Arrangement of spiral tubes for efficient filling and device for carrying out the same

Abstract

Improved packing efficiency of helical tube bundles of the same twist in a heat exchanger is achieved by selecting the angular orientation of the tube bundles so that the apexes of adjacent tube bundles are located between each other, forming bundle overlaps. An exemplary application is an EGR cooler.

Description

[Technical Field]

[0001] The present invention relates to bundles of helical tubes, and more particularly to an efficient configuration of bundles of helical tubes for heat transfer applications.

[0002] [Background technology]

[0003] Coiled tubes are a long-established technology for effectively exchanging heat between two fluids. In one application, such as that shown in U.S. Pat. No. 2,693,346, heat is transferred from a fluid inside the coil to a fluid flowing around the coil, e.g., high-pressure steam from a remote steam generator is passed through the coil to heat the water flowing around it. In another embodiment, as shown in U.S. Pat. No. 9,605,912, hot vehicle exhaust gases inside the coil transfer heat to engine coolant flowing around a coil for cooling.

[0004] A significant advantage of helical tubes or coils compared to straight tubes is that for a given enclosure (housing) length and tube diameter, the coils can provide substantially more surface area for heat exchange with the surrounding fluid. Multiple coils can be staggered around a common central axis to form coil bundles. Coil bundles can be adjacent to each other and precisely positioned to optimize the number of tubes within the enclosure.

[0005] U.S. Patent No. 9,605,912 discloses a helically coiled tube bundle configuration within a heat exchanger for transferring heat between two fluids, such as hot exhaust gas and a liquid coolant. In one embodiment, the heat exchanger includes a shell enclosing at least two tube bundles attached to tube headers at both ends. Each tube bundle is composed of multiple tubes twisted in the same helix around a common helical axis.

[0006] In a preferred configuration, two 3-tube bundles are formed with opposite helical twists. That is, the first tube bundle has tubes wound in a helix with a right-hand helix, and the second tube bundle has tubes wound in a left-hand helix. Each tube has the same diameter, pitch, and helix diameter, and the helix axes of the bundles are parallel to each other. Because the helices of the tubes in each bundle with opposite twists do not cross, the tube bundles can be positioned with their helix axes closer to each other than if all of the tube bundles had the same twist. This heat exchanger can be formed from multiple tube bundles arranged in a rectangular array, with each tube bundle having an opposite twist from each adjacent tube bundle. This configuration increases the number of helical tube bundles that can fit within the heat exchanger shell.

[0007] US Patent No. 9,964,077 discloses an efficient arrangement of two tube bundles formed in counter helical twists in a two or four bundle pattern. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 2,693,346 [Patent Document 2] U.S. Patent No. 9,605,912 [Patent Document 3] U.S. Patent No. 9,964,077 Summary of the Invention [Problem to be solved by the invention]

[0009] While the above patents disclose bundle arrangements in which the bundles have opposite helical twists, in some circumstances it may be desirable to have all of the helical tube bundles in a heat exchanger have the same twist. For example, if all tubes have the same twist, there is no need to maintain tooling and programs to create tubes with different twist directions. Furthermore, assembly is simpler because precise positioning of different bundles is not required, and inventory control of bundles is simplified because only one type of bundle exists. [Means for solving the problem]

[0010] Improved packing efficiency of helical tube bundles of the same twist within a heat exchanger can be achieved by selecting an angular orientation of the tube bundles such that they are topologically nested within one another, with the apexes of adjacent tube bundles located between each other.

[0011] [Brief explanation of the drawings]

[0012] [Figure 1] End and side views of a spirally wound tube.

[0013] [Figure 2] End and side views of a bundle of three spirally wound tubes.

[0014] [Figure 3] FIG. 2 is an enlarged end view of FIG.

[0015] [Figure 4] Diagram showing a pair of two adjacent bundles of spirally wound tubes.

[0016] [Figure 5] A diagram showing a pair of adjacent bundles of spirally wound tubes arranged so that the peaks of one bundle are aligned with the valleys of the other bundle.

[0017] [Figure 6] A diagram showing a pair of four-tube bundles.

[0018] [Figure 7] 1 is a diagram showing a pair of tube bundles positioned in phase according to claim 1 of the present invention.

[0019] [Figure 8] Diagram showing a pair of tube bundles with the apex of one tube centered within the bundle and showing where the tubes meet tangentially.

[0020] [Figure 9] FIG. 10 is a diagram showing the combination of tube bundles at the end portions.

[0021] [Figure 10] 10 shows the overlap when tube bundles are aligned and positioned in the same phase according to the present invention. FIG.

[0022] [Figure 11] FIG. 1 shows the dimensions at the end of a typical tube bundle.

[0023] [Figure 12] 2 illustrates an encasement for an embodiment of an EGR cooler of the present invention.

[0024] [Figure 13] FIG. 13 shows a preferred tube bundle for implementation of the embodiment of FIG. 12.

[0025] [Figure 14] FIG. 14 is an end view of a tube bundle configuration for implementation of the embodiment of FIG. 13.

[0026] [Figure 15]14 is a cross-sectional view of a multiple tube bundle in the embodiment of FIG. 13.

[0027] [Figure 16] FIG. 14 is a side view of the tube component of the embodiment of FIG.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] A spiral can be mathematically defined by a system of parametric equations. A mathematical spiral (defined as a curve whose tangent makes a constant angle with a fixed line) with diameter D and pitch P can be parameterized by θ: JPEG2025542069000002.jpg5764

[0030] Figure 1 shows a cylindrical tube 101 or wire centerline 100 formed into a spiral. When viewed from the centerline of the tube 101, the wave has a distance D between the peak 102 and the valley 103 of the centerline, and a wave length P from the peak 102 to the next peak 104. When viewed from the end, D is the coil diameter of the tube spiral, and d is the diameter of the tube itself. When tubes are added to the bundle, the coil diameter and tube diameter remain the same, so the wave is duplicated and shifted. See, for example, Figures 2, 4, and 6. The phase angle φ when the tubes are equally spaced around the spiral axis can be defined as: JPEG2025542069000003.jpg24127

[0031] Figure 2 shows a bundle of three tubes, represented by φ (instead of z). The waves of each additional tube are separated from each other by an angle φ. The equation for the centerline of each additional tube in the bundle is formed: JPEG2025542069000004.jpg20115Here, d represents the outer diameter of the tube, so as can be seen in Figure 3, the outer diameter of the spiral bundle is D+d.

[0032] As can be seen from FIG. 4, it is clear that two adjacent bundles can be spaced apart with the outer diameter of at least one bundle in close proximity. However, the waves in a helical tube bundle create crests 120 and troughs 130. When adjacent bundles have the same pitch, they are rotated and positioned, i.e., phased, so that the peaks of one bundle are aligned with the troughs of its adjacent bundle. Figure 5 shows that adjacent bundles can be phased with each other (e.g., by rotating the bundles to move the peaks and troughs of the helical tubes forward or backward relative to the adjacent bundle), thereby creating a gap 110 between the bundles. The largest available gap occurs when the peaks 120 of one bundle are aligned with the troughs 130 of the adjacent bundle. This gap means that adjacent bundles are oriented so that the peaks of one bundle are between the peaks of the adjacent bundle (Figure 6) and positioned so that the bundles overlap (Figure 7), resulting in bundles closer to each other than the outer diameter of a single bundle. This results in a bundle spacing < (D + d). For clarity, the existence of a clump overlap is described as the condition where a vertex of one clump is located between (i.e., a valley between) the vertices of an adjacent clump. In other words, at least one vertex of the clump is located so as to intersect with an imaginary line connecting the two closest vertices of the adjacent clumps.

[0033] As the number of tubes per bundle increases, the gaps, and therefore the potential amount of bundle overlap, decrease, as shown for the four-tube bundle in Figure 6, where the gap 111 between bundles is smaller than the gap 110 for the two-tube bundle. Although the potential bundle overlap is small, some portions of the vertices of adjacent tube bundles will always fit together.

[0034] To minimize the bundle spacing, if the apex 120 of one tube bundle is aligned with the center of the valley 130 of an adjacent bundle, the phase shift between the bundles will be: JPEG2025542069000006.jpg1464This is shown graphically in Figure 7.

[0035] Using this as a derivation, corresponding tubes in adjacent bundles are shifted so that the wave troughs of corresponding adjacent tubes are aligned in phase with the wave crests of the first tube. The crests and troughs of the sine waves are 180° apart. However, when there are more than two tubes per bundle, N>2, the phase shift can become larger than necessary, and corresponding tubes in adjacent bundles can be shifted to be in phase with different tubes in the initial bundle. In practice, bundles with an odd number of tubes do not need a phase shift to be in phase with adjacent bundles, while bundles with an even number of tubes require a minimum phase shift of (φ / 2).

[0036] The minimum bundle spacing occurs when the helical tubes or wires meet each other tangentially. Figure 8 shows adjacent tube bundles 115 and 116 positioned at minimum bundle spacing. The peak 120 of each bundle is always aligned with the valley 130 of the adjacent bundle. The walls of adjacent tubes meet tangentially at 125, the gap 110 between the tube bundles is minimized, and the center-to-center spacing is less than the outer diameter D+d of the tube bundles.

[0037] As mentioned above, pairs of helical tube bundles of the same twist can be placed adjacent to each other to be closer spaced than the standard D+d boundary. In a shell-and-tube heat exchanger, many tube bundles must be packed together. The fact that pairs of bundles can be aligned in phase with each other does not create close spacing throughout the enclosure.

[0038] It was discovered that a special situation occurs when the number of bundles in a pattern is an integer multiple of the number of tubes in the bundle, resulting in the last bundle of the pattern being in phase with the first bundle of the pattern. This results in maximum bundle overlap between the last bundle of the pattern and the first bundle of the pattern. This applies to pattern units of two or four two-tube bundles, three three-tube bundles, four four-tube bundles, and five five-tube bundles. See Figure 9. Any of these pattern units can be replicated throughout the enclosure, allowing adjacent bundles to be in phase with each other.

[0039] A tube-and-shell heat exchanger, with a case carrying one fluid and multiple tubes carrying another fluid, is one example of a device that can benefit from inserting the maximum practical number of tubes into the casing. A particular embodiment of this heat exchanger is an EGR cooler for cooling the exhaust gases of a diesel engine. EGR cooler designs are described in U.S. Pat. No. 9,605,912 and U.S. Pat. No. 9,964,077, which are incorporated herein by reference. [Patent Document 4] U.S. Patent No. 9,605,912 [Patent Document 5] No. 9,964,077. These patents describe the advantages of helically coiled tubing components and opposing twisted coil arrangements that increase the number of tubing within a defined cooler housing.

[0040] The improved configuration described in [Patent Document 4] (U.S. Pat. No. 9,605,912) only works for an even number of tubes per pattern unit. If a configuration with an odd number of tubes per pattern unit (e.g., three) is desired, at least two must have the same twist. While adjacent tube bundles with the same twist cannot be placed as closely together as adjacent bundles with opposite twists, packing efficiency is improved by the current discovery that adjacent bundles with the same twist can be spaced closer together than S=D+d when placed in phase.

[0041] The advantages achieved by positioning the tube bundle as described herein can be seen by calculating two parameters: bundle spacing and packing efficiency. Consider the case where the centerline of a constant diameter helix is ​​modeled by: JPEG2025542069000007.jpg1077The outer surface can be described by the following equation: JPEG2025542069000008.jpg13102 where, JPEG2025542069000009.jpg920 is the normal distance from the center line to the parallel curve, JPEG2025542069000010.jpg926 is the unit normal vector (note that the parameter θ has been replaced by t to avoid confusion). Distance JPEG2025542069000011.jpg920 is the radius of the tube, i.e.: JPEG2025542069000012.jpg2064Two adjacent bundle tubes have the following centerline equation: JPEG2025542069000013.jpg30102 The external surface is: JPEG2025542069000014.jpg34102Here, d1 is the pipe diameter of bundle 1 and d2 is the pipe diameter of bundle 2. Unit normal vector of JPEG2025542069000015.jpg1051 JPEG2025542069000016.jpg951 shows the top surface of the tube and is positive, whereas JPEG2025542069000017.jpg1251 shows the underside of the tube and is negative. The tubes have minimum spacing and contact tangents in the bundle. JPEG2025542069000018.jpg35116If y2(t) is as follows, then from this system of equations we can obtain the minimum spacing S min You can ask for: JPEG2025542069000019.jpg12102

[0042] In a simplified example utilizing tube bundles where adjacent tube bundles are identical, each tube has a constant helix diameter, pitch and tube diameter, and is fully phase aligned, this can be analyzed with reference to Figure 10. The centerline 121 of the tube in bundle 1 is: JPEG2025542069000020.jpg38115The centerline of the tube 122 in bundle 2, which is perfectly in phase with bundle 1, is: JPEG2025542069000021.jpg24166where, JPEG2025542069000022.jpg1364. Each tube in an adjacent bundle has an outer surface 123 and 124, which are offset by the tube radius 126. The centerlines of two adjacent tubes are spaced a regular distance apart, the tube diameter d 127 (2 tube radii). The outer surface 123 of the tube, parameterized by t, is: JPEG2025542069000023.jpg13102 where k=d / 2, so the contact point 125 occurs at: JPEG2025542069000024.jpg30102Therefore, the smallest possible bundle spacing S min or the maximum overlap of possible bundles q max depends on the number of tubes per bundle N, the pitch P, the helix diameter d, and the tube diameter d.

[0043] The performance of a heat exchanger is directly related to the amount of surface area available to transfer heat. The amount of heat transfer capacity that can be accommodated in a heat exchanger of a given size can be described by the volumetric efficiency of the heat exchanger. For a tube and shell heat exchanger, putting more tubes inside a heat exchanger of a given size allows for more heat transfer surface area, and therefore increases the volumetric efficiency. The packing efficiency of a tube and shell heat exchanger can be expressed as the fraction of the total volume that the tubes occupy. Since each tube typically has one inlet and one outlet and a constant diameter along its length, we can simplify from volumetric efficiency to a two-dimensional area efficiency: JPEG2025542069000025.jpg19115To compare the packing efficiency of different helical tube bundle pattern units, the packing area can be defined as the area of ​​a polygon with corners at the helical axes of the bundles in that pattern unit. The tube area is the cross-sectional area of ​​the polygonal tubes.

[0044] For comparison, the relationship between bundle overlap and packing efficiency was calculated using tubes in an EGR cooler. Generally, one of the design and manufacturing constraints for EGR heat exchangers is the tube-to-tube spacing. The tubes must have sufficient flow rate and surface area for heat exchange to avoid adverse effects such as localized boiling. The end bulkhead or tubesheet manufacturing requires a minimum web distance between holes. Reducing the tube-to-tube spacing improves packing efficiency. Therefore, for comparison, it is advantageous to keep the tube-to-tube spacing "t" constant across all bundle configurations. This spacing applies not only to the spacing between tubes in the same bundle, but also to the spacing between tubes in adjacent bundles.

[0045] Referring to Figure 11, for a constant pipe diameter d and pipe spacing t: JPEG2025542069000026.jpg2164

[0046] This model can be used to calculate bundle overlap, bundle spacing, and packing efficiency. The preferred standard spiral tube dimensions for an EGR cooler manufactured for use as disclosed in U.S. Pat. No. 9,605,912 are d=250", t=0.531" (depending on manufacturing tooling), and p=2.500". The results are shown in Table 1.

[0047] [Table 1]

[0048] It is also possible to achieve bundle spacing that is less than the outer diameter (D+d) by positioning in phase certain dissimilar adjacent bundles. Table 2 shows the bundle overlap, bundle spacing, and packing efficiency for a square pattern of four tube bundles per pattern with standard dimensions t=0.0531" where adjacent bundles have different pitches P, number of tubes N, and / or tube diameters d.

[0049] [Table 2]

[0050] Example

[0051] A preferred embodiment of the present invention is an EGR cooler having a 3x3 pattern unit (a three-tube bundle, three-bundle pattern). In the exemplary embodiment of FIG. 12, a heat exchanger 10 is configured as an EGR cooler having a gas inlet end 12 and a gas outlet end 14 that receives exhaust gas flow from a diesel engine. The gas inlet end 12 comprises a tube header comprising a bulkhead 16 having a plurality of perforations 18. A plurality of hollow passages, such as tubes 20, 22, and 24 (FIG. 15), are mechanically coupled to the bulkhead 16 (e.g., by welding, brazing, or a similar rigid attachment) to align with the perforations 18 to form a fluid-tight seal between the tubes and the bulkhead. A bulkhead 26 located at the gas outlet end 14 is of identical construction and will not be described in detail herein. The bulkhead 16 and bulkhead 26 are fluidly connected to the diesel engine exhaust system (e.g., by appropriate flange connections and exhaust system piping (not shown)).

[0052] A shell 28 extends between the bulkheads 16 and 26 and is mechanically coupled thereto (e.g., by welding, brazing, or similar rigid attachment) to form a fluid-tight seal between the bulkheads and the shell. The shell 28 includes a coolant inlet passage 30 and a coolant outlet passage 32 to allow coolant to flow within the shell 28. The coolant flows over tubes housed within the shell 28 and from the shell 28 to an external radiator or other means for rejecting heat from the tubes 20-24. While the exemplary embodiment of the heat exchanger 10 shown in FIG. 12 comprises a parallel-flow heat exchanger having the coolant inlet passage 30 adjacent the gas inlet end 12, the present invention is not limited to parallel-flow heat exchanger embodiments. For example, a counter-flow heat exchanger in which the coolant inlet passage 30 is adjacent the gas outlet end 14 is also within the scope of the present invention.

[0053] 13, the tubes running between the partitions 16 and 26 are arranged in a plurality of tube bundles, such as tube bundle 34, each having a relatively short straight section 36, 38, 40 at the gas inlet end 12 and a relatively short straight section 42, 44, 46 at the gas outlet end 14, between which three individual tubes 20, 22, 24 are wound helically, each having the same helical pitch, helix radius, and helical twist direction (e.g., right-handed or left-handed). All of the individual tubes 20, 22, 24 of tube bundle 34 share a common helix axis 48.

[0054] With further reference to FIG. 14 , tube bundle 34 is shown adjacent to second tube bundle 50 and third tube bundle 60. Tube bundle 50 is comprised of a plurality, e.g., three, tubes 52, 54, and 56, each of which has a relatively short straight section (not shown) at gas inlet end 12 and a relatively short straight section (not shown) at gas outlet end 14. Between the relatively short straight sections, each of the three tubes 52, 54, and 56 is wound helically, with each helix having the same helical pitch, helical diameter, and helical twist direction. All of the individual tubes 52, 54, and 56 of tube bundle 50 share a common helical axis 58, which is parallel to helical axis 48. Tube bundle 60 is comprised of a plurality, e.g., three, individual tubes 62, 64, and 66, each of which has a relatively short straight section (not shown) at gas inlet end 12 and a relatively short straight section (not shown) at gas outlet end 14. Between the relatively short straight sections, each of the three tubes 62, 64, and 66 is wound into a helix, each of which has the same helix pitch, helix diameter, and helix twist direction. All of the individual tubes 62, 64, and 66 of the tube bundle 60 share a common helix axis 68, which is parallel to helix axis 48 and also parallel to helix axis 58.

[0055] Tube bundles 34, 50, and 60 are positioned in phase with one another. The outer surface of tube 24, which forms the apex of tube bundle 34, aligns with the valley between tubes 64 and 66 (of tube bundle 60). The outer surface of tube 66 aligns with the valley formed by tubes 52 and 56 (of tube bundle 50). The outer surface of tube 52 aligns with the valley formed by tubes 22 and 24 (of tube bundle 34). As described in FIGS. 7 and 8, adjacent tube bundles are positioned so that the spacing between them is less than the sum of the tube bundle helical (coil) diameter (D) and the tube diameter (d). This distance is shown as 35, 55, and 65 for each bundle. In some embodiments, adjacent tube bundles are actually tangent to one another.

[0056] As shown in Figure 15, a 3x3 pattern unit containing three adjacent 3-tube bundles can be repeated to form a matrix of tube bundles.

[0057] With further reference to FIG. 16 of the exemplary embodiment, the heat exchanger 10 includes 14 tube bundles mounted between the partition walls 16 and 26, with the upper horizontal row of tube bundles consisting of tube bundle 34a, consisting of tubes 20a, 22a, and 24a, all of which have a left-handed twist. Immediately adjacent to tube bundle 34a is an identical tube bundle 34b, consisting of tubes 20b, 22b, and 24b, all of which also have a left-handed twist. Immediately below and adjacent to both tube bundles 34a and 34b is an identical tube bundle 34c, consisting of tubes 20c, 22c, and 24c, all of which have a left-handed twist. The three tube bundles are arranged in a triangular array, with their helical axes 48a, 48b, and 48c parallel to one another. As can be seen in Figure 16, the remainder of the tube bundles are arranged with their helical axes arranged in a series of triangular arrays, forming a triangular matrix such that the helical axis of each tube bundle is equidistant from the helical axes of all adjacent tube bundles, with each tube bundle adjacent to tube bundles having the same helical twist on all sides.

[0058] The exemplary embodiments described with reference to the drawings incorporating features of the present invention can be used as heat exchangers for a variety of purposes where it is desired to transfer heat from one fluid medium to another. One example is where the heat exchanger is used as an exhaust gas recirculation (EGR) cooler, but a heat exchanger incorporating features of the present invention can be used in connection with any suitable application to transfer heat from a fluid on one side of a barrier to a fluid on the other side of the barrier without the fluids contacting each other. A heat exchanger incorporating the teachings of the present invention can be suitably used to meet the specific needs of any type of fluid application, e.g., air-to-air, air-to-liquid, liquid-to-liquid, etc.

[0059] While exemplary embodiments have been described above with reference to the drawings, it will be apparent to those skilled in the art that variations and modifications of the above-described embodiments and methods may be made without departing from the invention. Furthermore, while in the exemplary embodiment, the tubes forming the tube bundle are circular in cross section, tubes having noncircular cross sections may be advantageously used in heat exchangers incorporating features of the invention and are within the scope of the invention. Also, while the helical axis of the tube bundle extends from partition to partition, the tube bundle need not be continuously helical from partition to partition, as long as it helices about a common helical axis for a portion of its length. The present invention is limited only to the extent required by the appended claims and the rules and principles of applicable law. Furthermore, references to directions such as "above" or "below" as used herein are intended to be illustrative and are not to be construed as limiting the invention. Unless otherwise defined, the terms "generally," "substantially," or "approximately," when used in connection with mathematical concepts or measurements, mean within ±10 degrees of the angle or within 10 percent of the measurement, whichever is greater.

Claims

1. A helical coil heat exchanger comprising a plurality of tube bundles of helical tubes, each tube bundle including a plurality of helical tubes of the same twist, each tube bundle having a common helical axis and an outer surface having peaks and valleys, the helical axes of each bundle being parallel to and radially offset from the helical axes of the other bundles, and each bundle being positioned so that the apex of one bundle is between the apex of its adjacent bundle.

2. 2. The heat exchanger of claim 1, wherein each bundle comprises a plurality of helical tubes having the same coil diameter, tube diameter, and pitch.

3. 3. The heat exchanger of claim 2, wherein all of the tube bundles have the same coil diameter, tube diameter, and pitch.

4. 4. The heat exchanger of claim 3, wherein the tube bundles have the same number of tubes per bundle.

5. 5. A heat exchanger according to claim 4, wherein the two tube bundles are arranged in groups of four adjacent bundles.

6. 5. The heat exchanger of claim 4, wherein the three tube bundles are arranged in groups of three adjacent bundles.

7. 5. The heat exchanger of claim 4 wherein the four tube bundles are arranged in groups of four adjacent bundles.

8. 5. The heat exchanger of claim 4, wherein the five tube bundles are arranged in groups of five adjacent bundles.

9. 5. The heat exchanger of claim 4, wherein each bundle has a coil diameter d, a tube diameter d, and a tube bundle center located on the tube bundle axis, and the distance between the centers of adjacent tube bundles is less than the sum of the coil diameter and the tube diameter.

10. 10. The heat exchanger of claim 9, wherein the tubes of adjacent tube bundles are tangent at points between the peaks and valleys of the tube bundle.

11. 1. A heat exchanger for transferring heat between a first fluid and a second fluid, comprising: a first tube bundle, a second tube bundle, a third tube bundle, and a shell surrounding the first tube bundle and the second tube bundle; the first tube bundle having a first set of three tubes for flowing a first fluid therethrough, each tube having an inlet forming a first set of inlets and an outlet forming a first set of outlets, the inlets of the first set attached at their inlet ends to inlet supports and the outlets of the first set attached at their outlet ends to outlet supports, each tube of the first set lying along a first common helical axis, each of the plurality of first tubes having the same twist direction, substantially the same helical pitch, helical radius, and symmetrical peaks and valleys along the bundle length; the second tube bundle having a second set of three tubes for the first fluid to flow therethrough, each tube of the second set having an inlet forming a second inlet set, each tube of the second set having an outlet forming a second outlet set, the second inlet set attached at its outlet end to an inlet support, the second inlet set attached at its outlet end to an outlet support, each tube of the second set oriented along a second common helical axis in the same helical sense as the first tube bundle, the helical path of the second set having substantially the same helical pitch, helical radius and symmetrical peaks and valleys along the bundle length as the tubes of the first set; the third tube bundle having a third set of three tubes for the first fluid to flow therethrough, each tube of the third set having an inlet forming a third inlet set, each tube of the third set having an outlet forming a third outlet set, the third inlet set being attached at its outlet end to an inlet support, each tube of the third set being oriented along a third common helical axis in the same helical sense as the first and second tube bundles, the helical path of the third set having substantially the same helical pitch, helical radius and symmetrical peaks and valleys along the bundle length as the first and second sets of tubes; the shell surrounds the first and second tube bundles, the shell having inlet and outlet ports for flowing a second fluid through the shell over the first, second, and third tube bundles and symmetrical peaks and valleys along the length of the tube bundles; the helical axes of the second and third tube bundles are parallel to each other and radially offset from each other, and the apex of each tube is located between the apexes of adjacent tube bundles; A heat exchanger characterized by:

12. 12. The heat exchanger of claim 11, wherein each tube bundle has a coil diameter D, a tube diameter d, and a tube bundle center located on the tube bundle axis, and the distance between the centers of adjacent tube bundles is less than the sum of the coil diameter length and the tube diameter length.

13. further including a plurality of additional adjacent tube bundles, each tube bundle consisting of a set of three tubes, each tube of which has a first fluid flowing therethrough, each tube set having an inlet forming an inlet set, each tube set having an outlet forming an outlet set, the inlet sets being attached at their inlet ends to inlet supports and the outlet sets being attached at their outlet ends to outlet supports, each of the plurality of tubes following a helical path along a common helical axis in the same twist sense as the first tube bundle, and each helical path of each of the additional tube sets having substantially the same helical pitch, helical radius and symmetrical peaks and valleys along the length of the bundle as the first tube set; 12. The heat exchanger of claim 11, wherein the helical axis of each of the additional tube bundles is parallel to the helical axes of the other tube bundles, and the additional tube bundles are arranged such that the apex of each bundle is located between the apexes of adjacent tube bundles.

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