U.S. patent application number 13/278281 was filed with the patent office on 2013-04-25 for tubular burner.
The applicant listed for this patent is Tadayuki Hiraga. Invention is credited to Tadayuki Hiraga.
Application Number | 20130101948 13/278281 |
Document ID | / |
Family ID | 48136246 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130101948 |
Kind Code |
A1 |
Hiraga; Tadayuki |
April 25, 2013 |
TUBULAR BURNER
Abstract
A flame hole member of a tubular burner has a front plate and a
rear plate both of sheet metal make. The front plate has a first
flame hole in the central portion of the front plate, and a
plurality of second flame holes located around a periphery of the
first flame hole, each of the second flame holes being of a slit
shape in a width below a quenching distance. The rear plate has a
first ventilation hole in the central portion of the rear plate,
and a plurality of second ventilation holes of smaller diameter
than the first ventilation hole, each of the second ventilation
holes being located around a periphery of the first ventilation
hole. At least one of the rear plate and the front plate is
provided with a cylindrical section for introducing into the first
flame hole.
Inventors: |
Hiraga; Tadayuki;
(Nagoya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hiraga; Tadayuki |
Nagoya-shi |
|
JP |
|
|
Family ID: |
48136246 |
Appl. No.: |
13/278281 |
Filed: |
October 21, 2011 |
Current U.S.
Class: |
431/354 |
Current CPC
Class: |
F23D 14/26 20130101;
F23D 14/08 20130101 |
Class at
Publication: |
431/354 |
International
Class: |
F23D 14/08 20060101
F23D014/08 |
Claims
1. A tubular burner comprising: a mixing tube inclusive of an inlet
port, at a rear end thereof, into which a fuel gas and primary air
flow, a venturi section having a smaller diameter than a diameter
of the inlet port, and a tapered tube section having a gradually
larger diameter from the venturi section toward a front of the
mixing tube; and a flame hole member having a plurality of flame
holes and being adapted to be fitted into a front end region of the
mixing tube such that a mixture of the fuel gas and primary air is
ejected through the flame holes for combustion, the flame hole
member being made up of a front plate of sheet metal make, and a
rear plate of sheet metal make located behind the front plate, the
front plate having a first flame hole in a central portion of the
front plate, and a plurality of second flame holes located around a
periphery of the first flame hole, each of the second flame holes
being of a slit shape in a width below a quenching distance, the
rear plate having a first ventilation hole in a central portion of
the rear plate, and a plurality of second ventilation holes of
smaller diameter than the first ventilation hole, each of the
second ventilation holes being located around a periphery of the
first ventilation hole, at least one of the rear plate and the
front plate having disposed therein a cylindrical section for
introducing into the first flame hole the mixture of the fuel gas
and primary air flowing into the first ventilation hole.
2. The tubular burner according to claim 1, wherein a rear region
of the cylindrical section is gradually reduced in diameter from
the first ventilation hole forward, and wherein the cylindrical
section in front of the rear region is formed into a cylindrical
shape of smaller diameter than the first ventilation hole.
3. The tubular burner according to claim 1, wherein a length of the
cylindrical section is equivalent to a longitudinal distance
between the rear plate and the front plate.
4. The tubular burner according to claim 1, wherein the cylindrical
section is disposed in the rear plate, and wherein a diameter of
the first flame hole is larger than an inner diameter at the front
end of the cylindrical section.
5. The tubular burner according to claim 1, wherein the second
flame holes are of slit shape elongated in a radial direction of
the front plate, wherein a plurality of inner second flame holes
are formed in a portion, closer to the first flame hole, of the
front plate at a circumferentially equal pitch, and wherein a
plurality of outer second flame holes are formed while being
circumferentially deviated by half a pitch from the inner second
flame holes so that the outer second flame holes are located
between: such an intermediate portion in the front plate as is
located in a diametrically inner end and a diametrically outer end
of the inner second flame holes; and such a portion in the front
plate as is located diametrically outward of the diametrically
outer end of the inner second flame holes.
6. The tubular burner according to claim 2, wherein the second
flame holes are of slit shape elongated in a radial direction of
the front plate, wherein a plurality of inner second flame holes
are formed in a portion, closer to the first flame hole, of the
front plate at a circumferentially equal pitch, and wherein a
plurality of outer second flame holes are formed while being
circumferentially deviated by half a pitch from the inner second
flame holes so that the outer second flame holes are located
between: such an intermediate portion in the front plate as is
located in a diametrically inner end and a diametrically outer end
of the inner second flame holes; and such a portion in the front
plate as is located diametrically outward of the diametrically
outer end of the inner second flame holes.
7. The tubular burner according to claim 3, wherein the second
flame holes are of slit shape elongated in a radial direction of
the front plate, wherein a plurality of inner second flame holes
are formed in a portion, closer to the first flame hole, of the
front plate at a circumferentially equal pitch, and wherein a
plurality of outer second flame holes are formed while being
circumferentially deviated by half a pitch from the inner second
flame holes so that the outer second flame holes are located
between: such an intermediate portion in the front plate as is
located in a diametrically inner end and a diametrically outer end
of the inner second flame holes; and such a portion in the front
plate as is located diametrically outward of the diametrically
outer end of the inner second flame holes.
8. The tubular burner according to claim 4, wherein the second
flame holes are of slit shape elongated in a radial direction of
the front plate, wherein a plurality of inner second flame holes
are formed in a portion, closer to the first flame hole, of the
front plate at a circumferentially equal pitch, and wherein a
plurality of outer second flame holes are formed while being
circumferentially deviated by half a pitch from the inner second
flame holes so that the outer second flame holes are located
between: such an intermediate portion in the front plate as is
located in a diametrically inner end and a diametrically outer end
of the inner second flame holes; and such a portion in the front
plate as is located diametrically outward of the diametrically
outer end of the inner second flame holes.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to a tubular burner having; a
mixing tube including at a rear end thereof an inlet port into
which a fuel gas and primary air flow; a venturi section having a
smaller diameter than the diameter of the inlet port; and a tapered
tube section having a gradually larger diameter from the venturi
section toward a front of the mixing tube. The tubular burner has a
flame hole member with a plurality of flame holes, the flame hole
member being adapted to be fitted into a front end region of the
mixing tube.
[0003] 2. Description of the Related Art
[0004] As this kind of burner, there is conventionally known one
which is described in U.S. Pat. No. 5,186,620. In the burner
described therein, a flame hole member is made of a sintered metal
of larger thickness. A plurality of flame holes which penetrate in
the back and forth (i.e., longitudinal) direction are formed in the
flame member so that a mixture of a fuel gas and primary air
(hereinafter also referred to as air-gas mixture) is ejected from
these flame holes for combustion.
[0005] The flow of the air-gas mixture from the mixing tube toward
the flame hole member has a directional component that is directed
toward the radially outward direction under the influence of the
tapered tube section. Therefore, if the flame hole member is made
smaller in thickness, the flames tend to be spread radially
outward. The above-mentioned conventional burner, on the other
hand, has a flame hole member of larger thickness. As a result, the
flow of the air-gas mixture is rectified at each of the flame holes
so as to be directed forward, thereby preventing the flames from
getting spread radially outward.
[0006] However, in the above-mentioned conventional burner, the
flame hole member is made of a sintered metal of higher material
cost, thereby bringing about a disadvantage of higher cost.
SUMMARY
Problems to be Solved by the Invention
[0007] In view of the above points, this invention has a problem of
providing a tubular burner in which a flame hole member is made of
a sheet metal plate to thereby reduce the cost, and in which the
flames can be prevented from getting spread diametrically
outward.
Means for Solving the Problems
[0008] In order to solve the above-mentioned problems, this
invention provides a tubular burner comprising: a mixing tube
inclusive of an inlet port, at a rear end thereof, into which a
fuel gas and primary air flow, a venturi section having a smaller
diameter than a diameter of the inlet port, and a tapered tube
section having a gradually larger diameter from the venturi section
toward a front of the mixing tube; and a flame hole member having a
plurality of flame holes and being adapted to be fitted into a
front end region of the mixing tube such that a mixture of the fuel
gas and primary air is ejected through the flame holes for
combustion. The flame hole member is made up of a front plate of
sheet metal make, and a rear plate of sheet metal make located
behind the front plate. The front plate has a first flame hole in
the central portion of the front plate, and a plurality of second
flame holes located around a periphery of the first flame hole,
each of the second flame holes being of a slit shape in a width
below a quenching distance. The rear plate has a first ventilation
hole in the central portion of the rear plate, and a plurality of
second ventilation holes of smaller diameter than the first
ventilation hole, each of the second ventilation holes being
located around a periphery of the first ventilation hole. At least
one of the rear plate and the front plate has disposed therein a
cylindrical section for introducing into the first flame hole the
mixture of the fuel gas and primary air flowing into the first
ventilation hole.
[0009] According to this invention, the flame hole member is made
of the front plate and the rear plate, i.e., a total of two plates
of sheet metal make. Therefore, as compared with the
above-mentioned conventional example in which the flame hole member
made of a sintered metal is used, the cost can be reduced. In
addition, according to this invention, although the flame hole
member is of sheet metal make, the flames can be prevented from
getting spread in a radially outward direction.
[0010] In other words, according to this invention, by providing
the cylindrical section for introducing the air-gas mixture flowing
into the first ventilation hole toward the first flame hole, the
flow of the air-gas mixture directed toward the first flame hole is
rectified by the cylindrical section. As a result, the air-gas
mixture is ejected strongly out of the first flame hole. On the
other hand, the flow velocity of the air-gas mixture that is
ejected from the second flame holes of slit shape in the front
plate through the second ventilation holes of relatively small
diameter in the rear plate can be kept relatively small. Therefore,
the air-gas mixture ejected from the second flame holes is
attracted into the flow of the air-gas mixture that is ejected from
the first flame hole at a high speed, thereby preventing the flames
from getting spread radially outward.
[0011] By the way, should the first flame hole be formed into a
pipe-shaped element that protrudes forward from the front plate
without providing the above-mentioned cylindrical section, there
may also be obtained an effect in that the flow of the air-gas
mixture to be ejected from the first flame hole is rectified to
thereby prevent the flames from getting spread in the radially
outward direction. In this arrangement, however, that heat quantity
from the flames which is inputted into the pipe-shaped element of
the first flame hole will increase and, as a result, back firing is
likely to occur due to overheating of the first flame hole. On the
other hand, according to this invention, without the necessity of
forming the first flame hole into the pipe-shaped element, there
can be obtained an effect of preventing the flames from getting
spread in the radially outward direction. Back firing due to
overheating of the first flame hole can thus be prevented. Further,
by forming the second flame holes into a slit shape in width that
is smaller than the quenching distance, back firing at the second
flame holes can also be prevented.
[0012] Further, according to this invention, preferably, a rear
region of the cylindrical section is gradually reduced in diameter
from the first ventilation hole forward, and the cylindrical
section in front of the rear region is formed into a cylindrical
shape of smaller diameter than the first ventilation hole.
According to this arrangement, in addition to the effect of
rectifying the flow of the air-gas mixture, there can also be
obtained an accelerating effect in that the flow velocity of the
air-gas mixture is made larger than the flow velocity thereof into
the first ventilation hole. The spreading of the flames in the
radially outward direction can thus be effectively prevented.
[0013] Furthermore, preferably, the length of the cylindrical
section is equivalent to the longitudinal distance between the rear
plate and the front plate. It is to be noted here that the term
"equivalent" includes all of the following cases, i.e.,: the case
in which the length of the cylindrical section is the same as the
longitudinal distance between the rear plate and the front plate;
and also the case in which the longitudinal length between the rear
plate and the front plate is slightly shorter than the longitudinal
length between the rear plate and the front plate. In the latter
case, a clearance may occur between the front end of the
cylindrical section that is disposed in the rear plate and the
front plate, or a clearance may occur between the rear end of the
cylindrical section that is disposed in the front plate and the
rear plate. Even in case such a clearance may occur, the air-fuel
gas that enters the cylindrical section or the air-fuel gas that
has flown into the first ventilation hole will never leak through
the clearance into the space outside the cylindrical section
between the front plate and the rear plate. The case in which such
a leak will not occur is also understood to fall under the meaning
of "equivalent." According to this arrangement, all of the air-gas
mixture entering the first ventilation hole is introduced into the
first flame hole, and the flow velocity of the air-gas mixture to
be ejected from the first flame hole becomes larger. As a result,
the flames can be effectively prevented from getting spread in the
radially outward direction.
[0014] Further, in case the cylindrical section is disposed in the
rear plate, the diameter of the first flame hole is preferably
larger than an inner diameter at the front end of the cylindrical
section. According to this arrangement, the air-gas mixture
entering the cylindrical section can smoothly be ejected from the
first flame hole without being hindered by the front plate. As a
result, the flow velocity of the air-gas mixture that is ejected
from the first flame hole becomes larger and also the pressure loss
becomes smaller.
[0015] By the way, in case the second flame holes are of slit shape
elongated in a radial direction of the front plate, preferably a
plurality of inner second flame holes are formed in a portion,
closer to the first flame hole, of the front plate at a
circumferentially equal pitch, and a plurality of outer second
flame holes are formed while being circumferentially deviated by
half a pitch from the inner second flame holes so that the outer
second flame holes are located between: such an intermediate
portion in the front plate as is located in a diametrically inner
end and a diametrically outer end of the inner second flame holes;
and such a portion in the front plate as is located diametrically
outward of the diametrically outer end of the inner second flame
holes. According to this arrangement, the second flame holes can be
disposed in the front plate in a well-balanced manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a sectional side view of a tubular burner
according to a first embodiment of this invention.
[0017] FIG. 2 is a perspective view of the tubular burner according
to the first embodiment of this invention.
[0018] FIG. 3 is a partly cut-away perspective view of the tubular
burner according to the first embodiment of this invention.
[0019] FIG. 4 is a partly cut-away perspective view of a tubular
burner according to a second embodiment of this invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] In FIG. 1 reference numeral 1 denotes a tubular burner
according to an embodiment of this invention. This burner 1 is used
as a heat source of a heating appliance, and is disposed so as to
lie opposite to an inlet end of a heat exchange pipe P which
performs heat exchanging with room air.
[0021] The burner 1 is made up of a mixing tube 2, and a flame hole
member 3 which is adapted to be fitted into a front end region of
the mixing tube 2. Also with reference to FIGS. 2 and 3, the mixing
tube 2 has: an inlet port 21 at a rear end thereof; a venturi
section 22 which is reduced in diameter relative to the inlet port
21; and a tapered tube section 23 which is gradually increased in
diameter from the venturi section 22 forward. In this arrangement,
a fuel gas ejected from a gas nozzle (not illustrated) which is
disposed so as to face the inlet port 21, and primary air flow from
the inlet port 21 into the mixing tube 2 so that a mixture of fuel
gas and primary air is generated within the mixing tube 2. The
mixing tube 2 is made of a thin sheet metal plate, and is formed by
combining together two sheet metal plates 2a, 2a made, e.g., of
press-formed stainless steel, and the like.
[0022] Although not illustrated, a plurality of the tubular burners
1 are disposed in parallel with one another. At the front end
region of the two sheet metal plates 2a, 2a that constitute the
mixing tube 2, there is each formed a dented portion 2b in a manner
to be away from the other sheet metal plate 2a. The clearance to be
generated between the two sheet metal plates 2a, 2a by means of
these dented portions 2b constitutes a slit-shaped carry-over flame
hole 2c which causes flames to be carried over to the adjoining
burners.
[0023] The front end region of the mixing tube 2 is formed in a
cylindrical shape which is elongated forward from an
enlarged-diameter region 23a of a curved shape at the front end of
the tapered tube section 23. The flame hole member 3 to be fitted
into the front end region of the mixing tube 2 is constituted by a
front plate 4 which is formed of a sheet metal plate of stainless
steel make and the like, and a disk shaped rear plate 5 which is
formed of a sheet metal of stainless steel make and the like and
which is located rearward of the front plate 4.
[0024] The front plate 4 has a tubular member 4a which is elongated
backward from a circular disk-shaped front portion so as to be
fitted into the inner circumference of the front portion of the
mixing tube 2. The front plate 4 is provided with a first flame
hole 41 in the central portion at the front face of the front plate
4, and a plurality of second flame holes 42 which are located
around the periphery of the first flame hole 41 and which are in
slit shape in a width (e.g., 0.7 mm) below a quenching
distance.
[0025] The second flame holes 42 are formed into slits which are
elongated in the radial direction of the front plate 4. In case
this kind of second flame holes 42 are formed simply at an equal
pitch in the circumferential direction, the distance between the
adjoining second flame holes 42, 42 becomes too large toward the
radially outward portion. As a solution, in this embodiment, a
plurality of inner second flame holes 42in are formed in a portion,
closer to the first flame hole, of the front plate 4 at a
circumferentially equal pitch. Also, a plurality of outer second
flame holes 42out are formed circumferentially deviated by half a
pitch from the inner flame holes 42in so as to be located between:
such an intermediate portion, in the front plate 4, as is located
in a diametrically inner end and a diametrically outer end of the
inner second flame holes 42in; and such a portion, in the front
plate 4, as is located diametrically outward of the diametrically
outer end of the inner second flame holes 42in. According to this
arrangement, the second flame holes 42 can be disposed in the front
plate 4 in a well-balanced manner.
[0026] The second flame holes 42 may alternatively be formed in a
slit shape elongated in the circumferential direction of the front
plate 4. In other words, on a plurality of circles that are coaxial
with the first flame hole 41, a plurality of the second flame holes
may be formed.
[0027] Further, at a front end of the tubular member 4a of the
front plate 4, there is formed a rounded corner portion 4b which is
away from the inner peripheral surface of the front end region of
the mixing tube 2. At the rounded corner portion 4b there is formed
a plurality of flame retention holes 43 of a slit shape at a
circumferential distance from one another.
[0028] The rear plate 5 is provided with a first ventilation hole
51 in the central portion of the rear plate 5, and a plurality of
second ventilation holes 52 which are of a smaller diameter than
that of the first ventilation hole 51 and which are located around
the periphery of the first ventilation hole 51. The rear plate 5
has further formed therein a cylindrical section 53 which projects
forward from the hole edge of the first ventilation hole 51. It is
thus so arranged that the air-gas mixture flowing into the first
ventilation hole 51 is introduced into the first flame hole 41
through the cylindrical section 53.
[0029] The rear region of the cylindrical section 53 is gradually
reduced in diameter from the first ventilation hole 51 toward the
front side. That portion of the cylindrical section 53 which lies
in front of the rear region (i.e., the front portion of the
cylindrical section 53) is formed into a cylindrical shape of
smaller diameter than that of the first ventilation hole 51.
Further, the length of the cylindrical section 53 is the same as
the longitudinal distance between the rear plate 5 and the front
plate 4 so that no clearance in the longitudinal direction occurs
between the front end of the cylindrical section 53 and the front
plate 4. Furthermore, the diameter of the first flame hole 41 is
larger than the inner diameter of the front end of the cylindrical
section 53. In this embodiment, the diameter of the first flame
hole 41 is made substantially equal to the outer diameter of the
front end of the cylindrical section 53.
[0030] According to the above-mentioned tubular burner 1 of this
embodiment, the flame hole member 3 is constituted by the front and
the rear, a total of two, plates 4, 5 of sheet metal make.
Therefore, as compared with the conventional example in which a
flame hole member made of a sintered metal is used, the cost can be
reduced. Further, if the flame hole member 3 is made of a sheet
metal plate, the air-gas mixture of the fuel gas and the primary
air is ejected with a directional component that is directed in a
radially outward direction under the influence of the tapered tube
section 23 of the mixing tube 2, and the flames are likely to be
spread in the radially outward direction. However, in this
embodiment, the flames can be prevented from spreading radially
outward, whereby the flames can surely be introduced into the heat
exchange pipe P. A description will now be made of the reasons.
[0031] In this embodiment, because the cylindrical section 53 is
disposed to introduce the air-gas mixture flowing into the first
ventilation hole 51 toward the first flame hole 41, the flow of the
air-gas mixture directed to the first flame hole 41 is rectified by
the cylindrical section 53. As a result, the air-gas mixture is
forcibly ejected forward from the first flame hole 41. On the other
hand, the flow velocity of the air-gas mixture to be ejected from
the slit-shaped second flame holes 42 in the front plate 4 via the
second ventilation holes 52 of relatively smaller diameter in the
rear plate 5 is kept relatively low. As a result, due to Bernoulli
law, the air-gas mixture ejected from the second flame holes 42 is
attracted by the flow of the air-gas mixture ejected at a high
speed from the first flame hole 41. Consequently, the flames to be
formed by the combustion of the air-fuel mixture ejected from the
second flame holes 42 are combined into the flame to be formed by
the combustion of the air-fuel mixture ejected from the first flame
hole 41, whereby aggregated flames Fa elongated forward are formed
and the flames can be prevented from getting spread radially
outward.
[0032] In this embodiment, since the front portion of the
cylindrical section 53 is formed into a cylindrical shape having a
diameter smaller than that of the first ventilation hole 51, there
can be obtained an accelerating effect in which the velocity of the
air-gas mixture is larger than the incoming velocity into the first
ventilation hole 51, in addition to the rectifying effect of the
air-gas mixture. Therefore, the velocity of the air-gas mixture
ejected from the first flame hole 41 becomes larger, whereby the
radially outward spreading of the flames can effectively be
prevented.
[0033] In case the cylindrical section 53 is not provided but the
first flame hole is formed into a pipe-shaped element that
protrudes forward from the front plate, there can also be obtained
an effect in that the flow of air-gas mixture ejected from the
first flame hole is rectified and that the spreading of the flames
in the radially outward direction can be prevented. In this
arrangement, however, the amount of heat from the flames to be
inputted into the pipe-shaped element in the first flame hole
becomes too large, and backfiring is likely to occur due to
overheating of the first flame hole. In this embodiment, on the
other hand, there can be obtained an effect in that, without
forming the first flame hole 41 into a pipe-shaped element, the
radially outward spreading of the flames can be prevented.
Backfiring due to overheating of the first flame hole 41 can thus
be prevented. In addition, by forming the second flame holes 42
into slit shape of a width below the quenching distance, backfiring
in the second flame hole 42 can also be prevented.
[0034] In place of the slit-shaped second flame holes 42,
backfiring can similarly be prevented by forming, as the second
flame holes, a multiplicity of circles of diameter smaller than the
quenching distance. It is, however, advantageous to arrange the
second flame holes 42 into slits like in this embodiment, because
the fabrication becomes easier and the pressure loss can be
reduced.
[0035] It is also possible to make the length of the cylindrical
section 53 smaller than the longitudinal distance between the rear
plate 5 and the front plate 4. In this arrangement, however, there
will occur a clearance in the longitudinal direction between the
front end of the cylindrical section 53 and the front plate 4. Part
of the air-gas mixture flowing into the cylindrical section 53 may
leak through this clearance into the space outside the cylindrical
section 53 between the front plate 4 and the rear plate 5. As a
result, the flow velocity of the air-gas mixture ejecting from the
first flame hole 41 will be lowered. In the arrangement of this
invention, on the other hand, the length of the cylindrical section
53 is made equal to the longitudinal distance between the rear
plate 5 and the front plate 4 so that no clearance in the
longitudinal direction occurs between the front end of the
cylindrical section 53 and the front plate 4. As a result, all of
the air-gas mixture flowing into the first ventilation hole 51 will
be introduced into the first fame hole 41. In conjunction with the
above-mentioned accelerating function, the velocity of the air-fuel
mixture ejected from the first flame hole 41 becomes still faster,
and the radially outward spreading of the flames can more
effectively be prevented.
[0036] In this embodiment, an arrangement has been made that the
length of the cylindrical section 53 is set to be the same as the
longitudinal distance between the rear plate 5 and the front plate
4. However, it need not be limited to such an arrangement. In other
words, take for example a case in which the length of the
cylindrical section 52 is slightly smaller than the longitudinal
distance between the rear plate 5 and the front plate 4 and, as a
result, a clearance occurs in the longitudinal direction between
the front end of the cylindrical section 53 and the front plate 4.
Even in such a case, if the air-gas mixture flowing into the
cylindrical section 53 does not leak into the space outside the
cylindrical section 53 between the front plate 4 and the rear plate
5, there can be obtained a similar effect as the one described
above.
[0037] Further, in this embodiment, the diameter of the first flame
hole 41 is made larger than the inner diameter of the front end of
the cylindrical section 53. Therefore, the air-gas mixture flowing
into the cylindrical section 53 is smoothly ejected from the first
flame hole 41 without being disturbed by the front plate 4. The
velocity of the air-gas mixture ejected from the first flame hole
41 becomes larger and the pressure loss becomes smaller.
[0038] Further, the air-gas mixture ejected from each of the flame
retention holes 43 gets collided with the inner circumference at
the front end of the mixing tube 2, and is then diffused in the
circumferential direction in the annular clearance that is
generated between the rounded corner portion 4b and the inner
circumference at the front end of the mixing tube 2. The air-gas
mixture is thereafter ejected forward from this clearance. Since
the velocity of ejection of the air-gas mixture from this clearance
is lowered due to the collision of the air-gas mixture with, and
diffusion thereof into, the inner circumference of the front end of
the mixing tube 2, there can be formed flames Fb that are hard to
be lifted off, thereby securing the flame retention property.
[0039] Now, a description will be made of a second embodiment of
this invention as shown in FIG. 4. The basic construction of the
second embodiment is not particularly different from that of the
first embodiment. The same reference numerals as those in the first
embodiment are therefore assigned to the similar members and the
parts. The difference of the second embodiment from the first
embodiment is that the diameter of the first flame hole 41 is made
larger than the outer diameter of the front end of the cylindrical
section 53.
[0040] Also in the second embodiment, the air-gas mixture entering
the cylindrical section 53 is smoothly ejected from the first flame
hole 41 without being disturbed by the front plate 4. Therefore, in
the same manner as in the first embodiment, the flow velocity of
the air-gas mixture ejected from the first flame hole 41 is
accelerated and also the pressure loss becomes smaller.
[0041] Descriptions have so far been made of embodiments of this
invention with reference to the accompanying drawings. This
invention is however not limited to the above embodiments. Although
the cylindrical section 53 is formed in the rear plate 5 in the
above embodiments, the following arrangement may also be made. For
example, the front plate 4 is provided with a cylindrical section
that protrudes backward from the hole edge of the first flame hole
41 toward the first flame hole 51 so that the air-gas mixture
flowing into the first flame hole 51 is introduced into the first
flame hole 41 through the cylindrical section. In this arrangement,
preferably, the length of the cylindrical section is made equal to
the longitudinal distance between the rear plate 5 and the front
plate 4 so that, between the rear end of the cylindrical section
and the rear plate 5, there occurs no clearance which allows
air-gas mixture flowing into the first ventilation hole 51 to leak
into the space outside the cylindrical section between the rear
plate 5 and the front plate 4. It is also possible to make the
length of the cylindrical section larger than the longitudinal
distance between the rear plate 5 and the front plate 4 so that the
rear end region of the cylindrical section is fitted into the first
ventilation hole 51. Further, in case the cylindrical section is
disposed in the front plate 4, it is preferable to gradually reduce
the diameter of the rear region of the cylindrical section from the
first ventilation hole 51 toward the front side so that the front
portion of the cylindrical section is formed into a cylindrical
shape having a smaller diameter than the first ventilation hole 51
but the same diameter as the first flame hole 41. However, in case
the cylindrical section is formed in the front plate 4, the
fabrication of the cylindrical section becomes troublesome.
Therefore, it is advantageous to form the cylindrical section 53 in
the rear plate 5 as in the above-mentioned embodiments.
[0042] In addition, the following arrangement may also be employed.
For example, the rear plate 5 is provided with a cylindrical
section that protrudes forward from the edge of the first
ventilation hole 51. The front plate 4 is provided with a
cylindrical section that protrudes backward from the edge of the
first flame hole 41. Then, both the cylindrical sections are fitted
between the rear plate 5 and the front plate 4 so that the air-gas
mixture flowing into the first ventilation hole 51 is introduced
into the first flame hole 41 through both the cylindrical sections.
It is possible to provide at least one of the front plate 4 and the
rear plate 5 with an independent cylindrical section other than
these plates 4, 5. Although the mixing tube 2 of sheet metal make
is used in the above-mentioned embodiments, it is also possible to
use a mixing tube made of a cast steel. Further, the flame
retention holes 43 in the above-mentioned embodiments may be
omitted. In addition, in the above-mentioned embodiments, this
invention was applied to a tubular burner for heating appliances.
This invention can, however, be applied to tubular burners which
are used in a combustion equipment other than a heating
appliance.
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