Influence of blade type of foam pump on theoretical lift

The influence of blade type on the theoretical lift is mainly to analyze the influence of blade angle B2A at the blade outlet on the theoretical lift h τ o. According to the size of B2A, the impeller is divided into three types: when B2A is less than 90 °, the bending direction of blade is opposite to the rotation direction of impeller, which is called backward curved blade impeller [figure 1-11 (a)]; when B2A is 90 °, the outlet of blade is radial, which is called radial blade impeller [figure 1-11 (b)]; when Ba is more than 90 °, the bending direction of blade is the same as the rotation direction of impeller, which is called forward curved blade impeller [figure 1-11 (c)].

From equation (1-16), it can be seen that for a given impeller (D2 and BS are constant values), when the rotating speed n is fixed, h and QT show a linear relationship, and its slope is related to, as shown in Figure 12.

H when B = 90 ". It is independent of Q. it is a horizontal line on H -. H ↑ and graph.

When a < 90 °, hx-q1 is a downward straight line with a negative slope.

When b2s > 90 °, HRO QR is an upward line with a positive slope of β = 90 °.

According to formula (1-16) and figure 1-12, when D2, N and QR are determined, the larger B2A is, the HR is. The bigger. Is this blade the better? Further analysis of HT is necessary. The relationship between static head 0 qrhp and B2A in.

2. Relationship between B2A and reaction degree

When the fluid passes through the impeller, its energy increases, and the increased energy is divided into kinetic energy and potential energy (position potential energy and pressure potential energy), corresponding to

The head can also be divided into dynamic head and static head.

From the velocity triangle of figure 1-7, we can get:

Substituting the above two formulas into formula (1-9), we can get:

The first item in the above formula is dynamic head ham, and the sum of the second and third items is static head hpot. Static head refers to the increase of static pressure energy when the liquid flows from the impeller blade inlet to the blade outlet. Dynamic head is the increase of speed energy, thus:

Considering the viscosity of the fluid, the greater the dynamic head is, the greater the fluid speed is. Because the flow resistance is proportional to the square of the velocity, the resistance loss is very large. Therefore, it is hoped that the static head will account for a higher proportion in the project.

The proportion of the static head hpor in the theoretical head HTO is called the degree of reaction, which is expressed by PRA:

According to the geometric relationship of the velocity triangle, we can get:

In general centrifugal pump, because the difference of flow area between the inlet and outlet of impeller is not big, that is, nd.b.t ≈ rd2brt2, C. has little change, it can be considered that CI, ≈ C2, and there is gin = 0 when there is no pre rotation at the inlet of impeller, then there are:

The formula (1-10), type (1-12) and type (1-19) are substituted (1-18): foam pump.

It can be seen from formula (1-20) that with the increase of B: n, the reaction degree PR decreases, and the proportion of static head HW obtained by the impeller in the theoretical head HT decreases, which is not desirable. Therefore, the impeller of centrifugal pump mostly adopts backward curved blade impeller, usually B, n = 15 ° ~ 40 °. In the later discussion, only the backward curved blade impeller is analyzed.