Indirect heat exchanger pressure vessel with controlled corrugated benders

Abstract

In one aspect of the disclosure, an indirect heat exchanger pressure vessel is provided that includes an inlet header for receiving a pressurized working fluid (e.g., water, ethylene glycol, ammonia, and / or carbon dioxide). The indirect heat exchanger pressure vessel includes an outlet header for collecting the pressurized working fluid, and a serpentine circuit tube connecting the inlet header and the outlet header. The serpentine circuit tube allows the pressurized working fluid to flow from the inlet header to the outlet header. The serpentine circuit tube includes a tube and a return bend connecting the tube. The return bend has a controlled corrugation portion that includes alternating ridges and grooves. The alternating ridges and grooves strengthen the return bend and allow the indirect heat exchanger pressure vessel to facilitate heat transfer of the working fluid at high internal working pressures.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 138,655, filed January 18, 2021, and U.S. Provisional Patent Application No. 63 / 270,953, filed October 22, 2021, both of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to indirect heat exchangers, and more specifically, to indirect heat exchangers having a serpentine loop having a plurality of shaped bends that convey pressurized working fluid through the serpentine loop and allow heat transfer between the working fluid inside the serpentine loop and a fluid outside the serpentine loop. The working fluid and the external fluid can be gas, liquid, or a mixture of gas and liquid, respectively. Background Technology

[0004] Heat exchangers are known to include direct heat exchangers and indirect heat exchangers. A direct heat exchanger transfers heat between a working fluid and another fluid through contact between the fluids themselves. An indirect heat exchanger transfers heat indirectly between a working fluid and another fluid through a separating medium.

[0005] Various types of heat exchange devices are known, including direct heat exchangers, indirect heat exchangers, or devices combining both. Known heat exchange devices include open-circuit heat exchange devices (such as open-circuit cooling towers) and closed-circuit heat exchange devices (such as closed-circuit cooling towers). An open-circuit cooling tower exchanges heat between a working fluid (such as water) and an external fluid (such as ambient air) by distributing the working fluid onto a fill. As the working fluid travels along the fill, it is directly cooled by the ambient air. In contrast, a closed-circuit cooling tower separates the working fluid from the external fluid.

[0006] Closed-loop heat exchanger equipment includes closed-loop cooling towers for fluids, evaporative condensers for refrigerants, dry coolers, air-cooled condensers, and ice storage systems. These heat exchange devices utilize one or more heat exchangers to transfer heat between a pressurized working fluid and an external fluid (such as ambient air, evaporative liquid, or a combination thereof).

[0007] For example, a heat exchanger device may include a closed-loop cooling tower with an indirect heat exchanger pressure vessel, the pressure vessel including an inlet manifold for receiving pressurized working fluid, an outlet manifold, and an indirect heat exchange coil connecting the inlet and outlet manifolds. The indirect heat exchange coil may include one or more serpentine loops configured to transfer heat between the pressurized working fluid inside the indirect heat exchange coil and a fluid (e.g., an evaporating liquid) outside the indirect heat exchange coil. The inlet manifold receives the internal working fluid from the upstream component of the heat exchanger before the working fluid is directed to the downstream component of the heat exchanger, while the outlet manifold collects the pressurized working fluid.

[0008] Indirect heat exchanger pressure vessels, including inlet and outlet manifolds and one or more serpentine loops, need to withstand high pressures suitable for specific applications and meet national and international engineering standards such as ASME Standard B31.5. For example, the indirect heat exchanger pressure vessel of a closed-loop cooling tower is rated to withstand internal pressures of 150 psig for fluids such as water, ethylene glycol, and brine. As another example, the indirect heat exchanger pressure vessel of an evaporative condenser may be able to withstand internal pressures of up to 410 psig or higher for typical refrigerants such as ammonia or R-407C. As yet another example, some evaporative condensers have indirect heat exchanger pressure vessels with internal pressure ratings of 1200 psig or higher for refrigerants such as carbon dioxide.

[0009] The serpentine loop of an indirect heat exchanger pressure vessel typically comprises straight sections and bends connecting the straight sections. The straight sections of the serpentine loop are usually connected by bends of approximately 180 degrees or by compound bends with multiple bends (e.g., two 90-degree bends connected by tube lengths). During the assembly of the heat exchange equipment, the serpentine loops can be stacked together, with the loops typically contacting each other in the area of ​​the bends, and the loops having a vertically staggered positioning.

[0010] Manufacturing serpentine tubes typically begins by forming elongated tubes from long, flat strips of metal (such as low-carbon steel or stainless steel). The flat metal strips are rolled into a roughly circular cross-section, and the longitudinal edges are welded together by continuous longitudinal welds to form a straight tube. Alternatively, a seamless tube forming process is used to form the straight tube. The resulting straight tube can then be bent at intervals along the tube to create a serpentine shape, where the straight tube routes are connected by bends. Tube bending is a complex process and is typically performed using hydraulically, electrically, or manually driven tube bending machines equipped with bending dies, clamping dies, pressing dies, and optionally, mandrels and wiper dies. Tube bending machines can be configured to form bends with any desired angle, reaching and including 180-degree bends (e.g., 80, 90, 100, or 180 degrees). As described above, the slewing bend of the serpentine loop pipe may include a compound bend, each compound bend having two or more bends, such as an 80-degree bend and a 100-degree bend connected by a straight pipe section.

[0011] To form a bend in the pipe, the pipe is fed into a pipe bender, and a portion of the pipe is positioned in the groove of the bending die. A clamping die and a holding die, each with a groove for the pipe, move against opposite sides of the pipe, such that the clamping die is positioned to support the pipe and the holding die clamps the portion of the pipe between the holding die and the bending die. The pipe bender then rotates or pivots the bending die and the holding die at the desired bending angle. As the bending die and the holding die pivot, the clamping die moves forward to support the pipe and ensure that the pipe follows the contour of the bending die. Once the bend is formed in the pipe, the clamping die and the clamping die retract from their clamping positions, the pipe is fed forward until the next bend position is positioned in the pipe bender, and then the bending die, the holding die, and the clamping die all return to their initial positions. This bending process is repeated for each bend to be formed in the serpentine loop pipe. Some pipes are bent only once to form a single bend, often referred to as hairpin pipes or crutch pipes, which can then be butt-welded together.

[0012] Bending pipes used to receive pressurized working fluids is a process that balances a variety of considerations, including performance, safety, and packaging standards for the specific application. Furthermore, during the bending process, unintended deformation within the pipe wall can lead to pipe failure due to the pressure of the working fluid inside, pipe corrosion, and / or the high pressure drop of the working fluid flowing through the pipe. In some pipe bending processes, an internal mandrel is pushed into the interior of the pipe to support the pipe wall during bending, and a release pliers die can be used to harden the pipe wall at the inner end of the bend to prevent unintended deformation within the pipe. The internal mandrel can be a sizing mandrel or can have one or more balls or rings; in this case, the internal mandrel is referred to as a spherical mandrel.

[0013] Pipe bending generally involves the following parameters:

[0014] OD = outer diameter of the pipe

[0015] WT = Pipe wall thickness

[0016] CLR = Centerline radius of the bend

[0017] The dimensions are measured using common measurement scales, such as inches or millimeters. These parameters are used to calculate the following two characteristic ratios:

[0018]

[0019]

[0020] The other two parameters in the bending process are the outer radius (OSR) of the bend, which is usually referred to as the outer arc surface (extrados), and the inner radius (ISR) of the bend, which is usually referred to as the inner arc surface (intrados).

[0021] The W and D ratios are further combined into a single coefficient, which indicates the complexity of the bend. This coefficient is calculated as follows:

[0022]

[0023] W, D and / or C B These values ​​can be used to determine whether a bend can be formed without an internal mandrel, known as empty bending, or whether an internal mandrel is necessary, in which case the process is called mandrel bending. For mandrel bending, these ratios help determine whether the required internal mandrel should be a multi-ball mandrel, a single-ball mandrel, or a simpler sizing mandrel. Finally, these ratios help determine whether a release clamp mold is needed in conjunction with the internal mandrel. For example, recommended processes for various bending complexities are shown in the table below:

[0024]

[0025] Table 1: Bending Complexity Values ​​and Recommended Bending Processes

[0026] Typically, you can find the W, D, and / or C on the industry standard pipe bending diagram. B The ratio is used to determine the required pipe bending process. For example, to determine the process parameters for a pipe with a bending outer diameter of 1”, a wall thickness of 0.05”, and a centerline radius of 2”, the ratio of W to D is:

[0027]

[0028]

[0029] Considering the W ratio of 20 and the D ratio of 2, industry standard pipe bending diagrams may recommend using a standard pitch internal mandrel with one ball, supplemented by a demolding clamp mold.

[0030] Alternatively, for the C of the bend in the example above B yes:

[0031]

[0032] Referring to the table above, this C B The value also indicates that the use of an internal mandrel is recommended, although a release clamp mold may be optional. The slight differences in the recommendations regarding mandrels and release clamps demonstrate the flexibility in bending configurations, where tool design and tube material selection can sometimes compensate for the lack of an internal mandrel and / or release clamp mold.

[0033] The above discussion covers the common bending diagrams and bending complexity values ​​(C) used in industry. B The range is based on the assumption that the profile of the tool groove (where the tube resides during the bending process) formed by the bending and clamping die is circular, complementary to the shape of the circular tube. However, recent advancements in bending tool design have allowed for the creation of bending tools with compound radii within the tool groove to compress and support the tube during the bending process, thus expanding the range of mandrel-less bending. B The values ​​range from approximately 5 to approximately 12.

[0034] In addition, especially when C B As the tube diameter approaches or exceeds 20, the use of internal mandrels and release pliers becomes increasingly necessary for successful tube bending. Internal mandrel bending processes have several drawbacks, including the need for additional tools, which increases costs; potential for increased scrap if the mandrel is used incorrectly; potential for increased cycle time; and the need for lubricants, which increases lubrication time and costs, as well as subsequent environmental remediation efforts.

[0035] When C B One issue with approaching and exceeding 20 is that the associated mandrel bends impose limitations on the continuous length of the tubing. Serpentine loop tubing can be quite long, reaching up to 400 feet for some applications. The physical limitations of mandrel rod length and setup mean that internal mandrels cannot be used to bend long, continuous serpentine loop tubing with multiple bends. This forces manufacturers to form one or two bends in shorter sections (sometimes called crooks) and then weld the sections together to form a larger loop. This not only involves additional labor and cost, but the additional welding increases the likelihood of leaks, and may not be permissible in many applications due to the high operating pressures the serpentine loop tubing will withstand.

[0036] When C B Another problem that can arise when the bend approaches or exceeds 20 is that the associated internal mandrel bend brings the neutral axis of the bend closer to the inside of the bend, potentially causing excessive thinning of the outer wall portion of the bend. Thinning of the outer wall portion of the bend weakens the serpentine loop, making it unable to withstand the pressure of the working fluid used in a particular application. Excessive thinning of the outer wall of the bend during its formation can also introduce variability in the process, leading to a reduction in the quality of the bend region.

[0037] The aforementioned issues make it desirable for manufacturers to avoid using internal mandrels for tubing bending. One way to avoid using internal mandrels for tubing with a given OD is to increase WT or CLR to an appropriate value so that the bend is within the range of mandrel-free bending. From an operational perspective, manufacturers whose products do not require such relatively thick walls may not choose to increase the wall thickness (WT). In some cases, thicker walls can increase the pressure drop on the fluid side, potentially reducing the thermal efficiency of the product, increasing the weight of the component, and potentially increasing the material cost of the serpentine loop. Furthermore, increasing CLR may not be an option when the serpentine loop needs to be installed within a given space for other operational considerations. In some cases, increasing CLR can also negatively impact the overall coil thermal and hydraulic efficiency. Summary of the Invention

[0038] In one aspect of this disclosure, an indirect heat exchanger pressure vessel is provided, comprising an inlet manifold for receiving a pressurized working fluid, an outlet manifold for collecting the pressurized working fluid, and a serpentine loop connecting the inlet manifold and the outlet manifold and allowing the pressurized working fluid to flow from the inlet manifold to the outlet manifold. The pressurized fluid may be, for example, water, ethylene glycol, a mixture of ethylene glycol, ammonia, or carbon dioxide, as some examples. The pressurized fluid may be a liquid such as water, or a liquid / gas combination such as a refrigerant liquid and a refrigerant vapor. The serpentine loop includes a conduit and a gyratory bend connecting the conduit. The gyratory bend includes a controlled pleated portion comprising alternating ridges and grooves. The controlled pleated portion of the gyratory bend provides a rigid structure that resists internal pressure during operation of the indirect heat exchanger pressure vessel. Furthermore, the controlled pleated portion provides a constructed bend centerline radius greater than the actual bend centerline radius of the gyratory bend. Compared to the slewing section of a conventional serpentine loop tube with the same outer diameter and wall thickness, the larger centerline radius of the structural bend reduces the bending complexity coefficient of the slewing section. This reduced bending complexity allows the slewing section with controlled folds to be bent without the use of an internal mandrel, simplifying the manufacturing process of the serpentine loop tube.

[0039] This disclosure also provides an indirect heat exchanger pressure vessel including an inlet manifold for receiving pressurized working fluid, an outlet manifold for collecting the pressurized working fluid, and a serpentine loop connecting the inlet and outlet manifolds to allow the pressurized working fluid to flow from the inlet manifold to the outlet manifold. The serpentine loop includes a conduit, a gyratory bend connecting the conduit, and a tangent at a junction between the gyratory bend and the conduit. The gyratory bend includes a bending angle and a controlled fold portion. The controlled fold portion is spaced apart from the tangent along the serpentine loop and has an angular range smaller than the bending angle around the inner side of the gyratory bend. In this way, the controlled fold portion can be formed using a bending die having a controlled fold forming feature corresponding to the entire inner arc surface of the gyratory bend, allowing the serpentine loop to slide longitudinally out of the bending die and increasing the speed at which the gyratory bend is formed in the serpentine loop. In one embodiment, the controlled fold portion includes a ridge having a smaller amplitude near the tangent point and increasing as the fold portion extends away from the tangent point, to reduce resistance to fluid flowing through the fold bend and to reduce internal fluid pressure drop at the fold bend relative to the non-conical or non-eased configuration of the fold ridge.

[0040] On the other hand, an indirect heat exchanger pressure vessel is provided, comprising an inlet manifold for receiving a pressurized working fluid, an outlet manifold, and a serpentine loop connecting the inlet and outlet manifolds to facilitate the flow of the pressurized working fluid from the inlet manifold to the outlet manifold. The serpentine loop includes a pair of pipes and a zigzag bend connecting the pipes. The zigzag bend includes an inner portion having a sinusoidal curve at its inner arc surface, the sinusoidal curve comprising crests and troughs. The inner portion of the bend includes an arcuate curve intersecting the sinusoidal curve, the arcuate curve comprising crest arcs intersecting crests and trough arcs intersecting troughs. The intersecting sinusoidal curve and arcuate curve provide smooth, continuously curved sidewalls for the serpentine loop, which enhances the resistance of the zigzag bend to internal pressure. In one embodiment, the sine wave curve has one or more end portions with shallower crests and troughs and a middle portion with deeper crests and troughs to reduce the internal fluid pressure drop through the sine wave curve (compared to a sine wave pattern with constant crests and troughs).

[0041] This disclosure also provides a closed-loop cooling tower including an indirect heat exchanger comprising a plurality of serpentine loops having conduits and gyratory bends connecting the conduits. The gyratory bends include gyratory bends with controlled gyration portions. The closed-loop cooling tower includes a fan operable to generate airflow relative to the serpentine loops, and an evaporative liquid distribution assembly configured to distribute evaporative liquid onto the serpentine loops. The closed-loop cooling tower further includes a reservoir for receiving evaporative liquid falling from the serpentine loops, and a pump operable to pump the evaporative fluid from the reservoir back to the evaporative liquid distribution assembly. The controlled gyration portions reinforce the serpentine loops to withstand internal pressure from the working fluid within the serpentine loops during cooling tower operation. The controlled folded bend also provides a constructed centerline radius for the folded bend that is larger than the actual centerline radius of the controlled folded bend, and offers a reduced bending complexity coefficient (compared to the slewing bend of a conventional serpentine loop with the same outer diameter and wall thickness). This reduced bending complexity coefficient allows the controlled folded bend to bend without the use of an internal mandrel, simplifying the manufacturing process of the serpentine loop. Attached Figure Description

[0042] Figure 1 It is a perspective view of an indirect heat exchange device with a serpentine loop tube, the tubes being connected by bends in the serpentine loop tube;

[0043] Figure 2 This is a schematic diagram of a heat exchange device including a serpentine loop tube;

[0044] Figure 3 This is a side view of a serpentine loop pipe, which has pipes connected by 180-degree bends;

[0045] Figure 4 yes Figure 3 The enlarged view of the curved section shown in the dashed circle shows the controlled folding portion inside the curved section;

[0046] Figure 5 It is along Figure 4 The cross-sectional view taken by line 5-5 shows the section of the bent portion at the groove of the folded part;

[0047] Figure 6 It is along Figure 4 The cross-sectional view taken by line 6-6 shows the section of the curved portion at the ridge of the folded part;

[0048] Figure 7 It is along Figure 4 The cross-sectional view taken by line 7-7 shows the cross-section of one of the pipes in the loop;

[0049] Figure 8 yes Figure 4 A perspective view of the curved portion, showing the folded portion inside the curved portion and the smooth outer wall portion outside the curved portion;

[0050] Figure 9A It is along Figure 8 The cross-sectional view taken by line 9A-9A shows the sine curve of the folded portion, which is spaced apart from the tangent points of the bend and the pipeline, so that the folded portion has an angle range that is smaller than the 180-degree bending angle of the bend.

[0051] Figure 9B It is similar to Figure 9A A cross-sectional view of a curved portion in another embodiment, the curved portion having a pleated portion having ridges and troughs of a sine curve with different amplitudes;

[0052] Figure 9C It is similar to Figure 9A A cross-sectional view of a curved portion in another embodiment, the curved portion having a pleated portion having ridges and troughs of sine curves with different periods and amplitudes;

[0053] Figure 10 , Figure 11 , Figure 12 , Figure 13A and Figure 13B The process of determining the sinusoidal curve of the bend is shown;

[0054] Figure 14 It is a graphical representation of a portion of the sine curve of the folded part of the bend, showing the peaks and troughs of the sine curve;

[0055] Figure 15 It is a graphical representation of a portion of the sinusoidal curve of the slew curve where a portion of the slew curve intersects with an arcuate curve of the slew curve, the arcuate curve including a crest arc intersecting with the crest of the slew curve and a trough arc intersecting with the trough of the slew curve;

[0056] Figure 16A yes Figure 15 The graphical representation of the crest arc shows a crest arc with a radius of curvature, an angular range, and a center, wherein the center is radially inward of the centerline of the serpentine loop tube;

[0057] Figure 16B It is similar to Figure 16A A graphical representation of a wave crest arc with a composite radius of curvature;

[0058] Figure 16C It is similar to Figure 16A A graphical representation of a wave crest arc with a shape defined by a portion of an ellipse;

[0059] Figure 17A yes Figure 15 The graphical representation of the trough arc shows that the trough arc has a radius of curvature that is substantially the same as that of the crest arc, a shorter angular range than that of the crest arc, and a center that extends radially outward from the centerline of the tube.

[0060] Figure 17B It is similar to Figure 17A A graphical representation of a trough arc with a composite radius of curvature;

[0061] Figure 17C It is similar to Figure 17B A graphical representation of a trough arc with a shape defined by a portion of an ellipse;

[0062] Figure 18 It is a perspective view, showing Figure 15 A portion of a sine curve, crest arcs and trough arcs, and a continuously curved, folded surface portion connecting the crest arcs and trough arcs;

[0063] Figure 19 This is a perspective view of a pipe bending machine, showing the bending die, clamping die, and holding die.

[0064] Figure 20 yes Figure 19 A side view of the bending die shows the ridges and grooves of the corresponding ridges and grooves that form the pleated portion of the tube;

[0065] Figure 21 , Figure 22 , Figure 23 , Figure 24 , Figure 25 and Figure 26 It shows the use of Figure 19 The process by which a pipe bending machine forms the bent section of a serpentine loop pipe;

[0066] Figure 27 Is using Figure 19 A top view of the lower part of the pipe and bending die of a pipe bending machine, showing the meshing engagement between the ridge of the pleated section of the bending part and the ridge of the bending die; and

[0067] Figure 28 , Figure 29 and Figure 30 These are front views of the curved sections with bending angles of 90 degrees, 80 degrees, and 100 degrees respectively;

[0068] Figure 31 It is a cross-sectional view of a serpentine coil including a pipe with a gradually flattening cross section;

[0069] Figure 32It is an elevational view of a composite bend of a pair of serpentine loop pipes, with three contact points between them. Each composite bend includes an 80-degree bend and a 100-degree bend.

[0070] Figure 33 It is a front view of the curved section with an asymmetrical pleated pattern;

[0071] Figure 34 It is used to form Figure 33 A perspective view of the lower part of the bending die for the bending section;

[0072] Figure 35 yes Figure 34 A perspective view of the lower part of the bending die and the corresponding upper part of the bending die;

[0073] Figure 36 It is a plan view of a tube with a flat cross-section, which includes a straight section and a zigzag section with pleats;

[0074] Figure 37A It is along Figure 36 The cross-sectional view taken from line 37A-37A shows the elliptical cross-section of the tube at the trough of the fold.

[0075] Figure 37B It is along Figure 36 The cross-sectional view taken along lines 37B-37B shows the elliptical cross-section of the tube at the crest of the folded portion; and

[0076] Figure 37C It is along Figure 36 The cross-sectional view taken from line 37C-37C shows the elliptical cross-section of the tube at one of its straight sections. Detailed Implementation

[0077] about Figure 1 The system provides an indirect heat exchanger pressure vessel, such as coil assembly 10, which can be used in heat exchange equipment such as evaporative condensers, closed-loop fluid coolers, or ice storage systems. Coil assembly 10 includes an inlet manifold 12, an outlet manifold 14, and a serpentine loop 16. The serpentine loop 16 includes conduits 18 connected to either a 180-degree bend 20 or a compound bend 21, the compound bend 21 including two 90-degree bends 23 and 25 separated by a straight section 27. The serpentine loop 16 allows working fluid to flow from the inlet manifold 12 through the serpentine loop 16 to the outlet manifold 14.

[0078] about Figure 2A heat exchange device, such as a cooling tower 24, is provided, comprising an external structure 26, one or more fans 28 including fan blades 30 and a motor 32, a direct heat exchanger such as a filler 34, and an indirect heat exchanger pressure vessel 36. As some examples, the cooling tower 24 may be an evaporative condenser, a closed-loop cooling tower, or a dry cooler heat exchanger. The indirect heat exchanger pressure vessel 36 includes an inlet manifold 38, one or more serpentine loop pipes 37 having loop lines 39 and bends 40, and an outlet manifold 42. Depending on the application, the inlet manifold 38 and the outlet manifold 42 may be interchanged. In some embodiments, the filler 34 is located above the indirect heat exchanger pressure vessel 36 and / or the filler 34 is located between the lines of the serpentine loop pipes 37.

[0079] about Figure 2 The cooling tower 24 includes an evaporative liquid distribution system 43, which includes a jet assembly 44 having nozzles or orifices 46 for distributing evaporative fluid, such as water, to the serpentine loop 37 and the filler 34. The evaporative liquid distribution system 43 includes a reservoir 50 for collecting the evaporative fluid from the filler 34 and the coil 36, and a pump 52 for pumping the collected evaporative fluid through a conduit 54 to the jet assembly 44. The cooling tower 24 also includes one or more air inlets 35, inlet louvers 58 to prevent evaporative liquid from leaving the cooling tower 24, an air outlet 59, and an eliminator 56 for collecting water mist from the air before it leaves the air outlet 59. A fan 28 is operable to generate or direct airflow upward relative to the serpentine loop 37 and the filler 34. In other embodiments, the cooling tower 24 may have one or more fans configured to direct airflow in an upward, downward, or lateral flow direction relative to the indirect and / or direct heat exchangers of the cooling tower 24.

[0080] about Figure 3 A serpentine loop 70 is provided, which can be used with heat exchange equipment, such as... Figure 1 The coil assembly 10 in the middle, or the above about Figure 2The cooling tower 24 under discussion. A serpentine loop 70 includes an internal passage 72 and tubular sidewalls 74 extending therearound it. The serpentine loop includes an end portion 76 connectable to an inlet manifold and an end portion 78 connectable to an outlet manifold. Depending on the application, end portion 76 may alternatively connect to the outlet manifold, and end portion 78 may connect to the inlet manifold. The serpentine loop 70 includes conduits 79 (e.g., conduits 80, 82) and bends 84. In one embodiment, conduits 79 may be parallel. In other embodiments, one or more conduits 80 extend laterally (e.g., obliquely) relative to each other to allow internal fluid to drain. The serpentine loop 70 may be self-draining, such that any liquid in the internal passage 72 flows downward toward the end portion 78 under gravity. The material of the serpentine loop 70, the outer diameter of the serpentine loop 70, the wall thickness of the sidewall 74, the number of pipes 79, the length of the pipes 79, the number of bends 84, the angle range of the bends 84, the centerline radius of the bends 84, and the inner / outer arc surface of the bends 84 can be selected for a specific heat exchange device. As another example in this regard, instead of a single angled bend 84 connecting a pair of pipes 79, the serpentine loop can have one or more bends 84, each comprising a pair of bends (e.g., 90 degrees) connected by straight sections, similar to... Figure 1 The composite bend 21 is shown. The conduit 80 may have a circular cross-section throughout. In other embodiments, the serpentine loop 70 includes one or more conduits 80 having a non-circular cross-section (e.g., elliptical or oblong).

[0081] The serpentine loop 70 can be formed from a single straight pipe, which is bent at intervals along the pipe to form bends 84. The serpentine loop 70 can also be formed by progressively rolling an elongated strip of material into a tubular shape and welding the longitudinal edges of the strip together to form a single weld extending along the length of the serpentine loop 70. In another method, the serpentine loop 70 can be made from multiple separately formed components. For example, the conduit 79 can be a separate component welded to the bend 84. Alternatively, the serpentine loop 70 can be formed by welding separate pipe segments together and then bending a longer welded pipe. The serpentine loop 70 can be made of a metallic material, such as carbon steel or stainless steel.

[0082] about Figure 4Each bend 84 includes an inner arc surface 90, an outer arc surface 92, a controlled wrinkle portion 94 on the inner side 96 of the bend 84, and a smooth outer surface 98 at the outer side 100 of the bend 84. The controlled wrinkle portion 94 includes a continuous bend of ridges 114 and grooves 116 and a controlled wrinkle surface 134. The continuous bend controlled wrinkle surface 134 is not disturbed by edges, corners, or planes to avoid localized stress areas. The continuous bend and the controlled wrinkle surface 134 are formed by the ridges 114 and grooves 116 of the bend 84, which are at least partially defined by intersecting sinusoidal curves 110 and arcuate curves 150, as described below relative to... Figure 15 As discussed in more detail. Figure 4 The bend 84 shown has a bending angle of 180 degrees. When this disclosure refers to a specific bending angle of a bend, it means that the bending angle is an approximation, such as + / - 5 degrees. In some embodiments, all bends 84 of the serpentine loop 70 have controlled wrinkle portions 94. In other embodiments, not all bends 84 have controlled wrinkle portions 94.

[0083] The serpentine loop 70 has a centerline 102 that extends through the conduits 80, 82 and the bend 84. A controlled folding portion 94 extends radially inward from the centerline 102 and is separated therefrom by a side surface portion 104. The smooth outer surface portion 98 and the side surface portion 104 allow the bend 84 to overlap with bends in other serpentine loops in a conventional arrangement, as with prior art pipes having smooth inner bends.

[0084] refer to Figure 4 At the inner arc surface 90 of the curved portion 84, the controlled wrinkled portion 94 has a sinusoidal curve 110 at the inner arc surface 90 of the curved portion 84, as described below regarding Figure 8 and 9A The discussed pleated portion 94 includes an alternating series of ridges 114 and grooves 116. In one embodiment, the bend 84 has relief portions 222, 224 located in the middle of the sine curve 110, and tangent points 122, 124 between the conduits 80, 82 and the bend 84. The relief portions 222, 224 facilitate providing a controlled pleated portion angle 240 smaller than the bend angle 220, as discussed in more detail below. The relief portions 222, 224 extend from the tangent points 122, 124 to points 216, 218. The pleated portion 94 further includes points 216, 218 and point 400 (see...). Figure 4The sine wave curve 110 extends between the starting and ending points 400 and tapered introductory portions 140 and 142. In one embodiment, relief portions 222 and 224 each have a first radius, and tapered introductory portions 140 and 142 each have a smaller second radius. The sine wave curve 110 starts at a point 400, extends through the crest 130 of the terminal ridge 118, undulates along the ridge 114 and groove 116, extends through the crest 132 of the terminal ridge 120, and finally reaches another point 400.

[0085] The ridge 114 includes terminal ridges 118 and 120, optionally having tapered inlet portions 140 and 142. The tapered inlet portions 140 and 142 provide a smooth transition between the relief portions 222 and 224 and the sinusoidal curve 110. The tapered inlet portions 140 and 142 allow the working fluid to flow smoothly through the bend 84 and aid material flow in the bend 84 during bending. The tapered inlet portions 140 and 142, the ridge 114, and the groove 116 reduce the internal fluid pressure drop caused by the working fluid flowing through the bend 84. Furthermore, the tapered inlet end portion 140 facilitates better drainage of the serpentine loop 70. The bend 84 may have two tapered inlet portions 140 and 142 if the working fluid can flow through the bend 84 in either direction 143 or 145. If the working fluid will flow through the bend 84 in only one direction 143, 145, then the bend 84 may have only one tapered inlet portion 140, 142.

[0086] about Figure 9B A cross-sectional view of bend 84' is provided, which is similar to bend 84 and has a sinusoidal curve 110' at the centerline of bend 84'. Bend 84' has ridges 114' and grooves 116', the amplitude of which varies around bend 84'. Specifically, ridges 114' and grooves 116' closer to pipes 80' and 82' have smaller amplitudes, while ridges 114' and grooves 116' closer to the middle of bend 84' have larger amplitudes. For example, ridges 114A' and 114B' have larger amplitudes than ridges 114C' and 114D'. The more gradually the amplitude of ridges 114' and grooves 116' increases compared to bend 84 in some applications, the less resistance is provided to the fluid flowing through bend 84', resulting in a reduced pressure drop across bend 84'. Compared to the bend 84 in some applications, the more gradually increasing amplitude of the ridge 114' and groove 116' can reduce stress in the material of the bend 84' during bending operations. In other embodiments, the amplitude of the sinusoidal curve of the bend 84' can be increased from one conduit adjacent to the bend 84' to another conduit adjacent to the bend 84'.

[0087] about Figure 9C A cross-sectional view of a bend 84” is provided, which is similar to the bend 84” and has a controlled folding portion 94” with a sinusoidal wave pattern 110” on the inner arc surface of the bend 84”. The controlled folding portion 94” includes a ridge 114” and a groove 116”. The controlled folding portion 94” includes a first portion 115”, which has ridges 114”A, 114”B and grooves 116”A, 116”B, having a first amplitude and a first period 117. The controlled folding portion 94” includes a second portion 119”, which has ridges 114”C, 114”D and grooves 116”C, 116”D, having a second amplitude greater than the first amplitude. The ridges 114”C, 114”D and the grooves 116”C, 116”D have a second period 121 less than the first period 117”. The controlled fold portion 94” also includes a third portion 123”, which has ridges 114”E, 114”F and grooves 116”E, 116”F, having a third amplitude substantially the same as the second amplitude of the second portion 119” and a third period 125” smaller than the second period 121”. The bend 84” receives fluid in the direction 127”, and the ridge 114”A includes a tapered inlet portion 129” to allow fluid to flow smoothly through the bend 84”. The tapered inlet portion 129” reduces the pressure drop across the bend 84” and improves fluid drainage from the bend 84”.

[0088] The characteristics of the sine wave curve 110 for a given gyrobola can be selected for a specific application. For example, the number of ridges / grooves, amplitude, period, and / or one or more tapered introductory sections can be selected for a specific application. The characteristics of the gyrobola can vary throughout the gyrobola; for example, the amplitude and period can vary throughout the gyrobola. The shape of the controlled folded section 94 is formed at least partially by two different intersecting cross-sectional profiles. Figure 4 and Figure 15 As shown, the controlled wrinkle portion 94 includes a sinusoidal portion 110 at the inner arc surface 90 of the curved portion 84. Another curve is an arcuate curve 150 comprising alternating crest arcs 152 and trough arcs 154. (As shown...) Figure 16A and Figure 17A As shown, crest arc 152 has a crest arc radius 152' and a center 182, and trough arc 154 has a trough arc radius 158 and a center 172. In this embodiment, crest arc 152 and trough arc 154 are substantially identical. As used herein, the term "substantially identical" means that the dimensions are practically the same, taking into account manufacturing variations, for example, differing from each other within + / - 10%. Crest arc 152 extends through an angle 160, which is greater than the angle 162 through which trough arc 154 extends.

[0089] like Figure 5 and Figure 15 As shown, the trough arc 154 forms a trough semicircular inner wall portion 170, which has a trough arc radius 158 and a center 172. Opposite to the trough semicircular inner wall portion 170, the bend 84 includes an outer wall portion 174 that may be semicircular. In some embodiments, due to the outer arc surface 92 of the bend 84 (see...) Figure 4 Tensioned during the bending process, the outer wall portion 174 can be curved, having a flattened portion. The curved portion 84 includes connecting wall portions 176, 178 that connect the trough-shaped semi-circular inner wall portion 170 to the outer wall portion 174. The connecting wall portions 176, 178 have curvatures that may differ from those of the inner wall portion 170 and the outer wall portion 174. The connecting wall portions 176, 178 provide a smooth transition between the geometries of the inner wall portion 170 and the outer wall portion 174 to minimize stress concentration at the junction between the geometries of the inner wall portion 170 and the outer wall portion 174. By reducing stress concentration at the junction between the geometries of the inner wall portion 170 and the outer wall portion 174, the connecting wall portions 176, 178 help the curved portion 84 withstand high internal working pressures.

[0090] like Figure 6 As shown in Figure 15, the crest arc 152 defines a crest semicircular inner wall portion 180, which has a crest arc radius 156 with a center 182. The bend 84 has an outer wall portion 184 opposite to the crest semicircular inner wall portion 180. Similar to the outer wall portion 174 (see Figure 15), the bend 84 has an outer wall portion 184 opposite to the crest semicircular inner wall portion 180. Figure 5 The outer wall portion can be semi-circular. In some embodiments, due to the outer arc surface 92 of the curved portion 84 (see...), Figure 4 Tensioned during the bending process, the outer wall portion 184 can be curved, having a flattened portion. The curved portion 84 further includes connecting wall portions 186, 188 that connect the crested semi-circular inner wall portion 180 and the outer wall portion 184. Similar to the outer wall portion 174, in some embodiments, the outer wall portion 184 may have a semi-circular or generally curved shape. Furthermore, the connecting wall portions 186, 188 provide a smooth transition between the geometries of the inner wall portion 180 and the outer wall portion 184 to minimize stress concentration at the junction between the geometries of the inner wall portion 180 and the outer wall portion 184. The connecting wall portions 186, 188 contribute to the ability of the curved portion 84 to withstand high internal working pressures. The crest arc 152 and the trough arc 154 may each have a single radius, as shown in the figure. Figure 16A and Figure 17A As shown in the diagram. In another embodiment, the crest arc 152 and / or the trough arc 154 have a composite radius or a compound radius. For example, and referring to... Figure 16BThe crest arc 152' has different radii 156A' and 156B'. Each radius of the crest arc 152' is tangent at the point where the radius joins the adjacent radius. Similarly, in Figure 17B In the middle, the trough arc 154' has different radii 158A' and 158B'.

[0091] In another embodiment, the crest arc 152 and / or the trough arc 154 have the shape of a portion of an ellipse. For example, Figure 16C The crest arc 152” is an arc defined by an angle 160” (e.g., 160 degrees) between points 426” and 430” of the ellipse 439, which has a major dimension 441 and a minor dimension 443. Similarly, Figure 17C The trough arc 154 in the ellipse 449 has a shape defined by an angle 162 (e.g., 142 degrees) between points 445 and 447 of the ellipse 449, which has a major axis 451 and a minor axis 453.

[0092] about Figure 7 The conduit 82 shown has a circular cross-section with its center at the conduit centerline 102. The sidewall 74 may also have a non-circular cross-section, such as an elliptical or rectangular cross-section. The sidewall 74 of the serpentine loop conduit 70 has a wall thickness 190 extending around the internal channel 72.

[0093] about Figure 8 The sections of conduits 80, 82, and bends 84 are shown in perspective. As seen above, the controlled pleats 94 have continuously curved controlled pleat surfaces 134, which include curved ridge surface portions 200 on opposite sides of each ridge 114 and curved groove surface portions 202 on opposite sides of each groove 116, connecting the curved ridge surface portions of adjacent ridges 114. The ridge surface portions 200 and groove surface portions 202 form the continuous, wavy appearance of the controlled pleats 94.

[0094] about Figure 9AThe serpentine loop 70 has an outer diameter of 210 and a wall thickness of 190. A centerline 102 extends through pipes 80, 82 and bend 84. The serpentine loop has joints 214, 215 between pipes 80, 82 and bend 84. At joints 214, 215, the pipe 70 includes tangents 122, 124 between pipes 80, 82 and bend 84. The bend 84 includes relief portions 222, 224 extending away from tangents 122, 124, and tapered inlet portions 140, 142 are radially inwardly inclined toward the crests 130, 132 of the end ridges 118, 120. The bend 84 has a center 230 and a centerline radius 232 extending from the center 230 to the centerline 102. In the illustrated embodiment, the bent portion 84 has a bending angle 220 of 180 degrees, and the controlled wrinkle portion 94 extends about the center 230 through a controlled wrinkle portion angle 240, which is smaller than the bending angle 220. For example, the controlled wrinkle portion angle 240 may be 5° or less, 10° or less, or 15° or less smaller than the bending angle 220. In one embodiment, the bending angle is 180 degrees, and the wrinkle portion angle 240 is approximately 166 degrees.

[0095] Refer again Figure 9A The controlled folding portion 94 positions the crest 250 of the ridge 114 on the inner arc surface 90 of the curved portion 84 (see...). Figure 4 The trough 252 of the groove 116 is positioned radially outward from the crest 250. By positioning the trough 252 outside the inner arc surface 90 of the bend 84, the folded portion 94 forms a structural bend centerline 254. The structural bend centerline 254 has a structural bend centerline radius 256, which is larger than the centerline radius 232 of the pipe centerline 102. Because the structural bend centerline radius 256 is larger than the bend centerline radius 232, for a given inner and outer arc surface of the bend, the bending complexity ratio of the bend 84 is smaller than that of a conventional bend with the same inner arc surface, outer arc surface, outer diameter, and wall thickness. Due to the larger structural bend centerline radius 256, the bend 84 has a lower bending complexity ratio.

[0096] For example, the following feature ratios can be provided for the curved portion of a specific application:

[0097]

[0098]

[0099]

[0100] Where OD refers to the outer diameter of the pipe, WT refers to the wall thickness, and CLR refers to the radius of the centerline of the bend. Assume these ratios for the bend are:

[0101] W1 = 20 and D1 = 2, therefore C B1 =10

[0102] Referring to Table 1 above, these values ​​indicate that if a conventional pipe bending machine is used, internal mandrel bending may be required.

[0103] Currently, certain parameters of the bend have been modified to exhibit improved serpentine tube characteristics, such as a tighter bend radius for the same wall thickness, reduced coil weight, lower internal fluid-side pressure drop, lower bend wall stress, increased tube strength, increased tube stiffness, and / or improved heat transfer efficiency. These changes affect the characteristic ratio. For example, a new characteristic ratio can be selected as:

[0104] W2 = 30 and D1 = 2, therefore C B2 =15

[0105] Currently, the complexity of bending characteristics is within the range that conventional pipe bending machines cannot compensate for, and such bends are usually manufactured using internal mandrels.

[0106] For the reasons mentioned above, internal mandrel bending is generally undesirable, making it impractical for manufacturers who use long and continuous tube sections to produce heat exchanger coils.

[0107] Refer again Figure 9A One way to overcome the need for an internal mandrel is to reduce bending complexity by increasing the bending radius (CLR). In our example, if we can increase the CLR of the bending radius while keeping the outer diameter and wall thickness constant, we can increase the bending radius (D) from 2 to 3 and obtain the following bending complexity (C). B )Compare:

[0108] W2 = 30 and D2 = 3, therefore C B2 =10

[0109] Because if C B2With a bend size in the range of 5 to 10, bends can be formed without an internal mandrel. However, for a given application, simply increasing the bend size CLR may be unacceptable because the new bends will be larger and take up more space than the original bends. For example, the center-to-center distance between the tubing will be greater, meaning fewer tubing will be available to fit a given sheath or coil height. Furthermore, because each bend in the serpentine coil will be taller, the serpentine coil will have fewer tubing for a given sheath or height, reducing its heat exchange capacity. Reducing the number of tubing in the serpentine coil to increase the bend size CLR is not an acceptable solution for many applications.

[0110] Refer again Figure 9A The controlled folding portion 94 of the bend 84 provides a constructed bend centerline radius 256, which is larger than the actual bend centerline radius 232, without increasing the distance between pipes 80 and 82. The larger constructed bend centerline radius 256 increases the CLR of the bend 84, which increases the D of the bend for a given OD and allows C... B It falls within the range where bending of the mandrel is not required.

[0111] More specifically, the controlled folding portion 94 provides a structurally oriented bend centerline 254 within the available space of the bend 84, thereby allowing sufficient length along the inner side of the bend 84 for the material to form ridges 114 and grooves 116 in a controlled manner without buckling. The folding portion 94 also maintains or improves other coil characteristics, such as internal fluid pressure drop and heat transfer efficiency. Other characteristics of the bend 84, such as reduced wall thinning on the outer arc surface, and the overall stiffness of the bend 84 are also improved.

[0112] refer to Figure 4 The alternating ridges 114 and grooves 116 of the controlled folded portion 94 provide space for the material of tube 70 to fold itself into a smaller usable arc length during bending of tube 70. The material of tube 70 folds along the inner arc surface of the bend 84 into a sine wave curve 110. Specific variables of the sine wave curve 110, such as the number of crests / troughs, the depth of the troughs (amplitude of the sine wave), the span of the arc, etc., are calculated for specific applications, as described below. This method can be used to calculate variables for various combinations of material, OD, WT, and CLR, and to optimize for various characteristics such as pressure drop and thermal efficiency.

[0113] The controlled corrugation section 94 offers advantages over conventional bends. For example, compared to other bends with corrugations, the sinusoidal curve 110 minimizes the stress generated in the material of the tube 70, allowing for much higher internal fluid pressures. The dimensions of the ridges 114 and grooves 116 (including the tapered inlet portions 140, 142) can be designed to limit obstruction to fluid flow within the bend 84 and minimize the internal fluid pressure drop through the bend 84. Compared to a conventional bend with the same bend centerline radius, the sinusoidal curve 110 increases the length of material along the inner arc surface 90, which increases the total surface area of ​​the bend 84 and improves heat transfer efficiency by increasing fluid turbulence within the bend region. Furthermore, the ridges 114 and grooves 116 operate as a corrugated structure, stiffening the bend 84 compared to a smooth, corrugated bend. Furthermore, compared to a smooth, wrinkle-free bend, the controlled wrinkle portion 94 pushes the neutral axis of the bend 84 outward toward the outer arc surface 92 of the bend 84, thereby reducing the material thinning of the bend 84 along the outer arc surface.

[0114] Reference Figure 10-13B A method is provided for determining the geometry of the bend 84 of a serpentine loop 70 in place of the bend 306 of a conventional serpentine loop 300, while fitting within the coiled sheath of the conventional serpentine loop 300 and utilizing a tighter bend radius for a given wall thickness.

[0115] about Figure 10 The conventional serpentine loop pipe 300 has pipe sections 302 and 304, a bend 306, an outer diameter 308, and a wall thickness 310. The bend 306 is a 180° bend and has an inner arc surface 312 and an outer arc surface 315 with an arc length 314. Initially, and regarding... Figure 11 The serpentine loop 70 has an outer diameter 210 that is the same as the outer diameter 308 and a wall thickness 190 that is smaller than the wall thickness 310. For example, both the outer diameter 308 and the outer diameter 210 can be 1.05 inches, the wall thickness 310 can be in the range of about 0.04 inches to about 0.07 inches (e.g., 0.048 inches), and the wall thickness 190 can be in the range of about 0.02 inches to about 0.05 inches (e.g., about 0.03 inches to about 0.04 inches). The outer diameter 210 is chosen to be the same as the outer diameter 308 such that bends 84 overlap with adjacent bends 84, just as bends 306 overlap with adjacent bends 306. For a given thickness 190, a tighter bend radius can improve the heat transfer efficiency between the working fluid inside the serpentine loop 70 and the fluid outside the serpentine loop 70. Furthermore, for a given wall thickness of 190, a tighter bend radius can reduce the internal fluid pressure drop in the serpentine loop 70 because the inner diameter of the pipe is increased.

[0116] refer to Figure 11 The method for determining the geometry of the bend 84 includes initially configuring the serpentine loop 70 with an initial bend 316 having connecting pipes 80 and 82. The initial bend 316 has a bending angle of 180° and a centerline radius 317, which is greater than... Figure 10 The centerline radius of the curved portion 306 shown is 313. (As shown...) Figure 10 and Figure 11 As shown, the initial curved portion 316 has an inner arc surface 320 with an arc length 318 greater than the arc length 314, because the center line radius 317 is greater than the center line radius 313.

[0117] about Figure 12 In order to make the curved part 84 like Figure 10 The conventional bend 306 is assembled within the same coil sleeve (meaning the center-to-center distance between the pipe sections is equal). The bend 84 has an outer arc surface 92 that matches the outer arc surface 315 of the bend 306, and the pipe 70 has an outer diameter 210 that matches the outer diameter 308. To provide matching outer arc surfaces 92 and 315, the method for determining the geometry of the bend 84 includes along directions 330 and 332 (…). Figure 11 Move the tangent points 122 and 124 of pipes 70 and 82 toward each other until: 1) the actual centerline radius 232 of the bend 84 is equal to the centerline radius 313 of the bend 306; 2) the arc length of the inner arc surface 90 of the bend 84 is equal to the inner arc surface 312 of the bend 306.

[0118] To compensate for the reduced vertical distance between tangent points 122 and 124, the material of the serpentine loop 70 inside the bend 84 is shaped to have a sinusoidal curve 110. The sinusoidal curve 110 has variables that define the shape of the sinusoidal curve 110, such as the length of the sinusoidal curve 110, the number of crests / troughs, the period, and / or the amplitude.

[0119] Now for reference Figure 13A The method for determining the geometry of the curved portion 84 next includes providing a line 339 having an inner arc length 340, which is related to the curve from... Figure 12 The inner arc surface 90 has an arc length of 336 that matches it. The inner arc surface 90 has an arc length of 336 that matches it. Figure 12 It extends between the transition points 122 and 124 in the middle.

[0120] The sine wave curve 110 is offset from the tangent points 122 and 124 of the bend 84 through two sections of the serpentine loop tube 70. The first section is the relief sections 222 and 224, which correspond to the offset angle, for example, offset by 7° on either side of the sine wave curve 110, and at angles 220° and 240° (see...). Figure 4 The measurements were taken between 140 and 142. The second part is the tapered introductory section 140, 142. The sine curve 110 begins and ends at point 400 (see...). Figure 4 To generate the offset of the sine wave curve 110 from the tangent points 122 and 124, the method for determining the geometry of the bend 84 includes removing lengths 342 and 344 from the length 340 to give a sine wave curve length 346 that is smaller than the inner arc length 340, such as... Figure 13A As shown in the diagram. Therefore, lengths 342 and 344 each comprise two length portions: 1) a length portion corresponding to one of the relief portions 222 and 224; and 2) a length portion corresponding to one of the tapered introduction portions 140 and 142. Lengths 342 and 344 are determined, for example, by solving for the length portions using the inner arc radius and angular offset.

[0121] Online 339 (see) Figure 13A The length of the arc is 340 and the arc length is 318 (see...). Figure 11 The difference between them is occupied by the total arc length of the sine wave curve 110, which is 346. (Reference) Figure 13A The total arc length of the sine wave curve 110, 346, can be expressed as:

[0122] Total arc length of the sine curve 346 =Inner arc length 340 -length 342,344 [Equation 1.1]

[0123] Once the total arc length 346 of the sine wave curve 110 is known, the total arc length 346 is divided by the number of crests 250A and troughs 252A, for example, in the range of 6 to 18 crests and troughs, for example, 8 to 12 crests and troughs, to determine the arc length 350 for each crest 250A and trough 252A. Each crest 250A and trough 252A has a radius 349 and an arc length 350, given by the following formula:

[0124] arc length 350 = radius 349 ×θ [Equation 1.2]

[0125] Where θ is the angular range of the crest portion 250A and the trough portion 252A. The radius of each crest portion 250A and trough portion 252A can be determined using the following operation.

[0126] refer to Figure 13B This provides the geometry 351, which has an arcuate line AD and a triangle formed by ABCD. Since triangle ABC is a right triangle, the following equation can be determined:

[0127]

[0128] The equation can be rearranged as follows:

[0129]

[0130] Substituting the relationship a = rxθ into equation 1.4, we get:

[0131]

[0132] At this point, the value of "a" is known, which is the total arc length of the sine curve 110, 346, divided by the peak portion 250 and the trough portion 252. Figure 13A The value of “c” is known (see [link]). Figure 13B c / 2), which is the length 346 divided by the number of selected crest portions 250 and trough portions 252.

[0133] Then, numerical methods such as the Newton-Raphson iteration can be used to solve the above equation to obtain θ. Once θ is determined, the radii of the crest portion 250A and the trough portion 252A can be determined by solving for radius 349 in equation 1.2.

[0134] The radius 349 and θ allow the amplitude of the sine wave curve 110 to be determined using the following equation:

[0135] amplitude 352 = radius 349 -(radius 349 ×cosθ)

[0136] It should be understood that special adjustments to the sine curve 110 can be used to customize the sine curve 110 for a specific application.

[0137] about Figure 12 The tapered inlet portions 140 and 142 are used to smoothly bend the material of the serpentine loop tube 70 to reduce the impact at the relief portions 222 and 224 (see...). Figure 4 The stress gradient at the transition between the sine wave curve 110 and the sine wave curve 110.

[0138] refer to Figure 14-18 The intersecting sinusoidal curve 110 and arcuate curve 150 of the controlled folded portion 94 will be discussed in more detail. The intersecting sinusoidal curve 110 and arcuate curve 150 provide a three-dimensional profile of the internal bend. The three-dimensional profile of the internal bend provides a corrugated structure with high strength to resist the internal fluid pressure within the serpentine loop 70. Even when the bend 84 is under high internal pressure, the intersecting sinusoidal curve 110 and arcuate curve 150 ensure that the bend 84 is subjected to low stress.

[0139] refer to Figure 14We will discuss one half of the sine wave curve 110, and the other half of the sine wave curve 110 and... Figure 9A The same as in the embodiment. The sine wave curve 110 begins at point 400 and is spaced apart from the tangent point 122 by the relief portion 222 and the tapered introduction portion 140. The tapered introduction portion 140 gradually slopes upward toward point 400 near the peak 250 of the end ridge 118. The sine wave curve 110 oscillates around a center line 406, which intersects the sine wave curve 110 at the transition 410 between the concave portion 412 and the convex portion 414 (when viewed from the center 230). Figure 14 In this embodiment, the centerline 406 of the sine wave curve 110 is located on the inner arc surface 90 of the bend 84 (see...). Figure 12 In another embodiment, the trough 252 of the sine wave curve 110 lies on the inner arc surface 90 of the bend 84, such that the inner arc surface 90 is tangent to the groove 116. In yet another embodiment, the peak 250 of the sine wave curve 110 lies on the inner arc surface 90 of the bend 84, such that the inner arc surface 90 is tangent to the ridge 114.

[0140] refer to Figure 14 The centerline 406 of the sine wave curve 110 has a radius of 416. In one embodiment, the centerline radius of the bend 84 is 232 (see...). Figure 12 The radius of the centerline 406 can be in the range of approximately 1.5 inches to approximately 2 inches, for example, in the range of approximately 1.7 inches to approximately 2 inches, such as 1.875 inches.

[0141] about Figure 15 The arc curve 150 includes a crest arc 152 that intersects the sine wave curve 110 at each crest 250, and a trough arc 154 that intersects the sine wave curve 110 at each trough 252. The crest arcs 152 and trough arcs 154 are spaced apart around the bend 84 at an angle 420, which can be in the range of, for example, about 4° to about 14°.

[0142] about Figure 16A The crest arc 152 has a center 182 that extends radially inward from the tube centerline 102 of the bend 84. The center 182 is located along the centerline plane 424 of the serpentine loop tube 70. The crest arc 152 extends through an angle 160, which can be in the range of, for example, 150° to approximately 170°, such as 160°. The crest arc 152 has an arc length 427 extending from end point 426 to end point 430.

[0143] about Figure 17A The trough arc 154 has a center 172 that extends radially outward from the centerline 102 of the serpentine loop 70. The trough arc 154 extends through an angle 162, which is less than... Figure 16A Angle 160. In one embodiment, angle 162 is in the range of about 100° to about 150°, for example 140°. The trough arc 154 has an arc length 432 between the endpoints 434, 436 of the trough arc 154, which is less than the arc length 427 of the crest arc 152.

[0144] about Figure 18 The continuously curved controlled folded portion 94 and the controlled folded surface 134 (e.g.) Figure 8 As shown, at least a portion of the surface portion 440 can be formed by connecting the crest arc 152 and the trough arc 154 to the surface portion 440, which has a convex surface portion 442, a concave surface portion 444, and a transition portion 446 that transitions between the convex surface portion 442 and the concave surface portion 444. The surface portion 440 can be mirrored to the opposite side of the ridge 114 across the vertical plane containing the crest arc 152.

[0145] In one embodiment, the continuously curved, wrinkled surface 134 is perpendicular to both the vertical plane containing the crest arc 152 and the vertical plane containing the trough arc 154. (See reference) Figure 15 The vertical plane containing the crest arc 152 is defined as perpendicular to the horizontal plane 424 (see...). Figure 8 The vertical plane contains the origin or center 230 and the crest point 250. The vertical plane containing the trough arc 154 is defined as perpendicular to the horizontal plane 424, and the vertical plane contains the center 230 and the trough 252. The vertical plane containing the crest arc 152 and the trough arc 154 is separated by an angle 420. Regarding... Figure 18 The concave surface portion 442 and the convex surface portion 444 connect the crest arc 152 and the trough arc 154, and provide a continuously curved controlled wrinkled surface 134. Figure 8 The wavy three-dimensional profile is described. Each concave surface portion 442 and convex surface portion 444 terminates at two or four pole splines, one of which begins at the crest endpoint 426. Figure 16A ) and ends at the endpoint of the trough arc 434 ( Figure 17A The other four polar spline curves begin at the peak arc endpoint 430 ( Figure 16A ) and ends at the endpoint of the trough arc 436 ( Figure 17A ).

[0146] refer to Figure 19 and Figure 20A pipe bending machine 500 is provided to bend sections of a serpentine loop pipe 70 into the bends 84 discussed above. The pipe bending machine 500 includes a bending die 502 and a clamping die 504 pivoting about an axis 506. The pipe bending machine 500 includes a clamping die 508 for supporting the outer side of the bend 84 and the tail of the serpentine loop pipe 70. The bending die 502 and the clamping die 504 include recesses 512, 514 with surfaces 516, 518 extending around them, which clamp the pipe once it has been advanced in direction 520 into the gap 522 between the bending die 502 and the clamping die 504. The clamping die 504 and the clamping die 508 can be actuated in direction 524 to secure a portion of the pipe between the clamping die 504 and the bending die 502. The clamping die 508 includes a recess that receives a portion of the tube, and the recess can be displaced in the direction 526 along the movement of the tube when the bending die 502 and the clamping die 504 pivot about axis 506 in direction 528 during the bending operation to support the outside of the tube.

[0147] like Figure 19 and Figure 20 As shown, the bending die 502 includes an upper portion 530, a lower portion 532, and a recess 534, in which a portion 534 receives a portion of the tube when the bending die 502 and the clamping die 504 pivot in direction 528. The bending die 502 has a pleated portion 536, which is a mirror image of a pleated portion 94 of the tube, such that the bending die 502 imparts a pleated pattern 94 into the tube. For example, the pleated portion 536 includes forming a groove 116 (…). Figure 8 The ridge 540 and the ridge 114 ( Figure 8 ) groove 542.

[0148] refer to Figure 20 The ridges 540 each have a middle portion 544 and opposing end portions 546. The middle portion 544 may have a first width around the bending die 502, and the end portions 546, 548 have a width around the bending die 502 that is greater than the width of the middle portion 544, such that the ridges 540 flare outward as they extend away from the centerline 550 of the bending die 502. The grooves 542 may correspondingly have a middle portion 552 and opposing end portions 554, 556, which are narrower around the bending die 502 than the middle portion 552 because the width of the ridges 540 increases as they extend away from the centerline 550. The ridges 540 and the grooves 542 have wavy, continuous curved surfaces 560, such that the pleated portions 536 form the continuous pleated surface 134 of the tube.

[0149] Reference Figure 21-25 A method for forming a bend 84 using a pipe bending machine 500 is provided. Figure 21-25 The pipe bending machine 500 shown has the same Figure 19 The pipe bender 500 shown has similar components, but the orientation of the components is different. For ease of discussion, similar reference numerals will be used to describe them. Figure 20 and Figure 21-25 Pipe bending machine.

[0150] like Figure 21 and Figure 22 As shown, tube 564 is pushed into tube bending machine 500 so that die 508 presses against the outer surface of tube 564. Figure 22 In the middle, the bending die 502 and the clamping die 504 join the portion 505 of the tube 564, and begin to pivot in the direction 565. Figure 22 The page.

[0151] Regarding 23 and Figure 24 The bending die 502 and the clamping die 504 pivot in direction 565 to begin forming a bend 570 in the tube 564. During the bending operation, the clamping die 508 continues to support the outside of the tube 506 and shifts in direction 526 to move together with the tube 564.

[0152] about Figure 25 The pipe bending machine 500 forms a bent section 570 by bending the pipe 564 by 180 degrees.

[0153] Figure 26 The diagram shows the upper part 530 of the bending die 502 moving upward from the lower part 532 along direction 569, the clamping die 504 moving away from the tube 564 (go to page), and the pressing die 508 retracting from the tube 564. The tube 564 then moves in direction 571 to position the next bending position along the tube 564 in the tube bending machine 500.

[0154] about Figure 27 The curved portion 570 shown has a pleated portion 572, which includes a ridge 574 and a groove 576 formed on the inner side of the curved portion 570. Figure 27 It also shows how the lower part 532 is positioned at the centerline 550 of the bending die 502 (see...). Figure 20 The upper portion 532 has a sinusoidal curve 578 at the bend 570, which imparts a sinusoidal curve 580 to the inside of the bend 570. More specifically, the lower portion 532 has a lower portion of a ridge 540 that forms a groove 576 in the bend 570, and the lower portion 532 has a lower portion of a groove 542 that receives the ridge 574 of the bend 570. In this way, the ridge 574 of the tube 564 and the ridge 540 of the bending die 502 form a tightly engaging structure. Furthermore, the ridge 540 and the groove 542, which have a wavy continuous surface, support the inside of the tube. The upper portion 530 of the bending die 502 ( Figure 26It forms a corresponding meshing engagement with the upper part of the curved portion 570.

[0155] about Figure 20 The pleated portion 536 of the bending die 502 includes (now referenced) Figure 27 The tapered transition portion 590 and the terminal ridge 592 cooperate to form the terminal ridge 594 of the curved portion 570. (As mentioned above...) Figure 9A The tapered transition portion 590 discussed provides a smooth inlet to the crest of the terminal ridge 594.

[0156] Based on the disclosure in this article, various types of bends can be provided. For example, Figure 28 The 90-degree bend 600 is shown. Figure 29 The 80-degree bend 620 is shown, and Figure 30 The 100-degree bend 640 is shown.

[0157] about Figure 31 A cross-sectional view of the serpentine loop 700, taken perpendicular to its length, is provided. The serpentine loop 700 is similar to the serpentine loop 70 and includes a conduit 701. The conduit 701 includes a conduit 702 with a circular cross-section and a conduit 704 with a non-circular cross-section (e.g., elliptical or oblong). The conduit 701 has a gradually flattening cross-section, with the conduit 706 having a width 707 that is wider than the width 709 of the conduit 708.

[0158] about Figure 32 A coil 800 is provided, comprising assembled serpentine loops 802 and 804. Each serpentine loop 802 and 804 includes conduits 803 and 805, a compound bend 806, and a connecting portion 816. The compound bend 806 includes a first bend 808 with a first bend angle 810 of 80 degrees and a second bend 812 with a second bend angle 814 of 100 degrees. The connecting portion 816 connects the first bend 808 and the second bend 812. The first bend 808 and the second bend 812 have internal controlled folds similar to the controlled folds discussed above. The serpentine loops 802 and 804 have three contact points 820, 822, and 824. Each serpentine loop 802 and 804 has a height or distance 830 between conduits 803 and 805. The serpentine loops 802 of the coil 800 are in contact with each other. In other embodiments, the coils may include non-contacting serpentine loops.

[0159] refer to Figure 33A portion of tube 896 is shown, comprising a straight portion 898 and a curved portion 900. The curved portion 900 is provided, which is similar in many respects to the curved portions discussed above. The curved portion 900 includes a pleated portion 902 having a ridge 904 and a groove 906. The pleated portion 902 includes a sinusoidal curve 903 along the inner arc surface of the curved portion 900, which begins and ends at points 903A and 903B. Tube 896 has tangent points 911 and 913 at the transition between the straight portion 898 and the curved portion 900.

[0160] The folded portion 902 is asymmetrical about the plane 908 that bisects the curved portion 900. Axes 915 and 912 extend perpendicularly to plane 908 and intersect tangent points 913 and 911, respectively. Tangent points 911 and 913 are offset by a distance 910 along plane 908, such that the folded portion 902 extends further along the tube 896 on one side of plane 908 than on the other. The portion of the folded portion 902 on one side of plane 908 (…) Figure 33 The upper part of the middle part has an offset portion 910A, which includes at least one ridge 904 and / or at least one groove 906 that are more than the portion of the pleated portion 902 on the other side of the plane 908.

[0161] The pleated portion 910 has an end groove 906A and an end ridge 904A. In one embodiment, the end ridge 904A lacks a tapered inlet portion. The offset portion 910A can provide a transition for flow in the pipe 896 between the adjacent straight portion 898 and the curved portion 900. Furthermore, the end ridge 904B has a tapered inlet portion 914 similar to the various end ridges discussed above.

[0162] about Figure 34 and Figure 35 A bending die 1000 is provided, which is similar to the bending die 502 discussed above, thus highlighting the differences. The bending die 1000 is used to form a bent portion 900 and includes an upper portion 1002 and a lower portion 1004. The upper portion 1002 and the lower portion 1004 have ridges 1006 and grooves 1008, which cooperate to form the ridges 904 and grooves 906 in the bent portion 900. The upper portion 1002 and the lower portion 1004 each have a pair of channels 1010 and 1012. The channel 1010 of the upper portion 1002 and the lower portion 1004 forms an opening 1013 on one side 1014 of the bending die 1000, and the channel 1012 of the upper portion 1002 and the lower portion 1004 forms another opening 1015 on a second side 1016.

[0163] Openings 1013 and 1015 allow the bending die 1000 to feed the tube into the opening 1013 or 1015 of the bending die 1000, and allow the bending die 1000 to rotate in the corresponding direction to form a bend 900 in the tube. For example and reference Figure 35 The first part of the tube can be advanced in the direction 1030 into the channel 1012 of the lower part 1004 of the bending die. The upper part 1002 is moved downward in the direction 1032 to engage with the lower part 1004 of the bending die to form an opening 1015 around the tube.

[0164] Then, the bending die 1000 rotates about axis 1036 in direction 1034, while the tail of the tube is supported by the clamping die. The bending die 1000 rotates in direction 1034 to impart the desired angle range to the bend 900. Once the bend 900 has been formed, the upper part 1002 of the bending die moves upward in direction 1033, and the tube is displaced relative to the bending die 1000 to position another portion of the tube in the bending die 1000 for bending. Continuing the example, the tube is repositioned to advance the second portion of the tube into the opening 1013, the bending die 1000 is closed, and the bending die 1000 is rotated in the opposite direction to direction 1034. The process of advancing and bending the tube is repeated until the desired number of bends has been imparted to the tube.

[0165] about Figure 36 A tube 1100 is provided, having a bend 1102 and a straight section 1103. The bend 1102 has a pleated portion 1104, similar to the pleated portions discussed above. The pleated portion 1104 has troughs 1106 and crests 1108. The tube 1100 has a flat cross-section at the troughs 1106, crests 1108, and / or the straight section 1103. The flat cross-section of the tube 1100 allows it to be tightly stacked with adjacent tubes, for example, in a coil assembly of a cooling tower. The flat cross-section of the tube 1100 also improves its thermal performance.

[0166] The flat cross-section of tube 1100 can be, for example, an elliptical cross-section. Regarding... Figure 37A The slewing bend 1102 includes a trough elliptical wall portion 1110 at the trough 1106. The trough elliptical wall portion 1110 has a primary dimension 1112 and a secondary dimension 1114.

[0167] about Figure 37BThe bend in the rotation 1102 has a crest elliptical wall portion 1116 at the crest 1108, which has a primary dimension 1120 and a secondary dimension 1122. The primary dimension 1120 of the crest 1108 is larger than the primary dimension 1112 of the trough 1106. In one embodiment, the secondary dimension 1122 of the crest 1108 is smaller than the secondary dimension 1114 of the trough 1106.

[0168] about Figure 37C The curved portion 1102 has a straight elliptical wall portion 1126 at the straight portion 1103, which has a primary dimension 1128 and a secondary dimension 1130. In one embodiment, the primary dimension 1128 of the straight portion 1103 is smaller than the primary dimensions 1112 and 1120, and the secondary dimension 1130 is larger than the secondary dimensions 1114 and 1122.

[0169] The flat cross-section of the portion of tube 1100 can be provided in a variety of different ways. For example, a tube bending machine used to bend the tube and impart a pleated portion 1104 can flatten the bend 1102 during the bending process. In another method, the tube initially has an elliptical cross-section, and the bending process imparts a pleated portion 1104 to the bend 1102 without further flattening the tube. In yet another method, a tube bending machine is used to form one or more bends in the tube, and a press is used to flatten the tube after the bending process.

[0170] Unless otherwise stated herein or clearly contradicted by the context, singular terms such as “a” or “one” are used to encompass both singular and plural. The terms “including,” “having,” “containing,” and “accommodating” will be interpreted as open-ended terms. The phrase “at least one” as used herein is intended to be interpreted in a disjunctive sense. For example, the phrase “at least one of A and B” is intended to encompass A, B, or A and B.

[0171] Although specific embodiments of the invention have been described and illustrated, it will be understood that many variations and modifications will occur to those skilled in the art, and the invention is intended to cover all such variations and modifications that fall within the scope of the appended claims. For example, the bends disclosed herein can be used in a variety of heat exchange devices, such as evaporative condensers, air-cooled condensers, closed-loop fluid coolers, closed-loop cooling towers, open-loop cooling towers, dry coolers, ice storage systems, heat storage coils, and / or water-cooled coils, as some examples.

Claims

1. An indirect heat exchanger pressure vessel comprising: an inlet header for receiving pressurized working fluid; an outlet header for collecting pressurized working fluid; a serpentine return circuit connecting the inlet header and outlet header and allowing the pressurized working fluid to flow from the inlet header to the outlet header; the serpentine return circuit comprising a tube and a return bend connecting the tube; wherein the return bend comprises an inner arc and an outer arc; the return bend comprising a side surface portion intermediate the inner arc and outer arc, the return bend having a controlled corrugation portion between the side surface portions; and the controlled corrugation portion comprising alternating ridges and troughs, wherein the controlled corrugation portion of the return bend comprises a sinusoidal curve at the inner arc of the return bend, the sinusoidal curve comprising peaks at the ridges and troughs at the troughs of the bend; wherein each ridge extends from the inner arc of the return bend toward the side surface portion of the return bend; and wherein each ridge increases in width as it extends from the inner arc of the return bend toward the side surface portion of the return bend, each ridge having a first width at the inner arc that is less than a second width thereof at either of the side surface portions.

2. The indirect heat exchanger pressure vessel of claim 1, wherein, the inlet header, the outlet header, and the serpentine return circuit are configured to operate at an internal pressure of at least 150 psig.

3. The indirect heat exchanger pressure vessel of claim 1, wherein, the inlet header, the outlet header, and the serpentine return circuit are configured to operate at an internal pressure of at least 410 psig.

4. The indirect heat exchanger pressure vessel of claim 1, wherein, the inlet header, the outlet header, and the serpentine return circuit are configured to operate at an internal pressure of at least 1200 psig.

5. The indirect heat exchanger pressure vessel of claim 1, wherein, the serpentine return circuit comprises a pair of cut points at a junction between the return bend and the tube of the serpentine return circuit; the return bend has a bend angle; the controlled corrugation portion of the return bend is spaced apart from the cut points along the serpentine return circuit; and wherein the controlled corrugation portion of the return bend has an angular range around the inside of the return bend that is less than the bend angle. the controlled corrugation portion of the return bend comprises an arcuate curve intersecting the sinusoidal curve of the bend, the arcuate curve comprising:

6. The indirect heat exchanger pressure vessel of claim 1, wherein, a peak arc intersecting the peaks; and a trough arc intersecting the troughs. at least one of the peak arcs has a first radius of curvature and at least one of the trough arcs has a second radius of curvature, wherein the first radius of curvature and the second radius of curvature are substantially the same.

7. The indirect heat exchanger pressure vessel of claim 6, wherein, the ridges comprise terminal ridges adjacent the tube of the serpentine return circuit; and 8. The indirect heat exchanger pressure vessel of claim 1, wherein, wherein at least one of the terminal ridges comprises a tapered lead-in portion to smooth the flow of the pressurized working fluid around the ridges and troughs. the return bend has a bend radius and comprises a tubular side wall extending around the interior of the return bend; 9. The indirect heat exchanger pressure vessel of claim 1, wherein, wherein the tubular side wall comprises: ​ a first semi-circular inner wall portion, a first outer wall portion, and a pair of first connecting wall portions at each ridge of the swivel bend, the first connecting wall portions being on opposite sides of the swivel bend interior connecting the first semi-circular inner wall portion and the outer wall portion, wherein the first semi-circular inner wall portion, outer wall portion, and the first connecting wall portions are radially aligned; and a second semi-circular inner wall portion, a second outer wall portion, and a pair of second connecting wall portions at each groove of the swivel bend, the second connecting wall portions being on opposite sides of the swivel bend interior connecting the second semi-circular inner wall portion and the second outer wall portion, wherein the second semi-circular inner wall portion, second outer wall portion, and the second connecting wall portions are radially aligned.

10. The indirect heat exchanger pressure vessel of claim 9, wherein, the first semi-circular inner wall portion has a first radius of curvature and the second semi-circular inner wall portion has a second radius of curvature that is substantially the same as the first radius of curvature.

11. The indirect heat exchanger pressure vessel of claim 9, wherein, the first semi-circular inner wall portion has a first angular range and the second semi-circular inner wall portion has a second angular range, wherein the first angular range and the second angular range are each greater than 90 degrees.

12. The indirect heat exchanger pressure vessel of claim 11, wherein, the first angular range is greater than the second angular range.

13. The indirect heat exchanger pressure vessel of claim 1, wherein, the pipe of the serpentine loop tube includes a plurality of pairs of pipes; and wherein the swivel bends include a plurality of swivel bends connecting the plurality of pairs of pipes.

14. The indirect heat exchanger pressure vessel of claim 1, wherein, the swivel bend includes: a first bend including a first controlled fold portion of the controlled fold portion; a second bend including a second controlled fold portion of the controlled fold portion; and a straight portion of the serpentine loop tube connecting the first bend and the second bend.

15. The indirect heat exchanger pressure vessel of claim 14, wherein, the first bend has a first bend angle that is greater than or equal to 90 degrees and the second bend has a second bend angle that is less than or equal to 90 degrees.

16. The indirect heat exchanger pressure vessel of claim 1, wherein, the swivel bend includes a plurality of swivel bends; and wherein the swivel bends of the serpentine loop tube have a common centerline.

17. The indirect heat exchanger pressure vessel of claim 1, wherein, the swivel bend has a bend angle of 180 degrees and the controlled fold portion of the bend has an arc length that is less than or equal to 180 degrees.

18. The indirect heat exchanger pressure vessel of claim 1, wherein, the pipe of the serpentine loop tube includes a pipe having a non-circular cross-sectional shape.

19. The indirect heat exchanger pressure vessel of claim 1, wherein, the controlled fold portion includes at least one tapered lead-in portion.

20. The indirect heat exchanger pressure vessel of claim 1, wherein, the serpentine loop tube has an outer diameter (OD), the serpentine loop tube has a wall thickness (WT), and the swivel bend has a centerline radius (CLR); wherein the coefficient of bending complexity (C B ) of the rotary bend is given by the following equation: wherein the bend complexity factor is greater than or equal to 10.

21. The indirect heat exchanger pressure vessel of claim 20, wherein, the bend complexity factor is less than or equal to 20.

22. The indirect heat exchanger pressure vessel of claim 1, wherein, the serpentine loop tube includes a plurality of serpentine loop tubes; and wherein the serpentine loop tubes contact each other.

23. The indirect heat exchanger pressure vessel of claim 1, wherein, the serpentine loop tube includes a plurality of serpentine loop tubes; and wherein the swivel bends of the serpentine loop tube do not contact each other.

24. The indirect heat exchanger pressure vessel of claim 1, wherein, the swivel bend of the serpentine loop tube has a non-circular cross-sectional shape.

25. The indirect heat exchanger pressure vessel of claim 1, wherein, the swivel bend of the serpentine loop tube has an elliptical cross-sectional shape.

26. The indirect heat exchanger pressure vessel of claim 1, wherein, the controlled fold portion is asymmetric about a plane bisecting the swivel bend.

27. The indirect heat exchanger pressure vessel of claim 1, wherein, The swivel bend has a bending angle of 180 degrees; and wherein the controlled pleat portion is asymmetric about a plane bisecting the swivel bend.

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