Patent Publication Number: US-2023138731-A1

Title: Fabricated heat exchange tube for microchannel heat exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 63/274,719, filed Nov. 2, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Embodiments of the present disclosure relate to the art of heat exchangers, and more particularly, to a microchannel heat exchanger having folded heat exchange tubes. 
     Heat exchange tubes typically used in existing microchannel heat exchangers are extruded. Because the weight and the cost of fabricated heat exchange tubes are reduced compared to extruded heat exchange tubes, fabricated heat exchange tubes are becoming more common in heating, ventilation, and air conditioning (HVAC) applications. However, when fabricated heat exchange tubes are used in place of extruded heat exchange tubes, in certain circumstances, the oil entrained within the refrigerant may accumulate within the heat exchange tubes, thereby reducing the efficiency of the system. 
     BRIEF DESCRIPTION 
     According to an embodiment, a heat exchange tube segment for use in a heat exchange includes a fabricated tube body having an upper surface, a lower surface, a leading edge, a trailing edge, and a plurality of fluidly distinct flow channels formed therein. The fabricated tube body has a length, width, height, and a total tube cross-sectional area measured between the upper surface, the lower surface, the leading edge, and the trailing edge. A ratio of the width to the height of the fabricated tube body is between about 10 and 20, and a ratio of the width to a number of the plurality of fluidly distinct flow channels is between 1 and 2.5. Each of the plurality of fluidly distinct flow channels forms an open area in a cross-section of the fabricated tube body, and a ratio of the open area to the total tube cross-sectional area is between 0.3 and 0.44. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the ratio of the width to the number of the plurality of fluidly distinct flow channels is between 1.3 and 2.5. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the ratio of the open area to the total tube cross-sectional area is between 0.36 and 0.40. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the plurality of fluidly distinct flow channels are configured to receive a refrigerant selected from methylene fluoride and difluoromethylene. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the fabricated tube body includes a single piece of material folded to form the upper surface, the lower surface, the leading edge, the trailing edge, and the plurality of fluidly distinct flow channels. 
     According to an embodiment, a heat exchanger includes a first manifold, aa second manifold, and a plurality of heat exchange tube segments extending between and fluidly coupling the first manifold and the second manifold. At least one the plurality of heat exchange tube segments further includes a fabricated tube body having an upper surface, a lower surface, a leading edge, a trailing edge, and a plurality of fluidly distinct flow channels formed therein. The fabricated tube body has a length measured parallel to the plurality of fluidly distinct flow channels, a width measured between the leading edge and the trailing edge, a height measured between the upper surface and the lower surface, and a total tube cross-sectional area measured between the upper surface, the lower surface, the leading edge, and the trailing edge. A ratio of the width to the height of the fabricated tube body is between about 10 and 20, a ratio of the width to a number of the plurality of fluidly distinct flow channels is between 1 and 2.5. Each of the plurality of fluidly distinct flow channels forms an open area in a cross-section of the fabricated tube body and a ratio of the open area to the total tube cross-sectional area is between 0.3 and 0.44. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the heat exchanger has a multi-pass configuration. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the heat exchanger has a first pass and a second pass, and a number of heat exchange tube segments associated with the first pass is greater than a number of heat exchange tube segments associated with the second pass. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments a ratio of the number of heat exchange tube segments associated with the first pass to the number of heat exchange tube segments associated with the second pass is between 1 and 3. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments a ratio of the number of heat exchange tube segments associated with the first pass to the number of heat exchange tube segments associated with the second pass is between 1.2 and 3. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the ratio of the width to the number of the plurality of fluidly distinct flow channels is between 1.3 and 2.5. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the ratio of the open area to the total tube cross-sectional area is between 0.36 and 0.40. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the plurality of fluidly distinct flow channels are configured to receive a refrigerant, the refrigerant being one of methylene fluoride and difluoromethylene. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the fabricated tube body comprises a single piece of material folded to form the upper surface, the lower surface, the leading edge, the trailing edge, and the plurality of fluidly distinct flow channels. 
     In addition to one or more of the features described herein, or as an alternative, further embodiments the heat exchanger is a condenser in a chiller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG.  1    is a perspective view of an exemplary chiller; 
         FIG.  2 A  is a perspective view of an exemplary heat exchanger according to an embodiment; 
         FIG.  2 B  is a side view of another exemplary heat exchanger according to an embodiment; 
         FIG.  3    is a cross-sectional view of an exemplary heat exchange tube segment of a heat exchanger according to an embodiment; 
         FIG.  4    is a cross-sectional view of an exemplary heat exchange tube segment according to an embodiment; 
         FIG.  5    is a cross-sectional view of another exemplary heat exchange tube segment according to an embodiment; 
         FIG.  6    is a perspective view of another exemplary heat exchange tube segment according to an embodiment; and 
         FIG.  7    is a perspective view of another exemplary heat exchange tube segment according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
       FIG.  1    shows an exemplary embodiment of a chiller or outdoor unit  20  comprising at least one coil unit  22 . The chiller  20  may be configured to perform heating, cooling, and air exchange via a vapor compression cycle as is known. In the illustrated, non-limiting embodiment, the chiller  20  includes a plurality of axially aligned or stacked coil units  22 , such as three coil units for example; however, it should be understood that a chiller  20  having any number of coil units  22  including a single coil unit, two coil units, or more than three coil units are within the scope of the disclosure. Each of the coil units  22  typically includes a frame  24  having a heat exchanger assembly  26  mounted therein. In embodiments of the chiller  20  including a plurality of coil units  22 , the heat exchanger assembly  26  of a coil unit  22  may, but need not be fluidly coupled with the heat exchanger assembly  26  of at least one other coil unit  22  relative to a flow of refrigerant. The refrigerant may be configured to flow through the heat exchanger assemblies  26  in series or in parallel. 
     Each coil unit  22  additionally includes a fan assembly  28  having at least one fan configured to move a flow of ambient air across the adjacent heat exchanger assembly  26 . A plurality of compressors  30 , such as positioned within the frame  24  of one or more of the coil units  22 , are fluidly coupled to the heat exchanger assemblies  26  and are configured to pump refrigerant through a vapor compression cycle. The compressors  30  may be arranged in series, or alternatively, may be arranged in parallel relative to the flow of refrigerant. For example, in the illustrated, non-limiting embodiment, three compressors  30  are illustrated as being fluidly coupled to the heat exchanger assemblies  26  of two coil units  22 . However, any number of compressors  30  may be in fluid communication with any number of heat exchanger assemblies  26 . The chiller or outdoor unit  20  illustrated and described herein are intended as an example only, and it should be understood that other configurations of the chiller and of the coil units are contemplated herein. 
     Referring now to  FIG.  2 A , a perspective view of an example of a heat exchanger  40 , such as suitable for use in a coil unit  22 , is illustrated. In an embodiment, the heat exchanger  40  is suitable for use as a condenser in a vapor compression cycle. As shown, the heat exchanger  40  includes a first manifold or header  42 , a second manifold or header  44  spaced apart from the first manifold  42 , and a plurality of heat exchange tube segments  46  extending in a spaced parallel relationship between and fluidly connecting the first manifold  42  and the second manifold  44 . In the illustrated, non-limiting embodiments, the first manifold  42  and the second manifold  44  are oriented generally vertically, and the heat exchange tube segments  46  extend generally horizontally between the two manifolds  42 ,  44 . The manifolds  42 ,  44  may comprise hollow, closed end cylinders having a circular cross-section. However, manifolds  42 ,  44  having other cross-sectional shapes, such as semi-elliptical, square, rectangular, hexagonal, octagonal, or other cross-sections for example, are within the scope of the disclosure. 
     In an embodiment, best shown in  FIG.  2 B , the heat exchanger  40  has a multi-pass configuration relative to a secondary fluid A (e.g., air, air having dilute ethylene gas therein, nitrogen, and the like). To achieve a multi-pass configuration, one or more partition plates  48  are mounted within at least one of the first manifold  42  and the second manifold. In the illustrated, non-limiting embodiment, a partition plate is arranged within the first manifold  42 , thereby separating the first manifold  42  into a first chamber  42   a  and a second chamber  42   b . In operation, refrigerant R is configured to flow from the first manifold  42  to the second manifold  44  through the portion of the heat exchange tube segments  46  fluidly connected to the first chamber  42   a  in a first direction. From the second manifold  44 , the flow of refrigerant will be directed in a second direction through the portion of heat exchange tube segments  46  arranged in fluid communication with the second chamber  42   b  of the first manifold  42 . In an embodiment, the refrigerant is selected from a HFC-32 Methylene Fluoride or a difluoromethylene (C H 2F 2 ). However, embodiments where the refrigerant is another suitable fluid are also within the scope of the disclosure. 
     With reference now to  FIG.  3   , each heat exchange tube segment  46  comprises a leading edge  50 , a trailing edge  52 , a first upper surface  54 , and a second lower surface  56 . The leading edge  50  of each heat exchange tube segment  46  is upstream of its respective trailing edge  52  with respect to the flow of the heat transfer fluid A through the heat exchanger  40 . The interior flow passage of each heat exchange tube segment  46  may be divided by interior walls  58  into a plurality of fluidly distinct flow channels  60  that extend longitudinally over the length of the heat exchange tube segment  46  and establish fluid communication between the respective first and second manifolds  42 ,  44 . The discrete flow channels  60  may have a circular cross-section, a rectangular cross-section, a trapezoidal cross-section, a triangular cross-section, or another non-circular cross-section (e.g., elliptical, star shaped, closed polygon having straight or curved sides). 
     The heat exchange tube segments  46  disclosed herein may further include a plurality of fins  62 . In an embodiment, each fin  62  is formed of a single continuous strip of fin material tightly folded in a ribbon-like serpentine fashion thereby providing a plurality of closely spaced fins that extend generally orthogonal to the heat exchange tube segments  46 . Typically, the fin density of the closely spaced fins of each continuous folded fin may be about 16 to 25 fins per inch, but higher or lower fin densities may also be used. Heat exchange between the refrigerant flow, R, and air flow, A, occurs through the outside surfaces  54 ,  56 , respectively, of the heat exchange tube segments  46 , collectively forming a primary heat exchange surface, and also through the heat exchange surface of the fins  62 , which forms the secondary heat exchange surface. 
     With reference now to  FIGS.  4 - 6   , in an embodiment, the heat exchange tube segments  46  are fabricated tube segments, having a tube body formed using one or more generally planar pieces or sheets of material  61 . The materials that may be used include, but are not limited to, sheet metal and non-metallic materials, such as polymers, thermally enhanced polymer based composites, or other suitable materials for example. In the illustrated, non-limiting embodiment of  FIG.  4   , a single, flat piece of material  61  is folded such that a single surface of the piece of material defines the leading edge  50 , trailing edge  52 , first surface  54 , and second surface  56  of the heat exchange tube segment  46 . By folding opposing edges of the sheet of material to extend between the first and second surfaces  54 ,  56  of the heat exchange tube segment  46 , a first portion  64  and a second portion  66  of the heat exchange tube segment  46  are formed, each having a single flow channel  60 . 
     In another embodiment, illustrated in  FIG.  5   , at least one of the opposing ends of the sheet of material  61  is bent to define a plurality of flow channels  60  within at least one of the first portion  64  and the second portion  66  of the heat exchange tube segment  46 . Although the ends of the sheet of material  61  are illustrated as being bent to form a plurality of similar flow channels  60  having a generally rectangular cross-section, embodiments where the flow channels  60  vary in size, shape, cross-sectional flow area, have varying surface characteristics (e.g., having differing surface roughness or textures, coatings, embossed patterns, and the like), or further include inserts of same or different configuration are also within the scope of the disclosure. Further, in the illustrated, non-limiting embodiment, the first portion  64  and the second portion  66  of a heat exchange tube segment  46  are substantially identical. However, embodiments where the first portion  64  and the second portion  66  vary in size and/or configuration, such as number and/or shape of flow channels  60 , are also within the scope of the disclosure. 
     Alternatively, the heat exchange tube segment  46  may have a two piece design where the flow channels  60  are formed using a corrugation form  68  inserted into an outer shell or sleeve  70  as shown in  FIG.  6   . The corrugated internal sheet  68  can be a different thickness and material than the outer shell  70  altogether, or can be made of the same or similar materials. The fabricated or folded heat exchange tube segments illustrated and described herein are intended as an example only. Further configurations and details for fabricated heat exchange tube segment are disclosed in U.S. Pat. Nos. 4,805,693; 5,491,997; 6,209,202; and 7,657,986, and U.S. application Ser. No. 16/067,009 filed on Jun. 28, 2018, the disclosures of each of which is incorporated herein by reference in its entirety. 
     In embodiments where a vapor compression cycle includes a plurality of compressors arranged in series relative to the flow of refrigerant, the total number of compressors used to propel the flow through the cycle may vary based on one or more operating conditions, such as the ambient air temperature or the load on the system. Accordingly, a velocity of the refrigerant in instances where all of the compressors are being used to move the refrigerant through the cycle is greater than the velocity of the refrigerant in instances where only one of the plurality of compressors is operational. When the refrigerant at this lower velocity associated with operation of only a portion of the compressors flows through a heat exchanger  40  having fabricated heat exchange tube segments  46 , excessive oil mixed with the refrigerant may accumulate within one or more of the flow channels  60  of a heat exchange tube segments  46 . Accordingly, one or more parameters of the fabricated heat exchange tube segment may be controlled to minimize the accumulation of oil within the flow channels. 
     With reference now to  FIG.  7   , an example of a fabricated heat exchange tube segment  46  configured to limit oil build-up therein is illustrated. As shown, the heat exchange tube segment  46  has a tube length L that extends parallel to the direction of flow of refrigerant R through the heat exchange tube segment  46 . A width W of the heat exchange tube segment  46  is measured parallel to the direction of the secondary fluid A provided to the heat exchanger  40 . The height H of the heat exchange tube segment  46  extends perpendicularly or orthogonally to both the length L and the width W of the heat exchange tube segment  46 . In an embodiment, each heat exchange tube segment  46  within the heat exchanger  40  has a substantially identical length, width W and height H. 
     In an embodiment, the ratio of the width W of the heat exchange tube segment  46  to the height H of the heat exchange tube segment  46  is between 10 and 20, and in some embodiments is between 12 and 20, 14 and 20, or 16 and 20. Further, in an embodiment, a ratio of the width W of the heat exchange tube segment  46  to the total number of flow channels  60  formed in the heat exchange tube segment  46  is between 1.3 and 2.5. The ratio of the width W to the total number of flow channels  60  may further be between 1.5 and 2.5, between 1.7 and 2.5, or between 2.0 and 2.5. 
     Further, a fabricated heat exchange tube segment  46  typically requires less material than an extruded heat exchange tube segment. Because of this, the open area defined by the plurality of fluidly distinct flow channels  60  occupies a greater percentage of the area of the heat exchange tube segment  46 . This percentage of the open area may be described as porosity. In an embodiment, a ratio of the cross-sectional area of the open areas of a heat exchange tube segment  46 , such as formed by the flow channels  60  for example, to the total tube cross-sectional area of a heat exchange the tube segment  46  is between about 0.30 and 0.44. For example, the ratio of the cross-sectional area of the open areas of the heat exchange tube segment  46  to the total tube cross-sectional area of a heat exchange tube segment  46  may be between about 0.34 and 0.44, between about 0.30 and 0.40, between about 0.36 and 0.44, between about 0.36 and 0.40, such as 0.38 for example. 
     With continued reference to  FIG.  7    and further reference to  FIG.  2 B , in embodiments where the heat exchanger  40  having a plurality of fabricated heat exchange tube segments  46  has a multi-pass configuration, such as a two-pass configuration for example, the number of heat exchange tube segments  46  associated with each pass may vary. For example, the number of heat exchange tube segments associated with the first pass may be greater than the number of heat exchange tube segments associated with the second pass. In an embodiment, the ratio of the heat exchange tube segments  46  associated with the first pass to the heat exchange tube segments  46  associated with the second pass is between 1 and 3. Further, the ratio of the heat exchange tube segments  46  associated with the first pass to the ratio of heat exchange tube segments  46  associated with the second pass may be between 1.2 and 3, between 1 and 2.5, or between 1.2 and 2.5. 
     By customizing the configuration of the fabricated heat exchange tube segments  46  and the heat exchanger  40 , the velocity of the refrigerant R may be improved, thereby mitigating the oil accumulation within the flow channels  60  of the heat exchange tube segments  46 . Further, the use of fabricated heat exchange tube segments as described herein provides a low-cost solution relative to an oil separator. It should be appreciated that the heating, ventilation, and air conditioning (HVAC) system described herein may be devoid of an oil separator, in certain instances. 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.