US3206624A

US3206624A - Hypersonic plasma thermocouple

Info

Publication number: US3206624A
Application number: US135381A
Authority: US
Inventors: Theodore P Cotter
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-08-31
Filing date: 1961-08-31
Publication date: 1965-09-14
Anticipated expiration: 1982-09-14

Description

p 1965 T. P. COTTER 3,206,624

HYPERSONIC PLASMA THERMOCOUPLE Filed Aug. 31, 1961 I[/III/I//IIIIIIIII/II/IIII[IIIIIII///I///I/III/ IIIII/II/IIII7////0 ,A III[li/IIIIII,,III/llIIIIIIIIIIII/I,IIIIIIIIIIIIIIIIIIIIIIIIIlil/,III IIIII W/T/VESSESJ INVENTOR. Bz'hedore P. Coffer United States Patent O 3,206,624 HYPERSONIC PLASMA THERMOCOUPLE Tleodore P. Cotter, Los Alamos, N. Mex., assignor to the United States of America as represented by the United States 'Atomic Energy Commission Filed Aug. 31, 1961, Ser. No. 135,381 4 Claims. (CI. 310-4) The present invention relates to a very simple direct current electrical power supply applicable to a vehicle moving in an ionized medium. The hypersonic plasma thermocouple of the present invention is an application of the basic phcnomenon of the development of a substantial thermal in a gaseous plasma which is supporting a temperature gradient. The principle is applicable to :any vehicle which is moving in any gaseous medium with a sufficiently high velocity as to create and maintain a region of ionized plasma of non-uniform temperature in its vicinity.

An object of the present invention is to provide a simple, low voltage, high direct current, electrical power supply for use by a reentry or other hypersonic vehicle.

It is a further object of the present invention to provide methods and means for converting the heat energy developed by a reentry vehicle into electrical energy to operate an electrical load carried by the vehicle.

A further object of the present invention is to provide methods and means of utilizing a portion of the normally dissipated heat energy developed by a vehicle which is moving in any gaseous medium with a sufliciently high velocity to create and maintain :a region of ionized plasma of non-uniform temperature in its vicinity.

The mechanism of heat transfer and hypersonic flow over a body is well known, see for example, chapters 12 and 13 of Space Technology, edited by H. Seifert and published by John Wiley & Sons, Inc.

Every conducting medium may be characterized by its relative thermoelectric power, a quantity expressed in units of potential difference per degree temperature difference. In metals, the thernoelectric powers are of the order of one microvolt per degree centigrade. These low values are commonly attrbuted to the fact that the electron gas in a metal is degenerate, i.e., the electron energy distribution is almost independent of temperature. In non-degenerate media, such :as the electron clouds in a vacuum, in a plasma, in a semiconductor or an electrolyte, the characteristic value of the thermoelectric power is about 1000 times as great, or more nearly a millivolt per degree centigrade.

The present invention and the results produced thereby can be more clearly understood by reference to the :attached drawings, hereby incorporated by reference, in

which- FIGURE l is a vertical cross section of a model simulating the possible appearance of the forward end of a vehicle incorporating the hypersonic plasma thermocouple of the present invention,

FIGURE 2 is a vertical cross section of a second additional embodiment of the invention,

FIGURE 3 is a vertical cross section of a third additional embodiment of the invention,

FIGURE 4 is a vertical cross section of a fourth additional embodiment of the invention, and

FIG. 5 is a vertical cross section of a fifth additional embodiment of the invention.

Near or at the forward end of the vehicle a refractory electrically conducting thermionic emitter is placed so as to be in contact with the ionized medium surrounding the vehicle. Further back along the vehicle, and separated from the emitter by an electrical insulator, is placed an electrically conducting collecting electrode, which is also 3,206,624 Patented Sept. 14, 1965 'ice in contact with the surrounding ionized medium. The existence of a temperature difference between the emitter and collector regions will give rise to an electromotive force of some few volts, from which source it is possible to draw very large Currents. An electrical load may now `be connected internal to the vehicle between the emitter and collector, and may be operated by this power supply.

Since the thermoelectric power of plasma in general is of the order of one millivolt per degree centigrade, and since it should be possible to obtain temperature differences of at least a thousand degrees centigrade between the emitter and collector regions, it is reasonable to expect the device to develop one or more volts of potential difference. Of course, there will be additional dependence of the voltage on the Work functions of' the particular emitter and collector materials chosenl The amount of current which may be drawn from the device will depend primarily upon the electron emission characteristics of the emitter, the geornetry of emitter and collector, and the electrical resistance of the plasma. With suflicient collector area and favorable location, and with adequate ion density in the plasma, one might expect to draw many amperes per square centimeter of emitting surface, for a wide variety of possible emitter materials. The electrons will fiow from the emitter to the collector through the external plasma, so that regarded as a power supply, the emitter would be the positive terminal of the device.

A series of five models was prepared, in order to simulate the possible appearance of the forward end of a vehicle incorporating a hypersonic plasma thermocouple power supply. A Giannini Plasmatron with a A3" diameter throat, Operating at 35 kilowatts input power, operating on either argon or an argon-air mixture, was used as a source of hot plasma.

The very simple structure of a device for use in carrying out the present invention is shown in five modifications in FIGURES 1 5. The main elements of such a device are the emitter electrode 1 placed at the forward end of the device, the collector electrode 2 placed further back along the device, and the electrical insulation sleeve 3 in FIGURES 1 and 2, and sprayed layer 5 in FIGURES 3, 4,'and` 5. The leading edges of 'the vehicle are illustrated in FIGURE 5 at 7. This representation of the leading edges is, of course, for the purposes of illustration, the only criterion as to the location being that it is desirable to place the emitter electrode 1 near the forward end of the device. The emitter and collector electrodes may be of the same material. The only criterion is that they be electrically conductive. FIGURES 3, 4, and 5 have additional element 6 which acts merely as a spacer and may be of the same material as the emitter and collector electrodes. In the tests reported below both electrodes were composed of Graphitite-G, a graphite manufactured by Graphite Specialties, Inc. The electrical insulation may be of any type, the material used in said tests was porcelain in FIGURES 1 and 2 and sprayed layers, .01 to .02 inch thick, of aluminum oxide in FIG-

URES

3, 4, and 5.

The electrodes may be connected to an electrical load in any known manner. In FIGURES 1 and 2 the electrical lead 4 was tungsten, and in FIGURES 3, 4, and 5 it was tantalum.

The models were placed in turn in the jet of the plasmatron with their axes parallel to the axis of the plasmatron jet. The electrical output was measured between the rear end of the collector afterbody and the rear cmergent end of the electrical connection 4 which connects with the emitter tip. In the experiments with FIGURES 1 and 2 these terminals were simply connected alternately with a voltmeter and an ammeter through a variable resistive load. For the experiments 3 with FIGURES 3, 4, and 5, a two channel recording system was provided so that voltage and current could be obtained simultaneously and continuously.

Experimental results are given in the following table. In all cases, after an initial transent period of about a second, the emitter tip became and remained the positive terminal of the device, as expected.

From the table it is seen that the largest open circuit voltage, 3 volts, was exhibited by FIGURES 1, 4, and 5. The largest short circuit current, 6.8 amperes, was produced by FIGURE 4. The largest power, 4 watts, was produced by FIGURE 1.

In the following table the model numbers 1 through 5 correspond respectively with the embodiments shown in FIGURES 1 through 5 of the drawing.

Performance of hypersonic plasma thermocouple models This invention is an extension of the basic phenomena of the development of a substantial thermal in a gaseous plasma which is supporting a temperature gradient as set forth and described in co-pending U.S. application Serial No. 821,339, the subject matter of which is incorporated herein by reference.

It is, therefore, apparent that the present invention provides a novel plasma thermocouple utilizing a portion of the heat accompanying a vehicle moving at hypersonic speeds in a gaseous atmosphere which has hitherto been dissipated. While presently preferred embodiments have been described, it is clear that many other modifications may be made without departing from the scope of the invention.

What is claimed is:

1. A hypersonic plasma thermocouple comprising a body portion mounted on a vehicle, said vehicle being capable of sufficent velocity through a gaseous medium to ionize the gas adjacent said vehicle and said body portion, a refractory electrically conducting thermionic emitter placed near the forward end of the body in contact with the ionized gas at one temperature, an electrically conducting collecting anode placed further back along the body in contact with the ionized gas at a lower temperature, and an electrical insulator separating said emitter and said collecting anode, whereby an electrical load may be connected between said emitter and sai-d collecting anode to be operated by this power supply.

2. A hypersonic plasma thermocouple mounted on a vehicle, said vehicle being capable of sufficient velocity in a gaseous medium to ionze the gas adjacent the vehicle, said hypersonic plasma thermocouple comprising an electrically conducting thermionic emitter placed in contact With the ionized gas at one temperature, and an electrically conducting collecting anode in contact with the ionized gas at `a lower temperature, said enitter and anode separated by an electrical insulator whereby an electrical load may be connected between said ernitter and said collecting anode.

3. A hypersonic plasma thermocouple as in claim 2 Wherein the ernitter and collecting anode are of the same material.

4. A hypersonic plasma thermocouple as in claim 2 Wherein the gaseous medium comprises air.

References Cted by the Examiner UNITED STATES PATENTS 2,5l0,397 6/50 Hansell 310-4 X FOREIGN PATENTS 866,434 5/41 France.

OTHER REFERENCES Journal of the Aeronautical Sciences, April, 1958, page 240.

ORIS L. RADER, Primary Exam'ner.

MILTON O. HIRSHFIELD, DAVID X. SLINEY,

Exam'ers.

Claims

2. A HYPERSONIC PLASMA THERMOCOUPLE MOUNTED ON A VEHICLE, SAID VEHICLE BEING CAPABLE OF SUFFCIENT VELOCITY IN A GASEOUS MEDIUM TO IONIZE THE GAS ADJACENT THE VEHICLE, SAID HPERSONIC PLASMA THERMOCOUPLE COMPRISING AN ELECTRICALLY CONDUCTING THERMIONIC EMITTER PLACED IN CONTACT WITH THE IONIZED GAS AT ONE TEMPERATURE, AND AN ELECTRICALLY CONDUCTING COLLECTING ANODE IN CONTACT WITH THE IONIZED GAS AT A LWER TEMPERATURE, SAID EMITTER AND ANODE SEPARATED BY AN ELECTRICAL INSULATOR WHEREBY AN ELECTRICAL LOAD MAY BE CONNECTED BETWEEN SAID EMITTER AND SAID COLLECTING ANODE.