US3457390A - High temperature resistance heater - Google Patents

Description

July 22, 1969 Filed April s.' 1967 FIGI FIG?) INVENTOR. FREDERICK... l

A TTORNE Y United States Patent O 3,457,390 HIGH TEMPERATURE RESISTANCE HEATER Frederick A. Beake, Hollis, N.H., assignor to Sanders Nuclear Corporation, Nashua, N.H., a corporation of Delaware Filed Apr. 5, 1967, Ser. No. 628,635 Int. Cl. Hb 3/44 US. Cl. 219-544 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The need for high temperature producing resistance heaters has become increased in recent years particularly in the thermoelectric generator field. Thermoelectric generators are often powered by isotopic thermal power sources which produce temperatures in excess of 2000 F. Frequently it is desirable to test such generators using heater sources other than isotopic sources which are difiicult to handle and require extreme safety precautions to prevent radiation damage to personnel and equipment. Thus, there has been a need for electrical heaters which will produce temperatures in excess of 2000 F. over long time periods and which are relatively inexpensive to construct, are compact and capable of producing uniform heat zones and are substantially insensitive to mechanical shock.

Known resistance heaters used for testing thermoelectric generators are frequently subject to short life and/ or inability to produce the high temperatures necessary for adequate testing. For example, during vibration test cycles of thermoelectric generators, known heaters often become open circuited or shorted at high temperatures. In many cases, commercially available heaters are limited to temperatures of approximately 1300 F.

SUMMARY OF THE INVENTION According to the invention a high temperature resistance heater has an annular core of a high temperature resistant insulating material. At least one winding is wound axially on the core and comprises a heavy gauge conductive wire with turns thereof spaced a predetermined distance apart to produce a uniform heat zone. End leads of the wire are used for attachment to electrical power sources. Preferably two windings are provided on an endless wall of the core with all turns of the winding spaced from each other to assure prevention of shorting. Thus, one winding can be used as a resistance heater while a second winding can provide a backup heater source I should the first heater become open circuited during testing.

DESCRIPTION OF THE DRAWINGS Patented July 22, 1969 FIG. 3 is a cross sectional view thereof taken through line 33 of FIG. 2.

PREFERRED EMBODIMENTS With reference now to the figures, a preferred embodiment 10 of a high temperature resistance heater of this invention is shown comprising a container 11, a heater core 12, windings 13 and 14, powdered dielectric 15 and a backing core 19.

The heater core 12 is preferably a cylinder of high temperature resistant dielectric material such as zirconia or stabilized quartz or other dielectric material which provides for uniform heat zones and is substantially insensitive to mechanical shock. The core 12 is preferably circular or annular in cross section although any endless wall construction such as finned core can be used to minimize space requirements. Thus, frustoconical, oval and irregular endless wall constructions are possible.

As best seen in FIGS. 2 and 3, a first winding 13 is wound axially about the core 12 passing from the outside surface thereof to the inside and back again with ends of the wall being notched as indicated at 16 to mechanically locate each end of the coil winding and prevent the turns thereof from shifting in position during mechanical vibration. In the preferred embodiment, a second winding 14 is provided with the turns thereof spaced from the turns of the first winding 13 as best shown in FIGS. 2 and 3 to assure electrical insulation between the two windings. Ends of winding 13 pass upwardly as indicated at 17 and 18 for connection to an electrical power source while ends 20 and 21 pass upwardly out of the casing for attachment to the same or a second power source.

The wire used for the windings is preferably a heavy gauge wire in the range of from 5 to 20 gauge. Standard heater resistance wire material such as Kanthal A, Nichrome, platinum and the like are used to permit high temperature generation for long periods of time without failure due to shorting or breakage of the wires.

The core 12 preferably comprises a cylinder having an outside diameter of from Ms inch to 10 inches, a thickness of from .030 inch to 0.5 inch and a length of from /2 inch to 3 feet. The core need not be cylindrical. Corrugated star, finned solid cylinders, oval or other cross-section cores can be used. In some cases the core can be arcuate, flat fluted or substantially planar if sufiicient support is providedto the winding by the surrounding insulation to prevent mechanical damage caused by vibration. Of course the specific dimensions of the core may vary outside the ranges given depending upon the particular intended application of the heater.

In the preferred embodiment, the heater core with its dual windings are positioned within a high temperature casing such as TD-l nickel, Inconel 600, LT-l, stainless steel and the like, 11 having a disc top 23 attached thereto through which the leads 17, 18, 20 and 21 pass insulated from the casing by suitable ceramic plugs such as indicated at 24 and 25. The leads 17, 18, 20 and 21 can pass through side walls of the casing as well as the bottom depending upon the mounting arrangement for the heater. Separating the heater core from the casing and supporting it within the casing is a high temperature resistant insulation or dielectric material 15 preferably comprsing an inorganic powdered dielectric such as zirconia, aluminum, magnesium or other earth oxides preferably resistant to temperatures above 2000 F. The dielectric 15 can be a cement like material such as Alundum cement (alumina with a binder which burns off at high temperature) or zirconia with a binder as is known in the art. The dielectric material 15 surrounds the core 12 and encloses the winding both within and about the core to aid in preventing vibration damage to the winding. Similarly the material of the casing 11 is stainless steel or other materal preferably not subject to breakdown and oxidation at temperatures in excess of 2000 F. in vacuum or inert atmospheres normally surrounding resistance heaters used to test thermoelectric generators and the like.

In the preferred embodiment, a backing core 19 preferably of the same material as the coil core 12 is employed to add to the mechanical stability of the heater In a specific embodiment of the axially wound high temperature resistant heater of the present invention formed as shown at 10, the coil core 12 is made of zirconia or stabilized quartz having a length of 3 inches and an outside diameter of 2 inches and a thickness of W inch. Kanthal A 14 gauge wire forms the windings 13 and 14 with each winding having 40 turns of wire about the annular core. An alumina powder is used as a filler for the stainless steel casing which has a diameter of 3 inches and the alumina completely fills the structure as shown in FIG. 3. When each of the windings is connected to a power source to produce a uniform temperature about the heater of at least 1200 F., the heater can be run for periods of at least 4000 hours under various conditions of vibration conforming to testing requirements for conventional thermoelectric generators.

While a specific embodiment of the invention has been shown and described, it should be understood that many variations thereof are possible. For example, one or more than two windings can be used insulated from each other on the annular core. In some cases, each of the winding will be connected to a power source providing different currents. In some cases, the gauge of one winding is different than the gauge of a second winding to allow flexibilty in use of the heater. Similarly, one winding can be used during testing with a second winding connected to a second power source through a circuit designed as a backup and actuated only upon failure of the first winding. In all cases, due to the heavy gauge wire and significant mass increase of high temperature resistant winding core, high temperatures can be obtained through the resistance wires and the heaters will operate for long periods of time under extreme conditions of mechanical shock.

It will be readily understood by those skilled in the art that many variations of this invention are possible. Therefore this invention is to be limited only by the spirit and scope of the following claims.

What is claimed is:

1. A high temperature resistance heater comprising,

a tubular core of a high temperature resistant insulating material,

said core defining an axis and a wall having a first end and a second end with said ends defining notches,

a heavy gauge conductive resistance wire wound axially about said core from one end to the other alternating either side of said wall defining turns thereof spaced at predetermined distance apart, said wire being positioned within said notches,

end leads provided by said wire for attachment to a power source,

a high temperature resistant metal casing enclosing said core, and

an inorganic heat conducting and electrical insulating material separating said core from said casing.

2. A high temperature resistance heater in accordance with claim 1 wherein said wall is endless and further comprising a second heavy gauge conductive wire wound axially about said core defining turns thereof spaced a predetermined distance apart and electrically insulated from I said first heavy gauge conductive wire.

3. A high temperature resistance heater in accordance with claim 1 wherein all elements thereof are stable at temperatures at least as high as 2000 F.

4. A high temperature resistance heater in accordance with claim 1 wherein said wire has a gauge size in the range of from 5 to 20 gauge.

5. A high temperature resistance heater in accordance with claim 1 wherein said core is in the form of a cylinder.

References Cited UNITED STATES PATENTS 1,713,845 5/1929 Lockwood 219-544 X 1,810,185 6/1931 Powell 219-546 X 2,223,617 12/1940 Johnston 13-22 2,372,212 3/1945 Lewin 338-237 2,476,613 7/ 1949' McKinley 219-544 2,913,695 11/1959 Borghult et al 338-317 2,864,929 12/1958 Schwing 219-523 3,237,144 2/1966 Ioeckel 338-316 3,313,921 4/1967 Mohn et al 219-553 VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

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