Ejector Apparatus And Method Of Utilizing Same

Abstract

A compound ejector apparatus comprising a primary nozzle, primary mixing chamber, secondary nozzle, secondary mixing chamber and diffuser, the primary nozzle functioning mainly as a super charger and the secondary nozzle functioning mainly as a mixer and which furnishes a major portion of the kinetic energy for the compression work taking place in the diffuser, each nozzle being supplied with a part of the motive fluid, wherein the motive fluid supplied to the secondary nozzle has a higher pressure than that supplied to the primary nozzle and wherein the amount of motive fluid supplied to the primary nozzle is only a small part of the total motive fluid supplied to the apparatus.

Parent Case Text

The present application is a continuation-in-part of copending application Ser. No. 44,962, filed on June 10, 1970, now abandoned.

Description

The present invention relates to an ejector apparatus and more particularly to a method and apparatus of improved efficiency.

When a fluid of high potential energy, hereinafter called motive fluid, passes through a converging or converging-diverging nozzle and discharges into a space filled with another fluid of lower potential energy, hereinafter called pumped fluid, the pressure of the motive fluid is reduced while its velocity greatly increases. The motive fluid may be, for example, high pressure steam, the pumped fluid may be low pressure steam, hereinafter called vapor, flowing from an evaporator. The pressure of the fluid stream, i.e., the motive steam continues to decrease after leaving the nozzle, the pressure falling below the evaporator pressure. The difference between the pressure of the pumped fluid (vapor) and the pressure of the fluid stream of the motive steam induces a flow of vapor into the fluid stream. The penetration of the vapor particles into the fluid stream can be compared to the phenomenon of diffusion inasmuch as a vapor particle must continually displace new particles of the fluid stream in order to advance into the fluid stream. This is because the vapor does not penetrate into a stationary medium but into a fluid stream having a high velocity which is moving perpendicularly to the direction of the penetration of the vapor. The velocity of the vapor flowing toward the motive fluid stream is far below the velocity of the fluid stream as the difference between the enthalpy of the vapor and the enthalpy of the fluid stream which is the potential difference producing the flow of vapor, is much smaller than the enthalpy difference which produces the fluid stream, namely the difference between the enthalpy of the high pressure stream and the enthalpy of the low pressure vapor. The velocity of penetration, accordingly similar to the velocity of diffusion, is low. Consequently, the vapor penetrates into only a thin surface layer of the fluid stream. The core of the fluid stream is not penetrated at all or barely reached and is as a result substantially inactive, i.e., it does not contribute substantially to the compression work. In fact it constitutes merely ballast. Thus the higher the velocity of the fluid stream, the thinner will be the vapor carrying layer of the fluid stream and the larger will be the inactive core.

The penetration of the low velocity vapor particles into the outer layer of the motive fluid stream results in a reduction of the velocity of that outer layer in the direction of flow while the velocity of the inner core of the motive fluid stream remains substantially the same. The resultant uneven velocity gradient across the fluid stream contributes to turbulence and, accordingly, to losses in kinetic energy.

It is, therefore, an object of the present invention to provide a method and apparatus for substantially reducing the velocity variations over the cross section of a fluid stream containing vapor particles.

It is a further object of the present invention to divide the plural functions normally performed by a single ejector and to provide a compound ejector including a primary nozzle which will perform primarily as a supercharger and a secondary nozzle which will perform primarily as a mixer and which will function to furnish the major part of the kinetic energy for the compression work.

These and further objects and advantages of the invention will become apparent from a consideration of the disclosure which follows.

The invention is illustrated by way of example in the accompanying drawing which forms a part of this application and in which:

FIG. 1 is an elevational cross sectional view of an embodiment of an ejector apparatus made in accordance with the teachings of the present invention;

FIG. 2 is an elevational cross sectional view of a further embodiment of an ejector apparatus made in accordance with the teachings of the present invention;

FIG. 3 is an elevational cross sectional view of a further embodiment of the invention;

FIG. 4 is an elevational cross sectional view of a further embodiment of the invention;

FIG. 5 is an elevational cross sectional view of a portion of a further embodiment of the invention;

FIG. 6 is an elevational cross sectional view of a portion of a further embodiment of the invention; and

FIG. 7 is an elevational cross sectional view of yet a further embodiment of the invention.

Referring to the drawings and more particularly to FIG. 1, a source of motive high-pressure fluid, as, for example saturated steam at 125 psia, is diagrammatically illustrated at 10. A portion of this high pressure fluid, hereinafter referred to as motive fluid, is directed via conduit 12 to the primary nozzle 16. While FIG. 1 shows an ejector having a single nozzle 16, it is understood that this single nozzle can be replaced by a number of smaller nozzles of similar design. Such an ejector having a plurality of small nozzles has the advantage that it has a better efficiency than an ejector of the same capacity having just one large nozzle. The motive fluid leaves the primary nozzle 16 as a high velocity fluid stream 17 and has a low pressure for example of 0.15 psia. On passage through the nozzle the fluid stream will no longer be saturated i.e., the stream will have a moisture content of approximately 17 percent. The velocity of the motive fluid stream 17 leaving nozzle 16 can be calculated from the formula

v=223.8 h.sub.1 - h.sub.2 ft./sec.

where h.sub.1 is the enthalpy of the motive high pressure fluid at its entry into the primary nozzle 16 and h.sub.2 is the enthalpy of the motive fluid stream 17 leaving the primary nozzle 16. In the instant embodiment, the velocity would be approximately equal to 3,800 ft./sec. (h.sub.1 =119BTU, h.sub.2 =900BTU). After the motive fluid stream 17 has been discharged from the primary nozzle 16, the fluid stream pressure will continue to decrease.

The primary nozzle 16 discharges the fluid stream into primary mixing chamber 18. A second fluid 21 comprising the so-called pumped fluid, in this example vapor, is supplied from a second fluid source in this case an evaporator diagrammatically and partially illustrated at 20. As just noted above, after the motive fluid is discharged from the nozzle 16 its velocity further increases and as a result its pressure falls below the evaporator pressure. The resultant pressure differential induces a flow of vapor designated in the drawing by the reference numeral 21 into the motive fluid stream 17 causing particles of vapor 21 to penetrate into the motive fluid stream 17. As this pressure differential is generally small, the velocity of the vapor 21 is far lower than the velocity of the motive fluid stream 17 passing through the mixing chamber. The time available for the vapor to penetrate into the motive fluid stream is very short because as soon as the vapor penetrates into the outer layer of the motive fluid stream 17 it is carried away. Thus, for example, with a distance of two feet from the end of the first ejector nozzle 16 to the point where the penetration ends and with a motive fluid stream velocity of only 2,500 ft./sec., this period of time of travel will amount to approximately 0.0008 seconds. Accordingly, the particles penetrate only into a very thin surface layer 26 of the motive fluid stream 17 and do not enter into the core 25. It is clear that the higher the velocity of the fluid stream 17 discharged from the primary nozzle 16 the thinner will be the vapor carrying layer and the larger will be the inactive core.

At the exit from the mixing chamber 18 there is arranged so as to annularly surround the stream 17, an annular chamber 30, which may be provided with either a single ring shaped nozzle 31 as illustrated or which may have a plurality of simple nozzles arranged in a circle concentric to the motive fluid stream path. A third fluid stream 29 which also constitutes motive fluid and which may be identical to the first fluid stream in composition and which, therefore, will have identical physical characteristics to that of the first fluid stream prior to the diversion thereof into separate conduits for introduction into the primary or secondary nozzle but which has a higher pressure as supplied to the secondary nozzle through a conduit 32 from the source 10 containing the motive high pressure fluid. The secondary nozzle is arranged to discharge this third fluid stream so that it will angularly intersect the fluid stream as composed of first fluid (motive) having second fluid (pumped) entrained in the outer layer thereof. The two converging fluid streams will undergo ready and thorough intermixing.

The reason for this is that the penetrating force of a fluid stream is a function of the total pressure (velocity pressure plus static pressure of that stream) while the resistance to penetration is a function only of the static pressure of the fluid stream being penetrated. This applies: (a) to the surface layer 26 of the first fluid stream 17 coming from the primary nozzle 16 and penetrating into the third fluid stream 29 of the secondary nozzle 31, (b) the core 25 of the first fluid stream 17 coming from the primary nozzle 16 and penetrating into the third fluid stream 29 of the secondary nozzle 31, and (c) the third fluid stream 29 of the secondary nozzle 31, penetrating into the entirety of the first fluid stream 17 coming from the primary nozzle 16. By ejecting the third fluid stream 29 so that it converges at an angle with the motive fluid stream 17 an intense interaction between the two streams will result thereby ensuring a homogeneous mixture and a very small velocity gradient across the fluid stream. The converging, but almost parallel flow of the first and third fluid streams is a factor which aids the interaction as the time available for mixing is made longer.

The compound ejector comprising a primary and a secondary nozzle in accordance with the invention permits higher compression ratios by the simple measure of increasing the pressure of the motive fluid supplied to the secondary nozzle while supplying the primary nozzle with a motive fluid of lower pressure. This difference in pressure can be brought about very simply by lowering the pressure of the motive fluid for the primary nozzle. This can be carried out manually or by means of a pressure reducing valve.

In accordance with a preferred embodiment of the invention, a pressure reducing valve 36 is provided in the conduit 12 leading from the motive fluid source 10 to the primary nozzle 16 for use in lowering the pressure of the motive fluid being supplied to the primary nozzle.

With a reduction of the motive fluid pressure, the velocity of the fluid stream discharged from the primary nozzle will be reduced permitting a longer period of time for the vapor in the mixing chamber to penetrate into the fluid stream. Accordingly, a reduction in this pressure within certain limits acts to increase the carrying capacity of the motive fluid stream. Further, by reducing the pressure of the motive fluid stream which is being directed to the primary nozzle, the relative velocity between the motive fluid stream and the vapor particles will be reduced and the shocks resulting from the high velocity fluid stream particles striking against the low velocity vapor particles will also be reduced and therewith a corresponding reduction in the loss of kinetic energy will take place.

As the loss by shock is a quadratic function of the difference of the velocities producing the shock, even a small reduction in the difference of the velocities results in a significant reduction of the loss.

Preferably, the apparatus in accordance with the invention can be modified in such a way that the pumped fluid (vapor) is admitted to the second mixing chamber 24 permitting vapor 21 to penetrate into the third fluid stream 29. This measure serves to increase the total carrying capacity of the motive fluid stream while still achieving good mixing in the second mixing chamber 24 as is shown in FIG. 3.

As can be appreciated the conventional two stage ejector apparatus utilizes first and second stage ejectors in series each of the ejectors handling the respective pumped fluid at rest (or having a very low velocity) and there is no division of functions between the first stage and second stage ejector and, consequently, each ejector works under unfavorable conditions and at a low efficiency. The present compound ejector apparatus divides the functions which are performed in duplicate by the conventional two stage ejectors, with the primary nozzle in accordance with the invention functioning mainly as supercharger while the secondary acts primarily as a mixer and supplies the major part of the energy required for the compression work. Each nozzle can accordingly be designed to fulfill its specific function and can be fed independently of the other by a motive fluid having the most convenient pressure or enthalpy.

The apparatus in accordance with the invention therefore permits higher compression ratios by the simple expedient of introducing the motive fluid into the secondary nozzle at a higher pressure than that which is used for the introduction of the motive fluid into the primary nozzle. This does not in any way adversely affect the carrying capacity of the motive fluid as the pressure of the fluid stream introduced into the primary nozzle can be kept sufficiently low. It can, therefore, be appreciated that in the ejector apparatus in accordance with the teachings of the present invention each nozzle performs a separate function which in combination achieve an outstanding amount of work as compared to the conventional arrangements.

For very high compression ratios requiring multistage compression, additional stages can be added to the compound secondary ejector. It is important to locate such additional stages at such points of the diffuser that the velocity of the fluid stream is still high enough that considerable losses by shocks are avoided. The design of the nozzle of a second or third stage ejector is similar to the design of a secondary nozzle of a compound ejector as for example illustrated in FIG. 4.

The greater the difference between the pressure in the evaporator and the motive fluid stream leaving the primary nozzle, the greater will be the velocity of the vapor and the greater will be the amount of vapor penetrating into the fluid stream. In other words, an increased over expansion increases the carrying capacity of the motive fluid stream. Over expansion cannot be carried too far because of the danger of shock which would then result in undesirable losses in kinetic energy. This danger increases with an increase in the motive fluid stream velocity and to be more precise with an increasing difference between the motive fluid stream velocity and the velocity of the pumped fluid vapor particles in the direction of flow. At lower velocities of the motive fluid stream, a higher degree of over expansion can be tolerated and this increases the utility of the present ejector apparatus as it can then use lower pressure motive fluid for the primary nozzle than can the conventional ejectors working against the same back pressure.

The same consideration applies to the secondary nozzle, The second fluid stream, i.e., fluid to be pumped is accelerated by the motive fluid stream discharged from the primary nozzle and thus the difference between the velocity of the first fluid stream carrying entrained second fluid and the velocity of the third fluid stream discharged from the secondary nozzle is reduced permitting higher over expansion.

FIG. 2 illustrates another embodiment of the invention wherein the secondary nozzle 31' does not concentrically surround the motive fluid stream 17' leaving the primary nozzle, but is comprised of a single nozzle which directs a motive fluid stream 29' to converge with the fluid stream 17' with the result that the vectorial forces of the converging fluid streams modify the direction of the mixture toward the diffuser.

As can be seen from FIG. 3, it is not necessary to have two separate feeds from the evaporator since the annular chamber 30 may be suspended from the upper portion of the apparatus thereby enabling a single feed to supply the pumped fluid 24 to the motive fluid stream 17.

Additionally, while the primary nozzle 16 and its corresponding nozzle 31 can be spaced along the path of flow as illustrated in FIGS. 1-4, it is also possible as is illustrated in the portion of the ejector apparatus shown in FIG. 5, for the primary nozzle 16 to be positioned so it surrounds the secondary nozzle 31 both cooperating to produce a converging homogenous fluid mixture entering the diffuser 24. The function of the ejector is the same with jets of the primary nozzle 16 accomplishing the entrainment of the vapor portion, and the jets of the secondary nozzle 31 accomplishing the work of compression. In this embodiment there is only a single mixing chamber 18.

FIGS. 6-7 illustrate two additional forms of the ejector. In FIG. 6 the first stage ejector comprises a nozzle 16 a mixing chamber 18 and a diffuser 50. Reduced steam pressure is used for the first stage and full steam pressure is used for the second stage ejector. The structure illustrated in FIG. 7 is substantially the same as that illustrated in FIG. 6 with the jets of the second stage ejector shown positioned to discharge fluid stream 29 to angularly intersect the fluid stream 17 of the first stage ejector.

It can be appreciated that the ejector apparatus made in accordance with the teachings of the present invention can utilize a gas and/or a liquid as the motive and pumped fluids.

The present ejector apparatus can be utilized in steam jet refrigeration systems, vacuum pumps, and gas ejectors as well as in many other similar applications.

Claims

What is claimed is:

1. An ejector apparatus comprising a source of motive fluid, primary nozzle means, means for supplying a portion of said motive fluid at a first pressure to said primary nozzle means, said primary nozzle means comprising means for discharging said motive fluid into a converging mixing chamber means as a first fluid stream having a reduced second pressure, means for supplying a second fluid stream to be pumped to said chamber means at a pressure greater than said second pressure whereby a portion of said second fluid stream will become entrained in said first fluid stream secondary nozzle means, means for supplying a further portion of said motive fluid at a third pressure greater than said first pressure to said secondary nozzle means, said secondary nozzle means comprising means for discharging said motive fluid as a third fluid stream to angularly intersect said first fluid stream with a portion of said second stream entrained therein within said chamber means thereby to effect mixing of said third fluid stream and first fluid streams with said second fluid stream entrained in it, said chamber means being substantially continuously converging between the nozzles whereby the velocity of said first fluid stream with a portion of said second stream entrained therein and the pressure thereof is maintained substantially constant, said secondary nozzle producing the major portion of the total kinetic energy necessary to produce the compression work by said apparatus and said primary nozzle producing but a minor portion of said total kinetic energy said mixing chamber issuing directly to a diffuser.

2. An ejector apparatus according to claim 1, wherein said secondary nozzle means includes an annular nozzle concentrically surrounding said first fluid stream.

3. An ejector apparatus comprising a source of motive fluid, primary nozzle means connected to said source, a converging mixing chamber means, said primary nozzle means constituting means for delivering a stream of motive fluid to said chamber means at a first pressure, conduit means supplying a stream of fluid to be pumped to said mixing chamber means at a second pressure higher than said first pressure whereby fluid to be pumped is entrained in said motive fluid stream from said primary nozzle to constitute therewith a primary fluid stream, secondary nozzle means delivering a second stream of motive fluid, said secondary nozzle means being angularly inclined to said primary fluid stream and issuing into said mixing chamber to intercept the primary fluid stream and to include between the primary stream and the second motive fluid stream an acute angle said chamber means being substantially continuously converging between the nozzles whereby the velocity of said first fluid stream with a portion of said second stream entrained therein and the pressure thereof are maintained substantially constant whereby said second motive fluid stream combines with said primary fluid stream, said mixing chamber issuing directly to a diffuser the motive fluid being delivered to said primary nozzle at a lesser pressure than to said secondary nozzle.