U.S. patent number 3,808,056 [Application Number 05/334,749] was granted by the patent office on 1974-04-30 for burner means for thermoelectric generator.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Thomas L. Nystrom, Edwin W. Pitcher.
United States Patent |
3,808,056 |
Pitcher , et al. |
April 30, 1974 |
BURNER MEANS FOR THERMOELECTRIC GENERATOR
Abstract
An improved burner assembly, especially useful to heat a
thermoelectric generator, comprising an ultrasonic atomizer for
atomizing liquid fossil fuels into a mist of fine particles; baffle
means for causing an appropriate mixture of fuel and air; and,
usually, a mantle for uniformly distributing the heat of combustion
over a cylindrical hot plate against which thermoelectric legs are
disposed.
Inventors: |
Pitcher; Edwin W. (White Bear
Lake, MN), Nystrom; Thomas L. (Falcon Heights, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
23308649 |
Appl.
No.: |
05/334,749 |
Filed: |
February 22, 1973 |
Current U.S.
Class: |
136/208; 431/1;
310/306 |
Current CPC
Class: |
B05B
17/063 (20130101); F23D 11/345 (20130101); H01L
35/30 (20130101) |
Current International
Class: |
H01L
35/30 (20060101); H01L 35/28 (20060101); F23D
11/00 (20060101); F23D 11/34 (20060101); B05B
17/04 (20060101); B05B 17/06 (20060101); H01v
001/30 () |
Field of
Search: |
;431/1 ;310/4R
;136/208 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dority, Jr.; Carroll B.
Attorney, Agent or Firm: Alexander, Sell, Steldt &
DeLaHunt
Claims
1. In a thermoelectric generator comprising a hot plate against
which thermoelectric legs are disposed, improved burner means for
heating said hot plate comprising, in alignment with said hot plate
on a central axis, (A) blower means spaced on said axis from said
hot plate and arranged to blow an oxidizing gas along said axis
toward the hot plate; (B) an ultrasonic atomizer downstream from
the blower means, connected to a source of liquid fuel, and having
a vibrating horn located on said axis from which the fuel emanates
downstream as a fine mist, (C) a cylindrical wall spaced radially
around said horn and in line with said blower means so as to convey
said oxidizing gas downstream from said blower means past said
horn; and (D) baffle means disposed around said horn and consisting
essentially of a set of overlapping vanes that are attached to the
inside of said wall, extend radially toward said axis, and are
disposed at an angle to said axis so as to form a first part of the
oxidizing gas that is conveyed downstream by the cylindrical wall
into a vortex; the innermost edge of the vanes being adjacent to,
but spaced from, said horn so as to define an area through which a
second part of said oxidizing gas passes unimpeded; and at least
part of the outermost edge of the vanes being spaced from the
cylindrical wall so as to permit a third part of said oxidizing gas
to pass unimpeded along the wall so as to contain said vortex into
a compact area, whereby the flame of fuel supplied by said
2. In a generator of claim 1 in which the hot plate is cylindrical,
a cylindrical burner housing aligned on said axis and extending
from said cylindrical wall, and a cylindrical, closed-end mantle
aligned on said axis, connected through an opening to said burner
housing, and juxtaposed within said cylindrical hot plate; the
mantle comprising a solid cylindrical wall perforated by a set of
holes distributed over the mantle
3. A generator of claim 1 in which the vanes are disposed at an
angle
4. A generator of claim 1 in which the vanes are disposed at an
angle
5. A generator of claim 1 in which the total surface area on one
side of
6. A generator of claim 1 in which the downstream part of the vanes
curves inwardly toward said axis from the point of connection of
the vanes to the
7. In a thermoelectric generator comprising a cylindrical hot plate
against which thermoelectric legs are disposed, improved burner
means for heating said cylindrical hot plate comprising, in
alignment with said cylindrical hot plate on a central axis, (A)
blower means spaced on said axis from said hot plate and arranged
to blow an oxidizing gas along said axis toward the hot plate; (B)
an ultrasonic atomizer downstream from the blower means, connected
to a source of liquid fuel, and having a vibrating horn located on
said axis from which the fuel emanates downstream as a fine mist;
(C) a cylindrical wall spaced radially around said horn and in line
with said blower means so as to convey said oxidizing gas
downstream from said blower means past said horn; (D) baffle means
disposed around said horn and consisting essentially of a set of
overlapping vanes that are attached to the inside of said wall,
extend radially toward said axis, have a total surface area on one
side equal to at least about 1.6 times the area subtended by the
vanes, and are disposed at an angle of between about 20.degree. and
70.degree. to said axis so as to form a first part of the oxidizing
gas that is conveyed downstream by the cylindrical wall into a
vortex; the innermost edge of the vanes being adjacent to, but
spaced from, said horn so as to define an area through which a
second part of said oxidizing gas passes unimpeded; and at least
part of the outermost edge of the vanes being spaced from the
cylindrical wall so as to permit a third part of said oxidizing gas
to pass unimpeded along the wall so as to contain said vortex into
a compact area, whereby the flame of fuel supplied by said
ultrasonic atomizer is kept compact; (E) a cylindrical burner
housing aligned on said axis and extending from said cylindrical
wall; and (F) a cylindrical, closed-end mantle aligned on said
axis, connected to said burner housing, and juxtaposed within said
cylindrical hot plate; the mantle comprising a solid cylindrical
wall perforated by a set of holes distributed over the mantle so as
to cause a uniform heating
8. A generator of claim 7 in which the vanes are disposed at an
angle
9. A generator of claim 7 in which the downstream part of the vanes
curves inwardly toward said axis from the point of connection of
the vanes to the cylindrical wall.
Description
The invention herein described was made in the course of or under a
contract or subcontract thereunder with the United States Army.
BACKGROUND OF THE INVENTION
Interest in heating thermoelectric generators with liquid fossil
fuels was enhanced several years ago when an ultrasonic atomizer
capable of atomizing liquid fuels into a mist of fine particles was
developed. The art had previously desired generators heated with
liquid fossil fuels.sup.1 but had been inhibited by deficiencies in
traditional techniques for atomizing such fuels.sup.2. Ultrasonic
atomizers gave promise of overcoming these deficiencies because of
the low fuel pressures used in ultrasonic atomization, the very
fine size of the atomized particles, and the compact size of the
mist of atomized particles. Designs for thermoelectric generators
using ultrasonic atomizers followed after the introduction of such
atomizers; see paper CP 66-3 presented at the American Petroleum
Institute Research Conference on DIstillate Fuel Combustion for
1966 (API Publication No. 1705)(for suggestions of other burner
assemblies generally intended for uses other than in thermoelectric
generators see other papers in the series CP 66-1 through CP 66-6
of that publication, API publications for other years, and U.S.
Pat. No. 3,275,059).
However, despite the prior suggestions for thermoelectric
generators incorporating burner systems based on ultrasonic
atomizers, and despite significant efforts based on those
suggestions, no successful thermoelectric generator of this type
has ever been produced until the present invention. None of the
previous suggestions was able to satisfy the rather severe
requirements for a burner system in a thermoelectric generator. A
primary requirement leading to other requirements is that the
burner system must be compact to make a generator compact. Yet the
system must operate at a peak efficiency so as to maximize the
efficiency of the generator. Further, the system must be capable of
long, unattended operation, and the burning must be stable so as to
provide a stable supply of heat distributed uniformly over the hot
ends of the thermoelectric legs in the generator.
We have found that a principal reason for the failure of the
previous designs lies in the scheme provided in those designs for
controlling the movement of fuel and air through the burner system.
The prior suggestions have not provided a mixing of fuel and air
that was rapid, thorough, and uniform enough; the mixture of fuel
and air was not compact enough; and too large volumes of air were
required. The failure of the burner systems previously suggested
for thermoelectric generators--they have generally been incapable
of long, stable, and trouble-free operation, and they have been
inefficient in use of fuel and in use of generated electricity to
power movement of air--may be traced directly to failure to
properly control the movement of fuel and air through the burner
system. Proper control of that movement of fuel and air is critical
to providing long-lasting, efficient burner systems based on
ultrasonic atomizers for use in thermoelectric generators.
SUMMARY OF THE INVENTION
The present invention provides a new burner assembly that, as a
result of its control of atomized liquid fossil fuel and oxidizing
gas moving through the assembly, is useful in a thermoelectric
generator to achieve high efficiency and reliable operation.
Briefly, a burner assembly of the invention, which is especially
useful in those thermoelectric generators that include a
cylindrical hot plate against which the hot-junction ends of
thermoelectric legs are disposed, comprises, in alignment with said
cylindrical hot plate on a central axis, (A) blower means spaced on
said axis from said hot plate and arranged to blow an oxidizing gas
along said axis toward the hot plate; (B) an ultrasonic atomizer
between the blower means and hot plate, connected to a source of
liquid fuel, and having a vibrating horn located on said axis from
which the fuel emanates downstream as a fine mist; (C) a
cylindrical wall spaced radially around said horn and connected to
said blower means so as to convey said oxidizing gas downstream
from said blower means past said horn; and (D) baffle means
disposed around said horn and consisting essentially of a set of
overlapping vanes that are attached to the insides of said wall,
extend radially toward said axis, and are disposed at an angle to
said axis so as to direct a first part of the oxidizing gas
conveyed downstream by the cylindrical wall into a vortex; the
innermost edge of the vanes being adjacent to, but spaced from,
said horn so as to define an area through which a second part of
said oxidizing gas passes unimpeded; and the outermost edge of at
least part of the vanes being spaced from the cylindrical wall so
as to permit a third part of said oxidizing gas to pass unimpeded
along the wall so as to contain said vortex into a compact area,
whereby the flame of fuel supplied by said ultrasonic atomizer is
kept compact. A cylindrical burner housing is generally aligned on
said axis and extends from said cylindrical wall; and a
cylindrical, closed-end mantle is aligned on said axis, connected
to said burner housing, and juxtaposed within said cylindrical hot
plate. This mantle preferably comprises a solid cylindrical wall
perforated by a set of holes distributed over the mantle so as to
provide a uniform distribution of heat over the cylindrical hot
plate.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view of a thermoelectric generator of
the invention, with parts broken away;
FIG. 2 is a section along the lines 2--2 of FIG. 1;
FIG. 3 is an end view of components from the thermoelectric
generator of FIG. 1, including a baffle means and ultrasonic
atomizer mounted inside a cylindrical wall;
FIG. 4 is a schematic view of a vane of the baffle means of the
thermoelectric generator shown in FIG. 1, shown with respect to a
longitudinal axis through the generator; and
FIG. 5 is a sectional view of the baffle means, ultrasonic
atomizer, and cylindrical wall of the thermoelectric generator of
FIG. 1, taken along the lines 5--5 of FIG. 3.
DETAILED DESCRIPTION
A typical thermoelectric generator 10 of the invention is shown in
FIGS. 1-5. This generator comprises an array of thermoelectric legs
11 (only three representative legs are shown in FIG. 1) disposed
regularly around a cylindrical hot plate 12 and arranged in
heat-conductive relation with the hot plate (the legs 11 are
pressed by spring-biased followers 5 that slide in bores 6 in a
cold plate 7, and the cold plate 7 is surrounded by a cold shell 8,
to which heat-dissipating fins 9 are attached; the hot plate in a
thermoelectric generator of the invention could, in less preferred
embodiments, be flat, and "cylindrical" hot plates may have a
cross-sectional shape other than a true cylinder, even being square
in some cases).
Heat is supplied to the inside of the cylindrical hot plate 12 with
a burner means of the invention that comprises, in alignment on a
central axis 13, a blower means 14; an ultrasonic atomizer 15
connected by tube means 16 to a source of fuel; a cylindrical wall
17 spaced radially around the atomizer; baffle means 18 disposed
around the tip of a horn 19 of the ultrasonic atomizer 15; a
cylindrical burner housing 20 which receives the blower means 14,
atomizer 15, cylindrical wall 17 and baffle means 18 and which
extends beyond the cylindrical wall 17 in a right-angle extension
to form a combustion chamber 21; and a cylindrical mantle 22
connected to said burner housing. An insulating jacket 23 surrounds
the burner housing 20 and is filled with a generally fibrous
thermal insulation. Openings 24 are provided in the housing 20 in
this embodiment to reduce impedance to the flow of air caused by
the blower means 14.
Ultrasonic atomizers have been described in several patents
including U.S. Pat. Nos. 3,275,059 and 3,214,101. As shown best in
FIGS. 2-5, a typical atomizer useful in the invention comprises a
stepped horn 19 that will vibrate at an ultrasonic frequency and
that includes a base portion 19a and a tip portion 19b, a dummy
horn 25 to balance the vibrating horn, two piezoelectric crystals
26 between the vibrating horn and dummy horn, an electrode 27
positioned between the piezoelectric crystals and connected through
leads 28 to an ultrasonic-frequency electric power source, and
flanges 29 on the vibrating and dummy horns by which the atomizer
parts are clamped together and to a mounting bracket 30 with screws
31. Plastic sleeves 31a around the screws 31 extend between the
flanges 29 and through the electrode 27.
The atomizer 15 is attached to the cylindrical wall 17 by screws 32
which extend through arms 33 of the mounting bracket and through
tabs 34 extending inwardly from the cylindrical wall. A fuel
passage 35 runs from the tube means 16 through the vibrating horn
19 to an outlet 36 in the center of the end of the tip portion 19b
of the horn. Fuel fed through the passage 35 forms as a thin film
on the end of the vibrating horn and then is vibrated off the horn
as a mist of fine particles or droplets.
The baffle means 18 of the thermoelectric generator of the
invention illustrated in the drawings consists of vanes 37 fastened
(as by welding) at a point 38 on the outer edge to the inside of
the cylindrical wall 17 and positioned at an angle to the axis 13
(that is, the angle .theta. shown in FIG. 4). The forward edge 39
of the vanes 37 terminates in a plane that extends approximately
through the longitudinal axis 13. Over most of their outer edge,
the vanes 37 are spaced from the inside of the cylindrical wall 17
to form a space 40. And the downstream portions 41 of the vanes 37
are gradually curved inwardly, which increases the distance of
those portions of the vanes from the inside of the cylindrical wall
17. The innermost edge of the vanes is spaced from the horn to form
a central space 42 around the horn.
Oxidizing gas (generally air) passing through the baffle means 18
and atomized fuel from the atomizer 15 mix and pass into the
combustion chamber 21 formed by the burner housing 20. Ignition
means are provided inside the combustion chamber by two wires 43
and 44 of a high-temperature-resistant alloy separated narrowly at
their ends to form a sparking gap. The wire 43 is connected to the
outer insulating jacket 23, which in turn is connected to ground
through a grounding lug not shown, while the wire 44 is insulated
from the housing 20, jacket 23, and other structure and is
connected to a source of electric voltage through an insulated lead
45 (see FIG. 2).
In the illustrated thermoelectric generator, the burner housing 20
is formed with a right angle so that the burning and heated fuel
and oxidizing gas mixture moves upwardly into the mantle. In other
embodiments, which are generally preferred for efficiency of
burning, the blower means 14, ultrasonic atomizer 15, burner
housing 20 and mantle 22 are arranged on a straight longitudinal
axis (note that for purposes herein the blower means, ultrasonic
atomizer, burner housing, and mantle are all regarded as being on
the same longitudinal axis 13, though that axis is bent at a right
angle).
As previously noted, the baffle means 18 shapes oxidizing gas blown
past the horn of the atomizer by the blower means 14 into three
components: a component deflected by the vanes 37 into a swirl or
vortex pattern; a center stream passing through the space 42
between vanes 37; and an outside annular component passing along
the inside of the cylindrical wall 17 through the space 40 between
the outer edge of the vanes and the inside of the cylindrical wall
17. Each of these components has an important function. Because of
the low pressure caused by the swirling movement within the vortex
component, the mist of atomized fuel is rapidly drawn into the
stream of oxidizing gas. Also, the low pressure of the vortex
component causes the flame to remain closely spaced from the horn.
Even if the flame is extinguished because of an air bubble in the
fuel supply, the heat of the system will quickly reignite fuel just
off the end of the horn. And burning generally can be initiated
with fuel and air flowing at their maximum rate, which makes
electronic control apparatus in the generator less costly and
complex.
The center component moving through the space 42 between the vanes
37 keeps the flame away from the atomizer horn 19, and cools the
horn. The outside annular component traveling through the space 40
provides an outer envelope that tends to confine the vortex
component. It has been found that if the vortex component spreads
outwardly too much, fuel is deposited on the sides of the burner
housing, resulting in carbon accumulation and reducing the
efficiency and the uniformity of the heating operation. In general,
baffle configurations that provide for movement of oxidizing gas
having the described three components are useful in the
invention.
To develop a vortex component of sufficient magnitude to achieve a
desired mixing of oxidizing gas and fuel, there are preferably five
or move vanes in the baffle means. Also, the angle .theta. between
the vanes and the axis 13 is generally more than about 20.degree.,
and preferably is more than about 40.degree.. On the other hand,
the angle .theta. is generally less than about 70.degree., and
preferably is less than about 60.degree., so as to avoid formation
of "dead" spaces (areas in which the air is not moving), to
minimize impedance for the blower means, to cause a desired amount
of oxidizing gas to enter the vortex, and to keep the flame spaced
from the tip of the atomizer horn. The vanes overlap sufficiently
so that a summation of the surface areas on one side of the vanes
is at least 1.2 times, and preferably at least 1.6 times, as great
as the area subtended by the vanes (that is, the area on a plane
perpendicular to the central axis of the baffle means that would be
covered if the vanes were projected onto the plane).
As the heated gases of the combustion process pass into the mantle
22 from the combustion chamber 21 inside the burner housing 20,
there is a pressure drop, because the cross-sectional area of the
mantle is greater than the cross-sectional area of the housing 20
(in this embodiment by about 600 percent); and this pressure drop
draws the heated gases into the mantle. It is desirable for almost
all burning to occur before the mixture of fuel and oxidizing gas
leaves the housing 20, though the flame will often extend into the
mantle. Because the burning is in large part completed within the
housing 20, the distribution of heat throughout the mantle 22 is
subjected to more control.
Once in the mantle, the heated gases travel through openings 46 in
the mantle, then upwardly through the space 47 between the mantle
and the hot plate, which is preferably divided into longitudinally
extending passageways by heat-collecting fins 48, and then out
through openings 49 in the top of the mantle. The center portion of
the top end of the mantle in FIG. 1 is closed so as to force the
gases out through the openings 46. The hot plate 12 is heated both
by convection of the heated gases in the space 47 and also by
radiation from the heated mantle. The openings 46 in the mantle are
arranged in a pattern that is empirically determined to cause
heating of the hot plate 12 uniformly over its surface, and thus
will provide a more uniform, efficient operation of the
thermoelectric legs. In the illustrated embodiment, there is a
greater open area (because of more and/or larger openings 46) at
the two axial ends of the mantle than there is in the area between
those two end portions, with the largest open area being at the
downstream end of the mantle.
As a specific example of a thermoelectric generator of the
invention, one illustrative thermoelectric generator was made in
the arrangement shown in the drawing with parts of the following
description: The blower means 14 comprised a vane-axial-type fan,
capable of blowing about 10 cubic feet of air per minute at a
pressure drop of 0.55 inch of water column. The inside diameter of
the cylindrical wall 17 was 1.95 inches. There were six vanes 37 in
the baffle means 18, disposed at an angle of 52.degree. to the
longitudinal axis 13 of the baffle means, and occupying about 1.8
times the area subtended by the vanes. Of the total cross-sectional
area inside the cylindrical wall 17, 2.5 percent was occupied by
the diameter of the tip 19b of the vibrating horn of the atomizer,
about 5 percent was occupied by the space 42 between the tip of the
horn and the inside edge of the vanes 37, about 70 percent was
occupied by the vanes, and about 22 percent was occupied by the
space 40 between the outer edge of the vanes and the inside of the
cylindrical wall. The ultrasonic atomizer 15 was a full-wave,
resonant, stepped-down ultrasonic atomizer, vibrating at about 77
kilohertz. The burner housing 20 had a height from the point 50 in
FIG. 1 of 4 inches and an inside diameter of 2 inches. The mantle
22 had an inside diameter of 5.25 inches and a length of 8.5
inches; and the cylindrical hot plate 12 had an inside diameter of
6 inches. Five-hundred-twelve thermoelectric legs were disposed
around the hot plate 12, and the hot end of the legs was generally
heated during operation of the generator to a temperature of
1050.degree.F, with a variation between hot ends of less than
50.degree.F.
* * * * *