Patent Publication Number: US-2022228817-A1

Title: Indirect Heat Exchanger Pressure Vessel with Controlled Wrinkle Bends

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 63/138,655, filed Jan. 18, 2021, and U.S. Provisional Patent Application No. 63/270,953 filed, Oct. 22, 2021, which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD 
     This disclosure relates to indirect heat exchangers and, more particularly, to indirect heat exchangers having serpentine circuit tubes with multiple formed bends that convey a pressurized working fluid through the serpentine circuit tube and permit heat transfer between the working fluid inside of the serpentine circuit tube and a fluid external to the serpentine circuit tube. The working fluid and the external fluid may each be gas, liquid or a mixture of gas and liquid. 
     BACKGROUND 
     Heat exchangers are known that include direct heat exchangers and indirect heat exchangers. A direct heat exchanger transfers heat between a working fluid and another fluid via contact between the fluids. An indirect heat exchanger transfers heat between a working fluid and another fluid indirectly through a medium separating the fluids. 
     Various types of heat exchange apparatuses are known that include direct heat exchangers, indirect heat exchangers, or both. Known heat exchange apparatuses include open circuit heat exchange apparatuses such as open circuit cooling towers and closed circuit heat exchange apparatuses such as closed circuit cooling towers. Open circuit cooling towers may exchange heat between a working fluid, such as water, and an external fluid such as ambient air by distributing the working fluid onto fill. The working fluid is directly cooled by ambient air as the working fluid travels along the fill. Closed circuit cooling towers, by contrast, keep the working fluid separated from the external fluid. 
     Closed circuit heat exchanger apparatuses include closed circuit cooling towers for fluids, evaporative condensers for refrigerants, dry coolers, air cooled condensers, and ice thermal storage systems. These heat exchange apparatuses utilize one or more heat exchangers to transfer heat between a pressurized working fluid and an external fluid such as ambient air, an evaporative liquid, or a combination thereof. 
     For example, a heat exchanger apparatus may include a closed circuit cooling tower having an indirect heat exchanger pressure vessel including an inlet header that receives a pressurized working fluid, an outlet header, and an indirect heat exchange coil connecting the inlet and outlet headers. The indirect heat exchange coil may include one or more serpentine circuit tubes configured to transfer heat between the pressurized working fluid inside the indirect heat exchange coil and a fluid, such as an evaporative liquid, external to the indirect heat exchange coil. The inlet header receives the internal working fluid from an upstream component of the heat exchange apparatus and the outlet header collects the pressurized working fluid before the working fluid is directed to a downstream component of the heat exchange apparatus. 
     Indirect heat exchanger pressure vessels, which includes the inlet header, outlet header, and one or more serpentine circuit tubes, are required to withstand high pressures appropriate for the specific application and satisfy domestic and international engineering standards such as ASME Standard B31.5. For example, an indirect heat exchanger pressure vessel of a closed circuit cooling tower may be rated to withstand an internal pressure of 150 psig for fluids such as water, glycols and brines. As another example, the indirect heat exchanger pressure vessel of an evaporative condenser may be able to withstand an internal pressure of up to 410 psig or higher for typical refrigerants such as ammonia or R-407C. As yet another example, some evaporative condensers have indirect heat exchanger pressure vessels with internal pressure ratings of 1200 psig or greater for refrigerants such as CO 2 . 
     Serpentine circuit tubes of indirect heat exchanger pressure vessels typically include straight lengths and bends connecting the straight lengths. The straight lengths of the serpentine circuit tubes are typically joined with bends of approximately 180 degrees or by compound bends having multiple bends, such as two 90 degree bends joined by a tube length. 
     The serpentine circuit tubes may be stacked together during assembly of the heat exchange apparatus with the serpentine circuit tubes contacting one another, typically in the area of the return bends, and with the serpentine circuit tubes having a vertically staggered positioning. 
     Serpentine circuit tubes are often made by first forming an elongated tube from a long, flat strip of metal such as mild steel or stainless steel. The flat strip of metal is roll formed into a generally circular cross section and the longitudinal edges are welded together with a continuous, longitudinal weld to form a straight tube. In another approach, a seamless tube forming process is used to form the straight tube. The resulting straight tube may then be bent at spaced locations along the tube to form the tube into a serpentine shape with straight runs connected by bends. Tube bending is a complicated process and often utilizes a hydraulically, electrically, or manually-powered tube bender having a bend die, a clamp die, a pressure die, and optionally a mandrel and wiper die. The tube bender may be setup to form bends with any desired angle up to and including 180 degree bends, such as 80 degrees, 90 degrees, 100 degrees, or 180 degrees. As noted above, the return bends of a serpentine circuit tube may include compound bends each having two or more bends, such as an 80 degree bend and a 100 degree bend, connected by a length of straight tube. 
     To form a bend in a tube, the tube is fed into the tube bender and a portion of the tube is nestled in a recess of the bend die. The pressure die and clamp die, with recesses for the tube, are moved against the opposite side of the tube such that the pressure die is positioned to support the tube and the clamp die clamps the tube portion between the clamp die and the bend die. The tube bender then rotates or pivots the bend die and the clamp die through the desired bend angle. The pressure die moves forward as the bend die and clamp die pivot to support the tube and ensure the tube follows the profile of the bend die. Once the bend has been formed in the tube, the clamp die and pressure die retract from their clamped positions, the tube is fed forward until the next bend location of the tube is positioned in the tube bender, and the bend die, clamp die, and pressure die all move back to their initial positions. The bending process is repeated for each bend to be formed in the serpentine circuit tube. Some tubes are bent only once to form single-bend tubes, which commonly are referred to as hairpin or candy-cane tubes, that can be subsequently butt welded together. 
     The bending of a tube that is to receive a pressurized working fluid is a process that balances various considerations including performance, safety, and packaging criteria for a particular application. Further, unintended deformations in the tube wall during the bending process may lead to tube failures due to the pressure of the working fluid within the tube, corrosion of the tube, and/or a higher pressure drop of the working fluid 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 may be used to stiffen the tube wall at a trailing end of the inside of the bend to prevent unintended deformations in the tube. The internal mandrel may be a plug mandrel or may have one or more balls or rings, in which case the internal mandrel is referred to as a ball mandrel. 
     Tube bending generally involves the following parameters:
         OD=Outside diameter of the tube   WT=Wall thickness of the tube   CLR=Centerline radius of the bend       

     The dimensions are measured using a common measurement scale, such as inches or millimeters. These parameters are used to calculate the following two characteristic ratios: 
     
       
         
           
             
               Wall 
               ⁢ 
               
                   
               
               ⁢ 
               Factor 
             
             = 
             
               W 
               = 
               
                 OD 
                 WT 
               
             
           
         
       
       
         
           
             
               D 
               ⁢ 
               
                   
               
               ⁢ 
               of 
               ⁢ 
               
                   
               
               ⁢ 
               Bend 
             
             = 
             
               D 
               = 
               
                 CLR 
                 OD 
               
             
           
         
       
     
     Two other parameters that are featured in the bending process are the Outside Radius (OSR) of the bend, usually referred to as the extrados, and the Inside Radius (ISR) of the bend, usually referred to as the intrados. 
     The W and D ratios are further consolidated into a single factor that is indicative of the complexity of the bend. This factor is calculated as: 
     
       
         
           
             
               Bend 
               ⁢ 
               
                   
               
               ⁢ 
               Complexity 
             
             = 
             
               
                 C 
                 B 
               
               = 
               
                 
                   W 
                   D 
                 
                 = 
                 
                   
                     O 
                     ⁢ 
                     
                       D 
                       2 
                     
                   
                   
                     C 
                     ⁢ 
                     L 
                     ⁢ 
                     R 
                     × 
                     W 
                     ⁢ 
                     T 
                   
                 
               
             
           
         
       
     
     The values of W, D, and/or CB may be used to determine whether a bend can be formed without an internal mandrel, called empty bending, or if an internal mandrel will be required, in which case the process is called mandrel bending. For mandrel bending, these ratios help determine whether the internal mandrel required should be a multiple ball, single ball or a simpler plug mandrel. Finally, these ratios help determine whether a wiper die will be required in combination with the internal mandrel. As an example, process recommendations for various bend complexities are shown in the table below: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Table of Bend Complexity Values 
               
               
                 and Recommended Bending Process 
               
            
           
           
               
               
            
               
                 C B  value 
                 Recommended Bending Process 
               
               
                   
               
               
                 Less than 5 
                 Empty Bending 
               
               
                  5-10 
                 Internal Mandrel recommended; Wiper Die not required 
               
               
                 10-20 
                 Internal Mandrel either Plug or Ball required; Wiper 
               
               
                   
                 Die optional 
               
               
                 20-50 
                 Internal Mandrel with multiple balls required; Wiper 
               
               
                   
                 Die required 
               
               
                 Greater than 50 
                 High Pressure Internal Mandrel and Wiper Die required 
               
               
                   
               
            
           
         
       
     
     It is typical to look up the W, D, and/or CB ratios on industry standard tube bending charts to decide the type of bending process required. For example, to determine the process parameters to bend a tube with outside diameter of 1″ and a wall thickness of 0.05″ with a centerline radius of 2″, then the ratios W and D are: 
     
       
         
           
             
               W 
               = 
               
                 
                   1 
                   
                     
                       0 
                       . 
                       0 
                     
                     ⁢ 
                     5 
                   
                 
                 = 
                 
                   2 
                   ⁢ 
                   0 
                 
               
             
             ⁢ 
             
               
 
             
             ⁢ 
             
               D 
               = 
               
                 
                   2 
                   1 
                 
                 = 
                 2 
               
             
           
         
       
     
     An industry standard tube bending chart may recommend, in view of the W ratio of 20 and the D ratio of 2, that a regular pitch internal mandrel with 1 ball, supplemented with a wiper die, should be used. 
     Alternately, the CB for the example bend above is: 
     
       
         
           
             
               C 
               B 
             
             = 
             
               
                 
                   2 
                   ⁢ 
                   0 
                 
                 2 
               
               = 
               
                 1 
                 ⁢ 
                 0 
               
             
           
         
       
     
     Referring to the table above, this CB value also indicates that an internal mandrel is recommended, although a wiper die could be optional. The small differences in recommendations on mandrels and wipers are indicative of a certain amount of flexibility in bend configurations where tool design and tube material choices can sometimes compensate for the absence of an internal mandrel and/or wiper die. 
     The conventional bending charts used in industry and the bend complexity value (CB) ranges discussed above are based on the assumption that the profile of the tooling groove formed by the bending and clamp dies, where the tube is seated during the bending process, is circular, complementing the shape of the round tube. However, bending tool design has made several advances in recent years and it is possible to design bend tooling with a composite radius in the tooling groove to compress and support the tube during the bending process and extend the range of empty bending up from a CB value of approximately 5 to approximately 12. 
     Beyond this, especially as CB approaches and exceeds 20, it becomes progressively more necessary to use internal mandrels and wiper dies to successfully bend the tube. The internal mandrel bending process has several disadvantages including that using a mandrel requires additional tooling which adds cost, may increase scrap if mandrels are not used correctly, may add to cycle time, and requires the use of lubricants which adds time and cost for the lubricant and subsequent environmental mitigation. 
     One issue as CB approaches and exceeds 20 is that the associated mandrel bending imposes a limit on the continuous length of the tube. Serpentine circuit tubes can be very long, up to 400 feet long for some applications. The physical limits on the length of the mandrel rod and setup mean that internal mandrels cannot be used to bend long, continuous serpentine circuit tubes with several bends. This forces a manufacturer to form one or two bends in short segments of tube, sometimes called candy canes, and then butt weld the tube segments together to create larger circuits. Not only does this involve additional labor and cost, but additional butt welds increase the possibility of leaks and may not be permitted in many applications due to the high operating pressure the serpentine circuit tube will experience. 
     Another issue that may arise as CB approaches and exceeds 20 is that the associated internal mandrel bending moves the neutral axis of the bend closer to the inside of the bend and may cause excessive thinning of the outside wall portion of the bend. Thinning of the outside wall portion of the bend may weaken the serpentine circuit tube such that the serpentine circuit tube cannot withstand the pressure of the working fluid for a particular application. Excessive thinning of the outside bend wall also creates variability in the process when forming the bends causing reduced quality in the bend areas. 
     The above issues make it desirable for a manufacturer to avoid the use of internal mandrels for tube bending. One way to avoid using internal mandrels for a tube with a given OD is to increase WT or increase CLR to a suitable value to bring the bend within the range of empty bending. Increasing the wall thickness (WT) may not be an option for manufacturers whose products do not require such relatively thick walls from an operational perspective. In certain cases, the thicker walls may increase the fluid side pressure drop, may make the products less thermally efficient, increase the weight of the assembly, and may increase the material cost of the serpentine circuit tube. Further, increasing CLR may not be an option where the serpentine circuit tube needs to fit in a given space for other operational considerations. Increasing CLR can also have negative impact on overall coil thermal and hydraulic efficiency in some cases. 
     SUMMARY 
     In one aspect of the present disclosure, an indirect heat exchanger pressure vessel is provided that includes an inlet header to receive a pressurized working fluid, an outlet header to collect the pressurized working fluid, and a serpentine circuit tube connecting the inlet and outlet headers and permitting the pressurized working fluid to flow from the inlet header to the outlet header. The pressurized fluid may be, for example, water, glycol, a glycol mixture, ammonia, or CO 2  as some examples. The pressurized fluid may be a liquid such as water or a liquid/gas combination such as refrigerant liquid and refrigerant vapor. The serpentine circuit tube includes runs and a return bend connecting the runs. The return bend includes a controlled wrinkled portion including alternating ridges and grooves. The controlled wrinkled portion of the return bend provides a rigid structure that resists internal pressure during operation of the indirect heat exchanger pressure vessel. Further, the controlled wrinkled portion provides a constructive bend centerline radius that is larger than an actual bend centerline radius of the return bend. The larger constructive bend centerline radius reduces the bend complexity factor for the return bend compared to a return bend of a conventional serpentine circuit tube having the same outer diameter and wall thickness. Due to the reduced bend complexity factor, the return bend having controlled wrinkled portions may be bent without the use of an internal mandrel which simplifies the manufacturing process of the serpentine circuit tube. 
     The present disclosure also provides an indirect heat exchanger pressure vessel including an inlet header to receive a pressurized working fluid, an outlet header to collect the pressurized working fluid, and a serpentine circuit tube connecting the inlet and outlet headers to permit flow of pressurized working fluid from the inlet header to the outlet header. The serpentine circuit tube includes runs, a return bend connecting the runs, and tangent points at junctures between the return bend and the runs. The return bend includes a bend angle and a controlled wrinkled portion. The controlled wrinkled portion is spaced from the tangent points along the serpentine circuit tube and has an angular extent about an inside of the return bend that is less than the bend angle. In this manner, the controlled wrinkled portion may be formed using a bend die having corresponding controlled wrinkle-forming features for less than the entire intrados of the return bend to permit the serpentine circuit tube to be slid out lengthwise from the bend die and increases the rapidity at which return bends may be formed in the serpentine circuit tube. In one embodiment, the controlled wrinkled portion includes ridges having amplitudes that are smaller adjacent the tangents points and increase as the wrinkled portion extends away from the tangent points to reduce resistance to fluid flow through the return bend and reduce the internal fluid pressure drop at the return bend relative to a non-tapered or non-eased configuration of the wrinkle ridges. 
     In another aspect, an indirect heat exchanger pressure vessel is provided that includes an inlet header to receive 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 return bend connecting the runs. The return bend includes an inner portion having a sinusoidal wave pattern at an intrados of the return bend, the sinusoidal wave pattern including peaks and valleys. The inner portion of the bend includes an arc pattern intersecting the sinusoidal wave pattern, the arc pattern comprising peak arcs intersecting the peaks and valley arcs intersecting the valleys. The intersecting sinusoidal wave pattern and arc pattern provide a smooth, continuously curving side wall of the serpentine circuit tube which strengthens the return bend against internal pressure. In one embodiment, the sinusoidal wave pattern has one or more end portions with shallower peaks and valleys and an intermediate portion with deeper peaks and valleys to reduce the internal fluid pressure drop across the return bend compared to a sinusoidal wave pattern having a constant peak and valley size. 
     The present disclosure also provides a closed circuit cooling tower including an indirect heat exchanger comprising a plurality of serpentine circuit tubes having runs and return bends connecting the runs. The return bends include wrinkled bends having controlled wrinkled portions. The closed circuit cooling tower comprises a fan operable to generate 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 comprises a sump to receive falling evaporative liquid 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 wrinkled bends strengthen the serpentine circuit tubes to withstand internal pressure from the working fluid within the serpentine circuit tubes during operation of the cooling tower. The controlled wrinkled bends also provide a constructive centerline radius of the wrinkled bends that is larger than the actual centerline radius of the controlled wrinkled bends and provides a reduced bend complexity factor compared to a return bend of a conventional serpentine circuit tube having the same outer diameter and wall thickness. The reduced bend complexity factor permits the controlled wrinkled bend to be bent without the use of an internal mandrel which simplifies the manufacturing process of the serpentine circuit tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an indirect heat exchange apparatus having serpentine circuit tubes with runs connected by bends of the serpentine circuit tubes; 
         FIG. 2  is a schematic view of a heat exchange apparatus including serpentine circuit tubes; 
         FIG. 3  is a side elevational view of a serpentine circuit tube having runs connected by 180 degree bends; 
         FIG. 4  is an enlarged view of the bend shown in a dashed circle of  FIG. 3  showing a controlled wrinkled portion of an inside of the bend; 
         FIG. 5  is a cross-sectional view taken across line  5 - 5  in  FIG. 4  showing a cross-section of the bend at a groove of the wrinkled portion; 
         FIG. 6  is a cross-sectional view taken across line  6 - 6  in  FIG. 4  showing the cross-section of the bend at a ridge of the wrinkled portion; 
         FIG. 7  is a cross-sectional view taken across line  7 - 7  in  FIG. 4  showing the cross-section of one of the runs of the circuit tube; 
         FIG. 8  is a perspective view of the bend of  FIG. 4  showing the wrinkled portion of the inside of the bend and a smooth outer wall portion of the outside of the bend; 
         FIG. 9A  is a cross-sectional view taken across line  9 A- 9 A in  FIG. 8  showing a sinusoidal pattern of the wrinkled portion that is spaced from tangent points of the bend and the runs so that the wrinkled portion has an angular extent that is less than the 180 degree bend angle of the bend; 
         FIG. 9B  is a cross-sectional view similar to  FIG. 9A  of another embodiment of the bend having a wrinkled portion with a varying amplitude of ridges and valleys of the sinusoidal pattern; 
         FIG. 9C  is a cross-sectional view similar to  FIG. 9A  of another embodiment of the bend having a wrinkled portion with a varying period and a varying amplitude of ridges and valleys of the sinusoidal pattern; 
         FIGS. 10, 11, 12, 13A, and 13B  show a process of determining the sinusoidal pattern of the bend; 
         FIG. 14  is a graphical representation of a portion of the sinusoidal pattern of the wrinkled portion of the return bend showing peaks and valleys of the sinusoidal pattern; 
         FIG. 15  is a graphical representation of a portion of the sinusoidal pattern of the return bend intersecting with an arc pattern of the return bend, the arc pattern including a peak arc that intersects a peak of the sinusoidal pattern and a valley arc that intersects a valley of the sinusoidal pattern; 
         FIG. 16A  is a graphical representation of the peak arc of  FIG. 15  showing the peak arc having a radius of curvature, an angular extent, and a center, wherein the center is radially inward of a center line of the serpentine circuit tube; 
         FIG. 16B  is a graphical representation similar to  FIG. 16A  of a peak arc having a composite radius of curvature; 
         FIG. 16C  is a graphical representation similar to  FIG. 16A  of a peak arc having a shape defined by a portion of an ellipse; 
         FIG. 17A  is a graphical representation of the valley arc of  FIG. 15  showing the valley arc having substantially the same radius of curvature as the peak arc, a shorter angular extent than the peak arc, and a center, wherein the center is radially outward from a center line of the tube; 
         FIG. 17B  is a graphical representation similar to  FIG. 17A  of a valley arc having a composite radius of curvature; 
         FIG. 17C  is a graphical representation similar to  FIG. 17B  of a valley arc having a shape defined by a portion of an ellipse; 
         FIG. 18  is a perspective view showing a portion of the sinusoidal pattern, the peak arc, and the valley arc of  FIG. 15  and a continuous, curved wrinkled surface portion connecting the peak arc and the valley arc; 
         FIG. 19  is a perspective view of a tube bender showing a bend die, a pressure die, and a clamp die of the tube bender; 
         FIG. 20  is a side elevational view of the bending die of  FIG. 19  showing ridges and grooves that form corresponding ridges and grooves of the wrinkled portion of the tube; 
         FIGS. 21, 22, 23, 24, 25, and 26  show a process of forming a bend of a serpentine circuit tube using the tube bender of  FIG. 19 ; 
         FIG. 27  is a top plan view of the tube bent using the tube bender of  FIG. 19  and the lower part of the bending die that shows the meshed engagement between the ridges of the bend wrinkled portion and the ridges of the bend die; and 
         FIGS. 28, 29, and 30  are elevational views of bends having, respectively, ninety degree, eighty degree, and one-hundred degree bend angles; 
         FIG. 31  is a cross-sectional view of a serpentine circuit coil having runs with progressively flattening cross-sections; 
         FIG. 32  is an elevational view of compound bends of a pair of serpentine circuit tubes with three points of contact therebetween, each compound bend including a bend of 80 degrees and a bend of 100 degrees; 
         FIG. 33  is an elevational view of a bend having an asymmetrical wrinkle pattern; 
         FIG. 34  is a perspective view of a lower portion of a bend die used to form the bend of  FIG. 33 ; 
         FIG. 35  is a perspective view of the bend die lower portion of  FIG. 34  and a corresponding bend die upper portion; 
         FIG. 36  is a plan view of a tube having a flattened cross-section, the tube including straights and a return bend with a wrinkled portion; 
         FIG. 37A  is a cross-sectional view taken across line  37 A- 37 A in  FIG. 36  showing an elliptical cross-section of the tube at a valley of the wrinkled portion; 
         FIG. 37B  is a cross-sectional view taken across line  37 B- 37 B in  FIG. 36  showing an elliptical cross-section of the tube at a peak of the wrinkled portion; and 
         FIG. 37C  is a cross-sectional view taken across line  37 C- 37 C in  FIG. 36  showing an elliptical cross-section of the tube at one of the straights of the tube. 
     
    
    
     DETAILED DESCRIPTION 
     Regarding  FIG. 1 , an indirect heat exchanger pressure vessel such as a coil assembly  10  is provided that may be used in a heat exchange apparatus, such as an evaporative condenser, closed circuit fluid cooler, or an ice thermal storage system. The coil assembly  10  includes an inlet header  12 , outlet header  14 , and serpentine circuit tubes  16 . The serpentine circuit tubes  16  each include runs  18  that are connected with 180 degree bends  20  or compound bends  21  including two 90 degree bends  23 ,  25  separated by a straight length  27 . The serpentine circuit tubes  16  permit working fluid to flow from the inlet header  12 , through the serpentine circuit tubes  16 , and to the outlet header  14 . 
     Regarding  FIG. 2 , a heat exchange apparatus such as a cooling tower  24  is provided that includes an outer structure  26 , one or more fans  28  including fan blades  30  and motor(s)  32 , a direct heat exchanger such as fill  34 , and an indirect heat exchanger pressure vessel  36 . The cooling tower  24  may be an evaporative condenser, closed circuit cooing tower, or dry cooler heat exchanger as some examples. The indirect heat exchanger pressure vessel  36  includes inlet header  38 , one or more serpentine circuit tubes  37  with circuit runs  39  and bends  40  and outlet header  42 . The inlet and outlet headers  38 ,  42  may be reversed depending on the application. In some embodiments, the fill  34  is above the indirect heat exchanger pressure vessel  36  and/or the fill  34  is located between runs of the serpentine circuit tubes  37 . 
     Regarding  FIG. 2 , the cooling tower  24  includes an evaporative liquid distribution system  43  including a spray assembly  44  having spray nozzles or orifices  46  that distribute an evaporative fluid, such as water, onto the serpentine circuit tubes  37  and the fill  34 . The evaporative liquid distribution system  43  includes a sump  50  for collecting evaporative fluid from the fill  34  and the coil  36  and a pump  52  that pumps the collected evaporative fluid through a pipe  54  to the spray assembly  44 . The cooling tower  24  further includes one or more air inlets  35 , inlet louvers  58  which keep the evaporative liquid from leaving cooling tower  24 , an air outlet  59 , and an eliminator  56  to collect water mist from the air before the air leaves the air outlet  59 . The fan  28  is operable to generate or induce air flow upwards relative to the serpentine circuit tubes  37  and the fill  34 . In other embodiments, the cooling tower  24  may have one or more fans configured to induce airflow in upflow, downflow, or crossflow directions relative to the indirect heat exchanger and/or direct heat exchanger of the cooling tower  24 . 
     Regarding  FIG. 3 , a serpentine circuit tube  70  is provided that may be utilized with a heat exchange apparatus, such as the coil assembly  10  in  FIG. 1 , or the cooling tower  24  discussed above with respect to  FIG. 2 . The serpentine circuit tube  70  includes an internal passageway  72  and a tubular side wall  74  extending thereabout. The serpentine circuit tube includes an end portion  76  that may be connected to an inlet header and an end portion  78  that may be connected to an outlet header. Depending on the application, the end portion  76  may alternatively be connected to an outlet header and the end portion  78  may be connected to an inlet header. The serpentine circuit tube  70  includes runs  79 , such as runs  80 ,  82 , and bends  84 . In one embodiment, the runs  79  may be parallel. In other embodiments, one or more of the runs  80  extend transversely, e.g., sloped, relative to one another to allow for internal fluid draining. The serpentine circuit tube  70  may be self-draining such that any liquid in the internal passageway  72  travels down toward the end portion  78  under the effect of gravity. The material of the serpentine circuit tube  70 , outer diameter of the serpentine circuit tube  70 , wall thickness of the side wall  74 , number of runs  79 , length of runs  79 , number of bends  84 , angular extent of bends  84 , centerline radius of the bends  84 , and intrados/extrados of the bends  84  may be selected for a particular heat exchange apparatus. As another example in this regard, instead of a single angle bend  84  connecting a pair of runs  79 , the serpentine circuit tube may have one or more bends  84  that each include a pair of bends, such as 90 degrees, connected by a straight segment similar to the compound bend  21  shown in  FIG. 1 . The runs  80  may have circular cross-sections throughout the runs  80 . In other embodiments, the serpentine circuit tube  70  includes one or more runs  80  with non-circular cross-sections such as cross sections that are elliptical or obround. 
     The serpentine circuit tube  70  may be formed from a single straight tube that is bent at spaced locations along the tube to form the bends  84 . The serpentine circuit tube  70  may be formed by progressively roll forming an elongated strip of material into a tubular shape and welding longitudinal edges of the elongate strip together to form a single weld running along the length of the serpentine circuit tube  70 . In another approach, the serpentine circuit tube  70  may be made from a plurality of separately formed components. For example, the runs  79  may be separate components that are welded to the bends  84 . Alternately the serpentine circuit tube  70  may be formed by welding separate lengths of tube together and then bending the longer welded tube. The serpentine circuit tube  70  may be made of a metallic material, such as carbon steel or stainless steel. 
     Regarding  FIG. 4 , each bend  84  includes an intrados  90 , an extrados  92 , and a controlled wrinkled portion  94  of an inside  96  of the bend  84  and a smooth outer surface  98  at an outside  100  of the bend  84 . The controlled wrinkled portion  94  includes a continuously curving and controlled wrinkled surface  134  of the ridges  114  and the grooves  116 . The continuously curving controlled wrinkled surface  134  is uninterrupted by edges, corners, or flats to avoid localized areas of stress. The continuously curving and controlled wrinkled surface  134  is shaped by ridges  114  and grooves  116  of the bend  84  that are, in turn, defined at least in part by an intersecting sinusoidal wave pattern  110  and an arc pattern  150  as discussed in greater detail below with respect to  FIG. 15 . The bend  84  shown in  FIG. 4  has a 180 degree bend angle. When the subject disclosure refers to a particular bend angle of a bend, it is intended that the bend angle is an approximate value, such as +/−5 degrees. In some embodiments, all of the bends  84  of the serpentine circuit tube  70  have controlled wrinkled portions  94 . In other embodiments, fewer than all of the bends  84  have controlled wrinkled portions  94 . 
     The serpentine circuit tube  70  has a tube center line  102  extending through the runs  80 ,  82  and in the bend  84 . The controlled wrinkled portion  94  is radially inward from the tube center line  102  and separated therefrom by a side surface portion  104 . The smooth outer surface portion  98  and the side surface portion  104  permits the bend  84  to be stacked with bends of other serpentine circuit tubes in conventional arrangements as would a prior art tube having a smooth inner bend. 
     Referring to  FIG. 4  at the intrados  90  of the bend  84 , the controlled wrinkled portion  94  has a sinusoidal wave pattern  110  at the intrados  90  of the bend  84  as discussed below with respect to  FIGS. 8 and 9A . The wrinkled portion  94  includes an alternating series of ridges  114  and grooves  116 . In one embodiment, the bend  84  has relief portions  222 ,  224  intermediate the sinusoidal wave pattern  110  and tangent points  122 ,  124  between the runs  80 ,  82  and the bend  84 . The relief portions  222 ,  224  facilitate provision of a controlled wrinkled portion angle  240  that is less than a bend angle  220  as discussed in greater detail below. The relief portions  222 ,  224  extend from the tangent points  122 ,  124  to points  216 ,  218 . The wrinkled portion  94  further includes tapered lead-in portions  140 ,  142  extending between points  216 ,  218  and points  400  (see  FIG. 4 ) wherein the sinusoidal wave pattern  110  begins and ends. In one embodiment, the relief portions  222 ,  224  each have a first radius and the tapered lead-in portions  140 ,  142  each have a smaller, second radius. The sinusoidal wave pattern  110  starts at one point  400 , extends through a peak  130  of the end ridge  118 , undulates through the ridges  114  and grooves  116 , extends through a peak  132  of the end ridge  120 , until reaching the other point  400 . 
     The ridges  114  include end ridges  118 ,  120  that optionally have tapered lead-in portions  140 ,  142 . The tapered lead-in portions  140 ,  142  provide a smooth transition between the relief portions  222 ,  224  and the sinusoidal wave pattern  110 . The tapered lead-in portions  140 ,  142  smooth flow of the working fluid through the bend  84  and assists the material of the bend  84  to flow during bending. The tapered lead-in portions  140 ,  142 , ridges  114 , and grooves  116  reduce the internal fluid pressure drop caused by the working fluid flowing through the bend  84 . Further, the tapered lead-end portion  140  facilitates better draining of the serpentine circuit tube  70 . The bend  84  may have both tapered lead-in portions  140 ,  142  if the working fluid may flow through the bend  84  in either direction  143 ,  145 . If the working fluid will only be flowing through the bend  84  in one direction  143 ,  145 , the bend  84  may have only one tapered lead-in portion  140 ,  142 . 
     Regarding  FIG. 9B , a cross-sectional view of a bend  84 ′ is provided that is similar to the bend  84  and has a sinusoidal wave pattern  110 ′ at a midline of the bend  84 ′. The bend  84 ′ has ridges  114 ′ and grooves  116 ′ that vary in amplitude around the bend  84 ′. Specifically, the ridges  114 ′ and grooves  116 ′ closer to runs  80 ′,  82 ′ have small amplitudes and the ridges  114 ′ and grooves  116 ′ near a middle of the bend  84 ′ have larger amplitudes. For example, ridges  114 A′,  114 B′ have larger amplitudes than ridges  114 C′,  114 D′. The more gradual increase in the amplitude of the ridges  114 ′ and grooves  116 ′ provide a reduced resistance to fluid flow through the bend  84 ′ such that the bend  84 ′ has a reduced pressure drop across the bend  84 ′ compared to the bend  84  in some applications. The more gradual increase in the amplitude of ridges  114 ′ and grooves  116 ′ may also reduce stress in the material of the bend  84 ′ during the bending operation compared to the bend  84  in some applications. In other embodiments, the amplitude of the sinusoidal wave pattern of the bend  84 ′ may increase from adjacent one run connected to the bend  84 ′ to adjacent the other run connected to the bend  84 ′. 
     Regarding  FIG. 9C , a cross-sectional view of a bend  84 ″ is provided that is similar to the bend  84  and has a controlled wrinkled portion  94 ″ with a sinusoidal wave pattern  110 ″ at an intrados of the bend  84 ″. The controlled wrinkled portion  94 ″ includes ridges  114 ″ and grooves  116 ″. The controlled wrinkled portion  94 ″ includes a first portion  115 ″ having ridges  114 ″A, B and grooves  116 ″A, B with a first amplitude and a first period  117 ″. The controlled wrinkled portion  94 ″ includes a second portion  119 ″ having ridges  114 ″C, D and grooves  116 ″C, D with a second amplitude greater than the first amplitude. The ridges  114 ″C, D and grooves  116 ″ C, D have a second period  121 ″ that is less than the first period  117 ″. The controlled wrinkled portion  94 ″ further includes a third portion  123 ″ having ridges  114 ″E, F and grooves  116 ″E, F with a third amplitude that is substantially the same as the second 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 direction  127 ″ and the ridge  114 ″A includes a tapered lead-in portion  129 ″ to smooth fluid flow through the bend  84 ″. The tapered lead-in portion  129 ″ reduces pressure drop across the bend  84 ″ and improves draining of fluid in the bend  84 ″. 
     The characteristics of the sinusoidal wave pattern  110  utilized for a given return bend may be selected for a particular application. For example, the number of ridges/grooves, amplitude, period, and/or one or more tapered lead-in portions may be selected for a particular application. The characteristics of the return bend may vary throughout the return bend, such as the amplitude and period varying throughout the return bend. The shape of the controlled wrinkled portion  94  as formed at least in part by two different intersecting cross-sectional profiles. Regarding  FIGS. 4 and 15 , the controlled wrinkled portion  94  includes a sinusoidal wave portion  110  at the intrados  90  of the bend  84 . The other pattern is an arc pattern  150  that includes alternating peak arcs  152  and valley arcs  154 . Referencing  FIGS. 16A and 17A , the peak arc  152  has a peak arc radius  152 ′ and a center  182  and the valley arc  154  has a valley arc radius  158  and a center  172 . In this embodiment, the peak arc  152  and valley arc  154  are substantially the same. As used herein, the term substantially the same refers to dimensions that are effectively the same when taking manufacturing variation into account, such as within +/−10% of one another. The peak arc  152  extends through an angle  160  that is greater than an angle  162  through which the valley arc  154  extends. 
     Returning to  FIGS. 5 and 15 , the valley arc  154  forms a valley semicircular inner wall portion  170  having the valley arc radius  158  and the center  172 . Opposite the valley semicircular inner wall portion  170 , the bend  84  includes an outer wall portion  174  that may be semicircular. In some embodiments, the outer wall portion  174  may be curved with a flattened portion due to extrados  92  (see  FIG. 4 ) of the bend  84  being tensioned during the bending process. The bend  84  includes connecting wall portions  176 ,  178  that connect the valley semicircular inner wall portion  170  to the outer wall portion  174 . The connecting wall portions  176 ,  178  have a curvature that may be dissimilar from the inner and outer wall portions  170 ,  174 . The connecting wall portions  176 ,  178  provide a smooth transition between the geometries of the inner and outer wall portions  170 ,  174  to minimize stress concentration at the junctures between the geometries of the inner and outer wall portions  170 ,  174 . By reducing stress concentration at the juncture between the geometries of the inner and outer wall portions  170 ,  174 , the connecting wall portions  176 ,  178  assist in the bend  84  being able to withstand high internal operating pressure. 
     Regarding  FIGS. 6 and 15 , the peak arc  152  defines a peak semicircular inner wall portion  180  having the peak arc radius  156  with the center  182 . The bend  84  has an outer wall portion  184  opposite the peak semicircular inner wall portion  180 . Like the outer wall portion  174  (see  FIG. 5 ), the outer wall portion may be semicircular. In some embodiments, the outer wall portion  184  may be curved with a flattened portion due to the extrados  92  (see  FIG. 4 ) of the bend  84  being tensioned during the bending process. The bend  84  further includes connecting wall portions  186 ,  188  connecting the peak semicircular inner wall portion  180  and the outer wall portion  184 . Like the outer wall portion  174 , the outer wall portion  184  may have a semicircular shape or generally curved shape in some embodiments. Further, the connecting wall portions  186 ,  188  provide a smooth transition between the geometries of the inner and outer wall portions  180 ,  184  to minimize stress concentration at the junctures between the geometries of the inner and outer wall portions  180 ,  184 . The connecting wall portions  186 ,  188  contribute to the ability of the bend  84  to withstand high internal operating pressure. The peak arc  152  and valley arc  154  may each have a respective single radius as shown in  FIGS. 16A and 17A . In another embodiment, the peak arc  152  and/or the valley arc  154  has a compound or composite radius. For example, and with reference to  FIG. 16B , the peak arc  152 ′ has different radii  156 A′,  156 B′. Each radius of the peak arc  152 ′ is tangent at the point where the radius joins an adjacent radius. Likewise in  FIG. 17B , the valley arc  154 ′ has different radii  158 A′,  158 B′. 
     In another embodiment, the peak arc  152  and/or the valley arc  154  has a shape that is a portion of an ellipse. For example, the peak arc  152 ″ of  FIG. 16C  is an arc defined by an angle of  160 ″, such as 160 degrees, between points  426 ″,  430 ″ of an ellipse  439  having a major dimension  441  and a minor dimension  443 . Similarly, the valley arc  154 ″ in  FIG. 17C  has a shape that is defined by an angle  162 ″, such as 142 degrees, between points  445 ,  447  of an ellipse  449  having a major axis  451  and a minor axis  453 . 
     Regarding  FIG. 7 , the run  82  is shown with the side wall  74  having a circular cross-section with a center at the tube center line  102 . Side wall  74  may also have a non-circular cross section such as elliptical or oblong cross-section. The side wall  74  of the serpentine circuit tube  70  has a wall thickness  190  that extends about the inner passageway  72 . 
     Regarding  FIG. 8 , the sections of the runs  80 ,  82  and the bend  84  are shown in a perspective view. As noted above, the controlled wrinkled portion  94  has a continuously curving controlled wrinkled 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  connecting the curved ridge surface portions of adjacent ridges  114 . The ridge surface portions  200  and groove surface portions  202  form the continuous, undulating appearance of the controlled wrinkled portion  94 . 
     Regarding  FIG. 9A , the serpentine circuit tube  70  has an outer diameter  210  and the wall thickness  190 . The tube center line  102  extends through the runs  80 ,  82  and the bend  84 . The serpentine circuit tube has junctures  214 ,  215  between the runs  80 ,  82  and the bend  84 . At the junctures  214 ,  215 , the tube  70  includes the tangent points  122 ,  124  between the runs  80 ,  82  and the bend  84 . The bend  84  includes the reliefs  222 ,  224  extending away from the tangent points  122 ,  124  and the tapered lead-in portions  140 ,  142  ramp radially inward toward the peaks  130 ,  132  of the end ridges  118 ,  120 . The bend  84  has a center  230  and a center line radius  232  extending from the center  230  to the tube center line  102 . In the embodiment shown, the bend  84  has a bend angle  220  of 180 degrees and the controlled wrinkled portion  94  extends about the center  230  through a controlled wrinkled portion angle  240  that is less than the bend angle  220 . For example, the controlled wrinkled portion angle  240  may 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 wrinkled portion angle  240  is approximately 166 degrees. 
     Referring again to  FIG. 9A , the controlled wrinkled portion  94  positions peaks  250  of the ridges  114  at the intrados  90  (see  FIG. 4 ) of the bend  84  and positions valleys  252  of the grooves  116  radially outward from the peaks  250 . By positioning the valleys  252  outward of the intrados  90  of the bend  84 , the wrinkled portion  94  creates a constructive bend center line  254 . The constructive bend center line  254  has a constructive bend center line radius  256  that is greater than the center line radius  232  of the tube centerline  102 . Because the constructive bend center line radius  256  is larger than the bend center line radius  232 , the bend complexity ratio of the bend  84  for a given bend intrados and extrados is less than the bend complexity ratio of a conventional bend having the same intrados, extrados, outer diameter, and wall thickness. The bend  84  has a lower bend complexity ratio because of the larger constructive bend center radius  256 . 
     For example, a tube bend for a particular application may be provided with the following characteristic ratios: 
     
       
         
           
             
               Wall 
               ⁢ 
               
                   
               
               ⁢ 
               Factor 
             
             = 
             
               
                 W 
                 1 
               
               = 
               
                 
                   OD 
                   1 
                 
                 
                   W 
                   ⁢ 
                   
                     T 
                     1 
                   
                 
               
             
           
         
       
       
         
           
             
               D 
               ⁢ 
               
                   
               
               ⁢ 
               of 
               ⁢ 
               
                   
               
               ⁢ 
               Bend 
             
             = 
             
               
                 D 
                 1 
               
               = 
               
                 
                   C 
                   ⁢ 
                   L 
                   ⁢ 
                   
                     R 
                     1 
                   
                 
                 
                   OD 
                   1 
                 
               
             
           
         
       
       
         
           
             
               Bend 
               ⁢ 
               
                   
               
               ⁢ 
               Complexity 
             
             = 
             
               
                 C 
                 
                   B 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
               = 
               
                 
                   W 
                   1 
                 
                 
                   D 
                   1 
                 
               
             
           
         
       
     
     Wherein OD refers to tube outer diameter, WT refers to wall thickness, and CLR refers to the bend centerline radius. Assuming that the values of these ratios for the tube bend are:
         W 1 =20 and D 1 =2 therefore C B1 =10       

     Referring to Table 1 above, these values indicate that internal mandrel bending may be required if a conventional tube bender is used. 
     Now certain parameters of the bend are changed to show improved serpentine tube characteristics such as tighter bend radius for the same wall thickness, reduced coil weight, reduced internal fluid side pressure drop, reduced bend wall stresses, increased tube strength, increased tube stiffness, and/or increased heat transfer efficiency. These changes affect the characteristic ratios. For example, the new characteristic ratios may be selected as:
         W 2 =30 and D 1 =2 therefore C B2 =15       

     The Bend Complexity characteristic ratio is now in the range where conventional tube benders can no longer compensate, and an internal mandrel is conventionally used to make this bend. 
     Internal mandrel bending is often undesirable for a variety of reasons as discussed above, making internal mandrel bending impractical for manufacturers that utilize long continuous lengths of tube to fabricate heat exchanger coils. 
     Referring again to  FIG. 9A , one way to overcome the internal mandrel requirement is to lower the Bend Complexity by increasing the Bend CLR. In our example, if we can increase the CLR of the bend while the tube outer diameter and wall thickness remains the same, we can increase the D of the bend from two to three and obtain the following bend complexity (CB) ratio:
         W 2 =30 and D 2 =3 therefore C B2 =10       

     Because the CB 2  ratio is in the range of five to ten, the bend may be formed without an internal mandrel. However, simply increasing the bend CLR for a given application may not be acceptable because the new bend would be larger and occupy more space than the original bend. For example, the center-to-center distance between tube runs would be greater which means fewer tube runs could be fit into a certain envelop or coil height. Further, because each bend of the serpentine circuit tube would be taller, the serpentine circuit tube would have fewer runs for a given coil envelope or height which would reduce heat exchange capacity of the serpentine circuit tube. Reducing the number of runs of a serpentine circuit coil to increase the bend CLR is not an acceptable solution for many applications. 
     Referring again to  FIG. 9A , the controlled wrinkled portion  94  of the bend  84  provides the constructive bend center line radius  256  that is larger than the actual bend center line radius  232  without increasing the distance between the runs  80 ,  82 . The larger constructive bend center line radius  256  increases the CLR of the bend  84 , which increases the D of the bend for a given OD and permits the CB to be in a range such that mandrel bending is not required. 
     More specifically, the controlled wrinkled portion  94  provides a constructive bend center line  254  in the available space of the bend  84  thereby allowing for sufficient length along the inside of the bend  84  for the material to form the ridges  114  and grooves  116  in a controlled manner without buckling. The wrinkled 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 of the thinning of the wall on the extrados and overall stiffness of the bend  84  are also improved. 
     Referring to  FIG. 4 , the alternating ridges  114  and grooves  116  of the controlled wrinkled portion  94  provide space for the material of the tube  70  to fold itself into the smaller available arc length during bending of the tube  70 . The material of the tube  70  is folded in the sinusoidal wave pattern  110  along the intrados of the bend  84 . The specific variables of the sinusoidal wave pattern  110 , e.g., number of peaks/valleys, depth of the valleys (amplitude of the sinusoidal wave), span of arc, etc. are calculated for a particular application as discussed below. This method can be used to calculate the variables for various combinations of material, OD, WT and CLR, and to optimize for various characteristics such as pressure drop and thermal efficiency. 
     The controlled wrinkled portion  94  provides advantages over conventional tube bends. For example, compared to other bends having wrinkles, the sinusoidal wave pattern  110  minimizes the stresses developed in the material of the tube  70  which allow for much higher internal fluid pressures. The ridges  114  and grooves  116 , including the tapered lead-in portions  140 ,  142  may be sized to limit obstruction to the flow of fluid within the bend  84  and minimize internal fluid pressure drop through the bend  84 . The sinusoidal wave pattern  110  increases the length of the material along the intrados  90  compared to a conventional bend having the same bend center line radius which increases the total surface area of the bend  84  and improves heat transfer efficiency by increasing fluid turbulence within the bend area. Further, the ridges  114  and grooves  116  operate as corrugated structure that stiffens the bend  84  as compared to a smooth, non-wrinkled bend. Still further, the controlled wrinkled portion  94  pushes the neutral axis of the bend  84  outward toward the extrados  92  of the bend  84  thereby reducing thinning of the material of the bend  84  along the extrados compared to a smooth, non-wrinkled bend. 
     Regarding  FIGS. 10-13B , a process is provided for determining the geometry of the bend  84  of the serpentine circuit tube  70  to replace a bend  306  of a conventional serpentine circuit tube  300  while, at the same time, fitting within the coil envelope of the conventional serpentine circuit tube  300  and utilizing a tighter bend radius for a given wall thickness. 
     Regarding  FIG. 10 , the conventional serpentine circuit tube  300  has runs  302 ,  304 , a bend  306 , an outer diameter  308 , a wall thickness  310 . The bend  306  is a 180° bend and the bend  306  has an intrados  312  with an arc length  314  and an extrados  315 . Initially and with respect to  FIG. 11 , the serpentine circuit tube  70  is provided with the outer diameter  210  that is the same as 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  may both be 1.05 inches, the wall thickness  310  may be in the range of approximately 0.04 inches to approximately 0.07 inches, such as 0.048 inches, and the wall thickness  190  may be in the range of approximately 0.02 inches to approximately 0.05 inches, such as approximately 0.03 inches to approximately 0.04 inches. The outer diameter  210  is selected to be the same as the outer diameter  308  so that the bend  84  stacks with adjacent bends  84  as would the bend  306  when stacked with adjacent bends  306 . The tighter bend radius for a given thickness  190  may improve the efficiency of heat transfer between the working fluid inside of the serpentine circuit tube  70  and the fluid outside of the serpentine circuit tube  70 . Further, the tighter bend radius for a given wall thickness  190  may reduce the internal fluid pressure drop in the serpentine circuit tube  70  since the inner diameter of the tube run increases. 
     Referencing  FIG. 11 , the process of determining the geometry of the bend  84  includes initially setting the serpentine circuit tube  70  to have an initial bend  316  connecting the runs  80 ,  82 . The initial bend  316  has a 180° bend angle and a center line radius  317  that is larger than a center line radius  313  of the bend  306  shown in  FIG. 10 . Referencing  FIGS. 10 and 11 , the initial bend  316  has an intrados  320  with an arc length  318  that is larger than the arc length  314  due to the center line radius  317  being greater than the center line radius  313 . 
     Regarding  FIG. 12 , in order for the bend  84  to fit within the same coil envelope as the conventional bend  306  of  FIG. 10 , meaning the center-to-center distance between the tube runs is equivalent, the bend  84  has the extrados  92  that matches the extrados  315  of the bend  306  and the tube  70  has the outer diameter  210  that matches the outer diameter  308 . To provide the matching extrados  92 ,  315 , the process of determining the geometry of the bend  84  includes moving the tangent points  122 ,  124  of the runs  70 ,  82  toward one another in directions  330 ,  332  ( FIG. 11 ) until: 1) the bend  84  has the actual center line radius  232  equal to the center line radius  313  of the bend  306 ; and 2) an arc length of the intrados  90  of the bend  84  equals the intrados  312  of the bend  306 . 
     To compensate for the reduced vertical distance between the tangent points  122 ,  124 , the material of the serpentine circuit tube  70  at the inside of the bend  84  is shaped to have the sinusoidal wave pattern  110 . The sinusoidal wave pattern  110  has variables that define the shape of the sinusoidal wave pattern  110 , such as the length of the sinusoidal wave pattern  110 , number of peaks/valleys, period, and/or amplitude. 
     Referring now to  FIG. 13A , the process of determining the geometry of the bend  84  next includes providing a line  339  having an intrados arc length  340  that matches the arc length  336  of the intrados  90  from  FIG. 12 . The arc length  336  of the intrados  90  extends between the transition points  122 ,  124  in  FIG. 12 . 
     The sinusoidal wave pattern  110  is offset from the tangent points  122 ,  124  of the bend  84  by two portions of the serpentine circuit tube  70 . The first portion is the relief portions  222 ,  224  corresponding to the offset angle, such as 7° on either side of the sinusoidal wave pattern  110 , and measured between angles  220 ,  240  (see  FIG. 4 ). The second portion is the tapered lead-in portions  140 ,  142 . The sinusoidal wave pattern  110  starts and ends at points  400  (see  FIG. 4 ). To create the offset of the sinusoidal wave pattern  110  from the tangent points  122 ,  124 , the process of determining the geometry of the bend  84  includes removing lengths  342 ,  344  from the length  340  to give a sinusoidal pattern length  346  that is less than the intrados arc length  340  as shown in  FIG. 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 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 intrados radius and the angular offset. 
     The difference between the length  340  of the line  339  (see  FIG. 13A ) and the arc length  318  (see  FIG. 11 ) is taken up by the total arc length  346  of the sinusoidal wave pattern  110 . Referencing  FIG. 13A , the total arc length  346  of the sinusoidal wave pattern  110  may be expressed as: 
       Total arc length of sinusoidal pattern 346 =Intrados arc length 340 −Lengths 342,344    (1.1)
 
     Once the total arc length  346  of the sinusoidal wave pattern  110  is known, the total arc length  346  is divided by the number of peak portions  250 A and valley portions  252 A, such as in the range of 6 to 18 peaks and valleys, such as 8 to 12 peaks and valleys, to determine the arc length  350  for each peak portion  250 A and valley portion  252 A. Each peak portion  250 A and valley portion  252 A has a radius  349  and an arc length  350  given by: 
       Arc Length 350 =Radius 349 ×θ  (1.2)
 
     Wherein θ is the angular extent of the peak portion  250 A and valley portion  252 A. The radius of each peak portion  250 A and valley portion  252 A may be determined using the following operations. 
     Referencing  FIG. 13B , a geometric shape  351  is provided having an arcuate line AD and triangles formed by ABCD. Because the triangle ABC is a right triangle, the following equation may be recognized: 
     
       
         
           
             
               
                 
                   
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         θ 
                         2 
                       
                       ) 
                     
                   
                   = 
                   
                     AB 
                     CA 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1.3 
                   
                   ] 
                 
               
             
           
         
       
     
     The equation may be rearranged to be: 
     
       
         
           
             
               
                 
                   
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         θ 
                         2 
                       
                       ) 
                     
                   
                   = 
                   
                     c 
                     
                       2 
                       ⁢ 
                       r 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1.4 
                   
                   ] 
                 
               
             
           
         
       
     
     The relationship of a=r×θ may be substituted into equation 1.4 to result in: 
     
       
         
           
             
               
                 
                   
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ( 
                       
                         θ 
                         2 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       c 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                     
                     
                       2 
                       ⁢ 
                       a 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1.5 
                   
                   ] 
                 
               
             
           
         
       
     
     At this point, the “a” value is known, i.e., the total arc length  346  of the sinusoidal wave pattern  110  divided by the number of peak portions  250  and valley portions  252  ( FIG. 13A ). The “c” value is known (see c/2 in  FIG. 13B ), i.e., the length  346  divided by the number of peak portions  250  and valley portions  252  selected. 
     The foregoing equation may then be solved for theta using a numerical method such as Newton-Raphson iteration. Once theta has been determined, the radius of the peak portions  250 A and valley portions  252 A may be determined by solving for radius  349  in equation 1.2. 
     The radius  349  and theta permits the amplitude of the sinusoidal wave pattern  110  to be determined using the following equation: 
       Amplitude 352 =Radius 349 −(Radius 349 ×cos θ)
 
     It will be appreciated that ad-hoc adjustment to the sinusoidal wave pattern  110  may be utilized to tailor the sinusoidal wave pattern  110  for a particular application. 
     Regarding  FIG. 12 , the tapered lead-in portions  140 ,  142  to smooth the bending of the material of the serpentine circuit tube  70  to reduce stress risers at the transition between the reliefs  222 ,  224  (see  FIG. 4 ) and the sinusoidal wave pattern  110 . 
     Regarding  FIGS. 14-18 , the intersecting sinusoidal wave pattern  110  and arc pattern  150  of the controlled wrinkled portion  94  will be discussed in greater detail. The intersecting sinusoidal wave pattern  110  and arc pattern  150  provide a three-dimensional profile of the inner bend. The three-dimensional profile of the inner bend provides a corrugated structure that has a high strength to resist internal fluid pressure within the serpentine circuit tube  70 . The intersecting sinusoidal wave pattern  110  and arc pattern  150  cause the bend  84  to experience low stress even when the bend  84  is under a high internal pressure. 
     Referencing  FIG. 14 , one half of the sinusoidal wave pattern  110  will be discussed, with the other half of the sinusoidal wave pattern  110  being identical in the embodiment of  FIG. 9A . The sinusoidal wave pattern  110  begins at point  400  and is spaced from the tangent point  122  by the relief  222  and the tapered lead-in portion  140 . The tapered lead-in portion  140  ramps gradually upward toward the point  400  proximate a peak  250  of the end ridge  118 . The sinusoidal wave pattern  110  oscillates about the center line  406 , which intersects the sinusoidal wave pattern  110  at transitions  410  between concave portions  412  and convex portions  414  (when viewed from the center  230 ). In the embodiment of  FIG. 14 , the centerline  406  of the sinusoidal wave pattern  110  is located on the intrados  90  of the bend  84  (see  FIG. 12 ). In another embodiment, the valleys  252  of the sinusoidal wave pattern  110  are on the intrados  90  of the bend  84  such that the intrados  90  is tangent to the grooves  116 . In yet another embodiment, the peaks  250  of the sinusoidal wave pattern  110  are on the intrados  90  of the bend  84  such that the intrados  90  is tangent to the ridges  114 . 
     In reference to  FIG. 14 , the centerline  406  of the sinusoidal wave pattern  110  has a radius  416 . In one embodiment, the bend  84  has a centerline radius  232  (see  FIG. 12 ) in the range of approximately 1.5 inches to approximately 2 inches, such as in the range of 1.7 inches to approximately 2 inches, such as 1.875 inches. The centerline  406  may have a radius in the range of approximately 1 inch to approximately 1.5 inches, such as in the range of approximately 1.3 inches to approximately 1.4 inches, such as 1.35 inches. 
     Regarding  FIG. 15 , the arc pattern  150  includes the peak arc  152  that intersects the sinusoidal wave pattern  110  at each peak  250 , and a valley arc  154  that intersects the sinusoidal wave pattern  110  at each valley  252 . The peak arc  152  and valley arc  154  are separated about the bend  84  by an angle  420  that may be in the range of, for example, approximately 4° to approximately 14°. 
     Regarding  FIG. 16A , the peak arc  152  has the center  182  of the peak arc  152  radially inward from the tube center line  102  of the bend  84 . The center  182  is positioned along a midline plane  424  of the serpentine circuit tube  70 . The peak arc  152  extends through an angle  160  that may be in the range of, for example, 150° to approximately 170°, such as 160°.The peak arc  152  has an arc length  427  that extends from end point  426  to end point  430  of the peak arc  152 . 
     Regarding  FIG. 17A , the valley arc  154  has the center  172  thereof radially outward from the center line  102  of the serpentine circuit tube  70 . The valley arc  154  extends through an angle  162  that is less than the angle  160  in  FIG. 16A . In one embodiment, the angle  162  is in the range of approximately 100° to approximately 150°, such as 140°. The valley arc  154  has an arc length  432  between end points  434 ,  436  of the valley arc  154  that is less than the arc length  427  of the peak arc  152 . 
     Regarding  FIG. 18 , the continuously curving controlled wrinkled surface  134  (as shown in  FIG. 8 ) of the controlled wrinkled portion  94  may be formed at least a part by connecting the peak arc  152  and the valley 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 and concave surface portions  442 ,  444 . The surface portion  440  may be mirrored across a vertical plane that contains peak arc  152  to the opposite side of the ridge  114 . 
     In one embodiment, the continuously curving wrinkled surface  134  is perpendicular to a vertical plane that contains the peak arc  152 , as well as a vertical plane that contains the valley arc  154 . Referencing  FIG. 15 , the vertical plane that contains peak arc  152  is defined as being perpendicular to the horizontal plane  424  (see  FIG. 8 ), and contains the origin or center  230  and peak point  250 . The vertical plane that contains valley arc  154  is defined as being perpendicular to the horizontal plane  424  and contains the center  230  and valley  252 . The vertical planes that contain the peak and valley arcs  152 ,  154  are separated by angle  420 . Regarding  FIG. 18 , the concave surface portions  442  and convex surface portions  444  connect the peak and valley arcs  152 ,  154  and provide the undulating three-dimensional profile of the continuously curving controlled wrinkled surface  134  (FIG.  8 ). Each concave and convex surface portion  442 ,  444  terminates at two, four pole splines, one of which starts at peak arc end point  426  ( FIG. 16A ) and ends at valley arc end point  434  ( FIG. 17A ), while the other four pole spline starts at peak arc end point  430  ( FIG. 16A ) and ends at valley arc end point  436  ( FIG. 17A ). 
     Regarding  FIGS. 19 and 20 , a tube bender  500  is provided to bend a segment of the serpentine circuit tube  70  into the bend  84  discussed above. The tube bender  500  includes a bend die  502  and a clamp die  504  that is pivotal about an axis  506 . The tube bender  500  includes a pressure die  508  for supporting an outside of the bend  84  and a trailing portion of the serpentine circuit tube  70 . The bend die  502  and the clamp die  504  include recesses  512 ,  514  with surfaces  516 ,  518  extending thereabout that clamp onto a tube once the tube has been advanced in direction  520  onto a gap  522  between the bend die  502  and the clamp die  504 . The clamp die  504  and the pressure die  508  may be actuated in direction  524  to secure a portion of the tube between the clamp die  504  and the bend die  502 . The pressure die  508  includes a recess that receives a portion of the tube and may be shifted in direction  526  along with movement of the tube upon the bend die  502  and clamp die  504  being pivoted about the axis  506  in direction  528  to support the outside of the tube during the bending operation. 
     Regarding  FIGS. 19 and 20 , the bend die  502  includes an upper part  530 , a lower part  532 , and a recess  534  that receives a portion of the tube therein as the bend die  502  and clamp die  504  are pivoted in direction  528 . The bend die  502  has a wrinkled portion  536  that is the mirror image of the wrinkled portion  94  of the tube so that the bend die  502  imparts the wrinkled pattern  94  into the tube. For example, the wrinkled portion  536  includes ridges  540  that form the grooves  116  ( FIG. 8 ) and grooves  542  that form the ridges  114  ( FIG. 8 ). 
     Referencing  FIG. 20 , the ridges  540  each have an intermediate portion  544  and opposite end portions  546 . The intermediate portion  544  may have a first width about the bend die  502  and the ends  546 ,  548  have widths around the bend die  502  that are larger than the width of the intermediate portion  544  such that the ridges  540  flare outwardly as they extend away from a midline  550  of the bend die  502 . The grooves  542  may correspondingly have an intermediate portion  552  and opposite end portions  554 ,  556  that are narrower around the bend die  502  than the intermediate portion  552  due to the increasing width of the ridges  540  as the ridges  540  extend away from the midline  550 . The ridges  540  and the grooves  542  have undulating and continuous curved surfaces  560  such that the wrinkled portion  536  forms the continuous wrinkled surface  134  of the tube. 
     Regarding  FIGS. 21-25 , a method of forming the bend  84  using the tube bender  500  is provided. The tube bender  500  shown in  FIGS. 21-25  has similar components as the tube bend  500  shown in  FIG. 19  but with a different orientation of the components. Similar reference numbers will be used to describe the tube benders of  FIGS. 20 and 21-25  for ease of discussion. 
     Regarding  FIGS. 21 and 22 , a tube  564  is advanced into the tube bender  500  so that the pressure die  508  supports an outer surface of the tube  564 . In  FIG. 22 , the bend die  502  and clamp die  504  engage a portion  505  the tube  564  and begin to pivot in direction  565  into the page of  FIG. 22 . 
     Regarding  FIGS. 23 and 24 , the bend die  502  and clamp die  504  are pivoted in direction  565  to begin forming the bend  570  in the tube  564 . The pressure die  508  continues to support the outside of the tube  506  and is shifted in direction  526  to move with the tube  564  during the bending operation. 
     Regarding  FIG. 25 , the tube bender  500  has formed the bend  570  by bending the tube  564  180 degrees. 
       FIG. 26  shows the upper part  530  of the bend die  502  shifted upward in direction  569  from the lower part  532 , the clamp die  504  shifted away from the tube  564  (into the page), and the pressure die  508  is retracted from the tube  564 . The tube  564  is then shifted in direction  571  to position the next bend location along the tube  564  in the tube bender  500 . 
     Regarding  FIG. 27 , the bend  570  is shown having the wrinkled portion  572  including ridges  574  and grooves  576  formed in the inside of the bend  570 .  FIG. 27  also shows how the lower part  532  have a sinusoidal pattern  578  at the midline  550  (see FIG.  20 ) of bend die  502  that imparts a sinusoidal wave pattern  580  to the inside of the bend  570 . More specifically, the lower part  532  has the lower portions of the ridges  540  that form the grooves  576  in the bend  570  and the lower part  532  has the lower portions of the grooves  542  that receive the ridges  574  of the bend  570 . In this manner, the ridges  574  of the tube  564  and the ridges  540  of the bend die  502  form a tightly meshed configuration. Further, the ridges  540  and grooves  542  with the undulating, continuous surface thereon supports the inside of the tube. The upper part  530  ( FIG. 26 ) of the bend die  502  forms a corresponding meshed engagement with the upper portion of the bend  570 . 
     Regarding  FIG. 20 , the wrinkled portion  536  of the bend die  502  includes, now referring to  FIG. 27 , a tapered transition portion  590  and an end ridge  592  that cooperate to form an end ridge  594  of the bend  570 . The tapered transition portion  590  provides a smooth lead-in to a peak of the end ridge  594  as discussed above with respect to  FIG. 9A . 
     Various types of bends may be provided in accordance with the disclosure here. For example,  FIG. 28  shows a 90 degree bend  600 ,  FIG. 29  shows an eighty degree bend  620 , and  FIG. 30  shows a one-hundred degree bend  640 . 
     Regarding  FIG. 31 , a cross-sectional view of a serpentine circuit tube  700  is provided that is taken normal to the length of the serpentine circuit tube  700 . The serpentine circuit tube  700  similar to serpentine circuit tube  70  and includes runs  701 . The runs  701  include runs  702  having a circular cross-section and runs  704  having a non-circular cross-section, such as elliptical or obround. The runs  701  have cross-sections that progressively flatten with the run  706  having a width  707  that is wider than a width  709  of the run  708 . 
     Regarding  FIG. 32 , a coil  800  including assembled serpentine circuit tubes  802 ,  804  is provided. Each serpentine circuit tube  802 ,  804  includes runs  803 ,  805 , a compound bend  806  including first bend  808  having an first bend angle  810  of 80 degrees, a second bend  812  having a second bend angle  814  of 100 degrees, and a connecting portion  816  connecting the first and second bends  808 ,  812 . The first and second bends  808 ,  812  have inner controlled wrinkled portions that are similar to the controlled wrinkled portions of the bends discussed above. The serpentine circuit tubes  802 ,  804  have three contact points  820 ,  822 ,  824 . Each serpentine circuit tube  802 ,  804  has a height or distance  830  between the runs  803 ,  805 . The serpentine circuit tubes  802  of coil  800  contact one another. In other embodiments, the coil may include serpentine circuit tubes that do not contact one another. 
     With reference to  FIG. 33 , a portion of a tube  896  is shown that includes straights  898  and a bend  900 . The bend  900  is provided that is similar in many respects to the bends discussed above. The bend  900  includes a wrinkled portion  902  having ridges  904  and grooves  906 . The wrinkled portion  902  includes a sinusoidal pattern  903  along an intrados of the bend  900  that starts and ends at points  903 A,  903 B. The tube  896  has tangent points  911 ,  913  at transitions between the straights  898  and the bend  900 . 
     The wrinkled portion  902  is asymmetrical about a plane  908  that bisects the bend  900 . Axes  915 ,  912  extend perpendicular to the plane  908  and intersect, respectively, the tangent points  913 ,  911 . The tangent points  911 ,  913  are offset along the plane  908  a distance  910  such that the wrinkled portion  902  extends farther along the tube  896  on one side of the plane  908  than the other. The portion of the wrinkled portion  902  on the one side of the plane  908  (the upper portion in  FIG. 33 ) has an offset portion  910 A including at least one ridge  904  and/or at least one groove  906  more than the portion of the wrinkled portion  902  on the other side of the plane  908 . 
     The wrinkled portion  910  has an end groove  906 A and an end ridge  904 A. In one implementation, the end ridge  904 A lacks a tapered lead-in portion. The offset portion  910 A may provide a transition for flow in the tube  896  between the nearby straight  898  and the bend  900 . Further, the end ridge  904 B has a tapered lead-in portion  914  similar to various end ridges discussed above. 
     Regarding  FIGS. 34 and 35 , a bend die  1000  is provided that is similar to the bend die  502  discussed above such that differences will be highlighted. The bend die  1000  is used to form the bend  900  and includes an upper portion  1002  and a lower portion  1004 . The upper and lower portions  1002 ,  1004  have ridges  1006  and grooves  1008  that cooperate to form the ridges  904  and grooves  906  in the bend  900 . The upper and lower portions  1002 ,  1004  each have a pair of channels  1010 ,  1012 . The channels  1010  of the upper and lower portions  1002 ,  1004  form an opening  1013  at one side  1014  of the bend die  1000  and the channels  1012  of the upper and lower portions  1002 ,  1004  form another opening  1015  at the second side  1016 . 
     The openings  1013 ,  1015  permit the bend die  1000  to have a tube fed into either opening  1013 ,  1015  of the bend die  1000  and allow the bend die  100  to be turned in the corresponding direction to form the bend  900  in the tube. For example and with reference to  FIG. 35 , a first portion of a tube may be advanced in direction  1030  into channel  1012  of the bend die lower portion  1004 . The upper portion  1002  is shifted downward in direction  1032  into engagement with the bend die lower portion  1004  to form the opening  1015  around the tube. 
     The bend die  1000  is then turned in direction  1034  about axis  1036  while a trailing portion of the tube is supported by a pressure die. The bend die  1000  is turned in direction  1034  to impart the desired angular extent to the bend  900 . Once the bend  900  has been formed, the bend die upper portion  1002  is shifted upward in direction  1033  and the tube is shifted relative to the bend die  1000  to position another portion of the tube in the bend die  1000  for bending. Continuing with the example, the tube is repositioned to advance a second portion of the tube into opening  1013 , the bend die  1000  is closed, and the bend die  1000  is turned in a direction opposite direction  1034 . The process of advancing and bending the tube is repeated until the desired number of bends have been imparted to the tube. 
     Regarding  FIG. 36 , a tube  1100  is provided having a return bend  1102  and straights  1103 . The return bend  1102  has a wrinkled portion  1104  that is similar to the wrinkled portions discussed above. The wrinkled portion  1104  has valleys  1106  and peaks  1108 . The tube  1100  has a flattened cross-section at the valleys  1106 , the peaks  1108 , and/or the straights  1103 . The flattened cross-section of the tube  1100  may enable the tube  1100  to be tightly packed with adjacent tubes, such as in a coil assembly of a cooling tower. The flattened cross-section of the tube  1100  may also improve thermal performance of the tube  1100 . 
     The flattened cross-section of the tube  1100  may be, for example, an elliptical cross section. Regarding  FIG. 37A , the return bend  1102  includes a valley elliptical wall portion  1110  at the valley  1106 . The valley elliptical wall portion  1110  has a major dimension  1112  and a minor dimension  1114 . 
     Regarding  FIG. 37B , the return bend  1102  has a peak elliptical wall portion  1116  at the peak  1108 , the peak elliptical wall portion  1116  having a major dimension  1120  and a minor dimension  1122 . The major dimension  1120  of the peak  1108  is larger than the major dimension  1112  of the valley  1106 . In one embodiment, the minor dimension  1122  of the peak  1108  is smaller than the minor dimension  1114  of the valley  1106 . 
     Regarding  FIG. 37C , the return bend  1102  has a straight elliptical wall portion  1126  at the straight  1103 , the straight elliptical wall portion  1126  having a major dimension  1128  and a minor dimension  1130 . In one embodiment, the major dimension  1128  of the straight  1103  is smaller than the major dimensions  1112 ,  1120  and the minor dimension  1130  is larger than the minor dimensions  1114 ,  1122 . 
     The flattened cross-section of the portions of the tube  1100  may be provided in a number of different approaches. For example, the tube bender used to bend the tube and impart the wrinkled portion  1104  may flatten the bend  1102  during the bending procedure. In another approach, the tube initially has an elliptical cross-section and the bending procedure imparts the wrinkled portion  1104  to the bend  1102  without further flattening of the tube. In yet another approach, a tube bender is used to form one or more bends of a tube and a press is used to flatten the tube after the bending procedure. 
     Uses of singular terms such as “a,” “an,” are intended to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms. It is intended that the phrase “at least one of” as used herein be interpreted in the disjunctive sense. For example, the phrase “at least one of A and B” is intended to encompass A, B, or both A and B. 
     While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended for the present invention to cover all those changes and modifications which fall within the scope of the appended claims. For example, the bends disclosed herein may be utilized in in various heat exchange apparatuses, such as an evaporative condenser, air cooled condenser, closed circuit fluid cooler, closed circuit cooling tower, open circuit cooling tower, dry cooler, ice thermal storage system, thermal storage coils, and/or a hydro-cooling coil, as some examples.