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BURNER MANIFOLD APPARATI;~S FOR USE IN A
CHEMICAL VAPOR DEPOSITION PROCESS
Background of the Invention
This invention relates to novel burner manifold apparatuses. More
particularly,
this invention relates to burner manifold apparatuses for rnicromachined
burners, such
as micromachined silicon burners.
It is known to form various articles, such as cr<acibles, tubing, lenses, and
optical
waveguides, by reacting a precursor in the flame of a burner to produce a soot
and then
depositing the soot on a receptor surface. This process is particularly useful
for the
IO formation of optical waveguide preforms made from doped and undoped silica
soot,
including planar waveguides and waveguide fibers.
The waveguide formation process generally involves reacting a silicon-
containing precursor in a burner flame generated by a combustible gas, such as
a
mixture of methane and oxygen, and depositing the silica soot on an
appropriately
i5 shaped receptor surface. In this process, silicon-containing materials
typically are
vaporized at a location remote from the burner. The vaporized raw materials
are
transported to the burner by a carrier gas. There, they are volatilized and
hydrolyzed to
produce soot particles. The soot particles then collect on the receptor
surface. The
receptor surface may be a flat substrate in the case of planar waveguide
fabricatian, a
20 rotating starting rod (bait tube) in the case of vapor axial deposition
(VAD) for
waveguide fiber fabrication, or a rotating mandrel in the case of outside
vapor
deposition (OVD) for waveguide fiber fabrication.
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Numerous burner designs have been developed for use in vapor delivery
precursor processes, and at least one liquid delivery precursor process has
been
contemplated, as disclosed in co-pending application serial no. 08/767,653 to
Hawtof et
al, incorporated herein by reference. Whether the precursor is delivered to
the burner in
S vapor form or liquid form, it is important that the burner receives a
distributed, even
stream of precursor. This consideration is particularly important during
waveguide
manufacture to form accurate refractive index profiles.
In the recent past, burners for deposition of metal oxide soot have been
proposed having orifices and supply channels on a small scale. The channels
and
orifices in these burners may have widths or diameters less than 150 microns,
for
example, as disclosed in commonly-owned provisional application serial no.
60/068,255 entitled "Burner and Method For Producing Metal Oxide Soot,"
incorporated herein byreference.
As a result, there has arisen a need for a burner manifold that may be used in
conjunction with these rnicrornachined burners and may distribute fluid
uniformly and
evenly to the burners. In conventional large-scale burners, this uniformity
was achieved
by equally large concentric rings. This solution, however, is not practical
for use with
micromachined burners.
Summary of the Invention
With the advent of micromachined burners, it is desirable to have a burner
manifold apparatus that evenly and uniformly distributes fluid (either vapor
or liquid} to
the micromachined burners.
A burner manifold apparatus in accordance with the present invention
comprises fluid inlets, fluid outlets, and a plurality of fl'.uid passages.
The fluid
passages extend between the fluid inlets and the fluid outlets to deliver
reactants to the
combustion site of a chemical vapor deposition process.. The fluid passages
converge
toward each other from the fluid inlets to the fluid outlets in that inlets of
the fluid
passages are spaced farther apart than outlets of the fluid passages. This
arrangement
facilitates delivery of reactant precursor fluid from a macro scale delivery
system to a
micro scale burner. The fluid passages preferably have a smaller cross-
sectional area at
their outlet than at their inlet.
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The fluid passages generally are isolated from one another so that some fluid
passages transport reactant precursor materials and otlher fluid passages
transport
combustion materials. The fluid passages at the fluid outlets are preferably
shaped to
match the geometry of the burner. In a preferred embodiment, the fluid outlets
are slot
shaped or formed as a series of in-line round holes.
The burner manifold apparatus further includea at least one pressure inducing
restriction device for passing fluid therethrough in evenly distributed,
narrow elongated
streams. The pressure inducing restriction device is positioned between the
fluid inlets
and the fluid outlets. The pressure inducing restriction device preferably
comprises a
plate having a series of slots or linearly arrayed apertures for emitting
fluid therefrom in
generally linear streams of droplets.
One embodiment of the present invention includes a manifold base having a top,
a bottom, a front wall, a back wall, and two side wall;. The manifold base
defines
horizontal passages therethrough that extend between. the side walls, vertical
passages
extending from a position within the manifold base tc> the top of the manifold
base, and
fluid inlet ports. Each fluid inlet port is located on either the front wall
or the back wall
of the manifold base, and each is in fluid communication with at least one of
the
horizontal and vertical passages. The horizontal passages preferably are
parallel to the
top and the bottom of the manifold base, and the vert:icai passages preferably
are
parallel to the side walls of the manifold base.
The burner manifold apparatus of the first embodiment also includes a plate
mounted to the top of the manifold base. The plate defines a plurality of
apertures
therethrough. At least one aperture is positioned at a location above an exit
of each of
the vertical passages of the manifold base to allow passage of fluid from the
vertical
passages through the plate.
The vertical passages of the manifold base are; symmetric about a first axis
bisecting the top of the manifold base. The vertical passages preferably
include a
central vertical passage and pairs of vertical passages, each pair defined by
two vertical
passages spaced equidistant from the first axis. Each. pair intersects a
particular
horizontal passage to create an array of passages witrun the manifold to
distribute fluid
symmetrically abaut the first axis.
The apparatus of the f rst embodiment further includes a manifold burner mount
mounted to the top of the plate. The manifold burner mount defines fluid
passages that
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extend from a bottom of the manifold burner mount to a top of the manifold
burner
mount. These fluid passages are arranged to converge; such that a distance
between
adjacent fluid passages is greater at the inlet of the manifold burner mount
than at the
outlet of the manifold burner mount.
The burner manifold apparatus further compriises a first gasket positioned
between the manifold base and the plate. The first gasket has slots therein in
alignment
with ,grooves in the top of the manifold base. A second gasket preferably is
positioned
between the plate and the manifold burner mount. This second gasket has slots
in
alignment with the slots in the first gasket. A burner l;asket may be placed
upon the
manifold burner mount. The burner gasket has slots iin alignment with the
exits of the
fluid passages in the manifold burner mount.
Securing elements, such as clamps, may be mounted to the top of the manifold
burner mount for releasably securing a burner to the manifold burner mount.
The
clamps each have an outer edge and an inner edge, an:d the inner edge has a
shoulder
that engages the burner. Further, the inner edge of each clamp has a tapered
surface
that tapers away from the top of the manifold burner mount.
A second embodiment of the subject burner rr~anifold apparatus includes a
plurality of manifold elements positioned in a stacked arrangement on top of a
base
element. The manifold elements fluidly communicate with each other via fluid
passages therein. Each of the manifold elements has .a different number of
fluid
passages, preferably increasing by two for each successive element located
higher on
the stack. These fluid passages converge toward eac)~~ other at the outlet of
the-manifold
apparatus. Each of the manifold elements has at least one fluid inlet port,
and
preferably two, with the exception of the lowermost manifold element.
The fluid passages preferably are linear and e~aend vertically through the
manifold elements. The outermost fluid passages of Each of the manifold
elements
communicate with a fluid inlet port, and inner fluid passages are isolated
from the
outermost fluid passages to isolate the fluids introduced into different
manifold
elements. The fluid passages of adjacent manifold elf;irients are in vertical
alignment.
Like the fluid passages in the burner mount of the first embodiment, the fluid
passages
of this second embodiment are symmetric about a cen.trai fluid passage.
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Gaskets are disposed between adjacent ones of the manifold elements. The
gaskets have slots therethrough to allow passage of fluid. The gaskets
preferably are
formed from an elastomer material.
In a third embodiment of the invention, the burner manifold comprises a
tapered
5 section having a first end and a second end, where thc: first end has a
larger surface area
than the second end. The fluid inlets are located at th.e first end of the
manifold, and the
fluid outlets are located at the second end of the manifold. The tapered
section
preferably has a truncated cone shape.
The burner manifold may also comprises a top section coextensive with the
tapered section. The top section has a first end adjoining the second end of
the tapered
section, and a second end for carrying a burner.
The tapered section and the top section of this, third embodiment define a
plurality of fluid passages therethrough to convey fluiid from the first end
of the tapered
section to the second end of the top section. In a preferred embodiment, the
fluid
passages run generally parallel to each other and converge toward each other
from the
fluid inlets at the first end of the tapered section to the fluid outlets at
the second end of
the top section. Selected ones of the fluid passages rnay be blocked or
plugged to
select, by elimination, which passages provide fluid flow.
In this third embodiment, the burner manifold. is formed by an extrusion
process. The burner manifold tapers from a first end to a second end or,
alternatively,
has a tapered section located between the first end and the second end. This
can be
done, for example, by plastically transforming a prefc>rm of parallel channels
(honeycomb substrate) into a funnel of funneling channels. Two suitable
transforming
processes are hot draw down and reduction extrusion. "Hot draw down" is a
viscous
forming process earned out on viscously sintered pre:forms and is described in
commonly-owned provisional application no. 60/091.,107 entitled "Redrawn
Capillary
Imaging Reservoir", incorporated herein by reference. "Reduction extrusion" is
a
plastic forming process carried out on unsintered particulate preforms as
illustrated in
Coming's Provisional P13569 entitled "The Manufacture of Cellular Honeycomb
Structures", incorporated herein by reference. Particc~lates of metal,
plastic, ceramic
and/or glass are compounded and extruded to make the preform. The top section
of the
manifold may be cylindrical, rectangular, or any othen~ shape suitable for
carrying a
burner.
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A fourth embodiment of the invention includes a plurality of burner mounts, a
plurality of plates, and a single manifold base. The rr~anifold has a
thickness dimension
between the front wall and the back wall that is greater than a thickness
dimension of
the burner mounts and the plates such that a plurality of burner mountlplate
combinations may be mounted to the manifold.
The burner manifold apparatus of the present :invention achieves a number of
advantages over conventional burner manifolds. For example, the burner
manifold
apparatus bridges the gap between the conventional 'Smacro" world of manifolds
and
the "micro" world of micromachined silicon wafer burners.
Another advantage is that the burner manifold apparatus is capable of use in
conjunction with a burner having a linear flame array that evenly distributes
fluid
through the manifold and to either side of the burner's linear flame array.
Still another advantage is that the burner manifold apparatus may securely and
precisely mount a micromachined burner wafer in place.
A further advantage is that the burner manifold apparatus may be arranged
adjacent other assemblies to form an array of adjacent burners; which generate
closely
adjacent burner flames.
Yet a further advantage is that the burner manifold apparatus may be produced
by an extrusion process or, alternatively, a hot draw down process.
Still a further advantage of the burner manifold apparatus is that the burner
may
be mounted to the burner mount by an anodic bond, without the need for clamps
or
other mechanical attachment means.
The manifold of the present invention also enaibles and facilitates the use of
miniature micromachined burners in applications for depositing silica soot, in
particular
for making high purity soot fox optical waveguide manufacturing processes.
Additional advantages of the invention will be set forth in the description
which
follows, and in part will be obvious from the description, or may be learned
by practice
of the invention. The advantages of the invention may be realized and obtained
by
means of the instrumentalities and combinations particularly pointed out in
the
appended claims.
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Brief Description of the Drawings
The accompanying drawings, which are incorporated in and constitute a part of
the specification, illustrate a presently preferred embodiment of the
invention, and,
together with the general description given above and the detailed description
of the
preferred embodiment given below, serve to explain tlhe principles of the
invention.
Fig. 1 is an exploded perspective view of a burner manifold apparatus for use
with a micromachined burner wafer in accordance with the invention;
Fig. 2 is a side elevation view, in partial cross section, of the burner
manifold
apparatus and a micromachined burner wafer in accordance with the invention;
Fig. 3 is a top plan view of the burner manifold apparatus, with a burner
mounted thereto, in accordance with the invention;
Fig. 4 is a top plan view of a burner manifold of the burner manifold
apparatus
in accordance with the invention;
Fig. 5 is a side elevation view, in cross section., ofthe burner manifold
along
section line B-B in Fig. 4;
Fig. 6 is a top plan view of a pressure plate of the burner manifold apparatus
in
accordance with the invention;
Fig. 7 is an exploded perspective view of a second embodiment of a burner
manifold apparatus in accordance with the invention;
Fig. 8 is a side elevation view, in cross section, of apparatus parts of the
burner
manifold apparatus shown in Fig. 7, with fluid fittings;
Fig. 9 is a top plan view of the burner manifold apparatus shown in Fig. 7;
Fig. 10 is a side elevation view of a third embodiment of a burner manifold in
accordance with the invention;
Fig. 11 is a bottom plan view of the burner manifold shown in Fig. 10;
Figs. 12A and 12B are top plan views of an alternative design for the third
embodiment shown in Fig. 10; and
Fig. 13 is an exploded perspective.view of a fourth embodiment of a burner
manifold apparatus in accordance with the invention.
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Detailed Description of the Preferred Embodiments
Micromaehined burners, such as those disclosed in commonly-owned
provisional application serial no. 601068,255 to Hawtof et al., have
stimulated the need
for a new, sophisticated burner manifold apparatus for manifolding the flow of
fluid to
the micromachined burners. These micromachined burners are typically
constructed as
wafers and are fabricated on a small scale. For example, burners used for the
production of silica soot for waveguide fber preform may be approximately 1
inch long
by I inch wide. The length and width of the burners can be smaller or larger,
limited by
semiconductor wafer fabrication procedures.
I O These wafer burners are fabricated with precision channels or orifices
having
widths or diameters, respectively, typically smaller than I50 microns, and in
some
embodiments, smaller than IO microns. The channels or orifices preferably are
micromachined in a linear array through the burner. Such micromachining can be
achieved using conventional techniques used in the fabrication of integrated
circuits,
such as Lithography, masking, etching, photochemical processes, reactive ion
etching
(RIE), ultrasonic machining, vertical wall micromachining, and
crystallographic
etching. The specific technique used depends on the burner material,
particularly the
crystal structure and orientation.
Since micromachined burners are much smaller than conventional burners and
are linearly symmetric about their center, conventional manifolds do not work.
A need
has arisen for a burner manifold suited to the new "micro" world of linearly
arrayed
wafer burners, representing a significant change from the conventional "macro"
world
of relatively large, ringed burners.
The burner manifold apparatus of the present invention includes fluid inlets,
fluid outlets, and a plurality of fluid passages extending between the fluid
inlets and the
fluid outlets. The fluid passages converge toward each other from the fluid
inlets to the
fluid outlets. For example, with fluid passages of a rectangular cross
section, the
longitudinal axes of the fluid passage cross sections ape spaced farther apart
at the inlet
end of the passages than at the outlet end to facilitate delivery of precursor
reactants
from a macro scale delivery system to the preferred miicro burner. In this
way, the
wider spaced inlets facilitate easy piping, whereas the closely spaced outlets
enable
alignment with the orifices of a miniature burner. Likewise, the fluid
passages
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preferably have a smaller cross-sectional area at the fluid outlets than at
the fluid inlets.
Thus, the burner manifold apparatus is particularly suited for use with a
micromachined
burner.
Referring now to the drawings, wherein like numerals indicate like parts, and
initially to Fig. 1, there will be seen a first embodiment of a burner
manifold apparatus,
generally indicated 10, in accordance with the invention. The burner manifold
apparatus 10 generally includes a manifold base 12, a pressure plate 14, and a
manifold
burner mount 16. The manifold base 12 illustrated in Fig. 1 has a top 18, a
bottom 20,
a front wall 22, a back wall 23 (in Fig 4), and side walls 24. Horizontal
passages, such
as passages 26 and 27 (see Figs. 2 and 5), extend betvveen the side walls 24
of the
manifold base 12. The manifold base 12 also has vertical passages 30a-30f (see
Figs.
4-5) extending from a position within the manifold base I2 to the top 18 of
the
manifold base 12. With the exception of a central vertical passage 30a, each
vertical
passage 30b-30f intersects and extends upward from a particular horizontal
passage, as
will be explained below in more detail.
It will be understood that the horizontal and vertical passages may be
constructed such that the horizontal and vertical passages are not
perpendicular to each
other. Moreover, whereas the horizontal and vertical passages illustrated are
preferably
linear, they may also be constructed with curvatures and undulations.
The manifold base 12 further has fluid inlet ports 32a, 32b located on either
the
front wall (32a) or the back wail (32b). The fluid inlea ports serve as ports
for fluid
lines to introduce vapors and/or liquids into the manii:old. Each fluid inlet
port fluidly
communicates with at least one of the horizontal and vertical passages. The
horizontal
passages, the vertical passages, and the fluid inlet ports intersect with each
other to
facilitate symmetric distribution of fluid within the manifold.
Turning to Figs. 2, 4, and 5, the vertical passages 30a-30f are symmetric
about a
first axis A-A bisecting the top 18 of the manifold base 12. The vertical
passages
include a central passage 30a and pairs of vertical passages 30b-30f. Each
pair 30b-30f
is def ned by two vertical passages that are spaced equidistant from the first
axis A-A to
distribute fluid symmetrically about the first axis A-A.. Each pair 30b-30f
intersects a
particular horizontal passage to create an array of fluid passages within the
manifold
base 12. In another embodiment, the pairs 30b-30f may be symmetric about a
central
passage 30a that lies off of the first axis A-A.
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The vertical passages 30b-30f are located at diifferent cross-sectional planes
within the manifold, where the planes are defined parallel to section line B-B
and
extend through the manifold top-to-bottom. Vertical ;passages 30a and 30b fall
on the
same plane, as shown in Fig. 4. The vertical passage 30a and pair 30b are
located on
5 section line B-B; pairs 30c and 30d are offset from section line B-B, closer
to the front
wall 22 of the manifold base I2; and pairs 30e and 30f are offset from section
line B-B,
closer to the rear wall 23 of the manifold base 12. The vertical passages 30b-
30f (and
their associated horizontal passages) are fluidly independent from each other
so that, for
example, a first fluid can be piped through vertical passages 30b and a second
fluid can
10 be piped through vertical passages 30c. One of skill in the art will
recognize that the
exact placement of the vertical passages at various planes within the manifold
base 12
can be altered, as long as their symmetry about the first axis A-A is
maintained.
As to the horizontal passages; such as passages 26 and 27, they are located at
different heights in the manifold base I2 and span the manifold base 12
between the
side walls 24. The height location of the horizontal passages is marked by the
location
of the fluid inlet ports 32a, 32b shown in Fig. 2. For example, Fig. 2 shows a
horizontal passage 26 located at a height marked by lowermost inlet port 32b
and a
horizontal passage 27 located at a height marked by ar:other higher inlet port
32b. Each
horizontal passage is fed by a single fluid inlet port 32a, 32b. Put another
way, each
fluid inlet port 32a, 32b intersects a particular horiizont;al passage, wiith
the exception of
the fluid inlet port that intersects central vertical passage 30a (and that
fluid inlet port is
shown as the topmost of inlet ports 32a in Fig. 2). By virtue of this
arrangement, a
single fluid feed line splits the fluid internally in the manifold for even
distribution
between two vertical passages located equidistant from the central vertical
passage 30a.
We have shown only two representative horizontal passages in Fig. 2, although
there are five horizontal passages in a preferred embodiment of the manifold
base 12,
located at heights marked by the five lower inlet ports :32a, 32b. We have
illustrated the
horizontal passages 26 and 27 with different dashed line styles to emphasize
that the
horizontal passages lie in different front-to-back planes within the manifold
base 12.
For example, horizantal passage 26 lies at the central plane defined by
section line B-B
in Fig. 4. Horizontal passage 27, which, in this embodiment of the invention,
fluidly
communicates with the vertical passages 30f, lies in a plane closer to the
back wall 23
of the manifold base 12.
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In addition, the vertical passages 30b-30f are not of a uniform length.
Rather,
the length of the vertical passages 30b-30f varies, depending upon which
horizontal
passage the vertical passages 30b-30f intersect. For example, as shown in Fig.
2, the
vertical passages 30f, which intersect the horizontal passage 27, will be
shorter than the
vertical passages 30b, which intersect the horizontal passage 26.
In slightly different terms than presented above, the orientation of the
passages
and ports in the manifold may be described by reference to an x-y-z coordinate
system
(shown beside Fig. 2). The vertical passages 30a-30f .extend in the y-
direction and shift
along both the x-axis and the z-axis relative to each other. The horizontal
passages, for
example 26 and 27 in Fig. 2, extend in the x-direction and shift along both
the y-axis
and the z-axis relative to each other. Finally, the fluid inlet ports 32a, 32b
extend along
the z-axis and shift along both the x-axis and the y-axiis relative to each
other.
To prevent the flow of fluid out of the manifold, the horizontal passages are
fitted on either end with plugs 33, as shown in Fig. 5.
The invention thus provides an intricate and effective array of fluid
passageways
within the manifold base that ensures an even distribution of the various
fluids
introduced through the inlet ports to both sides of the first axis A-A.
The top 18 of the manifold base i 2 includes grooves 34 positioned above the
exits of the vertical passages 30a-30f. The grooves 34 are elongate and extend
in a
direction parallel to the side walls 24 of the manifold ibase 12. The grooves
34
represent the spaced apart locations of the inlets of the; fluid passages in
that the vertical
passages 30a-30f are fluid inlets.
A pressure plate 14, a top plan view of which its shown in Fig. 6, rests atop
the
manifold base 12. The pressure plate 14 is separated :from the manifold base
12 by a
first gasket 36, as shown in Fig. 1. To allow the passage of fluid from the
manifold
base 12 to the pressure plate 14, the first gasket 36 includes slots 40 that
are in
alignment with the grooves 34 of the top 18 of the manifold base 12. The
pressure
plate 14 in turn includes an array of apertures 38 in aliignment with the
grooves 34. The
apertures 38 are smaller in size than the exits of the vc;rtical passages 30a-
30f. These
apertures 38 are small enough to create a high back pressure and equalize the
fluid flow
through the apertures on either side of the first axis A-A. For example, with
vertical
passages 30f, the associated fluid inlet port 32b is closer to the left
passage 30f than the
right passage 30f. The pressure plate 14 ensures that :fluid introduced
through inlet port
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32b, which, unhindered, would migrate up the left passage 30fmore quickly than
up the
right passage 30f, disperses evenly between the two passages. The pressure
plate 14 in
effect blacks the rapid exit of fluid from the manifold base 12 via a path of
least
resistance. Thus, fluid exits the manifold base 12 through the pressure plate
14 in a
substantially uniform fashion through each of the apertures 38, symmetrically
about the
first axis A-A, and at a substantially constant pressure.
In the embodiment illustrated, the top 18 of the manifold base 12 has a cut-
out,
sized to accommodate the frst gasket 36, the pressure plate 14, and at least a
portion of
a second gasket 42, as best seen in Fig. 2. The second gasket 42 separates the
pressure
plate I4 from the manifold burner mount 16. Like the first gasket 36, the
second gasket
42 has slots 44. These slots 44 are in alignment with the slots 40 of the
first gasket 36,
and thus with the grooves 34 in the manifold base 12 and the aperture array 38
in the
pressure plate 14.
The manifold burner mount 16 is positioned above the second gasket 42. The
manifold burner mount 16 has a top 46 and a bottom 48 and includes fluid
passages 50
that extend from top 46 to bottom 48. The entrances 52 to the fluid passages
50 from
the second gasket 42 are in alignment with the slots 4E4 in the second gasket
42 and the
apertures 38 in pressure plate 14. Fluid passing through the pressure plate 14
travels to
the fluid passages 50 in the manifold burner mount 16. The fluid is
symmetrically
distributed at the time it passes through the pressure plate 34, and it
remains evenly
distributed as it passes through the manifold burner mount 16 to a
micromachined
burner mounted thereon. In the embodiment of Fig. 2, the two outermost
vertical
passages 30f are spare vertical passages and do not adjoin any fluid passages
50 in the
burner mount; however, it will be understood that these outermost vertical
passage 30f
may be used with burner mounts having additional fluid passages.
As explained above, the manifold burner mount 16 is designed for use with a
micromachined burner, preferably a micromachined burner having channels or
orifices
of a small scale. To facilitate this use, the fluid passages 50 are disposeii
such that the
distance between adjacent fluid passages 50 is greater at the bottom 48 of the
manifold
burner mount I6 than at the top 46. The fluid passages SO are preferably
linear and
converge, without intersecting, at the top 46 of the manifold burner mount i
6, where
they meet vertical passages extending through microxnachined burner 58, as
shown in
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Fig. 2. The orientation of the passages that extend through the burner 58 is
shown in
Figs. 2 and 3:
Like the passages through the burner 58, the fluid passages 50 through the
manifold burner mount 16 are generally rectangular, having a longitudinal axis
extending between a back wall 52 and a front wall 54. The outlets 49 of the
fluid
passages 50 form a linear array, symmetric about a central fluid passage. This
linear
array produces one or more linear streams of fluid to the burner 58 mounted
atop the
manifold burner mount 16, and, when the fluid streams combine, the burner 58
generates a flame. The central fluid passage 50 is typically for the
silica/dopant
precursor materials (which can be liquid or vapor), arid the remaining fluid
passages 50
are for gases that react and combust with silica and dopants.
The unique structure of the manifold burner mount 16 bridges the gap between
the "macro" world of manifold and the "micro" world. of micromachined
siliconized.
wafer burners. The outlets 49 of the fluid passages 54) converge such that
they are
I5 spaced closer together than the inlets of the fluid passages 50 (and,
hence, the vertical
fluid passages 30a-30f).
The manifold burner mount 16 may be manufactured by plunge Electrical
Discharge Machine (EDM) technology, either using a~ wire or a plunge which
vaporizes
the metal that comes into contact with the tip of the plunge.
The burner manifold apparatus 10 in accordance with this first embodiment
further includes a burner gasket 60, which is mounted between the top 46 of
the
manifold burner mount 16 and the burner 58. The burner gasket 60 has slots 62
for
alignment with the outlets of the fluid passages 50, including the central
passage, in the
manifold burner mount 16. These slots 62 are also aligned with the slots 64
that form
the linear array in the burner 58. The top 46 of the manifold burner mount 16
has a cut-
out for receiving the burner gasket 60 for accurate placement and alignment of
the
gasket 60.
The burner mount apparatus 10 in this first embodiment also includes burner
securing elements 66 mounted on the top 46 of the rnanifald burner mount 16.
The
securing elements 66 secure the burner 58 and burner gasket 60 to the burner
mount top
46. The securing elements 66 preferably comprise a pair of clamps releasably
secured to
the top 46 of the manifold burner mount 16 by screws 68 and spring rings 69.
The
spring rings 69 are positioned between the clamps 66 and the burner mount top
46. The
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14
clamps 66 have screw holes 71 for receiving the screvvs 68. The spring rings
69 have a
slightly larger diameter than the holes 71 in the clamps 66 and the
coextensive holes in
the burner mount top 46.
The clamps 66 each have an outer edge 70 andL an inner edge 72. The inner
S edge 72 of each clamp 66 has a downwardly facing shoulder 74, as shown in
Fig. 2,
which engages opposite sides of the burner 58 to clamp the burner 58 in place
against
the burner gasket 60. Above the shoulder 74, the inner edge 72 has a tapered
surface 76
tapers away from the burner 58.
To secure the manifold burner mount 16 to the. manifold base 12, the apparatus
10 includes channels 78 that extend completely through the manifold base 12,
adjacent
the side walls 24, and through at least a portion of the manifold burner mount
16. The
apparatus 10 further includes screws 80 for receipt by the channels 78 to
attach the
manifold base I2 to the manifold burner mount 16.
When completely assembled, the burner mount apparatus 10 has a generally
rectangular configuration, with the thickness dimension from the front wall 22
to the
back wall 23. As shown in Fig. 13, the manifold base 116 may be elongated in
the z-
direction such that several burners and burner mount assemblies may be mounted
thereon, side by side. In a preferred embodiment, three fluid lines may be
introduced at
the front wall 118 and the back wall 120 of the burner manifold I I6, totaling
six fluid
lines. The holes 32 extend between the front wall 118 and the back wall 120,
feeding
the several vertical passages 30a-30f in the manifold.
This embodiment enables efficient transference of fluid to several different
burner mounts, resulting in several linear arrays of flame generated by the
side by side
burners. The fluids introduced into the manifold base 116 are distributed
evenly
throughout the manifold base 116, so that the burners produce essentially
uniform
burner flames.
Figs. 7-9 illustrate a second embodiment of the: subject burner manifold
apparatus. As shown in Fig. 8, this burner manifold apparatus, generally
indicated 82,
includes a base element 84 and a plurality of manifold elements 86a-86f
positioned in a
stacked arrangement on top of the base 84. The base 8.4 is preferably solid,
as shown in
cross section in Fig. 8. Each of the manifold elements 86a-86f has a different
number
of fluid passages 88, the number of fluid passages 88 increasing for each
element that is
closer to the top of the stack. For example, the lowerniost manifold element
86a has a
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single fluid passage fed by a single fluid feed line through a port 90. The
fluid passages
are isolated from one another, two new outer fluid passages being introduced
into the
stacked arrangement with each successive manifold element from bottom to top.
For
example, manifold element 86b has three fluid passages, manifold element 86c
has ftve
5 fluid passages, and so on. In this manner, the fluid remains contained until
it reaches
the topmost manifold element 86f and the burner (not shown).
The manifold elements 86b-86f each have two ports 90 so that two fluid feed
lines are needed for each of these elements 86b-86f. 7.'he ports 90 face
opposite
directions for each successive manifold element 86b-86f for ease of attachment
of the
10 fluid feed lines. Fluid is split evenly between the two ports 90 of each
manifold
element 86b-86f. This differs from the first embodiment, where a particular
fluid is
introduced into the burner mount via a single fluid inlet port and then split
internally to
opposite sides of the burner mount.
The manifold apparatus 82 of this second embodiment further comprises
15 gaskets 92 positioned between adjacent manifold elements 86a-86f (the
gaskets are not
shown in Fig. 8). The gaskets 94 may, for example, b~e formed from an
elastomer
material, such as Viton, a product of DuPont Dow Ela.stomers. The gaskets
include
slots 94 that align with the fluid passages in the manifbld elements 86a-86f.
All of the
gaskets 92 may be formed with the same number of slots 94, as illustrated by
the two
gaskets shown in Fig. 7; only those slots in alignment with fluid passages
being used
(for example, only the central slot being used for the gasket positioned
between
elements 86a and 86b). The slots 94, like the fluid passages 88, are
rectangular in
shape.
Fig. 9 shows a top view of,the topmost manifold element 86f in the stacked
arrangement. Here it is apparent that the fluid passages 88 are rectangular in
shape,
with a longitudinal axis extending between a front wall 96 of the manifold
element 86f
and a back wall 98. The fluid passages form a linear ~uray such that a burner,
for
example, burner 58 in Fig. 1, placed on top of the topmost manifold element
86f would
produce a linear flame. And, as with the first embodiment, the fluid passages
are
symmetric about a central fluid passage and converge at the fluid outlets of
the fluid
passages. In addition, the cross section of the fluid inlets are greater than
the cross
section of the associated fluid outlets.
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The manifold elements 86a-86f may be releasably connected by four long rods
(not shown), each channeled in a vertical direction through a set of bores 100
formed in
each corner of the manifold elements 86a-86f, the base element 84, and the
gaskets 92.
The rods may be threaded on each end fox receipt of a nut to secure the rod in
place on
the topmost manifold element 86f and the base elerner~t 84. Also shown in the
top view
of Fig. 9 are bores I O1 for receipt of alignment pins {not shown).
Like the first embodiment, this second embodiment may be used with a
micromachined burner to produce a linear flame for u:>e during a flame
hydrolysis
process.
Figs. 10-12 show a third embodiment of the subject invention. A burner
manifold, generally indicated 102, provides a web-like; or honeycomb structure
capable
of use with micromachined silicon wafer burners. Thc; burner manifold 102
includes a
tapered section 104 and a top section 106. The top section has a first end 107
and a
second end 108. A burner may be mounted to the second end 108 of the top
section
106.
The tapered section 104 has a first end 110 and a second end 112. The first
end
I IO has a larger diameter than the second end 1 I2. The top section 106 is
coextensive
with the tapered section 104; the first end 107 of the top section 106 adjoins
the second
end I 12 of the tapered section 104.
The tapered section 104 and the top section 106 define a plurality of fluid
passages 114 therethrough. The fluid passages 114 convey fluid from the first
end 110
of the tapered section 104 to the second end 108 of thc~ top section 106. The
fluid
passages 114 converge, yet remain isolated from each other, in the tapered
section 104
and this fluid passage convergence is carried over into the top section 106,
as shown in
Fig. 10.
As shown in Fig. 11, the fluid passages may have rectangular cross sections,
forming slots, similar to the shape of the passages in tl~e first two
embodiments. Here,
the top section 106 has a rectangular cross section; however, it will be
understood that
the top section 106 can have any conf guration suitable for use with a
rnicromachined
burner. For example, the top section may be cylindrical, as shown in Fig. 12A
and
indicated 115. This cylindrical top section 115 has fluid passages 116.
In one aspect of the invention, selected ones oj" the fluid passages rnay be
filled
or plugged with a fill material to block the passage of fluid therethrough.
Blocking of
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17
selected fluid passages makes it possible to form fluid passages of any cross-
sectional
shape. For example, selected fluid passages may be blocked to farm rectangular
slots
similar to those shown in Fig. 11, each rectangular slot being comprised of
several
unblocked fluid passages surrounded by blocked fluid/ passages, as,illustrated
in Fig.
12B. The unblocked passages 116, in combination, have a rectangular cross-
section.
This third embodiment may also be formed with only the tapered section. The
tapered section has a first end for carrying a micromac:hined burner and a
second end,
the first end having a smaller surface area than the second end. The tapered
section
defines a plurality of fluid passages therethrough to convey fluid from the
first end to
the second end, and selected ones of the fluid passages may be blocked to
prevent fluid
from passing therethrough.
The burner manifold 102 may be manufactured by reduction extrusion and/or
hot draw down processes and preferably comprises a /;lass material, such as
PYREX, so
that a silicon burner can be bonded directly to the second end 108 via an
anodic bond,
alleviating the need for clamps to secure the burner to the manifold.
Alternatively, the
burner manifold 102 may be composed of a silica material or a ceramic
material. The
silica and ceramic manifolds can be formed by cold reduction extrusion.
Typically, to manufacture the manifold of Figs. 10-12, a preform of parallel
channels (honeycomb) is extruded from particulate material compounded with
liquid
additives. In the special case of amorphous particles that viscously sinter,
the viscously
sintered preform can be hot drawn down viscously to make a taper of channels,
a funnel
of funnels. In the general case, the particulate preforrri (wet-green and
plastic) can be
reduction extruded into a taper. The channels of the particulate preform can
then be
backfilled with a material, such as a polycrystalline wax, which matches the
plasticity
and incompressibility of the webs of the particulate preform sufficiently so
as to then
allow the assembled structure (plastic composite) to plastically deform in a
reasonably
self similar manner as it is extruded into a die of the desired manifold
shape. Suitable
particulate materials include glass, ceramic, metal and/or plastics. After
reduction
extrusion of the backfilled honeycomb preform, the backfill is removed from
the
channels, and the particulate taper is sintered. With a /large array of
channels, selected
channels can be permanently filled or plugged to conveniently create a desired
flow
pattern through the taper. In this manner, the ensemble of fluid passages can
take on
any pixeiated shape, depending on which passages are blocked and which are
not. The
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backfill material may be removable (by a variety of methods) so as to leave an
array of
fluid passages, or it may be permanent so as to form an array of filaments, or
some
combination of the two.
Manufacture of this third embodiment by extrusion is a particularly convenient
method for impressing a taper on a honeycomb structure, and can be carried out
by
forcing the honeycomb from a suitable supporting enclosure (i.e., the barrel
ofa ram
extruder) partially into or through a tapered barrel, mild or extrusion die of
a desired
prismatic, conical, or other tapering form. The extrusion path preferably has
an inlet
cross section close in size and shape to that of the supporting enclosure for
the starting
honeycomb. The extrusion path preferably offers a smooth transition to an
outlet or
receptacle having a different cross-sectional size and/'or shape,
corresponding to a
predetermined channel size and shape for the final honeycomb product.
Any size reduction carned out between the die inlet and outlet will dictate a
corresponding increase in cell density and overall reduction in cell wall
thickness in the
reshaped product, while any change in outlet shape will modify the final cell
shapes
and/or cell wall thickness distributions in that product. Both are
accomplished without
any loss of channel integrity, because flow paths do not cross.
Additional advantages and modifications will readily occur to those skilled in
the art. Therefore, the invention in its broader aspects is not limited to the
specific
details, and representative devices, shown and described herein. Accordingly,
various
modifications may be made without departing from the spirit or scope of the
general
inventive concept as defined by the appended claims.
