WO2022208272A1

WO2022208272A1 - A heat exchanger and a method to fabricate

Info

Publication number: WO2022208272A1
Application number: PCT/IB2022/052787
Authority: WO
Inventors: Peter Hofbauer; Akshay Jadhav; Adrian Tusinean; David Yates
Original assignee: Thermolift, Inc.
Priority date: 2021-03-28
Filing date: 2022-03-27
Publication date: 2022-10-06

Abstract

A heat exchanger and a method to fabricate a heat exchanger are disclosed. A brazing compound is applied to a surface of a host piece, such a host cylinder. A flat, rectangular piece of metallic material is corrugated and crushed to form pluralities of crests and troughs. The troughs are flattened before abutting with the brazing compound on the host cylinder. The crushed folded fin is brazed to the host cylinder. In some embodiments, a folded fin is brazed to both the inside and outside cylindrical surfaces of the host cylinder. The resulting heat exchanger has high effectiveness and is low cost.

Description

A Heat Exchanger and a Method to Fabricate

Field

[0001] The present disclosure relates to a two-fluid heat exchanger and a method to fabricate such heat exchanger.

Background

[0002] Heat exchangers are well-known in the field. Heat exchangers that are highly effective, that conform to a volume available in a device in which the heat exchanger is installed, utilize inexpensive, standard materials, and are simple to manufacture are desirable.

Summary

[0003] T o provide a heat exchanger that improves on the prior art, a method to fabricate a heat exchanger is disclosed that includes: applying a brazing compound on a surface of a host piece; obtaining a flat, rectangular piece of metallic material; corrugating the rectangular piece to form a corrugated piece, the corrugated piece having pluralities of crests and troughs; crushing the corrugated piece to cause adjacent walls of the corrugated piece to touch; abutting troughs of the crushed, corrugated piece with the surface of the host piece having brazing compound thereon; and brazing the host piece and the crushed, corrugated piece. The method further includes installing at least one of a clamp and a fixture onto the abutted crushed-corrugated piece to the host piece to squeeze the two together. In some embodiments, the troughs of the crushed-corrugated piece are flattened prior to abutting the trough with the host piece.

[0004] In some embodiments, the host piece is a host cylinder. The surface onto which brazing compound is applied is an inside surface of the host cylinder. The method further includes: inserting a fixture within the host cylinder that presses against crests of the crushed, corrugated piece. In other embodiments, the surface onto which brazing compound is applied is an outside surface of the host cylinder. The method includes: installing at least two clamps around the crushed, corrugated piece; and tightening the clamps to press troughs of the crushed, corrugated piece into the outside surface of the cylinder.

[0005] In some embodiments, a folded fin is placed on the inside and the outside surfaces of a host cylinder, including: inserting a fixture within the host cylinder, the fixture pressing against crests of the first crushed, corrugated piece to thereby press troughs of the first crushed, corrugated piece into the inside surface of the host cylinder. Also, at least two clamps or straps are installed around the second crushed, corrugated piece. The clamps or straps are tightened to press troughs of the second crushed, corrugated piece into the outside surface of the cylinder.

[0006] In some embodiments, the host piece is flat. The surface of the host piece is a first surface of the host piece and the crushed corrugated piece is a first crushed corrugated piece. The method includes applying the brazing compound on a second surface of a host piece, obtaining a second flat, rectangular piece of metallic material, corrugating the second rectangular piece to form a second corrugated piece, the second corrugated piece having pluralities of crests and troughs, crushing the second corrugated piece to cause adjacent walls of the second corrugated piece to touch, abutting troughs of the second crushed, corrugated piece with the second surface of the host piece having brazing compound thereon, and brazing the host piece and the two crushed, corrugated pieces.

[0007] Also disclosed is a method to fabricate a thermodynamic apparatus that includes: obtaining first and second flat rectangular pieces of metallic material; corrugating the rectangular pieces to form first and second corrugated pieces, the corrugated pieces having pluralities of crests and troughs; crushing the first corrugated pieces so that adjacent walls of the first corrugated piece abut; crushing the second corrugated pieces so that adjacent walls of the second corrugated piece abut; machining a host cylinder of the thermodynamic apparatus; applying brazing compound onto inner and outer cylindrical surfaces of the host cylinder; placing the first crushed, corrugated piece into the host cylinder with troughs of the first crushed, corrugated piece abutted against the inside cylindrical surface of the host cylinder; wrapping the second crushed, corrugated piece around the outside cylindrical surface of the host cylinder with troughs of the second crushed, corrugated piece abutted against the outside cylindrical surface of the host cylinder; and brazing the first and second crushed, corrugated pieces and the host cylinder. The method further includes flattening the troughs of the two crushed, corrugated pieces. [0008] The method further includes: installing at least two straps around the crushed, corrugated piece and tightening the straps to press troughs of the second crushed, corrugated piece into the outside surface of the cylinder. The method further includes: inserting a fixture within the host cylinder, the fixture pressing against crests of the first crushed, corrugated piece.

[0009] In some embodiments, the crests of the first crushed, corrugated piece are flattened. In some of embodiments, a displacer is inserted within the first crushed, corrugated piece.

[0010] In some embodiments, an insulating ring is placed around the crests of the second crushed, corrugated piece.

[0011] In some embodiments, the host cylinder, first and second crushed- corrugated pieces, and the insulating ring are mounting into a housing. The housing has a liquid inlet and a liquid outlet that communicates fluidly with the second crushed, corrugated piece.

[0012] Also disclosed is a heat exchanger that has: a host piece having a brazing compound applied to two surfaces, a first folded fin comprised of a first flat, rectangular piece of metallic material that is corrugated and then crushed to have pluralities of crests and troughs, and a second folded fin comprised of a second flat, rectangular piece of metallic material that is corrugated and then crushed to have pluralities of crests and troughs. The troughs of the first folded fin are abutted to a first of the two surfaces of the host piece. The troughs of the second folded fin are abutted to a second of the two surfaces of the host piece. The first and second folded fins and the host piece are brazed together. [0013] The host piece is a host cylinder with the first of the two surfaces being an inside cylindrical surface of the host cylinder and the second of the two surfaces being an outside cylindrical surface of the host cylinder; and troughs of the first and second folded fins are flattened. In some embodiments, the heat exchanger includes: an insulating ring disposed outside of the second folded fin. [0014] The corrugated metallic piece is interchangeably called a folded fin or folded fins within this disclosure. Also, a folded fin applied to an outside surface of a host cylinder is held in place by clamps or straps, the terms being nearly interchangeable.

Brief Description of Drawings

[0015] Figures 1 and 2 are flowcharts showing processes involved in fabricating a heat exchanger according to embodiments of the present disclosure;

[0016] Figures 3-6 show a folded fin at several stages of fabrication;

[0017] Figure 7 shows two folded fins held into place on a host cylinder by a fixture and straps;

[0018] Figure 8 is a portion of a host cylinder, in cross section, with a folded fin on an inside surface;

[0019] Figure 9 shows a cross-section of a portion folded fin embodiment with a host cylinder;

[0020] Figure 10 is a folded fin embodiment with a flat-plate host; and [0021] Figure 11 shows a portion of a thermodynamic device having a heat exchanger having folded fins on a host cylinder.

Detailed Description

[0022] As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures maybe combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure maybe desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations, whether or not explicitly described or illustrated.

[0023] A process by which a heat exchanger is manufactured is described first in a flowchart in Figure 1, followed by sketches below. In block 410 in Figure 1, a host cylinder is cast or machined and the host cylinder has a brazing compound smeared on its inside surface. In block 400, a sheet is cut out of a thermally-conductive material, with aluminum as one non-limiting example. In block 402, the sheet is corrugated to form crests and troughs, i.e., a folded fin. In block 404, the folded fin structure is crushed to cause adjacent walls near the troughs abut each other. In some embodiments, the folded fin structure is further crushed so that adjacent walls near to the crests also abut. In block 406, the troughs are flattened. In block 408, the folded fin is formed into a cylinder. In block 412, the folded fins are placed within the host cylinder with the flattened troughs against the inside surface of the host cylinder. In block 414, a fixture is placed within the folded fins to press the troughs of the folded fins against the wall of the host cylinder. In block 416, the folded fins are brazed together with the host cylinder. In block 418, the fixture is removed after the assembly has sufficiently cooled. The assembly is heat treated in block 420 followed by final machining operations in block 422.

[0024] In some embodiments, such as one that will be discussed in more detail below, it is desirable that the inside surface of the folded fin be nearly cylindrical. In such embodiments, an additional process is included. In block 424 in Figure 1, the crests are flattened by a rolling process or any suitable process.

[0025] A folded fin heat exchanger can be made on the outside surface of a host cylinder via the processes shown in Figure 2. In block 438, a host cylinder is cast or machined and the host cylinder has a brazing compound smeared on its outside surface. In block 430, a sheet is cut out of a thermally-conductive material. In block 432, the sheet is corrugated to form crests and troughs, i.e., a folded fin. In block 434, the folded fin structure is crushed to cause adjacent walls near the troughs abut each other. In block 436, the troughs are flattened. The folded fin is wrapped around the outside surface of the host cylinder with the troughs against the cylinder in block 440. To maintain a contact between the troughs and the cylinder surface, clamps are placed around the crests in block 442. In block 444, the assembly is brazed. The clamps are removed in block 448 after the assembly has sufficiently cooled. The assembly is heat treated in block 450. Final machining operations are performed in block 452.

[0026] The flow charts in Figures 1 and 2 are not meant to specify a particular order.

The blocks in Figures 1 and 2 could be arranged in other suitable embodiments. Furthermore, parts of the operations in any given block could be performed before or after other operations.

[0027] In yet another embodiment, brazing compound is smeared on both sides of the host cylinder and folded fins are put on the inside surface and the outside surface with a fixture and clamps, respectively to hold the troughs of the folded fins against the cylinder. Processes in Figures 1 and 2 are appropriately used to create a double heat exchanger on the inner and outer surface of the host cylinder.

[0028] The manufacture of some embodiments is shown in the following figures.

Starting in Figure 3, a rectangular piece 160 of a flat material is shown. To serve as a fin, it is a material with high thermal conductivity. Because of the desire to put severe bends into the material, it is also a material that is sufficiently ductile to bend without cracking. The material is then corrugated, as shown in Figure 4, to form a folded fin 160. Folded fin 160 has crests 162 and troughs 164. As shown by arrows on either side of folded fin 160, folded fin 160 is pressed together to form a new version of a folded fin 160 in which walls near crests 162 abut at 166 and walls near troughs 168 abut at 168, as shown in Figure 5. As described in Figures 1 and 2, troughs flattened, the result of which is shown in Figure 6. [0029] A host cylinder is readied for attachment of one or more folded fins, machined in any suitable manner with brazing compound applied to the surface(s) of the cylinder to which the folded fins are to be brazed. An example of a host cylinder 180 is shown in Figure 7. Host cylinder 180 has flanges 182 and 184. A folded fin 190 has been formed into a cylinder and placed within the inner surface of cylinder 180 with the flattened troughs of folded fin 190 placed against the surface. A second folded fin 102 is wrapped around the outside surface of cylinder 180, again with the flattened troughs abutting the surface of cylinder 180. Flattening of the troughs allows more surface area in contact with the cylinder which aids in both creating a stronger braze connection and providing more surface area for heat transfer so that the resulting assembly has high heat transfer effectiveness. Folded fin 190 is pressed against the wall of cylinder 180 by a fixture 200. Fixture 200 has a series of vertical fingers 202 that spring outwardly to press on folded fin 190. Two clamps 206 are shown in Figure 7 that draw folded fin 192 into the outer surface of cylinder 180. As many clamps as desired may be placed around the folded fins to provide the desired clamping load. In addition to the normal function that flanges 182 and 184 provide, that also delimit folded fin 192 in place in a desired vertical position. [0030] A portion of a heat exchanger 220 according to embodiments of the present disclosure is shown in Figure 8. A folded fin 224 is brazed onto a cylinder 222. Folded fin 224 presents a plurality of passages 226 through which fluid can flow. Troughs of folded fin 224 are flattened, yet leave a small triangular opening 228 between cylinder 222 and folded fin 224. Fluid can flow through the triangular openings 228, which form long thin passages, in addition to passages 226.

[0031] A portion of a heat exchanger 8 is shown in cross section in Figure 9. A host cylinder 12 is disposed within a housing 10. Host cylinder 12, with centerline 6, has flanges 13 on each end. A folded fin 14 is brazed onto an inside surface of host cylinder 12 and a folded fin 16 is brazed onto an outside surface of host cylinder 12. An insulating ring 20 is placed between housing 10 and folded fin 16. Insulating ring 20 has grooves with 0-rings 22 in the back side of insulating ring 20. A liquid is provided through housing 10 at a fitting 30 through folded fin 16. The liquid exits through housing 10 at a fitting 32. In the embodiment in Figure 9, a gas flows through the passages in folded fin 14. The heat exchanger exchanges energy between the gas through passages folded fin 14 and the liquid that passes through folded fin 16.

[0032] In Figure 10, a flat version of a folded-fin heat exchanger 240 is shown. A host plate 252 has two folded fins (252 and 260) brazed onto upper and lower surfaces of host plate 250. The embodiment in Figure 10, shows cross flow where flowthrough passages 254 of folded fin 252 travels into the page. Flowthrough passages of folded fin 260 are shown as an inlet flow by an arrow 262 at the left-hand side of folded fin 260 and an outlet flow by an arrow 264 at the right-hand side of folded fin 260. A parallel flow arrangement is another alternative. Only the guts of heat exchanger 240 of shown in Figure 10. It would be provided within a housing that has provisions for conducting a first fluid (liquid or gas) through folded fin 252 and a second fluid (liquid or gas) through folded fin 260.

[0033] A portion of a thermodynamic apparatus 300 is shown in Figure 11, which is the cold end of a thermal-compression heat pump. A cold displacer 302 reciprocates within a cylinder 304. Displacer 302 is coupled to a mechatronics driver (not shown) via a rod 306. Displacer 302 is shown in an upper position in which there is volume in a cold chamber 310. When displacer 302 is reciprocated downward, there is almost no volume within cold chamber 310. Cold chamber is defined by a dome 312, an end cap of cold displacer 302, and cylinder 304. A host cylinder 320 has flanges 322 and 324. Dome 312 and host cylinder 320 are contained within housing portions 314 and 316. Host cylinder 320 has a folded fin 340 that is coupled to the outside cylindrical surface of host cylinder 320 and a folded fin 330 that is coupled to the inside cylindrical surface of host cylinder 320. Folded fin 340 is arranged vertically between flanges 322 and 324. In the case of thermodynamic apparatus 300, a gas is contained within cold chamber 310 and within passageways in folded fin 330. When displacer 302 is moved downward, the gas in cold chamber 310 is pushed into the passageways in fold fin 330 and toward another chamber (not shown) in the thermodynamic apparatus. When, displacer 302 is moved upward, gas in the passages within folded fin 330 is pulled into cold chamber 310. Two non-limiting examples of gases within cold chamber 310 are hydrogen and helium. The other fluid with which the gas exchanges heat is a liquid in the example in Figure 11. A water inlet 342 through housing 316 is provided to one end of folded fin 340. A water outlet 344 pierces housing 316 and is fluidly coupled to the other end of folded fin 340. An insulating ring 350 is provided between housing 316 and folded fin 340.

[0034] While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.

Claims

We claim:

1.A method to fabricate a heat exchanger, comprising: applying a brazing compound on a surface of a host piece; obtaining a flat, rectangular piece of metallic material; corrugating the rectangular piece to form a corrugated piece, the corrugated piece having pluralities of crests and troughs; crushing the corrugated piece to cause adjacent walls of the corrugated piece to touch; abutting troughs of the crushed, corrugated piece with the surface of the host piece having brazing compound thereon; and brazing the host piece and the crushed, corrugated piece.

2. The method of claim 1, further comprising: installing at least one of a clamp and a fixture onto the abutted crushed-corrugated piece to the host piece to squeeze the two together.

3. The method of claim 1, further comprising: flattening the troughs of the crushed- corrugated piece prior to abutting the trough with the host piece.

4. The method of claim 1 wherein: the host piece is a host cylinder; and the surface onto which brazing compound is applied is an inside surface of the host cylinder, the method further comprising: inserting a fixture within the host cylinder that presses against crests of the crushed, corrugated piece.

5. The method of claim 1 wherein: the host piece is a host cylinder; and the surface onto which brazing compound is applied is an outside surface of the host cylinder, the method further comprising: installing at least two clamps around the crushed, corrugated piece; and tightening the clamps to press troughs of the crushed, corrugated piece into the outside surface of the cylinder.

6. The method of claim 4, further comprising: flattening crests of the crushed-corrugated piece.

7. The method of claim 1 wherein: the host piece is a host cylinder; the crushed, corrugated piece is a first crushed, corrugated piece; and the surface onto which brazing compound is applied is an inside surface of the host cylinder, the method further comprising: applying the brazing compound on an outer, cylindrical surface of the host cylinder; obtaining a second flat, rectangular piece of metallic material; corrugating the second rectangular piece to form a second corrugated piece, the second corrugated piece having pluralities of crests and troughs; crushing the second corrugated piece to cause adjacent walls of the second corrugated piece to touch; abutting troughs of the second crushed, corrugated piece with the outer cylindrical surface of the host cylinder having brazing compound thereon; and brazing the hot piece and crushed, corrugated piece.

8. The method of claim 7, further comprising: inserting a fixture within the host cylinder, the fixture pressing against crests of the first crushed, corrugated piece to thereby press troughs of the first crushed, corrugated piece into the inside surface of the host cylinder; installing at least two clamps around the second crushed, corrugated piece; and tightening the clamps to press troughs of the second crushed, corrugated piece into the outside surface of the cylinder.

9. The method of claim 1, wherein: the host piece is flat; -li the surface of the host piece is a first surface of the host piece; and the crushed corrugated piece is a first crushed corrugated piece, the method further comprising: applying the brazing compound on a second surface of a host piece; obtaining a second flat, rectangular piece of metallic material; corrugating the second rectangular piece to form a second corrugated piece, the second corrugated piece having pluralities of crests and troughs; crushing the second corrugated piece to cause adjacent walls of the second corrugated piece to touch; abutting troughs of the second crushed, corrugated piece with the second surface of the host piece having brazing compound thereon; and brazing the host piece and the two crushed, corrugated pieces.

10. A method to fabricate a thermodynamic apparatus, comprising: obtaining first and second flat rectangular pieces of metallic material; corrugating the rectangular pieces to form first and second corrugated pieces, the corrugated pieces having pluralities of crests and troughs; crushing the first corrugated pieces so that adjacent walls of the first corrugated piece abut; crushing the second corrugated pieces so that adjacent walls of the second corrugated piece abut; machining a host cylinder of the thermodynamic apparatus; applying brazing compound onto inner and outer cylindrical surfaces of the host cylinder; placing the first crushed, corrugated piece into the host cylinder with troughs of the first crushed, corrugated piece abutted against the inside cylindrical surface of the host cylinder; wrapping the second crushed, corrugated piece around the outside cylindrical surface of the host cylinder with troughs of the second crushed, corrugated piece abutted against the outside cylindrical surface of the host cylinder; and brazing the first and second crushed, corrugated pieces and the host cylinder.

11. The method of claim 10, further comprising: flattening the troughs of the two crushed, corrugated pieces.

12. The method of claim 10, further comprising: installing at least two straps around the crushed, corrugated piece; and tightening the straps to press troughs of the second crushed, corrugated piece into the outside surface of the cylinder.

13. The method of claim 10, further comprising: inserting a fixture within the host cylinder, the fixture pressing against crests of the first crushed, corrugated piece.

14. The method of claim 13, further comprising: flattening crests of the first crushed, corrugated piece.

15. The method of claim 14, further comprising: inserting a displacer within the first crushed, corrugated piece.

16. The method of claim 10, further comprising: placing an insulating ring around the crests of the second crushed, corrugated piece.

17. The method of claim 16, further comprising: mounting the host cylinder, first and second crushed-corrugated pieces, and the insulating ring into a housing, the housing having a liquid inlet and a liquid outlet.

18. A heat exchanger, comprising: a host piece having a brazing compound applied to two surfaces; a first folded fin comprised of a first flat, rectangular piece of metallic material that is corrugated and then crushed to have pluralities of crests and troughs; a second folded fin comprised of a second flat, rectangular piece of metallic material that is corrugated and then crushed to have pluralities of crests and troughs, wherein: the troughs of the first folded fin are abutted to a first of the two surfaces of the host piece; the troughs of the second folded fin are abutted to a second of the two surfaces of the host piece; and the first and second folded fins and the host piece are brazed together.

19. The heat exchanger of claim 18, wherein: the host piece is a host cylinder with the first of the two surfaces being an inside cylindrical surface of the host cylinder and the second of the two surfaces being an outside cylindrical surface of the host cylinder; and troughs of the first and second folded fins are flattened.

20. The heat exchanger of claim 19, further comprising: an insulating ring disposed outside of the second folded fin.