CFD proved to be useful for exploring this kind of feature, a task whose accomplishment by means of experimental methods is not trivial. Such analysis helps to understand the flow pattern behind head and flow rate degradation when the Reynolds number is decreased. The results from this work are helpful as they provide a basis to estimate performance degradation for general scenarios. ARTICLE HISTORY
Centrifugal pumps operate below their nominal capacity when handling gas–liquid flows. This problem is sensitive to many variables, such as the impeller speed and the liquid flow rate. Several works evaluate the effect of operating conditions in the pump performance, but few bring information about the associated gas–liquid flow dynamics. Studying the gas phase behavior, however, can help understanding why the pump performance is degraded depending on the operating condition. In this context, this paper presents a numerical and experimental study of the motion of bubbles in a centrifugal pump impeller. The casing and the impeller of a commercial pump were replaced by transparent components to allow evaluating the bubbles' trajectories through high-speed photography. The bubble motion was also evaluated with a numerical particle-tracking method. A good agreement between both approaches was found. The numerical model is explored to evaluate how the bubble trajectories are affected by variables such as the bubble diameter and the liquid flow rate. Results show that the displacement of bubbles in the impeller is hindered by an increase of their diameter and impeller speed but facilitated by an increase of the liquid flow rate. A force analysis to support understanding the pattern of the bubble trajectories was provided. This analysis should enlighten the readers about the dynamics leading to bubble coalescence inside an impeller channel, which is the main reason behind the performance degradation that pumps experience when operating with gas–liquid flows.
This work presents a numerical investigation of the free surface flow in a gas-liquid separator with a cylindrical expansion chamber using Computational Fluid Dynamics. The centrifugal flow is set through a tangentially oriented nozzle at the chamber wall and is modeled using an inhomogeneous Eulerian-Eulerian multiphase flow model with the free surface approach to capture the phases interface. Fluid dynamics is examined for a range of fluid viscosities and flow rates for a single-phase liquid flow at the inlet. Liquid-gas bubbly-flow at the inlet is also considered to investigate some aspects of the phases separation inside the cylindrical chamber. Analysis of the flow field reveals that the impact of the fluid at the chamber wall combined with the centrifugal movement push part of the fluid upwards, stabilizing a liquid level above the nozzle. Near the inlet, the flow dynamics is characterized by a strong centrifugal motion, which decreases continuously below the entrance position due to gravity and viscous effects. The liquid level over the chamber wall and the centrifugal intensity increase with the flow rate, but decrease with viscosity. Viscosity also tends to enlarge the liquid layer thickness over the chamber wall and diminish the residence time of the liquid from the inlet down to the chamber’s bottom exit. Investigation of liquid-gas bubbly-flows in this equipment shows that separation occurs mainly near the chamber entrance due to the sudden expansion and the formation of a thin fluid layer over the chamber wall. In a percentage basis, phases tend to be more effectively separated for higher inlet gas volume fractions, lower liquid viscosities and bigger gas bubbles. These conclusions give technically interesting information for dimensioning hydrocyclones for gas-liquid flow separation.
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