Apparatus and method for manufacturing internally finned pressure vessels

Abstract

1. An apparatus for making an internally finned pressure vessel, the apparatus comprising: a plurality of locating discs, each of the locating discs defining a plurality of circumferentially spaced slots extending radially from a periphery of the locating disc into the locating disc; and one or more rods extending through the plurality of locating discs, the plurality of locating discs being held in axial alignment by the one or more rods. 2. A method of making an internally finned pressure vessel, the method comprising the steps of providing an apparatus, loading a plurality of fins into the slots of the locating discs, inserting the apparatus containing the plurality of fins into the pressure vessel, attaching the plurality of fins to the pressure vessel by a brazing process, and removing the apparatus from the pressure vessel.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to thermal energy conversion, and more particularly to pressure vessels for storing or transporting fluids. [Background technology]

[0002] In a thermal energy conversion engine, energy in the form of heat must be removed or added to a fluid stored at high pressure. Typical shapes of containers for storing or transporting fluids at high pressure are spherical or cylindrical. Because liquids and gases generally have much lower thermal conductivities than solid materials, the distance that heat must travel in the fluid must be reduced to maximize heat transfer efficiency. The structural integrity of the vessel containing the high-pressure fluid must not be affected by the heat transfer enhancement. Summary of the Invention

[0003] The present disclosure contemplates various apparatus and methods for overcoming the above-mentioned problems associated with the related art. One aspect of an embodiment of the present disclosure is an apparatus for making an internally finned pressure vessel. The apparatus may include a plurality of locating discs, each of which defines a plurality of circumferentially spaced slots extending radially from a periphery of the locating disc into the locating disc, and one or more rods extending through the plurality of locating discs, the plurality of locating discs being held in axial alignment by the one or more rods.

[0004] The positioning disc may be made of stainless steel or a nickel-chromium based alloy. The apparatus may include a pair of biasing discs, one on either side of the plurality of positioning discs, held in axial alignment with the plurality of positioning discs by the one or more rods, each of the biasing discs defining a plurality of circumferentially spaced slots extending radially from a periphery of the biasing disc into the biasing disc, the slots in the biasing disc terminating further from an axis defined by the axial alignment of the plurality of positioning discs than the slots in the positioning disc. The biasing discs may be made of rubber.

[0005] The one or more rods may include a central rod lying on an axis defined by the axial alignment of the plurality of positioning discs. The apparatus may include a pair of leveling discs, one on each side of the plurality of positioning discs and held in axial alignment with the plurality of positioning discs by the central rod, each of the leveling discs forming a surface that overlaps the slot in the positioning disc. The leveling discs may be made of stainless steel. The one or more rods may further include one or more off-axis rods parallel to the central rod. The positioning disc may be secured to the one or more off-axis rods by the central rod, the central rod being movable relative to the one or more off-axis rods along the axis. The positioning disc may be secured to the one or more off-axis rods by a plurality of nuts threadably connected to the one or more off-axis rods. The one or more off-axis rods may be made of stainless steel or a nickel-chromium alloy.

[0006] The apparatus may include a pair of retaining rings mountable on opposite sides of the plurality of locating discs, each retaining ring having a relaxed diameter greater than the diameter defined by the inner ends of the slots in the locating discs, and the retaining rings may be made of stainless steel.

[0007] The one or more rods may include a central rod lying on an axis defined by the axial alignment of the plurality of positioning discs. The apparatus may include a leveling disc on one side of the plurality of positioning discs and held in axial alignment with the plurality of positioning discs by the central rod, the leveling disc forming a surface that overlaps the slot in the positioning disc. The leveling disc may be made of stainless steel. The apparatus may include an adjustment assembly including a fixture connected to the leveling disc by the central rod and one or more adjustment screws configured to protrude from the fixture in the longitudinal direction defined by the central rod. The fixture may be made of stainless steel. The fixture may include a bar extending transversely to the central rod.

[0008] The one or more rods may include one or more grouping rods connecting a first subset of the plurality of locating discs to define a first group of locating discs, one or more grouping rods connecting a second subset of the plurality of locating discs to define a second group of locating discs, and one or more rods connecting the first group of locating discs to the second group of locating discs. The apparatus may comprise one or more spacer tubes through which the one or more rods connecting the first group of locating discs to the second group of locating discs extend, the one or more spacer tubes being positioned between the first group of locating discs and the second group of locating discs.

[0009] Another aspect of an embodiment of the present disclosure is a brazing jig for making an internally finned pressure vessel, the brazing jig may include a plurality of axially aligned locating disks, each of the locating disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the locating disk into the locating disk, and a pair of retaining rings mountable on opposite sides of the plurality of locating disks, each retaining ring having a relaxed diameter greater than the diameter defined by inner ends of the slots in the locating disk.

[0010] Another aspect of an embodiment of the present disclosure is a brazing jig for manufacturing an internally finned pressure vessel, the brazing jig may include a plurality of axially aligned locating disks, each of the locating disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the locating disk into the locating disk, a rod extending through the plurality of locating disks, and a leveling disk on one side of the plurality of locating disks and held in axial alignment with the plurality of locating disks by the rod, the leveling disk defining a surface that overlaps the slots of the locating disk.

[0011] Another aspect of an embodiment of the present disclosure is a method of making an internally finned pressure vessel. The method may include providing an apparatus including a plurality of locating disks, each of the locating disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the locating disk into the locating disk, the apparatus further including one or more rods extending through the plurality of locating disks, the plurality of locating disks being held in axial alignment by the one or more rods. The method may further include loading a plurality of fins into the slots of the locating disk, inserting the apparatus containing the plurality of fins into a pressure vessel, attaching the plurality of fins to the pressure vessel by a brazing process, and removing the apparatus from the pressure vessel.

[0012] The positioning disc may be made of stainless steel or a nickel-chromium based alloy. The fins may be made of aluminum.

[0013] The apparatus may include a pair of biasing disks, one on each side of the plurality of positioning disks, held in axial alignment with the plurality of positioning disks by the one or more rods, each of the biasing disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the biasing disk into the biasing disk, the slots in the biasing disk terminating further from an axis defined by the axial alignment of the plurality of positioning disks than the slots in the positioning disk. The method may include inserting the apparatus including the plurality of fins into the pressure vessel, tack welding the plurality of fins to the pressure vessel, and then removing the pair of biasing disks before attaching the plurality of fins to the pressure vessel by a brazing process. The biasing disks may be made of rubber.

[0014] The one or more rods may include a central rod lying on an axis defined by the axial alignment of the plurality of positioning discs. The apparatus may include a pair of leveling discs, one on each side of the plurality of positioning discs, held in axial alignment with the plurality of positioning discs by the central rod, each of the leveling discs defining a surface that overlaps the slot in the positioning disc. The method may include abutting the plurality of fins against a surface of a first leveling disc of the pair of leveling discs, and abutting the plurality of fins against a surface of a second leveling disc of the pair of leveling discs while the fins are abutting the surface of the first leveling disc. Abutting the plurality of fins against the surface of the second leveling disc may include moving the second leveling disc along the axis relative to the central rod. The leveling discs may be made of stainless steel.

[0015] The method may include welding a pair of end caps to the pressure vessel, one on each side of the plurality of fins, and the end caps may be made of aluminum. Another aspect of an embodiment of the present disclosure is a method of making a pressure vessel with multiple internal fins. The method may include providing an apparatus including multiple locating disks, each of the locating disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the locating disk into the locating disk, and the apparatus may further include one or more rods extending through the multiple locating disks, the multiple locating disks being held in axial alignment by the one or more rods. The method may further include loading multiple fins into the slots of the locating disk, inserting the apparatus containing the multiple fins into a pressure vessel, attaching the multiple fins to the pressure vessel by a brazing process, removing the apparatus from the pressure vessel, loading a new multiple fins into the slots of the locating disk, inserting the apparatus with the new multiple fins into a new pressure vessel, and attaching the new multiple fins to the new pressure vessel by a brazing process.

[0016] These and other features and advantages of the various embodiments disclosed herein will be better understood with regard to the following description and drawings, in which like numbers refer to like parts throughout. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a partially exploded perspective view of an apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a side view of the brazing jig of the apparatus. [Figure 3] FIG. 1 is a perspective view of a brazing jig having multiple fins. [Figure 4] 4 is a cross-sectional view taken along line 4-4 in FIG. 3. [Figure 5] Same view as Figure 4, but with multiple fins inserted into the brazing jig. [Figure 6] FIG. 1 is a perspective view of the brazing jig and fins and the pressure vessel. [Figure 7] FIG. 1 is a perspective view of the pressure vessel shown in an exploded view with the brazing jig and fins inserted into the pressure vessel and the tack welding jig of the apparatus. [Figure 8] 1 is a perspective view of a pressure vessel and a brazing jig and a tack welding jig inserted into the pressure vessel along with fins. [Figure 9] 9 is a cross-sectional view taken along line 9-9 in FIG. 8. [Figure 10] FIG. 1 is a perspective view of an internally finned pressure vessel made in accordance with an embodiment of the present disclosure. [Figure 11] 11 is a cross-sectional view taken along line 11-11 in FIG. [Figure 12] 12 is a cross-sectional view taken along line 12-12 in FIG. 11. [Figure 13] FIG. 10 is a partially exploded perspective view of an apparatus according to another embodiment of the present disclosure. [Figure 14] 1 is a perspective view of a pressure vessel (shown in phantom) and a device inserted into the pressure vessel with fins. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present disclosure encompasses various apparatus and methods for making internally finned pressure vessels. The detailed description set forth below in connection with the accompanying drawings is intended as a description of some currently contemplated embodiments. It is not intended to represent the only forms in which the disclosed subject matter may be developed or utilized. The description describes functions and features in connection with illustrated embodiments. However, it is understood that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second is used solely to distinguish one entity from another, without necessarily requiring or implying any actual relationship or order between such entities.

[0019] FIG. 1 is a partially exploded perspective view of an apparatus 100 according to one embodiment of the present disclosure. The apparatus 100 may be used to fabricate internally finned pressure vessels (see FIGS. 10-12 ), which may be used to store or transport high-pressure fluids, such as the working fluid of a thermal energy conversion system. Unlike more typical pressure vessel designs in which the fins are located on the exterior, the internally finned pressure vessel can improve the rate of heat transfer from the thermally conductive exterior of the pressure vessel to the low-thermal-conductivity fluid contained within. When fabricating such internally finned pressure vessels, attaching fins to the interior of the tubes by drilling or welding through the tubes from the outside can compromise the integrity of the vessel and is impractical, especially considering that the fins need to be as thin as possible to add minimal weight and maximize void space in the vessel for the working fluid. By positioning the fins on the interior of the vessel for brazing, the apparatus 100 avoids these difficulties and enables the fabrication of internally finned pressure vessels with high structural integrity and minimal weight and obstruction to radial and / or axial fluid flow.

[0020] As shown in FIG. 1 , the apparatus 100 may include a plurality of positioning disks 110, each of which defines a plurality of circumferentially spaced slots 112 extending radially from its periphery into the positioning disk 110. In the example of FIG. 1 , five positioning disks 110 are shown, although fewer or more positioning disks 110 may be used depending on the length of the internally finned pressure vessel being manufactured. The positioning disks 110 may be made of stainless steel or a nickel-chromium alloy (e.g., Inconel) to withstand brazing temperatures. The apparatus 100 may further include one or more rods 120 extending through and holding the plurality of positioning disks 110 in axial alignment, a pair of biasing disks 130, and a pair of leveling disks 140. In general, the positioning disk 110 and associated rods 120 may be considered to constitute a brazing jig used in the brazing process, while the biasing disk 130, leveling disk 140, and associated rods 120 may be considered to constitute a separate tack welding jig used prior to the brazing process, as described below. In this regard, the one or more rods 120 may include a central rod 122 associated with the tack welding jig and one or more off-axis rods 124 associated with the brazing jig and extending parallel to the central rod 122.

[0021] 2 is a side view of the brazing jig. As shown, the positioning disks 110 can be secured to the rods 124 by a plurality of nuts 160 threadably connected to the rods 124. For example, the rods 124 can be threaded to allow the nuts 160 to traverse their length up and down, and each of the positioning disks 110 can be secured to the rods 124 by positioning a nut 160 on either side of the positioning disk 110. To change the longitudinal position of the positioning disks 110 along the rods 124 (e.g., to change the spacing between the positioning disks 110), the nuts 160 can be loosened, allowing the positioning disks 110 to slide freely along the rods 124, and the nuts 160 can be retightened around the positioning disks 110 at the desired longitudinal position. In this regard, the positioning discs 110 may each define one or more holes 114 through which the rods 120 extend (see FIG. 1 where the central hole 114 is visible and the off-axis holes 114 are hidden by the nuts 160).

[0022] FIG. 3 is a perspective view of a brazing jig having a plurality of fins 200. FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 3. As shown in FIGS. 3 and 4, a method of fabricating an internally finned pressure vessel may include loading a plurality of fins 200 into slots 112 in positioning disks 110. Twenty fins 200 are shown, with four of the fins 200 omitted from FIG. 3 to more clearly illustrate the brazing jig. Correspondingly, each of the positioning disks 110 has twenty slots 112. However, any number of fins 200 and slots 112 is contemplated, depending on the heat transfer needs of the internally finned pressure vessel being fabricated. Each positioning disk 110 may be positioned such that the slots 112 of one positioning disk 110 are aligned with corresponding slots 112 of the other positioning disks 110, as shown. Thus, each fin 200 may be retained by a set of corresponding slots 112, one for each positioning disk 110. The fins 200 may be made of aluminum or another material that can be attached to the interior of the pressure vessel by brazing. In the example shown, the fins 200 are all the same length but alternate between two widths, and the slots 112 correspondingly alternate between two radial depths into the positioning disk 110. For an internally finned pressure vessel having a circular cross-section as shown, the use of alternating fin widths and slot depths may allow for an increased number of fins 200 while maintaining a desired minimum distance between the fins 200. However, other configurations are possible, including those having only a single fin width and a single slot depth.

[0023] FIG. 5 is the same view as FIG. 4 , but with multiple fins 200 inserted into the brazing jig. FIG. 6 is a perspective view of the brazing jig and fins 200 along with a pressure vessel 300 (e.g., a tube). Prior to insertion into the pressure vessel 300, the fins 200 may be prevented from falling out of the slots 112 by various means, including, for example, a press fit between the fins 200 and the slots 112 (i.e., friction between the fins 200 and the walls of the slots 112) or a temporary wrapping or tie circumferentially surrounding the brazing jig with the fins 200 loaded. Alternatively, the brazing jig may be positioned vertically so that the fins 200 are held in the slots 112 by gravity, either upright as shown in FIG. 6 or slightly tilted toward the brazing jig, and then the pressure vessel 300 may be lowered over the brazing jig and fins 200. In this manner, the pressure vessel 300 itself may serve to hold the fins 200 in the slots 112. Thus, the brazing jig including the fins 200 may be inserted into the pressure vessel 300 .

[0024] 7 is a perspective view of a pressure vessel 300 with the brazing jig and fins 200 inserted, and the tack welding jig of the apparatus 100 shown in an exploded view. As described above, the tack welding jig may include the biasing disks 130, leveling disks 140, and associated rods 120 (e.g., center rod 122) of the apparatus 100. Like the positioning disks 110 of the apparatus 100, each of the biasing disks 130 may define a plurality of circumferentially spaced slots 132 extending radially from its periphery into the biasing disk 130. Each biasing disk 130 may be positioned such that its slots 132 are aligned with corresponding slots 112 of the positioning disk 110. If the slots 112 of the positioning disk 110 have alternating slot depths as described and shown above, the corresponding slots 132 of the biasing disk 130 may likewise have corresponding alternating slot depths.

[0025] The slots 132 of the biasing disk 130 may terminate farther from an axis 170 defined by the axial alignment of the plurality of positioning disks 110 than the corresponding slots 112 of the positioning disk 110. For example, the distance d2 (see FIG. 1 ) between a given slot 132 of the biasing disk 132 and the center of the biasing disk 132 may be greater than the distance d1 between the corresponding slot 112 of the positioning disk 110 and the center of the positioning disk 110. By terminating the slots 132 of the biasing disk 130 at a greater distance d1 from the axis 170 than the corresponding slots 112 of the positioning disk 110, the biasing disk 130 can apply a biasing force to the fins 200 that tends to push the fins 200 outward against the inner wall of the pressure vessel 300. This achieves close contact between the fins 200 and the pressure vessel 300. The biasing disk 130 may be made of rubber or another material that has sufficient resilience to allow the fins 200 to fit into the slots 132 in the pressure vessel 300 against such biasing forces.

[0026] As shown in FIG. 7 , with the brazing jig and fins 200 inserted into the pressure vessel 300, fabrication of the internally finned pressure vessel may continue by placing a pair of biasing disks 130 on either side of the multiple positioning disks 110 of the brazing jig. To this end, like the positioning disks 110, the biasing disks 130 may each be formed with one or more holes 134 through which a rod 120 extends. Because the biasing disks 130 are not used to position the fins 200 during brazing, the biasing disks 130 may simply lie flat against the outermost positioning disks 110. The off-axis holes 134 of the biasing disks 130 may be large enough to accommodate the outermost nut 160 in addition to the off-axis rods 124 protruding from the outermost positioning disks 110. The off-axis rods 124 need not extend beyond the biasing disks 130 and, in some cases, may terminate just after the outermost positioning disks 110 upon entering the biasing disks 130. As mentioned above, the resiliency of biasing disk 130 allows slots 132 of biasing disk 130 to fit around fin 200, even though slots 132 terminate farther from axis 170 than slots 112 of positioning disk 110. In this manner, biasing disk 130 may be used to hold fin 200 firmly against the inner wall of pressure vessel 300 for a tack welding process as described below, and then may be removed for a subsequent brazing process.

[0027] The central rod 122 of the tack welding jig may pass completely through the brazing jig through the central hole 114 of the positioning disk 110 and, if used, through the central holes 134 of the biasing disks 130 on either end thereof, allowing free movement of the central rod 122 relative to the positioning disk 110, the biasing disks 130, and the off-axis rods 124. Creation of the internally finned pressure vessel may continue by placing a pair of leveling disks 140 on the ends of the central rod 122. The leveling disks 140 may be made of stainless steel or aluminum, for example, and may each form a surface that overlaps the slot 112 of the positioning disk 110 and, if used, the slot 132 of the biasing disk 130. For example, the radius d3 (see FIG. 1 ) of the leveling disk 140 may be greater than the distance from the center of either of the slots 112, 132 of the positioning disk 110 and the biasing disk 130. In particular, the surface of each leveling disk 140 can prevent the fins 200 from moving longitudinally beyond the leveling disk 140. Thus, the leveling disks 140 can be used to ensure alignment of the fins 200 along the length of the pressure vessel 300 prior to brazing (or tack welding). For example, the fins 200 can first abut against the surface of one of the leveling disks 140 (e.g., the bottom leveling disk 140 in FIG. 7 ), which can be secured to the central rod 122 by nuts 150. While the fins 200 abut against the surface of one leveling disk 140, the other leveling disk 140 (e.g., the top leveling disk) can be moved along the axis 170 relative to the central rod 122, for example, by sliding the leveling disk 140 downward until it abuts the fin 200 and securing the leveling disk 140 in its new position with another nut 150. For this purpose, the leveling discs 140 may each form a central hole 144 through which a rod 122 extends, and the end of the central rod 122 may be threaded as shown in FIG. 7 (or alternatively, the entire central rod 122 may be threaded).

[0028] FIG. 8 is a perspective view of a pressure vessel 300 with the entire apparatus 100, including the brazing jig and tack welding jig, inserted therein along with the fins 200. FIG. 9 is a cross-sectional view taken along line 9-9 in FIG. 8. As described above, the fins 200 are sandwiched between the leveling disks 140 of the tack welding jig to ensure that the fins 200 are longitudinally aligned relative to one another in the brazing jig. Meanwhile, intimate contact between the fins 200 and the pressure vessel 300 can be ensured by an outward force applied by the biasing disks 130 (partially hidden in FIG. 8). Thus, the method for making an internally finned pressure vessel can proceed with tack welding multiple fins 200 to the pressure vessel 300. For example, tack welds, e.g., less than 1 inch, may be applied to both ends of the pressure vessel 300 to secure each of the fins 200 to the interior wall of the pressure vessel 300. The tack welds function to temporarily hold each of the fins 200 on the pressure vessel 300 in the desired position established by the positioning disc 110 and fine-tuned by the biasing disc 130 and leveling disc 140 .

[0029] Once each of the fins 200 is tack welded at both ends, the tack welding jig may be removed from the pressure vessel 300. In particular, the nuts 150, leveling disks 140, biasing disks 130, and center rod 122 may be removed. The brazing jig, now with the fins 200 tack welded to the pressure vessel 300, may remain on the pressure vessel 300. The multiple fins 200 may then be attached to the pressure vessel 300 by a brazing process. For example, a filler metal (e.g., 88% aluminum and 12% silicon) may be applied to the base of the fins 200 in either paste or wire form. The entire pressure vessel 300, including the fins 200 and brazing jig (e.g., positioning disks 110, rods 124, and nuts 160), may be preheated in an air furnace and subsequently immersed in a molten salt bath to melt the filler metal and bond the fins 200 to the vessel 300. As mentioned above, the positioning disk 110, rod 124, and nut 160 may be made of stainless steel or a nickel-chromium alloy (e.g., Inconel) so that brazing of the fin 200 to a brazing jig may be avoided. However, various other combinations of materials may be used with appropriate control of the brazing temperature. By leaving the brazing jig in the pressure vessel 300 during the brazing process, excessive warping of the fin 200 may be prevented. After the brazing process is completed, the brazing jig may be removed from the pressure vessel 300.

[0030] Figure 10 is a perspective view of an internally finned pressure vessel 300 made in accordance with one embodiment of the present disclosure. Figure 11 is a cross-sectional view taken along line 11-11 in Figure 10. Figure 12 is a cross-sectional view taken along line 12-12 in Figure 11. The internally finned pressure vessel 300 having a plurality of fins 200 may be made using the apparatus 100 having the brazing jig and tack welding jig described above, for example, by loading a plurality of fins 200 into the slots 112 of the positioning disk 110, inserting the brazing jig into the pressure vessel 300, biasing the fins 200 against the interior wall of the pressure vessel 300 using the biasing disk 130 of the tack welding jig, leveling the fins 200 using the leveling disk 140 of the tack welding jig, tack welding the fins 200 to the pressure vessel 300, removing the tack welding jig, brazing the fins 200 to the pressure vessel 300, and removing the brazing jig. The internally finned pressure vessel 300 may be completed by closing the ends with a pair of end caps. For example, a pair of aluminum end caps may be welded to the pressure vessel 300, one on either side of the fins 200, so that the vessel 300 can withstand high internal and external pressures while maximizing radial heat transfer from the external environment to the contained working fluid. The apparatus 100, including the brazing and tack welding jigs, may then be reused to fabricate additional internally finned pressure vessels 300. In this regard, new fins 200 may be loaded into the slots 112 of the positioning disk 110, and the remainder of the process may be repeated to attach the new fins 200 to the new pressure vessel 300.

[0031] Generally, thermal energy conversion engines may require improved heat transfer for both moving and stationary fluids, making a simple increase in the convective heat transfer coefficient by increasing fluid velocity insufficient. In the absence of convection, the heat transfer rate is controlled solely by the thermal resistance to conduction in the fluid and solid materials of the pressure vessel. Thermal resistance may be reduced by reducing the distance energy must travel in a low-thermal-conductivity medium and by increasing the interfacial area between the fluid and the solid material. Both measures may be achieved using extended surfaces, such as fins. Heat transfer from such extended surfaces may be used to increase the rate of heat transfer without increasing the convection coefficient or temperature difference between the solid material and the fluid. Unlike more typical designs in which pressure vessel fins are located externally and intended to increase the rate of heat transfer from a solid with a high thermal conductivity to air with a very low thermal conductivity, an internally finned pressure vessel 300 constructed in accordance with the present disclosure may improve the rate of heat transfer from the exterior of the thermally conductive pressure vessel to a low-thermal-conductivity fluid contained within. By using the disclosed apparatus 100, the difficulties associated with attaching fins to the interior of a pressure vessel may be overcome, allowing for the manufacture of an internally finned pressure vessel 300 having high structural integrity with minimal weight and obstruction to fluid flow. Advantageously, the internally finned pressure vessel 300 manufactured according to the disclosed embodiments and shown in FIGS. 10-12 does not form separate compartments within the pressure vessel 300, thus allowing for unimpeded radial flow in the cross-sectional plane of the pressure vessel 300. This can be important because certain working materials may exhibit substantial volume changes when undergoing thermal expansion and / or phase changes.

[0032] U.S. Pat. No. 7,987,674, the disclosure of which is expressly incorporated herein by reference, describes a power generation system in which a phase change material (PCM) working material melts (expands) at warm temperatures, e.g., 15°C, and freezes (contracts) at colder temperatures, e.g., 8°C. Tubes containing the PCM, which can be a paraffin such as pentadecane, are fitted with a flexible central tube containing hydraulic oil. As the PCM melts (expands), it pushes the oil through a hydraulic motor, generating rotational mechanical energy, which is then converted to electricity using conventional methods. The elapsed time the unit must remain at the PCM's freezing and melting temperatures is important because it determines the amount of energy that can be generated in a specific time frame. To keep freezing and melting times short, previous units have been constructed using many small-diameter tubes, minimizing the distance energy must be transmitted through the PCM, which has low thermal conductivity. The drawbacks of this concept are the increased system complexity and the high overall system mass per unit of PCM volume. The disclosed apparatus 100 allows for the creation of one large diameter tube 300 instead of many smaller tubes while maintaining fast freezing and melting times. Through the process described above, radially arranged thin aluminum fins 200 are mechanically and thermally attached to the inner wall of the tube 300, allowing heat to be transported to the PCM.

[0033] In the illustrated examples above, it is assumed that the pressure vessel 300 is cylindrical. However, the disclosed subject matter is not intended to be so limited. For example, in the case of a spherical pressure vessel 300, the fins 200 may be thicker or outwardly curved in the center, and the positioning disk 110 may be larger toward the center of the brazing jig. In such cases, the relationship between the slot distances d1, d2 of the positioning disk 110 and the biasing disk 120 (see FIG. 1 ) may be modified as needed to generate the desired outward bias, accounting for differences in the size of the positioning disk 110 and / or the thickness of the fins 200.

[0034] FIG. 13 is a partially exploded perspective view of an apparatus 1100 according to another embodiment of the present disclosure. Similar to apparatus 100, apparatus 1100 may be used to fabricate internally finned pressure vessel 300 (see FIGS. 10-12). Apparatus 1100 may be identical to apparatus 100 except as shown and described herein, and may include a plurality of positioning discs 1110, which may be identical to positioning disc 110 except as follows, each of positioning discs 1110 similarly defining a plurality of circumferentially spaced slots 1112 extending radially from its periphery into positioning disc 1110. FIG. 13 illustrates, for example, that each slot 1112 may extend between its two ends 1113 a, 1113 b, with only ends 1113 a, 1113 b of each slot 1112 contacting fins 200. This structure may help provide some flexibility to the resulting "fingers" of the positioning disk 1110 formed between each two adjacent slots 1112, allowing the clearance at the ends 1113 a, 1113 b of each slot 1112 to be small enough to force-fit the fins 200 into the slot 1112. It is also contemplated that widening each slot 1112 between its ends 1113 a, 1113 b may facilitate the free passage of fluid in the longitudinal direction of the apparatus 100 during the brazing process (as the fins 200 are gripped only at the ends 1113 a, 1113 b) and may also reduce the amount of material (and therefore weight) of the positioning disk 1110.

[0035] The device 1100 may further comprise one or more rods 1120, which may be identical to the rods 120 except as described herein, and may similarly comprise a central rod 1122 identical to the central rod 122, and one or more off-axis rods 1124 identical to the off-axis rods 124, which similarly extend through the plurality of positioning discs 1110. The positioning discs 1110 may similarly be secured to the rods 1124 by a plurality of nuts threadably connected to the rods 1124, as described with respect to the device 100, and may similarly each define one or more holes 1114 through which the rods 1120 extend. Advantageously, the one or more rods 1120 of the device 1100 may further comprise grouping rods 1126 that are shorter than the rods 1124 and can be used to connect subsets of the positioning discs 1110 to form groups thereof. 13, two such groups are formed, with three grouping rods 1126 (thicker rods) connecting the upper two locating discs 1110 to form the first group, and three more grouping rods 1126 connecting the lower two locating discs 1110 to form the second group. Spacing between the two groups of locating discs 1110 may be achieved using spacer tubes 1180, with longer rods 1124 spanning both groups extending through their respective spacer tubes 1180. Grouping the locating discs 1110 in this manner may allow for easier removal of the components of the apparatus 1100 from each end after brazing.

[0036] Instead of the slotted biasing disk 130 described above in connection with the device 100 of FIG. 1, the device 1100 may include one or more pairs of retaining rings 1130, as shown in FIG. 13 (only the retaining ring 1130 at the top of the device 1100 is clearly visible). The pair of retaining rings 1130 may include one retaining ring 1130 at the top of the device 1100 and another retaining ring 1130 at the bottom of the device 1100. Similar to the biasing disk 130, the retaining rings 1130 (which may be, for example, tapered cross-section retaining rings) may apply a biasing force to the fins 200 tending to push the fins 200 outward against the inner wall of the pressure vessel 300. To this end, each retaining ring 1130 may have a relaxed diameter greater than the diameter defined by the inner ends 1113b of the slots 1112 (particularly, a relaxed radius greater than the difference between the radius of the pressure vessel 300 and the radial length of the fins 200). In this manner, a tight fit between the fins 200 and the pressure vessel 300 is achieved when the retaining rings 1130 are first compressed to seat in the bore formed by the collective interiors of the fins 200 and then expanded against the fins 200, allowing them to firmly press the fins 200 outward against the inner wall of the pressure vessel 300. The retaining rings 1130 may be made of a material that can withstand brazing temperatures, such as stainless steel. Each individual retaining ring 1130 may have a gap through which it compresses. Depending on the size of the gap between the retaining rings 1130 (particularly whether it is larger than the circumferential pitch of the fins 200), a second pair of retaining rings 1130 may be employed (as seen at the top of the apparatus 1100 in FIG. 13 ), with the gap of one ring 1130 offset from the gap of the other ring 1130 to effectively eliminate the gap and apply force to all of the fins 200.

[0037] Instead of two leveling discs 140 as described above in connection with the apparatus 100 of FIG. 1 , the apparatus 1100 may advantageously use only a single leveling disc 1140 (which may otherwise be identical to either of the leveling discs 140), which may be provided at one end of the central rod 1122. The leveling disc 1140 may form a surface that overlaps with the slot 1112 of the positioning disc 1110 and may prevent longitudinal movement of the fin 200 from exceeding the leveling disc 1140. By orienting the apparatus 1100 with the leveling disc 1140 at the bottom, longitudinal movement of the fin 200 away from the leveling disc 1140 (i.e., upward) may be prevented or at least limited by gravity. The leveling disc 1140 may thus be used to ensure alignment of the fin 200 in the longitudinal direction of the pressure vessel 300 before and during brazing. The leveling disk 1140 can prevent the fins 200 from falling out of the pressure vessel 300 during brazing if the frictional force applied by the retaining ring 1130 is insufficient. Multiple fins 200 can abut against the surface of the leveling disk 1140, which can be secured to the central rod 1122 by a nut 1150. To this end, the leveling disk 1140 can form a central hole 1144 through which the rod 1122 extends, and the end of the central rod 1122 can be threaded as shown in FIG. 13 (or alternatively, the entire central rod 1122 can be threaded). The use of only a single leveling disk 1140 allows the fins 200 to expand freely when heat is applied during the brazing process, thereby preventing excessive warping that can occur when the fins 200 are confined between two leveling disks 140 of the apparatus 100.

[0038] To adjust the longitudinal position of the fin 200 within the pressure vessel 300 prior to brazing, the apparatus 1100 may further include an adjustment assembly 1190 including a fixture 1192 and one or more adjustment screws 1194. The fixture 1192 (which may be, for example, a stainless steel bar) may be connected to the leveling disk 1140 by a central rod 1122 (which is secured by another nut 1150). The adjustment screw 1194 may be positioned to protrude from the fixture 1192 in the longitudinal direction defined by the central rod 1122, and may, for example, extend through the fixture 1192 as shown.

[0039] 14 shows the apparatus 1100 positioned within the pressure vessel 300 with the fins 200 inserted into the slots 1112 of the positioning disk 1110 (and biased outward against the interior wall of the pressure vessel 300 by the retaining ring 1130, as described above). As shown, the fixtures 1192 of the adjustment assembly 1190 may be positioned by a central rod 1122 above the positioning disk 1110 and the fins 200, and may be shaped to extend transversely to the central rod 1122 so as to span the interior of the pressure vessel 300 when the apparatus 1100 is positioned therein (e.g., extending from one side of the pressure vessel 300 to the other, in the case of the bar shown). Adjustment screws 1194 may be positioned to abut the pressure vessel 300 on either side of the apparatus 1100 to allow the height of the fixtures 1192 to be adjusted relative to the pressure vessel 300. In the embodiment shown, for example, fixture 1192 is positioned above pressure vessel 300, and adjustment screw 1194 extends from fixture 1192 to contact the longitudinal edge of pressure vessel 300 at different locations along its periphery. In this manner, adjustment screw 1194 may be turned to adjust the height of fixture 1192 relative to pressure vessel 300. Because fixture 1192 is connected to leveling disk 1140, which holds fins 200 (positioning disk 1110 is held in a fixed position along central rod 1122 by, for example, nut 1123), adjusting the height of fixture 1192 in this manner causes the entire apparatus 1100, and in particular the fins 200 held by leveling disk 1140, to move longitudinally upward or downward relative to pressure vessel 300. (The pressure vessel 300 may be placed on a stand or any surface during this adjustment, as well as during subsequent brazing.) Once the fins 200 are positioned in the desired longitudinal position within the pressure vessel 300, they may be brazed to the interior wall of the pressure vessel 300 to produce an internally finned pressure vessel 300.

[0040] The bar shown represents one relatively simple example of a fixture 1192, which may be positioned to support an adjustment screw 1194 that abuts the pressure vessel 300 at two points (e.g., on both sides). However, other types of fixtures 1192 are also contemplated, such as fixtures 1192 with three or more arms for supporting an adjustment screw 1194 that abuts the pressure vessel 300 at three or more points (e.g., equally spaced points around the periphery) (e.g., star- or spider-shaped fixtures 1192), or disk-shaped fixtures 1192 that support any number of adjustment screws 1194 around their periphery.

[0041] The process for creating an internally finned pressure vessel 300 using apparatus 1100 may be the same as when using apparatus 100, except for the details described above. One exemplary method includes grouping the locating disks 1110 as desired using rods 1124, 1126 and spacers 1180, loading multiple fins 200 into slots 1112 of the locating disk 1110, inserting the aligned locating disk 1110 with multiple fins 200 into the pressure vessel 300, installing a retaining ring 1130 to bias the fins 200 against the interior surface of the pressure vessel 300, inserting a center rod 1122 and attaching a leveling disk 1140 and adjustment assembly 1190 to the alignment disk 1110. 1100 to either end of the pressure vessel 300, aligning the fins 200 relative to the leveling disk 1140, adjusting the longitudinal position of the fins 200 relative to the pressure vessel 300 using an adjustment assembly 1190, attaching the plurality of fins 200 to the pressure vessel 300 by a brazing process, and removing the apparatus 1100 from the pressure vessel 300 after brazing (a new plurality of fins 200 may then be loaded for use in fabricating another internally finned pressure vessel 300 using the same apparatus 1100). Advantageously, the components of the apparatus 1100 may be made from a material, such as stainless steel, that can withstand high brazing temperatures, allowing the entire apparatus 1100 to remain in place during brazing. As a result, a preliminary tack welding step is unnecessary and can be omitted, simplifying and shortening the fabrication process.

[0042] The above description is provided by way of example, not limitation. Given the above disclosure, those skilled in the art will be able to devise variations within the scope and spirit of the invention disclosed herein. Furthermore, the various features of the embodiments disclosed herein can be used alone or in various combinations with each other and are not intended to be limited to the specific combinations described herein. Accordingly, the scope of the claims is not limited by the embodiments shown.

Claims

1. 1. An apparatus for making an internally finned pressure vessel, comprising: a plurality of positioning discs, each of said positioning discs defining a plurality of circumferentially spaced slots extending radially from a periphery of said positioning disc into said positioning disc; one or more rods extending through the plurality of positioning discs, the plurality of positioning discs being held in axial alignment by the one or more rods.

2. The device of claim 1 , wherein the positioning disc is made of stainless steel or a nickel-chromium alloy.

3. 2. The apparatus of claim 1, further comprising a pair of biasing disks, one on either side of the plurality of positioning disks and held in axial alignment with the plurality of positioning disks by the one or more rods, each of the biasing disks defining a plurality of circumferentially spaced slots extending radially from a periphery of the biasing disk into the biasing disk, the slots in the biasing disk terminating farther from an axis defined by the axial alignment of the plurality of positioning disks than the slots in the positioning disk.

4. 4. The device of claim 3, wherein the biasing disc is made of rubber.

5. 2. The apparatus of claim 1, wherein the one or more rods include a central rod on an axis defined by the axial alignment of the positioning discs, and the apparatus further comprises a pair of leveling discs, one on each side of the positioning discs and held in axial alignment with the positioning discs by the central rod, each of the leveling discs forming a surface that overlaps with the slot in the positioning disc.

6. 6. The apparatus of claim 5, wherein the leveling disc is made of stainless steel.

7. The apparatus of claim 5 , wherein the one or more rods further include one or more off-axis rods parallel to the central rod.

8. The apparatus of claim 7 , wherein the positioning disc is secured to the one or more off-axis rods by the central rod being movable relative to the one or more off-axis rods along the axis.

9. The apparatus of claim 8 , wherein the positioning disc is secured to the one or more off-axis rods by a plurality of nuts threadably connected to the one or more off-axis rods.

10. 2. The apparatus of claim 1, further comprising a pair of retaining rings mountable on opposite sides of the plurality of positioning discs, each retaining ring having a relaxed diameter greater than the diameter defined by the inner ends of the slots in the positioning discs.

11. The apparatus of claim 10 , wherein the retaining ring is made of stainless steel.

12. The one or more rods include a central rod that lies on an axis defined by the axial alignment of the plurality of positioning discs, and the apparatus further comprises:

2. The apparatus of claim 1, further comprising a leveling disk on one side of the plurality of positioning disks and held in axial alignment with the plurality of positioning disks by the central rod, the leveling disk forming a surface that overlaps the slot in the positioning disk.

13. 13. The apparatus of claim 12, wherein the leveling disc is made of stainless steel.

14. 13. The apparatus of claim 12, further comprising an adjustment assembly comprising a fixture connected to the leveling disc by the central rod and one or more adjustment screws configured to protrude from the fixture in a longitudinal direction defined by the central rod.

15. 15. The apparatus of claim 14, wherein the fixture is made of stainless steel.

16. 15. The apparatus of claim 14, wherein the fixture comprises a bar extending transversely to the central rod.

17. 2. The apparatus of claim 1, wherein the one or more rods include one or more grouping rods connecting a first subset of the plurality of positioning discs to define a first group of positioning discs, one or more grouping rods connecting a second subset of the plurality of positioning discs to define a second group of positioning discs, and one or more rods connecting the first group of positioning discs to the second group of positioning discs.

18. 18. The apparatus of claim 17, further comprising one or more spacer tubes through which the one or more rods extend connecting the first group of positioning discs to the second group of positioning discs, the one or more spacer tubes being disposed between the first group of positioning discs and the second group of positioning discs.

19. 1. A brazing jig for making an internally finned pressure vessel, comprising: a plurality of axially aligned positioning discs, each of said positioning discs defining a plurality of circumferentially spaced slots extending radially from a periphery of said positioning disc into said positioning disc; a pair of retaining rings installable on opposite sides of the plurality of positioning disks, each retaining ring having a relaxed diameter greater than the diameter defined by the inner ends of the slots in the positioning disks;

20. 1. A brazing jig for making an internally finned pressure vessel, comprising: a plurality of axially aligned positioning discs, each of said positioning discs defining a plurality of circumferentially spaced slots extending radially from a periphery of said positioning disc into said positioning disc; a rod extending through the plurality of positioning discs; a leveling disk located on one side of the plurality of positioning disks and held in axial alignment with the plurality of positioning disks by the rod, the leveling disk forming a surface that overlaps with the slots in the positioning disk.

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