Gas–Liquid Two-Phase Performance of Centrifugal Pump Under Bubble Inflow Based on Computational Fluid Dynamics–Population Balance Model Coupling Model

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Denghui He ◽  
Zhenguo Ge ◽  
Bofeng Bai ◽  
Pengcheng Guo ◽  
Xingqi Luo
Keyword(s):  
Centrifugal Pump ◽  
Volume Fraction ◽  
Simulation Method ◽  
Coupling Model ◽  
Balance Model ◽  
Eulerian Model ◽  
Two Phase ◽  
Air Mass ◽  
Gas Volume Fraction ◽  
Gas Volume

Abstract In this study, a numerical simulation method based on Eulerian–Eulerian model and population balance model (PBM) (i.e., computational fluid dynamics (CFD)–PBM coupling model) was developed to investigate the gas–liquid two-phase performance of centrifugal pump under bubble inflow. The realizable k–ε model turbulence model was implemented in ansysfluent solver. The air and water were employed as the working fluids, which was consistent with the experiment. The water head and pressure increment obtained by the experiment were used to validate the numerical method. The results show that the CFD–PBM coupling model is superior to the Eulerian–Eulerian model, particularly in the “surging” conditions. Using the CFD–PBM coupling model, the influences of parameters, such as inlet gas volume fraction, liquid phase flowrate, and rotational speed, on the head and efficiency of the centrifugal pump were investigated. Under the design condition, when the inlet gas volume fraction increases from 3% to 5%, the bubbles form air mass and stagnate in the impeller channel. The stagnated air mass can hardly be discharged with the liquid phase. Thus, the pump head drops suddenly, i.e., the surging occurs. The two-phase performance of centrifugal pump can be improved under the surging condition by increasing the liquid flowrate and the rotational speed to a certain value. The results contribute to an alternative simulation method to investigate the characteristics of bubble flow in pump and shed new lights on the understanding of the performance of centrifugal pumps under two-phase flow conditions.

Experimental Study of Two-Phase Air/Water Flow in a Centrifugal Pump Working With a Closed or a Semi-Open Impeller

2018 ◽  
Author(s):  
Michael Mansour ◽  
Bernd Wunderlich ◽  
Dominique Thévenin
Keyword(s):  
Centrifugal Pump ◽  
Volume Fraction ◽  
Operating Conditions ◽  
Superior Performance ◽  
Flow Conditions ◽  
Two Phase ◽  
Volume Fractions ◽  
Acrylic Glass ◽  
Gas Volume Fraction ◽  
Gas Volume

The characteristics of a transparent centrifugal pump of radial type were investigated for different conditions when conveying two-phase (air/water) flows. A closed impeller and a geometrically similar semi-open impeller, both made out of acrylic glass, were employed for comparison purposes when increasing air loading. The performance of the pump was measured for either a constant gas volume fraction or a constant air flow rate at the pump inlet. Hysteresis effects were studied by considering three different experimental approaches to reach the desired operating conditions. A constant rotational speed of 650 rpm was set for all experiments. The whole system was made of transparent acrylic glass to allow high-quality flow visualization. A systematic experimental database was produced based on shadowgraphy imaging, so that the resulting two-phase regimes could be properly identified. The results show that for gas volume fractions between 1 and 3%, the deterioration of pump performance parameters is much lower in the semi-open impeller compared to that of the closed impeller. Nevertheless, in the gas volume fraction range between 4 and 6%, the trend is reversed; the semi-open impeller performance is reduced compared to the closed impeller, particularly in overload conditions. At even higher gas loading, the semi-open impeller shows again superior performance. Flow instabilities and pump surging were much stronger in the closed impeller. The main reason for that was the occurrence of alternating gas pockets on the blades of the closed impeller. Additionally, pump surging was observed only in a very limited range of flow conditions in the semi-open impeller. Comparing the different experimental procedures to set the desired flow conditions, no significant hysteresis effects could be observed in the closed impeller. However, in the semi-open impeller obvious hysteresis in the performance could be seen for gas volume fractions between 4 and 6%. All the obtained experimental results will be useful to check and validate computational models used for CFD in a comparison study.

scholarly journals Numerical Investigation on Bubble Distribution of a Multistage Centrifugal Pump Based on a Population Balance Model

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 908 ◽  
Author(s):  
Sina Yan ◽  
Shuaihui Sun ◽  
Xingqi Luo ◽  
Senlin Chen ◽  
Chenhao Li ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Volume Fraction ◽  
Balance Model ◽  
Population Balance Model ◽  
Two Phase ◽  
Pressure Surface ◽  
Bubble Distribution ◽  
Impeller Outlet ◽  
Gas Volume Fraction ◽  
Gas Volume

This work aimed to study the bubble distribution in a multiphase pump. A Euler-Euler inhomogeneous two-phase flow model coupled with a discrete particle population balance model (PBM) was used to simulate the whole flow channel of a three-stage gas-liquid two-phase centrifugal pump. Comparison of the computational fluid dynamic (CFD) simulation results with experimental data shows that the model can accurately predict the performance of the pump under various operating conditions. In addition, the liquid phase velocity distribution, gas-phase distribution, and pressure distribution of the second stage impeller at a 0.5 span of blade height under three typical working conditions were compared. Results show that the region with high local gas volume fraction (LGVF) mainly appears on the suction surface (SS) of the blade. With the increase in inlet gas volume fraction (IGVF), vortices and low velocity recirculation regions are generated at the impeller outlet and SS of the blade, the area with high LGVF increases, and gas–liquid separation occurs at the SS of the blade. The liquid phase flows out of the impeller at high velocity along the pressure surface of the blade, and the limited pressurization of fluid mainly happens at the impeller outlet. The average bubble size at the impeller outlet is the smallest while that at the impeller inlet is the largest. Under low IGVF conditions, bubbles tend to break into smaller ones, and the broken bubbles mainly concentrate at the blade pressure surface (PS) and the impeller outlet. Bubbles tend to coalesce into larger ones under high IGVF conditions. With the increase in IGVF, the bubble aggregation zone diffuses from the blade SS to the PS.

scholarly journals Effect of Gas Volume Fraction on the Energy Loss Characteristics of Multiphase Pumps at Each Cavitation Stage

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2293
Author(s):  
Jianwei Shi ◽  
Sijia Tao ◽  
Guangtai Shi ◽  
Wenwu Song
Keyword(s):  
Energy Loss ◽  
Volume Fraction ◽  
Axial Flow ◽  
Two Phase ◽  
Multiphase Pump ◽  
Cavitation Phenomenon ◽  
Flow Loss ◽  
Gas Volume Fraction ◽  
Critical Cavitation ◽  
Gas Volume

In the process of conveying a medium, when the inlet pressure is low, the cavitation phenomenon easily occurs in the pump, especially in the gas–liquid two-phase working condition. The occurrence of the cavitation phenomenon has a great impact on the performance of the multiphase pump. In this paper, the SST (sheard stress transport) k-ω turbulence model and ZGB (Zwart–Gerber–Belamri) cavitation model were used to simulate the helical axial flow multiphase pump (hereinafter referred to as the multiphase pump), and the experimental verification was carried out. The effect of gas volume fraction (GVF) on the energy loss characteristics in each cavitation stage of the multiphase pump is analyzed in detail. The study shows that the critical cavitation coefficient of the multiphase pump gradually decreases with the increase in GVF, which depresses the evolution of cavitation, and the cavitation performance of the multiphase hump is improved. The ratio of total loss and friction loss to total flow loss in the impeller fluid domain gradually increases with the development of cavitation, and the pressurization performance of the multiphase pump gradually decreases with the development of cavitation. The results of the study can provide theoretical guidance for the improvement of the performance of the multiphase pump.

Numerical Study of Reactor Cooling Pumps Under Two-Phase Gas-Liquid Flow

2014 ◽  
Author(s):  
Peng Wang ◽  
Shouqi Yuan ◽  
Xiuli Wang ◽  
Guidong Li ◽  
Banglun Zhou ◽  
...  
Keyword(s):  
Computational Models ◽  
Volume Fraction ◽  
Numerical Study ◽  
Linear Increase ◽  
Suction Surface ◽  
Two Phase ◽  
Gas Volume Fraction ◽  
Head Pressure ◽  
Simulation Results ◽  
Gas Volume

In this paper, the unsteady pressure field and head-drop phenomenon caused by one of the most dangerous accidents in reactor plants known as Loss of Coolant Accident (LOCA) in its worse condition called small LOCA have been investigated numerically by computational fluid dynamics (CFD) in a nuclear reactor cooling pump. Five computational models with different blades had been calculated using Eulerian-Eulerian two fluid models using a multiphase approach. Simulation results show increasing gas volume fraction results in a sharp decline of the head pressure and pump efficiencies for each of 5 kinds of pumps modeled. This is especially evident for both the head pressure of impeller types C and impeller E. Here only have operating at half (58m and 54.9m)of the design condition when the gas volume fraction is 25%. The analysis of inner flow field of the five model pumps shown that the lower pressure area appeared at the inlet and outlet of the impeller as well as a small part distribution at the inlet of the diffuser, which is the main reason made the gas bubbles tend to concentrate at the impeller eye on the suction surface, the distribution of two phases appeared by non-linear increase and random located in whole passages. The experimental and simulation results are compared and are in good agreement with values obtained for the global performance at lower gas contents (below20%). When the gas contents increases to 25%, the bubbles occupy the passages, which effectively causes unsteady flow in the gas phase cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the two-phase flow under certain gas contents (below 20%) in the reactor cooling pump.

Measurement of a Void Fraction in Bubbly Gas-Water Two Phase Flows Using Differential Pressure Technique

2012 ◽  
Vol 152-154 ◽  
pp. 1221-1226
Author(s):  
H.A.M. Hasan Abbas
Keyword(s):  
Experimental Study ◽  
Void Fraction ◽  
Volume Fraction ◽  
Differential Pressure ◽  
Flow Density ◽  
Two Phase Flows ◽  
Two Phase ◽  
Gas Volume Fraction ◽  
Fraction Measurement ◽  
Gas Volume

Multiphase flows, where two or even three fluids flow simultaneously in a pipe are becoming increasingly important in industry. In order to measure the flow rate of gas-water two phase flows accurately, the void fraction (gas volume fraction) in two phase flows must be precisely measured. The differential pressure technique has proven attractive in the measurement of volume fraction. This paper presents the theoretical and experimental study of the void fraction measurement in bubbly gas water two phase flows using differential pressure technique (the flow density meter).

Bubbly, Two-Phase Flow in the Anode Channel of a Passive, Tubular Direct Methanol Fuel Cell

2011 ◽  
Author(s):  
Hafez Bahrami ◽  
Amir Faghri
Keyword(s):  
Experimental Data ◽  
Direct Methanol Fuel Cell ◽  
Volume Fraction ◽  
Catalyst Layer ◽  
Two Phase ◽  
Direct Methanol ◽  
Cell Current ◽  
Gas Volume Fraction ◽  
Gas Volume ◽  
Methanol Fuel Cell

A numerical study is presented to investigate the turbulent, two-phase, steady state, isothermal, bubbly flow characteristic in the anode channel of a passive, tubular direct methanol fuel cell (DMFC) in order to accurately predict the gas volume fraction distribution along the channel. Accumulation of carbon dioxide gas bubbles at the channel’s wall hinders the diffusion of the fuel from the channel to the catalyst layer. The conservation governing equations of the mass and momentum for both the continuous (methanol and water solution) and dispersed (CO2 bubbles) phases in the bubbly regime are solved using the multi-fluid technique. Turbulence in the liquid phase is formulated by employing the classical, two-equation k–ε model. Due to the lack of experimental data regarding the gas volume fraction in the anode channel of DMFCs, the proposed model was initially applied to the bubble plum in a cylindrical liquid bath in which air is injected into the water from a nozzle located at the bottom-center of the bath. The results are compared with the existing experimental data in the literature for the gas volume fraction and the liquid velocity in the bath. Finally, the model is successfully extended to the anode channel of a tubular DMFC operating passively in the vertical orientation in which the CO2 gas bubbles are injected through the wall. The rate of gas injection depends on the cell current density which is assumed to be uniform along the anode catalyst layer and the channel’s wall. It is found that the gas volume fraction significantly changes along the channel from a large value at the bottom of the channel to a lower value at the top. The flow field inside the channel is also investigated for different cell current densities.

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