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Description  |
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This invention relates to fluid delivery nozzles and more particularly to
nozzles which exhibit high thrust and low noise.
Various types of fluid delivery nozzles have been proposed for use in
manufacturing establishments where a stream of air is directed to perform
a function such as ejecting parts or blowing refuse from a machine or work
station. In such applications, it is desirable that the stream be
concentrated and that the working force of the stream be substantial. It
is also desirable that the noise levels not be excessive. One type of
nozzle which has been considered which produces high thrust and low noise
levels is described in my copending U.S. patent application Ser. No.
580,921 filed Aug. 26, 1974 which is a continuation-in-part of my U.S.
patent application Ser. No. 500,647 filed Aug. 26, 1974, now abandoned.
The nozzles described in the aforesaid copending U.S. application make use
of a modification of the Coanda or wall attachment principle to entrain
ambient air in a high velocity small mass air stream. As disclosed in U.S.
Pat. Nos. 2,052,869 and 3,047,208 and as exemplified in nozzle
applications by U.S. Pat. Nos. 3,743,186, 3,801,020, 3,806,039 and
3,705,367, the Coanda effect basically involves discharging a small volume
of a primary fluid under a high velocity from a nozzle having a shaped
surface adjacent the nozzle, whereby the stream of primary fluid tends to
follow the shaped surface and as it does, it induces a surrounding
secondary fluid -- notably, ambient air -- to flow with it along the
shaped surface. The result produces an exhaust stream which combines both
fluids. Thus, nozzles constructed in accordance with the principles
established by Coanda exhibit high thrust due to the amplification in flow
produced by the Coanda effect.
The nozzles described in my above-noted copending application feature
amplification of air flow produced by the Coanda effect and at the same
time provide reduced noise levels. In one embodiment, the nozzle is a
single stage amplification device which comprises an inlet for connection
to a source of high pressure air, an air passageway for conducting an air
stream from the inlet to the nozzle discharge opening, at least one port
intermediate the inlet and the discharge opening for conducting
pressurized air out laterally from the passageway, and means including an
appropriately shaped outer nozzle surface for causing the compressed air
exiting the port to induce a flow of ambient air along the outer surface
of the nozzle toward the nozzle's exit end so as to provide a working
stream which combines the pressurized air discharged from the main
passageway and the induced ambient air. Since the mass of the resulting
working stream is greater than that of just the pressurized air stream
which exits the passageway, it accordingly enhances the working force of
the combined stream substantially over that of only the discrete
pressurized air stream which exits the passageway. A selected
air-permeable flow-modifying element is disposed in the air passageway for
the purpose of causing the stream flowing in the passageway to assume a
laminar or near-laminar flow characteristic, whereby to reduce noise while
at the same time permitting the air stream in the passageway to exit the
nozzle at a high velocity. The flow-modifying element also provides a back
pressure which forces air to exit the passageway via the port(s) whereby
to promote the desired induction of ambient air. In a second embodiment I
describe a two-stage amplification nozzle which is basically the same as
the single stage device, but modified to include a second stage element.
The two-stage amplification nozzle provides increased thrust over the
single stage nozzle while maintaining relatively low-noise levels.
It has been determined that the air volume entrainment is not only a
function of the velocity of the air stream exiting from the side ports but
is also proportional to the length over which the inducing air stream
moves before entering the main stream of the nozzle. However, in both of
the aforementioned embodiments the length of the outer-surface over which
the air streams exiting the ports must travel is fixed. As a consequence,
a fixed optimum relationship can be achieved between the output thrust and
the input flow rate. If the latter is increased substantially from the
level at which the optimum condition is achieved, the output thrust will
increase at a rate slower than the rate of increase before reaching
optimum.
Accordingly, it is the primary object of the present invention to provide
an improved amplification air nozzle of the type described which will
maintain an optimum relationship between the output thrust and the input
flow rate through a large range of input flow.
A further object is to provide a nozzle of the type described which has a
higher output thrust capability per given input flow than is possible with
nozzles of the type described in my copending application.
Another object of the present invention is to provide an improved air
nozzle which automatically increases ambient air entrainment with
increases in the input flow rate over a large range of input flow.
A further object of the present invention is to provide an improved air
nozzle of the type described in which the length over which the air stream
moves along the outer surface before entering the main air stream of the
nozzle varies with the rate of input flow.
Yet another object of the present invention is to provide an improved air
nozzle of the character described, which is extremely simple in
construction, reliable and durable in use and economical to manufacture.
The foregoing objects and other objects hereinafter disclosed or rendered
obvious are achieved by an improved nozzle which comprises an inlet for
connection to a source of high pressure air, an air passageway for
conducting an air stream from the inlet to a nozzle discharge opening, one
or more ports intermediate the inlet and the discharge opening for
conducting pressurized air out laterally from the passageway, and means
including an appropriately shaped outer nozzle surface for causing the
compressed air exiting the one or more ports to induce a flow of ambient
air along the outer surface of the nozzle toward the nozzle's exit end so
as to provide a working stream which combines the pressurized air
discharged from the main passageway and the induced ambient air. The
improved nozzle further includes means for varying the length of the outer
surface of the nozzle over which the air exiting one or more of the ports
must travel, as a function of the input flow rate. Since the mass of the
resulting working stream increases with the length of the outer surface
over which the air exiting one or more of the ports travels, the optimum
relationship between the enhanced output and the flow input is maintained
over a relatively greater range of inputs. A selected air-permeable
flow-modifying element is disposed in the passageway for the purpose of
causing the stream flowing in the passageway to assume a laminar or more
nearly laminar flow characteristic without any substantial drop in air
pressure, whereby to reduce noise while at the same time permitting the
air stream in the passageway to exit the nozzle at a high velocity. The
flow-modifying element also provides a back pressure which forces air to
exit the passageway via the one or more ports whereby to promote the
desired induction of ambient air.
Other features and many of the attendant advantages of this invention are
disclosed by the following detailed description which is to be considered
together with the accompanying drawings wherein:
FIG. 1 is a longitudinal section of a preferred embodiment of the
invention;
FIG. 2 is a diagrammatic view on an enlarged scale of a piece of knitted
metal wire mesh;
FIG. 3 is a sectional view of a die for forming the flow-modifying element;
FIG. 4 is a cross-sectional view of the guide ring of the FIG. 1
embodiment; and
FIG. 5 is a longitudinal section of the FIG. 1 embodiment in a partially
extended position.
The same numerals are used in the several figures to designate identical
parts.
Turning to FIG. 1, the illustrated nozzle comprises a plug 2 which has a
reduced diameter threaded extension 4 at its rear or inlet end for
connection to a conduit 6, the latter leading to a source (not shown) of a
pneumatic medium such as compressed air. The main portion of the plug,
which is at the forward or outlet end thereof, is in the form of a
cylindrical body 8. The body 8 and the threaded extension 4 have a common,
centrally located and smooth surfaced bore 10 that has a circular
cross-section and serves as an inlet and flow passageway for the
pressurized pneumatic medium. The forward end of the body 8 is
counterbored so as to form an annular flange 12 and a recess 14. The body
8 also includes an outer cylindrical surface 16 and a radially-directed
annular flange 18 which extends outwardly from the surface 16 to form an
annular shoulder 20.
Attached to the plug 2 is a forwardly extending hollow cylindrical housing
or sleeve 22. The latter has a smooth inner cylindrical surface 24 which
is coaxially aligned with bore 10 and sized to make a tight friction fit
with the outer surface 16 of the plug 2, while its rear end surface
contacts the shoulder 20. A roll pin 26 extends radially through the
sleeve 22 into the plug 2 to insure that the sleeve 22 will remain secured
to plug 2 when the nozzle is connected to a source of high pressure air.
The forward end of sleeve 22 is bevelled to provide a frusto-conical outer
surface 28. The forward end of sleeve 22 is provided with an inner
cylindrical surface 30 which is of a reduced diameter and coaxially
aligned with the cylindrical surface 24. The surfaces 24 and 30 are joined
together by an inner radially-directed shoulder 32.
A tubular member, identified generally at 34, is coaxially and slidably
mounted within sleeve 22. Member 34 has a centrally located smooth
surfaced bore 10A that is the same diameter as and is aligned with bore
10. The element 34 is also counterbored at its forward end to provide an
inner radially-directed annular 36 and an inner cylindrical surface 38.
The inside of the forward end of element 34 is provided with a
frusto-conical surface 40 which forms an outwardly tapered or flared
opening for the tubular member. The exterior of tubular member 34
comprises a flange portion 42 at its rear or upstream end and a main
portion 44. Flange portion 42 has a flat annular rear surface 46, a
cylindrical outer surface 48 and a flat annular front end surface 50.
Surface 48 is sized so that the member 34 can freely move axially with
respect to the inner surface 24 of sleeve 22. The main portion 44 has a
cylindrical outer surface 52 that has a smaller diameter than surface 48
so as to provide an annular chamber 54 between it and the sleeve 22. The
diameter of the surface 52 is also made smaller than the inner cylindrical
surface 30 of the shell so as to provide an annular passageway or orifice
55 between the two surfaces. By way of example, in the preferred
embodiment of the invention, the gap between surfaces 30 and 52 is between
about 0.003 and 0.008 inch.
Additionally, the main portion has at least one and preferably several
ports 56 which are positioned between the flange 42 and the annular
shoulder 36 and lead from bore 10A to chamber 54. Preferably, but not
necessarily, ports 56 are closer to flange 42 than shoulder 36 and their
axes extend at a right angle to bore 10A.
In order to help maintain tubular member 34 coaxial with sleeve 22, a guide
ring 57 is provided between them at the forward end of the sleeve. The
guide ring is sized to make a tight friction fit with the inner surface 24
of sleeve 22 and, as shown in FIG. 4, the inside of the ring is preferably
provided with three inwardly-extending radially-directed segments 59 which
are equiangularly spaced around the guide tube and define slots 61. The
segments 59 are dimensioned to have first enough clearance with the tube
member 34 so that the latter can move freely through the ring. The slots
61 provide air gaps between ring 57 and the tube member connecting the
chamber 54 with the orifice 55. In the preferred embodiment of the
invention, the internal diameter of each slot is made 0.020 inch larger
than the outside diameter of the tube member 34.
In order to maintain the ring 57 at the forward end of the sleeve 22 and
the tube member in the retracted position, biasing means in the form of a
compression coil spring member 63 is provided. The spring member 63 is
positioned in the chamber 54 so that one end urges ring 57 against the
inner shoulder 32 and its other end contacts the surface 50 of flange
portion 42. Spring 63 acts to keep the rear surface 46 of flange 42
against the annular front end flange 12 of plug 2. Spring member 63 is
sized so that it can be compressed and relaxed without being binded by the
inner surface 24 of sleeve 22 and the external surface 52 of tube member
34. The spring constant of member 63 is selected according to the maximum
pressure of the fluid introduced through conduit 6, as will be more
apparent hereinafter.
Secured to the downstream end of tubular member 34 is a nozzle element
identified generally as 58. The latter has a centrally located
smooth-surfaced bore 10B that is of a smaller size than and is aligned
with bore 10A. Nozzle element 58 comprises an end section 62, a throat
section 64, and a main section 66. End section 62 has a flat annular rear
surface 68, a cylindrical outer surface 70, and a flat annular front end
surface 72. Surface 70 is sized to make a tight friction fit with the
inner surface 38 of the tubular element 34. At least one roll pin 71 is
used to insure that the nozzle element 58 remains fixed with respect to
tubular element 34. The roll pin extends radially through the tubular
element 34 into a blind hole in the end section 62 of the nozzle element.
Throat section 64 has a cylindrical outer surface 74 that has a smaller
diameter than surface 72 whereby to provide a second annular chamber 76
between it and the tubular element. Additionally, the throat section has
at least one and preferably several ports 78 that lead from bore 10B to
chamber 76. Preferably, but not necessarily, the axes of ports 78 extend
at a right angle to bore 10B.
The exterior of main section 66 has a generally bulbous shape characterized
by a rear frusto-conical surface 80, a front frusto-conical surface 82,
and a convex circumferentially-extending transition surface 84. The nozzle
section is sized so that its rear surface 80 is spaced from the adjacent
surface 40 of the tubular element. Preferably, the shape of the rear
frusto-conical surface 80 is linear and is set so that, with increasing
distance from throat section 64, it converges toward the adjacent surface
40 of the tubular element, whereby to form an annular passageway or
orifice 86 that communicates with chamber 76, and whose cross-sectional
area decreases progressively with increasing distance from chamber 76.
Preferably, but not necessarily, the axial length of the outer surface of
the annular throat section is set so that its junction with surface 80 is
aligned radially with the junction of surfaces 38 and 40 of the tubular
element, as shown. The frusto-conical surface 80 preferably is long enough
so that its forward end projects radially to or beyond the outer surface
of the tubular element, whereby the transition surface 84 is in position
to intercept ambient air flowing along the outer surfaces of the shell 22
and tubular element 34 toward the nozzle element 58. The surface 82 is
formed so that its front end terminates close to the axial bore 10B.
Preferably, its front end intersects or nearly intersects the axial bore
so that the nozzle element has a relatively narrow front edge as shown at
88. While a relatively thin knife edge may be advantageous for optimum
merging of ambient air with the air stream exiting from bore 10B, it is
preferred that edge 88 be somewhat blunt so as to minimize possible injury
to workmen. In any event, the slope and length of surface 82 are set so
that the induced ambient air and the pressurized air stream from bore 10B
will merge in a smooth transition without the creation of noise producing
eddies and vortices.
It is also essential that the slopes of confronting surfaces 40 and 80 and
the minimum gap therebetween be set so that air will exit the orifice 86
as a thin film which will tend to adhere to and flow along surface 80 over
surface 84 and along surface 82 in the manner shown by the arrows 90. By
way of example, in a preferred embodiment of the invention, the surface 82
has a slope of about 20.degree. with respect to the common axis of bores
10, 10A, and 10B, surfaces 40 and 80 have slopes with respect to the same
axis of 20.degree. and 30.degree. respectively, and the gap between
surfaces 40 and 80 is between about 0.003 and 0.008 inch.
It is also essential, for better promotion of laminar flow and to reduce
noise, that the bore 10B have a diameter substantially the same as or
smaller than bore 10A, since this arrangement provides a smooth transition
from bore 10A to bore 10B and thus avoids or minimizes creation of eddies
and turbulence in the air stream as it passes into bore 10B from bore 10A.
Also forming part of the nozzle assembly is a flow-modifying noise-reducing
element 92 which is essentially a cylindrically shaped plug and
preferably, but not necessarily, is formed with flat end surfaces as
shown. Noise-reducing element 92 is made of a knitted wire mesh fabric and
may be formed in situ or preformed and installed after formation.
The element 92 is made generally in accordance with the teachings of U.S.
Pat. No. 2,334,263 issued Nov. 16, 1943 to R. L. Hartwell for Foraminous
Body and Method of Producing Same. Element 92 consists of a compressed
mass of metal wire characterized by a closely packed, interlocked wire
structure that forms a coherent body. The element is fabricated from
knitted metal wire mesh of selected gauge. The mesh may be knit flat or
tubular and may be of selected mesh loop size. Preferably it is knitted as
a tube or sock on a circular knitting machine. In its simplest form, the
knitted wire mesh tube may be knitted from a single continuous length of
metal wire which is so manipulated as to form a continuous tube in which
successive turns of the wire form lengths which extend circumferentially
of the tube and are interlocked by stitches. Each length is bent locally
beyond its elastic limit as a result of the formation and interlocking of
loops or stitches as the tube is knitted. Thus each circumferential
length, in effect, forms a flattened spring which may be stretched or
compressed. The finished tube or sock is flattened longitudinally so as to
form a two-ply ribbon. Preferably, but not necessarily, the flattened tube
may be corrugated traversely to provide further interlocking between the
lengths of wire in the plies thereof. Corrugating the fabric is known in
the art as "crimping" and the product is commonly called "crimped knitted
wire mesh fabric". The tube may be corrugated at a right angle to its
axial length or at a different angle, e.g., 45.degree., in the manner
disclosed by the Hartwell patent. FIG. 3 presents a side view of a portion
of a knitted wire mesh fabric tube as above described. The fabric is seen
to comprise circumferential turns of wire 94 with each turn having loops
or stitches which are interlocked with adjacent turns. In this case, the
fabric is crimped along spaced diagonal lines 96.
Knitted wire mesh fabric and the method of making the same are well known
(in this connection see also U.S. Pats. Nos. 3,346,302, 2,680,284,
2,869,858 and 2,426,316).
In the practice of this invention, the knitted wire mesh fabric is
preferably made of a stainless steel wire, although other steels and
alloys may be used.
Preferably the flow-modifying element 92 is made by flattening a knitted
wire mesh fabric tube upon itself to form a flat two-ply ribbon, and then
rolling the ribbon upon itself. The ribbon is wound up in the manner shown
in FIG. 2 of U.S. Pat. No. 3,346,302 (except that it is not wound upon a
mandrel) and FIG. 2 of the Hartwell patent, with the result that the
rolled up body is generally cylindrical and the width or transverse
dimension of the ribbon extends parallel to the body's longitudinal axis.
More specifically, the cylindrical body consists in cross-section of a
continuous spiral convolute. In this generally cylindrical body the
lengths of wire making up each turn of the fabric tube are now largely so
oriented as to extend from one end of the body to the other in directions
generally parallel with the body's longitudinal axis. This cylindrical
body is then compressed and molded into a flow-modifying noise-reducing
element of desired density and shape.
FIG. 3 shows a forming die assembly made of tool steel for forming the
element 92 in situ. The forming die assembly comprises a stationary die
100 having a cavity 102 shaped to receive the forward portion of the main
section 66 of the nozzle element and a cylindrical extension 104 at the
base of the cavity which is sized to fit snugly within the bore 10B. The
upper surface of extension 104 has a flat end surface 106. A die sleeve
108 fits down over the rear portion of main section 66 and seats on the
flat upper surface 110 of die 100. Sleeve 108 makes a close fit with the
surfaces 82 and 70 of the nozzle element and is held against lateral
movement by dowels 114 which are embedded in the upper surface 110 of the
die and make a sliding fit in holes in the sleeve. The die assembly also
comprises a piston unit consisting of an elongate piston 116 and a piston
head 118 secured to the piston by a screw 120. The bottom end of piston
116 is enlarged and has a cylindrical outer surface 122 sized to make a
close sliding fit with bore 10B.
In molding the element 92 in situ, the die assembly is mounted in a press
(not shown) having a stationary bed and a vertically reciprocal pressure
head, with the die member 100 being fixed to the bed and the piston
assembly being mounted to the pressure head in vertical alignment with the
die member. With the die assembly open, the nozzle element 58 is inserted
in the cavity of die 100 and sleeve 108 is positioned as shown so as to
hold the nozzle element centered. Then the rolled-up or folded knitted
wire mesh fabric is inserted into the upper end of the nozzle element and
the piston unit is operated to drive the fabric body into the housing. The
length of knitted wire mesh fabric tube employed in forming the element 92
is set so that when the element is formed it has a density which is a
predetermined percentage of the density of the metal of which the wire
mesh fabric is made. The cylindrical wire mesh body formed by rolling up
the flattened wire mesh fabric tube is inserted in the bore 10B so that
the rolled up layers of the wire mesh fabric tube extend axially of and
are compressed radially by the surrounding surface of the nozzle element,
i.e., the cylindrical knitted mesh body is inserted so that its axis of
convolution extends parallel to the axis of bore 10B. The fabric body is
compressed and molded by the compressive co-action of die extension 104
and the end of the piston 116. The extent of penetration of the piston
unit determines the final size and density of the mass 92 of knitted wire
mesh fabric, and preferably the desired density is achieved when the
piston unit bottoms on the upper end of die sleeve 108. The formed element
92 and housing nozzle element 58 are tightly gripped together by a
friction fit and the element is self-supporting and has excellent
structural integrity.
The nozzle element in the embodiment just described is preferably made of
material that is softer than the material of which the element 92 is made.
Preferably, nozzle element 58 is made of aluminum or an aluminum alloy
while element 92 is made of stainless steel knitted wire mesh. As a
consequence, as the element 92 is formed in situ, portions of the wire of
which it is made will abrade and in some places actually cut into the
interior surface of the nozzle element, with the result that the element
is mechanically interlocked with the housing. Additionally, the formed
element has a certain amount of spring action and as a consequence, it
exerts a radial force against the surrounding nozzle element which further
improves the mechanical gripping action between the two parts. A
connection of almost equal strength can be achieved between the nozzle and
element 92 where the latter is preformed since the preformed element also
has a certain spring action. Accordingly, by making the preformed element
slightly oversized, it is possible to assure a strong press-fit connection
to the nozzle element. Again due to the difference in materials hardness,
as the preformed element is forced into bore 10B, portions of the wire of
which it is formed will abrade and cut into the interior surface of nozzle
element 58 so that it is mechanically interlocked with the nozzle element.
As the rolled up or convoluted body of knitted wire mesh fabric is
compacted and molded into the element 92, it is tightly compressed in
directions transverse to the width of the flattened tube or ribbon, i.e.,
it is compressed both radially and axially, with the result that the turns
or length of wire are crimped at innumerable points beyond their elastic
limits so that they take a more or less permanent set. Additionally, as
the wire mesh fabric is compressed, the wire is so deformed as to produce
a compressed mass or body consisting of a very great number of uniformly
distributed, randomly directed, relatively short spans or lengths of wire
which contact each other at innumerable points within the mass, with the
result that these spans or lengths are intimately interlocked
substantially uniformly throughout the entire volume of the mass with
portions of the spans of wire being spaced to form small pockets and
passageways of capillary size. The net result is a relatively dense yet
porous cohesive or self-supporting body consisting of fine, intermingled
and interconnected spring wire spans which are capable of some movement
relative to one another in response to absorbed energy. This
self-supporting body is characterized by substantial structural integrity,
controlled density, a uniform and fine porosity, and a controlled spring
constant. The multiplicity of short spans of wire, the uniformity of
distribution and random directions of such spans, and the innumerable
points of contact between them, all contribute to the capability of the
element to modify the flow of air through bore 10B so that it will exit
the nozzle as a laminar flow jet stream.
The plug 2, sleeve 22, tubular member 34, and spring member 63, may be made
of the same material as the nozzle element or a different material. Thus,
for example, if nozzle element 22 is made of aluminum, any one of or all
of the plug, sleeve, tubular member and spring member may be made of
aluminum or stainless steel. The sleeve 22 and tubular member 34 may be,
and preferably are, secured respectively to the plug 2 and nozzle element
58 by a press-fit as previously described, or it may be secured by other
means known to persons skilled in the art. The guide ring 57 is preferably
made of a hard, durable plastic material such as polyvinyl chloride, which
can easily withstand the compression forces of the spring 63.
Operation of the device of FIG. 1 as an air nozzle will now be described
with reference to FIG. 5. Assume that conduit 6 is connected to a
regulated source of air under pressure, e.g., 100 psi, through a flow rate
control valve. The compressed air enters the nozzle through the conduit 6,
flows along bores 10, 10A and 10B and through element 92, and escapes via
the exit orifice defined by annular end surface 88 of the nozzle element.
Since the wire mesh plug 92 offers some resistance to free flow of the
compressed air, a back pressure is created upstream of the element.
Consequently, part of the pressurized air supplied to the bore 10B is
diverted out of that bore through ports 78 into chamber 76 and then flows
out of chamber 76 via the small gap annular orifice 86 formed between the
surfaces 40 and 80. In passing out of this small gap orifice, the
pressurized air forms a very thin film moving at a high velocity. Since
air moving at a high velocity has a static pressure less than atmospheric
pressure, a differential pressure effect in the form of a partial vacuum
is created which on one side makes the air film cling to and follow the
exterior contour of the nozzle element 58 as shown by arrows 90, and on
the other side draws in ambient air as shown by arrows 91. The thin air
film and the induced ambient air flow together along surface 82 and merge
with the air stream discharged from bore 10B, thus in effect amplifying
the air flow directed by the nozzle. It is to be noted that transition
surface 84 acts to guide the air flowing out of orifice 86.
In addition to part of the pressurized air being diverted through ports 78,
the back pressure created upstream of the element 92 also causes some of
the air to be diverted out of the bore 10A through ports 56 into chamber
54. This diverted air then flows through the gaps provided by | | |
