We present extensive results on the performance of an unshrouded centrifugal pump impeller handling solid-liquid mixtures. The effect of the clearance between the impeller tip and the casing and of the solid concentration, density and mean diameter on the pump performance characteristics is investigated. The results are discussed and utilized, together with data available in the literature, to establish a correlation allowing the prediction of the head reduction factor for shrouded/unshrouded impeller centrifugal pumps handling solid-liquid mixtures

Performance Characteristics of a Centrifugal Pump Impeller With Running Tip Clearance Pumping Solid-Liquid Mixtures

Purpose




To analyze the work principle and capacity of energy conversion in each segment of profile lines, the energy transfer from impeller to transmission medium is separated into head coefficient and load coefficient to analyze the energy transfer process. The concepts of airfoil lift coefficient and drag coefficient are used; the third manifestation of the Euler equations is used as well.




Design/methodology/approach




The numerical simulation of energy conversion mechanism based on load criteria of vane airfoil has been established in screw centrifugal pump to explain its energy conversion mechanism in an impeller. Upon this basis, the velocity and pressure along the entire blade are investigated through the numerical simulation of internal solid–liquid flow in the pump. The energy conversion process under load criteria in the blade airfoil has also been obtained.




Findings




The research suggests that the mathematical model of energy conversion mechanism based on the load criteria of the vane airfoil is reliable in the screw centrifugal pump. The screw centrifugal blade has twice or even several times the wrap angle than the ordinary centrifugal blade. It is a large wrap angle that forms the unique flow channel which lays the foundation for solid particles to pass smoothly and for soft energy conversion. At the same time, load distribution along the profile line on the long-screw centrifugal blade is an important factor affecting the energy conversion efficiency of the impeller.




Originality/value




The quantitative analysis method of energy in the screw centrifugal pump can help the pump designer improve certain features of the pump and shorten the research cycle.

Mathematical model of energy conversion mechanism in screw centrifugal pump based on load criteria of blade airfoil

Equations of motion of solid particles in a pump impeller having a low specific speed were solved numerically in the flow field obtained with assumptions of an inviscid and incompressible three-dimensional potential flow, and general movements of solid particles in the pump were clarified. Trajectories of the sand particles and manganese ores, with diameters ranging from 1 to 5 mm, were obtained for different flow capacities. The positions and velocities with which the particles impact on the boundary surface of the pump were also discussed in order to estimate erosion damage in pumps.

Calculation of the Three-Dimensional Behaviour of Spherical Solid Particles Entrained in a Radial-Flow Impeller Pump:

When a jet stream containing the small particles impinges on a plane wall, the particles are possible to collide with the wall. Under the assumption that the flow is incompressible and irrotational, the fluid is governed by stokes drag law, and the interaction between particles is neglected, the classification of various types in the collision between the particles and the wall, the critical conditions above which the particles collide with the wall, the extent of the region in which the collision arise, the distribution of the collision frequency along the wall, the ratio of collision particles to total of particles, the position at which the collision frequency becomes maximum and so on are found theoretically by choosing the stokes number and the angle between the axis of the jet and the wall as the parameters.

On the collision between small particles and a plane wall in a jet

The movement of small particles, distributed uniformly in an unsteady flow in a square chamber having an inlet and an outlet, are simulated numerically. Particles are classified into three types according to their final state : exhaust type in which the particles are exhausted through the outlet, circulation type in which the particles circulate in the chamber and adhesion type in which the particles adhere to the wall of the chamber. The influences of the initial position of a particle, the particles adhere tot eh wall of the chamber. The influences of the initial position of a particle, the Reynolds number R and the dimension ratio N characterizing whether a particle is coarse or fine, on the ratios of the number of particles of each type to the total number of particles are examined. The number of particles of exhaust type has a maximum at a certain N. The particles of circulation type are finally gathered in a certain orbit. The particles of adhesion type adhere to the wall in the vicinity of the stagnation points.

Movement of Small Particles Caused by an Air Flow in a Chamber

Equations of motion of solid particles in a pump impeller having low specific speed were solved numerically with assumptions of an inviscid and incompressible quasi-three dimensional flow, and the general behavior of solid particles in the pump was clarified. The particle trajectories and forces acting on particles, the diameters of which range from 0.1 to 0.5 mm and the specific-gravities from 1.8 to 5.4 were obtained for different flow capacities. The locations and the velocities, with which the particles impinge on the boundary surface of the pump, were also discussed in order to predict the erosion damage in pumps.

Kiyoshi MlNEMURA

Papers

Behavior of Solid Particles in a Radial-flow Pump Impeller