Patent Application
20150075759
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.
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.
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:
a) & 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
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.
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
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
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.
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 202a 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
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
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. (
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 1/16th 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 ⅛th 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
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
It should also be apparent that a polymer heat exchanger, such as the heat exchanger 100 illustrated in
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.
