scholarly journals Investigation of the combined effect of air pockets and air bubbles on fluid transients

2017 ◽  
Vol 20 (2) ◽  
pp. 376-392 ◽  
Author(s):  
Oscar Pozos-Estrada
Keyword(s):  
Bubbly Flow ◽  
Combined Effect ◽  
Hyperbolic Partial Differential Equations ◽  
Experimental Investigations ◽  
Air Bubbles ◽  
Two Phase ◽  
Pressure Transients ◽  
Air Pocket ◽  
Experimental Apparatus ◽  
Air Pockets

Abstract This paper presents numerical and experimental investigations of the combined effect on pressure transients of air pockets and homogenous water–air bubble mixtures. An air pocket can accumulate at a high point of a pipeline along the control section located at the transition between pipes with sub- and supercritical slope, forcing open channel flow conditions underneath the pocket that ends in a hydraulic jump at the downward sloping pipe. The turbulence action at the jump generates small air bubbles that are entrained and transported along the pipe producing a two-component bubbly flow within the continuous liquid phase. A numerical model is developed, combining the explicit–implicit scheme proposed by McGuire and Morris and the method of characteristics for solving the quasi-linear hyperbolic partial differential equations for transient two-phase flow expressed in conservation form. To verify the proposed model, an experimental apparatus made of PVC was used to carry out hydraulic transient experiments. Tests were conducted in a tank–pipe–valve system and a valve with a pneumatic actuator at the downstream end generated transients. Numerical results at the test section pipe compares favorably with experimental data. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content.

Effects of water–air mixtures on hydraulic transients

2010 ◽  
Vol 37 (9) ◽  
pp. 1189-1200 ◽  
Author(s):  
Oscar Pozos ◽  
Alejandro Sanchez ◽  
Eduardo A. Rodal ◽  
Yuri V. Fairuzov
Keyword(s):  
Bubbly Flow ◽  
Experimental Investigations ◽  
Hydraulic Transients ◽  
Two Phase ◽  
Pressure Transients ◽  
Air Content ◽  
Air Pocket ◽  
Pressurized Pipelines ◽  
Air Pockets ◽  
The Impact

The purpose of this study is to investigate pressurized pipelines and the potential effects on pressure transients of air entrained at the downstream end of large entrapped air pockets followed by a hydraulic jump in pressurized pipelines. The homogeneous two-phase flow model is used to simulate the transient response of the bubbly mixture after a pump shutdown. The results show that pressure transients are significantly reduced with increasing air-pocket volumes and bubbly flow air content. Experimental investigations were carried out to analyze the impact of different air-pocket volumes located at high points of pressurized pipelines. A case study of an existing pumping system was considered to exemplify the impact of the bubbly flow air content on hydraulic transients.

On the Hydraulics of Downward Sloping Pipes With Entrapped Air Pockets

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
H. A. Warda ◽  
E. M. Wahba ◽  
E. N. Ahmed
Keyword(s):  
Hydraulic Jump ◽  
Open Channel ◽  
Numerical Results ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Dynamics Model ◽  
Computational Fluid Dynamics Model ◽  
Air Pocket ◽  
Entrapped Air ◽  
Air Pockets

Abstract In this study, air–water flow in a downward sloping pipe subsequent to the entrapping of an air pocket is investigated both numerically and experimentally. A transient, two-dimensional computational fluid dynamics model is applied to study the different possible flow regimes and their associated phenomena. The numerical model is based on the Reynolds-averaged Navier–Stokes (RANS) equations and the volume of fluid (VOF) method. Both numerical and experimental investigations provide visualization for the hydraulic jump, the blowback regime, and the full gas transport regime. The numerical results predict that the flow structure in the pipe downstream the toe of the hydraulic jump is subdivided into three distinct regions including the jet layer, the shear zone, and the circulation region, which agrees qualitatively with the previous investigations of the hydraulic jump characteristics in open channel flow. Numerical results are in reasonable agreement with the experimental measurements of the circulation length and the hydraulic jump head loss.

Bubble Size Reduction Using Mesh Bubble Breakers in Two-Phase Vertical Co-Flow

2015 ◽  
Author(s):  
Alan Kalbfleisch ◽  
Kamran Siddiqui
Keyword(s):  
Pore Size ◽  
Bubble Size ◽  
Slug Flow ◽  
High Speed ◽  
Imaging System ◽  
Bubbly Flow ◽  
High Speed Imaging ◽  
Two Phase ◽  
Vertical Column ◽  
Experimental Apparatus

Bubble breakers have been shown to reduce the bubble size and hence increasing the bubble surface-to-volume ratio facilitating higher mass transfer. We report on an experimental study investigating the effect of mesh-type bubble breaker on two-phase co-flow in a vertical column. A range of gas-liquid flow rates ratios (GLR) has been considered that covers the two-phase regimes from bubbly flow to slug flow. A vertical glass tube was used as the experimental apparatus which provides full optical access. A high speed imaging system was used to capture the flow dynamics for bubble characterization. The results show that the bubble size generated by the mesh bubble breaker is greatly affected by the pore size. For a bubbly flow regime, the initial bubble size was reduced by approximately 60%–70% for a pore size of 1mm and by about 45%–50% for a pore size of 4mm. It is found that the transition from bubbly flow to slug flow can be affected by the mesh bubble breaker. The results show that in general, the mesh bubble breaker increases the GLR limit for the transition from bubbly to slug flow.

Co-Current Air-Water Two Phase Flow Patterns in Horizontal and Vertical Circular Tube Under Various Inlet Conditions

2011 ◽  
Author(s):  
S. Zeguai ◽  
S. Chikh ◽  
O. Rahli ◽  
L. Tadrist
Keyword(s):  
Annular Flow ◽  
Two Phase Flow ◽  
Bubbly Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Transition Flow ◽  
Two Phase ◽  
Experimental Apparatus ◽  
Inner Diameter ◽  
Inlet Conditions

An experimental apparatus is setup to analyze a co-current air-water two phase flow in a 3 mm inner diameter tube with horizontal and vertical orientations. Air is axially injected through a nozzle of 260 μm of inner diameter. Air and water flow rates are accurately controlled at the inlet, covering a range of apparent velocities JL = 0.00118 to 0.0786 m/s, JG = 0.002 to 3.538 m/s for the horizontal tube and JL = 0.00078 to 0.0589 m/s, JG = 0.003 to 3.538 m/s for the upward flow. A fast camera with 250 fps is utilized to visualize the flow patterns. The experiments showed that the flow structures are very sensitive to inlet conditions. Within the covered range of velocities, several flow patterns were observed, namely bubbly flow, bubbly-slug transition flow, slug flow, slug-annular transition flow, annular flow, wavy annular flow and annular flow with dry zones. In the bubbly flow regime, a particular bubbly helical flow is observed before the dispersed bubbly flow.

A Review on Electrical Submersible Pump Head Losses and Methods to Analyze Two-Phase Performance Curve

2021 ◽  
Vol 16 ◽  
pp. 14-31
Author(s):  
Salman Shahid ◽  
Sharul Sham Dol ◽  
Abdul Qader Hasan ◽  
Omar Mustafa Kassem ◽  
Mohamed S. Gadala ◽  
...  
Keyword(s):  
Multiphase Flow ◽  
Oil And Gas ◽  
Air Bubbles ◽  
Two Phase ◽  
Pump Impeller ◽  
Head Losses ◽  
Electrical Submersible Pumps ◽  
Pump Head ◽  
Intake Pressure ◽  
Air Pockets

Electrical submersible pumps (ESP) are referred to as a pump classification whose applications arebased upon transporting fluids from submersible elevations towards a fixed pipeline. Specific ESP pumps areutilized in offshore oil and gas facilities that are frequently employed in transport of Liquefied Natural Gas(LNG) terminals. Transport of LNG is a multiphase process that causes operational challenges for ESP due topresence of air pockets and air bubbles; presenting difficulties, such as cavitation and degradation to pumpcomponents. This performance degradation causes an economic risk to companies as well as a risk to pumpperformance capabilities, as it will not be able to pump with the same pressure again. Operational references formultiphase flow in ESP are limited; thus, this research paper reports multistage pumping, review offundamentals, previous experimental as well as modelling work benefitting future literature for a potentialsolution. Industries consume power to cope up with the losses associated with pumping two-phase fluidscausing company’s fortune. Preceding experimental work on single along with multiphase flow illustrate adistinct flow pattern surrounding the area around pump impeller while the pump is in operation. Throughexperimental observation, four flow patterns were observed and studied when gas was varied at different flowrates. Increasing the intake pressure proved to increase pump performance at two-phase flow. Experimentalstudy of multiphase flow with LNG fluid is expensive; thus, experimental validation is accomplished on asingle stage pump with external intervention of air bubbles to simulate LNG vaporization at fixed pressure andtemperature difference.

Devolatilization of Molten Polymers During Multiphase Flow in a Double Screw Extruder

2002 ◽  
Author(s):  
Ingo Gestring ◽  
Dieter Mewes
Keyword(s):  
Mass Transfer ◽  
Flow Field ◽  
Bubbly Flow ◽  
Volatile Component ◽  
Bubble Nucleation ◽  
Experimental Investigations ◽  
Complex Flow ◽  
Screw Extruder ◽  
Two Phase ◽  
Flow Mechanisms

Devolatilization is a thermal separation process in order to remove low molecular solvents from mixtures of polymers. Extruders with partly filled devolatilization zones are often used for this process. The two-phase flow of the polymer and the evaporating monomers and solvents is complex due to free surfaces. In film flow and two-phase bubbly flow the polymer is heated by dissipation and cooled by evaporation of the low molecular solvent. Temperature and concentration fields are difficult to predict in extruders because of the complex flow field. Therefore the experimental investigations are carried out in special designed apparatus with a flow field similar to that in extruders and in a transparent double-screw extruder to investigate the different flow mechanisms. In order to nucleate bubbles of the volatile component the polymers must be supersaturated and some kind of deformation must exist. The bubble nucleation is shear induced. The changes in concentration during two-phase bubbly flow result in decreasing temperatures. The mass transfer rates are increased due to the large inner surfaces of the bubbles in the foam and so is the cooling by evaporation. The higher the foam expansion the better is the mass transfer.

Investigation on slug flow phenomenon in Alborz morning glory spillway and preventing its destructive effects

2020 ◽  
Vol 31 (06) ◽  
pp. 2050084
Author(s):  
Behrouz Aghebatie ◽  
Khosrow Hosseini
Keyword(s):  
Slug Flow ◽  
Temporal Variations ◽  
Morning Glory ◽  
Air Bubbles ◽  
Two Phase ◽  
Pressure Drops ◽  
Flow Phenomenon ◽  
Large Pressure ◽  
Micro Channels ◽  
Air Pockets

Slug flow is a flow pattern which occurs in conveyance systems containing a two phase-fluid flow. Large air bubbles entrapped along these systems interrupt the flow and conduct to undesirable pressures and their fluctuations. Most of the previous concerning studies on slug flow phenomenon were performed in micro-channels with small scales in which the expansion of the air bubbles was negligible. In contrast, we investigated the systems with large pressure drops which conduct to abrupt increases on the volume of air phase. In this research, the verification tests applying CFD techniques were performed in OpenFOAM software by interFoam solver. The performance of morning glory spillways is investigated under steady states. While during the occurrence of flood, by increasing the depth over the spillway crest, the discharge is augmented which conducts to entrap the air pockets with pressure and velocity fluctuations. These fluctuations influence on the life of structures and their performances. This study aimed on unsteady flow in a glory morning spillway and its consequences and proposing the measures for reducing the destructive effects of slug flow. The pressure and velocity fluctuation were considered as the indices for the performance of a hydraulic structure. Spatial and temporal variations of pressure and velocity along the spillway are evaluated. Also, the influences of spillway geometry on slug flow and the measures to attenuate its destructive effects are analyzed. The results showed that the better performances of morning glory spillway are coincided by the diameter of tunnel superior than the height of water above the crest.

Experimental Analysis of a Two Phase Air-Water Flow in a Tube of Small Size Diameter Under Various Inlet Conditions

2010 ◽  
Author(s):  
S. Zeguai ◽  
S. Chikh ◽  
O. Rahli ◽  
L. Tadrist
Keyword(s):  
Water Flow ◽  
Bubbly Flow ◽  
Water Flow Rate ◽  
Flow Regimes ◽  
Vertical Tube ◽  
Two Phase ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Inner Diameter ◽  
Inlet Conditions

An experimental apparatus is setup to analyze a two phase air-water upward flow in a vertical tube with an inner diameter of 3 mm. Air is axially injected through a microduct of 260 μm inner diameter. Various inlet conditions for air pressure and water flow rate are tested covering a wide range of superficial velocities JL = 0.221 to 0.312 m/s and JG = 0.061 to 0.083 m/s for a given position of air injection (x = 8cm). A fast camera with 250 fps is used to visualize different flow regimes. Experiments showed that the flow type is very sensitive to inlet conditions and several flow regimes were observed namely: the bubbly flow, the slug flow and the annular flow.

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