A lot of factors affecting the performance of centrifugal pump and performance conversion factors affecting the performance of centrifugal pump, including liquid properties (density and viscosity etc.), structure and size of the pump (such as D2 and beta 2), the speed of the pump n. When any of these parameters change, will change the performance of the pump, the pump manufacturers need to provide the performance parameters or characteristics of the curve.
1 liquid physical properties (properties of matter affect liquid)
(1) the effect of density (density)
The centrifugal pump flow, pressure head has nothing to do with the liquid density, the efficiency is not as the liquid density change, so when the transmission of liquid density changes, H-Q and -Q curve is basically unchanged, but the pump shaft power and the liquid density is proportional to the. At this point, the N-Q curve is no longer applicable, N need to re calculate the 2-16.
(2) the effect of viscosity (Viscosity)
When the transport of liquid viscosity greater than the viscosity of water at room temperature, increasing the energy loss of the liquid inside the pump, causing pump flow, pressure head is reduced, lower efficiency, but increase the shaft power, pump characteristics are changed. When the liquid viscosity is greater than 20cSt gamma (CST), the performance of centrifugal pump to press type correction, i.e.
(2-17)
Type
CQ, cH, C, respectively -- the correction coefficient of centrifugal pump flow, pressure head and efficiency, its value from figure 2-13, Richard 2-14;
Q, H, n -- respectively when the water flow in a centrifugal pump flow, pressure head and efficiency;
Q ', H', 'n -- respectively centrifugal pump for high viscosity fluid flow, pressure head and efficiency.
The viscosity coefficient conversion diagram is drawn from the average value of a number of tests on a single stage centrifugal pump, and the pressure head of each stage should be used for the multi-stage centrifugal pump. Two drawings are applicable to Newtonian fluids, and can only be used in the scale range, not to be extrapolated. Figure QS in the 2-13 of the transfer of water when the rated flow, the unit is m3/min. The use of viscosity coefficient conversion chart 2-3.
Viscosity conversion coefficient of large flow centrifugal pump
Viscosity conversion coefficient of small flow centrifugal pump
2 the influence of the centrifugal pump speed (of rotate speed affect)
By the basic equation of the centrifugal pump, when the pump speed change, the pump flow, pressure head will change, and cause the pump efficiency and power of the corresponding changes. When the liquid viscosity is small, the efficiency change is not obvious, the flow of the pump at different speed, the relationship between the head and the power and speed can be expressed as follows.
(2-18)
Type
The performance of Q1, H1 and N1------ speed is n1;
The performance of Q2, H2 and N2------ speed is n2;
Formula 2-18, known as the law of proportionality of centrifugal pumps. The applicable condition is that the speed change of the centrifugal pump is not more than 20%.
3 centrifugal pump impeller diameter influence (of impeller diameter affect)
When the centrifugal pump speed is certain, the basic equation of the pump shows that the flow, pressure head and impeller diameter. For the same type of pump, can be replaced with a smaller diameter of the impeller (except for the impeller outlet width slightly changed, the other size unchanged), then the pump flow, pressure head and power and the impeller diameter of the approximate relationship between the
(2-19)
Type
Q ', H', N '- speed for D2' when the pump performance;
The performance of Q, H and N------ speed is D2;
The formula 2-19 is called the law of the centrifugal pump's cutting. Its applicable condition is fixed speed, the diameter of the impeller turning is not greater than 5%D2.