Abstract:
An insulated heat exchanger tube assembly is disclosed herein comprising a heat exchanger tube, an insulating portion form-fitted around the heat exchanger tube, the insulating portion comprising a polymeric foam, and a polymeric film formed over and adhered to the insulating portion. A heat exchanger formed from the tube and a method of forming an insulated heat exchanger tube also are disclosed. The tube assembly is useful in making a heat exchanger that requires minimal floor space and can be efficiently assembled.

Description:
BACKGROUND 
       [0001]    Heat exchanger tubes can be coiled to permit a substantial length of tubing material to be conveniently disposed within the confines of a heat exchanger housing. When the tubes are used in connection with hot and/or cold fluid, the tubes may have insulation placed on the outer surface thereof. 
         [0002]    Tube-in-tube heat exchangers are used in a variety of applications for transferring heat from one fluid to another. Particular configurations of tube-in-tube heat exchangers are described in U.S. Pat. Nos. 5,004,047 and 6,012,514. 
         [0003]    Traditionally, tube-in-tube heat exchangers used in geothermal heat pumps employ coiled tube-in-tube heat exchanger tubes. The coiled tubes are wrapped with an insulating material after the tubing is installed. The insulated material is wrapped and taped around an individual tube, or around a coil of tubing material. This process can be time-consuming, and often is performed by a different contractor than the person who installs and/or maintains the heat exchanger. 
         [0004]    It would be useful to further improve the effectiveness of insulated heat exchange tube material, as well as the efficiency of installation. 
       SUMMARY 
       [0005]    One embodiment is an insulated heat exchanger tube assembly comprising a heat exchanger tube, an insulating portion form-fitted around the heat exchanger tube, the insulating portion comprising a polymeric foam, and a polymeric film formed over and adhered to the insulating portion. 
         [0006]    Another embodiment is a heat exchanger tube comprising the insulated tube assembly described in the previous paragraph. 
         [0007]    A further embodiment is method of making a heat exchanger tube assembly, comprising obtaining a mold having an inner surface, placing a film material on the inner surface of the mold, placing a heat exchanger tube inside the mold, feeding an insulating, foamable material into the mold in liquid form around the heat exchanger tube, and curing .the insulating material to form an insulating foam layer that surrounds the heat exchanger tube and adheres to the film material. 
         [0008]    Yet another embodiment is a method of making a mold to be used in the process described in the previous paragraph. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an insulated heat exchanger tube assembly in accordance with a first embodiment. 
           [0010]      FIG. 2  is a side view of the insulated heat exchanger tube assembly of  FIG. 1 , partially cut away. 
           [0011]      FIG. 3  is a sectional view of the insulated heat exchanger tube assembly of  FIG. 1 , taken along line  3 - 3  of  FIG. 2 . 
           [0012]      FIG. 4  is an end view of the insulated heat exchanger tube assembly of  FIG. 1 . 
           [0013]      FIG. 5  is a perspective view of the interior of a mold used to apply the insulation to the insulated heat exchanger tube assembly of  FIG. 1 . 
           [0014]      FIG. 6  shows the front exterior of a mold that can be used to apply the insulation to the insulated heat exchanger tube assembly of  FIG. 1 . 
           [0015]      FIG. 7  shows a delivery system for the liquid foam for the insulated heat exchanger tube assembly of  FIG. 1 . 
           [0016]      FIG. 8  shows a heating ventilation air conditioning (HVAC) unit containing an insulated heat exchanger tube assembly of  FIG. 1   
           [0017]      FIG. 9  shows a HVAC unit containing multiple insulated heat exchanger tube assemblies of  FIG. 1 . 
           [0018]      FIG. 10  is a perspective view of an insulated heat exchanger tube assembly in accordance with a second embodiment. 
           [0019]      FIG. 11  shows a HVAC unit containing insulated heat exchanger tube assemblies of both  FIG. 1  and  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A new and improved insulated heat exchanger tube assembly has been developed can be efficiently installed and is suitable for use in a small space. The insulated heat exchanger tube assembly is compact in size and is configured for convenient positioning any one of a variety of angles within a heat exchanger. The insulated heat exchanger tube assembly can be used in a variety of types of HVAC units, and is particularly useful for use in heat pumps, including geothermal heat pumps. In embodiments, the tube itself is coiled, and the insulation is applied by molding the foam insulation around the coiled tube. In some cases, the heat exchanger tube has a tube-in-tube configuration. 
         [0021]    Definitions 
         [0022]    As used herein, an “insulating portion” refers to a shaped insulated piece of material that provides an insulating function by surrounding a heat exchanger pipe that is configured to contain hot and/or cold fluid. The insulating portion in combination with the outer film layer form an insulating housing. As used herein a “mold” is an enclosure configured to hold a heat exchange pipe and to receive a liquid insulating material that subsequently is cured to form a solid insulating material. The insulating material is a foam. 
         [0023]    Referring first to  FIGS. 1-4 , a perspective view of an insulated heat exchanger tube assembly is shown and is designated as  10 . The assembly  10  includes a coiled tube  12  having a first end  14  and a second end  16 . In the embodiment shown in  FIG. 1 , the coiled tube  12  has a tube-in-tube configuration with an inner tube  18  and an outer tube  20 . However, a single coiled tube also can be used in accordance with embodiments described herein. The coiled portion of the tube  12  is surrounded by an insulation portion  22 . The first and second ends  14 ,  16  of the coiled tube  1 . 2  extend outwardly from the insulating portion  22 . A film portion  24  surrounds the insulation portion  22 . The insulating portion  22  and the film portion  24  together form an insulating housing  26 . 
         [0024]    In the embodiment shown in  FIG. 1 , the insulating portion  22  covered by the film  24  has an eight-sided “donut” shape defined by eight outer side walls  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  44 , a flat front wall  46 , and opposite flat back wall  48 , and an annular central wall  50  defining a central opening  52 . In other embodiments, there is no central opening, and/or there are more or fewer than eight side walls. In embodiments, the outer surface of the insulated portion is donut-shaped with a curved outer wall and either flat or curved front and back walls. Selection of configuration may depend, in part, upon the thickness, length and shape of the coiled tube being insulated. 
         [0025]    When a tube-in-tube heat exchange tube is used in the assembly, the outer tube  20  typically, but not necessarily, is formed from a first type of thermoplastic or thermoset polymer or a metal. Suitable metals include, but are not limited to, steel, copper or an alloy of copper and nickel, and the inner tube  18  preferably, but not necessarily, is formed from a second type of material, such as copper, an alloy of copper and nickel, titanium or a titanium alloy. In embodiments the outer tube  20  comprises carbon steel and the inner tube  18  comprises copper with or without nickel included. In embodiments, the inner tube has a diameter in the range of about ⅛ inch to 3 feet, or ½ inch to 1 foot, or ½ inch to 1.5 includes. In embodiments, the outer tube has a diameter in the range of about ⅛ inch to 3 feet, or ½ inch to 1 foot, or ½ inch to 1.5 includes. The inner tube is made from a material that is resistant to corrosion by the fluids that flow on both sides of the tube wall. The inner tube  18  can have a smooth or twisted (fluted) configuration, or can have other heat transfer enhancements. The outer tube  20  is made of a material that is resistant to corrosion by the fluid that flows in the annular opening  52 . 
         [0026]    The film portion  24  surrounding the insulation is applied during the molding process. The film typically is a flexible polymeric thermoplastic or thermoset material having a thickness in the range of 0.3-50 mils, or 0.5-5 mils. In embodiments, the film is polyethylene, such as low density polyethylene or high density polyethylene. The film has a sufficient high melt temperature that it will remain contiguous with itself during the molding process. The film is sufficiently thin that it conveniently can be folded and creased to conform to the shape of the mold cavity. 
         [0027]    The insulating portion  22  is formed from a thermoplastic or thermoset polymeric foam material. Non-limiting examples of suitable foam materials include polyurethanes, polyvinylchlorides, polystyrenes and polyimides. In embodiments, the insulating material has a density in the range of about 0.4-2.0 lb/ft3, or 0.8-1.2 lb/ft3, and an appropriate insulating R factor that typically, but not necessarily, is in the range of 2-30, depending on the material and the thickness used. The foam is formed over the heat exchanger tube by molding using a process described below. Because foaming takes place when the foam surrounds the tube, the foam is form-fitted around the tube outer surface, and fills the space between adjacent coils. Upon curing, the foam adheres to the film. In embodiments, the foam also adheres to the heat exchanger pipe. In embodiments, a two-part polyurethane system is used in which an isocyanate (component A) and a polymeric resin that will react with the isocyanate (component B), such as a polyol, are dispensed from separate vessels into a mixing nozzle, which is then used to spray the liquid mixture into the mold. In certain embodiments, the octagonal assembly has a length in the range of 4 inches to 5 feet, a width in the range of 4 inches to 5 feet, and a thickness in the range of ½ inch to 5 feet. 
         [0028]    In order to form the assembly, the following process can be used. A film is placed along the walls of a mold  60 , such as the mold shown in  FIGS. 5-6 . The mold  60  includes a cavity  62  defined by mold bottom  64 , side wall  66 , and a top  68 . In the embodiment shown, the side wall  66  forms an octagonal shape. In embodiments, a vacuum mold is used. Suction is applied to the mold to hold the pre-made film in place. A coiled heat exchange tube  12  is placed in the mold and is held in the center of the mold using supports  70 ,  72 , along the front wall of the mold. The supports  70 ,  72  can be configured to conform to the size and shape of the tubing material being insulated. The foam material is sprayed into the mold, over the film, as a liquid. After spraying, a piece of film is placed on the inner side of the mold top, the top is put on the mold and the foamed is cured. After curing is at least partially complete, the assembly is removed from the mold and cooled. 
         [0029]      FIG. 7  shows a dispensing system  78  for a 2-part polyurethane foam coating in which the isocyanate is dispensed from a first tank  80  and the reacting resin, such as a polyol, is dispensed from a second tank  82 . The two materials are mixed and then dispensed through a nozzle into the mold cavity  62 . 
         [0030]      FIG. 8  shows a HVAC unit  86  in which the insulated coil assembly  10  is mounted. Because the insulation is formed on the tube before the tube is installed, a separate post-installation wrapping step is not needed to apply insulation. In the configuration that is shown, the assembly is mounted on the bottom interior wall  88  of the heat exchanger, next to side wall  90 , with the pipes extending outward from the assembly in a horizontal direction. In other embodiments, the pipes can extend vertically upward or downward, or the assembly can be set with a different side wall on the bottom inner wall of the heat exchanger such that the pipes extend upward or downward at an angle. The octagonal shape facilitates a universal configuration. The heat exchanger dimensions can be configured to receive an insulated tube assembly having particularly defined dimensions.  FIG. 9 . shows a HVAC unit  92  with two insulated heat exchanger tube assemblies  10  mounted side-by-side in a space-efficient manner. 
         [0031]    Referring next to  FIG. 10 , a perspective view of a second embodiment of an insulated heat exchanger tube assembly is shown and is designated as  110 . The assembly  110  includes a U-shaped tube  112  having a first end  114  and a second end  116 . In the embodiment shown in  FIG. 10 , the U-shaped tube has a tube-in-tube configuration with an inner tube  118  and an outer tube  120 . However, a single U-shaped tube also can be used in accordance with embodiments described herein. The tube  112  is surrounded by an insulation portion  122 . A film portion  124  surrounds the insulation portion  122 . The insulating portion  122  and the film portion  124  together form an insulating housing  126 . 
         [0032]      FIG. 11  shows the insulated heat exchanger tube assembly  110  of  FIG. 10  installed in a HVAC unit  186  on the bottom wall  188  next to an insulated heat exchanger assembly that contains a coiled tube. 
         [0033]    It will be appreciated that features disclosed above and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Furthermore, currently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.