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This application claims the priority of provisional UK patent application no. 0000279.0 filed Jan. 8, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices and methods for reducing fluid pressure and velocity and enhancing fluid flow within a pipe or other flowbore. The devices and methods of the present invention have a particularly useful application in pipelines where crude oil or natural gas is flowed which contains abrasive agents. 
     2. Description of the Related Art 
     Production pipelines and conduits are used to transmit hydrocarbons, in the form of crude oil or natural gas, from a producing well to a storage facility or distribution point. One important aspect to the design for systems of these conduits is the ability of the conduits to manage fluid pressure and enhance the flow of fluid within the conduit. When hydrocarbons first leave the well and enter the conduit they are often under vary high pressure, and this pressure must be quickly and efficiently reduced. 
     A related problem is that the hydrocarbons, particularly natural gas, carry sand and other solids that will quickly abrade and/or clog flow reducing restrictions in the conduit. Efficient pressure reduction is necessary to preclude damage to the more vulnerable portions of the pipeline system. In addition, it is important that the pressure reduction means itself is highly resistant to abrasion and other wear damage that will be inflicted by the solids. 
     It would be desirable to have devices and methods that address the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     Arrangements are described wherein flow enhancing restrictors are located within a fluid conduit to provide pressure and velocity reduction as well as flow enhancement. The flow enhancers may be used in combination with a conventional choke valve or as a stand-alone pressure reduction means. Alternative exemplary embodiments for flow enhancers are described. Each of the flow enhancers has a generally cylindrical base with at least one fluid passage disposed therethrough. Each of the flow enhancers also provides a dome that projects upwardly from the center of the base to assist in directing fluid flow and receiving the abrasive forces associated with the fluid. The dome, in each of the embodiments, assists in directing fluid into the fluid passages of the flow enhancer and also provides a wear surface upon which abrasives are recieved. 
     It is an object of this invention to provide an efficient and long-lasting method of achieving a pressure drop within a fluid conduit, particularly where highly abrasive fluids are being transmitted. It is a further object of this invention to provide a fluid flow enhancer device that is highly resistant to abrasive action. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of an exemplary choke valve of the type used within pipelines which incorporates a fluid flow enhancer constructed in accordance with the present invention. 
     FIG. 2 is an isometric view of a first embodiment for a fluid flow enhancer. 
     FIG. 3 is a side isometric view of a second embodiment for a fluid flow enhancer. 
     FIG. 4 is a further isometric view of the fluid flow enhancer illustrated in FIG.  3 . 
     FIG. 5 is an isometric view of a third, and most preferred, embodiment for a fluid flow enhancer constructed in accordance with the present invention. 
     FIG. 6 is a plan view of the fluid flow enhancer depicted in FIG.  5 . 
     FIG. 7 is a side cross-section of the fluid flow enhancer shown in FIGS. 5 and 6. 
     FIG. 8 illustrates staged enhancers located within a fluid flow conduit to achieve a greater pressure drop. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, there is shown an exemplary choke valve  10  that incorporates a fluid flow enhancer as contemplated by the present invention. The choke valve  10  includes a valve body  12  that is typically constructed of a strong and chemically resistant metal. The body  12  defines a fluid inlet  14  and fluid outlet  16  which are set at right angles to one another thereby providing an elbow configuration for the valve body  12 . 
     The fluid outlet  16  houses, at its upper end, a stem and tip assembly  20  which is concentrically located within a flow cage  22  that is set within the body  12 . The stem and tip assembly  20  may be moved linearly within the body  12  by a manual handwheel, via an automated control, or using other techniques known in the art. Linear movement of the stem and tip assembly  20  actuates the choke mechanism  23  of the choke valve  10 . The choke mechanism  23  is used to regulate fluid flow within the valve  10  and includes a tip member  26  and surrounding flow cage  22 . 
     The lower end of the stem and tip assembly  20  is secured by autofrettage at interface  24  to a tip member  26 . The tip member  26  is a substantially cylindrical piece having a central dome-shaped chamber  28 . The central chamber  28  is surrounded by a number of fluid flow openings within the tip member  26 . The fluid flow openings are of differing sizes and are positioned in mutual opposition to one another so that openings of equal sizes are located directly across from one another. For example, fluid flow openings  30  are of equal sizes and are located antagonistically from one another. The same is true of openings  32 . Openings  34  (one shown) and  36  (one shown) have the same arrangement. A pressure balance chamber  38  is defined within the domed geometry of the tip member  26  and the stem and tip assembly  20 . The chamber  28  has an enlarged lower opening  40  that is located across from the pressure balance chamber  38 . 
     The flow cage  22  radially surrounds the tip member  26  and is retained within the valve body  12  by a bonnet (not shown) onto a valve seat  46  at its lower end. A valve seat insert  48  is disposed within the valve seat  46 . The flow cage  22  is a tubular member that contains a plurality of radial fluid communication openings  50 , four of which are shown. The tip member  26  can be moved upwardly and downwardly within the body  12  by linear movement of the stem and tip assembly  20  to modulate fluid entry into the chamber  28 . Such rotation will align the fluid openings  49  in the flow cage  22  with various fluid openings  30 ,  32 ,  34 ,  36  in the tip member  26  to permit different flow rates into the choke mechanism  23 , as those of skill in the art will appreciate. 
     A fluid flow enhancer  50  is located within the fluid outlet  16  below the valve seat  46 . The flow enhancer  50  is retained within the outlet  16  by a pair of bushings  52  and  54  that are located concentrically on either side of it. Other retention means may also be used. It is pointed out that, while the described embodiment illustrates a flow enhancer  50  incorporated within the valve  10 , the flow enhancer might also be of the design of flow enhancer  50 ′ or  50 ″, which will be described shortly or another type of flow enhancer falling within the scope of the claims. 
     In operation, fluid enters the fluid inlet  14  and encounters the choke mechanism  23 . Fluid enters the fluid openings  49  of the flow cage  22  and one or more of the fluid openings of the tip member  26 . Because the fluid is under pressure, the opposing openings create opposing fluid jets within the chamber thereby effectively creating a fluid pressure drop. The fluid exits the choke mechanism  23  through the opening  40  and is directed along the fluid outlet  16  to the flow enhancer  50 . As the fluid passes through the fluid passages  62  of the flow enhancer  50 , a fluid pressure drop and fluid velocity reduction is achieved. If desired, there may be multiple flow enhancers  50  located in a stacked relation downstream from the choke mechanism  23 . 
     There is a particular advantage in locating one or more flow enhancers  50  immediately downstream from the choke mechanism  23 . Fluid velocities within the flow cage  22  and tip  26  will be reduced. The introduction of a pressure drop across the one or more enhancers  50  means that the pressure drop through the choke mechanism  23  is reduced. Therefore, the choke mechanism  23  is also subjected to less wear and abrasion from solids. When the flow enhancer  50  is included downstream of the choke mechanism  23 , adjustment will need to be made to the choke mechanism  23  to ensure adequate flow rate exits the flow enhancer  50 . In other words, the choke mechanism  23  will have to be opened somewhat to compensate for the pressure reduction across the flow enhancer  50 . 
     The structure of the exemplary fluid flow enhancer  50  is better understood with reference to FIG. 2 wherein this component is shown apart from the check valve  10  and its structure may be seen in greater detail. The flow enhancer  50  has a unitary body  58  that is formed of a strong material that is resistant to chemicals and mechanical abrasion. Tungsten carbide and precipitation-hardened stainless steel are two examples of suitable materials. The body  58  has a substantially cylindrical base  60  having a diameter that is sized to fit within the interior diameter of a desired conduit. A plurality of fluid passages  62  penetrate axially and completely through the base  60 . In current preferred embodiments, there are eight fluid passages  62 , although depending on flow conditions there may be more or fewer than that number. The diameter of the fluid passages must be sufficient at least for any solids that might be encountered to pass through the passages  62  without obstruction. Preferably, the passages  62  have a much greater diameter than necessary for that purpose. However, the diameter of the passages  62  is typically established to provide the pressure drop necessary across the flow enhancer. 
     A dome  64  projects upwardly from the center of the cylindrical base  60 . The dome  64  has a smaller diameter than the base  60  so that fluid may flow around the dome  64 . In this embodiment, the dome  64  includes a reduced diameter lower neck section  66  and an enlarged upper head section  68  having a radial outer surface  70  that is substantially flat. The upper head section  68  also presents a substantially flat upper surface  72 . 
     The geometry of the components of the flow enhancer body  52  is important in terms of its functions for flow control. As FIG. 1 indicates, fluid flow approaches the flow enhancer  50  from the upper end. Thus, the flat upper surface  72  advantageously encounters the majority of abrasive material that is carried in the fluid. Because the upper surface  72  is substantially flat, abrasive particles impinge normally to the surface  72 . Therefore, the amount of abrasion and wear upon the upper surface  72  and the flow enhancer body  52  as a whole is minimized. 
     FIGS. 3 and 4 depict an alternative embodiment for a fluid flow enhancer  50 ′. For clarity, like components among the alternative embodiments are numbered alike. In this embodiment, the dome  64 ′ has a tapered side wall  74  extending from the rounded upper surface  72 ′ downward to the base  60  so that the head section  68 ′ is smaller than the neck section  66 ′. There are indentations  78  in the tapered side wall  74  that increase in width but decrease in depth as the base  60  is approached. The indentations  78  extend upwardly from the side walls of the fluid passages  62  and, in use, provide an increased wear area upon which abrasives can act. This feature extends the life span of the fluid flow enhancer  50 ′ in resisting abrasion and wear around the openings  62 . A primary advantage to this embodiment is that wear patterns are more balanced as compared to the flow enhancer  50  described earlier because the radially internal portions of the fluid openings  62  of flow enhancer  50 ′ are provided a greater exposure to the passing fluid. Thus, wear upon the flow enhancer  50 ′ is more even, and the wear enhancer  50 ′ should not be required to be replaced as often. 
     FIGS. 5-7 illustrate a third embodiment for a fluid flow enhancer  50 ″ that is currently the most highly preferred version. Fluid flow enhancer  50 ″ includes a recessed central valley  80  that results in the base  60  presenting a raised peripheral rim  82 . The dome  64  projects upwardly from the recessed valley  80  but has a reduced height so that its rounded upper surface  72 ″ is approximately level with the top of the rim  82  (see FIG.  7 ). In this embodiment as well, the dome  64  has a reduced diameter head section  68 ″ and a neck section  66 ″ with a somewhat larger diameter, thereby resulting in a tapered side wall  74 . The advantage associated with this embodiment of fluid flow enhancer is that the wear patterns surrounding the inlets of the fluid passages  62  are the most balanced as between all three of the flow enhancers  50 ,  50 ′ and  50 ″. As a result, it is expected that this design will have the longest life span in operation. 
     FIG. 8 illustrates a pair of flow enhancers  50 ″ a  and  50 ″ b  positioned in a staged or tandem relation within a flow conduit  86 . It is noted that the flow conduit  86  may be representative of a location immediately downstream from a choke valve choke mechanism, such as the choke mechanism  23  described earlier. Alternatively, the flow conduit  86  may be representative of any location within a pipe or other fluid conduit wherein it is desired to reduce fluid pressure. In that case, the flow enhancers  50 ″ are used as a stand-alone measure for fluid pressure reduction. The lower end  88  of the flow enhancer  50 ″ b  rests against a seat member  90  that is secured within the conduit  86 . A tubular spacer element  92  is disposed between the upstream flow enhancer  50 ″ a  and the downstream flow enhancer  50 ″ b.    
     In operation, fluid is flowed through the conduit  86  in the direction indicated by the arrows  94 . In the upper portion  96  of the conduit  86 , the fluid is under high pressure. Upon encountering the upstream flow enhancer  50 ″ a , the fluid is directed through the restricted diameter fluid passages  62  of the flow enhancer  50 ″ a , its passage being assisted by the tapered side wall  74 . Because a pressure drop occurs across the upper flow enhancer  50 ″ a , the fluid is at a reduced pressure when it resides within area  98  of the conduit  86 . The fluid then encounters the downstream flow enhancer  50 ″ b  and is directed through its fluid passages  62 . A second, staged pressure reduction occurs across the downstream flow enhancer  50 ″ b  and, therefore, the fluid is at a further reduced pressure in area  100  of the conduit  86 . If desired, additional flow enhancers may be located downstream of flow enhancer  50 ″ b  to provide further staged pressure reductions. 
     While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.

Summary:
Flow enhancing restrictors are located within a fluid conduit to provide pressure reduction and flow enhancement. The restrictors may be used in combination with a conventional choke valve or as a stand-alone pressure reduction means. Alternative exemplary embodiments for flow enhancers are described. Each of the flow enhancers has a generally cylindrical base with at least one fluid passage disposed therethrough. Each of the flow enhancers also provides a dome that projects upwardly from the center of the base to assist in directing fluid flow and receiving the abrasive forces associated with the fluid.