US3251396A

US3251396A - Ceramic burner plate

Info

Publication number: US3251396A
Application number: US303233A
Authority: US
Inventors: Joseph E Nitsche
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1963-08-20
Filing date: 1963-08-20
Publication date: 1966-05-17
Anticipated expiration: 1983-05-17
Also published as: CH451445A; SE302499B; BE651873A; GB1071827A; NL6409335A

Description

May 17, 1966 J. E. NlTscHE 3,251,396

CERAMIC BURNER PLATE Filed Aug. 2G, 1963 4 Sheets-Sheet l L www MNHN JMW INVENTOR. Joseph E. Nfsche BWM H/` ATTORNEY May 17, 1966 .1. E. NlTscHE CERAMIC BURNER PLATE lg 5 A 4 Sheets-Sheet 2 Filed Aug. 20, 1963 32|" 39 3&2" 3,9

27 Fig. N

Fig.8

INVENTOR. Joseph E. Nitsch@ BYCQMW fi,

H/S ATTORNEY Mayl?, 1966 J. ENITSCHE 3,251,396

CERAMIC BURNER PLATE Filed Aug. 20, 1965 4 Sheets-Sheet 5 |500 ik d. l 1400 lu I300 0 l5 30 45 60 G-EM/ss/a/v ANGLE WNVTSECM DEGEUg/WENORMAL BY Fig..9 3L' @www H/S ATTORNEY May 17, 1966 J. E. NITSCHE CERAMIC BURNER PLATE 4 Sheets-Sheet 4 Filed Aug. 2o, 1963 wkum zt E E o 3o Q EMISS/ON ANGLE INVENTOR. Joseph E. Nfsche DEGREES FROM NORMAL TO SURFACE Fig. IO

H/S ATTORNEY United States Patent O York Filed Aug. 20, 1963, Ser. No. 303,233 6 Claims. (Cl. 158-116) This invention relates to ceramic burner plates for infrared radiation gas burners and the like. In particular, it comprises a burner plate having an improved and novel combustion surface configuration or geometry.

In recent years, ceramic burner plates have been constructed in the form of a perforated or honeycomb structure having a plurality of small unobstructed gas passages or open-ended cells lseparated from each other by thin ceramic Walls and uniformly distributed throughout the structure. These burner plates have overcome many of the limitations and problems (eg. back-firing, high pressure drop, poor efficiency, etc.) associated with older and more well-known ceramic lburner plates, such as porous ceramic slab-like blocks or ceramic blocks with a limited number of widely scatteredperforations separated by thick walls. In these more recently developed burner plates, the gas passages extend in a uniform manner through the burner plate from one major face of the plate to an opposed or opposite major face thereof. One of these major faces constitutes an external combustion surface when the plate is pl-aced over an opening in a gas burner mixing chamber in such a manner that the other major face confronts `the interior of the mixing chamber. The combustion surface of these plates is made with a fiat, generally smooth configuration to provide an infrared radiating surface as the gaseous fuel burns on the combustion surface after passing through the gas passages from the mixing chamber. Typical examples of this type of ceramic burner plate are those disclosed in United States patent application Serial No. 189,785, filed April 24, 1962, by C. L. Goss and L. C. Lipt-ak, now Patent No. 3,161,227, and in UnitedStates Patent No. 2,775,294 to G. Schwank.

The ceramic honeycomb or perforated structures suitable for use as burner plates must be constructed with certain essential and necessary dimensional characteristics for attaining the unique, improved advantages over the old porous block plates including the avoidance of detrimental ashback. First, the gas passages should have a cross-sectional area at the combustion surface that does not exceed 0.006 square inch and a minimum length of about 0.2 inch. These gas passages, of course, should be substantially uniformly distributed! throughout the burner plate and their cross-sectional areas in the aggregate should provide at least 20%, and more preferably at least 50%, of the total area of the combustion or radiating surface. When this total aggregate open area is 50% or more, the ceramic Walls will necessarily be quite thin (i.e. 0.01 inch or less) and the upwardly flowing gas will extract most of the heat conducted down the wall of most any suitable ceramic material used, thereby 'preventing the well-known undesirable effect of flashbac-k from occurring. In the case where the total aggregate open area is less than 50%, with correspondingly thicker walls, the ceramic walls should desirably have a low heat conductivity on the order of less than 0.0014 cal/sec. cm. C. since the greater mass of the Walls makes it less possible for the upwardly owing gases to extract enough heat from higher heat conductivity ceramic fwalls to prevent flashback. p

It has been found that the flat combustion surface of these burner plates is not uniformly heated by the burning fuel because of slight differences in the thickness of ICC the cell walls and hydraulic diameters of the cells, which is an inherent result of the methods of manufacturing these plates. These differences create sufficient combustion variation to cause uneven heating and, as a result, the fiat surface has a mottled appearance. This mottled surface appearance, varies considerably in temperature from the orange-white-high temperature areas to the dull redor gray low temperature areas. Such a surface condition is undesirable since the maximum conversion of the available B.t.u. content of the gas into infrared energy is not being achieved.

It is an object of this invention to provide a ceramic, honeycomb or perforated burner plate having a novel combustion surface configuration of geometry whereby the thermal gradients or uneven heating of the radiating combustion surface due to slight differences in the thickness of the cell walls and hydraulic diameters of the cells is greatly reduced.

It is another object of this invention to provide a ceramic, honeycomb or perforated burner plate having a novel combustion surface configuration or geometry whereby .much more efficient combustion is effected by the resulting thermo-catalytic combustion.

It is a further object of this invention to provide a ceramic, perforated or honeycomb burner platehaving a novel combustion surface configuration or geometry which affords a maximum realization of the available heat content of the gaseous fuel and thereby results in greatly increased temperature of the radiating combustion surface and in greater burner efficiency.

It is stil-l another object of this-invention to provide Va ceramic, honeycomb or perforated burner plate having a novel combustion surface configuration or geometry which will have a higher emissivity thereby resulting in greater radiant output and in greater burner efficiency.

It is a still further object of this invention'to provide a novel combustion surface configuration or geometry which willyield, for all emission angles of 0 to 60 yfrom the normal to the combustion surface, combustion surface temperatures of at least about l500 F. and total radiation of at least 25,000 B.t.u./hour/squ-are foot.

These and other objects, which will become apparent to those skilled in the art from the detailed description given hereinafter and from the accompanying drawings, are attained in accordance with my discoveries by providing a ceramic gas burner plate comprising a thin wall, ceramic perforated or honeycomb structure constructed with the dimensional characteristics specified hereinabove and having t'wo opposed major faces with a plurality of small gas flow passages extending between the opposed major faces, and with one major face comprising a plurality of cylindrical Vcavities defined by indented surface portions having critical dimensional characteristics and disposed substantially uniformly over the entire area, or a given portion, of this one major face in critical spaced relation. must be within the range of about 1A; inch to 1 inch. The depth of the cavities should be such that the ratio of the depth to the diameter falls within the range of 0.5 to 5. The spacing between any two adjacent cylindrical cavities taken along a straight line joining centers of the cavities and defined by the unindented portions of t-he combustion surface must not exceed `about 1/2 inch. Cylindrical cavities according to this invention also include those having a nub protruding up centrally from the bottom of the cavities. In 'this latter case, the diameter of the cavities must be within the range of 3%; inch to 1 inch and the diameter of the nubs must be small enough (not less than about 1/s inch diameter to avoid fragility) to provide at least about 1A; inch annular space The diameter of the cylindrical cavities' between the nub and the cavity wall. The height of the nub may be as ymuch as the full depth of the cavity. The cylindrical cavities may also be made with a minor lower portion of smaller diameter than a main upper portion, but not less than the l/s inch diameter specified above. When the one major face that is to confront the interior of the mixing chamber is made generally fiat, the above-described minimum gas passage length is that distance between the lowermost part of the cylindrical cavities and the ilat, unindented major face.

The invention will be better understood by reference to the drawings wherein:

FIGURE l is a plan view of the combustion face of a radiant burner with one illustrative embodiment of the present invention, portions of the latter being broken away to expose the interior mixing chamber and the edges of walls 39 forming a part of the bases (or indented surfaces) of cylindrical cavities 32 being omitted for clarity in illustration of the cavity configuration;

FIGURE 2 is a sectional view of a` radiant burner like that shown in FIGURE l taken along line lI-IL the edges of walls 30 forming a part of the cylindrical sides of the cylindrical cavities 32 being omitted for clarity in illustration of the cavity configuration;

FIGURE 3 is a fragmentary schematic view of the combustion surface of another embodiment of the present invention;

FIGURE 4 is a fragmentary schematic view vof the combustion surface of a third embodiment of the present invention;

FIGURES 5A and 5B are fragmentary, side sectional views in schematic form of two more embodiments of the present invention;

FIGURE 6 is an enlarged fragmentary side sectional view of an embodiment of the present invention, the detail of the visible edges of walls 30 forming la part of the cylindrical cavities 32 being omitted for clarity in illustration of the radiation pattern of surface particles;

FIGURE 7 is an enlarged fragmentary side sectional view of a burner plate of the type prior to the present invention;

FIGURE 8 is an enlarged fragmentary sectional view taken along line VIII-VIII of FIGURE 6;

FIGURE 9 is a graph showing the combustion surface temperatures of several different burner plates asmeasured at various emission angles from the normal to the combustion or radiant surface; and

FIGURE l0 is a graph showing the 'total radiation from the combustion surface of several different burner plates as determined for various emission angles from the normal to the combustion or radiant surface.

Referring now to FIGURES l and 2, the radiant gas burner is typically composed of -a body member 10 having side walls 12 and a bottom wall 14. Attached to body member 10 is a centrally disposed inlet tube 16 extending from one side Wall 12. The cover member or burner plate of the radiant burner is a ceramic honeycomb structure 18 comprising one embodiment of the present invention. The zone 20 within the body 10 between the burner plate 18 and the bottom Wall 14 comprises a mixing chamber where air and the fuel, such as natural gas, propane, butane, manufactured gas, town gas or the like, thoroughly mix after entering from inlet tube 16 and prior to passing upwardly through the cover plate 18 for combustion on the upper surface thereof.

The honeycomb burner plate .18 is tted and attached to 4the body 10 at the upper portion 22 of the side Walls 12 by any suitable means, such as cement or packing 24.

As is shown in the drawings, the honeycomb burner plate 1S is characterized by a large number of unobstructed gas paths or open-ended cells that extend from the bottom or inlet surface 27 of the burner plate through to its top, combustion or radiant surface 28. These unobstructed gas paths are defined and sep- 4, arated from one another by thin ceramic walls 30. By unobstructed, I means that no structure exists within the gas flow paths that would prevent ow. The ceramic walls defining those ow paths can be arranged in triangular, circular or polygonal shape as desired.

The major characterizing feature of the invention is the geometry or confiuration of the combustion or radiant surface. As is illustrated by the embodiments shown in FIGURES l, 2 and 5, the combustion surface 28 (or 28 or 28") comprises a plurality of cylindrical cavities defined by identations 32 (or 32 or 32) disposed substantially uniformly over the entire area (or a given portion if desired) of surface 28 (or 28 or 28"). FIG- URE 3 illustrates another embodiment of the invention wherein cylindrical cavities 34 are disposed in alternately staggered rows, in contradistinction to the rectilinear arrangement of cavities 32 as shown in FIGURE 1. FIG- URE 4 illustrates a still further embodiment of the present invention wherein cylindrical cavities 36 are arranged in the rectilinear pattern (similar .to that of cavities 32 in FIGURE l) and additionally smaller cylindrical cavities 37 are positioned at points generally equidistant from the centers of four adjacent larger cylindrical cavities 36.

As previously mentioned, the cylindrical cavities may have a nub protruding upward centrally from their bottom (indented) surface, and FIGURES 5A and 5B illustrate this embodiment form. FIGURE 5A schematically shows the cylindrical cavities 32 in the combustion surface 28 and cylindrical nubs 3S extending centrally upward only a fraction of the total depth of cavities 32. FIGURE 5B schematically shows a similar arrangement but with nubs 39 extending upward substantially the full depth of cavities 32".

In the use of a burner plate of the invention, a source of a gaseous fuel and air enter the burner body 10 through the inlet tube 12 or any other suitable inlet means. The fuel and air can be provided by sources connected to a mixing head that is attached to the inlet means, or the pressure of the fuel gas can be used with suitable means to aspirate air into the stream.

Other. procedures, none of which form any part of the invention can be used as well. Thegases enter the enlarged space 20 within the burner body 10 and thoroughly mix therein. For mixing purposes, the inlet tube can be designed so that the gases irnpinge on a wall of the bodymember 10, or baffles (not shown) can be included within the body or tube to effect that object. The mixed gases then pass through the gas paths 25 in the burner plate to the upper surface 28 where they are combusted, heating the surface of the plate to incandescence, or to nearly incandescence. Any suitable conventional combustion initiator can be used as desired.

The significant improvements afforded by the burner plate of the invention are believed to be due to interparticle reinforcement. Thus, as shown in FIGURE 6, surface particles 40, 41 along indented surface portions 32 forming the cylindrical cavities in surface 28 radiate heat energy in a hemispherical pattern as indicated at 42, 43. With a burner plate according to this invention, having a combustion surface comprising a multitude of closely spaced cylindrical cavities, it can be seen that a substantial amount of the hemispherical radiation of each surface particle within the cylindrical cavity areas will impinge on other surface particles within the same cylindrical cavities. This effect, which I call interparticle reinforcement, results in increasing the overall temperature (and emissivity) of the combustion or radiating surface 28 for any given volume of gaseous fuel per unit of time. In turn, this higher surface temperature promotes thermocatalytic combustion and more complete combustion of the gaseous fuel thereby liberating maximum heat content from the fuel to further increase the combustion surface temperature. As will be apparent, the higher surface temperatures, provided by the burner plate of the invention, increase the amount of radiant energy relative to convected energy for any given unit volume of gaseous fuel combusted; thus the invention affords a significantly greater infrared burner eiciency. A

The significance of the improved burner plate of the invention can best be seen by comparing FIGURES v6 and 7. FIGURE 7 shows a burner plate of the type made prior to this invention having a at combustion surface 44. A surface particle 45 radiates energy in the hemispherical pattern as shown at 46. vAs can beseen, substantially none of the hemispherical `radiation impinges on othersurface particles. Thus, interparticle reinforcement is substantially wholly absent.

As was mentioned earlier, a particularly undesirable problem was the development of thermal gradients on the radiating combustion surface due to the slight diiferences in the thickness of the cell Walls and hydraulic diameters of the cells. This problem can best be understood by reference to FIGURE 8. The honeycomb structure is made of thin ceramic sheets 30 sintered together as at points 47 to form the thin walls dening the gas paths 25. The wall thickness at points 47 are essentially double that of the remaining wall portions. It is at these points that the dark or cool zones are seen on the edges of the thin ceramic walls making up a at combustion surface. However, with a lburner plate according to this invention, the hemispherical reinforcement radiation within the multitudinous cylindrical cavities causes the thicker Wall edge points- 47 to heat up more uniformly with the other thinner areas on the indented portions 32 of the combustion surface 28. It can also be seen in FIGURE 8 that if the cross-sectional areas of the gas passages vary one from another (e.g. if the cross-sectional area of passage 25a is somewhat larger than that of passage 25h), the hydraulic radius then varies and the gas mixture velocity through these passages also varies since the pressure drop from the inlet end of the passages to the outlet end of the passages is the same for each passage. This variation in the velocity of the gas/air mixtures causes an uneven burning condition at the combustion surface. This results in uneven surface temperatures and the characteristic mottled appearance of the combustion surface. However, with a burner plate according to this invention, this tendency toward uneven surface temperatures, due to slight variations in the hydraulic diameter of the gas/ air mixture ilow passages, is substantially reduced. This is substantially a result of the interparticle reinforcement described above.

In the areas where the hydraulic diameter is less than the normal (and on a fiat combustion surface results in darker color and lower temperature), interparticle reinforcement due to the cylindrical cavity coniiguration or geometry of the combustion surface raises the temperature. This results because the total` radiation from the lhotter areas is greater than that from the cooler areas as taught by the Stephan-Boltzman law. Thus, since in the cylindrical cavities, the cooler areas are seen by the hotter areas, the cooler areas receive radiation energy from the hotter areas and the temperature differential between the two areas is substantially reduced.

By way of illustration, and not of limitation, the following is given as the best mode contemplated of making burner plates according to this invention. A ceramic honeycomb body is prepared by coating a suitable carrier with a mixture of a pulverized ceramic and a binder, crimping the resulting coated carrier and then assembling it to the desired shape, alone or with another coated carrier that need not be crimped. The assembled body is then heated to a temperature suicient to sinter it to a unitary structure as more fully detailed hereinafter. This procedure is, generally, the process set forth in the copending application of R. Z. Hollenbach, Serial Number 759,706, filed September 8, 1958 and now Patent No. 3,112,184, to which reference may be had.

The purpose of the binder is to bond the unred ceramic material to the carrier, to impart green strength to the coated carrier and to retain the formed unred article in the desired shape after forming and prior to sintering. It is preferred to use an organic binder that is curable or thermo-setting and that can be removed by decomposition and/ or volatilization when the honeycomb body is fired, such as epoxy resins.

The purpose of the carrier is to provide support for the unired coating to allow it to be formed to the desired shape prior to sintering the ceramic coating. Tea bag paper is a preferred carrier because it will substantially decompose upon firing and thus result in an article consisting almost entirely of ceramic material.

Other suitable binders and carriers are disclosed in the aforementioned Hollenbach patent, to which reference can be made.

:In order to produce a -burner plate structure with optimum desirable characteristics of strength, low coeicient of thermal expansion (e.g. -10 to -l-2O 107/ C.), thermal shock resistance and high specific heat, it is preferred to use lithium alumino-silicate ceramic materials such, for example, as glass or crystalline petallite and beta spodumene, glass-ceramics having a lithium aluminosilicate :base (e.g. those made in accordance with Example I of United States Patent No. 2,920,971 to Stookey), as well as mixtures of any of the foregoing materials. Pet-allite glass-ceramic mixtures generally include about l0 to 40 weight percent of the glass-ceramic and the remainder petallite. Beta spodumene-petallite mixtures usually contain about 1 to 4 parts of petallite for each 4 to 1 parts -of beta spodumene. These materials normallly are used in particle size of about 200 mesh (Tyler) or finer.

Structures are assembled from ceramic coated carriers in Ia variety of ways, and the resulting structures are called honeycombs, a term which in this specification means a unitary body having a 'multitude of unobstructed gas paths of predetermined size and shape, each such gas path being defined by thin ceramic walls and extending between terminating end opposed major surfaces. These lstructures can be assembled from multiple layers of ceramic-coated carriers corrugated with the same pattern with alternate laye-rs of laterally disposed a distance equal to half of the width of the individual pattern so that the layers do not nest with each other. They can a-lso be made from multiple layers of corrugated ceramic coated carriers with alternate layers having the corrugation somewhat angled in opposite directions from the perpendicular to the edge of the sheet. The honeycomb structure can also be formed from roll-ing of alternate layers of crimped and uncrimped coated carriers until the desired shape is formed. The structure can also be formed by assembly into a stack alternate crimped and uncrimped coated carriers until the desired dimensions are attained. The structure is made large enough to form the cylindrical 'cavities in one major surf-ace, as by cutting, drilling or grinding, and to provide a minimum gas flow path length as described herein-above. In order to ensure good results, the minimum gas ow path length should be 0.375.

Other ways of making and assemblin-g these honeycombs will be apparent to those skilled in the art. For' example, the thin ceramic sheets from which the honeycomb structure is constructed can be produced by extrusion, knife casting and the like ceramic processes.

The iiring of the green structure or matrix, however formed, is accomplished in the normal manner for ceramic firing by placing the structure in a furnace and heating it at a rate slow enough to prevent breakage up to a temperature high enough to cause the ceramic particles to sinter. While the firing schedule, including heating -rates and sintering temperatures, will vary depending upon the ceramic material utilized, the size and shape of the structure formed, and the atmosphere used, the details of such schedules are not critical and suitable conditions are readily determinable by one skilled in the art of tiring ceramic particles.

The invention will be described further in conjunction with the following exam-ples in which the details are given by way of illustration and not by way of limitation.

A ceramic composition was made of 75 parts by weight of petallite and 25 parts by weight of a glass-ceramic having the following approximate com-position, by oxide analysis, in weight percent: 70% S102, 18% A1203, 5% TiOg, 3% LiOz, 3% MgO and 1% ZnO. The composition was ball-milled to a -200 mesh (Tyler) particle size. A solution of the following composition was added to 2160 grams of the ceramic material in the ball mill:

640 cc. of isopropanol 860 cc. of ethyl-acetate 180 cc. of Versamid 115 480 cc. of Hysol 6111 Versamid 115 is ,the trade name of a thermoplastic polymer supplied by General Mills, Inc. It is prepared by condensation of polymerized unsaturated fatty acids, such as dilinoleic acid, with aliphatic amines, such as ethylene diamine. Hysol 6111 is the trade name of an epoxy resin solution, supplied by Houghton Laboratories, Incorporated, containing 57% by weight of epoxy resin having a viscosity of about 2.5-4.0 poise at 25 C., an epoxide equivalent (grams of resin containing 1 g. chemical equivalent of epoxy) of 5951-50, and a melting range of 73-S5 C.

The ceramic material and ythe binder were further ball milled for about three hours yto produce a uniform suspension. A porous natural cellulose paper, commonly known as 31/2 pound tea bag paper, cut to a width of 4 inches ywas then dipped into the suspension and dried by heating to 120 C. for 2 minutes. The dried, coated paper `was then heated to 180 C. and crimped to produce a pattern, taken in cross-section, substantially in .the shape of a triangle with a height of about 0.04 inch and an open base of about 0.075 inch wide. The crimped, unfired, vcoated paper is rolledup simultaneously with a sheet of -tea bag paper of the same width, which has been coated in the same manner but not crimped, upon a 2-inch diameter reel until an annular cylinder with an Ioutside diameter of about 20 inches was obtained. Preferably the uncrimped coated paper is not dried prior to the Iroll-up operation, but, as in the present example, this coated paper is dried by forcing air heated to about 120 C. through the channels of the annular cylinder as they are formed during the roll-up operation.

The u nred honeycomb body was then placed in a furnace chamber and heated in accordance with the following schedule:

Temperature range: Firing rate Room temp. to 700 C. 350 C./hr. Hold at 700 C. 1 hour. 700 C. to 1220 C Furnace rate. Hold at 1220 C. 30 minutes. Cool to room temp; Furnace rate. Relire to 1240 C. 300 C./hr. Hold at l240 C. 7 hours.

Thereafter the honeycomb is cooled to handling Itemperature.

Burner plate blanks were then sawed from the above honeycomb structure to a size of 7% inches long by 5% inches Wide and a thickness suicient to provide a proper gas ow path length after the cylindrical cavities were cut in one major face of the blanks. Next, the cylindrical cavities were cut and the resulting finished burner plates were attached to a burner body as shown in FIGURES 1 and 2.

Table I gives the dimensional characteristics, in inches, of four burner plates constructed from the abovedescribed blank-s with the cylindrical cavities arranged. as -Shown in FIGURE 3:

Ceramic infrared gas -burner plates prepared just as described were actually tested. The same amount of input gas and air were used on each `plate test. The gas input was 13.2 s.c.f.h. of natural gas with a heat content of 1000 B.t.u. per cubic foot, which produced 50,000 Btu. per square foot. This gas was mixed with an amount of -air to produce theoretically combustion of the gas. After a warm-up period of at least 30 minutes, the burner -plate temperatures were recorded for emission angles from 0 to 60. These temperature (i.e. equivalent black body temperatures) were determined by focusing a radiation detector with its axis disposed at various angles from the normal t-o the cornbustion surface. The output signal of the radiation detector was then fed into a conventional millivolt recorder, which was calibrated in terms of degrees Fahrenheit. The results are as shown in FIGURE 9 (see

curves

2, 3, 4 and 5, respectively).

Example Nos. 3, 4 and 5 are specific illustrations of the prese-nt invention and FIGURE 9 clearly illustrates the utility of these burner plates to produce temperatures of at least about 1500 F. for all emission angles from 0 to 60. Moreover, Iit can be seen that the lowest optimum temperatures for these plates are well in excess of 1600 F.

Curve 2 (Example 2) in FIGURE 9 illustrates the very adverse effect of having too small a ratio of cavity depth to cavity diameter.

Curve 1 of FIGURE 9 illustrates the normal temperature -pattern for a prior type burner plate having a at combustion surface as illustrated in FIGURE 7. This plate was made of the same blank material as those described above and had a blank thickness of 1/2 inch.

In FIGURE 10, correspondingly numbered curves illustrate the superior total radiation obtainable for the burner plate Examples Nos. 3, 4 and 5. In each case, the .total radiation (as calculated yfrom the Stephan- Boltzman law using the data of FIGURE 9) exceeds 25,000 B.t.u./hour/square foot for all emission angles from 0 to 60 and the lowest optimum total radiation is at least 32,000 B.t.u./hr./ft.2. Similar total radiation data are shown for Example No. 2 and the prior fiat combustion surface plate in

curves

2 and 1, respectively.

A comparison of

curves

1, 2 and 4 in FIGURES 9 and l0 clearly shows the greatly superior character and performance of a burner plate according to the present invention.

Another illustration of this invention is that of a burner plate whose performance data is shown in curves 6 of FIGURES 9 and 10. This burner plate was made from a blank as described above with the cylindrical cavities arranged as shown in FIGURE 4. The large cavities 36 had a diameter of 3A inch and a depth of 3A; inch. Both spacings C and D were 1 inch. The blank thickness was 5A; inch. The small cavities 37 had a diameter of 1/i inch and Va depth of 1A inch.

It has also been found that burner plates according to the prese-nt invention provide results (as stated above) which are much superior to other types and shapes of cavities or indentations such as inverted pyramids or cones. This is illustrated by curves 7 in FIGURES 9 and 10, which are the data obtained from a burner plate made from a blank, as described above, having a blank thickness of 3A inch, and having inverted cone cavities 'arranged as show-n in FIGURE 3. The diameter of the cone cavities at the combustion surface were inch.

The included angle formed by the wall of the cone on an axial plane was 60. The spacing A was 1/z inch 'and the spacing B was inch.

yCeramic radiant gas burner plates according to this invention are found to be much more free from dark or cold zones on the radiating surface. Moreover, signiticantly greater combustion of the gaseous fuel, ie. natural gas and air, is also obtained yas is evidenced by the considerable reduction of the CO content of the combusted gases being given ot from the burner plate.

In accordance with the provisions of the patent statutes, I have explained the principle of my invention and have illust-rated and descri-bed what I now believe to represent its best embodiment. However, it should be understood that, although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such details bev limitations upon the sc-ope of the invention, except insofar as set forth in the claims.

I claim:

1. A gas burner plate comprising a thin walled ceramic honeycomb having an inlet surface and an opposed combustion surfaceLa plurality of unobstructed gas passages uniformly distributed throughout the honeycomb and extending between and terminating in said surfaces, said passages being dened and separated from one another by thin walls of ceramic, each said passage having a crosssectional area not exceeding 0.006 square inch, the aggregate cross-sectional areas of the gas passages providing an open space of at least 20% of the area of said combustion surface, at least a portion of said combustion surface having a conigurationcomprising a plurality of cylindrical cavities defined by indented surface portions, the diameter of said surface portions being within the range of about 1/3 inch to l inch, the depth of said surface portions below the -unindented portions of said combustion surface being such that the ratio of said depth to the diameter of said surface portions falls within the range of 0.5 to 5, the spacing between adjacent cylindrical cavities taken along a straight line joining centers of said cavities and detined by the unindented portions of said combustion surface not exceeding about V2 inch, and the length of all said gas passages lbeing at least about 0.2 inch. l

2. A gas burner plate according to claim 1 in which the aggregate cross-sectional areas of the gas passages provide an open space of at least of the area of said combustion surface.

3. A gas burner plate according to claim 1 in which said cylindrical cavities are disposed in a rectilinear pattern.

4. A gas burner plate according to claim 3 in which additional cylindrical cavities are positioned at points generally equidistant from the centers of four adjacent cylindrical cavities forming part of the rectilinear pattern, and

said additional cylindrical cavities being substantially smaller than said adjacent cylindrical cavities.

5. A gas burner plate according to claim l in which said cylindrical cavities are disposed in alternate staggered rows.

6. A gas burner plate according to claim 1 in which the `diameter of said indentedV surface portions is Within the range of about inch to 1 inch and including a nub protruding upward centrally from said indented surface portions, said nub having a diameter not less than about 1/8 inch and no larger than a size providing at least about a 1A; inch annular space between said nubs and the walls of said cavities extending from said indented surface portions to the unindented portions of said combusion surface.

References Cited by the ExaminerV UNITED STATS PATENTS 1,901,086 3/1933 Cox.

3,155,142 11/1964 Stack 158-99 3,161,227 12/1964 Goss et al. 158-116 X 3,170,504 2/1965 Lanning 158-116 3,179,155 4/1965 Partiot 158-116 3,179,157 4/1965 Partiot 158-116 FREDERICK L. MATTESON, JR., Primary Examiner.

H. B. RAM'EY, Assistant Examiner.

Claims

1. A GAS BURNER PLATE COMPRISING A THIN WALLED CERAMIC HONEYCOMB HAVING AN INLET SURFACE AND AN OPPOSED COMBUSTION SURFACE, A PLURALITY OF UNOBSTRUCTED GAS PASSAGES UNIFORMLY DISTRIBUTED THROUGHOUT THE HONEYCOMB AND EXTENDING BETWEEN AND TERMINATING IN SAID SURFACES, SAID PASSAGES BEING DEFINED AND SEPARATED FROM ONE ANOTHER BY THIN WALLS OF CERAMIC, EACH SAID PASSAGE HAVING A CROSSSECTIONAL AREA NOT EXCEEDING 0.006 SQUARE INCH, THE AGGREGATE CROSS-SECTIONAL AREAS OF THE GAS PASSAGES PROVIDING AN OPEN SPACE OF AT LEAST 20% OF THE AREA OF SAID COMBUSTION SURFACE, AT LEAST A PORTION OF SAID COMBUSTION SURFACE HAVING A CONFIGURATION COMPRISING A PLURALITY OF CYLINDRICAL CAVITIES DEFINED BY INTENDED SURFACE PORTIONS, THE DIAMETER OF SAID SURFACE PORTIONS BEING WITHIN THE RANGE OF ABOUT 1/8 INCH TO 1 INCH, THE DEPTHOF SAID SURFACE PORTIONS BELOW THE UNINDENTED PORTIONS OF SAID COMBUSTION SURFACE BEING SUCH THAT THE RATIO OF SAID DEPTH TO THE DIAMETER OF SAID SURFACE PORTIONS FALLS WITHIN THE RANGE OF 0.5 TO 5, THE SPACING BETWEEN ADJACENT CYLINDRICAL CAVITIES TAKEN ALONG A STRAIGHT LINE JOINING CENTERS OF SAID CAVITIES AND DEFINED BY THE UNIDENTED PORTIONS OF SAID COMBUSTION SURFACE NOT EXCEEDING ABOUT 1/2 INCH, AND THE LENGTH OF ALL SAID GAS PASSAGES BEING AT LEAST ABOUT 0.2 INCH.