Effects of wear ring clearance on hydraulically generated vibration and noise of a centrifugal pump volute

The wear ring clearance of centrifugal pumps is of significant importance for numbers of effects. In the paper, these effects including the performance, pressure pulsations, hydraulically generated vibration and noise level are investigated. For the purpose, a numerical method combined the FEM and BEM analysis was developed to predict the vibration and sound radiation of the volute. The numerical simulations with and without leakage flow paths being considered were compared. Additionally, the simulation results were validated by the vibration acceleration of the monitoring points on the volute. On this basis, the effects of wear ring clearance were analyzed. The results show that the quality of vibration simulation for centrifugal pumps can be improved by involving the leakage flow paths in simulations. Based on an overall consideration of the performance, pressure pulsations, vibration and noise, the optimum wear ring clearance is supposed to be 0.6 mm for the centrifugal pump (nqSI= 26.7). The results can be used to guide the optimum design of the pump wear ring clearance

Research on unsteady performance of a two-stage self-priming centrifugal pump

In order to study the unsteady performance of a two-stage self-priming centrifugal pump, the unsteady numerical calculation in a two-stage self-priming centrifugal pump was performed and energy characteristics experiments and self-priming experiments were carried out. The pressure pulsation and radial force in the pump were then analyzed. The results show that numerical calculation values are close to the experiment values. Head deviation of the pump is less than 3 %, and efficiency deviation of the pump is less than 2 percentage points. Compared with monitoring point P1, the pressure fluctuation coefficient of monitoring point P3 at the design flow rate is reduced by 61 %. Compared with monitoring point P8, the pressure fluctuation coefficient of monitoring point P5 is reduced by 70 %. The radial force on the radial guide-vane is obviously smaller than that on the volute. Under the same flow rate, radial force on the volute of second-stage pump is almost 20 times larger than that on the radial guide-van of first-stage pump

Investigation of radial force and hydraulic performance in a centrifugal pump with different guide vane outlet angle

In order to investigate the effect of the guide vane outlet angle on the performance of centrifugal pumps, a centrifugal pump with guide vanes was used as the research model and its specific speed is 165. Keep all the other geometry parameters of the pump as constants, the guide vane outlet angle was designed to be 28°, 20°, 15°,10°, 5° and 3° respectively. The whole flow field in the pump under different guide vane outlet angles was simulated by commercial code CFX and the simulation was unsteady. The simulation results were validated by experiment results. According to the simulations, the hydraulic performance, internal flow and radial force of the pump under different guide vane outlet angles were compared and analyzed in detail. The research results indicate that the head and efficiency of the pump are the best when the guide vane outlet angle is 10°. With the decrease of the blade outlet angle of guide vane, the length of flow channels in the guide vane become bigger and its width gets smaller, the uniformity of inner flow in the centrifugal pump gets better, and therefore the radial force on the impeller reduces. With the decrease of the guide vane blade outlet angle, the pulsation frequency of radial force does not change, but the pulsation amplitude of the radial force reduces obviously. The vector distribution of the unsteady radial force is symmetric around the origin and mainly lies in 5 regions, which is same as the blade number of impeller

Effect of suction chamber baffles on pressure fluctuations in a low specific speed centrifugal pump

In order to study the effect of suction chamber baffles on hydraulic performance and unsteady characteristics in a low specific speed centrifugal pump, a model pump was design with enlarging flow mothed and four schemes of suction baffle, including no baffle (scheme 0), only one baffle in the suction (scheme 1), two baffles (scheme 2) and three baffles in the suction (scheme 3), were considered. Commercial code FLUENT was applied to simulate the flow of the pump. RNG k-ε turbulence model was adopted to handle with the turbulent flows in the pump. The sliding mesh technique was applied to take into account the impeller-volute interaction. Based on the simulation results, the hydraulic performance and pressure fluctuations were obtained and analyzed in detail. The head value of no baffle in the suction (scheme 0) is lower than that with baffles in the suction (scheme 1, scheme 2, scheme 3) at each condition point. Hump point in scheme 0 is at φ= 0.00596 (1.2 times Qo). The hump point in scheme 1, scheme 2, scheme 3 is at 0.8Qo, 1.0Qo, 1.0Qo, respectively. The ε value of scheme 1 is the smallest and that of scheme 0 is the largest in the four schemes. Six wave troughs are observed clearly at each monitoring point as the impeller rotates in a circle. Each time the impeller is turned 10 degrees, there are six obvious troughs around the impeller. With the rotation of the impeller, peak value of pressure fluctuations at blade passing frequency (BPF) is gradually decrease. At low flow (ϕ= 0.002383), the main frequency of pressure fluctuation at P36 and P1 under scheme 0, scheme 2 and scheme 3 is 295 Hz, which is corresponding to BPF. The pressure fluctuation levels are decreased by –2.72 %, –2.13 %, and –2.21 % respectively when the number of baffle in the suction is one, two, three, respectively. And decrease rate of pressure fluctuation (∆Cp) on scheme 1 is maximum. It indicates that Adding baffles to the suction chamber is beneficial to reduce the amplitude of pressure pulsation at BPF in the volute. The best number of baffles in the suction is one. Based on scheme 1 simulation results, the prototype was manufactured and the performance experiments were carried out. A good agreement of the head and efficiency between numerical results and experimental results are observed

Effects of wear ring clearance on hydraulically generated vibration and noise of a centrifugal pump volute

The wear ring clearance of centrifugal pumps is of significant importance for numbers of effects. In the paper, these effects including the performance, pressure pulsations, hydraulically generated vibration and noise level are investigated. For the purpose, a numerical method combined the FEM and BEM analysis was developed to predict the vibration and sound radiation of the volute. The numerical simulations with and without leakage flow paths being considered were compared. Additionally, the simulation results were validated by the vibration acceleration of the monitoring points on the volute. On this basis, the effects of wear ring clearance were analyzed. The results show that the quality of vibration simulation for centrifugal pumps can be improved by involving the leakage flow paths in simulations. Based on an overall consideration of the performance, pressure pulsations, vibration and noise, the optimum wear ring clearance is supposed to be 0.6 mm for the centrifugal pump (nqSI= 26.7). The results can be used to guide the optimum design of the pump wear ring clearance

Effect of the blade outlet angle on unsteady characteristics of a single channel pump

To study the effect of β2 on energy performance and unsteady characteristics of the single-channel pump, the experimental tests about the energy characteristics, head pulsation, pressure fluctuation and radial force have been conducted by the synchronous test. 3 different impellers with the blade outlet angle β2 of 8°, 16° and 25° respectively are studied. The results show that with the increase of β2 from 8° to 25°, the head increases gradually and the maximum increase amplitude reaches 22.6 %. As β2 changes from 8° to 25°, there is a maximum efficiency. The mixing loss at the impeller outlet can be decreased by reducing β2. With the increasing of β2, the minimum head in time domain gradually lag and the maximum head gradually advances. The pressure fluctuation in each measuring point shows the trend of increasing first and then decreasing with the increasing of the flow rate. With β2 increasing, the radial force also increases and the maximum increase amplitude of minimum radial force is larger than 8 %. The research can provide some reference for the optimization of single channel pumps

Effect of inlet splitter on pressure fluctuations in a double-suction centrifugal pump

In order to investigate the effect of inlet splitter on pressure fluctuations in a double-suction centrifugal pump, three research schemes, including no splitter (scheme I), a splitter along the flow passage centerline (scheme II) and a splitter above the flow passage centerline in the suction (scheme III), were designed. The flow in the pump was simulated by commercial code FLUENT. The viscous Navier-Stokes equations were handled with an unsteady calculation and the sliding mesh technique was applied to take into account the impeller-volute interaction. Based on the simulation results, the hydraulic performance and pressure fluctuations were obtained and analyzed in detail. The hydraulic performance agrees well with the experimental results. The pressure fluctuations under three schemes are different. The maximum amplitude of the pressure fluctuations in scheme II is the minimum. For monitoring points near volute tongue, rotating frequency and its harmonies are dominant under three research schemes. The maximum amplitude of pressure fluctuations of three schemes are all at the blade passing frequency. In particular, the maximum pressure fluctuation amplitude of scheme II was less than that of scheme I and scheme III, which illustrated that it is effective to reduce the peak value of pressure fluctuations in double suction centrifugal pump by installing a splitter in the suction properly

Research on pressure fluctuation characteristics of a centrifugal pump with guide vane

In order to study the pressure pulsation characteristics of a centrifugal pump with a guide vane, a pump with specific speed ns= 190 was chosen as the research object. The numerical simulation was carried out using the standard k-ε turbulence model. The pressure pulsation characteristic was researched at a set monitoring point. The reliability of the numerical simulation was verified with experiment results. The pressure pulsation characteristic curves of each calculation domain were obtained by dimensionless data processing. The results elucidate that the rotor/stator interaction at the outlet of the impeller is the main source for the pressure pulsation. With increasing distance, the pressure pulsation gradually decreases; the pressure pulsation amplitude of the pressure surface is larger than the suction surface; the pressure pulsation in the flow channel of the guide vane remains the same; the pressure fluctuation near the outlet of the annular volute chamber is larger, and the pressure pulsation near the upstream of the flow channel is quite complicated. The pressure pulsation at the annular volute and axial symmetry is the same

Utilization of post-exposure prophylaxis potentially contributed to the changes of risk behaviors among men who have sex with men in China

BackgroundThe HIV infection status among men who have sex with men (MSM) in China is a cause for concern. Post-exposure prophylaxis (PEP) serves as a highly effective biomedical preventive measure against HIV infection. Substantial evidence has established an association between PEP utilization and risk behaviors among MSM, but whether the utilization of PEP has an impact on risk behaviors remains unknown. This study sought to elucidate the impact of PEP usage on risk behaviors among MSM and provide recommendations for developing targeted HIV prevention programs.MethodsA cohort study was conducted in Qingdao, China, from April 2021 to January 2022. Participants were enlisted by volunteers from community-based organizations through a snowball sampling method. Face-to-face interviews were conducted to collect sociodemographic and behavioral information of participants. The study encompassed a retrospective investigation, baseline survey, and follow-up survey, representing periods before, during, and after PEP usage, respectively. Generalized estimating equations, fitting a Poisson regression model, were applied to scrutinize changes in risk behaviors of MSM during and after PEP usage, in comparison to before PEP usage.ResultsA total of 341 MSM were recruited in the cohort study, with 179 individuals completing the follow-up survey. In comparison to before PEP usage, there was a significant increase in the proportion of Rush Popper usage (17.6% vs. 23.8% vs. 29.6%) and commercial sexual partners (10.9% vs. 17.6% vs. 21.8%) among MSM during and after PEP usage. Before PEP usage, 88.7% of MSM reported having ≥3 temporary sexual partners in the last 6 months. This proportion exhibited no significant change during PEP usage (91.8%), but it significantly increased to 97.8% after PEP usage (P < 0.05). Notably, there was a significant decrease in group sex during and after PEP usage compared to before PEP usage (30.8% vs. 21.4% vs. 21.2%).ConclusionThe utilization of PEP may impact risk behaviors among MSM, potentially leading to increased Rush Popper usage, temporary sexual partners, and commercial sexual partners after PEP usage, accompanied by a decrease in group sex. Further research is imperative to elucidate the impact of PEP utilization on MSM and develop targeted HIV prevention programs

Vision, challenges and opportunities for a Plant Cell Atlas

With growing populations and pressing environmental problems, future economies will be increasingly plant-based. Now is the time to reimagine plant science as a critical component of fundamental science, agriculture, environmental stewardship, energy, technology and healthcare. This effort requires a conceptual and technological framework to identify and map all cell types, and to comprehensively annotate the localization and organization of molecules at cellular and tissue levels. This framework, called the Plant Cell Atlas (PCA), will be critical for understanding and engineering plant development, physiology and environmental responses. A workshop was convened to discuss the purpose and utility of such an initiative, resulting in a roadmap that acknowledges the current knowledge gaps and technical challenges, and underscores how the PCA initiative can help to overcome them.</jats:p