Abstract:
A heat exchange system comprising a housing ( 66 ) elongated along a longitudinal axis (x-x) having an upper portion ( 22 ) defining an upper zone, a middle portion ( 23 ) defining a transitional zone, and a lower portion ( 24 ) defining a lower zone, a heat exchange conduit ( 25 ) elongated along the longitudinal axis interior to the housing and configured and arranged to transmit a fluid from a fluid input ( 26 ) to a fluid output ( 27 ) through the upper zone, the transitional zone and the lower zone, a burner ( 28 ) configured and arranged to produce combustion flue gases that can flow through at least a portion of the upper zone, the transitional zone and the lower zone, a hot flue gas flow path ( 35 ) between the upper zone and the lower zone, a baffle ( 30 ) disposed inside of the heat exchange conduit relative to the longitudinal axis and in the lower zone of the lower portion of the housing, and a gas flow diverter ( 40 ) disposed inside to the heat exchange conduit relative to the longitudinal axis and above the baffle and at least partially in the transitional zone, the gas flow diverter configured and arranged relative to the heat exchange conduit so as to divert the flue gas in the flue gas flow path into a first flow path ( 36 ) outside of the diverter relative to the longitudinal axis and a second flow path at least partially separated from the first flow path by the diverter.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the field of heat exchangers, and more particularly to an improved coil tube heat exchanger. 
       BACKGROUND ART 
       [0002]    Heat exchangers having cylindrical shells and helical tubes for heating fluid in the tubes are well known in the prior art. Generally, fluid flowing in the tubes is heated by flowing combustion gases provided by a burner located interior to the coils. U.S. Pat. No. 6,026,801 is directed to a coil heat exchanger having an interior plug. U.S. Patent Publication No. 2011/0041781 is directed to a coil tube heat exchanger having a dual-diameter outer cylindrical housing, a buffer tank within the helix coil of the heat exchanger and a rope seal disposed between adjacent coil loops of a portion of the helix coil. U.S. Pat. No. 7,523,721 is directed to a heat exchanger that includes a partition that partitions the space surrounding a coil tube into first and second regions to increase heat exchange efficiency. U.S. Pat. No. 8,343,433 is directed to a tube reactor having parallel reactor tubes. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides a heat exchange system ( 20 ) comprising a housing ( 66 ) elongated along a longitudinal axis (x-x) having an upper portion ( 22 ) defining an upper zone, a middle portion ( 23 ) defining a transitional zone, and a lower portion ( 24 ) defining a lower zone, a heat exchange conduit ( 25 ) elongated along the longitudinal axis interior to the housing and configured and arranged to transmit a fluid from a fluid input ( 26 ) to a fluid output ( 27 ) through the upper zone, the transitional zone and the lower zone, a burner ( 28 ) configured and arranged to produce combustion flue gases that can flow through at least a portion of the upper zone, the transitional zone and the lower zone, a hot flue gas flow path ( 35 ) between the upper zone and the lower zone, a baffle ( 30 ) disposed inside of the heat exchange conduit relative to the longitudinal axis and in the lower zone of the lower portion of the housing, and a gas flow diverter ( 40 ) disposed inside to the heat exchange conduit relative to the longitudinal axis and above the baffle and at least partially in the transitional zone, the gas flow diverter configured and arranged relative to the heat exchange conduit so as to divert the flue gas in the flue gas flow path into a first flow path ( 36 ) outside of the diverter relative to the longitudinal axis and a second flow path ( 37 ) at least partially separated from the first flow path by the diverter. 
         [0004]    The heat exchange conduit may comprise a helical heat exchange tube extending between the input and the output. The helical heat exchange tube may have an inner diameter ( 52 ) between the upper and lower zones that varies by less than 20 percent, and the inner diameter of the helical heat exchange tube between the upper and lower zones may be substantially uniform. 
         [0005]    The housing may comprise a cylindrical shell ( 21 ) and the heat exchange tube and the shell may be concentric. The baffle may comprise a cylindrical outer surface ( 31 ) and the outer surface of the baffle may be concentric with the heat exchange tube. The burner may be disposed at least partially within the upper zone of the upper portion of the housing. The burner may comprise a cylindrical outer surface ( 29 ) and the outer surface of the burner may be concentric with the heat exchange tube. The hot flue gas flow path may be inside of the heat exchange conduit relative to the longitudinal axis in the upper zone and between the heat exchange conduit and the burner in the upper zone. 
         [0006]    The first flow path may be outside of the diverter relative to the longitudinal axis and the second flow path may be inside of the diverter relative to the longitudinal axis. The diverter may comprise an annular ring and the annular ring may be concentric with the heat exchange tube. The diverter may be integral to the baffle. The diverter may be configured and arranged so as to divide the flue gas flow path into a third flow path ( 138 ) at least partially separated from the first flow path ( 136 ) and the second flow path ( 137 ). The second flow path may be inside of the diverter relative to the longitudinal axis and the third flow path may be between the first flow path and the second flow path. 
         [0007]    The baffle may comprise a water tank. The housing may have an inner diameter ( 50 ), the heat exchange tube may have an outer diameter ( 51 ) and the outer diameter of the heat exchange tube may be substantially equal to the inner diameter of the housing. The burner may be located exterior to the housing. The gas flow diverter may comprise a porous media. The upper zone may be configured to provide radiant heat transfer and convective heat transfer to a fluid flowing in the heat exchange conduit, wherein the heat exchange conduit, the baffle, the gas flow diverter and the housing are configured and arranged to provide a gas flow through the transition zone such that heat transfer to the fluid in the heat exchange conduit maintains the fluid at a temperature that is below the fluids boiling point, and the lower zone is configured to provide convective heat transfer to the fluid flowing in the heat exchange conduit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective and partial cut-away view of an embodiment of an improved heat exchanger. 
           [0009]      FIG. 2  is an enlarged view of the heat exchanger shown in  FIG. 1 , taken within the indicated area A of  FIG. 1 . 
           [0010]      FIG. 3  is a perspective view of the diverter ring and baffle shown in  FIG. 1 . 
           [0011]      FIG. 4  is a vertical cross-sectional view of the diverter ring and plug shown in  FIG. 3 , taken generally on line  4 - 4  of  FIG. 3 . 
           [0012]      FIG. 5  is a perspective and partial cut-away of the heat exchanger shown in  FIG. 1  showing positions for temperature readings. 
           [0013]      FIG. 6  is a perspective view of an alternative embodiment of the diverter ring and baffle shown in  FIG. 1 . 
           [0014]      FIG. 7  is a vertical cross-sectional view of the ring and baffle shown in  FIG. 6 , taken generally on line  7 - 7  of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0016]    Referring now to the drawings, and more particularly to  FIG. 1  thereof, an improved heat exchange system is provided, of which an embodiment is generally indicated at  20 . Heat exchanger  20  is shown as broadly including housing  66 , having a generally cylindrical outer shell  21  orientated about central vertical axis x-x, helical coiled tube  25  concentric with shell  21 , upper premix burner  28  concentric with shell  21 , and lower baffle  30  concentric with shell  21 . 
         [0017]    As shown, housing  66  includes a single diameter can or shell  21  having upper portion  22 , middle portion  23  and lower portion  24 . The inner diameter  50  of shell  21  is uniform through upper, middle and lower portions  22 ,  23  and  24 . Alternatively, the inner diameter  50  of shell  21  may vary by less than 20% through upper, middle and lower portions  22 ,  23  and  24 . Top cap  64  of housing  66  includes upper fuel inlet  33  and bottom cap  65  of housing  66  includes lower flue gas outlet  34 . 
         [0018]    Housing  66  contains a helical coiled tube  25  elongated along axis x-x. Tube  25  extends from bottom water inlet  26  to top water outlet  27  and is generally concentric with shell  21 . In use, water is received through inlet  26  and is moved through coiled tube  25  and out through output  27 . 
         [0019]    A radial fire burner  28  and cylindrical baffle  30  are disposed axially and concentrically within shell  21  and inside the lumen of helical coiled tube  25 . One or more igniters are located in close proximity to burner  28  for the purpose of igniting an air-fuel mixture that is received in burner  28  through inlet  33 . Baffle  30  is positioned in the lower portion  24  of shell  21  and is disposed radially inside of coiled tube  25 . Baffle  30  comprises outer surface  31  and top  60 , which define inner hollow pocket  32 . Inner hollow pocket  32  may be open to flue gas, but does not communicate with water flowing through the coil. 
         [0020]    In use, the coil-turns of helical tube  25  in the upper zone receive radiation heat from combustion flame of burner  28 . 
         [0021]    In use, fuel air mixture is provided to the combustion chamber of burner  28  through inlet  33 . Hot flue gas, generated in the combustion chamber of burner  28 , flows down through the upper zone in flow path  35 . In the lower zone, the flue gas passes by the coil-turns around center cylindrical baffle  30  and exits heat exchanger  20  through flue gas outlet  34 . Water flows in the opposite direction upward from inlet  26 , through coil tubes  25  and then out through output  27 . Heat, received by coil tube  25  from flue gas, is transferred to the water flowing inside coil tube  25 . Thus, cold water flows in at the bottom end of coil tube  25 , is heated, and then exits the top end of coil tube  25 . Thus, the overall flow direction of water is upward and the overall flow direction of hot gas is downward, which establishes a counter-flow heat transfer process. The water inside coil tube  25  receives heat when flowing through each coil-turn and its temperature is elevated as it receives such heat. The coil-turns around burner  28  generally receive radiation heat from surface  29  of burner  28  and from combustion flames. Some convection heat transfer exists but at a lower heat flow rate, due to the low local flue gas flow velocity around these coil-turns in the upper zone. In the coil-turns in the lower zone around center cylindrical baffle  30 , heat is transferred primarily through convection, with or without condensation. 
         [0022]    As shown in  FIGS. 1-5 , a specially configured heat transfer load reducing ring, or diverter ring,  40  is disposed slightly above top surface  60  of baffle  30  of heat exchanger  20  and inside the lumen of coiled tube  25 . Diverter ring  40  is thus disposed to the inside of coiled tube  25  relative to axis x-x. As shown in  FIG. 4 , heat transfer reducing ring  40  is generally a cylindrical ring-shaped annular structure elongated along axis x-x, and is bounded by upwardly-facing annual horizontal surface  41 , outwardly-facing vertical cylindrical surface  42 , downwardly and outwardly-face frusto-conical surface  43 , downwardly-facing annual horizontal surface  44 , inwardly-facing vertical cylindrical surface  45 , and upwardly and inwardly-facing frusto-conical surface  46 , joined at its outer marginal end to the inner marginal end of surface  41 . Surfaces  46  and  45  generally define axial through-way  47 . 
         [0023]    As shown in  FIGS. 3 and 4 , diverter ring  40  is supported on top surface  60  of baffle  30  by four circumferentially spaced legs or posts  48   a - d.  Posts  48   a - d  extend from top surface  60  of baffle  30  to provide an annular space between top surface  60  of baffle  30  and bottom surface  44  of diverter ring  40 . In this embodiment, diverter ring  40  and baffle  30  are formed integrally from the same material. However, it is contemplated that diverter ring  40  may be an entirely separately formed element that is supported above baffle  30  in the transitional zone of heat exchanger  20  by alternate means. 
         [0024]    As shown in  FIGS. 3 and 4 , an outer layer of insulation  63  is provided on outer surface  42  of diverter ring  40 , outer surface  31  of baffle  30 , and the outer surfaces of support legs  48   a - d.  In this embodiment, insulation covering  63  on the outer surfaces of baffle  30  and ring  40  is a ceramic fiber blanket. 
         [0025]    As shown in  FIG. 2 , heat load reducing ring  40  generally separates or spreads the hot flue gas flowing from the upper zone in flue gas flow path  35  into two paths  36  and  37  in the transition zone. In particular, part  36  of the hot flue gases in path  35  flows over top surface  41  of ring  40  and radially outwardly of diverter ring  40  and hits coil-turns C and B of tube  25 . As described further below, after passing by coil-turns C and B, the flue gas in this flow path  36  is already cooled down. Part  37  of hot flue gases in flow path  35  flows inside of surfaces  46  and  44  and below surface  44  of diverter ring  40  and is combined with the cooled flue gases in flow path  36  and hits coil-turn A of tube  25 . Thus, flow path  37  passes by inside surface  45  relative to axis x-x and through the gaps between posts  48   a - d,  bottom surface  44  of diverter ring  40  and top surface  60  of baffle  30 . The again combined hot flue gases are then forced by surface  31  of baffle  30  to flow by the lower coil-turns of tube  25  in the lower zone one-by-one. 
         [0026]    A number of unexpected beneficial results are achieved with heat transfer load reducing ring  40 . In particular, coil-turns C and B, on the outside of diverter ring  40  relative to axis x-x, receive the hottest flue gases but only with respect to part of the total mass flow of flue gases in flow path  35 . Coil-turn A, below heat transfer reducing ring  40 , received the total amount of flue gas but at a lower temperature. Thus, the concentrated heat transfer load of flue gases in flow path  35  was spread onto multiple coil-turns of tube  25  in this transitional zone by diverter ring  40 . In particular, and with reference to  FIG. 5  and the Table 1 below, flue gas temperatures were measured in heat exchanger  20  and compared to a similarly configured heat exchanger which did not include diverter ring  40 . The locations of temperature readings in these respective test heat exchangers are indicated in  FIG. 5 . Essentially, these measurements were taken on the inside and outside of each coil-turn of tube  25 . Location references from  FIG. 5  are set forth in columns  1  and  2 . Temperatures taken with heat exchanger  20  having diverter ring  40  at references  1 - 16  are shown in columns  3  and  4 , respectively. Temperature readings at such locations for a heat exchanger without diverter ring  40  are shown in column  5  and  6 , respectively. The temperatures in flue collector outlet  34  were also taken and are shown in Table 1 below. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Location of 
                   
                   
               
               
                 Temperature 
                 Including Heat Load 
                 Not Including Heat 
               
               
                 Measurement 
                 Reducing Ring 
                 Load Reducing Ring 
               
             
          
           
               
                 Inside of 
                 Outside of 
                 Inside of 
                 Outside of 
                 Inside of 
                 Outside of 
               
               
                 Coil 
                 Coil 
                 Coil 
                 Coil 
                 Coil 
                 Coil 
               
               
                   
               
             
          
           
               
                 2 
                 1 
                 1651 
                 535 
                 1527 
                 480 
               
               
                 4 
                 3 
                 1745 
                 555 
                 1642 
                 370 
               
               
                 6 
                 5 
                 1551 
                 615 
                 1720 
                 349 
               
               
                 8 
                 7 
                 1087 
                 485 
                 1769 
                 315 
               
               
                 10 
                 9 
                 656 
                 276 
                 982 
                 430 
               
               
                 12 
                 11 
                 272 
                 214 
                 291 
                 221 
               
               
                 14 
                 13 
                 202 
                 161 
                 211 
                 175 
               
               
                 16 
                 15 
                 155 
                 152 
                 161 
                 147 
               
             
          
           
               
                 Temperature in Flue 
                 130 
                 133 
               
               
                 Collector 
               
               
                   
               
             
          
         
       
     
         [0027]    As shown above, the temperature variation around the coil-turns indicates that the heat transfer load on coil-turn B and all the coil-turns above coil-turn B, is low. Coil-turn A has a very high transfer load. It cools the flue gas from about 1760° F. down to about 982° F. Considering the total flue gas temperature drop is about 1760° F. to 133° F. across the whole heat exchanger and assuming 15% of total heat is latent heat, due to the condensing of water vapor in the flue gas, 40% of the total heat transfer load of the whole heat exchanger is on coil A. By adding diverter ring  40 , it was found that a much more even heat transfer load is applied to these coil turns. Part of the hottest flue gas (for example 50 percent of the total flue gas) at 1745° F. hit coil-turns C and B. After it is cooled, this flow  36  mixed with the flue gas flowing through second flow path  37  (at 1745° F.) and reached a mix temperature of about 1087° F. Then the total amount of flue gas at 1087° F. hit coil-turn A. Coil-turn A cooled it down to 716° F. Again, assuming 15% of the total heat is latent heat, the heat transfer load on coils C, B and A were about 16%, 14% and 18%, respectively, of the total heat exchanger heat transfer load. Comparing the heat transfer load distribution for heat exchanger  20  compared to a heat exchanger without diverter ring  40 , diverter ring  40  successfully spread the concentrated heat transfer load onto these three critical coil-turns. 
         [0028]    In addition, heat transfer load reducing ring  40  provided benefits with respect to boiling noise. Considering a 100 MBH boiler, the design water flow rate through the heat exchanger is 8 gallons per minute. The corresponding temperature differential across the heat exchanger is 20° F. when the boiler runs on full fire. On boilers without diverter ring  40 , it was observed that when the temperature differential across the heat exchanger reached 26° F., boiling noises started. In other words, when the water flow rate was reduced to 6 gallons per minute, boiling started. Boiling noise came from the coil-turn at the top surface  60  of baffle  30 . By adding diverter ring  40 , surprising results occurred. The heat exchanger water flow rate was reduced down to 2 gallons per minute. The corresponding temperature differential across the heat exchanger was more than 80° F. No boiling noises were identified. The test was conducted with 100 percent antifreeze solution and the heating system had zero gauge pressure on its fluid. Thus, diverter ring  40  eliminated locate concentrated heat transfer loads. The hot gas flow in each of paths  36  and  37  may be 10% to 90% of the total hot gas flow. 
         [0029]      FIGS. 6 and 7  show a second embodiment  140  of a heat transfer load reducing ring. Gas flow diverter  140  comprises two ring members  141  and  142 , each having the same configuration as diverter ring  40 . As shown, the combination of baffle  30  and lower diverter ring  141  is the same as shown in  FIG. 4 . Diverter ring  141  is supported on top surface  160  of baffle  30  by four integral posts  148   a - d.  However, in this embodiment, a second diverter ring having a configuration the same as diverter ring  40  is further provided on top of intermediate ring  141 . As shown, upper diverter ring  142  is supported on top of lower diverter ring  141  by for posts  149   a - 149   d  that are supported by and formed integrally with upwardly-facing annular horizontal surface  171  of lower diverter ring  141 . As shown, an outer layer of insulation  163  is provided on the outer surfaces of the baffle, rings and posts. 
         [0030]    With this embodiment, flue gas in flow path  135  is further dispersed and spread relative to the associated coil-turns of helical tube  25 . With reference to  FIG. 6 , flow path  135  is initially separated by the top of upper ring  142  into flow path  136  and flow path  133 . Part  136  of the hot flue gases in path  135  flows over the top surface of upper ring  142  and radially outwardly of diverter ring  142 . Part  133  of hot flue gases in flow path  135  flows inside of upper ring  142  relative to axis x-x. Part  133  of hot flue gases is further separated into flow paths  137  and  138 . Flow path  138  passes through the gaps between posts  149   a - d  before recombining with flow path  136  outwardly of diverter ring  140  relative to axis x-x. The remaining part  137  of flue gases  133  flows inside of lower ring  141  relative to axis x-x and through the gaps between posts  148   a - d  before recombining with flow path  136  outwardly of diverter ring  140  relative to axis x-x. The again combined hot flue gases are then forced by surface  31  of baffle  30  to flow by the lower coil-turns of tube  25  in the lower zone one-by-one. It is contemplated that multiple other configurations may be used to spread or divide the flue gas in the flue gas path across multiple coil-turns. For example, a diverter ring with a higher number of flow channels may be employed or the diverter ring may comprise a porous media material defining many numerous flow paths that disperse or spread the flue gas. 
         [0031]    Diverter ring  40  may be made of metal or non-metal material, coil  25  may be a smooth tube coil or may be a tube with extended surfaces such as a finned coil. Burner  28  may be external to housing  20 . For example, an outside burner may be used to generate hot gas that is then transferred inside housing  65 . Baffle  30  may be formed of a metal or non-metal material. In addition, baffle  30  may include a heat exchanger component, such as a water tank. The heat exchanger may or may not employ addition flow guiding baffles on the coils. 
         [0032]    The present invention contemplates that many changes and modifications may be made. Therefore, while the presently-preferred form of the improved heat exchanger has been shown and described, and a number of alternatives discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.