U.S. patent application number 11/540689 was filed with the patent office on 2008-04-03 for heat exchanger tube with enhanced heat transfer co-efficient and related method.
This patent application is currently assigned to General Electric Company. Invention is credited to Ronald S. Bunker, Giuseppe Malcaus.
Application Number | 20080078534 11/540689 |
Document ID | / |
Family ID | 39272850 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080078534 |
Kind Code |
A1 |
Bunker; Ronald S. ; et
al. |
April 3, 2008 |
Heat exchanger tube with enhanced heat transfer co-efficient and
related method
Abstract
A method of enhancing the heat transfer coefficient of a tube
flowing a fluid in the tube in heat exchange relation with a second
fluid external to the tube includes forming a patterned array of
grooves on the interior surface of the tube. Each tube has a
depth-to-width ratio of 0.10 to 0.30, and the grooves may be formed
by mechanical pressing, pulsed ECM or electrodischarge
processes.
Inventors: |
Bunker; Ronald S.;
(Niskayuna, NY) ; Malcaus; Giuseppe; (Firenze,
IT) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
39272850 |
Appl. No.: |
11/540689 |
Filed: |
October 2, 2006 |
Current U.S.
Class: |
165/133 |
Current CPC
Class: |
F28F 1/40 20130101 |
Class at
Publication: |
165/133 |
International
Class: |
F28F 1/40 20060101
F28F001/40 |
Claims
1. A method of enhancing the heat transfer coefficient of a tube
flowing a fluid in the tube in heat exchange relation with a second
fluid external to the tube comprising forming a patterned array of
grooves on the interior surface of the tube.
2. The method of claim 1 wherein said grooves have a depth of
greater than about 0.2% of the internal tube diameter.
3. The method of claim 1 wherein said grooves have a depth of
between 1% and 5% of the internal tube diameter.
4. The method of claim 1 wherein said grooves have a semi-spherical
cross section.
5. The method of claim 1 wherein said grooves have a depth-to-width
ratio of 0.10 to 0.30
6. The method of claim 1 wherein said grooves are formed by a
mechanical pressing.
7. The method of claim 1 wherein said grooves are formed by pulsed
ECM or electro-discharge processes.
8. The method of claim 1 wherein said grooves are
criss-crossed.
9. The method of claim 1 comprising forming each grooves with a
flat bottom and angled side walls.
10. The method of claim 1 comprising forming at least some of the
grooves to run generally parallel to each other but with varying
spacing therebetween.
11. The method of claim 1 comprising forming the tube to vary
density of the grooves along the length of the tube.
12. A heat exchanger tube comprising a hollow tube having an
interior surface covered substantially by an array of grooves, said
grooves having a depth-to-width diameter ratio of 0.10 to 0.30.
13. The heat exchanger tube of claim 12 wherein said grooves have a
depth of greater than about 0.2% of the internal tube diameter.
14. The heat exchanger tube of claim 13 wherein said grooves have a
depth of between 1% and 5% of the internal tube diameter.
15. The heat exchanger tube of claim 12 wherein said grooves have a
semi-spherical cross section.
16. The heat exchanger tube of claim 12 wherein said grooves are
criss-crossed.
17. A heat exchanger comprising a plurality of interconnected tubes
adapted to carry a first fluid in heat exchange relationship with a
second fluid flowing across said plurality of interconnected tubes,
each tube having an interior surface covered substantially by an
array of intersecting grooves in a criss-crossed pattern, said
grooves having a depth-to-tube diameter ratio of 0.10 to 0.30.
18. The heat exchanger of claim 17 wherein said grooves have a
depth of greater than about 0.2% of the internal tube diameter.
19. The heat exchanger of claim 18 wherein said grooves have a
depth of between 1% and 5% of the internal tube diameter.
20. The heat exchanger of claim 17 wherein said grooves have a
semi-spherical cross section.
Description
BACKGROUND
[0001] The present invention relates to heat exchangers and
particularly to air cooled heat exchangers having an increased heat
transfer co-efficient between the fluid flowing within the tube and
the tube itself.
[0002] Heat exchangers providing heat exchange between a fluid
within a series of tubes and cooling air flowing about the tubes
are well known. Enhancements to these heat exchangers have taken
the form of a plurality of fins applied externally about the tubes
enhancing the heat exchange between the cooling air flowing about
the tubes and fins and the fluid flowing within the tubes. Various
methods for increasing the exchange surface and heat transfer
co-efficient are well known in other environments, such as the use
of brazed micro turbulators on internal surfaces of gas turbine
parts, and internal tube dimpling. See, for example, U.S. Pat. Nos.
6,598,781 and 6,644,921. However, these processes have not been
applied to air cooled heat exchangers, and do not address the
enhancement of heat transfer between the fluid within a tube and
the tube itself. Accordingly, there remains a need for increased
heat exchange between the fluid inside a tube and the tube wall in
an air cooled heat exchanger.
BRIEF SUMMARY
[0003] In accordance with an exemplary embodiment, heat exchange
between fluid inside the tube and the tube wall is enhanced through
the creation of a pattern of small grooves in the internal tube
surface in order to create vortices in the fluid flow.
[0004] The creation of grooves on the internal surface of the tube
and, in one exemplary embodiment, specifically a criss-crossed
grooved pattern on the internal surface, can be accomplished by
pulsed electrochemical machining (ECM), electrodischarge or simple
tool pressing operations. The cross grooving at shallow depth and
with spherical cross-sections serves to create low level fluid
vortices for mixing fresh fluid to the walls and increasing heat
transfer with little or no added pressure losses as compared to a
smooth tube.
[0005] Accordingly, in one aspect, the invention relates to a
method of enhancing the heat exchange coefficient of a tube flowing
a fluid in the tube in heat exchange relation with a second fluid
external to the tube comprising forming a patterned array of
grooves on the interior surface of the tube.
[0006] In another aspect, the invention relates to a heat exchanger
tube comprising a hollow tube having an interior surface covered
substantially by an array of grooves, said grooves having a
depth-to-width ratio of 0.10 to 0.30.
[0007] In still another aspect, the invention relates to a heat
exchanger comprising a plurality of interconnected tubes adapted to
carry a first fluid in heat exchange relationship with a second
fluid flowing across said plurality of interconnected tubes, each
tube having an interior surface covered substantially by an array
of grooves in a criss-crossed pattern, said grooves having a
depth-to-width diameter ratio of 0.10 to 0.30.
[0008] The invention will now be described in connection with the
drawings identified below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic illustration of a prior art heat
exchanger;
[0010] FIG. 2 is a schematic illustration of a tube with fins
forming part of a prior art heat exchanger of FIG. 1;
[0011] FIG. 3 is a partial perspective view of a heat exchanger
tube having an internal surface with a criss-crossed pattern of
grooves formed therein; and
[0012] FIG. 4 is a partial perspective view of an unwrapped
interior tube surface illustrating the criss-crossed groove pattern
formed in the tube of FIG. 3.
DETAILED DESCRIPTION OF THE DRAWINGS
[0013] Referring to the drawings, particularly to FIG. 1, there is
illustrated a conventional heat exchanger generally designated 10.
Heat exchanger 10 is comprised of a plurality of interconnected
tubes 12 for carrying/circulating a fluid to be cooled. The hot
fluid is typically conveyed back and forth in opposite directions
(or in one way only) in the tubes 12 that may be arranged in a
large grid-like pattern. As illustrated in FIG. 1, the tubes 12
extend from a hot fluid inlet 14, back and forth in the grid
pattern and terminate at an outlet port 16. It will be understood
that the tubes can be arranged in many different configurations,
e.g., one above the other, in layers offset one above the other or
in any other well-known and suitable configuration. It will also be
appreciated that, in use, the tubes 12 are in heat exchange
relation with a cooling fluid e.g., air, flowing across the
grid-like pattern. It will also be appreciated that the tubes may
carry a fluid to be heated by flowing a heated fluid across the
tubes.
[0014] To facilitate the heat transfer, and using as an example
heat exchange between tubes carrying a hot fluid and cooling air
passing over and about the tubes, a fan 18 with fan blades 20 is
disposed, for example, below the tubes 12 for driving the cooling
air through and across the grid. Thus, the air and the tubes 12 are
in heat exchange relation one with the other such that the heated
fluid passing through the tubes 12 is cooled and exits the heat
exchanger at outlet port 16 at a lower temperature than fluid at
the inlet 14. This invention also contemplates situations where
only the latent heat is involved, such that the fluid will have
energy removed, but will not actually be cooled.
[0015] An enlarged schematic illustration of a finned tube 12 is
shown in FIG. 2. Thus, each tube 12 in the heat exchanger may carry
multiple fins 22 which are attached to the tubes in a conventional
manner. It will be appreciated that the fins increase the effective
surface area of the interface between the cooling air and hot fluid
enabling enhanced thermal cooling of the hot fluid.
[0016] Further enhancement of heat transfer in connection with fins
is described in commonly owned co-pending application Ser. No.
11/493,022, filed Jul. 26, 2006.
[0017] As used herein, the term "fluid" embraces liquids, gases,
steam, two phase mixtures, and multi-component fixtures. Also, heat
exchanger's incorporating tubes as described herein may be of the
type for condensing evaporated fluid.
[0018] Referring now to FIGS. 3 and 4, the interior surface 24 of a
tube 26 (shown in "unwrapped form" in FIG. 4) may be treated
mechanically by a tool pressing operation, or by pulsed ECM or
electrodischarge processes to provide shaped surfaces within the
tubes. One exemplary pattern shown to enhance heat transfer is a
criss-crossed array of grooves 28 of shallow depth that serve to
create lower level fluid vortices for mixing fresh fluid to the
walls and increasing heat transfer with little or no added pressure
losses compared to a smooth tube. In FIG. 4, groove centerlines 30
and 32 illustrate a pair of intersecting grooves 28, noting that
regions 34 represent the original internal surface of the tube,
raised relative to the grooves 28. The grooves 28 may be pressed
simultaneously or formed in two sets of spiral or helical grooves,
one in a clockwise direction and the other in a counter-clockwise
direction, by different tools moving through the tube. The
differently directed grooves may be at the same or differing
relative angles.
[0019] In one example, a one-inch diameter tube having a wall
thickness of 0.1 inch may have a groove depth of greater than 50
microns (about 2 mils or 0.2% of tube ID), and preferably in a
range of 10 to 50 mils (or 1% to 5% of tube ID). The depth-to-width
ratio may be in a range of 0.10 to 0.30. The grooves are generally
semi-spherical in cross-section, with no sharp features to create
added stresses, and preferably extend along the entire length of
the tube.
[0020] Other patterns of intersecting grooves may be employed and
remain within the scope of the invention. For example, the grooves
when viewed in the unwrapped form illustrated in FIG. 4 may be
curved along the length dimension thereof.
[0021] The groove geometry may also be varied in any of the
following manners:
[0022] (a) The spacing between parallel running grooves, i.e., the
perpendicular distance between two grooves may be varied without
the grooves actually overlapping.
[0023] (b) The cross-sectional shape may only approximate a
generally semispherical shape, for example, the groove may have a
flat bottom with flat angled sidewalls.
[0024] (c) Groove density may vary, i.e., there may be a variation
in the spacing of the grooves within the same length tube. In other
words, constant spacing leads to a constant density (grooves per
unit length), while changing the spacing as a function of distance
along with tube length will alter the effects along the length.
This can be achieved, for example, by varying the rate of draw of
the tube during manufacture such that the tube may be tailored to
have more heat transfer in one region and less in another
region.
[0025] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *