Patent Publication Number: US-2011056667-A1

Title: Integrated multi-circuit microchannel heat exchanger

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional patent application No. 61/080780, which was filed Jul. 15, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     In recent years, much interest and design effort has been focused on the efficient operation of the heat exchangers (and condensers, gas coolers and evaporators in particular) of refrigerant systems. One relatively recent advancement in heat exchanger technology is the development and application of parallel flow, or so-called microchannel or minichannel, heat exchangers (these two terms will be used interchangeably throughout the text), as the condensers, gas coolers and evaporators. 
     These heat exchangers are provided with a plurality of parallel heat exchange tubes, typically of a non-round shape, among which refrigerant is distributed and flown in a parallel manner. The heat exchange tubes are orientated generally substantially perpendicular to a refrigerant flow direction in inlet, intermediate and outlet manifolds that are in flow communication with the heat exchange tubes. The heat exchange tubes typically have a multi-channel construction, with refrigerant distributed within these multiple channels in a parallel manner. Heat transfer fins may be inter-disposed and rigidly attached to the heat exchange tubes. The primary reasons for the employment of the parallel flow heat exchangers, which usually have aluminum furnace-brazed construction, are related to their superior performance, high degree of compactness, structural rigidity, lower weight, lower refrigerant charge and enhanced resistance to corrosion. 
     At times, there may be reasons to have multiple distinct refrigerant circuits within a single heat exchanger core and construction in a refrigerant system. As one example, a dual circuit refrigerant system having two completely separate refrigerant independent circuits with separate compressors and heat exchangers, etc. can be provided to achieve capacity control and efficiency improvement. In other applications, it may be desirable to route the total refrigerant flow only through a portion of the heat exchanger, while utilizing the entire heat exchanger frontal area. Furthermore, it may be desirable to implement multiple independent refrigerant paths of a single refrigerant circuit through the heat exchanger core to improve the heat exchanger effectiveness. 
     To date, the provision of the multiple distinct refrigerant circuits utilizing total frontal or cross-sectional area of the heat exchanger has required distinct heat exchangers, at least when a microchannel heat exchanger is used. More traditional heat exchangers, such as a round tube and plate fin heat exchangers, can be formed to be of a multi-circuit intertwined configuration utilizing the total frontal area of the heat exchanger, however, microchannel heat exchangers have not been easily tailored to include such multiple circuit configurations. 
     SUMMARY OF THE INVENTION 
     A microchannel heat exchanger includes two separate manifolds leading into a plurality of separate microchannel tube banks. In embodiments, the separate tube banks extend parallel to each other along a first direction through one dimension of a heat exchange area. The banks from the at least two manifolds are interspersed along a second direction which is perpendicular to the first direction. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a 3D view of an inventive heat exchanger. 
         FIG. 1B  shows a first schematic that might utilize the inventive heat exchanger. 
         FIG. 1C  shows a second schematic that might utilize the inventive heat exchanger. 
         FIG. 2  shows an enlarged manifold section of the  FIG. 1A  heat exchanger. 
         FIG. 3  is an end view of  FIG. 2 . 
         FIG. 4A  shows detail of the manifold section of the inventive heat exchanger. 
         FIG. 4B  shows an alternate feature of the inventive heat exchanger. 
         FIG. 5  is a cross-sectional view of a heat exchange tube. 
         FIG. 6A  shows a 3D view of another embodiment of the inventive heat exchanger. 
         FIG. 6B  is an end view of the  FIG. 6A  embodiment. 
         FIG. 6C  shows an enlarged manifold section of the  FIG. 6A  heat exchanger. 
         FIG. 7A  shows a 3D view of another embodiment of the inventive heat exchanger. 
         FIG. 7B  is an end view of the  FIG. 7A  embodiment. 
         FIG. 7C  shows an enlarged manifold section of the  FIG. 7A  heat exchanger. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a microchannel heat exchanger  20  having a heat exchanger frontal or cross-sectional surface area  21 . An inlet pipe  24  supplies refrigerant into a first inlet manifold  22 , and an inlet pipe  28  supplies refrigerant into a second inlet manifold  26 . The two inlet pipes  24  and  28  can be connected to completely separate independent refrigerant circuits, or can be connected to a common refrigerant source of a single refrigerant circuit. Outlet manifolds  30  and  32  lead to outlet pipes  29  and  31 , communicating the refrigerant downstream to independent refrigerant circuits or to a single refrigerant circuit respectively. Although references to a refrigerant and to a refrigerant system are made throughout the text, any suitable heat transfer fluid, such as, for instance, water, ethylene glycol, propylene glycol or oil, and an associated system, can be utilized instead. Furthermore, although microchannel heat exchangers of the invention are schematically shown in a single-pass configuration (see for instance  FIG. 1A ), any number of passes can be implemented in a similar manner, and all such multi-pass microchannel heat exchangers (see  FIG. 4B ) are within the scope of the invention. 
     When the inlet pipes  24  and  28  and the outlet pipes  29  and  31  communicate refrigerant to separate independent refrigerant circuits of a refrigerant system, capacity control and efficiency improvement are achieved at part-load operation, as the entire frontal surface area  21  is utilized in heat transfer interaction with the air flowing across heat exchanger external surfaces, while only one of the refrigerant circuits is operating. When the inlet pipes  24  and  28  and the outlet pipes  29  and  31  communicate refrigerant to a single refrigerant circuit of a refrigerant system, at certain conditions, it may be desired to flow refrigerant only through a portion of the heat exchanger  20 , while still utilizing the entire heat exchanger frontal area  21  for better performance. Such conditions may arise, for instance, for the purposes of head pressure control or maintaining minimum refrigerant velocity for proper oil circulation throughout a refrigerant system and return to the compressor. Furthermore, it may be desirable to implement multiple independent refrigerant paths of a single refrigerant circuit through the heat exchanger core to improve refrigerant distribution and the heat exchanger effectiveness. As known, refrigerant distribution is particularly important for two-phase refrigerant flows, such as a refrigerant flow entering an evaporator. 
       FIG. 1B  shows a basic exemplary multi-circuit refrigerant system that might utilize the inventive heat exchanger  20 . In this multi-circuit refrigerant system, there are two entirely separate independent refrigerant circuits  300  and  301 , each incorporating its own expansion device  302 , separate evaporator heat exchangers  304  and  308 , and separate compressors  306 . As can be appreciated, for both circuits, the refrigerant is routed through the single heat exchanger  20 . The  FIG. 1B  is quite simplified, and the flow through the heat exchanger  20  can be better appreciated from a review of  FIG. 1A . However, the power of this system configuration to provide the multiple refrigerant circuits, while still requiring only a single heat exchange  20  with fully utilized frontal area  21 , especially for part-load conditions when only some of the refrigerant circuits are operational, is apparent. The system may be a heat pump or an air conditioner, and the heat exchanger  20  may be the indoor heat exchanger or the outdoor heat exchanger. In addition, the heat exchanger  20  can be utilized for other applications such as a reheat function, as an example, if appropriate refrigerant circuitry is provided. 
       FIG. 1C  shows yet another application of the inventive heat exchanger  20 . In this application, a single refrigerant line  401  leads to branch refrigerant lines  402  and  404 , connecting to the refrigerant manifolds associated with the inventive heat exchanger  20 . Refrigerant flow control devices such as valves  406  control refrigerant flow to the branch refrigerant lines  402  and  404 , and then to the heat exchanger  20 . In this manner, the total volume of refrigerant passing through the heat exchanger  20 , refrigerant velocity and heat transfer area utilization for the heat exchanger  20  can be controlled. The various reasons for providing such control are known in the art, but the use of a microchannel heat exchanger providing intertwined refrigerant circuits within a single heat exchanger structure is inventive. 
       FIG. 2  shows a detail of the inlet manifolds  22  and  26 . The outlet manifolds  30  and  32  are constructed and connected to the heat exchanger core in a similar manner. As can be appreciated, connecting tubes  33  from each manifold  22  and  26  alternatively lead to separate independent banks of heat exchange tubes  34  extending perpendicular to the plane of the frontal heat exchange surface area  21  along a first direction. Each manifold has plural connecting tubes  33  connected to plural refrigerant heat exchange tubes  34 . As can be appreciated from this figure, the heat exchange tube banks  34  connected to the two manifolds  22  and  26  have an alternating pattern along a second direction along the manifold axis, which is generally perpendicular to the first direction. For instance, in some applications, the first direction is a horizontal direction and the second direction is a vertical direction; in other applications the first direction is a vertical direction and the second direction is a horizontal direction. 
       FIG. 3  shows the end view of the heat exchanger  20  and its manifolds  22  and  26  leading to the connecting tubes  33 . Notably, while the manifolds are shown extending generally vertically, with the heat exchange tube banks extending generally horizontally, the manifolds can extend generally horizontally with the heat exchange tube banks extending generally vertically. 
     The heat exchanger  20  typically includes external heat transfer fins, like a standard microchannel heat exchanger construction, but they have been omitted to simplify the understanding of the drawings. 
       FIG. 4A  shows a detail of the inlet pipe  28  leading into the inlet manifold  26 , into the connecting tube  33 , and into the bank of heat exchange tubes  34 . As known, the heat exchange tube  34  for a microchannel heat exchanger typically has a plurality of parallel refrigerant channels  100  separated by dividing walls  101 , as shown in  FIG. 5 . The parallel refrigerant channels  100  each preferably have a hydraulic diameter that is less than 5 mm, and may be less than 3 mm. Notably, the term “hydraulic diameter” does not imply that the channels are circular in cross-section. 
       FIG. 4B  shows an alternative heat exchanger pass arrangement  200 . This is a multi-pass heat exchanger construction, wherein the manifolds  22  and  30  are actually subdivided into multiple manifold chambers and incorporate inlet and outlet manifold chambers  205  and  206  as well as intermediate manifold chambers  207  and  208  respectively. As an example, refrigerant flows through the heat exchange tube bank  34  extending from the inlet manifold chamber  205  of the manifold  22  toward the intermediate manifold chamber  207  of the manifold  30 , but then reverses flow direction through another heat exchange tube bank  201  to reach the intermediate manifold chamber  208  of the manifold  22 , and then reverses direction once again to flow through yet another heat exchange tube bank  202  to reach the outlet chamber  206  of the manifold  30 . Divider plates  204  subdivide each of the manifolds  22  and  30  into the manifold chambers  205  and  208  and manifold chambers  207  and  208  respectively. Within this embodiment, heat exchange tube banks of the other refrigerant circuit would be intertwined with the heat exchange tube banks  34 ,  201  and  202 .  FIG. 4B  is a very simplified view. As can be appreciated, connecting refrigerant tubes  33  extending laterally from the manifolds  22  and  30  would typically be utilized within this embodiment, but are omitted in the  FIG. 4B  for simplicity. 
       FIGS. 6A and 6B  show another embodiment  75  wherein an inlet manifold  82  has three adjacent connecting tubes  84 , and hence three adjacent heat exchange tubes, and an inlet manifold  80  has only two adjacent connecting tubes  86 , and hence only two adjacent heat exchange tubes. As before, the alternating pattern repeats itself along the manifold axis. In this manner, the relative size of the heat exchanger portion connected to each inlet manifold can be controlled. Of course, ratios other than 3:2 can be utilized. This unequal circuit split may become advantages, for instance, when refrigerant circuits and associated compression systems are of a different size and capacity, allowing for different stages of capacity modulation and unloading. It has to be understood that a single connecting refrigerant tube  84  or  86  of a larger diameter, that leads to adjacent heat exchange tubes, can be utilized instead. 
       FIG. 6C  is a perspective 3D view showing a detail of the manifold structure. The power of the inventive system is apparent, in that it provides high flexibility control over capacity modulation by utilizing the distinct number of heat exchange tube banks of a variable size. As is apparent, refrigerant will flow into each of the manifolds  80  and  82 , into the respective connecting refrigerant tubes  86  and  84 , and then into the associated heat exchange tube banks. This embodiment can utilize the multi-pass alternative as shown in  FIG. 4B , or can be utilized in a single-pass configuration. 
       FIGS. 7A and 7B  show the power and flexibility of the inventive concept wherein an embodiment  90  has an inlet manifold  92  with associated connecting refrigerant tubes  94 , an inlet manifold  96  with associated connecting refrigerant tubes  98 , an inlet manifold  110  with associated connecting refrigerant tubes  112 , and an inlet manifold  114  with associated connecting refrigerant tubes  116 . More than four independent refrigerant circuits flowing through the heat exchanger  90  can be utilized. 
       FIG. 7C  is a perspective 3D view showing the detail of the manifold arrangement of the  FIG. 7A . Additional manifolds can be interfit into available space around the heat exchanger structure as shown in  FIG. 7C . As illustrated, the inlet manifolds  96  and  114  are located on one side of the core heat transfer area  21 , while the manifolds  92  and  110  are positioned on an opposed side of the core heat transfer area  21 . As before, refrigerant flowing through the several inlet manifolds passes into respective connecting refrigerant tubes, and into respective heat exchange tube banks. Again, multi-pass configurations such as shown in  FIG. 4B  can also be utilized within this embodiment. 
     The connecting refrigerant tubes  33  may have different cross-sectional areas, including (but not limited to) round, oval, rectangular, and square cross-sections. All these connecting refrigerant tube configurations are within the scope of the invention. Furthermore, in some design arrangements, the connecting refrigerant tubes  33  may not be required, when the heat exchange tubes  34  are bent in an alternating pattern such that they fit directly into different inlet and outlet manifolds positioned as exhibited in multiple Figures illustrating the invention. Such design arrangements, although feasible, may not be desirable from manufacturability and reliability perspectives. Lastly, inlet and outlet manifolds may be positioned at the same end of the heat exchanger core  21 , depending on the refrigerant pass arrangement within the heat exchanger core. 
     The inventive heat exchanger can be utilized within all types of refrigerant systems, such as air conditioning systems, refrigeration systems and heat pump systems, as well as within other auxiliary systems, such as, for instance, water cooling or heating systems, process gas/air cooling or heating systems, and oil cooling or heating systems. Moreover, the inventive heat exchanger can be utilized as an evaporator, condenser, gas cooler, reheat heat exchanger or any other heat exchanger within commercial and residential air conditioning and heat pump systems, marine container units, refrigeration truck-trailer units, merchandisers, bottle coolers, supermarket refrigeration systems, etc. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.