Note: Descriptions are shown in the official language in which they were submitted.
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HIGH-EFFICIENCY ENHANCED BOILER
BACKGROUND OF THE INVENTION
(1) Technical Field
The present invention relates generally to a heat exchanger, and more
specifically to a
"direct-fired" or "indirect-fired" boiler for generating steam, hot water, hot
oil, and hot
molten metals.
(2) Related Art
All boilers operate according to the physical sciences of thermodynamics and
heat
transfer. Essentially, forced hot gas is cooled within the boiler by
transferring heat to a heat
transfer medium, often water, to generate steam or hot water. Depending upon
system
requirements, direct-fired boilers and/or indirect-fired boilers are commonly
placed in service
to produce steam and hot water. In the case of a direct-fired boiler, a fueled
burner or
combustor is fired into the boiler, generating heat within the boiler itself.
The fueled burner
establishes a flame, producing a hot fluid, which is in heat transfer relation
with a cooler heat
transfer medium. A temperature differential between the hot fluid and the heat
transfer
medium drives the heat transfer process by way of conduction, convection, and
radiation.
In a similar manner, a "waste heat recovery" or indirect fired boiler makes
use of
residual heat from an isolated thermodynamic process. However, radiation heat
transfer is a
less significant heat transfer mechanism for the indirect-fired boiler. For
boilers of either
direct-fired or indirect-fired construction, the heat transfer medium is
usually water and/or
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st i eam, due in large part to their widespread availability and substantial
heat capacity.
Another advantage of water/steam heat transfer media is that it presents no
imminent
environmental threat.
A conventional type of direct-fired boiler, commonly called a "firetube"
boiler,
employs a fueled burner to generate heat. The burner is fired into a single
main tube, called
the firetube. This firetube absorbs the majority of the radiation emitted from
the combustion
process. In addition, convective/conductive couples drive heat transfer
between the hot fluid
and the heat transfer medium throughout the device. Conventional firetube
boilers typically
contain one to three additional banks of significantly smaller tubes, called
passes. For
example, a firetube boiler design that includes two banks of tubes in addition
to the firetube is
termed a "three-pass firetube boiler," elicited from the path of the hot
fluid. The course of
flow for the "three-pass firetube boiler" occurs after the fueled burner
generates hot gas inside
the firetube, which is then driven through a first bank of smaller tubes
flowing opposite the
firetube, and then diverted through a second bank of smaller tubes flowing
parallel to the
firetube. A channel, called the "turn-around pass," is located between each
pass, wherein the
hot gas reverses direction. The hot gas cools while flowing through the tube
passes of the
firetube boiler by transferring energy to the heat transfer medium. For either
design, all tube
banks, less the "turn-around pass," are in heat transfer relationship with the
heat transfer
medium. In a similar manner, although a "waste heat recovery" or indirect-
fired boiler does
not require a firetube, the hot gas does flow sequentially from tube bank to
tube bank as
required to enact the heat transfer. As a result, heat transfer to the heat
transfer medium is
largely dependent upon the total length of the tubes it contacts. This can
result in larger and
more expensive devices.
Accordingly, a need exists for a heat exchange device capable of greater
efficiency in
the transfer of heat from its fluid to its heat transfer medium.
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SUMMARY OF THE INVENTION
In devices known in the art, "conventional firetube" and "waste heat recovery"
boilers
each require many small tubes making successive passes within the boiler. In
one
embodiment of the invention, however, an enhanced conduit replaces numerous
conventional
small tubes. In some embodiments, the enhanced conduit incorporates a
plurality of fins,
each of which extends through a wall of the conduit. In other embodiments, the
enhanced
conduit incorporates a plurality of tubes along its inner surface, through
which a heat transfer
medium flows. Both designs enhance the heat transfer relationship between the
hot fluid and
the heat transfer medium by providing a continuous heat transfer relationship
with the heat
transfer medium, increasing the surface area involved in the heat transfer
relationship and
enhancing convection/conduction couples. For some applications, all of the
tube banks of
other devices in the art can be replaced by one continuous enhanced conduit.
In other
applications, the heat transfer fluid flows through the enhanced conduit while
the hot fluid
flows along an outer surface of the enhanced conduit.
The High-Efficiency Enhanced Boiler (HEEB) of the present invention offers
improvements over conventional designs. A first improvement is a continuous
heat transfer
relation by surrounding the enhanced conduit with heat transfer medium. A
second
improvement is the possibility of substantial turndown ratios. A third
improvement is the
feasibility of manufacturing devices for applications requiring steam
pressures in excess of
21.4 atmospheres absolute, whereas conventional firetube boilers have
practical limitations.
Finally, the HEEB is readily configurable to generate superheated steam.
Therefore, a first objective of the present invention is to provide a High
Efficiency
Enhanced Boiler capable of generating superheated steam or steam/hot water
output. A
second objective of the present invention is to provide an effective method
for direct-fire or
indirect-fire heat transfer to a molten metal heat transfer medium. A third
objective of the
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present invention is to provide a High Efficiency Enhanced Boiler for "waste
heat recovery"
or indirect-fired boiler applications. A fourth objective of the present
invention is to provide
a boiler with an enhanced conduit capable of removing heat from the burner
flame by
proximally located fins.
A first aspect of the invention is directed toward a device for transferring
heat from a
fluid to a heat transfer medium comprising a vessel for containing the heat
transfer medium, a
conduit extending through a wall of the vessel, the conduit having a first
surface in contact
with the heat transfer medium and a second surface in contact with a fluid
within the conduit,
and a plurality of fins, each fin extending through a wall of the conduit,
contacting the heat
transfer medium and the fluid, wherein heat is transferred from the fluid to
the heat transfer
medium via the plurality of fins.
A second aspect of the invention is directed toward a device for transferring
heat from
a fluid to a heat transfer medium comprising a vessel containing the heat
transfer medium, a
conduit extending through a wall of the vessel, the conduit having a first
surface in contact
with the heat transfer medium and a second surface in contact with a fluid
within the conduit,
and at least one tube, wherein the heat transfer medium flows within the tube
and the fluid
flows around the tube.
A third aspect of the invention is directed toward a device for transferring
heat from a
fluid to a heat transfer medium comprising a vessel containing the heat
transfer medium, a
first conduit extending through a wall of the vessel, the first conduit having
a first surface in
contact with the heat transfer medium and a second surface in contact with a
fluid within the
first conduit, a plurality of fins, each fin extending through a wall of the
first conduit, wherein
heat is transferred from the fluid to the heat transfer medium via the
plurality of fins, and at
least one tube, wherein the heat transfer medium flows within the tube and the
fluid flows
around the tube, and wherein heat is transferred from the fluid to the heat
transfer medium via
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the tube.
According to a further aspect of the present invention, there is provided a
device
for transferring heat from a fluid to a heat transfer medium comprising:
a vessel constructed and arranged to contain the heat transfer medium;
a conduit extending through a wall of the vessel, the conduit having a first
surface
for contacting the heat transfer medium and a second surface for contacting a
fluid within
the conduit;
a helical member residing around and along a length of the first surface of
the
conduit constructed and arranged to angularly direct a flow of the heat
transfer medium
along the first surface of the conduit; and
a plurality of fans helically arranged adjacent the helical member, each fm
extending through a wall of the conduit, and constructed and arranged to
contact the heat
transfer medium and the fluid, the helical arrangement of the plurality of
fins being
capable of imparting an angular flow to the fluid,
wherein heat is transferred from the fluid to the heat transfer medium via the
plurality of fins.
According to a further aspect of the present invention, there is provided a
device
for transferring heat from a fluid to a heat transfer medium comprising:
a vessel constructed and arranged to contain the heat transfer medium;
a conduit extending through a wall of the vessel, the conduit having a first
surface
for contacting the heat transfer medium and a second surface for contacting a
fluid within
the conduit;
a helical member residing around and along a length of the first surface of
the
conduit constructed and arranged to angularly direct a flow of the heat
transfer medium
along the first surface of the conduit; and
a plurality of fins helically arranged adjacent the helical member, each fin
extending through a wall of the conduit, and constructed and arranged to
contact the heat
transfer medium and the fluid, the helical arrangement of the plurality of
fins being
capable of imparting an angular flow to the fluid,
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wherein heat is transferred from the fluid to the heat transfer medium via the
plurality of fms.
According to a further aspect of the present invention, there is provided a
device
for transferring heat from a fluid to a heat transfer medium comprising:
a vessel constructed and arranged to contain the heat transfer medium;
a first conduit extending through a wall of the vessel, the conduit having a
first
surface for contacting the heat transfer medium and a second surface for
contacting a fluid
within the conduit;
a helical member residing around and along a length of the first surface of
the
conduit constructed and arranged to angularly direct a flow of the heat
transfer medium
along the first surface of the conduit;
a plurality of fins helically arranged adjacent the helical member, each fin
extending through a wall of the conduit, thereby being constructed and
arranged to contact
the heat transfer medium and the fluid, the helical arrangement of the
plurality of fms
being constructed and arranged to impart an angular flow to the fluid, wherein
heat is
transferred from the fluid to the heat transfer medium via the plurality of
fins; and
at least one tube extending through a wall of the conduit,
wherein the heat transfer medium flows within the tube and the fluid flows
around the at
least one tube, and wherein heat is transferred from the fluid to the heat
transfer medium
via the at least one tube.
According to a further aspect of the present invention, there is provided a
device
for transferring heat from a fluid to a heat transfer medium comprising:
a vessel constructed and arranged to contain the fluid;
a conduit extending through a wall of the vessel, the conduit having a first
surface
for contacting the fluid and a second surface for contacting a heat transfer
medium within
the conduit; and
a helical member residing around and along a length of the first surface of
the
conduit;
a plurality of fins, each fin extending through a wall of the conduit, and
constructed and arranged to contact the heat transfer medium and the fluid,
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wherein heat is transferred from the fluid to the heat transfer medium via the
plurality of fins.
According to a further aspect of the present invention, there is provided a
device
for transferring heat from a fluid to a heat transfer medium comprising:
a vessel constructed and arranged to contain the fluid;
a conduit extending through a wall of the vessel, the conduit having a first
surface
for contacting the fluid and a second surface for contacting a heat transfer
medium within
the conduit; and
a helical member residing around and along a length of the first surface of
the
conduit;
a plurality of fins, each fin extending through a wall of the conduit, and
constructed and arranged to contact the heat transfer medium and the fluid,
wherein heat is transferred from the fluid to the heat transfer medium via the
plurality of fins.
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The foregoing and other features of the invention will be apparent from the
following
more particular description of embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments of this invention will be described in detail, with reference
to the
following figures, wherein like designations denote like elements, and
wherein:
FIG. 1 shows a side-view of one embodiment of the invention.
FIG. 2 shows a front-view of one embodiment of the invention.
FIG. 3 shows a side elevational view of one embodiment of the invention.
FIG. 4 shows a cross-sectional view of one embodiment of the invention.
FIG. 5 shows a side elevational view of the device of FIG. 4.
FIG. 6 shows a side elevational view of the device of FIG. 4.
FIG. 7 shows a cross-sectional view of one embodiment of the invention.
FIG. 8 shows a top-view of the device of FIG. 7.
FIG. 9 shows a front-view of the device of FIG. 7.
FIG. 10 shows a cross-sectional view of one embodiment of the invention.
FIG. 11 shows a side elevational view of the device of FIG. 10.
FIG. 12 shows a side elevational view of the device of FIG. 10.
FIG. 13 shows a cross-sectional view of one embodiment of the invention.
FIG. 14 shows a cross-sectional view of one embodiment of the invention.
FIG. 15 shows a top view of the device of FIGS. 13 and 14.
FIG. 16 shows a cross-sectional view of one embodiment of the invention.
FIG. 17 shows a side elevational view of the device of FIG. 16.
FIG. 18 shows a side elevational view of the device of FIG. 16.
FIG. 19 shows a side elevational view of an enhanced conduit apparatus
according to
the invention.
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FIG. 20 shows a housing enclosing the apparatus of FIG. 19.
FIG. 21 shows a cross-sectional view of the apparatus of FIG. 19.
FIG. 22 shows a side elevational view of an alternate embodiment of an
enhanced
conduit apparatus according to the invention.
FIG. 23 shows a side cross-sectional view of the apparatus of FIG. 22.
FIG. 24 shows a front cross-sectional view of the apparatus of FIG. 22.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1 through 6 depict a boiler 1 of the present invention, which includes a
vessel
for containing a heat transfer medium. In some embodiments, vessel 10 is
pressurized
internally and designed according to American Society of Mechanical Engineers
(ASME)
codes for boilers and pressure vessels. The ASME codes are one of a few
fabrication
standards honored worldwide. Typically, internal design pressures for this
class of vessel
range from 1.1 to 21.4 atmospheres absolute, although there are vessels in
existence that
exceed pressures of 21.4 atmospheres absolute. For reasons of safety and
reliability, the
ASME codes and others restrict the materials and fabrication methods for
vessels with
internal design pressures over 2.0 atmospheres absolute. Therefore, only code
recognized
materials, such as, but not limited to, SA516 GR70, SA240 304, SA312 TP304,
and SA106
B, are acceptable for fabrication of vessel 10. In addition, the adherence to
a Code infers that
only a facility skilled in the art can fabricate a device such as vessel 10.
Additionally,
insulation (not shown) covers the exterior surface of vessel 10 for reasons of
efficiency and
safety.
Four basic penetrations are commonly made to vessel 10. In actuality, and
commonly
known to those of ordinary skill in the art, several penetrations of vessel 10
are required.
Process and policy require penetrations for boiler inspection, boiler
drainage, pressure relief,
and sensing/gauging. Although the previously mentioned compulsory penetrations
are not
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shown, it is assumed that these requirements are met in the final or code-
authorized design.
The sump 20 proximal to the top of vessel 10 is indicative of a steam boiler.
By
design, sump 20 is known to moderate surging, a problem associated with steam
production.
Consequently, in order to maintain a sufficient level of a heat transfer
medium (e.g., water in
the case of a steam boiler), a feedwater inlet 30 is located near the bottom
of vessel 10. Any
steam having left sump 20 continues upstream to deliver the stored energy and
then returns
downstream as condensate to feedwater inlet 30, thus completing the cycle.
This process is
typical of a closed steam/water system. In reality, system losses require that
provisions be
made to replenish the heat transfer medium (e.g., make-up water). Furthermore,
deaerators
and water treatments are meant to protect the system components from oxidation
and
chemical attack. However, since deaeraters and chemical treatments are known
to those of
ordinary skill in the art, further explanation will not be given.
The final two penetrations shown in the vessel 10 are the hot fluid inlet 40
and the
flue outlet 50 of enhanced conduit 60. Situated entirely within vessel 10,
enhanced conduit
60 forms a non-communicating pressure boundary between a hot fluid contained
within it and
a heat transfer medium within vessel 10. Thus, enhanced conduit 60 is entirely
in heat
transfer relation with the hot fluid and the heat transfer medium. Often, the
hot fluid is hot air
generated from a burner, although other fluids or liquids may be used. For
example, it may
be desirable to cool a molten metal or salt. In such a situation, the molten
meal or salt may be
passed through enhanced conduit 60, transferring its heat to a heat transfer
medium.
Similarly, although the embodiments of the invention are often depicted as
steam
boilers, necessitating that the heat transfer medium be water, other fluids or
liquids are also
allowable. For example, the heat transfer medium may be any liquid, gas, or
similar material
with suitable heat transfer properties.
In a "single pass firetube boiler," enhanced conduit 60 extends horizontally
near a
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central axis of vessel 10, as shown in FIGS. 4 through 6. A fuel-fired burner
70, generates
heat and energy, which are forced into enhanced conduit 60. Burner fuel may
include, for
example, coal, distillate oil, natural gas, methanol, ethanol, propane, and
liquefied petroleum
gas. A forced draft subassembly (not shown) regulates the flow of gas to
burner 70 so that the
proper ratio of oxygen-to-fuel can be attained, and forces or drives the hot
gas into enhanced
conduit 60.
Essentially, enhanced conduit 60 is under the same pressure as vessel 10,
except that
the pressure is exerted on an internal surface of vessel 10 and an external
surface of enhanced
conduit 60. Once again, the ASME code or other accepted design standard is
invoked to
comply with engineering requirements. In general, with respect to the length
of enhanced
conduit 60, external pressure is more severe than internal pressure in terms
of local stress.
Generally, when external pressure applied to a conduit exceeds allowable
stress limits,
buckling or failure occurs. Accordingly, in one embodiment of the invention,
the cross-
sectional geometry of enhanced conduit 60 is circular. However, other shapes,
including but
not limited to square, rectangular, or ellipsoidal, are possible and within
the scope of the
present invention.
Within enhanced conduit 60, a plurality of fins 80 extend intimately into the
path of
the hot fluid. Fins 80 establish a series of obstructions that force the hot
fluid to assume a
path around individual fins 80 in a manner that elicits turbulence, thereby
enhancing heat
transfer. Furthermore, a portion of each fin 80 extends through a wall of
enhanced conduit 60
and contacts the heat transfer medium. Fins 80 thereby increase heat transfer
through
turbulent mixing of the hot fluid and by increasing the surface area exposed
to the hot fluid
and/or the heat transfer medium. Each fin 80 may be oriented through a wall of
enhanced
conduit 60 in any number of angles relative to the long and short axes of
enhanced conduit
60. As such, fins 80 may be oriented to direct the flow of the hot fluid
and/or the heat
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transfer medium along a particular path.
Each fin 80 is fabricated from materials that demonstrate structural stability
while
providing good heat transfer characteristics. Possible fin 80 materials
include, but are not
limited to, generic steels, metals (including copper, molybdenum, etc.),
ceramics, refractory
materials, and engineered composites. A largely material-dependent objective
of the present
invention is the ability to extract heat by placing fins 80 in close proximity
to the flame of
burner 70. One example (not shown) of a fin configuration capable of meeting
this objective
comprises a cylindrical generic steel body fitted with a spherical molybdenum
tip.
For simplicity in depiction, cylindrical-shaped fins 80 are shown. However,
other fin
shapes or combinations of shapes are possible and considered to be within the
scope of the
present invention. Such shapes include, for example, square, elliptical,
aerodynamic,
rectangular, and spherical. In addition, such fins may be constructed with
through holes, with
threaded holes, with blind holes, and may be tapered or threaded. As an
example (not shown)
of a multi-geometric combination, the fin shape may be cylindrical at one end,
tapered in the
middle, and rectangular with blind holes toward its opposite end. Each fin 80
may be
mechanically fastened to enhanced conduit 60 in an ASME code or other
acceptable method,
forming a pressure-rated joint.
In general, the heat transfer medium is water/steam, although molten metal
(heat
transfer salt) and hot oil systems are possible. As suggested earlier,
widespread availability
and substantial heat capacity are factors favoring water/steam as the most
common heat
transfer medium. At startup, vessel 10, around the outside surface of enhanced
conduit 60, is
filled with the heat transfer medium (e.g., water). Demand for steam signals
burner 70 to
ignite fuel into a combustible flame. The flame is directed at hot fluid inlet
40 of enhanced
conduit 60, whereby heat is drawn off by fins 80 located near the outer flame
boundary. Fins
80 extract substantial energy from the flame by
radiation/conduction/convection heat transfer
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to the heat transfer medium over the length of the flame. At the extreme
boundary of
combustion, where the flame ceases to exist, fins 80 remove heat from the hot
fluid stream by
convection/conduction couples. Additionally, the portion of each fin 80
extending within
enhanced conduit 60 causes turbulence in the hot fluid stream, accelerating
convection heat
transfer, while the portion of each fin 80 extending outside enhanced conduit
60 provides
more surface area for convective heat transfer to occur. More particularly, a
balanced energy
flow exists in the region of each fin 80. The exhausted hot gas leaves
enhanced conduit 60
through the flue outlet 50 on route to the stack (not shown). As the heat
transfer medium
(e.g., water) is heated, it evaporates and exits at sump 20. From sump 20, the
steam goes to
the load (not shown), where condensation occurs. The steam condenses to water
and is
pumped into inlet 30 in order to maintain a constant level of heat transfer
medium within
boiler 1.
EXAMPLE 1
Referring to FIGS. 7-12, a direct-fired 3-pass 30-horsepower boiler 100 is
shown,
fabricated in accordance with the present design criteria for a pressure of 10
atmospheres and
requiring a one million BTU (British thermal units) natural gas burner.
Cylindrical vessel
110 has dimensions of 42-inches O.D. wide by 60-inches O.D. long, with ten-
inch diameter
enhanced conduit 160 winding through the interior of the vessel. Hot fluid
enters boiler 100
through hot fluid inlet 140, passes through enhanced conduit 160, and exits
through flue
outlet 150. Condensate returns to boiler 100 through feedwater inlet 130.
There are 280 3/4"
diameter fins 180 located circumferentially throughout enhanced conduit 160 in
sets of ten.
Fins 180 are mechanically fastened to enhanced conduit 160 by virtue of a self-
locking taper
and seal welding. The temperature of the exhausted flue gas is approximately
230 C. The
thermal efficiency of such a design is increased, in part, due to the fact
that "turn-around
passes" are maintained in heat transfer relationship with the heat transfer
medium within the
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boiler.
EXAMPLE 2
Referring now to FIGS. 13-18, a direct-fired boiler 200 is shown with a coiled
enhanced conduit 260. The long axis of cylindrical vessel 210 is oriented
vertically, rather
than horizontally as in Example 1. Rather than completing a series of
reversals in direction as
in Example 1, enhanced conduit 260 is coiled within vessel 210, completing a
total of three
revolutions. Hot fluid enters boiler 200 through hot fluid inlet 240, passes
through enhanced
conduit 260, and exits through flue outlet 250. As in Example 1, enhanced
conduit 260
contains a plurality of fins 280 located around its circumference and along
its length. Fins
280 may be fastened to enhanced conduit 260 by any of a number of means
described above.
EXAMPLE 3
Referring to FIGS. 19-21, a 4-pass conduit 360 is shown. Unlike earlier-
described
embodiments, wherein a heat transfer medium sits within a vessel, the depicted
embodiment
incorporates a housing 360A around the apparatus 360. Housing 360A directs a
heat transfer
medium along an outer surface of a pass 362, 364, 366, 368 as the hot fluid is
directed along
an inner surface of the same pass. In some embodiments, such as that shown in
FIG. 20, the
apparatus has a "reverse flow," wherein as the hot fluid enters first pass 362
(often a firetube),
the heat transfer medium enters through a heat transfer medium inlet 368B at a
distal end of
the fourth pass housing 368A, flows in a direction substantially opposite that
of the hot fluid,
and exits through a heat transfer medium outlet 362B at a proximal end of the
first pass
housing 362A.
In the embodiment depicted in FIG. 19, three of the four passes 362, 364, 366
are
enhanced, each containing a plurality of fins 380 extending through a wall of
the pass.
Optionally, one or more enhanced pass 362, 364, 366 may contain a helical
member 390
along its outer surface. Located in such a manner, helical member 390 contacts
or resides
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close to an inner surface of each enhanced pass housing 362A, 364A, 366A of
apparatus
housing 360A and directs the heat transfer medium along the surface of the
pass 362, 364,
366, effectively increasing contact between the pass and the heat transfer
medium.
Accordingly, in order to increase contact between fins 380 and the heat
transfer medium,
helical member 390 preferably lies parallel to the pattern of fins 380. Such
an arrangement
effectively creates channels between the surface of a pass 362, 364, 366 and a
pass housing
362A, 364A, 366A, in which are situated a plurality of fins 380.
Each pass 362, 364, 366, 368 is connected to another by a turn-around pass
363, 365,
367 which substantially reverses the direction of flow of the fluid within
enhanced conduit
360. For example, the fluid within enhanced conduit 360 initially flows
through first pass
362 in direction A. Upon passage through first turn-around pass 363, the fluid
substantially
reverses direction, entering second pass 364 in direction B. Similarly, upon
passage through
second turn-around pass 365, the fluid again substantially reverses direction,
entering third
pass 366 in direction C. Finally, the fluid passes through third turn-around
pass 367 and
enters a non-enhanced pass 368 in direction D before flowing through flue
outlet 350.
FIG. 21 shows a side cross-sectional view of the apparatus in order to depict
the
obstructions within each enhanced pass 364, 366 created by the interior
projections of fins
380. Also depicted are the channels created between helical member 390 and
enhanced pass
housings 364A, 366A.
As depicted, only passes 362, 364, 366 contain fins 380 and, optionally,
helical
member 390. However, it should be recognized that turn-around passes 363, 365,
367 may be
enhanced with fins 380 and/or helical member 390 in addition to or instead of
passes 362,
364, 366.
EXAMPLE 4
Referring to FIGS. 22-24, a modified 4-pass enhanced conduit 460 is shown.
Unlike
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the device in FIG. 19, wherein fourth pass 368 is an unenhanced conduit,
modified enhanced
conduit 460 includes a fourth pass 468 comprised of a plurality of tubes 494.
The plurality of
tubes 494 is preferably arranged in a circular pattern, as depicted most
clearly in FIG. 24,
although other shapes are allowable. Similarly, while a plurality of tubes 494
is depicted, a
single tube is also within the scope of the invention.
Heat transfer medium enters an opening 498 in an end of each tube 494 and
flows
through tube 494, increasing the heat transfer from the hot fluid within
fourth pass 468 to the
heat transfer medium. Due to the transfer of heat from the hot fluid to the
heat transfer
medium, the difference in temperature between the hot fluid and the heat
transfer medium is
generally smaller along fourth pass 468 than along earlier passes 462, 464,
466. Where such
a smaller temperature difference exists, it has been found that such a
plurality of tubes more
efficiently transfers heat from the hot fluid to the heat transfer medium than
does a plurality
of fins 480 or a plurality of fins 40 and helical members 490, such as those
along earlier
passes 462, 464, 466.
Optionally, one or more baffles 496, 497 maybe placed along the length of the
plurality of tubes 494. Such baffles may be outer baffles 496, located around
tubes 494, or
inner baffles 497, located within the plurality of tubes 494. Outer baffles
496 are preferably
ring shaped so as to fit around a circular arrangement of the plurality of
tubes 494, although
other shapes are allowable. Outer baffles 496 preferably contact or reside
close to an inner
surface of fourth pass housing 468A. Inner baffles are preferably disc shaped
so as to fit
within a circular arrangement of the plurality of tubes 494, although other
shapes are
allowable. Outer baffles 496 and inner baffles 497 disrupt the flow of the hot
fluid within
pass 468. Inner baffles 497 force the hot fluid outside the plurality of tubes
494 to a location
between the plurality of tubes 494 and fourth pass housing 468A, while outer
baffles 496
force the hot fluid in the opposite direction, i.e., into the center of the
plurality of tubes 494.
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CA 02535855 2006-12-14
WO 2005/021122 PCT/US2004/027812
This disruption of the flow of the hot fluid increases heat transfer from the
hot fluid to the
heat transfer medium.
While this invention has been described in conjunction with the specific
embodiments
outlined above, it is evident that many alternatives, modifications and
variations will be
apparent to those skilled in the art. Accordingly, the embodiments of the
invention as set
forth above are intended to be illustrative, not limiting. Various changes may
be made
without departing from the spirit and scope of the invention as defined in the
following
claims.
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