HK1019781B - A pump impeller - Google Patents

Description

Pump impeller

The present invention relates to a pump impeller, and more particularly to a centrifugal or semi-axial flow pump impeller for pumping fluids, primarily sewage.

There are numerous types of pumps and pump impellers described in the literature for this purpose, but all suffer from certain disadvantages. Most importantly, both involve clogging and inefficiency problems.

Sewage contains many types of sewage, the amount and composition of which depend on the type of area where the sewage is discharged and the season of discharge. In urban areas, plastics, hygiene articles, textiles, etc. are most prevalent; whereas in industrial areas wear resistant particles may be discharged. Experience has shown that the worst problem is rags and the like, which stick to the leading edge of the blade and which are then wound around the hub of the impeller. Such events result in frequent maintenance and reduced efficiency of use.

In agriculture and the pulp industry, special pumps of various types are used, which should be able to handle straw, grass, leaves and other various organic materials. To this end, the leading edge of the blade is swept back so that dirt is transported outwardly to the outer periphery of the blade without adhering to the leading edge. Various types of shredding methods are used to cut these materials so that they flow more smoothly. Examples are listed in patent documents SE-435952, SE-375831 and US-4347035.

Since the sewage in the sewage contains other types of sewage that are more difficult to treat and since the operating time of sewage pumps is generally much longer, the above-mentioned special pumps do not meet the requirements for pumping sewage, both from a reliability point of view and from an efficiency point of view.

A sewage pump is often operated for 12 hours a day, which means that the energy consumption is strongly dependent on the total power of the pump.

Tests prove that the efficiency of the sewage pump is improved by 50 percent compared with the original sewage pump. Since the lifetime cost of an electrically driven pump is generally governed by the total energy consumption cost (c: a 80%), it is clear that the dramatic efficiency improvement is of paramount importance.

The description of pump impeller design in the literature is extremely generalized, particularly with respect to the problem of blade leading edge sweep. There is no clear definition of the sweep.

The test shows that: the design of the sweep angle distribution over the leading edge is very important in order to obtain the self-cleaning capability of the pump impeller. The characteristics of the various contaminants also require different sweep angles to ensure good pump performance.

Nothing is given in the literature to tell how to cause dirt to slide and be transported radially outwardly along the leading edge of the blade. It is noted that general statements such as leading edge should be obtuse, swept back, etc. See patent document SE-435952.

When pumping smaller contaminants such as grass and other organic matter, a smaller leading edge sweep angle may be sufficient to cause radial transport of the contaminants and be shredded in the groove between the pump impeller and the pump body. In practice, this shredding is achieved by the shredded waste coming into contact with the impeller and the pump body when the impeller rotates at a peripheral speed of 10 to 25 m/s. This shredding process can be improved by providing cutting means such as slots or the like. In comparison with SE-435952, pumps of this type are used for conveying pulp, manure, etc.

When designing a pump impeller with leading edge swept blades, there is a conflict in considering the relationship between the swept angle distribution, the pump performance, and other design parameters in order to achieve self-cleaning capability. In general, increasing the sweep angle means reducing the risk of clogging, but at the same time the efficiency is reduced.

The invention results in the possibility of designing the leading edge of the blade in an optimum manner, in such a way that sewage containing rags, fibres etc. can be pumped reliably and economically with different functions and qualities.

The invention essentially comprises three parts, which are described in the claims.

The first part, as shown in fig. 5, determines a set of data for the sweep angle distribution that provides good performance and efficiency for the pump. The range of data is related to size, peripheral speed and material friction. The independent variables used for the description, referred to herein as nominal radii, are defined as follows:

nominal radius ═ r-r₁)/(r₂-r₁) Equation 1

In the formula, r₁At the hub connection point (the point where the leading edge of the blade connects to the hub)Radius r₂Is the radius of the outer periphery of the leading edge, and the radius r, in a cylindrical coordinate system with the origin on the axis of the impeller, is defined as the shortest distance between an actual point and a point on the extension line of the impeller axis.

The basis of the first part of the invention is that the swept angle of the leading edge increases significantly from a minimum of 40 degrees at the point of connection with the hub to a maximum of 55 degrees at the outer periphery. The upper limit of 60 to 75 degrees defines the thicker line in the graph beyond which efficiency and reliability are negatively affected.

The second part of the invention relates to a special embodiment which has a very advantageous capability, wherein the sweep angle will be almost independent of the operating point, i.e. independent of the different flows and lifts, and which also corresponds to different velocity triangles (C, U, W).

The definition of the sweep angle will be explained below with reference to the drawings.

Fig. 1 is a three-dimensional view of a pump impeller according to the present invention. Fig. 2 is a schematic diagram of a radial cross-section of a pump according to the present invention. Fig. 3 is an axial schematic view of the suction end of the impeller. FIG. 4 is an enlarged partial view of the leading edge of one of the impeller blades. FIG. 5 is a graph showing the relationship between leading edge sweep and nominal radius according to the present invention.

In each figure, 1 denotes an impeller hub, 2 denotes a blade, which has a leading edge 3; 4 denotes the connection point of the leading edge to the hub; 5 denotes the outer periphery of the leading edge; 6 denotes the normal to a point on the leading edge; 7 denotes the inner wall of the pump body; 8 denotes the end face of the hub; 9 denotes the direction of rotation, α denotes the sweep angle, W_RRepresents the projected relative velocity (projected relative velocity), i.e. the velocity of the fluid in the operating coordinate system; z represents the direction of the impeller axis.

In order to design the desired pump impeller geometry in an optimum manner, it is a prerequisite that the described sweep angle is defined correctly. The exact sweep angle α is generally a function of the geometric parameters of the leading edge in both the meridional view (r-z) and the axial view (r- θ), see FIGS. 2 and 3.

The exact definition will be a function of the curve describing the shape of the leading edge 3 and the local relative velocity W on this curve. This can be expressed mathematically as follows:

with the conventional velocity triangle notation (C, U, W), the relative velocity W (r) is a function of the position vector r in the running cylindrical coordinate system. Under normal conditions, the relative velocity W (r, theta, z) may also use its component (W)_r，W_θ，W_z) And (4) expressing.

The three-dimensional curve along the leading edge 3 can be described in the corresponding operating coordinate system as a function R, which depends on the position vector R, i.e. R ═ R (R, θ, z).

An infinitesimal vector parallel to the leading edge at each point on the leading edge can be defined as d R. By the definition of scalar product, the exact expression of the sweep angle alpha can be obtained, where alpha is the normal of d R and W_RAngle between the projection and the projection relative velocity W_RIs defined as W_ROrthographic projection with an angle of incidence of zero in the W direction. This means that W_RAnd W are equal at or close to the nominal operating point, sometimes referred to as the sweet spot.

α＝π/2-arc cos[(d R· W_R)/(|d R|·| W_R|)]Equation 2

Assuming that the absolute inlet velocity does not contain any circumferential component, i.e. in the normal direction, W_θEqual to the peripheral speed of the impeller.

With these definitions and assumptions, the following will beIt will be seen that alpha is independent of flow. These are the cases: the leading edge lies in a plane which is essentially perpendicular to the impeller axis Z direction and the leading edge lies at an absolute inlet velocity which is essentially axial. This means that the radial component W_RClose to zero. For the same reason, W_RIs equal to the peripheral speed of the impeller, i.e. in the theta direction, independently of the flow rate. As described above, when dRz is zero, W_RThe influence of the axial component of (a) on a can be neglected. This is defined in terms of a scalar product. Therefore, in equation 2, the flow-related variable W_RAlpha is not affected because the numerator and denominator change proportionally.

According to a preferred embodiment of the invention, the leading edge of the blade is located in a plane essentially perpendicular to the axis of the impeller. As is common knowledge, a pump often operates over a wide range of flow and head variations, and the preferred embodiment allows its self-cleaning capability to be maintained independent of different operating conditions.

The third part of the invention relates to a preferred embodiment where the connection of the leading edge to the hub is adjacent the end face 8 of the hub 1, i.e. the hub has no central protruding boss. This reduces the risk of dirt wrapping around the central portion of the impeller.

Claims (4)

1. A centrifugal or semi-axial flow pump impeller for a pump for pumping sewage, characterized by:

the impeller is provided with one or several blades (2) whose leading edge (3) is swept back towards the periphery, the precise sweep angle (α) being defined as: at each point on the leading edge, the normal (6) to the leading edge and the projected relative velocity (W) of the pumped medium at that point_R) The sweep angle is limited to 40-55 degrees at the connection point (4) of the front edge and the hub (1), to 60-75 degrees at the outer periphery (5) of the front edge, and to the rear of the other pointsThe sweep angle varies approximately smoothly between the two.

2. The pump impeller of claim 1, wherein:

the normal (b) of a point on the leading edge (3) and the projected relative velocity (W) of the pumped medium at that point_R) The value of the included angle (alpha) is limited within the range of 45-55 degrees at the connecting point (4) of the front edge and the hub (1), is limited within the range of 62-72 degrees at the outer periphery (5) of the front edge, and the values of alpha of the rest points are changed between the front edge and the hub approximately and smoothly.

3. The pump impeller of claim 1, wherein:

the leading edges (3) of the blades (2) lie in a plane substantially perpendicular to the impeller axis (Z), wherein the absolute velocity of the pumped medium is mainly in the axial direction.

4. The pump impeller of claim 1, wherein:

the connection point (4) of the leading edge (3) to the hub (1) is located adjacent to the end face (8) of the hub.