Note: Descriptions are shown in the official language in which they were submitted.
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This application is a division of application 290,308, filed
November 7, 1977.
The present invention relates to transducer assemblies and to
apparatus employing same for achieving efficient combustion of fuels. An
example of same is found in the United States patent to H. L. Berger,
3,861,852, issued January 21, 1975.
One problem associated with transducer assemblies of the type used
in apparatus for achieving combustion of fuels is the non-uniform delivery
of fuel to the atomizing surface with consequent non-uniform distribution of
fuel from same. It has been discovered that with such prior art assemblies,
fuels which have low surface tension as, for example, hydrocarbon fuels, begin
to atomize within the fuel passage leading to the atomizing surface. This
premature atomization creates bubbles within the fuel passage. The bubbles
eventually work their way to the atomizing surface, but their arrival at the
atomizing surface results in a temporary interruption in fuel flow to portions
of the surface and, as a result, non-uniform distribution of fuel over the
surface. The bubble remains intact for a short period of time on the atomiz-
ing surface and thus the surface area beneath the bubble during the interval
is not wet with fuel.
According to the present invention there is provided an ultrasonic
transducer having an elongated, longitudinally vibrating probe with a flanged
tip, said flanged tip comprising a vibrating surface capable of causing atom-
ization of a liquid, the transducer further comprising a liquid delivery pas-
sage extending axially through said probe to said atomizing surface and a
decoupling sleeve mounted within said passage and extending to said atomizing
surface for acoustically isolating the interior surface of said passage from
liquid flowing therethrough.
In the accompanying drawings, which illustrate an exemplary embodi-
ment of the present invention and related structures that may advantageously
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be used in conJunction therewith:
Figure 1 is a cross sectional view of a first section of a transduc-
er assembly;
Figure 2 is a cross sectional view of a second section Or the trans-
ducer assembly; and
Figure 3 is a cross sectional view of a complete transducer assem~
bly: -
~eferring to the dra~ing, the design oP a transducer assembly may
be optimized, for among other things, maximum Q, by con~tructing a first
transducer assembly section comprising a driving element and t~o identical
horn sections (Figure 1) such that the resulting structure forms a symmetric
geometry with respect to the longitudinal axis. This first assembly section
is referred to as a double-dummy ultrasonic horn. In the next operation the
resonant frequency of the first section is measured, and a second section is
added (Figure 2) that includes an amplification step and an atomizing sur-
face, and whose theoretical resonant frequency matches the empirically
mea~ured frequency of the first section, thereby forming a complete trans-
ducer assembly (Figure 3) designed for maximum Q and for use in achieving
efficient c bustion of fuels.
Referring first to Figure 1 the first section 11 of the transducer
assembly i8 seen a8 including front 12A and rear 13 ultrasonic horn sections
and a driving element 14 comprising a pair of piezoelectric discs 15, 16 and
an electrode (not shown) positioned therebetween, excited by bigh frequency
electrical energy fed thereto from a te i nal lô.
Driving element 1~ is sandwiched between flanged portions 19, 20
of horn sections 12A, 13 and securely clamped therein by mean~ of a clamping
assembly that includes a mounting ring 21 (for secur~ng the assembly to other
apparatus) and a plurality of assembly bolts 22 which pass through holes in
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terminal 18, flange sections 19 and 20 into threaded openings in mounting
ring 21. The assembly bolts 22 are electrically isolated from the terminal
18 by means of insulators 23.
The first section 11 further includes a fuel tube 24 for introduc-
ing fuel into a channel within the transducer assembly and a pair of sealing
gaskets 26, 27 compressed between horn flange sections 19, 20.
In a typical embodiment: the horn sections 12A, 13 and flange
sections 19, 20 are preferably of good acoustic conducting material such as
aluminum, titanium or magnesium; or alloys thereof such as Ti-6A R-4v
titanium-aluminum alloy, 6061-T6 aluminum alloy, 7025 high strength aluminum
alloy, AZ 61 magnesium alloy and the like; the discs 15, 16 are of lead-
zirconate-titanate such as those manufactured by Vernitron Corporation or of
lithium miobate such as those manufactured by Valtec Corporation; the elec-
trode is of copper; the terminal 18, mounting ring 21, and assembly bolts 22
are of steel; the insulators 23 are of nylon, polytetrafluoroethylene ~such
as sold by Dupont under the trade mark Teflon) or some plastic with good
electrical insulating properties; and, the sealing gaskets 26, 27 are of
silicone rubber.
The first section 11 is seen to have symmetric half-wavelength
geometry, yet it contains all the ana lous features of the transducer assem-
bly, i.e. clamping at non-nodal planes, copper electrode, screw clamping and
mounting bracket. The properties of this first section are established and
its characteristic frequency, for maximum Q, quantitatively measured. Typical-
ly the frequency is measured and found to be 85KHZ. This completes the first
step in the design of the transducer assembly.
Referring to Figure 2, another half-wave section 29 is added to the
first section 11. The section 29 is seen as including a large diameter seg-
ment 12B, a small diameter segment 30 so as to form an amplification step
31, a flanged tip 32 with atomizing surface 33, a central passage 34 for
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delivering fuel to the atomizing surface 33 and internally mounted decoupling
sleeve 35. The decoupling 81eeve i8 a substance such as Te n on which does
not couple well acoustically to the fuel hole.
It will be observed by those skilled in the art that this section
contains few anamolies since it is a pure theoretical structure as well. Its
characteristic frequency for maximum Q is computed and selected 80 as to
match that of the first section 11.
In order to complete the design, the two sections 11 and 29 are
formed integrally so as to yield a transducer assembly (Figure 3) optimized
for maximum Q and for use in achieving efficient combustion of fuels.
Prior art transducer assemblies used for ultrasonic atomization of
fuel have, in the past, typically employed a flanged tip 32 with atomization
surface 33. The presence of the flanged tip with its atomization surface 33
increases atomization capabilities due to increased atomizing surface area.
The addition of such flange has been at the expense of atomizer
efficiency.
Referring to Figure 2, let A = length of horn front section 12B,
B ~ length of small diameter segment 30 and C = thickness of flanged tip sec-
tion 32.
In prior art assemblies that do not use a flange, A = 1 since they
are both quarter wave length sections.
In prior art assemblies utilizing a flange A = 1.
BIC
It has been determined that maintaining the ratio at 1, even a M er
addition o~ the flange, is inefficient and reduces power transfer, but by
maintaining the ratio A ~ 1 efficiency levels can be maintainea at pre-
~C
flange addition levels. Thus, for example, if
~3 = diameter of flange section 32
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D2 = diameter of small diameter segment 30 for
3 = 1.53
~2
A (without flange) = A = 1
B+C B
and A (with flange) = 1.12
B+C
and the efficiency levels achieved with the flange match those of the assembly
with the flange. .
~ he foregoing analysis applies to assemblies of aluminum, titanium,
magnesium and previously mentioned alloys, and assumes that for both mate-
rials the velocity of sound in same is approximately the same. For other
0 materisls with different velocities of sound the ratio A will differ, but
BIC
always be greater than 1.
The long-term reliability of the device is dramatically enhanced by
sealing the discs 15 since fuel contamination is no longer possible. The
space between the clamping flange sections 19, 20 is filled with a silicone
rubber compound as by sealing gaskets 26, 27. In the past, fuel creepage onto
the faces of the discs 15, 16 has caused degradation of sPm~ and has resulted
in poor long-term atomizer performance. The phenomenon causes a 1088 in
mechanical coupling between elements of the horn. The gaskets 26, 27 solve
the problem and atomizer performance is not affected by the added mass as has
been confixmed by before and after measurement of impedance, operating fre-
quency and flange displacement. The slightly higher internal heating caused
by sealing the discs 15 does not reduce the atomizer's useful life since
internal temperatures are still well below the m~ximum operating temperature
for piezoelectric crystals. The gaskets 26, 27 are of a compressible material
and have an inner periphery conforming to but initially sl~ghtly greater than
the outer circumference of the discs 15, 16. Upon clamping the inner periph-
ery of gaskets 26, 2~ come into light contact with the outer circumference of
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the discs 15, 16.
The present application is concerned with the elimination of pre-
mature atomization Or fuel in the fuel passage leading to the atomizing sur-
fsce. As noted previously, in prior art structures the fuel can begin to
atomize within the fuel passage leading to the atomizing surface. This pre-
mature atomization creates voids within the fuel passage at the fuel-wall
interface which leads to the formation of bubbles within the fuel passage.
The bubbles eventually work their way to the atomizing surface, but their
arrival at the atomizing surface results in a temporary interruption in fuel
flow to a portion of the surface and as a result, non-uniform distribution of
fuel over the surface. The bubble remains intact for a short period of time
on the atomizing surface and thus the surface area beneath the bubble during
that interval is not wet with fuel. The net effect of thls non-uniform and
constantly varying distribution of fuel on the surface is a spatially un-
stable spray of fuel, a condition which leads to unstable combustion.
The foregoing problem is eliminated by the provision of a decoupling
sleeve 35 within the fuel passage 3~l that extends up to, say within 1/32 of
an inch of the atomizing surface 33. The sleeve is typically i e of plastic
and press fit into passage 34 extending inwardly to large diameter segment
12b. The difference in acoustical transmitting properties between the mate-
rial of the sleeve 35 and the horn section 29 is such that the vibrating
motion of section 29 is not imparted to the fuel within the fuel passage 3
encompassed by the sleeve 35.
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