Patent Publication Number: US-2022221226-A1

Title: Flat tube and heat exchanger

Description:
TECHNICAL FIELD 
     The invention relates to a flat tube for a heat exchanger as well as to a heat exchanger having such flat tubes. 
     BACKGROUND 
     In heat pump applications and heat exchangers having exclusively one single passage it is a problem that under unfavorable environment conditions the single passage may freeze up easily. This problem could be solved in that, for example, a refrigerant pressure drop in a heat exchanger block having flat tubes is increased, e.g. by an increased deflection of the refrigerant in the heat exchanger block. An increase of the pressure drop goes hand in hand with increasing a boiling temperature of the refrigerant as a result of which the temperature of the flat tubes or of the heat exchanger block can be increased and thus the risk of a freezing can be at least reduced. This can be achieved for example by a meander-like or multi-loop flow through the heat exchanger. 
     From CN 103 644 685 A, a heat exchanger having two inflow collectors and two outflow collectors is known. This heat exchanger has two types of flat tubes stacked upon one another alternatingly. The flat tubes of a second type are substantially straight. The flat tubes of first type have a sharp bend or fold near their longitudinal ends, in which bend or fold a central heat exchange portion of the respective flat tubes merges into an angled portion of these flat tubes. Accordingly, a first of the inflow and a first of the outflow collectors are arranged in line with flat tubes of the second type and a second of the inflow and a second of the outflow collectors are each arranged aside of the flat tubes of the second type and connected to the angled portions of the flat tubes of the first type. 
     However, the sharp bend or fold near the longitudinal ends of the flat tubes (of the first type) leads to increased internal mechanical stresses in the area of the sharp bend or fold. Thus, such usual flat tubes may be prone to material failure either during their manufacturing or whilst operation of the heat exchanger due to the coolant or refrigerant pressure they have to withstand when the heat exchanger is operated. 
     SUMMARY 
     The present disclosure presents new ways for the development of flat tubes for heat exchangers. 
     A general idea of the invention therefore is to configure the bent portion of the flat tube for a heat exchanger as to have a first and a second bend, via which a heat exchange portion of the flat tube merges into an angled portion of the flat tube. 
     Advantageously, this results in an increased bending radius opposite that of usual bent flat tubes and thus allows for improved strength of the flat tube and less likely failure during its manufacturing or operation. 
     The invention concerns a flat tube for a heat exchanger, having a tube body delimiting at least one coolant channel through which a coolant or a refrigerant can flow. The tube body has an outer top and an outer bottom surface arranged opposite one another at a thickness of the tube body as well as two outer side surfaces arranged opposite one another at a width of the tube body, the outer side surfaces connecting the outer top to the outer bottom surface. It goes without saying that the expressions “outer top surface” and “outer bottom surface” only refer to a preferred orientation of the flat tube, wherein this orientation can be deviated from without leaving the scope of the invention. Thus, if practical, the flat tube in its operation position can be orientated as to have its outer bottom surface facing upwards or downwards or sideways with respect to gravity. The tube body has a heat exchange portion substantially extending along an extension direction. The tube body has an angled portion substantially extending along a transverse direction that is inclined with respect to the extension direction. Preferably, the first bend has an S- or Z-like shape comprising two sub-bends, one of which is directed against and one of which is directed in the offset direction, wherein both sub bends together cause the tube body to withdraw counter to the offset direction whilst distancing from the heat exchange portion in the extension direction. The tube body also has a bent portion connecting the heat exchange portion to the angled portion. The angled portion is arranged at a distance from the heat exchange portion measured in an offset direction substantially perpendicular to both the extension and the transverse direction. The bent portion in its first end region facing the heat exchange portion has a first bend counter to the offset direction. In its second end region facing the angled portion, the bent portion has a second bend in the offset direction. This allows for a particular big bending radius of the bent portion, such that the mechanical strength of the flat tube can be enhanced and its manufacturing can be simplified. 
     According to a preferred embodiment of the flat tube, the second bend is a twist-bend. By that, both the inclination of the angled portion opposite the heat exchange portion and the distance between the angled portion and the heat exchange portion along the offset direction can be achieved in a single and thus inexpensive deformation process. 
     According to another preferred embodiment of the flat tube, the extension direction substantially follows a straight line. This allows for particular effective heat exchange. 
     In another preferred embodiment of the flat tube, the transverse direction is substantially perpendicular to the extension direction. Such a flat tube is particularly cost-effective to produce. 
     In another preferred embodiment of the flat tube, the distance at which the angled portion is arranged opposite the heat exchange portion is smaller than a minimum bending radius of the second bend. This way, a mechanical load when bending the flat tube to its final shape whilst manufacturing can be kept below a failure load. 
     According to another preferred embodiment of the flat tube, the minimum bending radius of the second bend is 3 to 6 times the tube thickness. This ratio of the bending radius of the second bend to the tube thickness has proven to be particularly suitable. In addition or as an alternative, the minimum bending radius of the second bend is 0.70 to 0.95 times the tube width. In addition or as an alternative, heat transfer fins can be present at the outer top and/or bottom surface, wherein the heat fins protrude from the respective outer top and/or bottom surface along a fin height, which fin height is measured perpendicularly opposite the respective outer top and/or bottom surface, the minimum bending radius of the second bend being 0.70 to 0.95 times the fin height. 
     According to another preferred embodiment of the flat tube, the tube body delimits numerous coolant channels arranged in a queue along the width of the tube, wherein between directly adjacent coolant channels a division wall extending along the thickness of the tube body is present. Such a flat tube allows for particularly even heat exchange distribution at its outer upper and bottom surfaces. Furthermore, such flat tubes can have a particularly small thickness. 
     In another preferred embodiment of the flat tube, the tube body has a uniform material or consists of a uniform material, which material preferably is a metal. This enhances the heat transfer/exchange and allows bending a semi-finished straight flat tube as to match the geometry of the flat tube according to this embodiment of the invention. 
     According to another preferred embodiment of the flat tube, the bent portion in a view perpendicular both to the extension and to the offset direction has an S- or Z-like geometry. This means that if the first bend comprises two sub-bends, which together form an S- or Z-like shape, the second bend steadily adds to the S- or Z-like shape as to form the S- or Z-like geometry of the bent portion. By that, the bending radius of the second bend can be increased. 
     The invention also relates to a heat exchanger, which has first flat tubes, which accord to the invention as described above, wherein longitudinal ends of their angled portions facing away from their bent portions are received in associated second openings of a second collector. Thus, the afore-mentioned advantages of the flat tube according to the invention transfer to the heat exchanger, accordingly. Furthermore, the heat exchanger has second flat tubes, wherein first longitudinal ends of these second flat tubes are received in associated third openings of a third collector and second longitudinal ends of the second flat tubes, which are arranged opposite their first longitudinal ends, are received in associated fourth openings of the first collector. The first and fourth openings are arranged spaced apart from one another. 
     According to a preferred embodiment of the heat exchanger, the first flat tubes and the second flat tubes are arranged alternatingly along a stacking direction that corresponds to, in particular equals, the offset direction of the first flat tubes. By the alternating arrangement of the individual flat tubes a defrosting capacity can be increased. Thereby, a defrosting cycle can be shortened and the overall energy efficiency of the heat exchanger can be increased. 
     In another preferred embodiment of the heat exchanger, an intermediate space is present between adjacent flat tubes, in which heat transfer fins are accommodated. This enhances the heat exchange/transfer between a fluid led through the intermediate space and the coolant or refrigerant flowing through the flat tubes, since the heat transfer fins effectively increase a heat exchange surface area of the heat exchanger. 
     Preferably, whilst assembling the heat exchanger, the heat transfer fins are held in place by the first bend. 
     According to another preferred embodiment of the heat exchanger, in a view along the stacking direction the heat exchange portions of the first flat tubes completely overlap the second flat tubes, whereas the angled portions of the first flat tubes do not. This allows for particularly well heat exchange whilst keeping a profile of the heat exchanger and an air pressure drop low. 
     In another preferred embodiment of the heat exchanger, the second flat tubes are substantially straight. Such second flat tubes can easily be taken from stock without any manufacturing or modification process on them to be carried out but cutting to length. 
     According to another preferred embodiment of the heat exchanger, the second flat tubes as well as the first flat tubes accord to the invention as described above. Then, the transverse direction of the first flat tubes differs from that of the second flat tubes. Such a heat exchanger can be set up in a particular compact design. 
     Further important features and advantages of the invention become evident from the drawings and from the associated detailed description by way of the drawings. 
     It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention. 
     Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference numbers relate to same or similar or functionally same components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It shows, in each case schematically: 
         FIG. 1A  shows an example of a flat tube according to the invention in a view against a transverse direction; 
         FIG. 1B  shows the example of  FIG. 1A  in a view along an offset direction; 
         FIG. 2A  shows another example of the flat tube according to the invention in a view along the offset direction; 
         FIG. 2B  shows the example of  FIG. 2A  in a view opposite the transverse direction; 
         FIG. 3A  shows, partially, an example of a heat exchanger according to the invention in a view against the transverse direction; 
         FIG. 3B  shows a first flat tube of the heat exchanger of  FIG. 3A  in a view along the offset direction; 
         FIG. 4A  shows the heat exchanger of  FIG. 3A  in a plan view along the offset direction; and 
         FIG. 4B  shows another example of the heat exchanger according to the invention in a plan view along the offset direction. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows an example of a flat tube  1  according to the invention in a view against a transverse direction  10 , which flat tube  1  is configured to be implemented in a heat exchanger  30  according to the invention, the latter being depicted in  FIGS. 3A, 4A and 4B  and described later on.  FIG. 1B  shows the example of  FIG. 1A  in a view along an offset direction  12 . As to be seen from  FIGS. 1A and 1B , the flat tube  1  has a tube body  2 , which delimits at least one coolant channel  3  through which a coolant or a refrigerant can flow. In the example of  FIG. 1A , the tube body  2  delimits numerous coolant channels  3 , which are arranged in a queue along the width W of the tube  1 . A division wall  17  extending along the thickness T of the tube body  2  is present between two directly adjacent coolant channels  3 . For example, tube body  2  has a uniform material or consists of such a uniform material. The material of the tube body  2  for instance is a metal. 
       FIG. 2A  illustrates another example of the flat tube  1  according to the invention in a view along the offset direction  12 .  FIG. 2B  shows the example of  FIG. 2A  in a view against the transverse direction  10 . In other words, the perspective of  FIG. 2A  corresponds to that of  FIG. 1B , whereas the perspective of  FIG. 2B  is similar to that of  FIG. 1A . For the sake of clarity and better understanding, the coolant channels  3  of the tube body  2  are not shown in the example of  FIGS. 2A and 2B . 
     As to be seen from  FIGS. 1A, 1B, 2A and 2B , the tube body  2  has an outer top surface  4  and an outer bottom surface  5 , which are arranged opposite one another at a thickness T of the tube body  2 . Tube body  2  also has two outer side surfaces  6 , which are arranged opposite one another at a width W of the tube body  2 . The outer side surfaces  6  connect the outer top and the outer bottom surface  4 ,  5 . Tube body  2  has a heat exchange portion  7 , which substantially extends along an extension direction  8 . Tube body  2  has an angled portion  9 , which substantially extends along a transverse direction  10  that is inclined with respect to the extension direction  8 . Tube body  2  has a bent portion  11 , which connects the heat exchange portion  7  to the angled portion  9 . 
     It is to be seen from  FIGS. 1A and 2B , that the angled portion  9  is arranged at a distance D from the heat exchange portion  7 , which distance D is to be measured in the offset direction  12 . The offset direction  12  is substantially perpendicular to both the extension and the transverse direction  8 ,  10 . The bent portion  11  has a first bend  14 , which is present in a first end region  13  of the bent portion  11  that faces the heat exchange portion  7 . The first bend  14  of the bent portion  11  is bent counter to the offset direction  12 . Furthermore, the bent portion  11  has a second bend  16 , which is present in a second end region  15  that faces the angled portion  9 . The second bend  16  is bent in the offset direction  12 . In other words, in the first end region  13  the tube body  2  is set back opposite the heat exchange portion  7  counter to the offset direction  12  due to the first bend  14 . Accordingly, in the second end region  15  the tube body  2  is protruding from the heat exchange portion  7  and from the first end region  13  in the offset direction  12  due to the second bend  16 . The bent portion  11 , for example, has an S- or Z-like geometry  19 . Between the first bend  14  and the second bend  16  a step bend  22  (see  FIGS. 2A and 2B ) can be present. The first bend  14  can have an S- or Z-like shape consisting of two sub-bends, one of which is directed against and one of which is directed in the offset direction, wherein both sub bends together cause the tube body  2  to withdraw counter to the offset direction  12  whilst distancing from the heat exchange portion  7  in the extension direction  8 . When the first bend  14  comprises of two sub-bends, which both together have the S- or Z-like shape, the second bend  16  may steadily add to the S- or Z-like geometry as to form the S- or Z-like geometry  19  of the bent portion  11 . 
     Additionally,  FIGS. 1A, 1B, 2A and 2B  show that the extension direction  8  substantially follows a straight line. The transverse direction  10  in the examples of  FIGS. 1A, 1B, 2A and 2B  is substantially perpendicular to the extension direction  8 . It goes without saying that as an alternative the transverse direction  10  in contrast to the right angle of  FIGS. 1A, 1B, 2A and 2B  may be inclined by a different angle opposite the extension direction  8 . The transverse direction  10  can follow a straight or a curved line. The distance D at which the angled portion  9  is arranged opposite the heat exchange portion  7  is smaller than a minimum bending radius R of the second bend  16 . The minimum bending radius R of the second bend  16  for example is 3 to 6 times the tube thickness T of the tube body  2 . The minimum bending radius R can be 0.70 to 0.95 times the tube width W. The minimum bending Radius R can be determined by an inner height H of the bent portion  11 , which is measured along the offset direction  12 . When progressively distancing from the heat exchange portion  7 , the bent portion  11  firstly is set back counter to the offset direction  12  by the first bend  14 , then the bent portion  11  by its second bend  16  begins rising in the offset direction  12  as to cross a plane containing the heat exchange portion  7  and lastly transfer into the angled portion  9  in the offset direction  10 . 
     According to  FIGS. 1A, 1B, 2A and 2B , the second bend  16  is a twist-bend  18 . This means that in the second bend  16  the tube body  2  is bent and twisted at the same time, such that on the one hand the distance D between the angled portion  9  and the heat exchange portion  7  is bridged and on the other hand the exact same surface area of the tube body  2 , which in the heat exchange portion  7  represents the top surface  4 , mutates to the bottom surface  5  in the area of angled portion  9 . Thus, the tube body  2  can be twisted 180° in the second bend  16 . 
     As mentioned above, the flat tube  1  may be used in a heat exchanger  30  according to the invention. In  FIG. 3A  an example of the heat exchanger  30  according to the invention is partially depicted in a view against the transverse direction  10 . The heat exchanger  30  has first flat tubes  1  according to the invention, one of which is illustrated separately in  FIG. 3B  in a view along the offset direction  12 . Alternatively, the first flat tubes  1  of the heat exchanger  30  may accord to the examples of  FIGS. 1A, 1B, 2A and 2B  as described above. The first flat tubes  1  of the heat exchanger  30  each have a first longitudinal end  20  of their heat exchange portions  7 , which faces away from their bent portions  11 . 
       FIG. 4A  shows the heat exchanger  30  in a plan view along the offset direction  12 . As to be seen from  FIGS. 3A and 4A , the first longitudinal ends  20  of the first flat tubes  1  are received in associated first openings  39  of a first collector  36  of the heat exchanger  30 . Each of the first flat tubes  1  also has a second longitudinal end  21  of their angled portions  9 , which faces away from their bent portion  11 . These second longitudinal ends  21  are received in associated second openings  40  of a second collector  37  of the heat exchanger  30 . The heat exchanger  30  furthermore has second flat tubes  31 . These second flat tubes  31  have first longitudinal ends  32 , which are received in associated third openings  41  of a third collector  38  of the heat exchanger  30 . The second flat tubes  31  also have second longitudinal ends  33 , which are arranged opposite their first longitudinal ends  32 , which are received in associated fourth openings  42  of the first collector  36  of the heat exchanger  30 . The first and the fourth openings  39  and  42  are arranged spaced apart from one another. 
     As to be seen from  FIG. 3A , heat transfer fins  34  can be present at the outer top and bottom surface  4 ,  5 , wherein the heat fins  34  protrude from the respective outer top and bottom surface  4 ,  5  along a fin height HF. The fin height HF is measured perpendicularly opposite the respective outer top and bottom surface  4 ,  5 . The minimum bending radius R of the second bend  16  is 0.70 to 0.95 times the fin height HF. 
     According to  FIGS. 3A and 4A , in the heat exchanger  30 , the first flat tubes  1  and the second flat tubes  31  are arranged alternatingly along a stacking direction that corresponds to the offset direction  12  of the first flat tubes  1 . For instance, this stacking direction equals the offset direction  12  of the first flat tubes  1 . Between two adjacent flat tubes  1 ,  31  an intermediate space  35  can be present in the heat exchanger  30 , in which the heat transfer fins  34  of the heat exchanger  30  are accommodated. In a view along the stacking direction the heat exchange portions  7  of the first flat tubes  1  for example completely overlap the second flat tubes  31 , whereas the angled portions  9  of the first flat tubes  1  do at least partially not overlap the second flat tubes  31 . For example, the second flat tubes  31  may substantially be straight. For instance, whilst assembling the heat exchanger  30 , the heat transfer fins  34  can be held in place by the first bends  14  of the first flat tubes  1 . 
     In an alternative example of the heat exchanger, which is—in a plan view along the offset direction  12 —shown in  FIG. 4B  as an example, the second flat tubes  31  are configured to substantially accord to the flat tube  1  of the invention as exemplary depicted in  FIGS. 1A, 1B, 2A and 2B  and described above, wherein the transverse direction  10  of the first flat tubes  1  differs from the transverse direction  10 ′ of the second flat tubes  31 . Thus, both the first and the second flat tubes  1  and  31  in the heat exchanger  30  may accord to the flat tube  1  according to the invention, wherein they are mounted in different, in particular mirrored, orientations in the heat exchanger  30 . In the example of  FIG. 4B , the first and the second flat tubes  1  and  31  are formed as identical parts, that only differ in their orientation in the heat exchanger  30 . 
     While the above description constitutes the preferred embodiments of the present invention, the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.