Ejecting pipe, negative pressure air suction device and method for generating stable negative pressure

Abstract

According to the injection pipe, the negative pressure air suction device and the method for generating the stable negative pressure, the negative pressure air suction device comprises a nozzle and an injection pipe which are sequentially communicated, the inlet end of a jet flow expansion cavity is arranged around the outer portion of an outlet of the nozzle, and an annular vacuum channel communicated with the jet flow expansion cavity is formed in the butt joint position of the nozzle and the injection pipe; the injection pipe is provided with a through internal airflow channel, and the internal airflow channel sequentially comprises a jet flow expansion cavity, a backflow restraining area, a jet flow injection cavity and an exhaust port. The inlet end of the jet flow expansion cavity is provided with an inlet contraction section protruding inwards, and a shock wave control face used for controlling shock waves is connected behind the inlet contraction section. The backflow restraining area comprises at least one structure composed of a channel sudden expansion section and a downstream channel transition section, and thickening of a boundary layer is effectively restrained. By controlling jet flow expansion, precise suction and boundary layer inhibition, stable high-speed airflow is formed, and finally stable negative pressure is generated and maintained at the annular vacuum channel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum obtaining, in particular to an ejector pipe, a negative pressure air suction device and a method for generating stable negative pressure. BACKGROUND

[0002] In the field of vacuum obtaining devices, gas injection type negative pressure air suction devices are a kind of widely used equipment, and the basic principle is to use high-speed jet flow to form a low-pressure area in the ejector pipe to achieve suction or maintain a vacuum environment. The suction performance of this type of device mainly depends on the jet expansion ratio, that is, the ratio of the total pressure of the inlet gas to the minimum static pressure in the ejector pipe. The higher the maximum speed in the jet flow, the lower the static pressure at the corresponding position, the larger the expansion ratio, the lower the static pressure that can be obtained, and the lower the vacuum pressure that can be achieved.

[0003] The existing gas injection type negative pressure air suction device usually adopts a single cylindrical channel structure, or a slightly differentiated jet expansion cavity and jet injection cavity, and the two are connected by a conical surface. Although this structure can form the basic functions of jet expansion and injection, it has obvious limitations when pursuing higher expansion ratio and lower static pressure.

[0004] 1. Uncontrollable low-pressure area position and low connection efficiency: In a simple cylindrical ejector pipe, the jet flow expands freely, and the position and shape of the lowest static pressure area (low pressure distribution zone) are unstable and difficult to predict. This results in the connection position of the vacuum cavity and the ejector pipe often failing to correspond to the low pressure area, resulting in low suction efficiency and failing to fully utilize the vacuum potential of the jet flow.

[0005] 2. Shock wave interference and flow instability: High-speed jet flow is prone to complex shock wave systems during expansion. The traditional structure lacks effective control of the shock wave, which may cause the shock wave to oscillate in the cavity or interfere with the wall boundary layer, causing flow separation and destroying the stability of the flow field, thereby causing vacuum pressure fluctuations and limiting the maximum expansion ratio.

[0006] 3. Thickening of the boundary layer narrows the effective flow passage: Under high-speed flow, the wall of the ejector pipe will form and thicken the boundary layer, which essentially reduces the effective area of the gas flow passage. Especially when pursuing a large expansion ratio and designing a longer flow passage, the thickening of the boundary layer will seriously hinder the development of the core high-speed flow, like a "blockage layer" formed on the inner wall of the pipe, making it impossible to achieve the theoretical high expansion ratio. SUMMARY

[0007] The technical problem solved by the present application is how to accurately guide and control the flow field to achieve higher expansion ratio and higher and more stable vacuum performance.

[0008] According to a first aspect, in one embodiment, a ejector pipe for a negative pressure inhalation device is provided, the ejector pipe has a through internal airflow passage, the internal airflow passage comprises, in sequence along the airflow direction: a jet flow expansion cavity, an inlet end of the jet flow expansion cavity is provided with an inwardly protruding inlet contraction section, a rear of the inlet contraction section is connected with a shock wave control surface, the shock wave control surface is used for controlling the shock wave angle and position in the jet flow expansion process; a backflow suppression zone, the backflow suppression zone comprises at least one set of backflow suppression structures arranged on an inner wall of the internal airflow passage, the backflow suppression structures are arranged axially spaced, and the number of the backflow suppression structures is determined according to the length of the ejector pipe and the flow state; any of the backflow suppression structures comprises an annular channel expansion section and a channel transition section downstream of the channel expansion section; a jet flow entraining cavity, an upstream end of the jet flow entraining cavity is smoothly connected with a downstream end of the backflow suppression zone; and an exhaust port, the exhaust port is arranged at a terminal point of the internal airflow passage, and is used for exhausting the mixed gas flow guided through the jet flow entraining cavity.

[0009] In another embodiment, the channel transition section is a tapered or straight channel section, and an inner wall surface of the channel transition section is a smooth continuous curved surface, used for guiding the smooth transition of the airflow and suppressing the flow separation.

[0010] In another embodiment, a diameter of the channel expansion section is greater than a diameter of the jet flow expansion cavity adjacent upstream of the channel expansion section, and the channel transition section is arranged as a conical surface converging to the axis.

[0011] In another embodiment, a diameter expansion direction of the channel expansion section is perpendicular to the axis of the ejector pipe.

[0012] In another embodiment, the shock wave control surface is arranged as a conical surface or a rotationally curved surface with continuous curvature in the circumferential direction.

[0013] In another embodiment, a diameter of the jet flow expansion cavity is greater than a diameter of the jet flow entraining cavity.

[0014] According to a second aspect, in one embodiment, a negative pressure inhalation device is provided, comprising a nozzle and the ejector pipe described in the above scheme, the nozzle has a through internal injection passage, and the internal injection passage is communicated with the internal airflow passage; an inlet end of the jet flow expansion cavity surrounds an outside of an outlet of the nozzle, and an annular vacuum passage is formed between the inlet end of the jet flow expansion cavity and the outlet of the nozzle; one end of the annular vacuum passage is communicated with the jet flow expansion cavity, and the communicated position of the annular vacuum passage is located in a jet low pressure distribution area of the jet flow expansion cavity; the other end of the annular vacuum passage is used for connecting a vacuum cavity to be pumped.

[0015] In another embodiment, the gas flow inlet of the annular vacuum channel is in communication with the vacuum cavity, the gas flow outlet of the annular vacuum channel is in communication with the jet expansion cavity to guide the gas in the vacuum cavity to the low pressure area of the jet expansion cavity, and the annular vacuum channel is in the same direction as the suction direction of the gas flow in the jet expansion cavity.

[0016] In another embodiment, the internal jet channel includes, in sequence along the gas flow direction, a compressed gas inlet for introducing compressed gas, a convergent throat, and a divergent channel in communication with the jet expansion cavity.

[0017] According to a third aspect, a method for generating stable negative pressure is provided in an embodiment, using the negative pressure air suction device described in the above scheme, comprising the following steps: The high pressure gas is accelerated into a supersonic jet through the nozzle; The supersonic jet enters the jet expansion cavity of the ejector pipe and impacts on the shock control surface to form an expansion flow field with a predetermined low pressure distribution area; The gas in the annular vacuum channel is sucked through the inlet contraction section at the low pressure distribution area of the jet expansion cavity; The mixed gas flow forms a stable high-speed gas flow through the backflow suppression structure to suppress the thickening of the boundary layer and flow separation of the internal gas flow channel, and maintain the stability of the core flow field; The mixed gas is discharged through the exhaust port of the jet expansion cavity and a stable negative pressure is formed in the annular vacuum channel.

[0018] According to the above-mentioned embodiments of the ejector pipe, the negative pressure air suction device and the method for generating stable negative pressure, through the cooperative design of the inlet contraction section and the shock control surface, a stable and controllable low pressure distribution area is formed in the jet expansion cavity. The annular vacuum channel directly and accurately communicates the low pressure area with the vacuum cavity to be pumped, significantly improving the suction efficiency. The shock control surface accurately restricts the jet expansion angle and the shock shape, and the backflow suppression structure periodically "resets" the wall boundary layer, which together ensures the stability of the core high-speed flow field and effectively avoids pressure fluctuations. Due to the effective suppression of the boundary layer, the effective flow area of the flow channel is increased, so that the jet can achieve a larger expansion ratio, thereby obtaining a stable vacuum with extremely low pressure at the annular vacuum channel. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The overall structure of the negative pressure air suction device in an embodiment is shown schematically; Figure 2 The overall structure of the negative pressure air suction device in an embodiment is shown schematically; Figure 1 The detailed structure of the negative pressure air suction device in an embodiment is shown schematically; Figure 3 The velocity distribution nephogram of the negative pressure air suction device in an embodiment is shown. Figure 4 Pressure distribution cloud chart of the negative pressure inhalation device in one embodiment; Figure 5 Schematic diagram of steps of the method for generating stable negative pressure in one embodiment.

[0020] Attachment mark: 1. Nozzle; 11. Compressed gas inlet; 12. Contraction throat; 13. Injection channel; 2. Ejector tube; 21. Jet expansion cavity; 22. Inlet contraction section; 23. Shock wave control surface; 24. Backflow suppression zone; 25. Channel sudden expansion section; 26. Channel transition section; 27. Jet injection cavity; 28. Exhaust port; 3. Annular vacuum channel; 4. Vacuum cavity. DETAILED DESCRIPTION

[0021] The application will be further described in details through specific embodiments and with reference to the drawings. In different embodiments, similar elements are marked with similar element numbers. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in details for those skilled in the art according to the description in the specification and general technical knowledge in the art.

[0022] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. Meanwhile, the steps or actions in the method description can also be adjusted or replaced in order as those skilled in the art can easily recognize. Therefore, the order in the specification and the drawings is only for clear description of one embodiment, and does not mean the necessary order, unless otherwise stated that the order must be followed.

[0023] In this paper, the serial numbers of components, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any order or technical meaning. Unless otherwise specified, "connection" and "coupling" in this application include direct and indirect connection (coupling).

[0024] For the gas injection negative pressure air intake device, the greater the jet expansion ratio (the ratio of the total pressure of the gas at the inlet of the gas injection negative pressure air intake device to the minimum static pressure in the draft tube 2) is, the higher the maximum speed in the jet is, and the lower the static pressure at the corresponding position is. The gas injection negative pressure air intake device always pursues a greater jet expansion ratio to obtain a lower static pressure. The structure of the draft tube 2 of the existing gas injection negative pressure air intake device is mostly a single cylindrical passage without distinction between the jet expansion chamber 21 and the jet draft chamber 27, but this does not affect the automatic formation of the jet expansion section and the jet draft section in the passage; a few jet expansion chambers 21 have a diameter slightly larger than that of the jet draft chamber 27, and the transition between the jet expansion chamber 21 and the jet draft chamber 27 is a conical surface, which is beneficial to obtain a greater jet expansion ratio.

[0025] In the gas injection negative pressure air intake device, the following two problems will affect the maximum value of the jet expansion ratio. One is the boundary layer flow in the expansion chamber and the jet draft chamber 27, and the other is the boundary layer flow in the jet expansion chamber 21 and the jet draft chamber 27. By using a cylindrical jet expansion chamber 21 and a jet draft chamber 27, the only adjustable parameters of the draft tube 2 are the diameter of the draft tube 2, the axial position of the draft tube 2 and the nozzle 1, and the length of the draft tube 2 itself. Therefore, when a larger jet expansion ratio is selected, the thickness and flow of the boundary layer in the jet expansion chamber 21 and the jet draft chamber 27 will increase, and the geometric space occupied by the boundary layer will also increase, which will limit the jet expansion ratio. At the same time, the jet velocity distribution in the expansion chamber is basically fixed, and the pressure distribution at the connection between the vacuum chamber 4 and the jet is not exactly at the position with the lowest pressure, so that the pressure in the vacuum chamber 4 cannot be as low as possible.

[0026] The technical problem solved by the present application is how to accurately guide and control the flow field to obtain a higher expansion ratio and thus achieve higher and more stable vacuum performance.

[0027] To solve the above technical problems, in the embodiment of the present application, a kind of ejector pipe for negative pressure air intake device is disclosed, internal airflow passage includes in turn jet expansion cavity 21, backflow suppression zone 24, jet ejecting cavity 27 and exhaust port 28.Jet expansion cavity 21 entrance end is equipped with the entrance contraction section 22 that protrudes to interior, it is followed by the shock wave control surface 23 for controlling shock wave.Surrounding flow suppression zone 24 includes at least a group of structures consisting of passage sudden expansion section 25 and downstream passage transition section 26, effectively suppresses boundary layer thickening.A kind of negative pressure air intake device is also disclosed, including the above-mentioned ejector pipe 2 and nozzle 1.Nozzle 1 expansion channel outlet extends into jet expansion cavity 21 of ejector pipe 2, and annular vacuum passage 3 is formed between the two, which efficiently connects the vacuum cavity 4 to be pumped with low pressure area in jet expansion cavity 21.A kind of method for generating stable negative pressure is also disclosed, using the above-mentioned device, by controlling jet expansion, accurate suction and suppressing boundary layer, forming stable high-speed airflow, finally generating and maintaining stable negative pressure at annular vacuum passage 3. Embodiment one:

[0028] Please refer to Figure 1 and Figure 2 , a kind of ejector pipe for negative pressure air intake device, ejector pipe 2 has through internal airflow passage, internal airflow passage includes in turn arranged in airflow direction: jet expansion cavity 21, its entrance end is equipped with the entrance contraction section 22 that protrudes to interior, the rear of entrance contraction section 22 is connected with shock wave control surface 23, shock wave control surface 23 is used to control the shock wave angle and position in jet expansion process;Surrounding flow suppression zone 24, it includes at least a group of surrounding flow suppression structures arranged on the inner wall of internal airflow passage, surrounding flow suppression structures are arranged along the axial direction of ejector pipe 2 with interval, its number is determined according to the length of ejector pipe 2 and flow state;Any surrounding flow suppression structure includes annular passage sudden expansion section 25 and passage transition section 26 located downstream thereof;Jet ejecting cavity 27, the upstream end of jet ejecting cavity 27 is smoothly connected with the downstream end of surrounding flow suppression zone 24;And exhaust port 28, exhaust port 28 is arranged as the terminal point of internal airflow passage, for discharging the mixed gas flow guided through jet ejecting cavity 27.

[0029] The ejector pipe 2 of the embodiment is a hollow tubular member, which integrates four functionally clear and cooperatively working sections in sequence along the airflow direction: the jet expansion cavity 21, the surrounding flow suppression zone 24, the jet ejecting cavity 27, and the exhaust port 28, optimizing the flow field, suppressing the boundary layer, and providing a basis for generating stable negative pressure.

[0030] Specifically, please refer to Figure 1 and Figure 2 , the jet expansion cavity 21 is located at the inlet end of the ejector pipe 2, and the entrance contraction section 22 at the inlet thereof protrudes towards the axis to form a tapered inlet structure, and the profile of the entrance contraction section 22 is a smooth converging curved surface, thereby playing a preliminary converging role on the incoming airflow.

[0031] Please refer to Figure 1 and Figure 2 , the shock control surface 23 is immediately downstream of the entrance contraction section 22, and the shock control surface 23 is usually provided as a fixed-angle conical surface, for example, 15°-30°, which can effectively adapt to the expansion characteristics of the supersonic jet; the shock control surface 23 can also be provided as a rotating curved surface with continuously variable curvature, and the curvature radius gradually increases along the flow direction of the airflow, which can better fit the jet expansion trajectory.

[0032] When the airflow passes through, the entrance contraction section 22 can be equivalent to an accurate low-pressure gas suction point, and a local low-pressure area is formed in the entrance contraction section 22. The shock control surface 23 actively meets and guides the supersonic jet from the upstream; through its specific angle, the outer boundary of the jet expansion and the shock shape generated thereby are accurately controlled, and the originally free and unstable expansion process is changed into a controlled and stable expansion process, thereby forming a low-pressure distribution zone with fixed position and stable pressure distribution in the jet expansion cavity 21, that is, the shock control surface 23 accurately controls the shock angle and position in the jet expansion process through its own structural form, thereby optimizing the pressure distribution and velocity field distribution in the jet expansion cavity 21, and creating a favorable low-pressure environment for subsequent gas suction.

[0033] Further, please refer to Figure 1 and Figure 2 , the backflow suppression zone 24 is specifically formed by one or more completely identical backflow suppression structures distributed along the axial direction, and the specific number can be determined according to the actual length of the ejector pipe 2 and the flow state of the internal airflow, and three groups are provided in the present application.

[0034] Specifically, please refer to Figure 1 and Figure 2 , the channel sudden expansion section 25 has a diameter larger than that of the adjacent jet expansion cavity 21 upstream thereof, and the diameter expansion direction of the channel sudden expansion section 25 is perpendicular to the axis of the ejector pipe 2, forming a radial sudden expansion structure, thereby forming an annular cavity. This structure can disturb the airflow and break the continuous thickening trend of the boundary layer.

[0035] Please refer to Figure 1 and Figure 2 , the channel transition section 26 immediately downstream of the channel sudden expansion section 25 is a tapered or straight cylindrical channel section, and the inner wall surface thereof is a smooth continuous curved surface; in the present embodiment, the channel transition section 26 is tapered, for example, a conical surface channel converging to the axis direction is provided, and the included angle between the generatrix of the conical surface and the axis of the ejector pipe 2 is controlled within a certain angle range, for example, 5°-15°, which can guide the smooth transition of the airflow and effectively suppress the flow separation, and ensure the orderly flow of the airflow along the channel wall surface.

[0036] The sudden expansion of the passage sudden expansion section 25 induces a stable backflow vortex zone at its corner when the airflow passes through. Through the periodic design of sudden expansion and convergence, the continuous thickening of the boundary layer in the entire flow passage is effectively suppressed, ensuring that the core high-speed airflow has sufficient flow area. The backflow vortex zone formed can act as an isolation structure, effectively hindering the momentum transfer of the main flow to the wall surface, thereby disrupting the normal development of the wall boundary layer. The subsequent passage transition section 26 smoothly accelerates the convergence of the core airflow, avoiding flow separation due to sudden changes in cross section.

[0037] Further, please refer to Figure 1 and Figure 2 The upstream end of the jet injection cavity 27 is smoothly connected to the downstream end of the backflow suppression zone 24 and the last passage transition section 26. The jet injection cavity 27 can be designed as a passage structure with a relatively small and constant or tapered diameter, and the diameter of the jet injection cavity 27 is smaller than the diameter of the jet expansion cavity 21. In the embodiment of the application, the jet injection cavity 27 is preferably a retrieval channel structure, which can further accelerate and converge the mixed gas flow treated by the backflow suppression zone 24, and enhance the kinetic energy of the gas flow.

[0038] Please refer to Figure 1 and Figure 2 The exhaust port 28 is the outlet of the injection pipe 2 and serves as the terminal point of the internal airflow passage. It is used to discharge the mixed gas flow guided by the jet injection cavity 27, and the cross section of the exhaust port 28 can be designed as circular or square according to actual installation requirements. In the embodiment, the exhaust port 28 adopts a circular structure to reduce the resistance when the gas is discharged.

[0039] When the airflow passes through, the guided mixed gas flow of the jet injection cavity 27 stably flows to the exhaust port 28 for discharge. The small diameter of the jet injection cavity 27 helps to maintain the speed of the airflow, ensuring sufficient momentum to discharge the gas.

[0040] The injection pipe 2 of the embodiment integrates the inlet contraction section 22, the shock control surface 23 and the backflow suppression structure, providing an environment of optimized flow field, stable low pressure zone and suppressed boundary layer, which provides a basis for generating stable negative pressure. Embodiment two:

[0041] Please refer to Figure 1 and Figure 2A negative pressure suction device, comprising a nozzle 1 and an ejector pipe 2 in the above embodiments, the nozzle 1 has a through internal jet channel 13, and the internal jet channel 13 is communicated with the internal airflow channel of the ejector pipe 2; the inlet end of the jet expansion cavity 21 is arranged around the outside of the outlet of the nozzle 1, and an annular vacuum channel 3 is formed at the abutting position of the two, one end of the annular vacuum channel 3 is communicated with the jet expansion cavity 21, and the communicated position of the annular vacuum channel 3 is located in the jet low-pressure distribution area of the jet expansion cavity 21, and the other end of the annular vacuum channel 3 is used for connecting a vacuum cavity 4 to be pumped.

[0042] Specifically, please refer to Figure 1 and Figure 2 , the outlet position of the internal jet channel 13 at the rear end of the nozzle 1 is integrally protrudingly arranged, and the outer wall of the protruding part is arranged as a tapered curved surface converging to the axis direction, so that the inlet end of the jet expansion cavity 21 is arranged around the outside of the outlet of the nozzle 1. An annular gap is reserved between the outer wall of the protruding part at the rear end of the nozzle 1 and the inner wall of the inlet converging section 22 of the ejector pipe 2, which forms the above-mentioned annular vacuum channel 3. One end (airflow inlet) of the annular vacuum channel 3 is communicated with the vacuum cavity 4 needing to be pumped, and the other end (airflow outlet) is communicated with the inside of the jet expansion cavity 21 at the converging position of the inlet converging section 22, so as to guide the gas in the vacuum cavity 4 to the low-pressure area of the jet expansion cavity 21.

[0043] Please refer to Figure 1 and Figure 2 , the trend of the annular vacuum channel 3 is consistent with the suction direction of the airflow in the jet expansion cavity 21, which reduces the airflow flow resistance, so as to efficiently guide the gas in the vacuum cavity 4 to the low-pressure area of the jet expansion cavity 21, that is, to make the pumped gas be introduced into the low-pressure area of the jet core in the most direct way with the smallest flow resistance, and the suction position of the vacuum cavity 4 is always accurately aligned with the stable low-pressure distribution zone formed by the shock control surface 23, so as to realize the most efficient suction.

[0044] Further, please refer to Figure 1 and Figure 2 , the internal jet channel 13 includes a compressed gas inlet 11, a converging throat 12 and an expanding channel in sequence along the airflow direction, wherein the compressed gas inlet 11 is used for introducing compressed gas, the converging throat 12 is arranged with a contracted inner diameter and has the smallest cross-sectional area, and the diameter of the expanding channel gradually increases from the converging throat 12 to the outlet of the internal jet channel 13, which is used for being communicated with the jet expansion cavity 21. The nozzle 1 as a whole constitutes a Laval nozzle structure, which can efficiently convert high-pressure gas into supersonic jet flow.

[0045] Specifically, please refer to Figure 1 and Figure 2 , the interface size of the compressed gas inlet 11 is designed according to the specification of the gas supply pipeline, and is usually arranged as a threaded interface for convenient connection.

[0046] Please refer to Figure 1 and Figure 2 , the inner diameter of the converging throat 12 gradually shrinks along the airflow direction, and the minimum inner diameter is the throat. The converging throat 12 is used to preliminarily accelerate and compress the entering high-pressure gas, and to increase the kinetic energy of the gas.

[0047] Please refer to Figure 1 and Figure 2 , the diverging channel is immediately downstream of the converging throat 12, and the inner diameter of the diverging channel gradually expands along the airflow direction, so as to further accelerate the airflow accelerated by the converging throat 12 to a supersonic state, forming a supersonic jet flow with high kinetic energy.

[0048] When the gas is introduced, the high-pressure gas enters from the compressed gas inlet 11, is accelerated to the speed of sound at the converging throat 12, and then is further expanded to a supersonic jet flow in the diverging channel, so as to serve as a power source for the subsequent negative pressure air suction device.

[0049] The negative pressure air suction device of the embodiment forms a stable and position-controllable low pressure distribution area in the jet expansion chamber 21 through the coordinated design of the inlet converging section 22 and the shock wave control surface 23 of the ejector pipe 2. The annular vacuum channel 3 directly and accurately connects the low pressure area with the vacuum cavity 4 to be pumped, which significantly improves the pumping efficiency. The shock wave control surface 23 accurately restricts the jet expansion angle and the shock wave form, and the backflow suppression structure periodically "resets" the wall boundary layer, which together ensures the stability of the core high-speed flow field and effectively avoids pressure fluctuations. Due to the effective suppression of the boundary layer and the increase of the effective flow area of the flow channel, the jet flow can achieve a larger expansion ratio, so as to obtain a stable vacuum with extremely low pressure at the annular vacuum channel 3, forming an equipment capable of generating an extremely low and stable vacuum pressure.

[0050] That is, in the embodiment, when the compressed air pressure introduced into the negative pressure air suction device is in the range of 5.5-7.5 atm, the air suction flow is 926 NL / min (55.5 m' / h), the compressed air consumption is 900 NL / min (54 m' / h), and the ultimate vacuum degree can be finally stabilized at -100 kPa. Embodiment Three:

[0051] The embodiment actively constructs and maintains a stable negative pressure area in the annular vacuum channel 3 through the control of the expansion, injection and flow stability of the supersonic jet flow. Please refer to Figure 3 , Figure 4 , ​ and ​ , which disclose a method for generating a stable negative pressure, using the negative pressure air suction device in the above-mentioned scheme, comprising the following steps: S1: jet acceleration and expansion; High pressure gas is introduced into the internal injection channel 13 through the compressed gas inlet 11 of the nozzle 1; The high pressure gas first flows through the convergent throat 12, is accelerated initially and compressed to supersonic speed at the convergent throat 12; Then enters the divergent nozzle 1, is fully expanded in the divergent channel, and finally forms a stable supersonic jet flow from the nozzle 1 outlet and is injected into the jet expansion chamber 21 of the ejector 2.

[0052] In the present embodiment, the inlet gas pressure is between 5.5 atm and 6.5 atm, and a vacuum degree of -100 kPa can be stably obtained.

[0053] S2: low pressure zone formation; The nozzle 1 forms a supersonic jet flow into the jet expansion chamber 21 of the ejector 2 and impacts on the shock control surface 23. Due to the guiding effect of the structure of the shock control surface 23, the shock control surface 23 precisely restricts the expansion of the jet flow to form an expanded flow field with a predetermined low pressure distribution zone, i.e. a stable and controllable low pressure distribution zone in shape and position is formed in the jet expansion chamber 21.

[0054] S3: suction; At the same time of the low pressure zone formation in S2, the gas in the vacuum chamber 4 is directly sucked to the low pressure distribution zone through the annular vacuum channel 3 under the action of pressure difference, and is mixed with the driving jet flow. At this time, the annular vacuum channel 3 forms a gas flow from the low pressure chamber to the jet expansion chamber 21, realizing the gas suction process of the low pressure chamber. The inlet convergent section 22 ensures that the suction action occurs at the point with the lowest pressure.

[0055] S4: flow field stabilization and maintenance; The mixed gas flow continues to flow downstream and passes through the backflow suppression structure composed of the channel sudden expansion section 25 and the channel transition section 26 in turn. Through the periodic design of the diameter sudden expansion of the channel sudden expansion section 25 and the convergence of the channel transition section 26, the thickening of the wall boundary layer is periodically suppressed, preventing it from blocking the flow channel, so that the mixed gas flow forms a stable high-speed gas flow through the backflow suppression structure, maintaining the stability of the core flow field.

[0056] S5: negative pressure generation and exhaust; The mixed gas is discharged through the exhaust port 28 of the jet expansion chamber 27, and as S2 and S3 continue, a stable pressure difference is formed in the annular vacuum channel 3, i.e. the required stable negative pressure is generated and maintained in the vacuum chamber 4.

[0057] The above application of specific examples to the present invention is only used to help understand the invention and does not limit the invention. For those skilled in the art to which the present invention belongs, according to the idea of the present invention, several simple deductions, deformations or substitutions can be made.

Claims

1. An ejector tube for a negative pressure suction device, said ejector tube (2) having a through internal airflow channel, characterized in that, The internal airflow channels include those arranged sequentially along the airflow direction: The jet expansion cavity (21) has an inlet contraction section (22) protruding inward at its inlet end. A shock wave control surface (23) is connected behind the inlet contraction section (22). The shock wave control surface (23) is used to control the shock wave angle and position during the jet expansion process. The backflow suppression zone (24) includes at least one set of backflow suppression structures disposed on the inner wall of the internal airflow channel. The backflow suppression structures are arranged at intervals along the axial direction of the ejector tube (2), and their number is determined according to the length of the ejector tube (2) and the flow state. Each of the backflow suppression structures includes an annular channel expansion section (25) and a channel transition section (26) located downstream therefrom. The upstream end of the jet ejection cavity (27) is smoothly connected to the downstream end of the backflow suppression zone (24); And an exhaust port (28), which is set as the end point of the internal airflow channel for discharging the mixed airflow guided by the jet ejector cavity (27).

2. The ejector tube as described in claim 1, characterized in that, The channel transition section (26) is a tapered or straight channel section, and the inner wall surface of the channel transition section (26) is a smooth continuous curved surface, which is used to guide the airflow to transition smoothly and suppress flow separation.

3. The ejector tube as described in claim 2, characterized in that, The diameter of the channel expansion section (25) is larger than the diameter of the upstream adjacent jet expansion cavity (21), and the channel transition section (26) is configured as a conical surface converging in the axial direction.

4. The ejector tube as described in claim 3, characterized in that, The diameter expansion direction of the channel expansion section (25) is perpendicular to the axis of the ejector tube (2).

5. The ejector tube as claimed in claim 1, characterized in that, The shock wave control surface (23) is configured as a conical surface or a continuously curvatured surface of revolution along the circumferential direction.

6. The ejector tube as claimed in claim 1, characterized in that, The diameter of the jet expansion cavity (21) is larger than the diameter of the jet ejection cavity (27).

7. A negative pressure suction device, characterized in that, Includes a nozzle (1) and an ejector tube (2) as described in any one of claims 1-6, wherein the nozzle (1) has a through internal injection channel (13) and the internal injection channel (13) is in communication with the internal airflow channel; The inlet end of the jet expansion chamber (21) surrounds the outlet of the nozzle (1), and an annular vacuum channel (3) is formed between the two. One end of the annular vacuum channel (3) is connected to the jet expansion chamber (21), and the connection position of the annular vacuum channel (3) is located in the jet low pressure distribution area of ​​the jet expansion chamber (21). The other end of the annular vacuum channel (3) is used to connect to the vacuum chamber (4) to be evacuated.

8. The negative pressure suction device as described in claim 7, characterized in that, The airflow inlet of the annular vacuum channel (3) is connected to the vacuum chamber (4), and the airflow outlet of the annular vacuum channel (3) is connected to the jet expansion chamber (21) to guide the gas in the vacuum chamber (4) to the low-pressure area of ​​the jet expansion chamber (21). The direction of the annular vacuum channel (3) is consistent with the suction direction of the airflow in the jet expansion chamber (21).

9. The negative pressure suction device as described in claim 7, characterized in that, The internal injection channel (13) includes, in sequence along the airflow direction, a compressed gas inlet (11), a constriction throat (12), and an expansion channel. The compressed gas inlet (11) is used to introduce compressed gas. The constriction throat (12) has a constricted inner diameter. The expansion channel is used to communicate with the jet expansion chamber (21).

10. A method for generating a stable negative pressure, characterized in that, The negative pressure suction device as described in any one of claims 7-9 includes the following steps: High-pressure gas is accelerated into a supersonic jet through nozzle (1); The supersonic jet enters the jet expansion cavity (21) of the ejector tube (2) and impacts the shock wave control surface (23) to form an expansion flow field with a predetermined low-pressure distribution area; In the low-pressure distribution zone of the jet expansion chamber (21), the gas in the annular vacuum channel (3) is drawn in through the inlet contraction section (22); The mixed airflow is converted into a stable high-speed airflow through the recirculation suppression structure to suppress boundary layer thickening and flow separation in the internal airflow channels and maintain the stability of the core flow field. The mixed gas is discharged through the jet ejector cavity (27) and discharged through the exhaust port (28), forming a stable negative pressure in the annular vacuum channel (3).

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