US3511259A - Venturi pump for mixing two fluid streams within a large range of flow rates - Google Patents

Description

May 12, 1970 K. TOURE 3, 1 5

VENTURI PUMP FOR MIXING TWO FLUID STREAMS WITHIN A LARGE RANGE OF FLOW RATES Filed April 5, 1967 s Sheets-Sheet 1 AM) a uni 3511259 'I EAMS WITHIN A LARGE May 12, 1970 K. TOURE VENTURI I-UMP FOR MIXING TWO FLUID RANGE OF FLOW R Filed April 5, 1967 3 Sheets-Sheet 2 Fill mm May 12, 1970 K. TO E 3,511,259

VENTURI PUMP FOR MIXING TWO F D STREAMS WITHIN A LARGE RANGE OF FLOW RATES Filed April 5, 1967 3 Sheets-Sheet 5 m um United States Patent 3,511,259 VENTURI PUMP FOR MIXING TWO FLUID STREAMS WITHIN A LARGE RANGE OF FLOW RATES Klber Tour, Paris, France, assignor to Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France, a company of France Filed Apr. 3, 1967, Ser. No. 627,932 Claims priority, application France, Apr. 4, 1966,

rm. 0]. 605a 11/35 US. Cl. 137114 4 Claims ABSTRACT OF THE DISCLOSURE A venturi pump for mixing two fluid streams with variable flow rates the sum of which is substantially constant, comprising a mixing chamber with constant cross-sectional area, two admission channels opening into said mixing chamber, and means responding to the flow rates of one of the fluid streams for increasing the cross-sectional area of one of the channels and simultaneously decreasing the cross-sectional area of the other channel.

Background of the invention The present invention relates to the mixture of fluid streams and is applicable, in particular, to plants adapted to supply a receiver or fluid consumer with a widely variable flow rate of a fluid subjected to a high pressure as in the case, in particular, for plants feeding fuel into gas turbine or reaction jet engines.

Description of prior art Prior plants include generally volumetric pumps driven at a constant speed so as to supply fluid under the desired high pressure. In order to adjust the flow rate of fluid fed into the receiver, it is possible to resort, as is wellknown in the art, either to a variable capacity pump or else to a pump with an unvarying flow rate or fixed displacement pump associated with an adjustable by-pass. The former pump arrangement is of a more intricate structure and of a higher cost price than the latter and it is furthermore less sturdy. It has therefore been thought preferable generally to resort to a fixed displace ment pump while the flow rate fed into the receiver is adjusted by acting on the flow rate of the recycled stream flowing through the by-pass.

In all conventional recycling arrangements, the potential pressure energy of the recycled fluid is dissipated and is entirely lost in the form of heat. This results, on the one hand, in a loss of efliciency and, on the other hand, in a serious drawback since the temperature of the recycled fluid rises gradually. Said rise in temperature may speedily become objectionable for a proper operation of the plant by reason of the consequent rise in vapor pressure of the fluid sucked in by the pump from a fluid supply. In fact, the formation of vapor bubbles may lead, as is well-known, to vapor lock phenomena in the fluid-conveying channels and to cavitation in the pump, which phenomena appear earlier when the suction pressure of the pump is lower.

In order to reduce said drawback, it has already been proposed to recover the potential pressure energy carried by the recycled fluid by making the latter act as an inducing fluid inside a venturi pump inserted ahead of the main pump and fed by the fluid hailing from the fluid supply which acts as the induced fluid. This reduces, in principle, both the work of the main pump which is fed by a fluid the pressure of which is higher than that of the fluid hailing from the fluid supply and the heating of the fluid due to its recycling.

These known arrangements do not operate however in a satisfactory manner flow rate the ranges of through put of the inducing and induced fluids passing in the corresponding channels formed for them in the venturi pump. As a matter of fact, it is known that the theory of such arrangements is governed by the so-called Eulers theorem (relating to the momenta) which relies on the values of the mass flow rates of the fluids considered and also of their velocities at the entrance into the mixing area. The selection of said velocity values is far from being indiflerent. On the one hand, incidentally, it is necessary for the velocity of the inducing fluid to be sufficiently above the velocity of the induced fluid in order to ensure an actual transfer of energy to the latter. On the other hand, the velocities of the two fluids should not be too different if it is desired to retain a suflicient efficiency for the apparatus. In practice, the selection of said velocities is the result of an averaging between opposed requirements.

Assuming M1 and M2 designate the mass flow rates of the fluid sent, respectively, into the receiver and into the recycling channel, while M designates the constant mass flow rate passing through the main pump, the following equality is true at any moment.

M=M1+M2 or, again assuming the fluid is non-compressible Q=Q +Q Q, Q1 and Q2 being the corresponding volumetric flow rates.

If S1 and S2 designate the corresponding cross-sections of the passageways afforded for the induced and inducing fluids at their input into the mixing area, while V1 and V2 designate the corresponding velocities, the following equalities are also true at any moment The amounts Q1 and Q2 vary to a large extent in opposite directions. Consequently, if as, in known arrangements, the amounts Q1 and Q2 or only one of them does not match accurately the cross-sectional area of the corresponding passageway in the venturi pump, the latter will not operate within the matching range for which it has been calculated. The gain of energy for which it has been designed may then be partly cut out and the rise in temperature in the recycled fluid is retained with all the accompanying drawbacks. If, for instance, one of the passageways is too small for the flow rate it is intended to convey, there may arise in said passageway a loss of head produced by a throttling and consequently a further loss of energy accompanied by a further release of heat.

Summary of the invention The invention has for its object to avoid the abovementioned drawbacks ascribable to a lack of matching between the cross-sectional areas of the passageways afforded in the venturi pump for an inducing fluid, and an induced fluid the flow rates of which vary to a large extent and in opposite directions.

To this end, the passageways for the inducing and induced fluids are each provided in the vicinity of its opening into the mixing area with means adjusting the cross sectional area of the passageway, the position of which means depend on the value of the flow rate which has been previously detected in said passageway. Each of said arrangements is adapted to increase the area of the crosssection of the passageway controlled thereby whenever the fluid throughput in said cross-section increases. Since the two throughputs vary in opposite directions, the crosssectional areas vary also in opposite directions.

According to a preferred embodiment, the two adjusting means are carried by a common movable system the position of which may be adjusted under the control of the flow rate of fluid sent into the receiver or of the flow rate of recycled fluid. Said arrangements are efficiently incorporated with a venturi pump for fluid-recycling systems with a view to providing a higher efficiency than all the known venturi pumps while it allows recycling of the fluid under conditions such that the rise in temperature of the latter may be lower than that observed in conventional systems.

Brief description of the drawings FIG. 1 is a general diagram of a plant feeding fuel into a reaction jet engine to which plant the present invention is applicable;

FIG. 2 is a longitudinal cross-section of an arrangement according to the invention;

FIGS. 3a and 3b are diagrammatic longitudinal crosssections showing the two extreme positions of the arrangement illsutrated in FIG. 2.

Description of the preferred embodiment Turning to FIG. 1 illustrating diagrammatically a plant feeding fuel into a reaction jet engine 1 propelling an aircraft, the fuel carried by a container 3 housed, for instance, within the air craft wing 4 is fed into a channel 5 controlled by a valve 6 through the agency of a low pressure booster pump 7 constituted preferably by a submerged centrifugal pump ensuring the preliminary compression of the fuel. After said fuel has passed through a venturi pump 8, designed in accordance with the invention and described with further detail hereinafter, said fuel enters through a channel 9 into pumping group 10. Said group 10 is constituted in the embodiment described by a mean pressure booster pump 11, preferably of a centrifugal type, and a main high pressure pump 12 inserted in series with the pump 11 with the interposition of a filter 13. The pump 12 is a fixed displacement pump, for instance, of the gear pump type.

At the output of the pumping group 10, to be termed hereinafter merely the pump 10, the fuel is sent into conventional metering means 14 provided, for instance, with a measuring needle 15 and thence through a channel 16 towards fuel nozzles 17 fitted in a combustion chamber 18 of the reaction jet engine 1 which is drawn again separately on the right-hand side of FIG. 1. A by-pass 19, controlled by the metering means 14, returns a fraction of the fuel into the suction end of the pump 10 through the venturi pump 8. The filter 13 is adapted to prevent the progression of the solid particles which may possibly clog the metering means 14 and the injector 17. The presence of said filter leads, however, to a substantial loss of head and, consequently, there is inserted between the low pressure booster pump 7 and the main high pressure pump 12 an auxiliary booster pump similar to the pump 11 for the purpose of compensating said loss of head and also making up for the reduction in pressure at the suction end of the main pump when the aircraft flies at a high altitude. Such an auxiliary booster pump 11 is, however, not essential and the compression ensured by the booster pump 7 is generally suflicient.

From an operative standpoint, the system including the two pumps 11 and 12 may be considered as a single pump 10 showing the characteristic properties of a fixed displacement pump. When said pump is driven at a constant speed, it feeds an also constant fluid flow rate Q.

The fuel flow rate Q1 fed into the fuel nozzles 17 varies considerably with the load to which the plant is submitted and the altitude of flight. Consequently, the fuel flow rate Q2 which is recycled in the channel 19 varies also considerably in a direction opposed to the fuel flow rate Q1 since the sum of the two flow rates is equal to the total constant flow rate Q through the pump 10.

An auxiliary control system 20 receives through a connection 21, a pulse which is a function of the flow rates Q1 and Q2 and which adjusts, through the agency of a control connection 22, the value of the cross-sectional areas afforded for the inducing and induced fluids at their entering in the mixing section of the venturi pump 8, as will be described hereinafter.

The mixing venturi pump, designed in accordance with the invention, is illustrated in FIG. 2 which shows again the channels 5 and 19 conveying the corresponding fluid flow rates Q1 and Q2 of the inducing and induced fluid and also the channel 9 feeding into the pump 10 the total flow rate Q equal to the sum of the partial flow rates Q1 and Q2. The channels 5 and 19 open into the chambers 23 and 24, respectively. The chamber 24 terminates with a nozzle 25 and the chamber 23 with an annular passageway 26, both said nozzle and annular passageway opening into the mixing chamber 27 followed by the above-mentioned channel 9. In order that the respective cross-sectional areas S1 and S2 of the nozzle 25 and annular passageway 26 constantly match the flow rates which are to pass through them and which are both defined by the metering means 14, there are provided in accordance with the invention two members 28 and 29 which allow adjusting said cross-sectional areas, their operation being such that when one of said cross-sectional areas increases, the other decreases, and conversely. The member 28 is constituted by a needle or core adapted to move axially between two extreme positions which are illustrated in FIGS. 3a and 3b, respectively, so as to close to a varying extent the nozzle 25; while the member 29 comprises by a sleeve sliding axially inside a bore 30 in the body of the mixing chamber, the end 31 of said member 29 facing the outer downstream edge 32 of the nozzle nose so as to cooperate therewith in closing, to a varying, extent, the annular passageway 26 between two limit positions, which are clearly illustrated in FIGS. 3a and 3b respectively.

It is convenient to provide a common movable support for the members 28 and 29. To this end, the needle 28 is connected with the sleeve 29 through the agency of ribs 33. The sleeve 29 is provided outwardly with an enlarged section 34 acting as a piston slida-bly carried inside a cylinder 35 closed by the covers 36 and 37.

The piston 34 defines with the cylinder 35 two chambers 38 and 39 into which it is possible to send, selectively, a fluid under pressure depending on the position assumed by a slide valve (not shown) pertaining to the auxiliary control system 20. It is also possible, as illustrated, to subject only one end of the piston to a fluid pressure by feeding only one of the chambers, for instance, the chamber 38, with compressed fluid entering through the channel 22, while the opposite surface of the piston is subjected to the action of a spring 40. The auxiliary control system 20 is connected at 41 and 42 respectively with a supply of compressed fluid and with a chamber subjected to a reduced pressure. Under the action of pulses sent through the connection 21, the slide valve connects the channel 22 with the channel 41 or with the channel 42. It is also possible to provide a feedback by feeding the control system 20 with an additional pulse which is a function of the position of the piston 34. The connection 21 transmits a pulse which is a function of one of the flow rates Q1 and Q2. In the event said fiow rate being controlled by the shifting of a measuring needle 15 (FIG. 1) the pulses may be produced for instance by the displacement of said needle.

FIGS. 3a and 3b show the two extreme positions which may be occupied by the movable system 28, 29 of the arrangement illustrated in FIG. 2. For one of said positions (FIG. 3a) the throughput Q1 is at a maximum and the throughput Q2 at a minimum and possibly near zero. Said position corresponds to the case where the fuel nozzles absorb the totality or almost the totality of the flow rate delivered by the pump 10, the recycled flow rate being reduced to a minimum. To said minimum flow rate there corresponds, as is apparent to a minimum cross-sectional area for the recycled fluid and a maximum cross-sectional area for the fluid hailing from the container 3.

For the position illustrated in FIG. 3b, the recycled flow rate is at a maximum and the throughput hailing from the container 3 is very low. The movable system 28, 29 is shifted so as to match the modified partial flow rates Q1 and Q2 in a manner such that the mixing venturi pump may continue operating satisfactorily.

The invention has been described in its application to an arrangement feeding fuel into a reaction jet engine Obviously, however, said application has been mentioned solely by way of example and the invention is applicable to all fluid recycling and compressing arrangements, chiefly, hydraulic control systems including a fixed displacement pump associated with a by-pass.

What I claim is:

1. A venturi pump adapted to mix a first and a second fluid stream with variable flow rates the sum of which is substantially constant, said pump comprising: a mixing chamber having a substantially constant cross-sectional area; a first admission channel for the first fluid stream, said first channel opening into said mixing chamber through a first opening; means for adjusting the cross sectional area afforded by said first opening; a second admission channel for the second fluid stream, said second channel opening into said mixing chamber through a second opening; means for adjusting the cross-sectional area afforded by said second opening; means responding to the flow rate value of one of the fluid streams and adapted to control said first and second adjusting means so as to increase the cross-sectional area afforded by one of the openings when the flow rate through said opening increases and to simultaneously decrease the cross-sectional area afiorded by the other opening.

2. A venturi pump as claimed in claim 1, comprising means connecting together said first and said second adjusting means.

3. A venturi pump as claimed in claim 1, wherein the means for adjusting said first opening include a shiftable shaped central core, and wherein the means for adjusting said second opening comprise a sleeve coaxial with said core and rigidly connected therewith.

4. A venturi pump as claimed in claim 1, wherein said control means comprises a power unit adapted to drive said first and second adjusting means, and means responding to the fluid flow of one of the fluid streams and adapted to produce pulses controlling said power unit.

References Cited UNITED STATES PATENTS 2,642,813 6/1953 Woodrufi 103-271 3,043,104 7/1962 Magnus 230-112 X 2,928,376 3/1960 Levetus 137-36 X 3,068,878 12/1962 Turnbull 137-56 3,258,919 7/1966 Klein 137-81.5 X 3,279,484 10/1966 Brinkel 137-36 X 3,374,800 3/1968 Wheeler 137-36 X CLARENCE R. GORDON, Primary Examiner U.S. Cl. X.R.

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