Investigation of single and two-phase flows in a radial centrifugal rotor through particle image velocimetry

Abstract

Two-phase gas-liquid flows are commonly found in many industrial applications, e.g., chemical, nuclear, and oil industries. Several pieces of equipment handling two-phase flows show lower performance when compared to those under single-phase operation. Particularly, Electric Submersible Pumps (ESPs) can operate with gas-liquid flows during oil and gas production, representing an off-design condition that degrades their performance. Experimental studies have been performed to understand how the gas phase impairs the pump’s head, efficiency, and power consumption during two-phase flow operations. Visualization studies have also shown the gas phase behavior inside the pump channels, with the occurrence of different flow patterns that depend on the operating conditions. However, studies aiming at understanding how the gas phase affects the liquid flow field are scarce. In this context, this work employs Particle Image Velocimetry (PIV) to evaluate the liquid flow field in a radial centrifugal rotor operating with single and two-phase air-water flows. Different liquid and gas flow rates were tested, as well as different rotating speeds. Results for single-phase flow show that the rotor behaves according to kinematic similarity, and rotational periodicity between adjacent channels was observed, even at part-load operations. Analyses in different planes have shown that the velocity magnitude is higher near the hub than near the shroud, while turbulence intensities have the opposite behavior. This difference can be attributed to the flow direction change from the intake pipe to the rotor channels. Results for two-phase flow have shown that velocity reduces, whereas turbulent kinetic energy and turbulent shear stress increase for a small gas volume fraction. However, increasing the mean bubble diameter at the intake has reduced the turbulent kinetic energy. This effect could be due to energy absorption on the bubbles’ surface. Moreover, the velocity at the rotor inlet has increased by increasing the mean bubble diameter, possibly due to an area restriction caused by the bubbles. Furthermore, the turbulence has increased by increasing the liquid flow rate while keeping the gas flow rate fixed. The findings from this work have shed light on the gas-phase effect over the liquid flow field, especially on turbulence. Furthermore, the results herein presented can be used for numerical modeling validation, improving models such as turbulence enhancement or suppression caused by bubbles.