WO2023203500A1

WO2023203500A1 - Heat exchanger tube

Info

Publication number: WO2023203500A1
Application number: PCT/IB2023/053992
Authority: WO
Inventors: Meethan GOKOOL
Original assignee: Bosch Management Services (Pty) Ltd
Priority date: 2022-04-19
Filing date: 2023-04-19
Publication date: 2023-10-26

Abstract

A heat exchanger tube (10, 210, 310) for use in a heat exchanger. A first fluid is conveyed inside the tube (10, 210, 310) and a second fluid is conveyed externally to the tube (10, 210, 310). The heat exchanger tube (10, 210, 310) has a wall (12, 212, 312) defining an internal surface (14, 214, 314) across which the first operating fluid flows, in use, and an external surface (16) across which the second fluid flows, in use. The wall (12, 212, 312) carries deformations (18, 218, 318) which deform both the internal (14, 214, 314) and external (16, 216, 316) surfaces such that the heat transfer area of the internal (14, 214, 314) and external (16, 216, 316) surfaces across which the first and second fluids flow respectively is increased to improve the heat transfer characteristics of the heat exchanger tube (10, 210, 310).

Description

HEAT EXCHANGER TUBE

BACKGROUND TO THE INVENTION

This invention relates to a heat exchanger tube.

Heat exchanger tubes are commonly used in various industrial applications for transferring heat between two fluids. In the sugar industry, heat exchanger tubes are commonly used in a number of applications including vacuum pans for processing sugar syrup. The processing of sugar syrup typically involves three main phases, namely concentration, pan boiling and pan tightening. In the concentration phase the preheated sugar syrup is concentrated through boiling until the desired concentration is achieved. In the pan boiling phase, sugar syrup concentration is maintained as sugar crystals are grown. Thereafter, the pan tightening phase begins during which the concentration of the sugar syrup is increase and the sugar crystal developed until the desired crystal size is reached. The ability to evaporate liquid from the sugar syrup effectively is a key element to increasing and maintaining its concentration. The rate of evaporator is dependent on heat transfer between the fluid outside the heat exchanger tubes and the sugar syrup carried within them. The heat exchanger tubes therefore play an important role in the efficiency of the vacuum pan and, accordingly, the sugar manufacturing process.

Heat exchanger tubes currently being used in vacuum pans are typically plain, smooth-walled tubes with limited surface area available for heat transfer. Furthermore, these known smooth-walled heat exchanger tubes create a laminar boundary layer on their smooth surfaces. This laminar boundary layer limits heat transfer and, accordingly, the achievable evaporation rate in the vacuum pan.

Alternative heat exchanger tubes that aim to address at least some of the shortcomings of smooth-walled tubes carry diametric or tangential fins on their external surfaces to increase the surface area through which heat transfer takes place. The limited heat transfer area of smooth-walled heat exchanger tubes makes them less efficient and, accordingly, inferior when compared to that of finned tubes. However, a significant disadvantage of the finned heat exchanger tubes is that their external or major diameters are altered, typically increased, as a result of the fins and, accordingly, cannot necessarily be retrofitted to existing heat exchangers. Finned heat exchanger tubes are also susceptible to fouling and have the disadvantage of increased difficulty in cleaning.

It is accordingly an object of the invention to provide a heat exchanger tube that will, at least partially, address the above disadvantages.

It is also an object of the invention to provide a heat transfer tube which will be a useful alternative to existing heat transfer tubes.

It is yet another object of the invention to provide a method of increasing the efficiency of a heat exchanger, particularly but not exclusively one used in the sugar industry. SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided a heat exchanger tube for use in a heat exchanger in which a first fluid is conveyed inside the tube and a second fluid is conveyed externally to the tube, the heat exchanger tube including a wall defining an internal surface across which the first operating fluid flows, in use, and an external surface across which the second fluid flows, in use, wherein the wall carries deformations which deform both the internal and external surfaces such that the heat transfer area of the internal and external surfaces across which the first and second fluids flow respectively is increased to improve the heat transfer characteristics of the heat exchanger tube.

The wall of the heat exchanger tube may be embossed. The deformations are preferably part of an embossed pattern carried by the wall of the heat exchanger tube.

The deformations may be shaped to deform the wall radially inward towards the axial centreline of the heat exchanger tube without increasing the external diameter of the tube. The deformations may be indentations created in the wall of the heat exchanger tube.

The deformations may have substantially circular profiles when viewed in plan.

The deformations may be arranged in annular rings that are spaced apart axially along at least part of the longitudinal length of the heat exchanger tube. The deformations of adjacent annular rings may be off-set to create a staggered arrangement of deformations, thereby to disturb the fluid boundary layer to create turbulent flow of fluid across the internal and/or external surface(s) of the heat exchanger tube. In one embodiment the deformations of adjacent annular rings are off-set to create a spiral arrangement or pattern to promote centrifugal fluid separation via density within the tube, thereby to enhance heat transfer by promoting the flow of higher density particles closer to the wall.

The distance between adjacent deformations in an axial direction may be reduced to create continuous deformations in the form of ridges on the internal surface and grooves on the external surface.

In one embodiment the deformations may be axially aligned to create continuous, linear deformations that run longitudinally along the wall to increase surface area for heat transfer while limiting fluid turbulence.

In accordance with another aspect of the invention there is provided a method of improving the efficiency of a heat exchanger, the method including increasing internal and external heat transfer surface areas of a heat exchanger tube over which a first and second fluid flow respectively, wherein the internal and external heat transfer surface areas are increased by deforming a wall of the heat exchanger tube.

The method may include increasing the surface area available for heat transfer per axial increment by creating deformations in or on the wall of the heat exchanger tube.

The step of deforming the wall of the heat exchanger tube may include embossing deformations into the wall.

The method may include disturbing a fluid boundary layer on an internal surface and/or an external surface of the heat exchanger tube, thereby increasing the turbulence of the fluid flow across the internal heat transfer surface area and/or the external heat transfer surface area.

In accordance with another aspect of the invention there is provided a method of manufacturing the heat exchanger tube according to the first aspect of the invention, the method including creating the deformations in an embossing process, selected from a forming, stamping, imprinting, pressing, rolling, tooling, punching, casting or moulding process, a machining processing or additive manufacturing process.

In accordance with another aspect of the invention there is provided for the use of a heat exchanger tube according to the first aspect of the invention in a cross-flow heat exchanger. The cross-flow heat exchanger may be one used in a sugar processing plant, typically in a vacuum pan, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a heat exchanger tube in accordance with the invention;

Figure 2 shows an enlarged perspective view of the heat exchanger tube of Figure 1 ;

Figure 3 shows a side view of the heat exchanger tube of Figure 1 ;

Figure 4 shows a cross-sectional end view of the heat exchanger tube of Figure 1 taken along A - A;

Figure 5 shows a cross-sectional end view of the heat exchanger tube of Figure 1 taken along B - B;

Figure 6 shows a cross-sectional side view of the heat exchanger tube of Figure 1 taken along C-C; Figure 7 shows an enlarged detail view of the cross-sectional view of Figure 6 on which the internal and external flow patterns across the surface of the tube are illustrated;

Figure 8 shows a perspective view of a second embodiment of a heat exchanger tube in accordance with the invention;

Figure 9 shows a side view of the heat exchanger tube of Figure 8;

Figure 10 shows an end view of the heat exchanger tube of Figure 8;

Figure 11 shows a perspective view of a third embodiment of a heat exchanger tube in accordance with the invention;

Figure 12 shows a side view of the heat exchanger tube of Figure 1 1 ;

Figure 13 shows an end view of the heat exchanger tube of Figure 11 ; and

Figure 14 shows a graphical representation of experimental results of the performance of the heat exchanger tube of Figure 8 in comparison to a known, smooth walled tube.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Additionally, the words "lower", "upper", "upward", "down" and "downward" designate directions in the drawings to which reference is made. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Referring to the drawings, in which like numerals indicate like features, a nonlimiting example of a heat exchanger tube in accordance with the invention is generally indicated by reference numeral 10.

It is envisaged that the heat exchanger tube 10 will be particularly useful in a heat exchanger (not shown in the drawings) such as a cross-flow heat exchanger, for example. However, is should be understood that the invention is not limited to a cross-flow heat exchanger and could be used in any other type of heat exchanger, such as a concurrent or counter current heat exchanger. Irrespective of the type of heat exchanger, the tube 10 is used to transfer heat between two operating fluids.

The tube 10 has a wall 12 defining an internal surface 14 and an external surface 16. In use, a first operating fluid is conveyed inside the tube 10 and, accordingly, flows across or over the internal surface 14 while a second operating fluid is conveyed outside or externally to the tube and, accordingly, flows across or over the external surface area 16.

The wall 12 of the tube 10 carries deformations 18. The deformations 18 deform both the internal 14 and external 16 surfaces such that both the internal and external surface areas across which the first and second fluids flow respectively are increased. The deformation of the wall 12 is shown in detail in Figures 4 to 7.

Best seen in Figures 4 and 5, the deformations 18 deform the wall 12 radially inward. In other words, the deformations 18 are shaped so as to deform the wall 12 inward toward the axial centreline 20 of the heat exchanger tube 10. The deformations 18 are in the form of indentations created in the wall 12 of the tube 10. It can be seen that the deformations 18 do not alter the major or external diameter of the tube 10 substantially, preferably at all.

In the preferred embodiment of the invention the deformations 18 are embossed. The deformations 18 are preferably in the form of an embossed pattern carried by the wall 12. The words “emboss”, “embossed” and “embossing” should be interpreted broadly to include a process of creating the deformations 18 by forming, stamping, imprinting, pressing, rolling, tooling, punching, casting, moulding or any other similar process. In one method of manufacturing the tube 10, a forming process, either hot or cold forming, is used to create the deformations 18 in the wall 12. The deformations 18 are integrally formed in the wall 12 of the heat transfer tube 10, typically in a single process or action. In other words, the deformations 18 are not separate or distinct to the wall 12 of the tube 10 but are instead defined by the tube. It is envisaged that other manufacturing methods could be used, such as machining or additive manufacturing, for example, where the deformations 18 are created in or on the wall 12 of the tube 10.

In this illustrated embodiment of the tube 10, the deformations 18 have substantially circular profiles when viewed in plan. The deformations 18 are typically between about 5 and 15 mm, preferably about 10 mm, in diameter. The deformations 18 are typically between about 2 and 10 mm, preferably about 5 mm, deep. It should be understood that the depth of the deformations 18 can also be described as their height or the distance by which they extent above the internal surface 14. The thickness of the wall 12 of the tube 10 is typically between about 0.5 mm and 5 mm depending on the application in which the tube 10 is used. It has been found that in the exemplified sugar manufacturing application, a tube 10 with a wall thickness of about 1.5 mm and deformations 18 of about 10 mm in diameter and about 5 mm in depth achieves the desired advantages.

The deformations 18 are also arranged in annular rings 22 that are spaced apart axially along at least part of the longitudinal length of the tube 10. Furthermore, the deformations 18 of adjacent annular rings 22 are off-set to create a staggered arrangement of deformations. The staggered arrangement acts to disturb the fluid boundary layers on the internal 14 and external 16 surfaces further to create more turbulent flow of fluid across the internal 14 and external 16 surfaces of the tube 10.

It should be understood that the heat exchanger tube 10 of the invention is not limited to any particular deformation profile and that the embossed pattern could include deformations of any shape and/or size. The invention is also not limited to any particular arrangement of pattern in which the deformations 18 are arranged. Instead, the important aspect of the invention is that the wall 12 is covered, at least partially, with deformations 18 that deform both the internal 14 and external 16 surfaces of the heat exchanger tube 10.

Returning now to the illustrated embodiment of the heat exchanger tube 10, the turbulent flow of the first and second fluids across the internal 14 and external 16 surfaces is indicated in Figure 7 by the reference numerals 24 and 26 respectively. From this figure it can be seen how the fluid boundary layers on the internal 14 and external 16 surfaces are disturbed by the deformations 18 so as to improve the heat transfer between the first and second fluids.

From the above description of the heat exchanger tube 10 of the invention it should be understood that the embossed pattern of deformations 18 improves the heat transfer characteristics of the heat exchanger tube and, accordingly, the heat exchanger. The efficiency is improved by the increase in the heat transfer surface area of the tube 10 and the creation of turbulent flow in the boundary layer as a result of the addition of the embossed deformations 18 in the wall 12. It should be understood that the surface area density, i.e. the surface area available for heat transfer per axial increment, is increased as a result of the deformations 18. The addition of the embossed deformations 18 modifies the tube wall structure such that there are indentations which extend from the outer surface 16 of the wall 12 towards the axial centreline 20 of the tube. Although the formations 18 are described and illustrated as indentations, it is envisaged that they could also take the form of protrusions on the exterior surface 16 of the tube 10. In such alternative embodiment the deformations will extent outward away from the axial centreline of the tube 10. In this alternative embodiment, the surface area density will be increased and a turbulent boundary layer will be achieved substantially the same as in the illustrated embodiment of the tube 10.

In use the heat exchanger tube 10 is used to improve the efficiency and, accordingly, performance of a heat exchanger. In the exemplified use case the heat exchanger tube 10 is used to improve the efficiency of a cross-flow heat exchanger used in a vacuum pan in a sugar manufacturing process. In particular, the embossed deformations 18 on the tube 10 result in increased evaporation rates to increase the concentration of fluids in the sugar manufacturing process. The additional heating surface area and increased turbulence resulting from the embossed deformations 18 decrease the required size and/or energy consumption of the equipment and/or increase the throughput or processing capacity. Another significant advantage of the heat exchanger tube 10 of the invention is that it can be retrofitted to existing heat exchangers. This is achievable because the deformations 18 do not change the external or major diameter of the tube 10 materially, preferably at all. Accordingly, the external or major diameter of the tube 10 of the invention is no larger than that of a known heat transfer tube currently being used in the heat exchanger. It is believed that the tube 10 is particularly suitable for retrofitting applications in which additional capacity or energy efficiency can be realised with existing equipment by replacing the existing tubes with the embossed tubes 10 of the present invention. From the above description it should be understood that due to the ease at which the heat exchanger tube 10 can be retrofitted to existing heat exchangers an increase in performance can be realised at very low cost and labour.

Referring now to Figures 8 to 10 of the drawings, a non-limiting example of a second embodiment of the heat exchanger tube in accordance with the invention is generally indicated by reference numeral 210. The features of the heat exchanger tube 210 are indicated using the same refence signs used above in describing the features of the heat exchanger tube 10 but are preceded by the numeral 2. The heat exchanger tube 210 is substantially similar to the heat exchanger tube 10 and, accordingly, only the most significant differences will be described.

In this second embodiment the deformations 218 carried on the wall 212 of the tube 210 are off-set to create a spiral arrangement or pattern. In particular, the deformations 218 of adjacent annular rings 222 are off-set to create the spiral arrangement of deformations. This spiral arrangement of embossed deformations 218 promote centrifugal fluid separation via density within the tube 210. This further enhances fluid heat transfer by promoting the flow of higher density particles closer to the tube wall 212.

Referring now to Figures 1 1 to 13 of the drawings, a non-limiting example of a third embodiment of the heat exchanger tube in accordance with the invention is generally indicated by reference numeral 310. The features of the heat exchanger tube 310 are indicated using the same refence signs used above in describing the features of the heat exchanger tube 10 but are preceded by the numeral 3. The heat exchanger tube 310 is substantially similar to the heat exchanger tubes 10 and 210 and, accordingly, only the most significant differences will be described.

In this third embodiment, the deformations 318 carried on the wall 312 of the tube 310 are aligned to create linear deformations that run longitudinally along the wall 312. In particular, the embossing intervals between aligned deformations 318 are reduced to create continuous, linear deformations. As a result, the wall 312 carries a series of continuous, linear and elongate deformations 318 that are arranged circumferentially around the wall 312. The deformations 318 essentially create continuous grooves on the exterior surface 16 and continuous ridges on the internal surface 14. In this embodiment, the grooves and ridges are semi-circular in cross-section. The shape or profile of the grooves and ridges are not limited being semi-circular in cross-sectional and could vary depending on the tooling and/or manufacturing technique used. Although the continuous deformations 318 are illustrated to be linear it is envisaged that in alternative embodiments not illustrated in the drawings the deformations could create any other pattern, such as a spiral pattern similar to the one used in the tube 210 according to the second embodiment, for example. It should therefore be understood that the deformations could be off-set while being continuous.

The linear arrangement of deformations 318 used in this third embodiment of the tube 310 illustrated in the drawings provides added surface area for heat transfer while limiting fluid turbulence. It is envisaged that the tube 310 will be particularly useful in applications in which laminar flow is preferred to protect product integrity while still achieving the advantages of the increased heat transfer area and reduced internal volume of the tube 310.

It should be understood that, in addition to the advantages as set out above in respect of the second 210 and third 310 embodiments of the heat exchanger tube of the invention, the same advantages as described in respect of the first embodiment 10 of the heat exchanger tube are achieved insofar as the features of the second and thirds embodiments are consistent with the features of the first embodiment of the heat exchanger tube.

In all three illustrated embodiments of the heat exchanger tubes 10, 210, 310, the deformations 18, 218, 318 span a major section of the length of the tube. It is envisaged that the deformations 18, 218318 could span the entire length of the tube 310. It is further envisaged that the formations 18, 218, 318 could span sections of the tube. For example, the deformations 18, 218, 318 do not necessarily need to be continuous along the entire portion of the tube 10, 210, 310 on which they are formed. The formations 18, 218, 318 could be divided into axial sections.

Experimental testing was conducted using a heat exchanger tube 210 according to the second embodiment of the invention for comparison with known smooth-walled heat exchanger tubes. The comparative results are shown in the graphical representation of Figure 14, which plots the equivalent specific evaporation rate (kg/(h.m²) against the Massecuite Brix (%) for both heat exchanger tubes. The results for the heat exchanger tube 210 according to the present invention are indicated by the series designated by the reference numeral 30 while the results for the smooth-walled heat exchanger tube are indicated by the series designated by the reference numeral 40.

As shown in Figure 14 the results are shown across the three different phases of the pan cycle discussed above. During the concentration phase, the heat exchanger tube 210 showed an improvement of more than 50% compared to the smooth-walled tube. During the pan boiling phase, the heat exchanger tube 210 showed an improvement of more than 25 to 35%. In the final, pan tightening phase the improvement was more than 20%. During testing the use of the heat exchanger tube 210 resulted in an overall pan cycle time improvement of more than 30% compared to the smooth-walled tube. This improvement significantly enhanced pan floor capacity.

In the exemplified use case, when the tubes 10 are used in a batch pan, the deformations 18 protruding into the internal volume of the tube decreases the internal tube volume and thereby the pan graining volume, i.e. the initial volume. The reduction in the pan graining volume, in turn, has the advantage of decreasing the start-up time, i.e. the pan start-up inertia, and accordingly increases its productivity. The reconfiguration of the wall 12 to incorporate the embossed pattern of deformations 18, increases the heating surface areas on both the internal 14 and external 16 surfaces of the tube 10. This addresses the shortcoming of known heat exchanger tubes, which have deformations such as fins that affect only one side of the tube. Another advantage over the known tubes currently used in the sugar industry is the ability of the deformations 18 to disrupt the fluid boundary layer by increasing turbulence in the fluid flow, which in turn improves heat transfer. In other words, the embossed pattern of deformations 18 prevents the formation of a laminar boundary layer of fluid associated with the known heat exchanger tubes currently being used in the industry. The increase in turbulence of the fluid within the tube 10 contributes to the heating efficiency of the tube and therefore the equipment in which it is incorporated.

Also, the embossed formations are formed in the wall 12 so that they extend radially inward such that the major diameter of the tube 10 is not altered, thereby allowing for the retrofitting of the tube to existing heat exchangers. Another advantage of the tube 10 of the invention is that both the interior 14 and exterior 16 surfaces are deformed in a single process, without increasing the external diameter of the tube 10.

Although the exemplified use case is in the sugar industry, the heat exchanger tube 10, 210, 310 of the invention can be used in various other industries and applications. The heat exchanger tube 10, 210, 310 of the invention provides a cost-effective alternative to conventional means of increasing equipment capacity and improving energy efficiency in various other industries where shell and tube heat exchangers are used. The heat exchanger tube 10, 210, 310 of the invention is ideal for retrofit applications across various industries. The heat exchanger tube 10, 210, 310 allows for simple and inexpensive upgrades, with minimal or no vessel modifications being required.

It will be appreciated that the above description only provides some embodiments of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention. It is easily understood from the present application that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments.

The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.

Claims

1. A heat exchanger tube (10, 210, 310) for use in a heat exchanger in which a first fluid is conveyed inside the tube (10, 210, 310) and a second fluid is conveyed externally to the tube (10, 210, 310), the heat exchanger tube (10, 210, 310) including a wall (12, 212, 312) defining an internal surface (14, 214, 314) across which the first operating fluid flows, in use, and an external surface (16, 216, 316) across which the second fluid flows, in use, wherein the wall (12, 212, 312) carries deformations (18, 218, 318) which deform both the internal (14, 214, 314) and external (16, 216, 316) surfaces such that the heat transfer area of the internal (14, 214, 314) and external (16, 216, 316) surfaces across which the first and second fluids flow respectively is increased to improve the heat transfer characteristics of the heat exchanger tube (10, 210, 310).

2. A heat exchanger tube (10, 210, 310) according to claim 1 , wherein the wall (12, 212, 312) of the heat exchanger tube is embossed.

3. A heat exchanger tube (10, 210, 310) according to claim 2, wherein the deformations (18, 218, 318) are part of an embossed pattern carried by the wall (12, 212, 312) of the heat exchanger tube.

4. A heat exchanger tube (10, 210, 310) according to any one of claims 1 to 3, wherein the deformations (18, 218, 318) are shaped to deform the wall (12, 212, 312) radially inward towards the axial centreline (20, 220, 320) of the heat exchanger tube (10, 210, 310) without increasing the external diameter of the tube.

5. A heat exchanger tube (10, 210, 310) according to claim 4, wherein the deformations (18, 218, 318) are indentations created in the wall (12) of the heat exchanger tube (10, 210, 310).

. A heat exchanger tube (10, 210, 310) according to any one of claims 1 to 5, wherein the deformations (18, 218, 318) have substantially circular profiles when viewed in plan. . A heat exchanger tube (10, 210, 310) according to any one of claims 1 to 6, wherein the deformations (18, 218, 318) are arranged in annular rings that are spaced apart axially along at least part of the longitudinal length of the heat exchanger tube (10, 210, 310). . A heat exchanger tube (10, 210, 310) according to claim 7, wherein the deformations (18, 218, 318) of adjacent annual rings are off-set to create a spiral arrangement or pattern to promote centrifugal fluid separation via density within the tube (10, 210, 310), thereby to enhance heat transfer by promoting the flow of higher density particles closer to the wall (12). . A heat exchanger tube (10, 210) according to claim 7, wherein the deformations (18, 218) of adjacent annular rings are off-set to create a staggered arrangement of deformations, thereby to disturb the fluid boundary layer to create turbulent flow of fluid across the internal (14, 214) and/or external (16, 216) surfaces of the heat exchanger tube. 0. A heat exchanger tube (10, 210, 310) according to any one of claims 1 to 9, wherein the distance between adjacent deformations (318) in an axial direction is reduced to create continuous deformations in the form of ridges on the internal surface (314) and grooves on the external surface (316). 1. A heat exchanger tube (310) according to claim 10, wherein the deformations (318) are axially aligned to create continuous, linear deformations that run longitudinally along the wall (312) to increase surface area for heat transfer while limiting fluid turbulence. A method of improving the efficiency of a heat exchanger, the method including increasing internal and external heat transfer surface areas of a heat exchanger tube (10, 210, 310) over which a first and second fluid flow respectively, wherein the internal and external heat transfer surface areas are increased by deforming a wall (12, 212, 312) of the heat exchanger tube. A method according to claim 12, including increasing the surface area available for heat transfer per axial increment by creating deformations (18, 218, 318) in or on the wall (12, 212, 312) of the heat exchanger tube. A method according to claim 13, wherein the step of deforming the wall (12, 212, 312) of the heat exchanger tube (10, 210, 310) includes embossing deformations (18, 218, 318) into the wall. A method according to any one of claims 12 to 14, including disturbing a fluid boundary layer on an internal surface (14, 214) and/or an external surface (16, 216) of the heat exchanger tube (10, 210), thereby increasing the turbulence of the fluid flow across the internal heat transfer surface area and/or the external heat transfer surface area. A method of manufacturing the heat exchanger tube (10, 210, 310) according to any one of claims 1 to 1 1 , the method including creating the deformations (18, 218, 318) in an embossing process, selected from a forming, stamping, imprinting, pressing, rolling, tooling, puncing, casting or moulding process, a machining processing or additive manufacturing process. Use of a heat exchanger tube (18, 218, 318) according to any one of claims 1 to 11 in a cross-flow heat exchanger. Use of a heat exchanger tube (18, 218, 318) according to any one of claims 1 to 11 in a cross-flow heat exchanger in a sugar processing plant.