GB2185533A - Ejector pumps - Google Patents

Abstract

An ejector pump (26) comprises a main flow pipe (34) into which a flow of primary air (30) is discharged from an annular convergent/divergent nozzle (36). Primary air (30) is fed into a gallery (32) from a feed pipe (28) connected to a source of pressurised air and thence flows through the nozzle (36). By utilising a convergent/divergent nozzle (36) the primary air is accelerated to a very high velocity and is therefore able to entrain a large main flow through the pump. <IMAGE>

Description

SPECIFICATION Improvements in or relating to ejector pumps This invention relates to an ejector pump of the type wherein a flow of primary air is adapted to induce a much largerflowofsecondaryairwithouttheuseof moving mechanical parts.

There is known pump apparatusforinducing a flow of gas without the use of any moving parts. The apparatus may comprise a tubular flow inducing unit having an internal venturi defining a main flow stream through the unit. A primary flow ofairis caused to enterthe venturi through a circumferentially extending slot in the venturi. The primaryflowadheretotheinnersurfaceofthe venturi by the coanda effect and thereby entrains a much largermainflowthroughthe duct. Such apparatus and variations thereof is more particularly described in UK Patent 2077356B to Clifford N Beck.

A drawback of the known type of ejector pump is the limit to the amount offlow that can be entrained for a given size of pump. The entrained flow rate is proportional to the primary flow rate which itself is limited bythecoanda being lost due to separation.

It is an object of the invention to provide an improved ejector pump which has a greaterflow capacity for a given size of pump.

The invention will now be described byway of an example with reference to the accompanying drawings in which: Figure 1 depicts an ejector pump ofthe known type, Figure2 depicts a pump constructed in accordance with the present invention, and, Figure 3 shows a more detailed view of part ofthe structure of the pump in Figure 2.

Referring to Figure 1, an ejector pump 10 ofthe type known in the art comprises aventuri 1 through which a main flow of air 14 is induced to flow. A circumferentially extending inlet port 16 is provided in the venturi body and a flow of primary air 18 is pumped through a supply pipe 20 and into a gallery 22,andthencethroughthe port 16 and intothe ventu ri. The primary air is entrained intotheventuri in the direction of arrow A. A main flow of airs entrained into the venturi in the direction of arrow A bythe primary air. The main airflow rate is substantially proportional to theflow rate of primary air.If the primary flow is increased beyond a certain figurethe performance ofthe pump will deteriorate due to separation of the primary flow.

Referring to Figures 2 and 3 there is shown an ejector pump 26 according tothe present invention.

The pump 26 comprises a feed pipe 28 which supplies primary air 30 to a gallery 32 which extends circumferentially round a main flow pipe 34. The pumpfurthercomprises an annular convergent/divergent nozzle 36 through which primary air 30 flows from the gallery 32 into the main flow pipe 34. Apparatus not shown is provided for supplying aflowof primary airtothefeed pipe, such apparatus may comprise a mechanical pump.

In operation, the feed pipe 28 supplies primary air 30to the gallery32 and thence primary air 30 is discharged into the main flow pipe from the annular convergent/divergent nozzle 36 in the direction of arrow B in Figure 2. The coanda effect is not utilised.

Instead, the convergent/divergent nozzle is shaped and dimensioned with respect to the pressure ratio across itto accelerate the primary airtothe highest possible velocity. For maximum efficiency it is desirableto avoid overexpansion orunderexpansion ofthe flow. Underexpansion of the flow would not exploitthefull potential ofthe primary flow pressure and underexpansion would cause shock losses and thereby reduce performance. Isentropicflow is therefore the optimum flow regime ofthe primary air through the nozzle. The primary flow discharging into the main flow pipe 34 causes a main flowto be entrained through the pump 26 in the direction of arrow B.The difference in velocity between the primary airandthe surrounding air sets up a shear force which accelerates the surrounding and deaccelerates the primary air. To reach equilibrium a main flow through the pump is thereby created.

Furthermore, the local static pressure of the fast moving primaryairwill be less than ambient pressure and will therefore aid entrainment.

After the primary flow has deaccelerated and the main flow has accelerated such that there is a uniform velocity downstream from the nozzle 36 a diffuser may be added to reduce the velocity of the flow and increase the static pressure up to ambient conditions.

In this specification air has been described as the working fluid althoughthe invention is equally applicable to any fluid.

1. An ejector pump, comprising structure defining a main flow path through the pump, means for introducing a flow of primaryworking fluid into the main flow path including convergent/divergent nozzle structure for accelerating the primary working fluid and thereby causing the mainflowthroughthe pump.

2. An ejector pump as claimed in claim 1 wherein the means for introducing the primary working fluid into the main flow path includes at least one feed pipe communicating art a first end with a source of pressurised working fluid and ata second end with a gallery disposed around the main flow path defining structure.

3. An ejector pump as claimed in claim 1 orclaim 2 the convergent/divergent nozzle structure comprises an annular convergent/divergent nozzle shaped and dimensioned to accelerate the working fluid to a velocity in excess of the local speed of sound.

4. An ejector pump as claimed in claim 2 and claim 3 wherein the convergent/divergent nozzle structure is adapted and positioned to communicate between the gallery and the main flow path and to directtheflowofprimaryworking fluid in the direction of main flow through the pump.

5. An ejector pump as claimed in any one ofthe preceding claims wherein the structure defining a main flow path comprises a tubular pipe adapted to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to ejector pumps This invention relates to an ejector pump of the type wherein a flow of primary air is adapted to induce a much largerflowofsecondaryairwithouttheuseof moving mechanical parts. There is known pump apparatusforinducing a flow of gas without the use of any moving parts. The apparatus may comprise a tubular flow inducing unit having an internal venturi defining a main flow stream through the unit. A primary flow ofairis caused to enterthe venturi through a circumferentially extending slot in the venturi. The primaryflowadheretotheinnersurfaceofthe venturi by the coanda effect and thereby entrains a much largermainflowthroughthe duct. Such apparatus and variations thereof is more particularly described in UK Patent 2077356B to Clifford N Beck. A drawback of the known type of ejector pump is the limit to the amount offlow that can be entrained for a given size of pump. The entrained flow rate is proportional to the primary flow rate which itself is limited bythecoanda being lost due to separation. It is an object of the invention to provide an improved ejector pump which has a greaterflow capacity for a given size of pump. The invention will now be described byway of an example with reference to the accompanying drawings in which: Figure 1 depicts an ejector pump ofthe known type, Figure2 depicts a pump constructed in accordance with the present invention, and, Figure 3 shows a more detailed view of part ofthe structure of the pump in Figure 2. Referring to Figure 1, an ejector pump 10 ofthe type known in the art comprises aventuri 1 through which a main flow of air 14 is induced to flow. A circumferentially extending inlet port 16 is provided in the venturi body and a flow of primary air 18 is pumped through a supply pipe 20 and into a gallery 22,andthencethroughthe port 16 and intothe ventu ri. The primary air is entrained intotheventuri in the direction of arrow A. A main flow of airs entrained into the venturi in the direction of arrow A bythe primary air. The main airflow rate is substantially proportional to theflow rate of primary air.If the primary flow is increased beyond a certain figurethe performance ofthe pump will deteriorate due to separation of the primary flow. Referring to Figures 2 and 3 there is shown an ejector pump 26 according tothe present invention. The pump 26 comprises a feed pipe 28 which supplies primary air 30 to a gallery 32 which extends circumferentially round a main flow pipe 34. The pumpfurthercomprises an annular convergent/divergent nozzle 36 through which primary air 30 flows from the gallery 32 into the main flow pipe 34. Apparatus not shown is provided for supplying aflowof primary airtothefeed pipe, such apparatus may comprise a mechanical pump. In operation, the feed pipe 28 supplies primary air 30to the gallery32 and thence primary air 30 is discharged into the main flow pipe from the annular convergent/divergent nozzle 36 in the direction of arrow B in Figure 2. The coanda effect is not utilised. Instead, the convergent/divergent nozzle is shaped and dimensioned with respect to the pressure ratio across itto accelerate the primary airtothe highest possible velocity. For maximum efficiency it is desirableto avoid overexpansion orunderexpansion ofthe flow. Underexpansion of the flow would not exploitthefull potential ofthe primary flow pressure and underexpansion would cause shock losses and thereby reduce performance. Isentropicflow is therefore the optimum flow regime ofthe primary air through the nozzle. The primary flow discharging into the main flow pipe 34 causes a main flowto be entrained through the pump 26 in the direction of arrow B.The difference in velocity between the primary airandthe surrounding air sets up a shear force which accelerates the surrounding and deaccelerates the primary air. To reach equilibrium a main flow through the pump is thereby created. Furthermore, the local static pressure of the fast moving primaryairwill be less than ambient pressure and will therefore aid entrainment. After the primary flow has deaccelerated and the main flow has accelerated such that there is a uniform velocity downstream from the nozzle 36 a diffuser may be added to reduce the velocity of the flow and increase the static pressure up to ambient conditions. In this specification air has been described as the working fluid althoughthe invention is equally applicable to any fluid. CLAIMS

1. An ejector pump, comprising structure defining a main flow path through the pump, means for introducing a flow of primaryworking fluid into the main flow path including convergent/divergent nozzle structure for accelerating the primary working fluid and thereby causing the mainflowthroughthe pump.

2. An ejector pump as claimed in claim 1 wherein the means for introducing the primary working fluid into the main flow path includes at least one feed pipe communicating art a first end with a source of pressurised working fluid and ata second end with a gallery disposed around the main flow path defining structure.

3. An ejector pump as claimed in claim 1 orclaim 2 the convergent/divergent nozzle structure comprises an annular convergent/divergent nozzle shaped and dimensioned to accelerate the working fluid to a velocity in excess of the local speed of sound.

4. An ejector pump as claimed in claim 2 and claim 3 wherein the convergent/divergent nozzle structure is adapted and positioned to communicate between the gallery and the main flow path and to directtheflowofprimaryworking fluid in the direction of main flow through the pump.

5. An ejector pump as claimed in any one ofthe preceding claims wherein the structure defining a main flow path comprises a tubular pipe adapted to receive means for introducing the flow of primary working fluid into the pipe.

6. An ejector pump as claimed in any one ofthe preceding claimswhereinthemainflowthroughthe pump is caused by entrainment of the mai n worki ng fluid andthe main working fluid isfurtherentrained by the effectofthe reduced static pressure ofthe primary fluid as it is discharged from the convergent/divergent nozzle structure.

7. An ejector pump as claimed in any one ofthe preceding claimswhereinthe pump further comprises a diffuser section ofthe main flow path at a location downstream oftheconvergent/divergent nozzle structure; the diffuser being constructed and arranged to retard the velocity ofthe main flow and thereby increase the static pressure.

8. An ejector pump as claimed in any one of the preceding claims wherein the working fluid is air.

9. An ejector pump substantially as described herein with reference to Figures 2 and 3.