Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

2020 ◽  
pp. 095765092093934
Author(s):  
Cong Wang ◽  
Yongxue Zhang ◽  
Jianjun Zhu ◽  
Zhiyi Yuan ◽  
Bohui Lu
Keyword(s):  
Centrifugal Pump ◽  
Flow Characteristics ◽  
Low Frequency ◽  
Two Phase ◽  
Free Gas ◽  
Gas Entrainment ◽  
Natural Cavitation ◽  
Low Specific Speed ◽  
Critical Cavitation ◽  
Churn Flow

An experimental study on gas–liquid two-phase flow characteristics in a low-specific-speed centrifugal pump is presented via employing multiple investigation techniques, such as visualization observation, measurements of acoustic emission and vibration, etc. Specially, three different flow conditions were inspected, namely gas locking initiation, critical cavitation with/without free-gas presence, etc. For gas locking, the drastic deterioration of the pump performance and the disrupted balance of shaft were observed. Especially, at low rotational speeds, the gas locking accompanied with intermittent or churn flow can be triggered by even lower inlet gas volumetric fractions. When it came to the cavitation flow, a small amount of gas entrainment could induce the rapid deterioration of cavitation and stimulate much higher amplitude in low-frequency band of shaft rotation. The relationship between the gas bubble trajectory and the vibration level under the backflow is discussed. The results reveal that the combined effect of the free-gas entrainment and cavitation on the pump instability is much stronger than that under natural cavitation or free-gas entrainment flow, whose fault diagnosis can be determined by the data manifested in different spectral segments.

Effects of short blades on performance and inner flow characteristics of a low-specific-speed centrifugal pump

2017 ◽  
Vol 231 (4) ◽  
pp. 290-302 ◽  
Author(s):  
Can Kang ◽  
Ning Mao ◽  
Chen Pan ◽  
Yang Zhu ◽  
Bing Li
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Low Flow ◽  
Back Surface ◽  
Flow Rates ◽  
Pump Operation ◽  
Low Specific Speed ◽  
Specific Speed

A low-specific-speed centrifugal pump equipped with long and short blades is studied. Emphasis is placed on the pump performance and inner flow characteristics at low flow rates. Each short blade is intentionally shifted towards the back surface of the neighboring long blade, and the outlet parts of the short blades are uniformly shortened. Unsteady numerical simulation is conducted to disclose inner flow patterns associated with the modified design. Thereby, a comparison is enabled between the two schemes featured by different short blades. Both practical operation data and numerical results support that the deviation and cutting of the short blades can eliminate the positive slope of pump head curve at low flow rates. Therefore, the modification of short blades improves the pump operation stability. Due to the shortening of the outlet parts of the short blades, velocity distributions between impeller outlet and radial diffuser inlet exhibit explicitly altered circumferential flow periodicity. Pressure fluctuations in the radial diffuser are complex in terms of diversified periodicity and amplitudes. Flow rate influences pressure fluctuations in the radial diffuser considerably. As flow rate decreases, the regularity of the orbit of hydraulic loads exerted upon the impeller collapses while hydraulic loads exerted upon the short blades remain circumferentially periodic.

scholarly journals Investigation on centrifugal pump performance degradation under air-water inlet two-phase flow conditions

2018 ◽  
pp. 41-48 ◽  
Author(s):  
Qiaorui Si ◽  
Qianglei Cui ◽  
Keyu Zhang ◽  
Jianping Yuan ◽  
Gérard Bois
Keyword(s):  
Centrifugal Pump ◽  
Pressure Pulsation ◽  
Flow Characteristics ◽  
Performance Degradation ◽  
Inlet Pressure ◽  
Pulsation Frequency ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Flow Rates ◽  
Pump Performance

In order to study the flow characteristics of centrifugal pumps when transporting the gas-liquid mixture, water and air were chosen as the working medium. Both numerical simulation and experimental tests were conducted on a centrifugal pump under different conditions of inlet air volume fraction (IAVF). The calculation used URANS k-epsilon turbulence model combined with the Euler-Euler inhomogeneous two-phase model. The air distribution and velocity streamline inside the impeller were obtained to discuss the flow characteristics of the pump. The results show that air concentration is high at the inlet pressure side of the blade, where the vortex will exist, indicating that the gas concentration have a great relationship with the vortex aggregation in the impeller passages. In the experimental works, pump performances were measured at different IAVF and compared with numerical results. Contributions to the centrifugal pump performance degradations were analyzed under different air-water inlet flow condition such as IAVF, bubble size, inlet pressure. Results show that pump performance degradation is more pronounced for low flow rates compared to high flow rates. Finally, pressure pulsation and vibration experiments of the pump model under different IAVF were also conducted. Inlet and outlet transient pressure signals under four IAVF were investigated and pressure pulsation frequency of the monitors is near the blade passing frequency at different IAVF, and when IAVF increased, the lower frequency signal is more and more obvious. Vibration signals at five measuring points were also obtained under different IAVF for various flow rates.

Flow Distribution and Slug Flow Characteristics for Hydraulically Equilibrium Air-Water Two-Phase Flows in a Vertical 2×3 Rod Channel

2003 ◽  
Author(s):  
Keiko Kano ◽  
Michio Sadatomi ◽  
Akimaro Kawahara ◽  
Tsukasa Kuno
Keyword(s):  
Flow Characteristics ◽  
Prediction Method ◽  
Flow Distribution ◽  
Bubble Velocity ◽  
Accurate Estimation ◽  
Two Phase ◽  
Taylor Bubble ◽  
Rod Bundle ◽  
Superficial Gas Velocity ◽  
Churn Flow

To complete subchannel analysis for predicting thermal-hydraulic behavior of coolant in a BWR rod bundle channel, accurate estimation of fluid transfer between subchannels is necessary. In order to validate a prediction method, flow distributions data of gas and liquid phases are essential. But, such data reported so far are limited to those in a two-subchannel system alone. Then we have measured flow distributions of both phases and Taylor bubble velocity in a multi-subchannel system as called 2×3 rod bundle channel. It has been found that flow distributions of gas and liquid in bubble and annular flows under a hydraulically equilibrium flow condition are close to those of single-phase flow, but in slug-churn flow the distributions are different. In slug-churn flow, both superficial gas velocity and Taylor bubble velocity are higher in larger subchannel. These experimental data are presented and discussed in this paper.

An Experimental Study on the Gas Entrainment in Horizontally and Vertically Installed Centrifugal Pumps

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Martin Neumann ◽  
Thomas Schäfer ◽  
André Bieberle ◽  
Uwe Hampel
Keyword(s):  
Centrifugal Pump ◽  
Gas Flow ◽  
Gamma Ray ◽  
Minor Effect ◽  
Centrifugal Pumps ◽  
Flow Conditions ◽  
Two Phase ◽  
Inlet Flow ◽  
Pump Performance ◽  
Gas Entrainment

In this work, we have studied how gas accumulates in an industrial centrifugal pump under various steady-state two-phase flow conditions. Thereby, we considered both horizontal and vertical pump installation positions. Phase fractions within the impeller region of the pump have been quantitatively disclosed using high-resolution gamma-ray computed tomography (HireCT) and applying time-averaged rotation-synchronized CT scanning technique. The study was made for inlet volumetric gas flow rates between 0% and 5%. To account for different inlet flow conditions, which are assumed to occur during unwanted gas entrainment by hollow vortices, we produced disperse and swirling gas–liquid inlet flows. In this way, the influence of inlet flow boundary conditions on the pump performance as well as gas fraction distributions and gas holdup within the impeller wheel region could be successfully analyzed and compared with respect to the impeller alignment. It was shown that the installation position offers only a minor effect on the pump performance in comparison to the inlet flow conditions. In addition, for the first time, thin gas films at the pressure side of the impeller wheel blades could be visualized in an industrial centrifugal pump.

Bubble Behaviour in Three Phase Capillary Microreactors

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Mark J Simmons ◽  
David C Y Wong ◽  
Paul J Travers ◽  
James S Rothwell
Keyword(s):  
High Speed ◽  
Flow Characteristics ◽  
Flow Regimes ◽  
Two Phase ◽  
Microchannel Reactors ◽  
Flow Maps ◽  
Three Phase ◽  
Monolith Reactors ◽  
Produce Flow ◽  
Churn Flow

Two-phase flow characteristics in vertical capillary downflow were investigated in order to obtain understanding of the behaviour of three-phase monolith reactors. Experiments were conducted using air and dyed water in round and square capillary tubes of 2 mm and 3 mm diameter. The flow regimes and transitions observed were recorded using high speed videography and this data was used to produce flow maps for each tube. The gas and liquid superficial velocities used ranged from 0.001 to 10 m/s and 0.0001 to 1 m/s respectively. The flow regimes and their transitions were found to be a strong function of tube geometry and surface tension effects, and some differences were observed between capillaries of round and square section. This has significant implications for the design of microchannel reactors. Annular, slug-annular, slug, bubbly and churn flow regimes were observed in the round tubes; channelling/irregular flow was observed in the square tubes in place of annular and slug-annular flow.

A Study on the Internal Flow Characteristics of a Very Low Specific Speed Centrifugal Pump by PTV

2006 ◽  
Vol 9 (1) ◽  
pp. 9-18
Author(s):  
Young-Do Choi ◽  
Jun Matsui ◽  
Junichi Kurokawa ◽  
Young-Ho Lee
Keyword(s):  
Centrifugal Pump ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Low Specific Speed ◽  
Specific Speed

Visualization Study of Gas-Liquid Two-Phase Flow in a Hydrophobic Pipe

2007 ◽  
Author(s):  
Takayoshi Kikuchi ◽  
Tatsuya Hazuku ◽  
Yutaka Fukuhara ◽  
Tomoji Takamasa ◽  
Takashi Hibiki
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Two Phase ◽  
Experimental Conditions ◽  
Churn Flow ◽  
Effect Of Surface

To evaluate the effect of pipe wall surface wettability on flow characteristics in a vertical upward gas-liquid two-phase flow, a visualization study was performed using an acrylic pipe and a hydrophobic pipe. Such basic flow characteristics as flow patterns, pressure drop and void fraction were investigated in these pipes. In the hydrophobic pipe, an inverted-churn flow regime was observed in a region where the churn flow regime was observed in the acrylic pipe, while a droplet flow regime was observed in the region where an annular flow regime was observed in the acrylic pipe. At a high gas flow rate, the average void fraction in the hydrophobic pipe was higher than in the acrylic pipe. The effect of surface wall wettability on frictional pressure loss was confirmed to be insignificant under the present experimental conditions.

Evaluation of Rotor–Stator Interface Models for the Prediction of the Hydraulic and Suction Performance of a Centrifugal Pump

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Hyeon-Seok Shim ◽  
Kwang-Yong Kim
Keyword(s):  
Centrifugal Pump ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Hydraulic Efficiency ◽  
Two Phase ◽  
Single Passage ◽  
Critical Cavitation ◽  
Rans Analysis ◽  
Suction Performance ◽  
Rotor Model

The effects of a rotor–stator interface model on the hydraulic and suction performance of a single-stage centrifugal pump have been evaluated. A three-dimensional Reynolds-averaged Navier–Stokes (RANS) analysis was performed using the shear-stress transport turbulence model. The cavitating flow was simulated using a homogeneous two-phase mixture model and a simplified Rayleigh–Plesset cavitation model. Three performance parameters were selected to compare different cases: the hydraulic efficiency, head coefficient, and critical cavitation number for a head-drop of 3%. Frozen-rotor and stage models were evaluated for the rotor–stator interface. The evaluation was done using three different computational domains: one with a single passage of the impeller with a vaneless diffuser, one with a single passage of the impeller with the whole shape of volute casing, and another with the whole passage of the impeller with the whole shape of volute casing. Two different volute shapes were also tested. The results show that it is desirable to use the whole domain of the impeller and volute with the frozen-rotor model for accurate prediction of the suction performance. The stage model is not recommended for the prediction of the suction performance of the centrifugal pump with the volute in severe off-design conditions.

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