Abstract:
A gas turbulator is inserted in a tube of a heat exchanger to increase turbulence of gases passing through the tubes of the heat exchanger. The turbulator consists of a longitudinal metal strip running the length of the heat exchanger tube. Longitudinal tabs are punched from the interior of the metal strip. The tabs protrude in opposite directions from the plane of the longitudinal strip to form a series of slanted flip up tabs and flip down tabs in a side elevation view of the turbulator.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Provisional Patent Application No. 62/335,330, filed on May 12, 2016, the disclosure of which is relied upon and incorporated herein in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a tubular heat exchanger for an indirect gas-fired air handling unit and more particularly to a turbulator for insertion into the tubes of the tubular heat exchanger. 
       BACKGROUND OF THE INVENTION 
       [0003]    A turbulator is a device that is positioned inside the tubes of a tubular heat exchanger. The turbulator prevents laminar gas flow from developing inside the heat exchanger tubes. Turbulent gas flow is preferred because turbulent gas flow inside the heat exchanger tubes promotes heat being transferred from the heated combustion gas to the tube material. High turbulence, however, also causes resistance to the gas flow through the heat exchanger tubes in the form of a pressure drop along the length of the heat exchanger tubes. 
       SUMMARY OF THE INVENTION 
       [0004]    An indirect gas-fired air handling unit of the present invention includes a drum and tube heat exchanger comprising a drum combustion chamber and a tubular heat exchanger. The combustion chamber is fitted with a burner. The heated combustion gas from the burner in the combustion chamber flows through the tubes of the tubular heat exchanger before exiting through the exhaust flue. Flip-up-down single H-type turbulators of the present invention are inserted in the heat exchanger tubes to increase heat transfer from the heated gas to the heat exchanger tubes. The flip-up-down single H-type turbulators of the present invention also reduce manufacturing time for the drum and tube heat exchangers. 
         [0005]    Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of an indirect gas-fired air handling unit with a drum and tube heat exchanger in accordance with the present invention. 
           [0007]      FIG. 2  is perspective view of the drum and tube heat exchanger with the front plate removed to reveal internal detail in accordance with the present invention. 
           [0008]      FIG. 3  is a side perspective view of the ends of the tubes of the heat exchanger with some of the turbulators partially withdrawn for the purposes of illustration. The heat exchanger is mounted in a demonstration cabinet with a door replacing the standard front plate for the purposes of demonstrating the present invention. 
           [0009]      FIG. 4  is an enlarged side perspective view of the ends of the tubes of the heat exchanger with some of the turbulators partially withdrawn for the purposes of illustration. The heat exchanger is mounted in a demonstration cabinet with a door replacing the standard front plate for the purposes of demonstrating the present invention. 
           [0010]      FIG. 5A  is a top plan view of a turbulator in accordance with the present invention. 
           [0011]      FIG. 5B  is an enlarged top plan view of the turbulator in accordance with the present invention. 
           [0012]      FIG. 6A  is a side elevation view of the turbulator in accordance with the present invention. 
           [0013]      FIG. 6B  is an enlarged side elevation view of the turbulator in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]      FIGS. 1-4  illustrate the indirect gas-fired air handling unit  10  with a drum and tube heat exchanger  34  in which turbulators  40  of the present invention are used.  FIGS. 5A-6B  illustrate the construction of the turbulators  40  of the present invention. 
         [0015]      FIG. 1  illustrates an indirect gas-fired and fire air handling unit  10  with a drum and tube heat exchanger  34  such as the AW-I indirect gas-fired air handling unit manufactured and sold by E. H. Price Ltd., Winnipeg, Manitoba, Canada. The air handling unit  10  comprises a cabinet  12 , the drum and tube heat exchanger  34  including a gas-fired burner (not shown), a fan  22  driven by a motor  24 , and controls  32  for controlling the operation of the fan  22  and the gas-fired burner. The fan  22  draws outside air into the cabinet  12  through air inlet  26  and filter  30 , directs the air past the drum and tube heat exchanger  34  where the air absorbs heat, and forces the heated air out of the supply air outlet  28  into the occupied space of a building. 
         [0016]      FIG. 2  shows the drum and tube heat exchanger  34  in greater detail. Particularly, the drum and tube heat exchanger  34  has a drum shaped combustion chamber  36  and a tubular heat exchanger  37 .  FIGS. 3 and 4  show an inlet side  41  of the tubular heat exchanger  37  in greater detail. A gas-fired burner (not shown) is mounted to fire into the combustion chamber  36 . Combustion air is drawn into the combustion chamber  36  through a combustion air inlet (not shown). The heated combustion gases exit the combustion chamber  36  through combustion chamber outlet  17 . A conduit chamber  39  connects the combustion chamber outlet  17  to the inlet side  41  of the tubular heat exchanger  37 . In  FIG. 2 , a standard front plate for the conduit chamber  39  has been removed to show the internal detail of the heat exchanger tubes  38  at the inlet side  41  of the tubular heat exchanger  37 . In  FIG. 3  the heat exchanger  34  is mounted in a demonstration cabinet  12 . The standard front plate has been removed from the heat exchanger  34  and replaced by a door  35  to allow easy access to the conduit chamber  39  during demonstrations and testing. Depending on the model of the indirect gas-fired air handling unit  10 , the drum and tube heat exchanger  34  may have anywhere from 14 to 38 heat exchanger tubes  38 . Moreover, the heat exchanger tubes  38  may vary in size from 2 inches in diameter to 3.5 inches in diameter. 
         [0017]    As more clearly shown in  FIGS. 3 and 4 , flip-up-down single H-type turbulators  40  are inserted into the heat exchanger tubes  38 . In  FIGS. 3 and 4 , the turbulators  40  have been partially pulled from the heat exchanger tubes  38  for the purposes of illustration. 
         [0018]    Turning to  FIGS. 5A-6B , the turbulator  40  is shown in greater detail. The turbulator  40  is constructed from a longitudinal strip of metal  42  with a length equal to that of the heat exchanger tubes  38  and a width approximately equal to the diameter of the heat exchanger tubes  38 . H-shaped cuts  48  are made in the longitudinal strip  42  as shown in  FIGS. 5A and 5B . Each H-shaped cut  48  creates a pair facing tabs, flip up tab  44  and a flip down tab  46 . The flip up tab  44  remains connected to the longitudinal strip  42  along a flip up hinge line  45 , and the flip down tab  46  remains connected to the longitudinal strip  42  along a flip down hinge line  47 . The flip up tab  44  is bent upward from the plane of the longitudinal strip  42  along the flip up hinge line  45 , and the flip down  46  is bent downward from the plane of the longitudinal strip  42  along the flip down hinge line  47 . The elevation views in  FIGS. 6A and 6B  show the orientation of the flip up tab  44  and the flip down tab  46  once those tabs have been bent along the hinge lines  45  and  47  respectively. 
         [0019]    The material for the turbulators  40  is stainless steel conforming to ASTM A240 Gr.409, Gr.304, or Gr.316 and has a thickness between 0.030 inch and 0.060 inch. The width of the longitudinal strip  42  conforms to the diameter of the particular heat exchanger tube  38 . The width of the tabs  44  and  46  is between 40% and 60% of the width of the longitudinal strip  42 . The length of each pair of the tabs  44  and  46  is approximately twice the length of the outside diameter of the tube  38  and between 4 inches and 7 inches. The total length of all of the tabs  44  and  46  is between 50% and 80% of the length of the longitudinal strip  42 . The tabs  44  and  46  are bent at an angle  52  to the plane of the longitudinal strip  42  of between 15° and 25°. While the FIGS. illustrate tabs  44  and  46  that are essentially rectangular in shape, tabs in the shape of squares, triangles, circles, ellipses, pentagons, hexagons, octagons, or other geometric shapes are useful in implementing the present invention. 
         [0020]    As previously indicated, the flip-up-down single H-type turbulators  40  of the present invention are intended for installation in the indirect gas-fired air handling unit  10 , as for example the Price AW-I air handling unit. The AW-I air handling unit  10  has a heat release of 250 MBTU/hr. up to 6 MMBTU/hr. of heat output. The AW-I air handling unit  10  with prior art spiral turbulators has an efficiency of approximately 80%. 
         [0021]    When the flip-up-down single H-type turbulators  40  of the present invention are installed in heat exchanger tubes  38  the AW-I air handling unit  10  in place of conventional spiral turbulators, a 4% increase in heat transfer occurs as evidenced by a drop in the flue temperature from 620° F. to 480° F. The flue gas pressure drops approximately 0.65 inch of water column (w.c.) as measured across the heat transfer tubes  38  when using the flip-up-down single H-type turbulators  40  of the present invention. 
         [0022]    The flip-up-down single H-type turbulators  40  also produce increased performance even with burners that have a cylindrical flame. A cylindrical flame is longer in the direction of the length of the drum combustion chamber  34  than it is wide at the root of the flame. An efficiency of greater than 83% occurred when using a GP C-Series burner manufactured and sold by C.I.B. UNIGAS S.p.A., Via L. Galvani, 9-35011, Campodarsego (PD), Italy. Other burners have a short flame relative to the size of the flame root at maximum fire. A burner with a long cylindrical flame is able to effectively impart radiant energy onto the interior of the drum combustion chamber  36  which is on a parallel axis. At the same heat release, a burner with a short and wide flame is not able to effectively impart radiant energy onto the interior of the drum combustion chamber  36 . This means that if the heat exchanger  37  needs to exchange the same amount of energy, the heat exchanger tubes  38  will need to transfer more with the short and wide flame. The H-type turbulator  40  allows for more energy to be transferred by the heat exchanger tubes  38  when the drum combustion chamber  36  is not as effective because of the flame shape. However, even when the flame is cylindrical, a shape which allows for good heat transfer through the drum, the H-type turbulators  40  still allow for improved heat transfer in the tubular heat exchanger  37 . The H-type turbulators  40  ensure that laminar flow does not set up inside the heat exchanger tube  38 , thereby ensuring that good heat transfer can take place between the hot flue gasses and the wall of the heat exchanger tube  38  due to the turbulent flow. 
         [0023]    The effect of the additional pressure drop on the C-Series burner (a cylindrical flame burner) is balanced by balancing the orifice size on the tubular heat exchanger  37 . The orifice of the tubular heat exchanger  37  is downstream of the heat exchanger tubes  38  which contain the turbulators  40 . The orifice size can be increased when using a C-Series burner to reduce the pressure drop the orifice imparts on the flow of hot flue gases, to offset the increased pressure drop that the H-type turbulator  40  imparts on the flow of hot flue gases. 
         [0024]    The flip-up-down single H-type turbulator  40  is easy to manufacture. The H-shaped cut  48  ( FIGS. 5A and 5B ) is made by a laser, and the tabs  44  and  46  are bent by hand. The heat exchanger tube  38  acts as a go/no-go jig, preventing tabs  44  and  46  from being bent too far, and also showing where tabs should be bent more. The configuration of the turbulator  40  does not require high degree of accuracy. 
         [0025]    While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.