Abstract:
Newly-developed manufacturing techniques have opened up new possibilities in fabricating designs of components that were previously infeasible. One such component is a heat exchanger. A crossflow heat exchanger is disclosed that includes a plurality of internal passages for conducting a first fluid. The internal passages that form a spiral with adjacent passages separated by a gap of a predetermined distance or less. The second fluid passes through the gaps. The internal passages may be a plurality of parallel passages arranged along a first line. From upstream to downstream, each of the passages form an inlet spiral connected to an inner ring connected to an outlet spiral. The gaps are less than a predetermined distance related to a Reynolds number that is less than that at which laminar flow exists.

Description:
FIELD 
       [0001]    The present disclosure relates to heat exchangers for special applications such as a heat pump. 
       BACKGROUND 
       [0002]    There are many heat exchanger configurations that have been used over the years. Many of these designs have been constrained by manufacturing limitations. However, with the advent of new manufacturing techniques, heat exchangers that might have not been conceived of previously might now be fabricated. 
       SUMMARY 
       [0003]    A heat pump presently being developed has a heat exchanger specification of high effectiveness and favorable packaging. A heat exchanger having such characteristics is disclosed herein as one example of such a heat exchanger to provide the desired characteristics for the heat pump. 
         [0004]    A cross flow heat exchanger is disclosed that has an inlet for a first fluid, an outlet for the first fluid, an inlet spiral having a plurality of passages therein, an inlet manifold fluidly coupling the inlet with the plurality of passages of the inlet spiral, an outlet spiral having a plurality of passages therein, and an outlet manifold fluidly coupling the outlet with the plurality of passages of the outlet spiral. The passages of the inlet spiral are fluidly coupled to the passages of the outlet spiral. Interior walls of the passages of the inlet and outlet spirals are in contact with the first fluid. The exterior walls of the inlet and outlet spirals are in contact with a second fluid. The inlet spiral is nested with the outlet spiral. A gap between adjacent turns of the inlet and outlet spirals is less than a predetermined distance. 
         [0005]    The predetermined distance is less than a distance at which a predetermined Reynolds number exists. The predetermined Reynolds number is that which is defined to lead to laminar flow for the given geometry of the gaps. 
         [0006]    The crossflow heat exchanger may include a plurality of braces mechanically coupling adjacent turns of the inlet and outlet spirals. 
         [0007]    In some embodiments, the passages of the inlet spiral and the passages of the outlet spiral are fluidly coupled via a collector ring. In another embodiment, the passages of the inlet spiral and the passages of the outlet spiral are coupled via a transition section. 
         [0008]    In some embodiments, the passages of the inlet spiral are arranged along a first line, the passages of the outlet spiral are arranged along a second line, and the first line and the second line are parallel. 
         [0009]    The passages of the inlet and outlet spirals are circular, elliptical, polygonal, or any suitable shape. 
         [0010]    A heat pump is disclosed that includes a cylinder, a hot displacer disposed in the cylinder, a cold displacer disposed in the cylinder, and a crossflow heat exchanger disposed between the hot displacer and the cold displacer. The crossflow heat exchanger includes: an inlet spiral having a rectangular cross section and defining a plurality of passages arranged longitudinally, an inlet manifold coupled to an upstream end of the inlet spiral with the inlet spiral defining an inlet volume that fluidly couples with the plurality of passages of the inlet spiral, an outlet spiral having a rectangular cross section and defining a plurality of passages arranged longitudinally, and an outlet manifold coupled to a downstream of the outlet spiral with the outlet spiral defining an outlet volume that fluidly couples with the plurality of passages of the outlet spiral, wherein the passages of the inlet spiral are fluidly coupled to the passages of the outlet spiral. 
         [0011]    The passages of the inlet spiral are coupled to the passages of the outlet spiral via a transition section, a central collector ring, or any suitable transition. 
         [0012]    Turns of the inlet spiral interleave with turns of the outlet spiral, and gaps exists between adjacent turns. 
         [0013]    The cylinder is filled with a working fluid. And reciprocation of one of the displacers in the cylinder causes the working fluid to pass through the gaps. 
         [0014]    A pressurized fluid supply is coupled to the inlet manifold. 
         [0015]    Turns of the inlet spiral interleave with turns of the outlet spiral, and a gap exists between adjacent turns. The heat exchanger further includes a plurality of braces mechanically coupling adjacent turns. 
         [0016]    A liquid flows from the inlet manifold into passages in the inlet spiral into passages in the inlet ring into passages in the outlet spiral into the outlet manifold. 
         [0017]    A crossover passage in parallel with gaps between inlet spirals through which the second fluid may bypass the heat exchanger. 
         [0018]    Newer fabrication techniques, such as 3-dimensional printing and hydroforming, facilitate manufacture complicated shapes is facilitated. Some of the embodiments in the present disclosure, which may have been very difficult to fabricate with prior fabrication techniques, may now be readily fabricated via such newer methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a top view of a heat exchanger according to an embodiment of the disclosure; 
           [0020]      FIG. 2  is a core of the heat exchanger of  FIG. 1 ; 
           [0021]      FIG. 3  is a cross-sectional, isometric view of the heat exchanger of  FIG. 1 ; 
           [0022]      FIG. 4  a cross-sectional view of a portion of the heat exchanger of  FIG. 1 ; 
           [0023]      FIGS. 5-9  are illustrations of alternative cross-sectional shapes for inlet and outlet spirals of a heat exchanger; 
           [0024]      FIGS. 10-12  are representations of alternative embodiments of heat exchanger spirals; 
           [0025]      FIG. 13  is a schematic of a heat pump with a centrally-located heat exchanger; 
           [0026]      FIG. 14  is a cross-sectional view of a heat exchanger showing a bypass passage; 
           [0027]      FIGS. 15-17  illustrate various stages of an embodiment in which a heat exchanger is assembled using sintering; and 
           [0028]      FIG. 18  is an illustration of a spiral heat exchanger according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0030]      FIG. 1  shows a top view of a heat exchanger  100 , which has a frame  102  having two nested spirals  110  and  112 . The term involute is an alternative term for spiral. In some applications, frame  102  of heat exchanger  100  is welded to a cylinder (not shown) in which it is disposed. In other applications, frame  102  is a sealing member and has any number of O-rings, or other suitable type of seals in grooves in frame  102 , to seal against a cylinder (not shown). Inlet spiral  110  has three turns  111  interleaved with turns  113  of outlet spiral  112 . A spiral may alternately called and involute. 
         [0031]    A gap  106  between adjacent turns has a distance  108  less than a predetermined distance. In one embodiment, a liquid circulates in passages within spirals  110  and  112  and a gas travels through gaps  106  (into, or out of, the plane of  FIG. 1 ) between adjacent turns of spirals  110  and  112 . The predetermined distance, in one embodiment, is a distance in which laminar flow would exist if the length of the flow were to be enough to set up laminar flow. There is a Reynolds number which is based on the geometry, the velocity expected, and parameters of the fluid itself, below which is defined to provide laminar flow. Braces  104  are provided to maintain the gaps of predetermined distance of spirals  110  and  112  with a gap that is less than or equal to the gap that provides laminar flow. Manifold housing  114  is an inlet area and manifold housing  116  is an outlet area, which will be discussed below. A central collector  118  has an internal passage that fluidly couples with passages in spirals  110  and  112 . 
         [0032]    In  FIG. 2 , a representation of a core  120  of heat exchanger  100  (of  FIG. 1 ). The core is essentially the “negative” of heat exchanger  100 , i.e., the part where the fluid would flow inside heat exchanger  100 . Core  120  has an inlet  122  and an outlet  124 . Inlet  122  leads to an inlet spiral passages (only one of which is visible)  132  via an adapter  136  to a central collector  134 . The fluid moves from central collector  134  to outlet spiral passages (only one of which is visible)  130  via an adapter  138 . Outlet spiral passages  130  fluidly couple to outlet  124 . Inlet spiral passages  132  interleave with outlet spiral passages  130 , although offset by 180 degrees in the embodiment shown in  FIG. 2 . The three-turn embodiment with 180 degree offset in  FIG. 2  is provided by way of example only and not intended to be limiting as the turns can be any suitable number and the offset can be altered to accommodate desired inlet and outlet locations or for other purposes. 
         [0033]    In  FIG. 3 , an isometric view of a section of heat exchanger  100  is shown. The cross section is taken through two of braces  104 . In  FIG. 2 , outlet spiral passage  130  appears as a single spiral. However, in the embodiment in  FIG. 3 , there are four parallel outlet spirals passages arranged along a line, such as illustrated with one of the turns shown arranged along dash dot line  140 . In place of four openings along line  140 , a single slot could be provided. However, in some embodiments in which the pressure difference between the inside and the outside is great, a plurality of passages essentially provides bracing and prevents collapse that might occur with a single slot. Similarly, inlet spiral passage  132  has four parallel spirals. The passages of one of the turns is shown lying in a line, as illustrated with dash-dot line  142 . Central collector  134  is shown as a single slot. Thus, the four passages of the inlet spiral passage  132  combine to form a single slot passage of central collector  134  and then manifolds into four passages of outlet spiral passage  130 . Central collector  134  has beefier walls than spiral passages  130  and  132 . If thinner walls for the central collector are desired, the central collector may alternatively have a plurality of passages that correspond to the passages in the spirals. 
         [0034]    In  FIG. 4 , a portion of heat exchanger  100  is shown in cross section. An inlet  152  leads to a manifold  154  that fluidly couples with inlet spiral passages  132 . A similar manifold is provided for the outlet spiral passages (not shown). 
         [0035]    The cross section of heat exchanger  100  shown in  FIG. 3  is taken through brace  104 . Thus, passages  132  appear to be in a block with an array of passages. In  FIG. 5 , a single turn of a spiral  200  is shown in cross section with the cross section taken at a place away from a brace. Within that turn are multiple circular passages  200 . In an alternative, passage  206  in turn  204  are substantially square. Passages  206  have rounded corners to avoid stress risers. In turn  208 , passages  210  are substantially rectangular. Any suitable passage shape can be used. In the embodiments shown in  FIGS. 3-7  the spiral has straight sides. However, in an alternative configuration shown in  FIG. 9 , adjacent turns  220  and  222  of spirals have a gap distance  224  that is consistent along the gap. 
         [0036]    An alternative heat exchanger  240  configuration is also contemplated, as shown in  FIG. 10 . Heat exchanger  240  has an inlet spiral  242  interleaved with an outlet spiral  244 . In the embodiment in  FIG. 10 , the spirals are not regular, but have kinks in them. Herein, such a configuration or other similar configurations with slight kinks are called spirals. Heat exchanger  240  has a central opening  248  to accommodate a post. In other configurations, opening  248  is filled with a plug so that gasses flow through the gaps between adjacent turns of the spirals. The gaps in  FIG. 10  are exaggerated for illustration convenience. The gaps are to be consistent and are generally narrow. To fill any blank spaces that would allow gases to flow rather than between the spirals, plugs  250  and  252  are provided. A transition section  246  is provided to connect inlet spiral  242  with outlet spiral  244 . Another heat exchanger  260  alternative is shown in  FIG. 11  with inlet spiral  262 , outlet spiral  264 , plugs  270  and  272 , opening to accommodate a post  268 , and transition section  266 . And yet, another alternative heat exchanger  280  is shown in  FIG. 12 . Heat exchange  280  has: inlet spiral  282 , outlet spiral  284 , plugs  290  and  292 , opening to accommodate a post  288 , and transition section  296 . 
         [0037]    The illustrations in  FIGS. 10-12  show the inlet and outlet spirals to be single lines for illustration simplicity. In reality, the turns of the spirals are wider than is implied in the Figures and the gap between adjacent turns is a predetermined width. That predetermined width is based on the properties of the gas that travels through the gap and the velocity of the gas traveling through the gap such that the Reynolds number is in a range defined to provide laminar flow. 
         [0038]    An illustration of a heat pump  300  is shown in cross section in  FIG. 13 . Heat pump  300  has a cylinder  302  in which a hot displacer  304  and a cold displacer reciprocate. A heat exchanger  310  is located within cylinder  302 . A top edge of heat exchanger  310  is substantially at the bottom end of travel of hot displacer  304 ; a bottom edge of heat exchanger  310  is substantially at the top of travel of cold displacer  306 . Heat exchanger  310  has an inlet  314  and an outlet  316  and passages fluidly coupling inlet  314  with outlet  316 . The fluid within heat exchanger  310  is a liquid, but alternatively a gas. Flow within heat exchanger  310  is in the plane of such heat exchanger. Flow on the exterior surface is substantially perpendicular to the flow with heat exchanger  10 . Gas flows through gaps  312 . 
         [0039]    If both cold and hot displacers  304  and  306  move upward or downward, the gases flow from one side of heat exchanger  310  to the other side. If only one of the displacers moves, the gases that flow through heat exchanger  310  bypasses the cylinder. That is, for example, if cold displacer  306  moves upwardly while hot displacer  304  is stationary, gases from the volume within cylinder  302  that is above displacer  306  flow through gaps  312  into the volume above heat exchanger  310  through a bypass tube  340 , a regenerator  342 , a bypass tube  344 , and a heat exchanger  346  then into the volume within cylinder  302  that is below displacer  306 . Gases reverse that flow path when hot displacer  304  moves upwardly while hot displacer  306  is stationary. Another bypass path is provided that has a bypass tube  334 , a regenerator  332 , a bypass tube  330 , and a heat exchanger  336 . These elements provide desired function in the context of a heat pump, in particular a Vuilleumier heat pump, further description of which can be found elsewhere. The heat exchanger disclosed herein is suitable for such a heat pump, but this is a non-limiting application. 
         [0040]    In  FIG. 14 , a cross section through a heat exchanger  400  shows bypass passages  430  and  440 . There are a plurality of such passages around the periphery of heat exchanger  400 . The cross section in  FIG. 14  happens to cut through two such passages  430  and  440 . Unlike the cross section in  FIG. 3  that is through a brace section, the cross section of  FIG. 14  is away from the brace section. A turn of the inlet spiral in which passage  402  is located is displaced by a gap  406  from a turn of the outlet spiral in which passage  404  is located. 
         [0041]    One of the processes by which a heat exchanger according to the present disclosure can be manufactured is via 3D printing. Alternatively, a sintering process is used. In  FIG. 15 , two portions  450  are shown in cross section. The two portions  450  are shown sintered together at interface  452  in  FIG. 16 . An assembly  456  of a grid of such portions  450  is shown in which the portions are sintered at interfaces  452  and interfaces  454 . Gaps  458  less than a predetermined width are provided between each column. 
         [0042]    In some applications, it is desirable to have an annular heat exchanger, such as a heat exchanger  500  shown in  FIG. 18 . An inlet  502  leads inwardly and couples to a turnaround  504  which causes heat exchanger  500  to spiral outwardly to outlet  506 . Heat exchanger  500  allows for space  510  in the center to provide the annular shape. In the case of a Vuilleumier heat pump, displacers can reciprocate through the middle of heat exchanger  500 . 
         [0043]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.