US2519785A - Thermopile - Google Patents

Description

Aug. 22, 1950 F. OKOLICSANYI THERMOPILE Filed Aug. 1, 1945 lawn/mm a 'UUU INVE NTOK: Fef-enc Qkoli c 541 l Patented Aug. 22, 1950 UNITED STATES PATENT OFFICE Ferene okolicsanjif l l a rpgt effhndon, England Application August 1, 1945, Serial No. 608,208 In Great Britain August 14, 1944 Claims. (Cl. 136-4) This invention relates to thermopiles and has for its main object the provision of an improved thermopile which can be utilized to produce a current capableof doing useful work, in contradistinction to its normal function of acting as a pure temperature-measuring device.

A further object of this invention is to provide a method of constructing a thermopile which enables the provision of a very large number of thermo-couples to be achieved. Known methods of thermopile construction involving individually soldered joints are quite unsuitable for thi purpose, since they do not enable mass-production of the articles to be effected; furthermore, the

existence of thousands of soldered joints is a source of weakness, for a single bad joint will increase the electrical resistance of the whole device to a prohibitive extent.

According to this invention there is provided a thermopile comprising a fiat block formed of layers of electrically insulating material whose surfaces are at right angles to the upper and lower faces of the block, and which carry on these surfaces a series of thermo-couples consisting of films of materials of difierent thermo-electric powers arranged alternately so that consecutive junctions lie alternately near the upper and lower edges of the layers.

The method of depositing the films will depend upon the materials employed for the thermo-- couples and to some extent upon the form in which they are commercially available. One of the well-known spraying processes is usually the most suitable, since these exist for dealing with metals either in wire or powder form. Alternative processes are painting, cathode sputtering, or pressing thin foils of metal into intimate contact with the insulating material. The spraying process has the advantage that by theuse of suitable masks, the films can be deposited in the required pattern quickly and accurately.

The choice of the pairs of materials forthe thermo-couples will be governed by alarge number of factors,'and will depend not only on their thermo-electric powers, but also on the working I temperature it is'desired to employ, on their electrical conductivity which must not be too low and on the case with which they can be handled in practice to produce the necessary thin films or foils. The following pairs of materials are quoted as examples, and it is obvious that many others exist.

1. Constantan and iron. These materials have the advantage of being able to withstand temperatures up to at least 1000 C. but show a rather low thermo-electric eflfect, namely 50 microvolts/ C. l

2. Bismuth and a bismuth-tin alloy containing 6 per cent of tin. These show a higher thermo-electric effect of'100 micro-volts/ C. but can withstand temperatures up to 200 C. only.

3. A bismuth-tellurium alloy with the constituents in substantially equal proportions, and the intermetallic compound of bismuth and tellurium, BizTes. These show a high thermo-electric effect of 250 micro-volts/ C. and can withstand temperatures up to 550 C.

Preferred forms of thermopile according to the invention will now be described by way of example with reference to the accompanying drawn s in which: l

Figure 1 shows an insulating tape carrying a series of thermo-couples;

Figures Za-c show the masks employed in depositing the metal films on the tape;

Figures 3ac show the method of forming a thermopile from the tape;

Figure 4 shows the use of a sheet of insulating material carrying a series of thermo-couples, and

Figures Sw-b showa tape with an alternative arrangement of metal films for the thermocouples.

Referring to Figure 1, a long tape lof glassfibre fabric carries on one surface a series of thermo-couples each consisting of a pair of sprayed films 2, 3 of two different metals, the films being arranged in zig-zag formation as shown, the junction points of each pair'of films lying near one or other of the edges of the tape. To ensure good electrical contact each junction point is covered by a film 4 of copper or other good conductor. The films also serve, by virtue of their heat capacity, to preserve a more uniform temperature at the junctions. Output connections leading to terminals 5 are secured to each end of the series, so that the whole will con- 3 stitute a thermopile. The various-films are deposited on the tape by sprayin with the aid of the apertured masks shown in Figures 20-0. The masks are made of thin copper foil and are used in succession, the final spraying producing the copper films l with the aid of the mask shown in Figure 2c. The tape and the particular mask in.

use can be stretched on a frame, and holes 6 in the mask and tape can be used to obtain proper registration, or they may be wound or! one drum past the spray on to theother if the tape is very long.

It is very desirable that the electrical resistance of the elements 2, 3 should be as nearly equal as possible and this can be achieved by a proper choice of the length, width and thickness of the two films.

The tape is then wound into a fiat spiral on a former I as shown in Figures 3a and 3b. A second tape 8 of the same material is interwound with the first to provide the necessary electrical insulation. When air cooling is employed it is desirable to provide means to assist this, and for this a purpose a tapering strip of copper foil 9 (Figure 3c) is interwound with the two strips, as 7 shown.

Instead of using the second tape 8, the insulation of the thermo-couples can be achieved by coating the surface and edges of the tape with a very thin layer of a suitable heat-resisting enamel.

In Figure 4 a sheet ID of glass-fibre fabric instead of a tape is employed, and after spraying through "suitable masks the series of thermocouples 2, 3, the copper films covering the junctions, and the copper films ll connecting the ends of each row in series, the whole sheet is coated with a thin film of protective enamel and then folded along the dotted lines I! to form a rectangular block.

An alternative arrangement of the films on the tape is shown in Figures a and 5b. Two broad bands l3, M of copper are sprayed. along the edges of the tape and across the unoccupied central portion are alternate strips 2, 3 of the two materials, as shown in Figure 5a. Portions 15 of the copper bands are then removed as shown in Figure 5b. As a result there is formed a zig-zag chain of the materials. There is littl or no temperature gradient in the areas of copper, which serve as heating and cooling fins. Both surfaces of the tape can be so treated and its subsequent treatment is the same as already described. Slits can be made in the portions of the tape at the points l5, or these portions of the tape entirely sulated from, the hot junctions. The copper plate is heated by any suitable means and serves to ensure a uniform distribution of heat.

For small electrical outputs, air cooling assisted by suitable cooling fins as already described, is adequate.

By heating the plate IS with a conventional heater winding fed with A. C. or D. C. current, the device can be used for obtaining a smooth direct current from one of undesirable characteristics, for example, for supplying power to small radio receivers.

I claim:

1. A thermopile comprising a long electrically insulating tape wound into a spiral and carrying a series of thermo-couples consisting of films of materials of different thermo-electric powers'arranged alternately so that consecutive junctions lie alternately near the lower and upper edges of the tape including means for air cooling said thermopile comprising a metallic ribbon interwound with said spiral and insulated from the thermocouples therein, said ribbon having areas extending longitudinaly beyond said spiral for exposure to the surrounding atmosphere.

2. A thermopile comprising a long electrically insulating tape wound into a spiral and carrying a series of thermo-couples consisting of alternating strips of sprayed metals of different thermoelectric powers, the strips extending across the width of the tape in zig-zag formation including means for air cooling said thermopile comprising a metallic ribbon interwound with said spiral and insulated from the thermocouples therein, said rib n having areas extending longitudinally be ond said spiral for exposure to the surrounding atmosphere.

3. A thermopile according to claim 1 wherein the electrically insulating material comprises a fabric woven from vitreous fibres.

4. A thermopile according to claim 1 wherein each junction is covered by a film of a good electrically conducting metal.

5. A thermopile according to claim 1 wbe ein a second tape of electrically insulating mate'- rial-is interwound therewith.

FERENC OKOLICSANYI.

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

removed together with the copper, so that when the tape is in the final form of a spiral, the portions carrying the copper fins can be bent outwardly to increase the separation between the same.

When utilizing the thermopile care must be taken to ensure rapid and uniform transfer of heat to the hot junctions, and from the cold junctions. For heating, the thermopile can be mounted on a copper plate l6 (Figure 3a) which will be in close proximity to, yet electrically in- UNITED STATES PATENTS Number I Name Date 1,269,778 Becker June 18, 1918 1,618,743 Adams Feb. 22, 1927 1,638,943 Little Aug. 16, 1927 1,667,142 Darrah Apr. 24, 1928 2,381,819 Graves et al. Aug. 7, 1945 2,385,481 Wills Sept. 25, 1945 FOREIGN PATENTS Number Country Date 10,036/13 Great Britain Mar. 26, 1914 France Apr. 25, 1933

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