|Publication number||US3371618 A|
|Publication date||Mar 5, 1968|
|Filing date||Feb 18, 1966|
|Priority date||Feb 18, 1966|
|Publication number||US 3371618 A, US 3371618A, US-A-3371618, US3371618 A, US3371618A|
|Original Assignee||John Chambers|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Referenced by (55), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
March 5, 1968 J. CHAMBERS 3,371,618
Filed Feb. 18, 1966 s Sheets-Sheet 1 LOW 2 23 11- INVENTOR Joli/v CHAMBERS MM, 7% 7w 9 .5
ATTORNEY 5 March 5, 1968 J. CHAMBERS 3,371,618
PUMP I Filed Feb. 18. 1966 e Sheets-Sheet 2 -l3| SECONDARY FLOW :21
MiXED FLUIDS E2 -'III7/III/ IIIV/IIII'IIII/II/7 MIXED m- FLUIDS x llpxqln' llx'ai 53 MIXED FLUIDS 'IIIIIIIIIIIIIIIIIIIIIIIIIIIN' INVENTOR JOHN CHAMBERS BY MMWM 7 5 ATTORNEY 5 March 5, 1968 J. CHAMBERS 3,371,618
Filed Feb. 18. 1966 6 Sheets-Sheet .5
INVENTOR JOHN CHAMBERS BY Mywm A'ITO NEYS J. CHAMBERS March 5, 1968 PUMP '6 Sheets-Sheet 5 Filed Feb. 18, 1966 CONSTANT PRESSURE STRAIGHT 6 DISTANCE FRCM NOZZLE- INCHES 4 PRESSURE TAP- NUMBERS INVENTOR JOHN CHAMBERS BY 77m 9 5 WM'M WRNEYS,
Filed Feb. 18. 1966 J-CHAMBERS MDGNG SECHON PUMP MFFUSER MDGNG QQI:
SECTDN MFFUSER I 6 Sheets-Sheet 6 United States Patent PUM John Chambers, Rte. 1, Box M41, Del Mar, Calif. 92014 Filed Feb. 18, 1966, Ser. No. 528,464 11 Claims. (Cl. 103-258) ABSTRACT OF THE DISCLOSURE This invention relates to improvements in jet pumps and more specifically to improvements in jet pumps which minimize or eliminate the energy losses attributable to expansion of the primary or motive fluid and/oiof the secondary or induced fluid in the mixing chamber where the latter becomes entrained in the former.
Jet pumps have particular utility as condensers, mixers and fluid circulating apparatus where it is desired to modify the temperature of the circulating fluid or to mix fluids having different physical characteristics. A major difficulty, however, with existing jet pumps is that satisfactory mixing of the primary and secondary fluids cannot be attained without high energy losses due to expansion of the motive fluid and turbulence at the contact region of the fluids in the mixing chamber.
Known jet pump constructions of both the single and plural secondary fluid inlet types are exemplified by United States Patent No. 571,022 issued Nov. 10, 1896 to L. Schutte for Exhauster and United States Patent No. 1,111,541 issued Sept. 221914 to E. Koerting for Injector. The effectiveness of the plural secondary inlets is, in the Schutte and Koerting devices however, partially lost by the use of improperly designed mixing chambers. Primary fluid exiting from the pump nozzle has a low static pressure and expands outwardly toward the sides of the mixing chamber in a conical configuration. The straight-walled cylindrical mixing chamber retards expansion of the escaping primary fluid which intercepts the chamber side walls before complete mixing is accomplished and, thus, decreases its axial velocity and raises its static pressure a short distance axially from the nozzle. The secondary fluid entrance openings farthest spaced axially from the nozzle, thus, do not contribute efficiently to the mixing operation. For maximum etficiency,
the static pressure of the drive and driven fluids in the mixing chamber and the static pressure of the drive fluid should be constant throughout the length of the mixing chamber and, approach but be slightly above the drive fluid vapor pressure. Such a constant pressure is impossible to maintain throughout a cylindrical, diverging or improperly designed converging mixing chamber.
Also, although the Schutte suction inlets are inclined in the direction of primary fluid flow, once the secondary fluid enters the mixing chamber a high degree of turbulence is eiiected in the mixing operation thereby reducing the overall pump efiiciency. The regular annular arrangement of inlets in the Schutte device further attributes to low combining efficiency since mixing occurs only at axially and radially spaced intervals along the mixing chamber rather than continuously along its length.
The primary object of this invention is to provide a highly eflicient jet pump which combines two fluids of substantially equal density by entraining a secondary fluid in a primary fluid in increments along the length of a mixing chamber under constant or substantially constant static pressure conditions whereby losses attributable to expansion of the fluids in the mixing chamber are substantially eliminated.
Another object of this invention is to provide a jet pump which maintains the static pressure of the drive fluid constant and but slightly above the fluid vapor pressure throughout the mixing chamber to obtain maximum pumping efliciency while preventing cavitation due to a vaporization of the motive fluid.
Still another object of this invention is to provide a jet pump having means for feeding secondary fluid into the mixing chamber substantially parallel with the axis of the primary fluid flow through the mixing chamber.
Another object of this invention is to provide a jet pump and method of operation wherein the relative velocities and flow rates of the drive and driven fluids are coordinated with the configuration and dimensions of the mixing chamber so that complete mixing of the fluids is accomplished before interception of the chamber side walls by the expanding drive fluid.
Yet another object of this invention is to provide a jet pump having a divergent-walled mixing chamber for maintaining substantially constant low static fluid pressure throughout the chamber.
A further object of this invention is to provide a jet pump having adjustable wedges for selectively changing the weight ratio of primary fluid to secondary fluid while at the same time maintaining a high degree of pumping efliciency.
Another object of this invention is to provide a jet pump having diverter vanes mounted on the inner surfaces of the mixing chamberwalls in a position sufficient to direct secondary fluid flow through inlets in the mixing chamber walls substantially parallel to primary fluid flow through the mixing chamber.
Yet another object of this invention is to provide a method for entraining a first fluid in a second fluid by accelerating the second fluid to provide a low pressure region at several locations along the flow of the second fluid and guiding flow of said first fluid into the low pressure regions at the several locations so that the first fluid travels substantially parallel with the second fluid providing a large interface area between the first and second fluids along which the static pressure of the two fluids remains substantially constant.
Still another object of this invention is to provide a cylindrical jet pump which can be operated at efliciencies above 50%, said pump having a mixing chamber which converges to a diameter at its downstream end which exceeds the diameter of the jet discharge orifice for the drive fluid by an amount substantially equal to twice the tangent of approximately 252 times the length of the mixing chamber.
Yet another object is to provide a method of operation of a jet pump so that the weights of the primary and secondary streams and the densities of the fluids are correlated with the jet pump dimensions according to the fiollowing relationship:
2 tan 252 approximately v is the exit velocity of the mixture from the mixing chamber in feet per second;
p is the density of the primary and secondary fluids which are substantially equal; and
D, is the pump nozzle discharge orifice diameter.
These and other objects of the present invention will become more apparent from the following description and appended claims when read in conjunction with the accompanying drawings wherein:
FIGURE 1 is a sectional view of a prior art jet pump;
FIGURE 2 is a sectional view of one form of jet pump of this invention;
FIGURE 3 is a top view of the interior portion of the jet pump of FIGURE 2 taken substantially along line 3--3 of FIGURE 2;
FIGURE 4 is an enlarged view of the diverter vanes from the jet pump of FIGURE 2;
FIGURE 5 is a transverse sectional view substantially along line 5-5 of FIGURE 2;
FIGURE 6 is a top view similar to FIGURE 3 of another embodiment of the jet pump of this invention;
FIGURE 7 is a sectional view of the jet pump of FIG- URE 2 with an adjustable wedge;
FIGURES 8, 9 and 10 are sectional views of other embodiments of the jet pump of this invention;
FIGURE 11 is an axial sectional view of still another embodiment of the jet pump of this invention;
FIGURES 12-15 are transverse sectional views substantially along lines 1212 to 15-15 of FIGURE 11;
FIGURE 16 is a plot of the relation of the efliciency of constant pressure mixing jet pumps constructed in accord with the present invention to the ratio of their throat and suction velocities;
FIGURE 17 illustrates a test pump set up and the measured and the critical pressure curves for that pump;
FIGURE 18 illustrates one arrangement for compounding jet pumps constructed in accord with the present invention; and
FIGURE 19 illustrates a second arrangement for compounding jet pumps constructed in accord with my invention.
Referring to the drawings wherein like numerals are used throughout to identify like parts, FIGURE 1 discloses a basic prior art jet pump comprising a primary motive or driving fluid flow conduit 10 bounded by straight rectilinear, usually cylindrical side walls 11 which converge axially to form a nozzle 12 axially spaced from an entrainment area or mixing chamber 14 having opposed rectilinear side walls 16 and a flanged inlet end portion 18. The space between the tip of nozzle 12 and the surrounding portions of wall 18 provides an annular inlet throat for the secondary fluid into the jet pump mixing chamber. As the primary or driving fluid accelerates to flow through converging nozzle 12, its static pressure decreases. Upon admission of primary fluid into mixing chamber 14, through nozzle 12 its fluid velocity gradually decreases from a maximum at the jet outlet to the velocity of the mixture and its static pressure gradually increases, creating a low pressure region at the nozzle outlet and a progressively increasing pressure region throughout the mixing chamber length (see FIGURE 6, page 177, University of California Publications in Engineering, vol. 3, No. 3). The secondary fluid which is at a higher static pressure than that present in the mixing chamber is thus induced into the low pressure region of the mixing chamber. The prior art jet pump of FIGURE 1 effects mixing of the primary and secondary fluids substantially by a batch process, wherein the secondary fluid mixes with the primary fluid in the mixing chamber effectively only at one axial location. Consequently, turbulence and secondary flow losses are extremely high.
FIGURE 2 shows a jet pump in accord with this invention. The primary or driving fluid conduit 19 is axially disposed within a pump housing 21 and comprises upper and lower side walls converging axially into nozzle 24 which is integral with axially diverging side walls 26 of an entrainment area or mixing chamber 25. The included angle between the walls 26 is preferably in the order of 6 to 12. Thus, the upper and lower boundaries of the primary flow conduit and the mixing chamber are formed of integral opposed walls having straight sections 20, converging arcuate sections forming nozzle 24 and diverging wall portions 26 and the walls 26 are located substantially along the natural angle of divergence of the jet and form a physical boundary between the region in which the secondary fluid inlet velocity is measurable and the zone of mixture of primary and secondary fluids.
Secondary fluid flow conduits 23 are formed by the spacing of primary conduit side walls 20 and housing walls 22. The secondary fluid is at a low energy state in conduits 23 and the primary fluid which is at a higher energy level imparts its energy to the secondary fluid during entrainment thereof.
The pump primary conduit and mixing chamber walls may be mounted in the pump housing, as shown in FIG- URE 5, by welding or otherwise attaching the axially extending side edges of walls 26 in fluid tight relation to housing 21. Alternatively, integral pump primary flow conduit 19, nozzle 24 and mixing chamber side walls 26 may be formed as a unitary casting of cylindrical crosssection which may be mounted within a cylindrical housing by suitable brackets and supports (not shown).
The mixing chamber side walls 26 are provided with a plurality of axially spaced inlets 28 which may be either transversely extending slots 31 forming an oblique angle with the pump axis as shown in FIGURE 3, or spaced through-apertures 32 as shown in FIGURE 6. In these embodiments, each secondary flow inlet is provided with an axially extending fluid diverter vane 30 protruding into the mixing zone and arranged to direct secondary flow substantially parallel to primary fluid flow through mixing chamber 25. The mixing operation of the jet pump of FIGURE 2 is, thus, continuous and differential wherein the secondary fluid is mixed with the primary fluid in small increments axially along the mixing chamber. The preferable axial spacing of openings 31 or 32 is just sufficient to allow thorough mixing of the secondary fluid from the first inlet with the drive fluid before secondary fluid from the second inlet contacts the drive fluid and so on successively and continuously along the mixing chamber. The exact size and spacing of the openings 31 or 32 depends upon the viscosity of the drive fluid and the pumping velocity, the critical factor being the maintenance of the static pressure within the mixing zone substantially constant along the entire length of the walls 26.
The diverter vanes 30 reduce impact losses between the secondary fluid and primary fluid by lowering turbulence at the points of impact. The substantially parallel travel of the fluids through mixing chamber 25 provides a large fluid interface area for mixing without excessive turbulence.
Each vane, as best illustrated in FIGURE 4, axially tapers in the direction of fluid flow from the entrance edge 36 of inlet 28 forming an arcuate tapered wedge having be obtained in reducing turbulence and impact losses by' arranging the slots at an oblique angle to the axis of the pump. It has been empirically determined that for most eflicient pump operation, the slots should intersect the pump axis at an angle of about 30. Similarly, apertures 32 may be aligned to form rows which intersect the axis of the pump at an oblique angle. Such a distribution of secondary fluid inlets systematically further increases the primary-secondary fluid interface area in the mixing chamber to provide optimum mixing conditions throughout the mixing zone.
Primary fluid flow conduit 19, nozzle 24 and diverging side walls 26 of the mixing chamber form smooth curves and may be highly polished to present substantially frictionless surfaces for low resistance to fluid flow during pump operation if contact occurs. With such construction, the frictional flow losses are substantially reduced over the prior art jet pumps. Energy losses due to expansion of the primary fluid in the mixing chamber are substantially eliminated since side walls 26 diverge at about the angle of expansion of the primary stream in the mixing chamber thereby eliminating interception of the side walls before complete mixing is accomplished.
In operation of the jet pump, the primary fluid is initially forced through conduit 19 under a predetermined head provided either by the force of gravity or an auxiliary pumping unit (not shown). The fluid accelerates when it enters the convergent section of nozzle 24 because of the difference in cross-sectional area between the inlet portion of primary conduit 19 and the convergent section of nozzle 24. In jet pumps utilizing liquids, the exit velocity is chosen slightly below that which would reduce the liquid pressure to its flash point or vapor pressure. When the fluids are vapors or gases, I prefer to use nozzle exit velocities which are slightly subsonic, in the order of 1300 ft./sec. for example, to avoid the problems inherent in supersonic nozzle design. This increase in velocity causes a reduction in the fluid static pressure pv, which effects a low pressure area surrounding the drive fluid jet as it extends into the mixing chamber. Secondary fluid from secondary conduits 23 being at a higher pressure is induced through inlets 28 into fluid communication and entrainment with the drive fluid in the mixing chamber. The diverging chamber side walls enable the chamber to be so designed that the static pressure of the drive fluid is maintained constant and if liquids are involved but slightly above the liquids vapor pressure throughout the chamber length to provide a high entrain-' ing force without cavitation or fluid expansion losses.
If the secondary fluid is a condensable vapor such as steam and the primary fluid a cooler liquid such as water, the steam will condense upon contact with the water in the mixing chamber. If the steam enters the mixing chamber at a severe angle to the axis of the water flow, it will penetrate the water surface and condense in the stream of water rather than at the interface on the surface of the water stream. Instantaneous condensation of the steam bubbles within the water causes high turbulence and cavitation which contribute to extremely low efliciency of jet pumps. Cavitation is substantially reduced, however, in the jet pump shown in FIGURE 2 by diverter vanes 30 and diverging side walls 26 of the mixing chamber which direct secondary fluid flow substantially parallel with the stream of primary fluid in the mixing chamber thereby increasing the interface area between the primary and secondary fluids and substantially preventing impingement of walls 26 prior to complete mixing of the fluids. Arranging slots 31 of FIGURE 3 or holes 32 of FIGURE 6 obliquely to the axis of the jet pump, as explained, creates an even greater interface area between the primary and secondary fluid thereby further increasing the efficiency of the pump by continuously contacting the upper and lower surfaces of the drive fluid with secondary fluid. A comparison of FIGURES 1 and 2 shows several basic structural differences between the jet pump of the instant invention and that of the prior art. For example, in the high efliciency jet pump of FIGURE 2, nozzle 24 and mixing chamber walls 26 are integral such that the front throat portion 27 of mixing chamber 25 is the same diameter as nozzle 24. Mixing chamber walls 26 are divergent rather than straight thereby providing a greater cross-sectional area for mixing as the axial distance from nozzle 24 increases and preventing interception of the.
chamber side walls before complete mixing is accomplished. Also, the mixing chamber is provided with a plurality of secondary fluid inlets 28 rather than a single annular inlet such as that between nozzle 12 and side wall edges 18 of the FIGURE 1 prior art pump. Each of the inlets of the high efiiciency pump of FIGURE 2 is further provided with a diverter vane 30 which directs the incoming secondary fluid substantially parallel with the expanding accelerated primary fluid in the mixing chamber thereby providing a greater interface area between the primary and secondary fluids reducing penetration of the primary fluid into the secondary fluids and turbulence within the primary fluid. The greater surface contact area of the parallel streams of fluids enables condensation to be completed at the interface rather than within the primary fluid as commonly occurs in prior art pump structures. Each feature of the jet pump of FIGURE 2, thus, contributes to the increases in efliciency over prior art pumps.
It is possible to determine the dimensions for maximum efliciency of the jet pump of FIGURE 2 from a consideration of the energy relationships in the mixing chamber. From the general energy balance, the sum of the primary fluid energy and the secondary fluid energy minus the primary and secondary fluid expansion losses and the primary fluid impact losses equals the final fluid energy in the mixer exit portion.
The primary fluid expansion loss can be expressed as and the secondary fluid expansion loss can be expressed as V 2 V Z fag g fdwa) where secondary fluid at distance x from the primary fluid nozzle) s=secondary fluid entrance conditions.
The impact loss for the primary driving fluid can be expressed as p v x s 2 f g dwa where V =secondary fluid velocity, ft./sec. w =secondary weight flow rate, lb./sec.
The'primary and secondary fluid energies may be expressed according to thermodynamic incompressible fluid flow equations as respectively and the final output energy in the mixing chamber may be expressed as where:
w=flow rate, lbs/sec.
. p pressure, lbs./ft.
Thus, the energy balance for the jet pump of FIGURE 2 may be expressed as:
y g dw fdw f g dw The general solution to the foregoing energy balance equation after differentiation and mathematical reduction to lowest terms is:
where c is a constant equal to It has been found empirically that the value for at maximum efficiency of the pump is about 6 to 12 (see Applied Thermodynamics by Faires, pages 142, published by MacMillan Co., copyright 1936 and 1938). Also at maximum efficiency p v the static pressure of fluid moving through mixing chamber is a constant value slightly above the vapor pressure of the primary driving fluid. Thus, by assigning arbitary desired values to the velocities and flow rates, the relative dimensions of the primary conduit, the secondary conduit and the mixing chamber can be determined for maximum efficiency operation of the jet pump.
Although the energy balance equation used as a basis for deriving the general design solution was based on an incompressible fluid behavior, the general solution is valid for a gaseous fluid providing that both primary and secondary fluids enter the entrainment area at approximately the same temperature.
A jet pump having a square cross-section with an inclusive angle of 6 for the diverging mixing chamber side walls and a plurality of slots arranged at to the pump axis with none of the slots overlapping axially was designed using the foregoing design equations and the following conditions for water as both the primary and secondary fluid:
a primary fluid pressure head of 70 feet measured in feet of water absolute (/1 a secondary fluid pressure head of 34 feet measured in feet of water absolute (/1 the flow rates of the primary fluid and secondary fluid were made equal at 2.4 lbs. per second a final static pressure of the mixed fluids of zero (pv=0); a secondary fluid velocity of 46.8 feet per second; and
a primary fluid velocity of 67.2 feet per second.
The designed jet pump for an output of 4.8 pounds per second had a slot depth of .0614 inch, a nozzle area of .000625 square feet, and a mixing chamber length of 1.44 inches.
Jet pumps normally have an average efficiency value of about 25%. The jet pump of the above design had an efficiency of greater than 50%. The efficiency of a jet pump as used for comparison here is defined as the ratio of the pumping energy given up by the drive fluid to the pumping energy absorbed by the secondary fluid. It is calculated by multiplying the ratio of the difference between the fluid head in the mixing chamber and the fluid head in the secondary conduit to the difference between the fluid head in the primary conduit and the fluid head in the mixing chamber by the ratio of the flow rate in the secondary conduit to the flow rate in the primary conduit or expressed mathematically:
As shown in FIGURE 7, a control rod or axially adjustable wedge 48 may be used in combination with the jet pump of this invention. Adjustable wedge 48 comprises a solid wedge shaped end portion 50 having opposed arcuate surfaces 52 joined to a shaft portion 54. Shaft portion 54 may be slidably mounted in a suitable fixture such as bracket 56 fixedly mounted on jet pump housing wall 22. Shaft 54 is axially slidable in bracket 56 so that wedge portion 50 can be moved toward and away from nozzle 24. By selectively positioning wedge portion 50, the weight ratio of the primary drive fluid to the secondary fluid can be selectively varied. Also, the angle at which the primary fluid travels through entrainment area 25 can be varied, compensating for any variations in the flow properties of the secondary fluid entering the entrainment area through inlets 28. For example, a variation in secondary fluid density may cause certain secondary fluids not to flow parallel with the primary fluid flow since the diverter vanes are designed for a fluid of a specific density. Thus, by varying the path of the driving fluid, the angular contact between the primary fluid and secondary fluid can still be controlled so that the fluids move substantially parallel to each other providing the desired large interface contact area between the fluids.
Adjustable wedge 48 is also valuable in maintaining a high degree of efficiency when the weight ratio of the primary drive fluid to the secondary fluid has been changed, consequently varying the relative flow properties of the fluids in the mixing chamber. By selectively positioning adjustable wedge 48, any changes in the weight ratios of the two fluids can be compensated for so that the flow directions are maintained substantially constant. The beneficial effects of a mixing chamber having diverging walls also can be obtained as shown in FIG- URE 8, by varying the inlet configuration for the primary drive fluid. In this embodiment of the invention, the primary conduit 119 is enclosed by upper and lower walls 120 integrally connected to a converging nozzle portion 124 which is integrally joined with a pair of drive fluid injecting unit walls 126 having a plurality of openings 128 therein. Injector walls 126 converge to a wedgeshaped transverse end edge 130. The effect obtained by the diverging mixing chamber walls of the jet pump of FIGURE 2 is obtained in the jet pump of FIGURE 8 by means of converging walls 126 which provide diverging low presure mixing zones 127 with the pump housing 131. Diverging zones 127 are dimensioned to maintain a constant static pressure throughout. Openings 128 are preferably provided with vanes as shown in FIGURE 4 to direct the primary fluid substantially parallel with the induced secondary fluid flow into low pressure regions 127. In the jet pump of FIGURE 8, secondary flow is induced into the mixing chamber in increments due to the successive reduction in pressure at axially spaced inlets 128. As previously discussed, fluid mixing occurs at the large interface area between the primary and secondary fluids.
Another embodiment of this invention is shown in FIG- URE 9, as having a housing 132 with straight side wall portions 133, converging wall portions 134 and diverging wall portions 136. The primary flow conduit 140 is bounded by walls 142 which are integral with pump nozzle 144. The secondary fluid flow conduit 146 is formed between housing straight portions 133 and primary conduit walls 142.
Nozzle 144 is integral with a pair of slightly converging injector walls 148 having primary fluid inlets 150 axially spaced therein and angled to permit primary fluid flow into the mixing portion 152 of the pump in increments as in FIGURE 8. Slightly converging walls 148 and diverging walls 136 of the pump housing form a pair of substantially divergent mixing chambers 151 therebetween.
Walls 148 of the primary flow injector are integrally joined with a wedge shaped block 154 having opposed arcuate surfaces 153 which extend axially toward the pump outlet providing smooth surfaces for guiding and intermingling mixed fluids from the upper and lower mixing zones as they travel axially toward the pump out let to the right of FIGURE 9.
In the embodiments shown in FIGURES 8 and 9, it should be clear that either the drive fluid or the driven fluid may flow through the outer conduit depending on the location of the pump nozzle. For example, as shown in FIGURE 10;, the central conduit may carry the sec ondary fluid fiow and the outer coaxial conduit may carry primary fluid flow. In such a pump the injector portion 160 is connected directly to the secondary flow conduit walls 162.
I have further discovered that it is possible to obtain high jet pump efliciencies without using a plurality of inlets from the secondary fluid conduit into the mixing chamber and without using a diverging mixing chamber.
It is essential, however, that the pump he closely designed to maintain a constant primary fluid static pressure throughout the mixing chamber and that the expanding drive fluid not intercept the mixing chamber side walls prior to complete mixing of the fluids. This embodiment of the invention is representediin FIGURE 11 which shows a cylindrically-cross-sectioned jet pump.
As previously explained (Applied Thermodynamics by Faires, page 142, published by-MacMillan Company, copyright 1936, and 1938) the natural expansion angle for fluids, after passing through a constrictive throat or orifice, for minimum turbulence is in the orderof 6 to 12". Experiments have shown that in a jet pump, a jet pump, a jet of primary or motive fluid discharging from a circular orifice into a coaxial mixingchamber will expand in a cone form having an apex angle of 5 44' plus or minus a few minutes, as shown in FIGURE 11, until the periphery of the expanding jet intercepts the chamber side wall. If the secondary fluid is induced into the mixing chamber in surrounding relation to the primary fluid orifice at a lower velocity than the velocity of the primary fluid, the portion of the chamber between the plane of the primary fluid orifice and the plane of intercept of the conical stream of primary fluid with the chamber wall will form the mixing zone for the primary and secondary fluids and at that intercept plane, the mixed fluid will have a velocity determined by the energy of the primary and secondary fluids as they enter the mixing chamber and the losses within the mixing chamber.
In the embodiment illustrated in FIGURE 11, the cylindrical primary conduit 166 extends through an openi ig in secondary conduit wall 168 and is in fluid tight relation with the edges of the opening. The primary fluid discharge nozzle 170 has a sharply axially tapered lip 172 so that, at the discharge orifice 174, the paths of flow of the primary and secondary fluids are substantially parallel as in the FIGURE 2, 7, 8 and 9 embodiments. The fluid velocities measurable within the mixing zone (the region between the section planes 1212 and 1515) are, as illustrated in FIGURES ll, 14 and 15, in the center; the discharge velocity of the primary fluid from the jet (V,-) at the periphery; the velocity of the secondary fluid (V 'as it enters the mixing chamber; and, in between, the velocity of the mixture v(V as it exists at the downstream end of the mixing chamber as represented by the section plane 1515. As is apparent from FIGURES 11-15, the cross-sections of the regions in which the velocities Vj and V exist gradually decrease in area along the length of the mixing chamber from maximums in the plane 12-12 to zero at the downstream end of the mixing chamber in the plane 15-15; and the region intermediate the planes 1212 and 1515, the crosssection in which the velocity V exists, gradually expands in cross-section from a continuous line at the plane 12-12 of the primary nozzle until it is equal in crosssection to the cross-section of the mixing chamber at its downstream end in the plane 15-15.
I have found that, if the mixing chamber is properly designed for the required flow conditions so that the static pressures, pv (where p is the pressure in pounds per square foot and v is the specific volume in cubic feet per pound), are constant, for example, and if the primary, secondary and mixed stream are equal and constant (p -v =p v p v =c), the boundary layers 176 and 178 between the regions in which the velocities V V and V exist throughout the mixing chamber are quite sharply defined and the efiiciency of the jet pump is, as a result, greatly increased.
For blunt enclosed nozzles, a region of turbulence exists at-the initial juncture of the primary and secondary streams. While the configurations of the regions in which the velocities V and V exist in the mixing chamber remains substantially the same as illustrated in FIGURES 12-15, the Value of the velocity V within-the intermediate region between boundary layers 176 and 178 is not uniform n-or, except at the downstream end of the mixing chamber (the plane 1515), equal to the velocity V The velocity within this region between boundary layers 176 and 178 is a diflerential variable (dV gradually increasing in value from the plane 1212 of the jet orifice to the value V at the plane 1515 at the 'downstream end of the mixing chamber. As a result, the losses in the mixing chamber are higher when a blunt end nozzle is used than when a sharply tapered nozzle as illustrated in FIGURE 11 is used.
I have found that the static pressure pv within the mixing chamber can be maintained constant if and only if the wall 180 of the mixing chamber converges throughout its length between the planes 1212 and 1515, i.e., if the mixing chamber is of gradually decreasing cross-sectional area normal to the jet axis from the plane 12-12 of initial intermixture of the primary and secondary fluids to the plane 1515 of intercept withthe chamber wall of the lines tangent to the primary jet orifice and intersecting'the jet axis at an angle of about 544. (as indicated by the conical boundary layer 176), i.e., the plane at which the stream discharged from the nozzle would normally intercept the chamber wall. Considered another way and applied specifically to orifices and chambers of circular cross-sections about a common axis, as illustrated in FIGURES 12-15, the mixing chamber must converge throughout its length from plane 1212 to plane 15'15 and have a diameter D, at its downstream end at the plane 1515 which exceeds the diameter of the discharge orifice for the primary stream D, by an amount in the range substantially equal to twice the tangent of 252 times (i.e., approximately .10014 times) the length of the mixing chamber. Stated mathematically, D =D +2 tan (252')x. When this relation exists, the jet pump can be operated at efiiciencies above 50% as compared with a normal 20 to 25% efiiciencies found in jet pumps, see Mechanical Engineering Handbook by Marks, 5th edition, McGraw-Hill Book Company, at page 1833.
The design equations for a pump of the type of FIG- URES 11-15 follows. The General Energy Equation for a standard jet pump having a parallel sided mixing chamber is: primary fluid energy+secondary fluid energyimpact lossexpansion lossfriction loss=mixed energy. Stated mathematically:
The friction loss may be ignored providing V is small. Since the secondary fluid is the fluid that rubs the sides of the mixing chamber and it is constant throughout the mixing process it can be computed readily if V is larger.
Ignoring friction loss and solving the energy equation for the pump of FIGURE 11 it reduces to:
When W W V V are selected for design condition this equation is solved for V V is the velocity after the primary and secondary fluid are mixed.
When V is determined the area of the throat is:
The diameter of the throat then is:
Solving for V, by quadratic equation:
v 70 F. for water=.01606 fb.
A .00260045 ft.
Total area=A,-|A,=.68968 in. +.l1946 in.
Inlet total diameter= =l 015 in 3.1416
Since p v =p v =p v for a constant pressure mixing process,
Efficiency-- v2 Eflicieney For w -w,,
V-V., 2 2 From General Energy Equation solving for VP,
Efficiency V mV Substituting,
2 2 Efiiciency= (mvs) 5 It should be noted, as is apparent from FIGURE 16, that when the V,/ V ratio (m) is infinite, the efficiency is 50.0%. 1
As proof of the foregoing theory, I have constructed a jet pump substantially in accord with FIGURE 11 but with a straight section of uniform cross-section interposed between the mixing chamber and the diffuser as is illustrated at the top of FIGURE 17. FIGURE 17 pro- 20 vides a comparison between the theoretical pressure curve and the actual measurements which were made.
For this test of the constant pressure mixing pump illustrated in FIGURE 17, the inlet pressure was 20.5 p.s.i.g.; and at the flo-W orifice, for the primary fluid 25 Ap"H =4.8 and for the secondary fluid ApH =4.8.
The total flow by weight measurement was 332 min.=39.6 g.p.m.
The pressure reading, which are plotted in the center of FIGURE 17, were:
7. It will be noted that there is a dotted path between pressure tap No. 6 and pressure tap No. 7, since I am not quite sure of the pressure plot between these two plots. However, from past testing I know basically what is happening. The location of the throat in this test model is not quite properly located from the nozzle. The throat location is too far away and the natural expansion of the primary jet has intercepted the sides of the mixing chamber before the throat is intercepted. This causes an over expansion of the primary jet and an expansion loss. Immediately after the interception of the mixing wall by the primary jet there has to be a contraction or the mixture has to speed up thereby decreasing its static pressure in order to go through the smaller area of the throat. From pressure taps No. 7 through No. 10 the mixture is getting back to equilibrium conditions after the contraction. From pressure tap No. 10 to No. 11 is the standard pressure loss due to friction. The reason why the pressure did not go back to approximately pressure ft. H O gage at pressure tap No. 10 is due to the friction loss between pressure tap No. 7 and pressure tap No. 10 and the slight expansion loss experienced by the main or primary fluid jet over expanding.
From past experience a correction of .050" or less in throat location will correct this situation.
This difference between the theoreticaland test curves does not indicate an error of any appreciable magnitude in the formula for mixing length but rather the critical importance of departures from it. For example, if the primary fluid jet nozzle is not accurately aligned with the Press. Tap No 1 2 3 4 5 6 7 8 9 10 11 "H 15 10 0 1. 9 2. 4 2. 3 1. 9 2. 2 Ft. H 0 17 113 0 227 283 283 2. l5 2. 72 2. 61 2. 15 2. 49
The jet and throat velocities were:
Jet velocity 20.0 g.p.m., design 53.8 ft./sec., actual 53.84 ft./sec.
Throat velocity 40.0 g.p.m., design 34.35 ft./sec., ac-
tual 34.35 ft./sec.
From the measured data:
The actual efliciency was therefore:
w,(H.-H, 2.781(16.20 1.52 Emc1ency w, (H, H. 2.7s1 44.97 16.20)
The V /V ratio was:
3.005" from the nozzle or at .005" past pressure tap No.
axis of the mixing chamber, then there will be an interception of the mixing wall by the primary fluid before the throat is reached. Also, as indicated above, the theoretical angle of expansion of the primary jet as found experimentally by myself of 5 44' may be a few minutes in error.
It will be noted from FIGURE 16 that the test pump gave an efliciency of 51% as opposed to 63% from the theoretical efficiency at a V V ratio of 3.69. By properly locating or adjusting the throat location an efliciency of 63% would have been obtained.
A straight section after the convergent mixing section was included in the test pump illustrated at the top of FIGURE 17 to detect if the throat location was correct. In an actual jet pump with proper throat location this straight section is unnecessary as indicated in FIGURE 11.
The jet pump as depicted in FIGURE 11 and expanded upon in FIGURE 12 through FIGURE 15 is superior in all cases to the differential jet pump depicted in FIG- URE 2 through FIGURE 10. There are two reasons for this: (1) the FIGURE 11 pump is easier to build and design, (2) of the two losses (neglecting friction) occurring in a standard jet pump, expansion loss and impact loss the pump of FIGURE 11 completely eliminates the expansion loss and the differential pump of FIGURES 2-10 does not completely eliminate it. 7
Since the pump of FIGURE 11 completely eliminates the expansion loss and only the impact loss is left, by compounding the pump of FIGURE 11 the efliciency of this pump may be increased at any V /V ratio and the 15 impact loss may be reduced thereby. This may be done in the manner illustrated in FIGURES 18 and 19.
As indicated above, the efficiency of the FIGURE 11 jet pump is dependent only upon the V,,/ V ratio for any particular w /w ratio and the loss is impact only at The closer the V /V ratio becomes to unity, the higher the efliciency will be. For any particular V V ratio for a single stage, the ratio may be made more nearly unity by compounding the pump and still operating at the overall V /V ratio for a single stage pump, thereby increasing the efliciency as graphed for a single stage pump in FIGURE 16.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
What is claimed and desired to be secured by United States Letters Patent is:
1. The combination in a jet pump or the like of axially elongated housing means, means providing a first fluid conduit means in said housing means, means providing a second conduit means in said housing means in overlying relationship to said first conduit means, means for elfecting flows of primary and secondary fluids through said first and second conduit means, means providing in said housing means a diverging mixing chamber for the primary and secondary fluids, means for accelerating the primary fluid and directing said accelerated fluid from the conduit means in which it is flowing into said diverging mixing chamber at the upstream end thereof, means for introducing the secondary fluid into said diverging mixing chamber for entrainment by the primary fluid in distinct increments at intervals spaced along said mixing chamber and in a direction substantially parallel to the flow of primary fluid, said mixing chamber being dimensioned to maintain the static pressure on the fluids flowing therethrough substantially constant from the upstream end thereof to the downstream end thereof and the angle of divergence being approximately equal to the angle of expansion of the primary fluid in said mixing chamber to minimize energy losses attributable to expansion of the primary fluid; and discharge means communicating with the downstream end of the mixing chamber for conducting from said chamber the primary and secondary fluids introduced therein from said first and second conduit means.
2. The combination of claim 1, wherein the mixing chamber providing means comprises a diverging apertured member extending from the outlet of the first fluid conduit means generally to the downstream end of the flow passage in said housing means and flow directing means on said member adjacent each of the apertures therethrough for directing fluid flowing from said second conduit means through said apertures into said passage into contact with the fluid flowing into said passage from said first conduit means in streams which are generally parallel to the longitudinal axis of the flow passage.
3. The combination of claim 2, wherein the apertures in said diverging member are oriented at an oblique angle relative to the longitudinal axis of the flow passage.
4. The combination of claim 1, together with means disposed in said housing means for selectively varying the ratio of primary fluid to secondary fluid in the fluid flowing through the mixing chamber.
5. The combination of claim 1, wherein the angle of divergence of said mixing chamber is in the range of from about 6 to about 12.
6. The combination in a jet pump or the like of axially elongated housing means, a first fluid conduit means having an outlet communicating with the interior of the housing means at a first, upstream end thereof, a second fluid conduit means having an outlet surrounding the outlet of the first conduit means, said second fluid conduit means communicating with the interior of the housing means at the upstream end thereof, means for eifecting flows of primary and secondary fluids through said first and second fluid conduit means into said housing means, means including a converging section of said housing means for providing in said housing means a primary and secondary fluid flow passage having an inlet communicating with the outlets from the first and second fluid conduit means and for maintaining the static pressure exerted on the fluid therein generally uniform the length of the passage, and discharge means communicating with a second, downstream end of the housing means for conducting from said flow passage the primary and secondary fluids introduced therein from said first and second conduit means.
7. The combination of claim 6, wherein the diameter of the downstream end of the covering housing means section exceeds the diameter of the outlet of the first conduit means by an amount in the range of one-tenth of the length of the converging section.
8. The combination of claim 6, wherein said first conduit means terminates in orifice means capable of producing contact of the primary and secondary fluid along interfaces which are generally parallel to the converging section of the housing means and thereby minimizing turbulence-induced energy losses in said flow passage.
9. A multistage jet pump or the like in which the initial stage comprises housing means, a first fluid conduit means having an outlet communicating with the interior of the housing means at a first, upstream end thereof, a second fluid conduit means having an outlet surrounding the outlet of the first conduit means, said second fluid conduit means communicating with the interior of the housing means at the upstream end thereof, means for effecting flows of primary and secondary fiuids' through said first and second fluid conduit means into said housing means, means for providing in said housing means a primary and secondary fluid flow passage having an inlet communicating with the outlets from the first and second fluid conduit means and for maintaining the static pressure exerted on the fluid therein generally uniform the length of the pas sage, and in which each succeeding stage comprises housing means, fluid conduit means having an outlet communicating with the interior of the housing means at a first, upstream end thereof, means for effecting a flow of fluid through said fluid conduit means into said housing means, means for providing in said succeeding stage housing means a primary and secondary fluid flow passage having an inlet communicating with the outlet from the fluid conduit means and for maintaining the static pressure exerted on the fluid therein generally uniform the length of the passage, and means providing fluid communication between the upstream end of said flow passage and the downstream end of the primary and secondary fluid flow passage of the preceding stage, and including discharge means communicating with a second downstream end of the housing means of the last stage for conducting from the flow passage thereof the fluid introduced therein.
10. The multistage jet pump of claim 9, wherein there are at least two initial stages as aforesaid, the downstream ends of the primary and secondary fluid flow passages of said initial stages being connected in parallel to the upstream end of the primary and secondary fluid flow passage of the succeeding stage of the pump.
11. The combination in a compound jet pump or the like of axially elongated housing means, a first fluid conduit means having an outlet communicating with the inten'or of the housing means at a first, upstream end therea second fluid conduit means having an outlet surrounding the outlet of the first conduit means, said second fluid conduit means communicating with the interior of the housing means at the upstream end thereof, means for effecting flows of primary and secondary fluids through said first and second fluid conduit means into said housing means, means for providing in said housing means a series of primary and secondary fluid flow passages of successively smaller cross sectional area and for maintaining the static pressure exerted on the fluid therein generally uniform the length of each said passage, the first of said passages having an inlet communicating With the outlets from the first and second fluid conduit means, and each succeeding flow passage having an inlet communicating with the outlet of the preceding passage, and discharge means communicating with a second, downstream end of the housing means for conducting from the last of said flow passages the primary and secondary fluids introduced into said housing means from said first and second conduit means.
References Cited UNITED STATES PATENTS Re. 19,581 5/1935 Justheim 230-92 561,160 6/1896 Du Faur 230-92 571,022 11/1896 Schutte 230-95 580,762 4/1897 Brooke 103-265 904,276 11/ 1908 Prache 230-95 1,228,608 6/1917 Scanes 230-95 1,936,246 11/1933 Carter et a1. 230-92 2,172,522 9/1939 Sline 230-95 2,180,259 11/1939 Sargent 230-95 15 3,123,285 3/1964 Lee 230-95 DONLEY J. STOCKING, Primary Examiner.
W. I. KRAUSS, Assistant Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,371,618 March 5,
John Chambers It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:
Column 6, line 19, for column 7, about lines 24 to equation reading ZV-V same c61umn 7, line 38, for line 66, for
"increases" read increase 32, for that portion of the read "pages" read column 12 Column 15 line 22 for "covering" read converging Signed d sealed this 24th day of June 1969.
2 V =ZV V read (SEAL) Attest:
Edward M. Fletcher, J r.
WILLIAM E. SCHUYLER, JR.
Attesting Officer Commissioner of Patents
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