Abstract:
When a fluid passes through a conventional elbow, turbulence is created in the fluid flow. The fluid may not stabilize and return to a laminar flow until 40-50 pipe diameters downstream. Turbulence in a piping system can cause a variety of problems such as measurement error, noise, vibration, and/or erosion. The flow diffuser of the present invention may be configured as a 90° elbow for use in a piping system to reduce turbulence and/or pulsation as the fluid passes through the improved elbow. The elbow can restore substantially laminar flow in a space of about four pipe diameters, with nominal pressure drop.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of Ser. No. 09/360,424 filed Jul. 23, 1999, now U.S. Pat. No. 6,289,934 issued on Sep. 18, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flow diffuser with an elongate discharge nozzle which can be used as a 90° elbow in piping systems. The flow diffuser can be located in or immediately upstream of a measurement station or custody transfer station to improve measurement accuracy. The flow diffuser promotes laminar fluid flow and reduces pulsation in gas pipelines. 
     2. Description of the Prior Art 
     In piping systems, orderly or streamlined flow is desirable. When a fluid passes through a conventional valve or a 90° turn at a conventional elbow, the fluid flow becomes disorderly or turbulent. This turbulent fluid does not return to a streamlined or laminar flow for at least 40-50 pipe diameters downstream of an elbow. (Assuming that the downstream piping is axially aligned with the outlet of the valve or elbow and has the same inside diameter.) 
     Turbulence can be caused by a number of factors including, but not limited to, boundary layer separation, sometimes referred to as flow separation, vortices, pressure waves and/or cavitation. Turbulence in pipe systems often causes noise, vibration, erosion and/or stress cracking. Reduction of turbulence is desirable in valves, at elbows and in piping systems generally, both upstream of gas or liquid measurement and downstream of compressor stations. 
     Turbulence also causes a drop in fluid pressure. Each time a fluid flows through a valve or elbow, there is an incremental drop in fluid pressure between the inlet and the outlet. In transmission pipelines, pressure drops are undesirable. If the fluid pressure drops low enough, additional pumping stations may be required. In any event, adding pressure to the fluid in the pipeline increases transportation costs. Because the elbow of the present invention reduces turbulence, it has less of a pressure drop when compared with conventional 90° elbows. 
     Elbow induced turbulence has been recognized and addressed by a number of prior art designs including the vanes of U.S. Pat. No. 5,197,509 and No. 5,323,661 which are located upstream from an elbow. These vanes impart rotation to the fluid as it passes through the elbow to reduce downstream turbulence. Others have considered the deleterious effects of elbow induced turbulence and have included rotation vanes both upstream and downstream of an elbow as described in U.S. Pat. No. 5,529,084. These inventions seek to create non-turbulent or laminar flow after fluid passes through a conventional elbow. 
     The use of curved vanes to influence fluid flow for various reasons is not a new concept. In U.S. Pat. No. 1,570,907, a plurality of vanes were used in a locomotive to separate water from steam. 
     Japanese Patent Application Serial Number Sho58 (1983)-13899 was filed on Jan. 31, 1983 by Yamatake Honeywell Co. Ltd. for a Valve Seat for Control Valve and Its Manufacturing Method. This prior art valve discloses a comb-like cylinder equipped with multiple teeth of rectangular cross-section formed as one piece with the ring-shaped valve seat. These teeth may be formed at the lower end of the valve seat on the outlet side or may be formed at both the upper and the lower end of the valve seat. The manufacturing method of the valve seat occurs sequentially. First, multiple slits are formed in the radial direction on the cylindrical wall joined to the ring-shaped valve seat as one piece. Then the rectangular teeth forming these slits are twisted plastically (i.e., by exerting torsional moments at the tip of the teeth large enough to cause permanent deformation) so that each slit is oriented in the direction of the fluid flow at its respective position. Because of the rectangular shape of these teeth, they promote turbulence instead of encouraging laminar flow. 
     In some piping systems, granular or particulate material will quickly wear out a conventional elbow. One way to address this problem is by increasing the radius of curvature of the elbow to about 10 pipe diameters. However, this is not an entirely acceptable solution, especially in areas where space is at a premium. There have been many attempts to solve this erosion problem, including the use of inserts in the elbow, the insert being a disposable item intended to be replaced when it wears out. Examples of this type of replaceable insert in an elbow can be found in the following U.S. Pat. No. 1,357,259; No. 2,911,235; No. 3,942,684; and No. 5,590,916. 
     Other proposed solutions to this erosion problem include a circular pocket off the elbow. This pocket accumulates a certain quantity of the particulate material which serves as a pad to absorb the blow of the subsequent material to reduce the erosive effects thereof as shown in U.S. Pat. No. 4,387,914 and No. 5,060,984. 
     Conventional valves are also known to create turbulence and a pressure drop between the inlet and the outlet. Robert H. Welker, the inventor herein and the inventor of U.S. Pat. No. 5,730,416, has developed various approaches to deal with valve induced turbulence. In another patent, U.S. Pat. No. 5,769,388, Mr. Welker has developed a plurality of vanes and passageways in the valve to reduce turbulence. The apparatus shown in U.S. Pat. No. 5,769,388 has certain shortcomings because of the short discharge nozzle which tapered at an included angle of approximately 12°. There is still a need to reduce turbulence in elbows, in valves and in piping systems in general. 
     In a gas pipeline, pulsation is normally caused by reciprocating compressors and can be caused to a lesser degree by certain types of check valves. Pulsation in a gas pipeline is typically the result of the pistons in a reciprocating compressor pushing the gas out in distinct pressure waves which may move five to ten miles downstream of a pumping station. Pulsation is never desirable. 
     Liquid pipelines reduce pulsation by installing pulsation dampeners, many of which commercially available. Pulsation in a liquid pipeline can cause failure. The present invention should reduce pulsation in a liquid pipeline. 
     The present invention should also reduce pulsation in gas pipelines. Pulsation in gas pipelines can cause measurement error at custody transfer stations and other measurement installations. Pulsation pressure waves require sensitive instruments to be detected. 
     The traditional solution to reduce pulsation in a gas pipeline is a pulsation dampener, for example, those produced by Burgess Manning Corp. of Cisco, Tex. 76437. 
     Prior art pulsation dampeners typically cause at least a 15 psi permanent pressure drop in the pipeline. The present invention will reduce pulsation in a gas pipeline with only a nominal pressure drop, i.e., less than 5 psi. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention can be used as a 90° elbow in piping systems to reduce turbulence and pulsation. The elbow, sometimes referred to as a flow diffuser, is connected to an inlet conduit and an outlet conduit. The flow diffuser includes a convenient top entry design allowing access to the removable flow conditioner. Downstream of the flow conditioner is a transition zone, and an elongate tapered discharge nozzle. Fluid flows from the inlet conduit into the flow diffuser, through the flow conditioner, the transition zone, and the elongate tapered discharge nozzle to the outlet conduit. 
     The removable flow conditioner includes a plurality of vanes defining a plurality of passageways to guide the fluid flow from the inlet into the transition zone and elongate tapered discharge nozzle. The purpose of the guide vanes is to reduce asymmetric flow, swirling, jetting and other turbulence and to promote a symmetric velocity profile and/or laminar flow as the fluid turns a 90° corner. In gas pipelines, the vanes also reduce pulsation. The flow conditioner can be fabricated as a replaceable part to facilitate maintenance of the flow conditioner. One way to develop a symmetric velocity profile is the design of the vanes and passageways in the replaceable flow conditioner. The width of the outlets from the passageways may be non-uniform in order to promote streamlined flow. 
     After the flow diffuser has been fabricated, it is desirable to test and align the flow conditioner for maximum effectiveness before it is shipped to the field. This alignment process may only require minor adjustments to properly orient the flow conditioner relative to the discharge nozzle. After the adjustments have been made the flow conditioner will need to be locked in place. In some embodiments, the adjustment mechanism and the locking mechanism are separate structures. In one alternative embodiment with opposing set screws, the adjustment mechanism also locks the flow diffuser in place. In some situations it may also be desirable to further calibrate/adjust the flow diffuser in tandem with a meter after both have been installed in the field. 
     The flow diffuser can be used in piping systems with liquids, gases, and steam, as well as two-phase flow, three-phase flow, and dry particulate and granules. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above-identified features and advantages of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiment thereof which is illustrated in the appended drawings. 
     It is noted, however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Reference the appended drawings, wherein: 
     FIG. 1 is a section view of the flow diffuser in exploded view. 
     FIG. 2 is a section view of the flow diffuser of FIG. 1 fully assembled. 
     FIG. 3 is a section view of the flow diffuser along the line  3 — 3  of FIG.  2 . 
     FIG. 4 is an enlarged partial section view of the adjustable flow conditioner, vanes and passageways of FIG.  3 . 
     FIG. 5 is an enlarged partial section view of the adjustment assembly, the locking assembly, and the adjustable flow conditioner of FIG.  2 . 
     FIG. 6 is an enlarged perspective view of the removable flow conditioner of FIG.  3 . 
     FIG. 7 is a section view of the rectangular inlet of the discharge passageway in the elongate discharge nozzle at the line  7 — 7  of FIG.  1 . 
     FIG. 8 is a section view of the polygonal interior surface of the discharge passageway in the elongate discharge nozzle at the line  8 — 8  of FIG. 1 
     FIG. 9 is a section view of the polygonal interior surface of the discharge passageway in the elongate discharge nozzle at the line  9 — 9  of FIG.  1 . 
     FIG. 10 is a section view of the circular outlet of the discharge passageway in the elongate discharge nozzle at the line  10 — 10  of FIG.  1 . 
     FIG. 11 is an enlarged perspective view of the bottom of the removable flow conditioner of FIG.  3 . 
     FIG. 12 is an enlarged partial section view of an alternative embodiment of the adjust assembly using opposing set screws to rotate the flow conditioner. 
     FIG. 13 is an enlarged perspective view of an alternative embodiment of the adjustment mechanism using an eccentric cam. 
     FIG. 14 is a top view of the eccentric cam. 
     FIG. 15 is a schematic view of the test apparatus used during the adjustment process for the flow diffuser. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a flow diffuser is generally identified by the numeral  10  and is shown in exploded view. The top of the flow diffuser  10  is generally identified by the arrow  11  and the bottom is generally identified by its numeral  13 . The flow diffuser is configured as a 90° elbow  10  to be used in a piping system, not shown. The flow diffuser  10  has a body  12  which defines an inlet  14  and an outlet  16 . An inlet conduit, not shown in the drawing, has a flange that aligns and mechanically connects by a bolt circle to the inlet flange  18  of the elbow  10 . The inlet flange  18  has a plurality of bolt holes, for example at  20  and  22  which receive the bolts for securing the inlet conduit flange to the inlet flange  18  of the flow diffuser  10 . An outlet conduit, not shown in the drawing, has a flange which aligns and is connected to the outlet flange  24  of the flow diffuser  10  by a bolt circle. The outlet flange  24  of the flow diffuser  10  has a plurality of bolt holes, for example at  26  and  28  which align with the bolt holes in the outlet conduit flange. The alignment and connection of the inlet conduit flange and the outlet conduit flange to the flanges  18  and  24  of the elbow  10  in a piping system is well known to those skilled in the art. 
     To reduce turbulence and/or pulsation the inside diameter of the inlet  14  should be about the same as the inside diameter of the inlet conduit. To reduce turbulence and/or pulsation the inside diameter of the outlet  16  should be about the same as the inside diameter of the inlet conduit. To reduce turbulence and/or pulsation, the inside diameter of the outlet conduit should also be about the same as the inside diameter of the inlet conduit. 
     In FIG. 1 bolt holes  20 ,  22 ,  26  and  28  are shown at a 12 o&#39;clock and 6 o&#39;clock position merely for illustrative purposes. One skilled in the art will recognize that the actual locations of these bolt holes are out of hand about 16″ from the position shown in these drawings for a 4-inch flange. 
     Fluid flows from the inlet conduit, not shown, into the inlet  14 , past the throat  29 , through the flow conditioner  30 , into the transition zone  32 , through the discharge passageway  33  of the elongate tapered discharge nozzle  34 , through the outlet  16 , and finally into the outlet conduit, not shown in the drawing. The present invention can reduce turbulence and/or pulsation in gas pipelines, such as those that transport natural gas and other hydrocarbons, and it can reduce turbulence in liquid pipelines such as those that transport water, gasoline, diesel and other hydrocarbons. It can be used for two-phase flow, such as a cold slurry or natural gas with entrained liquids. It can also be used with three-phase flow, such as oil, water and gas. It can be used with steam and it can be used with dry particulate or granules. For purposes of this application, all of the foregoing will simply be referred to as fluid. 
     The elbow  10  includes a removable cap  36 . The cap  36  can be threadably attached to the body  12 , or attached by other means well known in the art, such as a plurality of bolts  15  and  17 . The elbow includes several primary components, as follows: a removable and adjustable flow conditioner  30 , a transition zone  32 , and a discharge passageway  33  in the elongate tapered discharge nozzle  34 . The flow conditioner  30  is manufactured as a separate part that is inserted into receptacle  38  in the body  12  by removing the cap  36 . Once the removable flow conditioner  30  is inserted into the receptacle  38  of the body  12 , the cap  36  is replaced and secured. In some conditions, the flow conditioner may experience more wear than other components in the elbow  10 . To facilitate maintenance and prolong the life of the flow diffuser  10 , the flow conditioner is replaceable. 
     When fluid passes through a conventional 90° elbow in a piping system, turbulence is generated because of the 90° turn. Conventional wisdom indicates that laminar flow does not return to the fluid stream after it passes through a 90° elbow until as much as 40 to 50 pipe diameters past the elbow (assuming an axially aligned straight discharge pipe having the same inside diameters as the elbow). For example, with a conventional 2 inch elbow and 2 inch piping system, laminar flow may not return until as much as 80 inches to 100 inches downstream of the elbow. It is desirable for many reasons to restore laminar flow as quickly as possible after a fluid passes through a 90° elbow. A length of 40 or 50 pipe diameters is simply impractical in many real world applications. 
     The present invention restores substantially laminar flow to a fluid stream after it passes through the 90° turn within about 4 pipe diameters after the transition zone  32 . Reducing the distance necessary to achieve substantially laminar flow from 40 or 50 pipe diameters to about 4 pipe diameters is an advantage in a number of situations, especially in close quarters, such as offshore drilling or production platforms. In addition, the flow diffuser  10  is able to restore laminar flow after the fluid passes through this 90° turn with reduced noise and vibration when compared with conventional elbow. 
     Reduction in noise and vibration is accomplished because of the reduced turbulence in the elbow  10  when compared with prior art elbows. Pulsation in gas pipelines is reduced because molecules entering the elbow at the same time arrive at the outlet at slightly different times due to some having to travel through a longer passageway (flow path). Therefore, the voids between pressure waves are filled in; thus, no pressure wave will exist at the outlet  16 . 
     To function properly, the flow conditioner  30  must be aligned properly in the receptacle  38 . An adjustment assembly generally identified by the numeral  31  allows proper alignment of the flow conditioner  30  with the discharge passageway  33  of the elongate tapered discharge nozzle  34 . The adjustment assembly  31  includes an adjustment stem  35  with a pivot point  37  on one end and an adjustment knob  39  on the other end. A plurality of gear teeth  41  are formed on the stem  35  proximate the pivot point  37 . The gear teeth  41  are sized and arranged to engage teeth  69  formed in the flow conditioner  30 . Rotation of the knob  39  imparts rotation to the stem  35  and teeth  41  which engage the teeth  69  on flow conditioner  30 . Thus, rotation of knob  39  causes the flow conditioner  30  to rotate in the receptacle  38 . The stem  35  fits through a bore  43  in the cap  36  and is sealed by a plurality of chevron seals  45 . 
     After proper adjustment of the flow conditioner  30 , it is necessary in this embodiment to use a locking assembly  47  to lock the flow conditioner  30  in place. An elongate stem  49  has a point  51  on one end and a knob  53  on the other end. The point  51  bears against the flow conditioner  30  to lock it in the proper orientation. A lock nut  55  locks the stem  49  against the cap  36 . The stem  49  fits through a bore  57  in the cap  36  and is sealed by an O-ring  59  which is positioned in groove  61 . 
     FIG. 2 is a section view of the flow diffuser  10  of FIG. 1, with the cap  36  and flow conditioner  30  assembled for operation. The flow conditioner  30  has a flat bottom plate  42 . The guide vanes  50  A-P extend upward from the bottom  42  of flow conditioner  30 . As a matter of manufacturing choice, it would be equivalent to invert the flow conditioner  30  so the vanes extended downward from a flat top plate, not shown. If the flow conditioner was produced in this equivalent fashion, minor changes would need to be made to the receptacle and cap so the conditioner would align with the transition zone  32  and the passageway  33  of elongate discharge nozzle  34 . Body  12  forms a side wall  44  surrounding the flow conditioner  30 . The side wall  44 , the cap  36  and the bottom plate  42  contain the fluid flow in the flow conditioner  30 . The flow conditioner  30  includes an inlet port and an outlet port identified generally by the dotted curved line  46  better seen in FIG.  3 . The outlet port  46  is defined by the side wall  44 , the cap  36  and the bottom surface  42  of the flow conditioner  30 . 
     The inlet  14  feeds the fluid through an inlet port  79  into an inlet zone  48  better seen in FIG. 3. A generally conical protrusion  54  is attached to the cap  36  by bolt  62  which is sealed to cap  36  by seal  64 . The conical protrusion  54  extends into the inlet zone  48  of flow conditioner  30 . The area of the inlet zone  48  is reduced by the area of the generally conical protrusion  54 ; however, in the preferred embodiment, the inlet zone  48  has an area at least twice the cross-sectional area of the inlet  14 . The conical protrusion  54  is replaceable, but as a matter of manufacturing choice, it would be equivalent to form the conical protrusion as a part of the cap  36  or as a part of the flow conditioner  30 . 
     FIG. 3 is a section view of the flow diffuser  10  along the line  3 — 3  of FIG. 1 except the conical protrusion  54  is not shown. In other words, FIG. 3 is a section view of the flow diffuser  10  viewed from the top  11 . The rear vane  50  A has a cutout area  56  and a plurality of teeth  69  formed therein. The teeth  41  formed on the stem  35  of the adjustment assembly  31  engage the teeth  69  on the rear vane  50  A of flow conditioner  30 . Rotation of knob  39  causes stem  35  and teeth  41  to rotate. This imparts rotation to the flow conditioner  30  in receptacle  38 . The flow conditioner  30  is adjusted after manufacture and before the flow diffuser  10  is shipped to the field. 
     Vanes  50  A-P define a plurality of passageways  52  A-P. In the preferred embodiment, 16 passageways are shown; however, a larger number or a smaller number of passageways can be used depending on the fluid matrix, pressure, pipe size and other operational parameters. The side wall  44  of the body  12  together with the cap  36  and the bottom  42  direct fluid flow as it exits the passageways  52  A-P. The guide vanes have a generally heart-shaped outline. Each passageway  52  has a beginning  58  and an ending  60 . The beginning  58  in fluid communication with the inlet zone  48  and the ending  60  is in fluid communication with the transition zone  32 . In the preferred embodiment, the area of each beginning  58  has a cross-sectional area that is about twice as large as the cross-sectional area of the end  60 . The width of each passageway  52  at the beginning  58  is preferably equal to the circumference of the inlet zone  48  divided by the number of passageways  52 . The area of the beginning  58  and the end  60  of each passageway  52  may be modified during manufacture depending on the fluid matrix, pressure, pipe size and other operational parameters. The ends  60  of each passageway  52  A-P may have different widths in order to achieve the optimum velocity profile described in FIG. 15, below. 
     The taper of the discharge nozzle  34  is important to reduce turbulence of the fluid as it passes from the transition zone  32  towards the outlet conduit. Applicant prefers a taper with an included angle of about 5°-7.5°. The included angle of taper will determine the length of the discharge nozzle  34  as shown in the table below. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Discharge Nozzle Lengths 
               
             
          
           
               
                 Diameter of 
                   
                   
               
               
                 Inlet Conduit 
                 7° Included Angle 
                 5° Included Angle 
               
               
                   
               
             
          
           
               
                 1″ 
                 App. 4.1″ 
                 App. 6.53″ 
               
               
                 2″ 
                 App. 8.2″ 
                 App. 13.05″ 
               
               
                 4″ 
                 App. 16.4″ 
                 App. 26.11″ 
               
               
                 6″ 
                 App. 24.5″ 
                 App. 39.16″ 
               
               
                 8″ 
                 App. 32.7″ 
                 App. 52.22″ 
               
               
                 12″ 
                 App. 49.1″ 
                 App. 78.33″ 
               
               
                   
               
             
          
         
       
     
     As indicated in this table, a discharge nozzle  34  tapered at a 7° included angle will have a length approximately 4 times the diameter of the inlet conduit. A discharge nozzle tapered at a 5° angle will be longer and have a length approximately 6½ times the diameter of the inlet conduit. 
     As shown in FIG. 3, the interior surface  66  of the discharge nozzle  34  has a taper of 3.5° on all surfaces as measured from lines extended parallel to the outlet conduit. The tapered discharge nozzle  34  extends from the line  7 — 7  to the line  10 — 10 . The parallel lines in the drawing extend parallel to the walls of the outlet  16 . The outlet  16  has parallel sides aligned with the outlet conduit to reduce turbulence. 
     In FIG. 4, an enlarged section view of the flow conditioner  30  similar to the view in FIG. 3 without the conical protrusion  54 . Fluid flows form the inlet  14  into the inlet zone  48  which has a larger area than the cross-sectional area of the inlet  14 . The fluid encounters the conical protrusion  54 , the guide vanes  50  A-P and the beginning  58  of each curvilinear passageway  52  A-P as shown by the flow arrows. The fluid then passes through the passageways  52  A-Q and moves into the transition zone generally identified by the numeral  32 . The transition zone  32  is defined by an upper portion  70  and a lower portion  72  of the body  12  and a curved outer wall  74 , which is likewise a portion of the body  12 . In the preferred embodiment, the curved outer wall  74  has a radius about 2½ times the diameter of the inlet  14 . The transition zone  32  is in fluid communication with the outlet opening  46  of the flow conditioner  30 , and the elongate tapered discharge nozzle  34 . The diameter of the flow conditioner from point R to point S in the preferred embodiment is approximately 3 times the diameter of the inlet  14 . 
     Some of the passageways, i.e.,  52  H and  52  I are aligned radially relative to the inlet zone  48  and some are curvilinear, i.e.,  52  A and  52  P. This combination of radial and curvilinear passageways reduces turbulence as fluid passes through the flow diffuser  10 . In addition, all of the vanes  50  A- 50  P have a streamlined leading edge  81  and a streamlined trailing edge  83  which also reduces turbulence as fluid passes through the flow diffuser  10 . 
     FIG. 5 is an enlarged section view of the adjustment assembly  31  and the locking assembly  47 . The removable cap  36  is attached to the body  12  by a plurality of bolts. Bolt  17  passes through bore  19  in cap  36  and threadibly engages bore  21  in body  12 . In this view, the point  51  of stem  49  is in engagement with the top surface of the rear vane  50  A of the flow conditioner  30  to hold it in a fixed position. Lock nut  55  is abutting cap  36 , thus holding the stem  49  in a locked position. An O-ring groove  63  surrounds the cap  36 . O-ring  65  is positioned in the groove  63  to form a seal between the body  12  and the removable cap  36 . Chevron seals  45  form a seal between the stem  35  and the bore  43  of the cap  36 . O-ring  59  forms a seal between the stem  49  and the bore  57  of the cap  36 . Adjustment of the flow conditioner  30  occurs after the diffuser  10  has been manufactured but before it has been shipped to the field. 
     FIG. 6 is a perspective view of the top side of the removable flow diffuser  30 . Vanes  50  A-P extend upward from a flat bottom plate  42 . Teeth  69  are formed in a cutout  56  in the rear vane  50  A. The center vane  50  I is located opposite the rear vane  50  A. 
     FIG. 7 is a section view of the discharge nozzle  34  along the line  7 — 7  of FIG.  1 . The interior surface  86  of the discharge nozzle  34  defines a discharge passageway  33  with a generally rectangular shaped inlet  88 . In the preferred embodiment, the height of the rectangular shaped inlet  88  is about {fraction (1/2+L )} the diameter of the inlet  14  and the width of the rectangular inlet  88  is about 1.5 times the diameter of the inlet  14 . However, other dimensional configurations for this rectangle fall within the scope of this invention and may be adjusted, depending upon the fluid matrix, pressure, pipe size, and other operational parameters. 
     FIG. 8 is a section view of the discharge nozzle  34  along the line  8 — 8  of FIG.  1 . The interior surface  86  begins to change shape from the generally rectangular inlet  88  to a polygon as shown in the drawing. Other polygonal shapes fall within the scope of this invention, provided that the interior surface  86  maintains a taper with an included angle of about 5°-7.5°. 
     FIG. 9 is a section view of the discharge nozzle  34  along the line  9 — 9  of FIG.  1 . The interior surface  86  is polygonal. Other polygonal shapes fall within the course of this invention, provided that they are tapered as discussed above. 
     FIG. 10 is a section view along the line  10 — 10  of FIG. 1 showing the discharge nozzle  34  as it converges to a circular outlet  90 . The diameter of the circular outlet  90  is approximately equal to the diameter of the inlet  14 . The inlet conduit and the outlet conduit should be approximately equal in diameter and cross-sectional area to reduce turbulence. The cross-sectional area of the discharge passageway  33  as it extends from line  7 — 7  to line  10 — 10  for a 7° included angle is about 4 times the diameter of the inlet  14 . The length of the discharge nozzle  34  from the line  7 — 7  to the line  10 — 10  with a 5° included angle is about 6½ times the diameter of the inlet  14 . FIG. 10 the elbow  10  is viewed from the bottom  13 . 
     FIG. 11 is a bottom perspective view of the removable flow conditioner  30 . The vanes  50  A-P extend upward from the flat bottom plate  42 . An inlet port  79  is formed in the bottom plate  42 . In the rear of the flow conditioner  30  is the rear vane  50  A. A cutout  56  is formed in the rear vane  50  A and the bottom plate  42 . Teeth  69  are formed in the cutout  56  to permit adjustment of the flow conditioner  30 . 
     FIG. 12 is an alternative embodiment of the adjustment assembly. In this alternative embodiment of the adjustment assembly, no separate locking assembly is needed, because opposing set screws  132  and  134  are self locking. 
     In FIG. 12 a modified flow diffuser  130  has a lug  136  formed on the rear vane  150  A. Set screw  132  engages one side  138  of the lug  136  and set screw  134  engages the other side  140  of the lug  136 . The set screw  132  threadibly engages bore  142  in the body  12  and set screw  134  threadibly engages bore  144  in the body  12 . When set screw  132  is turned clockwise and set screw  134  is turned counter-clockwise, the flow diffuser  130  rotates counter-clockwise, and vice versa. 
     A seal  146  surrounds the head of screw  148  and creates a seal between the body  12  and the screw  148 . The screw  148  must be removed from bore  142  in order to rotate the set screw  132 . A seal  150  surrounds the head of screw  152  and creates a seal between the body  12  and the screw  152 . The screw  152  must be removed from bore  144  in order to rate the set screw  134 . 
     FIG. 13 is a second alternative embodiment of the adjustment assembly. In the second alternative embodiment of the adjustment assembly  231 , a separate locking mechanism must be used to fix the position of the flow conditioner  230 . 
     In FIG. 13, a modified flow conditioner  230  has a slot  232  formed in the rear vane  250  A. The stem  35  has an eccentric cam  234  formed on the end opposite the knob  39 . A projection  236  extends from the eccentric cam  234  and engages the slot  232  in the rear vane  250  A. When the knob  39  is rotated clockwise, the projection  236  bears against slot  232 , causing the flow conditioner  230  to rotate clockwise and vice versa. 
     FIG. 14 is a top view of the eccentric cam  234 . The projection  236  is shown in phantom. 
     FIG. 15 is a schematic of the test apparatus used to adjust the flow conditioner after manufacture, but before it is shipped to the field. A newly manufactured flow diffuser  10  is placed approximately six pipe diameters upstream of the manometer  300  and is connected to a pressurized source of fluid, not shown. A shut off valve, not shown, is placed between the source of pressurized fluid and the flow diffuser  10 . A valve, not shown, is opened and pressurized fluid flows through the flow diffuser  10  past the manometer  300 . The flow conditioner  30  is rotated using the adjustment mechanism  31  based on the readout from the manometer  300 . After precise alignment is achieved, the locking assembly  47  is secured and the flow conditioner  30  is fixed in position. The flow diffuser  10  is then ready to be shipped to the field for installation. 
     This final adjustment process is necessary because there may be slight manufacturing imperfections in the flow conditioner  30  which might create a bias in the fluid flow exiting the flow conditioner  30 . Another reason for this final adjustment process is because precise prealignment of the flow conditioner  30  with the passageway  33  in the elongate discharge nozzle  34  during manufacture is difficult because the flow conditioner  30  is removable. Prior art prealignment pins simply do not always achieve the desired precision due to manufacturing tolerances and assembly requirements. Precise alignment can be achieved when fluid is passing through the flow diffuser  10 . Adjustments to the flow conditioner  30  are typically very slight, and may only be 0.010 inch in one direction or the other. 
     The manometer  300  has a high pressure side  302  and a low pressure side  304 . In between is a U-shaped tube  306  typically filed with water. The normal readout from a manometer is in inches of water. 
     The high pressure side  302  is attached to an adjustable pitot probe  308  that can be moved up and down through the center of the pipeline as shown in phantom. The low pressure side  304  is connected to an inlet  310  that is fixed in position near the wall of the pipeline. 
     The goal of the adjustment procedure is to achieve a symmetric velocity profile in the flowing fluid downstream of the flow diffuser  10 . The shape of a symmetric velocity profile is sketched in FIG.  15 . 
     If the flow diffuser is inefficient or improperly adjusted, asymmetric and/or turbulent fluid flow may result. Asymmetric and turbulent flow are undesirable. If the adjustment procedure is not precise, the velocity profile may be flattened or there may be overrounding, both of which are undesirable. Overrounding results in a conical velocity profile which is sometimes referred to as a jet. 
     The American Gas Association (AGA) has various accuracy standards for flow meters. Asymmetric flow, jetting, swirling and/or pulsations may adversely affect accurate flow measurement. According to AGA Transmission Measurement Committee Report No. 9 at Section 7.2.2 “asymmetric velocity profiles may persist for 50 pipe diameters downstream from the point of initiation. Swirling velocity profiles may persist for 20 pipe diameters or more.” The present invention is designed to produce a symmetric velocity profile without swirling or jetting. One way to enhance measurement accuracy is to use a sufficient length of straight pipe (i.e., diameters) upstream of the meter so the fluid will develop a symmetric velocity profile before it enters the meter. Another way to enhance measurement accuracy is to place a well designed flow diffuser upstream of the meter so the fluid will develop a symmetric velocity profile before it enters the meter. Various flow diffusers (also called flow conditioners) are available for this purpose, such as the Vortab from Vortab Company of San Marcos, Calif.; the CPA 50E plate from Canadian Pipeline Accessories Company, Ltd. of Calgary, Alberta, Canada; or the GFC (Gallagher Flow Conditioner) from Savant Measurement Corp. of Kingwood, Tex. 
     The adjustment procedure for the present invention using the apparatus in FIG. 15 is as follows. First, the pitot probe  308  is placed in the center  312  of the pipe to measure the pressure of the flowing fluid in the center of the pipe. Then the pitot probe  308  is placed near each pipe wall  314  and  316  to measure the pressure of the flowing fluid near the walls. The highest pressure should be in the center  312  of the pipeline and the lowest pressures should be near the walls  314  and  316 . 
     A symmetric velocity profile is desirable and has the same velocity on either side of the center-line of the pipe. The optimum velocity profile has a gentle curve or rounded nose as shown in FIG.  15 . The adjustable pitot probe  308  is moved back and forth across the diameter of the pipeline from wall  314  to wall  316  to measure the velocity of the flowing fluid. The flow conditioner  30  should be adjusted so the velocity profile is as close as possible to the optimum shape shown in FIG.  15 . After adjustment, the flow conditioner  30  should be locked in place with the locking mechanism  47 . In some situations, it may also be desirable to further calibrate/adjust the flow diffuser  10  in tandem with a meter after both have been installed in the field. 
     Similar adjustments can be made to the flow conditioner  130  with the first set screws  132  and  134  in the first alternative embodiment of FIG. 12, except there is no separate locking assembly. In other words, the opposing set screws  132  and  134  can be tightened against the lug  136  to lock the flow conditioner  130  in place. 
     Similar adjustments can also be made to the flow conditioner  230  with eccentric cam  234  in the second alternative embodiment shown in FIGS. 13 and 14. In the second alternative embodiment a separate locking assembly  47  is required to fix the position of the flow conditioner  230 . 
     In some situations it may be difficult to obtain a pressurized fluid source to adjust the flow conditioners  30 ,  130  or  230 . In these situations, the center vane  50  I may be optically aligned with the center of the passageway  30  of the elongate discharge nozzle  34 .