US3179155A - Deep combustion radiant surfaces with special slotting - Google Patents

Description

April 20, 1965 M. PARTIOT 3,179,155

DEEP COMBUSTION RADIANT SURFACES WITH SPECIAL SLOTTING Filed June 17. 1960 2 Sheets-Sheet 1 FIG. I.

FIG. 5.

Maurice Parriof BY 2| 4f -v A TTO RNEYS April 20, 1965 M. PARTIOT 3,179,155

DEEP COMBUSTION RADIANT SURFACES WITH SPECIAL SLO'I'TING Filed June 1'7, 1960 2 Sheets-Sheet 2 FIG. 7.

ATTORNEYS INVENTOR .m w m JV 0 o I 9 I a P q I I .MI-vu w 0 M W m. m G H Y O B 3 A W a 6 ll 2 Q United States Patent 3,179,155 DEEP COMBUSTION RADIANT SURFACES WITH SPECIAL SLQTTING Maurice Partiot, 12 Rue de Plateau Saint Antoine, Le Chesnay, Seine-et-Oise, France Filed June 17, 1960, Ser. No. 36,767 11 Claims. (Cl. 158-116) The present invention concerns the design of radiant ceramic plate so that the flame produced by the combustion of flammable gas mixtures is caused to penetrate to a controlled depth in the combustion surface of the ceramic and provide a combustion region of predetermined thickness.

It is an object of the invention to provide means to achieve practically complete combustion of a gaseous mixture by reverberation of the radiant energy of combustion.

It is an object of the invention to raise the temperature of the radiant combustion face of a ceramic plate to maximize the rate and completeness of combustion of a gaseous mixture.

It is an object of the invention to provide a combustion region of controlled depth below the outer radiant surface of a ceramic plate.

It is an object of the invention to provide a radiant ceramic plate having holes therethrough for the sup ly of a combustible gaseous mixture with outer radiant face slotted between holes to provide a combustion region of controlled depth.

It is an object of the invention to provide sufficient space within the combustion region to allow for the expansion of combustible gases without an increase in velocity which would drive them out of the combustion zone before they have finished burning and at the same time provide sufficient velocity to support the Coanda effect which causes the combustion gases to follow closely the surface of the ceramic plate around a bend.

It has been found that combustion in a radiant surface plate provided with holes, but unslotted, is confined to a region Which begins about one thirty-second of an inch 1: to one sixteenth of an inch below the radiant surface. As discussed above, this is not sufficient to provide the depth of combustion region needed to produce the full benefits of the invention. In order to obtain the desired increased temperature of the surface and the more complete oxidation of the gaseous mixture, a deeper combustion region about one-eighth inch to one quarter of an inch i) thick is provided. With holes or passages of about one square millimeter in cross-section area, a slot of about 0.7 mm. to one mm. in width and joining rows of holes permits combustion to occur at the bottom of the slot. As a result, an increased amount of heat is transferred to the material of the ceramic plate,

increasing its temperature and both the rate and completeness of the combustion of the gaseous mixture.

Several arrangements are proposed, according to the purpose described, and are best adapted to meet variable gas mixture compositions under varied pressure feed at the gas injector nozzle.

In general, in each of the several arrangements, the upper radiant surface defines a plurality of hollows, i.e. cavities or slots, which extend below the radiant surface a depth in excess of the maximum cross-sectional dimension of any passage and with a plurality of said passages opening into each hollow, the novel construction resulting in combustion deeply within the hollows to provide thereby a substantially hotter radiant surface.

One disposition consists in joining all the holes or passages in any of one or more rows of such passages at the radiant surface of the plate by a slot three to four millimeters deep and from five-tenths to eight-tenths of a millimeter wide. The flame will reach deeper into the holes from backfiring.

In another embodiment of the invention, the slots are only five-tenths of a millimeter wide and are terminated by an angle bevel about 60 from the outer surface which gives the slot an opening of about one millimeter wide at said surface. The slot totals between three and four millimeters deep, and the bevelled portion of the slot reaches about one to two millimeters below the outer surface as compared to a hole diameter ranging from about one millimeter to one and a half millimeters. The slots are aligned with respect to the rows of holes preferably so that an aggregate of about one quarter to three quarters of the circumference of the hole section is cut open by said slots to a depth greater than half the total depth of said slots below the outer face of the ceramic block.

In still other embodiments of this invention, each slot or cavity is so disposed as to join, at the bottom of the slot or cavity, passages which are respectively associated with different rows of such passages. More specifically, each of the generally opposing side walls forming a part of any one slot or cavity intersects one or more of the passages below the radiant surface of the grid and cuts away a portion of the passage-defining Wall most deeply on that portion thereof which faces an opposing wall of the slot or cavity. This results in a tendency for the gas mixture passing through such intersected passage to be directed at least in part away from the axis of the passage and in a direction generally toward an opposing wall of the slot or cavity. Such a construction results in deep combustion within the slots or cavities and in a much higher radiant temperature of the Walls of the slots or cavities because of the mutually radiant reverberation that takes place.

The combustion takes place in a zone slightly below the bottom of the narrowed bevelled portion and is completed closely above the outer surface level of the radiant plate. The bevel serves the dual purpose of allowing the flame to enter substantially below the outer surface and of spilling the hot combustion gases over the outer surface between the slots. The walls of the slot and bevel opposing each other reverberate their radiation to each other and finally to outside space; the mutual reverberation serves to increase the temperature of the bevel surfaces and the rate of combustion of the mixture.

The temperature of the radiant plate with bevelled slots joining the holes is raised by as much as fifty to eighty degrees centigrade, as compared to the: temperature of a ceramic plate which is flat, with all the holes being flush with the outside flat radiant unslotted surface of the plate.

If the combustion region is too deep the burning gases penetrate too far into the manifold as the apparatus operates at low pressure, usually at seven or eleven inches of water at the gas main. At usual gas main pressures, the combustion is practically complete when gases reach the outer surface of the ceramic plate, and the overheating of the walls of the slots caused by their mutual reverbera tion prompts the combustion to occur at a deep level in the non-slotted holes adjacent to said slots.

In the usual type of radiant surfaces for domestic purposes, the composition of the ceramic is the same throughout the whole thickness as well as in the slotted part and in the non-slotted part. However, when higher' temper- 3 atures and higher heat outputs are contemplated, the outer surface composition is changed at a depth between oneeighth A3") of an inch and one quarter 0A) of an inch. The usual vegetable fillers are replaced by more heat-resistant materials such as gypsum, zirconium oxide, and materials having high emissivity such as carborundum or other refractory materials which stay black at higher temperatures and radiate as black bodies with a higher proportion of infra-red output. Although the clay binder is apt to melt and flow somewhat, the fillers or other oxide or carbide aggregates are sintered so as to present a high durability at operating temperatures.

Other objects will appear from the following description and from the drawings, in which like numerals refer to like parts throughout.

FIGURE 1 is a fragmentary plan view of one form of a deep combustion radiant plate according to the invention, showing slotted construction.

FIGURE 2 is a sectional View taken along line 2-2 of FIGURE 1.

FIGURE 3 is a fragmentary plan View of a modified form of deep combustion radiant plate, yielding a strong construction.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 3.

FIGURE 5 is a fragmentary plan view of a further modified form of a deep combustion radiant plate with slots astride adjacent rows of holes.

FIGURE 6 is a sectional View taken along line 6-6 of FIGURE 5.

FIGURE 6A is a horizontal view showing the relative positions of reverberatory parts of a ceramic plate according to the invention.

FIGURE 7 is a fragmentary plan view of a fourth embodiment of the invention resembling FIGURE 6, but having every third row unslotted.

FIGURE 8 is a sectional view taken along line 8-3 of FIGURE 7.

FIGURE 9 is a fragmentary sectional view of a deep combustion radiant slotted plate having blind holes opened by slots.

FIGURE 10 is a fragmentary sectional view of a deep combustion radiant slotted plate having slotted blind holes and open holes in alternate rows.

FIGURE 11 is a fragmentary plan view of a plate according to the invention with blind holes and cross bevels to increase heat exchange or reverberation.

FIGURE 12 is a section taken along line 12-12 of FIGURE 11.

In FIGURE 1 ceramic radiant plate is provided with rows of holes 21 extending through the plate 243 and serving to conduct the gaseous mixture to the combustion region. Holes 26 are connected by slots 22, permitting combustion to begin at the bottom of the slots 22. Each slot has opposing side walls which are generally parallel to each other and to the axes of the passages and are spaced apart a distance which is less than the diameter of any passage intersected thereby. Consequently, opposing ribs are formed in the space between successively joined passages ofany row, and these ribs extend downwardly to the bottom of the slot where each intersected passage opens into the slot and where increased space is provided to permit the issuing gas stream to expand without any substantial increase in its velocity. Thus, combustion takes place within the slots and ribs are heated and form mutually reverberatory radiant surfaces. This construction provides greater area for the hot gases to contact the ceramic material of plate 20, space for the gases to expand without substantial increase in velocity, produces a higher temperature in the combustion region by reverberation and a greater net production of heat flowing from the faster rate of combustion and the greater completeness of oxidation of the hydrogen and carbon molecules comprising the combustible portion of the gaseous mixture being burned.

FIGURES 3 and 4 illustrate a form of the invention for use in ceramic plates which are highly porous and lacking in the structural strength of the denser, more compact ceramic materials. The slots 22 are applied to alternate rows of holes 21 so as to avoid weakening of the ceramic structure of the plate 2i). A bevel 23 is provided at the outer ends of slots 22, making the slots about one millimeter wide at the surface of plate 20 with the bevelled portion of the slots 22 extending between one and two millimeters below the surface. This construction provides additional room for expansion of the hot gases without substantial increase in velocity.

FIGURES 5 and 6, two adjacent rows of holes 21, are connected by wider slots 24 which are bevelled at 23. In this construction the combustion region reaches a little below the bottom of the slots 24 and the expanding gases of combustion spread to contact and overheat the fin or partition 25 between adjacent pairs of rows of holes 23 The reverberation of the heated walls of the slotted hole rows is partly directed outside the combustion region by the bevels 23. The slots astride the adjacent rows of holes are from one to two millimeters wide.

Thus, as can readily be seen from FIGURES 5 and 6, 7

each of the generally opposing side Walls which in part form any slot intersects a plurality of passages substantially below the upper surface of the radiant grids and by their intersection cut away a portion of the otherwise encircling wall which defines the passage, and cuts away such wall most deeply in that portion thereof which generally faces the opposing wall of the slot or cavity. Because of this, there is a tendency for some of the gas mixture passing through each hole or passage 21 to be deflected away from the axis of such passage and in a direction toward an opposing wall of the common slot joining the two passages 21 shown in FIGURE 6.

In FIGURES 7 and 8 a similar construction is shown but with the slots 24 astride two rows of holes 21 out of three, leaving a row of unslotted holes 21.

FIGURE 9 shows the use of blind holes 26 open and joined by slots 27. Blind holes create turbulence and aid in locating the combustion region at a predetermined depth. Slots 2.7 connect with the outer surface of the plate 2% through an outer wider slot 28 providing space for expansion of the heated gases.

In FIGURE 10 the use of slotted blind holes is employed in alternate rows with intermediate rows of open holes.

FIGURES 11 and 12 show two adjacent rows of blind holes 26 joined by wider slots 29. The surface of the plate 10 is formed with cross bevels 30 to increase heat exchange and also to allow for heated gas expansion without substantial velocity increase thus reducing any tendency of the hot gases to drive themselves away from the radiant surface. Shoulders 31 increase turbulence within the combustion region and help assure completeness of the combustion.

While there have been described above what are presently believed to be the preferred forms of the invention, variations thereof will be obvious to those skilled in the art and all such changes and variations which fall within the spirit of the invention are intended to be covered by the generic terms in the appended claims, which are variably worded to that end.

Reference is made to my copending application Serial No. 43,802, filed on July 19, 1960, now abandoned, for Deep Combustion Radiant Surfaces and to my other two copending applications, Serial No. 800,793 filed March 20, 1959, now abandoned, and Serial No. 821,038, filed June 17, 1959, now abandoned.

In prior constructions of radiant plates there has been a tendency to let a good part of the heat of combustion be carried away from the refractory plate which is intended to be heated to a maximum degree to convert as much of the heat of combustion into radiant heat as possible, leaving a minimum to be carried away by convection of the gas. With previous constructions the expansion of the gas during combustion imparts a relatively high velocity to the exhaust gas which is especially noticeable at the low gas feed pressures employed and the resulting low radiation output. One purpose of the invention is to provide enough space to permit expansion of the burning gas without substantial increase in velocity of fiow, which rather stays the same or even decreases. The velocity is preferably adjusted to follow closely the surface of the ceramic around a bend, in accordance with boundary layer conditions and the Coanda effect with its concomitant stagnation point and production of turbulent eddies close to the plate surfaces.

I claim:

1. A radiant grid element for a gas burner comprising a unitary block of refractory material defining a myriad of minute-bore elongated passages extending therethrough from a first boundary surface of said block toward a second boundary surface thereof for conducting from said first surface a myriad of streams of a combustible gas mixture toward said second surface for combustion adjacent said second surface, said block at said second boundary surface defining therein a plurality of cavities each having generally opposing wall surfaces that extend below said second surface an amount in excess of the maximum crosssectional dimension of any said passage, a plurality of said passages opening into each said cavity, some of said plurality of passages being intersected only by one of said opposing wall surfaces and others of said plurality of passages being intersected only by another of said opposing wall surfaces, each said passage-intersecting wall surface at least in part cutting away a portion of the material of said block which would otherwise define the intersected passage up to said second boundary surface, said cut-away portion being that passage-defining portion which is nearest an opposing wall surface of said cavity and forming an escape means which passes a portion of the gas mixture entering said intersected passage at an angle away from its axis and in a direction toward said opposing wall surface of said cavity, the arrangement of said passages and their dimensions together with the shape and size of said cavities and said escape means comprising a means which is jointly operable to cause at least some of the gas mixture to burn at substantially the bottoms of the respective cavities, the thickness of said block at its minimum within said cavities and the nature of the refractory material of said block comprising a means which is jointly operable to prevent said first surface from reaching the ignition temperature of said gas mixture, and each said passage being many times longer than its width and sufiiciently narrow to prevent the flame from backpropagating therethrough to said first surface.

2. The radiant grid element of claim 1 in which the cavity wall surfaces are substantially parallel to the axes of said passages, said escape means comprising an aperture communicating between said passage and said cavity below the level of said second boundary surface.

3. The radiant grid element of claim 1 wherein the cross-sectional area of each said passage is between about one square millimeter and one and one-half square millimeters and each said cavity comprises a slot having a 6. The radiant grid element of claim 1 wherein said second boundary surface is substantially fiat and parallel to said first boundary surface except for the passages and cavities defined in said second boundary surface.

7. A radiant grid element for a gas burner comprising a unitary block of refractory material defining a myriad of minute-bore elongated passages extending therethrough from a first boundary surface of said block to a second boundary surface thereof, each said passage defining a separate and distinct path for the flow from said first surface of a stream of combustible gas mixture toward said second surface for combustion adjacent to said second surface, said block at said second boundary surface defining therein a plurality of slots each having generally opposing side walls which over a major portion of the depth of said slots are generally parallel to the axes of said passages, said side walls of said slots being spaced apart a minimum distance which is less than the maximum crosssectional dimension of any said path-defining passage, each said slot having its said side Walls intersecting and joining at least two adjacent said passages, the intersection of the bottom-most portion of said slot with one of said side walls of said passages joined thereby defining a space of substantially increased cross-sectional area relative to that of any passage to lower the velocity of the gas mixture in such space and thereby induce combustion in and near the bottom of said slots, the said slot Walls forming in the region between the passages joined by said slots a pair of mutually opposing ribs which extend downwardly below said second boundary surface to the level at which the joined passage is intersected by the bottom of the associated slot, the arrangement of said passages and their dimensions together with the depth and width of said slots comprising means which is jointly operable to cause at least some of the gas mixture to burn at substantially the bottoms of the respective slots, the thickness of said block at its minimum within each said slot and the nature of the refractory material of said block. comprising means which is jointly operable to prevent said first surface from reaching the ignition temperature of said gas mixture, and each said passage being many times longer than its maximum cross-sectional dimension and sufficiently narrow to prevent the flame from back-propagating therethrough to said first surface.

8. The radiant grid element as defined in claim 7 wherein the opposing side walls of each said slot diverge outwardly at their upper portions nearest said second surface.

9. The radiant grid element of claim 7 wherein said second boundary surface is substantially flat and parallel to said first boundary surface except for the passages and slots defined on said second boundary surface.

10. The radiant grid element of claim 7 wherein said opposing side Walls are substantially planar.

11. The radiant grid element of claim 7 in which said minute-bore passages are arranged in rows and each alternate row is intersected by a respective one of said slots.

References Cited in the file of this patent UNITED STATES PATENTS 1,113,174 Lucke et a1 Oct. 6, 1914 1,215,229 Willson Feb. 6, 1917 1,308,364 Lucke July 1, 1919 1,901,086 Cox Mar. 14, 1933 FOREIGN PATENTS 485,086 Germany Oct. 26, 1929 144,694 Austria Feb. 25, 1936 551,940 Belgium Nov. 14, 1956 558,007 Belgium June 29, 1957

Claims (1)

1. 7. A RADIANT GRID ELEMENT FOR A GAS BURNER COMPRISING A UNITARY BLOCK OF REFRACTORY MATERIAL DEFINING A MYRIAD OF MINUTE-BORE ELONGATED PASSAGES EXTENDING THERETHROUGH FROM A FIRST BOUNDARY SURFACAE OF SAID BLOCK TO A SECOND BOUNDARY SURFACE THEREOF, EACH SAID PASSAGE DEFINING A SEPARATE AND DISTINCT PATH FOR THE FLOW FROM SAID FIRST SURFACE OF A STREAM OF COMBUSTIBLE GAS MIXTURE TOWARD SAID SECOND SURFACE FOR COMBUSTION ADJACENT TO SAID SECOND SURFACE, SAID BLOCK AT SAID SECOND BOUNDARY SURFACE DEFINING THEREIN A PLURALITY OF SLOTS EACH HAVING GENERALLY OPPOSING SIDE WALLS WHICH OVER A MAJOR PORTION OF THE DEPTH OF SAID SLOTS ARE GENERALLY PARALLEL TO THE AXES OF SAID PASSAGES, SAID SIDE WALLS OF SAID SLOTS BEING SPACED APART A MINIMUM DISTANCE WHICH IS LESS THAN THE MAXIMUM CROSSSECTIONAL DIMENSION OF ANY SAID PATH-DEFINING PASSAGE, EACH SAID SLOT HAVING ITS SAID SIDE WALLS INTERSECTING AND JOINING AT LEAST TWO ADJACENT SAID PASSAGES, THE INTERSECTION OF THE BOTTOM-MOST PORTION OF SAID SLOT WITH ONE OF SAID SIDE WALLS OF SAID PASSAGES JOINED THEREBY DEFINING A SPACE OF SUBSTANTIALLY INCREASED CROSS-SECTIONAL AREA RELATIVE TO THAT OF ANY PASSAGE TO LOWER THE VELOCITY OF THE GAS MIXTURE IN SUCH SPACE AND THEREBY INDUCE COMBUSTION IN AND NEAR THE BOTTOM OF SAID SLOTS, THE SAID SLOT WALLS FORMING IN THE REGION BETWEEN THE PASSAGES JOINED BY SAID SLOTS A PAIR OF MUTUALLY OPPOSING RIBS WIHICH EXTEND DOWNWARDLY BELOW SAID SECOND BOUNDARY SURFACE TO THE LEVEL AT WHICH THE JOINED PASSAGE IS INTERSECTED BY THE BOTTOM OF THE ASSOCIATED SLOT, THE ARRANGEMENT OF SAID PASSAGES AND THEIR DIMENSIONS TOGETHER WITH THE DEPTH AND WIDTH OF SAID SLOTS COMPRISING MEANS WHICH IS JOINTLY OPERABLE TO CAUSE AT LEAST SOME OF THE GAS MIXTURE TO BURN AT SUBSTANTIALLY THE BOTTOM OF THE RESPECTIVE SLOTS, THE THICKNESS OF SAID BLOCK AT ITS MINIMUM WITHIN EACH SAID SLOT AND THE NATURE OF THE REFRACTORY MATERIAL OF SAID BLOCK COMPRISING MEANS WHICH IS JOINTLY OPERABLE TO PREVENT SAID FIRST SURFACE FROM REACHING THE IGNITION TEMPERATURE OF SAID GAS MIXTURE, AND EACH SAID PASSAGE BEING MANY TIMES LONGER THAN ITS MAXIMUM CROSS-SECTIONAL DIMENSION AND SUFFICIENTLY NARROW TO PREVENT THE FRAME FROM BACK-PROPAGATING THERETHROUGH TO SAID FIRST SURFACE.

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