U.S. patent application number 14/119560 was filed with the patent office on 2014-08-07 for manipulation of flames and related methods and apparatus.
This patent application is currently assigned to President and Fellows of Harvard College. The applicant listed for this patent is Kyle J.M. Bishop, Ludovico Cademartiri, Ryan C. Chiechi, Charles R. Mace, Aaron D. Mazzeo, Robert Shepherd, George M. Whitesides. Invention is credited to Kyle J.M. Bishop, Ludovico Cademartiri, Ryan C. Chiechi, Charles R. Mace, Aaron D. Mazzeo, Robert Shepherd, George M. Whitesides.
Application Number | 20140220500 14/119560 |
Document ID | / |
Family ID | 48044351 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140220500 |
Kind Code |
A1 |
Cademartiri; Ludovico ; et
al. |
August 7, 2014 |
MANIPULATION OF FLAMES AND RELATED METHODS AND APPARATUS
Abstract
Manipulation of flames is described using electric fields. In
those instances in which electric fields are used, the electric
fields may be time-varying gradient electric fields, and in some
instances may be oscillating electric fields. The manipulation may
include extinction, suppression, control of mixing of the flame,
concentration, and/or bending, among other types.
Inventors: |
Cademartiri; Ludovico;
(Somerville, MA) ; Mace; Charles R.; (Auburn,
NY) ; Shepherd; Robert; (Somerville, MA) ;
Mazzeo; Aaron D.; (Cambridge, MA) ; Bishop; Kyle
J.M.; (University Park, PA) ; Chiechi; Ryan C.;
(Cambridge, MA) ; Whitesides; George M.; (Newton,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cademartiri; Ludovico
Mace; Charles R.
Shepherd; Robert
Mazzeo; Aaron D.
Bishop; Kyle J.M.
Chiechi; Ryan C.
Whitesides; George M. |
Somerville
Auburn
Somerville
Cambridge
University Park
Cambridge
Newton |
MA
NY
MA
MA
PA
MA
MA |
US
US
US
US
US
US
US |
|
|
Assignee: |
President and Fellows of Harvard
College
Combridge
MA
|
Family ID: |
48044351 |
Appl. No.: |
14/119560 |
Filed: |
May 31, 2012 |
PCT Filed: |
May 31, 2012 |
PCT NO: |
PCT/US12/40171 |
371 Date: |
April 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61559677 |
Nov 14, 2011 |
|
|
|
61491836 |
May 31, 2011 |
|
|
|
Current U.S.
Class: |
431/8 |
Current CPC
Class: |
F23C 99/001 20130101;
F23N 5/00 20130101 |
Class at
Publication: |
431/8 |
International
Class: |
F23N 5/00 20060101
F23N005/00 |
Goverment Interests
GOVERNMENT FUNDING
[0002] Research leading to various aspects of the present invention
were sponsored, at least in part, by the Department of Defense
under DARPA Award #w911nf-09-1-005. The U.S. government has certain
rights in the invention.
Claims
1. A method, comprising: manipulating a flame by applying a
time-varying three-dimensional gradient electric field to the
flame.
2. The method of claim 1, wherein the time-varying
three-dimensional gradient electric field has a magnitude given by
E.apprxeq.1 MV/m, a gradient between dE/dr.apprxeq.10.sup.7
V/m.sup.2 and dE/dr.apprxeq.10.sup.9 V/m.sup.2, and a frequency
given by f.apprxeq.1000 Hz.
3. The method of claim 1, wherein the flame is generated by a
liquid fuel source.
4. The method of claim 1, wherein the flame is generated by a
gaseous fuel source.
5. The method of claim 1, wherein the flame is generated by a solid
fuel source.
6. The method of claim 1, wherein the flame is a toluene flame.
7. A method, comprising: extinguishing a flame by application of an
oscillating three-dimensional gradient electric field to the
flame.
8. The method of claim 7, wherein the oscillating three-dimensional
gradient electric field has a gradient of approximately
dE/dr.apprxeq.=10.sup.8 V/m.sup.2 at a center of the flame.
9. The method of claim 7, wherein extinguishing the flame by
application of an oscillating three-dimensional gradient electric
field comprises inducing lift off of the flame by application of
the oscillating three-dimensional gradient electric field.
10. The method of claim 7, comprising using an electrode to apply
the oscillating three-dimensional gradient electric field to the
flame.
11. The method of claim 7, comprising applying the oscillating
three-dimensional gradient electric field in a direction
substantially perpendicular to a direction of flow of the
flame.
12. A method, comprising: suppressing a flame by application of an
oscillating three-dimensional gradient electric field.
13. The method of claim 12, wherein the oscillating
three-dimensional gradient electric field has a gradient of
approximately dE/dr.apprxeq.10.sup.8 V/m.sup.2 at a center of the
flame and a magnitude of approximately 1 MV/m at the center of the
flame.
14. The method of claim 12, wherein suppressing a flame comprises
preventing contact between a flame and a fuel source.
15. The method of claim 14, wherein preventing contact between the
flame and the fuel source comprises creating an outflow from the
flame that diverts the fuel source from the flame.
16. A method, comprising: bending a flame by application of an
oscillating three-dimensional gradient electric field to the
flame.
17. The method of claim 16, wherein the oscillating
three-dimensional gradient electric field has a gradient of
approximately dE/dr.apprxeq.10.sup.8 V/m.sup.2 at a center of the
flame and a magnitude of approximately 1 MV/m at the center of the
flame.
18. A method, comprising: controlling mixing in a flame by
application of an oscillating three-dimensional gradient electric
field to the flame.
19. The method of claim 18, wherein the oscillating
three-dimensional gradient electric field has a gradient of
approximately dE/dr.apprxeq.10.sup.8 V/m.sup.2 at a center of the
flame and a magnitude of approximately 1 MV/m at the center of the
flame.
20. A method, comprising: concentrating a flame by application of
an oscillating electric field to the flame.
21. The method of claim 20, wherein the oscillating
three-dimensional gradient electric field has a gradient of
approximately dE/dr.apprxeq.10.sup.8 V/m.sup.2 at a center of the
flame and a magnitude of approximately 1 MV/m at the center of the
flame.
22. The method of claim 20, comprising applying the oscillating
gradient electric field in a direction substantially parallel to a
direction of flow of the flame.
23. A method, comprising: manipulating a flame by applying a
time-varying electric field to the flame, the time-varying electric
field being non-uniform in three dimensions.
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Application Ser. No. 61/491,836
filed May 31, 2011 entitled "CONTROL AND EXTINCTION OF FLAMES BY
OSCILLATING ELECTRIC FIELD GRADIENTS" and U.S. Provisional
Application Ser. No. 61/559,677 filed Nov. 14, 2011 as Attorney
Docket No. H0498.70424US00 and entitled "MANIPULATION OF FLAMES AND
RELATED METHODS AND APPARATUS," the entire contents of both of
which is incorporated herein by reference.
BACKGROUND
[0003] Combustion processes, and the flames associated therewith,
are common. Yet, our understanding of fire, and how to control it
remains incomplete.
BRIEF SUMMARY
[0004] According to one aspect, manipulation of flames using
electric fields is described. The manipulation may be performed by
applying a time-varying gradient electric field to the flame. The
flame may be any of various types, as the present aspect is not
limited in this manner.
[0005] According to another aspect, a method comprises
extinguishing a flame by applying an oscillating gradient electric
field to the flame. According to another aspect, a method comprises
suppressing a flame by applying an oscillating gradient electric
field to the flame. According to another aspect, a method comprises
bending a flame by application of an oscillating gradient electric
field to the flame. According to another aspect, a method comprises
controlling mixing in a flame by application of an oscillating
gradient electric field to the flame. According to another aspect,
a method comprises concentrating a flame by application of an
oscillating gradient electric field to the flame.
[0006] Further aspects and embodiments are described below.
BRIEF DESCRIPTION OF DRAWINGS
[0007] Various aspects and embodiments of the technology will be
described with reference to the following figures. It should be
appreciated that the figures are not necessarily drawn to scale.
Items appearing in multiple figures are indicated by the same or a
similar reference number in each of the figures in which they
appear.
[0008] FIG. 1 illustrates a non-limiting embodiment of a system
which may be used to manipulate a flame by application of a
time-varying electric field to the flame.
[0009] FIG. 2 shows a graph of the values of the probability of
extinction, P, and the angle of deflection (a) in degrees as a
function of frequency in Hertz (Hz) for the voltage V=20 kV of the
signal applied to an electrode and the distance .delta.=6 mm of the
electrode from the a flame.
[0010] FIG. 3 shows the dependence on electric field frequency of
the probability of extinction, P, of a methane/air conical
diffusion flame as a function of the peak voltage of the sinusoidal
voltage signal applied to the electrode.
[0011] FIG. 4 shows the dependence of the critical electric field
frequency (in Hz) at which flame extinction ensues on the peak
voltage (in kV) applied to the electrode, as obtained from the data
shown in FIG. 2.
[0012] FIG. 5 illustrates dependence on electric field frequency of
the probability of extinction, P, of a methane/air conical
diffusion flame as a function of the distance between the tip of
the metal electrode and the mouth of the burner.
[0013] FIG. 6 shows the dependence of the critical frequency on the
distance between the tip of the Pt electrode and the mouth of the
burner as obtained from the data shown in FIG. 4.
[0014] FIG. 7 illustrates a non-limiting example of a configuration
for concentrating a flame using an electric field.
[0015] FIGS. 8A-8D each illustrate a photograph of a non-limiting
configuration for concentrating a flame with an electric field as
well as a plot of temperature data resulting therefrom.
[0016] FIG. 9 illustrates a non-limiting configuration in which a
time-varying electric field may be used to suppress a flame.
[0017] FIG. 10 illustrates a non-limiting example of a
configuration which may be used to increase flow of a fluid by
creating a plume.
[0018] FIGS. 11A and 11B illustrate non-limiting examples of a
suitable configuration for the electrode 104 and sheath 116 of FIG.
1.
[0019] FIG. 12 illustrates a non-limiting example of a
configuration which may be used to suppress or extinguish flames
using a combination of thermal quenching and electric fields.
[0020] FIG. 13 illustrates a non-limiting example of a
configuration in which a mobile electrode may be used to manipulate
a flame.
DETAILED DESCRIPTION
[0021] According to various aspects of the present application,
methods and apparatuses for manipulating flames are provided. The
manipulation may take various forms, including, but not limited to,
extinguishing a flame, suppressing a flame, bending a flame,
controlling mixing of the flame, and concentrating the flame. Such
manipulation may be useful in various applications in which control
of a flame is desired.
[0022] According to a first aspect of the present application, a
flame may be manipulated by applying an electric field to the
flame. The electric field may be a time-varying electric field, and
in some embodiments may be an oscillating electric field (e.g.,
oscillating between a positive electric potential and a negative
electric potential). Moreover, in some embodiments the electric
field may have a gradient associated therewith, rather than being a
uniform electric field. In some embodiments, the electric field may
exhibit a gradient in three dimensions, though not all embodiments
are limited in this respect. Thus, according to a non-limiting
embodiment of the present aspect, a flame may be manipulated with
an oscillating gradient electric field. The electric field may be
applied to the flame with one or more electrodes, as non-limiting
examples.
[0023] The aspects described above, as well as additional aspects,
are described further below. These aspects may be used
individually, all together, or in any combination of two or more,
as the technology is not limited in this respect.
[0024] Manipulation of Flames Using Time-Varying Electric
Fields
[0025] According to a first aspect, manipulation of flames is
accomplished using time-varying electric fields. In one embodiment,
the time-variation may be sinusoidal, and the electric field may be
an oscillating electric field. The electric field may, in some
embodiments, have a gradient, which may facilitate achieving
certain types of manipulation. Various non-limiting examples are
described further below.
[0026] Manipulation of flames using a time-varying electric field
may depend, at least partially, on some parameters of the flame as
well as some parameters of the electric field. For example, flame
parameters which may influence whether, and to what extent, the
flame may be manipulated by application thereto of a time-varying
electric field include the amount of soot in the flame and the size
of the flame source (e.g., the size of the burner used to create
the flame if a burner is used). Parameters of the electric field
that may impact the effectiveness of manipulation include the field
strength, field gradient, and field frequency (e.g., in those
embodiments in which an oscillating electric field is used). The
distance of the electric field source (e.g., an electrode) from the
flame as well as the electrode configuration may also impact the
effectiveness of manipulation.
[0027] Applicants have appreciated that flames are charge neutral
polarizable media. The effect of electric field stimulation on a
flame can be understood by considering the concentration of ions
that is present in most flames, which may range, for example, from
approximately 10.sup.8 to approximately 10.sup.11 ions per cubic
centimeter (ions/cm.sup.3). Despite their low concentration, the
driven motion of these ions in response to an external electric
field, and the consequent transfer of momentum to neutral
molecules, imparts upon the flame a collective behavior. For
sufficiently strong electric fields, this process can result in
macroscopic gas flows--so-called ionic or electric wind--with
speeds of up to ten meters per second. When placed in the proximity
of a flame, the resulting gas flows may serve to manipulate the
flame. However, not all embodiments described herein relating to
manipulation of flames with electric fields are limited to
manipulation arising from generation of an electric wind, as other
physical mechanisms may also or alternatively be implicated. In
fact, in at least some embodiments, manipulation of a flame is
achieved without an ionic wind.
[0028] According to one non-limiting embodiment, a flame may be
extinguished by application thereto of a time-varying gradient
electric field. The electric field may be applied by an electrode
placed in proximity to the flame. Various types of electrodes may
be used. According to one embodiment, a rod-shaped electrode may be
used (e.g., a wand-shaped electrode). According to one embodiment,
a point electrode, e.g., from a wire, may be used. According to
another embodiment, a wire electrode may be used. Alternatively,
plate shaped electrodes may be used in some embodiments. The
electrode may be covered/insulated in some embodiments, for example
to minimize or prevent formation of a corona on the electrode. The
electrode may have any suitable size, shape, and material to
provide a desired electric field. As will be appreciated from the
following non-limiting examples, manipulation of flames (e.g.,
extinction) may be achieved according to some non-limiting
embodiments with one or more electrodes (e.g., with one electrode,
two electrodes, three electrodes, or more). Extinction may occur
when lift off is achieved, which may represent the displacement of
the combustion zone of the flame from the burner.
[0029] In some embodiments, the electrode (or electrodes) used to
apply a time-varying electric field may be stationary. In other
embodiments, the electrode(s) may be mobile. Further explanation of
a non-limiting example of the use of mobile electrodes to apply a
time-varying electric field to a flame is provided in FIG. 13.
[0030] A non-limiting example of a configuration in which a flame
may be extinguished using an oscillating gradient electric field is
illustrated in FIG. 1. The illustrated system 100 includes a
chamber 102, an electrode 104, a counter electrode 106, an electric
signal source 108, a burner 110, and a flame 112. Diffusers 114 are
also included to introduce oxygen into the chamber. A sheath 116
(e.g., made of borosilicate glass or any other insulating material)
encloses at least one end of electrode 104 proximate the flame. The
electrode 104 may be spaced from the flame by a distance
.delta..
[0031] A non-limiting example of a suitable configuration for the
electrode 104 and sheath 116 is illustrated in FIGS. 11A and 11B,
which include various dimensions. It should be appreciated that
other configurations are also possible.
[0032] As shown, the flame 112 may be deflected from the vertical
118 by an angle .alpha. in response to application thereto of an
oscillating gradient electric field from the electrode 104. The
electric field may have any suitable frequency and magnitude to
deflect the flame by a desired angle .alpha., as the various
aspects described herein are not limited to use of electric fields
having any particular magnitude and/or frequency. For purposes of
explanation, some non-limiting examples are described further
below.
[0033] It should be appreciated that the illustrated electrode
configuration is non-limiting. While a wire-shaped electrode is
illustrated, other shapes may be used, including rod-shaped
electrodes, and in some embodiments plate shaped electrodes, though
these are only non-limiting examples. In the illustrated
configuration, the resulting electric field may exhibit a gradient
in three dimensions, though not all embodiments are limited in this
respect. The configuration may allow for achieving larger fields
strengths and/or field gradients than may be possible in
configurations in which the electric field gradient is limited to
only two dimensions. Thus, a configuration in which a gradient is
exhibited in three dimensions may facilitate achieving various
types of manipulation of a flame, such as extinction.
[0034] Also worth noting is that in some embodiments (e.g., the
configuration of FIG. 1), the flame may be positioned substantially
between the electrode and the counter electrode (e.g., the flame
may be located on a line between the electrode and the counter
electrode). Such a configuration may facilitate achieving the types
of manipulation described herein.
Example 1
[0035] A non-limiting example of the operation of system 100 is now
provided for purposes of illustration. It should be appreciated
that the manner of operation and the specific parameters listed are
non-limiting.
[0036] The methane burner 110 was enclosed in a 0.1 m.sup.3 cubic
chamber 102 of 0.5 cm-thick panels of ROBAX.RTM., a refractory,
electrically insulating, and highly transparent glass ceramic. The
top panel was instead a glass-filled PTFE sheet (0.32 cm.times.61
cm.times.61 cm) with a hole 120 (15 cm diameter) in its center,
which served as a chimney for the combustion products. The burner
comprised a cylindrical tube of machinable Al.sub.20.sub.3 (0.32 cm
inner diameter; 2 cm outer diameter; 25 cm in length) and was
lodged tightly into a hole in the center of the bottom panel of the
chamber. Methane was introduced from the bottom hole of the burner
through a one-way valve, and the flow was monitored by a gas flow
meter. The methane flow was kept at 540.+-.23 ml/min for all
experiments reported here.
[0037] Air was introduced into the system via two flexible bubble
diffusers (Flexible Bubble Wand, Marineland), which lined the
bottom inside perimeter of the chamber. The diffusers were covered
with a PTFE mesh (635 um.times.127 um rhombic-shaped holes) to
further diffuse the inlet air flow and connected to a compressed
air tank through a flow meter. The air flow rate was maintained at
19.+-.2 l/min for all experiments.
[0038] The electrode 104 was a Pt wire (0.5 mm diameter) with a
rounded parabolic-like tip created via chemical etching, though the
aspects described herein as utilizing a rounded parabolic-like
electrode are not limited to the manner in which the electrode is
created. Furthermore, other electrode geometries are also possible,
as a rounded parabolic-like electrode tip is a non-limiting
example. The electrode was encased in custom-made borosilicate
glass sheath (2 mm thick on the sides of the wire, 5 mm thick at
the tip). The purpose of the sheath was to (i) electrically
insulate the flame from the electrode (e.g., to prevent are
formation between the electrode and the flame) and (ii) to prevent
the formation of the so-called ionic wind emanating from the corona
discharge at the electrode tip. The electrode was connected to an
AC power amplifier (TREK 30/20A), driven by a signal generator
(Agilent 33220A). The amplifier's output current and voltage were
monitored with an oscilloscope (Tektronix TDS 2024D).
[0039] The electrode 104 was positioned horizontally at a height of
1.5 cm above the burner 110, and its tip was oriented towards the
center of the burner (cf. FIG. 1) The sheathed electrode was
supported by a stack of glass slides positioned 7 cm from the
burner and fastened with insulating tape.
[0040] The counter electrode 106 was a 45 cm.times.45 cm.times.1 cm
aluminum plate, fastened to the interior side of the chamber
opposite the electrode and the flame. The distance between the
electrode tip and the plate was .delta.=25.5 cm.
[0041] Before an experiment, the interior of the chamber was
cleaned of soot. The flame and the air flow were turned on at least
one hour before the beginning of the experiment to allow the
thermalization of the setup. The temperature at the internal
surface of the side panels of the box was found to stabilize at
39.+-.2.degree. C.
[0042] The flame was subjected to AC fields using a sinusoidal
waveform of various amplitudes (15-30 kV) and frequencies (10-2000
Hz). The distance between the tip of the electrode (i.e., the outer
surface of the glass sheath) and the mouth of the burner was varied
from 6 to 15 mm.
[0043] For a constant voltage and a distance .delta.<11 mm, as
the frequency of the oscillation of the voltage (and therefore the
electric field) was increased, the flame was increasingly
deflected. This deflection of the body of the flame is constant in
time and no obvious turbulence is observed. As the frequency is
further increased and the deflection approaches 90.degree. the
flame is extinguished with increasing probability.
[0044] For a given voltage, V, frequency, f, and distance, .delta.,
the angle of deflection .alpha. and the probability of extinction,
P, were measured. Movies (at 1 frame per second) were collected of
all events. The angle of deflection a of the flame for a certain
set of experimental parameters was determined by averaging all of
the stills (still images) from all events performed under those
conditions. The resulting image was then analyzed to determine the
major axis of "inertia" of the flame. The manner of analysis is
described in the Appendix of the present application, though it
should be appreciated that the various aspects of the technology
described herein are not limited to the manner in which deflection
is calculated, or to calculating deflection of the flame at
all.
[0045] The probability of extinction, P, was estimated as the
fraction of successful extinction events (within a set of 10-30)
following the application of the field for 10 sec. If the flame was
extinguished by the field, it was reignited, and the flame was left
burning undisturbed for 30 seconds before attempting another
extinction event. If the flame was not extinguished by the field
within 10 seconds following the application of the field, the field
was turned off. The flame was then left undisturbed for 30 seconds
before starting another event. These 30 second pauses between
events prevented correlation between events.
[0046] Manipulation of flames using time-varying electric fields
may apply to various flame types (i.e., flames resulting from
combustion of various types of fuels), unless otherwise stated,
including liquid, gas, and solid flames, flames categorized as
National Fire Protection Association (NFPA) Class A (e.g., paper,
wood, plastic, etc.), Class B (liquid and gaseous fuel sources),
and/or Class C, flames from gels, or any other types of flames.
Ethanol, methanol, toluene, and hexane are non-limiting examples of
liquid flame types to which one or more aspects of the present
application may apply. In some embodiments, diffusion flames may be
used. In some embodiments, flames having conductive particulates
may exhibit the greatest degree of response to an applied electric
field. The breadth in flame types to which the presently described
techniques may apply is due at least in part to the fact that
oscillating gradient electric fields operate on a minority
component of the flame which has a characteristic which is shared
across flames of the most diverse kinds: electric charge, and not
on parameters such as fuel and oxidizer availability, heat, or the
radical chain reaction. Thus, again, ethanol, methanol, toluene,
and hexane are only non-limiting examples of fuel sources to which
aspects of the present application may be applied. Other types of
flames are also possible.
[0047] The electric field may have any suitable magnitude and
frequency to extinguish a given flame. In some embodiments, such as
that of FIG. 1, the electric field may be an alternating current
(AC) electric field having a sinusoidal waveform. The signal
generating the electric field may have any suitable voltage to
generate a suitable magnitude electric field. As a non-limiting
example, the voltage of the applied signal may be between 15-30 kV,
between 10-50 kV (e.g., 10 kV, 15 kV, 20 kV, etc.), between 20-25
kV, or have any other suitable value. The frequency of oscillation
of the applied signal (the signal applied to the electrode 104),
and therefore of the electric field itself, may be, for example,
between 10-2000 Hz, between 100-50000 Hz, between 100-300 Hz,
between 300-600 Hz, between 400-500 Hz, between 100-1000 Hz (e.g.,
100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, eta), or any other
suitable value, as these are non-limiting examples. According to a
non-limiting embodiment, an electric field having the following
parameters may be used to manipulate, and in some instances
extinguish, a flame: E.apprxeq.1 MV/m, dE/dr.apprxeq.10.sup.8
V/m.sup.2, and f.apprxeq.1000 Hz). Other values are possible.
[0048] The electric field may have any suitable gradient. According
to some embodiments, the gradient may be a three-dimensional
gradient, while in others the gradient may exist in fewer than
three dimensions (e.g., two dimensions). The gradient may range, in
some non-limiting embodiments, between approximately
dE/dr.apprxeq.10.sup.6 V/m.sup.2 and dE/dr.apprxeq.10.sup.10
V/m.sup.2 (e.g., dE/dr.apprxeq.10.sup.7 V/m.sup.2,
dE/dr.apprxeq.10.sup.8 V/m.sup.2, dE/dr.apprxeq.10.sup.9 V/m.sup.2,
etc.). Other gradient values are also possible.
[0049] The distance from the electrode generating the electric
field to the source of the flame (e.g., to a burner when a burner
is used) may take any suitable value. According to some
embodiments, the closer the electric field source is to the flame
the more easily the flame may be extinguished. According to some
embodiments, the source electrode may be between approximately 5 mm
and 30 mm from the source of the flame (e.g., between 6 mm and 15
mm, between 10 mm and 25 mm, etc.), or any other suitable
distance.
[0050] The impact of the electric field characteristics and the
distance from the electrode to the flame on the deflection and
extinction of flames is illustrated in some non-limiting example
graphs, and now explained. Generally, both the angle of deflection,
.alpha., and the probability of extinction, P, increase with
increasing frequency. More specifically, the dependence of P on
frequency exhibits a threshold-like behavior, whereby the flame is
reliably extinguished primarily, and in some situations only, above
a certain "critical" frequency, which we define as the frequency at
which P=50%.
[0051] FIGS. 2 and 3 illustrate data indicative of this
generalization. FIG. 2 shows a graph of the values of P and .alpha.
(in degrees) as a function of frequency (in Hz) for V=20 kV and
.delta.=6 mm. Above the graph is a set of three pictures of the
flame 210 taken at the indicated frequencies (20 Hz, 310 Hz, and
400 Hz), showing the increasing deflection in the flame 210 with
increasing frequency. The positions of the burner 212 and of the
electrode 214 are also indicated.
[0052] The probability of extinction, P, increases with increasing
voltage of the applied signal, and therefore with increasing
electric field strength. FIG. 3 illustrates a graph showing a
non-limiting example of data supporting this statement. This plot
shows the dependence on frequency (in Hz) of the probability of
extinction, P, of a methane/air conical diffusion flame as a
function of the peak voltage of the sinusoidal voltage signal
applied to the electrode. No extinction was observed for V<16 kV
within the range of frequencies experimentally tested.
[0053] The critical frequency, f.sub.c, decreases with increasing
voltage (see also FIG. 4, which shows the dependence of the
critical frequency (in Hz) at which flame extinction ensues on the
peak voltage (in kV) applied to the electrode, as obtained from the
data shown in FIG. 2), in a manner that can be fitted by a decaying
exponential (see FIG. 4):
[0054] (f.sub.c=.ae butted..sup.-bV, where f.sub.c is the critical
frequency, V is the voltage of the applied signal,
a=1.1.times.10.sup.5 Hz and b=0.28 V.sup.-1) or with a power law
(see FIG. 4) (f.sub.c=cV.sup.-d with c=3.2.times.10.sup.9 Hz and
d=5.4).
[0055] FIG. 5 illustrates dependence on frequency (in Hz) of the
probability of extinction, P, of a methane/air conical diffusion
flame as a function of the distance between the tip of the metal
electrode and the mouth of the burner. The data represent five
distances: 6 mm, 10 mm, 11 mm 12.5 mm and 15 mm. It can be seen
that P decreases with increasing distance. The extinction behavior
is similar for .delta.=6, 10, and 11 mm, while there is no
extinction for .delta.>12.5 mm. While at 11 mm of distance, the
response of the flame to the field is repulsive, at 12.5 mm the
response is a mixture of attractive and repulsive, with the flame
becoming shorter and wider, as if stretched horizontally by the
field. The critical frequency of suppression may be independent of
distance, as long as the distance is sufficiently small to elicit
the suppressive "response" (see FIG. 6, which shows the dependence
of the critical frequency (in Hz) on the distance (in mm) between
the tip of the Pt electrode and the mouth of the burner as obtained
from the data shown in FIG. 4). Such behavior may arise from a very
sharp distance dependence (e.g., a power law with large exponent)
of the effective force operating on the flame.
[0056] Extinction of a flame by application of a time-varying
electric field thereto, when P=.about.50%, may progress in stages.
The flame is initially strongly deflected (.about.70-90 degrees).
The flame loses all traces of soot emission (possibly due to
cooling, or more plausibly due to the efficient removal of soot
particles from the hot zone). The flame front oscillates
erratically at about 2-5 cm from the burner, as if pushed by two
opposing driving forces. On one side the flame propagation which
drives the flame front back to the burner. On the other side, the
effective force generated by the electric field is pushing it away
from the burner. This behavior fades as P increases to 100% with
increasing frequency. In such conditions extinction happens within
the first second of the application of the field. At frequencies
much lower than the critical frequency (P.about.0), the flame
remains "attached" to the burner and is only deflected.
[0057] Though the various aspects described herein are not limited
to utilizing any particular physical mechanism for extinguishing
flames, it is noted that in at least some embodiments the
extinction of the flame may be caused at least in part by forcing
the combustion region away from the fuel source using an
oscillating gradient electric field. The electric field may
accelerate the ions within the flame, resulting in a transfer of
momentum having a non-zero net average, and thus leading to
repulsion of the flame from the electrode applying the electric
field. When the speed of repulsion of the flame is less than the
speed of propagation of the flame to the burner, the flame may not
be extinguished but rather may be deflected. When the speed at
which the flame is projected away from the burner (the fuel source)
is greater than the speed at which the flame can propagate to the
burner (which happens to be approximately 1 m/s for a CH.sub.4/air
diffusion flame), the flame may be blown off the fuel source and
thus extinguished.
[0058] The behavior of flames in response to the application of a
time-varying electric field may be due, at least in part, to the
Ponderomotive Force. The Ponderomotive force, F.sub.p, may take the
form:
Fp = - q 2 o ( E o 2 ) 4 m .omega. 2 [ 1 + ( .lamda. / m .omega. )
2 ] ##EQU00001##
[0059] where m and q are, respectively, the mass and charge of the
particle, E.sub.o is the magnitude of the electric field given by
E(r,t)=E.sub.o(r)cos(.omega.t), and .lamda. is a damping factor
which accounts for the viscous drag due to the surrounding fluid
(e.g., air).
[0060] The Ponderomotive Force may cause ions of either polarity
(positive or negative) to be repelled from the electrode applying
the oscillating gradient electric field. The particles may
oscillate and drift towards regions of low electric field density.
When the amplitude of the oscillations is small with respect to
length scales of the electric field gradients, the oscillation
center moves as if acted upon by a force, which is the so-called
Ponderomotive Force. The Ponderomotive force acts symmetrically on
both positive and negative charged species, may require oscillating
electric fields in at least some situations, and generally
increases with increasing field gradients. The Ponderomotive Force
may also act most effectively in at least some embodiments on large
particles, such as soot in a flame.
[0061] It is also noted that the manipulation of flames using
oscillating gradient electric fields, as described herein, need not
require contact between the electrode(s) applying the electric
field and the flame.
[0062] As should be appreciated from the foregoing, application of
a time-varying gradient electric field may bend (or deflect) a
flame, for example prior to extinguishing the flame. Thus,
according to one embodiment, a flame may be manipulated by bending
the flame via application of a time-varying (e.g., oscillating)
gradient electric field thereto. The field have any suitable
frequency, magnitude, gradient, and spacing from the flame to
generate a desired degree of bending. Similarly, a flame may be
squashed (e.g., minimized) or stretched if a time-varying electric
field is applied parallel to the direction of the flame.
[0063] According to another non-limiting embodiment, mixing of a
flame may be controlled at least in part by application thereto of
a time-varying gradient electric field. As explained previously,
application of a time-varying gradient electric field to a flame
may generate motion of ionic particles within the flame, which may
itself give rise to collective motion of the flame, for example as
a result of ionic particles of the flame transferring momentum to
neutral particles of the flame. The resultant motion may enhance,
or alternatively suppress depending on the conditions, mixing of
the flame. Thus, various applications in which control over flame
mixing is desired may be realized.
[0064] According to another non-limiting embodiment, concentration
of a flame may be achieved by application of a time-varying
gradient electric field thereto. FIG. 7 illustrates a non-limiting
example of a configuration which may be used. As shown, an electric
field source may be configured substantially parallel to the
direction of flow of the flame. For example, a burner 702 may have
an electrode 704 configured with respect thereto such that an
electric field 706 is generated in a direction substantially
parallel to the direction of propagation of the flame 708. A
time-varying applied signal 710 (e.g., an alternating current (AC)
signal) may be applied to the electrode to generate the electric
field. A grid 712 may be positioned a distance d from the top of
the burner. The distance d may be between approximately 5-15 cm
(e.g., 10 cm), or have any other suitable value, as these are
non-limiting examples. Application of the electric field may result
in concentration of the flame across a smaller area of the grid 712
than would occur absent the electric field. Thus, in some
non-limiting embodiments, the width (from left to right in FIG. 7)
of the flame 708 may be greater when no electric field is applied
than when the electric field 706 is applied (i.e., the electric
field 706 may "shrink" the width of the flame, thus concentrating
the flame). A non-limiting example of operation of the
configuration of FIG. 7 is now described, together with results
therefrom in FIGS. 8A-8D.
Example 2
[0065] FIGS. 8A-8D illustrate the setup of an apparatus conforming
to the general configuration of FIG. 7, and which may be used to
concentrate a flame. The bottom photograph in each of FIGS. 8A-8D
illustrates the physical setup, showing a perspective view of the
metal grid. The dark spot in the center of the metal grid
represents the area of the grid contacted by the flame. As
described further below, it can be seen that the area changes
depending on the parameters of the applied electric field. The top
image in each of FIGS. 8A-8D represents a thermal image taken of
the metal grid for the corresponding physical setup.
[0066] The setup comprises a ceramic burner flowing .about.1 L/min
of methane. The methane is lit. The flame is then arrested by the
thick metal grid placed flat above the flame. The grid functions as
the ground, while a ring electrode is applied to the burner.
[0067] FIG. 8A illustrates the scenario in which no electric field
is applied. The maximal temperature observed on the top of the grid
was 631.degree. C.
[0068] FIG. 8B illustrates the scenario in which a voltage of 18 kV
at 100 Hz is applied to the ring electrode surrounding the burner,
as mentioned previously in the manner illustrated by the
configuration of FIG. 7. Thus, an electric field is applied to the
flame. The maximal temperature increased by approximately 100
degrees to 731.degree. C. (which appeared to be the equilibrium)
compared to that of FIG. 8A within 40 seconds. In these conditions
there is the occurrence of slight sparking between the
electrodes.
[0069] To verify if the sparks are responsible for this increase in
temperature, the conditions of FIGS. 8C and 8D were tested. FIG. 8C
illustrates a scenario in which no electric field is applied, as in
FIG. 8A. FIG. 8D illustrates the scenario in which a voltage of 9
kV at 100 Hz (a voltage at which no sparking occurred) is applied
to the ring electrode surrounding the burner. The temperature still
increased by 50 degrees compared to that of FIG. 8C in
approximately 40 seconds.
[0070] Thus, it should be appreciated from FIGS. 8A-8D and the data
illustrated therein that according to one or more embodiments a
flame may be concentrated over a smaller area when an electric
field is applied.
[0071] According to another non-limiting embodiment, a flame may be
stabilized by the application of a time-varying electric field, and
in some instances a time-varying gradient electric field, thereto.
The flame may be stabilized in that its ability to remain in
existence when it otherwise would be extinguished may be increased.
A non-limiting example of a configuration resulting in
stabilization of a flame is that illustrated in FIG. 7. Application
of the electric field to the flame as illustrated may allow the
flame to exist at higher fuel flow rates than would be possible
absent the electric field. The electric field may have any suitable
strength and frequency to accomplish this result.
[0072] According to another non-limiting embodiment, an electric
field may be used to suppress a flame. The electric field may, for
example, be configured to create a boundary between a fuel source
and a flame, such that the fuel source does not ignite. A
non-limiting example is illustrated in FIG. 9.
[0073] As shown, a flame 902 may be positioned near a fuel source
(e.g., a burner) 904. The fuel 906 emitted by the fuel source 904
may initially propagate toward the flame 902. However, application
of a time-varying gradient electric field, in the manner described
previously herein, from an electrode 908 (as a result of
application of an applied signal 910) may prevent the flame from
igniting the fuel source, thus suppressing the flame. The electric
field may create an outflow from the flame (in the direction of the
arrows) which may divert the fuel from the flame. This, however, is
a non-limiting example.
[0074] According to another non-limiting embodiment, a time-varying
electric field may be used to increase the flow and nebulization of
a fluid. A non-limiting configuration is illustrated in FIG. 10. As
shown, container 1002 may include a fuel 1004 and a plume 1006.
Application of a time-varying gradient electric field thereto in
the manner previously described herein, using an electrode 1008 may
increase the plume.
[0075] According to another non-limiting embodiment, a Davy Lamp
configuration is used to manipulate a flame. In some such
embodiments, a flame arrestor grid may be used as one electrode. A
combination of thermal quenching and electric fields may be used to
extinguish the flame. FIG. 12 illustrates a non-limiting
embodiment.
[0076] As shown in FIG. 12, the apparatus 1200 may include a first
electrode 1202 and a second electrode 1204. A power supply 1206 may
apply a voltage difference between the electrodes 1202 and
1204.
[0077] The electrode 1202 may be a metal mesh structure having a
mesh size sufficient to allow a fuel source to pass through. In
some non-limiting embodiments, the electrode 1202 may be considered
a flame arrestor grid, as will be further appreciated from the
discussion below. The mesh size should be such that liquid can
rapidly pass through, but not so large that the flame is not
quenched (as described below). Non-limiting examples for suitable
mesh sizes are between 1 mm and 1 cm.
[0078] The electrode 1204 may be any suitable electrode formed of
any suitable material.
[0079] The power supply 1206 may apply a direct current (DC) or AC
signal to the electrodes 1202 and 1204. Non-limiting examples of
suitable voltages for AC signals include greater than 5 kV at a
frequency greater than 1 Hz (e.g., between 1 Hz and 1 kHz, or even
greater). Non-limiting examples of suitable DC signals include -5
kV, between 5 kV and 50 kV, 50 kV, greater than 50 kV, or any other
suitable voltages.
[0080] If fuel on the electrode 1202 catches fire 1208, a suitable
electric potential may be applied to the electrode 1202 by the
power supply 1206. The fire may be extinguished, for instance
because contact with the electrode 1202 may thermally quench the
fire 1208 resulting in extinguished fuel 1210 passing through the
mesh of electrode 1202 to the electrode 1204. The thermal quenching
may separate the flame from the liquid fuel and allow the liquid
fuel to pass through the mesh. The electric field from the
electrode 1202 may also facilitate extinguishing the flame, in
addition to the thermal quenching. For instance, the flame may be
extinguished in approximately 1/3 the time as would occur without
the field (e.g., in approximately 4 seconds compared to 12 seconds
which may be required without the electric field). Applying the
electric field may also stabilize the flame.
[0081] The electrodes 1202 and 1204 may take any suitable
configuration with respect to each other. For example, they may be
separated by between 1 mm and 1 meter, greater than 1 m, or any
other suitable distance. The electrode 1204 may be below the
electrode 1202 or above it, as the relative orientation is not
limiting.
[0082] The configuration of FIG. 12 may be used in various
products. For example, a floor or flooring system may be
constructed in the configuration illustrated. Other applications
are also possible.
[0083] In some embodiments, an electrode may be moved relative to a
flame, for example by swiping the electrode across a flame. A
non-limiting example of a suitable configuration is illustrated in
FIG. 13. As shown, the apparatus 1300 includes a fuel source 1302
(e.g., gal, liquid, solid, etc.) which may create multiple flames
1304. Ten flames 1304 are shown, but the number is non-limiting,
and may even include only a single flame in some embodiments. An
electrode, such as the sheathed wire electrode of FIGS. 11A and 11B
may be oriented as indicated at 1306 (i.e., with the electrode
oriented into and out of the page) and may be moved in the
direction indicated by arrow 1308 across the flames. The electrode
may be connected to a current source (AC or DC) of any suitable
potential (e.g., greater than 5 kV in some non-limiting
embodiments). Moving the electrode in the direction shown may
deflect the flames and may extinguish the flames in some
embodiments (e.g., with an oscillating signal of approximately 1
kHz and electric potential greater than 30 kV, as non-limiting
examples). The closer the electrode is to the origin of the flames,
the greater the likelihood of extinguishing the flames. For
example, positioning the electrode within approximately 1 cm of the
flame origin may increase the likelihood of extinguishing the
flames.
[0084] From the foregoing, it should be appreciated that various
types of manipulation of flames using electric fields may be
achieved. In some non-limiting embodiments, the electric fields may
be oscillating electric fields having a gradient in three
dimensions (referred to herein as "three-dimensional gradient
fields"). In some embodiments, the electric fields are generated
using fewer than three electrodes. The electrode(s) may be
insulated to prevent generation of an ionic wind. Thus, the
manipulation described according to various embodiments may be
achieved without the need for an ionic wind.
[0085] Various techniques for manipulating flames have been
described. As mentioned previously, it should be appreciated that
the various aspects described herein may be used individually or in
any combination of two or more, unless otherwise stated.
[0086] As mentioned previously, one or more aspects of the present
application may relate to manipulation of flames, and the
manipulation may take one or more of various forms. Non-limiting
examples of manipulation may include extinguishing a flame,
suppressing a flame, bending a flame, controlling the mixing within
the flame, and concentrating the flame. However, other forms of
manipulation may also be possible, and the various aspects
described herein are not limited to any particular form of
manipulation unless otherwise stated.
[0087] Also, as mentioned previously, the aspects described herein
may apply to various flame types (i.e., flames resulting from
combustion of various types of fuels), unless otherwise stated. For
example, ethanol, methanol, toluene, and hexane are non-limiting
examples of fuel sources to which aspects of the present
application may be applied. Other types of flames are also
possible.
[0088] Moreover, various benefits may be realized by the
application of one or more of the aspects described (though it
should be appreciated that not all aspects necessarily provide each
benefit). For example, one or more aspects may be used to put out a
fire without the need for adding a suppressant (e.g., a chemical
suppressant), which may reduce damage to items (e.g., personal and
real property) as well as avoiding the need for toxic chemicals. In
some embodiments, a fire may be put out from a distance. Moreover,
manipulation of flames of different compositions may be achieved
with the same technique of manipulation. Other aspects may provide
improved combustion, e.g., more efficient combustion with the
production of fewer combustion byproducts. Various other benefits,
alternatively or in addition, may be realized by one or more
aspects, as those listed are non-limiting examples.
[0089] One or more aspects and embodiments of the present
application involving the performance of methods may utilize
program instructions executable by a device (e.g., a computer, a
processor, or other device) to perform, or control performance of,
the methods. In this respect, various inventive concepts may be
embodied as a computer readable storage medium (or multiple
computer readable storage media) (e.g., a computer memory, one or
more floppy discs, compact discs, optical discs, magnetic tapes,
flash memories, circuit configurations in Field Programmable Gate
Arrays or other semiconductor devices, or other tangible computer
storage medium) encoded with one or more programs that, when
executed on one or more computers or other processors, perform
methods that implement one or more of the various embodiments
discussed above. The computer readable medium or media can be
transportable, such that the program or programs stored thereon can
be loaded onto one or more different computers or other processors
to implement various ones of the aspects discussed above. In some
embodiments, computer readable media may be non-transitory
media.
[0090] Having thus described several aspects and embodiments of the
technology, it is to be appreciated that various alterations,
modifications, and improvements will readily occur to those skilled
in the art. Such alterations, modifications, and improvements are
intended to be within the spirit and scope of the technology.
Accordingly, the foregoing description and drawings provide
non-limiting examples only.
[0091] Also, the phraseology and terminology used herein is for the
purpose of description and should not be regarded as limiting. The
use of "including," "comprising," or "having," "containing,"
"involving," and variations thereof herein, is meant to encompass
the items listed thereafter and equivalents thereof as well as
additional items.
APPENDIX
Quantifying Flame Deflection
[0092] In order to measure the angle of deflection, the flame is
filmed during the application of the electric field using a digital
camera at a frame rate of 1 fps. The frames are then superimposed
on one another to create a composite, grayscale image as shown
below.
The angle of deflection is then measured by calculating the
principle axes of "inertia" of the flame's image. First, the center
of "mass" is calculated as
x cm = i j x j M ij and y cm = i j y i M ij ( 0.1 )
##EQU00002##
where M.sub.ij is the intensity of pixel (i,j). The inertial tensor
is then calculated as
I = [ i , j ( y i - y cm ) 2 M ij i , j x i y j M ij i , j x i y j
M ij i , j ( x j - x cm ) 2 M ij ] ( 0.2 ) ##EQU00003##
The eigenvectors of the inertial tensor represent the "principle
axes" of the flame; the one of interest, v, points along the long
axis of the flame. The angle of deflection is then calculated as
.theta.=tan.sup.-1(|v.sub.x/v.sub.y|).
* * * * *