Patent Publication Number: US-2015075759-A1

Title: Polymer manifold and methods of fabrication

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to manifolds and heat exchangers formed from polymer materials and associated fabrication techniques. 
     Heat exchangers are used in a wide variety of applications and have a wide variety of geometries and designs for specific applications. Most often, heat exchangers are formed from metal materials such as copper, aluminum or stainless steel due to the favorable heat transfer characteristics that are displayed by such materials. Although metal heat exchanger designs work well for many applications, metals tend to be more expensive and/or more subject to corrosion than certain other materials such as plastics. Therefore, there are some applications where it is desirable to form a heat exchanger from lower cost polymer materials. 
     One class of heat exchangers uses a flow of a heat exchange fluid (heat exchange medium) through a heat transfer medium to affect heat exchange. For example, a feed stream can be supplied to a heat exchange device and divided into multiple streams that pass through the heat transfer medium. Such a heat exchanger typically employs inlet and outlet manifolds to divide and reunite the feed stream into/from a number of relatively narrow tubes that pass through the heat transfer medium. The fabrication of such manifolds can be difficult when the tubes and/or manifolds are formed from a plastic (or other polymer) material. Co-owned U.S. patent application Ser. No. 13/071,322 describes a few methods of manufacturing polymer manifolds and polymer heat exchangers. Although the described polymer manifold and polymer heat exchanger designs work well, there are continuing efforts to provide improved manifold and heat exchanger designs. The present application describes a low cost polymer manifold design that is well suited for use in a variety of heat exchanger designs. The polymer manifold may also have extensive applications outside of the heat exchanger field. 
     SUMMARY OF THE INVENTION 
     A variety of polymer manifold structures and methods of forming polymer manifolds are described. In one aspect a polymer manifold is formed by welding distal tips of a multiplicity of polymer tubes to a polymer retainer. The tubes pass through guide passages that extend between opposing faces of the retainer and the distal tip of each tube is welded to a manifold face of the retainer. The welds between the tubes and the manifold face form sealed connections between the tubes and the manifold face. 
     In some embodiments a locking plate is positioned adjacent the retainer. The locking plate also includes a multiplicity of guide passages, with each locking plate guide passage being aligned with an associated retainer guide passage and receiving an associate one of the tubes therethrough. During assembly, the locking plate and/or the retainer can be moved slightly relative to the other to hold the tubes in place during welding to the retainer. 
     The manifold may also include a coupling member that facilitates connection to complementary devices. In some embodiments, the coupling member includes a cap that covers the manifold face and forms a manifold plenum adjacent the manifold face. 
     In some embodiments, such polymer manifolds are provided on both ends of the tubes. 
     In a method aspect, the tubes are positioned in the retainer such that distal tips of the tubes extend slightly beyond the manifold face of the retainer. These protruding portions of the tubes are then welded to the manifold face of the retainer. In some embodiment, a heated platen is used to melt the tube tips and heat fuse the tubes to the manifold face of the retainer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and the advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagrammatic perspective illustration of a polymer heat exchanger incorporating manifolds in accordance with the present invention. 
         FIG. 2  is a diagrammatic perspective illustration of a polymer manifold in accordance with one embodiment of the present invention. 
         FIGS. 3(   a ) &amp;  3 ( b ) are respectively perspective and cross section side views of an embodiment of a retainer suitable for use in the polymer manifold illustrated in  FIG. 2 . 
         FIG. 4  is a cross section view of a locking plate embodiment suitable for use in the polymer manifold of  FIG. 2 . 
         FIG. 5  is a flow chart illustrating one method of fabricating a polymer manifold in accordance with some embodiments of the invention. 
         FIGS. 6(   a )- 6 ( f ) are a series of diagrammatic side sectional views that illustrate various steps in a process of fabricating a manifold in accordance with a process embodiment of the invention. 
     
    
    
     In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates generally to polymer heat exchangers. In general, polymer materials may be used to form a low cost heat exchanger that can perform well in a variety of applications. 
     Referring initially to  FIG. 1 , a polymer heat exchanger in accordance with one embodiment will be described. In the illustrated embodiment, the heat exchanger  100  includes a multiplicity of plastic tubes  110  and a pair of manifold assemblies  200 . The manifold assemblies  200  are positioned on opposing ends of tube  110  to facilitate connection to larger diameter input and output lines or other component such as plenums, etc. 
     The diameter and length of the tubes  110  may be widely varied to meet the needs of any particular application. Preferably, the tubes will have small diameters and relatively thin walls. By way of example, polymer tubes having an outer diameter in the range of approximately 0.08 to 0.25 inches work well for many applications, although both larger and smaller tube diameters may be used in particular applications. Inner tube diameters may also vary widely although it should be appreciated that thin walls are generally preferred since thin walls will generally improve the heat exchangers thermal performance by decreasing the temperature drop across the tube walls. 
     The tubes  110  and various components of the manifold assemblies  200  may be formed from a wide variety of plastics and other polymers. By way of example, Polyethylene, Polypropylene, Polyamide, Polysulfone, and Polyphenylene Sulfide work well for both the tubes and the manifold assemblies. Of course, in other embodiments, a wide variety of other plastics and polymers may be used. The tubes and components of the manifold assemblies may be formed from the same materials, substantially the same materials or different materials depending on the requirements of any particular application. 
     A representative manifold assembly  200  is illustrated in the partially cut-away, perspective, cross-sectional view of  FIG. 2 . Each manifold assembly  200  includes a perforated retainer plate  202  that serves as a manifold plate, a locking plate  209  and a manifold cap  205 . The cap  205  defines an internal chamber  207  that serves as a manifold plenum and integrates a tube stub  208  suitable for coupling to a feed or drain line. The tubes  100  pass through the locking plate  209  and the perforated retainer  202 . Distal ends of the tubes are welded to the exterior face  213  of the perforated retainer plate  202  in a manner that seals the retainer plate openings. Thus, face  213  effectively serves a manifold surface. This structure is described in more detail below. 
     Although a particular cap geometry is shown, it should be appreciated that the actual geometry of both the manifold cap  205  and its associated chamber  207  may be widely varied. In the illustrated embodiment, the cap  205  is butt welded to the retainer plate  202 . Of course, in other embodiments, a variety of alternative coupling structures can be used to connect the manifold cap to the tube assembly. By way of example, other welding techniques (e.g., socket welding), threaded connections, and or other conventional coupling techniques can be used to secure the tube assembly to the manifold cap. 
       FIGS. 3(   a ) and  3 ( b ) illustrate a representative embodiment of a perforated retainer  202  in more detail. The perforated retainer  202  has a generally cylindrical or puck like geometry although a variety of other shapes and sizes can be used. In the illustrated embodiment, selected peripheral segments  327  of the perforated retainer puck are flattened to facilitate handling. The retainer is formed of a polymer or plastic material. Examples of suitable materials include, but are not limited to, polyethylene, polypropylene, polyamide, polysulfone, and polyphenylene sulfide materials. The perforated retainer  202  includes a first face that serves as manifold surface  213 , an opposing second face  305 , and a plurality of guide passages  307  that extend therebetween. The passages  307  are sized, spaced, and arranged such that a plurality of tubes  110  can be inserted into the guide passages  307  and then affixed in place. 
     The diameter of the guide passages  307 , like the diameter of the associated tubes, can be varied. The actual number of guide passages  307  in any particular implementation is variable and generally determined by the size of the retainer, the arrangement of the passages, the desired fluid flow, and the diameter of the tubes  110  associated with the manifold  100 . By way of example, in some implementations, on the order of 40 to 70 guide passages  307  are formed in the perforated retainer  202  to accommodate a like number of tubes  110 . The guide passages  307  can be arranged in a wide variety of configurations and arrays in accordance with the needs of any particular application. In general, the tolerances between the diameter of the passages and the outer diameter of the tubes are such that the tubes can be readily inserted into the guide passages without undue difficulty. In one specific example, the perforated retainer  202   a  has a diameter of about 3 inches and a thickness of about ½ of an inch, with sixty (60) guide passages  307  each having a diameter of approximately ¼ inch. Other retainer embodiments can assume a wide variety of sizes, shapes, and thicknesses as well as support a wide range of guide passages (sizes, shapes, and passage arrangements). 
     The locking plate  209  may have a geometry that is generally similar to the perforated retainer  202 —although its thickness may vary as discussed below. Typically, the guide passage pattern of the locking plate  209  will match that of the perforated retainer. In some embodiments, at least a portion of the guide passages in the locking plate may be tapered somewhat to facilitate insertion of the tubes  110 . Once such geometry is illustrated in  FIG. 4 . In the illustrated embodiment the guide passages  337  in locking plate  209  include a short tapered portion  337   a  and a narrower cylindrical portion  337   b.  In other embodiments, the guide passages may be tapered along their entire length. The openings on the face abutting the retainer plate are slightly narrower than the openings on the opposing proximal face. Such a taper can make it easier to insert the tubes  110  during assembly of the manifold. When such a taper is used, the actual taper angle may vary widely. By way of example, a taper angle of approximately 45 degrees works well in many applications. 
     The thickness of the locking plate may be widely varied. In many embodiments, the locking plate  209  is formed from a polymer material similar to the retainer  202  and/or the tubes  110 . An advantage of using a polymer material for the locking plate is that after attachment of the tubes, the locking plate can optionally be welded to the retainer to provide additional strength which is particularly useful in higher pressure applications. 
     Referring next to  FIG. 5  a process suitable for fabricating a manifold assembly  200  using the locking plate approach will be described. Initially a perforated retainer and a locking plate are positioned adjacent one another and oriented such that their respective openings are aligned. Thereafter, tubes  110  are inserted into each of the aligned passages  307 ,  317 —typically from the tapered end of the locking plate  209 . (Step  510  as illustrated in  FIG. 6(   a )). Preferably the tubes are inserted such that their distal ends protrude slightly from past the manifold face  213 . The tubes can be inserted manually or in an automated fashion. For example, a jig can be used assist in the insertion of the tubes. 
     The inserted tubes are aligned such that each of the tubes extends a predetermined distance past the manifold face  213 . The alignment of the tubes can be accomplished in any suitable manner such as by using a registration block during or after insertion. (Step  520 ). 
     The distance  112  that the distal tips  118  of tubes  110  protrude past the manifold face  213  is selected to provide the proper amount of material for welding as will be described in more detail below. The appropriate protrusion distance will vary somewhat based on a number of factors, but generally tends to be dependent on the size of the tubes (e.g., diameter and wall thickness), the materials used and the spacing between the guide passages. 
     Once the tubes are properly positioned, they are locked in place. In the illustrated embodiment, the locking of the tubes is accomplished by translating or otherwise moving the locking plate  209  relative to the retainer (step  530 ) which exerts a force on the tubes thereby holding them in place for the subsequent welding operation. In other embodiments the locking plate can be rotated relative to the retainer to hold the tubes in place (although this approach does not work well for centrally located tubes) or other mechanisms can be used to hold the tube in place. 
     Once the tubes are properly positioned and locked in place, the distal tips  118  of tubes  110  are welded (or otherwise affixed) to the perforated retainer  202 . (Step  540 ). In one embodiment, this can be achieved by melting the tips  118  of the tubes  110  and welding the melted tips to the first surface of the retainer  202 . This approach forming a high quality seal that affixes the tubes  110  to the retainer  202 . 
     In one approach, the tubes are affixed by applying a heated platen  601  against the extended distal tips  118  of the tubes  110  and gently pushing the platen  601  against the tubes in the direction of the manifold face  213  of the perforated retainer  202 . ( FIG. 6(   c )). In this way the heated platen  601  melts the distal tips of tubes  110 . As the tips melt, the protruding portion of the tubes “collapse” allowing the platen  601  to move towards the manifold face until the platen is only separated from the manifold face by the molten plastic. As the platen moves towards the retainer, the melted plastic spreads out on the manifold face—preferably away from the open entrances to the tubes. In this position, the platen heats the manifold face which effectively welds the tips of the tubes to the manifold face  213  of retainer  202 . 
     The platen may be formed from a variety of different materials that facilitate good weld formation. By way of example the platen may be formed from a material having good heat conduction properties such as aluminum and may be covered with a thin coat of a material such as Teflon or other suitable fluoropolymer to prevent sticking. The results can be high quality bonds that affix the tubes  110  to the retainer  202  and seal the connections. When polypropylene is used as the material for both tubes  110  and the retainer  202 , heating a platen  601  to a temperature in the range of 250-400° F. is suitable to facilitate the melting/welding of the tube tips 
     It should be appreciated that the amount of plastic material that is used in the weld is most directly controlled by the distance that the tube tips  118  protrude beyond the manifold face  213 . It has been found that by controlling the amount of material melted (i.e., the tube tip protrusion) and the pressure applied by the platen  601  during welding, good welds can be formed that do not unduly occlude the tubes. If the tube tips extend too far (resulting in too much material being melted) or too much pressure is used during the welding operation, then larger amounts of plastic will flow into the distal ends of the tubes, thereby clogging the tubes and/or good welds between the tubes and the retainer will not be formed. Conversely, if the tips do not extend out far enough or too little pressure is used during the welding operation, then poor welds will form and the resulting manifold structure will not be strong. In some embodiments, the movement of the platen can be controlled to provide a designated standoff distance from the manifold face to help maintain weld quality. 
     As suggested above, a number of factors will influence the quality of the welds and the optimal protrusion of the tube tips will vary with factors such as the diameter of the tubes, the wall thickness of the tubes, the materials used to form the tubes, etc. In one particular embodiment, polypropylene tubes having a 3/16 inch outer diameter with a 0.018 inch (18 mil) wall thickness, the distal tips  118  of the tubes  110  protrude a specified distance  112  that is about 1/16 th  of an inch beyond the manifold face  213 . Additionally, the spacing between guide passages  307  should be selected such that there is room for the melted plastic from the protruding tube tips  118  to spread sufficiently to avoid blocking the adjacent tubes. In this embodiment, the spacing distance (between guide passages) is at least ⅛ th  of an inch, edge-to-edge. It should be noted that the distance that the tips protrude and the spacing between adjacent tubes is subject to a wide range of variability depending on the specific design. The appropriate tip protrusion and tube spacing for any particular design can be determined experimentally. 
     The bonds between the tubes  110  and the retainer  202  is diagrammatically illustrated in  FIG. 6(   e ). As seen therein, when the appropriate volume of plastic material is provided and the appropriate pressure is used, the melted plastic material will primarily spread outward from the openings  114  of the tubes  110 . Thus, the melted portion of the plastic  115  does not noticeably occlude the openings  114 . However, it should be appreciated that if the protruding tube segments are too long, bulges of plastic material (not shown) may form adjacent the distal end of the tube which extend into the tube opening  114 , thereby partially or fully occluding the tubes. 
       FIG. 6(   f ) is a more detailed frontal view of a portion of the perforated retainer  202  showing the tubes  110  secured thereto. As stated above, the melted tube ends  113  are not intended to substantially occlude the tube opening  114 . The separation  116  between the guide passages  307  is chosen such that the melted plastic from one of the tubes does not interact with the melted plastic from adjacent tubes in a manner that can cause undue blockage of an adjacent tube. Often the skirts  119  of plastic formed around adjacent tubes will merge together in places, although often not to the extent that the entire surface of the retainer is covered. In other implementations, the guide passages can be located far enough apart such that the skirts  119  associated with adjacent tubes generally do not touch. 
     A significant advantage of the described approach is that when controlled properly, the tube openings are not significantly occluded during the welding operation. Thus, there is no need to machine out, or otherwise enhance or form openings in the tube channels after the welding operation which can significantly reduce production costs. Of course, the openings could be drilled out, routed or otherwise machined if necessary or desired—however, it is believed that the elimination of the need for such steps will be highly desirable in most applications. 
     Since control of the weld volume is desirable, it is helpful to hold the tubes and retainer firmly in place relative to each other during the welding operation. When desired, this can be done using a jig or other suitable fixture. Although such arrangements work well, they can be a bit expensive—particularly in low volume manufacturing environments. Therefore, in the embodiments shown above, the locking plate  209  is used to hold the tubes in place during the welding operations. As mentioned above, this can be done by simply translating or otherwise moving at least one of the retainer  202  and the locking plate  209  relative to the other. This movement binds the tubes, thereby immobilizing the tubes, which are effectively locked into place. After the welding has been completed, the locking translation may be released, thereby freeing the tubes. If desired, the locking plate can be removed and potentially reused. However, that is not always appropriate (as for example when manifolds are provided at both ends of the tubes.) Therefore, it is often easiest to form the locking plates from the same plastic material as the retainer and to use the locking plate as additional reinforcement for the manifold. 
     In an alternative embodiment having manifolds provided at both ends of the tubes  110 , a single locking plate can potentially be used in conjunction with the formation of both manifolds with the locking plate being slid along the tubes from adjacent the first retainer to a position adjacent the second retainer 
     In the embodiment of  FIG. 3 , a plastic manifold cap  205  is used to cover the manifold face to thereby form a manifold plenum  207 . The cap may also serve as a coupling member that is suitable for connecting the manifold  200  to complimentary components such as a heat exchanger feed line, a heat exchanger exhaust line, fluid tanks, a heat exchanger mounting fixture, etc. (none shown). In the embodiment depicted in  FIG. 3 , the cap  205  has a tube stub  208  suitable for engaging an input or outlet source or conduit. Of course, any other suitable coupling structure can be used in place of or in addition to the cap/tube stub structure. By way of example, various adaptors, housings or end caps may be used. Such structures or alternatively the retainer itself (and locking plate when appropriate) can be threaded to facilitate coupling to input or outlet sources. In other embodiments, manifold plates and bolts may be used in conjunction with a gasket to secure and seal the assembly. In yet another example particularly suitable for higher pressure applications, locking plate  209  make take the form of a metal plate having a larger size or diameter than the retainer  202  and the locking plate itself can serve as a coupling member with a gasket provided between the metal locking plate and a complementary structure to seal the manifold. Thus, it should be appreciated that the geometry of the housing/coupling member may be widely varied. 
     It should also be apparent that a polymer heat exchanger, such as the heat exchanger  100  illustrated in  FIG. 1  can readily be assembled by providing the described polymer manifolds on both ends of a bundle of polymer tubes. Such heat exchangers have many applications. One specific example is to use the described heat exchanger in the tank portion of the polymer solar collector described in U.S. Pat. No. 8,161,963 which is incorporated herein by reference. Although a specific application of the heat exchanger within a solar collector tank is mentioned, it should be appreciated that the described heat exchanger may be applied in a wide variety of applications outside of the solar field as well. 
     A significant advantage of the described approach is that it allows the substantially simultaneous sealing of many small diameter tubes with respect to a manifold chamber to create a high tube density manifold without the need for precise tube alignment, over molding or additional machining operations to form open channels in the manifold. Thus, a very low cost arrangement for forming a plastic or other polymer heat exchanger manifold that includes openings to a relatively large number of heat exchange tubes is described. The number of tubes that are joined in a manifold may be widely varied. By way of example numbers on the order of 20 to 250 tubes are believed appropriate for many applications although either more or fewer tubes may be used. 
     Although only a few embodiments of the invention have been described in detail, it should be appreciated that the invention may be implemented in many other forms without departing from the spirit or scope of the invention. For example, although the manifold formation has been described primarily in the context of a heat exchanger manifold, it should be appreciated that the described polymer manifold may be used in a wide variety of applications and its uses are not in any way limited to heat exchanger manifolds. 
     In the primary described embodiments, the polymer tubes are platen welded to the polymer retainer. Although platen welding works well and has been specifically described, it should be appreciated that there are a number of other plastic welding/fusing techniques that may be suitable including, for example, ultrasonic bonding, thermosonic bonding, infrared welding, laser welding, hot gas welding, and a variety of other heat fusing techniques and any of these may be used in other embodiments. All of these techniques are considered plastic “welding” or “fusing” within the context of this application. 
     The process of forming a manifold has been described in the context of a particular sequence of steps. It should be appreciated that in alternative embodiments, the sequence of the steps can sometimes be altered and some of the steps may be skipped, while others may be added. For example, the tubes may be inserted into the retainer in and aligned in a single operation or the distal tips of the tubes may be gradually egressed out of the retainer during the welding operation rather than using fixed protrusions. In other examples, the locking plate can be eliminated in some embodiments and/or the manifold housing may be assembled in a wide variety of manners. 
     The method of forming a manifold has been described primarily in the context of forming a heat exchanger manifold. However, it should be appreciated that the described approach to may be used to attach a plurality of tubes to a variety of structures. For example, U.S. Pat. Nos. 3,934,323 and 6,038,768 describe approaches for attaching riser tubes to a header in a solar collector application. It should be appreciated that the approach described herein is well suited for use as an alternative approach to forming such header manifolds. Therefore, the present embodiments should be considered illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.