US 3209193 A
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P 1965 c. SHEER ETAL 3,209,193
METHOD OF ENERGY TRANSFER TO FLUIDS Filed Feb. 12, 1962 2 Sheets-Sheet l 4/ MD PART 70 55 /0N/Z E D 0% flIIIIIMIIIIII/IIMIM/II/JMWIM IIIIIIIIIMIIIIw/MI/II/I/I/wl[11 70 as ION/ZED INVENTORS 674/124 [SJ/4552 BY 5407054 AfJQM W A1 iORNEY p 1965 c. SHEER ETAL 3,209,193
METHOD OF ENERGY TRANSFER TO FLUIDS Filed Feb. 12., 1962 2 Sheets-Sheet 2 Tuclj- YIIII/I/l/IIIIIIIIIIII/III//IIII IN VEN TORS (HA EL 55 53 /554 ATTORNEY United States Patent 3,209,193 METHOD OF ENERGY TRANSFER TO FLUIDS Charles Sheer, Teaneck, N.J., and Samuel Korman, Hewlett, N.Y., assignors to Sheer-Korman Associates, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 12, 1962., Ser. No. 172,735 5 Claims. (Cl. 313-231) This invention relates to an apparatus and method of transferring large amounts of energy to fluids. It is a purpose to impart such energy quickly and effectively with no dilution or contamination of the energized fluid by extraneous matter.
It is an object of this invention to produce a plasma of any gaseous fluid in the form of a well defined jet.
This case is a continuation-in-part of our copending application 749,132 filed July 17, 1958 and of application 19,914 filed April 4, 1960. This case contains the subject matter of those earlier cases but contains also an improved form of process and apparatus for carrying out the invention, and it gives a more complete disclosure of the manner of use and the underlying technology by which the results are achieved.
With the filing of these cases the former cases above referred to are hereby abandoned.
Although this field of imparting energy to fluids has attracted the attention of scientists for many decades, the phenomena governing such transfer when an electric arc is used as the energy source, is virtually unknown. Indeed, few physical systems have been found so intractable with regard to quantitative treatment, or even the development of an adequate qualitative description of the basic mechanisms. In this respect the electric arc has defied the evolution of a comprehensive formal description, this ditficulty' being a common feature of the class of systems which involve the flow of electrical energy through compressible fluids. As a result, the development of engineering tools which make practical use of their inherently valuable properties and which are the normal progeny of realistic physical models and valid mathematical formulation has been painfully slow.
In the face of this difliculty the pressure for a better understanding of the dominant energy transfer processes has been steadily mounting. The trend of modern space sciences, for example, has imposed inescapable requirements for the capability of generating, sustaining and controlling hyperthermal environments whose creation is beyond the limits of the existing state of the art. Similarly, the increasing demands of industry for exotic, high temperature materials has focussed attention on the generation of the ultra-high energy density zones essential to the production of such materials. Under the stimulus of these requirements an intensified effort has been carried on for the last decade or so, directed towards the achievement of a fluid flow system in which an ultra-high temperature zone can be generated, maintained, and manipulated in a practical manner.
From the end-use viewpoint, the central problem has been not merely the more or less transient generation of a volume of high temperature fluid, but rather the development of means for rapid and efficient transfer of energy whereby a useful working volume of fluid at ultrahigh temperatures may be created and sustained in a rapidly moving fluid system.
In the attempt to advance technology towards this objective, by far the largest majority of systems studied have been electrothermal in character. This is understandable in view of the inadequacy of even the most exothermic chemical reactions known to provide the required degree of energy concentration. For most of the desired applications, the same has been found true of 3,209,193 Patented Sept. 28, 1965 mechanical gas-kinetic systems, while nuclear sources are prohibitively expensive, and, except in rare instances, impracticable.
Consequently, most attention has been directed toward the direct transfer of electrical energy to the working fluid. In particular, the electric arc discharge is the most promising electrothermal system, owing to its intrinsic property of dissipating large amounts of energy in a relatively small volume of space.
Although known and used for well over a century, it has been only within the past decade that any real progress has been made toward the understanding of basic arc mechanisms. However, a review of the literature clearly indicates that our level of comprehension of these mechanisms, particularly with regard to ergodic phenomena, is still embryonic. Unfortunately such progress as has been made almost exclusively encompasses quiescent or nonflowing arc systems. Considering the volume of published works on arc phenomena, the attention paid to the effects of gas convection on are characteristics has been quite casual and confined largely to the natural atmospheric convection established in the vicinity of the discharge by virtue of the existing thermal gradients. On the other hand the continuous generation of a plasma stream inevitably implies the interaction of a sizeable quantity of moving gas with the arc discharge zone. Further, it is reasonable to expect the behavior of an arc to be altered under conditions of forced convection. Such alteration in behavior has indeed been observed by the inventors and forms the basis of the new and improved method of energizing a stream of fluid in an electric arc with which this invention is concerned. In a conventional high intensity are, the effluent plasma is generated by continuous vaporization of the solid material of which the anode is made. The rapid and eflicient vaporization of the anode in this case occurs as the result of the concentration of a major portion of the are energy into a very thin layer in contact with the anode surface. This layer is established only over the area of anode surface in contact with the arc discharge, i.e., where the stream of electrons carrying the arc current enters the surface. This layer is known as the anode fall space and its thickness depends on a variety of factors, such as the nature of the atmosphere and anode material, the arc and current voltage, and the ambient pressure. For arcs operating near one atmosphere pressure it is usually about 0.1 mm. thick.
A similar thin layer, known as the cathode fall space, is also established over the contact area on the cathode surface. The main gas conduction zone, extending for almost the entire inter-electrode gap distance is called the conduction column. The major distinction between the conduction column and either fall space is the fact that the voltage gradient in the former is relatively low whereas in the fall spaces the gradient is high.
All electric arcs are characterized by these three regions in the gas conduction zone. However, various types of arc behavior can usually be associated with the distribution of potential drop among the three regions. This in turn determines the portion of the input energy which is dissipated in each region.
In the common (low intensity) arc, for example, about 10% of the arc voltage (and energy dissipation) occurs across each fall space, while the remaining 80% occurs across the conduction column.
On the other hand, in the consumable-anode hierarc, from 60 to of the voltage drop occurs across the anode fall space. The electric field is so high that the material is converted into a plasma jet soon after it enters the field. The space in which this occurs is called the anode fall space. It is so called, no doubt, because the fall in voltage in that space is so high.
The inventors believe that this remarkable focusing effect, which concentrates such a large faction of the input energy near the anode surface, is due to the interaction within the anode fall space between the vapor stream arising from the anode surface, and the counterflowing stream of energetic electrons which carry the arc current. This interaction causes the potential distribution to shift markedly, when the anode current density is raised above a critical value. The net effect is to concentrate a major fraction of the are energy into anode fall space where it becomes available not only for the continuous generation of anode vapor, at the surface, but also for transferring energy efficiently to the outflowing vapor stream, heating it to ultra-high temperatures, and converting it effectively into a hyperthermal vapor plasma jet.
The above phenomenon has provided a useful technique for generating a continuous, rapid-flowing, ultrahigh temperature gas stream. It has found valuable application in many instances where the preferred composition of the stream was the vapor of a refractory solid which could be fabricated into a conductive electrode. The consumable anode hierarc, however, is not suitable for generating a hyperthermal environment when it is desired to use a non-refractory medium for the plasma jet. Thus it would be virtually impossible to inject an external fluid into the anode fall space of a consumable-anode hierarc so as to absorb an appreciable fraction of the energy dissipated in this region; and in any case the effluent plasma would necessarily be contaminated with the refractory anode vapor.
Techniques have been described in the prior art for generating a high-temperature plasma by employing a low intensity or common are using a medium which is a gas or a liquid at ordinary temperatures. These are all based on the technique of passing the working fluid through the conduction column of a low intensity are. In such devices as much as possible of the energy dissipated in the two falls spaces is removed by water-cooling the electrodes, and is therefore run to waste. Further, in order to stabilize the arc discharge under the forced convection of large amounts of fluid through the conduction column, it has been found necessary to confine or constrict the conduction column by providing fixed, cool boundaries eveloping the gas conduction zone; e.g. by means of a swirling liquid vortex or a watercooled metal channel.
Although these techniques permit stable operation of the are under forced convection and produce high temperature plasma jets, a further appreciable amount of energy is lost by heat transfer through the confining cool boundaries.
Such devices are therefore incapable of generating a plasma jet of the desired high energy content without either serious energy losses or limited operating life owing to thermal destruction of the arc electrodes and/ or confining channel. In addition the plasma generated by these devices is generally characterized by some degree of objectionable contamination with electrode vapor except under extreme conditions of rapid fluid flow rate, in which case the energy content of the effiuent jet becomes undesirably low. Further, the plasma jet from such a system usually emerges in a highly turbulent flow pattern, which, for some purposes, is also objectionable.
It is the purpose of this invention to provide a means of continuously generating a plasma jet from any desired fluid by means of a free-burning are without the use of artificially cooled boundaries or thermal constraints of any kind.
It is also an object of this invention to transfer energy from an electric arc to a continuous stream of fluid by causing the injected fluid to alter the arc characteristics so as to simulate the energy-focusing property of the consumable anode hierarc but without vaporization of the anode material.
It is further an object of this invention to provide a means for transferring the major portion of the energy absorbed by the anode as well as that dissipated in both the anode fall space and conduction column, to the working fluid, thus achieving high energy transfer efficiency simultaneously with a high effluent plasma temperature, but without significant erosion of the electrodes or supporting structures.
It is a further object of this invention to provide a plasma generator capable of operating over a very wide range of fluid flow rates without arc instability and for which there is no detectable contamination of the effluent jet with electrode vapor over the entire range of operation.
It is still further object of this invention to provide a plasma generator capable of producing a much smoother and less turbulent plasma jet than heretofore possible.
In order to achieve the purposes of this invention, it is essential that the stream of injected fluid be exposed to the energy of the arc in accordance with a specialized and unique procedure. The means, method, and apparatus required to accomplish this are set forth in the following description.
Whereas the cathode of the are used as the energy source may be of conventional design, i.e. a cylindrical rod of refractory, conducting material, such as graphite or tungsten, the anode structure on the other hand must be designed with certain special features. In particular, a portion of the anode structure must consist of a conducting porous plug, preferably of cylindrical cross section, and mounted securely in a suitable metallic holder. During operation, the arc control parameters, namely, the gap distance, are current, and applied voltage, should be so adjusted that the active anode area just covers completely the exposed surface of the porous plug. In this connection, the term active anode area is defined as that area of the anode which is engaged in receiving current from the arc, thereby serving as the anodic terminus of the discharge. Thus, in this application, it is desired that while the entire front face of the porous plug act as the current-receiving surface, no segment of the supporting structure surface comprises part of the active anode area.
It is clear, therefore, that the anodic terminus of the arc will contain a myriad of tiny orifices distributed over the active surface. Moreover, the internal structure of the porous plug must be such that said multiplicity of surface openings are connected to similar openings on the rear face by a network of passageways through its body. This arrangement provides for the transpiration of fluid through the porous anode under the influence of suitable fluid pressure at the rear face. The density of passageways through the plug body should be sufiicient to provide adequate fluid permeability, i.e. to permit the maximum fluid flow rate consistent with the mechanical strength, for the plug as a whole, necessary to withstand the pressure drop between rear and front surfaces.
It is of paramount importance to the successful operation of this invention that as much as possible, i.e. approaching of the injected fluid pass through the anode fall space of the arc. Since the fall space becomes established as a thin, high-potential gradient layer in contact only with the active anode area, it will be clear that the above-described method of fluid injection, i.e. by transpiration through a porous anode, provides a practical means for accomplishing this essential process and which at the same times does not require autogenous vaporization of the anode material from its active surface. The word autogenous is used to indicate the distinction between gases which, as in former cases are generated by vaporizing the anode as in a hierarc, as compared to all gases which are fed into the are already in vapor form, as in this case. Specifically the condition which must be created at the anodic terminus is the following:
The fluid issuing from the active surface should emerge as a multiplicity of tiny gas jets of such size, number and distribution that the individual jets diffuse laterally and merge into a gaseous flow continuum, proceeding perpendicularly away from the surface, before it has penetrated an appreciable distance, into the anode fall space. This situation assures maximum exposure of the fluid to the high energy density of the fall space, and more importantly, will influence the character of the arc discharge so as to focus a major fraction of the energy into the fall space, in the region where the gas continuum forms, with the net result that the gas absorbs a large portion of the energy that would otherwise be carried into the anode surface. In this case the transpiration fluid behaves analogously to the continuous vapor stream arising from the active anode surface of the consumable-anode hierarc, insofar as its interaction with the counterfiux of high speed electrons in the anode fall space is concerned.
The crucial factor in the technique embodied in this invention is the rapid formation of a gas continuum from the discrete emerging jets of transpiration fluid. Further, this must occur early enough in the period of transit through the fall space so that a large percentage of the fluid molecules will have the oportunity to collide with current-carrying electrons after the latter have been significantly accelerated by the high potential gradient which exists only in the fall space.
The inventors have determined that the following operating criteria are necessary in order to establish this condition in practice, or, having established this condition, to optimize the performance of the device in terms of its energy transfer properties.
First, the fluid must be injected into the zone only by transpration through a porous anode, as described above. This method of injection not only cools the anode by convective heat transfer to the transpiring fluid within the porous body, but also causes such transferred heat to be usefully absorbed by the working fluid, preheating it to a certain degree before it is energized in the are itself. The amount of energy represented by such preheating would be largely wasted by any other method of injection. Further, if the injected fluid is normally in the liquid state, the preheat energy can be utilized to advantage in converting the liquid to a gas before it emerges into the fall space. It is essential that the fluid issue from the porous anode in the gaseous state, since it is only in this state that the desired flow continuum can be formed by lateral diffusion in a distance small compared to the anode fall space thickness.
Second, the active anode area must be integrally congruent with the surface of emergence of the transpiration fluid. In other words, the current-receiving surface of the anode and the surface containing the multiplicity of exit pores should coincide. If the anodic terminus covers any part of the non-porous supporting structure, then some of the are energy will be absored by the anode without coming into contact with the emerging gas stream, and will therefore be wasted. Conversely, if the active anode area does not cover the entire surface of the porous plug, then some of the emerging gas will not pass through the arc discharge and will therefore not be directly energized. The unexposed portion of the emergent gas will then mix with and cool the energized portion, thus reducing the temperature of the resultant plasma jet.
Third, the exit orifices on the active porous surface should be as uniformly distributed as it is practicable to obtain. A porous plug characterized by a highly inhomoeneous density of surface openings will not be as effective as one having the same total number of pores but distributed uniformly over the active surface. Thus, for example, in the inhomogeneous case, it will require a greater distance for the gas flow continuum to form in those areas where the openings are sparse than where they are concentrated. This in turn is due to the fact that, when the openings are far apart, it will take longer for the individual gas jets to diffuse laterally and merge into a continuous stream. If in these sparse areas the average interpore separation it too great, the jets may penetrate the entire fall space before merging. Therefore stagnant areas will exist adjacent to those solid portions of the surface most remote from the orifices. Such regions of the surface will absorb all of the local fall space energy while the fluid escapes clear through the fall space without maximum exposure. Consequently, not only will the energy transfer be reduced in the sparse areas, but, more significantly, local hot spots will develop in these regions which lead to either thermal erosion of the porous body or a serious limitation in the maximum usable power level of the device.
Fourth, the diameter of the openings in the active surface must be small enough so that the pores do not appreciably affect the thickness and continuity of the anode fall space. It is desired for example to maintain essen tially the same fall space geometry as occurs when the active anode area consists of a continuous, non-porous, solid surface. This criterion is extremely important in achieving a gas flow continuum well within the space region and in securing maximum exposure of the injected fluid to the energy dissipated in this region. The optimum results are obtained when the pore diameter is very small compared to the fall space thickness. The results here referred to are of course those features which render the device valuable as a plasma generator; namely, high percentage of energy transfer to the fluid, high effluent plasma temperature, long electrode operating lifetime, resistance to flame-out, high percentage of ionization, stable operation without confining channels, non-turbulent flow, and freedom from contamination of the plasma with electrode vapor.
As the pore size is increased from a value very much less than the anode fall space thickness, no very great changes in these features are observed until the pore diameter approaches the thickness of the fall space in dimension. At this point the results obtained begin to decrease rapidly from the optimum, until, when the pore diameter exceeds the fall space thickness, a radical change in the operating characteristics is observed. In this condition, the energy transfer efiiciency drops to about half of the optimum value, while the electrode erosion for a given power level becomes more severe. Further the are becomes much more sensitive to flame-out, and it becomes impossible to achieve stable operation at reasonable fluid flow rates without the use of a confining channel for the conduction column. The inventors have interpreted this phenomenon as a transition from one set of conditions under which the injected fluid can form a flow continuum inside the anode fall space into another set of conditions under which it cannot. The view is based on a consideration of the characteristics of anode fall space formation as influenced by the shape of the active anode surface. The fall space always forms contiguous to the active electrode area as a result of electrical and thermal boundary conditions governing the transition between a gaseous and a solid conductor. As mentioned earlier, these conditions relate to the nature of the gas and electrode material, the arc gap, voltage and current, and the operating pressure. In the aggregate these parameters determine the thickness of the high voltage gradient layer and the voltage across it. Whatever these factors are, the fall space always follows the contour of the active anode surface, so long as the subjacent surface is engaged in receiving current from the discharge. On the other hand the fall space peters out next to any region where the current entering the surface falls off. If We consider the situation directly above a hole in the surface, it is clear that if the hole is small compared to the thickness of the fall space under the prevailing conditions the electric field distribution in the volume of fall spaced directly above the hole will not appreciably differ from that above a solid portion of the surface. Accordingly, the current will flow toward the surface for most of the fall space thickness as though the hole were not there. Only in the last minute fraction of its path through the fall space will the field pattern be perturbed causing the current to swerve away from the hole axis to reach the electrode surface. Accordingly the same high potential gradient will be established over most of the fall space above the hole as is found above a solid portion. Hence all the gas escaping from the hole will traverse a high voltage gradient layer before reaching the low potential gradient zone of the conduction column.
On the other hand, as the hole is made larger, the electric field will become perturbed from a normal distribution at a greater distance from the surface, causing the current to deflect away from the hole axis at an earlier stage in its transit across the fall space. The net result is that both the fall space thickness and the voltage drop across it are decreased, as compared to that above an equivalent solid portion of the surface. Finally, when the hole is made larger than the normal fall space thickness, the zone above the hole becomes almost wholly devoid of current and the voltage gradient in this region drops to a negligible value. Hence, when gas issues from the hole, only that fraction which diffuses laterally into the fall space region above the adjacent solid area will pass through a high voltage gradient region. The remaining gas moving near the hole axis will traverse a zone which is stagnant with respect to electron flow and will pass directly into the conduction column without interacting with electrons accelerated to hyperthermal energies. In the extreme case of a hole very large compared to the normal fall space thickness, practically all of the gas issuing from the hole will pass through this electronically stagnant region into the conduction column without coming into contact with the fall space. This situation is typical of the case in the prior art in which the gas is injected through a single large hole in a tubular anode and for which the active anode surface is establishing around the entire pe riphery of the annular electrode tip. In this case, as well as the case of a porous anode whose orifices are all very large compared to the anode fall space, the fluid never enters or comes into intimate contact with the fall space, but instead is energized entirely by its passage through the conduction column. Thus none of the advantages of this invention are available for these cases, and they behave similarly to other prior art devices in which the fluid is blown directly into the conduction column from the outside. It is significant that satisfaction of the pore size criterion does not merely provide for the transfer of fall space energy in addition to column energy to the fluid, plus the feature of electrode cooling, but also leads to a radical alteration in the character of the fall space itself. Thus, the successful injection of the fluid in the form of a continuous stream which can interact within the fall space in counterflux with the current flow is responsible for the focusing etfect by which a much larger portion of the are energy is concentrated in the fall space region than is the case for a quiescent are (no fluid flow). In this respect the inventors have found that, when the stipulated criterion is met, the voltage across the fall space increases and the space itself divides into several distinct regions having a total thickness considerably greater than the normal thickness which prevails in the absence of fluid flow. However, this situation and the concomitant valuable results cannot be achived unless the pore size is made smaller than the thickness of the fall space, which forms at the active anode surface in the absence of fluid flow; i.e., when all parameters pertaining to regular operation are established except that the fluid flow has not yet been turned on.
In applying this criterion to a practical device it is necessary to know the minimum quiescent fall space thickness likely to be encountered over a specified range of operating conditions, and to use a porous material whose average pore diameter is less than this value. Since the thickness is a variable quantity, the correct dimension is most readily determined empirically while operating the device, under the desired conditions but without fluid flow. If desired, a solid anode may be used for this purpose initially. In some instances the value of the fall space thickness for a given type of atmospheric and anode material under the required range of operating conditions may be found in the published literature. In any case, straightforward techniques for measuring this quantity directly are well known in the art.
Also, in selecting a porous material it is often convenient to use commercially available materials such as porous graphite. In this event the pore size criterion may be related to the average orifice diameter, since the pores in such materials generally have a statistical distribution of sizes. However, when such materials are used, it is important to make sure that the material does not have too many large size pores in this distribution. Such pores are likely to be too large to satisfy the size criterion, and at the same time account for a disproportionately large percentage of the total gas flow.
Fifth, the flow rate of gas through the anode fall space relative to the counterflow of arc current must be in excess of the value required to effect a transition to a quasi-hierarc mode. The latter refers to a transition analogous to that which occurs in the case of the vaporizing anode hierarc. It will be recalled that this is due to the copious flow of vapor through the anode fall space and causes a redistribution of the are energy so as to concentrate a major fraction into the fall space. This was previously referred to as the focusing effect and results in a significant increase in the energy transferred to the vapor.
The inventors have demonstrated that a similar effect can be produced with an external fluid, introduced into the arc in accordance with the first four operating criteria listed earlier, when the fluid flow rate is raised above a specific value. In the consumable-anode type hierarc. the criterion for initiating this mode of operation is to increase the anode current density until a critical value is reached sufficient to cause rapid vaporization of the anode substance.
Although in the present case no requirement for vaporization exists, a distinct transition of analogous character may be observed at a specific flow rate of fluid through the anode fall space. This transition may be recognized in the following manner: The are is first established at the current level required for the arc terminus to cover the entire face of the porous anode. Then the gas flow is turned on and gradually increased, with the current kept fixed at its initial value, While the voltage across the arc is noted. At the transition point, a sharp rise in arc voltage is observed. Simultaneously, the brilliance of the elfluent plasma increases markedly while the anode face temperature drops. Thus, while the power dissipated in the arc rises to about double that just before the transition, the thermal loading of the anode itself drops significantly. Further, the additional energy is transferred almost exclusively to the eflluent plasma, resulting in an extremely eflicient mode of operation.
The accompanying drawings illustrate the means by which this invention is carried out.
In the drawings:
FIG. 1 shows a medial section through a simple device by which the invention of this application is carried out;
FIG. 2 is a similar view of an alternative device;
FIG. 3 is an end view of the device of FIG. 1 looking in the direction of the arrow;
FIG. 4 is a central section on the center line of the porous block of FIG. 3; and
FIG. 5 is a central section of a more developed form of the device.
The transpiration gas flow alone may be caused to pre vent undue heating of the porous block, but for some cases we prefer where practical to provide a cooling mechanism for that purpose such for example as here disclosed.
Referring now to the drawings, FIGS. 1, 3 and 4, the numeral 10 comprises a tube terminating in a porous block 11. concentrically disposed within tube 10 is a second tube 12 which terminates short of the porous block. Thus a fluid to be treated may be projected through the inner tube against the block 11, returning in the annular space. Part of this fluid will transpire through the pores while the remainder will impinge against the rear face of the block 11 to cool it.
In the construction of FIG. 2 there is provided an outer tube 20 closed at the end by a porous block 24, and having at each side a lateral wall 21 and 22 each providing a channel for a cooling fluid in and out. This porous block 24 may if desired be provided with transverse channels 23 leading from one side to the other communicating on one side with channel 22 and on the other with channel 21, so that a cooling fluid may be caused to traverse the anode block from side to side to keep it from overheating. These additional cooling channels are useful when it is desired to extend the power handling capability of a given device to a higher level.
In the construction of FIG. the anode comprises a porous block which may be of porous carbon 30, which is clamped between an outer casing 32 and a central pillar 31. Electrical connection is made through central pillar 31 through flexible braided conductors 310. In order to avoid the possibility of the arc jumping to the outer casing 32, the latter is completely insulated electrically from the arc circuit by means of insulating gasket 30:: and insulating inserts 30b and 30c.
The porous block 30 is shown as conical, mating with the interior of the outer casing, and is firmly held against the casing by the central pillar 31, which also serves as the electrical contact. Firm contact is achieved by means of the coiled spring 31b.
The central pillar has a tube 33 clear through it to permit gases to be conducted to the rear face of the porous block.
As shown, the outer casing 32 is hollow as shown at 35 to permit it to be water cooled, and if desired the central pillar 31 may be hollow so that it too can be water cooled through a pipe 36.
The electrode 34 is negatively energized and the porous block 30 is positively energized, so that an arc may be struck between them. In operation the fluid is introduced through the tube 33 under suflicient pressure to cause it to transpire through porous block 30 into the arc.
The arc is now struck between the cathode 34 and the porous anode block 30, and the fluid is forced through the porous block. The flow of the gas contrary to the direction of the flow of the current keeps the porous block from vaporizing and establishes a fall space immediately beyond the face of the porous block, in which the major portion of the energy of the arc is concentrated.
The pores of the porous block anode in either form permit suflicient fluid to transpire through it to form, when energized, a plasma jet which can carry away from the anode substantially all the energy fed to it, while the cooling fluid passing through and against the porous block assists in preventing it from overheating.
When the required criteria are fulfilled, the porous block may be kept relatively cool, by transferring its energy to the fluid passing through it, while the fluid itself issues into the fall space.
When the fluid is passed through the arc in accordance with the five criteria described above, a new form of plasma generator is created which has a number of distinct advantages over any other form of arc plasma device revealed in the prior art. Although competitive devices have individually achieved high energy transfer efliciency, or long operating lifetime, and/or absence of electrode contamination in the plasma jet, none of such devices is capable of achieving all of these desirable features at the same time. In addition, the prior art devices must be operated within narrow limits of fluid flow rate, the lower limit being set by the onset of severe electrode erosion while the upper limit is established by fiameout (i.e. blowing out of the arc). Finally, in the prac tical operating range of the prior art devices, which introduce the fluid directly into the arc column, the plasma jet is characterized by a high degree of turbulence, which is often undesirable.
Conversely, the inventors have demonstrtted that the device described in the present application, when constructed and operated in accordance with the stipulated criteria, comprises a plasma generator which combines high energy transfer efliciency to 97%), high enthalpy for the eflluent plasma (1 to 5 kilo-calories per gram-mole (of argon) per kilowatt of input power), long operating lifetime (300 to 600 hours), and no observable trace of electrode vapor in the plasma jet over a wide range of operating conditions.
In addition, this fluid transpiration arc plasma generator is capable of providing these advantages over a wide range of fluid flow rates because of its unique insensitivity to flame-out. This in turn is due to an abnormally high degree of ionization, which was discovered to be an inherent property of this device. Or, in other words, the plasma generated by the fluid transpiration arc possesses an unusually high electrical conductivity, thus providing an added useful feature for many applications. Finally, it has been demonstrated that the flow regime characteristic of the plasma jet generated by this device is considerably less turbulent than that of other known devices operating under analogous conditions of flow-rate are power and ambient pressure.
What is claimed:
1. The process of energizing a fluid by means of an electric hierarc having a porous anode and a cathode, which comprises passing the fluid through the active anode surface of the arc into and through the anode fall space, the anode having pores of such size and density and distribution that the transpired fluid merges into a continuum over the entire active surface of the anode as it leaves the anode, so that said fluid continuum will be energized Within the fall space of the arc, the disposition being such that said continuum is coextensive with the face of the anode.
2. A device for producing a plasma jet from a fluid material comprising a porous anode, means for projecting said fluid material through said anode, a cathode beyond said anode, means for establishing a hierarc between said material issuing from said porous anode and said cathode, said hierarc energy being suflicient to convert the transpired material into a palsma jet.
3. A plasma generator comprising a porous anode, means for passing fluid through said porous anode to form a stream, a cathode adjacent to said stream, means for energizing said cathode suflicient to produce a high energy are through said fluid to said porous anode.
4. A plasma generator comprising a porous anode and a cathode in substantial alignment therewith, means to establish a hierarc between said anode and said cathode including means for passing a stream of a gas to be ionized through said porous anode into said hierarc, said anode being out of alignment with said gas stream.
5 A process for imparting a high energy to a fluid WhlCh comprises passing said fluid continuously through the pores of a porous anode to exit toward a cathode while maintaining a hierarc current between said cathode and said anode through issuing fluid.
References Cited by the Examiner FOREIGN PATENTS 1,233,796 '10/60 France.
DAVID J. GALVIN, Primary Examiner. GEORGE N. WESTBY, ARTHUR GAUSS, Examiners.