Study of the Hydraulic Performances of Two Inducers in Water - CO2 Mixture - Toward Performance Improvement with Suppression of Pre-Rotation

2021 ◽  
Author(s):  
Petar Tomov ◽  
Loic Pora ◽  
Richard Paridaens ◽  
Magne Théodore ◽  
Mohamed Kebdani ◽  
...  
Keyword(s):  
High Speed ◽  
Flow Instability ◽  
Low Flow ◽  
Rotating Flow ◽  
Geometrical Parameters ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Co2 Gas ◽  
The Impact ◽  
Working Liquid

Abstract The inducers increase the pressure available at the inlet of the impellers of centrifugal pumps. This technological solution may induce instabilities, such as pre-rotating flow at partial flow rates. The scientific literature offers studies on the cavitation in the inducers, as well as on the associated instabilities. However, studies describing devices that improve the behavior in these unstable regimes are rare. This is particularly true for fluids like aviation fuels or liquids with dissolved gases. In the present work we expose, an experimental study for two axial inducers carried out at low flow rates in cavitating and non-cavitating regimes in a closed loop equipped with a transparent test pipe. The working liquid is water with and without dissolved CO2. We employ a camera and a high-speed camera to take the photographs of the dynamics of the cavitation structures. The experimental campaign provided results of head breakdown comparison. The added dissolved CO2 gas at a concentration of 300 mg/L does not change the overall inducers' performance in non-cavitating regime. The paper presents also the impact of some of inducers' geometrical parameters on their cavitating performance. The authors observed pre-rotating flow instability, which they tried to decrease by incorporating a grooved ring into the inlet side of the inducers. It is found that pre-rotating structures are much less developed in the upstream when a grooved ring is employed.

A CFD Study on Cavitating Flow in High-Speed Centrifugal Pumps under Low Flow Rates

2014 ◽  
Vol 945-949 ◽  
pp. 914-923 ◽  
Author(s):  
Jian Ping Yuan ◽  
Yu Wen Zhu ◽  
Ai Xiang Ge
Keyword(s):  
Total Pressure ◽  
High Speed ◽  
Volume Fraction ◽  
Experimental Methods ◽  
Cavitation Number ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Blade Passage ◽  
Critical Cavitation

Cavitation is one of the most important aspects that need to be considered while designing centrifugal pumps, since it is a major contributor to failure and inefficiency. In order to study the cavitating performance in high-speed centrifugal pumps under low flow rates, the pump named IN-32-32-100 with two different impellers was investigated based on numerical and experimental methods. The impeller case 1 is the impeller with six blades. The impeller case 2 is the impeller with four long and four splitter blades. The research results show that the cavities of two impellers occur at the impeller inlet. The region of developed cavities extends and the volume fraction in the blade passages gradually increases with the decrease of inlet total pressure at the flow rate of 0.5Qd. The cavities distribute asymmetrically in each blade passage and the vapor fraction of one blade passage is significantly larger compared with them of blade passages. The inner flow of the pump can be effectively improved with more uniform pressure distribution by applying splitter blades. The critical cavitation number of the impeller case 1 and impeller case 2 corresponding to the sudden head-drop point are 3.2m and 3.55m, respectively. Compared with impeller case 2, cavitating performance of the pump with impeller case 1 is better. The numerical results agree well with the experimental data, which shows that the numerical method in the present study can to some extent accurately predict the cavitating development inside the high-speed centrifugal pump.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

Bubble behaviour in a horizontal high-speed solid-body rotating flow

2021 ◽  
Vol 925 ◽  
Author(s):  
Majid Rodgar ◽  
Hélène Scolan ◽  
Jean-Louis Marié ◽  
Delphine Doppler ◽  
Jean-Philippe Matas
Keyword(s):  
Aspect Ratio ◽  
Solid Body ◽  
High Speed ◽  
Lift Coefficient ◽  
Rotating Flow ◽  
Axis Of Rotation ◽  
Large Fluctuations ◽  
The Mean ◽  
Drag And Lift ◽  
The Impact

We study experimentally the behaviour of a bubble injected into a horizontal liquid solid-body rotating flow, in a range of rotational velocities where the bubble is close to the axis of rotation. We first study the stretching of the bubble as a function of its size and of the rotation of the cell. We show that the bubble aspect ratio can be predicted as a function of the bubble Weber number by the model of Rosenthal (J. Fluid Mech., vol. 12, 1962, 358–366) provided an appropriate correction due to the impact of buoyancy is included. We next deduce the drag and lift coefficients from the mean bubble position. For large bubbles straddling the axis of rotation, we show that the drag coefficient $C_D$ is solely dependent on the Rossby number $Ro$, with $C_D \approx 1.5/Ro$. In the same limit of large bubbles, we show that the lift coefficient $C_L$ is controlled by the shear Reynolds number $Re_{shear}$ at the scale of the bubble. For $Re_{shear}$ larger than 3000 we observe a sharp transition, wherein large fluctuations in the bubble aspect ratio and mean position occur, and can lead to the break-up of the bubble. We interpret this regime as a resonance between the periodic forcing of the rotating cell and the eigenmodes of the stretched bubble.

Experimental Tests With Centrifugal Pumps: Degradation of Performance, Instability and Dynamic Phenomena With Non-Newtonian Suspensions of Kaolin in Water

2019 ◽  
Author(s):  
Matteo Occari ◽  
Enrico Munari ◽  
Valentina Mazzanti ◽  
Michele Pinelli ◽  
Francesco Mollica ◽  
...  
Keyword(s):  
Experimental Tests ◽  
Newtonian Fluids ◽  
Low Flow ◽  
Time Varying ◽  
Centrifugal Pumps ◽  
Strong Reduction ◽  
Flow Rates ◽  
Specific Speed ◽  
Dynamic Phenomena ◽  
Newtonian Behavior

Abstract The performance of pumps when working with non-Newtonian fluids significantly change with respect to water. In several experimental tests with non-Newtonian fluids, significant deration of head and the presence of head instability were observed. The present work aims to better understand this phenomenon since the reasons that originate it are not clear. Two small size centrifugal pumps were experimentally tested with different mixtures of kaolin-in-water, which showed a verified non-Newtonian behavior. The rheology of the mixtures and the particle size distribution of kaolin powder were measured to characterize the fluids. Similar to previous tests, a strong reduction of head and the appearance of instability were observed at low flow rates and, in some cases, also at higher flow rates. This behavior was related to the presence of air trapped into the fluid that, within the pump, generated a phenomenon known as gas-locking, which in literature it has been studied in detail with water but not with non-Newtonian fluids. Moreover, in some working conditions, non-stable time-varying phenomena are observed and their consequence on performance commented. Comparing the two pumps, characterized by a similar specific speed but by a different geometry, the head drop manifested itself with different intensity.

Suppression of Self-Excited Flow Instability in a Radial Diffuser Using Rough Surfaces

2006 ◽  
Author(s):  
Saad A. Ahemd ◽  
Hayder Salem
Keyword(s):  
Flow Rate ◽  
Smooth Surface ◽  
Flow Instability ◽  
Rough Surfaces ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Flow Limit ◽  
Stable Operating

Flow instabilities in a compression system at low flow rates set the flow limit of the stable operating range. Experiments to investigate the feasibility of controlling the stall in the radial diffuser of a low speed centrifugal compressor were carried out. The technique was very simple and involved using rough surfaces (i.e., sand papers) attached to the diffuser shroud. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the mass flow rate could be reduced to 70% of its value with the smooth surface) when the rough surfaces were positioned on the diffuser shroud.

Analysis of the Behavior of Droplet Impinging on a Curved Dry Wall in a Rotating Flow Field

2020 ◽  
Author(s):  
Shuo Ouyang ◽  
Zhenqin Xiong
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Nuclear Power ◽  
Rotating Flow ◽  
Droplet Deformation ◽  
Wind Speeds ◽  
Boundary Information ◽  
Different Diameters ◽  
The Impact ◽  
Steam Separator

Abstract Steam water separator is the core equipment of nuclear power plant. It is very vital for improving the efficiency of the steam separator to study the impact characteristics between the droplets and the curved dry wall of the steam separator under the action of the rotating air flow. In this paper, the characteristics of droplet impinging on the dry wall in the rotating flow field are analyzed by establishing a visualization experimental device. A high-speed camera was used to capture the impact of droplets with different diameters on the dry wall of a non-wetting curved surface at different gas velocities. At the same time, using image processing tool in MATLAB to obtain image boundary information. The characteristics of spreading factor, droplet deformation factor and initial diffusion velocity of droplets impacting the surface dry wall under different wind speeds are studied.

Comparison of Inlet Curved Disk Arrangements for Suppression of Recirculation in Centrifugal Pump Impellers

2016 ◽  
Author(s):  
Munther Y. Hermez ◽  
Badih A. Jawad ◽  
Liping Liu ◽  
Vernon Fernandez ◽  
Kingman Yee ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Operating Cost ◽  
Three Dimensional ◽  
Centrifugal Pumps ◽  
Unstable Flow ◽  
Pump Impeller ◽  
Flow Rates ◽  
Flow Recirculation ◽  
Flow Field Characteristics

The present work aims to numerically study the inlet flow recirculation and modified impeller interaction in a centrifugal pump. An optimization of modified shrouded impeller with curved disk arrangement to suppress the unsteady flow recirculation is pursued. This modification will enhance the impeller characteristics with a wider operation range at both low and high flow rates in a high speed centrifugal pump type. The unstable flow in the centrifugal pumps is a common problem that leads to damage in the pump’s internal parts, consequently increases the operating cost. At certain flow rates, generally below the Best Efficiency Point (BEP), all centrifugal pumps are subject to internal recirculation occurs at the suction and discharge areas of the impeller. For decades, experimental work has been done to investigate the complex three-dimensional flow within centrifugal pumps impellers, before computational work gains momentum due to advancement of computing power and improved numerical codes. In this study the impeller with a curved disk arrangement has been investigated by using a three-dimensional Navier-Stokes code with a standard k-ε turbulence model. The purpose is to evaluate and select the optimum impeller modification that would increase the pump suction flow rate range. Three-dimensional numerical Computational Fluid Dynamics (CFD) tools are used to simulate flow field characteristics inside the centrifugal pump and provide critical hydraulic design information. In the present work, ANSYS v.16.1 Fluent solver is used to analyze the pressure and velocity distributions inside impeller suction and discharge passages. The ultimate goal of this study is to manufacture and validate the most optimized and efficient centrifugal pump impeller with a curved disk. The best case curve identifies the highest increase of total pressure difference by 22.1%, and highest efficiency by 92.3% at low flowrates.

scholarly journals Electromagnetic fields related to high speed transportation systems

2018 ◽  
Vol 4 (2) ◽  
pp. 152-166 ◽  
Author(s):  
Roland Kircher ◽  
Johannes Klühspies ◽  
Ryszard Palka ◽  
Eckert Fritz ◽  
Kenji Eiler ◽  
...  
Keyword(s):  
Energy Balance ◽  
Electromagnetic Fields ◽  
Health Risks ◽  
Power Supply ◽  
High Speed ◽  
Transportation Systems ◽  
Geometrical Parameters ◽  
Potential Health ◽  
Maglev System ◽  
The Impact

Issue: The potential health risks on passengers and the environment related to electromagnetic fields caused by the operation of electrically driven high speed transportation systems has become a major issue. Especially the magnetic flux density or induction can generate physiological effects in body tissues. Aim: In this paper, we compare calculated and experimental values of electromagnetic fields in rail-wheel systems such as ICE with the Maglev-systems Transrapid and the JR Maglev-system, based on available data. Method: To estimate the impact on passengers, the field contributions generated by the power supply system as well as by the drive and suspension systems are taken into account. For the comparison, the peak values of the electromagnetic fields have been considered. Results: The results show, that there are no health risks from the electric fields. Regarding the magnetic induction, the calculated the peak values remain well below the limits given by national regulations. In the case of the Transrapid and the JR Maglev system, the measured peak values in the environment and inside the vehicle depend on the levitation and the guidance technology and the geometrical parameters. The JR Maglev system requires effective magnetic shielding measures which are connected with heavy materials. Since such materials may have a negative influence on the energy balance and the economics of operation, R&D efforts are focusing on the optimization of materials and the structure of shields. Conclusion: In high speed transportation systems there are no potential risks from electrical fields. Regarding magnetic fields, the induction generated by the power supply and the drive system remain well below the frequency dependent limits. The situation is different for magnetic levitation systems, depending on the suspension and guidance technology. Especially the JR Maglev requires effective shielding measures. The shielding materials may have a negative impact on the energy balance.

scholarly journals The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study.

F1000Research ◽  
2017 ◽  
Vol 6 ◽  
pp. 1997 ◽  
Author(s):  
Fredrik Leijonhufvud ◽  
Fredrik Jöneby ◽  
Jan G. Jakobsson
Keyword(s):  
Gas Flow ◽  
Anaesthetic Agent ◽  
Point Of View ◽  
Low Flow ◽  
Test Lung ◽  
Minimal Alveolar Concentration ◽  
Flow Rates ◽  
Optimal Flow ◽  
Gas Consumption ◽  
The Impact

Low-flow anaesthesia is considered beneficial for the patient and the environment, and it is cost reducing due to reduced anaesthetic gas consumption. An initial high-flow to saturate the circle system ( wash-in) is desirable from a clinical point of view. We measured the wash-in and wash-out times (time to saturate and to eliminate the anaesthetic agent, AA), for sevoflurane and desflurane, in a test-lung with fixed 3 MAC vaporizer setting at different fresh gas flow (FGF) and calculated the consumption of AA. We tried to find an optimal flow rate for speed and gas consumption, comparing two anaesthesia machines (AMs): Aisys and Flow-i. Time to reach 1 minimal alveolar concentration (MAC) (wash-in) decreased (p<0.05) at higher flow rates (1 – 2 – 4) but plateaued at 4-4.8 l/min. The consumption of AA was at its lowest around 4-4.8 l/min (optimal flow) for all but the Aisys /desflurane group. Wash-out times decreased as FGF increased, until reaching plateau at FGF of 4-6 l/min. Aisys had generally shorter wash-in times at flow rates < 4 l/min as well as lower consumption of AA. At higher flow rates there were little difference between the AMs. The “optimal FGF” for wash-out, elimination of gas from the test-lung and circle system, plateaued with no increase in speed beyond 6 l/min. A fresh gas flow of 4 l/min. seems “optimal” taking speed to reach a 1 MAC ET and gas consumption into account during wash-in with a fixed 3 MAC vaporizer setting, and increasing fresh gas flow beyond 6 l/min does not seem to confirm major benefit during wash-out.

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