Tag: two-phase flow
TR-PIV and CNN-based analysis of liquid–liquid two-phase flow in a centrifugal pump impeller
Centrifugal pumps are widely used in engineering applications, consuming a considerable amount of energy across the globe. However, in many cases they operate under off-design conditions, such as multiphase flows, implying in an even higher energy consumption. A prominent example is the mixture of water and viscous oil, where the phases may exhibit a dispersed flow pattern depending on superficial velocities. Understanding the flow dynamics within the impeller during two-phase liquid–liquid operation is crucial for grasping the mechanisms underlying energy dissipation and pump performance. In this work, we investigate experimentally oil–water flows in dispersed regime within a centrifugal pump impeller, and propose a framework for automatically identifying the dispersed phase and measuring the velocity field of the continuous phase. For that, we carried out time-resolved particle image velocimetry (TR-PIV) in a transparent pump operating under two-phase flow conditions. An image processing technique based on deep learning was developed to dynamically mask oil droplets (dispersed phase) and distinguish them from water-seeded particles (continuous phase) in the raw TR-PIV data. Additionally, a method to evaluate the phase-ensemble average velocity was designed and implemented. The results revealed that neglecting dynamic masking in the TR-PIV images caused an inversion of velocity values between the pressure and suction blades, driven by the accumulation of oil droplets in recirculation zones near the suction blade. This result highlights the importance of accurately tracking the dispersed phase. Our findings indicate higher turbulent kinetic energy (TKE) values at lower flow rates when the dispersed phase consists of larger oil droplets. These findings expand our understanding of multiphase flows in centrifugal pumps, which can be proven useful for validating numerical simulations, proposing new mathematical models, and contributing to the design of improved and energy-saving impellers.
Flow visualization in centrifugal pumps: A review of methods and experimental studies
Methods for flow visualization have been decisive for the historical development of fluid mechanics. In recent years, technological advances in cameras, lasers, and other devices improved the accuracy and reliability of methods such as High-Speed Imaging (HSI) and Particle Image Velocimetry (PIV), which have become more efficient in visualizing complex transient flows. Thus, the study of centrifugal pumps now relies on experimental techniques that enable a quantitative characterization of single- and two-phase flows within impellers and diffusers. This is particularly important for oil production, which massively employs the so-called Electrical Submersible Pump (ESP), whose performance depends on the behavior of bubbles and drops inside its impellers. Visualization methods are frequently used to study gas-liquid flows in pumps; however, the visualization of liquid-liquid dispersions is complex and less common, with few publications available. Methods to characterize the motion of gas bubbles are often unsuitable for liquid drops, especially when these drops are arranged as emulsions. In this context, there is room to expand the use of visualization techniques to study liquid-liquid mixtures in pumps, in order to improve the comprehension of phenomena such as effective viscosity and phase inversion with focus on the proposition of mathematical models, for example. This is a main motivation for this paper, which presents a review of researches available in the literature on flow visualization in centrifugal pumps. A broad set of studies are reported to provide the reader with a complete summary of the main practices adopted and results achieved by scientists worldwide. The paper compares the methods, investigates their advantages and limitations, and suggests future studies that may complement the knowledge and fill the current gaps on the visualization of single-phase flows, gas-liquid, and liquid-liquid mixtures.