Note: Descriptions are shown in the official language in which they were submitted.
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BACKG~O~JND OF THE INVENTION
Field of the Invention
5 The invention relates to a propulsive apparatus for displacing a main fluid
within a duct, and resembles a iet pump or ejector pump as used for pumping
fluids, or solids suspended in fluids.
Prior Art
Jet pumps or ejector pumps have been used for many years and are
characterised by a duct into which one or more jets of driving liquid are
directed. The driving liquid propels the main fluid within the duct by transfer
of the momentum of the driving liquid to the main fluid. The present
15 invention relates to a particular type of jet pump known as a "peripheral jetpump", in which a series of jets ars spaced around the periphery, thus
leaving the centre of the duct free of obstructions. This permits the pump
to pump objects suspended in the main fluid having a maximum si~e which is
slightly less than cross-section of the duct. Many applications for this type
20 o~ pump have been devised, such as pumping fish, fruit, or vegstables or
other objects that are fragile and would be damaged by other types of pumps
or conveying systems.
In general, prior art jet pumps are characterised by relatively low efficiency
25 when compared with conventional fluid pumps, but this low efficiency i3
tolerated for the benefits of relatively gentle handling of delicate solids.
The low efficiency of prior art jet pumps requires the use of relatively high
powered units to pump the driving liquid, and this results in high energy
costs and considerable space requirsments where the pump is to be used.
30 When such pumps ars used for pumping fish on small fishing boats, the size ofthe power plant necessary to power the driving liquid can become excessive
and thus limits the use oF such pumps. ~n example of an ejector pump using
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two sets of jet nozzles inclined at different angles to the duct axis and
spaced along the axis is shown in U.S. Patent 4,155,682, issued to Hillis.
Spacing between the two sets of jet nozzles increases length of the jet pump
necessary for mixing of the fluids, and use of two separate sets of nozzles
5 increases cost of the pump.
The height to which the pump can maintain a column of water is limited by
pun p efficiency and available power. When using various types of pumps, it
is known to inject air into the column of water and fish as it is drawn from a
10 fish net or hold of a boat. The injected air reduces effective density of theliquid or liquid/solid mixture within the column and this is commonly called
an "air assist" lift pump. An example of a fish pump using air assist is shown
in U.S. Patent 2,736,121, issued to Kimmerle. This pump is characterised
by complexity, and therefore cost and the number of parts which can
15 damage fish drawn through the pump. A pump using air assist in combination
with a jet pump i9 shown in Japanese publication 56-41500, but this has a
central obstruction in the duct which limits size of product being handled
and also could damage the product.
2 0 SUMM~RY OF THE I~lVENTlnN
The present invention reduces the difficulties and disadvantages of the prior
art by providing a propulsive apparatus or jet pump with improved
efficiency, which permits a reduction in the size of power unit for moving a
25 given amount of fluid, or alternatively increases the height to which a fluid can be drawn. This improvement in efficiency is attained without
increasing complexity of the apparatus, because most of the apparatus has
basically no moving parts. Similarly to prior art peripheral ~et pumps, the
invention provides a duct without obstruction, thus permitting movement of
30 solids having a maximum size slightly less than the size of the duct.
Furthermore, pressure of the working liquid is relatively low, so that
impinyement of the working liquid on the solids causes negligible damage.
Air assist in combination with a diverging or diffusing outlet portion further
improves lift capability.
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A propulsive apparatus according to the invention is for displacing
a main liquid and includes a duct, a driving liquid manifold and
first and second sets of inwardly facing jet nozzles. The dust
extends along a duct axis and is for receiving the main liquid, and
has a duct side wall to define in part a mixing portion have a
constant cross-sectional area. The duct side wall also defines in
part inlet and outlet portions spaced on upstream and downstream
sides respectively of the mixing portiGn. The driving liquid
manifold cooperates with the duct and is adapted to receive
pressurized driving liquid. The jet nozzles are disposed adjacent a
transverse plane of the duct, and cooperate with the duct side wall
and the manifold to pass the driving liquid into the mixing portion.
The first and second sets of jet nozzles have respective first and
second jet axes inclined at respective first and second angles to
the duct axis, in which the first angle is greater than the second
angle. The first and second sets of jet nozæles alternate with each
other and extend peripherally around the side wall so that at least
one nozzle of the first set alternates with at least one nozzle of
the second set. The two sets of jet nozzles have a total
cross-secti~nal area which is within a range of approximately 3~ to
15~ of the cross-sectional area of the mixing portion. By
positioning the two sets of nozzles in the same diametrical plane,
mixing of the jets of driving fluid with the main fluid occurs in a
shorter space, thus permitting reduction in length of the apparatus
and manufacturing costs by having only one ring of nozzles.
Preferably, the nozzles have outlets essentially flush wlth the side
wall and are spaced equally from the duct axis.
In one embodiment a gas manifold cooperates with the auct and is
adapted to receive pressurised gas. This embodiment also includes a
plurality of gas nozzles cooperating with the duct side wall and the
gas manifold to pass the gas into at least one of the duct portions.
To improve performance, the outlet portion diverges downstream from
the mixing portion so as to have a larger cross-sectional area than
the mixing portion.
A detailed disclosure following, related to drawings, describes a
preferred embodiment of the invention which is capable of expression
in structure other than that particularly described and illustrated.
DESCRIPTION ~F TH~: DRAWINGS
Figure 1 is a simplified perspective of a propulsive apparatus
according to the invention incorporated into a system for
pumping fish from a net etc, into a container,
Figure 2 is a simplified fragmented section on a longitudinal axial
plane of the apparatus, as would be seen on line 2-2 of
Figure 3,
Figure 3 is a simplified transverse section of the apparatus, as seen
on line 3-3 of Figure 2,
Figure 4 is a simplified fragmented section of a first jat nozzle on
line 4-4 of Figure 3,
Figure 5 is a simplified fragmented section of a second jet nozzle on
line 5-5 of Figure 3,
20 Figure 6 are experimental performance curves comparing a pump o-f
the invention with a generally similar prior art pump
having jet nozzles all of the same angle,
Figure 7 are experimental performance curves comparing
improvements in performance of a pump of the invention
with and without air assist and a diffusing outlet portion.
C~ETAIIED DIS~OSURE
Figure 1
A fish pump system 10, adapl:ed particularly for use on the decl~ oF a fishing
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vessel, not shown, utilises a propulsive apparatus 12 according to the
invention. The apparatus 12 has a duct 13, a driving liquid manifold 14, and
inlet ar d outlet portions 16 and 18 respectively which are disposed on
upstream and downstream sides respectively of the maniFold. The manifold
5 14 has a manifold inlet 17 which receives pressurised driving liquid i.e,
water, through a manifold delivery pipe 20. An engine 22 drives a liquid
pump 23 which supplies pressurised water to the delivery pipe 20. The
pump receives water through a watPr supply or suction hose 21 which draws
water from a convenient body of water 19 which is usually surrounding the
10 fishing ves3el. However, when unloading in a harbour where water might be
polluted, a separate supply o-f cleaner water might be required.
The engine 22 also drives an air compressor, not shown, which delivers
compressed air through an air delivery pipe 25 which feeds air to an air assist
15 or gas manifold 27 surrounding the outlet portion 18 i.e., air i9 injected on a
downstream side of the apparatus 12. If desired, an alternative air assi~t
or gas manifold can be fitted adjacent the inlet portion 16 of the duct, as
shown at 28, and thus i~ fitted on the upstream side of the propulsive
apparatus 12. The air delivery pipe 2S is shown partially in broken outline
20 for supplying air to both the downstream located manifold 27, and/or the
upstream located manifold 28 or to other locations to suit particular
requirements. The outlet portion 18 discharges water and fish into a transfer
duct 31, which in turn is connected to a deceleraticn/dewatering unit 34
which separates solids, that i3 the fish, from the water, the fish being
25 discharged through a discharge chute 36.
Figure3 2 through 5
Re-ferring mostly to Figure 2, the duct 13 has a duct side wall 42 extending
30 along and surrounding a duct longitudinal axis 44. A pair of diametrically
opposed lugs 43 extend from the side wall 42 for supporting the duct with
cables, etc, not shown. As shown in Figure 1, the duct is mounted so that the
axis 44 is generally vertical, and water flows from the inlet portion 16 per an
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arrow 46 through the outlet portion 18 and into the hose 31. The duct 13
has a central or mixing portion 50 of constant cross-sectional area, i.e., the
central portion of the duct is parallel sided, and extends between the inlat
portion 16 and the outlet portion 18. Thus it can be seen that the duct side
wall 42 defines in part the inlet and outlet portions 16 and 18 spaced on
upstream and downstream sides respectively of the mixing portion 50.
Most of the inlet portion is of the same cross-se:ctional as the mixing
portion, i.e., is also parallel sided. However, an upstream opening 48 of the
inlet portion 16 is flared so as to present a "bell-mouth" of larger diameter
than the central portion to facilitate smooth entry of water thereinto. The
manifold 28 extends around the inlet portion 16 and a plurality of openings
49 penetrate the duct side wall to serve as gas nozzles to direct gas from the
manifold into the inlet portion of the duct. For a 12 inch (305mm)
diameter duct, 32 openings of 0.25 inches (6.35mm) diameter are adequate.
While the duct axis 44 can be at inclinations other than vertical, if air assistis used care must be taken to reduce chances of air collecting in the hose.
The outlet portion 18 is a hollow frustum and has an upstream edge of the
same diameter as the central portion secured with releasable clamp means
52 to the central portion 50 of the duct for convenience of assembly and
storage. The transfer hose 31 has a larger diameter than the mixing portion
50, and thus the outlet portion 18 diverges downstream from the mixing
portion to a downstream edge 54 which cooperates smoothly with the hose
31. The outlet portion 18 preferably has a maximum total angle of about
30 for reduction of flow velocity with minimum losses. Preferably the
outlet portion 18 causes an increase in cross-sectional duct area of between
50 to 100% of the duct cross-sectional area at the mixing portion 50, and
this is considered important for improved lift when used in conjunction with
air injection. The manifold 27 is positioned ad3acent the edge 54, i.e., at
the junction between the hose 31 and the outlet portion 18, although it could
be located at an inter iection between the mixing portion 50 and outlet
portion lB, as shown in broken outline at 27.1. Generally it is more
convenient to locate the gas injection mani fold remote from the clamp
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means 52. In either location of the manifold 27, i.e. adjacent
downstream (27) or upstream (27.1) portions of the outlet portion,
similarly to the manifold 28, a plurality of gas nozzles 53
penetrates the duct side wall to pass gas from the manifold into
the gas outlet portion.
The driving liquid manifold 14 has a tubular portion 55, and
annular upstream and downstream end plates 56 and 57 which enclose
the duct side wall 42 to form an annular chamber 58. The manifold
delivery pipe 20 cooperates with the manifold inlet 17 which is
secured parallel to the duct 13 as shown. The tubular portion 55
has a pair of openings 63 which provide communication between the
manifold inlet 17 and the annular chamber 58 defined by the
manifold. Flow losses are reduced by having the manifold 14 much
larger in cross-section than the duct 13. An annular nozzle ring
62 forms a portion of the duct side wall 42 and cooperates with
the downstream end plate 57 as seen in Figure 2. The ring 62 has
first and second sets of inwardly facing jet nozzles 64 and 65
disposed adjacent a transverse diametrical plane 67 of the duct.
It can be seen that the jet nozzles cooperate with the duct side
wall and the manifold 14 to pass the driving liquid into the
mixing portion 50. Preferably the mixing portion 50 has a minimum
mixing length 68 of about 3 times its diameter 69, measured from
the diametrical plane 67 containing the jet nozzles to the
beginning of the outlet portion 18, that is the intersection
between the portions 18 and 50. This is to permit some mixing of
the driving liquid with the main fluid prior to entering the
outlet portion 18 which acts as a diffuser.
As seen in Figure 4, a typical first jet nozzle 64 has a first
axis 70 inclined to the duct axis, shown diagrammatically
transposed at 44.1, at a first angle 71 as shown. Similarly, as
seen in Figure 5, a typical second jet nozzle 65 has a second jet
axis 73 inclined at a second angle 74 to the duct axis, as shown
diagrammatically transposed at 44.2. As seen in Figure 3, the
first and second sets of jet nozzles 64 and 65 are positioned
peripherally around the side wall so as to alternate with each
other. For best performance, the first angle 71 of the first set
of nozzles 64 is between about 15 and 30, and the second angle
of the second set of nozzles 65 is between 10 and
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20. Also, the first angle is always greater than the second angle,
and preferably the first and second angles are separated by no less
than about 5 degrees. As seen in Figure 2, the first and second jet
axes converge inwardly to intersect the duct axis 44, and all axes
pass through the common diametrical plane 67 adjacent the side wall
42. Because of the difference in angles between the two sets of
nozzles, the axes 73 of the second set of jet nozzles intersect the
duct axis 44 at an intersection 72 positioned downstream from an
intersection 75 of the axis 4~ with axes 70 of the first set of jet
nozzles. Furthermore both sets of jet nozzles penetrate the duct
side wall 42 smoothly, without a step in the side wall or a change
in duct diameter. That is, outlets from the nozzles are essentially
flush with the duct side wall and are spaced egually from the duct
axis. This is considered to reduce turbulence considerably when
compared with nozzles of the prior art which are commonly located in
steps on the side wall. A side wall without steps reduces flow
losses in the main flow as it passes the nozzles because there is no
significant change in duct diameter across the jet nozzles. A
smooth duct side wall, adjacent joins in the duct portions as well
as adjacent the nozzles, is important also to reduce or eliminate
possible damage to the product, i.e., fish, being handled.
The angles specified above represent ranges of angles with
acceptable limits of angles for pumping fish. Improved pumping
efficiency is attained when the first angle is between 18 and 25,
the second angle is between 12 and 19, and the first and second
angles are within a range of between 5 and 10 of each other~ As
will be described, the graphical results presented in Figures 6 and
7 relate to an improved pump in which the first angle is 25 and the
second angle is 18.
Referring again to Figure 4, the first jet nc2zle 64 has a jet
length 76 measured along the axis 70, and a parallel jet bore 77,
being the narrowest diameter of the jet nozzle. PreEerably, the
ratio of the jet bore diameter to jet length~ i.e. the ratio
jet bore:jet length is between 1:2 and 1:6, although
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variations outside this range are permitted for certain liquids. It is added
that a shorter jet length to bore ratio would tend to result in a spray of
driving liquid from the nozzle which diverges too rapidly, and thus loses
momentum too quickly with consequent loss of pumping efficiency. A
larger ratio would likely result in a jet that Focuses driving liquid too
sharply, causing impact damage to a delicate product being pumped. The
nozzle 64 has an entrance cone 79 which converges inwardly to meet the jet
bore. Preferably, the entrance cone 79 has a length ao that is
approximately three times the jet bore 77. Preferably, the entrance cone
has an included angle of about 15to 25to reduce losses. The second jet
nozzles 65 are generally similar in geometry to the first jet nozzles, with of
course the exception of the more shallow angle of inclination to the duct
axis 44.
An important factor to consider is the overall cross-sectional area of the jet
nozzles when compared with the overall duct cross-sectional area in the
mixing portion 50. Preferably, the two sets of jet nozzles 64 and 65 have a
total cross-sectional area which is within a range of approximately 3% to
15% of the cross-sectional area of the central or mixing portion 50. In the
example shown, there is a jet nozzle positioned every 22.5 degrees around
the periphery of the nozzle ring 62. Thus there are eight first jet nozzles
and eight second jet nozzles spaced equally apart. To be within the jet
nozzle/duct cross-sectional area ratio above, for a duct having a diameter
of 8 inches (2û3mm), each nozzle has a jet bore diameter of between 0.346
inches (8.79mm) and 0.775 inches (19.69mm). If the said cross-sectional
area ratio is much smaller than 3%, the pump effectiveness would be
reduced considerably unless very high driving liquid pressures were used
which might damage the product. If the cross-sectional area ratio were
much larger than 15%, the manifold pipe 20 would be exc~ptionally large5
and much power would be required by the pump 23 to supply adequate
volume flow of driving liquid.
OPER~TION
In operation, referring mostly to Figure 1, the apparatus 10 is positioned by
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hanging from the lifting lugs 43 so that the inlet portion 16 is immersed in
the fish net or hold of a ship containing fish to be pumped, or other liquid or
liquid/solid material to be pumped. The pump 23 supplies water under
pressure to the manifold 14, and the sets of nozzles 64 and 65 (Figure 2)
direct a plurality of jets of high pressure water into the duct 13. The jets
from the nozzles induce a flow of main fluid in direction of the arrow 46 up
the duct, by transferring momentum from the jets themselves to the main
fluid and solids suspended within the fluid. For improved performance, air
is admitted from the air delivery pipe 25 into either the manifold 27 or 28,
or both, although it would seem that best results have been obtained by
admitting air into the manifold 28. When using air assist lift, it has been
found best when this is used in conjunction with the diverging outlet portion,
as shown at 18. The diverging outlet portion 18 acts as a diffuser and
reduces speed of the flow through the duct, and as seen in Figure 7,
admission of air into the duct appear~ to increase considerably the lift that
was available from this typ0 of pump. Water and fish within the water are
passed along the duct 31 to the decelerating/dewatering device 34, and fish
are rejected from the chute 36, while water is returned to the body of water
19 for re-use if required, or to waste.
Operating parameters vary considerably depending on the product being
handled, and height to which the product must be lifted prior to discharge.
As will be seem by reference to Figure 7, injection of air considerably
improves the lift, with only a small increase in horse power required for this
injection. Air pressure in the manifold 27, 27.1 and/or 28 typically is
relatively low, i.e., between 5 and 10 PSI (34.5 kPa and 68.9 kPa), when
compared with the higher pressure in the driving liquid manifold 14, which is
within the range of 50 to 150 PSI (344 kPa and 1.03 MPa). Injection of air
either upatream or downstream of the jet nozzles causes a dramatic increase
30 in pump suction flow and performance with very small increase in power
requirements to pressurize the air.
In one set of testa, the pumping apparatus 12 had an 8 inch (203mm)
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diameter duct expanding to a 12 inch (305mm) outlet portion at lifts of 20
feet (6.1metres) from waterline to discharge point. When the jet pump was
used without air injection, the pump suction flow was measured as 650
USGPM (0.41 m /sec) at the inlet portion 16, and this required
approximately 75 horspower (55.9 l~w) to drive the pump 23. When air was
injected at approximately 100 CFM (0.0472 m /sec), using about 10
horsepower (7.5 Kw), the suction flow of the system at inlet portion 16 was
doubled to 1300 USGPM (0. 82m /sec). This shows that the addition of a
small energy increment in the form of power for compressing the air
effectively doubled the performance of the pump. This improvement in
performance is attributed to the fact that the buoyancy of air induces flow
of pumped mixture which flows upwardly with it. Also, air mixing with water
decreases the effective density of the resulting air and water mixture which
allows the pump to operate at a lower purnping head at a more efficient
point on its operating curve. Air Flow was approximately 150 CFM per
square foot of cross-sectional area (0.76m /sec per square metre of cross-
sectional area) of the transfer hose 31. The pressure requirements were
only that re~uired to ovarcome hose losses, and the static head within the
hose 31. No additional benefits were measured when higher air flows were
used.
Figure 6
The graph of Figures 6 supports the applicant's claims that the use of first
and second jet nozzles of differing angles of a certain range provides
improved benefits over a row of jet nozzles all at the sarne angle. The
graph shows the relationship betwean input power, i.e., horsepower,
determined at two different locations and suction velocity, measured in feet
per second measured at the upstream open;ng 48. It was possible to make a
direct comparison of the improvement in performance using a ring of jets all
of the same angle which is similar to the~ prior art jet pumps, compared with
a ring of jets of two separate angles as described herein. These tests were
performed on the same duct of 1n inch (254mm) diameter, generating a lift
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of 10 feet (3m) without use of air injection for assistance. The axis angle
of single angle prior art jet nozzle was 15, whereas the first and second
angles of the jets of the invention were 25 degrees and 18 degrees. In the
single angle pump, the nozzle/duct area ratio was 10%, whereas in the two
angle pump the area ratio was 9%. The minor differences in angles and area
ratios are considered to be insignificant. The operating parameters for the
four curvss are as below.
CURVE AN~ F T~PE INPllr POWER
I~TER~vlINATION POI;~IT
A Single angle,prior art Engine 22
B Double angle,invention Engine 22
C Single angle,prior art Manifold 14
15 D Double angle,invention Manifold 14
The curvea A and B show that the total input power required at the engine
22, for the same suction flow, the double angle design of the invention
requires about 25 horsepower (18.6 KW) less than a single angle prior art
20 pump. Curves C and D show a similar difference when power requirements
are determined at the driving fluid manifold 14, with the invention requiring
approximately lB horsepower (13.4 KW) less than a single angle pump.
These graphs illustrate that efficiency gains at the jet nozzles have a
magnifying effect due to other losses in the power delivery system, and will
25 result in even greater power savings or pumping efficiency gains at the final drive unit.
Fi~ure 7
30 The graph of Figure 7 shows 9ix performance curves obtained when testing a
propulsive apparatus 12 having an 8 inch (203 cm) diameter duct, in which
the jet nozzle bore is û.625 inch (15.9mm), the first angle is Z5 and the
second angle i9 18 . The graph compares suction velocity in feet per
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second, measured at the inlet portion 16, against jet pressure, measured in
PSI at the manifold 14. These curves illustrate the effectiveness of the
diverging outlet portion 18, termed diffuser and the use of air injection,
which, at this time was injected at the upstream inlet portion 16.
The operating parameters for the six curve~s of Figure 7 are as below.
CURVE HIEIGHT OF LIFT AIR IN;IECTION DIFFUSER
10 A 11.5 feet (3.5m) No No
B 11.S feet (3.5m) Yes No
C 11.5 feet (3.5m) No Yes
D 11.5 feet (3.5m) Yes Yes
E 20 Feet (6m) No Yes
15 F 20 feet (6m) Yes Yes
As can be seen, the curve A is a datum or baseline curve, with no air
injection or outlet diffuser. Curve El shows that air injection by itself i.e.,
20 without a diFfuser, provides only a small efficiency improvement with
slightly more suction. Curve C shows that the outlet diffuser, by itself,
results in no significant change in power requirements. Thus air injection or
an outlet diffuser when applied singly, has little effect. Curve D shows a
considerable improvement by combining simultaneously air injection with
25 the diffu~er, which produces a large improvement in suction flow with the
same input power, or therefore a large gain in pumping efficiency of the jet
pump. CurvE~ F shows a marked improvement when using air injection with
an outlet diffuser over Curve E, which is the same lift height without air
injsction. Note that these last two curves relate to a higher lift than the
30 previous four curvas and it can be seen that air injection produces an even
greater benefit than with the lower lifts.
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This improvement in efficiency is attributed to the fact that the
diffuser appears to reduce speed of the pump discharge such that the
injected air is more effective in assisting the pumping action. This
injection of air must be applied without loss of injected air around
the outside of the pump, that is escaping from the inlet nozzle,
especially when the air injection is applied at the inlet portion 16.
Field tests have shown that fish pumping rates as high as 65 tons
per hour (16.4kg/sec) with a 6 inch (152mm) diameter duct causes
minimal damage to herring. Softer species of fish and larger fish
such as salmon can be handled with minimal damage at high pumping
rates.
ALTERNATIVES AND EQUIVALENTS
As previously stated, the air injection is preferred upstream of the
jet nozzles in conjunction with a diffusing outlet portion. Clearly
air can be omitted totally or admitted alternatively or irl addition
to the inlet portion 16. While the device is shown using water as
the main fluid other liquids or gases such as air can be substituted
as the main fluid. ~owever, if air or other gases were used as a
substitute for the driving liquid, jet axes angles other than those
listed and a change in duct or nozzle geometry would likely be
required. Thus this invention is considered inappropriate for using
a gas as the sole means of propelling the main fluid flow through
the duct. While the first and second sets of jet nozzles are shown
to alternate singly with each other around the periphery of the
duct, the nozzles could alternate in pairs around the duct. That
is, there would be a pair of nozzles having the first angle disposed
between two pairs of nozzles having the second angle, and vice
versa, around the duct. Thus, in summary, at least one nozzle of
the first set alternates with at least one nozzle of the second
set. The benefits of the invention appear to result from the
intimate mixing of the jets of driving liquid from the two sets of
nozzles which are closely adjacent each other peripherally as well
as axially.
An important aspect of the invention relates to the two sets of jet
nozzles in
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which the jet angles of inclination of one set are dissimilar to the jet angles
of the other set. This provides benefits over a single set of jet nozzles all
of the same jet angle. However a second aspect of the im~ention relates to
air injection in combination with an outlet diffuser, i.e., the duct outlet
5 portion diverges downstream from the mixing portion. This second aspect
provides benefits in addition to the first aspect of the invention, however it
could also provide benefits when used with a jet pump having one set of jet
nozzles having jet axes inclined at similar angles to the duct axis. The jet
nozzles could be inclined at angles of between 10 and 30 and would be
10 adjacent a transverse plane of a duct having a mixing portion of constant
cross-sectional area. These equal angled jet nozzles only of this
alternative would resemble the jet nozzles of some prior art jet pumps.
While the device i9 shown for pumping fish from a net etc., it can be used to
15 harvest shell fish from the sea bed, or used as a propulsive apparatus to
propel or displace floatlng vessels or vehicles
