US3073984A

US3073984A - Toroidal arc apparatus

Info

Publication number: US3073984A
Application number: US80438A
Authority: US
Inventors: Richard C Eschenbach; Robert J Wickham
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1961-01-03
Filing date: 1961-01-03
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15

Description

Jan. 15, 1963 R. c. ESCHENBACH ETAL TOROIDAL ARC APPARATUS Filed Jan. 3, 1961 INVENTORS RICHARD C. ESCHENBACH ROBERT J. WICKHAM ATTORNEY 3,073,984 TOROEDAL ARC APPARATUS Richard C. Eschenhach, Indianapolis, and Robert .l. Wickham, llainfield, Ind., assignors to Union Carbide Corporation, a corporation of New York Filed .lan. 3, 1961, Ser. No. 30,438 6 Claims. (Cl. 313-231) The present invention relates to an apparatus for the are treating of air and other gases. More particularly, it relates to such an apparatus utilizing the energy from a toroidal are.

For the purpose of this invention a toroidal arc is defined as an are maintained in the annular space between two concentric electrodes in which the path of the arc termination on each electrode is approximately a circle, and in which gas flows through the annular arc space between the two electrodes.

The use of high temperature, high velocity gas streams has become very important in many industrial processes in recent years. In particular, the aircraft industry requires a source of such gas streams for wind tunnels and materials testing equipment. Generally, there are two possible sources of such high temperature, high velocity gas streams: these are gas flames and electric arcs. The former involves the combustion of gases and is quite limited in achieving the high temperatures and velocities that are required.

The electric arc has been used for many years for such purposes as metal welding and cutting, coating, cracking of hydrocarbons and other similar purposes. Attempts have been made in the past to develop electric arc devices for heating gas streams; however, these have been successful in only limited areas.

The principal requirements of an electric arc gas heater are that it must be capable of utilizing extremely high power inputs to the arc and then utilizing this power to heat up the gas and increase its velocity. Secondly, the device must be capable of continuous operation with ambient temperatures of up to 20,000 F. to produce velocities many times the speed of sound. And lastly, the gas must be substantially free of contaminants such as material eroded from the electrode. Developing such a device requires far more than scaling up known welding devices since the power, temperature and gas velocities encountered are of a far different order.

It is accordingly the primary object of the present invention to provide a non-consumable electrode electric arc energized gas heater.

It is a further object to provide such a heater utilizing a toroidal are. 7

It is a further object to provide a low velocity high enthalpy heater.

It is a still further object to provide such a heater which is capable of operation for extended periods of time.

Other objects and advantages will be apparent from the description and drawings in which:

FIG. 1 is a side elevation in cross-section of a preferred embodiment of the present invention.

The objects of the present invention are accomplished in general by an electric arc gas heater which comprises an elongated fluid-cooled, non-consumable stick electrode having an elongated tubular fluid-cooled nozzle electrode located coaxial with and substantially surrounding the stick electrode to form an elongated and annular ice arc path therebetween. Means are provided at one end of the nozzle electrode for introducing an annular gas stream therein, in an axial or swirling fashion, and into the arc path about and in intimate contact with the stick electrode, the outer diameter of said gas stream being initially substantially less than the inner diameter of the nozzle electrode. The nozzle and stick electrodes are electrically insulated from each other and both are connected to an are power source. Arc rotation means in the form of a magnetic field coil is wrapped circumferentially around the nozzle electrode.

The above-described arc device is especially useful in combination with a plenum chamber located at the outlet end of the nozzle electrode, said plenum chamber being in turn provided at its outlet end with a nozzle for directing the gas into a wind tunnel or like device.

Referring generally to FIG. 1, the device comprises a cylindrical nozzle electrode 60 having an axially mounted stick electrode 10 extending through the center thereof and forming an arc chamber 63 therebetween. Provision is made for passing a gas stream to be heated into the arc chamber at one end thereof and then through the arc chamber and out the other end. Such gas may be introduced axially or in a swirling fashion. A field coil 61 surrounds the nozzle electrode to establish a very strong magnetic field in the arc chamber. When an arc is established between the nozzle and the stick electrode the resultant arc rotates rapidly around the stick electrode and uses an appreciable area of the electrodes, thus heating the gas stream through an appreciable fraction of the volume of said chamber. The heated gas stream is then passed into a plenum chamber 86 which is electrically insulated from the nozzle electrode, where pressure is built up and then passes out through exit nozzle 94. The gas stream emanating from the exit nozzle has extremely high temperature and supersonic velocity.

The specific apparatus embodiment set forth in the drawing will now be described in greater detail. Stick electrode 10 passes through support member 12 and is supported therein by insulating members 14 and 16 Stick electrode ll is hollow and is provided with a tubular member 18 therein forming fluid coolant inlet path 20 and outlet path 22. An are power source (not shown) is connected to electrode 10 by means of terminal 24.

A gas inlet chamber 30 having one or more inlets 32 is provided adjacent the support member 12. This chamber is formed by tubular member 34 and is closed at the upstream end by insulating nut 16 and lock nut 36. Insulating member 40 and constriction 42 are located at the downstream end of the chamber, the constriction 42 forming an annular opening around stick electrode 10.

The tubular nozzle electrode 60 surrounds the stick electrode immediately downstream from the constriction 42 forming an arc chamber 63 therebetween. The nozzle electrode is supported by threaded member 62, a tubular Water jacket 64 and nozzle nut 66. Member 62 engages insulating member 40 and in turn supports tubular member 64 and nozzle nut 66 which in turn supports the downstream end of nozzle electrode 60. The constriction 42 is mounted in the upstream end of the nozzle electrode and is held in gas-tight abutment with insulating member 40. Member 64 forms an annular coolant path 68 surrounding the nozzle electrode having inlet 70 and outlet 72. An arc current power connection is provided at 74.

Insulating members 76, 78, and located at the downa stream end of the nozzle electrode support two tubular members 82 and 84, which define a plenum chamber 36 and an annular coolant passage 88 therefor, having inlet and outlet paths 99 and 92. The downstream end of the plenum chamber 86 is provided with an exit nozzle 94, and a support member 96 which engages members 82 and 84. The exit nozzle is held in place in member 96 by retaining ring 98 and is surrounded by a coolant passage 99 having inlet 100 and outlet 101.

The magnetic field coil 61 is wrapped around the exterior of nozzle electrode 66 and is provided with a suitable direct current power source to establish a strong magnetic field within the arc chamber 63. The field coil is conveniently constructed by forming same from copper tubing and then passing coolant directly therethrough.

In a typical operating cycle of the instant device, a small amount of atmospheric air is introduced under pres sure into the chamber through the apertures 32 so as to direct the air axially along the stick electrode 10' through the constriction 42 and out the exit 94. By proper design of the apertures, a vortex or swirling flow of air may be established if desired. The constriction 42 is a desirable feature of the apparatus in that it is necessary that a sufficient gas velocity be maintained to move the arc along the length of the stick electrode 10 after it has once been established at the point of constriction. A suitable diameter for the constriction has been found to be 1 /4 when used in conjunction with a stick electrode having a diameter of 1". The apertures 32 should be placed a sufficient distance from the constriction 42 so as to allow the gas flow to become streamlined before reaching the constriction. A suitable distance has been found to be from 4" to 7". The constriction additionally protects the insulator from being destroyed from heat radiation.

An appropriate power supply is connected to the stick electrode 10 at 24 and to the nozzle electrode nut 66 at 74, the nozzle nut being in electrical contact with the nozzle electrode 60. Direct current with straight or reverse polarity may be used as desired. The are is established between the stick electrode 10 and the nozzle electrode at the constriction 42 by any suitable means such as a high frequency pilot arc. The quantity of air is then increased as desired. The arc that is finally established moves away from the constriction 42 and moves f Both of the electrodes are preferably constructed of copper because of its high electrical and thermal conductivity. Such material is also useful to minimize electrode damage in the presence of oxidizing atmospheres. Aluminum could also be used as a cathode material. Further,

when using gases that are not oxygen bearing, tungsten,

molybdenum and brass could be used.

The coolant is supplied to the nozzle electrode 60 through the inlet around and through the annular space 71 formed by the nozzle electrode 6% and the nozzle sleeve 64, and thence out the outlet 72. These water cooling passages are a necessary feature of the device. When relatively large current densities are present, as in this apparatus, efficient electrode cooling is necessary so that the electrodes will not be melted because of the arc intensity. It has been found that high velocity water cooling is effective because of high heat transfer coefficients. Therefore, the cooling fluid should be supplied at high pressure. In the present apparatus, if the cooling space 71 is too large, the high pressure, high velocity cooling will result in a greater quantity of fluid being supplied to the device than is needed. Therefore, the cooling space 71 should be small enough to minimize the excessive flow of fluid and yet be large enough to insure a continuous flow. An annular space width of about .015, for example, has

been found suitable for cooling space 71 when the water is supplied at a pressure of 250 p.s.i.g.

Coolant is supplied to the stick electrode 10 by injecting cooling water into and through the annular space 20 formed by the concentric tubes 10 and 18 and then out through the space 22 formed by the inner tube 18. The cupped portions 11 allow a greater surface area of the tip portion of the electrode to be subjected to the cooling water.

In the preferred form of the invention, the stick electrode 10 projects beyond the nozzle nut 66. When an elongated stick electrode is used, the arc tends to concentrate at the tip of the electrode. In the present apparatus, however, an arc is desired which extends along the arc chamber between the stick electrode and the nozzle electrode and which substantially fills the cross section of such chamber. Therefore, care is taken to prevent the are from being localized at the tip of the stick electrode. This is preferably accomplished by extending the electrode 10 beyond the outlet of the nozzle electrode 60 and its nozzle nut 66. This apparatus configuration also reduces electrode erosion by enabling the arc to be maintained along the stick electrode in a less concentrated fashion. It is desirable therefore that the stick electrode project beyond the nozzle nut a minimum distance. A distance of 1" has been found to be suitable when a 1 dia. inner electrode is used.

Extending the stick electrode past the nozzle electrode eliminates the undesirable localizing of the are at the tip of the stick electrode. However, there is also a tendency for the arc to localize at a spot along the stick or nozzle electrode. This difficulty is overcome in the present invention by the addition of the copper field coil 61 which produces a magnetic field having a strong component parallel to the axis of the torch. This component rotates or spins the are around the outer periphery of the stick electrode and the inner periphery of the nozzle electrode. Such coil may be cooled by any suitable means, with water cooling being preferred. The field coil may be either connected in series to the power supply of the electrodes or it may have a separate supply of its own.

Another advantage of the rotating or spinning arc lies in the more effective heating of the air or gas that is passing through the nozzle area. Specifically, since the arc is rotating, the complete cross-sectional area through which the air travels may be considered to be subjected to the heat generated by the arc.

The are rotation induced by the field coil also materially increases the current carrying capacity of the electrodes. Specifically, for a given electrode area, there can only be so much current applied to the area where the arc is instantaneously localized before melting or severe arc erosion occurs. By using the field coil the arc will tend to effectively spread out over a greater electrode area. Thus, the arc area will be increased so as to permit greater overall currents with workable current densities.

The field coil will also stabilize the arc. That is, for a given current and gas flow the strength of the field coil should be of sufficient strength in order to prevent the are from wandering and eventually blowing out. For example, when the current to the device was 600 amperes and the gas flow was 830 c.f.h. the arc failed or blew out when the strength of the coil became as low as 24 kiloampere turns.

This combination of heating the complete arc chamber cross-sectional area and providing for increased arc current densities results in a more effective method of producing a hot gas efiluent.

Referring once again to the drawing, the hot gas effluent emanating from the arc chamber passes through the plenum chamber 86 from the nozzle electrode outlet, out through the nozzle exit 94.

In order to achieve high exit velocities when the ciliaent exhausts into a chamber or room at atmospheric pressure, it is necessary that high pressures of the order of 100-200 p.s.i.g. be built up within the plenum chamber.

This is accomplished by the constricted outlet nozzle 94.

i. .Thesize of the constriction would be dependent upon the 2 pressures that are desired and which can be maintained aw-ithout damage to the apparatus. Although the drawing discloses a diverging, velocity increasing nozzle, it is to be understood that a converging or a straight nozzle could be used if so desired.

As stated above, the plenum chamber is electrically insulated from the electric arc device by the insulators 76,

78 and 80. These insulators are an important feature of the chamber. Specifically, if the chamber were at the same potential as the nozzle electrode, the arc would tend to wander from the nozzle electrode to the walls of the chamber. Suitable materials for the insulators 78 and 80 have been found to be Bakelite, Formica and nylon. Insulator 76 also protects insulators 7-8 and 80 from the heat of the nozzle electrode 60. Therefore, it is preferably constructed of fused silica, boron nitride or Transite. It is to be understood, however, that materials exhibiting like properties could alternatively be used.

Cooling of the chamber 86 and its exit nozzle 94 is accomplished by passing fluid coolant through the annular passageways 88 and 99 respectively.

While the present apparatus has been described with reference to producing a high temperature, high velocity gas stream, it is also useful as a relatively low velocity, high enthalpy heater. That is, because of the relatively large volume arc chamber existing. between the central electrode 10 and the surrounding electrode 60, the gas passing through the heater itself will be at a relatively low velocity. Such low velocity will enable the gas to be more effectively heated because of the increased length of time that the gas is within the arc chamber. The device therefore is useful without the plenum chamber 86 as a low velocity, high enthalpy heater. Such a device would be useful for materials testing, for example.

When being used primarily as a high enthalpy, gas heater the length of the nozzle electrode should terminate just beyond the area where the arc is localized. The inner stick electrode would then project beyond the nozzle a minimum required distance of about one inch. Any increase in length beyond these requirements will result in lower gas enthalpies since more of the heat being generated will be dissipated into the electrodes as the gas passes out of the device.

The following examples illustrate the use of the instant arc 'gas heater. Apparatus of the type shown in FIG. 1 without the plenum chamber 86 and nozzle was used in Example 1. In Example 2 the plenum chamber was used.

Example 1 In this example a 1 dia. stick electrode with an overall length of approximately 25" including a 1" projection beyond the nozzle nut was used. The nozzle electrode was 12" long with a 2' ID. The constriction at the entrance to the nozzle electrode was A" in length with a 1%" ID. A water-cooled field coil was positioned around the nozzle electrode. The field power was 25 kilo-ampere turns and the direction of the field was upstream. Air was supplied to the chamber through two apertures positioned approximately 6 /2" from the constriction so as to create a streamlined axial flow at the rate of 320 c.f.h. With the nozzle electrode acting as the cathode, 1400 amperes was supplied to the device. Under these conditions the total power developed was 235 kw., the arc voltage was 168 v., the power to the gas was 76 kw., and the calculated enthalpy of the gas was 10,000 B.t.11./ lb.

It is seen that a relatively large amount of current can be used without damage to the apparatus. This is evidenced by the fact that the arc efiiuent was blue indicat ing no electrode erosion. Due to the rotation of the arc through the gas flow, the high currents effectively heated the gas as indicated by the high enthalpy. It is apparent that the high velocity cooling combined with the arc rotation enables high currents to be used withou damage to the apparatus. 1-

Example 2 In this example the dimensions of the electric arc device and the field coil conditions were the same as in Example 1. The plenum chamber was approximately 6" in length with an ID. of 27s". The exit nozzle had a A" throat diameter and a length of 1%". Air was supplied in the same manner as in Example 1 at 1500 c.f.h. With the nozzle acting as the anode, 400 amperes was supplied to the device. Under these conditions the total power developed was 106 kw., the arc voltage was 265 v., the power to the gas was an estimated 21 kw. and the enthalpy was 650 B.t.u./ lb. The pressure developed within the plenum chamber was 106 p.s.i.g. resulting in a calculated gas exit velocity of 3000 ft./sec. which is between Mach 1 and 2 under these conditions.

From the above description and examples it may be seen that the device of the present invention provides a practical means of obtaining a high temperature, high velocity gas stream which may, in turn, be used for materials testing or in combination with a wind tunnel for aeronautical structures and for many other uses. While a preferred embodiment of the invention has been specifically set forth, it is to be understood that certain substitutions and modifications could be made by a per-t son skilled in the art without departing from the spirit and scope of the invention. For example, while a cylindrical-nozzle electrode has been shown, a convergent, divergent or combination thereof could be used.

What is claimed is:

1. An electric arc gas heater which comprises a hollow, elongated fluid-cooled, non-consumable stick electrode, a chamber surrounding said electrode at one end thereof, means for supplying a stream of gas to said chamber, an elongated, fluid-cooled nozzle electrode surrounding said stick electrode coaxially therewith and forming an elongated annular arc path therebetween, said nozzle electrode being located adjacent the chamber and extending toward the other end of the stick electrode, flow-restriction means between the chamber and the nozzle electrode for directing the gas stream in an annular flow pattern into the annular arc path surrounding said stock electrode, a fluid-cooled plenum chamber attached at one end to the nozzle electrode, coaxial with and surrounding the other end of the stick electrode, and closure means at the other end of said plenum chamber containing a nozzle means mounted coaxially with respect to said plenum chamber axially spaced from said adjacent end of the stock electrode, means electrically insulating the first chamber, the stick electrode, the nozzle electrode, and the plenum chamber from each other, means for supplying electric power to the stick electrode and the nozzle electrode, and means for providing a strong magnetic field in the annular arc path having lines of force parallel to the axis of said stick electrode.

2. An electric arc gas heater as set forth in claim 1 wherein the last named means comprises a field coil wrapped around the nozzle electrode.

3. An electric arc gas heater as set forth in claim 2 wherein the plenum chamber and the nozzle electrode form a single cylindrical chamber, and wherein the stick electrode extends into the plenum chamber.

4. An electric arc gas heater as set forth in claim 1 wherein annular coolant passages are provided within the stick electrode, and surrounding the nozzle electrode, the plenum chamber and the nozzle means.

5. An electric arc gas heater which comprises an elongated tubular water-cooled nozzle electrode, an elongated water-cooled stick electrode extending axially through said nozzle electrode and forming an elongated arc chamber therebetween, means at one end of said nozzle electrode for supporting said stick electrode therein and electrically insulated therefrom, further means at said one end in combination with said last named means for passing an annular gas stream surrounding and in intimate contact with the stick electrode into the elongated arc chamber at one end and out the other end thereof, electric power means connected to the nozzle and stick electrode for establishing and maintaining an arc therebetween, and a magnetic field coil surrounding said nozzle electrode for establishing a strong magnetic field within the arc chamher.

6. An electric arc gas heater as set forth in claim 5 8 including a plenum chamber affixed to the other end of the nozzle electrode and electrically insulated therefrom and having a flow constriction in the outlet end thereof opposite from said nozzle electrode whereby gas pressure is caused to build up within the arc and plenum chambers,

References Cited in the file of this patent UNITED STATES PATENTS Partiot 'Jan. 8, 1952