U.S. patent application number 13/149146 was filed with the patent office on 2012-12-06 for fin and tube heat exchanger.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to William Joseph Antel, JR., Sebastian Walter Freund.
Application Number | 20120305227 13/149146 |
Document ID | / |
Family ID | 46207872 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120305227 |
Kind Code |
A1 |
Freund; Sebastian Walter ;
et al. |
December 6, 2012 |
FIN AND TUBE HEAT EXCHANGER
Abstract
The present application provides a fin and tube heat exchanger.
The fin and tube heat exchanger may include a number of tubes with
a number of substantially spirally wound circular fins positioned
on each of the tubes. The tubes may include a first set of tubes
including a plurality of tube pairs each including a tube in a
first row of tubes and a tube in a second row of tubes of the first
set of tubes. The tubes may further include a second set of tubes
including a plurality of tube pairs including a tube in a third row
of tubes and a tube in a fourth row of tubes of the second set of
tubes. The first set of tubes further including a transverse offset
position as compared to the second set of tubes.
Inventors: |
Freund; Sebastian Walter;
(Unterfoehring, DE) ; Antel, JR.; William Joseph;
(Freising, DE) |
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
46207872 |
Appl. No.: |
13/149146 |
Filed: |
May 31, 2011 |
Current U.S.
Class: |
165/172 |
Current CPC
Class: |
F28B 1/06 20130101; F28D
1/05333 20130101; F28D 7/163 20130101; F28F 1/36 20130101 |
Class at
Publication: |
165/172 |
International
Class: |
F28F 1/12 20060101
F28F001/12 |
Claims
1. A fin and tube heat exchanger, comprising: a plurality of tubes;
and a plurality of substantially spirally-wound circular fins
positioned on each of the plurality of tubes; the plurality of
tubes comprising a first set of tubes comprising a plurality of
tube groupings and a second set of tubes comprising a plurality of
tube groupings; wherein the first set of tubes comprises a
transverse offset position as compared to the second set of
tubes.
2. The fin and tube heat exchanger of claim 1, wherein the first
set of tubes comprises at least a first row of tubes and a second
row of tubes and wherein each of the plurality of tube groupings of
the first set of tubes comprises at least one tube in the first row
of tubes and one tube in the second row of tubes.
3. The fin and tube heat exchanger of claim 2, wherein the first
row of tubes and the second row of tubes comprise an inline
position relative to a flow across the first row of tubes and the
second row of tubes.
4. The fin and tube heat exchanger of claim 2, wherein the second
set of tubes comprises at least a third row of tubes and a fourth
row of tubes and wherein each of the plurality of tube groupings of
the second set of tubes comprises at least one tube in the third
row of tubes and one tube in the fourth row of tubes.
5. The fin and tube heat exchanger of claim 4, wherein the third
row of tubes and the fourth row of tubes comprise an inline
position relative to a flow across the third row of tubes and the
fourth row of tubes.
6. The fin and tube heat exchanger of claim 1, wherein the
transverse offset position comprises about a half of a transversal
tube spacing.
7. The fin and tube heat exchanger of claim 1, wherein the
plurality of tube groupings comprises a plurality of tube
pairs.
8. The fin and tube heat exchanger of claim 1, wherein the first
set of tubes and the second set of tubes are longitudinally spaced
apart to form a gap therebetween.
9. The fin and tube heat exchanger of claim 1, wherein the first
set of tubes and the second set of tubes are transversally spaced
apart to form a gap therebetween each tube grouping.
10. The fin and tube heat exchanger of claim 1, wherein the first
set of tubes and the second set of tubes are longitudinally spaced
apart to form a gap therebetween and the plurality of tubes
groupings of the first set of tubes and the second set of tubes are
transversally spaced apart to form a gap therebetween each tube
grouping.
11. The fin and tube heat exchanger of claim 1, wherein a first
plurality of substantially spirally-wound circular fins positioned
on a first tube of one of the plurality of tube groupings and a
second plurality of substantially spirally-wound circular fins
positioned on a second tube of one of the plurality of tube
groupings includes cut portions to provide close longitudinal
spacing between the first tube and the second tube of each of the
plurality of tube groupings.
12. The fin and tube heat exchanger of claim 1, wherein the fin and
tube heat exchanger comprises an air-cooled condenser.
13. The fin and tube heat exchanger of claim 1, wherein the fin and
tube heat exchanger comprises a heat recovery steam generator.
14. The fin and tube heat exchanger of claim 1, wherein the
plurality of tubes may include additional sets of tubes, comprised
of additional rows of tubes with the same repeated pattern.
15. A fin and tube heat exchanger, comprising: a plurality of
tubes; and a plurality of substantially spirally-wound circular
fins positioned on each of the plurality of tubes; the plurality of
tubes comprising: a first set of tubes comprising a first row of
tubes and a second row of tubes, wherein a plurality of tube pairs
are defined therein by a tube in the first row of tubes and an
inline tube in the second row of tubes; and a second set of tubes
comprising a third row of tubes and a fourth row of tubes, wherein
a plurality of tube pairs are defined therein by a tube in the
third row of tubes and an inline tube in the fourth row of tubes,
wherein the first set of tubes comprises a transverse offset
position as compared to the second set of tubes.
16. The fin and tube heat exchanger of claim 15, wherein the first
row of tubes and the second row of tubes comprise an inline
position relative to a flow across the first row of tubes and the
second row of tubes.
17. The fin and tube heat exchanger of claim 16, wherein the third
row of tubes and the fourth row of tubes comprise an inline
position relative to a flow across the third row of tubes and the
fourth row of tubes.
18. The fin and tube heat exchanger of claim 15, wherein the
plurality of substantially spirally-wound circular fins comprises a
substantially concentric position about each tube.
19. The fin and tube heat exchanger of claim 15, wherein the first
set of tubes and the second set of tubes are longitudinally spaced
apart to form a gap therebetween.
20. The fin and tube heat exchanger of claim 15, wherein the
plurality of tubes pairs of the first set of tubes and the second
set of tubes are transversally spaced apart to form a gap
therebetween each tube pair.
21. The fin and tube heat exchanger of claim 15, wherein the
plurality of tubes may include additional sets of tubes, comprised
of additional rows of tubes with the same repeated pattern.
22. A fin and tube heat exchanger, comprising: a plurality of
tubes; and a plurality of substantially spirally-wound circular
fins positioned on each of the plurality of tubes, the plurality of
tubes comprising: a first set of tubes comprising a first row of
tubes and a second row of tubes, wherein the first row of tubes and
the second row of tubes comprise an inline position relative to a
flow across the first row of tubes and the second row of tubes, and
wherein a plurality of tube pairs are defined therein, each of the
plurality of tube pairs comprising a tube in the first row of tubes
and a tube in the second row of tubes; and a second set of tubes
comprising a third row of tubes and a fourth row of tubes, wherein
the third row of tubes and the fourth row of tubes comprise an
inline position relative to a flow across the third row of tubes
and the fourth row of tubes, and wherein a plurality of tube pairs
are defined therein, each of the plurality of tube pairs comprising
a tube in the third row of tubes and a tube in the fourth row of
tubes, wherein the first set of tubes comprises a transverse offset
position as compared to the second set of tubes.
23. The fin and tube heat exchanger of claim 22, wherein the
plurality of tubes may include additional sets of tubes, comprised
of additional rows of tubes with the same repeated pattern.
Description
BACKGROUND
[0001] The present application relates generally to fin and tube
heat exchangers and more particularly relates to a semi-staggered
arranged compact fin and tube heat exchanger with substantially
spirally wound circular fins so as to maximize heat transfer while
minimizing the pressure loss therethrough.
[0002] In heat exchange applications that have a high mass flux and
limited frontal area it is advantageous to utilize a design with a
low-pressure drop but that maintains a relatively high heat
transfer. A broad variety of fin and tube type heat exchangers and
similar structures are commercially available and suitable for use
in the above described heat exchange application. One of the main
design goals in the construction of fin and tube type heat
exchangers focuses on maximizing heat transfer while minimizing the
pressure loss therethrough. Generally described, the extent of the
pressure loss may be directly related to the operating costs and
the overall energy losses and efficiency of the heat exchanger and
its use.
[0003] When designing a heat exchanger, a large fraction of the
pressure loss for a finned tube is due to profile drag. Unlike skin
friction on the fin surface, profile drag has little benefit for
the heat transfer. To address this profile drag, known tube bundle
arrangements generally are configured either in an in-line or a
staggered alignment. One example of known fin and tube heat
exchanger designs includes the use of in-line tube bundles with
densely-spaced and spirally-wound circular fins. In an in-line
arrangement, each tube is configured in the wake of the preceding
tube so as to lower the overall drag. The use of such in-line
arrangement of circular fins, however, may cause relatively large
bypass flows, wake regions, and lower heat transfer coefficients
because of the generally reduced air velocity therethrough.
Moreover, the bypass flow may exacerbate fouling problems about the
fins and the spaces therebetween as well as depress the heat
transfer coefficients. In-line arrangements, with low velocity
between the tubes, have weak wake regions and lower pressure loss.
In addition, the heat transfer coefficient on the fins as well as
on the tubes is lower, since a strong bypass flow exists, as
compared to a staggered arrangement where stronger flow mixing and
less bypassing of the finned area occurs due to a transverse offset
of a tube relative to a preceding tube. The staggered arrangement
generally may be favored as such an arrangement gives a higher heat
transfer coefficient with somewhat less bypass flow as compared to
an in-line arrangement. The pressure loss of such a staggered
arrangement, however, may be relatively high due to profile drag
caused by the tubes.
[0004] Oval and elliptical shaped tubes and fins also have been
used to reduce drag and pressure losses, but such tubes generally
may not withstand the very high pressures found in some power plant
cycles. Oval tubes too are known to have small wake regions and
lower profile drag than circular tubes and hence lower pressure
loss. Finned tubes having such an oval profile have a wide radius
that is oriented parallel to the flow. Thus the profile drag due to
the tube itself is low. The heat transfer coefficient on oval
finned tubes is, enhanced by horseshow and wake vortices, slightly
higher than on circular tubes. However, oval tubes have much lower
pressure ratings, are more difficult to manufacture than circular
tubes and are susceptible to deformation from pressure effects. To
alleviate this problem, manufacturers have incorporated a vertical
strut in the center of the tube for stability.
[0005] In heat exchange applications that have a high mass flux and
limited frontal area it is advantageous to utilize a design with a
low-pressure drop, but that maintains a relatively high heat
transfer. An example of this application would be an air-cooled
condenser. An air-cooled condenser relies upon forced convection
from a fan to operate, thus a lower pressure drop results in less
fan power and thus better operating efficiency.
[0006] Accordingly, there is a desire for an improved compact fin
and tube heat exchanger to increase the heat transfer rate per unit
pressure loss so as to provide a smaller and less expensive heat
exchanger with lower energy losses and lower overall life cycle
costs. Such a fin and tube heat exchanger preferably may be used
for a variety of gas to liquid or gas to steam heat transfer
applications and specifically may be used for air-cooled condensers
utilized in power plant operations and the like.
BRIEF DESCRIPTION
[0007] The present application is directed to an embodiment of a
fin and tube heat exchanger. The fin and tube heat exchanger may
include a plurality of tubes; and a plurality of substantially
spirally-wound circular fins positioned on each of the plurality of
tubes. The plurality of tubes comprising a first set of tubes
comprising a plurality of tube groupings and a second set of tubes
comprising a plurality of tube groupings. The first set of tubes
comprises a transverse offset position as compared to the second
set of tubes.
[0008] Another embodiment of the present application is directed to
a fin and tube heat exchanger including a plurality of tubes; and a
plurality of substantially spirally-wound circular fins positioned
on each of the plurality of tubes. The plurality of tubes
comprising a first set of tubes comprising a first row of tubes and
a second row of tubes, wherein a plurality of tube pairs are
defined therein by a tube in the first row of tubes and an inline
tube in the second row of tubes. The plurality of tubes further
comprising a second set of tubes comprising a third row of tubes
and a fourth row of tubes, wherein a plurality of tube pairs are
defined therein by a tube in the third row of tubes and an inline
tube in the fourth row of tubes. The first set of tubes comprises a
transverse offset position as compared to the second set of
tubes.
[0009] The present application further provides yet another
embodiment of a fin and tube heat exchanger. The fin and tube heat
exchanger may include a plurality of tubes; and a plurality of
substantially spirally-wound circular fins positioned on each of
the plurality of tubes. The plurality of tubes comprising a first
set of tubes and a second set of tubes. The first set of tubes
comprising a first row of tubes and a second row of tubes, wherein
the first row of tubes and the second row of tubes comprise an
inline position relative to a flow across the first row of tubes
and the second row of tubes. A plurality of tube pairs are defined
therein. Each of the plurality of tube pairs comprising a tube in
the first row of tubes and a tube in the second row of tubes. The
second set of tubes comprising a third row of tubes and a fourth
row of tubes. The third row of tubes and the fourth row of tubes
comprise an inline position relative to a flow across the third row
of tubes and the fourth row of tubes. A plurality of tube pairs are
defined therein. Each of the plurality of tube pairs comprising a
tube in the third row of tubes and a tube in the fourth row of
tubes. The first set of tubes comprises a transverse offset
position as compared to the second set of tubes.
[0010] These and other features and improvements of the present
application will become apparent to one of ordinary skill in the
art upon review of the following detailed description when taken in
conjunction with the several drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The above and other aspects, features, and advantages of the
present disclosure will become more apparent in light of the
subsequent detailed description when taken in conjunction with the
accompanying drawings in which:
[0012] FIG. 1 is a schematic view of a gas turbine engine;
[0013] FIG. 2 is a schematic view of a system for use in a power
plant including an air-cooled condenser;
[0014] FIG. 3 is a three-dimensional view of a portion of a
semi-staggered fin and tube heat exchanger as may be described
herein;
[0015] FIG. 4 is an end view of a portion of a semi-staggered fin
and tube heat exchanger as may be described herein;
[0016] FIG. 5 is an end view of a portion of a semi-staggered fin
and tube heat exchanger illustrating transverse fin and tube
spacing as may be described herein;
[0017] FIG. 6 is an end view of a portion of a semi-staggered fin
and tube heat exchanger illustrating longitudinal fin and tube
spacing as may be described herein;
[0018] FIG. 7 is an end view of a portion of a semi-staggered fin
and tube heat exchanger illustrating fin and tube spacing as may be
described herein;
[0019] FIG. 8 is a perspective view of a portion of a
semi-staggered fin and tube heat exchanger as may be described
herein;
[0020] FIG. 9 is an end view of a portion of a semi-staggered fin
and tube heat exchanger as may be described herein illustrating
computational fluid dynamics and resultant streamlines; and
[0021] FIG. 10 is diagram of a portion of a semi-staggered fin and
tube heat exchanger as may be described herein illustrating
computational fluid dynamics and resultant streamlines and heat
transfer coefficient.
DETAILED DESCRIPTION
[0022] Referring now to the drawings, in which like numerals refer
to like elements throughout the several views, FIG. 1 shows a
schematic view of a gas turbine engine 100 as may be described
herein. The gas turbine engine 100 may include a compressor 110.
The compressor 110 compresses an incoming flow of air 120. The
compressor 110 delivers the compressed flow of air 120 to a
combustor 130. The combustor 130 mixes the compressed flow of air
120 with a compressed flow of fuel 140 and ignites the mixture to
create a flow of combustion gases 150. Although only a single
combustor 130 is shown, the gas turbine engine 100 may include a
number of combustors 130.
[0023] The flow of combustion gases 150 is in turn delivered to a
turbine 160. The flow of combustion gases 150 drives the turbine
160 so as to produce mechanical work via the turning of a turbine
shaft 170. The mechanical work produced in the turbine 160 drives
the compressor 110 and an external load such as an electrical
generator 180 and the like via the turbine rotor 170.
[0024] The flow of now spent combustion gases 150 then may be
delivered to a heat recovery steam generator 190 or other types of
heat exchanger. The flow of the spent combustion gases 150 to the
heat recovery steam generator 190 may heat a flow of feedwater and
steam 200 therethrough for use in, for example, a steam turbine,
process heating, fuel preheating, and/or for other types of work.
The flow of the combustion gases 150 then may be vented through a
stack or otherwise disposed.
[0025] The gas turbine engine 100 may use natural gas, various
types of petroleum-based liquid fuels, synthesis gas, and other
types of fuels. The gas turbine engine 100 may be any number of
different turbines offered by General Electric Company of
Schenectady, N.Y. or otherwise. The gas turbine engine 100 may have
other configurations and may use other types of components. Other
types of gas turbine engines also may be used herein. Multiple gas
turbine engines 100, other types of turbines, and other types of
power generation equipment may be used herein together.
[0026] Generally described, the heat recovery steam generator 190
may be a non-contact heat exchanger that allows feedwater for the
steam generation process and the like to be heated by the otherwise
wasted flow of the spent combustion gases 150. The heat recovery
steam generator 190 may be a large duct with tube bundles
interposed therein such that water is heated to steam as the flow
of combustion gases 150 pass through the duct. Other heat recovery
steam generator configurations and other types of heat exchange
devices may be used herein.
[0027] FIG. 2 shows a schematic view of a system 210 for use in a
power plant, such as a combined cycle power plant as may be
described herein. For combined cycle power plants to be used in
water scarce regions of the world, an air-cooled condenser may be
installed due to the unavailability of water. The power plant
includes an energy source, such as a gas turbine 220, which
generates heat 225 during operations thereof, a heat recovery steam
generator (HRSG) 230, which is coupled to the gas turbine 220, a
cooling tower 235 and steam turbines 240, such as a high pressure
steam turbine (HPST) 245, an intermediate pressure steam turbine
(IPST) 250 and a low pressure steam turbine (LPST) 255. The HRSG
230 generates steam by way of the heat generated by the gas turbine
220 and includes heat exchangers, such as super heaters,
evaporators, and pre-heaters, which are disposed along an axis
thereof, and by which portions of the generated steam are diverted
to the HPST 245, the IPST 250, and the LPST 255. The HPST 245, the
IPST 250 and the LPST 255 generate power, such as electricity, by
way of the diverted steam, and output spent steam supplies. An
air-cooled condenser 260 is configured to fluidly receive and to
air-cool at least a steam supply 265. The air-cooled condenser 260
operates with electrically driven fans and cools the steam supply
265 via a supply of air 270. It is noted that the power plant shown
in FIG. 2 is merely exemplary and that other configurations of the
same are possible.
[0028] Referring now to FIGS. 3 and 4, illustrated is a portion of
a semi-staggered fin and tube heat exchanger 300 as may be
described herein. The semi-staggered fin and tube heat exchanger
300 may be used as part of the heat recovery steam generator 190 of
FIG. 1, or as part of the air-cooled condenser 265 of FIG. 2, or
for any type of heat exchange device or purpose.
[0029] The semi-staggered fin and tube heat exchanger 300 includes
a number of tubes 310 protruding therethrough with a number of
substantially spirally-wound circular fins 320 positioned thereon.
Any number of tubes 310 and substantially spirally-wound circular
fins 320 may be used herein. The semi-staggered fin and tube heat
exchanger 300 may be relatively compact as compared to existing fin
and tube heat exchangers, but may have any desired size, shape,
and/or configuration.
[0030] The semi-staggered fin and tube heat exchanger 300 may
include the tubes 310 positioned in a semi-staggered relationship.
Specifically, a first set 330 of tubes 310 may be staggered or
transversely offset from a second set 340 of tubes 310. The first
set 330 of tubes 310 may include a first row 332 and a second row
334 with the tubes 310 having an in-line position 331 with respect
to a flow of air 305 therethrough. Furthermore, a plurality of tube
pairs 335 (as indicated by the dotted line, FIG. 4) are defined in
the first set of tubes 330, each tube pair 335 including one tube
310 in the first row 332 of tubes and one tube 310 in the second
row 334 of tubes.
[0031] The second set 340 of tubes 310 may include a third row 342
and a fourth row 344 with the tubes 310 therein also having the
in-line position 331. A plurality of tube pairs 345 (as indicated
by the dotted line) are defined in the second set of tubes 340,
each tube pair 345 including one tube 310 in the third row 342 of
tubes and one tube 310 in the fourth row 344 of tubes. Although
pairs of tubes 310 are shown in the first set 330 and the second
set 340, any number of rows 332, 334 and 342, 344 may be used
herein with any number of tubes 310 therein. Where additional rows
are included in each tube set, tube groupings, similar to tube
pairs 335 and 345, may be defined therein. The first set 330 and
the second set 340 may have an offset position 350 (FIG. 4) with
respect to each other to form the semi-staggered relationship. The
offset position 350 may be about of half of the transverse spacing
of a fin 320. More specifically, each subsequent tube row in a tube
set, such as first set 330 or second set 340, is transversally
offset by half the transversal spacing between the individual tubes
310. Other types of offsets, spacings, and configurations may be
used herein.
[0032] Referring now to FIGS. 5-7, alternate embodiments of the
semi-staggered fin and tube heat exchanger 300 are illustrated. As
previously described, like numerals refer to like elements
throughout the several views. Accordingly, the semi-staggered fin
and tube heat exchanger 300 may include the tubes 310 positioned in
a semi-staggered relationship. Specifically, the first set 330 of
tubes 310 may be staggered or transversally offset from the second
set 340 of tubes 310. Further spacing of the tubes 310 may include,
and as best illustrated in FIG. 5, a gap 400 between each tube pair
335 in the first set 330 of spirally wound circular fins 310 or
each tube pair 345 in the second set 340 of spirally wound circular
fins 310. The size and shape of the gap 400 may vary. More
specifically, each tube pairs 335, 345 may be spaced a transverse
distance, D.sub.T, from a next tube pair 335, 345 dependent upon
specific design requirements. As best illustrated in FIG. 6,
further spacing of the tubes 310 may include a gap 400 between the
first set 330 of spirally wound circular fins 310 and the second
set 340 of spirally wound circular fins 310. Again, the size and
shape of the gap 400 may vary. More specifically, as illustrated in
FIG. 6, the first set of tubes 330 may be spaced a longitudinal
distance, D.sub.L, from the second set of tubes 340 dependent upon
specific design requirements. Finally, as best illustrated in FIG.
7, further spacing of the tubes 310 may include a plurality of gaps
400 between each tube pair 335 in the first set 330 of spirally
wound circular fins 310 or each tube pair 345 in the second set 340
of spirally wound circular fins 310, indicated at D.sub.T and a gap
400 between the first set 330 of spirally wound circular fins 310
and the second set 340 of spirally wound circular fins 310,
indicated at D.sub.L. The design of the heat exchanger 300 may vary
the longitudinal spacing (D.sub.L) and transverse spacing (D.sub.T)
to meet the process or heat exchanger needs. It is anticipated that
other types of positionings or spacings may be used herein. As is
shown in FIGS. 4-6, the fins 320 of the semi-staggered fin and tube
heat exchanger 300 may be in the form of substantially
spirally-wound circular fins 310. Each spirally-wound circular fin
310 may have a substantially concentric position 355 about each
tube 310.
[0033] Referring now to FIG. 8, illustrated is a single pair of
tubes, such as a tube pair 335 or 345. In this particular
embodiment, each of the substantially spirally-wound circular fins
310 of the tube pair 335, 345 includes a cut portion 410. In a
preferred embodiment, approximately 0.25'' is cut off the fin
height of 0.5 on one side of the fin structure. The cut portions
410 provide closer spacing of the tubes 310 in each tube pair 335,
345, and as a result, the distance between the rows 332, 334 and
342, 344 of each tube set 330, 340 may be minimized.
[0034] As described above, an in-line tube arrangement generally
has the benefit of a lower pressure loss while a staggered
arrangement generally leads to higher heat transfer. In use, the
semi-staggered fin and tube heat exchanger 300 described herein
thus combines the advantages of both positionings. Specifically in
this example, the second row 334 of the first set 330 and the
fourth row 344 of the second set 340 are generally positioned in
the wake of the first row 332 of the first set 330 and the third
row 342 of the second set 340, respectively. This staggered or
transversely off-set position 350 thus reduces the aerodynamic
profile drag that may account for part of the pressure loss,
particularly given the relatively small distances between the
in-line rows 332, 334 and 342, 344 of the tubes 310. Similarly,
staggering the first set 330 and the second set 340 of the tubes
310 may generate or enhance horseshoe and wake vortices so as to
enhance heat transfer on the substantially spirally wound circular
fins 320.
[0035] Referring now to FIGS. 9 and 10, computational fluid
dynamics (CFD) analyses carried out on the semi-staggered tube
bundle arrangement are disclosed herein. The semi-staggered tube
arrangement of the described fin and tube heat exchanger 300 aims
at a reduction of pressure loss by forming the tube pairs 335, 345,
comprised of a tube 310 of every first 332 and second row 334
in-line to the flow direction 305, while every consecutive third
342 and fourth 344 row is staggered with an offset of half the
transverse spacing (D.sub.T). With the in-line rows spaced closely
in a longitudinal direction (D.sub.L), the result is a reduction in
profile drag as only half the tubes 310 cross-sectional areas are
facing the flow 305. A CFD model was set up to make use of
symmetries and periodic inlet-outlet conditions. The geometry
tested included solid fins having approximately a 2'' OD and
including cut portions 410 on one side to a height of approximately
0.25'' to make the in-line tubes 310 fit tightly together. The mass
flux corresponds to the experimental mass flow of 400 g/s.
[0036] Referring more specifically to FIG. 10, the results plot
shows the streamlines 500 the heat transfer coefficients on the
fins 320 and tubes 310. The heat transfer coefficients are highest
on a leading edge 312 of the fins 310 of the first row 332. In
between the in-line tubes 310 little fluid passes over the fins
320, leading to the low heat transfer coefficient and heat flux.
The fins 320 act merely to conduct and transfer the heat
circumferentially towards the inside of the tube.
[0037] The distribution of the local heat transfer coefficients
over the fins 320 appears quite uneven, ranging from 10 W/m.sup.2K
between the in-line tubes 310 to more than 100 W/m.sup.2K at the
leading edge 312 of the fins 320 and on the tube wall facing the
flow 305. The average heat transfer coefficient on a second fin 320
of an in-line tube pair 335, 345 is lower than on the fin 320
facing the flow 305. A local maximum exists at the trailing edge
322 of the second fin 320, caused by an eddy vortex in the
recirculation zone. The surface heat flux (not shown) distribution
essentially follows the heat transfer coefficient, but the
difference of the average over the first and second fin 320 is less
pronounced, supporting the case for this arrangement as the second
fin 320 contributes almost as much to heat transfer as the first.
Furthermore, quantitative results show that the ratio of air-side
conductivity over pressure loss for this configuration is high,
indicating that for a given mass flux and overall conductivity such
a heat exchanger would offer a low pressure loss penalty.
[0038] The semi-staggered fin and tube heat exchanger 300 thus
provides the staggered sets 330, 340 of the tubes 310 with the
offset position 350. Each tube 310 may have a number of
substantially spirally wound circular fins 320 thereon. This tube
arrangement aims at a reduction of pressure loss by setting two
tubes of every first and second row in-line to the flow direction,
while every consecutive third and fourth row is staggered with an
offset of half the transverse spacing. With the in-line rows spaced
closely longitudinal, this leads to a reduction in profile drag as
only half the tubes cross-sectional areas are facing the flow. The
fins 320 may include cut portions 410 so as to minimize the
distance between the rows, 332, 334 and 342, 344 of each tube pair
335, 345 in each set 330, 340 while the fins 310 may also have
small gaps 400 therebetween. The semi-staggered fin and tube heat
exchanger 300 thus provides a lower pressure loss as compared to
conventional fin and tube designs with a higher heat transfer per
tube. Additional technical advantages of the semi-staggered fin and
tube heat exchanger 300 described herein are due to the utilization
of standard circular tubes. The substantially spirally wound
circular tubes 310 described herein have excellent pressure
characteristics. Thus a heat exchanger utilizing the fin and tube
heat exchanger 300 design described herein may operate at a wide
range of pressures with no risk of tube deformation or bursting,
that may be an issue with alternative oval tubes. In addition, no
re-tooling of the tube production line is necessary. The tubes
utilized may be standard finned substantially circular tubes known
in the art. Implementation of the embodiments of the fin and tube
heat exchanger 300 described herein may require a modified header
design that is easily accomplished. The semi-staggered fin and tube
heat exchanger 300 may be more compact with lower operating costs
and fewer tube rows for a given duty. The semi-staggered fin and
tube heat exchanger 300 may be used for a variety of gas to liquid
or gas to steam heat transfer applications and specifically may be
used for power plant operations and the like. Smaller, better, and
less expensive heat exchangers generally provide for a more cost
effective energy system with a smaller footprint and lower
operating costs.
[0039] It should be understood that the foregoing relates only to
the preferred embodiments of the present application and that
numerous changes and modifications may be made herein by one of
ordinary skill in the art without departing from the general spirit
and scope of the invention as defined by the following claims and
the equivalents thereof.
* * * * *