Indirect heat exchanger pressure vessel with controlled corrugated bends

Abstract

In one aspect of the present 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 pressurized working fluid, and a serpentine loop tube connecting the inlet header and the outlet header. The serpentine loop tubes allow pressurized working fluid to flow from the inlet header to the outlet header. The serpentine loop pipe comprises a pipeline and a rotary bending part connected with the pipeline. The turning bend has a controlled pleat portion that includes alternating ridges and grooves. The alternating ridges and grooves reinforce the turning bends and allow the indirect heat exchanger pressure vessel to facilitate heat transfer of the working fluid at high internal working pressures.

Description

[0001] This application is a divisional application of the invention patent application No. 2022800007323 entitled "Indirect Heat Exchanger Pressure Vessel with Controlled Wrinkled Bending Section".

[0002] Cross-references to related applications

[0003] 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

[0004] 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

[0005] 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.

[0006] 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.

[0007] 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).

[0008] For example, a heat exchanger apparatus can include a closed circuit cooling tower having an indirect heat exchanger pressure vessel that includes an inlet header that receives pressurized working fluid, an outlet header, and an indirect heat exchange coil connecting the inlet header and the outlet header. The indirect heat exchange coil can include one or more serpentine loop tubes configured to transfer heat between the pressurized working fluid inside the indirect heat exchange coil and a fluid (e.g., evaporative liquid) outside the indirect heat exchange coil. The inlet header receives the internal working fluid from an upstream component of the heat exchanger apparatus before the working fluid is directed to a downstream component of the heat exchanger apparatus, and the outlet header collects the pressurized working fluid.

[0009] The indirect heat exchanger pressure vessel, including the inlet header, the outlet header, and the one or more serpentine loop tubes, is required to withstand high pressures appropriate for the particular application and to meet engineering standards, both domestic and international, such as ASME Standard B31.5. For example, the indirect heat exchanger pressure vessel of a closed circuit cooling tower can be rated to withstand an internal pressure 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 can be able to withstand an internal pressure of up to 410 psig or more for typical refrigerants (e.g., ammonia or R-407C). As yet another example, some evaporative condensers have an indirect heat exchanger pressure vessel rated for an internal pressure of 1200 psig or more for refrigerants such as carbon dioxide.

[0010] The serpentine loop tubes of the indirect heat exchanger pressure vessel typically include straight lengths and bends connecting the straight lengths. The straight lengths of the serpentine loop tubes are typically connected by a bend of approximately 180 degrees or by a compound bend having multiple bends (e.g., two 90 degree bends connected by a tube length). During assembly of the heat exchanger apparatus, the serpentine loop tubes can be stacked together with the serpentine loop tubes typically contacting each other in the area of the return bends and with the serpentine loop tubes having a vertically staggered orientation.

[0011] Manufacturing a serpentine loop tube typically begins with forming an elongated tube from a long, flat strip of metal, such as low carbon steel or stainless steel. The flat metal strip is rolled into a generally circular cross-section, and the longitudinal edges are welded together by a continuous longitudinal weld to form a straight tube. In another method, a seamless tube forming process is used to form the straight tube. The resulting straight tube can then be bent at spaced locations along the tube to form the tube into a serpentine shape, with the straight tube sections being connected by bends. Tube bending is a complex process, and typically uses a hydraulic, electric, or hand driven tube bender having a bending die, a clamping die, a pressing die, and optionally a mandrel and wiper die. The tube bender can be set to form bends having any desired angle, up to and including 180 degree bends (e.g., 80 degrees, 90 degrees, 100 degrees, or 180 degrees). As noted above, the return bends of a serpentine loop tube can include compound bends, each having two or more bends, such as an 80 degree bend and a 100 degree bend connected by a section of straight tube.

[0012] To form a bend in a tube, the tube is fed into the tube bender, and a portion of the tube is seated in the recess of the bending die. The pressing die, which has a recess for the tube, and the clamping die are moved against opposite sides of the tube so that the pressing die is positioned to support the tube and the clamping die clamps the tube portion between the clamping die and the bending die. The tube bender then rotates or pivots the bending die and clamping die through the desired bending angle. As the bending die and clamping die pivot, the pressing die moves forward to support the tube and ensure that the tube follows the contour of the bending die. Once the bend is formed in the tube, the clamping die and pressing die are retracted from their clamping position, the tube is fed forward until the next bending location of the tube is positioned in the tube bender, and then the bending die, clamping die, and pressing die are all moved back to their initial positions. This bending process is repeated for each bend to be formed in the serpentine loop tube. Some tubes are bent only once to form a single-bend tube, which are often referred to as hairpin tubes or crutch tubes, which can then be butt welded together.

[0013] Bending of tubes for receiving pressurized working fluid is a process that balances a variety of considerations, including performance, safety, and packaging standards for a particular application. In addition, during the bending process, unintended deformation in the tube wall can lead to tube failure due to the pressure of the working fluid within the tube, corrosion of the tube, and / or high pressure drop of the working fluid flowing through the tube. In some tube bending processes, an internal mandrel is advanced into the interior of the tube to support the tube wall during bending, and a wiper die can be used to harden the tube wall at the inside tail end of the bend to prevent unintended deformation within the tube. The internal mandrel can be a sizing mandrel or can have one or more balls or rings, in which case the internal mandrel is referred to as a ball mandrel.

[0014] Pipe bending generally involves the following parameters:

[0015] OD = Outside diameter of the pipe

[0016] WT = Wall thickness of the pipe

[0017] CLR = Centerline radius of the bend

[0018] Dimensions are measured using common measurement scales, such as inches or millimeters. These parameters are used to calculate the following two characteristic ratios:

[0019]

[0020]

[0021] Two additional parameters in the bending process are the outside radius of the bend (OSR), which is often referred to as the extrados, and the inside radius of the bend (ISR), which is often referred to as the intrados.

[0022] The W and D ratios are further combined into a single factor, which indicates the complexity of the bend. This factor is calculated as follows:

[0023]

[0024] The values of W, D, and / or C B can be used to determine whether a bend can be formed without an internal mandrel, referred to as empty bending, or whether an internal mandrel is necessary, in which case the process is referred to as mandrel bending. For mandrel bending, these ratios help determine whether the internal mandrel required should be a multiple ball mandrel, a single ball mandrel, or a simpler sizing mandrel. Finally, these ratios help determine whether a knockout caliper mold needs to be used in conjunction with the internal mandrel. For example, the recommended bending processes for a variety of bending complexities are shown in the following table:

[0025]

[0026] Table 1: Bend complexity values and recommended bending process table

[0027] The W, D, and / or C B ratios are typically looked up on industry standard pipe bending charts to determine the type of pipe bending process required. For example, to determine the process parameters for a pipe with a bend outside diameter of 1”, a wall thickness of 0.05”, and a centerline radius of 2”, the ratios of W and D are:

[0028]

[0029]

[0030] Considering the W ratio of 20 and the D ratio of 2, an industry standard tube bending chart can recommend that a standard pitch internal mandrel with 1 ball should be used, supplemented with stripper jaw dies.

[0031] Alternatively, for the C B value of the above example bend is:

[0032]

[0033] Referring to the above table, this C B value also indicates that an internal mandrel is recommended, although stripper jaw dies can be optional. The slight difference in the recommendations regarding mandrels and stripper jaws indicates that there is some flexibility in the bending configuration, where tool design and tube material selection can sometimes make up for the lack of an internal mandrel and / or stripper jaw dies.

[0034] The range of conventional bending charts and bend complexity values (C B ) discussed above that are used in the industry are based on the assumption that the profile of the tool slot (where the tube is located during the bending process) formed by the bending and clamping dies is circular, complementary to the shape of a round tube. However, there have been some advances in the design of bending tools in recent years, and it is possible to design a bending tool with a compound radius in the tool slot to compress and support the tube during the bending process, and to expand the range of mandrel-less bending, C B values from about 5 to about 12.

[0035] In addition to this, especially when C B approaches and exceeds 20, there is an increasing need to use internal mandrels and stripper jaw dies to successfully bend the tube. The internal mandrel bending process has several drawbacks, including the need for additional tooling to use the mandrel, which increases cost; can increase scrap if the mandrel is used incorrectly; can increase cycle time; and requires the use of lubricants, which increases the time and cost of lubrication and subsequent environmental remediation efforts.

[0036] When C BOne issue that arises near and beyond 20 is that the associated mandrel bending places a limit on the continuous length of the tube. Serpentine loop tubes can be very long, up to 400 feet for some applications. The physical limitations of the mandrel rod length and setup mean that an internal mandrel cannot be used to bend long and continuous serpentine loop tubes with multiple bends. This forces manufacturers to form one or two bends in short tube segments (sometimes referred to as canes), then butt weld the tube segments together to form a larger loop. This not only involves additional labor and cost, but the additional butt welds increase the likelihood of leaks, and can not be allowed in many applications since the serpentine loop tube will be subjected to high working pressures.

[0037] When C B Another issue that can arise near and beyond 20 is that the associated internal mandrel bending brings the neutral axis of the bend closer to the inside of the bend, and can cause the outer wall portion of the bend to be excessively thinned. Thinning of the outer wall portion of the bend weakens the serpentine loop tube, such that the serpentine loop tube cannot withstand the pressure of the working fluid for a particular application. Excessive thinning of the outer wall of the bend also creates variability in the process when forming the bend, resulting in a decrease in quality of the bend area.

[0038] The above issues make it desirable for manufacturers to avoid using internal mandrels for tube bending. One way to avoid using an internal mandrel for a tube with a given OD is to increase the WT to a suitable value or increase the CLR to a suitable value to bring the bend within the range of mandrel-free bending. Manufacturers whose products do not require such relatively thick walls from an operational standpoint can not choose to increase the wall thickness (WT). In some cases, a thicker wall can increase the pressure drop on the fluid side, can decrease the thermal efficiency of the product, increase the weight of the assembly, and can increase the material cost of the serpentine loop tube. Additionally, increasing the CLR can not be an option in cases where the serpentine loop tube needs to fit within a given space for other operational considerations. Increasing the CLR can also have a negative impact on overall coil thermal and hydraulic efficiency in some cases. SUMMARY

[0039] 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, an outlet header for collecting the pressurized working fluid, and a serpentine circuit tube connecting the inlet header and the outlet header and allowing the pressurized working fluid to flow from the inlet header to the outlet header. The pressurized fluid can be, for example, water, glycol, glycol mixture, ammonia, or carbon dioxide, as some examples. The pressurized fluid can be a liquid such as water, or a liquid / gas combination such as refrigerant liquid and refrigerant vapor. The serpentine circuit tube includes a tube run and a return bend connecting the tube run. The return bend includes a controlled crease portion that includes alternating ridges and grooves. The controlled crease portion of the return bend provides a rigid structure that resists internal pressure during operation of the indirect heat exchanger pressure vessel. In addition, the controlled crease portion provides a constructed bend centerline radius that is greater than an actual bend centerline radius of the return bend. The greater structural bend centerline radius reduces a bend complexity factor of the return bend compared to a return bend of a conventional serpentine circuit tube having the same outer diameter and wall thickness. As a result of the reduced bend complexity factor, the return bend having the controlled crease portion can be bent without the use of an internal mandrel, which simplifies the manufacturing process of the serpentine circuit tube.

[0040] The disclosure also provides an indirect heat exchanger pressure vessel that includes an inlet header for receiving a pressurized working fluid, an outlet header for collecting the pressurized working fluid, and a serpentine circuit tube connecting the inlet header and the outlet header to allow the pressurized working fluid to flow from the inlet header to the outlet header. The serpentine circuit tube includes a tube run, a return bend connecting the tube run, and a tangent point at a junction between the return bend and the tube run. The return bend includes a bend angle and a controlled crease portion. The controlled crease portion is spaced apart from the tangent point along the serpentine circuit tube and has an angular extent around an inside of the return bend that is less than the bend angle. In this manner, the controlled crease portion can be formed using a bending die having a corresponding controlled crease forming feature that is less than an entire inside arc face of the return bend to allow the serpentine circuit tube to slide longitudinally out of the bending die and improve the speed of forming the return bend in the serpentine circuit tube. In one embodiment, the controlled crease portion includes a ridge having a smaller wave amplitude near the tangent point and increasing as the crease portion extends away from the tangent point to reduce resistance to fluid flowing through the return bend and reduce internal fluid pressure drop at the return bend relative to a non-tapered or non-eased configuration of the crease ridge.

[0041] In another aspect, an indirect heat exchanger pressure vessel is provided that includes an inlet header for receiving a pressurized working fluid, an outlet header, and a serpentine circuit tube connecting the inlet header and the outlet header to facilitate flow of the pressurized working fluid from the inlet header to the outlet header. The serpentine circuit tube includes a pair of runs and a reverse bend connecting the runs. The reverse bend includes an inner portion having a sinusoidal wave curve at an inner arc of the reverse bend, the sinusoidal wave curve including a peak and a valley. The inner portion of the bend includes an arcuate curve intersecting the sinusoidal wave curve, the arcuate curve including a peak arc intersecting the peak and a valley arc intersecting the valley. The intersecting sinusoidal wave curve and arcuate curve provide a smooth, continuous curved sidewall of the serpentine circuit tube that enhances the resistance of the reverse bend to internal pressure. In one embodiment, the sinusoidal wave curve has one or more end portions having shallower peaks and valleys and a middle portion having deeper peaks and valleys to reduce internal fluid pressure drop through the reverse bend (as compared to a sinusoidal wave pattern having constant peaks and valleys).

[0042] The present disclosure also provides a closed circuit cooling tower including an indirect heat exchanger having a plurality of serpentine circuit tubes having runs and reverse bends connecting the runs. The reverse bends include a pleated bend having a controlled pleat portion. The closed circuit cooling tower includes a fan operable to generate an airflow relative to the serpentine circuit tubes and an evaporative liquid distribution assembly configured to distribute evaporative liquid onto the serpentine circuit tubes. The closed circuit cooling tower further includes a sump for receiving evaporative liquid falling from the serpentine circuit tubes and a pump operable to pump evaporative fluid from the sump back to the evaporative liquid distribution assembly. The controlled pleated bend strengthens the serpentine circuit tube to withstand internal pressure from working fluid within the serpentine circuit tube during operation of the cooling tower. The controlled pleated bend also provides a centerline radius of construction of the pleated bend that is greater than an actual centerline radius of the controlled pleated bend and provides a reduced bend complexity factor (as compared to a reverse bend of a conventional serpentine circuit tube having the same outer diameter and wall thickness). The reduced bend complexity factor allows the controlled pleated bend to be bent without the use of an internal mandrel, which simplifies the manufacturing process of the serpentine circuit tube. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a perspective view of an indirect heat exchange apparatus having a serpentine circuit tube, the runs of which are connected by a bend of the serpentine circuit tube;

[0044] Figure 2 is a schematic view of a heat exchange apparatus including a serpentine circuit tube;

[0045] Figure 3 is a side view of a serpentine circuit tube having runs connected by a 180 degree bend;

[0046] Figure 4 is an enlarged view of the curved portion shown in dashed circle in Figure 3 , showing the controlled fold portion inside the curved portion;

[0047] Figure 5 is a cross-sectional view taken along line 5-5 in Figure 4 , showing the curved portion cross-section at the trough of the fold portion;

[0048] Figure 6 is a cross-sectional view taken along line 6-6 in Figure 4 , showing the curved portion cross-section at the ridge of the fold portion;

[0049] Figure 7 is a cross-sectional view taken along line 7-7 in Figure 4 , showing the cross-section of one of the circuit tubes;

[0050] Figure 8 is a perspective view of the curved portion of Figure 4 , showing the fold portion inside the curved portion and the smooth outer wall portion outside the curved portion;

[0051] Figure 9A is a cross-sectional view taken along line 9A-9A in Figure 8 , showing the sinusoidal curve of the fold portion spaced apart from the tangent points of the curved portion and the tubes such that the fold portion has an angular range less than the 180-degree bend angle of the curved portion;

[0052] Figure 9B is a cross-sectional view of the curved portion of another embodiment similar to Figure 9A , the curved portion having a fold portion with a sinusoidal curve having ridges and troughs of different amplitudes;

[0053] Figure 9C is a cross-sectional view of the curved portion of another embodiment similar to Figure 9A , the curved portion having a fold portion with a sinusoidal curve having ridges and troughs of different amplitudes and without a period;

[0054] Figure 10 , Figure 11 , Figure 12 , Figure 13A and Figure 13B show the process of determining the sinusoidal curve of the curved portion;

[0055] Figure 14 is a graphical representation of a portion of the sinusoidal curve of the fold portion of the curved portion, showing the peaks and troughs of the sinusoidal curve;

[0056] Figure 15It 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;

[0057] 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;

[0058] Figure 16B It is similar to Figure 16A A graphical representation of a wave crest arc with a composite radius of curvature;

[0059] 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;

[0060] 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.

[0061] Figure 17B It is similar to Figure 17A A graphical representation of a trough arc with a composite radius of curvature;

[0062] 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;

[0063] 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;

[0064] Figure 19 This is a perspective view of a pipe bending machine, showing the bending die, clamping die, and holding die.

[0065] 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;

[0066] Figure 21 , Figure 22 , Figure 23 , Figure 24 , Figure 25 and Figure 26 It shows the use ofFigure 19 the process of a tube bender forming a bend of a serpentine circuit tube;

[0067] Figure 27 is a top view of a tube being bent by a tube bender and a lower portion of a bending die showing the engagement between the ridge of the bend wrinkle portion and the ridge of the bending die; and Figure 19

[0068] Figure 28 Figure 29 Figure 30 are elevational views of bends having bend angles of ninety degrees, eighty degrees, and one hundred degrees, respectively;

[0069] Figure 31 is a cross-sectional view of a serpentine circuit coil including a tube having a cross-section that tapers to flatten;

[0070] Figure 32 is an elevational view of a compound bend of a pair of serpentine circuit tubes having three points of contact therebetween, each compound bend including an 80 degree bend and a 100 degree bend;

[0071] Figure 33 is an elevational view of a bend having an asymmetric wrinkle pattern;

[0072] Figure 34 is a perspective view of a lower portion of a bending die for forming the bend of Figure 33

[0073] Figure 35 is a perspective view of a lower portion of a bending die and a corresponding upper portion of a bending die of Figure 34

[0074] Figure 36 is a plan view of a tube having a flattened cross-section, the tube including a straight portion and a return bend having a wrinkle portion;

[0075] Figure 37A is a cross-sectional view taken along line 37A-37A in Figure 36

[0076] Figure 37B is a cross-sectional view taken along line 37B-37B in Figure 36

[0077] Figure 37C is a cross-sectional view taken along line 37C-37C in Figure 36 DETAILED DESCRIPTION ​​​​​​​​

[0078] With reference to Figure 1 , an indirect heat exchanger pressure vessel, such as coil assembly 10, is provided that can be used in a heat exchange device, such as an evaporative condenser, closed circuit fluid cooler, or ice storage system. Coil assembly 10 includes an inlet header 12, an outlet header 14, and a serpentine circuit tube 16. Serpentine circuit tube 16 includes a tube 18 connected to a 180 degree bend 20 or a compound bend 21 that includes two 90 degree bends 23, 25 separated by a straight section 27. Serpentine circuit tube 16 allows working fluid to flow from inlet header 12, through serpentine circuit tube 16, to outlet header 14.

[0079] With reference to Figure 2 , a heat exchange device, such as cooling tower 24, is provided that includes an outer structure 26, one or more fans 28 including fan blades 30 and a motor 32, a direct heat exchanger such as fill 34, and an indirect heat exchanger pressure vessel 36. As some examples, cooling tower 24 can be an evaporative condenser, closed circuit cooling tower, or dry cooler heat exchanger. Indirect heat exchanger pressure vessel 36 includes an inlet header 38, one or more serpentine circuit tubes 37 having circuit tubes 39 and bends 40, and an outlet header 42. Inlet header 38 and outlet header 42 can be interchanged depending on the application. In some embodiments, fill 34 is located above indirect heat exchanger pressure vessel 36 and / or fill 34 is located between the tubes of serpentine circuit tubes 37.

[0080] With reference to Figure 2 , cooling tower 24 includes an evaporative liquid distribution system 43 that includes a spray assembly 44 having nozzles or orifices 46 that distribute an evaporative fluid, such as water, onto serpentine circuit tubes 37 and fill 34. Evaporative liquid distribution system 43 includes a sump 50 for collecting evaporative fluid from fill 34 and coil 36, and a pump 52 that pumps the collected evaporative fluid through a pipe 54 to spray assembly 44. Cooling tower 24 also includes one or more air inlets 35, inlet louvers 58 that prevent evaporative liquid from exiting cooling tower 24, an air outlet 59, and an eliminator 56 for collecting water mist from air before the air exits air outlet 59. Fans 28 are operable to create or direct an airflow to flow upward relative to serpentine circuit tubes 37 and fill 34. In other embodiments, cooling tower 24 can have one or more fans configured to direct an airflow in an upward flow, downward flow, or lateral flow direction relative to the indirect heat exchanger and / or direct heat exchanger of cooling tower 24.

[0081] With reference to Figure 3 , a serpentine circuit tube 70 is provided that can be used with a heat exchange device, such asFigure 1 coil assembly 10 in FIG. 1, or the cooling tower 24 discussed above with respect to Figure 2 The serpentine loop tube 70 includes an internal passage 72 and a tubular sidewall 74 extending therearound. The serpentine loop tube includes an end portion 76 connectable to an inlet header and an end portion 78 connectable to an outlet header. Depending on the application, the end portion 76 can instead be connected to the outlet header, and the end portion 78 can be connected to the inlet header. The serpentine loop tube 70 includes runs 79 (e.g., runs 80, 82) and bends 84. In one embodiment, the runs 79 can be parallel. In other embodiments, one or more of the runs 80 extend laterally (e.g., obliquely) relative to one another to allow internal fluid drainage. The serpentine loop tube 70 can be self-draining such that any liquid in the internal passage 72 flows downward under the force of gravity toward the end portion 78. The material of the serpentine loop tube 70, the outer diameter of the serpentine loop tube 70, the wall thickness of the sidewall 74, the number of runs 79, the length of the runs 79, the number of bends 84, the angular extent of the bends 84, the centerline radius of the bends 84, and the inside / outside arc of the bends 84 can be selected for a particular heat exchange apparatus. As another example in this regard, instead of a single angled bend 84 connecting a pair of runs 79, the serpentine loop tube can have one or more bends 84 each including a pair of bends (e.g., 90 degrees) connected by a straight section, similar to the compound bend 21 shown in FIG. 1. Figure 1 The runs 80 can have a circular cross-section throughout the run 80. In other embodiments, the serpentine loop tube 70 includes one or more runs 80 having a non-circular cross-section (e.g., an elliptical or obround cross-section).

[0082] The serpentine loop tube 70 can be formed from a single straight tube that is bent at spaced locations along the tube to form the bends 84. The serpentine loop tube 70 can be formed by progressively rolling an elongated strip of material into a tubular shape and welding the longitudinal edges of the elongated strip together to form a single weld extending along the length of the serpentine loop tube 70. In another method, the serpentine loop tube 70 can be made from a plurality of separately formed components. For example, the runs 79 can be separate components that are welded to the bends 84. Alternatively, the serpentine loop tube 70 can be formed by welding separate tube sections together and then bending the longer welded tube. The serpentine loop tube 70 can be made from a metallic material, such as carbon steel or stainless steel.

[0083] with respect to 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.

[0084] 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.

[0085] 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, the relief portions 222 and 224 each have a first radius, and the 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.

[0086] 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.

[0087] 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'.

[0088] With reference to Figure 9C , a cross-sectional view of a bend 84" is provided that is similar to bend 84 and has a controlled corrugation portion 94" with a sinusoidal wave pattern 110" at the inner arc 90 of bend 84". The controlled corrugation portion 94" includes ridges 114" and troughs 116". The controlled corrugation portion 94" includes a first portion 115" having ridges 114"A, 114"B and troughs 116"A, 116"B having a first wave amplitude and a first period 117". The controlled corrugation portion 94" includes a second portion 119" having ridges 114"C, 114"D and troughs 116"C, 116"D having a second wave amplitude that is greater than the first wave amplitude. The ridges 114"C, 114"D and troughs 116"C, 116"D have a second period 121" that is less than the first period 117". The controlled corrugation portion 94" further includes a third portion 123" having ridges 114"E, 114"F and troughs 116"E, 116"F having a third wave amplitude that is substantially the same as the second wave amplitude of the second portion 119" and a third period 125" that is less than the second period 121". The bend 84" receives fluid in a direction 127" and the ridges 114"A include a tapered lead-in portion 129" to smoothly flow the fluid through the bend 84". The tapered lead-in portion 129" reduces pressure drop across the bend 84" and improves discharge of the fluid in the bend 84".

[0089] The characteristics of the sinusoidal wave curve 110 for a given turn bend can be selected for a particular application. For example, the number of ridges / troughs, the wave amplitude, the period, and / or one or more tapered lead-in portions can be selected for a particular application. The characteristics of the turn bend can vary throughout the turn bend, for example, the wave amplitude and period vary throughout the turn bend. The shape of the controlled corrugation portion 94 is formed at least in part by two different intersecting cross-sectional profiles. As shown in Figure 4 and Figure 15 , the controlled corrugation portion 94 includes a sinusoidal wave portion 110 at the inner arc 90 of the bend 84. Another curve is an arcuate curve 150 that includes alternating peak arcs 152 and trough arcs 154. As shown in Figure 16A and Figure 17A , the peak arcs 152 have a peak arc radius 152' and a center 182 and the trough arcs 154 have a trough arc radius 158 and a center 172. In this embodiment, the peak arcs 152 and the trough arcs 154 are substantially the same. As used herein, the term "substantially the same" means dimensions that are virtually the same, for example, within + / - 10% of each other, when manufacturing variations are taken into account. The peak arcs 152 extend through an angle 160 that is greater than an angle 162 through which the trough arcs 154 extend.

[0090] AsFigure 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.

[0091] 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 peak arc 152' has different radii 156A', 156B'. Each radius of the peak arc 152' is tangent at the point where the radius meets the adjacent radius. Likewise, in Figure 17B The valley arc 154' has different radii 158A', 158B'.

[0092] In another embodiment, the peak arc 152 and / or the valley arc 154 has the shape of a portion of an ellipse. For example, Figure 16C The peak arc 152" is an arc defined by an angle 160" (e.g., 160 degrees) between points 426", 430" of an ellipse 439 having a major dimension 441 and a minor dimension 443. Similarly, Figure 17C The valley arc 154" has a shape defined by an angle 162" (e.g., 142 degrees) between points 445, 447 of an ellipse 449 having a major axis 451 and a minor axis 453.

[0093] With regard to Figure 7 The tubing 82 is shown with a sidewall 74 having a circular cross-section with a center at the tube centerline 102. The sidewall 74 can also have a non-circular cross-section, such as an elliptical or rectangular cross-section. The sidewall 74 of the serpentine return tube 70 has a wall thickness 190 extending around the interior passage 72.

[0094] With regard to Figure 8 The segments of tubing 80, 82 and bend 84 are shown in perspective view. As seen above, the controlled fold portion 94 has a continuous curved controlled fold surface 134 including 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, which connect curved ridge surface portions of adjacent ridges 114. The ridge surface portions 200 and groove surface portions 202 form a continuous, undulating appearance of the controlled fold portion 94.

[0095] With regard to Figure 9AThe serpentine loop tube 70 has an outer diameter 210 and a wall thickness 190. The tube centerline 102 extends through the runs 80, 82 and the bend 84. The serpentine loop tube has junctions 214, 215 between the runs 80, 82 and the bend 84. At the junctions 214, 215, the tube 70 includes tangent points 122, 124 between the runs 80, 82 and the bend 84. The bend 84 includes reliefs 222, 224 that extend away from the tangent points 122, 124, and the tapered lead-in portions 140, 142 are angled radially inward toward the crests 130, 132 of the terminal ridges 118, 120. The bend 84 has a center 230 and a centerline radius 232 that extends from the center 230 to the tube centerline 102. In the illustrated embodiment, the bend 84 has a bend angle 220 of 180 degrees, and the controlled crimp portion 94 extends around the center 230 through a controlled crimp portion angle 240 that is less than the bend angle 220. For example, the controlled crimp portion angle 240 can be 5° or less, 10° or less, or 15° or less than the bend angle 220. In one embodiment, the bend angle is 180 degrees, and the crimp portion angle 240 is about 166 degrees.

[0096] Referring again to Figure 9A , the controlled crimp portion 94 positions a crest 250 of the ridge 114 at the inside camber 90 of the bend 84 (see Figure 4 ), and positions a trough 252 of the groove 116 radially outward from the crest 250. By positioning the trough 252 outside of the inside camber 90 of the bend 84, the crimp portion 94 creates a constructed bend centerline 254. The constructed bend centerline 254 has a constructed bend centerline radius 256 that is greater than the centerline radius 232 of the tube centerline 102. Because the constructed bend centerline radius 256 is greater than the bend centerline radius 232, for a given bend inside and outside cambers, the bend 84 has a lower bend complexity ratio than a conventional bend having the same inside and outside cambers, outer diameter, and wall thickness. Because the constructed bend center radius 256 is greater, the bend 84 has a lower bend complexity ratio.

[0097] For example, a bend for a particular application can be provided with the following characteristics:

[0098]

[0099]

[0100]

[0101] where OD refers to the outside diameter of the tube, WT refers to the wall thickness, and CLR refers to the bend centerline radius. Assume the values of these ratios for the bend are:

[0102]

[0103] Referring to Table 1 above, these values indicate that if a conventional tube bender is used, internal mandrel bending can be required.

[0104] Now, certain parameters of the bend have been changed to show improved serpentine tube characteristics, such as tighter bend radius at the same wall thickness, reduced coil weight, reduced internal fluid side pressure drop, reduced bend wall stress, increased tube strength, increased tube stiffness, and / or increased heat transfer efficiency. These changes affect the characteristic ratio. For example, the new characteristic ratio can be selected as:

[0105]

[0106] Now, the bend complexity characteristic ratio is in a range that cannot be compensated for by a conventional tube bender, and internal mandrel is typically used to manufacture this bend.

[0107] For a variety of reasons as described above, internal mandrel bending is typically undesirable, which makes internal mandrel bending impractical for manufacturers that utilize long and continuous tube lengths to manufacture heat exchanger coils.

[0108] Referring again to Figure 9A One method to overcome the need for internal mandrel is to reduce the bend complexity by increasing the bend CLR. In our example, if we can increase the CLR of the bend while keeping the tube outside diameter and wall thickness constant, we can increase the bend D from 2 to 3 and obtain the following bend complexity (C B ) ratio:

[0109]

[0110] Because if the C B2 ratio is in the range of 5 to 10, the bend can be formed without internal mandrel. However, simply increasing the bend CLR can not be acceptable for a given application because the new bend will be larger and take up more space than the original bend. For example, the center-to-center distance between the tubes of the tube row will be larger, which means that there will be fewer tube rows of tubes that can fit into a particular shell or coil height. Furthermore, because each bend of the serpentine circuit tube will be taller, the serpentine circuit tube will have fewer tube rows for a given coil shell or height, which will reduce the heat exchange capacity of the serpentine circuit tube. Reducing the number of tube rows of a serpentine circuit coil to increase the bend CLR is not an acceptable solution for many applications.

[0111] Referring again to Figure 9A , the controlled buckled portion 94 of the bend 84 provides a constructed bend centerline radius 256 that is greater than the actual bend centerline radius 232 without increasing the distance between the tubes 80, 82. The greater 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 for a C B within a range that does not require mandrel bending.

[0112] More specifically, the controlled buckled portion 94 provides a constructed bend centerline 254 in the available space of the bend 84, allowing sufficient length along the inside of the bend 84 for the material to form the ridges 114 and troughs 116 in a controlled manner without buckling. The buckled 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 a reduction in wall thinning on the outer arc, and the overall stiffness of the bend 84 are also improved.

[0113] Referring to Figure 4 , the alternating ridges 114 and troughs 116 of the controlled buckled portion 94 provide space for the material of the tube 70 to fold itself into a smaller available arc length during bending of the tube 70. The material of the tube 70 folds into a sinusoidal curve 110 along the inner arc of the bend 84. Specific variables of the sinusoidal curve 110, such as the number of peaks / troughs, the depth of the troughs (amplitude of the sinusoid), the span of the arc, etc., are calculated for a particular application, as described below. This method can be used to calculate variables for a variety of combinations of material, OD, WT, and CLR, and optimized for a variety of characteristics, such as pressure drop and thermal efficiency.

[0114] The controlled corrugated portion 94 provides advantages over conventional bends. For example, the sinusoidal curve 110 minimizes the stress induced in the material of the tube 70 compared to other bends with corrugations, which allows for much higher internal fluid pressures. The dimensions of the ridges 114 and the grooves 116, including the tapered lead-in portions 140, 142, can be designed to limit the impedance to fluid flow within the bend 84 and minimize the internal fluid pressure drop through the bend 84. The sinusoidal curve 110 increases the length of material along the inner arc 90 compared to a conventional bend with the same bend centerline radius, which increases the overall surface area of the bend 84 and improves heat transfer efficiency by increasing fluid turbulence within the bend area. Furthermore, the ridges 114 and the grooves 116 operate as a corrugated structure, which stiffens the bend 84 compared to a smooth, uncorrugated bend. Still further, the controlled corrugated portion 94 pushes the neutral axis of the bend 84 outward toward the outer arc 92 of the bend 84, which reduces the thinning of the material of the bend 84 along the outer arc compared to a smooth, uncorrugated bend.

[0115] Referring to Figure 10-13B A method is provided for determining the geometry of the bends 84 of a serpentine loop tube 70 to replace the bends 306 of a conventional serpentine loop tube 300 while fitting within the coil envelope of the conventional serpentine loop tube 300 and utilizing tighter bend radii for a given wall thickness.

[0116] With respect to Figure 10 The conventional serpentine loop tube 300 has runs 302, 304, bends 306, an outer diameter 308, a wall thickness 310. The bends 306 are 180° bends, and the bends 306 have an inner arc 312 with an arc length 314 and an outer arc 315. Initially, and with respect to Figure 11 The serpentine loop tube 70 is provided with an outer diameter 210 that is the same as the outer diameter 308 and a wall thickness 190 that is less than the wall thickness 310. For example, the outer diameter 308 and the outer diameter 210 can both 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 selected to be the same as the outer diameter 308 so that the bends 84 stack with adjacent bends 84 just as the bends 306 stack with adjacent bends 306. For a given thickness 190, tighter bend radii can increase the heat transfer efficiency between the working fluid inside the serpentine loop tube 70 and the fluid outside the serpentine loop tube 70. Furthermore, for a given wall thickness 190, tighter bend radii can decrease the internal fluid pressure drop in the serpentine loop tube 70 because the inner diameter of the runs of the tube is increased.

[0117] Referring to Figure 11 , the method of determining the geometry of the bend 84 includes initially setting the serpentine loop tube 70 to have an initial bend 316 that connects the runs 80, 82. The initial bend 316 has a bend angle of 180° and a centerline radius 317 that is greater than the centerline radius 313 of the bend 306 shown in Figure 10 . As shown in Figure 10 and Figure 11 , the initial bend 316 has an inside arc 320 that has an arc length 318 that is greater than the arc length 314 because the centerline radius 317 is greater than the centerline radius 313.

[0118] With respect to Figure 12 , to fit the bend 84 within the same coil jacket as the conventional bend 306 of Figure 10 (which means that the center-to-center distance between the runs of the tube is equal), the bend 84 has an outside arc 92 that matches the outside arc 315 of the bend 306, and the tube 70 has an outside diameter 210 that matches the outside diameter 308. To provide the matching outside arcs 92, 315, the method of determining the geometry of the bend 84 includes moving the cut points 122, 124 of the runs 70, 82 toward each other in directions 330, 332 (shown in Figure 11 ) until: 1) the effective centerline radius 232 of the bend 84 is equal to the centerline radius 313 of the bend 306; and 2) the arc length of the inside arc 90 of the bend 84 is equal to the arc length of the inside arc 312 of the bend 306.

[0119] To compensate for the reduced vertical distance between the cut points 122, 124, the material of the serpentine loop tube 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 peaks / troughs, the period, and / or the amplitude.

[0120] Referring now to Figure 13A , the method of determining the geometry of the bend 84 next includes providing a line 339 that has an inside arc arc length 340 that matches the arc length 336 of the inside arc 90 from Figure 12 . The arc length 336 of the inside arc 90 extends between the cut points 122, 124 in Figure 12 .

[0121] The sinusoidal curve 110 is offset from the cut points 122, 124 of the bend 84 by two portions of the serpentine loop tube 70. The first portion is a relief portion 222, 224 that corresponds to an offset angle, such as 7° offset on either side of the sinusoidal curve 110, and is at the angles 220, 240 (seeFigure 4 measured between points 400. The second portion is the tapered lead-in portion 140, 142. The sinusoidal curve 110 begins and ends at points 400 (see Figure 4 To produce the offset of the sinusoidal curve 110 from the tangent points 122, 124, the method of determining the geometry of the bend 84 includes removing lengths 342, 344 from the length 340 to give a sinusoidal curve length 346 that is less than the inside arc length 340, as shown in Figure 13A Thus, the lengths 342, 344 each include two length portions: 1) a length portion corresponding to one of the relief portions 222, 224; and 2) a length portion corresponding to one of the tapered lead-in portions 140, 142. The lengths 342, 344 are determined, for example, by solving for the length portions using the inside arc radius and the angular offset.

[0122] The difference between the length 340 of the line 339 (see Figure 13A ) and the arc length 318 (see Figure 11 ) is occupied by the total arc length 346 of the sinusoidal curve 110. Referring to Figure 13A The total arc length 346 of the sinusoidal curve 110 can be expressed as:

[0123] [Equation 1.1]

[0124] Once the total arc length 346 of the sinusoidal curve 110 is known, the total arc length 346 is divided by the number of peak portions 250A and trough portions 252A, for example in the range of 6 to 18 peaks and troughs, for example 8 to 12 peaks and troughs, to determine the arc length 350 for each peak portion 250A and trough portion 252A. Each peak 250A and trough 252A has a radius 349 and an arc length 350 given by:

[0125] [Equation 1.2]

[0126] where θ is the angular extent of the peak portions 250A and trough portions 252A. The radius of each peak portion 250A and trough portion 252A can be determined using the following operation.

[0127] Referring to Figure 13B A geometry 351 is provided having the arc AD and a triangle formed by ABCD. Because the triangle ABC is a right triangle, the following equation can be determined:

[0128] [Equation 1.3]

[0129] The equation can be rearranged as:

[0130] [Equation 1.4]

[0131] The relationship a = rx0may be substituted into Equation 1.4 to obtain:

[0132] [Equation 1.5]

[0133] At this point, the value of "a" is known, i.e., the total arc length 346 of the sinusoidal curve 110 divided by the number of peak portions 250 and valley portions 252 (n) selected. Figure 13A The value of "c" is known (see c / 2 in Equation 1.5), i.e., the length 346 divided by the number of peak portions 250 and valley portions 252 selected. Figure 13B

[0134] The above equation can then be solved using a numerical method such as the Newton-Raphson iteration to obtain 0. Once 0 is determined, the radii of the peak portion 250A and the valley portion 252A can be determined by solving for the radius 349 in Equation 1.2.

[0135] The radius 349 and 0 allow the amplitude of the sinusoidal curve 110 to be determined using the following equation:

[0136]

[0137] It should be appreciated that special adaptations of the sinusoidal curve 110 can be used to customize the sinusoidal curve 110 for a particular application.

[0138] With respect to Figure 12 , the tapered lead-in portions 140, 142 are used to smoothly bend the material of the serpentine return tube 70 to reduce stress steps at the transitions between the relief portions 222, 224 (see Figure 4 ) and the sinusoidal curve 110.

[0139] With reference to Figure 14-18 , the intersecting sinusoidal curve 110 and arcuate curve 150 of the controlled corrugated portion 94 will be discussed in greater 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 that has high strength to resist internal fluid pressure within the serpentine return tube 70. The intersecting sinusoidal curve 110 and arcuate curve 150 cause the bend 84 to be subjected to low stress even when the bend 84 is under high internal pressure.

[0140] With reference to Figure 14 , one half of the sinusoidal curve 110 will be discussed, the other half of the sinusoidal curve 110 being a mirror image of Figure 9A ​the same as in the embodiment of FIG. 1. The sinusoidal curve 110 begins at a point 400 and is spaced apart from the tangent point 122 by the relief 222 and the tapered lead-in portion 140. The tapered lead-in portion 140 gradually slopes upwardly toward the point 400 near the peak 250 of the terminal ridge 118. The sinusoidal curve 110 oscillates about a centerline 406 that intersects the sinusoidal curve 110 at the transition 410 between the concave portion 412 and the convex portion 414 (when viewed from the center 230). In Figure 14 In the embodiment of FIG. 1, the centerline 406 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 (see FIG. 2). In another embodiment, the trough 252 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 such that the inner arc 90 is tangent to the groove 116. In yet another embodiment, the peak 250 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 such that the inner arc 90 is tangent to the ridge 114. Figure 12 In the embodiment of FIG. 1, the centerline 406 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 (see FIG. 2). In another embodiment, the trough 252 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 such that the inner arc 90 is tangent to the groove 116. In yet another embodiment, the peak 250 of the sinusoidal curve 110 lies on the inner arc 90 of the bend 84 such that the inner arc 90 is tangent to the ridge 114.

[0141] With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches. Figure 14 Figure 12 With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches.

[0142] With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches. Figure 15 With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches.

[0143] Figure 16A With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches.

[0144] With reference to FIG. 2, the centerline 406 of the sinusoidal curve 110 has a radius 416. In one embodiment, the centerline radius 232 (see FIG. 2) of the bend 84 is in the range of about 1.5 inches to about 2 inches, such as in the range of 1.7 inches to about 2 inches, such as 1.875 inches. The radius of the centerline 406 can be in the range of about 1 inch to about 1.5 inches, such as in the range of about 1.3 inches to about 1.4 inches, such as 1.35 inches. Figure 17A ​​The trough arc 154 has a center 172 that is radially outward from the centerline 102 of the serpentine return tube 70. The trough arc 154 extends through an angle 162 that is less than the angle 160 in Figure 16A In one embodiment, the angle 162 is in the range of about 100° to about 150°, such as 140°. The trough arc 154 has an arc length 432 between the end points 434, 436 of the trough arc 154 that is less than the arc length 427 of the peak arc 152.

[0145] With respect to Figure 18 , the continuously curved controlled fold surface 134 (as shown in Figure 8 ) of the controlled fold portion 94 can be formed at least in part by connecting the peak arc 152 and the trough arc 154 with a surface portion 440 having a convex surface portion 442, a concave surface portion 444, and a transition 446 that transitions between the convex surface portion 442 and the concave surface portion 444. The surface portion 440 can be mirrored across a vertical plane containing the peak arc 152 to the opposite side of the ridge 114.

[0146] In one embodiment, the continuously curved fold surface 134 is perpendicular to a vertical plane containing the peak arc 152 and a vertical plane containing the trough arc 154. With reference to Figure 15 , the vertical plane containing the peak arc 152 is defined as perpendicular to the horizontal plane 424 (see Figure 8 ) and contains the origin or center 230 and the peak point 250. The vertical plane containing the trough arc 154 is defined as perpendicular to the horizontal plane 424 and contains the center 230 and the trough point 252. The vertical planes containing the peak arc 152 and the trough arc 154 are separated by the angle 420. With respect to Figure 18 , the concave surface portion 442 and the convex surface portion 444 connect the peak arc 152 and the trough arc 154 and provide the undulating three-dimensional profile of the continuously curved controlled fold surface 134 (as shown in Figure 8 ). Each concave surface portion 442 and convex surface portion 444 terminates in two, four pole splines, one of which begins at the peak arc end point 426 (as shown in Figure 16A ) and ends at the trough arc end point 434 (as shown in Figure 17A ), and the other four pole splines begin at the peak arc end point 430 (as shown in Figure 16A ) and end at the trough arc end point 436 (as shown in Figure 17A ).

[0147] With reference 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.

[0148] 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 to 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] about Figure 25 The pipe bending machine 500 forms the bent section 570 by bending the pipe 564 by 180 degrees.

[0154] Figure 26 The diagram shows the upper part 530 of the bending die 502 moving upward along direction 569 from the lower part 532, 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.

[0155] 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.

[0156] 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 work together 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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 manifold for receiving pressurized working fluid; An outlet manifold for collecting pressurized working fluid; A serpentine loop connecting the inlet manifold and the outlet manifold to allow pressurized working fluid to flow from the inlet manifold to the outlet manifold, the serpentine loop including a conduit and a bend connecting the conduit, the bend including: The internal portion has a sine wave curve at the inner arc surface of the rotary bend, the sine wave curve including peaks and troughs; The inner portion of the curved section includes an arc-shaped curve that intersects with the sine wave curve, and the arc-shaped curve includes a crest arc that intersects with the wave crest and a trough arc that intersects with the wave trough.

2. The indirect heat exchanger pressure vessel according to claim 1, wherein, The crest arc has a first radius of curvature, and the trough arc has a second radius of curvature; as well as The first radius of curvature of the crest arc and the second radius of curvature of the trough arc are basically the same.

3. The indirect heat exchanger pressure vessel according to claim 1, wherein, The angle range of the crest arc is greater than the angle range of the trough arc.

4. The indirect heat exchanger pressure vessel according to claim 1, wherein, The serpentine loop has a centerline; Wherein, each of the wave crest arcs has a center radially inward from the center line; and The trough arcs each have a center radially outward from the center line.

5. The indirect heat exchanger pressure vessel according to claim 1, wherein, The rotary bending section has a centerline plane, and the sine curve is located in the centerline plane; Wherein, the wave crest arc is perpendicular to the midline plane; and The trough arc is perpendicular to the midline plane.

6. The indirect heat exchanger pressure vessel according to claim 1, wherein, The sine curve includes the terminal peak portion adjacent to the conduit; and At least one of the terminal crest portions includes a tapered introduction section.

7. The indirect heat exchanger pressure vessel according to claim 1, wherein, The sine curve has a period and an amplitude; and Wherein, at least one of the period and the amplitude varies around the gyroscopic bend.

8. The indirect heat exchanger pressure vessel according to claim 7, wherein, The sine curve includes a first minimum amplitude adjacent to one of the pipes, a second minimum amplitude adjacent to the other pipe, and a maximum amplitude between the first minimum amplitude and the second minimum amplitude along the inner arc surface of the bend.

9. The indirect heat exchanger pressure vessel according to claim 1, wherein, The crest arc and trough arc each have an angle range of at least 100 degrees.

10. The indirect heat exchanger pressure vessel according to claim 1, wherein, The crest arcs respectively include a first radius of curvature and a second radius of curvature; as well as The trough arcs respectively include a third radius of curvature and a fourth radius of curvature; and The first radius of curvature and the third radius of curvature are substantially the same, and the second radius of curvature and the fourth radius of curvature are substantially the same.

11. The indirect heat exchanger pressure vessel according to claim 1, wherein, The crest arc has a shape defined by a portion of a first ellipse; as well as The trough arc has a shape defined by a portion of the second ellipse.

12. The indirect heat exchanger pressure vessel according to claim 11, wherein, The first ellipse has a first principal dimension and a first major dimension; Wherein, the second ellipse has a second principal dimension and a second secondary dimension; and Wherein, the first major dimension is substantially the same as the second major dimension, and wherein the first major dimension is substantially the same as the second major dimension.

13. A closed-loop cooling tower, comprising: An indirect heat exchanger, the indirect heat exchanger comprising a plurality of serpentine loop tubes, the serpentine loop tubes comprising pipes and gyratory bends connecting the pipes; The rotary bending section includes a folded bending section with controlled folds; A fan, operable to generate airflow relative to the serpentine loop tube; An evaporating liquid distribution assembly configured to distribute evaporating liquid onto the serpentine loop pipe; A storage tank for receiving evaporated liquid from the serpentine loop; and A pump operable to pump evaporating fluid from the reservoir to the evaporating liquid distribution assembly.

14. The closed-loop cooling tower according to claim 13, wherein, The indirect heat exchanger includes an inlet manifold for receiving pressurized working fluid and an outlet manifold for collecting pressurized working fluid. The serpentine loop connects the inlet manifold and the outlet manifold, allowing pressurized working fluid to flow from the inlet manifold to the outlet manifold; and The inlet manifold, the outlet manifold, and the serpentine loop are configured to operate at an internal pressure of at least 150 psig.

15. The closed-loop cooling tower according to claim 13, wherein, The slewing bend of each serpentine loop includes a first folded bend, and the serpentine loop includes a tangent at the junction between the first folded bend and the adjacent pipe of the serpentine loop. The first folded bending portion has a bending angle; The controlled fold portion of the first folded rotary bend is spaced apart from the tangent point along the serpentine loop tube; as well as Wherein, the controlled fold portion of the first folded folded bending portion has an angle range smaller than the bending angle around the inner side of the first folded folded bending portion.

16. The closed-loop cooling tower according to claim 13, wherein, The controlled fold portion includes a sinusoidal curve at the inner arc surface of the fold bending portion, the sinusoidal curve including peaks and troughs; as well as The controlled fold portion further includes an arc curve intersecting the sine wave curve, the arc curve including a crest arc intersecting the crest and a trough arc intersecting the trough.

17. The closed-loop cooling tower according to claim 16, wherein, Each of the serpentine loop pipes has a centerline; Wherein, the crest arc of each serpentine loop has a center radially inward of the centerline of the serpentine loop; and The trough arc of each serpentine loop has a center radially outward from the centerline of the serpentine loop.

18. The closed-loop cooling tower of claim 13, further comprising a direct heat exchanger, wherein the evaporating liquid distribution assembly is configured to distribute the evaporating liquid onto the direct heat exchanger.

19. An indirect heat exchanger pressure vessel, comprising: An inlet manifold for receiving pressurized working fluid; An outlet manifold for collecting pressurized working fluid; A serpentine loop pipe connects the inlet manifold and the outlet manifold to allow pressurized working fluid to flow from the inlet manifold to the outlet manifold, the serpentine loop pipe including a conduit and a swivel bend connecting the conduit; The serpentine loop has a tangent point at the junction between the rotary bend and the pipe, wherein the rotary bend includes: Bending angle; Controlled folding portion; The controlled folded portion is spaced apart from the tangent point along the serpentine loop; and The controlled fold portion has an angle range smaller than the bending angle around the inner side of the rotary bending portion.

20. The indirect heat exchanger pressure vessel according to claim 19, wherein, The controlled fold portion of the rotary bending section includes a ridge and a groove; and The ridge includes an end ridge spaced apart from the tangent point.

21. The indirect heat exchanger pressure vessel according to claim 19, wherein, The controlled fold portion of the rotary bend includes an end ridge spaced apart from the tangent point; and At least one of the terminal ridges includes a tapered inlet portion to allow the working fluid to flow smoothly around the folded portion.

22. The indirect heat exchanger pressure vessel according to claim 21, wherein, Both of the end ridges include a tapered inlet portion to allow the working fluid to flow smoothly around the folded portion.

23. The indirect heat exchanger pressure vessel according to claim 19, wherein, The controlled fold portion of the slewing section includes alternating ridges and grooves, the ridges and grooves having amplitudes that vary around the slewing section.

24. The indirect heat exchanger pressure vessel according to claim 23, wherein, The ridges and grooves include a plurality of first ridges and grooves, the amplitude of which increases as the plurality of first ridges and grooves extend around the gyroboid portion away from one of the tangent points.

25. The indirect heat exchanger pressure vessel according to claim 24, wherein, The ridge and groove include a plurality of second ridges and grooves, the plurality of second ridges and grooves being located between a plurality of first ridges and grooves and the other tangent point; and Specifically, when the plurality of second ridges and grooves extend away from the plurality of first ridges and grooves toward another tangent point, the amplitude of the plurality of second ridges and grooves decreases.

26. The indirect heat exchanger pressure vessel according to claim 19, wherein, The controlled fold portion of the slewing bend has an angle range that is at least five degrees smaller than the angle of the slewing bend around the inner side of the slewing bend.

27. The indirect heat exchanger pressure vessel according to claim 19, wherein, The serpentine loop has an outer diameter (OD) and a wall thickness (WT). Wherein, the slewing bend has a centerline radius, and the controlled fold portion of the slewing bend provides a structural centerline radius (CCLR) of the slewing bend, the structural centerline radius (CCLR) being larger than the centerline radius; and The bending complexity coefficient (C) of the rotary bending section B It is determined by the following relationship: Among them, C B The rotary bend can be bent without an internal spindle.

28. The indirect heat exchanger pressure vessel according to claim 27, wherein, C B Approximately 10 or less.

29. The indirect heat exchanger pressure vessel according to claim 19, wherein, The serpentine loop tube includes an outer diameter (OD) and a wall thickness (WT), wherein: 。 30. The indirect heat exchanger pressure vessel according to claim 19, wherein, The inlet manifold, outlet manifold, and serpentine return pipe are configured to operate at an internal pressure of at least 150 psig.

31. The indirect heat exchanger pressure vessel according to claim 19, wherein, The inlet manifold, outlet manifold, and serpentine return pipe are configured to operate at an internal pressure of at least 410 psig.

32. The indirect heat exchanger pressure vessel according to claim 19, wherein, The inlet manifold, outlet manifold, and serpentine loop are configured to operate at an internal pressure of at least 1200 psig.

33. The indirect heat exchanger pressure vessel according to claim 19, wherein, The rotary bend includes a first rotary bend adjacent to one of the pipelines, a second rotary bend adjacent to the other pipeline, and a connecting portion connecting the first bend and the second bend. The bending angle includes the first bending angle of the first bending portion and the second bending angle of the second bending portion; The controlled fold portion includes a first controlled fold portion of the first curved portion and a second controlled fold portion of the second curved portion; and Wherein, the first folded portion has a first angular range smaller than the first bending angle surrounding the inner side of the first curved portion; and The second controlled fold portion has a second angle range smaller than the second bending angle around the inner side of the second curved portion.

34. The indirect heat exchanger pressure vessel according to claim 19, wherein, The bending angle is 180 degrees, and the angle range of the controlled fold portion is less than 170 degrees.

35. The indirect heat exchanger pressure vessel according to claim 19, wherein, The rotary bending section has a bending complexity coefficient greater than or equal to 10.

36. The indirect heat exchanger pressure vessel according to claim 19, wherein, The rotary bending section has a bending complexity coefficient of less than or equal to 20.

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