Patent Publication Number: US-2021164739-A1

Title: Heat exchangers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/117,374, filed Aug. 30, 2018, which is a divisional application of U.S. patent application Ser. No. 14/993,843 filed Jan. 12, 2016, issued as U.S. Pat. No. 10,088,250. The contents of each above referenced application are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to heat exchangers, and, in particular, to a cylindrical counter-flow heat exchanger. 
     2. Description of Related Art 
     Heat exchangers are used in a variety of systems, for example, in engine and environmental control systems of aircraft. These systems tend to require continual improvement in heat transfer performance, reductions in pressure loss, and reductions in size and weight. Heat exchangers typically include a plate/fin construction in the core of the heat exchanger. 
     Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for systems and methods that allow for improved heat exchangers. The present invention provides a solution for these problems. 
     SUMMARY OF THE INVENTION 
     A counter-flow heat exchanger comprising a heat exchanger core including an inner wall and an outer wall radially outward and spaced apart from the inner wall. A first flow path is defined within the inner wall and a second flow path is defined between the inner wall and the outer wall. The heat exchanger core includes a primary flow inlet, a primary flow outlet and a middle portion therebetween. The inner and outer walls are concentric at the primary flow inlet of the heat exchanger core. The inner wall defines a first set of channels extending axially from the primary flow inlet to the middle portion of the heat exchanger core diverging away from a radial center of the heat exchanger core. The inner wall and the outer wall define a second set of channels extending axially from the primary flow inlet to the middle portion of the heat exchanger core converging toward the radial center of the heat exchanger core. 
     In accordance with certain embodiments, the inner wall is corrugated to form the first and second sets of channels. Respective channels of the first and second sets of channels can alternate circumferentially with one another. The heat exchanger core can be a circular cylinder. At the primary flow inlet of the heat exchanger core, in a cross-section taken perpendicular to a primary flow direction, the inner and outer walls can define an annulus therebetween including the second flow path. A diameter of the heat exchanger core at the primary flow inlet can be smaller than a diameter of the heat exchanger core in the middle portion. At least one channel of the first set of channels can split into multiple sub-channels to maintain a width smaller than a maximum threshold. At least two channels of the second set of channels can unite into a single joined channel to maintain a width greater than a minimum threshold. 
     It is contemplated that at least one of the first and second flow paths can include vanes to assist with flow distribution. The heat exchanger core can be substantially linear and can define a longitudinal axis between the primary flow inlet and the primary flow outlet. A radial center of the inner wall can be aligned with the longitudinal axis. Additional cylindrical walls can be disposed radially inward from the outer wall and concentric with the heat exchanger core. The additional cylindrical walls can be radially spaced apart from one another and are in fluid communication with the first and second flow paths. Annular ring sections can be defined between two adjacent cylindrical walls. Each annular ring section can include a portion of a channel from the first set of channels and a portion of a channel from the second set of channels. The portion from the first set of channels in a first annular ring section can be offset radially and circumferentially from the portion from the first set of channels in a second annular ring section. The second annular ring section can be adjacent to the first annular ring section. The portion from the second set of channels in the first annular ring section can be offset radially and circumferentially from the portion from the second set of channels in the second annular ring section. The additional cylindrical walls can be circular cylindrical walls. The additional cylindrical walls can be disposed in the middle portion of the heat exchanger core. The inner and outer walls can be concentric at the primary flow outlet of the heat exchanger core. 
     The heat exchanger core can be cylindrical, wherein at an outlet of the heat exchanger core, in a cross-section taken perpendicular to a primary flow direction, an annulus can be defined between the inner and outer walls. From the middle portion of the heat exchanger core to the primary flow outlet, the first set of channels can extend axially away from the middle portion to the primary flow outlet converging toward the radial center of the heat exchanger core and the second set of channels can extend axially away from the middle portion to the primary flow outlet diverging away from the radial center of the heat exchanger core. In accordance with another aspect, a method of manufacturing a counter-flow heat exchanger core includes forming a heat exchanger core body using additive manufacturing. The heat exchanger core body is similar to the heat exchanger core described above. Additive manufacturing can be via direct metal laser sintering. 
     These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a top view of a schematic depiction of an exemplary embodiment of a counter flow heat exchanger, showing the heat exchanger core and the primary flow direction; 
         FIG. 2  is a schematic cross-sectional view of the heat exchanger of  FIG. 1  at the primary flow inlet of the heat exchanger core, showing inner and outer walls and an annulus formed therebetween; 
         FIG. 3  is a schematic cross-sectional view of the heat exchanger of  FIG. 1  between the primary flow inlet of the heat exchanger core and a middle portion of the heat exchanger core, showing the converging and diverging sets of channels; 
         FIG. 4  is a schematic cross-sectional view of the heat exchanger of  FIG. 1  between the primary flow inlet of the heat exchanger core and a middle portion of the heat exchanger core, showing the channels of the first set of channels separating into sub-channels; 
         FIG. 5  is a schematic cross-sectional view of the heat exchanger of  FIG. 1  in the middle portion of the heat exchanger core, showing the additional cylindrical walls; and 
         FIG. 6  is a schematic cross-sectional view of a portion of the heat exchanger of  FIG. 1  in the middle portion of the heat exchanger core, showing adjacent annular sections between the additional cylindrical walls off-set from one another. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a perspective view of an exemplary embodiment of a heat exchanger in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of imaging systems in accordance with the disclosure, or aspects thereof, are provided in  FIGS. 2-5 , as will be described. Embodiments of heat exchanger  100  provide a fractal heat exchanger core that results in increased performance, and reduced size and weight as compared with traditional plate fin heat exchangers. As shown in  FIG. 1 , a counter-flow heat exchanger  100  includes a heat exchanger core  102  that defines a longitudinal axis X. Heat exchanger core  102  includes a primary flow inlet  104 , a primary flow outlet  106  and a middle portion  108  therebetween. The primary flow direction is indicated schematically by the arrow  101 . Heat exchanger core  102  is circular cylinder that includes conical tapering portions at its inlet and outlet,  104  and  106 , respectively. A diameter of heat exchanger core  102  at primary flow inlet  104  is smaller than a diameter of the heat exchanger core  102  in middle portion  108 . It is also contemplated that the diameter of core  102  at inlet  104  and in middle portion  108  can be the same, e.g. core  102  can have a constant diameter. Heat exchanger core  102  has circular cross-sections along its length, e.g. those taken perpendicular to the flow direction and longitudinal axis X. It is contemplated that heat exchanger core  102  can have a variety of other suitable shapes, for example, it can be an oval cylinder, an elliptical cylinder, a rectangular cylinder, or a square cylinder. In accordance with some embodiments, additional elliptically shaped walls, similar to additional walls  130  can be used inside a rectangular cylinder core. The heat exchanger core is substantially linear and defines a longitudinal axis between the primary flow inlet and the primary flow outlet. A radial center of the inner wall is aligned with the longitudinal axis. 
     As shown in  FIG. 2 , a cross-section of heat exchanger core  102  at primary flow inlet  104  is shown. At primary flow inlet  104 , heat exchanger core  102  includes an inner wall  110  and an outer wall  112  radially outward and spaced apart from inner wall  110 . A first flow path  114  is defined within inner wall  110  and a second flow path  116  is defined between inner wall  110  and outer wall  112 . Inner and outer walls,  110  and  112 , respectively, define an annulus  115  that includes second flow path  116 . Inner and outer walls  110  and  112 , respectively, are cylindrical and concentric at primary flow inlet  104  of heat exchanger core  102 . Inner and outer walls,  110  and  112 , respectively, are concentric at primary flow outlet of the heat exchanger core. 
     As shown in  FIG. 3 , as inner wall  110  extends away from primary flow inlet  104  it becomes corrugated and defines a first set of channels  118  extending axially from primary flow inlet  104  to middle portion  108  of heat exchanger core  102  diverging away from a radial center A of heat exchanger core  102 . Inner wall  110  and outer wall  112  define a second set of channels  120  extending axially from primary flow inlet  104  to middle portion  108  of heat exchanger core  102  converging toward radial center A of heat exchanger core  102 . Respective channels  122  and  124  of the first and second sets of channels  118  and  120 , respectively, alternate circumferentially with one another to provide additional surface area for heat transfer. In accordance with the embodiment of  FIG. 3 , two channels  122  from first set of channels  118  alternate with one channel  124  from second set of channels  120 . First and second flow paths  114  and  116 , respectively, include vanes  125  to assist with flow distribution with only minimal pressure drop. 
     With reference now to  FIG. 4 , as inner wall  110  extends further axially away from flow inlet  104  toward and into middle portion  108 , channels  122  of the first set of channels  118  split into multiple sub-channels  126  to maintain a width smaller than a maximum threshold. At least two channels  124  of the second set of channels  120  unite into a single joined channel  128  to maintain a width greater than a minimum threshold. 
     As shown in  FIG. 5 , additional cylindrical walls  130  are disposed radially inward from outer wall  112  and are concentric with heat exchanger core  102 . Additional cylindrical walls  130  are radially spaced apart from one another and are in fluid communication with first and second flow paths  114  and  116 , respectively. Additional cylindrical walls  130  are circular cylindrical walls. Additional cylindrical walls  130  are disposed in middle portion  108  of the heat exchanger core  102 . It is also contemplated that additional cylindrical walls like cylindrical walls  130  could be used in other portions of heat exchanger core  102 . 
     As shown in  FIG. 6 , in accordance with an embodiment of core  102 , annular ring sections  132  are defined between two adjacent additional walls  130  are circumferentially offset with respect to an adjacent annular ring so that a checker-board pattern is formed, e.g. alternating first and second flow paths  114  and  116 , respectively, in a radial direction as well as in a circumferential direction. The cross-section of  FIG. 6  is taken at a similar location as the cross-section of  FIG. 5 . Each annular ring section  132  includes a portion  122 ′ of one of channels  122  from first set of channels  118  and a portion  124 ′ of one of channels  124  from second set of channels  120 . Portion  122 ′ from first set of channels  118  in a first annular ring section  132   a  is offset radially and circumferentially from portion  122 ′ from first set of channels  118  in a second annular ring  132   b  section. Second annular ring section  132   b  is adjacent to first annular ring section  132   a . Portion  124 ′ from the second set of channels  120  in first annular ring section  132   a  is offset radially and circumferentially from portion  124 ′ from second set of channels  120  in second annular ring section  132   b.    
     With reference now to  FIGS. 1-5 , at outlet  106  of the heat exchanger core  102  inner and outer walls  110 , and  112 , respectively, are similar to how they were arranged at inlet  104 , shown in  FIG. 2 , e.g. at a cross-section taken perpendicular to longitudinal axis X at outlet  106  inner and outer walls  110 , and  112 , respectively, would be concentric circles. To transition back to concentric circles, from middle portion  108  of the heat exchanger core  102  to primary flow outlet  106 , the first set of channels  118  extends axially away from middle portion  108  to the primary flow outlet  106  converging back toward radial center A of heat exchanger core  102  and second set of channels  120  extends axially away from middle portion  108  to primary flow outlet  106  diverging away from radial center A of the heat exchanger core. By utilizing a counter-flow configuration, heat exchanger  100  provides for reduced size and increased performance by better balancing the hot and cold fluids running through core  102 , e.g. through first and second flow paths  114  and  116 , respectively. Heat exchanger  100  also increases the heat exchanger effectiveness for a given overall heat transfer area. The counter-flow configuration enables high temperature and high pressure operation by reducing the temperature differential across the heat exchanger planform since the cold side outlet and hot side inlet are aligned with one another. By gradually transitioning from the inlet  104 , as shown in  FIG. 2 , to the core  108 , as shown in  FIG. 5 , pressure drops can be reduced and there is not a large discontinuity in stiffness or thermal response as in traditional headering. 
     It is contemplated that a method of manufacturing a counter-flow heat exchanger core, e.g. heat exchanger core  102 , includes forming heat exchanger core  102  using additive manufacturing such as, direct metal laser sintering, for example. It is contemplated that the heat exchanger core can be manufactured in the flow direction, e.g. along longitudinal axis X to avoid horizontal surfaces. It is also contemplated that instead of being a linearly extending cylinder, the heat exchanger could be built along a sinusoidal path creating wavy or ruffled sets of channels as opposed to straight ones for increased heat transfer or bend around obstructions. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for heat exchangers with superior properties including improved heat transfer resulting from a larger primary flow area, with a relatively small amount of secondary flow area. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.