U.S. patent application number 16/850673 was filed with the patent office on 2020-10-22 for perturbing air cooled condenser fin.
The applicant listed for this patent is The Babcock & Wilcox Company. Invention is credited to Tony F. HABIB, Billy G. SPRINGER, JR., Ted L. THOME.
Application Number | 20200333077 16/850673 |
Document ID | / |
Family ID | 1000004796048 |
Filed Date | 2020-10-22 |
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United States Patent
Application |
20200333077 |
Kind Code |
A1 |
THOME; Ted L. ; et
al. |
October 22, 2020 |
PERTURBING AIR COOLED CONDENSER FIN
Abstract
An air cooled condenser fin comprises flow channel walls
defining an air flow channel. The flow channel walls include planar
sections separated by intermittent flow interruptions which are
spaced apart along the air flow channel. The intermittent flow
interruptions are defined by the flow channel walls. The
intermittent flow interruptions may for example comprise splits
formed by a staggered arrangement in which the planar sections of
the flow channel walls before and after each split are staggered;
or intermittent sinusoidal waves formed into the flow channel
walls; or louvers formed into the flow channel walls to create
openings passing through the flow channel walls at the louvers. The
intermittent flow interruptions may be spaced apart along the air
flow channel by at least 5 hydraulic diameters, and in some
embodiments by 5-10 hydraulic diameters. A plurality of such air
cooled condenser fins are suitably employed with the air flow
channels arranged in parallel.
Inventors: |
THOME; Ted L.; (Cuyahoga
Falls, OH) ; HABIB; Tony F.; (Lancaster, OH) ;
SPRINGER, JR.; Billy G.; (Canal Winchester, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Babcock & Wilcox Company |
Akron |
OH |
US |
|
|
Family ID: |
1000004796048 |
Appl. No.: |
16/850673 |
Filed: |
April 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62835706 |
Apr 18, 2019 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28B 1/06 20130101; F28F
3/025 20130101 |
International
Class: |
F28B 1/06 20060101
F28B001/06; F28F 3/02 20060101 F28F003/02 |
Claims
1. An air cooled condenser fin comprising: flow channel walls
defining an air flow channel; wherein the flow channel walls
include planar sections separated by intermittent flow
interruptions which are spaced apart along the air flow channel;
wherein the intermittent flow interruptions are defined by the flow
channel walls.
2. The air cooled condenser fin of claim 1 wherein the intermittent
flow interruptions comprise splits formed by a staggered
arrangement in which the planar sections of the flow channel walls
before and after each split are staggered.
3. The air cooled condenser fin of claim 2 wherein the staggering
of the flow channel walls after each split is about one-half of a
width of the air flow channel.
4. The air cooled condenser fin of claim 2 wherein the splits are
spaced between 5 hydraulic diameters and 10 hydraulic diameters
apart along the air flow channel.
5. The air cooled condenser fin of claim 2 wherein the splits are
spaced apart along the air flow channel by at least 5 hydraulic
diameters.
6. The air cooled condenser fin of claim 1 wherein the intermittent
flow interruptions comprise intermittent sinusoidal waves formed
into the flow channel walls.
7. The air cooled condenser fin of claim 6 wherein the intermittent
sinusoidal waves are spaced between 5 hydraulic diameters and 10
hydraulic diameters apart along the air flow channel.
8. The air cooled condenser fin of claim 6 wherein the intermittent
sinusoidal waves are spaced apart along the air flow channel by at
least 5 hydraulic diameters.
9. The air cooled condenser fin of claim 1 wherein the intermittent
flow interruptions comprise louvers formed into the flow channel
walls to create openings passing through the flow channel walls at
the louvers.
10. The air cooled condenser fin of claim 9 wherein the louvers are
angled between 1 degree and 30 degrees to an air flow direction of
the air flow channel.
11. The air cooled condenser fin of claim 9 wherein the flow
channel walls are secured to a tube of an air cooled condenser.
12. The air cooled condenser fin of claim 9 wherein the louvers are
spaced between 5 hydraulic diameters and 10 hydraulic diameters
apart along the air flow channel.
13. The air cooled condenser fin of claim 9 wherein the louvers are
spaced apart along the air flow channel by at least 5 hydraulic
diameters.
14. The air cooled condenser fin of claim 1 wherein the
intermittent flow interruptions are spaced between 5 hydraulic
diameters and 10 hydraulic diameters apart along the air flow
channel.
15. The air cooled condenser fin of claim 1 wherein the
intermittent flow interruptions are spaced apart along the air flow
channel by at least 5 hydraulic diameters.
16. An air cooled condenser comprising a plurality of air cooled
condenser fins as set forth in claim 1 wherein the air flow
channels of the air cooled condenser fins are arranged in
parallel.
17. An air cooled condenser comprising: steam/condensate tubes;
fins attached to the steam/condensate tubes; wherein the fins
comprise flow channel walls defining parallel air flow channels,
the flow channel walls including planar sections separated by
intermittent flow interruptions which are spaced apart along the
air flow channels; wherein the intermittent flow interruptions are
defined by the flow channel walls.
18. The air cooled condenser of claim 17 wherein the intermittent
flow interruptions comprise splits formed by a staggered
arrangement in which the planar sections of the flow channel walls
before and after each split are staggered.
19. The air cooled condenser of claim 18 wherein the staggering of
the flow channel walls after each split is about one-half of a
width of the air flow channel.
20. The air cooled condenser of claim 17 wherein the intermittent
flow interruptions comprise intermittent sinusoidal waves formed
into the flow channel walls.
21. The air cooled condenser of claim 17 wherein the intermittent
flow interruptions comprise louvers formed into the flow channel
walls to create openings passing through the flow channel walls at
the louvers.
22. The air cooled condenser of claim 21 wherein the louvers are
angled between 1 degree and 30 degrees to an air flow direction of
the air flow channel.
23. The air cooled condenser of claim 17 wherein the intermittent
flow interruptions are spaced between 5 hydraulic diameters and 10
hydraulic diameters apart along the air flow channel.
24. The air cooled condenser of claim 23 wherein the air flow
channels are rectangular with the hydraulic diameter D.sub.H,fin of
each air flow channel being: D H , fin = 2 ( S f i n .times. H f i
n ) S f i n + H f i n ##EQU00005## where H.sub.fin is a fin height
and S.sub.fin is a separation between the fin walls defining each
air flow channel.
25. The air cooled condenser of claim 23 wherein the hydraulic
diameter D.sub.H,fin of each air flow channel is: D H , fin = 4 A P
##EQU00006## where A is the cross-sectional area of each air flow
channel and P is the perimeter of the cross-section of each air
flow channel.
26. The air cooled condenser of claim 17 wherein the intermittent
flow interruptions are spaced apart along the air flow channel by
at least 5 hydraulic diameters.
27. The air cooled condenser of claim 26 wherein the air flow
channels are rectangular with the hydraulic diameter D.sub.H,fin of
each air flow channel being: D H , fin = 2 ( S f i n .times. H f i
n ) S f i n + H f i n ##EQU00007## where H.sub.fin is a fin height
and S.sub.fin is a separation between the fin walls defining each
air flow channel.
28. The air cooled condenser of claim 26 wherein the hydraulic
diameter D.sub.H,fin of each air flow channel is: D H , fin = 4 A P
##EQU00008## where A is the cross-sectional area of each air flow
channel and P is the perimeter of the cross-section of each air
flow channel.
29. The air cooled condenser of claim 17 further comprising:
distribution headers connected to feed steam into the
steam/condensate tubes; and an air moving system comprising a fan
arranged to drive an airflow across the fins attached to the
steam/condensate tubes.
30. The air cooled condenser of claim 29 further comprising: risers
connected to feed the steam into the distribution headers; wherein
the steam/condensate tubes, the distribution headers, the risers,
and the air moving system are arranged to form the air cooled
condenser as an A-frame type air cooled condenser.
31. The air cooled condenser of claim 17 wherein at least 70% of
the intermittent flow interruptions are positioned within a first
one-half of a length of the fins closest to an air flow entrance of
fins.
32. A method of cooling using an air cooled condenser fin, the
method comprising: flowing air through an air flow channel defined
by flow channel walls; and interrupting the flowing of air at
intermittent flow interruptions defined by the flow channel walls
which are spaced apart along the air flow channel.
33. The method of claim 32 wherein the intermittent flow
interruptions are placed at locations where a boundary layer of the
flowing air has normalized.
34. The method of claim 32 wherein the intermittent flow
interruptions are spaced apart along the air flow channel by at
least 5 hydraulic diameters.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/835,706 filed Apr. 18, 2019. U.S. Provisional
Application No. 62/835,706 filed Apr. 18, 2019 is incorporated
herein by reference in its entirety.
BACKGROUND
[0002] The following relates to air cooled condensers, heat
exchanger fins and arrays thereof for air cooled condensers, and so
forth.
[0003] Traditional heat exchange fins are of the straight or plain
variety. Heat transfer occurs through a fin channel wherein air
enters in the channel and establishes a fluid boundary layer. Heat
transfer normalizes once the fluid boundary layer is established.
Some straight fins may have blemishes or other features on their
surface as a result of manufacturing processes. As such traditional
fin designs may not be entirely straight nor uniform from fin to
fin within a fin array.
[0004] A known modification of the straight fin design is to
include perforations in the fins to disturb air flow with the flow
channel, i.e. pressed or cut perforations. They offer cross channel
flow paths and are commonly used in automotive applications. The
perforations, while effective at disturbing the fluid boundary
layer increasing heat transfer, can be impractical in certain
applications as they increase the pressure drop of the air
flow.
[0005] Another known fin design employs offset fins. In this design
the straight path is cyclically offset within a channel to disturb
the boundary layer. This design, as with the perforations, increase
heat transfer capability but in doing so also increases pressure
drop.
[0006] Another known fin design employs wavy or ruffled fins. In
this design the straight fins are curved to form sinusoidal waves.
The periodic waves enables disruption of the fluid boundary layer.
Haushalter, U.S. Pat. No. 5,209,289 issued May 11, 1993, discloses
a modified fin array incorporating wavy offsets in a unique
combination.
[0007] Bugler et al., U.S. Publication No. 2018/0023901 A1
published Jan. 25, 2018, discloses a heat exchange tube fin design
in which a plurality of arrowhead shapes are pressed into or
embossed onto each fin. The pressed arrowhead shapes are grouped
into nested pairs, and one of the arrowheads in a pair is pressed
as a positive relative to the fin plane and the other of the pair
is pressed as a negative relative to the fin plane. The arrowhead
pairs are placed in rows parallel to the air flow direction and
arrowhead pairs in one row are preferably staggered relative to the
arrowhead pairs in the adjacent row along the fin in the air flow
direction.
BRIEF SUMMARY
[0008] In some aspects disclosed herein, an air cooled condenser
fin comprises flow channel walls defining an air flow channel. The
flow channel walls include planar sections separated by
intermittent flow interruptions which are spaced apart along the
air flow channel. The intermittent flow interruptions are defined
by the flow channel walls.
[0009] In some illustrative embodiments, the intermittent flow
interruptions comprise splits formed by a staggered arrangement in
which the planar sections of the flow channel walls before and
after each split are staggered. In some embodiments, the staggering
of the flow channel walls after each split is about one-half of a
width of the air flow channel.
[0010] In some illustrative embodiments, the intermittent flow
interruptions comprise intermittent sinusoidal waves formed into
the flow channel walls.
[0011] In some illustrative embodiments, the intermittent flow
interruptions comprise louvers formed into the flow channel walls
to create openings passing through the flow channel walls at the
louvers. In some embodiments, the louvers are angled between 1
degree and 30 degrees to an air flow direction of the air flow
channel. In some embodiments, the flow channel walls are secured to
a tube of an air cooled condenser.
[0012] In any of the foregoing embodiments, the intermittent flow
interruptions are in some more specific embodiments spaced between
5 hydraulic diameters and 10 hydraulic diameters apart along the
air flow channel.
[0013] In any of the foregoing embodiments, the intermittent flow
interruptions are in some more specific embodiments spaced apart
along the air flow channel by at least 5 hydraulic diameters.
[0014] In some aspects disclosed herein, a plurality of air cooled
condenser fins as set forth in any of the preceding paragraphs is
provided, in which the air flow channels of the air cooled
condenser fins are arranged in parallel.
[0015] In some aspects disclosed herein, an air cooled condenser
comprises steam/condensate tubes and fins attached to the
steam/condensate tubes. The fins comprise flow channel walls
defining parallel air flow channels. The flow channel walls include
planar sections separated by intermittent flow interruptions which
are spaced apart along the air flow channels. The intermittent flow
interruptions are defined by the flow channel walls. The
intermittent flow interruptions in some embodiments comprise splits
formed by a staggered arrangement in which the planar sections of
the flow channel walls before and after each split are staggered.
The staggering of the flow channel walls after each split is, in
some more specific embodiments, about one-half of a width of the
air flow channel. The intermittent flow interruptions in some
embodiments comprise intermittent sinusoidal waves formed into the
flow channel walls. The intermittent flow interruptions in some
embodiments comprise louvers formed into the flow channel walls to
create openings passing through the flow channel walls at the
louvers. The louvers are, in some more specific embodiments, angled
between 1 degree and 30 degrees to an air flow direction of the air
flow channel. In any of the foregoing embodiments of this
paragraph, the intermittent flow interruptions may in some more
specific embodiments be spaced between 5 hydraulic diameters and 10
hydraulic diameters apart along the air flow channel. In any of the
foregoing embodiments of this paragraph, the intermittent flow
interruptions may in some more specific embodiments be spaced apart
along the air flow channel by at least 5 hydraulic diameters.
[0016] Some embodiments of an air cooled condenser as set forth in
the immediately preceding paragraph further comprise distribution
headers connected to feed steam into the steam/condensate tubes,
and an air moving system comprising a fan arranged to drive an
airflow across the fins attached to the steam/condensate tubes.
Some more specific embodiments further include risers connected to
feed the steam into the distribution headers, wherein the
steam/condensate tubes, the distribution headers, the risers, and
the air moving system are arranged to form the air cooled condenser
as an A-frame type air cooled condenser or other types.
[0017] In some aspects disclosed herein, a method of cooling using
an air cooled condenser fin is disclosed. The method comprises
flowing air through an air flow channel defined by flow channel
walls, and interrupting the flowing of air at intermittent flow
interruptions defined by the flow channel walls which are spaced
apart along the air flow channel. In some more specific
embodiments, the intermittent flow interruptions are placed at
locations where a boundary layer of the flowing air has normalized.
In some more specific embodiments, the intermittent flow
interruptions are spaced apart along the air flow channel by at
least 5 hydraulic diameters.
[0018] These and other non-limiting aspects and/or objects of the
disclosure are more particularly described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention may take form in various components and
arrangements of components, and in various process operations and
arrangements of process operations. The drawings are only for
purposes of illustrating preferred embodiments and are not to be
construed as limiting the invention. This disclosure includes the
following drawings.
[0020] FIG. 1 diagrammatically shows differential temperature
versus length for a planar fin.
[0021] FIG. 2 diagrammatically shows heat transfer coefficient
versus length for a planar fin.
[0022] FIG. 3 diagrammatically shows incremental air pressure drop
versus length for a planar fin.
[0023] FIG. 4 diagrammatically shows a perspective view of a
portion of an air cooled condenser fin having a single
split-fin.
[0024] FIG. 5 diagrammatically shows a top view of a portion of an
air cooled condenser fin array including a plurality of splits of
the type shown in FIG. 4.
[0025] FIG. 6 diagrammatically shows a perspective view air flow
velocity map for the split fin air flow.
[0026] FIG. 7 diagrammatically shows a perspective view of a
portion of an air cooled condenser fin having intermittent
sinusoidal waves.
[0027] FIG. 8 diagrammatically shows a perspective view of a
portion of an air cooled condenser fin having louvers.
[0028] FIG. 9 diagrammatically shows a top view of a portion of an
air cooled condenser fin array including a plurality of louvers of
the type shown in FIG. 8.
[0029] FIG. 10 plots heat transfer coefficient of an air cooled
condenser fin with splits, versus position.
[0030] FIG. 11 plots heat transfer coefficient of an air cooled
condenser fin with intermittent sinusoidal waves, versus
position.
[0031] FIG. 12 diagrammatically shows a typical air cooled
condenser application of the disclosed improved fins, where the
illustrative air cooled condenser is of the forced draft A-frame
type.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] For certain applications, such as air-cooled condensers,
excessive pressure drop creates design constraints when applying
fins to a tube geometry. A need exists for new and improved fin and
fin array designs that minimize heat exchanger footprint opposite
need for additional power input needed to move air/overcome
excessive pressure drops of existing designs.
[0033] Air-cooled condenser applications have some requirements
regarding the steam flow area and resultant pressure drop that
places constraints on the minimum sizing of the heat exchanger fin
tube base. Use of existing non-planar fin designs (Louvered,
Offset, Wavy, etc.) requires additional power input (larger air
mover sizing) to apply the fin to the required tube geometry.
Further, redesigning tube geometry to incorporate a non-planar fin
design in a lower power input design is often uneconomical.
[0034] Flow on the air-side of an air-cooled condenser generally
operates in the laminar regime, which is defined by Reynolds
numbers less than 2000. In this regime, momentum and energy
transport occur via the mechanism of molecular diffusion, which is
driven by gradients in the velocity profile. The velocity gradients
near the fin wall are especially important in determining the
momentum and energy transport rates in the local region as the air
flows through the fin channel. As the air in the free-stream
approach region enters the fin channels, extremely high velocity
gradients result, based on the large velocity differential between
the entering air velocity and the zero-velocity condition at the
fin wall. This results in large friction factors and heat transfer
coefficients at the lead edge of the fin. As the flow progresses
down the fin channel, the velocity profile approaches the fully
developed profile (generally parabolic). As this transition occurs,
the local velocity gradients at the fin wall are reduced, and the
local friction factor and heat transfer coefficient values
gradually approach the fully developed values. This transition
often occurs within ten (10) hydraulic diameters from the entrance
to the fin section. The hydraulic diameter, D.sub.H, is a commonly
used term when handling flow in non-circular tubes and channels,
and is defined as
D H = 4 A P ( 1 ) ##EQU00001##
where A is the cross-sectional area of the flow and P is the wetted
perimeter of the cross-section (where the wetted perimeter includes
all surfaces acted upon by shear stress from the fluid). For a
closed rectangular channel of dimensions a.times.b, the hydraulic
diameter D.sub.H is given by:
D H , rect = 4 A P = 4 ( a .times. b ) a + b + a + b = 2 a b a + b
( 2 ) ##EQU00002##
The entrance region of the fin is therefore more effective in terms
of heat transfer than the remainder of the fin, although the
increase in heat transfer comes at the cost of added pressure
drop.
[0035] With reference to FIGS. 1-3, numerical simulations of
differential temperature versus length (FIG. 1), heat transfer
coefficient versus length (FIG. 2), and incremental air pressure
drop versus length (FIG. 3) are shown for a planar fin. In FIGS. 1,
2, and 3, the entrance region is to the left, with the air flow
proceeding along the channel of length L to the exit side of the
fin on the right of the curve. The most effective region of heat
transfer in a planar fin of an air cooled condenser is at the air
entrance into the fin channel. This is evident in FIG. 2 where the
heat transfer coefficient decreases rapidly as air flows along the
channel length.
[0036] FIG. 4 is a graphic representation showing a single
split-fin 10 as disclosed herein. The split-fin takes advantage of
the enhanced heat transfer which occurs at the lead edge of a fin
channel entrance to reduce the total surface area of the overall
fin assembly. The split-fin arrangement of FIG. 4 comprises a
straight fin section 12 having a fin channel 14 that is
subsequently split into two fin channels 16, 18 at a split point 20
along the length of the fin channel 14. The split 20 preferably
occurs at or around the point where air flow has fully developed in
the first channel section 14. As air flow (indicated by arrows F in
FIG. 4) enters the staggered fin arrangement 20, it is split into
subsequent sections, i.e. split air flows 16, 18. The fin wall of
the downstream fin section 22 is located at or near the center of
the upstream flow path or channel 14 (in other words, the
staggering of the fin walls after the split is about one-half of a
width of the air flow channel), thereby being exposed to high
velocity gradients near the wall, similar to what occurs at the
entrance of the first fin section 12. This process is repeated at
each flow split, resulting in increased heat transfer at the lead
edge region of every fin section 12, 22. A more compact fin
assembly configuration results; requiring less fin surface area and
comparatively less material needed to construct the fin array than
traditional designs.
[0037] With reference to FIG. 5, when the split-fin is formed into
a fin array, each flow split results in increased heat transfer
coefficient and friction factor in the local region near the
respective fin section entrance. FIG. 5 illustrates a fin array
including successive illustrated fin sections 12a, 12b, 12c with
respective channels 14a, 14b, 14c, with fin split point 20ab at the
junction of fin sections 12a, 12b and fin split point 20bc at the
junction of fin sections 12b, 12c. This is repeated for as many fin
split sections exist in the assembly. The local increases in
friction factor result in an increase in pressure drop, which is
generally undesirable. Heat transfer from the fin to the air
depends on two factors, the local heat transfer coefficient, and
the local bulk air-to-fin temperature difference. The flow splits
20 increase the local heat transfer coefficient, which is
beneficial. As with friction factor, the local increase in heat
transfer coefficient resulting from each flow split 20 is
consistent throughout the fin assembly. However, as the air flow F
proceeds through the assembly, the temperature difference between
the air and the fin is continuously reduced. Therefore, the
effectiveness of the flow splits 20 with respect to increased local
heat transfer decreases the farther the particular flow split is
from the fin assembly entrance. For this reason, it is beneficial
to cluster the flow splits 20 near the entrance to the assembly and
use a more continuous section at the trail end of a fin assembly
comprising multiple split-fins.
[0038] With reference to FIG. 6, in another embodiment, an air
cooled condenser utilizes single row finned tubes and includes a
split-feature within the air flow channel which disturbs the
boundary layer along the flow channel wall. FIG. 6 shows a
perspective view air flow velocity map for the split fin air
flow.
[0039] The concepts of split-fins is not intended to be limited by
the preceding discussion. Split features may be repeating or
intermediate. Flow channel walls may be discontinuous or
continuous. Flow along the wall of a planar fin may be perturbed by
the channel being cut, and a new channel formed with the opening
offset from the outlet of the original channel. Fin channels may
consist of single or multiple splits.
[0040] Channel length of the fin sections 12 is preferably
determined by finding the point along the wall in which the air
flow boundary layer approaches fully developed profile. In one
embodiment having multiple splits the splits are spaced between
about 5 hydraulic diameters and about 10 hydraulic diameters
apart.
[0041] With reference to FIG. 7, in an alternative embodiment one
or more fin channels in the fin array may include intermittent
sinusoidal waves. A graphic representation of a fin 30 having a
channel 34 with an intermittent sinusoidal wave 32 is shown in FIG.
7. Flow F along the wall of the channel 34 is redirected by the
sinusoidal wave 32 in the transverse direction of air flow F. Wave
geometry of the sinusoidal wave 32 is designed to optimize full
channel recirculation downstream from the disturbance. Planar fin
wall is placed between the multiple waves 32 until boundary layer
normalizes to reduce pressure drop. The sinusoidal waves 32 are
preferably spaced between about 5 hydraulic diameters and about 10
hydraulic diameters apart.
[0042] With reference to FIGS. 8 and 9, in yet another embodiment,
louvered fins 40 are disclosed. In this embodiment, openings 42
between adjacent fin channels 44 are used. Openings may take the
form of louvers 46 angled between about 1 and about 30 degrees to
the direction of flow. FIGS. 8 and 9 provide graphic
representations of the openings 42 between adjacent fin channels
44. As seen in FIG. 8, the openings 42 do not comprise the entirely
of the flow channel wall. While FIGS. 8 and 9 show alignment
between openings in adjacent channels, such alignment is not
present in some embodiments; rather, in these embodiments the
opening may alternatively be offset. FIG. 8 also illustrates the
louvered fins 40 soldered (or otherwise attached) to a tube 48 as
is common in the case of an air cooled condenser (where the steam
or other fluid being condensed flows through the tube 48). It is
noted that FIGS. 8 and 9 show the louvers in the "pointing
downstream" configuration. In this configuration the tips of the
louvers are pointing roughly in the direction of the flow from
upstream to downstream. In a variant embodiment, the louvers may be
reversed, so as to point "into" the flow in the upstream direction.
Either configuration can be employed effectively.
[0043] The innovations disclosed herein may be used on a single
channel, a combination of channels, and/or combined with one
another to form new and unique fin arrays that improve heat
transfer over a variety of tube geometries that may be subject to
space constraints and otherwise have limitations on ability to
overcome pressure drop concerns. Further advantageous is the
reduction in materials requirements for fin arrays enabled by the
approaches disclosed herein.
[0044] FIGS. 10 and 11 plots show simulated data relating to heat
transfer coefficient of the split-fin and intermittent wave,
respectively, against position. As shown in these figures, the heat
transfer peaks at the location of the flow interruption and
decreases along the length of the channel as the boundary layer is
reestablished and the difference in temperature between the two
fluids, air and steam, is gradually reduced.
[0045] With reference now to FIG. 12, a typical air cooled
condenser application of the disclosed improved fins is shown. An
illustrative air cooled condenser shown in FIG. 12 is of the forced
draft A-frame type. An electric power generator 52 is driven by a
steam turbine 54 using steam 56. Exhaust steam 58 discharged from
the steam turbine 54 flows into a main steam duct 60 and a
distribution manifold 62, that distributes the steam to a set of
air cooled condensers, an illustrative one of which is shown in
FIG. 12. The steam flows up through risers 64 which are connected
to feed the steam into distribution headers 66 which in turn are
connected to feed the steam into bundles 70 that include
steam/condensate tubes (e.g., the illustrative steam/condensate
tube 48 shown in FIG. 8) with fins (such as split fins 10 as shown
in FIGS. 4-6; or fins 30 with intermittent sinusoidal waves 32 as
shown in FIG. 7; or fins 40 with louvers 46 as shown in FIGS. 8 and
9) soldered or otherwise attached to the steam/condensate tubes. An
air moving system 72, such as a fan, drives an airflow across the
fins of the bundles 70 in order to cool and condense the steam in
the tubes to form condensate. FIG. 12 further shows the condenser
superstructure including a fan deck 74 supported by support
structure 76 and bracing 78, and a windwall structure 80 atop the
fan deck 74. While the illustrative air cooled condenser is of the
forced draft A-frame type, the disclosed improved fins are suitably
employed in conjunction with air cooled condensers of other types,
such as an induced draft V-frame condenser type, a flat condenser
type, or so forth.
[0046] The inventors have performed computer simulations of the
performance of various designs of split fins 10 (FIGS. 4-6), fins
30 with intermittent sinusoidal waves 32 (FIG. 7), and fins 40 with
louvers 46 (FIGS. 8 and 9). In these simulations, the fins were
modeled as rectangular channels with rectangular dimension
H.sub.fin being the fin height (that is, the distance the fin
extends away from the steam/condensate tube to which it is
soldered) and dimension S.sub.fin being the separation between the
fin walls defining the air flow channel. Using the hydraulic
diameter for a rectangular channel given in Equation (2), this
yields the following hydraulic diameter D.sub.H,fin for the
fins:
D H , f i n = 4 A P = 2 a b a + b = 2 ( S f i n .times. H f i n ) S
f i n + H f i n ( 3 ) ##EQU00003##
More generally, for an air flow channel of arbitrary cross
sectional dimensions the first expression of Equation (3) holds,
i.e.
D H , f i n = 4 A P ##EQU00004##
where A is the cross-sectional area of the air flow channel and P
is the perimeter of the cross-section of the air flow channel, and
with a tube bundle length "L" (also indicated as bundle length 82
if FIG. 12). The simulations were for a design of the bundles 70
that included 11 fins per inch. The simulations also modeled the
energy (in horsepower which is related to pressure loss across a
bundle) of the air moving system (e.g. fan) 72 and the bundle tube
length 82. In addition to modeling performance of the designs of
the split fins 10, fins 30 with intermittent sinusoidal waves 32,
and louvered fins 40, simulations were performed to model the
performance of conventional planar fin and continuous wavy fin
designs. The simulations concluded that utilizing the planar fin
design with the intermittent perforations, i.e., split fins 10,
fins 30 with intermittent sinusoidal waves 32, and louvered fins 40
would enable reduction of the tube bundle length 82 by
approximately 10% with only a moderate increase of 30% in the fan
energy consumption (horsepower). The cost savings in reducing the
tube bundle length by 10% is order magnitude greater than the cost
of higher energy fan. On the other hand, the bundle with the
continuous wavy fin design would reduce the tube bundle length by
16% but at the price of 700% increase in energy consumption which
is prohibitive.
[0047] These simulations confirm the mechanism for improved
performance disclosed herein, namely that employing mostly planar
fins but with intermittent flow interruptions positioned at points
where the boundary layer normalizes can achieve the desired heat
transfer efficiency improvement while only imposing a modest
increase in pressure drop. It was found that the intermittent flow
interruptions are in some embodiments preferably spaced between
about 5 hydraulic diameters and about 10 hydraulic diameters apart
to optimally balance heat transfer efficiency (improved by the
intermittent flow interruptions) against pressure drop introduced
by the interruptions. The intermittent flow interruptions can be
fin splits 20 (as in the embodiments of FIGS. 4-6), intermittent
sinusoidal waves 32 (as in the embodiment of FIG. 7), louvers 46
(as in the embodiments of FIGS. 8 and 9), or more generally any
other type of intermittent interruption. The simulations also found
that placing the intermittent flow interruptions nearer the
entrance side of the fin maximizes the heat transfer benefit while
imposing the least additional pressure drop. For example, in some
nonlimiting embodiments at least 70% of the intermittent flow
interruptions are positioned within the first one-half of the fin
length L (that is, within the half-fin length closest to the
entrance side of the fin). In some other nonlimiting embodiments,
at least 80% of the intermittent flow interruptions are positioned
within the first one-third of the fin length L (that is, within the
first third of the fin length that is closest to the entrance side
of the fin).
[0048] It should be noted that the term "planar fin" is used herein
in its usual and ordinary meaning in the art, as a fin that
channels air flow principally along a single planar channel. In a
planar section of a fin, the flow channel walls defining the air
flow channel may have some deviations from geometrically perfect
planar form, for example due to unintended manufacturing-induced
variations, dimples, wall curvature, or so forth. Such a
imperfections typically do not have a meaningful impact on air flow
and hence are considered "planar" fin sections as used herein.
Likewise, the term "intermittent flow interruption" as used herein
is an intentional (i.e. design-basis) modification to a fin wall or
walls, or a fin split, that is sufficient to induce air flow
interruption as described herein. Hence, unintended
manufacturing-induced variations, dimples, wall curvature, or so
forth are not considered "intermittent flow interruptions" as used
herein.
[0049] Illustrative embodiments including the preferred embodiments
have been described. While specific embodiments have been shown and
described in detail to illustrate the application and principles of
the invention and methods, it will be understood that it is not
intended that the present invention be limited thereto and that the
invention may be embodied otherwise without departing from such
principles. In some embodiments of the invention, certain features
of the invention may sometimes be used to advantage without a
corresponding use of the other features. Accordingly, all such
changes and embodiments properly fall within the scope of the
following claims. Obviously, modifications and alterations will
occur to others upon reading and understanding the preceding
detailed description. It is intended that the present disclosure be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or the
equivalents thereof.
* * * * *