Patent Application
20180185942
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
High performance heat exchangers that achieve very low approach temperatures (for example, effectiveness greater than 99%) and very low pressure drops (for example, less than 5% or 1% calculated as (change in pressure)/(inlet pressure) across the heat exchanger) generally require very small diameter (for example, less than 10 mm) fluid passages with long lengths (for example, 0.5 m or 1 m or greater). Forming a large quantity of fluid passages (for example, greater than 100,000) with the above noted dimensions and then assembling enough of them in parallel to achieve large heat duties, such as might be used on a grid-scale energy generation or storage system, represents a significant manufacturing challenge.
Conventional methods of constructing shell-and-tube heat exchangers with long length, small diameter tubes have significant limitations. To form the tubes, mandrel rod drawing or floating plug drawing is typically used, but there are limitation such as manufacturing throughput, the need for intermediate tube diameters for drawing over the mandrel or plug, and additional secondary operations, such as mandrel reeling (removal). Finally, a dense array of individual tubes must then be coupled to an input plenum and output plenum in a time consuming and sometimes low-reliability assembly process.
Disclosed herein are modular tube apparatuses for shell-and-tube heat exchangers, and molds and methods for forming the apparatuses.
Example mold assemblies may include a bottom mold portion that may include a bottom block that may include a top surface and a plurality of cavities in the bottom block extending downwardly from the top surface to a first depth. Example mold assemblies may further include a top mold portion that may include a top plate positioned opposite and at a first distance from the top surface of the bottom block and a plurality of protrusions extending downwardly from the top plate, wherein each protrusion of the plurality of protrusions forms a seal at the top surface of the bottom block. Example mold assemblies may further include a middle mold portion that may include a wall that forms a seal between the top plate and the bottom block around the periphery of a void space between the top plate and the bottom block.
Example methods may include providing a modular tube apparatus casting, wherein the casting may include a connecting plate and a plurality of cylinders extending downward from the connecting plate. Example methods may further include providing an electrochemical machining assembly, wherein the assembly may include a base and a plurality of wire cathodes, wherein each wire cathode may include a spherical tip, and wherein each wire cathode of the plurality of wire cathodes may be arranged to align with a respective cylinder of the plurality of cylinders. Example methods may further include contacting the spherical tips of the plurality of wire cathodes to the casting and moving the plurality of wire cathodes through the plurality of cylinders to form a plurality of hollow tubes.
Other example methods may include providing a modular tube apparatus casting, wherein the casting may include a connecting plate and a plurality of cylinders extending downward from the connecting plate. Example methods may further include providing an electrochemical machining assembly, wherein the assembly comprises a base and a plurality of wire cathodes, wherein each wire cathode may include a spherical tip, wherein each wire cathode of the plurality of wire cathodes may be arranged to align with a respective cylinder of the plurality of cylinders. Example methods may further include contacting the spherical tips of the plurality of wire cathodes to the casting and moving the plurality of wire cathodes through the plurality of cylinders to form a plurality of hollow tubes.
These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.
Example methods and systems are described herein. It should be understood that the words “example” and “exemplary” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “example,” “exemplary,” or “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. More generally, the embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed methods systems and can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.
Example embodiments herein generally relate to modular tube portions of shell-and-tube heat exchanger apparatuses, and molds and methods for forming the modular tube portions. In a preferred embodiment, a modular tube apparatus for use in a shell-and-tube heat exchanger may include a connecting plate with an arrangement of receiving cups on one side and small diameter long tubes on the other side. The modular apparatus may be configured such that multiple apparatuses may be connected in series with the tubes of one apparatus mating to the receiving cups of the next apparatus in series to form a very long tube assembly with a high-density of small diameter tubes. This beneficially provides a high heat transfer design within a shell-and-tube heat exchanger. Preferably, this type of modular apparatus may be formed as a unitary homogenous body within a casting mold specifically designed to allow the formation of a connecting plate with integral long small diameter cylinders. In a preferred embodiment, solid cylinders may be electrochemically machined to remove material from the center of the tubes to create the long small diameter tubes. The connecting plate may additionally include one or more through holes to, for example, allow a thermal fluid to flow through the apparatus and aid heat transfer with a working fluid flowing through the tubes.
The apparatus 100 is preferably cast as a metal or metal matrix composite with a unitary body in a permanent mold. Preferred metals include, as non-limiting examples, stainless steel alloys Type 304 or Type 316. The unitary body may be a homogenous casting with metal or metal matrix composite removed via electrochemical machining from small-diameter long-length cylinders to form the small-diameter long-length tubes 104.
For purposes of illustrative clarity only, the apparatus 100 is shown with a five-by-five array of tubes 104 for a total of twenty-five tubes 104. Preferably for a heat exchanger requiring a high heat load, such as one is configured for use in a grid scale energy storage system, a modular tube apparatus, such as apparatus 100, may have on the order of approximately 101, 102, 103, 104, 105 or more tubes per apparatus. The use of the five-by-five array is for illustration only and embodiments including up to and beyond 105 tubes per apparatus are within the scope claimed herein.
In the illustrated embodiment, the tubes 104 are preferably formed as substantially cylindrical tubes. Because the apparatus 100 is preferably cast as unitary body in a permanent mold, it may be necessary to include draft on cast parts that must be removed from the permanent mold, and/or on permanent mold portions that must be removed from cast parts. Accordingly, and for purposes herein, the term “substantially cylindrical” should be understood to mean cylindrical with a 0° or greater draft angle along an exterior surface that may be in contact with a mold wall surface. For practical purposes, the tubes 104 may have an approximately 1.5° draft angle on the exterior surface. Likewise for the connecting plate 102. However, depending on the mold constraints, the draft angle may be less than or greater than 1.5° for various parts. The wall thickness of tubes 104 that are cast may be constant or varied along the length of the tube by varying the cathode or cathode path used for electrochemical machining. Additionally, draft angles may be varied along the length of the tubes 104. For illustrative clarity only, and not as a limitation, all draft angles are drawn at 0° in the illustrative Figures.
Preferably, each of the tubes 104 may be approximately 10 mm or less in width or diameter at the distal end with a length of 100 mm, 500 mm, 1000 mm to 2000 mm or longer. Both smaller and larger diameter tubes 104 are considered and both shorter and longer lengths are considered as well. Length to diameter ratio (or length to width ratio if non-cylindrical) may be tuned for desired thermal transfer properties of the heat exchanger, casting shrinkage and deformation, practical draft angles, or other considerations. For illustrative clarity only, the tubes 104 in
While cylindrical tubes, and matching cylindrical receiving cups, are preferred shapes of tubes 104 and receiving cups 106 due to fluid flow characteristics, mating requirements (including susceptibility to twist), and heat transfer properties, other shapes are also considered, so long as the distal end of a tube 104 is configured to mate with a receiving cup 106 to form a fluid seal. Non-limiting examples include square, hexagonal, or octagonal tubes. The fluid seal may preferably be formed through the use of a brazing material at one or more mating surfaces of the tubes 104 and receiving cups 106, but other non-limiting examples may include compression fitting, locking taper with perpendicular compressive force, welding, gasketing, or other configurations.
A fillet or chamfer 104a may be included at the interface of each tube 104 with the bottom surface of the connecting plate 102. The fillet or chamfer 104a may provide strength at that stress-prone area and/or may provide structural material below the receiving cup, as is evident in the cross-sectional view of
While an internal fluid (e.g., a working fluid) may flow through the apparatus 100 in enclosed paths through receiving cups 106, internal connecting fluid paths 112 (illustrated in
To enhance and/or allow flow of the external fluid, a second set of fluid paths 108 may extend completely through the connecting plate 102 from the top surface to the bottom surface. The fluid paths 108 may be arranged as shown or in other regular or irregular patterns. Additional or alternatively shaped fluid paths may be added via a mold or other means to optimize the flow of the thermal fluid through the plate 102 to optimize the heat transfer. This may beneficially provide better flow and/or circulation of the external fluid; and, in an embodiment where a shell is sealed to the external periphery of the connecting plate 102, the fluid paths 108 provide a means of fluid flow between apparatuses, such as apparatus 100, connected in series.
In this illustrated embodiment of modular apparatus 100, where the tubes 104 are illustrated as substantially cylindrical, the width 104d of the distal open end of each tube 104 may also be considered the outer diameter of the tube 104. Similarly, where the receiving cups 106 are also illustrated as substantially cylindrical, the bottom width 106d of the receiving cup 106 may be considered the inside diameter of the bottom of the receiving cup 106. In other non-cylindrical embodiments, the widths 104d and 106d may be considered the widths of respective opposing surfaces. For example, for a tube 104 and respective receiving cup 106, each with a regular polygonal contour, the widths 104d and 106d may be measured as flat-to-flat, vertex-to-vertex, or flat-to-vertex.
The distal open end of each tube 104 has an outer contour that conforms to an internal contour of the respective receiving cup 106. In the illustrated cylindrical embodiment, the outer contour of the distal open end of tube is substantially cylindrical with an outer circumferential surface 116. Similarly, the internal contour of the respective receiving cup 106 is substantially cylindrical with an internal circumferential surface 114. The widths 106d and 104d may be sized such that the internal circumferential surface 114 may form a fluid seal with a mating outer circumferential surface 116. Brazing may be used to form the fluid seal, though other configurations are considered, as described above.
Alternatively or additionally, the fluid seal may occur at another surface along the internal and external contours. For example, the fluid seal may occur at a mating interface between the bottom surface of the tube 104 and the annular bottom surface of the receiving cup 106. Again, brazing may be used to form the seal, though other configurations are considered.
As shown in
In a modular tube apparatus cast with the top mold portion embodiment shown in
In a modular tube apparatus cast with the top mold portion embodiment shown in
In a modular tube apparatus cast with the top mold portion embodiment shown in
Referring now to
In the alternative embodiment shown in
In the alternative embodiment shown in
For purposes of illustrative clarity only, the example mold portions 300, 301, 303 and 400 illustrated in
In the example embodiment depicted in
In one embodiment shown in
Protrusions 308 may also extend downward from top plate 302 all the way through the void space 502 and form a seal with the top surface 402 of the bottom block 406. In the illustrated embodiment, the protrusions 308 may extend to and contact a flat top surface 402 of the bottom block 406 to form through-hole fluid paths in a cast connecting plate, such as fluid paths 108; however, other configurations are also possible to form through-hole fluid paths through the connecting plate. For example, top surface 402 may include slight recesses into which protrusions 308 seat, while still forming a seal with the top surface 402 around the perimeter of the protrusions 308.
In an alternative embodiment, shown in
As previously described, bottom block 406 may include a chamfer 404a at each cavity 404 opening at the top surface of the bottom block. The chamfer 404a partially defines a void space 504 configured to provide strength and/or structural material below the receiving cup 106 in the cast apparatus.
In an alternative embodiment, shown in
Mold assemblies for casting unitary modular tube apparatuses such as mold assembly 500, are preferably permanent molds, though portions or sections may be non-permanent (e.g., sand casting). To the extent that mold assembly 500 includes permanent mold portions, it may be necessary to include draft on areas that must be separated from the casting. For practical purposes, draft angles may be approximately 1.5°. However, depending on the mold constraints of a particular embodiment, the draft angle may be less than or greater than 1.5°. Accordingly, and for purposes herein, the term “substantially cylindrical” should be understood to mean cylindrical with a 0° or greater draft angle. Draft angles may be varied along the length of the cavity 404.
Preferably, each of the cavities 404 may have a width or diameter 404d of approximately 10 mm or smaller in diameter at the bottom with a length 404L of 100 mm, 500 mm, 1000 mm to 2000 mm or longer. Both smaller and larger widths/diameters 404d are considered and both shorter and longer lengths 404L are considered as well. Length to diameter ratio (or length to width ratio if non-cylindrical) may be tuned for desired thermal transfer properties of the heat exchanger, casting shrinkage and deformation, practical draft angles, or other considerations. For illustrative clarity only, the cavities 404 in
Cavities 404, protrusions 306, and partial cores 304, are preferably shaped as substantially cylindrical due to fluid flow characteristics, mating requirements (including susceptibility to twist), and heat transfer properties. However, other shapes are also considered. As long as the distal end of a formed tube may mate with a formed receiving cup to form a fluid seal, other configurations are considered, including the non-limiting examples of square, hexagonal, or octagonal forms.
In the illustrated embodiment of mold assemblies 500, 501, and 503 where the cavities 404 are illustrated as substantially cylindrical, the width 404d of the bottom end of each cavity 404 may also be considered the inner diameter of the cavity 404. Similarly, where the protrusions 306 are also illustrated as substantially cylindrical, the bottom width 306d of the protrusions 306 may be considered the outside diameter of the bottom of the protrusions 306. In other non-cylindrical embodiments, the widths 404d and 306d may be considered the widths of respective opposing surfaces. For example, regular polygonal contours, the widths 404d and 306d may be measured as flat-to-flat, vertex-to-vertex, or flat-to-vertex.
The mold assemblies 500, 501, and 503 are preferably constructed as reusable permanent molds and of materials sufficient to withstand repeated high-temperature casting of materials such as metal or metal matrix composites, including stainless steel alloys Type 304 or Type 316. For example, each mold may be formed as a ceramic mold using laser-based rapid prototyping, a graphite or graphite/metal composite mold, or other rapid prototyping formed mold that may allow the long and thin forms required of the cavities. For metal casting, and particularly stainless steel casting, the mold assembly should be capable of withstanding a casting temperature of approximately 1350° C.
Various casting methods may be used with the mold assemblies 500, 501, and 503. For example, centrifugal, spin, vacuum, low-pressure, liquid metal pumping, and high-pressure casting methods may be employed depending on mold design parameters and desired or acceptable finish and/or porosity.
Risers, gates, vents, sprues/ports and runners may be necessarily and additionally present in any claimed mold assembly, including mold assemblies 500, 501, and 503. Inclusion of some or all of such casting mold structures is considered, though not shown, and such casting mold structures may be included in example mold assemblies 500, 501, and 503 and other embodiments.
A casting and electrochemical machining process may be accomplished by providing a mold assembly according to embodiments herein, coupling together the portions of the mold assembly to form a mold chamber, infiltrating the mold chamber with a molten material, decoupling some or all the mold portions in a manner sufficient to remove the cast modular tube apparatus, and electrochemically machining the cast modular tube apparatus to form a plurality of tubes comprising distal open ends and hollow portions.
Electrochemical machining is a method of removing metal by advancing a charged electrode (e.g., cathode) into a conductive workpiece (e.g., anode) in the presence of a conductive fluid (electrolyte). In various embodiments described herein, a cathode assembly comprising a plurality of wire cathodes may be used to simultaneously create multiple tubes in modular tube apparatus by forming hollow portions in multiple solid or partially hollow cylinders. A current may be passed through the cathode assembly and the electrolyte to the plurality of cylinders in order to remove cast material from the plurality of cylinders to form a plurality of tubes.
As a specific example method to cast and electrochemically machine an embodiment of the modular tube apparatus 100 described herein, the following steps may be accomplished.
A bottom mold portion may be provided. The bottom mold portion may include a bottom block with a top surface. A plurality of cavities in the bottom block may extend downward from the top surface into the interior of the bottom block.
A top mold portion may be provided. The top mold portion may include a top plate positioned opposite and at a first distance from the top surface of the bottom block. In one embodiment, a first plurality of protrusions may extend downward from the top plate. Each protrusion of the plurality may form a seal at the top surface of the bottom block. In another embodiment, the plurality of protrusions may be absent.
In one embodiment, a second plurality of protrusions may extend downward from the top plate to a length less than the first distance. Each protrusion of the second plurality may be disposed opposite a respective cavity of the plurality of cavities. Each protrusion of the first plurality may define an outer contour that conforms to an internal contour at a base of the respective cavity.
In another embodiment, a plurality of partial cores may extend downward from each protrusion of the second plurality of protrusions or from the top plate if the second plurality of protrusions is not present. Each core may be disposed within the respective cavity and form a respective void space in each cavity.
A middle mold portion may be provided. The middle mold portion may include a wall that forms a seal between the top plate and the bottom block around the periphery of a void space between the top plate and the bottom block.
The top mold portion, middle mold portion, and bottom mold portion may be coupled together to form a mold chamber. As non-limiting examples, the portions may be bolted or clamped together with internal and/or external bolts or clamps.
The mold chamber may take the negative form of a modular tube apparatus with solid or partially hollow cylinders in place of the tubes and with or without additional risers, gates, ports, or structural supports, and the negative form be configured to account for shrinkage or growth in the casting material. The mold chamber may be infiltrated with a molten material. Preferably materials include Type 304 or 316 stainless steel.
Following a dwell period after infiltration, one more mold portions mays be decoupled and removed. In the embodiment illustrated as mold assembly 500, the top portion 300 with may be decoupled and removed. The cast modular tube apparatus with the connecting plate and a plurality of cylinders may be retained in the bottom mold portion for subsequent electrochemical machining, or it may be removed and placed in a fixture for subsequent electrochemical machining.
As shown in
A plurality of the wire cathodes 602 may be configured to pass through the plurality of cylinders 604 simultaneously such that material is removed from each of the plurality of cylinders 604 at the same time. Each of the plurality of wire cathodes 602 may comprise a rod portion with a spherical tip 606 at the distal ends. The diameter of the spherical ends 606 may be larger than the diameter to of the wire cathode's rod portion. The diameter of the spherical tips 606 may be approximately the same as the desired internal diameter of the tubes 604, such as the hollow portion 110 of the respective tube 104 in
The method may further comprise electrochemically machining a plurality of receiving cups, such as receiving cups 106. The inner diameters of the receiving cups may be approximately the same size as the outer diameter of each of the plurality of tubes. To create the receiving cups, cathode assembly 600 may be moved in, for example, three axes during the electrochemical machining process so that the spherical tips 606 create the receiving cup.
The method may be used to form a plurality of modular tube apparatuses. The plurality of modular tube apparatuses may be joined by methods known in the art, such as brazing, soldering, or welding.
During the electrochemical machining process, the metal anode is consumed and metal is put into the electrolyte. The metal put into the electrolyte may be recovered for future use. Such recovery methods may include electrochemical methods (e.g., plating the metal onto another electrode) or filtration methods.
The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary embodiment may include elements that are not illustrated in the Figures. Additionally, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein.
