CN105909567B - A kind of ejector improving jet-type centrifugal pump cavitation performance - Google Patents

Abstract

The invention relates to an ejector for improving the cavitation performance of a jet centrifugal pump, which comprises a nozzle, a drainage section, a mixing section, a throat, a diffusion section and a booster hole. When the jet-type centrifugal pump is operating under high-flow conditions, a booster hole is designed at the throat of the ejector. The booster hole introduces the high-pressure liquid in the pump chamber into the low-pressure area of the throat, increases the pressure in the low-pressure area of the throat, and suppresses the jet flow. Vibration and noise induced by cavitation inside the throat of the ejector can improve the phenomenon that the head of the jet centrifugal pump drops sharply due to cavitation inside the throat of the ejector, shift the breaking point of the lift to the large flow rate, and increase the operating range of the jet centrifugal pump .

Description

An Ejector for Improving the Cavitation Performance of a Jet Centrifugal Pump

technical field

The invention relates to an ejector which is the main part of a jet-type centrifugal pump, in particular to an ejector which can improve the cavitation performance of the jet-type centrifugal pump.

Background technique

The jet-type centrifugal pump is an electric pump designed in combination with a jet and a centrifugal pump. It has the advantages of compact structure, convenient operation, no need for irrigation for the second start, no need to install a bottom valve, and self-priming. It is used in garden drip irrigation, It is widely used in water-saving systems such as agricultural sprinkler irrigation. Compared with traditional centrifugal pumps, jet centrifugal pumps operate on the principle that the high-pressure liquid flowing from the pump guide vanes into the pump cavity forms a partial vacuum in the mixing section through the nozzle jet, so that the liquid in the pump inlet pipe passes through the pump under the action of atmospheric pressure. The drainage section enters the mixing section of the ejector, and then mixes with the liquid ejected from the nozzle, and flows into the centrifugal impeller through the throat and the diffuser section, and is discharged from the guide vane. Part of the liquid is discharged from the pump chamber, and the other part passes through the inlet of the ejector. Continue to mix with the liquid in the inlet pipe and flow into the impeller, so the cycle runs. Based on the particularity of the working principle of the jet centrifugal pump, according to the research, it is found that during the operation, the lowest internal pressure of the jet centrifugal pump is generated in the throat area, which determines that the cavitation of this type of pump will not occur at the impeller inlet Instead, it occurs somewhere in the throat of the ejector. As the flow rate increases, cavitation will occur inside the throat of the ejector, which will lead to a sharp drop in the head of the jet centrifugal pump, and at the same time induce vibration and noise, limiting its flow operating range.

Therefore, it is very important to design an ejector that improves the cavitation performance of a jet centrifugal pump by introducing the high-pressure liquid in the pump chamber into the throat area of the ejector to increase the pressure in this area during the operation of large flow .

Contents of the invention

The object of the present invention is to provide an ejector for improving the cavitation performance of a jet-type centrifugal pump, which includes a nozzle, a drainage section, a mixing section, a throat, a diffusing section and a booster hole. A certain number of booster holes are set in the throat of the ejector to introduce the high-pressure liquid in the pump chamber into the low-pressure area of the throat of the ejector to increase the pressure in this area and suppress the cavitation-induced vibration and noise inside the throat of the ejector , to improve the sharp drop in the head of the jet centrifugal pump caused by cavitation inside the throat of the ejector, shift the breaking point of the lift to the high flow rate, and increase the flow operating range of the jet centrifugal pump.

To achieve the above object, the present invention adopts the following scheme:

First, determine the nozzle diameter according to the design requirements

In the formula: Q ₁ is the injection flow rate of the nozzle, among which, the injection flow rate Q ₁ of the nozzle is equal to the inlet flow rate Q ₀ of _the centrifugal impeller minus the inlet flow rate Q ₂ of the pump _. According to the design requirements;

μ is the correction coefficient of the velocity slip between solid particles and liquid, and its value is 1 in the clear water medium;

α is the inlet function of the ejector throat, and the empirical value is 1~1.05;

Δp ₀ is the pressure difference between the inlet of the nozzle and the inlet of the drainage section, and the pressure at the inlet of the drainage section can be approximated as the pressure at the inlet of the pump;

γ is the bulk density of the liquid.

And then determine:

Throat diameter: Among them, the area ratio R represents the ratio of the throat area to the nozzle area, and its value is related to the flow ratio M, and the flow ratio M represents the ratio of the centrifugal impeller inlet flow _Q0 to the nozzle injection flow _Q1 ;

Nozzle cylindrical outlet length: L ₁ = (0.3～0.5) D ₁ ;

Throat-mouth distance: L ₂ = (0.5～1)D ₂ , the throat-mouth distance is the length of the mixing section, that is, the distance from the outlet of the nozzle to the inlet of the throat;

Throat length: L ₃ =(1.5～3)D ₂ ;

The length of the diffusion section: L ₄ =(2~5)D ₂ , wherein, L ₄ is determined by the diffusion angle β, and β is 5°~8°.

In the above scheme, the ratio of the distance L ₀ from the booster hole to the inlet of the throat to the length L ₃ of the throat is 1/6˜1/2.

In the above scheme, the outflow direction of the liquid in the booster hole should minimize the impact loss with the incoming flow of the throat, that is, the direction of the angle between the booster hole and the wall of the throat is θ, and 30°≤θ≤90 °.

In the above solution, the ratio of the diameter D ₀ of the pressurizing hole to the diameter D ₂ of the throat is 1/20˜1/12.

In the above solution, the number of pressurization holes is 2≤N≤4, and the number is evenly distributed in the circumferential direction.

The beneficial effects of the present invention are:

The ejector with this structure can effectively improve the vibration and noise induced by cavitation inside the throat of the ejector when operating under high flow conditions; This leads to the problem of a sharp drop in the head, shifting the breaking point of the head to a large flow rate, and increasing the operating range of the jet centrifugal pump.

Description of drawings

Fig. 1 is the schematic diagram of the jet type centrifugal pump of existing two kinds of different ejector structures, and figure (a) is the jet type centrifugal pump that ejector is straight pipe shape, and figure (b) is the jet type centrifugal pump with ejector band elbow;

Fig. 2 is the jet device schematic diagram of existing two kinds of different structures, and figure (a) is the jet device that is straight pipe shape, and figure (b) is the jet device with bent pipe;

Fig. 3 is the injector schematic diagram of two kinds of different structures described in the present invention, and figure (a) is the injector that is straight pipe shape, and figure (b) is the schematic diagram of F-F direction cross-section in figure (a), and figure (c) is belt The ejector of elbow, figure (d) is the schematic diagram of F-F to section in figure (c);

Fig. 4 is a schematic diagram of the internal flow of the ejector with two different structures according to the present invention.

Explanation of reference signs:

1-inlet pipeline, 2-jet, 21-nozzle, 22-drainage section, 23-mixing section, 24-throat, 25-diffusion section, 26-boosting hole, 3-centrifugal impeller, 4-guide vane , 5-pump cavity, 6-outlet pipeline, 7-motor.

Detailed ways

Fig. 3 is a schematic structural view of an ejector 2 that can improve the cavitation performance of a jet-type centrifugal pump according to the present invention. The ejector 2 of the jet-type centrifugal pump includes a nozzle 21, a drainage section 22, and a mixing section 23 , Throat 24, diffuser section 25 and booster hole 26.

As shown in Figure 2, when the jet centrifugal pump operates under the condition of large flow, cavitation will occur inside the throat of the jet, which will cause the pump head to drop sharply and induce vibration and noise at the same time. As shown in Figure 4, after the pressure boosting hole 26 is designed at the throat 24 of the ejector 2, the pressure boosting hole 26 will introduce the high-pressure liquid in the pump chamber 5 into the low-pressure area of the throat 24, increasing the pressure in the low-pressure area of the throat 24, To improve the anti-cavitation performance of the injector 2 of the jet centrifugal pump. achieve the desired effect of the design.

As shown in Figure 3, the included angle θ between the pressurization hole 26 and the wall of the throat pipe 24 is 30°≤θ≤90°. Preferably, when the length _L3 of the throat pipe 24 of the ejector 2 is longer, the pressure increase hole 26 and The angle θ between the walls of the throat pipe 24 is 30°≤θ≤60°. The ratio of the distance L ₀ from the booster hole 26 to the inlet of the throat 24 to the length L ₃ of the throat 24 is 1/6˜1/2. The ratio of the diameter D ₀ of the pressurizing hole 26 to the diameter D ₂ of the throat 24 is 1/20˜1/12. The number of booster holes 26 is 2≤N≤4, and the number is evenly distributed in the circumferential direction.

Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, rather than to limit them; wherein the booster hole for increasing the liquid flow pressure in the low-pressure area of the throat is an indispensable part of the solution, but It is not limited thereto, as long as the ejector can introduce the high-pressure liquid in the pump cavity into the low-pressure area of the throat through the booster hole, so as to improve the cavitation performance, all schemes are included in the protection of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these The modification or replacement does not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (3)

1. An ejector for improving the cavitation performance of a jet-type centrifugal pump is characterized in that it comprises a nozzle (21), a drainage section (22), a mixing section (23), a throat (24), a diffuser section (25) and A booster hole (26), the booster hole (26) is arranged at the throat (24) of the ejector (2), and the distance from the booster hole (26) to the inlet of the throat is _L0 and the length of the throat is L The ratio of ₃ is 1/6～1/2, and the direction of the included angle between the booster hole (26) and the wall surface of the throat pipe (24) is θ, 30°≤θ≤90°; The ratio of the diameter _D0 of the pressurizing hole (26) to the diameter _D2 of the throat (24) is 1/20-1/12; The diameter of the nozzle (21) is D ₁ , In the formula: Q ₁ is the injection flow rate of the nozzle, among which, the injection flow rate Q ₁ of _{the nozzle is equal to the inlet flow rate Q 0 of} the centrifugal impeller minus the inlet flow rate _{Q 2 of} the pump. out; μ is the correction coefficient of the velocity slip between solid particles and liquid, and its value is 1 in the clear water medium; α is the inlet function of the ejector throat, and the empirical value is 1~1.05; Δp ₀ is the pressure difference between the inlet of the nozzle and the inlet of the drainage section, and the pressure at the inlet of the drainage section can be approximated as the pressure at the inlet of the pump; γ is the bulk density of the liquid; The diameter of the throat (24) is D ₂ : Among them, the area ratio R represents the ratio of the throat area to the nozzle area, and its value is related to the flow ratio M, and the flow ratio M represents the ratio of the centrifugal impeller inlet flow _Q0 to the nozzle injection flow _Q1 ; The cylindrical outlet length of the nozzle (21) is L ₁ : L ₁ =(0.3-0.5)D ₁ . 2. An ejector for improving the cavitation performance of a jet-type centrifugal pump according to claim 1, characterized in that: the number of the booster holes (26) is N, 2≤N≤4, and the circumferential direction is uniform distributed. 3. An ejector for improving the cavitation performance of a jet-type centrifugal pump according to claim 1, characterized in that: the length of the mixing section (23) is the throat-mouth distance, and the throat-mouth distance L ₂ =(0.5～ 1) D ₂ , that is, the distance from the outlet of the nozzle to the inlet of the throat; The length of the throat (24) is L ₃ : L ₃ =(1.5～3)D ₂ ; The length of the diffusion section (25) is L ₄ : L ₄ =(2-5)D ₂ , where L ₄ is determined by the diffusion angle β, and β is 5°-8°.