Centrifugal pump basic equations

Centrifugal pump is based on the rotation of the impeller to pump water, then, working water flow in the rotating impeller is how to exercise it? How much head can a rotating impeller produce? For these laws of motion, we will learn more about each one by deducing and analyzing the basic equations of a centrifugal pump.
      Liquid flow in the impeller
      Figure 2-17 shows the plane and section of a centrifugal impeller. Flow from the suction pipe along the axis of the pump at an absolute speed of CO into the inlet from the impeller, the liquid particles enter the impeller, they undergo a composite circular motion. Therefore, to study the flow of liquid particles in the impeller, there are two coordinate systems: (1) the rotating impeller is the kinematic coordinate system: (2) the stationary pump casing or the pump base is a static coordinate system. The flow of water in the impeller groove flows along the blade at a velocity W, which is the movement of the mass point of the liquid on the kinematic coordinate system, referred to as the relative motion, at the same time as the water flow again has a circumference that rotates with the impeller Become involved speed, the combination of the above two speeds, namely the liquid mass point on the pump shell absolute speed C. In other words, for a pump housing, the flow of water will move at an absolute speed c. Then the angle of the compound of water flow in the impeller is called the angle between a1 and a2 and the angle between W1 and negative U1, which becomes B1 and B2. In the design of pump, B1 is also called the water inlet angle of the blade, B2 is the blade's water exit angle.

Figure 2-17 Centrifugal pump impeller speed of water flow

      When the blade outlet is radial, B2 = 90, as shown in Figure 2-18 (b) below. When both B1 and B2 are less than 90 °, the blade rotates backwards with respect to the direction of rotation, as shown in Figure 2-18 (A). When B2 is greater than 90. , The blades and the rotation direction of the front curved blade, as shown in Figure 2-18 (c) below. Therefore, the size of angle B2 reflects the camber of leaves, which is an important data for the shape of leaves and the energy of leaves. Centrifugal pump impeller used in the actual project,

Mostly curved leaves. Backward curved blade flow path is relatively gentle, small curvature, smaller hydraulic loss within the vat, help to improve the efficiency of the pump. Generally forward curved blades, short and curved channel, the impeller in the water flow curve loss, low hydraulic effect. B2 commonly used in general centrifugal pump value of 20. -30


    In the discussion that follows, we will all target curved blades later and usually replace the velocity flattened quadrilateral with velocity triangles. Figure 2-19 shows the velocity triangles at the impeller exit. Diagram of the speed of the tangential speed C2 with symbols, radial speed with the symbol C said.

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