BACKGROUND

[0001] The invention relates generally to heat exchangers and, more particularly, to a finned tube heat exchanger.

[0002] A finned tube heat exchanger includes a tube and fins disposed on the outer surface of the tube. Several designs for the fins are known in the art, including a serrated fin configuration. A serrated fin configuration can be formed on a tube by creating serrations in a sheet of metal and then winding the serrated sheet around the tube to define a plurality of fins or finlets.

[0003] Fins including serrations, slits, and bending aspects are known in the art. Kenichi (EP 0854344 A2) discloses a heat exchanger having finned tubes. The finned tubes are fabricated by attaching fins having the shape of a circular plate to the outer surface of the tube. Each fin is provided with bent portions that are formed by forming radial slits in a peripheral portion of the fin to divide the peripheral portion into a plurality of segments and then bending each segment in an axial direction of the tube along a bending line extending from a point on the radial slit. The bent portions can be formed in the same direction or in alternately opposite directions. The bent portions or tips accomplish increased flow mixing. The resultant bent tips are basically vortex generators. The goal of a vortex generator is to generate a vortex that brings higher energy particles from a free stream to low energy particles. The vortex generators reenergize boundary layers and prevent flow separation with slow recirculation. Therefore, the bent portions affect the flow and prevent or lessen the flow separation, but do not act as prime heat transfer surfaces. As a result, the heat transfer capability is compromised.

[0004] Shigenaka (U.S. Pat. No. 5,617,916) discloses a fin tube heat exchanger formed by winding a serrated fin strip around a tube. The fins are twisted at a twist angle relative to a contact line along the base portion of the fin strip which is in contact with the tube. The fins are also inclined at an inclination angle relative to a straight line perpendicular to an axis of the tube. This design of heat exchanger increases flow mixing. Increased flow mixing leads to higher heat transfer. However, increased flow mixing also leads to increased pressure losses. All the fins have the same level of inclination and twist angles. Therefore, an upstream fin will shade a downstream one that will only see a low speed recirculation. This twisting and inclination may increase heat transfer due to increased mixing, but the effect may become detrimental after some point. There may be increased pressure losses since the flow will most likely separate.

[0005] In order to reduce the costs, it is desirable to increase the heat transfer performance of finned tubes, while reducing the cost of manufacturing the finned tubes.

[0006] An increase in heat transfer is normally associated with an increase of the pressure drop in the system. Typically, increased heat transfer can be achieved by increasing the turbulence of the flow or the effective heat transfer area. It is possible to achieve a higher heat transfer by increasing the turbulence levels of the flow, but this increase is normally penalized by an increase in the pressure drop of the heat exchanger. Serrated fins are used to generate turbulence in the flow in order to increase the heat transfer performance of the heat exchanger. However, serrated fins generate increased pressure drops compared to a simple solid fin and have less material and area for heat transfer.

[0007] In addition, fin tubes with serrated helically wound straight fins form a boundary layer along the plane of the straight fins that reduces the heat transfer below what can be achieved when breaking up this boundary layer. In order to

accommodate large heat loads with small temperature differences, large surfaces areas are required, resulting in large numbers of tubes and high material costs. Winding and welding a long sheet metal strip with small pitch takes time for manufacturing. [0008] It would therefore be desirable to provide finned tube heat exchangers having augmented heat transfer capability without unfavorable pressure drops, smaller required area, fewer tubes and faster manufacturing.

BRIEF DESCRIPTION

[0009] These and other shortcomings of the prior art are addressed by the present disclosure, which includes a finned tube heat exchanger with enhanced serrated fins.

[0010] Briefly, one aspect of the present disclosure resides in a heat exchanger. The heat exchanger includes a tube , a first fin strip and at least one additional fin strip , a first set of finlets and at least one additional set of finlets. The first fin strip and the at least one additional fin strip are wound in parallel onto the tube as intertwined helices to define a first helical path and at least one additional helical path. The first fin strip and the at least one additional fin strip are coupled thereto an exterior surface of the tube. The first set of finlets extends from the first fin strip along the first helical path. The at least one additional set of finlets extend from the at least one additional fin strip along the at least one additional helical path.

[0011] Another aspect of the disclosure resides in a heat exchanger. The heat exchanger includes a tube, a first fin strip and a second fin strip wound in parallel onto the tube as intertwined helices to define a first helical path and a second helical path, a first set of finlets and a second set of finlets. The first fin strip and the second fin strip are coupled thereto an exterior surface of the tube. The first set of finlets extends from the first fin strip along the first helical path. The second set of finlets extends from the second fin strip along the second helical path. The first set of finlets and the second set of finlets are formed by at least one of bending and twisting the first set of finlets and the second set of finlets in an alternating arrangement along a single helical path relative to the first fin strip and the second fin strip before helically winding and attaching the first fin strip and the second fin strip on the outer surface of the tube. [0012] Yet another aspect of the disclosure resides in a heat exchanger. The heat exchanger includes a tube, a first fin strip and a second fin strip, a first set of finlets and a second set of finlets. The first fin strip and the second fin strip are wound in parallel onto the tube as intertwined helices to define a first helical path and a second helical path. The first fin strip and the second fin strip are coupled thereto an exterior surface of the tube. The first set of finlets extends from the first fin strip along the first helical path. The second set of finlets extends from the second fin strip along the second helical path,. The first set of finlets comprises a first plurality of finlets that are bent relative to a continuous base fin of the first fin strip and in an alternating pattern with a second plurality of finlets that are twisted relative to a helix angle of the helical path of the first fin strip. The second set of finlets comprises a third plurality of finlets that are bent relative to a continuous base fin of the second fin strip and in an alternating partem with a fourth plurality of finlets that are twisted relative to a helix angle of the helical path of the second fin strip.

[0013] Various refinements of the features noted above exist in relation to the various aspects of the present disclosure. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of the present disclosure without limitation to the claimed subj ect matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: in accordance with one or more embodiments shown or described herein; [0015] FIG. 1 is a plan view of a partially wound finned tube heat exchanger with enhanced serrated fins, in accordance with one or more embodiments shown or described herein;

[0016] FIG. 2 illustrates a side elevation view of a portion of a finned tube heat exchanger including two or more helical fin strips, in accordance with one or more embodiments shown or described herein;

[0017] FIG. 3 illustrates a partial perspective view of the finned tube heat exchanger of FIG. 2, in accordance with one or more embodiments shown or described herein;

[0018] FIG. 4 is a partial plan view of a first fin strip of another embodiment of a finned tube heat exchanger including enhanced serrated fins taken along line 4-4 of FIG. 5, in accordance with one or more embodiments shown or described herein;

[0019] FIG. 5 illustrates a side elevation view of a portion of the finned tube heat exchanger of FIG. 4, in accordance with one or more embodiments shown or described herein, where a plurality of finlets include bent finlets and twisted finlets in an alternating pattern relative to each fin strip and offset axially from fin strip to fin strip;

[0020] FIG. 6 illustrates a partial perspective view of the finned tube heat exchanger of FIG. 5, in accordance with one or more embodiments shown or described herein;

[0021] FIG. 7 illustrates a side elevation view a portion of another embodiment of a finned tube heat exchanger, in accordance with one or more embodiments shown or described herein, where a plurality of finlets include bent finlets and twisted finlets in an alternating pattern relative to each fin strip and in alignment axially from fin strip to fin strip; [0022] FIG. 8 illustrates a partial perspective view of the finned tube heat exchanger of FIG. 7, in accordance with one or more embodiments shown or described herein;

[0023] FIG. 9 illustrates a side elevation view of a portion of another embodiment of a finned tube heat exchanger, in accordance with one or more embodiments shown or described herein, where a plurality of finlets include bent finlets and twisted finlets in an alternating partem relative to each fin strip and offset axially from fin strip to fin strip;

[0024] FIG. 10 illustrates a partial perspective view of the finned tube heat exchanger of FIG. 9, in accordance with one or more embodiments shown or described herein;

[0025] FIG. 11 illustrates a frame for housing finned tubes, in accordance with one or more embodiments shown or described herein; and

[0026] FIG. 12 is a flow diagram of an exemplary method of assembling a heat exchanger, such as the exemplary heat exchanger shown in any of FIGs. 1-11, in accordance with one or more embodiments shown or described herein.

DETAILED DESCRIPTION

[0027] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents. [0028] The embodiments described herein provide a finned heat exchanger including two or more fin strips each disposed in a helical configured path about a tube. In addition, the embodiment described herein provide a finned heat exchanger including a plurality of enhanced serrated fin strips each defining a plurality of finlets that are bent relative to a continuous base fin of each fin strip and in an alternating partem with a plurality of finlets that are twisted relative to the continuous base fin of the fin strip. The alternating finlets being one of aligned or offset axially from fin strip to fin strip.

[0029] Unless otherwise indicated, approximating language, such as

"generally," "substantially," and "about," as used herein indicates that the term so modified may apply to only an approximate degree, as would be recognized by one of ordinary skill in the art, rather than to an absolute or perfect degree. Approximating language may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about,"

"approximately," and "substantially," is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations are identified. Such ranges may be combined and/or interchanged, and include all the sub-ranges contained therein unless context or language indicates otherwise.

[0030] Additionally, unless otherwise indicated, the terms "first," "second," etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer.

Moreover, reference to, for example, a "second" item does not require or preclude the existence of, for example, a "first" or lower-numbered item or a "third" or higher- numbered item. As used herein, singular forms such as "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0031] Embodiments disclosed herein include serrated finned tube heat exchangers. The finned tube heat exchanger includes a tube and at least two intertwined helically wound fin strips defining a plurality of finlets extending from the outer surface of the tube. In an embodiment, the fin strips are arranged and designed in a manner to define a plurality of finlets that augment heat transfer capability and reduce or minimize pressure drops compared to a standard serrated finned tube heat exchanger. In one embodiment, the fin strips include serrations to define a plurality of finlets that are disposed along a first helical path and at least one additional helical path. In an embodiment, the plurality of finlets may be correspondingly bent relative to a continuous base fin of the fin strip in one or more directions relative to an axial direction of the tube. In another embodiment, a portion of the plurality of finlets may be correspondingly bent relative to a continuous base fin of the fin strip and relative to an axial direction of the tube, while another portion of the plurality of finlets may be twisted relative to an angle of the helix and relative to an axial direction of the tube. The bent finlets and the twisted finlets configured in an alternating geometric predetermined arrangement along a single helical path.

[0032] Referring to FIG. 1 , illustrated is an embodiment of a finned tube heat exchanger 10 including a tube 12, a first fin strip 14 and at least one additional fin strip 16 during the winding process. In an embodiment, each of the first fin strip 14 and the at least one additional fin strip 16 is comprised of a sheet metal. To increase the manufacturing speed at which the finned tube heat exchanger 10 can be produced, the first fin strip 14 and the at least one additional fin strip 16 are wound in parallel onto the tube 12 as intertwined helices (described presently) defining a first helical path and a second helical path (described presently) and thereby allowing the tube 12 to move at approximately twice the speed through the finning tool (not shown).

[0033] The first fin strip 14 includes a plurality of serrations 18 to define a continuous base fin 15 and a first set of finlets 20 extending from an outer surface 22 of the tube 12. The at least one additional fin strip 16 includes a plurality of serrations 18 to define a continuous base fin 17 and at least one additional set of finlets 24 extending from the outer surface 22 of the tube 12. In the illustrated embodiment, the at least one additional fin strip comprises second fin strip 16 defining the continuous base fin 17 and second set of finlets 24.

[0034] Referring more specifically to FIGs. 2 and 3, the tube 12 has a length along an axis 26 passing through a center of the tube 12. The first fin strip 14 is disposed around the outer surface 22 of the tube 12 in a first helical configuration as indicated by helical path 28. Similarly, the second fin strip 16 is disposed around the outer surface 22 of the tube 12 in a second helical configuration as indicated by helical path 30. In the illustrated embodiment, an angle of helix, as indicated by "a" of each helical path 28, 30 is in a range of 2° to 8° relative to axis 26. A steeper helix angle "a" allows for fewer revolutions of the tube 12 and a higher throughput during the finning process.

[0035] The first set of finlets 20 and the second set of finlets 24 can be formed by first creating the serrations 18 on each of the first fin strip 14 and the second fin 16. For clarity, finlets in the second set of finlets 24 are shown as shaded in FIG. 2 to differentiate from the first set of finlets 20. Subsequent to forming the serrations 18, each of the first fin strip 14 and the second fin strip 16 is then helically wound in parallel, about the tube 12 along the helical paths 28, 30, respectively, as illustrated by dashed lines, and attached on the outer surface 22, such as by high frequency (HF) welding. In the illustrated embodiment of FIGs. 1-3, each finlet in the first set of finlets 20 and the second set of finlets 24 is bent at an angle "δ" relative to its respective fin strip 14, 16. The finlets 20, 24 can be bent in any angle, where "δ" ranges from -90 degrees to +90 degrees relative to the plane of the first fin strip 14 and the second fin strip 16, respectively. In this particular embodiment, each of the finlets 20, 24 are all bent in the same direction relative to the axis 26, and more particularly, relative to an axial direction 27 of the tube 12 and in alignment axially relative to the axis 26. The axial direction 27 of the tube 12 is along the axis 26 of the tube 12. In an alternate embodiment, each of the finlets 20, 24 are all bent in the same direction relative to the axis 26 and relative to the axial direction 27 of the tube 12 and offset axially relative to the axis 26 (described presently).

[0036] FIGS. 4-6 illustrate various views of another embodiment of a finned tube heat exchanger 40. It should be understood that like elements have like numbers throughout the embodiment. In addition, in an effort to provide a concise description of the various embodiments, features previously described may not be described in each disclosed embodiment. Similar to the first embodiment, in this particular embodiment, a first fin strip 14 is positioned in a first helical path 28 around the tube 12. The first fin strip 14 includes serrations 18 defining a continuous base fin 15 and a first set of finlets 20. As best illustrated in FIG. 4, in a partial cross-sectional view taken through line 4-4 of FIG. 5, the first fin strip 14 is wound around the tube 12 so as to define the first helical path 28 and the first set of finlets 20 are oriented alternately to define a first plurality of bent finlets 42 and a second plurality of twisted finlets 44.

[0037] As best illustrated in FIGs. 5 and 6, the first set of finlets 20, are oriented in a first direction "δ" relative to the axial direction 27 of the tube 12 and at a twist angle "βι" opposing an angle "a" of the first helical path 28. More particularly, the first plurality of finlets 42 are bent at an angle "δ" in an axial direction 27, and the alternating second plurality of finlets 44 are twisted at an angle "βι" opposing an angle "a" of the first helical path 28, thus remaining in line with the helical path 28. The twist angle "βι" is measured relative to a contact line along the continuous base fin of the respective fin strip 14 which is in contact with the tube 12. In an embodiment, the first plurality of finlets 42 may remain in line with the helical path 28, when bent at a substantially 0° angle "δ", or not in line with the helical path 28 when bent at an angle larger than 0° relative to the base fin 15.

[0038] As best illustrated in FIGs. 5 and 6, the second set of finlets 24 are oriented in a similar alternating bent and twist configuration. For clarity, finlets in the second set of finlets 24 are shown as shaded in FIG. 5 to differentiate from the first set of finlets 20. More particularly, a third plurality of finlets 42 are bent at an angle "δ" in an axial direction 27, and an alternating fourth plurality of finlets 44 are twisted at an angle "β ₂ " opposing an angle "a" of the second helical path 30, thus remaining in line with the helical path 30. The twist angle "β ₂ " is measured relative to a contact line along the continuous base fin of the respective fin strip 16 which is in contact with the tube 12. In an embodiment angle "βι" is equal to angle "β ₂ ". In an embodiment angle "βι" is not equal to angle "β ₂ ". In an embodiment, the third plurality of finlets 42 may remain in line with the helical path 30, when bent at a substantially 90° angle "δ", or not in line with the helical path 30 when bent at an angle other than 90° relative to the continuous base fin 17.

[0039] As illustrated, each of the first plurality of finlets 42 and the third plurality of finlets 42 are all bent in the same direction relative to the axis 26 and relative to the axial direction 27 of the tube 12 and offset axially between the first helical path 28 and the second helical path 30, relative to the axis 26. In an alternate embodiment, the first plurality of finlets 42 and the third plurality of finlets 42 are bent in opposed directions relative to the axis 26 and relative to the axial direction 27 of the tube 12 and/or in alignment axially between the first helical path 28 and the second helical path 30, relative to the axis 26.

[0040] Bending of the finlets 42 and twisting of the finlets 44 provides for improved heat transfer. More specifically, the heat transfer of the finlets 42 and 44 is enhanced as the geometric variation of the finlet surface causes orientation towards a gas flow path 32 and breaks up a boundary layer that would form if all the finlets 42, 44 were straight and oriented the same way. In addition, the geometry of the finlets 42, 44 provides for alignment of the flow direction in one plane orthogonal to the tube axis 26 despite the helix angle "a" of the first fin strip 14 and the second fin strip 16. The finlets 42, 44 protruding from the continuous base fins 15, 17 as described, are configured alternating, either straight (i.e. unbent so as to be aligned with the continuous base fins 15, 17, twisted with an angle "β" opposing the helix angle "a", or bent out of the plane of the continuous base fins 15, 17 to either side. While the bent finlets 42 mainly break up the boundary layer created by any straight fin upstream, the twisted finlets 44 turn the flow back from the plane with the helix angle "a" into a direction perpendicular to the tubes 12. Turning the flow through the twisted finlets 44 allows a steeper helix angle "a" with less pressure loss.

[0041] FIGs. 7 and 8, illustrate a finned tube heat exchanger 50, generally similar to the embodiment of FIGs. 5 and 6, wherein the first set of finlets 20 are oriented alternately, in a first direction at a bend angle "δ" relative to the axial direction 30 of the tube 12 and at a twist angle "β" opposing an angle "a" of a first helical path 28. More particularly, a first plurality of finlets 42 are bent at an angle "δ" in an axial direction 27, and an alternating second plurality of finlets 44 are twisted at an angle "β" opposing an angle "a" of the first helical path 28, thus remaining in line with the helical path 28. The second set of finlets 24, including a third plurality of finlets 42 and a fourth plurality of finlets 44, are oriented in a similar alternating bent and twist configuration. For clarity, finlets in the second set of finlets 24 are shown as shaded in FIG. 7 to differentiate from the first set of finlets 20. As illustrated, each of the bent finlets 42 in the first set of finlets 20 and the second set of finlets 24 are all bent in the same direction relative to the axis 26 and relative to the axial direction 27 of the tube 12 and in contrast to the embodiment of FIGs. 5 and 6 are aligned axially between the first helical path 28 and the second helical path 30, relative to the axis 26. Similarly, each of the twisted finlets 44 in the first set of finlets 20 and the second set of finlets 24 are all at a twist angle "β" opposing an angle "a" of a respective helical path 28, 30 and in contrast to the embodiment of FIGs. 5 and 6 are aligned axially between the first helical path 28 and the second helical path 30, relative to the axis 26.

[0042] FIGs. 9 and 10, illustrate another embodiment of a finned tube heat exchanger 60, generally similar to the embodiment of FIGs. 5 and 6, wherein the first set of finlets 20 are oriented alternately, in a first direction at a bend angle "δι" relative to the axial direction 27 of the tube 12 and at a twist angle "βι" opposing an angle "a" of a first helical path 28. More particularly, a first plurality of finlets 62a are bent at an angle "δι" in an axial direction 27, and an alternating second plurality of finlets 64a are twisted at an angle "β" opposing an angle "a" of the first helical path 28, thus remaining in line with the helical path 28. The second set of finlets 24 are oriented in a similar alternating bent and twist configuration, but in contrast to the previous embodiment of FIGs. 5 and 6, in this embodiment, a third plurality of finlets 62b of the second set of finlets 24 are bent at an angle "δ ₂ " in an axial direction 27 opposite to that of the first plurality of finlets 62a. For clarity, finlets in the second set of finlets 24 are shown as shaded in FIG. 9 to differentiate from the first set of finlets 20. An alternating fourth plurality of finlets 64b of the second set of finlets 24 are twisted at an angle "β" opposing an angle "a" of the second helical path 30, thus remaining in line with the helical path 30. As illustrated, each of the first plurality of finlets 62a, in the first set of finlets 20 and each of the third plurality of finlets 62b in the second set of finlets 24 are all bent in an opposed direction relative to the axis 26 and relative to the axial direction 27 of the tube 12. Similar to the embodiment of FIGs. 5 and 6, the finlets 62a and 62b are offset axially between the first helical path 28 and the second helical path 30, relative to the axis 26, but may alternatively be aligned as previously described. Similarly, each of the twisted finlets 64a, 64b in the first set of finlets 20 and the second set of finlets 24, respectively, are all at a twist angle "β" opposing an angle "a" of a respective helical path 28, 30 and offset axially between the first helical path 28 and the second helical path 30, relative to the axis 26.

[0043] In the disclosed embodiments of FIGs. 3-10, the arrangement of the first and second set of finlets 20 and 24 results in a configuration where every finlet in a single fin strip 14, 16 is oriented differently relative to a contiguous finlet along the respective helical path 28, 30. More particularly, the finlets in a single fin strip 14, 16 are oriented in an alternating geometric configuration, thus resulting in a higher heat transfer coefficient on the finlets. This higher heat transfer coefficient leads to a smaller required area and fewer tubes 12. In addition, faster manufacturing saves machinery and personnel costs and reduces delivery time.

[0044] The boundary layer formed at the surface of each finlet 20, 24 is one of the leading obstacles to better heat transfer. The inclusion of the bent finlets and twisted finlets will allow for the shedding of vortices, increasing the mixing of a downstream flow and enhancing mixing and disrupting of boundary layers. Also, the alternating geometric configuration of the finlets within each fin strip 14, 16 results in a flow condition that is closer to a three dimensional flow field than a two

dimensional flow.

[0045] The alternating bent/twisted finlets 20, 24 in the embodiments described above provide higher heat transfer coefficients compared to standard serrated fin and also solid fin tube configurations. Pressure losses are higher as well, but using a wider heat exchanger with shorter

[0046] The finned tubes disclosed herein can be arranged in modules as shown in FIG. 1 1. In this particular illustration, the finned tubes as previously described are generally referenced 70. A frame 72 can be used to house bundles of the finned tubes 70. The frame 72 can include a mechanism 74 to mount the finned tubes 70 in a specific position such that the tubes 70, and more particularly the finlets 20, 24, are directly in the path of the free stream.

[0047] An exemplary method 70 of assembling a heat exchanger, such as heat exchanger 10, 40, 50, 60, is illustrated in the flow diagram of FIG. 12. With reference also to FIGs. 1 -1 1, in the exemplary embodiment, the method 80 includes providing a tube 12, a first fin strip 14 and at least one additional fin strip 16, in a first step 82. Next, in step 84, a plurality of serrations 18 are formed in the first fin strip 14 to define a continuous base fin 15 and a first set of finlets 20. In addition, a plurality of serrations 18 are formed in the at least one additional fin strip 16 to define a continuous base fin 17 and at least one additional set of finlets 24, in step 86. Next, in a step 88, the first fin strip 14 and the at least one additional fin strip 16 are helically wound in parallel onto the tube 12 as intertwined helices to define a first helical path 28 and at least one additional helical path 30. During or subsequent to the winding process, the first fin strip 14 and the at least one additional fin strip 16 are coupled thereto an exterior surface 22 of the tube 12. After the first fin strip 14 and the at least one additional fin strip 16 are coupled to the tube 12, the first set of finlets 20 are one of bent or twisted relative to the continuous base fin 15 of the first fin strip 14 in one or more directions, relative to an axial direction 27 of the tube 12, in a step 90. Simultaneous, or subsequent thereto, in a step 92, the at least one additional set of finlets 24 are one of bent or twisted relative to the continuous base fin 17 of the at least one additional fin strip 16 in one or more directions relative to an axial direction 27 of the tube 12. In an embodiment, the first set of finlets 20 and the second set of finlets 24 are oriented in a similar direction relative to an axial direction 27 of the tube 12. In an embodiment, the first set of finlets 14 are oriented in a first direction relative to an axial direction 27 of the tube 12 and the second set of finlets 24 are oriented in a second direction relative to the axial direction 27 of the tube 12.

[0048] The finned tube heat exchangers thus provide a way to augment heat transfer without unfavorable pressure drops. In the alternating bent/twisted finlet configurations disclosed herein, heat transfer capability can be enhanced with only a small increase in pressure drop compared to a standard serrated finned tube. In addition, the to increase the manufacturing speed at which the finned tube heat exchanger can be produced, multiple fin strips are wound in parallel onto the tube as intertwined helices thereby allowing the tube to move at a greater speed through a finning tool during the manufacturing process.

[0049] It is to be understood that not necessarily all such obj ects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other obj ects or advantages as may be taught or suggested herein.

[0050] Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.

[0051] While only certain features of the disclosure have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The representative examples and embodiments provided herein include features that may be combined with one another and with the features of other disclosed embodiments or examples to form additional embodiments that are still within the scope of the present disclosure. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.