US2792440A - Thermoelectric generator - Google Patents

Description

May 14, 1957 c. BIGGLE THERMOELECTRIC GENERATOR Filed. Oct. 8. 1954 2 Sheets-Sheet l INVENTOR, [AugE/va- G 5/6'6L5 A TTaQ/VEK May 14, 1957 L. c. BIGGLE 2,792,440

THERMOELECTRIC GENERATOR 2 Sheets-Sheet 2 Filed Oct. 8. 1954 INVENTOR,

lAuef/vafi G 5/6615 THERMOELECTRIC GENERATOR Laurence C. Biggie, Altadena, Calif., assignor to General Controls (10., Glendale, Califi, a corporation of California Application October 8, 1954, Serial. No. 461,125

6 Claims. (Cl. 1364) This invention relates to thermoelectric generators and more particularly to those of the type which comprise a. thermocouple unit and a pilot gas-burner adapted to produce flame for heating the hot-junction or hot-junctions of the unit, as well as for igniting the main burner of a furnace.

An object of' this invention is to provide a thermoelectric generator havinghigh thermal efliciency and which employs but a single small flame for heating the thermocouple unit and for igniting the main burner.

Another object of the invention is to provide an ar rangement whereby a stable blue flame is produced at the pilot burner when the'same is supplied with unaerated fuel gas.

Another object is to provide an arrangement: whereby the flame of the pilot burner is protected from drafts.

Another object is to provide a thermoelectric generator which can be mounted very close to the main-burner flame and yet operate efliciently.

For full understanding of the invention, and further appreciation of its objects and advantages, reference is to be had to the following detailed description and accompanying drawing, and to the appended claims;

In the drawing:

Figure 1 is a front elevation of a thermoelectric generator embodying this invention;

Figure 2 is an end. elevation of the generator of Fig. 1 and shows, in addition, a fragment of a main gas burner in suitable relative position;

Figure 3. is a vertical sectional view, to enlarged scale, ofthe generator shown in Figs. 1 and 2;

Figure 4 is. a horizontal. section taken along. the irregular line 44 of Fig. 3;

Figure 5 is a vertical sectionalview. of a. modified form of thermocouple unit according to this invention;

Figure 6 is a bottom view of the unit shown in. Fig. 5;

Figure 7 is a diagram showing the arrangement of. the thermocouples in the unit of Figs. 5 and 6; and

I Figure 8' is a. sectional view of. a modified burner head, and a fragment of a thermocouple unit with which it cooperates.

Referring first more particularly to the thermoelectric generator shown in Figs. 1-4, the numeral 11 indicates a base or connection block having in its bottom and in one end threaded openings 12 and 13 which may be empioyed, selectively, for connecting the generator to a vertical or to a horizontal gas pipe by means of a fitting 14, the other opening then being closed by a plug 15. The openings 12 and 13 arein intercommunication by way of a small opening 16; The flow passage (not shown) through fitting 14 is greatly restricted and of smaller flow capacity than opening 16. A hole for a mounting bolt is indicated at 17.

The opening 12 has a reduced upward extension for a burner tube 18 whose lower end is sealingly secured to the block as by solder and is flared as indicated at 19 to strengthen the connection. At its top the tube 18 is 2,792,446 Patentecl May 14, 1957 pinched or flattened to form a burner tip 20 having a narrow elongated flame-orifice 21.

At the top of block 11 is a plate 22, three edges of which are bent downwardly to provide sides 23 which engage the top surface of the block at its margin so that there is aspace 24 between the block and plate 22. The plate has a central opening for the burner tube 18 and a pair of additional openings at opposite sides of the central opening (and at right-angles to the flattened burner tip 2 0) for receiving the ends of the side arms of an inverted U-shapecl tube 25, preferably of corrosion resistant metal such as stainless steel. Burner tube 18 and U-tube 25 are in a common general plane, the crook portions 26' of the U-tube being relatively closely above the burner tip 20; As can be seen in Fig. 3 the burner tube and U-tube are secured to plate 22 by welding 27, so that the flaring of end 19 of the burner tube serves to hold the plate and tubes in place on block 11.

Inside of U-tube' 25 is a thermocouple comprising a pair of' wires 28" and 29, of thermoelectrically dissimilar materials such as the alloys Chromel. and Copel, which are welded together at one end to form a hotjunction 30 located in the crook portion 26 of the U- tube. Around the wires 28, 29 is a braided sleeve 31 of electrical insulating material such as Fiberglas.

The thermocouple 28, 29, with sleeve 31 around it, is inserted in tube 25 while the same is straight, so that in bending the tube to U-shape its crook portion 26 becomes considerably flattened as can be seen in Figs. 1-3 of the drawing. By this procedure the portions of the thermocouple adjoining its hot-junction 30 are brought into good heat-transfer relation tothe crook 26. The bottom or cold-junction ends. of the thermocouple are welded to the wires 32,: 33 of an. armored cable 34 for connecting the output of the thermoelectric generator to a load.

The general shape of flame produced by gas issuing from the elongated burner-orifice 21, and impinging on the crook portion. 26. of the unit, is indicated in Figs. 1 and. 2 by the numerals 35 and 35'. In Fig. 2 a fragment of. a conventional main burner 36 has been added to indicate the blending relation of the mainfburner flame 37 and flame 35'.

It. will be observed thatthere is no provision. for mixing air with the gas flowing to the burner orifice so that the flame produced is more stable andnormally would be luminous or yellow. However, due to the spreading of theflame as it. straddles or' encircles the crook portion of the thermocouple unit, such a large surface area of the flame is presented to the atmosphere that. complete combustion of the gas is eflected and the flame is nonluminous or blue, and highly effective in heating the thermocouple.

I have found that if, in place of the slit type orifice 21, a single central orifice is provided, the. flame then produced wil normally stay on both sides of the plane of the termocouple unit. However, if that flame is diverted to one side of the unit, as by a momentary draft or. When it is lit, there is a tendency for the flame to remain only on that side, so that its effectiveness is impaired, Of more importance is thefact that the diverted flame may be only on the side awayfrom the main burner and therefore ineffective to perform its igniting function. There isno possibility of such an occurrence in connection with the arrangement of Figs. 1-4 of the present invention: be cause of the elongation of orifice 2'1. Furthermore,,since the burner is between. the arms of the thermocouple unit it is shield from drafts to a considerable degree.

The continuous stainless-steel U-tube affords good protection for the thermocouple against the high ambient temperature to which the unit is subjected close to the main burner. It is to be observed that in the present arrangement there is no welded connection exposed to exposure.

One reason for the efiiciency of operation of the thermoelectric generator of this invention is the fact that a very high proportion of the flame is utilized since it is applied to the thermocouple unit at the region immediately adjoining both sides of its hot-junction.

Because of the thinness of the wall of the U-tube 25 and the vertical arrangement of its side arms the loss of heat along the tube from its hot-junction region is minimized. The bottom or cold-junction ends of the thermocouple unit remain relatively cool in operation due to conduction of heat through plate 22, 23 to the block 11. The s ace 24 between the plate and the block is preferably filled with ceramic cement (not shown) to seal the interior parts from the atmosphere.

For its customary use in connection with pilot-flame safety controls the thermoelectric generator can be very small. In a practical embodiment substantially as shown in the drawing, the U-tube 25 and burner tube 18 are each 0.125 inch in diameter with a wall thickness of 0.008 inch. The consumption of gas is about A cubic foot per hour, the dimensions or orifice 21 being 0.010 x 0.171 inch and the diameter of the orifice in inlet fitting 14 about 0.010 inch.

The modified thermocouple unit shown in Figs. -7 is adapted to be mounted and heated in the same manner as the thermocouple unit of Figs. 1-4. Inasmuch as the U-tube may be of the same construction and size as that shown in Figs. 14 it has been assigned the reference numeral 25'. Inside of U-tube 25' is a plurality of thermocouple elements 4148 in the form of ribbons whose dimensions may conveniently be 0.014 x 0.062 inch when the U-tube has an internal diameter of 0.109 inch. The ribbons are of thermoelectrically dissimilar materials such as Chromel and Copel and they are interconnected in series to form a pair of thermopiles 41--44 and 4548, these thermopiles (after assembly in the U-tube and mounting of the same) being interconnected in series by a conducting strip 49. The ribbons or elements 41, 43, 45 and 47 are of one material, such as Chromel," and the ribbons 42, 44, 46 and 48 of a dissimilar material such as Copel. The ribbons are secured together at their ends by welding and are electrically insulated from each other by films of oxide formed on them by subjecting each of the pair of thermopiles, before assembly in the tube, to high temperature in an oxidizing atmos phere. The diagram of Fig. 7 illustrates the series arrangement of the elements and indicates the hot-junctions at 50, 51, 52 and 53, as Well as two of the intermediate cold-junctions at 54 and 55, the other intermediate coldjunction being formed, efiectively, by the connecting strip 49. The pair of thermopiles 41--44 and 45-48, with insulating sleeve 31' around it, is inserted in tube 25' before the same is bent to U-shape. The flame spreading-around or straddling the crook portion 26 of the unit effects substantially uniform heating of each of the hot-junctions 50-53.

In Fig. 8 there is shown a modified burner-tip 61, preferably of ceramic material and fitting in a burner tube 18" of the same size as the tube 18 of Figs. 1-4. The burner tip 61 has a pair of orifices 62, 63 arranged so that the gas issuing from them blends to form a single flame whose general shape, when straddling the crook portion 26" of a thermocouple unit of the same general construction as those shown in the other figures, is indicated at 64. I have found that in this arrangement the lower part of the flame spreads to the edge of the flat top of the burner tip, as shown, and there is no tendency for this flame to remain at one side of the hot-junction crook 26" if it is momentarily diverted to that side by a draft.

The specific embodiments of my invention herein shown and described are susceptible of modification without departing from the spirit of the invention, and I intend therefore to be limited only by the scope of the appended claims.

I claim as my invention:

1. A thermoelectric generator comprising an elongated U-shaped thermocouple unit having its hot-junction in the crook portion of the U, said crook portion being smoothly curved in cross section; and a gas-burner tube mounted centrally between the side arms of the unit and spaced therefrom, said burner tube extending in the general plane of the unit and having gas-discharge means adjacent said crook portion for producing a flame and directing it against the crook portion, said burner tube being otherwise imperforate so that primary air is absent from the gas issuing from said discharge means; said gas discharge means being so arranged that said flame encircles the smoothly curved crook portion and is of such size relative to the crook portion that it is limited to the general region thereof, said flame being spread to such extent by the crook portion that its area presented to the atmosphere is so large that the flame is nonluminous despite the absence of said primary air.

2. A thermoelectric generator according to claim 1 wherein said gas-discharge means consists of means defining a narrow flame-orifice elongated in a direction transverse to said general plane of said unit.

3. A thermoelectric generator according to claim 1 wherein said gas-discharge means has a flame orifice at both sides of said general plane of said unit.

4. A thermoelectric generator comprising anelongated U-shaped tubular member; a thermocouple within the hollow of said member and having its hot-junction in the crook portion of the member, said crook portion being smoothly curved in cross section; and a gas-burner tube mounted centrally between the side arms of the member and spaced therefrom, said burner tube extending in the general plane of the member and having gasdischarge means adjacent said crook portion for producing a flame and directing it against the crook portion, said burner tube being otherwise imperforate so that primary air is absent from the gas issuing from said discharge means; said gas-discharge means being so arranged that said flame encircles the smoothly curved crook portion and is of such size relative to the crook portion that it is limited to the general region thereof, said flame being spread to such extent by the crook portion that its area presented to the atmosphere is so large that the flame is nonluminous despite the absence of said primary air. r v

5. A thermoelectric generator according to claim 4 wherein said gas-discharge means consists of means defining a 'narrow flame-orifice elongated in a direction transverse to said general plane of said member.

6 A thermoelectric generator according to claim 4 wherein said gas-discharge means has a flame orifice at both sides of said general plane of said member.

References Cited in the file of this patent UNITED STATES PATENTS 1,752,117 Smith Mar. 25, 1930 2,052,181 Kroch Aug. 25, 1936 2,189,829 Wunsch et al. Feb. 13, 1940 2,268,959 Ray Jan. 5, 1942 2,339,809 Ray Jan. 25, 1944 2,372,506 Mantz Mar. 27, 1945 2,454,229 Sparrow Nov. 16, 1948

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