Velocity bias in intrusive gas-liquid flow measurements

Abstract

Gas–liquid flows occur in many natural environments such as breaking waves, river rapids and human-made systems, including nuclear reactors and water treatment or conveyance infrastructure. Such two-phase flows are commonly investigated using phase-detection intrusive probes, yielding velocities that are considered to be directly representative of bubble velocities. Using different state-of-the-art instruments and analysis algorithms, we show that bubble–probe interactions lead to an underestimation of the real bubble velocity due to surface tension. To overcome this velocity bias, a correction method is formulated based on a force balance on the bubble. The proposed methodology allows to assess the bubble–probe interaction bias for various types of gas-liquid flows and to recover the undisturbed real bubble velocity. We show that the velocity bias is strong in laboratory scale investigations and therefore may affect the extrapolation of results to full scale. The correction method increases the accuracy of bubble velocity estimations, thereby enabling a deeper understanding of fundamental gas-liquid flow processes.

Invariance Properties of the Entropy Production, and the Entropic Pairing of Inertial Frames of Reference by Shear-Flow Systems

“…First consider the unsteady purely translational (irrotational) motion of an isolated rigid sphere with velocity V (t) [m s −1 ] in a uniform flow field of velocity U(t) [m s −1 ], both relative to a common inertial frame of reference (Figure 6a without rotation). A force balance at low velocities yields [90][91][92][93][94][95][96][97][98]:…”

Bubble velocimetry using the conventional and CNN-based optical flow algorithms

“…Interfacial momentum exchange between continuous and dispersed phases is very important in understanding the physics of multiphase flows, in particular, for the gas-liquid two-phase flows, where the gas-liquid interface deforms in a complex manner and the mutual interaction between the phases are correlated [1][2][3][4][5][6][7][8][9][10] . Since the interfacial forces (e.g., drag, lift, added mass and basset history forces) acting on the rising bubbles in a liquid flow [11][12][13] and the bubbleinduced agitation (pseudo-turbulence) to the liquid flow [5,8,[14][15][16][17][18][19] are strongly determined by the bubble velocity (motion) relative to the liquid-phase, it is critical to have the detailed information of bubble velocities.…”

Analysis of rectangular free-falling jets in overtopping of concrete dams

“…Estudios posteriores han evidenciado la fuerte interacción entre los fenómenos de introducción de aire y los efectos de la intensidad turbulenta en flujos de agua-aire, teniendo en cuenta su aplicación al campo de las estructuras hidráulicas, por ejemplo, (Ervine et al 1980;Brocchini 2001;Felder 2013;Valero 2018;Krammer et al 2020;Hohermuth et al 2021).…”

“…Por ejemplo, Borges et al (2010) 2010) sugieren también que la dificultad en la precisión para detectar burbujas pequeñas puede deberse a la geometría de la sonda que produce un punto de estancamiento en la zona cercana al sensor de la sonda, provocando que las burbujas pequeñas de aire se alejen del sensor de la sonda. En línea a esa afirmación estudios recientes han demostrado que las interacciones entre las burbujas y la sonda conducen a una subestimación de la velocidad real de la burbuja debido a la tensión superficial (Hohermuth et al 2021).…”

“…Recientemente, se han producido avances en las metodologías para el procesamiento de las señales y obtención de los parámetros agua-aire (Krammer & Valero 2019;Krammer et al 2020;Hohermuth et al 2021).…”