Experimental Analysis of Gas–Liquid Flows in a Centrifugal Rotor

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Henrique Stel ◽  
Edgar M. Ofuchi ◽  
Rafael F. Alves ◽  
Sergio Chiva ◽  
Rigoberto E. M. Morales
Keyword(s):  
Liquid Flow ◽  
Experimental Analysis ◽  
Volume Fraction ◽  
Operating Conditions ◽  
Centrifugal Pumps ◽  
Phase Dynamics ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Gas Liquid Flow ◽  
Liquid Flows

Abstract This work presents an experimental analysis of gas–liquid flows in a centrifugal rotor prototype. Pressure rise curves are evaluated considering a wide range of liquid and gas flowrates and different rotating speeds. An innovative apparatus including a dynamic sealing system, back illumination, and filming in a rotating frame of reference is employed to visualize gas–liquid flow patterns at different operating conditions. Volume fraction measurement and bubble-size evaluation are also taken into account. The experimental apparatus allowed analyzing details of the gas-phase dynamics inside the rotor channels. That includes preferential bubble paths and zones of agglomeration, gas pocket formation, coalescence and breakup, and the effect of flow pattern transition on different degrees of performance degradation that centrifugal rotors are subject to when working with gas–liquid flows. Also, important information about the effect of the gas flowrate and the rotating speed on the performance of the assumed rotor prototype could be gathered. Discussions in this work should contribute to comprehend the behavior of gas–liquid flow in centrifugal pumps, a topic that is still far from being well understood. Qualitative and quantitative data here presented could also be valuable to guide the development of numerical models to solve this problem.

Experimental Visualization of Gas-Liquid Flow Patterns in a Centrifugal Rotor

2019 ◽  
Author(s):  
Henrique Stel ◽  
Edgar Minoru Ofuchi ◽  
Rafael Fabrício Alves ◽  
Sergio Chiva ◽  
Rigoberto E. M. Morales
Keyword(s):  
Flow Rate ◽  
Liquid Flow ◽  
Volume Fraction ◽  
Flow Patterns ◽  
Centrifugal Pumps ◽  
Gas Volume Fraction ◽  
Gas Liquid Flow ◽  
Liquid Flows ◽  
Complex Phenomena ◽  
Gas Volume

Abstract Centrifugal pumps operating with gas-liquid flows can undergo severe performance degradation. This can be attributed to an effect of the gas phase on the liquid flow orientation in the pump impeller channels, which induces additional hydraulic losses that negatively affect the delivered head and flow rate. Effort to investigate the effect of many operating parameters on the pump performance under multiphase flows can be found on numerous experimental investigations. Few studies, however, bring together flow visualization to understand the physics behind the behavior of centrifugal pumps with gas-liquid flows. One issue is that pumps involve rotating parts, metallic casing and limited visual access, sometimes making it hard to interpret flow patterns and to understand complex phenomena, such as bubble breakup and coalescence. Such issues usually lead to unsatisfactory image quality, which in turn makes it difficult to extract quantitative data from the obtained images, such as gas volume fraction and bubble size distribution. In an attempt to overcome many difficulties of previous investigations, this work presents an experimental study aimed to visualize gas-liquid flow patterns in a centrifugal rotor prototype using a novel approach. The experimental apparatus uses a plane and transparent rotor, assembled with an intake pipe and a discharge chamber by means of a dynamic seal system that dismisses the use of an enclosing pump casing. This makes possible to use back illumination of the impeller for visualization, which in turn is done by using a camera attached to the impeller axis for filming in a rotating frame of reference. This setup, which is new in the open literature, provides high image contrast and sharpness for clear interpretation of the flow patterns found inside the rotor channels for a wide range of operating conditions. This advantage, in turn, allows using image processing for quantitative assessment of gas volume fraction distributions. Pressure rise versus flow rate curves are measured together to investigate the rotor performance degradation associated with the gas-liquid flow patterns for a range of liquid and gas flow rates. Information obtained with the designed experimental setup at controlled conditions help not just to bring further understanding to the complex phenomena involved with multiphase flows in rotating devices, but also in the direction of validating a numerical model for reliable simulations of gas-liquid flows in centrifugal pumps, which is lacking in the current literature.

scholarly journals Velocity bias in intrusive gas-liquid flow measurements

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
B. Hohermuth ◽  
M. Kramer ◽  
S. Felder ◽  
D. Valero
Keyword(s):  
Liquid Flow ◽  
Breaking Waves ◽  
Correction Method ◽  
Force Balance ◽  
Bubble Velocity ◽  
Natural Environments ◽  
Flow Measurements ◽  
Gas Liquid Flow ◽  
Liquid Flows ◽  
Velocity Bias

AbstractGas–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.

Axial and Radial Investigation of Hydrodynamics in a Bubble Column; Influence of Fluids Flow Rates and Sparger Type

2006 ◽  
Vol 4 (1) ◽  
Author(s):  
Hélène Chaumat ◽  
Anne-Marie Billet ◽  
Henri Delmas
Keyword(s):  
Liquid Flow ◽  
Gas Flow ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Batch Mode ◽  
Flow Rates ◽  
Wide Range ◽  
Injection Zone

A detailed investigation of local hydrodynamics in a pilot plant bubble column has been performed using various techniques, exploring both axial and radial variations of the gas hold-up, bubble average diameter and frequency, surface area. A wide range of operating conditions has been explored up to large gas and liquid flow rates, with two sparger types. Two main complementary techniques were used: a quasi local measurement of gas hold-up via series of differential pressure sensors to get the axial variation and a double optic probe giving radial variations of gad hold-up, bubble average size and frequency and surface area.According to axial evolutions, three zones, where radial evolutions have been detailed, have been separated: at the bottom the gas injection zone, the large central region or column bulk and the disengagement zone at the column top. It was found that significant axial and radial variations of the two phase flow characteristics do exist even in the so called homogeneous regime. The normalized profiles of bubble frequency appear sparger and gas velocity independent contrary to bubble diameter, gas hold-up and interfacial area normalized profiles. In any case bubbles are larger in the sparger zone than elsewhere.The main result of this work is the very strong effect of liquid flow on bubble column hydrodynamics at low gas flow rate. First the flow regime map observed in batch mode is dramatically modified with a drastic reduction of the homogeneous regime region, up to a complete heterogeneous regime in the working conditions (uG> 0.02 m/s). On the contrary, liquid flow has limited effects at very high gas flow rates.A large data bank is provided to be used for example in detailed comparison with CFD calculations.

scholarly journals The flow and mass transfer characteristics of concentric gas-liquid flow in an advanced static mixer

2020 ◽  
pp. 24-24
Author(s):  
Huibo Meng ◽  
Zhonggen Li ◽  
Yanfang Yu ◽  
Mengqi Han ◽  
Shuning Song ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Liquid Flow ◽  
Operating Conditions ◽  
Static Mixer ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Local Mass ◽  
Transfer Characteristics ◽  
Local Mass Transfer ◽  
Gas Liquid Flow

The fluid dynamic and mass transfer characteristics of concentric upward gas-liquid flow were studied in the industrial static mixer with four equally spaced helical inserts (FKSM). The numerical simulations of gas volume fraction in Kenics mixer had a good agreement with the numerical and experimental results provided by Rabha et al. The characteristics of radial gas void fraction and local mass transfer coefficients in the FKSM were evaluated under different operating conditions. The velocity profiles of concentric air phase accelerated by the bubble forces firstly became sharp and narrow until z/l=-3.27 and then slowly decreased and stabilized at z/l=-1.5 before entering the first mixing element. Some extra unimodal profile of radial gas holdup gradually generated near the rectangle cross sections of mixing elements. The ?G gradually enlarged from r/R=0.2 to r/R=0.55 and then weakened from r/R=0.65 to r/R=0.874. The air void fractions in the bulk flow region decreased with the increasing initial uniform bubble diameter. The inlet effect of first leading edge enhanced the air phase dispersion and local mass transfer coefficients sharply increased from 2.04 to 3.69 times of that in the inlet. The local mass transfer coefficients in each mixing group had unimodal profiles.

Rayleigh-Taylor instability in oscillating liquid pistons

2018 ◽  
Vol 233 (4) ◽  
pp. 1236-1245 ◽  
Author(s):  
Samuel Langdon-Arms ◽  
Michael Gschwendtner ◽  
Martin Neumaier
Keyword(s):  
Taylor Instability ◽  
Operating Conditions ◽  
Surface Stability ◽  
Wide Range ◽  
Experimental Apparatus ◽  
In Series ◽  
Rayleigh Taylor Instability ◽  
Gas Expansion ◽  
Liquid Piston ◽  
The Impact

In this study, an experimental apparatus is used to excite four U-tube-shaped liquid pistons connected in series, and to study their behaviour. Some of the gas spaces are heated to induce piston oscillations; in others, gas expansion is utilised to produce a refrigeration effect. It was discovered that the liquid piston surface would become unstable and turbulent at relatively low gas charge pressures (2 bar–3 bar). Cylindrical polyethylene floats were employed at each piston surface in order to reduce the area of the free surface of each piston and allow experiments to be conducted over a wide range of operating conditions. Experiments were carried out using gas charge pressures in the range of 1 bar–6 bar. The resulting liquid piston oscillations were measured and analysed to assess the impact of any developing piston instability. Evidence of a liquid piston acceleration limit, likely resulting from the Rayleigh-Taylor instability phenomenon, is consistently observed during the experiments. The use of submerged polyethylene piston floats is found to increase the surface stability and enable maximum accelerations of 25 ms−2 to 30 ms−2.

Performance of Trickle Bed Reactor and Active Carbon in the Liquid Phase Oxidation of Phenol

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Nigus Gabbiye ◽  
Josep Font ◽  
Agusti Fortuny ◽  
Christophe Bengoa ◽  
Azael Fabregat ◽  
...  
Keyword(s):  
Liquid Flow ◽  
Active Carbon ◽  
Operating Conditions ◽  
Catalyst Stability ◽  
Wastewater Remediation ◽  
Air Oxidation ◽  
Trickle Bed Reactor ◽  
Phenolic Pollutants ◽  
Wide Range ◽  
Trickle Bed

Application of trickle-bed reactor and active carbon catalyst to catalytic wet air oxidation of phenolic pollutants is explored over a wide range of operating conditions. The study focuses on the assessment of key engineering aspects such as reactor start-up, gas-liquid flow directions and effects of temperature, pressure, phenol feed concentration and liquid flow rate on activity and stability performance of unsupported active carbon. Moreover, for analyzing the potential integration of CWAO as a pre-treatment in biological wastewater remediation, intermediate distribution and biodegradability enhancement of treated effluents are obtained from HPLC analysis and respirometry assays, respectively. Finally, since slow carbon burn-off is occurring at CWAO conditions, some promising options for improvement of catalyst stability are pointed out on both molecular (iron coating of active carbon) and reactor (periodic reactor operation) scale.

Experimental Study of Gas-Liquid Pressurization Performance and Critical Gas Volume Fractions of a Multiphase Pump

2021 ◽  
Author(s):  
Liang Chang ◽  
Qiang Xu ◽  
Chenyu Yang ◽  
Xiaobin Su ◽  
Xuemei Zhang ◽  
...  
Keyword(s):  
Liquid Flow ◽  
Volume Fraction ◽  
Extreme Points ◽  
Transition Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Multiphase Pump ◽  
Gas Liquid Flow ◽  
Relative Errors ◽  
Gas Volume

Abstract Gas entrainment may cause pressurization deterioration and even failure of pumps under conditions of high inlet gas volume fraction (GVF). When the inlet GVF increases to a critical value, an obvious deterioration performance of pump occurs. Air-water pressurization performance and inlet critical GVFs of a centrifugal multiphase pump are investigated experimentally under different inlet pressures and gas-liquid flow rates. To determine the first and second critical GVFs, a new method is proposed by computing the local extreme points of the second derivative of performance curves. New prediction correlations for two critical GVFs are established with relative errors lower than ±10% and ±8%. Boundaries of three different flow patterns and the transition flow rates are determined and presented by critical GVFs on the flow pattern diagram. Moreover, boundaries of maximum pressurization are determined by performance curve clusters and a power function correlation of gas-liquid flow rates when reaching the maximum pressurization is established. With the increase of inlet pressure from 1MPa to 5MPa, two-phase pressurization performance is significantly increased; occurrences of pressurization deterioration are obviously delayed with the first and second critical GVFs increasing by maximums of 8.2% and 7.1%.

Experimental Investigation Of Detailed Structure Of Gas-Liquid Flow In Rectangular Microchannel

2016 ◽  
Vol 11 (1) ◽  
pp. 73-79
Author(s):  
German Bartkus ◽  
German Bartkus ◽  
Vladimir Kuznetsov ◽  
Vladimir Kuznetsov
Keyword(s):  
Liquid Flow ◽  
High Speed ◽  
Rectangular Cross Section ◽  
Rectangular Channel ◽  
Detailed Structure ◽  
Rectangular Microchannel ◽  
Flow Rates ◽  
Wide Range ◽  
Gas Liquid Flow ◽  
Vertical Microchannel

The detailed structure of upward gas-liquid flow of water and nitrogen in a vertical microchannel with a rectangular cross-section 420 × 280 µm was experimentally investigated. The experiments were conducted using the methods of high-speed video and laser-induced fluorescence. In a wide range of flow rates the characteristic regimes of the gas-liquid flow were defined, velocity of elongated bubbles and the local thickness of the liquid film were measured. The dependence of the local film thickness on the capillary number was determined and it was found that the Taylor Law for rectangular channel is not fully implemented due to the deformation of the interface and the contraction of the liquid into the corners of the channel by capillary force.

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