Do you know how to improve the efficiency of the centrifugal pump?Today let us study it together!
General methods to improve the centrifugal pump efficiency
Improve pipeline system and reduce resistance. The length of the pipeline shall be shortened and kept as straight as possible, and the flow rate of the centrifugal pump shall be reduced to reduce the head loss along the pipeline; the number of gate valve, bottom valve, elbow, orifice plate and other components shall be reduced to reduce the local head loss. Reduce the surplus of centrifugal water pump outlet pressure to meet the requirements of pipeline system for outlet pressure.
Centrifugal ump is the most widely used general-purpose machinery, but also a large consumer of electricity and energy, so improving the efficiency of the centrifugal pump itself and the use efficiency of the pump plays an important role in energy conservation.
Improve the efficiency of the the centrifugal pump itself
The blade extends to the suction port and thins, so that the liquid is affected by the blade in advance, which can reduce the outer diameter of the impeller of the centrifugal pump, also can increase the length of the streamline in the blade passage, and reduce the relative diffusion; but the extension should be appropriate, too forward extension will make the area of the inlet et too small, so that the wall angle between the blade inlet and the blade cover plate will be smaller, but it will increase the hydraulic friction loss, squeeze the inlet flow channel, and affect the cavitation and efficiency Both are unfavourable.
2. In order to reduce the diffusion loss, the ratio of the outlet area to the inlet area of the runner between the adjacent blades should be controlled between 1.0 and 1.3. If the ratio is greater than 1.3, the channel diffusion is serious and the efficiency of the centrifugal pump is reduced.
3. The larger the hydraulic radius of the runner is, the better. Try to make the blade inlet section close to the square as much as possible to reduce the friction loss. From hydraulics, we know that the ratio of the cross-section area of the flow passage to the wet circumference is called the hydraulic radius, that is, the hydraulic radius - cross-section area of the flow passage / wet circumference. Large wetted perimeter, in fact, is the contact area between the liquid of the centrifugal pump and the wall. When the cross-section of the flow passage is changed from an approximate square to a long and narrow rectangle, it is essentially to let the liquid flow through the gap of the long and narrow cross-section, so the resistance must be large.
4. Because of the large hydraulic loss of the curved diffusion pipe, the diffusion section with a slight bend close to a straight line is mostly used now. For the anti guide vane, its inlet angle and position in the circumferential direction of the centrifugal pump shall be determined in combination with the outflow of liquid flow in the diffusion section. The principle is to form a continuous flow channel, so as to avoid the narrow inlet section of the anti guide vane, otherwise, eddy current and impact loss will be caused at the inlet of the anti guide vane.
5. For the multistage centrifugal pump, the impeller inlet is pre rotated (the outlet angle of the anti guide vane is less than 90). ）At the same time, the relative velocity diffusion is reduced when the outlet angle of the guide vane is less than 90. When the water flows into the impeller, there is a pre rotation, that is to say. 1, 0.
6. In order to make the "1vul" term in the theoretical head formula ht-u2vu2-lvul zero in the design, the outlet angle of the anti guide vane should be 90. For the last stage guide vane, the rotating component can be eliminated. However, experiments show that this is not good for efficiency and stable performance curve of the centrifugal pump, especially for some low specific speed pumps, in order to obtain the declining performance curve of the centrifugal pump, the outlet angle of the anti guide vane should be less than 90. Usually at 60. 80. Both ends of the blade should be thinner to avoid collision and eddy current loss.
Section of Blade Runner
7. Increase the width of impeller of the centrifugal pump outlet, reduce the absolute speed of impeller outlet, and reduce the hydraulic loss in the water chamber.
8. In order to reduce the pressure difference between the front and rear cover plate streamline and reduce the secondary return at the outlet, it is necessary to cut the impeller of the centrifugal pump outlet obliquely, reduce the length difference between the front and rear streamlines or select different blade outlet angles for different streamlines.
9. When the original design area is small, the flow will not be blocked.
(2) Reduce mechanical and friction losses
① The mechanical friction loss of the centrifugal pump caused by bearing and packing is very small, which has little effect on efficiency. The mechanical friction loss of packing seal is larger than that of mechanical seal. If mechanical seal shell 4 can be used, it is better.
② Improve the surface finish of impeller of the centrifugal pump and guide vane passage. If possible, it is best to use hand-held grinding wheel and other tools to polish the surface of the runner, so that the hydraulic friction loss will be significantly reduced.
③ The friction loss between the front and rear cover plate surface of the impeller of the centrifugal pump and the disk caused by the liquid is directly proportional to the 5th power of the outer diameter of the impeller. Selecting a larger blade outlet angle can reduce the outer diameter of the impeller of the centrifugal pump, thus reducing the disc friction loss. The friction loss of the disc is closely related to the surface roughness, and the outer wall of the impeller cover plate should be as smooth as possible. The disc friction loss can also be reduced by properly reducing the clearance between the impeller cover plate and the guide vane.
(3) Reduce leakage
In order to reduce the volume loss, it is necessary to reduce the clearance of each part of the centrifugal pump or lengthen the clearance between seals and adopt labyrinth seal to increase the leakage resistance.
The leakage part in the centrifugal pump pump occurs at the impeller and sealing ring, between stages of multistage centrifugal pump, axial force balancing device, etc.