Pump impellers rotation

Example 7.15. A centrifugal water pump impeller rotates at 1800r/min see Fig. 7.17. The water enters the blades at a radius of 1 in and leaves the blades at a radius of 6 in. The total flow rate is 100 gal/min. The tangential velocities in and out may be assumed equal to the tangential velocity of the rotor at those radii. What is the steady-state torque exerted on the rotor ... 

A pump impeller rotates at 500 rpm to pump 65 L/s through a suction diameter of 200 mm. Using Equation 8-20, determine the required NPSH. 

A centrifugal pump, in its simplest form, consists of an impeller rotating within a casing. The impeller consists of a number of blades,... 

F-G F Thermoforming, injection, blow, rotational and extrusion molds Business machine and camera housings, blowers, bearings, gears, pump impellers... 

The working or pumping vanes are backward in form relative to the impeller rotation. 

Centrifugal pumps utilize one or more impellers rotating at high speed within a casing to provide centrifugal force to the FW and to convert this force into pressure. 

The variables involved in the performance of a centrifugal pump include the fluid properties (p, and p), the impeller diameter (cl), the casing diameter (/)), the impeller rotational speed (N), the volumetric flow rate of the fluid (0, the head... 

The pressure developed by a centrifugal pump depends on the fluid density, the diameter of the pump impeller, the rotational speed of the impeller, and the volumetric flow rate through the pump (centrifugal pumps are not recommended for highly viscous fluids, so viscosity is not commonly an important variable). Furthermore, the pressure developed by the pump is commonly expressed as the pump head, which is the height of a column of the fluid in the pump that exerts the same pressure as the pump pressure. 

A Roots vacuum pump (see Fig. 2.17) Is a rotary positive-displacement type of pump where two symmetrically-shaped Impellers rotate Inside the pump casing past each other In close proximity. The two rotors have a aoss... 

Liquid-Piston Type This type is illustrated in Fig. 10-97. These compressors are offered as single-stage units for pressure differentials up to about 0.52 MPa (75 Ibf/in ) in the smaller sizes and capacities up to 6.8 X 10 mVh (4000 fF/min) when used with a lower pressure differential. Staging is employed for higher pressure differentials. These units have found wide application as vacuum pumps on wet-vacuum service. Inlet and discharge ports are located in the impeller hub. As the vaned impeller rotates, centrifugal force drives the sealing liquid... 

Equation (10.41) shows that H is the asymptote approached by (p/w) + z as r approaches infinity and V approaches zero. On the other hand, as r approaches zero, V approaches infinity, and (p/w) + z approaches minus infinity. Since this is physically impossible, the free vortex cannot extend to the axis of rotation. In reality, as high velocities are attained as the axis is approached, the friction losses, which vary as the square of the velocity, become of increasing importance and are no longer negligible. Hence the assumption that H is constant no longer holds. The core of the vortex tends to rotate as a solid body as in the central part of a pump impeller. 

Spiral vortex. If a radial flow is superimposed upon the concentric flow previously described, the path lines will then be spirals. If the flow goes out through a circular hole in the bottom of a shallow vessel, the surface of liquid takes the form of an empty hole, with an air core sucked down the hole. If an outlet symmetrical with the axis is provided, as in a pump impeller, we might have a flow either radially inward or radially outward. If the two plates are a constant distance B apart, the radial flow with a velocity Vr is then across a series of concentric cylindrical surfaces whose area is 0.2nrB. Thus Q = 2nrBVr is a constant, from which it is seen that rVr is a constant. Thus the radial velocity varies in the same way with r that the circumferential velocity did in the preceding discussion. Hence the pressure variation with the radial velocity is just the same as for pure rotation. Therefore the pressure gradient of flow applies exactly to the case of spiral flow, as well as to pure rotation. 

Secondary nucleation results from the presence of solute particles in solution. Recent reviews [16,17] have classified secondary nucleation into three categories apparent, true, euid contact. Apparent secondary nucleation refers to the small fragments washed from the surface of seeds when they are introduced into the crystallizer. True secondary nucleation occurs due simply to the presence of solute particles in solution. Contact secondary nucleation occurs when a growing particle contacts the walls of the container, the stirrer, the pump impeller, or other particles, producing new nuclei. A review of contact nucleation, frequently the most significant nucleation mechanism, is presented by Garside and Davey [18], who give empirical evidence that the rate of contact nucleation depends on stirrer rotation rate (RPM), particle mass density, Mj>, and saturation ratio. 

The activity inside the pump volute incurs several losses first is the backflow of the flow that had aheady been acted upon but is shpping back into the suction eye of the impeller or, in general, toward the suction side of the pump. Because energy had already been expended on this flow but failed to exit into the discharge, this backflow represents a loss. The other loss is the turbulence induced as the impeller acts on the flow and swirls it around. Turbulence is a loss of energy. As the impeller rotates, its tips and sides shear off the fluid this also causes what is called disk friction and is a loss of energy. All these losses cause the inefficiency of the pump is these losses. 

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