Very Low Specific Speed Centrifugal Pump—Hydraulic Design and Physical Limitations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Grunde Olimstad ◽  
Morten Osvoll ◽  
Pål Henrik Enger Finstad
Keyword(s):  
Centrifugal Pump ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Hydraulic Design ◽  
New Findings ◽  
Gear Pumps ◽  
Disk Friction ◽  
Low Specific Speed ◽  
High Head ◽  
Specific Speed

For low-flow and high-head applications, pump types such as progressive cavity or gear pumps are often used. However, centrifugal pumps are much more robust and wear resistant, and are beneficial if they can handle the rated head and flows. By challenging the limitations of low specific speed (Nq), centrifugal pumps can be made to handle a combination of low flow and high head, which previously required other pump types. Conventional centrifugal pumps have specific speed down to 10, while in this paper a design with specific speed of 4.8 is presented. The paper describes several iterative steps in the design process of the low Nq pump. These iterations were done one physical pumps, which were successively tested in a test rig. Motivation for each step is explained theoretically and followed up by discussion of the measured results. Four different geometries of the pump were tested, all of them manufactured by rapid prototyping in nylon material. A substantial question is how low the specific speed of a centrifugal pump can be. Limitations of low Nq pumps are discussed and new findings are related to volute cavitation. In addition, limitations due to disk friction, volute losses, leakage flow, and pump stability are discussed and show to limit the design space for the pump designer.

The effect of wear ring clearance on flow field in the impeller sidewall gap and efficiency of a low specific speed centrifugal pump

2017 ◽  
Vol 232 (17) ◽  
pp. 3062-3073 ◽  
Author(s):  
M DaqiqShirazi ◽  
R Torabi ◽  
A Riasi ◽  
SA Nourbakhsh
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Volumetric Efficiency ◽  
Centrifugal Pumps ◽  
Disk Friction ◽  
Low Specific Speed ◽  
Overall Efficiency ◽  
Specific Speed

In this paper, the flow in the impeller sidewall gap of a low specific speed centrifugal pump is analyzed to study the effect of wear ring clearance and the resultant through-flow on flow field in this cavity and investigate the overall efficiency of the pump. Centrifugal pumps are commonly subject to a reduction in the flow rate and volumetric efficiency due to abrasive liquids or working conditions, since the wear rings are progressively worn, the internal leakage flow is increased. In the new operating point, the overall efficiency of the pump cannot be predicted simply by using the pump characteristic curves. The flow field is simulated with the use of computational fluid dynamics and the three-dimensional full Navier–Stokes equations are solved using CFX software. In order to verify the numerical simulations, static pressure field in volute casing and pump performance curves are compared with the experimental measurements. The results show that, for the pump with minimum wear ring clearance, the disk friction efficiency is the strongest factor that impairs the overall efficiency. Therefore, when the ring clearance is enlarged more than three times, although volumetric efficiency decreases effectively but the reduction in overall efficiency is remarkably smaller due to improvement in the disk friction losses.

scholarly journals Effect of Short Blade Circumferential Position Arrangement on Gas-Liquid Two-Phase Flow Performance of Centrifugal Pump

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1317
Author(s):  
Biaobiao Wang ◽  
Haoyang Zhang ◽  
Fanjie Deng ◽  
Chenguang Wang ◽  
Qiaorui Si
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Two Phase Flow ◽  
Low Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Suction Surface ◽  
Two Phase ◽  
Low Specific Speed ◽  
Specific Speed

In order to study the internal flow characteristics of centrifugal pumps with a split impeller under gas-liquid mixed transportation conditions, this paper conducted a steady calculation of the flow field in the centrifugal pump under the conditions of different inlet gas volume fractions based on the Eulerian-Eulerian heterogeneous flow model, using air and water as the working media and the Schiller Nauman model for the interphase resistance. This paper takes a low specific speed centrifugal pump as the research object, through the controlling variables, using the same pump body structure and pump body geometric parameters and setting three different arrangements of long and short blades (each plan uses the same long and short blades) to explore the influence of the short blade arrangement on the low specific speed centrifugal pump performance under a gas-liquid two-phase flow. The research results show that, under pure water conditions, the reasonable arrangement of the short blade circumferential position can eliminate the hump of the centrifugal pump under low-flow conditions, can make the flow velocity in the impeller more uniform, and can optimize the performance of the pump. Under the design conditions and the gas-liquid two-phase inflow conditions, when the circumferential position of the short blades is close to the suction surface of the long blades, some of the bubbles on the suction surface of the long blade can be broken under the work of the pressure surface of the short blade and flow out of the impeller with the liquid, which improves the flow state of the flow field in the impeller.

Theory and application of two-dimension viscous hydraulic design of the ultra-low specific-speed centrifugal pump

2019 ◽  
Vol 234 (1) ◽  
pp. 58-71 ◽  
Author(s):  
Cong Wang ◽  
Yongxue Zhang ◽  
Hucan Hou ◽  
Zhiyi Yuan
Keyword(s):  
Boundary Layer ◽  
Centrifugal Pump ◽  
Diagnostic Model ◽  
Two Dimension ◽  
Cavitation Performance ◽  
Hydraulic Design ◽  
Displacement Thickness ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Low Efficiency

Low efficiency and bad cavitation performance restrict the development of the ultra-low specific-speed centrifugal pump (ULSSCP). In this research, combined turbulent boundary layer theory with two-dimension design and two-dimension viscous hydraulic design method has been proposed to redesign a ULSSCP. Through the solution of the displacement thickness in the boundary layer, a less curved blade profile with a larger outlet angle was obtained. Then the hydraulic and cavitation performance of the reference pump and the designed pump were numerically studied. The comparison of performance of the reference pump calculated by the numerical and experimental results revealed a better agreement. Research shows that the average hydraulic efficiency and head of the designed pump improve by 2.9% and 3.3%, respectively. Besides, the designed pump has a better cavitation performance. Finally, through the internal flow analysis with entropy production diagnostic model, a 24.8% drop in head loss occurred in the designed pump.

Optimal hydraulic design of an ultra-low specific speed centrifugal pump based on the local entropy production theory

2019 ◽  
Vol 233 (6) ◽  
pp. 715-726 ◽  
Author(s):  
Hucan Hou ◽  
Yongxue Zhang ◽  
Xin Zhou ◽  
Zhitao Zuo ◽  
Haisheng Chen
Keyword(s):  
Entropy Production ◽  
Centrifugal Pump ◽  
Orthogonal Design ◽  
High Energy ◽  
Geometrical Parameters ◽  
Production Theory ◽  
Local Entropy ◽  
Hydraulic Design ◽  
Low Specific Speed ◽  
Specific Speed

The ultra-low specific speed centrifugal pump has been widely applied in aerospace engineering, metallurgy, and other industrial fields. However, its hydraulic design lacks specialized theory and method. Moreover, the impeller and volute are designed separately without considering their coupling effect. Therefore, the optimal design is proposed in this study based on the local entropy production theory. Four geometrical parameters are selected to establish orthogonal design schemes including blade outlet setting angle, wrapping angle volute inlet width, and throat area. Subsequently, a 3D steady flow with Reynolds stress turbulent model and energy equation model is numerically conducted and the entropy production is calculated by a user-defined function code. The range analysis is made to identify the optimal scheme indicating that the combination of local entropy production and orthogonal design is feasible on pump optimization. The optimal pump is visibly improved with an increase of 1.08% in efficiency. Entropy production is decreased by 16.75% and 6.03% in impeller and volute, respectively. High energy loss areas are captured and explained in terms of helical vortex and wall friction, and the turbulent and wall entropy production are respectively reduced by 3.82% and 14.34% for the total pump.

scholarly journals Optimal Design of Slit Impeller for Low Specific Speed Centrifugal Pump Based on Orthogonal Test

2021 ◽  
Vol 9 (2) ◽  
pp. 121
Author(s):  
Yang Yang ◽  
Ling Zhou ◽  
Hongtao Zhou ◽  
Wanning Lv ◽  
Jian Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Centrifugal Pump ◽  
Large Scale ◽  
Internal Flow ◽  
Orthogonal Test ◽  
Centrifugal Pumps ◽  
Initial Model ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Four Levels

Marine centrifugal pumps are mostly used on board ship, for transferring liquid from one point to another. Based on the combination of orthogonal testing and numerical simulation, this paper optimizes the structure of a drainage trough for a typical low-specific speed centrifugal pump, determines the priority of the various geometric factors of the drainage trough on the pump performance, and obtains the optimal impeller drainage trough scheme. The influence of drainage tank structure on the internal flow of a low-specific speed centrifugal pump is also analyzed. First, based on the experimental validation of the initial model, it is determined that the numerical simulation method used in this paper is highly accurate in predicting the performance of low-specific speed centrifugal pumps. Secondly, based on the three factors and four levels of the impeller drainage trough in the orthogonal test, the orthogonal test plan is determined and the orthogonal test results are analyzed. This work found that slit diameter and slit width have a large impact on the performance of low-specific speed centrifugal pumps, while long and short vane lap lengths have less impact. Finally, we compared the internal flow distribution between the initial model and the optimized model, and found that the slit structure could effectively reduce the pressure difference between the suction side and the pressure side of the blade. By weakening the large-scale vortex in the flow path and reducing the hydraulic losses, the drainage trough impellers obtained based on orthogonal tests can significantly improve the hydraulic efficiency of low-specific speed centrifugal pumps.

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 Numerical Simulation of 3D Solid-Liquid Turbulent Flow in a Low Specific Speed Centrifugal Pump: Flow Field Analysis

2014 ◽  
Vol 6 ◽  
pp. 814108 ◽  
Author(s):  
Baocheng Shi ◽  
Jinjia Wei
Keyword(s):  
Turbulent Flow ◽  
Centrifugal Pump ◽  
Centrifugal Pumps ◽  
Numerical Convergence ◽  
Phase Calculation ◽  
Low Specific Speed ◽  
Specific Speed ◽  
3D Solid ◽  
Solid Liquid ◽  
Numeral Simulation

For numerically simulating 3D solid-liquid turbulent flow in low specific speed centrifugal pumps, the iteration convergence problem caused by complex internal structure and high rotational speed of pump is always a problem for numeral simulation researchers. To solve this problem, the combination of three measures of dynamic underrelaxation factor adjustment, step method, and rotational velocity control means according to residual curves trends of operating parameters was used to improve the numerical convergence. Numeral simulation of 3D turbulent flow in a low specific speed solid-liquid centrifugal pump was performed, and the results showed that the improved solution strategy is greatly helpful to the numerical convergence. Moreover, the 3D turbulent flow fields in pumps have been simulated for the bottom ash-particles with the volume fraction of 10%, 20%, and 30% at the same particle diameter of 0.1 mm. The two-phase calculation results are compared with those of single-phase clean water flow. The calculated results gave the main region of the abrasion of the impeller and volute casing and improve the hydraulic design of the impeller in order to decrease the abrasion and increase the service life of the pump.

scholarly journals Comparison of energy parameters of a centrifugal pump with a multi-piped impeller in cooperation either with an annular channel and a spiral channel

2018 ◽  
Vol 8 (1) ◽  
pp. 513-522 ◽  
Author(s):  
Bartłomiej Chomiuk ◽  
Janusz Skrzypacz
Keyword(s):  
Centrifugal Pump ◽  
Annular Channel ◽  
Operating Parameters ◽  
Centrifugal Pumps ◽  
Impeller Outlet ◽  
Flow Geometry ◽  
Quantitative Verification ◽  
Flow Through ◽  
Low Specific Speed ◽  
Specific Speed

Abstract The article presents results of numerical analyzes, which raise a subject of influence of the cooperation the multi-piped impeller with a rationalized flow geometry of annular casing and volute casing for liquid flow through centrifugal pump and their operating parameters in the extremely low specific speed nq<10. The multi-piped impeller (patented by authors) is a major alternative to classic vane impellers. The stator type is responsible for the conversion of the kinetic energy of the liquid by the impeller outlet into potential energy, which determines the overall efficiency of the pump. Also, the article presents qualitative and quantitative verification of results obtained by computer modeling and an attempt to estimate their accuracy. The article focuses mainly on the comparison of the performance parameters of the pump with a multi-piped impeller in cooperation with two stator types with a rationalized flow geometry. Both outlet elements were tested in various configurations of constructional features. The complexity of the construction of the stator can significantly affect the manufacturing costs of pump unit. Knowledge concerning construction of hydraulic elements of centrifugal pumps working in the range of parameters corresponding specific speed (nq<10) is insufficient. As shown in the paper, the annular type casing model pump cooperating with a multi-piped impeller, designed in accordance with literature, reached far poorer operating parameters than the rational annular construction in a configuration with the same impeller.

Hydraulic design and performance analysis of low specific speed centrifugal pump

2012 ◽  
Vol 15 (3) ◽  
pp. 032023 ◽  
Author(s):  
X Zhou ◽  
Y X Zhang ◽  
Z L Ji ◽  
L Chen
Keyword(s):  
Performance Analysis ◽  
Centrifugal Pump ◽  
Hydraulic Design ◽  
Low Specific Speed ◽  
Specific Speed ◽  
And Performance

Effect of the Section Area of Volute in Low Specific Speed Centrifugal Pumps on Hydraulic Performance

2009 ◽  
Author(s):  
Xiang Zhang ◽  
Yang Wang ◽  
Jianhui Fu ◽  
Cui Dai ◽  
Caihong Wang
Keyword(s):  
Flow Rate ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Blade Angle ◽  
Rate Condition ◽  
Section Area ◽  
Impeller Outlet ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Experimental Researches

The volute of low specific speed centrifugal pumps has a great impact on the performance of the pump in that the highest efficiency can only be achieved when the impeller is matched with a well-designed volute. At off-BEP conditions, the performance of pumps declines as a consequence of a mismatch between characteristics of the impeller and the volute. The section area is the most important factor of volute. Numerical simulations and experimental researches have been carried out on the routine-designed impeller and the non-overloading designed impeller (different impeller outlet blade angle between two types of impellers) in the hope of finding out the effect of the section area of volute on low specific speed centrifugal pumps. It has been found that the uneven flow rate on different volute sections caused by the backflow between volute and impeller is one of the reasons for the efficiency decline of pumps at off-BEP conditions, especially in the low flow rate condition. It has also been found that the routine-designed impeller is more easily affected by the section area of volute than non-overloading designed impeller.

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