Title of Invention	HEAT TRANSFER TUBE AND METHOD OF AND TOOL FOR MANUFACTURING THE SAME
Abstract	A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2) formed from ridges (1) formed along a surface of the tube at an angle relative to the longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from the inner surface in a direction that is not substantially perpendicular to the longitudinal axis, characterised in that the protrusions (2) are formed by the steps of: a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4); and b. lifting the ridge layers to form protrusions (2) having a protrusion height, protrusion thickness, and protrusion pitch.

Title of Invention

HEAT TRANSFER TUBE AND METHOD OF AND TOOL FOR MANUFACTURING THE SAME

Abstract

A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2) formed from ridges (1) formed along a surface of the tube at an angle relative to the longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from the inner surface in a direction that is not substantially perpendicular to the longitudinal axis, characterised in that the protrusions (2) are formed by the steps of: a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4); and b. lifting the ridge layers to form protrusions (2) having a protrusion height, protrusion thickness, and protrusion pitch.

Full Text	HEAT TRANSFER TUBE AND METHOD OF AND TOOL FOR MANUFACTURING THE SAME Field of the Invention This invention relates to a heat transfer tube having protrusions on the inner surface of the tube and a method of and tool for forming the protrusions on the inner surface of the tube. Background of the Invention This invention relates to a heat transfer tube having an enhanced inner surface to facilitate heat transfer from one side of the tube to the other. Heat transfer tubes are commonly used in equipment, such as, for example, flooded evaporators, falling film evaporators, spray evaporators, absorption chillers, condensers, direct expansion coolers, and single phase coolers and heaters, used in the refrigeration, chemical, petrochemical, and food-processing industries. A variety of heat transfer mediums may be used in these applications, including, but not limited to, pure water, a water glycol mixture, any type of refrigerant (such as R-22, R-134a, R-123, etc.), ammonia, petrochemical fluids, and other mixtures. An ideal heat transfer tube would allow heat to flow completely uninhibited from the interior of the tube to the exterior of the tube and vice versa. However, such free flow of heat across the tube is generally thwarted by the resistance to heat transfer. The overall resistance of the tube to heat transfer is calculated by adding the individual resistances from the outside to the inside of the tube or vice versa. To improve the heat transfer efficiency of the tube, tube manufacturers have striven to uncover ways to reduce the overall resistance of the tube. One such way is to enhance the outer surface of the tube, such as by forming fins on the outer surface. As a result of recent advances in enhancing the outer tube surface (see, e.g., U.S. Patent Nos. 5,697,430 and 5,996,686), only a small part of the overall tube resistance is attributable to the outside of the tube. For example, a typical evaporator tube used in a flooded chiller with an enhanced outer surface but smooth inner surface typically has a 10:1 inner resistance:outer resistance ratio. Ideally, one wants to obtain an inside to outside resistance ratio of 1:1. It becomes all the more important, therefore, to develop enhancements to the inner surface of the tube that will significantly reduce the tube side resistance and improve overall heat transfer performance of the tube. It is known to provide heat transfer tubes with alternating grooves and ridges on their inner surfaces. The grooves and ridges cooperate to enhance turbulence of fluid heat transfer mediums, such as water, delivered within the tube. This turbulence increases the fluid mixing close to the inner tube surface to reduce or virtually eliminate the boundary layer build-up of the fluid medium close to the inner surface of the tube. The boundary layer thermal resistance significantly detracts from heat transfer performance by increasing the heat transfer resistance of the tube. The grooves and ridges also provide extra surface area for additional heat exchange. This basic premise is taught in U.S. Patent No. 3,847,212 to Withers, Jr. et al. The pattern, shapes and sizes of the grooves and ridges on the inner tube surface may be changed to further increase heat exchange performance. To that end, tube manufacturers have gone to great expense to experiment with alternative designs, including those disclosed in U.S. Patent No. 5,791,405 to Takima et al., U.S. Patent Nos. 5,332,034 and 5,458,191 to Chiang et al., and U.S. Patent No. 5,975,196 to Gaffaney et al. In general, however, enhancing the inner surface of the tube has proven much more difficult than the outer surface. Moreover, the majority of enhancements on both the outer and inner surface of tubes are formed by molding and shaping the surfaces. Enhancements have been formed, however, by cutting the tube surfaces. Japanese Patent Application 09108759 discloses a tool for centering blades that cut a continuous spiral groove directly on the inner surface of a tube. Similarly, Japanese Patent Application 10281676 discloses a tube expanding plug equipped with cutting tools that cut a continuous spiral slot and upstanding fin on the inner surface of a tube. U.S. Patent No. 3,753,364 discloses forming a continuous groove along the inner surface of a tube using a cutting tool that cuts into the inner tube surface and folds the material upwardly to form the continuous groove. While all of these inner surface tube designs aim to improve the heat transfer performance of the tube, there remains a need in the industry to continue to improve upon tube designs by modifying existing and creating new designs that enhance heat transfer performance. Additionally, a need also exists to create designs and patterns that can be transferred onto the tubes more quickly and cost-effectively. As described hereinbelow, applicants have developed new geometries for heat transfer tubes as well as tools to form these geometries, and, as a result, have significantly improved heat transfer performance. Summary of the Invention This invention provides an improved heat transfer tube surface and a method of formation thereof that can be used to enhance heat transfer performance of tubes used in at least all of the above-referenced applications (i.e., flooded evaporators, falling film evaporators, spray evaporators, absorption chillers, condensers, direct expansion coolers, and single phase coolers and heaters, used in the refrigeration, chemical, petrochemical, and food-processing industries). The inner surface of the tube is enhanced with a plurality of protrusions that significantly reduce tube side resistance and improve overall heat transfer performance. The protrusions create additional paths for fluid flow within the tube and thereby enhance turbulence of heat transfer mediums flowing within the tube. This increases fluid mixing to reduce the boundary layer build-up of the fluid medium close to the inner surface of the tube, such build-up increasing the resistance and thereby impeding heat transfer. The protrusions also provide extra surface area for additional heat exchange. Formation of the protrusions in accordance with this invention can result in the formation of up to five times more surface area along the inner surface of the tube than with simple ridges. Tests show that the performance of tubes having the protrusions of this invention is significantly enhanced. The method of this invention includes using a tool, which can easily be added to existing manufacturing equipment, having a cutting edge to cut through ridges on the inner surface of the tube to create ridge layers and a lifting edge to lift the ridge layers to form the protrusions. In this way, the protrusions are formed without removal of metal from the inner surface of the tube, thereby eliminating debris which can damage the equipment in which the tubes are used. The protrusions on the inner surface of the tube can be formed in the same or a different operation as formation of the ridges. Tubes formed in accordance with this application may be suitable in any number of applications, including, for example, applications for use in the HVAC, refrigeration, chemical, petrochemical, and food-processing industries. The physical geometries of the protrusions may be changed to tailor the tube to a particular application and fluid medium. It is an object of this invention to provide improved heat transfer tubes. It is another object of this invention to provide an improved heat transfer tube having protrusions on its inner surface. It is yet another object of this invention to provide a method of forming an improved heat transfer tube having protrusions on its inner surface. It is a further object of this invention to provide an innovative tool for forming improved heat transfer tubes. It is a still further object of this invention to provide a tool for forming protrusions on the inner surface of heat transfer tubes. These and other features, objects and advantages of this invention will become apparent by reading the following detailed description of preferred embodiments, taken in conjunction with the accompanying drawings. Brief Description of the Accompanying Drawings FIG. la is a fragmentary perspective view of the partially-formed inner surface of one embodiment of a tube of this invention. FIG. lb is a side elevation view of the tube shown in FIG. la in the direction of arrow a. FIG. lc is a side elevation view similar to FIG. lb except that the protrusions protrude from the inner surface of the tube in a direction that is not perpendicular to tube axis s. FIG. 1d is a front elevation view of the tube shown in FIG. la in the direction of arrow b. FIG. le is a top plan view of the tube shown in FIG. la. FIG. 2 is a photomicrograph of an inner surface of one embodiment of a tube of this invention. FIG. 3 is a photomicrograph of an inner surface of an alternative embodiment of a tube of this invention. FIG. 4 is a side elevation view of one embodiment of the manufacturing equipment that can be used to produce tubes in accordance with this invention. FIG. 5 is a perspective view of the equipment of FIG. 4. FIG. 6a is a perspective view of one embodiment of the tool of this invention. FIG. 6b is a side elevation view of the tool shown in FIG. 6a. FIG. 6c is a bottom plan view of the tool of FIG. 6b. FIG. 6d is a top plan view of the tool of FIG. 6b. FIG. 7a is a perspective view of an alternative embodiment of the tool of this inventioa FIG. 7b is a side elevation view of the tool shown in FIG. 7a. FIG. 7c is a bottom plan view of the tool of FIG. 7b. FIG. 7d is a top plan view of the tool of FIG. 7b. FIG. 8a is a fragmentary perspective view of the partially-formed inner surface of an alternative embodiment of a tube of this invention where the depth of the cut through the ridges is less than the helical ridge height. FIG. 8b is a fragmentary perspective view of the partially-formed inner surface of an alternative embodiment of a tube of this invention where the depth of the cut through the ridges is greater than the helical ridge height. FIG. 9a is a fragmentary top plan view of the inner surface of another embodiment of a tube in accordance with this invention. FIG. 9b is an elevation view of the tube shown in FIG. 9a in the direction of arrow 22. FIG. 10a is a fragmentary view of an inner surface of a tube of this invention, showing the tool approaching the ridge in direction g for cutting a protrusion from the ridge in direction g. FIG. 1 0b is a fragmentary view of an alternative inner surface of a tube of this invention, showing the tool approaching the ridge in direction g for cutting a protrusion from the ridge in direction g. FIG. 1 la is a schematic of the inner surface of a tube in accordance with this invention showing the angular orientation between the ridges and grooves, whereby the ridges and grooves are opposite hand helix. FIG. 1 lb is a schematic of the inner surface of a tube in accordance with this invention showing the angular orientation between the ridges and grooves, whereby the ridges and grooves are same hand helix. FIG. 12 is a bar graph comparing the tube-side heat transfer coefficients of various tubes of the prior art and of tubes in accordance with this invention. FIG. 13 is bar graph comparing the overall heat transfer coefficients of various tubes of the prior art and of tubes in accordance with this invention. Detailed Description of the Drawings FIGS, la-e show the partially-formed inner surface 18 of one embodiment of the tube 21 of this invention. Inner surface 18 includes a plurality of protrusions 2. Protrusions 2 are formed from ridges 1 formed on inner surface 18. Ridges 1 are first formed on inner surface 18. The ridges 1 are then cut to create ridge layers 4, which are subsequently lifted up to form protrusions 2 (best seen in FIGS, la and lb). This cutting and lifting can be, but does not have to be, accomplished using tool 13, shown in FIGS. 6a-d and 7a-d and described below. It should be understood that a tube in accordance with this invention is generally useful in, but not limited to, any application where heat needs to be transferred from one side of the tube to the other side of the tube, such as in single-phase and multi-phase (both pure liquids or gases or liquid/gas mixtures) evaporators and condensers. While the following discussion provides desirable dimensions for a tube of this invention, the tubes of this invention are in no way intended to be limited to those dimensions. Rather, the desirable geometries of the tube, including protrusions 2, will depend on many factors, not the least important of which are the properties of the fluid flowing through the tube. One skilled in the art would understand how to alter the geometry of the inner surface of the tube, including the geometry of ridges 1 and protrusion 2, to maximize the heat transfer of the tube used in various applications and with various fluids. Ridges 1 are formed on inner surface 18 at a helix angle a to the axis s of the tube (see FIGS, la and le). Helix angle a may be any angle between 0°-90°, but preferably does not exceed 70°. One skilled in the art will readily understand that the preferred helix angle a will often depend, at least in part, on the fluid medium used. The height er of ridges 1 should generally be greater the more viscous the liquid flowing through tube 21. For example, a height er of greater than zero (preferably, but not necessarily, at least 0.001 inches) up to 25% of the inside diameter of the tube (Dj) will generally be desirable in a tube sample used with a water/glycol mixture for low temperature applications. For purposes of this application, Di is the inside diameter of tube 21 measured from inner surface 18 of tube 21. The axial pitch P of ridges 1 depends on many factors, including helix angle a, the number of ridges 1 formed on inner surface 18 of tube 21, and the inside diameter D of tube 21. While any pitch may be used, the ratio of is preferably at least 0.002, and the ratio of is preferably between approximately 0.001- 0.25. Again, however, one skilled in the art will readily understand that these preferred ratio values will often depend, at least in part, on the fluid medium used and operating conditions (e.g., the temperature of the fluid medium). Ridge layers 4 are cut at an angle 0 to axis s that is preferably between approximately 20°-50°, inclusive, and more preferably around 30°. The axial pitch of protrusions 2 may be any value greater than zero and generally will depend on, among other factors, the relative revolutions per minute between the tool (discussed below) and the tube during manufacture, the relative axial feed rate between the tool and the tube during manufacture, and the number of tips provided on the tool used to form the protrusions during manufacture. While the resulting protrusions 2 can have any thickness SPi the thickness Sp is preferably approximately 20-100% of pitch Pap. The height ep of protrusions 2 is dependent on the cutting depth t (as seen in FIGS, lb, 8a, and 8b) and angle 0 at which the ridge layers 4 are cut. The height ep of protrusions 2 is preferably a value at least as great as the cutting depth t up to three times the cutting depth t It is preferable, but not necessary, to form ridges 1 at a height erand set the cutting angle 0 at a value that will result in the height ep of protrusions 2 being at least approximately double the height of ridges 1. Thus, the ratio is preferably between approximately 0.002-0.5 (i.e., is double the preferred range of the ratio of approximately 0.001-0.25). FIGS, la and lb show cutting depth t equal to the height erof ridges 1 so that the base 40 of protrusion 2 is located on the inner surface 18 of tube 21. The cutting depth t need not be equal to the ridge height e, however. Rather, the ridges 1 can be cut only partially through ridges 1 (see FIG. 8a) or beyond the height of ridges 1 and into tube wall 3 (see FIG. 8b). In FIG. 8a, the ridges 1 are not cut through their entire height e,.so that the base 40 of protrusions 2 is positioned further from the inner surface 18 of tube 21 than the base 42 of ridges 1, which is located on the inner surface 18. In contrast, FIG. 8b illustrates a cutting depth t of beyond the ridge height e„ so that at least one wall of the protrusions 2 extends into tube wall 3, beyond the inner surface 18 and ridge base 42. When ridge layers 4 are lifted, grooves 20 are formed between adjacent protrusions 2. Ridge layers 4 are cut and lifted so that grooves 20 are oriented on inner surface 18 at an angle T to the axis s of tube 21 (see FIGS, le, 1 la, and 1 lb), which is preferably, but does not have to be, between approximately 80°-100°. The shape of protrusions 2 is dependent on the shape of ridges 1 and the orientation of ridges 1 relative to the direction of movement of tool 13. In the embodiment of FIGS, la-e, protrusions 2 have four side surfaces 25, a sloped top surface 26 (which helps decrease resistance to heat transfer), and a substantially pointed tip 28. The protrusions 2 of this invention are in no way intended to be limited to this illustrated embodiment, however, but rather can be formed in any shape. Moreover, protrusions 2 in tube 21 need not all be the same shape or have the same geometry. Whether the orientation of protrusions 2 is straight (see FIG. 10a) or bent or twisted (see FIG. 10b) depends on the angle p formed between ridges 1 and the direction of movement g of tool 13. If angle p is less than 90°, protrusions 2 will have a relatively straight orientation, such as is shown in FIG. 10a. If angle p is more than 90°, protrusions 2 will have a more bent and/or twisted orientation, such as, for example, is shown in FIG. 10b. During manufacture of tube 21, tool 13 maybe used to cut through ridges 1 and lift the resulting ridge layers 4 to form protrusions 2. Other devices and methods for forming protrusions 2 may be used, however. Tool 13 can be made from any material having the structural integrity to withstand metal cutting (e.g. steel, carbide, ceramic, etc.), but is preferably made of a carbide. The embodiments of the tool 13 shown in FIGS. 6a-d and 7a-d generally have a tool axis q, two base walls 30, 32 and one or more side walls 34. Aperture 16 is located through the tool 13. Tips 12 are formed on side walls 34 of tool 13. Note, however, that the tips can be mounted or formed on any structure that can support the tips in the desired orientation relative to the tube 21 and such structure is not limited to that disclosed in FIGS. 6a-d and 7a-d. Moreover, the tips may be retractable within their supporting structure so that the number of tips used in the cutting process can easily be varied. FIGS. 6a-d illustrate one embodiment of tool 13 having a single tip 12. FIGS. 7a- d illustrate an alternative embodiment of tool 13 having four tips 12. One skilled in the art will understand mat tool 13 may be equipped with any number of tips 12 depending on the desired pitch P,iP of protrusions 2. Moreover, the geometry of each tip need not be the same for tips on a single tool 13. Rather, tips 12 having different geometries to form protrusions having different shapes, orientations, and other geometries maybe provided on tool 13. Each tip 12 is formed by the intersection of planes A, B, and C The intersection of planes A and B form cutting edge 14 that cuts through ridges 1 to form ridge layers 4. Plane B is oriented at an angle FIG. 6b). Angle q> is defined as 90° - 9. Thus, angle (p is preferably between approximately 40°-70° to allow cutting edge 14 to slice through ridges 1 at the desirable angle 0 between approximately 20°-50°. The intersection of planes A and C form lifting edge 15 that lifts ridge layers 4 upwardly to form protrusions 2. Angle (pi_ defined by plane C and a plane perpendicular to tool axis q, determines the angle of inclination © (the angle between a plane perpendicular to the longitudinal axis s of tube 21 and the longitudinal axis of protrusions 2 (see FIG. 1c)) at which protrusions 2 are lifted by lifting edge 15. Angle = angle and thus angle on tool 13 can be adjusted to directly impact the angle of inclination 00 of protrusions 2. The angle of inclination 00 (and angle is preferably the absolute value of any angle between approximately -45° to 45° relative to the plane perpendicular to the longitudinal axis s of tube 21. In this way, protrusions can be aligned with the plane perpendicular to the longitudinal axis s of tube 21 (see FIG. lb) or incline to the left and right relative to the plane perpendicular to the longitudinal axis s of tube 21 (see FIG. lc). Moreover, the tips 12 can be formed to have different geometries (i.e., angle may be different on different tips), and thus the protrusions 2 within tube 21 may incline at different angles (or not at all) and in different directions relative to the plane perpendicular to the longitudinal axis s of tube 21. While preferred ranges of values for the physical dimensions of protrusions 2 have been identified, one skilled in the art will recognize that the physical dimensions of tool 13 may be modified to impact the physical dimensions of resulting protrusions 2. For example, the depth t that cutting edge 14 cuts into ridges 1 and angle affect the height ep of protrusions 2. Therefore, the height ep of protrusions 2 may be adjusted using the expression FIGS. 4 and 5 illustrate one possible manufacturing set-up for enhancing the surfaces of tube 21. These figures are in no way intended to limit the process by which tubes in accordance with this invention are manufactured, but rather any tube manufacturing process using any suitable equipment or configuration of equipment may be used. The tubes of this invention may be made from a variety of materials possessing suitable physical properties including structural integrity, malleability, and plasticity, such as, for example, copper and copper alloys, aluminum and aluminum alloys, brass, titanium, steel, and stainless steel. FIGS. 4 and 5 illustrate three arbors 10 operating on tube 21 to enhance the outer surface of tube 21. Note that one of the arbors 10 has been omitted from FIG. 4. Each arbor 10 includes a tool set-up having finning disks 7 which radially extrude from one to multiple start outside fins 6 having axial pitch The tool set-up may include additional disks, such as notching or flattening disks, to further enhance the outer surface of tube 21. Moreover, while only three arbors 10 are shown, fewer or more arbors may be used depending on the desired outer surface enhancements. Note, however, that depending on the tube application, enhancements need not be provided on the outer surface of tube 21 at all. In one example of a way to enhance inner surface 18 of tube 21, a mandrel shaft 11 onto which mandrel 9 is rotatably mounted extends into tube 21. Tool 13 is mounted onto shaft 11 through aperture 16. Bolt 24 secures tool 13 in place. Tool 13 is preferably locked in rotation with shaft 11 by any suitable means. FIGS. 6d and 7d illustrate a key groove 17 that may be provided on tool 13 to interlock with a protrusion on shaft 11 (not shown) to fix tool 13 in place relative to shaft 11. In operation, tube 21 generally rotates as it moves through the manufacturing process. Tube wall 3 moves between mandrel 9 and finning disks 7, which exert pressure on tube wall 3. Under pressure, the metal of tube wall 3 flows into the grooves between the finning disks 7 to form fins 6 on the exterior surface of tube 21. The mirror image of a desired inner surface pattern is provided on mandrel 9 so that mandrel 9 will form inner surface 18 of tube 21 with the desired pattern as tube 21 engages mandrel 9. A desirable inner surface pattern includes ridges 1, as shown in FIGS, la and 4. After formation of ridges 1 on inner surface 18 of tube 21, tube 21 encounters tool 13 positioned adjacent and downstream mandrel 9. As explained previously, the cutting edge(s) 14 of tool 13 cuts through ridges 1 to form ridge layers 4. Lifting edge(s) 15 of tool 13 then lift ridge layers 4 to form protrusions 2. When protrusions 2 are formed simultaneously with outside finning and tool 13 is fixed (i.e., not rotating or moving axially), tube 21 automatically rotates and has an axial movement hi this instance, the axial pitch of protrusions Pap is governed by the following formula: Where: Po is the axial pitch of outside fins 6; Z0 is the number of fin starts on the outer diameter of tube 21; and Zi is the number of tips 12 on tool 13. To obtain a specific protrusion axial pitch Pp, tool 13 can also be rotated. Both tube 21 and tool 13 can rotate in the same direction or, alternatively, both tube 21 and tool 13 can rotate, but in opposite directions. To obtain a predetermined axial protrusion pitch Pp, the necessary rotation (in revolutions per minute (RPM)) of the tool 13 can be calculated using the following formula: If the result of this calculation is negative, then tool 13 should rotate in the same direction of tube 21 to obtain the desired pitch Pp. Alternatively, if the result of this calculation is positive, then tool 13 should rotate in the opposite direction of tube 21 to obtain the desired pitch P. Note that while formation of protrusions 2 is shown in the same operation as formation of ridges 1, protrusions 2 may be produced in a separate operation from finning using a tube with pre-formed inner ridges 1. This would generally require an assembly to rotate tool 13 or tube 21 and to move tool 13 or tube 21 along the tube axis. Moreover, a support is preferably provided to center tool 13 relative to the inner tube surface 18. In this case, the axial pitch P of protrusions 2 is governed by the following formula: This formula is suitable when (1) the tube moves only axially (i.e., does not rotate) and the tool only rotates (i.e., does not move axially); (2) the tube only rotates and the tool moves only axially; (3) the tool rotates and moves axially but the tube is both rotationally and axially fixed; (4) the tube rotates and moves axially but the tool is both rotationally and axially fixed; and (5) any combination of the above. With the inner tube surface of this invention, additional paths for fluid flow are created (between protrusions 2 through grooves 20) to optimize heat transfer and pressure drop. FIG. 9a illustrates these additional paths 22 for fluid travel through tube 21. These paths 22 are in addition to fluid flow paths 23 created between ridges 1. These additional paths 22 have a helix angle α1 relative to the tube axis s. Angle α1 is the angle between protrusions 2 formed from adjacent ridges 1. FIG. 9b clearly shows these additional paths 22 formed between protrusions 2. Helix angle α1 and thus orientation of paths 22 through tube 21, can be adjusted by adjusting pitch P of protrusions 2 using the following expression If ridge helix angle a and angle T of grooves 20 are both either right hand or left hand helix (see FIG. 1 lb), then the "[-]" should be used in the above expression. Alternatively, if ridge helix angle a and angle T of grooves 20 are opposite hand helix (see FIG. 1 la), then the "[+]" should be used in the above expression. Tubes made in accordance with this invention outperform existing tubes. FIGS. 12 and 13 graphically illustrate the enhanced performance of two examples of such tubes (boiling tubes Tube No. 25 and Tube No. 14) by demonstrating the differences in the enhancement factors between these tubes. The enhancement factor is the factor by which the heat transfer coefficients (both tube-side (see FIG. 12) and overall (see FIG. 13)) of these new tubes (Tube No. 25 and Tube No. 14) increase over existing tubes (Turbo-B®, Turbo-BII, and Turbo B-III). Again, however, Tube Nos. 25 and 14 are merely examples of tubes in accordance with this invention. Other types of tubes made in accordance with this invention outperform existing tubes in a variety of applications. The physical characteristics of the Turbo-B®, Turbo-BD®, and Turbo B-m® tubes are described in Tables 1 and 2 of U.S. Patent No. 5,697,430 to Thors, et al. Turbo-B® is referenced as Tube II; Turbo-BII® is referenced as Tube III; and Turbo B-ID® is referenced as Tube IVH The outside surfaces of Tube No. 25 and Tube No. 14 are identical to that of Turbo B-III®. The inside surfaces of Tube No. 25 and Tube No. 14 are in accordance with this invention and include the following physical characteristics: FIG. 12 shows that the tube-side heat transfer coefficient of Tube No. 14 is approximately 1.8 times and Tube No. 25 is approximately 1.3 times that of Turbo B-III®, which is currently the most popular tube used in evaporator applications and shown as a baseline in FIGS. 12 and 13. Similarly, FIG. 13 shows that the overall heat transfer coefficient of Tube No. 25 is approximately 1.25 times and Tube No. 14 is approximately 1.5 times mat of Turbo B-III®. The foregoing is provided for purposes of illustrating, exlaining, and describing embodiments of this invention. Further modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention. WE CLAIM: 1. A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2) formed from ridges (1) formed along a surface of the tube at an angle relative to the longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from the inner surface in a direction that is not substantially perpendicular to the longitudinal axis, characterised in that the protrusions (2) are formed by the steps of: a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4) ; and b. lifting the ridge layers to form protrusions (2) having a protrusion height, protrusion thickness, and protrusion pitch. 2. The tube (21) as claimed in claim 1, in which others of the plurality of protrusions (2) extend from the inner surface (18) in a direction substantially perpendicular to the longitudinal axis (s). 3. The tube (21) as claimed in claim 1 or 2, wherein at least some of the plurality of protrusions (2) are bent and/or twisted. 4. The tube (21) as claimed in any preceding claim, wherein the protrusion (2) has a height that has a value no more than three times the cutting depth (t). 5. The tube as claimed in claim 4, wherein the cutting depth (t) is less than or approximately equal to the ridge height. 6. The tube as claimed in claimed in claim 4, wherein the cutting depth (t) is greater than the ridge height. 7. The tube (21) as claimed in any preceding claim, wherein at least one of the plurality of protrusions (2) has a height that has a value at least as great as the cutting depth (t). 8. The tube as claimed in any preceding claim, wherein the ridge (1) is cut through at an angle between 20° and 50°, preferably approximately 30°, relative to the longitudinal axis (s) of the tube. 9. The tube as claimed as claimed in any preceding claim, wherein the ridge (1) is formed along the inner surface (18) at an angle of no more than 70° relative to the longitudinal axis (s). 10. The tube (21) as claimed in any preceding claim, wherein the ratio of the tube (21) inside diameter (Di) to the height of the ridge (1) is in the range of 0.001 to 0.25. 11. The tube (21) as claimed in any preceding claim, wherein the ridge (1) has a height of at least 0.025 mm (0.001 inch). 12. The tube (21) as claimed in any preceding claim, having a plurality of said ridges (1) spaced at an axial pitch, wherein the ratio of the ridge axial pitch to ridge height is at least 0.002. 13. The tube (21) as claimed in any preceding claim, wherein the ridge height is greater than or equal to the cutting depth (t). 14. The tube (21) as claimed in any of claims 1 to 4 or 6 to 13, wherein the protrusion (2) comprises at least one wall that extends into the inner surface (18) of the tube beyond a base (42) of the ridge (1). 15. The tube (21) as claimed in any preceding claim, wherein the ratio of the height of each protrusion (2) to the tube inside diameter (Di) is between 0.002 and 0.5. 16. The tube (21) as claimed in any preceding claim, wherein the protrusion (2) comprises at least three side surfaces and a top surface (26). 17. The tube (21) as claimed in claim 16, wherein the top surface (26) is sloped. 18. The tube (21) as claimed in any preceding claim, wherein the protrusion (2) has a substantially pointed tip (28). 19. The tube (21) as claimed in any preceding claim, in which the plurality of protrusions (2) have a pitch and wherein the thickness of each of said plurality of protrusions is between 20% and 100% of the protrusion pitch. 20. The tube (21) as claimed in any preceding claim, comprising grooves (20) formed between the plurality of protrusions at an angle between 80° and 100° relative to the longitudinal axis of the tube. 21. Equipment, such as herein described, incorporating a tube (21) as claimed in any of claims 1 -20. 22. A tool for cutting the inner surface of a tube as claimed in claim 1, said tool comprising a tool axis and at least one tip formed by the intersection of at least a first plane, a second plane, and a third plane and having a cutting edge and a lifting edge. 23. The tool as claimed in claim 22, wherein the tool comprises at least one of carbide, steel, and ceramic. 24. The tool as claimed in claim 22, wherein the cutting edge is formed by the intersection of the first plane and the second plane. 25. The tool as claimed in claim 24, wherein the second plane is oriented at an angle between 40° and 70° relative to a plane perpendicular to the tool axis. 26. The tool as claimed in claim 22, wherein the lifting edge is formed by the intersection of the first plane and the third plane. 27. The tool as claimed in claim 26, wherein the third plane is oriented at an angle relative to a plane perpendicular to the tool axis. 28. The tool as claimed in claim 27, wherein the angle is zero. 29. The tool as claimed in claim 27, wherein the angle is not zero. 30. The tool as claimed in claim 29, wherein the angle is not more than approximately 45°. 31. The tool as claimed in claim 22, wherein said at least one tip comprises more than one tip. 32. The tool as claimed in claim 25, wherein said at least one tip comprises at least two tips and the angle of the second plane relative to the plane perpendicular to the tool axis of at least two of said at least two tips is not equal. 33. The tool as claimed in claim 27, wherein said at least one tip comprises at least two tips and the angle of the third plane relative to the plane perpendicular to the tool axis of at least two of said at least two tips is not equal. 34. A method of manufacturing a tube as claimed in claim 1, having a surface and a longitudinal axis, said method comprising : a. cutting through at least one ridge formed along the surface of the tube to a cutting depth and at an angle relative to the longitudinal axis to form ridge layers ; and b. lifting the ridge layers to form a plurality of protrusions, wherein at least some of the plurality of protrusions project from the surface in a direction that is not substantially perpendicular to the longitudinal axis, and wherein the protrusions are formed on the inner surface of the tube. 35. The method as claimed in claim 34, wherein each of the plurality of protrusions has a height that has a value no more than three times the cutting depth. 36. The method as claimed in claim 34, wherein the tube has an inside diameter and each of the plurality of protrusions has a height, and the ratio of each protrusion height to tube inside diameter is between 0.002 and 0.5. 37. The method as claimed in claim 34, wherein others of the plurality of protrusions extend from the surface in a direction substantially perpendicular to the longitudinal axis. 38. The method as claimed in claim 34, wherein the tube has grooves formed between the plurality of protrusions at an angle between 80° and 100° relative to the longitudinal axis of the tube. 39. The method as claimed in claim 34, wherein said at least one ridge is cut through at an angle between 20° and 50° relative to the longitudinal axis of the tube. 40. The method as claimed in claim 34, wherein said at least one ridge has a ridge height and the cutting depth approximately equals the ridge height, 41. The method as claimed in claim 34, wherein said at least one ridge has a ridge height and the cutting depth is not equal to the ridge height. 42. A method of manufacturing a tube as claimed in claim 1, having a surface and a longitudinal axis, said method comprising : a. cutting through at least one ridge formed along the surface of the tube to a cutting depth and at an angle relative to the longitudinal axis to form ridge layers ; and b. lifting the ridge layers to form a plurality of protrusions, wherein at least some of the plurality of the protrusions are at least partially twisted, and wherein the protrusions are formed on the inner surface of the tube. 43. The method as claimed in claim 42, wherein at least some of the plurality of protrusions extend from the surface in a direction that is not substantially perpendicular to the longitudinal axis. 44. The method as claimed in claim 43, wherein others of the plurality of protrusions extend from the surface in a direction substantially perpendicular to the longitudinal axis. 45. The method as claimed in claim 42, wherein the tube has an inside diameter and each of the plurality of protrusions has a height, and the ratio of each protrusion height to tube inside diameter is between 0.002 and 0.5. 46. The method as claimed in claim 42, wherein the tube has grooves formed between the plurality of protrusions at an angle between 80° and 100° relative to the longitudinal axis of the tube. 47. The method as claimed in claim 42, wherein each of the plurality of protrusions has a height that has a value no more than three times the cutting depth. 48. The method as claimed in claim 42, wherein said at least one ridge is cut through at an angle between 20° and 50° relative to the longitudinal axis of the tube. 49. The method as claimed in claim 42, wherein said at least one ridge has a ridge height and the cutting depth approximately equals the ridge height. 50. The method as claimed in claim 42, wherein said at least one ridge has a ridge height and the cutting depth is not equal to the ridge height. 51. The method as claimed in claim 34, wherein the cutting and lifting is performed using a tool comprising a tool axis and at least one tip formed by the intersection of at least a first plane, a second plane, and a third plane and having a cutting edge and a lifting edge. 52. The method as claimed in claim 51, wherein the cutting edge is formed by the intersection of the first plane and the second plane. 53. The tool as claimed in claim 52, wherein the second plane is oriented at an angle between 40° and 70° relative to a plane perpendicular to the tool axis. 54. The method as claimed in claim 52, wherein the lifting edge is formed by the intersection of the first plane and the third plane. 55. The method as claimed in claim 54, wherein the third plane is oriented at an angle relative to a plane perpendicular to the tool axis and the protrusions are oriented at an angle relative to a plane perpendicular to the longitudinal axis of the tube. 56. The method as claimed in claim 55, wherein the angle of the third plane is approximately equal to the angle of the protrusions. 57. The method as claimed in claim 55, wherein the angle of the third plane and the angle of the protrusions are no more than 45°. 58. The method as claimed in claim 55, which involves predetermining the protrusion height (ep) using ep = t I sin(90 - q) or ep = t / sin(6), where : t is the cutting depth ; cp is the angle between the second plane and a plane perpendicular to the tool axis ; and is the angle through which said at least one ridge layer is cut relative to the longitudinal axis of the tube. 59. The method as claimed in claim 51, which involves predetermining the protrusion thickness (Sp) using Sp = Pap. sin(90° - cp ) or Sp = Pap. sin (6), where : Pa.P is the protrusion pitch ; cp is the angle between the second plane and a plane perpendicular to the tool axis ; and 8 is the angle through which said at least one ridge layer is cut relative to the longitudinal axis of the tube. 60. A method of enhancing the inner surface of a tube as claimed in claim 1, said method comprising : a. mounting a tool onto a shaft, the tool comprising a tool axis and at least one tip formed by the intersection of at least a first plane, a second plane, and a third plane and having a cutting edge and a lifting edge ; b. positioning the tool in the tube ; c. causing relative rotation and relative axial movement between the tube and the tool to cut at least partially though at least one ridge formed along the surface of the tube to form ridge layers and lift the ridge layers to form protrusions. 61. The method as claimed in claim 60, wherein the tube rotates and moves axially and the tool neither rotates nor moves axially. 62. The method as claimed in claim 60, wherein the tool rotates and moves axially and the tube neither rotates nor moves axially. 63. The method as claimed in claim 60, wherein the tube rotates in a direction and the tool rotates in the direction of the tube. 64. The method as claimed in claim 60, wherein the tube rotates in a direction and the tool rotates in a direction opposite to the rotational direction of the tube. 65. The method as claimed in claim 60, wherein the tube moves axially and the tool rotates. 66. The method as claimed in claim 60, wherein the tube rotates and the tool moves axially. 67. The method as claimed in claim 60, which involves mounting a mandrel on the shaft to form said at least one ridge on the inner surface of the tube. 68. The method as claimed in claim 60, which involves rotating the shaft, wherein the tool has a locking means to lock the tool in rotation with the shaft. 69. The method as claimed in claim 68, wherein the locking means comprises a groove and the shaft comprises a protrusion that mates with the groove. 70. An evaporator incorporating at least one heat transfer tube as claimed in claim 1. 71. A condensor incorporating at least one heat transfer tube as claimed in claim 1. 72. A heat exchanger incorporating at least one heat transfer tube as claimed in claim 1. A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2) formed from ridges (1) formed along a surface of the tube at an angle relative to the longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from the inner surface in a direction that is not substantially perpendicular to the longitudinal axis, characterised in that the protrusions (2) are formed by the steps of: a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4); and b. lifting the ridge layers to form protrusions (2) having a protrusion height, protrusion thickness, and protrusion pitch.

Full Text

HEAT TRANSFER TUBE AND METHOD OF AND TOOL FOR MANUFACTURING THE SAME
Field of the Invention
This invention relates to a heat transfer tube having protrusions on the inner
surface of the tube and a method of and tool for forming the protrusions on the inner
surface of the tube.
Background of the Invention
This invention relates to a heat transfer tube having an enhanced inner surface to
facilitate heat transfer from one side of the tube to the other. Heat transfer tubes are
commonly used in equipment, such as, for example, flooded evaporators, falling film
evaporators, spray evaporators, absorption chillers, condensers, direct expansion coolers,
and single phase coolers and heaters, used in the refrigeration, chemical, petrochemical,
and food-processing industries. A variety of heat transfer mediums may be used in these
applications, including, but not limited to, pure water, a water glycol mixture, any type of
refrigerant (such as R-22, R-134a, R-123, etc.), ammonia, petrochemical fluids, and other
mixtures.
An ideal heat transfer tube would allow heat to flow completely uninhibited from
the interior of the tube to the exterior of the tube and vice versa. However, such free flow
of heat across the tube is generally thwarted by the resistance to heat transfer. The overall
resistance of the tube to heat transfer is calculated by adding the individual resistances
from the outside to the inside of the tube or vice versa. To improve the heat transfer
efficiency of the tube, tube manufacturers have striven to uncover ways to reduce the
overall resistance of the tube. One such way is to enhance the outer surface of the tube,
such as by forming fins on the outer surface. As a result of recent advances in enhancing

the outer tube surface (see, e.g., U.S. Patent Nos. 5,697,430 and 5,996,686), only a small
part of the overall tube resistance is attributable to the outside of the tube. For example, a
typical evaporator tube used in a flooded chiller with an enhanced outer surface but
smooth inner surface typically has a 10:1 inner resistance:outer resistance ratio. Ideally,
one wants to obtain an inside to outside resistance ratio of 1:1. It becomes all the more
important, therefore, to develop enhancements to the inner surface of the tube that will
significantly reduce the tube side resistance and improve overall heat transfer
performance of the tube.
It is known to provide heat transfer tubes with alternating grooves and ridges on
their inner surfaces. The grooves and ridges cooperate to enhance turbulence of fluid heat
transfer mediums, such as water, delivered within the tube. This turbulence increases the
fluid mixing close to the inner tube surface to reduce or virtually eliminate the boundary
layer build-up of the fluid medium close to the inner surface of the tube. The boundary
layer thermal resistance significantly detracts from heat transfer performance by
increasing the heat transfer resistance of the tube. The grooves and ridges also provide
extra surface area for additional heat exchange. This basic premise is taught in U.S.
Patent No. 3,847,212 to Withers, Jr. et al.
The pattern, shapes and sizes of the grooves and ridges on the inner tube surface
may be changed to further increase heat exchange performance. To that end, tube
manufacturers have gone to great expense to experiment with alternative designs,
including those disclosed in U.S. Patent No. 5,791,405 to Takima et al., U.S. Patent Nos.
5,332,034 and 5,458,191 to Chiang et al., and U.S. Patent No. 5,975,196 to Gaffaney et
al.

In general, however, enhancing the inner surface of the tube has proven much
more difficult than the outer surface. Moreover, the majority of enhancements on both
the outer and inner surface of tubes are formed by molding and shaping the surfaces.
Enhancements have been formed, however, by cutting the tube surfaces.
Japanese Patent Application 09108759 discloses a tool for centering blades that
cut a continuous spiral groove directly on the inner surface of a tube. Similarly, Japanese
Patent Application 10281676 discloses a tube expanding plug equipped with cutting tools
that cut a continuous spiral slot and upstanding fin on the inner surface of a tube. U.S.
Patent No. 3,753,364 discloses forming a continuous groove along the inner surface of a
tube using a cutting tool that cuts into the inner tube surface and folds the material
upwardly to form the continuous groove.
While all of these inner surface tube designs aim to improve the heat transfer
performance of the tube, there remains a need in the industry to continue to improve upon
tube designs by modifying existing and creating new designs that enhance heat transfer
performance. Additionally, a need also exists to create designs and patterns that can be
transferred onto the tubes more quickly and cost-effectively. As described hereinbelow,
applicants have developed new geometries for heat transfer tubes as well as tools to form
these geometries, and, as a result, have significantly improved heat transfer performance.
Summary of the Invention
This invention provides an improved heat transfer tube surface and a method of
formation thereof that can be used to enhance heat transfer performance of tubes used in
at least all of the above-referenced applications (i.e., flooded evaporators, falling film
evaporators, spray evaporators, absorption chillers, condensers, direct expansion coolers,
and single phase coolers and heaters, used in the refrigeration, chemical, petrochemical,

and food-processing industries). The inner surface of the tube is enhanced with a
plurality of protrusions that significantly reduce tube side resistance and improve overall
heat transfer performance. The protrusions create additional paths for fluid flow within
the tube and thereby enhance turbulence of heat transfer mediums flowing within the
tube. This increases fluid mixing to reduce the boundary layer build-up of the fluid
medium close to the inner surface of the tube, such build-up increasing the resistance and
thereby impeding heat transfer. The protrusions also provide extra surface area for
additional heat exchange. Formation of the protrusions in accordance with this invention
can result in the formation of up to five times more surface area along the inner surface of
the tube than with simple ridges. Tests show that the performance of tubes having the
protrusions of this invention is significantly enhanced.
The method of this invention includes using a tool, which can easily be added to
existing manufacturing equipment, having a cutting edge to cut through ridges on the
inner surface of the tube to create ridge layers and a lifting edge to lift the ridge layers to
form the protrusions. In this way, the protrusions are formed without removal of metal
from the inner surface of the tube, thereby eliminating debris which can damage the
equipment in which the tubes are used. The protrusions on the inner surface of the tube
can be formed in the same or a different operation as formation of the ridges.
Tubes formed in accordance with this application may be suitable in any number
of applications, including, for example, applications for use in the HVAC, refrigeration,
chemical, petrochemical, and food-processing industries. The physical geometries of the
protrusions may be changed to tailor the tube to a particular application and fluid
medium.
It is an object of this invention to provide improved heat transfer tubes.

It is another object of this invention to provide an improved heat transfer tube
having protrusions on its inner surface.
It is yet another object of this invention to provide a method of forming an
improved heat transfer tube having protrusions on its inner surface.
It is a further object of this invention to provide an innovative tool for forming
improved heat transfer tubes.
It is a still further object of this invention to provide a tool for forming protrusions
on the inner surface of heat transfer tubes.
These and other features, objects and advantages of this invention will become
apparent by reading the following detailed description of preferred embodiments, taken in
conjunction with the accompanying drawings.
Brief Description of the Accompanying Drawings
FIG. la is a fragmentary perspective view of the partially-formed inner surface of
one embodiment of a tube of this invention.
FIG. lb is a side elevation view of the tube shown in FIG. la in the direction of
arrow a.
FIG. lc is a side elevation view similar to FIG. lb except that the protrusions
protrude from the inner surface of the tube in a direction that is not perpendicular to tube
axis s.
FIG. 1d is a front elevation view of the tube shown in FIG. la in the direction of
arrow b.
FIG. le is a top plan view of the tube shown in FIG. la.
FIG. 2 is a photomicrograph of an inner surface of one embodiment of a tube of
this invention.

FIG. 3 is a photomicrograph of an inner surface of an alternative embodiment of a
tube of this invention.
FIG. 4 is a side elevation view of one embodiment of the manufacturing
equipment that can be used to produce tubes in accordance with this invention.
FIG. 5 is a perspective view of the equipment of FIG. 4.
FIG. 6a is a perspective view of one embodiment of the tool of this invention.
FIG. 6b is a side elevation view of the tool shown in FIG. 6a.
FIG. 6c is a bottom plan view of the tool of FIG. 6b.
FIG. 6d is a top plan view of the tool of FIG. 6b.
FIG. 7a is a perspective view of an alternative embodiment of the tool of this
inventioa
FIG. 7b is a side elevation view of the tool shown in FIG. 7a.
FIG. 7c is a bottom plan view of the tool of FIG. 7b.
FIG. 7d is a top plan view of the tool of FIG. 7b.
FIG. 8a is a fragmentary perspective view of the partially-formed inner surface of
an alternative embodiment of a tube of this invention where the depth of the cut through
the ridges is less than the helical ridge height.
FIG. 8b is a fragmentary perspective view of the partially-formed inner surface of
an alternative embodiment of a tube of this invention where the depth of the cut through
the ridges is greater than the helical ridge height.
FIG. 9a is a fragmentary top plan view of the inner surface of another embodiment
of a tube in accordance with this invention.
FIG. 9b is an elevation view of the tube shown in FIG. 9a in the direction of arrow
22.

FIG. 10a is a fragmentary view of an inner surface of a tube of this invention,
showing the tool approaching the ridge in direction g for cutting a protrusion from the
ridge in direction g.
FIG. 1 0b is a fragmentary view of an alternative inner surface of a tube of this
invention, showing the tool approaching the ridge in direction g for cutting a protrusion
from the ridge in direction g.
FIG. 1 la is a schematic of the inner surface of a tube in accordance with this
invention showing the angular orientation between the ridges and grooves, whereby the
ridges and grooves are opposite hand helix.
FIG. 1 lb is a schematic of the inner surface of a tube in accordance with this
invention showing the angular orientation between the ridges and grooves, whereby the
ridges and grooves are same hand helix.
FIG. 12 is a bar graph comparing the tube-side heat transfer coefficients of various
tubes of the prior art and of tubes in accordance with this invention.
FIG. 13 is bar graph comparing the overall heat transfer coefficients of various
tubes of the prior art and of tubes in accordance with this invention.
Detailed Description of the Drawings
FIGS, la-e show the partially-formed inner surface 18 of one embodiment of the
tube 21 of this invention. Inner surface 18 includes a plurality of protrusions 2.
Protrusions 2 are formed from ridges 1 formed on inner surface 18. Ridges 1 are first
formed on inner surface 18. The ridges 1 are then cut to create ridge layers 4, which are
subsequently lifted up to form protrusions 2 (best seen in FIGS, la and lb). This cutting
and lifting can be, but does not have to be, accomplished using tool 13, shown in FIGS.
6a-d and 7a-d and described below.

It should be understood that a tube in accordance with this invention is generally
useful in, but not limited to, any application where heat needs to be transferred from one
side of the tube to the other side of the tube, such as in single-phase and multi-phase (both
pure liquids or gases or liquid/gas mixtures) evaporators and condensers. While the
following discussion provides desirable dimensions for a tube of this invention, the tubes
of this invention are in no way intended to be limited to those dimensions. Rather, the
desirable geometries of the tube, including protrusions 2, will depend on many factors,
not the least important of which are the properties of the fluid flowing through the tube.
One skilled in the art would understand how to alter the geometry of the inner surface of
the tube, including the geometry of ridges 1 and protrusion 2, to maximize the heat
transfer of the tube used in various applications and with various fluids.
Ridges 1 are formed on inner surface 18 at a helix angle a to the axis s of the tube
(see FIGS, la and le). Helix angle a may be any angle between 0°-90°, but preferably
does not exceed 70°. One skilled in the art will readily understand that the preferred helix
angle a will often depend, at least in part, on the fluid medium used. The height er of
ridges 1 should generally be greater the more viscous the liquid flowing through tube 21.
For example, a height er of greater than zero (preferably, but not necessarily, at least
0.001 inches) up to 25% of the inside diameter of the tube (Dj) will generally be desirable
in a tube sample used with a water/glycol mixture for low temperature applications. For
purposes of this application, Di is the inside diameter of tube 21 measured from inner
surface 18 of tube 21. The axial pitch P of ridges 1 depends on many factors, including
helix angle a, the number of ridges 1 formed on inner surface 18 of tube 21, and the
inside diameter D of tube 21. While any pitch may be used, the ratio of is
preferably at least 0.002, and the ratio of is preferably between approximately 0.001-

0.25. Again, however, one skilled in the art will readily understand that these preferred
ratio values will often depend, at least in part, on the fluid medium used and operating
conditions (e.g., the temperature of the fluid medium).
Ridge layers 4 are cut at an angle 0 to axis s that is preferably between
approximately 20°-50°, inclusive, and more preferably around 30°. The axial pitch of
protrusions 2 may be any value greater than zero and generally will depend on, among
other factors, the relative revolutions per minute between the tool (discussed below) and
the tube during manufacture, the relative axial feed rate between the tool and the tube
during manufacture, and the number of tips provided on the tool used to form the
protrusions during manufacture. While the resulting protrusions 2 can have any thickness
SPi the thickness Sp is preferably approximately 20-100% of pitch Pap. The height ep of
protrusions 2 is dependent on the cutting depth t (as seen in FIGS, lb, 8a, and 8b) and
angle 0 at which the ridge layers 4 are cut. The height ep of protrusions 2 is preferably a
value at least as great as the cutting depth t up to three times the cutting depth t It is
preferable, but not necessary, to form ridges 1 at a height erand set the cutting angle 0 at a
value that will result in the height ep of protrusions 2 being at least approximately double
the height of ridges 1. Thus, the ratio is preferably between approximately
0.002-0.5 (i.e., is double the preferred range of the ratio of approximately
0.001-0.25).
FIGS, la and lb show cutting depth t equal to the height erof ridges 1 so that the
base 40 of protrusion 2 is located on the inner surface 18 of tube 21. The cutting depth t
need not be equal to the ridge height e, however. Rather, the ridges 1 can be cut only
partially through ridges 1 (see FIG. 8a) or beyond the height of ridges 1 and into tube wall
3 (see FIG. 8b). In FIG. 8a, the ridges 1 are not cut through their entire height e,.so that

the base 40 of protrusions 2 is positioned further from the inner surface 18 of tube 21 than
the base 42 of ridges 1, which is located on the inner surface 18. In contrast, FIG. 8b
illustrates a cutting depth t of beyond the ridge height e„ so that at least one wall of the
protrusions 2 extends into tube wall 3, beyond the inner surface 18 and ridge base 42.
When ridge layers 4 are lifted, grooves 20 are formed between adjacent
protrusions 2. Ridge layers 4 are cut and lifted so that grooves 20 are oriented on inner
surface 18 at an angle T to the axis s of tube 21 (see FIGS, le, 1 la, and 1 lb), which is
preferably, but does not have to be, between approximately 80°-100°.
The shape of protrusions 2 is dependent on the shape of ridges 1 and the
orientation of ridges 1 relative to the direction of movement of tool 13. In the
embodiment of FIGS, la-e, protrusions 2 have four side surfaces 25, a sloped top surface
26 (which helps decrease resistance to heat transfer), and a substantially pointed tip 28.
The protrusions 2 of this invention are in no way intended to be limited to this illustrated
embodiment, however, but rather can be formed in any shape. Moreover, protrusions 2 in
tube 21 need not all be the same shape or have the same geometry.
Whether the orientation of protrusions 2 is straight (see FIG. 10a) or bent or
twisted (see FIG. 10b) depends on the angle p formed between ridges 1 and the direction
of movement g of tool 13. If angle p is less than 90°, protrusions 2 will have a relatively
straight orientation, such as is shown in FIG. 10a. If angle p is more than 90°, protrusions
2 will have a more bent and/or twisted orientation, such as, for example, is shown in FIG.
10b.
During manufacture of tube 21, tool 13 maybe used to cut through ridges 1 and
lift the resulting ridge layers 4 to form protrusions 2. Other devices and methods for
forming protrusions 2 may be used, however. Tool 13 can be made from any material

having the structural integrity to withstand metal cutting (e.g. steel, carbide, ceramic,
etc.), but is preferably made of a carbide. The embodiments of the tool 13 shown in
FIGS. 6a-d and 7a-d generally have a tool axis q, two base walls 30, 32 and one or more
side walls 34. Aperture 16 is located through the tool 13. Tips 12 are formed on side
walls 34 of tool 13. Note, however, that the tips can be mounted or formed on any
structure that can support the tips in the desired orientation relative to the tube 21 and
such structure is not limited to that disclosed in FIGS. 6a-d and 7a-d. Moreover, the tips
may be retractable within their supporting structure so that the number of tips used in the
cutting process can easily be varied.
FIGS. 6a-d illustrate one embodiment of tool 13 having a single tip 12. FIGS. 7a-
d illustrate an alternative embodiment of tool 13 having four tips 12. One skilled in the
art will understand mat tool 13 may be equipped with any number of tips 12 depending on
the desired pitch P,iP of protrusions 2. Moreover, the geometry of each tip need not be the
same for tips on a single tool 13. Rather, tips 12 having different geometries to form
protrusions having different shapes, orientations, and other geometries maybe provided
on tool 13.
Each tip 12 is formed by the intersection of planes A, B, and C The intersection
of planes A and B form cutting edge 14 that cuts through ridges 1 to form ridge layers 4.
Plane B is oriented at an angle

FIG. 6b). Angle q> is defined as 90° - 9. Thus, angle (p is preferably between
approximately 40°-70° to allow cutting edge 14 to slice through ridges 1 at the desirable
angle 0 between approximately 20°-50°.
The intersection of planes A and C form lifting edge 15 that lifts ridge layers 4
upwardly to form protrusions 2. Angle (pi_ defined by plane C and a plane perpendicular

to tool axis q, determines the angle of inclination © (the angle between a plane
perpendicular to the longitudinal axis s of tube 21 and the longitudinal axis of protrusions
2 (see FIG. 1c)) at which protrusions 2 are lifted by lifting edge 15. Angle = angle
and thus angle on tool 13 can be adjusted to directly impact the angle of inclination 00
of protrusions 2. The angle of inclination 00 (and angle is preferably the absolute
value of any angle between approximately -45° to 45° relative to the plane perpendicular
to the longitudinal axis s of tube 21. In this way, protrusions can be aligned with the
plane perpendicular to the longitudinal axis s of tube 21 (see FIG. lb) or incline to the left
and right relative to the plane perpendicular to the longitudinal axis s of tube 21 (see FIG.
lc). Moreover, the tips 12 can be formed to have different geometries (i.e., angle may
be different on different tips), and thus the protrusions 2 within tube 21 may incline at
different angles (or not at all) and in different directions relative to the plane
perpendicular to the longitudinal axis s of tube 21.
While preferred ranges of values for the physical dimensions of protrusions 2 have
been identified, one skilled in the art will recognize that the physical dimensions of tool
13 may be modified to impact the physical dimensions of resulting protrusions 2. For
example, the depth t that cutting edge 14 cuts into ridges 1 and angle affect the height ep
of protrusions 2. Therefore, the height ep of protrusions 2 may be adjusted using the
expression

FIGS. 4 and 5 illustrate one possible manufacturing set-up for enhancing the
surfaces of tube 21. These figures are in no way intended to limit the process by which
tubes in accordance with this invention are manufactured, but rather any tube
manufacturing process using any suitable equipment or configuration of equipment may
be used. The tubes of this invention may be made from a variety of materials possessing
suitable physical properties including structural integrity, malleability, and plasticity, such
as, for example, copper and copper alloys, aluminum and aluminum alloys, brass,
titanium, steel, and stainless steel. FIGS. 4 and 5 illustrate three arbors 10 operating on
tube 21 to enhance the outer surface of tube 21. Note that one of the arbors 10 has been
omitted from FIG. 4. Each arbor 10 includes a tool set-up having finning disks 7 which

radially extrude from one to multiple start outside fins 6 having axial pitch The tool
set-up may include additional disks, such as notching or flattening disks, to further
enhance the outer surface of tube 21. Moreover, while only three arbors 10 are shown,
fewer or more arbors may be used depending on the desired outer surface enhancements.
Note, however, that depending on the tube application, enhancements need not be
provided on the outer surface of tube 21 at all.
In one example of a way to enhance inner surface 18 of tube 21, a mandrel shaft
11 onto which mandrel 9 is rotatably mounted extends into tube 21. Tool 13 is mounted
onto shaft 11 through aperture 16. Bolt 24 secures tool 13 in place. Tool 13 is preferably
locked in rotation with shaft 11 by any suitable means. FIGS. 6d and 7d illustrate a key
groove 17 that may be provided on tool 13 to interlock with a protrusion on shaft 11 (not
shown) to fix tool 13 in place relative to shaft 11.
In operation, tube 21 generally rotates as it moves through the manufacturing
process. Tube wall 3 moves between mandrel 9 and finning disks 7, which exert pressure
on tube wall 3. Under pressure, the metal of tube wall 3 flows into the grooves between
the finning disks 7 to form fins 6 on the exterior surface of tube 21.
The mirror image of a desired inner surface pattern is provided on mandrel 9 so
that mandrel 9 will form inner surface 18 of tube 21 with the desired pattern as tube 21
engages mandrel 9. A desirable inner surface pattern includes ridges 1, as shown in
FIGS, la and 4. After formation of ridges 1 on inner surface 18 of tube 21, tube 21
encounters tool 13 positioned adjacent and downstream mandrel 9. As explained
previously, the cutting edge(s) 14 of tool 13 cuts through ridges 1 to form ridge layers 4.
Lifting edge(s) 15 of tool 13 then lift ridge layers 4 to form protrusions 2.

When protrusions 2 are formed simultaneously with outside finning and tool 13 is
fixed (i.e., not rotating or moving axially), tube 21 automatically rotates and has an axial
movement hi this instance, the axial pitch of protrusions Pap is governed by the
following formula:

Where:
Po is the axial pitch of outside fins 6;
Z0 is the number of fin starts on the outer diameter of tube 21;
and
Zi is the number of tips 12 on tool 13.
To obtain a specific protrusion axial pitch Pp, tool 13 can also be rotated. Both
tube 21 and tool 13 can rotate in the same direction or, alternatively, both tube 21 and tool
13 can rotate, but in opposite directions. To obtain a predetermined axial protrusion pitch
Pp, the necessary rotation (in revolutions per minute (RPM)) of the tool 13 can be
calculated using the following formula:

If the result of this calculation is negative, then tool 13 should rotate in the same
direction of tube 21 to obtain the desired pitch Pp. Alternatively, if the result of this
calculation is positive, then tool 13 should rotate in the opposite direction of tube 21 to
obtain the desired pitch P.
Note that while formation of protrusions 2 is shown in the same operation as
formation of ridges 1, protrusions 2 may be produced in a separate operation from finning
using a tube with pre-formed inner ridges 1. This would generally require an assembly to
rotate tool 13 or tube 21 and to move tool 13 or tube 21 along the tube axis. Moreover, a
support is preferably provided to center tool 13 relative to the inner tube surface 18.
In this case, the axial pitch P of protrusions 2 is governed by the following
formula:

This formula is suitable when (1) the tube moves only axially (i.e., does not rotate)
and the tool only rotates (i.e., does not move axially); (2) the tube only rotates and the
tool moves only axially; (3) the tool rotates and moves axially but the tube is both
rotationally and axially fixed; (4) the tube rotates and moves axially but the tool is both
rotationally and axially fixed; and (5) any combination of the above.
With the inner tube surface of this invention, additional paths for fluid flow are
created (between protrusions 2 through grooves 20) to optimize heat transfer and pressure

drop. FIG. 9a illustrates these additional paths 22 for fluid travel through tube 21. These
paths 22 are in addition to fluid flow paths 23 created between ridges 1. These additional
paths 22 have a helix angle α1 relative to the tube axis s. Angle α1 is the angle between
protrusions 2 formed from adjacent ridges 1. FIG. 9b clearly shows these additional paths
22 formed between protrusions 2. Helix angle α1 and thus orientation of paths 22
through tube 21, can be adjusted by adjusting pitch P of protrusions 2 using the
following expression

If ridge helix angle a and angle T of grooves 20 are both either right hand or left
hand helix (see FIG. 1 lb), then the "[-]" should be used in the above expression.
Alternatively, if ridge helix angle a and angle T of grooves 20 are opposite hand helix
(see FIG. 1 la), then the "[+]" should be used in the above expression.
Tubes made in accordance with this invention outperform existing tubes. FIGS.
12 and 13 graphically illustrate the enhanced performance of two examples of such tubes
(boiling tubes Tube No. 25 and Tube No. 14) by demonstrating the differences in the

enhancement factors between these tubes. The enhancement factor is the factor by which
the heat transfer coefficients (both tube-side (see FIG. 12) and overall (see FIG. 13)) of
these new tubes (Tube No. 25 and Tube No. 14) increase over existing tubes (Turbo-B®,
Turbo-BII, and Turbo B-III). Again, however, Tube Nos. 25 and 14 are merely
examples of tubes in accordance with this invention. Other types of tubes made in
accordance with this invention outperform existing tubes in a variety of applications.
The physical characteristics of the Turbo-B®, Turbo-BD®, and Turbo B-m® tubes
are described in Tables 1 and 2 of U.S. Patent No. 5,697,430 to Thors, et al. Turbo-B® is
referenced as Tube II; Turbo-BII® is referenced as Tube III; and Turbo B-ID® is
referenced as Tube IVH The outside surfaces of Tube No. 25 and Tube No. 14 are
identical to that of Turbo B-III®. The inside surfaces of Tube No. 25 and Tube No. 14 are
in accordance with this invention and include the following physical characteristics:

FIG. 12 shows that the tube-side heat transfer coefficient of Tube No. 14 is
approximately 1.8 times and Tube No. 25 is approximately 1.3 times that of Turbo B-III®,
which is currently the most popular tube used in evaporator applications and shown as a

baseline in FIGS. 12 and 13. Similarly, FIG. 13 shows that the overall heat transfer
coefficient of Tube No. 25 is approximately 1.25 times and Tube No. 14 is approximately
1.5 times mat of Turbo B-III®.
The foregoing is provided for purposes of illustrating, exlaining, and describing
embodiments of this invention. Further modifications and adaptations to these
embodiments will be apparent to those skilled in the art and may be made without
departing from the scope or spirit of the invention.

WE CLAIM:
1. A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a
longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2)
formed from ridges (1) formed along a surface of the tube at an angle relative to the
longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from
the inner surface in a direction that is not substantially perpendicular to the longitudinal
axis, characterised in that the protrusions (2) are formed by the steps of:
a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4) ; and
b. lifting the ridge layers to form protrusions (2) having a protrusion height,
protrusion thickness, and protrusion pitch.
2. The tube (21) as claimed in claim 1, in which others of the plurality of protrusions
(2) extend from the inner surface (18) in a direction substantially perpendicular to the
longitudinal axis (s).
3. The tube (21) as claimed in claim 1 or 2, wherein at least some of the plurality of
protrusions (2) are bent and/or twisted.
4. The tube (21) as claimed in any preceding claim, wherein the protrusion (2) has a
height that has a value no more than three times the cutting depth (t).
5. The tube as claimed in claim 4, wherein the cutting depth (t) is less than or
approximately equal to the ridge height.
6. The tube as claimed in claimed in claim 4, wherein the cutting depth (t) is greater
than the ridge height.

7. The tube (21) as claimed in any preceding claim, wherein at least one of the
plurality of protrusions (2) has a height that has a value at least as great as the cutting
depth (t).
8. The tube as claimed in any preceding claim, wherein the ridge (1) is cut through at
an angle between 20° and 50°, preferably approximately 30°, relative to the longitudinal
axis (s) of the tube.
9. The tube as claimed as claimed in any preceding claim, wherein the ridge (1) is
formed along the inner surface (18) at an angle of no more than 70° relative to the
longitudinal axis (s).
10. The tube (21) as claimed in any preceding claim, wherein the ratio of the tube (21)
inside diameter (Di) to the height of the ridge (1) is in the range of 0.001 to 0.25.
11. The tube (21) as claimed in any preceding claim, wherein the ridge (1) has a
height of at least 0.025 mm (0.001 inch).
12. The tube (21) as claimed in any preceding claim, having a plurality of said ridges
(1) spaced at an axial pitch, wherein the ratio of the ridge axial pitch to ridge height is at
least 0.002.
13. The tube (21) as claimed in any preceding claim, wherein the ridge height is
greater than or equal to the cutting depth (t).
14. The tube (21) as claimed in any of claims 1 to 4 or 6 to 13, wherein the protrusion
(2) comprises at least one wall that extends into the inner surface (18) of the tube beyond
a base (42) of the ridge (1).

15. The tube (21) as claimed in any preceding claim, wherein the ratio of the height of
each protrusion (2) to the tube inside diameter (Di) is between 0.002 and 0.5.
16. The tube (21) as claimed in any preceding claim, wherein the protrusion (2)
comprises at least three side surfaces and a top surface (26).
17. The tube (21) as claimed in claim 16, wherein the top surface (26) is sloped.
18. The tube (21) as claimed in any preceding claim, wherein the protrusion (2) has a
substantially pointed tip (28).
19. The tube (21) as claimed in any preceding claim, in which the plurality of
protrusions (2) have a pitch and wherein the thickness of each of said plurality of
protrusions is between 20% and 100% of the protrusion pitch.
20. The tube (21) as claimed in any preceding claim, comprising grooves (20) formed
between the plurality of protrusions at an angle between 80° and 100° relative to the
longitudinal axis of the tube.
21. Equipment, such as herein described, incorporating a tube (21) as claimed in any
of claims 1 -20.
22. A tool for cutting the inner surface of a tube as claimed in claim 1, said tool
comprising a tool axis and at least one tip formed by the intersection of at least a first
plane, a second plane, and a third plane and having a cutting edge and a lifting edge.
23. The tool as claimed in claim 22, wherein the tool comprises at least one of
carbide, steel, and ceramic.

24. The tool as claimed in claim 22, wherein the cutting edge is formed by the
intersection of the first plane and the second plane.
25. The tool as claimed in claim 24, wherein the second plane is oriented at an angle
between 40° and 70° relative to a plane perpendicular to the tool axis.
26. The tool as claimed in claim 22, wherein the lifting edge is formed by the
intersection of the first plane and the third plane.
27. The tool as claimed in claim 26, wherein the third plane is oriented at an angle
relative to a plane perpendicular to the tool axis.
28. The tool as claimed in claim 27, wherein the angle is zero.
29. The tool as claimed in claim 27, wherein the angle is not zero.
30. The tool as claimed in claim 29, wherein the angle is not more than approximately
45°.
31. The tool as claimed in claim 22, wherein said at least one tip comprises more than
one tip.
32. The tool as claimed in claim 25, wherein said at least one tip comprises at least
two tips and the angle of the second plane relative to the plane perpendicular to the tool
axis of at least two of said at least two tips is not equal.

33. The tool as claimed in claim 27, wherein said at least one tip comprises at least
two tips and the angle of the third plane relative to the plane perpendicular to the tool axis
of at least two of said at least two tips is not equal.
34. A method of manufacturing a tube as claimed in claim 1, having a surface and a
longitudinal axis, said method comprising :
a. cutting through at least one ridge formed along the surface of the tube to a
cutting depth and at an angle relative to the longitudinal axis to form ridge layers ;
and
b. lifting the ridge layers to form a plurality of protrusions,
wherein at least some of the plurality of protrusions project from the surface in a direction
that is not substantially perpendicular to the longitudinal axis, and wherein the
protrusions are formed on the inner surface of the tube.
35. The method as claimed in claim 34, wherein each of the plurality of protrusions
has a height that has a value no more than three times the cutting depth.
36. The method as claimed in claim 34, wherein the tube has an inside diameter and
each of the plurality of protrusions has a height, and the ratio of each protrusion height to
tube inside diameter is between 0.002 and 0.5.
37. The method as claimed in claim 34, wherein others of the plurality of protrusions
extend from the surface in a direction substantially perpendicular to the longitudinal axis.
38. The method as claimed in claim 34, wherein the tube has grooves formed between
the plurality of protrusions at an angle between 80° and 100° relative to the longitudinal
axis of the tube.

39. The method as claimed in claim 34, wherein said at least one ridge is cut through
at an angle between 20° and 50° relative to the longitudinal axis of the tube.
40. The method as claimed in claim 34, wherein said at least one ridge has a ridge
height and the cutting depth approximately equals the ridge height,
41. The method as claimed in claim 34, wherein said at least one ridge has a ridge
height and the cutting depth is not equal to the ridge height.
42. A method of manufacturing a tube as claimed in claim 1, having a surface and a
longitudinal axis, said method comprising :
a. cutting through at least one ridge formed along the surface of the tube to a
cutting depth and at an angle relative to the longitudinal axis to form ridge layers ;
and
b. lifting the ridge layers to form a plurality of protrusions,
wherein at least some of the plurality of the protrusions are at least partially twisted, and
wherein the protrusions are formed on the inner surface of the tube.
43. The method as claimed in claim 42, wherein at least some of the plurality of
protrusions extend from the surface in a direction that is not substantially perpendicular to
the longitudinal axis.
44. The method as claimed in claim 43, wherein others of the plurality of protrusions
extend from the surface in a direction substantially perpendicular to the longitudinal axis.
45. The method as claimed in claim 42, wherein the tube has an inside diameter and
each of the plurality of protrusions has a height, and the ratio of each protrusion height to
tube inside diameter is between 0.002 and 0.5.

46. The method as claimed in claim 42, wherein the tube has grooves formed between
the plurality of protrusions at an angle between 80° and 100° relative to the longitudinal
axis of the tube.
47. The method as claimed in claim 42, wherein each of the plurality of protrusions
has a height that has a value no more than three times the cutting depth.
48. The method as claimed in claim 42, wherein said at least one ridge is cut through
at an angle between 20° and 50° relative to the longitudinal axis of the tube.
49. The method as claimed in claim 42, wherein said at least one ridge has a ridge
height and the cutting depth approximately equals the ridge height.
50. The method as claimed in claim 42, wherein said at least one ridge has a ridge
height and the cutting depth is not equal to the ridge height.
51. The method as claimed in claim 34, wherein the cutting and lifting is performed
using a tool comprising a tool axis and at least one tip formed by the intersection of at
least a first plane, a second plane, and a third plane and having a cutting edge and a lifting
edge.
52. The method as claimed in claim 51, wherein the cutting edge is formed by the
intersection of the first plane and the second plane.
53. The tool as claimed in claim 52, wherein the second plane is oriented at an angle
between 40° and 70° relative to a plane perpendicular to the tool axis.

54. The method as claimed in claim 52, wherein the lifting edge is formed by the
intersection of the first plane and the third plane.
55. The method as claimed in claim 54, wherein the third plane is oriented at an angle
relative to a plane perpendicular to the tool axis and the protrusions are oriented at an
angle relative to a plane perpendicular to the longitudinal axis of the tube.
56. The method as claimed in claim 55, wherein the angle of the third plane is
approximately equal to the angle of the protrusions.
57. The method as claimed in claim 55, wherein the angle of the third plane and the
angle of the protrusions are no more than 45°.
58. The method as claimed in claim 55, which involves predetermining the protrusion
height (ep) using ep = t I sin(90 - q) or ep = t / sin(6), where :
t is the cutting depth ;
cp is the angle between the second plane and a plane perpendicular to the tool
axis ; and
is the angle through which said at least one ridge layer is cut relative to the
longitudinal axis of the tube.
59. The method as claimed in claim 51, which involves predetermining the protrusion
thickness (Sp) using Sp = Pap. sin(90° - cp ) or Sp = Pap. sin (6), where :
Pa.P is the protrusion pitch ;
cp is the angle between the second plane and a plane perpendicular to the tool
axis ; and
8 is the angle through which said at least one ridge layer is cut relative to the
longitudinal axis of the tube.

60. A method of enhancing the inner surface of a tube as claimed in claim 1, said
method comprising :
a. mounting a tool onto a shaft, the tool comprising a tool axis and at least
one tip formed by the intersection of at least a first plane, a second plane, and a third
plane and having a cutting edge and a lifting edge ;
b. positioning the tool in the tube ;
c. causing relative rotation and relative axial movement between the tube and
the tool to cut at least partially though at least one ridge formed along the surface of the
tube to form ridge layers and lift the ridge layers to form protrusions.
61. The method as claimed in claim 60, wherein the tube rotates and moves axially
and the tool neither rotates nor moves axially.
62. The method as claimed in claim 60, wherein the tool rotates and moves axially
and the tube neither rotates nor moves axially.
63. The method as claimed in claim 60, wherein the tube rotates in a direction and the
tool rotates in the direction of the tube.
64. The method as claimed in claim 60, wherein the tube rotates in a direction and the
tool rotates in a direction opposite to the rotational direction of the tube.
65. The method as claimed in claim 60, wherein the tube moves axially and the tool
rotates.
66. The method as claimed in claim 60, wherein the tube rotates and the tool moves
axially.

67. The method as claimed in claim 60, which involves mounting a mandrel on the
shaft to form said at least one ridge on the inner surface of the tube.
68. The method as claimed in claim 60, which involves rotating the shaft, wherein the
tool has a locking means to lock the tool in rotation with the shaft.
69. The method as claimed in claim 68, wherein the locking means comprises a
groove and the shaft comprises a protrusion that mates with the groove.
70. An evaporator incorporating at least one heat transfer tube as claimed in claim 1.
71. A condensor incorporating at least one heat transfer tube as claimed in claim 1.
72. A heat exchanger incorporating at least one heat transfer tube as claimed in
claim 1.

A heat transfer tube (21) comprising an inner surface (18), an outer surface, and a
longitudinal axis (s), wherein the tube comprises a plurality of surface protrusions (2)
formed from ridges (1) formed along a surface of the tube at an angle relative to the
longitudinal axis (s), wherein at least some of the plurality of protrusions (2) project from
the inner surface in a direction that is not substantially perpendicular to the longitudinal
axis, characterised in that the protrusions (2) are formed by the steps of:
a. cutting through the ridges (1) to a cutting depth (t) to form ridge layers (4); and
b. lifting the ridge layers to form protrusions (2) having a protrusion height,
protrusion thickness, and protrusion pitch.

Documents:

1931-KOLNP-2004-(09-01-2012)-CORRESPONDENCE.pdf

1931-KOLNP-2004-(09-01-2012)-OTHER PATENT DOCUMENT.pdf

1931-KOLNP-2004-(09-01-2012)-PA-CERTIFIED COPIES.pdf

1931-KOLNP-2004-CORRESPONDENCE_.pdf

1931-KOLNP-2004-FORM 27_.pdf

1931-KOLNP-2004-FORM-27.pdf

1931-kolnp-2004-granted-abstract.pdf

1931-kolnp-2004-granted-assignment.pdf

1931-kolnp-2004-granted-claims.pdf

1931-kolnp-2004-granted-correspondence.pdf

1931-kolnp-2004-granted-description (complete).pdf

1931-kolnp-2004-granted-drawings.pdf

1931-kolnp-2004-granted-examination report.pdf

1931-kolnp-2004-granted-form 1.pdf

1931-kolnp-2004-granted-form 18.pdf

1931-kolnp-2004-granted-form 3.pdf

1931-kolnp-2004-granted-form 5.pdf

1931-kolnp-2004-granted-gpa.pdf

1931-kolnp-2004-granted-reply to examination report.pdf

1931-kolnp-2004-granted-specification.pdf

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Patent Number

227745

Indian Patent Application Number

1931/KOLNP/2004

PG Journal Number

04/2009

Publication Date

23-Jan-2009

Grant Date

20-Jan-2009

Date of Filing

15-Dec-2004

Name of Patentee

WOLVERINE TUBE INC.

Applicant Address

200 CLINTON AVENUE, SUITE 1000, HUNTSVILLE, AL

Inventors:

#	Inventor's Name	Inventor's Address
1	THORS PETUR	4222 WILLOW BEND ROAD SE, DECATUR. AL 35603
2	ZOUBKOV NIKOLAI	NOVOYSENEVSKI PR. 31-1-161, MOSCOW

PCT International Classification Number

F28F 1/42

PCT International Application Number

PCTUS2003/018304

PCT International Filing date

2003-06-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/387,328	2002-06-10	U.S.A.