Patent Publication Number: US-10767900-B2

Title: Burner with flow distribution member

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to burners for use in water heaters and boilers, and more particularly to a flow distribution member used with such burners for providing an improved pressure distribution of fuel and air mixture throughout the burner. 
     Description of the Prior Art 
     One well known architecture for water heaters and boilers is that utilized in the series of water heaters produced by Lochinvar LLC, the assignee of the present invention, as its POWER-FIN® water heaters and boilers. The general construction of such water heaters may be similar to that disclosed for example in U.S. Pat. No. 4,793,800 to Vallett et al. or that in U.S. Pat. No. 6,694,926 to Baese et al. 
     Such water heaters utilize a generally cylindrical burner concentrically received within a circular array of fin tubes. 
     Water heaters of this type use a premix blower to supply air and gas mixture to the cylindrical burner. One issue which is encountered in designing in such a water heater is the desire to provide a balanced uniform flow of fuel and air mixture throughout the burner, and particularly to avoid any negative pressure zones in the burner which could cause flashback into the burner. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment a pre-mix burner apparatus includes a burner having a generally cylindrical burner surface, the burner having a central axis and having a generally circular burner inlet at one end of the burner. The burner inlet has an inlet diameter. A flow distribution member is arranged to distribute flow of fuel and air mixture into the burner. The flow distribution member includes a closed axially central portion configured to block flow of fuel and air mixture axially centrally into the burner. The flow distribution member further includes a plurality of vanes extending radially outward from the closed axially central portion. The vanes are configured to generate a swirling flow of fuel and air mixture flowing past the vanes into the burner. 
     The closed axially central portion may be disc shaped and may have a disc diameter in a range from about 10 percent to about 20 percent of the inlet diameter. 
     The burner inlet may define an inlet plane generally perpendicular to the burner central axis, and each of the vanes may be oriented at a vane angle to the inlet plane in a range from about 30 degrees to about 60 degrees. 
     Each of the vanes may be planar. 
     Each of the vanes may be generally triangular in shape. 
     Each of the vanes may have a radial length in a range from about 40 percent to about 45 percent of the inlet diameter. 
     The array of vanes may include at least 12 and no greater than 20 vanes substantially equally circumferentially spaced about the central axis of the burner. 
     The flow distribution member may comprise a formed integral sheet, the vanes each being generally triangular shaped with two free sides and one attached side, the attached side extending generally radially relative to the central axis of the burner. 
     The flow distribution member may have a total open area in a range from about 50 percent to about 70 percent of a cross sectional area of the burner inlet. 
     The flow distribution member may include a plurality of spokes extending outward from the closed axially central portion, each of the vanes being attached to one of the spokes. 
     The flow distribution member may include a radially outer planar flange connected to radially outer ends of the spokes, the flange being configured to mount the flow distribution member. 
     The apparatus may further include a blower configured to provide fuel and air mixture to the burner inlet, the blower having a blower outlet having a blower outlet cross sectional area, wherein the burner inlet has an inlet cross sectional area greater than the blower outlet cross sectional area. 
     The vanes may be configured such that the spiral flow pattern adjacent and downstream of the burner inlet prevents flame flow back into the burner adjacent the burner inlet. 
     The burner apparatus may be used in combination with a water heater, the water heater being in heat exchange relationship with the burner. 
     In another embodiment a method is provided for operating a burner comprising: 
     (a) providing an inlet stream air mixture to an inlet of the burner, the inlet being generally circular; 
     (b) blocking an axially central portion of the inlet and thereby preventing axially central flow of the inlet stream into the inlet; and 
     (c) swirling the inlet stream and creating a spiral flow pattern as the stream passes through an annular area between the axially central portion and a diameter of the burner inlet, such that negative pressure is avoided in the burner adjacent the burner inlet. 
     The method may further include in step (a) the burner being a cylindrical burner having a cylindrical burner surface and having an axial length, and in step (c) the spiral flow pattern extending along the entire length of the burner. 
     The spiral flow pattern may cause the fuel and air mixture to exit the burner surface at substantially uniform velocities along the entire length of the burner. 
     The spiral flow pattern may avoid the creation of negative pressures at any location along the entire length of the burner. 
     The burner may be operated at an output in excess of 1.0 MM BTU/HR. 
     The inlet stream of step (a) may be provided by a blower having a blower outlet with an outlet cross sectional area less than an inlet cross sectional area of the burner inlet. 
     The method may further comprise the step of heating water with a heat exchanger in heat exchange relationship with the burner. 
     Numerous objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a water heater apparatus. 
         FIG. 2  is an enlarged schematic cross sectional view of the water heater apparatus of  FIG. 1 . 
         FIG. 3  is a perspective view of the pre-mix blower and the cylindrical burner utilized with the water heater apparatus of  FIGS. 1 and 2 . 
         FIG. 4  is a side elevation view of the blower and burner assembly of  FIG. 4 . 
         FIG. 5  is a cross sectional view taken along line  5 - 5  of  FIG. 4  showing the cross section of the burner apparatus with a flow distribution member in place at the inlet of the burner apparatus. 
         FIG. 6  is a plan view of the flow distribution member of  FIG. 5 . 
         FIG. 7  is a cross section view of the flow distribution member taken along lines  7 - 7  of  FIG. 6 . 
         FIG. 8  is a top perspective view of the flow distribution member of  FIG. 6 . 
         FIG. 9  is a an enlarged cross section view of the outer mounting flange portion of the flow distribution member of  FIG. 6 , from within the circled portion of the right hand side of  FIG. 7 . 
         FIG. 10  is a schematic cross-section view of the burner showing the spiral flow pattern downstream of the flow distribution member. 
         FIG. 11A  is a schematic elevation view of a test setup for testing the pressure distribution within a burner without a pressure distribution member. 
         FIG. 11B  is a schematic bottom view of the test setup of  FIG. 11A , showing the blower outlet cross-section superimposed on the burner inlet cross-section, and showing the location of the pressure test points within the four quadrants of the cross-section of the burner inlet. 
         FIG. 12A  is a schematic elevation of a test setup for testing the pressure distribution within a burner with the pressure distribution member. 
         FIG. 12B  is a schematic bottom view of the test setup of  FIG. 12A . 
         FIG. 13  is a visual depiction of the flow velocity/pressure distribution of a baseline burner without a flow distribution member, as computed using CFD (computational fluid dynamics) modeling. The left side of  FIG. 13  is a cross-section along centerline  112  of the blower outlet seen in  FIG. 11B . The right side of  FIG. 13  is a cross-section along centerline  114  of the blower outlet seen in  FIG. 11B . The table in the middle of  FIG. 13  identifies flow velocity range zones A, B, C etc. 
         FIG. 14  is a visual depiction of the flow velocity/pressure distribution of a burner with the flow distribution member disclosed herein, as computed using CFD (computational fluid dynamics) modeling. The left side of  FIG. 14  is a cross-section along centerline  112  of the blower outlet seen in  FIG. 11B . The right side of  FIG. 14  is a cross-section along centerline  114  of the blower outlet seen in  FIG. 11B . The table in the middle of  FIG. 14  identifies flow velocity range zones A, B, C etc. 
         FIG. 15  is a visual depiction of the flow velocity/pressure distribution of a comparable burner having a flow distribution member with an open center instead of the closed center disclosed herein, as computed using CFD (computational fluid dynamics) modeling. The left side of  FIG. 15  is a cross-section along centerline  112  of the blower outlet seen in  FIG. 11B . The right side of  FIG. 15  is a cross-section along centerline  114  of the blower outlet seen in  FIG. 11B . The table in the middle of  FIG. 15  identifies flow velocity range zones A, B, C etc. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, and particularly to  FIG. 1 , a water heater or boiler apparatus is shown and generally designated by the numeral  10 . As used herein, the term water heater refers to an apparatus for heating water, including both steam boilers and water heaters that do not actually “boil” the water. Much of this discussion refers to the apparatus  10  as a boiler  10 , but it will be understood that this description is equally applicable to water heaters that do not boil the water. The boiler  10  includes a heat exchanger  12  having a water side  14  having a water inlet  16  and a water outlet  18 . 
     The general construction of the heat exchanger  12  may be similar to that disclosed for example in U.S. Pat. No. 4,793,800 to Vallett et al., or that in U.S. Pat. No. 6,694,926 to Baese et al., the details of which are incorporated herein by reference. The heat exchanger may be a multiple pass exchanger having a plurality of fin tubes arranged in a circular pattern with a burner located concentrically within the circular pattern of fin tubes. In  FIG. 2  the heat exchanger  12  is shown to have upper and lower headers  20  and  22  connected by a plurality of vertically oriented fin tubes  24 . The burner apparatus disclosed herein may also be used with other arrangements of heat exchangers. 
     A burner  26  is concentrically received within the circular array of fin tubes  24 . The burner  26  is operatively associated with the heat exchanger  12  for heating water which is contained in the water side  14  of the heat exchanger  12 . Within each fin tube  24 , the water receives heat from the burner  26  that is radiating directly upon the exterior fins of the fin tubes  24 . 
     The burner  26  is of the type referred to as a premix burner which burns a previously mixed mixture of combustion air and fuel gas. In the system shown in  FIG. 1 , a venturi  28  is provided for mixing combustion air and fuel gas. Other types of mixing devices may be used in place of the venturi  28 . An air supply duct  30  provides combustion air to the venturi  28 . A gas supply line  32  provides fuel gas to the venturi  28 . A gas control valve  33  is disposed in supply line  32  for regulating the amount of gas entering the venturi  28 . The gas control valve  33  includes an integral shut off valve. A shut off valve  35  may also be disposed in supply line  32 . 
     In order to provide the variable output operation of the burner  26  a variable flow blower  34  delivers the premixed combustion air and fuel gas to the burner  26  at a controlled blower flow rate within a blower flow rate range. The blower  34  may be driven by a variable frequency drive motor  36 . Alternatively, a variable speed motor with a Pulse Width Modulation drive may be used to drive the blower  34 . 
     The gas line  32  will be connected to a conventional fuel gas supply (not shown) such as a municipal gas line, with appropriate pressure regulators and the like being utilized to control the pressure of the gas supply to the venturi  28 . 
     The gas control valve  33  is preferably a ratio gas valve for providing fuel gas to the venturi  28  at a variable gas rate which is proportional to the flow rate entering the venturi  28 , in order to maintain a predetermined air to fuel ratio over the flow rate range in which the blower  34  operates. 
     An ignition module  40  controls an electric igniter  42  associated with the burner  26 . 
     Combustion gasses from the burner  26  exit the boiler  10  through a combustion gas outlet  44  which is connected to an exhaust gas flue  46 . 
     The water inlet and outlet  16  and  18  may be connected to a flow loop  38  of a heating system. A pump  39  may circulate water through the flow loop  38  and thus through the water side  14  of the heat exchanger  12 . 
     A plurality of temperature sensors are located throughout the boiler apparatus  10  including sensor T 1  at the water inlet  16 , sensor T 2  at the water outlet  18 , and sensor T 3  at the exhaust gas outlet  44 . 
     A blower to burner transition duct  48  may connect a blower outlet  50  to a burner inlet  52 . A flow distribution member  54  may be located at the burner inlet  52 . 
     As best seen in  FIGS. 3-5 , the burner  26  has a generally cylindrical burner outer surface  56  generally concentrically disposed about a burner central axis  58 . The burner inlet  52  is a generally circular burner inlet  52  located at the upper end of the burner  26 . The burner inlet  52  has an inlet diameter  60 . The burner has a length  62  from the burner inlet  52  to a burner bottom  64 . In the embodiment illustrated, the cylindrical outer surface  56  of the burner  26  is covered with a foraminous material such as for example wire mesh, woven wire fabric, ceramic material or the like which is generally indicated by the patch of foraminous material  66  illustrated in  FIGS. 3 and 4 . It will be understood that the entire cylindrical outer surface  56  will be made up of such foraminous material  66 . In the embodiment shown, the bottom  64  of burner  26  is a closed non porous bottom. 
     Thus, as schematically illustrated in  FIG. 2 , generally radially outward extending flames  68  will form on the cylindrical exterior surface  56  of burner  26  and will heat the surrounding heat exchanger tubes  24 . 
     The blower outlet  50  of blower  34  has a blower outlet which may generally be rectangular in shape, and has a blower outlet cross sectional area which may be less than the circular inlet cross sectional area of the circular inlet  52  of burner  26 . This can best be appreciated by viewing the diverging enlarging cross section of the blower to burner transition duct  48  which is best seen in the cross sectional view of  FIG. 5 , and by viewing the superimposed rectangular blower outlet cross-section and burner inlet cross-section as seen in  FIG. 11B  described below. 
     When using a pre-mix blower such as blower  34  to supply fuel and air mixture to the cylindrical burner inlet  52 , in the absence of the flow distribution member  54 , the high velocity flow of fuel and air mixture exiting the blower  34  and entering the burner inlet  52  can cause a negative pressure zone at the inlet of the burner  52  and for a short distance downstream thereof, which can result in pulling flame back into the burner  26 . Also, the velocity profile exiting the blower outlet  50  across the cross section thereof is typically not even and equal across the entire cross sectional area of the blower outlet  50 , which can result in uneven loading of the burner  26 . Furthermore, high velocity flow from the blower outlet  50  through the burner  26  can cause noisy operation of the water heater apparatus  10  under normal running conditions. This problem may be more severe in arrangements where the blower outlet  50  cross-section is substantially smaller than the burner inlet  52  cross-section. But there can be other causes of unequal velocity profile entering the burner inlet  52 , such as for example the unequal distribution due to centrifugal effects within the blower  34 , or flow disturbances due to ducting between the blower  34  and the burner  26 . The flow distribution member  54  described herein may be used in any suitable situation, including arrangements where the cross-section of the blower outlet  50  is greater than the cross-section of the burner inlet  52 . 
     The flow distribution member  54  is provided to break up the flow pattern of the fuel and air mixture exiting the blower outlet  50  and to redirect that fuel and air mixture into a spiral flow pattern  106  (see  FIG. 10 ) as the fuel and air mixture flows downward through the burner  26  from the burner inlet  52  toward the burner bottom  64 . 
     This spiral flow pattern  106  creates an outward pressure at the neck of the burner adjacent and just downstream of the burner inlet  52 , and also throughout the entire burner length  62 , thus causing the fuel and air mixture to exit the burner  26  at an equal or approximately equal flame velocity throughout the entire length of the burner  26 , thus eliminating negative pressure zones. 
     Additionally, the flow distribution member  54  may eliminate the effect of blower velocity profile on the burner balancing. The inherently unequal velocity profile at the outlet  50  of the blower  34  is redirected into the spiral flow pattern  106  by the flow distribution member  54 , which results in a balanced burner  24 . 
     Finally, by breaking up the flow pattern exiting the blower outlet  50 , the flow distribution member  54  reduces the noise level of the combustion system of water heater  10  during normal operation. 
     One preferred construction of the flow distribution member  54  is shown in more detail in  FIGS. 6-9 . 
     The flow distribution member  54  includes a closed axially central portion  70  configured to block flow of fuel and air mixture axially centrally into the burner  26  along the burner axis  58 . 
     The flow distribution member  54  further includes a plurality of vanes  72  extending radially outward from the closed axially central portion  70 . The vanes  72  are configured to generate the swirling flow  106  of fuel and air mixture flowing past the vanes  72  into the burner  26 . 
     As best shown in  FIG. 6 , the closed axially central portion  70  is generally disc shaped and has a disc diameter  74  in a range from about 10 percent to about 20 percent of the inlet diameter  60 . 
     As seen in  FIG. 5 , the burner inlet  52  may be described as defining an inlet plane  76  generally perpendicular to the burner longitudinal axis  58 . Each of the vanes  72  may be described as being oriented at a vane angle  78  best shown in  FIG. 7 . The vane angle  78  may be in a range from about 30 degrees to about 60 degrees, and more preferably may be in a range of from about 35 degrees to about 45 degrees. It will be appreciated that for a planar vane  72 , the vane angle  78  is the angle between the plane of the vane  72  and inlet the plane  76 . The angle  78  as illustrated in  FIG. 7  is schematic only, and does not depict exactly the angle between the two planes. 
     In the embodiment illustrated, each of the vanes  72  may be described as being generally planar and as being generally triangular in shape. It will be appreciated, however, that the vanes  72  could also be curved. 
     In the embodiment illustrated in  FIGS. 6-9 , the flow distribution member  54  comprises a formed integral sheet of material such as stamped steel. The vanes  72  are each generally triangular shaped with two free sides  80  and  82  and one attached side  84 , as identified in  FIGS. 6 and 7 . The attached side  84  can be described as extending generally radially relative to the central axis  58  of the burner  26 , and may be described as defining a radial length  86  of the vane  72 . The radial length  86  is preferably in a range from 40 percent to 45 percent of the inlet diameter  60 . 
     In the embodiment illustrated in  FIGS. 6-8 , the flow distribution member  54  includes fourteen vanes  72  arranged in an array substantially equally circumferentially spaced about the central axis  58  of the burner  26 . The array of vanes preferably includes at least twelve and no greater than twenty vanes  72 . 
     The flow distribution member  54  includes a plurality of spokes  88  extending radially outward from the closed axially central portion  70 , to an annular outer flange portion  90 . 
     It will be appreciated in the view of  FIG. 7 , that the closed axially central portion  70 , the spokes  88  and the flange portion  90  are generally planar, and that the vanes  72  have been folded out of that plane along their fixed sides  84 . Each of the vanes  72  may be described as being attached to one of the spokes  88  at the attached side  84  of the vane  72 . 
     The flow distribution member  54  may be described as having a plurality of triangular openings in the plane or cross sectional area thereof, each of which openings is defined as a triangular opening between the attached side  84 , and a radially open edge  92  and an outer open edge  94 . The total open area of the flow distribution member  54  is preferably in a range from about 50 percent to about 70 percent of the cross sectional area of the circular burner inlet  52 . It will be appreciated that the effectiveness of this open area is also dependent upon the vane angle  78 . 
     The flow distribution member  54  may also have a radially outward upturned annular wall  96  formed thereon for aid in placement and retention of the flow distribution member  54  in the inlet  52  of the burner apparatus  26 . 
     EXAMPLE 
     One example of flow distribution member  54  has an outside diameter  98  of 7.727 inches. The closed axially central portion  70  has a disc diameter  74  of 1.0 inches. Each of the fourteen vanes  72  has a radial length  86  of 3.16 inches. Each of the first free sides  80 , and the corresponding outer open edge  94  has a length of 1.25 inches. This provides a flow distribution member  54  having a total open area of approximately 58 percent of the cross sectional area of the burner inlet  52 . The vanes  72  are at a vane angle  78  of approximately 40 degrees. 
     The flow distribution member  54  just described is designed for use with a burner  26  designed for a heat output at maximum rated capacity of 4.0 MM Btu/Hr. In general, the apparatus  10  may be described as having a heat output at maximum rated capacity in excess of 1.0 MM Btu/Hr. For the burner  26 , designed to have a maximum rated capacity of 4.0 MM Btu/Hr, the inlet stream  100  may have a flow velocity of 10.4 ft/sec at the inlet  52  of the burner  26  at low fire, and 52.2 ft/sec at high fire. 
     The example flow distribution member  54  was tested to compare pressure distribution in the burner, both with and without the flow distribution member. 
       FIG. 11A  is a schematic elevation view of the burner  26 , identifying six axial test locations  1  through  6  along the length of the burner from its inlet  52  to its bottom  64 . The burner  26  had a length  62  of 40 inches, and an inlet diameter  60  of 7.8 inches.  FIG. 11B  is a schematic bottom view of the burner  26 , showing superimposed on the burner cross- section the location of the blower outlet  50 . The blower outlet  50  had a width along centerline  112  of 3.6 inches and a length along centerline  114  of 6.7 inches. Also shown in  FIG. 11B  are the locations of pressure detection tubes in the four quadrants of the burner cross-section. The pressure detection tubes are inserted through the burner bottom  64  near the inside surface of the cylindrical burner so as to measure the air pressure in the burner  26  adjacent the burner wall. The pressure detection tubes  110 A-D are longitudinally movable so that their open end is located at the desired one of the test elevations  1 - 6  seen in  FIG. 11A . The locations of the pressure detection tubes also correspond to the orientation of the blower outlet  50 . Pressure detection tubes  110 A and  110 D are aligned with the centerline  112  across the width of the cross-section of the rectangular outlet  50 , and pressure detection tubes  110 B and  110 C are aligned with the centerline  114  across the length of cross-section of the rectangular outlet  50 . 
     The test was performed by blowing air into the burner  26  with the blower  34  operating at 5500 RPM, and measuring the air pressure in the four quadrants of the cross-section at each of the six different elevations  1 - 6  along the length of the burner  26 . The data is displayed in the following Table I, with the pressure data being displayed in “inches of water”. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                   
                 Distance 
                 Pressure 
                 Pressure 
                 Pressure 
                 Pressure 
               
               
                 Elevation 
                 From Burner 
                 Detection 
                 Detection 
                 Detection 
                 Detection 
               
               
                 Location 
                 Inlet (Inches) 
                 Tube 110D 
                 Tube 110C 
                 Tube 110B 
                 Tube 110A 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 3.25 
                 −0.02 
                 2.20 
                 0.85 
                 0.34 
               
               
                 2 
                 5.75 
                 0.29 
                 2.90 
                 1.70 
                 1.20 
               
               
                 3 
                 13.75 
                 1.20 
                 3.00 
                 1.50 
                 1.80 
               
               
                 4 
                 21.50 
                 1.50 
                 2.60 
                 1.50 
                 1.70 
               
               
                 5 
                 28.75 
                 1.60 
                 2.10 
                 1.30 
                 1.60 
               
               
                 6 
                 35.75 
                 1.50 
                 1.80 
                 1.20 
                 1.40 
               
               
                   
               
            
           
         
       
     
     As is seen in Table I, very low pressures are experienced for pressure detection tube  110 D at elevation locations  1  and  2 , and for pressure detection tube  110 A at elevation location  1 . These locations correspond to the width centerline  112  of the outlet  50 , and they are locations where back flow of flame into the burner could occur. Also there is a substantial lack of uniformity of the pressure data in the four quadrants for any selected elevational location near the burner inlet  52 . 
       FIGS. 12A and 12B  are similar to  FIGS. 11A and 11B , but are for the testing of the burner  26  with the flow distribution member  54 , constructed as per the example described above, in place. It is noted that in the quadrants of pressure detection tubes  110 D and  110 A, where the low pressure problems were observed in the testing of  FIGS. 11A and 11B , additional elevational test locations  1 . 1 - 1 . 5  were added in the upper portion of the burner  26  to further explore the pressure distribution. The test results using the flow distribution member  54  are seen in the following Table II: 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE II 
               
               
                   
               
               
                   
                 Distance 
                 Pressure 
                 Pressure 
                 Pressure 
                 Pressure 
               
               
                 Elevation 
                 From Burner 
                 Detection 
                 Detection 
                 Detection 
                 Detection 
               
               
                 Location 
                 Inlet (Inches) 
                 Tube 110D 
                 Tube 110C 
                 Tube 110B 
                 Tube 110A 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 3.25 
                 2.90 
                 1.50 
                 1.70 
                 2.10 
               
               
                 1.1 
                 3.75 
                 2.00 
                 NA 
                 NA 
                 2.20 
               
               
                 1.2 
                 4.25 
                 1.60 
                 NA 
                 NA 
                 2.40 
               
               
                 1.3 
                 4.75 
                 1.90 
                 NA 
                 NA 
                 2.30 
               
               
                 1.4 
                 5.25 
                 1.90 
                 NA 
                 NA 
                 2.20 
               
               
                 1.5 
                 5.75 
                 2.20 
                 NA 
                 NA 
                 2.30 
               
               
                 2 
                 13.75 
                 1.40 
                 1.50 
                 1.80 
                 1.20 
               
               
                 3 
                 21.50 
                 1.20 
                 1.10 
                 1.10 
                 1.10 
               
               
                 4 
                 28.75 
                 0.97 
                 0.97 
                 0.90 
                 0.97 
               
               
                 5 
                 35.75 
                 0.72 
                 0.84 
                 0.75 
                 0.76 
               
               
                   
               
            
           
         
       
     
     It is noted that as compared to Table I there are much higher pressures adjacent the burner inlet  52 , and there are no negative pressure zones. Also, with the use of the flow distribution member  54  there is much better cross-sectional pressure uniformity across the four quadrants for any given elevational location, as compared to the data of Table I. 
     CFD Modeling 
       FIGS. 13-15  represent CFD (computational fluid dynamics) modeling.  FIG. 13  represents the baseline modeling that was done for the burner  26  without the flow distribution member  54 .  FIG. 14  represents the modeling for the burner  26  using the flow distribution member  54 , having dimensions substantially like those of the example described above for the test data of  FIG. 12A and 12B .  FIG. 15  represents comparative CFD modeling that was done for a modified flow distribution member having an open center instead of having the closed center  70 . 
     In  FIG. 13 , there are two cross-sections shown, taken along the two centerlines  112  and  114  of the rectangular cross-section of the blower outlet  50  seen in  FIG. 11B . The cross-section on the left side of  FIG. 13 , is taken along the shorter centerline  112 , and the cross-section on the right side of  FIG. 13  is taken along the longer centerline  114 . Between the two cross-sectional views of  FIG. 13  there is a table showing zones of computed flow velocities, which correspond also to fluid pressure. Thus the zone indicated as “A” represents velocities in the range of from 107.732 ft/s down to 95.761 ft/s. Corresponding areas in the cross-sectional views having velocities within that range have been identified by the tag lines with the letter “A”. Similar identification is provided for zones of flow velocity B, C, etc. By comparison it is apparent that there is more lack of uniformity of flow velocities along the axis  112  than along the axis  114 . This is because there is a greater discontinuity between the cross-sectional shape of the blower outlet  50  and the burner inlet  52  along axis  112 . As can be seen on the cross-section on the left side of  FIG. 13 , there are significant areas having very low velocities in the I, H and G velocity zones, which are representative of low pressure or negative pressure areas where flash back could occur. It is apparent that these problematic areas are located along the centerline  112  across the narrow width of the blower outlet  50 . 
       FIG. 14  is presented in a format similar to  FIG. 13 , and is representative of a burner  26  including the flow distribution member  54  having a closed center  70  as described herein. Again, the cross-section on the left side of  FIG. 14  is taken along centerline  112 , and the cross-section on the right side of  FIG. 14  is taken along centerline  114 . In both cross-sections the flow velocities are much more uniform in all four quadrants at a given cross-section, than were the results of  FIG. 13 . Also there are no low or negative pressure zones near the burner inlet  52 . 
     Finally,  FIG. 15  is presented to contrast the performance of the flow distribution member  54  having the closed center portion  70 , to a flow distribution member having similar radial vanes but having an open center instead of the closed center  70 . As is apparent, there is a very high axial velocity stream near the inlet  52  surrounded by some relatively low velocity zones near the inlet  52 . There is a great lack of uniformity of flow velocities across each cross-section, especially near the burner inlet  52 . The flow distribution member modeled in  FIG. 15  creates very low flow velocities near the burner surface adjacent the burner inlet  52 , and under certain conditions such a design could suffer from flash back of flames into the burner. 
     Methods of Operation 
     The methods of operating the burner apparatus  26  may be described as follows with reference to the schematic illustration of  FIG. 10 . 
     An inlet stream  100  of fuel and air mixture is provided to the inlet  52  of burner  26  from the outlet  50  of blower  34  via the blower to burner transition duct  48 . 
     An axially central portion  102  of inlet  52  is blocked by the closed axially central portion  70  of flow distribution member  54  thereby preventing axially central flow of the inlet stream  100  into the inlet  52 . 
     This diverts the inlet stream  100  through an annular area  104  between the axial central portion  102  and the outside diameter  60  of the burner inlet  52 . Additionally, the vanes  72  swirl the inlet stream  100  as it passes across the vanes  72  thus creating the spiral flow pattern schematically illustrated at  106  in  FIG. 10 . The spiral flow pattern  106  extends along the entire length  62  of the burner  26 . 
     As a result of the spiral flow pattern  106  and the absence of axially central flow adjacent the inlet  52  to burner  26 , negative pressures are avoided along the entire length  62  of the burner  26 , particularly adjacent the burner inlet  52 . 
     Furthermore, the spiral flow pattern  106  causes the fuel and air mixture to exit the burner outer surface  56  at substantially uniform velocities along the entire length  62  of the burner  26 . 
     The vanes  72  serve as a directional guide to the fuel and air mixture. The angle  78  of the vanes  72  can vary, but should be great enough to create a swirling motion of the fuel and air mixture to form the spiral flow pattern  106 . 
     With the spiral flow pattern  106 , an outward pressure is provided against the perforated burner wall  56  which in turn provides an even and substantially equal flame pattern throughout the length  62  of the burner  26 . 
     Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned, as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled In the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.