HK1216661A1

HK1216661A1 - Tube bundle for shell-and-tube heat exchanger and a method of use

Info

Publication number: HK1216661A1
Application number: HK16104482.9A
Authority: HK
Inventors: 布拉若．留比契奇
Original assignee: 科氏传热有限合伙公司
Priority date: 2013-03-14
Filing date: 2014-01-31
Publication date: 2016-11-25
Also published as: CN105431702A; EP2972041A1; WO2014143435A1; CA2904471A1; US20140262172A1; KR20150126677A; EP2972041A4

Abstract

A tube bundle is provided for a shell-and-tube heat exchanger. The tube bundle includes a plurality of elongated tubes, each of which has an intermediate portion that has a cross section in the form of a flattened circle with at least one axis of symmetry. The tubes are arranged in concentric circles with the axis of symmetry extending tangentially to the circle to facilitate rotational flow of a shell-side fluid.

Description

Tube bundle for shell and tube heat exchanger and method of use

Background

This invention relates generally to shell and tube heat exchangers and, more particularly, to tube bundles for such heat exchangers and methods of use thereof.

Shell and tube heat exchangers are used in a variety of applications to cause heat exchange between fluid streams. In these heat exchangers, a first fluid, known as the tube-side fluid, passes through the elongated tubes of a bundle of tubes contained within a generally cylindrical shell. A large number of tubes are included in the tube bundle and they extend in parallel and spaced relationship to each other. The tubes are fixed at their opposite ends to a substantially planar head plate, also referred to as a tube sheet. The second fluid, commonly referred to as the shell-side fluid, flows within the shell in open spaces around the tubes and undergoes heat exchange with the first fluid stream flowing within the tubes.

Shell and tube heat exchangers are constructed in different known ways to provide the desired flow arrangement between the tube side fluid and the shell side fluid. For example, in a single pass tube and single pass shell arrangement, straight tubes are used and the inlet and outlet nozzles for the tube side fluid flow are located at opposite ends of the heat exchanger. Inlet and outlet nozzles for shell side fluid are also located at opposite ends of the heat exchanger. In this arrangement, the flow of the fluid streams may be co-current or counter-current. In co-current flow, inlet nozzles for both tube-side and shell-side fluids are located at the same end of the heat exchanger and outlet nozzles for the fluids are located at the opposite end of the heat exchanger. The tube-side and shell-side fluids then enter at the same end of the heat exchanger, flow along its length, and exit at the opposite end of the heat exchanger. In counter-flow, the inlet nozzles for the fluid are located at opposite ends of the heat exchanger and the outlet nozzles are also located at opposite ends of the heat exchanger. The fluid then enters the opposite end of the heat exchanger, flows in the opposite direction along its length, and exits at the opposite end of the heat exchanger.

In another flow arrangement, U-shaped tubes are used instead of straight tubes and the inlet and outlet nozzles for the tube-side fluid are located at the same end of the heat exchanger. The tube-side fluid flows along one arm (leg) of each U-shaped tube and then reverses direction and flows back along the other arm of the U-shaped tube. In this arrangement both the inlet and outlet nozzles for shell side fluid may be located at the same end of the heat exchanger as the inlet and outlet nozzles for tube side fluid, in which case longitudinal baffles are provided between the arms of the U-tubes forming separate flow paths which allow shell side fluid on one side of the longitudinal baffles to flow in one direction and then reverse and flow in the opposite direction along the other side of the longitudinal baffles.

Alternatively, the inlet and outlet nozzles for the shell-side fluid may be located at opposite ends of the shell, so that the shell-side fluid flows in only one direction along the length of the heat exchanger. Other multi-pass shells and multi-pass tube arrangements are conventionally used and are further defined in the standard of the institute of tubular heat exchanger manufacturers (the standard and digital heat exchanger exchange manufacturers association), which is incorporated herein by reference in its entirety.

In many applications, the tubes in the tube bundle pass through baffles spaced along the longitudinal length of the tube bundle to provide structural support to the tubes and thus reduce tube sag and vibration. Each baffle also serves to divert the flow of the shell-side fluid, thereby promoting its cross flow rather than along the tubes, for better heat transfer with the tube-side fluid. The baffles are typically in the form of single or double-part cut baffles in which a quarter circle or other area of the baffle is open to allow shell-side fluid to pass through; or in the form of a disk and donut (donut) baffle, in which case the shell-side fluid flows through an annular region around the disk baffle and through a central opening of the donut baffle.

During initial assembly of the tube bundle, tie bars are typically welded to the baffles to form a cage structure, with the baffles secured in spaced apart relation. The direction of rotation of each baffle is set so that the holes in the baffles, through which the tubes are inserted, are longitudinally aligned. Because the holes are only slightly larger than the tubes to reduce leakage of fluid through the holes, the longitudinal alignment of the holes must be within tight tolerances. Once the tubes are inserted through the holes in the baffles, the ends of the tubes are secured to one or more tubesheets to form a complete tube bundle.

The tube sheets in conventional shell and tube heat exchangers are typically formed of a high strength metal or metal alloy and have a thickness much greater than the shell to withstand the operating pressures within the heat exchanger and to compensate for the structural weakness created by the large number of holes receiving the tubes in the tube sheets. The manufacture of the tubesheet is a time intensive process because the holes typically must be drilled through the tubesheet thickness individually. The drilling operation creates holes of circular cross-section, limiting the tubes to those having the same circular cross-section. Although better heat exchange can be obtained when using tubes having an elliptical or other non-circular cross-section, heretofore, the circular cross-section of the holes in the tube sheet has prevented the use of tubes having an elliptical, oblong, oval or egg-shaped cross-section in shell-and-tube heat exchangers.

Summary of The Invention

In one aspect, the present invention relates to a tube bundle for a shell and tube heat exchanger. The tube bundle includes a plurality of hollow, elongated tubes extending in parallel and spaced relationship to one another and arranged in a series of concentric circular patterns. Each tube has: a first end for entry of a first fluid flowing within the tube along a longitudinal length of the tube; an opposite second end for the first fluid outflow conduit; and an intermediate portion between the first and second ends. The middle portion of each tube has an oblate cross-section. In one embodiment, the oblate shape has an axis of symmetry. In another embodiment, the oblate shape has two axes of symmetry, one axis being shorter than the other. The tubes are oriented such that the axis of symmetry or the longer of the axes of symmetry extends tangentially to the concentric circle in which the tubes are disposed.

The tube bundle further includes a first tube sheet having an aperture into which the first ends of the tubes extend and are secured, and a plurality of baffles at spaced locations along the longitudinal lengths of the tubes for supporting the tubes and directing the flow of a second fluid outside the tubes. Each baffle has a cutout portion for passage of fluid and a plurality of openings through which at least some of the tubes are inserted. The cutouts of adjacent ones of the baffles are rotationally offset about the central longitudinal axis of the tube bundle. The intermediate portion of each tube is at least a majority of the longitudinal length of each tube, at least 75% of the length of each tube, at least 90% of the length of each tube, or at least 95% of the length of each tube. In one embodiment, the first and second ends of the tubes have a circular cross-section, wherein the diameter of the second end is smaller than the diameter of the first end and equal to or smaller than the length of the short symmetry axis of the middle portion of the respective tube. The tube bundle also includes a plurality of flow deflectors, each plate extending in one direction between and contacting an adjacent one of the baffles and extending in an opposite direction along a cutout in said adjacent one of the baffles. The plates serve to induce a swirling flow of the shell side fluid.

In another aspect, the present invention relates to a shell and tube heat exchanger wherein the tube bundle is arranged as described above.

In a further aspect, the invention relates to a method of operating a heat exchanger and inducing a shell-side fluid swirl to promote heat transfer using the baffles described above with tube-side fluid.

Brief Description of Drawings

FIG. 1 is a perspective view from one end of a heat exchanger made in accordance with one embodiment of the present invention with shell portions of the heat exchanger broken away to show internal tube bundles;

FIG. 2 is a perspective view of the heat exchanger shown in FIG. 1 taken from the opposite end;

FIG. 3 is an enlarged fragmentary perspective view of the heat exchanger showing an end portion of the tube bundle;

FIG. 4 is an enlarged fragmentary perspective view illustrating the process of assembling the tube bundle by inserting individual tubes through openings in the baffles;

FIG. 5 is a side view of the heat exchanger taken in vertical section;

FIG. 6 is an enlarged fragmentary end view taken in vertical section along line 6-6 of FIG. 5 showing a pipe and tie rod inserted through a portion of one of the baffles;

FIG. 7 is a fragmentary end view of one of the tubes;

FIG. 8 is an elevation view taken from one end of the tube shown in FIG. 7;

FIG. 9 is an elevation view taken of the opposite end of the tube;

FIG. 10 is an illustration of variables used to calculate an elliptical cross-section of a portion of a tube;

FIG. 11 is a perspective view from one end of the heat exchanger with portions of the shell of the heat exchanger broken away to show another embodiment of the inner tube bundle and with most of the tubes removed to better illustrate other components of the tube bundle; and

FIG. 12 is a fragmentary perspective view of the tube bundle shown in FIG. 11 with the tubes removed to allow for an illustration of the flow path of the shell-side fluid.

Detailed Description

Turning now to the drawings in greater detail and initially to fig. 1-5, a heat exchanger constructed in accordance with the present invention is indicated generally by the numeral 10. Heat exchanger 10 is a shell and tube heat exchanger and includes an elongated shell 12 having a front end 14, an opposite end 16, and an open interior volume 18. The shell 12 is generally cylindrical in configuration, although other shapes may be used. The shell 12 is formed of a metal, polymer, or other material that is generally inert to the fluid within the shell 12 and is capable of withstanding the pressure and temperature within the shell 12 during operation of the heat exchanger 10.

An inlet nozzle 20 extends from the forward end 14 of the shell 12 for introducing shell-side fluid into the interior volume 18 of the shell 12. An outlet nozzle 22 extends from the shell 12 for removing shell-side fluid out of the interior volume 18 of the shell 12. In one embodiment, the outlet nozzle 22 is located at the end 16 opposite the front end 14 where the inlet nozzle 20 of the housing 12 is located. In another embodiment, the outlet nozzle 22 is located at the forward end 14 along with the inlet nozzle 20 and a longitudinally extending baffle (not shown) is located within the interior volume 18 of the housing 12. The longitudinally extending baffle urges shell side fluid from the inlet nozzle 20 toward the opposite end 16 of the shell 12, and then reverses direction to flow back toward the front end 14 on the opposite side of the baffle, where it exits the interior volume 18 of the shell 12 through the outlet nozzle 22. The inlet nozzle 20 and the outlet nozzle 22 extend generally radially from the shell 12, but they may extend from the shell 12 in other directions, such as tangential.

In the single pass tube side embodiment shown, an inlet channel or head 24 defining an internal cavity 25 and having an inlet nozzle 26 for tube side fluid is provided to close the open front end 14 of the housing 12. An outlet passage or head 28 defining an internal cavity 29 and having an outlet nozzle 30 for tube side fluid is provided to close the open end 16 of the housing 12. In a two-pass tube side embodiment, the inlet header 24 and the outlet header 28 are both located at the front end 14 of the shell 12 and the other end 16 of the shell is closed. In the illustrated embodiment, the inlet nozzle 26 and the outlet nozzle 30 extend along a longitudinal central axis of the shell 12, but they may extend in other directions, such as perpendicular to the longitudinal central axis of the shell 12.

A tube bundle 32 is located within the open interior volume 18 of the shell 12 and includes a plurality of hollow, elongated tubes 34 extending in parallel, spaced apart relation to one another and arranged in a preselected pattern. Each tube 34 has an open first end 36 for entry of a tube-side fluid flowing within the tube 34 along the longitudinal length of the tube 34, and an opposite open second end 38 for exit of the first fluid from the tube 34. The tube 34 is constructed of a thermally conductive, corrosion resistant material such as various metals including copper alloys, stainless steel, carbon steel, non-ferrous copper alloys, inconel (inconELalloys), nickel, hastelloy (Hastelloyalloys), and titanium.

The tube bundle 32 includes a plurality of plate-like baffles 40 located at spaced apart locations along the longitudinal length of the tubes 34. The baffles 40 serve to redirect the flow of shell-side fluid as it flows over the exterior of the tubes 34. The baffles 40 also serve to support and maintain the desired positioning of the tubes 34. As best shown in fig. 4, each baffle 40 has a separate opening 42 through which the tubes 34 extend. The opening 42 is sized slightly larger than the tube 34 to allow the tube 34 to be inserted longitudinally through the opening 42 while minimizing the amount of shell side fluid that can pass through the opening 42.

The baffles 40 are formed as incomplete disks and are sized so that their outer edges contact or are proximate to the inner surface of the shell 12. When the baffle 40 is disposed perpendicular to the central longitudinal axis of the shell, the baffle 40 may be formed as an incomplete annular disk. When the baffle 40 is inclined with respect to the vertical plane, the baffle 40 may be formed as a partially elliptical disk. The baffles 40 are referred to as incomplete disks because they each include a cutout 44 that allows shell-side fluid to pass through the baffles 40. In one embodiment, the cutout 44 transects the outer edge of the baffle 40. The cutouts 44 may be formed as sectors, segments, or other portions of the baffle 40. In one embodiment, cutout 44 is a sector having an angle of between 45 and 270 degrees, between 75 and 240 degrees, 85 and 230 degrees, 90 degrees, 135 degrees, or 180 degrees.

The cutouts 44 in adjacent baffles 40 are rotationally or otherwise offset from one another about the longitudinal central axis of the shell 12 to form the desired shell-side fluid flow path as shell-side fluid flows within the interior volume 18 of the shell 12 from the inlet nozzle 26 to the outlet nozzle 30. In one embodiment, the cutouts 44 in the baffles 40 are hemispherical and the cutouts 44 in adjacent baffles 40 are rotated 180 degrees from each other, creating a sinusoidal flow path for the shell-side fluid. In another embodiment, the cutouts 44 in the baffles 40 are quarter-circles and the cutouts 44 in adjacent baffles 40 are rotated 90 degrees from each other to create a helical flow of shell side fluid.

The tube bundle 32 may include tie rods 46 that extend through and are secured to the edge regions of the baffles 40 to secure the baffles 40 at the desired longitudinal spacing and rotational orientation. The number of tie rods 46 can be varied as desired. In one embodiment, four to twenty-four tie bars 46 are evenly spaced around the edge of baffle 40.

The tube bundle 32 includes at least one tube sheet 48 located at the forward end 14 of the shell 12 and separating the open interior volume 18 of the shell 12 from the interior cavity 25 of the inlet header 24. The tubesheet 48 is generally disk-shaped with an edge that seals against the inner surface of the shell 12 in a conventional manner. As best shown in fig. 5, the tubesheet 48 includes a plurality of apertures 49 that extend completely through the thickness between the opposite faces of the tubesheet 48. The first ends 36 of the tubes 34 are inserted through the holes 49 of the tube sheet 48 and secured therein. If the tubes 34 are U-shaped, the second ends 38 of the tubes 34 are inserted into and secured in other holes 49 in the tube sheet 48. In the embodiment shown, where the tubes 34 are straight, a second tube sheet 50 is located at the opposite end 16 of the shell 12 and separates the open interior volume 18 of the shell 12 from the interior cavity 29 of the outlet head 28. The second ends 38 of the tubes 34 are inserted through the holes 49 extending through the second tube sheet 50 and secured therein. As best seen in fig. 3, in the illustrated embodiment, the first and second ends 36 and 38 of the tubes 34 are received into sleeves 51 that fit into apertures 49 in the tube sheets 48 and 50.

The tube sheets 48 and 50 must withstand the operating pressures within the heat exchanger 10. Because the presence of the holes 49 significantly reduces the strength of the tubesheets 48 and 50, the tubesheets 48 and 50 are formed of a high strength material having a thickness several times the thickness of the shell 12. In one embodiment, each of the tube sheets 48 and 50 is formed of a high strength metal or metal alloy and has a thickness of two to ten inches. Because of the hardness and thickness of the material used for the tubesheets 48 and 50, in one embodiment of the tubesheets 48 and 50, the holes 49 are annular in cross-section and are formed in a drilling operation.

Between first and second ends 36 and 38 of tube 34The middle portion 52 of each tube 34 in between has an oblate cross-section. In one embodiment, the oblate shape has two axes of symmetry extending at orthogonal angles relative to each other, with one axis being shorter than the other, such that the cross-section of the tube 34 forms a geometric shape such as an ellipse or an ellipse. In another embodiment, the oblate shape has only one axis of symmetry, such that the cross-section of the tube 34 forms a geometric shape, such as an oval or egg shape. When the cross-section of tube 34 has two axes of symmetry, such as shown in FIG. 10, tube 34 has a long axis 54 of preselected length at the widest portion of the cross-section of tube 34 and a perpendicular shorter axis 56 at the narrowest portion of the cross-section of tube 34. In the embodiment shown in FIG. 10, the cross-section of the tube 34 is elliptical and the radius r₁And r₂At the point of tangency P of the two curves₁And P₂Are collinear. At the limit of its domain, the radius r₁At a focal point Q₁And Q₂Transverse to the major axis "a" of the ellipse, which is also the radius r₂The center point of (a). The ratio of the minor axis "b" of the ellipse to the major axis "a" of the ellipse ranges from 0.22 < b/a < 0.92.

The intermediate portion 52 of each tube 34 comprises at least a majority of the longitudinal length of each tube 26, at least 75% of the length of each tube 34, at least 90% of the length of each tube 34, or at least 95% of the length of each tube 34. As best seen in fig. 7-10, in one embodiment, the first end 36 of each tube 34 is circular in cross-section, having a larger diameter than the second end 36. The diameter of the first end 36 of each tube 34 is also greater than the length of the minor axis 56 (FIG. 10) of the cross-section of the intermediate portion 52 of the tube 34 and less than the length of the major axis 54 (FIG. 10) of each tube 34. The second end 38 of each tube 34 also has an annular cross-section with a diameter equal to or slightly less than the length of the minor axis 56 (fig. 10) of the cross-section of the intermediate portion 52 of the tube 34.

Each tube 34 may be manufactured from stock having a circular cross-section of the same diameter as the first end 36. The tube 34 is then flattened by one or more series of rollers to form the desired geometry for the cross-section of the intermediate section 52. The second end 38 is then formed by a tapering tool to obtain a circular cross-section with a smaller diameter. As can be seen in fig. 7, each tube 34 includes a transition segment 58 between the first end 36 and the intermediate portion 52 and a similar transition segment 60 between the second end 38 and the intermediate portion 52. The tubes 34 may be unmodified or they may have extended or increased inner and/or outer surfaces. In one embodiment, the extended surface is a scale (not shown) that extends longitudinally along the tube 34.

In one embodiment, the openings 42 in the baffle 40 have the same elliptical, oblong, oval, egg-shaped, or other geometric shape as the cross-sectional shape of the intermediate portion 52 of the tube 34. The opening 42 is slightly larger than the middle portion 52 of the tube 34 so that the tube 34 can be inserted through the opening 42 and maintain a tight fit within the opening 42 to reduce the amount of shell side fluid that can pass through the opening 42. As an example, the opening 42 is about 0.4mm larger than the outer dimension of the tube 34. The openings 42 may be arranged with their long axes extending vertically, horizontally, or in a direction between vertical and horizontal. The openings 42 may each be oriented in the same direction or they may be independently oriented.

The openings 42 in the baffles 40 are arranged to position the tubes 34 in a preselected series of concentric circular patterns, with the major axis 56 of each tube 34 extending tangentially to the associated ring.

In the embodiment shown in fig. 11 and 12, the tube bundle 32 further includes a plurality of baffles 62 extending generally perpendicular to the baffles 40 and arranged to direct the swirling flow in the shell-side fluid as indicated by lines 64 in fig. 11 and arrows 66 in fig. 12 flow along the length of the shell 12. Each plate 62 extends between adjacent pairs of baffles 40 or between an end baffle 40 and a tube sheet 48 or 50. Each plate 62 extends in one direction between adjacent baffles 40 and contacts adjacent baffles 40. Each of the plates 62 extends in opposite directions along the entire length of the cutout portions 44 of adjacent ones of the baffles 44. When one edge of the cutout 44 in one baffle 40 is longitudinally aligned with an opposite edge of the cutout 44 in the mating baffle 40, as shown in FIG. 2, the plates 62 can extend perpendicular to the baffles 40 and radially from the central longitudinal axis of the tube bundle 32. When the edges of the cutouts 44 are misaligned due to additional rotational positioning of the downstream baffle 40, the plate 62 will not extend perpendicular to the baffle 40 or radial to the central longitudinal axis, but will twist from that direction so that the edges of the plate 62 extend along the cutouts 44 of the adjacent baffle 40. The plates 62 may be generally planar or they may be curved in more than one direction to facilitate the flow of shell-side fluid along the faces of the plates 62.

During assembly of tube bundle 32, tube sheets 48 and 50 and baffles 40 are spaced a desired preselected distance from each other and their openings 42 are aligned. Tie rods 46 are then welded or otherwise secured to the baffles 40 to secure the baffles 40 in their spaced and rotated relationship to each other. One end of each tie rod 46 may be threaded into a threaded hole (not shown) in one of the tube sheets 48 and 50 and the other end of the tie rod 46 is secured to the last baffle 40 at the opposite end of the tube bundle 32.

Once the cage structure has been formed by the tube sheets 48 and 50, the baffles 40 and the tie rods 46, the smaller diameter second end 38 of each tube 34 is inserted through one of the holes 49 in the tube sheet 48 and the second end 38 is moved longitudinally through one of the openings 42 in the first baffle 40 at one end of the tube bundle 32. The tubes 34 are then rotated as necessary to align the long and short axes 54 and 56 of the intermediate portion 52 of the tubes 34 with the respective axes of the openings 42 in the end stop 40. The tubes 34 are then fed through the aligned openings 42 in successive baffles 40 until the first ends 36 of the tubes 34 pass through the last baffle 40 at the opposite end of the tube bundle 32 and are positioned within one of the holes 49 in the other tube sheet 50. The remaining tubes 34 are inserted in the same manner through holes 49 in the tubesheet 48, the openings 42 in each baffle 40, and holes 49 in the other tubesheet 50. In one embodiment, the first and second ends 36 and 38 of the tubes 34 that project slightly beyond the tube sheets 48 and 50 are then secured to the tube sheets 48 and 50, such as by being enlarged into the tube sheets 48 and 50 or welded to the tube sheets 48 and 50. The assembled tube bundle 32 is then inserted into the shell 12 of the heat exchanger 10 in a conventional manner

In use, a shell-side fluid is introduced into the interior volume 18 of the shell 12 of the heat exchanger 10 through the inlet nozzle 20. The shell-side fluid encounters the plate 62, which causes the shell-side fluid to swirl and then enter each cutout 44, which allows the shell-side fluid to pass through successive baffles 40 as the shell-side fluid flows along the length of the shell 12. The shell-side fluid is then removed from the interior volume 18 of the shell 12 through the outlet nozzle 22.

Tube-side fluid is introduced into the interior cavity 25 of the inlet head 24 through an inlet nozzle 26. The tube-side fluid is then distributed to a first end 36 of the tube 34 and flows along the length of the tube 34 before exiting a second end 38 of the tube 34. The tube side fluid then enters the internal cavity 29 of the outlet header 28 before exiting the heat exchanger 10 through the outlet nozzle 30.

As the shell-side and tube-side fluids flow in the heat exchanger 10, heat transfer occurs from one fluid to the other. The non-circular intermediate portions 52 of the tubes 34 in the tube bundle 32 provide higher tube-side and shell-side heat transfer coefficients than conventional round tubes because the flattened circular cross-section of the intermediate portions 52 of the tubes 34 has a greater surface area than the circular cross-section of the tubes 34 from which the intermediate portions 52 are formed. By arranging the tubes 34 in concentric circles (with the axis of symmetry or the longer of the two axes of symmetry extending tangentially to the circle), the desired shell side fluid swirl is promoted, thereby increasing the heat transfer performance of the tube bundle 32.

From the foregoing, it will be seen that this invention is one which is sufficiently modified to attain all the ends and objects set forth above, together with other advantages which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the present invention.

Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

1. A tube bundle for a shell and tube heat exchanger, the tube bundle comprising:

a plurality of hollow, elongated tubes extending in parallel and spaced apart relation to one another and arranged in a preselected pattern, each of said tubes having a first end for entry of a first fluid flowing within the tube along the longitudinal length of the tube and an opposite second end for exit of the first fluid from said tube and an intermediate portion between the first and second ends;

a first tube sheet having an aperture, a first end of the tube extending into the aperture and secured;

a plurality of baffles at spaced locations along the longitudinal length of the tubes for supporting the tubes and directing a second fluid to flow outside the tubes, each of the baffles having a cutout portion for fluid flow therethrough and a plurality of openings through which at least some of the tubes are inserted, wherein the cutout portions of adjacent ones of the baffles are rotationally offset about the central longitudinal axis of the tube bundle; and

a plurality of baffles, each of said plates extending in one direction between and in contact with adjacent ones of said baffles and extending in an opposite direction along said cutouts in said adjacent ones of said baffles.

2. The tube bundle of claim 1, wherein said intermediate portion of each tube has an oblate circular cross-section having at least one axis of symmetry.

3. The tube bundle of claim 2, wherein said preselected pattern of said tube arrangement is a series of concentric circles.

4. The tube bundle of claim 3, wherein said tubes are arranged within each of said concentric circles such that said at least one axis of symmetry of each tube extends tangential to said concentric circles.

5. The tube bundle of claim 4, wherein said oblate is in the form of an elliptical or oblong geometric shape.

6. The tube bundle of claim 4, wherein said oblate is in the form of an oval or egg-shaped geometry.

7. The tube bundle of claim 4, wherein said oblate has two axes of symmetry, one axis being shorter than the other.

8. The tube bundle of claim 4, wherein the cross-section of the middle portion of each tube has two axes of symmetry, one axis being shorter than the other, and wherein the first and second ends of the tubes are circular in cross-section and one of the first and second ends has a diameter that is less than the length of the short axis of symmetry.

9. The tube bundle of claim 4, wherein said intermediate portion of each tube having said flattened circular cross-section is a majority of the longitudinal length of each tube.

10. The tube bundle of claim 4, wherein said intermediate portion of each tube having said flattened circular cross-section is at least 75% of the longitudinal length of each tube.

11. The tube bundle of claim 4, wherein said intermediate portion of each tube having said flattened circular cross-section is at least 90% of the longitudinal length of each tube.

12. The tube bundle of claim 4, wherein said intermediate portion of each tube having said flattened circular cross-section is at least 95% of the longitudinal length of each tube.

13. The tube bundle of claim 4, wherein said cutout is a sector or segment of a baffle.

14. A tube bundle for a shell and tube heat exchanger, the tube bundle comprising:

a plurality of hollow, elongated tubes extending in parallel and spaced relationship to one another and arranged in a preselected series of concentric circular patterns, each of said tubes having a first end for entry of a first fluid flowing within the tube along the longitudinal length of the tube and an opposite second end for exit of the first fluid from the tube, and an intermediate portion between the first and second ends, wherein said intermediate portion of each tube has an oblate cross-section with at least one axis of symmetry, wherein said tubes are arranged within respective said concentric circles such that said at least one axis of symmetry of each tube extends tangential to said concentric circles;

a first tubesheet having an aperture into which a first end of the tube extends and is secured;

a plurality of baffles at spaced locations along the longitudinal length of the tubes for supporting the tubes and directing a second fluid flow outside the tubes, wherein each of the baffles is in the form of a partial disc and is disposed in a plane generally perpendicular to the central longitudinal axis of the tube bundle;

cutouts in each of the baffles and transverse to the baffle edges for passage of fluid, wherein the cutouts of adjacent ones of the baffles are rotationally offset about a central longitudinal axis of the tube bundle;

a plurality of openings in each of the baffles through which at least some of the tubes are inserted, wherein the openings are shaped to conform to a cross-section of a middle portion of the tubes; and

a plurality of baffles, each said plate extending in one direction between and contacting adjacent ones of said baffles and extending in an opposite direction along said cutouts in said adjacent ones of said baffles.

15. The tube bundle of claim 14, wherein said first tube sheet has additional openings into which the second ends of the tubes extend and are secured.

16. The tube bundle of claim 14, including a second tube sheet having an opening into which the second ends of the tubes extend and are secured.

17. The tube bundle of claim 14, wherein each of said tubes has said cross-section in the form of an oblate circle along its entire longitudinal length.

18. A shell and tube heat exchanger, comprising:

a shell having an interior volume in which the tube sheet of claim 1 is disposed;

an inlet nozzle extending from the shell for introducing shell-side fluid into the interior volume of the shell;

an outlet nozzle extending from the shell for removing shell-side fluid from the interior volume of the shell;

a further inlet nozzle for introducing a tube-side fluid to the first ends of the tubes within the tube bundle; and

another outlet nozzle for removing tube side fluid from the second ends of the tubes within the tube bundle.

19. A method of operating a shell-and-tube heat exchanger having a shell with an interior volume, wherein the tube sheet of claim 1 is disposed in the interior volume, the method comprising the steps of:

introducing a shell-side fluid into the interior volume of the shell at one end of the shell;

causing the shell-side fluid to swirl in the interior volume as the shell-side fluid encounters the respective plates and thereafter into the respective cutouts;

passing the shell-side fluid through cutouts in successive ones of the baffles as the shell-side fluid passes from the one end of the shell to the opposite end of the shell;

introducing a tube-side fluid to a first end of a tube;

flowing a tube-side fluid along a length of the tube;

wherein heat exchange occurs between the tube-side fluid and the shell-side fluid as the tube-side fluid flows along the length of the tubes and the shell-side fluid passes from one end of the shell to an opposite end of the shell within the interior volume.