U.S. patent application number 12/436294 was filed with the patent office on 2010-11-11 for finned tube heat exchanger.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Jorge Alejandro Carretero Benignos, Johannes Eckstein, Rodrigo Rodriguez Erdmenger, Sal Albert Leone, Thomas Francis Taylor, Hua Zhang.
Application Number | 20100282456 12/436294 |
Document ID | / |
Family ID | 42932614 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100282456 |
Kind Code |
A1 |
Benignos; Jorge Alejandro Carretero
; et al. |
November 11, 2010 |
FINNED TUBE HEAT EXCHANGER
Abstract
A heat exchanger comprises a tube and fins extending from an
outer surface of the tube. The fins comprise first and second sets
of fins with the first set of fins oriented in a first direction
with respect to an axial direction of the tube and the second set
of fins oriented in a second direction with respect to the axial
direction of the tube to expose at least a portion of the first and
second sets of fins to a free stream.
Inventors: |
Benignos; Jorge Alejandro
Carretero; (Munich, DE) ; Erdmenger; Rodrigo
Rodriguez; (Munchen, DE) ; Leone; Sal Albert;
(Scotia, NY) ; Taylor; Thomas Francis;
(Greenville, SC) ; Zhang; Hua; (Greer, SC)
; Eckstein; Johannes; (Ismaning, DE) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, BLDG. K1-3A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
42932614 |
Appl. No.: |
12/436294 |
Filed: |
May 6, 2009 |
Current U.S.
Class: |
165/182 |
Current CPC
Class: |
F28F 2215/04 20130101;
F28F 1/36 20130101; F28F 1/30 20130101 |
Class at
Publication: |
165/182 |
International
Class: |
F28F 1/24 20060101
F28F001/24 |
Claims
1. A heat exchanger, comprising: a tube; and fins extending from an
outer surface of the tube, the fins comprise first and second sets
of fins with the first set of fins oriented in a first direction
with respect to an axial direction of the tube and the second set
of fins oriented in a second direction with respect to the axial
direction of the tube to expose at least a portion of the first and
second sets of fins to a free stream.
2. The heat exchanger of claim 1, wherein the first and second sets
of fins are alternately arranged to expose each of the fins to the
free stream.
3. The heat exchanger of claim 1, wherein the fins are arranged in
a helical path around the outer surface of the tube.
4. The heat exchanger of claim 3, wherein the first direction is in
line with the helical path and the second direction is at an angle
with respect to the helical path.
5. The heat exchanger of claim 3, wherein the first direction and
the second direction are at an angle with respect to the helical
path.
6. The heat exchanger of claim 1, wherein the fins are formed by
creating slits on a fin strip and bending the first set of fins,
the second set of fins, or both the first and second sets of fins
with respect to the fin strip before helically winding and
attaching the fin strip on the outer surface of the tube.
7. A heat exchanger, comprising: a tube; and fins extending from an
outer surface of the tube, the fins comprise groups of contiguous
fins that are oriented alternately in first and second directions
with respect to an axial direction of the tube to expose the groups
of contiguous fins to a free stream.
8. The heat exchanger of claim 7, wherein the fins are arranged in
a helical path around the outer surface of the tube.
9. The heat exchanger of claim 8, wherein the first direction is in
line with the helical path and the second direction is at an angle
with respect to the helical path.
10. The heat exchanger of claim 8, wherein the first direction and
the second direction are at an angle with respect to the helical
path.
11. The heat exchanger of claim 7, wherein the fins are formed by
creating slits on a fin strip and bending a portion of fins with
respect to the fin strip to correspond to the first and second
directions before helically winding and attaching the fin strip on
the outer surface of the tube.
12. A heat exchanger, comprising: a tube; and fins extending from
an outer surface of the tube in a helical path, the fins comprise
serrated sections and solid sections that are disposed in a
predetermined arrangement along the helical path.
13. The heat exchanger of claim 12, wherein the serrated sections
and the solid sections are alternately disposed along the helical
path.
14. The heat exchanger of claim 12, wherein a portion of the
serrated sections are directly in the path of a free stream.
15. The heat exchanger of claim 12, wherein a portion of the solid
sections are directly in the path of a free stream.
16. The heat exchanger of claim 12, wherein the solid sections
comprise groove, dimples, corrugations, or other heat transfer
enhancing features.
17. The heat exchanger of claim 12, wherein each of the serrated
sections includes a plurality of individual fins that extend
substantially till the outer surface of the tube.
18. The heat exchanger of claim 17, wherein the fins comprise a fin
strip that is helically wound and attached to the outer surface of
the tube, with slits created on the fin strip corresponding to the
serrated sections before helically winding the fin strip.
19. A heat exchanger, comprising: a tube; and fins extending from
an outer surface of the tube in a helical path, the fins comprise
serrated sections and solid sections that are alternately disposed
along the helical path, wherein the tube is positioned such that a
portion of either the serrated sections or the solid sections are
directly in the path of a free stream.
20. The heat exchanger of claim 19, wherein the solid sections
comprise groove, dimples, corrugations, or other heat transfer
enhancing features.
21. The heat exchanger of claim 19, wherein each of the serrated
sections includes a plurality of individual fins that extend
substantially till the outer surface of the tube.
22. The heat exchanger of claim 21, wherein the fins comprise a fin
strip that is helically wound and attached to the outer surface of
the tube, with slits created on the fin strip corresponding to the
serrated sections before helically winding the fin strip.
Description
BACKGROUND
[0001] The invention relates generally to heat exchangers and, more
particularly, to a finned tube heat exchanger.
[0002] A finned tube heat exchanger includes a tube and fins
disposed on the outer surface of the tube. Several designs for the
fins are known in the art, including a serrated fin configuration.
A serrated fin configuration can be formed on a tube by creating
serrations in a sheet of metal and then winding the serrated sheet
around the tube.
[0003] Fins including serrations, slits, and bending aspects are
known in the art. Kimura (EP 0854344 A2) discloses a heat exchanger
having finned tubes. The finned tubes are fabricated by attaching
fins having the shape of a circular plate to the outer surface of
the tube. Each fin is provided with bent portions that are formed
by forming radial slits in a peripheral portion of the fin to
divide the peripheral portion into a plurality of segments and then
bending each segment in an axial direction of the tube along a
bending line extending from a point on the radial slit. The bent
portions can be formed in the same direction or in alternately
opposite directions. The bent portions or tips accomplish increased
flow mixing. The resultant bent tips are basically vortex
generators. The goal of a vortex generator is to generate a vortex
that brings higher energy particles from a free stream to low
energy particles. The vortex generators reenergize boundary layers
and prevent flow separation with slow recirculation. Therefore, the
bent portions affect the flow and prevent or lessen the flow
separation, but do not act as prime heat transfer surfaces. As a
result, the heat transfer capability is compromised.
[0004] Shigenaka (U.S. Pat. No. 5,617,916) discloses a fin tube
heat exchanger formed by winding a serrated fin strip around a
tube. The fins are twisted at a twist angle with respect to a
contact line along the base portion of the fin strip which is in
contact with the tube. The fins are also inclined at an inclination
angle with respect to a straight line perpendicular to an axis of
the tube. This design of heat exchanger increases flow mixing.
Increased flow mixing leads to higher heat transfer. However,
increased flow mixing also leads to increased pressure losses. All
the fins have the same level of inclination and twist angles.
Therefore, an upstream fin will shade a downstream one that will
only see a low speed recirculation. This twisting and inclination
may increase heat transfer due to increased mixing, but the effect
may become detrimental after some point. There may be increased
pressure losses since the flow will most likely separate.
[0005] In order to reduce the costs, it is desirable to increase
the heat transfer performance of finned tubes. An increase in heat
transfer is normally associated with an increase of the pressure
drop in the system. Typically, increased heat transfer can be
achieved by increasing the turbulence of the flow or the effective
heat transfer area. It is possible to achieve a higher heat
transfer by increasing the turbulence levels of the flow, but this
increase is normally penalized by an increase in the pressure drop
of the heat exchanger. Serrated fins are used to generate
turbulence in the flow in order to increase the heat transfer
performance of the heat exchanger. However, serrated fins generate
increased pressure drops compared to a simple solid fin and have
less material and area for heat transfer.
[0006] It would therefore be desirable to provide finned tube heat
exchangers having augmented heat transfer capability without
unfavorable pressure drops.
BRIEF DESCRIPTION
[0007] In accordance with one embodiment disclosed herein, a heat
exchanger comprises a tube and fins extending from an outer surface
of the tube. The fins comprise first and second sets of fins with
the first set of fins oriented in a first direction with respect to
an axial direction of the tube and the second set of fins oriented
in a second direction with respect to the axial direction of the
tube to expose at least a portion of the first and second sets of
fins to a free stream.
[0008] In accordance with another embodiment disclosed herein, a
heat exchanger comprises a tube and fins extending from an outer
surface of the tube. The fins comprise groups of contiguous fins
that are oriented alternately in first and second directions with
respect to an axial direction of the tube to expose the groups of
contiguous fins to a free stream.
[0009] In accordance with another embodiment disclosed herein, a
heat exchanger comprises a tube and fins extending from an outer
surface of the tube in a helical path. The fins comprise serrated
sections and solid sections that are disposed in a predetermined
arrangement along the helical path.
[0010] In accordance with another embodiment disclosed herein, a
heat exchanger comprises a tube and fins extending from an outer
surface of the tube in a helical path. The fins comprise serrated
sections and solid sections that are alternately disposed along the
helical path. A portion of either the serrated sections or the
solid sections are directly in the path of a free stream.
DRAWINGS
[0011] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0012] FIG. 1 illustrates a partial perspective view of an
embodiment of the finned tube heat exchanger in accordance with
aspects disclosed herein.
[0013] FIG. 2 illustrates a plan view of a fin strip in accordance
with aspects disclosed herein.
[0014] FIG. 3 illustrates a side view of the fin strip where only
alternate fins are bent with respect to the fin strip in accordance
with aspects disclosed herein
[0015] FIG. 4 illustrates a side plan view of the finned tube heat
exchanger in accordance with aspects disclosed herein.
[0016] FIG. 5 illustrates a front plan view of the finned tube heat
exchanger in accordance with aspects disclosed herein, wherein only
few fins are depicted for clarity.
[0017] FIG. 6 illustrates a partial sectional view of the finned
tube heat exchanger in accordance with aspects disclosed
herein.
[0018] FIG. 7 illustrates a plan view of a standard serrated finned
tube from one end.
[0019] FIG. 8 illustrates a side view of fin strip where alternate
fins are bent in opposite directions with respect to the fin strip
in accordance with aspects disclosed herein.
[0020] FIG. 9 illustrates a side plan view of another embodiment of
the finned tube heat exchanger in accordance with aspects disclosed
herein.
[0021] FIG. 10 illustrates a front plan view of the finned tube of
FIG. 9 in accordance with aspects disclosed herein, wherein only
few fins are depicted for clarity.
[0022] FIG. 11 illustrates a partial sectional view of the finned
tube of FIG. 9 in accordance with aspects disclosed herein.
[0023] FIG. 12 illustrates a partial sectional view of another
embodiment of the finned tube in accordance with aspects disclosed
herein.
[0024] FIG. 13 illustrates a graph comparing Colburn factors of the
finned tube heat exchanger with bent fins and a conventional
serrated finned tube heat exchanger without bent fins.
[0025] FIG. 14 illustrates a graph comparing friction factors of
the finned tube heat exchanger with bent fins and a conventional
serrated finned tube heat exchanger without bent fins.
[0026] FIG. 15 illustrates a side plan view of another embodiment
of the finned tube heat exchanger with serrated sections directly
in the path of a free stream in accordance with aspects disclosed
herein.
[0027] FIG. 16 illustrates a front plan view of the finned tube
heat exchanger of FIG. 15 in accordance with aspects disclosed
herein.
[0028] FIG. 17 illustrates a plan view of a fin strip with slits
formed only in selected locations in accordance with aspects
disclosed herein.
[0029] FIG. 18 illustrates a side plan view of the finned tube heat
exchanger with solid sections in the path of a free stream in
accordance with aspects disclosed herein.
[0030] FIG. 19 illustrates a side plan view of another embodiment
of the finned tube heat exchanger with heat transfer enhancing
features in accordance with aspects disclosed herein.
[0031] FIG. 20 illustrates a frame for housing finned tubes in
accordance with aspects disclosed herein.
DETAILED DESCRIPTION
[0032] Embodiments disclosed herein include serrated finned tube
heat exchangers. The finned tube heat exchanger includes a tube and
fins extending from the outer surface of the tube. The fins are
arranged and designed in a manner to augment heat transfer
capability and reduce or minimize pressure drops compared to a
standard serrated finned tube heat exchanger. In one embodiment,
the fins include serrated fins that are disposed along a helical
path corresponding to first and second directions with respect to
an axial direction of the tube. In another embodiment, the fins
include serrated and solid sections that are disposed in a
predetermined arrangement along a helical path. As used herein,
singular forms such as "a," "an," and "the" include plural
referents unless the context clearly dictates otherwise.
[0033] Referring to FIGS. 1-3, an embodiment of the finned tube
heat exchanger 10 includes a tube 12 and a plurality of fins 14
extending from an outer surface 16 of the tube 12. The tube 12 has
a length along an axis 18 passing through the center of the tube
12. The fins 14 are disposed around the outer surface 16 of the
tube 12 in a generally helical configuration. The fins 14 can be
formed by first creating slits 20 on a fin strip 22. The fin strip
22 is then helically wound and attached on the outer surface 16 of
the tube 12. In one embodiment, every alternate fin 14 is bent with
respect to the fin strip 20. A first set of fins 24 includes unbent
fins and a second set of fins 26 includes bent fins. The second set
of fins 26 can be bent in any angle ranging from -90 degrees to +90
degrees with respect to the plane of the fin strip 22.
[0034] FIGS. 4-6 illustrate various views of the finned tube heat
exchanger 10. Fins in the first set of fins 24 are shown as shaded
to differentiate from the second set of fins 26. The fin strip 22
is positioned in a helical path 28 around the tube 12. The first
set of fins 24 are oriented in a first direction `.theta.1` with
respect to the axial direction 30 of the tube 12. The axial
direction 30 of the tube is along the axis 18 of the tube 12. The
second set of fins 26 are oriented in a second direction `.theta.2`
with respect to the axial direction 30. Since only the second set
of fins 26 is bent, the first set of fins 24 are in line with the
helical path 28 and the second set of fins 26 are positioned at an
angle `.theta.3` with respect to the helical path 28. Fins in the
second set of fins 26 are therefore out of the plane of the helical
fin strip 22. In a standard serrated fin 32 as shown in FIG. 7, all
the fins 34 have the same orientation with respect to each other
and the fins 34 would generally be in line with a helical path,
i.e. .theta.1=.theta.2 and .theta.3=0.
[0035] In another embodiment as shown in FIG. 8, alternate fins are
bent in opposite directions with respect to the fin strip 22. For
example, the first set of fins 24 can be bent in any angle ranging
from 0 degrees to +90 degrees with respect to the plane of the fin
strip 22 and the second set of fins 26 can be bent in any angle
ranging from -90 degrees to 0 degrees with respect to the plane of
the fin strip 22. In this case, both the first set of fins 24 and
the second set of fins 26 will be at an angle with respect to the
helical path after the fin strip 22 is helically wounded around the
tube.
[0036] The arrangement of the first and second set of fins 24 and
26 results in a configuration where every fin is oriented
differently with respect to a contiguous fin along the helical path
28. Each fin is therefore exposed to a free stream of air (denoted
by arrows in FIG. 5) flowing towards the tube 12. A free stream air
is at a higher temperature and therefore there is more potential
for heat transfer. The boundary layer formed at the surface of each
fin 14 is one of the leading obstacles to better heat transfer. The
second set of fins 26 (bent fins) will shed vortices, increasing
the mixing of a downstream flow and enhancing mixing and disrupting
of boundary layers. Being out of plane, the second set of fins 26
will not be significantly affected by any boundary layer from an
upstream fin. This will reduce the local thermal resistance,
thereby enhancing heat transfer capability.
[0037] Also, the distance a flow travels after an unbent upstream
fin 24 and until an unbent downstream fin 24 is longer compared to
a conventional serrated fin, since the bent fin 26 does not block
the flow between an unbent upstream fin 24 and an unbent downstream
fin 24. The increased distance allows for wake dissipation and
increased speed at the leading edge of a downstream fin. Any
remaining wake is eliminated on impact with a downstream fin. The
different orientations of first sets of fins 24 (unbent fins) and
second set of fins 26 (bent fins) results in a flow condition that
is closer to a three dimensional flow field than a two dimensional
flow. In a conventional serrated configuration, in which fins 26
are not bent, the wake dissipation would be much shorter.
[0038] The finned tube heat exchanger 10 does not have unfavorable
effects compared to a standard serrated finned tube from pressure
or head loss perspective. Flow around the fins 14 would be in
laminar and low turbulence regimes. Wall friction losses should be
unchanged compared to a standard serrated finned tube because there
is no increase in area of the fins. Tip vortices generated by the
fins 14 are only displaced compared to a standard serrated finned
tube, without major change in magnitude.
[0039] In another embodiment 40 as shown in FIGS. 9-11, groups of
contiguous fins 42 are oriented alternately in first and second
directions with respect to an axial direction 44 of the tube 46.
For example, pairs of contiguous fins 42 are oriented alternately
in first and second directions. Fins oriented in the first
direction are shown as shaded to differentiate from the fins
oriented in the second direction. The first direction is at an
angle `.theta.1` with respect to the axial direction 44 of the tube
46 and the second direction is at an angle `.theta.2` with respect
to the axial direction 44 of the tube 46. This configuration can be
achieved by bending every alternate pair of contiguous fins 42
before winding the fin strip 48 around an outer surface 50 of the
tube 46. In another embodiment as shown in FIG. 12, pairs of
alternate fins can be bent such that both the first and second
directions are at an angle with respect to the helical path.
[0040] The first direction will be in line with the helical path 52
and the second direction will be at an angle `.theta.3` with
respect to the helical path 52. Every pair of contiguous fins 42 is
therefore exposed to a free stream of air (denoted by arrows)
flowing towards the tube 46. As discussed previously with respect
to the embodiment of FIGS. 4-6, the finned tube heat exchanger 40
also has enhanced heat transfer capability and does not have
unfavorable effects compared to a standard serrated finned tube
from pressure or head loss perspective.
[0041] The bent-fin embodiments described above provide higher heat
transfer coefficients compared to standard serrated fin and also
solid fin tube configurations. Experimental results show about an 8
percent increase in heat transfer coefficient compared to standard
serrated fins. This augmented heat transfer capability is achieved
without increasing pressure losses compared to the standard
serrated fin. Colburn factor (j) is used to characterize heat
transfer coefficient and friction factor (f) is used to
characterize pressure drop. The Colburn factor and friction factor
are experimentally determined and plotted versus mass flux, G, in
FIGS. 13 and 14, respectively, for the finned tube heat exchanger
with bent fins and a conventional serrated finned tube heat
exchanger without bent fins. The data in FIGS. 13 and 14 was
obtained in a wind tunnel experiment using heated air on the finned
tube side and water inside the tubes. The inlet air pressure and
temperature and outlet air pressure and temperature were measured
across a bundle including four rows of finned tubes arranged in a
staggered pattern. From these measurements, the Colburn factor and
friction factor as a function of mass flux were determined.
[0042] Referring to FIGS. 15-17, another embodiment of the finned
tube heat exchanger 60 includes a tube 62 and fins 64 extending
from an outer surface 66 of the tube 62 in a helical path 68. The
fins 64 include serrated sections 70 and solid sections 72. The
serrated sections 70 and solid sections 72 are alternately disposed
along the helical path 68. The serrated sections 70 include a
plurality of individual fins 74 that extend substantially until the
outer surface 66 of the tube 62. The fins 64 can be formed on a fin
strip 76. Slits 78 are created on the fin strip 76 corresponding to
the serrated sections 70. The fin strip 76 is then helically wound
and attached to the outer surface 66 of the tube 62. Portions of
the fin strip 76 without the slits form the solid sections 72.
[0043] In one embodiment, a single revolution on the fin strip 76
around the tube 62 includes two serrated sections 70 and two solid
sections 70 that are alternately arranged. Therefore, referring to
FIG. 15, all of the serrated sections 70 on the topside of the tube
62 are in line with each other and all of the solid sections 72 on
the bottom side of the tube 62 are in line with each other.
Similarly, all of the serrated sections 70 on the left side of the
tube 62 are in line with each other and all of the solid sections
72 on the right side of the tube 62 are in line with each
other.
[0044] The combination of serrated and solid sections 70 and 72
increases turbulence of the flow, enhancing heat transfer
capability, and minimizes the overall pressure drop. The solid
sections increase the available heat transfer area compared to
standard serrated finned tube (shown in FIG. 7) that has a
plurality of individual fins. A reduced number of individual fins
in the finned tube will result in lower pressure drops. The
orientation of the finned tube with respect to the flow can be
determined according to the flow conditions in order to provide a
balance between increased heat transfer and reduced pressure drop.
In the embodiment shown in FIG. 15, the finned tube 60 is
positioned such that the serrated sections 70 on one side of the
tube 62 are directly in the path of a free stream 80. In another
embodiment as shown in FIG. 18, the finned tube 60 is positioned
such that the solid sections 72 on one side of the tube 62 are
directly in the path of a free stream 80. The finned tube 60 can
further include heat transfer enhancing features 82 such as
grooves, dimples, or corrugations on the solid sections as shown in
FIG. 19.
[0045] The finned tubes 60 can be arranged in bundles as shown in
FIG. 20. A frame 84 can be used to house bundles of the finned
tubes 60. The frame 84 can include a mechanism 86 to mount the
finned tubes 60 in a specific position such that either the solid
sections on one side of the tube 60 or the serrated sections on
another side of the tube 60 are directly in the path of a free
stream. In one embodiment, the mechanism 86 can include a notch at
the end of the tube 60 and a mating feature for the notch on the
frame 84 so that the fins can be aligned appropriately with respect
to the flow.
[0046] The finned tube heat exchangers thus provide a way to
augment heat transfer without unfavorable pressure drops. In
bent-fin embodiments, heat transfer capability can be enhanced
without an increase in pressure drop compared to a standard
serrated finned tube. In solid-serrated section embodiments, heat
transfer capability can be enhanced and pressure drop can be
reduced compared to a standard serrated finned tube.
[0047] It is to be understood that not necessarily all such objects
or advantages described above may be achieved in accordance with
any particular embodiment. Thus, for example, those skilled in the
art will recognize that the systems and techniques described herein
may be embodied or carried out in a manner that achieves or
optimizes one advantage or group of advantages as taught herein
without necessarily achieving other objects or advantages as may be
taught or suggested herein.
[0048] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *