MXPA01004379A - Polyhedral array heat transfer tube - Google Patents

Abstract

A heat exchanger tube having an internal surface that is configured to enhance the heat transfer performance of the tube. The internal enhancement has a plurality of polyhedrons extending from the inner wall of the tubing. The polyhedrons have first and second planar faces disposed substantially parallel to the polyhedral axis. The polyhedrons have third and fourth faces disposed at an angle oblique to the longitudinal axis of the tube. The resulting surface increases the internal surface area of the tube and the turbulence characteristics of the surface, and thus, increases the heat transfer performance of the tube.

Description

POLYDRICAL DISTRIBUTION OF A STEAM TRANSFER PIPE FIELD OF THE INVENTION This invention relates to tubes used in heat exchangers and more particularly the invention relates to a heat exchanger tube having an internal surface that is capable of improving the heat transfer performance of the tube. BACKGROUND OF THE INVENTION The heat transfer performance of a tube having surface improvements is known to those skilled in the art which is superior to a flat wall tube. Surface improvements have been applied to both internal and external tube surfaces and include flanges, fins, coatings and inserts and the like. All improvement designs attempt to increase the surface heat transfer area of the tube. Most designs also attempt to increase turbulence in the fluid flowing through or on the tube in order to promote fluid mixing and decomposition of the boundary layer on the surface of the tube. ^^^^^^^^^ 6Aiiií ^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ g ^^^^^^^^^ ^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ & amp; ^^^^^ A large percentage of air and cooling conditioners, as well as cooling engines, heat exchangers, are of the plate and tube fin type. In such heat exchangers, the tubes are externally improved by the use of fixed plate fins on the outside of the tubes. Heat exchange tubes often also have internal heat transfer improvements in the form of modifications to the inner surface of the tube. In a significant proportion of the total length of the pipe in a heat exchanger air conditioning and refrigeration typical of plate fin and tube, the refrigerant exists in both liquid and vapor state. Below certain flow rates and due to the variation in density, the liquid refrigerant flows along the part The bottom of the tube and the refrigerant in the form of vapor flows along the top. The heat transfer performance of the tube is improved if it is improved in intermixing between the fluids in the two states, for example, by promoting the drainage of liquid from the upper region of the tube in a application of condensation or by allowing liquid to flow up the tube into a wall by capillary action in an evaporation application. It is also desirable that the same type of pipe be used in all the heat exchangers of a system. Consequently, the heat transfer tube must work satisfactorily in condensation and evaporation applications. In order to reduce the manufacturing costs of heat exchangers, it is also desirable to reduce the weight of the heat transfer tube while maintaining its performance. Consequently, what is needed is a heat transfer tube that provides adequate performance for both condensation and evaporation applications and that offers practical and economical features to end users.

BRIEF DESCRIPTION OF THE INVENTION The heat exchanger tube of the present invention meets the needs described above by providing a tube with features that improve heat transfer performance so that, with equal weight, the tube provides superior heat transfer performance compared to the tubes of the prior art and, with a reduced weight, the tube provides a heat transfer performance equal to the tubes of the prior art and a pressure drop performance that is superior to the tubes of the prior art. The heat exchanger tube of the present invention has an internal surface that is configured to improve the heat transfer performance of the tube. The internal improvement has a plurality of polyhedra extending from the inner wall of the pipe in a preferred embodiment. In a preferred embodiment, the polyhedra are distributed in rows that are substantially parallel to the longitudinal axis of the tubes. However, the rows may be offset from the longitudinal axis to approximately 40 °. The polyhedra have a first and second flat faces that are placed substantially parallel to the axis of the polyhedron. The polyhedra have a third and fourth faces placed at an angle oblique to the longitudinal axis of the tube. The resulting surface increases the area of the inner surface of the tube and therefore increases the heat transfer performance of the tube. In addition, polyhedra promote flow conditions within the tube that also promote heat transfer. The tube of the present invention is adaptable for manufacturing from a strip of copper or copper alloy by roll-stamping the breeding pattern on a surface of the strip to be rolled and welded by sewing the strip into a pipe. Such a manufacturing process is capable of rapidly and economically producing an internally complicated improved heat transfer pipe.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevation view of the heat exchanger tube of the present invention showing a cutout of a portion of the tube. Figure 2 is a perspective view of a section of the wall of the heat exchanger tube of the present invention. Figure 3 is a sectional view of the wall of the heat exchanger tube of the present invention taken along the line 3-3 of Figure 1. Figure 4 is a graph showing the relative performance of the tubes of the present invention compared to the prior art tube when the tube is used in a condensation application. Figure 5 is a graph showing the relative performance of the tubes of the present invention compared to a prior art tube, with respect to the pressure drop.

DESCRIPTION OF THE PREFERRED MODALITY In this specification, the term polyhedron is used and will be defined as a solid formed by substantially flat faces.

Referring initially to Figure 1, the tube 10 is preferably formed of copper, copper alloy or other heat conducting material. The tube 10 is preferably cylindrical with an outer diameter, an inner diameter and corresponding wall thicknesses. The inner surface is preferably formed with an internal surface enhancement 13. The heat exchanger tube 10 of the present invention is preferably formed by roll-pattering the breeding pattern 13 onto a surface on a copper or copper alloy strip prior to roll forming and seam welding of the strip in accordance with the invention. a tube 10. Again in FIG. 2, the surface enhancement 13 for a portion of the wall 16 is shown. A plurality of polyhedrons 19 extend outwardly from the wall 16. The polyhedrons 19 are preferably placed along the length of the wall. The longitudinal axis of the tube 10, however, can be deviated from the axis by an angle in any amount from 0 to 40 °. With the angle at 0 °, a first flat face 22 and a second flat face 25 are substantially parallel to the longitudinal axis of the tube 10. A third flat face 28 and a fourth flat face 31 are placed at an angle oblique to the longitudinal axis. This angle of incidence between the third and fourth faces 28 and 31 and the longitudinal axis, is the angle ß. This angle ß can acquire any value from 5 to 90 °, however, it is preferred that ß is in the range of 5 to 40 °.

The polyhedra 19 are placed on the wall 16 at a distance d between the center lines of the adjacent rows. The distance d can be in the range of 0.28 mm (0.011 inches) to 0.93 mm (0.037 inches), however, the preferred range is 0.38 mm (0.015 inches) to 0.68 mm (0.027 inches). The maximum length of the polyhedra 19 measured between the third and fourth faces 28 and 31 is 1. The length 1 can be from 0.13 mm to 0.635 mm (0.005-0.025 inches), however, the preferred length is approximately 0.37 mm ( 0.0145 inches). A recessed area 32 adjacent to the polyhedra 19 is decreased to a depth of D. D is in the range of -0.02 to 0.02 mm (-0.001 inches to 0.001 inches) but is preferably 0.13 mm (0.0005 inches) (where the negative values indicate the distance above the inner wall of the tube). The faces 28 and 31 form a vertex angle Y which is in the range of 20 to 50 °, and preferably to about 44 °. Again in Figure 3, the polyhedra 19 have a height H and have a maximum width w. The width w is in the range of 0.10 to 0.25 mm (0.004 to 0.01 inches) and preferably 0.14 mm (0.0056 inches). The polyhedra 19 has an angle 12 between opposite faces 22 and 25. The angle 12 is in the range of 10 to 50 ° and preferably is about 15 °. For all pipe sizes, the number of polyhedrons per 360 ° arc is determined by the step or d described above. For an optimum heat transfer consistent with a minimum fluid flow resistance, a tube constituting the present invention must have an internal enhancement with features as described above and having the following parameters: the polyhedral axis 99 of the polyhedrons should be placed at an angle between 0 and 40 ° with respect to the longitudinal axis of the tube; the ratio of the height H of the polyhedron to the inner diameter of the tube should be between 0.015 and 0.04. The angle of incidence ß between the longitudinal axis and the third and fourth faces 28 and 31 should be between 5o and 40 °. The recessed area 32 adjacent the polyhedron 19 preferably should extend within the interior surface of the wall 16 between -0.02 and 0.02 mm (-0.001 and 0.001 inches) and preferably 0.01 mm (0.0005 inches) (the values negative indicate the distance above the inner wall of the tube). The angle of the vertex lx between the opposite faces 28 and 31 should be in the range of 20 to 50 °, and preferably in 44 °. In addition, the ratio of the area S in cross section (shown in Figure 3) of the space between the polyhedra 19 with respect to the height H of the polyhedra 19 must be between 0.1 mm and 0.6 mm. By increasing the cross-sectional area between the polyhedra 19, the ratio of the area S in cross section to the height increases, and the weight and costs decrease ^ ___ ^^^^^^^^^^ H ^ ^ ái ^^^^^^^^ resulting from the pipeline, provided that the height (H) of the polyhedron remains unchanged. The polyhedra 19 (best shown in Figure 2) is formed by the material that remains after two patterns are stamped on the interior wall 16. The first pattern is preferably made along the longitudinal axis of the tube 10 and determines the length of the polyhedra 19, however, as stated above, they may be offset by up to 40 °. The second pattern is oblique to the longitudinal axis and determines the width of the polyhedra 19. The second pattern preferably extends further into the interior wall 16 of the tube 10 compared to the first pattern. The resulting surface improvement 13 should preferably be formed with an amount between 945 and 1732 polyhedra 19 per square centimeter (2,400-4,400 polyhedrons per square inch) of the inner wall 16. Although 945 to 1732 (2,400 to 4,400) are preferred this number it can vary from 787 to 3937 polyhedrons per square centimeter (2,000-10,000 polyhedrons per square inch). The improvement 13 can be formed on the interior of the tube wall 16 by any suitable process. In the manufacture of the welded seam metal pipe using high-speed automated processes, an effective method is to apply a pattern of improvement by roll-stamping on a surface of a metal strip before the strip is formed by rollers in a circular cross section and welded with seams in a tube 10. This can be carried out by placing two stamping stations by rollers in sequence in a production line to form by rollers and weld by sewing metal strips in pipe. The stations may be located in the supply source of the unworked metal strip and the portion of the production line where the strip is formed by rollers, in a tubular form. Each stamping station has a roll improvement pattern respectively and a backing roller. The backing and pattern rolls in each station are pressed together with sufficient force by suitable means (not shown), to cause the pattern surface on one of the rolls to be printed on the surface on one side of the strip and therefore both the longitudinal sides of the polyhedra are formed. The third and fourth faces 28 and 31 will be formed by a second roller having a series of raised projections that are pressed into the polyhedra 19. If the tube is manufactured by roll-forming, roll forming and seam welding, it is likely that there is a region along the line of the weld in the finished pipe 10 that lacks the configuration of the improvement that is present around the pipe 10 in a circumference, due to the nature of the manufacturing process, or having a configuration of different improvement. This region of different configuration does not adversely affect the thermal or fluid flow performance of the tube 10 in a significant manner. Again in Figure 4, h represents the heat transfer coefficient, IE represents the pipe with internal improvements and "uniform" represents a flat pipe. The curves in Figure 4 illustrate the relative condensation performances (h (IE) / h (uniform)) of three different internally improved tubes compared to a tube having a uniform interior surface, over a mass flow rate range of refrigerant R-22 through the tubes. The tube A is an embodiment of the present invention, which has an S / H ratio of 0.264 mm, a ß angle of 15 ° and the rows of the polyhedra are oriented substantially parallel to the longitudinal axis of the tube. Tube B represents a prior art tube having helical inner rims similar to those of the tube described in U.S. Patent Number 4, 658,892. The tube C is another embodiment of the present invention, which has an S / H ratio of 0.506 mm, a ß angle of 15 ° and the rows of polyhedrons are oriented substantially parallel to the longitudinal axis of the tube. The graph of Figure 4 illustrates that tube A works better than tube B, while tube C operates approximately equal to tube B, over a wide range of flow rates. Tube A is designed to have the same weight as tube B and tube C is designed to have a lighter weight than tube B. Accordingly, the present invention provides improved performance at an equal weight, and equal operation at a reduced weight, which reduces costs for the end user. Again in Figure 5, the curves show the relative performance with respect to the pressure drop of the tubes described above, A, B and C over a range of mass flow velocities of refrigerant R-22 through the tube. The graph in Figure 5 indicates that tube A has a relatively small amount of increase in pressure drop while tube C has a significant decrease in pressure drop over a wide range of coolant flow rates R-22 , all compared to tube B. Accordingly, the tube of the present invention provides superior performance for end users without adding significant complexity to their manufacturing processes. Although the invention has been described in connection with certain preferred embodiments, it is not intended to limit the scope of the invention to the particular forms that are established, but rather to cover the alternatives, modifications and equivalents that may be included within the scope of the invention. spirit and scope of the invention as defined by the appended claims.

Claims (21)

1. A heat exchanger tube, comprising: a tubular member having an inner surface defining an inner diameter and having a longitudinal axis; a plurality of polyhedra that are formed on the inner surface along at least one polyhedral axis, the at least one polyhedral axis is disposed at an angle of 0-40 ° of the longitudinal axis, each of the polyhedrons has four opposite sides and a height, the polyhedrons have first and second faces opposed to each other, the polyhedrons have a third and fourth faces opposite and inclined to each other and are arranged at an angle β of 5-14 ° of the polyhedral axis, the polyhedrons define a space between adjacent polyhedra having an area (S) in cross section, the S portion of a polyhedron height is around 0.1-0.6 mm.

2. Heat exchanger tube, as described in claim 1, wherein a portion of the inner surface adjacent the third and fourth faces is recessed below the remainder of the inner surface.

3. Heat exchanger tube, as described in claim 4, wherein the recessed portion is in the range of 0.02 mm above the inner surface to 0.02 mm below the inner surface.

4. Heat exchanger tube, as described in claim 1, wherein the distance between adjacent rows of polyhedra is approximately 0.28 mm at

0. 94 mm.

5. Heat exchanger tube, as described in claim 4, wherein there are 747 to 3937 polyhedra per square centimeter.

6. Heat exchanger tube, as described in claim 1, wherein there are approximately 945 to 1732 polyhedra per square centimeter.

7. Heat exchanger tube, as described in claim 1, wherein the vertex angle between the third and fourth adjacent faces of the polyhedrons is 20 to 50 Y

8. Heat exchanger tube, as described in claim 1, wherein the angle between the first and second adjacent faces is 10 to 50 Y

9. Heat exchanger tube, comprising: a tubular member that it has an interior surface that defines an inside diameter and that has a longitudinal axis; and a plurality of polyhedra that are formed on the inner surface along at least one polyhedral axis, the at least one polyhedral axis is arranged at an angle of about 0-40"with respect to the lingual axis, each of the polyhedra has four opposite sides and a height, the polyhedrons have first and second faces opposite each other, the polyhedrons have a third and fourth opposite faces and they are included among each other and placed at an angle of 5-14 ° with respect to the axis longitudinal, the polyhedra define a space between the adjacent polyhedrons that have an area (S) in cross section, the ratio of the area in cross section to the height is 0.1 mm to 0.6 mm, the polyhedrons arranged to exist between 747 and 1968 polyhedra per square centimeter of the pipe, the polyhedra having an apex angle between the third and fourth adjacent faces of the polyhedra is from 20 to 50 °

10. Heat exchanger tube, as described in claim 9, wherein the portion of the inner surface adjacent to the third and half faces is recessed below the remainder of the inner surface.

11. Heat exchanger tube, as described in claim 9, wherein the recessed portion is in the 0.02 mm range below the inner surface.

12. Heat exchanger tube, as described in claim 9, where the distance between adjacent rows of polyhedra is approximately 0.28 mm at

0. 94 mm.

13. Heat exchanger tube, as described in claim 9, wherein there are 747 to 3937 polyhedra per square centimeter.

14. Heat exchanger tube, as described in claim 9, wherein there are approximately 945 to 1732 polyhedra per square centimeter.

15. Heat exchanger tube, as described in claim 9, wherein the vertex angle between the third and fourth adjacent faces of the polyhedra is 20 to 50 °.

16. Heat exchanger tube, as described in claim 9, wherein the angle between the first and second adjacent faces is 10 to 50 °.

17. A heat exchanger tube, comprising: a tubular member having an inner surface defining an inner diameter and having a longitudinal axis; and a plurality of polyhedra that are formed on the inner surface, each of the polyhedra has four opposite sides and a height, the polyhedra are placed in rows that extend substantially parallel to the longitudinal axis, the polyhedra have a first and second opposite faces among themselves and extending substantially parallel to the longitudinal axis, the polyhedra have a third and fourth faces opposite and inclined to each other and placed at an oblique angle with respect to the longitudinal axis, the polyhedrons are placed along a polyhedral axis, the axis polyhedral is placed at an angle between 0 and 40 ° with respect to the longitudinal axis of the tubular member, the angle at which the third and fourth faces intersect the longitudinal axis is between 5 and 40 °, the polyhedra define a space between adjacent polyhedra that they have an area in cross section, the ratio of the area in cross section with respect to the height is between 0.1 mm and 0.6 mm, the They are distributed between 747 and 3937 polyhedra per square centimeter of pipe.

18. Heat exchanger tube, comprising: a tubular member having an inner surface defining an inner diameter and having a longitudinal axis; a plurality of polyhedra that are formed on the inner surface along at least one polyhedral axis, the at least one polyhedral axis is disposed at an angle of 0-40 ° of the longitudinal axis, each of the polyhedrons has four opposite sides and a height, the polyhedrons have first and second faces opposed to each other, the polyhedra have a third and fourth faces opposite and inclined to each other and are arranged at an angle β of 5-14 'of the polyhedral axis, the polyhedrons define a space between the adjacent polyhedrons that have an area (S) in cross section, the S portion of a height of the polyhedron is around 0.4-0.6 mm, the third and fourth faces have a cut arranged between them, the cut extended between the interior surface.

19. Heat exchanger tube, as described in claim 18, wherein the angle ß is about 15 °.

20. Heat exchanger tube, as described in claim 19, wherein the cut extends about 0.02 mm on the inner surface.

21. Heat exchanger tube, as described in claim 20, wherein there are about 945 polyhedrons per square centimeter.