RU113794U1 - SCREW CENTRIFUGAL PUMP - Google Patents

Abstract

A screw centrifugal pump containing a centrifugal wheel and an upstream screw wheel fixed to the bushing, mounted on one shaft, and a spiral outlet with a conical diffuser, the upstream screw wheel is made axial with screw blades of variable pitch, the upper edges of which outline a cylindrical or conical surface when the wheel rotates, and the said sleeve is made with a monotonically increasing diameter from inlet to outlet.

Description

The utility model relates to the field of pump engineering and can be used in pumps with high anti-cavitation and energy qualities.

A screw centrifugal pump is known, comprising a centrifugal wheel, an upstream auger wheel and a spiral outlet with a conical diffuser, in which an upstream auger wheel provides high anticavitation qualities of the pump and creates the necessary pressure for cavitationless operation of the centrifugal wheel (see the textbook B.V. Ovsyannikov, B.I. . Borovsky. "Theory and calculation of power units for liquid rocket engines", Moscow, "Engineering", 1979, p.204 - the closest analogue).

The upstream screw wheel has a small number of screw blades (Z _l = 2-3) of constant pitch, a cylindrical shape of the sleeve and the outer contour of the blades. The screw head pressure is created due to increased values of the angle of attack at the input edges of the blades (i = 4-10 °) with respect to the angle of leakage of the fluid flow. It is noted that in those cases when the screw head pressure created under such conditions is insufficient for cavitation-free operation of the centrifugal wheel, it is necessary to use a variable pitch screw wheel. However, recommendations for choosing the shape of the flowing part of the screw wheel of variable pitch are not given. In addition, it is known, see V.F. Chebaevsky, V.I. Petrov, “Cavitational characteristics of high-speed screw centrifugal pumps”, Moscow, “Mashinostroenie”, 1973, (p. 51), which is in the auger wheel of a constant step with increased angles of attack Separate flow zones are formed at the inlet and outlet, leading to an increase in hydraulic losses and the level of pressure pulsations, both in the screw wheel itself and in the centrifugal wheel following it. The presence of a tear-off zone at the sleeve at the exit of the auger wheel creates an increased unevenness of the velocity diagram and does not allow designing the input section of the centrifugal wheel for optimal geometric and kinematic parameters, ensuring maximum hydraulic efficiency of the screw-centrifugal pump.

The objective of the utility model is to increase efficiency (Efficiency) and reduce the level of pressure pulsations to an acceptable level, typical for conventional centrifugal pumps, while maintaining the high anticavitational qualities of screw centrifugal pumps achieved using constant-pitch auger wheels.

The technical result of the utility model is to improve the anti-cavitation qualities of a screw centrifugal pump by eliminating the formation of flow separation zones at the inlet and outlet of the auger wheel.

The problem is solved in that the screw centrifugal pump comprises a centrifugal wheel mounted on one shaft and an upstream auger wheel mounted on the sleeve, and a spiral outlet with a conical diffuser, the upstream auger wheel made osediagonal with screw blades of variable pitch, the upper edges of which outline a cylindrical or conical the surface during rotation of the wheel, and said sleeve is made with a monotonously increasing diameter from entrance to exit.

The outer contour of the wheel, outlined by the upper (outer) edges of the blades during its rotation, can have a cylindrical shape - when pumping clean liquids or a conical shape - when pumping liquids with high viscosity or content of mechanical impurities. This is due to the fact that when the auger wheel rotates, the viscous boundary layer and mechanical impurities flow along the blade to the periphery of the wheel and accumulate in the radial gap between the blades and the casing. As a result, there is increased resistance to rotation and even, with a cylindrical outer surface of the blades, jamming of the wheel is possible. Mentioned conical surface has a monotonously increasing diameter from entrance to exit.

The use of the osediagonal screw wheel as an upstream in the screw centrifugal pump allows to achieve the following technical results:

- to provide high anti-cavitation qualities of the pump at optimal angles of attack (i = 3-4 °) without the formation of a separation zone and reverse currents at the inlet;

- create the pressure required for cavitation-free operation of the centrifugal wheel without the formation of a tear-off zone at the sleeve at the exit of the screw wheel;

- design the inlet section of the centrifugal wheel for the optimal geometric and kinematic flow parameters (the optimum value of the flow coefficient φ ₀ ), ensuring the achievement of the maximum value of the hydraulic efficiency of the centrifugal wheel.

The essence of the utility model is illustrated using figures 1 and 2.

Figure 1 shows a longitudinal section of the proposed pump with screw blades, the upper edges of which outline a cylindrical surface during rotation of the wheel, and figure 2 shows a longitudinal section of the proposed pump with screw blades, the upper edges of which outline a conical surface during rotation of the wheel.

The screw centrifugal pump contains a centrifugal wheel 1, an upstream axially-auger screw wheel 2 with variable pitch helical blades, the upper edges of which outline a cylindrical (see Fig. 1) or conical (see Fig. 2) surface during rotation of the wheel. Wheel 2 is mounted on a cone-shaped sleeve 3, which, in turn, is also installed as wheel 1 on the shaft 4. A spiral bend is provided on the outside of the wheels 5. A “cone-shaped” sleeve in a screw wheel is understood to mean any shape with a monotonously increasing diameter from entrance to exit d _in (i) in the meridional section of the wheel in general terms described by a cubic parabola in the form:

Where

d _1B and d _2B are the diameters of the screw bush at the inlet and outlet, respectively;

a, b and c are the coefficients of the cubic parabola assigned when choosing the shape of the sleeve in compliance with the conditions

a + b + c = 1.0;

- relative current sleeve length

L _W - the total length of the sleeve

From the experience of computational and experimental studies of screw and axial-diagonal pumps, standard data on geometric parameters are established that limit the range of their changes, provided that the required characteristics are achieved:

- the relative diameter of the screw bush at the inlet

Where

D _1m is the outer diameter of the auger wheel at the inlet;

- the relative diameter of the bush of the screw on the output

Where

D _2m is the outer diameter of the auger wheel at the outlet.

From the experience of designing and operating conventional centrifugal pumps, it is known, see A. A. Lomakin, “Centrifugal and Axial Pumps”, M. - L. “Mechanical Engineering”, 1966. (p. 179) that the maximum hydraulic efficiency is achieved with a flow coefficient φ _{0 opt} - the ratio of axial speed to circumferential at the entrance to the centrifugal wheel

φ _{0 opt} = V ₀ / U ₀ = tgβ ₀ = 0.375-0.267,

which corresponds to the angle of flow leakage, respectively β ₀ = 20 ° -15 °.

Thus, when the centrifugal 1 and upstream 2 screw wheels rotate under the influence of hydrodynamic forces, the flow of the pumped liquid with optimal angles of attack enters the inter-blade channels of the axial diagonal screw wheel 1, in which, during the further flow, it acquires the peripheral velocity component and an increase in static pressure. As a result, the total pressure in the fluid flow rises to a value exceeding, with the necessary cavitation margin, the vapor pressure of the pumped fluid in the cross section at the inlet of the centrifugal wheel 2, profiled for optimal geometric and kinematic parameters, ensuring the maximum hydraulic efficiency of the screw centrifugal pump. In the spiral outlet 5, the pumped liquid is collected from the spinning centrifugal wheel 1 and the kinetic energy of the flow is converted into static pressure in the conical diffuser.

Claims (1)

A screw centrifugal pump comprising a centrifugal wheel and a preincluded auger wheel mounted on a sleeve mounted on one shaft, and a spiral outlet with a conical diffuser, an upstream auger wheel made axially diagonal with variable pitch helical blades, the upper edges of which outline a cylindrical or conical surface during rotation of the wheel, and said sleeve is made with a monotonously increasing diameter from inlet to outlet.