A Cavitation-Resistant Cryogenic Pump

Abstract

The present invention discloses an anti-cavitation cryogenic pump, which aims to solve the problem of performance degradation of cryogenic pumps due to cavitation under extremely low temperature conditions. The present invention includes an inducer anti-cavitation guide grid structure, an impeller cavitation suppression device and an axial force dynamic balancing device. Through the optimized design of these components, the occurrence of cavitation during the cryogenic liquid pumping process and its negative impact on pump efficiency, vibration and mechanical damage are significantly reduced. The guide grid structure in front of the inducer effectively suppresses the mainstream rotation of the inlet section, reduces the generation and distribution of cavitation bubbles, and improves the hydraulic performance of the pump. At the same time, the impeller cavitation suppression device can reduce the temperature of the cavitation area by controlling the temperature, further curbing the development of cavitation. In addition, the axial force dynamic balancing device maintains the axial force stability of the pump through the pressure difference on both sides of the balancing disk, extends the service life of the pump, and ensures efficient and reliable operation in a low temperature environment.

Description

Technical Field

[0001] The present invention relates to the field of centrifugal pump cavitation, in particular to an inducer anti-cavitation guide grid structure, an impeller cavitation suppression device and an axial force dynamic balancing device, and specifically to an anti-cavitation cryogenic pump. Background Art

[0002] Cryogenic pumps are equipment used to transport liquids (such as liquid nitrogen, liquid helium, etc.) under extremely low temperature conditions. They are widely used in cryogenic scientific research, aerospace, superconducting technology, and the storage and transportation of liquefied gases. Cavitation is one of the unique problems of hydraulic machinery. It is a complex multiphase flow phenomenon and an important non-steady-state flow structure and excitation source inside fluid machinery. The cavitation phenomenon caused by the collapse of bubbles will have a negative impact on the performance of the pump. Specifically, it is manifested in reduced pump efficiency, increased noise, increased vibration, and mechanical damage to components such as the inducer and impeller.

[0003] The inducer is one of the key components of the cryogenic pump. The cavitation process on the blade surface directly affects the overall performance of the cryogenic pump. In history, there have been many rocket launch failures caused by cavitation in the inducer of the cryogenic pump.

[0004] Compared with the cavitation process of room temperature fluids such as water, low-temperature cavitation contains more complex physical mechanisms. Taking liquid nitrogen as an example, the liquid / vapor density ratio is about two orders of magnitude smaller than the liquid / vapor density ratio of water. Therefore, in order to produce the same volume of gas phase, more liquid nitrogen needs to be vaporized. The latent heat of phase change cannot be ignored, which reduces the temperature of the liquid near the cavitation zone. There is a significant temperature drop in the cavitation zone. For example, the temperature drop in the liquid nitrogen cavitation zone can reach 2-3K. The temperature drop will also reduce the saturation pressure of the fluid, and the saturation pressure is more sensitive to the temperature drop of low-temperature cavitation. Therefore, the temperature drop in the cavitation zone of low-temperature liquids leads to a decrease in saturation pressure. The reduced saturation pressure in turn curbs the further occurrence of cavitation until a dynamic equilibrium is reached. This unique characteristic caused by the temperature drop is called thermal effect.

[0005] Centrifugal pumps generate axial force when working. If cavitation occurs, the vibration caused by the collapse of the cavitation bubbles will make the axial force more unstable, resulting in a shortened life of the pump components. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide an anti-cavitation cryogenic pump, aiming to solve the problem of performance degradation of the cryogenic pump due to cavitation under extremely low temperature conditions.

[0007] The object of the present invention is achieved by the following technical solutions: an anti-cavitation cryogenic pump, comprising a liquid inlet portion, a front impeller portion, a rear impeller portion, a motor system, a liquid outlet, a liquid outlet pipe and a pump shaft;

[0008] The liquid inlet portion includes an inlet guide grid, a front end cover, a front pump housing and an inducer; the front end cover is connected to the front pump housing through threads; the inducer is arranged in the front pump housing and fixed on the pump shaft; the inlet guide grid is circumferentially fixed inside the front pump housing and is located at the front end of the inducer;

[0009] The front impeller part includes a first-stage impeller, a first-stage diffuser and a temperature control box; the first-stage impeller is fixed on the pump shaft; the first-stage diffuser is arranged inside the temperature control box and is fixedly connected to the rear impeller part; the temperature control box is fixedly connected to the front pump casing;

[0010] The rear impeller part includes a secondary impeller, a secondary diffuser, a balancing disc, a balancing ring and a rear pump casing; the secondary impeller is fixed on the pump shaft; the balancing disc is fixed on the pump shaft; the secondary diffuser is connected to the motor system; the balancing ring is connected to the secondary diffuser; the front end of the rear pump casing is connected to the primary diffuser;

[0011] The motor system is fixed on the pump shaft, and a motor housing is provided outside the motor system, and the motor housing is connected to the rear end of the rear pump housing;

[0012] The liquid outlet is connected to the liquid outlet pipe, the liquid outlet pipe is connected to the outlet of the secondary diffuser, and the liquid outlet pipe is used to transport the cryogenic liquid to the liquid outlet.

[0013] Furthermore, a filter screen is provided on the front end cover of the liquid inlet portion.

[0014] Furthermore, the inner side of the temperature control box is a diaphragm structure connected to the flow field of the first-stage impeller, and the outer side is a thin-wall structure connected to the external cryogenic pump pool.

[0015] Furthermore, the thin-wall structure of the temperature control box is made of heat-conducting material.

[0016] Furthermore, an axial gap is left between the balancing disc and the balancing ring to form a balancing chamber.

[0017] Furthermore, an axial gap of 0.01-0.25 mm is retained between the balancing disc and the balancing ring.

[0018] Furthermore, a cavity behind the balancing disk is provided behind the balancing disk, and the cavity behind the balancing disk is connected to the inlet of the secondary impeller.

[0019] Furthermore, the rear cavity of the balancing disk is connected to the inlet of the secondary impeller through a pressure balancing pipe.

[0020] Furthermore, a liquid outlet shell is provided outside the liquid outlet pipe, and the liquid outlet shell is connected to the motor shell.

[0021] Furthermore, the liquid outlet housing is provided with a pipe joint and a flange for connecting to an external pipe system.

[0022] The beneficial effects of the present invention are:

[0023] The inlet guide grid structure can suppress the mainstream rotation in the inlet section, reduce the backflow intensity, reduce the critical cavitation number, and reduce the volume fraction distribution of cavitation bubbles under cavitation conditions, thereby improving the anti-cavitation performance and hydraulic performance of the pump.

[0024] The impeller cavitation suppression device absorbs the heat generated by the impeller rotation, cools the low-pressure area when the impeller is working, and reduces the occurrence of cavitation.

[0025] The axial force dynamic balancing device can reduce the axial force fluctuation caused by the vibration of the pump and extend the service life of the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall appearance of the present invention;

[0027] Figure 2 It is an overall schematic diagram of the pump casing of the present invention;

[0028] Figure 3 It is a schematic diagram of the internal section of the present invention;

[0029] Figure 4 It is a partial cross-sectional schematic diagram of the liquid inlet of the present invention;

[0030] Figure 5 It is a schematic diagram of the inlet guide grid of the present invention;

[0031] Figure 6 It is a partial cross-sectional schematic diagram of the front impeller of the present invention;

[0032] Figure 7 It is a partial cross-sectional schematic diagram of the rear impeller of the present invention.

[0033] Reference numerals:

[0034] 1-liquid inlet part, 101-filter screen, 102-inlet guide grid, 103-front pump housing, 104-induction wheel, 105-front cover;

[0035] 2-front impeller part, 201-temperature control box, 202-diaphragm, 203-first-stage impeller, 204-first-stage diffuser;

[0036] 3-rear impeller part, 301-secondary impeller, 302-secondary diffuser, 303-balance disc, 304-balance ring, 305-balance chamber, 306-pressure balance pipe, 307-rear pump casing, 308-balance disc rear cavity;

[0037] 4-motor system, 401-motor housing;

[0038] 5-liquid outlet, 501-liquid outlet pipe, 502-liquid outlet shell;

[0039] 6-Pump shaft. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 As shown, an anti-cavitation cryogenic pump mainly includes a liquid inlet part 1, a front impeller part 2, a rear impeller part 3, a motor system 4, a liquid outlet 5 and a pump shaft 6.

[0042] like Figure 2 As shown, the overall housing of the pump is in direct contact with the cryogenic liquid in the pump pool, and is composed of the front cover 105, the front pump housing 103, the temperature control box 201, the rear pump housing 307, the motor housing 401 and the liquid outlet housing 502. The pump shaft 6 is fixed by the overall housing of the pump. The housing of the pump impeller rotor part is composed of the front pump housing 103, the temperature control box 201 and the rear pump housing 307. The liquid outlet housing 502 is equipped with a pipe joint and a flange for connecting to an external pipeline system.

[0043] The liquid inlet part 1 includes an inlet guide fence 102, a front pump housing 103, an inducer 104 and a front end cover 105; the front end cover 105 is connected to the front pump housing 103 by threads; the inducer 104 is arranged in the front pump housing 103 and fixed on the pump shaft 6; the inlet guide fence 102 is circumferentially fixed inside the front pump housing 103 and is located at the front end of the inducer 104; the front end cover 105 is provided with a filter 101.

[0044] The front impeller part 2 includes a first-stage impeller 203, a first-stage diffuser 204 and a temperature control box 201; the first-stage impeller 203 is fixed on the pump shaft 6; the first-stage diffuser 204 is arranged inside the temperature control box 201 and is fixedly connected to the rear impeller part 3; the temperature control box 201 is fixedly connected to the front pump casing 103; the inner side of the temperature control box 201 is a diaphragm structure, which is connected to the flow basin part of the first-stage impeller 203, and the outer side is a thin-wall structure, which is connected to the external low-temperature pump pool; the thin-wall structure of the temperature control box 201 adopts heat-conducting material.

[0045] The rear impeller part 3 includes a secondary impeller 301, a secondary diffuser 302, a balancing disc 303, a balancing disc rear cavity 308, a balancing ring 304, a balancing chamber 305, a pressure balancing pipeline 306 and a rear pump casing 307; the secondary impeller 301 is fixed on the pump shaft 6; the balancing disc 303 is fixed on the pump shaft 6, and a balancing disc rear cavity 308 is arranged behind the balancing disc 303, and the balancing disc rear cavity 308 is connected to the inlet of the secondary impeller 301; the secondary diffuser 302 is connected to the motor system 4; the balance ring 304 is connected to the secondary diffuser 302; an axial gap of 0.01 to 0.25 mm is retained between the balance disk and the balance ring; the balance chamber 305 is a cavity formed between the balance disk 303 and the balance ring 304; the pressure balance pipe 306 is a pipe connecting the rear cavity 308 of the balance disk and the inlet of the secondary impeller 301; the front end of the rear pump casing 307 is connected to the primary diffuser 204.

[0046] The motor system 4 is fixed on the pump shaft 6 and directly transmits power to the inducer 104, the first-stage impeller 203 and the second-stage impeller 301 without using a coupling.

[0047] The liquid outlet 5 is connected to a liquid outlet pipe 501 , and the liquid outlet pipe 501 is connected to the outlet of the secondary diffuser 302 to transport the cryogenic liquid to the liquid outlet 5 .

[0048] The present invention is an immersed two-stage centrifugal pump, which is immersed in a pump pool as a whole, has no seals, and all moving parts are cooled and lubricated by low-temperature liquid. Under the action of the pump, the low-temperature liquid flows in from the liquid inlet part 1 and flows out from the liquid outlet 5.

[0049] More specifically, Figure 3 The figure shows a schematic diagram of the overall internal cross-section of the present invention, and the main flow-through components of the present invention are the filter screen 101, the inlet guide grid 102, the inducer 104, the primary impeller 203, the primary diffuser 204, the secondary impeller 301, the secondary diffuser 302, the liquid outlet pipe 501, and the liquid outlet 5. When the cryogenic pump is working, the cryogenic liquid enters the pump through the filter screen 101 due to the centrifugal force generated by the rotation of the impeller, reaches the inducer 104 through the inlet guide grid 102, and then is pressurized from the primary impeller 203, the primary diffuser 204 reduces the radial force, the secondary impeller 301 further pressurizes, and the secondary diffuser 302 further reduces the radial force, and then passes through the two axially symmetrical liquid outlet pipes 501 of the pump body and leaves the pump body from the liquid outlet 5.

[0050] The liquid inlet portion 1 of the present invention is as follows Figure 4 , 5As shown, the main components are the filter screen 101, the inlet guide grid 102, the front pump housing 103, the inducer 104 and the front cover 105. The number of the inlet guide grids 102 is 3, which are circumferentially distributed and fixed in front of the inducer 104 inside the front pump housing 103. The inlet guide grid 102 suppresses the circumferential rotation of the cryogenic fluid, thereby reducing the generation of cavitation. After the cryogenic liquid flow bypasses the inlet guide grid 102, cavitation development and shedding will occur at its tail. Compared with the rectangular guide grid, the elliptical guide grid has a relatively smooth transition between the inlet and outlet edges, so the disturbance generated is relatively small, and the intensity of cavitation development and shedding is weaker. On the other hand, the inlet guide grid 102 also changes the inlet liquid flow angle of the inducer 104 of the centrifugal pump, improves the suction performance of the inducer 104, and thus improves the hydraulic performance of the pump.

[0051] The front impeller part 2 of the present invention is as follows Figure 6 As shown, the main components are a temperature control box 201, a diaphragm 202, a primary impeller 203, and a primary diffuser 204. After the liquid enters the primary impeller 203, it flows to the impeller outlet under the action of centrifugal force. Due to the lack of a volute structure, a large amount of radial force is generated, which is eliminated by the primary diffuser 204.

[0052] It should be noted that the physical properties of cryogenic liquids and water are different, so the cavitation situation is different. Taking liquid nitrogen as an example, the liquid / vapor density ratio is about two orders of magnitude smaller than that of water, and the gas volume produced by cavitation of the same volume of fluid is smaller. The saturated vapor pressure of liquid nitrogen at 77 K can reach a temperature change rate of 10 kPa / K, while this value in water at 293 K is only 150 Pa / K. It is obvious that the saturated pressure is more sensitive to the temperature drop of cryogenic cavitation.

[0053] The temperature control box 201 is filled with low temperature liquid, and the pressure inside the box is slightly lower than the ambient pressure in the pump pool. Before the pump starts working, the entire pump is immersed in the pump pool, and the pressure inside and outside the diaphragm 202 is balanced. Since the initial pressure in the box is slightly lower than the ambient pressure in the pump pool, the diaphragm 202 is slightly concave inward to achieve pressure balance.

[0054] When the pump shaft rotates, due to centrifugal force, the pressure at the impeller inlet drops rapidly, the diaphragm 202 bulges rapidly due to pressure imbalance, and the pressure inside the temperature control box 201 drops accordingly. Since the initial pressure inside the temperature control box 201 is low, cavitation is more likely to occur, and the latent heat of phase change cannot be ignored, which reduces the liquid temperature in the cavitation zone. The temperature reduction will also reduce the saturated vapor pressure of the fluid, thereby suppressing the occurrence of cavitation in the flow channel and achieving the effect of suppressing cavitation.

[0055] The rear impeller part 3 of the present invention is as follows Figure 7As shown, the main components are the secondary impeller 301, the secondary diffuser 302, the balance disc 303, the balance ring 304, the balance chamber 305, the pressure balance pipeline 306, and the rear pump housing 307. The balance disc 303 rotates together with the pump shaft 6, and the balance ring 304 is fixed on the secondary diffuser 302. An axial clearance of 0.01 to 0.25 mm is reserved between the balance disc 303 and the balance ring 304.

[0056] Under the action of the secondary impeller 301, the liquid flow is further pressurized, and the radial force generated is eliminated by the secondary diffuser 302. The pressure of the balancing disc cavity 308 is equal to the pressure at the entrance of the secondary impeller 301 through the pressure balancing pipe 306, and the pressure is relatively low; the pressure of the liquid in the gap between the balancing disc 303 and the balancing ring 304 is close to the pressure at the outlet of the final impeller, and the pressure is relatively high, so a pressure difference is formed on both sides of the balancing disc 303, and the pressure difference acts on the pump shaft through the balancing disc 303, and the direction is opposite to the axial force of the impeller.

[0057] When the pump is working, when the axial force on the impeller is greater than the balancing force on the balancing disc 303, the balancing disc 303 will move in the suction direction, reducing the axial gap and increasing the fluid resistance of the liquid, thereby reducing the leakage. After the leakage is reduced, the pressure drop of the liquid flowing through the radial gap is reduced, thereby increasing the pressure in front of the balancing disc 303, and the above-mentioned axial balancing force increases accordingly. As the balancing disc 303 moves forward, the balancing force gradually increases until the balancing force and the axial force are balanced. Similarly, when the axial force is less than the balancing force, the balancing disc 303 will move backward, and the axial force and the balancing force will reach a new balance after moving a certain distance. Due to inertia, the moving balancing disc 303 will not stop at the new balance position immediately, but will continue to move to cause the balance to be destroyed, creating the condition for the rotor to move in the opposite direction. Similarly, since the vibration causes the axial force to fluctuate, the axial position of the balancing disc 303 will not be fixed, but will fluctuate to promote the dynamic balance of the axial force.

[0058] The contents described in the embodiments of this specification are merely an enumeration of implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also includes equivalent technical means that can be thought of by those skilled in the art based on the inventive concept.

Claims

1. A cavitation-resistant cryopump, characterized in that: It includes a liquid inlet part, a front impeller part, a rear impeller part, a motor system, a liquid outlet, a liquid outlet pipe and a pump shaft; The liquid inlet portion includes an inlet guide grid, a front end cover, a front pump housing and an inducer; the front end cover is connected to the front pump housing through threads; the inducer is arranged in the front pump housing and fixed on the pump shaft; the inlet guide grid is circumferentially fixed inside the front pump housing and is located at the front end of the inducer; The front impeller part includes a first-stage impeller, a first-stage diffuser and a temperature control box; the first-stage impeller is fixed on the pump shaft; the first-stage diffuser is arranged inside the temperature control box and is fixedly connected to the rear impeller part; the temperature control box is fixedly connected to the front pump casing; The rear impeller part includes a secondary impeller, a secondary diffuser, a balancing disc, a balancing ring and a rear pump casing; the secondary impeller is fixed on the pump shaft; the balancing disc is fixed on the pump shaft; the secondary diffuser is connected to the motor system; the balancing ring is connected to the secondary diffuser; the front end of the rear pump casing is connected to the primary diffuser; The motor system is fixed on the pump shaft, and a motor housing is provided outside the motor system, and the motor housing is connected to the rear end of the rear pump housing; The liquid outlet is connected to the liquid outlet pipe, the liquid outlet pipe is connected to the outlet of the secondary diffuser, and the liquid outlet pipe is used to transport the cryogenic liquid to the liquid outlet; The inner side of the temperature control box is a diaphragm structure connected to the flow area of ​​the first-stage impeller, and the outer side is a thin-wall structure connected to the external cryogenic pump pool; the thin-wall structure is made of heat-conducting material; The temperature control box is filled with low-temperature liquid, and the pressure in the temperature control box is slightly lower than the ambient pressure in the pump pool; before the pump starts working, the entire pump is immersed in the pump pool, and the pressure inside and outside the diaphragm is balanced. Since the initial pressure in the temperature control box is slightly lower than the ambient pressure in the pump pool, the diaphragm is slightly concave inward at this time to achieve pressure balance; When the pump shaft rotates, due to the action of centrifugal force, the pressure at the impeller inlet drops rapidly, the diaphragm bulges rapidly due to pressure imbalance, and the pressure inside the temperature control box decreases accordingly. Since the initial pressure in the temperature control box is low, cavitation is more likely to occur, and the latent heat of phase change cannot be ignored, which reduces the liquid temperature in the cavitation zone; the temperature reduction will also reduce the saturated vapor pressure of the fluid, thereby suppressing the occurrence of cavitation in the flow channel, so as to achieve cavitation suppression.

2. The anti-cavitation cryopump according to claim 1, characterized in that: A filter screen is arranged on the front end cover of the liquid inlet portion.

3. The anti-cavitation cryopump according to claim 1, characterized in that: An axial gap is left between the balancing disc and the balancing ring to form a balancing chamber.

4. The anti-cavitation cryopump according to claim 3, characterized in that: An axial gap of 0.01 to 0.25 mm is reserved between the balancing disc and the balancing ring.

5. The anti-cavitation cryopump according to claim 1, characterized in that: A cavity behind the balancing disk is provided behind the balancing disk, and the cavity behind the balancing disk is connected to the inlet of the secondary impeller.

6. The anti-cavitation cryopump according to claim 5, characterized in that: The rear cavity of the balancing disk is connected to the inlet of the secondary impeller through a pressure balancing pipeline.

7. The anti-cavitation cryopump according to claim 1, characterized in that: A liquid outlet shell is arranged outside the liquid outlet pipe, and the liquid outlet shell is connected to the motor shell.

8. The anti-cavitation cryopump according to claim 7, characterized in that: The liquid outlet shell is provided with a pipe joint and a flange for connecting to an external pipe system.

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