Patent Publication Number: US-8987640-B2

Title: Axial resistance sheathed heater

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 12/878,823, filed on Sep. 9, 2010, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The standard sheathed resistance element has been around for many decades. These standard elements typically use a spiral wound resistance wire with conductor leads on both ends, surrounded by dielectric and heat transfer material and compacted to extend the thermal and dielectric capabilities and make it formable with common bending practices. One of the limitations associated with the use of a coiled resistance element which per lineal inch of heater cause the fast buildup of resistance even with heavier resistance wires which would need to be wound on a very tight coil pattern to fit into a marginally sized tubular sheath. These units are excellent choices for common heating systems that do not demand the spatial conservation or ultra low resistances and disproportional large power levels. Standard maximum power:voltage (p:v) ratios for these customary units are 2000:120 (18 amps). 
     Other heater elements which are used in special resistive heating situations are the single ended compacted tubular elements which help overcome some of the built in deficiencies of the customary heater element designs described above. These units use a hairpin style resistive element within a compacted tubular sheath, giving it greater flexibility and usefulness in smaller equipment or process footprints. These would not lend themselves useful in low voltage high power applications as the system would need to accommodate the use of side-by-side massive conductor legs. This would make the heater sheath too massive for space constrained operations, also the mass of the element would cause a innate thermal burden on the resistive wire causing the resistance wire to prematurely expire. Standard theoretical p:v ratio achieved by such a unit could be up to 750:120 (6.25 amps) however the likelihood of heater longevity would be difficult to ascertain without formal study. 
     The final notable compacted sheath style heating element we observe is the single line style heater element (seen in U.S. Pat. No. 6,456,785 to Evans). This design overcomes further the deficiencies of the single ended heater design with hairpin resistive circuit by using straight single line resistance wire further compacted with slide splice ends and small diameter conductor pins the unit steps closer to achieving greater p:v ratios up to 2500:120 (21 amps) as a standard maximum. Auxiliary cooling and specialized conductor materials are required to achieve greater ratios so that the conductor pins do not overheat and melt making the unit difficult to commercialize and produce. With the low voltages the naturally occurring oxide layers developing between the resistance wire and the slide splice create a resistive break causing the unit to lose continuity after several hours of operation. 
     SUMMARY 
     Prior to the present invention, designing a practical compacted sheathed resistance heating element for low voltage-high power systems was not possible in a spatially practical single circuit design. With the advent of larger more powerful on-board power systems in all types of vehicles and shipboard processes, including electro-chemical battery supplies, fuel cells and hybridized electrical systems there is an increased capability associated with what is considered standard power overhead. The new systems make possible the use of resistive heating loads to replace the loss of internal combustion engines which would commonly produce waste energy in the form of heat to provide cabin heating. Power packs capable of large electrical discharge to produce heat for increasing the latent voltages seen in electro-chemical batteries or fuel cell systems which naturally produce greater potential at elevated temperatures. 
     The current invention also allows for a natural thermal management of the atypical current draw, whereas the leads will not require additional or specially constructed cooling to keep them within customary tolerance. These atypical current draws are not uncommonly up to 250 amps per circuit, whereas the source voltage is a nominal 24 volts and the power output is 6 kW, this circuit would yield a required resistive level of 0.096. 
     Embodiments of the invention significantly overcome such deficiencies and provide mechanisms and techniques that provide an axial resistance sheathed heater. The features of the invention, as explained herein, may be employed in devices such as those manufactured by Infinity Fluids Corp. of Sturbridge, Mass. 
     Note that each of the different features, techniques, configurations, etc. discussed in this disclosure can be executed independently or in combination. Accordingly, the present invention can be embodied and viewed in many different ways. Also, note that this summary section herein does not specify every embodiment and/or incrementally novel aspect of the present disclosure or claimed invention. Instead, this summary only provides a preliminary discussion of different embodiments and corresponding points of novelty over conventional techniques. For additional details, elements, and/or possible perspectives (permutations) of the invention, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure as further discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. 
       The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  comprises a cross-sectional view of a first embodiment of an axial resistance sheathed heater in accordance with embodiments of the invention; 
         FIG. 2  comprises a cross-sectional end view of the axial resistance sheathed heater of  FIG. 1  prior to reduction in accordance with embodiments of the invention; 
         FIG. 3  comprises a cross-sectional end view of the axial resistance sheathed heater of  FIG. 1  after reduction in accordance with embodiments of the invention; 
         FIG. 4  comprises a cross-sectional view of a second embodiment of an axial resistance sheathed heater in accordance with embodiments of the invention; 
         FIG. 5  comprises a cross-sectional end view of the axial resistance sheathed heater of  FIG. 4  prior to reduction in accordance with embodiments of the invention; and 
         FIG. 6  comprises a cross-sectional end view of the axial resistance sheathed heater of  FIG. 4  after reduction in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the electric heating industry there are many common designs which allow for customary heating of processes where higher voltages and large power production is required with standard sheath style compacted heater elements. Standard voltages from 90-575 volts are compensated for with higher resistances and increased sheath diameters. This also helps to mitigate the current flow across the element by increasing the potential across the circuit the natural response is to decrease the current flow. These designs are not as useful when lower voltages and greater powers are required as the lengths required to achieve lower power density makes them implausible to produce with any practical design. There are notable exceptions which address the lower resistances with greater surface areas to decrease the power density across the circuit like U.S. Pat. No. 6,456,785 issued to Evans, however this design fails to account for the greater amperages while maintaining power levels at lower voltages. The limiting factor is the cross sectional limitation of the splice, this does not allow large amperage flows across the circuit without causing the conductor pin and the slide splice to become too hot for sustainable application due to the inherent diameter restrictions. 
     With the new design, large power scheduling, decreased resistive requirements and non-standard amperage flows are overcome by the inherent design of the present invention. The present invention uses a bored conductor rod made from very low resistance metal or alloy, nickel 200, carbon alloy metals, copper alloy, etc. or larger diameter reduced tubing with greater cross section, allowing it to carry the substantial amperage loads associated with these low potential high output applications. These loads become exacerbated by the low-level voltage supply commonly seen in on board systems such as marine, automotive, space and military applications. It also allows the element to accommodate the large amperage flows associated with lower voltage higher amperage applications, such as marine. 
     Referring now to  FIGS. 1-3 , a first embodiment of an axial resistance sheathed heater  10  is shown. Heater  10  includes a conductor rod  14  of greater diameter which is then reduced in diameter over the outside of the resistance wire  16  or joined with metal addition, overcomes the natural continuity breaking oxide buildup potential, creating an indefinitely stable circuit. Carrying this concentric reduced diameter conductor rod  14  out of the exposed ends of retaining sheath  12  allows for very high amp capacity and reduces the possibility of further resistive breaks in the conductor legs at elevated amperage and temperatures, characteristics without the use of specialized materials or auxiliary cooling required as to not overheat and melt the conductor rods. By using the present invention achieving greater r:p ratios up to @5000:24 (208 amps) as a standard maximum is achievable and stable with non-auxiliary cooled conductor rods. This element would then be set into a flow housing exposing the naturally heated portion of the heater to the fluid or flow stream. The non-heated section would be isolated through a feed through device exposing the terminal/cold legs of the heater to ambient conditions where an operator or electrician would be capable of servicing the unit. 
     The present invention entails the use several components some standard materials found in customary heater product design, such as the dielectric heat transfer material  22  (e.g., Magnesium Oxide granules), used to envelop the resistance wire  16  and shield it from contact with the retaining sheath  12 . The resistance wire is comprised of a material such as nickel chromium wire, or suitable resistance wire or ribbon material such as stainless steel, alumel, nickel etc. Suitable retaining sheath  12  materials which maintain the ability to be reduced in diameter for the compaction process, mostly this material will be stainless steels, copper, alloy 800 etc. Low resistance machinable conductor leads  18 , manufactured from carbon/alloy steels, copper, brass etc. 
     These components are assembled in such a manner that a low ohm, high amperage heater can safely operate without the requirement of the non-fluid contact conductor ends being cooled by separate process or stream. 
     The present invention will have an axial resistance wire  16  embedded within a tubular retaining sheath  12 . This resistance wire  16  is selected to achieve a given resistance according to both the wattage and voltage being applied to it in the process. The resistance wire  16  is introduced by a high amperage conductor rod or tube  14 . The conductor rod  14  is reduced or affixed to the resistance rod/wire  16  prior to the introduction of the dielectric material  22 . The connection of the resistance wire to the rod may be achieved by having mating threads on each which are mated together or by standard metal joining techniques (including but not limited to welding, brazing, soldering or the like). The dielectric material  22  may be in the form of cast or extruded or granule spacing bodies. The tubular retaining sheath  12  is positioned over the entire length of the resistance wire  16  and major portion of the conductor rods  14 . The conductor rods  14  will extend beyond the boundary edge of the sheath  12  so that the heater circuit may be electrified after final manufacturing. The dielectric heat transfer material  22  is used to surround the resistive wire  16  within the retaining sheath  12  such that the resistive wire  16  is not in contact with the tubular retaining sheath  12 . The entire length of the tubular sheath  12 , dielectric heat transfer material  22  and the resistive wire  16  will be reduced in diameter by convention roll or rotary reduction technology. The heater  10  in some instances will not need to be reduced assuming the proper casting material or dielectric materials are selected and implemented.  FIG. 2  shows the heater of  FIG. 1  before the compacting process, and  FIG. 3  shows the heater of  FIG. 1  after the compacting process. 
       FIGS. 4 ,  5  and  6  are similar to  FIGS. 1 ,  2  and  3  respectively, except that in the embodiment of the heater  30  shown in  FIGS. 3 ,  4  and  5  the conductor rods  24  have a bore extending the length of the rod, whereas the conductor rods  14  of the heater  10  shown in  FIG. 1  have a bore extending only partially therein. 
     Unless otherwise stated, use of the word “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems. 
     Throughout the entirety of the present disclosure, use of the articles “a” or “an” to modify a noun may be understood to be used for convenience and to include one, or more than one of the modified noun, unless otherwise specifically stated. 
     Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, may be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein. 
     Although the methods and systems have been described relative to a specific embodiment thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, may be made by those skilled in the art. 
     Having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used. Accordingly, it is submitted that that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims.