U.S. patent application number 10/998828 was filed with the patent office on 2005-09-29 for duct.
Invention is credited to Holten, Wolfgang, Podhorsky, Miroslav, Schrey, Hans-Georg, Schug, Wolfgang.
Application Number | 20050211424 10/998828 |
Document ID | / |
Family ID | 34442924 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050211424 |
Kind Code |
A1 |
Podhorsky, Miroslav ; et
al. |
September 29, 2005 |
Duct
Abstract
The present invention relates to a duct for conducting a flowing
primary fluid, having a thermally conductive wall with exterior
ribs having an exterior side through which a secondary fluid can
pass, at least partially, whereby the duct wall comprises a
structured surface on its exterior side in addition to the ribs.
The invention further relates to a heat exchanger with an inventive
duct and an air condenser, particularly a natural-draught
condenser, with inventive heat exchangers.
Inventors: |
Podhorsky, Miroslav;
(Ratingen, DE) ; Schug, Wolfgang; (Ratingen,
DE) ; Holten, Wolfgang; (Dusseldorf, DE) ;
Schrey, Hans-Georg; (Ratingen, DE) |
Correspondence
Address: |
BAKER & HOSTETLER LLP
Washington Square
Suite 1100
1050 Connecticut Avenue, N.W.
WASHINGTON
DC
20036
US
|
Family ID: |
34442924 |
Appl. No.: |
10/998828 |
Filed: |
November 30, 2004 |
Current U.S.
Class: |
165/152 |
Current CPC
Class: |
F28F 3/04 20130101 |
Class at
Publication: |
165/152 |
International
Class: |
F28D 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2003 |
EP |
03027584.6 |
Claims
1. Duct (2) for conducting a flowing primary fluid, having a
thermally conductive wall (3) with exterior ribs (8, 9) having an
exterior side through which a secondary fluid can pass, at least
partially, characterized in that the ribs (8, 9) have a structured
surface (17), at least in part.
2. Duct according to claim 1, characterized in that the ribs (8, 9)
have a fully structured surface (17).
3. Duct according to claim 1, characterized in that the structured
surface (17) comprises formations (18).
4. Duct according to claim 1, characterized in that the structured
surface (17) comprises depressions (19).
5. Duct according to claim 1, characterized in that the structured
surface (17) is aligned with a flow direction of the secondary
fluid such that formations (18) and depressions (19) are arranged
in alternation in the flow direction.
6. Duct according to claim 1, characterized in that the formations
(18) and/or depressions (19) form a uniform pattern.
7. Duct according to claim 1, characterized in that the structured
surface (17) has a microstructure (21) and/or a macrostructure
(22).
8. Duct according to claim 1, characterized in that the size of the
formation (18) and/or the depression (19) of the macrostructure
(22) in the direction of the secondary fluid flow equals a few
tenths of a millimeter, in particular 0.30 mm to 1.00 mm.
9. Duct according to claim 1, characterized in that the size of the
formation (18) and/or the depression (19) of the microstructure
(21) in the direction of the secondary fluid flow equals a few
hundredths of a millimeter, in particular 0.05 mm to 0.15 mm.
10. Duct according to claim 1, characterized in that a plurality of
ribs is formed by a corrugated rib strip (8, 9).
11. Duct according to claim 1, characterized in that the corrugated
rib strip (8, 9) extends in the longitudinal direction of the duct
(2).
12. Duct according to claim 1, characterized in that the corrugated
rib strip (8, 9) is covered by a plate (11, 12) on its side facing
away from the duct wall (3), and forms a meander structure (15, 16)
through which the secondary fluid can pass.
13. Duct according to claim 1, characterized in that the corrugated
rib strip (8, 9) is soldered and/or glued at its turning points
(10, 13) to the duct wall (3) and the plate (11, 12).
14. Heat exchanger (1) having at least one duct (2) according to
claim 1.
15. Heat exchanger according to claim 14, characterized in that the
heat exchanger comprises a duct (2) with a passable meander
structure (15, 16) having exterior coverplates (11, 12) which form
a stackable duct configuration.
16. Heat exchanger according to claim 14, characterized in that the
heat exchanger comprises a plurality of stacked plate-shaped duct
configurations, whereby different fluids in alternation can pass
through adjoining plate-shaped duct configurations.
17. Air condenser for condensing steam, particularly turbine steam
of a power plant, whereby steam that is to be condensed can be fed
to heat exchangers (1) by way of a steam supply line and
partitions, and whereby lines are provided for condensate removal
and inert gas discharge, characterized in that at least one heat
exchanger (1) is a heat exchanger according to one of the preceding
claims 14 through 16.
18. Air condenser according to claim 17, characterized in that the
air condenser is a natural-draught condenser.
Description
[0001] The present invention relates to a duct, a heat exchanger,
and an air condenser according to the preambles of the independent
claims 1, 14, and 17.
[0002] In a variety of applications, fluids, i.e. liquids, gasses,
or mixtures thereof, such as water, steam, or air, are employed for
transporting heat. To transfer heat, apparatuses otherwise known as
heat exchangers are used. Heat exchangers usually have at least one
duct through which a first fluid, hereinafter the primary fluid, is
conducted. Heat is exchanged between the primary fluid and the
environment across the wall of the duct. The environment can be a
directly adjoining component, or a second fluid, hereinafter the
secondary fluid for purposes of distinction.
[0003] In power plant technology, the primary fluid is usually hot
water or steam and is conducted on the primary side of the heat
exchanger, also known as the steam side, i.e. the interior side for
prevention of mass loss. In contrast, the secondary fluid is
usually air, which surrounds and circulates around the heat
exchanger on its exterior side, the air side or secondary side. In
this case, the wall of the duct, besides conducting the primary
fluid, serves for the heat exchange between primary and secondary
fluids.
[0004] Heat exchangers with species-related ducts are employed a
variety of ways in the power plant field in order to extract
residual energy from a primary fluid that has passed through a heat
power process. For example, heat exchangers in air condensers are
used for recovering the boiler water from the exhaust steam of
turbines. After passing through the turbine, the steam condenses
into water in the heat exchanger of the air condenser, and the
water is fed back to the boiler. This closes the boiler water
cycle.
[0005] The ability of heat to be transferred over a surface will be
qualified by the heat transfer coefficient. The heat transfer
coefficient alpha (.alpha.) specifies which amount of heat,
measured with the energy unit Ws between a square meter of the
surface of a component and the adjacent air, will be transferred
when the temperature difference between the components surface and
the air amounts to one Kelvin. Alpha is not a pure value of a
substance (like heat conductivity, density, or viscosity), it is
dependent on the substance properties of the fluid, the roughness
of the wall, the temperature range and the flow relationship in
proximity of the wall. The heat transfer coefficient is set on the
primary side of a steam condenser with flowing steam at
approximately 3000 W/(m.sup.2 K), while a is approximately 50 to
100 times smaller on the secondary side to the air.
[0006] The known duct system for power plant heat exchangers
usually comprise walls with smooth surfaces on the inside so that
the primary fluid flowing through is presented with optimally
little resistance. That way, it is possible to minimize the energy
expenditure needed to keep the primary fluid in a flowing state.
Such heat exchanger pipes typically comprise ribs on their exterior
side that faces the secondary fluid, for purposes of enlarging the
heat transfer surface area. These ribs are frequently strips of
aluminum sheet a few centimeters high and only a few millimeters
thick that are soldered onto the exterior of the duct as a base
pipe. The base pipe typically consists of a pressure-resistant
steel pipe surrounded by an aluminum layer at least on the
outside.
[0007] The flow of the primary fluid or the secondary fluid in or
around the flow duct can occur in a laminar or turbulent fashion,
the flow state forming in dependence on the average flow rate, the
duct cross-section, and the cinematic viscosity of the relevant
fluid, among other factors. In this, a barrier emerges in the
region of the duct walls. Due to this boundary layer, the heat
exchange between the fluid and the duct wall occurs substantially
only with the part of the flow near of the duct wall. A majority of
the heat capacity of the fluids flowing by can therefore not be
used or only ineffectively. In the case of a laminar flow, the
thickness of this barrier is especially big.
[0008] It is therefore known at the technical level that so-called
turbulators within the flow duct assembly parts or in the flow duct
are to be provided. Turbulators are strong turbulence producing
structures, almost like holes, ribs punched out or tags that
provide for a better mixing of individual flow pieces with the
produced turbulence. In this way a clearly improved utilization of
the heat capacity of the fluid flowing by on the wall can be
achieved. Nevertheless, this leads to the fact that the technical
flow resistance is significantly increased. It is therefore a
clearly larger effort to displace or stop the primary or secondary
fluid in the flowing state.
[0009] The optimal performance of a heat exchanger depends, among
other factors, on the heat transfer coefficient and the flow
resistance in the heat exchanger duct. This leads to conflicting
demands on the flow relations in the heat exchanger. On one hand, a
largely laminary flow with optimally few deflections in the duct is
desirable in order to minimize flow losses. On the other had, a
turbulent flow can be desirable, because it makes possible a larger
heat transfer coefficient and therefore an improved heat
transfer.
[0010] The known heat exchangers only partly satisfy these demands.
Heat exchangers which exhibit a small pressure loss owing to their
substantially laminar flow or surge generally make possible only a
small heat exchange, so that a majority of the heat energy of the
passing primary or secondary fluids are emitted very slowly if at
all. On the other hand, heat exchangers make possible an
essentially good heat exchange with arranged inserts in the pipes
or with turbulators arranged outside, but necessitate an
introduction of the relevant fluids under high pressure so that
through the inserts or turbulators the emerging pressure loss is
equalized. It is usually necessary to provide means for increasing
pressure, such as compressors, pumps, or suchlike.
[0011] The object of the present invention is thus to design a
species-related duct for a heat exchanger which makes possible an
improved heat exchange between the primary fluid flowing in the
duct and the secondary fluid outside the duct, given a small
pressure loss.
[0012] The object is inventively achieved by a duct according to
claim 1, a heat exchanger according to claim 14, and an air
condenser according to claim 17. Preferred developments are derived
from the subclaims.
[0013] The present invention accordingly proposes a duct with a
wall for conducting a flowing primary fluid, whereby heat is
exchangeable between the primary fluid and the duct wall. The
highly heat-conductive duct wall inventively is comprised of ribs
with an additional structured surface on its exterior side facing
the secondary fluid.
[0014] The heat exchange between the primary fluid and the duct
wall thus occurs given a smooth internal wall. This brings a
reduction of pressure losses in flow of the primary fluid compared
to the known ducts, heat exchangers and air condensers. The
associated initial relatively minor heat exchange with the primary
fluid is inventively compensated by means of a heat exchange on the
exterior of the ducts which is intensified, and even surpassed, by
turbulences in the secondary fluid. The heat exchange between
primary fluid and secondary fluid is increased as a result of the
flow of the secondary fluid between the ribs being purposefully
mixed more strongly by means of structurings that generate
turbulence.
[0015] The structuring exhibits then by preference relatively
weakly rounded shapes with only slightly sharp edges. Thereby a
laminar flow of the flow duct in secondary fluid emerges only in
local and limited micro turbulence in the area of the wall surface.
The global flow of the secondary fluid then follows the further
laminar while through the micro turbulence a clear reduction of the
thickness of the barrier on the ducts outer wall is attained. This
solution has the advantage that only the most minimal increase of
the flow resistance happens on the secondary side, while the heat
transfer coefficient is greatly increased there. In other words,
the secondary flow is not so strongly disrupted that it fixes a
large turbulence field or an entirely turbulent flow in secondary
fluid.
[0016] The surprisingly beneficial effect of this configuration is
felt particularly strongly in power plant heat exchangers or air
condensers such as natural draught cooling towers, wherein air is
typically employed as the secondary fluid with little internal
friction compared with water. In the case of natural draught
condensers and industrial heat exchangers, this is augmented by the
quasi self-generated flow which the air generally exhibits with the
aid of physical effects, as a result of which the surface
structures for generating turbulence do not produce any notable
impairment of the flow of the secondary fluid or require the
enhanced propulsion capacities of pumps.
[0017] This micro turbulence inducing surface structures can be
configured fully or partly located in the flow walls of the ribs of
the flow ducts. Also the interaction of two different surfaces is
advantageous. In a preferred design plan the structured surface
exhibits a macrostructure and a microstructure. There also the
ribs' plate also provides the microstructure and the macrostructure
is then embossed and finally the ribs are brought to the base
duct.
[0018] The microstructure has to do with a molding such as round or
squared dents or buckling that extend either as bumps or
indentations over the outside of the flow duct. This special
shaping already has the known advantage of producing relatively low
flow resistance but also at the same time brings about a good
reduction of the barrier thickness in the secondary fluid. The
height or depth of the outer formation is by measured from the
unformed surface of the rib plate as approximately 0.05 mm to 0.15
mm.
[0019] The microstructure has to do with the preference of a
oblongness that is stretched in the direction of the flow where the
cross section is formed of soft waves or ripples. The height or the
depths of the waves are measured as approximately 0.3 mm to 1.0 mm
from the unformed surface of the rib plates.
[0020] The structure surface can then be built for example on the
rib surface itself or also through a lamination. For example, the
ribs can exhibit an embossing that the structure surface creates on
both rib sides. The duct, the rib or the lamination exhibit thereby
a sufficiently high friction coefficient to the secondary fluid in
order to reach the required micro turbulence.
[0021] With the structured surface, a decrease of the thickness of
the barrier through especially small and limited micro turbulence
in the flow of the secondary fluid in the area around the duct can
be achieved, which makes possible an increased heat transfer. A
boundary layer in the region of the exterior wall can be reduced.
At the same time, based on the unique position and shape, the
turbulence can be minimized to such a degree that the pressure loss
in the secondary fluid flow is not substantially increased.
[0022] In the first place, it is possible in this way to improve
the conflicting demands on a heat exchange between flowing fluid
and a duct wall. Based on the structured surface, it is now
possible to increase the heat transfer capacity substantially given
a slight pressure drop in the primary fluid
[0023] The properties of the duct wall and the nature of the
structured surface are advantageously adapted to the fluid flowing
through, so that an optimal effect can be achieved. For instance, a
very fine surface structure can be provided for a high-viscosity
fluid, whereas a rough structure can be provided for a
low-viscosity fluid. The flow rate of the fluid, which can also
affect the structured surface, must also be taken into account.
[0024] The structured surface can be provided partly on the side
facing the fluid. It is also advantageous when it extends over the
entire length and/or periphery of the duct. It is advantageously
disposed at the locations that are particularly important for the
heat transfer. Accordingly, the duct can comprise a smooth surface
in a region that is provided merely for propelling the fluid,
whereas an inventive surface is provided in a region of the
provided heat exchange.
[0025] In a development of the present invention, it is suggested
that the structured surface comprise formations, that is to say
elevations. These formations are advantageously formed in the duct
wall and protrude into the secondary fluid flow. They also enlarge
the surface area of the duct wall. The size, number, and
configuration of the formations relative to one another is selected
so that the influence on the pressure drop in the secondary fluid
flow is largely negligible. At the same time, the formations induce
turbulences of the fluid flows in the region of the duct wall
between the ribs. This surface can be produced inexpensively by
known means.
[0026] It is further proposed that the structured surface also
comprise depressions. With the depressions, as with the formations
that rise into the flow, it is possible to increase the turbulence
of the secondary fluid flow in the region of the duct wall. There
is further enlargement of the micro turbulence of the surface on
the exterior of the duct, which further enhances the heat exchange
with the secondary fluid. Moreover, a duct with external
depressions is very inexpensive to produce.
[0027] It is further proposed that formations and depressions be
arranged in alternation in the flow direction of the secondary
fluid. A particularly beneficial heat transfer can be achieved that
way given a heavily stirred secondary stream. Particularly when the
formations and depressions are arranged at intervals based on
fluidic considerations, the heat transfer capacity can be
substantially increased depending on the flow mechanics of the
fluid.
[0028] It is further provided that the formations and/or
depressions form a uniform pattern. Thus, for example, the
formations and/or depressions can be disposed staggered in the flow
direction. The shape of the formation and/or depression can also be
adjusted in order to achieve an optimal heat exchange capacity.
Thus, the shape can take the form of a spherical segment, conical
segment, pyramid or suchlike.
[0029] In a development of the present invention, it is proposed
that the deviation of the formation and/or depression from a center
line of the duct wall surface facing the fluid equals a few tenths
of a millimeter. An increase of the pressure drop can be further
reduced that way.
[0030] It is further provided that the deviation of the formation
and/or depression from the center line of the surface facing the
fluid equals a few hundredths of a millimeter. An increase of the
pressure drop can be reduced further. Different deviations from the
center line and shapes of the formations or depressions can be
combined.
[0031] In a preferred development of the invention, it is proposed
that a heat-conductive, permeable meander structure that is
oriented in the longitudinal direction of the duct is disposed in
at least one of the ducts, which is in thermal communication with a
neighboring cover plate at least partially at its reversal points.
"Meander structure" means an optimally uniform corrugated steel
tape that extends over the entire width and length of the duct. The
troughs of the corrugations of the steel tape form contact lines at
which the tape is soldered or glued to the base pipe of the duct.
On the other side, the peaks of the corrugations form contact lines
relative to the overlying coverplates. This results in a
rectilinear flow path through the meander structure in the
direction of secondary fluid flow, whereas the undulating rib strip
winds back and forth evenly in meandering fashion from a side
perspective. An enlargement of the heat transmitting surface can be
advantageously achieved this way. Furthermore, the meander
structure can also be provided with a structured surface, whereby
the heat transmission capacity can be further increased. The
thermal connection can be achieved by soldering, welding, gluing,
or suchlike.
[0032] Further proposed by the invention is a heat exchanger with
ducts that are passable by fluids which interact with one another
thermally, whereby at least one inventive duct is provided.
[0033] The heat transmission capacity of the inventive heat
exchanger can be advantageously increased this way without having
to enlarge its structural shape and/or accept a higher pressure
drop in the flow of the primary fluid. An existing device can thus
be retrofitted with an inventive heat exchanger with a higher heat
transmission capacity, with no additional space requirement.
Besides this, a smaller structural shape of the heat exchanger can
be achieved given the same heat capacity, in order to gain space in
an existing device, for example.
[0034] Beyond this, the rigidity of the duct that is provided with
such a surface, but also of the heat exchanger overall, can be
increased by means of the structured surface. It can thus withstand
an increased mechanical strain.
[0035] It is further proposed that the ducts at least partly form a
plate-shaped duct configuration. An easily adaptable structural
shape of the heat exchanger can be achieved by stacking
plate-shaped duct configurations.
[0036] According to a further embodiment, the heat exchanger
comprises a plurality of stacked plate-shaped duct configurations,
whereby different fluids in alternation can pass through
neighboring plate-shaped duct configurations. Thus, good
adjustability based on stacking enables a high heat transfer
capacity to be achieved from one fluid to another fluid passing
through different duct configurations.
[0037] Further proposed according to the invention is an air
condenser for condensing steam, particularly turbine steam of a
power plant, whereby steam that is to be condensed can be conducted
to the heat exchangers by way of a steam supply line and
partitions, and whereby lines are provided for condensate removal
and inert gas discharge, whereby the heat exchanger is an inventive
heat exchanger with the above described advantages. Based on the
correspondingly increased heat transfer capacity, the air condenser
can have a smaller structural shape and can be produced more
cost-effectively.
[0038] As described above, the preferred embodiment of the
inventive air condenser is a natural draught condenser, since here
the above-described benefits are particularly prominent.
[0039] The invention will now be described in detail in connection
with exemplifying embodiments that are represented in the drawing.
Substantially identical components are assigned identical reference
characters. Shown are:
[0040] FIG. 1: a perspective view of a part of an inventive heat
exchanger;
[0041] FIG. 2: a first embodiment of an inventive rib with a
microstructured surface;
[0042] FIG. 3: a second embodiment of an inventive rib with a
microstructured surface; and
[0043] FIG. 4: the section IV-IV, indicated in FIG. 2, of a third
embodiment of an inventive rib with a macrostructured surface.
[0044] FIG. 5: the enlarged segment of the sectional representation
indicated in FIG. 4, showing a fourth embodiment of the
macrostructured and microstructured surface according to the
invention.
[0045] FIG. 1 represents a part of an inventive heat exchanger 1
having an inventive duct 2 for conducting a primary fluid. The duct
2 comprises a wall 3 with a broad, flat base profile, which
consists of two parallel plates 4 and 5 disposed at a distance from
one another, which are connected laterally to semicircular pipe
profiles 6 and 7. In this instance, the duct wall 3 of the duct 2
is made of a pressure-resistant, corrosion-resistant steel coated
with aluminum on the outside.
[0046] Disposed on the flat sides 4, 5 of the duct wall 3 are two
corrugated aluminum tapes 8 and 9, also referred to as cooling
ribs, which form the external ribs of duct 2. Disposed on the
external reversal points 10 of the two corrugated rib strips 8, 9
are two coverplates 11 and 12, respectively. These coverplates 11,
12 increase the rigidity of the rib strips 8 and 9, increase the
heat exchanging surface of the duct 2, and make it possible to
stack several ducts 2 on or next to one another easily. Thus, heat
exchange plates 1 can be easily formed, and easily installed in
cooling towers and dismantled therefrom in stacked bundles.
[0047] At their inner reversal points 13, the corrugated tapes or
rib strips 8 and 9 are in thermal communication with the flat
exterior sides 4, 5 of the thermally transmitting wall 3 of duct 2.
In the present example, the thermal contact is realized as a glued
connection using a high-temperature-resistant and thermally
conductive glue. The contact can also be realized as a soldered or
welded joint. The rib strips 8, 9 are made of aluminum, as are the
coverplates 11, 12, whereby other materials that are good heat
conductors can also be utilized.
[0048] The undulating and externally covered rib strips 8 and 9
result in a variety of flow lanes 14 on the base profile for the
secondary fluid. In cross-section, the consecutive flow lanes 14
together with the rib strips 8, 9 that wind back and forth and the
coverplates 11, 12 form two meander structures 15 and 16,
respectively.
[0049] As a result of the alignment of the rib strips 8, 9
perpendicular to the flow direction of the primary fluid, the
primary fluid and secondary fluid can pass through the duct 2 in
crossflow. Steam passes through the duct 2 as the primary fluid in
the interior, whereas air can pass through the exterior lanes 14 as
the secondary fluid. The duct 2 with its wall 3, through which the
primary fluid passes, and the flow lanes 14 are thus disposed at
such a distance from each other that the two fluids cannot mix.
[0050] On its exterior, the wall 3 of duct 2 represented in FIG. 2
comprises a rib 8 having a structured surface 17. In this instance
the structured surface 17 comprises a microstructure, shown greatly
enlarged, whose bases are square- and triangular-shaped structures,
whereby alternating formations 18 and depressions 19 form a uniform
pattern in the direction of primary fluid flow. The formations 18
and depressions 19 are staggered and spaced apart.
[0051] The microstructured surfaces 17, shown greatly enlarged in
FIG. 3, extend only on the lateral margin zones of the rib sheets 8
or 9. The structured surfaces 17 comprise truncated pyramids 20 of
heat-resistant plastic with a rectangular base which are glued onto
the ribs 8. In this embodiment, elevations 18 are provided in
consecutive pairs in the flow direction, which are disposed a great
distance from one another. In this example, the height of the
elevations 18 relative to the surface of the rib sheet 8 is
approximately 0.07 mm.
[0052] As is evident from the section through a third alternative
embodiment of the structured surface 17 which is represented in
FIG. 4, this structured surface can also comprise a macrostructure
having round formations 18 and depressions 19 in the rib sheet 8.
These shapes can be pressed into the rib sheet 8 by spherical
embossing dies before the rib sheet is compressed into a ripple
shape and fastened to duct wall 3. The height or depth of the
formations 18 in the rib sheet 8 relative to the surface of the
sheet is approximately 0.3 mm.
[0053] FIG. 5 shows the section represented by "A" from the
sectional view of FIG. 4, greatly enlarged. In the fourth exemplary
embodiment of the structured surface of the rib shown here, a
microstructure 21 of pyramid-shaped nibs is provided on the
undulating macrostructure 22. Thus, this is an overlapping
configuration of microstructure and macrostructure, but is also an
embodiment in which the placement of microstructure next to
macrostructure is advantageous.
[0054] The exemplifying embodiments represented in the Figures
serve for illustration of the invention only, and do not represent
limitations of the invention. In particular, the shape of the
depressions and their configuration in the duct can be varied.
* * * * *