US2441672A - Thermopile for furnace control - Google Patents

Description

ay 18, 1948." -5 w; A. RAY'- f 2,441,672 Y v i THERMoPI-LE Eon FURNACE coNTRoL Filed July 21, 1942.

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Patented May 18, 1948 'UNITED STATESA PATENT .oFFlcl-z THERMOPILE FOR FURNACE CONTROL William A. Ray, Glendale, Calif., assigner to General Controls Co., a corporation appunti .my 21, 1942. sensi Nn. 451,191 4 cnam.. (ci. 13e- 4) This invention relates to a system for controlling a furnace. r

Such furnaces,'employing for example gaseous or liquid fuels or other sources of heat, are usually provided with safety systems or c'ontrol systems that operate automatically in response to an alteration in the operation of the source. When an oil burner is used, it is important to ensure that when it is desired to shut down the furnace, the blower motor is deenergized and that the igniting means remain inactive. Also there must be an assurance that the ignition means will be maintained active upon initiation of operation of the furnace, and will be rendered inactive upon igniting of the flame. It is also highly important that if the burner fails to function properly, preventing ignition, or if `the llame fails for any reason, the entire system be rendered inoperative after a short delay.

Such a system is described and claimed in Patent No. 2,113,858, granted on April 12, 1938, to William A. Ray, for Control unit. In this prior patent, the control system includes a thermopile,

intended to initiate controlling functions as required by the conditions of operation.

In systems of this character that utilize thermocouples or other heat responsive devices. it is highly desirable that such devices should be compensated for the ambient temperature in the For example, if the flame fails, the furnace chamber ambient temperature is still elevated. Until the slow process `of cooling is substantially. entirely completed, a heat' responsive device might continue to be affected by the ambient, with attendant failure of the control system.

It is one of the objects of this invention to make it possible to compensate for any change in the furnace ambient, in a simple and reliable manner.

It is another object of this invention to make it possible to place the hot and cold junctions into the furnace chamber, where they are substantially equally subjected to the furnace chamber ambient, and yet to ensure prompt response of the thermoelectric device in accordance with the flame condition.

These objects are attained by a construction of the thermoelectric device such that the flame selectively aects the hot junction or junctions to a much higher degree, than the cold junction or junctions. It is accordingly still another object of this invention to provide a thermoelectric structure capable oi being utilized in this manner.

It is still another object of this invention to utilize a concentrating means, similar to loptical reflectors or ref-ractors, for focusing heat from a flame selectively upon the hot junctions. while permitting the furnace ambient to affect all of the junctions substantially equally. In this way, as soon as the radiant source or ame is extinguished, the supplemental heating of the hot junction or junctions is discontinued; the thermoelectric device generates no operative electric power, although the temperature in the furnace chamber'may remain elevated for a long period thereafter.

This invention. possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of one embodiment of the invention. For this purpose there is shown a form in the drawings accom- `panying and forming part of the present specification. form will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this d etailed description is not to be taken in a limiting sense, since the scope of this invention is best defined by the appended claims.

Referring to the drawings:

4Figure 1 isa diagram of the control system, shown installed in connection with a furnace;

Fig. 2 is an enlarged fragmentary sectional view of a thermoelectric generator and its housing, utilized in connection with the control system;

Fig. 3 is a sectional view, taken along plane 3-3 of Fig. 2; and y Fig. 4 is an enlarged fragmentary sectional view illustrating the thermopile structure.

The furnace chamber I is formed by the aid o f appropriate refractorywalls 2, 3 and 4. Within the furnace chamber l is a source of radiant heat, such as a flame 5, shown as' projecting from the nozzle 6 of an-oil burner 1. The oil burner incorporates appropriate mechanism for subdividing the fuel into iine particles before the fuel emerges from nozzle 6. Other equivalent means for producing radiant heat may be utilized in the fu'mace chamber `i.4

If the source ofiradiant heat be an oilburner' name 5 such as illustrated, it is customary to pravide a blower motor 8 as well as an electric spark igniter I0. This spa/rk igniter i0 is shown as located at the placewhere the flame 5 emerges from the nozzle 6.

Automatic -controls for the igniter i0 as weil as for the motor 8 are provided by automatic control devices illustrated in general by the refcontrol devices II.

erence character II. 'I'hese automatic control vdevices obtain power from appropriate electric mains I2.

The initiation of operation of the oil burner structure including the blower motor 8 and the nozzle 6, may occur in response to an automatic control device such as a thermostat, included in group II. When this occurs, the circuit for the igniter I is also energized. If the flame 5 should fail to ignite after the fuel is supplied through nozzle 6, the automatic control devices II operate to correct this condition or to render the supply of fuel ineffective. Furthermore, if after the flame has been ignited, and later fails for any reason, similar corrective or safety automatic controls are provided by the aid of devices II.

The essential feature of such automatic controlling functions is a Vheat responsive device which is connected to the automatic control devices II, and which responds only to heat radiated from the flame 5, and does not respond to Y the furnace ambient temperature or to 'changes in the ambient temperature.

In the present instance such a heatresponsive device is shown as a thermopile structure I3. As is well understood, such a thermopile structure forms a therrnoelectric generator, including a plurality of hot junctions and cold junctions formed by thermoelectrically dissimilar conductors. The hot and cold junctions are arranged in alternating series relation. Furthermore, by the present arrangement as will hereinafter appear, temperature of the hot junctions is elevated over that of the cold junctions by an amount dependent upon the radiation of heat from flame 5. Accordingly, the energy generated by the thermopile structure I3 is that due solely to the surplus heat radiated by flame 5 upon the hot junctions. The furnace chamber ambient temperature is compensated, since the hot and` .cold junctions are equally affected thereby The thermopile structure I3 (Figs. 2 and 4) is housed in a tubular-like housing I4. This housing I4, which may be-made of appropriate heat resistant material, is shown as forming a passageway I5 having an inner opening directed toward the flame 5 and extendinginwardly beyond the .wall 4. The rear portion of the passage |5 is defined by a curved wall I6. Through the end wall I5 extend the conductors or leads I1 and I8 forming the terminals of the thermopile structure I3 and connected to the automatic In this way the electrical energy generated by the device I3 is caused to affect these control devices.

The thermopile structure I3 in this instance is shown as comprising five hot junctions I9, arranged symmetrically around the axis 20 of the passageway I5, shown as substantially cylindrical. These junctions I9 are formed between pairs Yof conductors 2| and 22 having'dissimilar thermoelectric properties. They are twisted around each other to form the junctions I9. They are supported in apertures in a refractory collar This collar 23 is shown a-s supported upon a post 24 supported on the end wall I6. Thus for example the post 24 may have a threaded exten- .sion 25 of reduced diameter which passes through `an aperture in the end wall I6 and which is engaged by the nut 26. Similarly, the inner end of the post 24 is provided with reduced threaded extension 2l over which the refractory collar 23 is placed. A nut 28 is threaded over the ex-` tension 21 to hold the collar 23 in place.

The ends of the conductors 2|, 22, on the opposite side of the collar 23 are similarly joined to form a series of cold junctions 29. The terminal conductors or leads I1 and I8 connect to the end conductors of the series.

The space I5 in which the thermopile structure I3 is located, being in communication with the furnace chamber I, is subjected to the ambient temperature of the furnace. The value of this ambient temperature, when the furnace has been shut down is a function of the heat content of the walls of the furnace and of the rate of heat transfer; and when flame 5 is propagated, the ambient temperature is very much greater, due to the transfer of heat from the flame to chamber I as well as to the walls 2, 3, 4. Under Y cold junctions I9 and 29.

' vof the llame 6, to a focus at 33 (Fig. 2).

either circumstance, the ambient furnace heat substantially uniformly affects both the hot and The inner surface 30 of the end wall I6 is formed-as a specularly Areflecting surface, It serves torconverge a heat ray 3| from a spot 32 This focal point 33 corresponds to one focus of the reflecting surface 30. The concentrated heat ray 3| at the locality 32 materially affects only the hot junctions I9. 'For this purpose the junctions I9 are turned inwardly so as to approach the axis 20 of the reflecting surface 30. This reflecting surface 30 may be formed as a surface of revolution defined by a substantially elliptical curve. The focus 33 -corresponds to one focus of the ellipse. The other focus of the ellipse is located at a point on axis 20 where the inwardly extended elements of ray 3| cross this axis;

By the aid of the reflector wall I6, the hot junctions I9 are thus selectively affected by the heat ray 3|, to the substantial exclusion of the cold junctions 29. Accordingly the thermopile structure I3 responds at all times to the difference in temperature between the ambient of the furnace chamber I, and the high temperature attained at focal point 33. The furnace ambient is therefore compensated for, since both the hot junctions I9 and cold junctions 29, being relatively close to each other, are substantially equally subjected to the heating effect caused by conduction and convection in tube I4, and are thus raised to substantially the same temperature. However, the hot junctions I9 are additionally subjected to the radiant heat of ray 3|, focused by the surface 30 upon the hot junctions, and are thereby raised to a higher temperature than junctions I9.

What is claimed is:

l. In a thermoelectric device for a furnace chamber having a source of radiant heat therein, means'forming a passage opening into said chamber and directed toward said source, a reflector closing the endof the passage remote Y from said source and having a concave surface .as by the furnace ambient temperature, said cold junctions being spaced llengthwise of said passage from lsaid focal region so as to be less affected by the heat in said region, while being subjected to the furnace ambient temperature.

'from said source and having a concave surface exposed to the direct rays from said source and thereby receiving heat therefrom, and reflecting said heat in a focal region in said passage, a thermoelectric generator supported in said passage comprising a plurality of thermocoupies spaced about the axis of said passage and extending parallel therewith, said thermocouples having hot and cold junctions and having portions inclined toward said axis to position the hot junctions in said focal region to be affected by the heat concentrated therein as well as by the furnace ambient temperature, the cold junctions being spaced from said region in a direction away from said source so as to be less affected by the heat of said region, while being subjected to the furnace ambient temperature.

3. In a thermoelectric device for a furnace chamber having a source of radiant heat therein, means forming a passage opening into said chamber and directed toward said source, a reilector closing the end of the passage remote from said source and having an area as large as the cross-sectional area of said passage and having a concave surface for receiving heat from 30 l Number said source and reflecting and concentrating said heat in a focal region of limited extent in relation to the size of the reector in said passage, a thermoelectric generator in said passage comprising a, plurality of pairs of elements of different thermoelectric properties spaced about the axis of said passage and extending lengthwise thereof, the elements of each pair having portions directed toward said axis and joined to form hot junctions located in said focal region 40 to be affected by the heat concentrated therein as well as by the furnace ambient temperature, said elements extending from said focal region in a direction away from said source, and being joined to connect said pairs in series, said connections forming the cold junctions and being positioned to be less affected by the heat in said focal region while subjected to the furnace ambient temperature.

4. In a thermoelectric device for a furnace chambei` having a source of radiant heat therein: means forming a passageway in communication with said chamber and directed toward said source; a thermoelectric generator having a plurality of hot and cold junctions; a. concave reflectorv dening the end of said passageway, said reector having an area substantially as large as that of the cross-section of the passageway; and a support mounted on said reector for the generator to position the hot junctions at the fo'cal region of the reflector.

W'JILEILIIAMv A. RAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,038,258 Zander Sept. 10, 1912 1,734,837 Thwing Nov. 5, 1929 1,891,039 Barton Dec. 13, 1932 2,113,858 Ray Apr. 12, 1938 2,149,853 McCabe ,Mar. '7, 1939 2,162,098 McCabe June 13, 1939 FOREIGN PATENTS Number Country Date 430,974 France Aug. 29, 1911

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