Abstract:
A device for separating liquid particles from an entraining gas or vapor stream. The device employs mechanical centrifugal forces to concentrate liquid droplets in a limited space for further extraction from the gas flow using an electrical field and an electrically charged collecting surface whereby the particles are attracted to and deposited on the surface for further extraction by the gas flow without reintrainment of the liquid back into the vapor stream. The device is constructed to provide an area of low gas velocity for removing the liquid from the device.

Description:
PRIORITY 
     Applicants claim priority based on their Provisional Patent Application filed Aug. 15, 2000 having Ser. No. 60/225,321. 
    
    
     BACKGROUND 
     Many types of industrial, commercial and even residential technical processes and apparatuses have vapor or gaseous flow streams in which liquid particles of various sizes are entrained. In some of these, the presence of the liquid particles negatively affects the apparatus longevity, the apparatus efficiency or possibly even human health. 
     The following paragraphs describe examples of such systems and such processes where the invention described and claimed herein can profitably be employed. 
     Air compressed by air compressors and subsequently cooled frequently has water particles entrained with the air. In one application the water particles enter tools causing corrosion and bearing damage. Other applications find the water separating in a compressed air reservoir or tank where the pooled water, if not drained, causes corrosion that weakens the tank walls, leading to potential catastrophic failure. 
     Refrigeration systems employ compressors lubricated by oils that, in varying amounts are always entrained with the compressed refrigerant discharged by the compressor. The oil lost from the compressor, if not replaced, can lead to compressor destruction from lack of lubrication. The oil conveyed through the system also causes loss of heat transfer capability in both the evaporator and the condenser. 
     Oil return in miscible oil-refrigerant systems is generally reasonably reliable because the viscosity of oil conveyed within the system has been lowered by a solution of the refrigerant into the miscible oil. By contrast, oil return in systems employing an immiscible oil-refrigerant pair is much less reliable because the solubility of the refrigerant in the oil is slight and therefore the oil retains its original higher viscosity making flow much less certain. While the system piping can be designed to provide sufficiently high vapor velocities to achieve reasonably satisfactory oil flow, there is a penalty of higher gas pressure drop resulting in reduced system efficiencies. In such refrigeration systems employing immiscible refrigerant-lubricant pairs, discharge line oil separators having the highest efficiencies provide a definite advantage. Moreover, drops of liquid refrigerant in the inlet of a refrigerant vapor pump or compressor can cause damage to the compressor. Therefore, such damage must be avoided by preventing liquid drops of a refrigerant from entering into the compressor inlet. 
     Comfort air conditioning systems lower air temperature and thereby cause moisture condensation. Some of the condensed moisture is carried along with the cooled airstream into the cooled space, thereby causing discomfort, damage to fabrics and furniture and damage to sensitive electronic equipment, where these are located within the cooled space. 
     PRIOR ART 
     To cope with these problems or other problems arising from liquid carry over in vapor streams, many types and designs of mechanical separators have been designed and many are offered commercially for specific uses. The following types are primarily descriptive of those available for use in refrigeration systems to minimize oil carryover in the compressor discharge stream. Some simply reduce the vapor velocity so that liquid particles settle out. Others swirl the gas to provide at least partial centrifugal separation, some provide baffles to secure separation by impingement, some provide fills or meshes which filter or otherwise trap liquid particles on the meshes or in the mesh interstices. However, all these designs have the fault that very small oil particles and liquid droplets escape through the separator and are carried into the refrigeration piping. Further, no special oil separator designs are suggested or provided for immiscible oil-refrigerant systems. 
     OBJECTS OF THE INVENTION 
     Objectives of this invention are focused on enhancing efficiency of liquid particle separation from a flowing vapor stream using electrical forces alone or a combination of electrical forces and centrifugal forces. The electrical forces are variously known as Electrostatic (ES) when applied to static situations and Electrohydrodynamic (EHD) when applied to situations involving their effects on moving fluids and on the solid and liquid particles carried by such moving fluids. 
     In accordance with a first objective, the invention provides separation of liquid droplets from a vapor/gas flow (or flow stream) by a system of electrically charged electrodes and electrical fields associated with those electrodes. 
     In accordance with a second objective, the invention provides a liquid/gas separator in which centrifugal forces are used to concentrate liquid drops close to a collecting electrode. 
     In accordance with a third objective, the invention provides electrical charging of liquid droplets in a gas flow stream by a first electrode. 
     In accordance with a fourth objective, the invention provides collection of liquid droplets on the surface of a second electrode within the gas flow stream. 
     In accordance with a fifth objective, the invention provides separation of liquid droplets from a vapor/gas stream by moving liquid droplets collected on the surface of the second electrode along the surface of the electrode from a region of higher vapor velocity to a region of lower vapor velocity. 
     Thus, the invention combines a mechanical centrifugal concentration of liquid droplets with electrical separation of said liquid droplets from the gas flow combined with removal of the separated particles from a region of higher vapor velocity to a region of lower vapor velocity, thereby minimizing reentrainment of the removed particles into the flow stream. 
     In accordance with a sixth objective, the invention provides a device for modifying the initially straight vapor flow into a twisted one in order to subject the liquid particles to a centrifugal force whereby the liquid droplets are concentrated close to the surface of the second collecting electrode. 
     In accordance with a seventh objective, the invention provides the second collecting electrode with an electrical field or potential of a character designed to attract liquid particles charged by the first electrode. 
     In accordance with a eighth objective, the invention provides a combination of charging and collecting electrodes in series. 
     Further objectives include providing a highly efficient device for separating liquid particles from a flowing vapor stream. 
     Providing such a device that is mechanically simple and easy to fabricate. 
     Providing such a device that employs means for imparting a high electrical potential or charge of a first polarity to the gas stream and the liquid particles entrained with the gas stream. 
     Providing such a device where the polarity of the electrical potential is uni-polar, that is non-alternating. 
     Providing such a device where the potential imparting means is substantially adjacent the device inlet. 
     To provide such a device having charged means of a second polarity for attracting the particles charged with the first polarity. 
     To provide such a device where the particle attracting means includes a cylindrical flow means having an electrical potential substantially equal to and of opposite polarity to the potential applied to the particles. 
     To provide such a device including at least two coaxial spaced apart cylindrical flow means. 
     To provide such a device including seriatim in the vapor flow stream a first electrode having a first polarity for initially charging liquid particles, a second electrode having a second opposite polarity for collecting some particles, a third electrode for charging remaining particles with the second polarity and a fourth electrode having the first polarity for attracting substantially all the remaining particles. 
     SUMMARY OF THE INVENTION 
     A device for separating liquid particles from a flowing gas stream, the device comprising seriatim: an inlet for receiving the liquid bearing gas stream, an element positioned in the flow stream bearing a signed electrical charge for charging the gas borne liquid particles, a second element positioned in the flow stream bearing an oppositely signed electric charge for attracting and receiving the liquid particles and conveying said particles out of the gas flow stream. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section of an elementary device employing the principle of the invention. 
     FIG. 2A is a section of a single stage separator of the invention showing details of construction. 
     FIG. 2B is a section of a receiving electrode of the device of FIG. 2A showing modifications of the shape of the outlet end. 
     FIG. 2C is a section of a part of the device of FIG. 2A showing all plastic construction with a metallic insert as the secondary collecting electrode and a flow device for producing a rotating flow over the secondary electrode. 
     FIG. 2D is a top view of the flow rotating device of FIG.  2 C. 
     FIG. 3 is a section of a two-stage embodiment of the invention. 
     FIGS. 4A,  4 B and  4 C show three constructions of a flow rotating device. 
     FIG. 5 is a schematic piping diagram of a compression type refrigeration system including identification of specific locations for application of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a crossection of a simplified device illustrating a principle of the invention. Pairs of components having opposite electrical charges are shown as operative elements. While the charged element most subject to the vapor-liquid mixture entering the separator is generally described herein for convenience as having a negative charge and the collecting element as having the positive charge, it should be understood that reverse polarities may be required for effective operation with other liquids and vapors and that the reversal of electrode polarities is secured simply by interchanging the connecting leads. 
     Electrohydrodynamic (EHD) separator  20  has an outer metallic shell  21  having an inlet  22  for flow of a mixture of vapor with entrained liquid particles having a range of sizes to be separated. The individual particles are not separately shown in the figures because of their small size. Positioned in the path of the liquid bearing vapor stream entering inlet  22  is an electrical charging element  24  connected to a high voltage source (not shown) by wire or conductor  26  that conveys a negative charge to element  24 . The inlet charging element  24  is typically in the form of a metallic screen through which the vapor-liquid mixture must pass. Separator  20  includes a vapor outlet  42  for flow of substantially liquid-free vapor and a liquid outlet  40  for flow of the separated liquid. Within shell  21  there is a more or less centrally positioned metallic collector tube  32  having a bottom closure  30 . Collector tube  32  is electrically charged with a high voltage having a polarity equal in potential or voltage but opposite in polarity to the electrical charge applied to inlet charging element  24  by the same high voltage source employed to apply the electrical charge to inlet element  24 . The bottom closure  30  has positioned therein at least one orifice  34  to allow liquid separated from the vapor flow stream that flows to the bottom of the collector tube  32  to freely exit collector tube  32  and thereby flow into the bottom of shell  21 . Separated liquid reaching the bottom of shell  21  flows to liquid outlet  40  and exits the separator therefrom. Because the vapor velocities within collector tube  32  may be high, it is likely that much of the separated liquid will not flow to the bottom  30  of the collector  32  but instead will be frictionally dragged by the rapidly moving vapor to the upper edge  38  of the collector tube. There, the separated liquid flows over the collector tube edge  38  via flow stream  36  and flows downward by gravity to the exterior bottom  30  of collector tube  32  from which it drops into the bottom of shell  21 , thence to liquid connection  40 . The vapor flow outlet  42  from the separator  20  is positioned at an upper level of the separator shell  21  thereby assuring substantially zero vapor flow around the exterior of collector tube  32  since a significant vapor velocity around the outside of collector tube  32  would interfere with liquid movement down the exterior of collector tube  32 . 
     Because the collector tube  32  is designed to be electrically charged, it is electrically separated or insulated from the shell  21  and from the separator inlet  22  by insulating connector  23 . In another embodiment there is no insulating connector  23  and the shell  21  and collector  32  are at ground potential. In this embodiment, only charging grid  26  is at a high potential with respect to the shell  21 , the collector tube  32  and ground. 
     Within the separator, flow inlet  22  is positioned an electrically charged grid  24  having an electrical connector  26  for connection to a high voltage generator. Collector tube  32  has electrical connection  28  for connection to a second pole of the high voltage generator. Construction of high voltage generators is well known to the electronics art. Examples of direct current high voltage generators are found in color television receivers utilizing cathode ray tubes, in color computer monitors having cathode ray tubes and many other household and commercial appliances. Typically such high voltage generators employ fly-back transformers and high voltage rectifiers but other constructions including high voltage generating transformers such as Tesla coils and static electricity generators are well known. 
     Typically, a direct current (DC) high voltage generator has terminals of positive and a negative polarity. While the flow inlet electrode  24  will here be specified as being connected to the negative terminal of the HV generator and the collector  32  to the positive terminal, the simplicity of reversing the connections to the generator and thereby the polarities of the terminals indicates that both polarities be tried to determine the most effective for each vapor-liquid combination. 
     In FIG. 2A (with reference to FIG. 5) there is displayed a crossectional view of a practical EHD separator  50  employing principles of the invention. In FIG. 2A separator  50  includes enclosing shell  51  that is most frequently of metallic construction. Typical shell constructional materials include copper and steel. Material selections depend on the temperatures and pressures of the liquid laden vapor entering the separator  50 . For refrigeration systems (FIG. 5) employing HCFC-22 and mineral oil, steel is generally the preferred material for separators intended for application in the hot, high pressure discharge line  102  (location D) for removal of oil discharged by the compressor along with the refrigerant vapor. The oil removed by the discharge line separator is then returned to compressor  100 . The discharge line conveys the hot gas from compressor  100  to condenser  104  where the vapor is cooled by air circulated by fan  106 . The condenser  104  cools and condenses the hot discharge gas to a liquid that is circulated to the evaporator  112  through liquid line  108  and expansion device  110 . 
     At suction location S in FIG. 5, by contrast, copper is the preferred shell  51  material for CFC, HCFC and HFC refrigerants. That is because the low pressure, relatively cold, suction conduit  116  (at location S) is subject to condensation of moisture from the atmosphere. The function of the separator  50  applied at location S is for removal of potentially damaging liquid refrigerant particles attempting to reach the compressor  100 . The liquid refrigerant borne by the cold suction stream can be emitted accidentally or intentionally from evaporator  112  over which air is circulated by fan  114  or from other sources. 
     Continuing reference to FIG. 2A, The collector tube  69  is preferably formed of copper or steel or other highly conductive material. 
     A second preferred construction shown in FIG. 2C provides support tube  77  formed of electrically insulating plastic having a conductive coating  78  of copper plated at least on its interior to function as the collector surface. 
     Inlet fitting  62  is adapted for connection to receive the flow of gas or vapor carrying the liquid particles to be removed by separator  50 . Within shell  51  are electrically insulating plastic or resin structures  52  and  58 . Both are formed of plastic material suited to the application. For service in a hot compressor discharge line the plastics should be of the thermosetting type or of a thermoplastic type specially designed to be stable under temperature conditions as high as 400F. Alternate supporting materials are ceramics. For relatively cool suction service, ordinary thermoplastics would be satisfactory. In other embodiments, both plastic structures  52  and  58  can be molded in a single piece. 
     Plastic element  52  performs several functions: It provides an interior flow passage for the vapor-liquid mixture to collector tube  69 ; It provides mechanical support for the collector tube  69 ; It provides material within which liquid flow passage  54  is formed for flow of separated liquid to liquid outlet  56  and it provides both an electrically insulating matrix for support of high voltage grid  64  that serves to electrically charge inflowing liquid particles entrained with vapor stream entering flow inlet  62  and it serves to support and electrically insulate conductor  66  that communicates the electrical potential from the external high voltage power supply to the grid  64 . 
     Plastic element  58  serves as electrical insulator and mechanical support and sealant for conductor  68  that communicates an electrical potential, having an opposite polarity from the polarity of grid  64 , to the collector tube  69 . Flow outlet  72  provides connection means between the separator  50  and vapor flow conduits external of the separator. Flow outlet  72  is positioned to ensure minimum or zero vapor velocity around the outside of collector tube  69 . 
     Liquid particles entrained with vapor entering separator inlet  62 , having been electrically charged with a polarity by passage through and contact with high voltage grid  64  are attracted to and deposited on the opposite polarity electrically charged collector tube  69 . The collected liquid particles are conveyed upward along the interior of collector tube  69  and flow over the outlet end of tube  69  in path  60  and down the outside periphery of tube  69  to liquid flow outlet conduit  54 . Very high vapor velocities within collector tube  69  can cause reentrainment of collected liquid particles at a sharp (small radius) end  70  of tube  69  collected on the interior of collector tube  69 . 
     FIG. 2B shows two modifications in the shape of the outlet end of tube  69 . In the right-hand modification, the end  71  has been rolled over into the shape  73  whose edge  74  does not contact the exterior of tube  69 . In the left-hand modification the end  71  of tube  69  has been rolled over into shape  75  so that the end  74 B of the rolled-over portion contacts the exterior of tube  69 . Both these constructions provide a larger radius at the outlet flow end  71  of collecting tube  69  thereby discouraging reentrainment of collected liquid into the vapor stream leaving collecting tube  69 . 
     Separator vapor outlet  72  is positioned so that liquid flowing down the outside of tube  69  does so in volume  63  within which there is essentially no vapor flow. This allows separated liquid to flow unimpeded to the liquid outlet conduit  54 . 
     FIG. 2C illustrates the construction of the collection portion of any version of the separator where the collector support tube  77  is part of the molded plastic construction and the collecting portion comprises a plated conducting layer  78 . In FIG. 2C only plastic part  52  is shown. High voltage connection  68  is connected to the metallic interior layer  78  by the connecting electrode and either a mechanical or soldered connection. 
     The effectiveness of a charged collecting element in attracting and separating oppositely charged entrained liquid particles from a flow stream is strongly related to the proximity of the particles to the collecting element. The disclosed invention employs centrifugal principles to move the liquid particles, desired to be separated from the vapor flow stream, close to the oppositely charged separating element. Referring again to FIGS. 2C and 2D and FIGS. 4A and 4B there is employed a flow rotating element  46  positioned in the flow stream between the initial particle charging element  64  and the oppositely charged collecting element  78  to secure the desired centrifugal effect. 
     The flow rotating element  46  comprises a cylindrical plug with an axis parallel to the general vapor flow direction. Plug  46  has formed within it one or more conduits or passages  48  positioned or oriented at an angle to the general flow direction  47  to cause rotation of the vapor stream and entrained liquid particles leaving plug  46  and entering collector tube  78 . The rotation of the vapor stream creates a centrifugal effect that causes the liquid particles to approach more closely the inner surface of collecting electrode  78 . 
     In FIG. 3 there is shown a two-stage embodiment  80  of the invention in which the vapor flow, having been partially depleted of its entrained liquid particles, is exposed to a reversed potential whereby the remaining liquid particles are substantially removed. In FIG. 3 the two stage separator  80  has a shell  81  substantially similar to the shell  51  of FIG. 2A except longer. The lower portion of the shell and its interior are substantially identical to the interior construction and operation of the separator  50  of FIG.  2 A and the elements have the same numbers for corresponding parts. However, plastic portion  58  of FIG. 2A has been extended and now labeled  82 . The element  82  has been provided with a supporting flange portion extended toward the shell axis for supporting a secondary collector tube  88 . The collector tube  88  may be a metal tube or a metallic layer  78  applied to the interior of a plastic tube  77 . The flange portion of the plastic part  82  has been provided with at least one flow channel  84  for flow of separated liquid. Liquid collected within the secondary collector tube  88  flows over the top edge of the secondary collector tube  88  in flow path  86  and flows to the liquid outlet  56  of the separator through the paths already identified. The lower portion of secondary collector tube  88  is formed into a flared portion so that liquid that flows down the tube  88  on flow stoppage drops into still volume  63  for flow to the separator outlet  56 . 
     Parts expected to have high relative electrical potentials imposed between them, such as tube  88  and both grid  90  and primary collector tube  69  should be separated by a distance sufficient to prevent electrical arc-over. This is especially important when the separator is to be applied in suction line or other very low pressure applications. 
     In another embodiment of the invention, the secondary collector tube  88  is formed with a larger inside diameter than the primary collector tube  69 , thereby providing a lower vapor velocity to facilitate liquid separation. Secondary charged grid  90  is positioned at the outlet of primary collector tube  69  and is connected to the same high voltage source so the secondary grid  90  has the same electrical polarity as primary collector tube  69 . Secondary charged grid  90  has the function of restoring a high level of electrical potential to yet unseparated liquid particles leaving primary collector tube  69 . Secondary collector tube  88  is electrically connected by connector  94  to the same electrical connection on the high voltage source as connector  66  thereby providing it with an electrical charge highly opposite to the electrical charge imposed on the remaining liquid particle by grid  90 . 
     In other embodiments, the connection to grid  90  is made to the same polarity electrical supply as inlet grid  64  and the connection to secondary collector tube  88  is made to the same polarity as the primary collector tube  69 . 
     In another embodiment of the invention, secondary collector  88  is connected to a potential source that generates a greater potential difference between the grid  90  and collector  88  than the potential between the primary grid  64  and the primary collector  69 . 
     Referring to FIG. 4A there is shown for improved clarity an isometric, partly cut away, view of the vapor rotating element  46  shown in FIGS. 2C and 2D. Inclined angled flow passages  48  are formed at an angle  49  with the primary flow direction at the flow inlet of element  46 . While the passages  48  are shown straight, they may be formed with increasing angle to the direction of the primary flow direction. 
     FIG. 4B illustrates a second embodiment of the flow rotating element identified here as  96 . Vanes  99  are provided at an angle  96  to the flow direction at the inlet of the device. While the vanes  99  are shown formed with curvature, in other embodiments, they are formed at a fixed angle to the general flow direction  47 . 
     FIG. 4C illustrates an alternate embodiment of the invention employing a spiral collecting tube that combines the collecting function as an electrically charged tube having a charge opposite that supplied to the liquid particles by inlet electrode  64  and a swirl device for generating a centrifugal force on the particles to be separated, thereby forcing them into closer proximity to the charged collecting element. The spiral charged collecting tube  118  has inlet  120  that is positioned at  120 A (FIG. 2A) in this alternate embodiment. The outlet  122  of the spiral collecting tube  118  functions just like outlet  70  of straight collecting tube  69  (FIG. 2A) emitting the substantially particle-free vapor for flow to separator outlet  72  and allowing the flow of the separated liquid over the edge of the outlet  122  and down the exterior, in a volume  63  having substantially zero vapor velocity. 
     While the vapor velocity in the collector tube depends on the refrigerant type and operating condition, typical dimensions (FIG. 1) for a 12,000 Btu/hr system employing R-134a are: 
     Inlet and outlet fittings  22 , 42 ; 0.75 in. inside diameter. Collector tube  32 , 1.25 inches inside diameter; 4 inches length; 
     Potential difference between primary electrode  24  and collecting electrode  32 ; 5 to 20 or more kilovolts. 
     Referring again to FIGS. 2A,  2 C and  4 A, for the same system and refrigerant, the inside diameter of inlet  62  and collector  69  is 0.74 inches; the length of collector tube  69  is  6  inches. The inside diameter of the angled swirl producing conduits  48  is 0.38 inches. 
     While the drawings and related text disclose that the interior of the charged collector tube  69  acts as the collecting surface, in other embodiments, the liquid bearing flow stream is directed over the exterior surface of collector tube  69  and the collected oil flows over the top  70  of the collector tube  69  into the interior of tube  69  from which it is drained away. 
     From the foregoing description, it can be seen that the present invention comprises an advanced liquid-gas separator employing both electrohydrodynamic principles and centrifugal separation principles useable in refrigeration systems, in separators for liquid water from air, from oil in engine exhausts and for other purposes. It will be appreciated by those skilled in the art that changes could be made to the embodiments described in the foregoing description without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment or embodiments disclosed, but is intended to cover all elements and modifications and equivalents thereof which are within the scope and spirit of the invention as defined by the appended claims and this disclosure.