Abstract:
The invention is for an apparatus and method for pumping of electrically conductive liquids such as liquid metals and electrolytes. The apparatus of the present invention is a self-contained direct current (DC) magneto-hydrodynamic (MHD) pump assembly formed by an upper core assembly, lower core assembly, and a flow channel. The flow channel is formed when the upper core assembly and the lower core assembly are put together. Permanent magnets are used to produce magnetic field inside the flow channel. When the flow channel is filled with electrically conductive liquid, the liquid comes into contact with electrodes within the lower core assembly. The electrodes may be used to draw electric current through the liquid, thereby generating MHD force onto it. As a result, a pressure may be generated within the liquid and/or the liquid may be caused to flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional patent applications U.S. Ser. No. 61/849,723, filed on Feb. 2, 2013 and entitled “THERMAL MANAGEMENT FOR SOLID STATE HIGH-POWER ELECTRONICS,” and U.S. Ser. No. 61/855,824, filed on May 25, 2013 and entitled “MAGNETOHYDRODYNAMIC ACTUATOR,” the entire contents of all of which are hereby expressly incorporated by reference. This patent application is a continuation-in-part patent application of: U.S. Ser. No. 13/986,084 filed on Mar. 30, 2013 and entitled THERMAL MANAGEMENT DEVICE FOR HIGH-HEAT FLUX ELECTRONICS; the entire contents of which are hereby expressly incorporated by reference. 
     
    
     GOVERNMENT RIGHTS NOTICE 
       [0002]    This invention was made with Government support under Contract No. FA9453-10-C-0061 awarded by the U.S. Air Force. The Government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates generally to a magnetohydrodynamic (MHD) pump and more specifically to a direct current MHD pump. 
       BACKGROUND OF THE INVENTION 
       [0004]    The subject invention is an apparatus and a method for pumping electrically conductive liquids. 
         [0005]    Many liquids are electrically conductive. A variety of electrically conductive liquids, such as certain liquid metals and certain aqueous electrolytes may be pumped to achieve specific desired outcome such as thermal management or actuation of components. 
         [0006]    It is well known in the art that electrically conductive liquids may be pumped by magnetohydrodynamic (MHD) effect. Pumps operating in accordance with the MHD effect are known as MHD pumps. One advantage of MHD pumps is that they may not require any moving components. MHD pumps can be generally classified according to the nature of the electric current used for their operation as 1) direct current (DC) MHD pumps and 2) alternating current (AC) MHD pumps. DC MHD pumps may have substantially lower power consumption because permanent magnets may be used to generate the required magnetic field. 
         [0007]    Prior art MHD pumps show significant complexity, which makes it challenging to scale them down in size to meet the compactness criteria required by many applications. Other challenges include corrosiveness of many liquid metals and electrolytes. MHD pumps are also susceptible to deleterious MHD effects such a Hartman layers, which reduce effectiveness. In addition, magnetic field produced permanent magnets in a gap of a given size is known to fall of as the magnet size is reduce, thus limiting the MHD pump performance. The static pressure “p” producible by an MHD pump may be theoretically expressed as p=B.I/h, where “B” is magnetic flux density (measured, e.g., in Tesla), “I” is electric current (measured, e.g., in Amperes), and “h” is the vertical height of the flow channel inside the MHD pump (measured, e.g., in meters). This formula offers the designer a variety of trades between p, B, I, and h. For example, to produce a target pressure value “p”, one may select a large value of magnetic flux density “B” (which may be produced by permanent magnet with no energy added) to conserve electric current “I” while maintaining the channel height “h” within practical range. 
         [0008]    In summary, prior art does not teach an MHD pump capable of producing high pressure at high flow rate that is also efficient, compact, simple, and easy to produce. It is against this background that the significant improvements and advancements of the present invention have taken place. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides an MHD pump assembly for pumping of electrically conductive liquids. 
         [0010]    In one preferred embodiment of the present invention, the MHD pump assembly comprises an upper core assembly, a lower core assembly, and a flow channel. The flow channel is formed by the upper core assembly and a lower core assembly when the two assemblies are put together. In particular, the upper core assembly and the lower core assembly are held together only by magnetic forces provided by permanent magnets within. The upper core assembly comprises a core structure, permanent magnet, and electrically insulating material. The lower core assembly comprises a core structure, permanent magnet, a pair of electrodes, and electrically insulating material. When the MHD pump assembly is formed, the core structures provide a low reluctance path for magnetic flux emanating from the permanent magnets to form a magnetic circuit, which passes through the flow channel. As a result, a very high magnetic flux density can be generated in the MHD pump flow channel between the electrodes. In addition, the core structures provide magnetic shielding to surrounding components. The permanent magnets are substantially wider than the electrodes to provide a substantially uniform magnetic flux density in the portion of the flow channel between the electrodes. This feature may allow the MHD pump assembly to operate at high efficiency. 
         [0011]    Accordingly, it is an object of the present invention to provide an MHD pump assembly for pumping of electrically conductive liquid. The MHD pump is capable of producing high pressure at high flow rate, while also being efficient, compact, simple, and suitable for large volume production. 
         [0012]    It is another object of the invention to provide means for pumping electrically conductive liquids. 
         [0013]    It is still another object of the invention to provide an MHD pump having very low stray magnetic field outside the pump volume. 
         [0014]    It is an additional object of the invention to provide an MHD pump robust to corrosion by gallium-based liquid metals. 
         [0015]    It is yet another object of the invention to provide an MHD pump with self-sealing capability. 
         [0016]    These and other objects of the present invention will become apparent upon a reading of the following specification and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an isometric view of the MHD pump in accordance with one embodiment of the invention. 
           [0018]      FIG. 2  is a cross-sectional view  2 - 2  of the MHD pump shown in  FIG. 1 . 
           [0019]      FIG. 3  is an isometric view of the upper core assembly. 
           [0020]      FIG. 4  is cross-sectional view  4 - 4  of the upper core assembly of  FIG. 3 . 
           [0021]      FIG. 5  is an isometric view of the upper core structure. 
           [0022]      FIG. 6  is an isometric view of the lower core assembly. 
           [0023]      FIG. 7  is a cross-sectional view  7 - 7  of the lower core assembly of  FIG. 6 . 
           [0024]      FIG. 8  is an isometric view of the lower core structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Selected embodiments of the present invention will now be explained with reference to drawings. In the drawings, identical components are provided with identical reference symbols in one or more of the figures. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses. 
         [0026]    Referring now to  FIG. 1 , there is shown an isometric view of the MHD pump assembly  10  in accordance with one embodiment of the subject invention generally comprising an upper core assembly  180 , a lower core assembly  182 , and a flow channel  104 . 
         [0027]    The flow channel  104  is formed by the upper core assembly  180  and the lower core assembly  182  when the two assemblies are put together.  FIG. 2  shows a cross-sectional view  2 - 2  of the MHD pump assembly shown in  FIG. 1  while exposing additional elements. The upper core assembly  180  is shown (flipped over) in  FIG. 3 .  FIG. 4  is a cross-sectional view  4 - 4  of the upper core assembly of  FIG. 3  showing an upper core structure  186  equipped with a magnet  128   a,  electrically insulating filler material  192   a,  and an electrically insulating film  198   a.  The upper core structure  186  (shown as a stand-alone component in  FIG. 5 ) is formed from a suitable ferromagnetic material capable of carrying magnetic flux at high flux density such as iron, steel, low carbon steel, core iron (e.g., Consumet® by Cartpenter Steel), substantially pure iron, nickel-iron alloys such as Hiperco®, or alike. The electrically insulating filler material  192   a  may be epoxy, plastic (e.g., Ultem®), ceramic potting compound, or other suitable material having good electrical insulating properties. The electrically insulating film  198   a  may be a suitable film formed from plastic (e.g., Mylar® or Kapton®), epoxy, epoxy paint or other material having good electrical insulating properties. The magnet  128   a  is a suitable permanent magnet magnetized through its large faces in a direction parallel to the broken line  181   a . The magnet  128   a  may be bonded to the upper core structure  186 . 
         [0028]    The lower core assembly  182  is shown in  FIG. 6 .  FIG. 7  is a cross-sectional view  7 - 7  of the lower core assembly of  FIG. 6  showing a lower core structure  190  equipped with a magnet  128   b,  electrically insulating filler material  192   b,  electrodes  130   a  and  130   b,  and an electrically insulating film  198   b.  The lower core structure  190  (shown as a stand-alone component in  FIG. 8 ) is formed from a suitable ferromagnetic material capable of carrying magnetic flux at high density such as iron, steel, low carbon steel, core iron (e.g., Consumet® by Cartpenter Steel), pure iron, nickel-iron alloys such as Hiperco®, or alike. The electrically insulating filler material  192   b  may be epoxy, or plastic (e.g., Ultem), ceramic potting compound, or other suitable material having good electrical insulating properties. The electrically insulating film  198   b  may be a suitable film formed from plastic (e.g., Mylar® or Kapton®), epoxy, epoxy paint, or other material having good electrical insulating properties. 
         [0029]    The lower core assembly  182  has a groove  188  designed to form a portion of the flow channel  104  when the MHD pump assembly  10  is formed. The groove  188  is formed by selected surfaces of the lower core structure  190 , electrically insulating filler material  192   b,  electrodes  130   a  and  130   b,  and the electrically insulating film  198   b.  The groove  188  has a width “W” and a height “H” ( FIG. 1 ). The width “W” and the height “H” may not have to be constant within the lower core assembly  182 . For example, the width “W” may be reduced between the electrodes  130   a  and  130   b.  Because the flow channel  104  is formed when the upper core assembly  180  and the lower core assembly  182  are put together, the width “W” and the height “H” of the flow channel  104  may be substantially same as those of the groove  188 . The magnet  128   b  is a suitable permanent magnet magnetized through its large faces in a direction parallel to the broken line  181   b . The magnet  128   b  may be bonded to the upper core structure  190 . 
         [0030]    The magnets  128   a  and  128   b  (see, e.g.,  FIGS. 2 ,  4  and  7 ) are suitable permanent magnets magnetized through their large faces in a direction parallel to the arrows  181   a  and  181   b , respectively. The magnets  128   a  and  128   b  are preferably rare earth permanent magnets formed from samarium-cobalt (SmCo) or from neodymium-iron-boron (NdFeB) materials. The magnetization of the magnets  128   a  and  128   b  should be arranged so that their magnetization vectors are substantially pointing in the same direction when the MHD pump assembly  10  ( FIG. 1 ) is formed. Because of the magnetization vector alignment, the upper core assembly  180  and the lower core assembly  182  attract each other. As a result, the MHD pump assembly  10  may be formed without any fasteners, thus allowing for simple construction and installation. 
         [0031]    The electrodes  130   a  and  130   b  are preferably made of tungsten, tantalum, or other suitable material having high electrical conductivity as well as robustness to erosion by electrical arc. Alternatively, the electrodes may be made of copper or copper alloy and they may be plated with a suitable refractory metal such as, but not limited to molybdenum, tungsten, tantalum, ruthenium, osmium, and iridium. The edge  152  of the electrodes facing the flow channel  104  may be curved (as shown in  FIG. 6 ) or it may be straight. Curved edge may make the electrode less susceptible to electrical arcing. 
         [0032]    The electrodes  130   a  and  130   b,  the insulating filler materials  192   a  and  192   b , and the insulating films  198   a  and  198   b  are preferably installed to prevent electrical contact between the electrodes and the upper core structure  196 , the lower core structure  190 , the magnet  128   a,  and the magnet  128   b.    
         [0033]    Preferably, the mating surfaces of the upper core assembly  180  and the lower core assembly  182  are fabricated so that upon forming the MHD pump assembly  10  with no additional seals are required. Alternatively, when the MHD pump assembly  10  is formed, a suitable adhesive or sealant (e.g., epoxy or cyanoacrylate adhesive) may be applied to the joints to seal the flow channel  104  and to prevent potential leakage of conductive liquid from the pump. 
         [0034]    It is important that all surfaces of AHS  10  that may come into contact with the liquid being pumped (such as liquid metal, electrolyte, or alike) be made of compatible materials. In particular, it is well know that liquid gallium and its alloys severely corrode many metals. Literature indicates that certain refractory metals such as tantalum, tungsten, and ruthenium may be stable in gallium and its alloys. See, for example, “Effects of Gallium on Materials at Elevated Temperatures,” by W.D. Wilkinson, Argonne National Laboratory Report ANL-5027, published by the U.S. Atomic Energy Commission (Aug. 1953). To protect against corrosion, vulnerable surfaces that may come into contact with the liquid metal coolant (for example portions of the body  102 ) may be coated with suitable protective film. Suitable protective coatings and films for copper parts (e.g., the body  102 ) may include sulfamate (electroless) nickel, electroplated ruthenium, titanium nitride (TiN), and diamond-like coating (DLC). Diamond-like coating may be obtained from Richter Precision in East Petersburg, Pa. The Applicant has determined that core structures  186  and  190  made of substantially pure iron or core iron (e.g., Consumet® by Cartpenter Steel) may not require a protective coating. Reduced need for protective coatings simplifies fabrication and reduces cost. 
         [0035]    In operation, the flow channel  104  of the MHD pump assembly  10  may be substantially filled with suitable electrically conductive liquid. The electrodes  130   a  and  130   b  may be electrically connected to the terminals of a source of direct electric current, such a battery or a power supply. For example, the electrode  130   a  may be electrically connected to a negative terminal (or the ground terminal) of the source of direct electric current, and the electrode  130   b  may be electrically connected to a positive terminal of the source of direct electric current. The liquid inside the flow channel  104  makes an electrical contact with the electrodes  130   a  and  130   b  and allows an electric current to flow from one electrode to another electrode. In particular, the current flows through the liquid metal located generally between the electrodes. Because the portion of the flow channel  104  between the electrodes is immersed in a magnetic field generated by the permanent magnets  128   a  and  128   b,  drawing of electric current though the liquid therein generates a force on the liquid. Such a force may be directed so as to flow the liquid inside the flow channel  104  or generate a pressure within. The direction of the electric current (as defined by the polarity of the electric current source) drawn though the liquid may be coordinated with the direction of the magnetic field generated by the magnets  128   a  and  128   b  to define the direction of liquid flow. 
         [0036]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” and “includes” and/or “including” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0037]    The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
         [0038]    The term “suitable,” as used herein, means having characteristics that are sufficient to produce a desired result. Suitability for the intended purpose can be determined by one of ordinary skill in the art using only routine experimentation. 
         [0039]    Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. In addition, the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. 
         [0040]    Different aspects of the invention may be combined in any suitable way. 
         [0041]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the present invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents. Thus, the scope of the present invention is not limited to the disclosed embodiments.