High Vacuum Ejector

Abstract

An ejector for generating a vacuum comprising a first stage. The first stage comprises a drive nozzle and a ring drive nozzle. The drive nozzle is for generating a drive jet of air from a flow of compressed air and directing the drive jet of air into a first stage expansion nozzle in order to entrain air in a volume surrounding the drive jet of air into the jet flow to generate a vacuum across the first stage. The ring drive nozzle is for generating a drive ring of air from the flow of compressed air and directing the drive ring of air onto the jet flow and the entrained air, and into an inlet of an exit expansion nozzle.

Claims

1. An ejector for generating a vacuum comprising: a first section comprising: a drive nozzle for generating a drive jet of air from a flow of compressed air and directing the drive jet of air into a first section expansion nozzle in order to entrain air in a volume surrounding the drive jet of air into a jet flow to generate a vacuum across the first section; and a ring drive nozzle for generating a drive ring of air from the flow of compressed air and directing the drive ring of air onto the jet flow and the entrained air, and into an inlet of an exit expansion nozzle.

2. The ejector of claim 1, wherein the first section expansion nozzle comprises a diverging section, the diverging section of the first section expansion nozzle diverges in a direction of airflow through the first section expansion nozzle.

3. The ejector of claim 1, wherein the drive ring of air is directed over an outlet of the first section expansion nozzle.

4. The ejector of claim 3, wherein the outlet of the first section comprises an outlet of the first section expansion nozzle and an outlet of the ring drive nozzle.

5. The ejector of claim 1, wherein the inlet of the exit expansion nozzle defines a stepwise expansion in the diameters between an outlet of the first section and the inlet of the exit expansion nozzle.

6. The ejector of claim 5, wherein an outlet of the first section expansion nozzle, an outlet of the ring drive nozzle and the stepwise expansion in the diameters between the outlet of the first section and the inlet of the exit expansion nozzle, are aligned along a direction of airflow through the ejector.

7. The ejector of claim 1, wherein the drive ring of air is directed onto the jet flow and the entrained air at the inlet of the exit expansion nozzle.

8. The ejector of claim 1, wherein the exit expansion nozzle comprises a diverging section, the diverging section of the exit expansion nozzle diverges in a direction of airflow through the exit expansion nozzle.

9. The ejector of claim 8, wherein the drive ring of air is directed onto the jet flow and the entrained air at least in the diverging section of the of the exit expansion nozzle.

10. The ejector of claim 8, wherein the diverging section of the exit expansion nozzle defines a stepwise expansion in the diameter of the diverging section.

11. The ejector of claim 1, wherein the exit expansion nozzle comprises a converging section, the converging section of the exit expansion nozzle converges in a direction of airflow through the exit expansion nozzle.

12. The ejector of claim 11, wherein the drive ring of air is directed onto the jet flow and the entrained air at least in the converging section of the of the exit expansion nozzle.

13. The ejector of claim 1, wherein the exit expansion nozzle comprises a straight section, the straight section of the exit expansion nozzle is straight in a direction of airflow through the exit expansion nozzle.

14. The ejector of claim 13, wherein the drive ring of air is directed onto the jet flow and the entrained air at least in the straight section of the of the exit expansion nozzle.

15. A method of generating a vacuum from a flow of compressed air, comprising: supplying the flow of compressed air to a drive nozzle to generate a drive jet of air; directing the drive jet of air into a first section expansion nozzle; generating a vacuum by entraining air in a volume surrounding the drive jet of air into a jet flow; supplying the flow of compressed air to a ring drive nozzle to generate a drive ring of air; and directing the drive ring of air onto the jet flow and the entrained air, and into an inlet of an exit expansion nozzle.

16. The method of claim 15, wherein the drive ring of air is directed onto the jet flow and the entrained air, and into the inlet of the exit expansion nozzle in order to accelerate the flow of air through the first section expansion nozzle.

17. The ejector of claim 9, wherein the diverging section of the exit expansion nozzle defines a stepwise expansion in the diameter of the diverging section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0037] FIG. 1A shows a longitudinal, axial sectional view through an embodiment of an ejector cartridge according to the present invention, as seen in a direction perpendicular to the direction of airflow through the ejector cartridge;

[0038] FIG. 1B shows a perspective side view of the ejector cartridge of FIG. 1A from the same direction as FIG. 1A;

[0039] FIG. 2 shows a longitudinal, axial sectional view of the drive nozzle, the first section expansion nozzle and the second housing 100A(b) of the embodiment shown in FIGS. 1A and 1B;

[0040] FIG. 3 shows a longitudinal, axial sectional view of parts of the first section expansion nozzle, ring drive nozzle and exit expansion nozzle of the embodiment shown in FIGS. 1A and 1B;

[0041] FIGS. 4 and 5 show sectional views of a prior art ejector cartridge, with FIG. 5 illustrating a cartridge being mounted into a housing unit of an ejector; and

[0042] FIG. 6 shows a prior art ejector unit including a booster stage incorporated into a common housing in parallel with the in-line series of multi-stage ejector nozzles.

DETAILED DESCRIPTION

[0043] Embodiments of the present invention will now be described with reference to the accompanying figures. Like reference numerals have been used to refer to like features throughout the description of the various embodiments.

[0044] FIGS. 1A and 1B show an embodiment of an ejector according to the present invention. The embodiment of FIGS. 1A and 1B is configured as an ejector cartridge 100. Such a cartridge is intended to be installed within an ejector housing module, or within a bore or chamber formed in an associated piece of equipment, which defines the volume to be evacuated by the ejector cartridge.

[0045] Although the most preferred embodiment of the ejector, as shown in the drawings, is designed to work with air as the drive fluid, and as the fluid to be evacuated, the ejector will be applicable to any gas as the drive fluid, and any gas as the fluid to be evacuated. The drive fluid will have a primary direction of movement, or flow, through the ejector. This direction is parallel to the longitudinal axis of the ejector, shown horizontally in the drawings, and starting from the inlet 114. In the following, this direction will be referred as the direction of airflow. Ejector cartridge 100 is a multi-section ejector having a first section 100A and a second section 100B. A vacuum may be generated across the first section 100A.

[0046] The first section 100A comprises a drive nozzle 120. The drive nozzle 120 has an inlet flow section 121 and an outlet flow section 122. The inlet flow section 121 is in fluid communication with an inlet 114 of the ejector cartridge 100 such that at least a portion of the compressed air supplied to the inlet 114 of the ejector cartridge 100 will be supplied to the inlet flow section 121 of the drive nozzle 120. The drive nozzle 120 is arranged to accelerate compressed air supplied to the inlet flow section 121 of the drive nozzle 120, so as to direct a jet flow of high-speed air (referred to as a drive jet of air) out of the outlet flow section 122 of the drive nozzle 120. The outlet flow section 122 of the drive nozzle 120 lies on the center axis CL of the ejector cartridge 100.

[0047] The flow of high-speed air is directed into a first section expansion nozzle 130 of the first section 100A. The outlet flow section 122 of the drive nozzle 120 is disposed within the first section expansion nozzle 130. Accordingly, the jet of high-speed air exiting the outlet flow section 122 of the drive nozzle 120 is immediately within the first section expansion nozzle 130.

[0048] The first section expansion nozzle 130 has at least one suction port 131 and a diverging section 135. The diverging section 135 of the first section expansion nozzle 130 defines an outlet 136 of the first section expansion nozzle 130. In this embodiment, the diverging section 135 of the first section expansion nozzle 130 is an outlet section of the first section expansion nozzle 130. The at least one suction port 131, an outlet of the outlet flow section 122 and the outlet 136 are arranged in this order along the airflow direction. In other words, the outlet 136 is downstream of the outlet of the outlet flow section 122, which is in turn downstream of the at least one suction port 131. Referring to FIG. 1B, in this embodiment, the first section expansion nozzle 130 has four suction ports 131, three of which can be taken from the figure, the fourth of which lying diametrically opposite the one facing the viewer.

[0049] When compressed air is supplied to the inlet flow section 121 of the drive nozzle 120 via the inlet 114 of the ejector cartridge 100, a high-speed air jet will be generated by the drive nozzle 120, so as to form a jet flow in which the drive air jet is directed into the first section expansion nozzle 130. In this way, air or other fluid medium in a volume surrounding the drive jet of air will be entrained into the jet flow and driven through the first section expansion nozzle 130 and out of the outlet 136 of the first section expansion nozzle 130. The jet flow and the entrained air will be driven into the second section 100B of the ejector cartridge 100.

[0050] The consumption and the feed pressure of the supplied compressed air can vary in accordance with ejector size and desired evacuation characteristics. For smaller ejectors, a consumption range from about 0.1 to about 0.2 Nl/s (normalized litres per second) at feed pressures of from about 0.4 to about 0.5 MPa will usually be sufficient, and large ejectors typically consume from about 2 to about 2.4 Nl/s at about 0.4 to about 0.5 MPa. Ranges in between for sizes in between are possible and common. Without wishing to be bound to these particular ranges, compressed air as used herein is to be understood to have such properties.

[0051] The first section 100A of the ejector cartridge 100 has a first housing 100A(a), a second housing 100A(b) and a third housing 100A(c), which together form a housing of the first section 100A. The suction port 131 of the first section expansion nozzle 130 extends through the first housing 100A(a) and provides fluid communication between the inside of the first section expansion nozzle 130 and the outside of the ejector cartridge 100.

[0052] The first section 100A of the ejector cartridge 100 has a ring drive nozzle 140. The ring drive nozzle 140 is formed from an outer surface of the first section expansion nozzle 130 and an inner surface of the housing of the first section 100A. The ring drive nozzle 140 defines a substantially rotationally symmetric body, forming a body of revolution about the center axis CL.

[0053] The ring drive nozzle 140 has an inlet flow section 141 and an outlet flow section 142. The inlet 114 of the ejector cartridge 100 is in fluid communication with both the inlet flow section 121 of the drive nozzle 120 and the inlet flow section 141 of the ring drive nozzle 140. Accordingly, a source of compressed air may supply compressed air into the inlet 114 of the ejector cartridge 100 so as to supply compressed air to both the inlet flow section 121 of drive nozzle 120 and the inlet flow section 141 of ring drive nozzle 140. The ring drive nozzle 140 is arranged to accelerate compressed air supplied to the inlet flow section 141 of the ring drive nozzle 140, so as to direct a drive ring of air out of the outlet flow section 142 of the drive ring nozzle 140. The drive ring of air is a ring of high-speed air. The drive ring of air is driven into the second section 100B of the ejector cartridge 100. The compressed air is supplied to the inlet flow section 141 of the ring drive nozzle 140 via the inlet 144 defined by a surface formed from the outer surface of the drive nozzle 120 together with an outer surface of the first section expansion nozzle 130, and an inner surface of the first housing 100A(a).

[0054] The drive ring of air is directed onto the jet flow and the entrained air after the jet flow and the entrained air is driven out of the outlet 136 of the first section expansion nozzle 130. The drive ring of air is directed onto the jet flow and the entrained air in the second section 100B of the ejector cartridge 100. As the drive ring of air is directed onto the jet flow and the entrained air, it may be possible to accelerate the flow of air through the first section expansion nozzle 130.

[0055] An outlet of the outlet flow section 142 of the ring drive nozzle 140 defines an outlet 143 of the ring drive nozzle 140. An outlet of the first section 100A comprises the outlet 136 of the first section expansion nozzle 130 and the outlet 143 of the ring drive nozzle 140. The air driven out of the outlet of the first section 100A is driven into the second section 100B.

[0056] The first section 100A is a drive section as it is the only section connected to the source of compressed air, and so drives the flow of compressed air through the subsequent section (second section 100B), before the fluid is ejected from the ejector cartridge 100. Moreover, as the at least one suction port 131 is provided in the first section 100A, a vacuum may be generated across the first section 100A. The second section 100B of the ejector cartridge 100 has an exit expansion nozzle 150. The exit expansion nozzle 150 has an inlet section 151 which defines an inlet 152 of the exit expansion nozzle 150. The exit expansion nozzle 150 has a first diverging section 155a and a second diverging section 155b which define a diverging section 155 of the exit expansion nozzle 150. In this embodiment, both the first diverging section 155a and the second diverging section 155b have the same rate of divergence. The diverging section 155 defines an outlet 157 of the exit expansion nozzle 150. The outlet 157 is the outlet of the ejector cartridge 100.

[0057] The inlet 152 of the exit expansion nozzle 150 is an inlet of the second section 100B. The air exiting the outlet of the first section 100A is directly introduced into the inlet 152 of the exit expansion nozzle 150 (i.e. the inlet of the second section 100A). The air then passes through the exit expansion nozzle 150 and exits the ejector cartridge 100 via the outlet 157.

[0058] The second section 100B facilitates the mixing of the jet flow and the entrained air, and the drive ring of air. Furthermore, the second section 100B and may be configured such that the change from the flow and pressure conditions immediately after the first section 100A, to the expansion of the flow into ambient pressure, is less abrupt. This may improve the efficiency of the ejector cartridge 100.

[0059] Referring to FIG. 1B, the ejector cartridge 100 is formed as a substantially rotationally symmetric body, forming a body of revolution about the center axis CL, with the exception of the suction ports 131. Although the suction ports 131 do not, strictly speaking, form bodies of revolution, they may be disposed with rotational symmetry about said axis of rotation CL, thus representing only minor discontinuities in what is otherwise a body of revolution about the center axis CL.

[0060] As shown in FIGS. 1A and 1B, the ejector cartridge 100 is a substantially cylindrical ejector cartridge having a substantially circular cross-sectional shape along its length in the plane perpendicular to the center axis CL, i.e., perpendicular to the direction of airflow through the ejector cartridge 100. However, it will be appreciated that it is not essential for the ejector cartridge 100 or the components thereof, to be formed with a circular cross-sectional shape. Nevertheless, a substantially cylindrical or tubular form is preferred for the ejector cartridge 100, since this permits the ejector cartridge 100 to be installed most easily within a bore hole or other ejector housing module, utilising appropriate seals such as the O-ring 112, shown in FIGS. 1A and 1B.

[0061] With reference also to FIGS. 2 and 3, the components of the ejector cartridge 100 will be described in more detail below. FIG. 2 shows the drive nozzle 120 and the first section expansion nozzle 130 of the ejector cartridge 100, and the second housing 100A(b) of the first section 100A. As explained above, the drive nozzle 120 is arranged to accelerate compressed air supplied to the inlet flow section 121 so as to direct a jet flow of high-speed air out of the outlet flow section 122. In this embodiment, the drive nozzle 120 is a converging-diverging nozzle. Accordingly, the inlet flow section 121 of the drive nozzle 120 has a converging section and the outlet flow section 122 of the drive nozzle 120 has a diverging section.

[0062] The first section expansion nozzle 130 has a first straight section 132, a first converging section 133a, a second converging section 133b, a second straight section 134 and a diverging section 135 arranged in this order with respect to the direction of airflow. The first converging section 133a and the second converging section 133b together form a converging section 133 of the first section expansion nozzle 130. In this embodiment, the first converging section 133a is more converging than the second converging section 133b. The diverging section 135 defines an outlet 136 of the first section expansion nozzle 130.

[0063] The suction port 131 of the first section expansion nozzle 130 is formed in the first straight section 132 of the first section expansion nozzle 130. An outlet of the outlet flow section 122 of the drive nozzle 120 is disposed within the first section expansion nozzle 130. The outlet of the outlet flow section 122 is disposed downstream of the suction port 131 of the first section expansion nozzle 130. The outlet of the outlet flow section 122 is disposed such that the jet flow of high-speed air exiting the outlet flow section 122 is directed into the converging section 133 of the first section expansion nozzle 130. Accordingly, the outlet of the outlet flow section 122 is disposed upstream of the first converging section 133a.

[0064] The second straight section 134 is disposed between the converging section 133 and the diverging section 135. As can be seen from FIG. 2, the first section expansion nozzle 130 has at least one fixing element 137 which fixes the first section expansion nozzle 130 to the second housing 100A(b) and, in turn, to the first housing 100A(a) and the third housing 100A(c). The at least one fixing element 137 extends through the channel formed from the outer surface of the first section expansion nozzle 130 and the inner surface of the second housing 100A(b). The at least one fixing element 137 is configured such that the impedance to the flow in the channel is minimised. In one embodiment, the at least one fixing element 137 comprises a web of material. The web of material may form a plane which has an axis parallel to the direction of airflow and a perpendicular axis perpendicular to the direction of airflow. In one embodiment, the at least one fixing element 137 comprises a sheet of material. The sheet of material may form a plane which has an axis parallel to the direction of airflow and a perpendicular axis perpendicular to the direction of airflow. In one embodiment, there are four fixing elements 137. In one embodiment, the fixing elements 137 are disposed with rotational symmetry about the axis of rotation CL. In one embodiment, the first section expansion nozzle 130, the at least one fixing element 137 and the second housing 100A(b) are formed as a single entity.

[0065] FIG. 3 shows parts of the first section expansion nozzle 130, ring drive nozzle 140 and exit expansion nozzle 150. As can be seen from FIG. 3, the ring drive nozzle 140 is a converging-diverging nozzle. Accordingly, the inlet flow section 141 of the ring drive nozzle 140 has a converging section and the outlet flow section 142 of the ring drive nozzle 140 has a diverging section. The outlet flow section 142 of the ring drive nozzle 140 directs air over the diverging section 135 of the first section expansion nozzle 130. The drive ring of air exiting the outlet flow section 142 passes over the outlet 136 of the first section expansion nozzle 130. The drive ring of air immediately enters the inlet section 151 of the exit expansion nozzle 150.

[0066] In this embodiment, the inlet section 151 is a converging section. The outlet of the first section 100A comprises the outlet 136 of the first section expansion nozzle 130 and the outlet of the outlet flow section 142 of the ring drive nozzle 140. The outlet of the first section 100A defines an outer outlet diameter. In this embodiment, the inlet 152 of the exit expansion nozzle 150 defines a stepwise expansion 160 between the outer outlet diameter of the first section 100A and the diameter of the inlet 152 of the exit expansion nozzle 150. Specifically, outer outlet diameter of the first section 100A is smaller than the diameter of the inlet 152. In other words, an outer diameter of the outlet of the outlet flow section 142 is smaller than the diameter of the inlet 152. In this embodiment, the outlet of the first section expansion nozzle 130, the outlet of the ring drive nozzle 140 and the stepwise expansion 160 are aligned along the direction of airflow through the ejector cartridge 100. The inlet section 151, straight section 153, and diverging section 155 of the exit expansion nozzle 150 are arranged in this order with respect to the direction of airflow.

[0067] The diverging section 155 defines a stepwise expansion 156 in the diameter of the diverging section 155. The stepwise expansion 156 in the diameter is formed part-way along the diverging section 155, in this example, nearer to the inlet section 151 of the exit expansion nozzle 150, rather than the outlet 157. The first diverging section 155a of the exit expansion nozzle 150 extends from the straight section 153 with a divergence angle which may be substantially constant, up to the point where the stepwise expansion in diameter is provided at a sharp corner 156a. Preferably, the sharp corner 156a is defined by an undercut in the diverging section 155 of the exit expansion nozzle 150. At the stepwise expansion 156 in diameter, the wall of the diverging section 155 reverses direction to form the sharp corner 156a, where the wall changes from diverging whilst extending in an axial direction towards the outlet 157 of the exit expansion nozzle 150, to being diverging whilst extending in an axial direction towards the inlet section 151 of the exit expansion nozzle 150, for a short distance, before reversing back to again diverge whilst extending in the axial direction towards the outlet 157 of the exit expansion nozzle 150. The last reversal back into a diverging shape is optional in that the second diverging section 155b as shown in the figures may initially, i.e. immediately downstream of the sharp corner 156a, may reverse back to continue in a cylindrical, straight-walled shape, before it continues in a diverging shape shortly before the outlet 157 of the exit expansion nozzle 150. A shape of the exit expansion nozzle 150 will be selected in accordance with the desired characteristics of the ejector, keeping in mind that the shape serves to render the change from the flow and pressure conditions in the exit expansion nozzle 150 to the expansion of the flow into ambient pressure less abrupt. In this manner, the design of the exit expansion nozzle can advantageously be used to influence pressure and flow rate conditions in the first section 100A. As a result, the skilled person will have greater freedom in designing the first section 100A of the ejector cartridge 100.

[0068] As shown in FIG. 3, the stepwise expansion in diameter 156 can be measured by comparing the diameter Di immediately before the stepwise expansion 156, at the sharp corner 156a, with the diameter Do immediately after the stepwise expansion 156, which is radially in line with sharp corner 155a, but on the second diverging section 155b of the diverging section 155. A stepwise change in diameter serves to trip the fluid flow in the diverging section 155 of the exit expansion nozzle 150, so as to generate a turbulent outlet flow along the nozzle wall, thereby reducing the friction at the outlet 156 of the exit expansion nozzle 150 and correspondingly improving the efficiency with which the ejector cartridge 100 can generate a vacuum from a given source of compressed air.

[0069] The ratio Di:Do is preferably between 5:6 and 5:8.

[0070] Although the above explanation is considered to fully clarify how the present invention may straightforwardly be put into effect by those skilled in the art, it is to be regarded as purely exemplary. In particular, there are a number of variations which are possible, as may be appreciated by those skilled in the art. For example, the ring drive nozzle 140 may be arranged in any manner as long as the drive ring of air is directed onto the jet flow and the entrained air, and into an inlet 152 of the exit expansion nozzle 150. Moreover, the ring drive nozzle 140 may not be formed from an outer surface of the first section expansion nozzle 130 and an inner surface of the housing of the first section 100A. Rather, the ring drive nozzle 140 may be formed from further elements.

[0071] In the embodiment shown in FIGS. 1 to 3, the inlet 114 is in fluid communication with both the inlet flow section 121 of the drive nozzle 120 and the inlet flow section 141 of the ring drive nozzle 140. Accordingly, in this embodiment, a source of compressed air may supply compressed air into the inlet 114 of the ejector cartridge 100 so as to drive both the drive nozzle 120 and the ring drive nozzle 140. However, in another embodiment, a first source of compressed air is configured to supply a first compressed air to the inlet flow section 121 of the drive nozzle 120 and a second source of compressed air is configured to supply a second compressed air to the inlet flow section 141 of the ring drive nozzle 140. Furthermore, either of the stepwise expansions 156, 160 may be omitted in other embodiments. Also, the stepwise expansion 156 may be formed nearer the outlet 156 of the exit expansion nozzle 150, rather than the inlet section 152.

[0072] Also, the exit expansion nozzle 150 may have any combination of: a converging section; a straight section 153; and a diverging section 155, arranged in any order. The drive ring of air may be directed onto the jet flow and the entrained air in any of these sections or any combination of these sections. Also, the first section expansion nozzle 130 may have any combination of: a first straight section 132; a converging section 133; a second straight section 134; and a diverging section 135, arranged in any order. The outlet of the outlet flow section 122 may be disposed such that the jet flow of high-speed air exiting the outlet flow section 122 is directed into any of these sections.

[0073] Throughout this disclosure, any reference to a converging section or a diverging section refers to a section which converges or diverges with respect to the direction of airflow, respectively. In other words, to a section in which the diameter decreases or increases with respect to the direction of airflow. All of the above are fully within the scope of the present invention, and are considered to form the basis for alternative embodiments in which one or more combinations of the above-described features are applied, without limitation to the specific combinations disclosed above.

[0074] In light of this, there will be many alternatives which implement the teaching of the present invention. It is expected that one skilled in the art will be able to modify and adapt the above disclosure to suite its own circumstances and requirements within the scope of the present invention, while retaining some or all technical effects of the same, either disclosed or derivable from the above, in light of his comment general knowledge in this art. All such equivalents, modifications or adaptations fall within the scope of the invention hereby defined and claimed.