Cavitation behavior is very important in pumps for long time operation. However, there is difficulty in predicting the cavitation phenomena of pumps by Computational fluid dynamics (CFD). In order to accurately ascertain cavitation behavior, a comparison between CFD and experimental data is a significant and essential process. The purpose of this study is to analyze cavitating behavior in multistage centrifugal pumps numerically and experimentally. For this investigation an experimental set up was used to obtain cavitation performance results. The CFD method was used to investigate the multistage centrifugal pump performance under developed cavitating conditions. The Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was adopted to account for turbulent flows. Numerical data were validated with experimental data and a good comparison of results was achieved. Numerically, cavitation performances were obtained for different pump stages and the effects on cavitation were described according to different NPSH (Net positive suction head). The occurrence of cavitation was also described according to NPSH3% in the head drop lines and water vapor volume fraction on the impeller blade. The rapid drop in head at low NPSH was captured for different flow conditions. It was found that for stage to stage performance, the head drop changes could be related to losses inside the pump. It was also shown that the simulation results can truly represent the development of the attached sheet cavitation in the impeller.
Net Positive Suction Head Pdf Download
Chapter 12. Pumping Systems Authors: Harold R. Duke Keywords: Affinity equations, Centrifugal, Efficiency, Engine, Head, Head-discharge curve, Impeller, Irrigation, Motor, Net positive suction head, Power, Pump curve, Pump stage, Pumping rate, System head, Total dynamic head, Vertical turbine.DOI: 10.13031/2013.23695 ( Free Abstract ) ( Download PDF )
Cavitation in reciprocating pump installations is a major cause of piping and pump vibration and mechanical failures. Cavitation occurs in pump systems when the negative peak of the dynamic pressure wave, added to the steady state pressure, approaches the vapor pressure of the liquid. Even in those systems which have ample net positive suction head (NPSH) according to Hydraulic Institute Standards [1], cavitation can occur. These standards specify that, in addition to the net positive suction head required (NPSHR) by the manufacturer, an allowance should be made for the inlet piping pressure drop and acceleration head. Acceleration head calculations are an attempt to account for the dynamic behavior of the system using quasi-static assumptions. In practice, these calculations can be inadequate since they ignore the dynamic acoustical response characteristics of the fluid.
This paper discusses the inadequacies of the acceleration head concept, and describes how pulsation can contribute to cavitation. Simulation of pump systems using a computer program to predict pulsation and the onset of cavitation is discussed. Using these techniques, cavitation and pulsation levels in the suction systems can be predicted and the need for additional suction head properly evaluated.
Gorman-Rupp VGH Series centrifugal pumps are engineered for maximum operating efficiency and minimal energy consumption when pumping dirty liquids and mild abrasives. The enclosed impeller design incorporates double curvature vanes for higher efficiency. The entrance of the volute casing has dynamic positioning vanes that direct the flow to the impeller for increased efficiency while reducing net positive suction head (NPSH). Impeller trims can provide maximum flexibility for your specific application.
Net positive suction head (or NPSH) is a term that indicates the pressure on the suction side of a pump to help you find out if the pressure is high enough to prevent cavitation. Cavitation is an event in which bubbles or cavities in a liquid occur in regions of relatively low pressure around the pump impeller. This phenomenon can cause severe damage to the impeller. It must be ensured that the net positive suction head available is greater than the net positive suction head required, with the appropriate safety margin.
This characteristic curve illustrates the net positive suction head required (NPSHR) trends versus the pump discharge. It can be seen from this figure that NPSHR gradually rises as the pump discharge increases. 2ff7e9595c
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