Centrifugal pump performance factors and their conversion (with photos)

Centrifugal pump production sector provides the characteristic curve is usually at a certain speed and room temperature (20 ℃) ​​under the conditions of water as the transmission medium measured out. If the use of the conditions of use of large differences in the nature of the liquid and water when the transmission is large, you have to consider the physical properties, speed and impact of different impeller diameter. When used should be converted. The following centrifugal pump performance factors and conversion to illustrate. 1, the impact of density ρ Centrifugal pump can be seen from the basic equation, the pressure head of the centrifugal pump, flow, and has nothing to do with the density, so its efficiency does not change with the density changes, so the centrifugal pump shaft power formula shows that the centrifugal pump Shaft power changes with the density of the liquid changes, so the original characteristic curve N ~ Q or performance of the shaft power should be converted accordingly: Where, N - operating conditions, the centrifugal pump shaft power, KW; ρ - Operating conditions, was transported liquid; N0 - test conditions, centrifugal pump shaft power, KW; ρ0 - 20 ℃ when the density of water, kg / m3. 2, the viscosity of the centrifugal pump due to the loss of flow resistance and liquid viscosity is being transported, the viscosity increases, the fluid through the impeller and the pump casing flow resistance increases, the pressure head, the flow decreases, the efficiency decreases, the shaft power Increase. In general, when the kinematic viscosity of the liquid is over ν> 0.2m2 / s, it should be converted by the following formula: where Q, H and η are the flow rate, pressure head and efficiency at the time of water conveyance; Q ' , H ', η' - the flow rate, head and efficiency of the liquid to be conveyed; CQ, CH, Cη - the conversion factor, the values ​​are less than one. Available from the relevant manuals. 3. Effect of speed n When the centrifugal pump speed changes, its flow, pressure head, shaft power and speed can be converted according to the following proportion of law: Where, Q1, H1, N1 - respectively when the speed of centrifugal pump performance n1 ; Q2, H2, N2 - Centrifugal pump performance when the speed is n2 respectively. It is worth noting that the basic assumption underlying the above relation is that its efficiency is constant after the speed is changed, so that the law of proportion is only right when the speed change is less than 20%. 4. Impeller diameter D2 When the centrifugal pump speed n is constant, the basic equation shows the pressure head, flow and the diameter of the hour wheel D2 related. The change can be converted according to the following cutting law: where, Q ', H', N '- respectively when the impeller diameter D2' pump performance; Q, H, N-- respectively when the impeller diameter D2 Pump performance. It is noteworthy that the above relationship is only applicable to the same type of centrifugal pump, use a small diameter impeller, but the diameter should not change.