Note: Descriptions are shown in the official language in which they were submitted.
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System and Method for Manufacturing and Operating a Coaxial Tube Heat
Exchanger
Cross Reference to Related Application
[0001] This application claims the benefit of U.S. Provisional Application No.
62/984,525, filed
March 3, 2020. The entire disclosure of U.S. Provisional Application No.
62/984,525 is hereby
incorporated herein by reference.
Field of the Invention
[0002] This invention relates generally to coaxial heat exchangers, and in
particular, to
manufacturing processes and equipment for producing coaxial heat exchangers,
such as for
HVAC systems and water source heat pumps.
Background
[0003] This section is intended to introduce the reader to various aspects of
the art that may
be related to various aspects of the presently described embodiments¨to help
facilitate a
better understanding of various aspects of the present embodiments.
Accordingly, it should
be understood that these statements are to be read in this light, and not as
admissions of
prior art.
[0004] Modern residential and industrial customers expect indoor spaces to be
climate
controlled. In general, heating, ventilation, and air-conditioning ("HVAC")
systems circulate
an indoor space's air over low-temperature (for cooling) or high-temperature
(for heating)
sources, thereby adjusting the indoor space's ambient air temperature. HVAC
systems
generate these low- and high-temperature sources by, among other techniques,
taking
advantage of a well-known physical principle: a fluid transitioning from gas
to liquid releases
heat, while a fluid transitioning from liquid to gas absorbs heat.
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[0005] In a typical system, a fluid refrigerant circulates through a closed
loop of tubing that
uses compressors and other flow-control devices to manipulate the
refrigerant's flow and
pressure, causing the refrigerant to cycle between the liquid and gas phases.
These phase
transitions generally occur within the HVAC's heat exchangers, which are part
of the closed
loop and designed to transfer heat between the circulating refrigerant and
outside
environment. This is the foundation of the refrigeration cycle. The heat
exchanger where the
refrigerant transitions from a gas to a liquid is called the "condenser," and
the condensing
refrigerant releases heat to the surrounding environment. The heat exchanger
where the
refrigerant transitions from liquid to gas is called the "evaporator," and the
evaporating
refrigerant absorbs heat from the surrounding environment.
[0006] A heat pump is a compression refrigeration system that is designed to
reverse the flow
of refrigerant to transition between heating and cooling modes. A reversing
valve controls
the direction of refrigerant flow through the refrigerant loop, thereby
determining whether
the heat pump is in heating mode or cooling mode. When the refrigerant flow is
reversed,
the potion of the refrigerant loop that previously functioned as an evaporator
functions as a
condenser and vice versa.
[0007] Water source heat pumps (WSHP) generally rely on two loops and one or
more heat
exchangers that transfer heat between the loops. Water source heat pumps
utilize a water
loop and a refrigerant loop. Depending on the mode of operation, heat is
absorbed by one
loop and transferred to the other. Heat is often transferred between the
refrigeration loop
and water loop using coaxial heat exchangers.
[0008] Coaxial heat exchanges, also called tube-in-tube heat exchangers, are
used in
numerous applications including various heating, ventilation, air
conditioning, and
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refrigeration (HVACR) applications. Like other forms of heat exchangers,
coaxial heat
exchangers are used to transfer heat from one fluid to another. While coaxial
heat
exchangers are also referred to as tube-in-tube heat exchangers, neither the
inner nor outer
tube is required to be round. Either the inner or outer tube may be
substantially any shape
that allows a fluid to flow through the tube. The inner tube and outer tube
are each designed
to resist the working pressures associated with the fluids within the inner
and outer tube
respectively. In some coaxial heat exchangers, a tube may contain grooves,
lobes, fins,
projections, or other elements that increase the surface area of a tube or
promote a higher
heat transfer coefficient, thereby allowing a greater exchange of heat between
a fluid on the
interior of the tube and a fluid on the exterior of the tube.
[0009] In WSHPs, coaxial heat exchangers are used to transfer heat between the
refrigerant
within the refrigerant loop and the water, water/anti-freeze solution, or
other fluid within the
water loop. Water/anti-freeze solutions include, but are not limited to,
water/methanol and
water/glycol solutions. The water or other fluid in the water loop then
transfers heat to the
outside environment, such as the air or ground.
Summary
[0010] Certain aspects of some embodiments disclosed herein are set forth
below. It should
be understood that these aspects are presented merely to provide the reader
with a brief
summary of certain forms the invention might take and that these aspects are
not intended
to limit the scope of the invention. Indeed, the invention may encompass a
variety of aspects
that may not be set forth below.
[0011] Embodiments of the present disclosure generally relate to a heating,
ventilation, air
conditioning or refrigeration (HVACR) system adapted utilizing a coaxial heat
exchanger that
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has been formed according to the disclosed methods. In some embodiments,
engineered
tubing may be hydrostatically expanded to achieve a higher degree of contact
and/or a press
fit with an intermediate member. It will be appreciated that expanding the
engineered tubing
may create a friction fit and/or interference fit with the intermediate
sleeve. The engineered
tubing and sleeve may be positioned within an outer jacket, thereby creating
an inner fluid
pathway and outer fluid pathway which may be used for fluid to fluid heat
exchange.
[0012] Some embodiments of the present disclosure generally relate to a
coaxial heat
exchanger for water source heat pumps comprising an extruded aluminum fin
member
comprising an interior and an exterior. In some embodiments, the interior of
the extruded
aluminum fin member has a substantially circular interior diameter and the
exterior of the
extruded aluminum fin member comprises a plurality of projecting structures.
Some
embodiments further comprise an engineered copper tube with a rifled interior.
In some
embodiments, the engineered copper tube is positioned within the extruded
aluminum fin
member and expanded using hydrostatic pressure to increase contact between the
exterior
of the engineered copper tube and the interior of the aluminum fin member.
Embodiments
further comprise an outer jacket positioned outboard of the extruded aluminum
fin member.
[0013] Some embodiments of the present disclosure generally relate to a method
for
manufacturing a coaxial heat exchanger, the method comprising the steps of
obtaining an
engineered inner tube comprising an interior and an exterior, wherein the
interior of the inner
tube includes a rifled texture; annealing the engineered inner tube;
positioning the
engineered inner tube within the interior volume of an intermediate member
comprising an
interior and an exterior wherein the exterior of the intermediate member
comprises
projecting structures; deforming the engineered inner tube using a pressure to
increase
contact between the exterior of the engineered inner tube and the interior of
the
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intermediate member; and positioning the intermediate member and engineered
inner tube
within an outer jacketing member.
[0014] Various refinements of the features noted above may exist in relation
to various
aspects of the present embodiments. Further features may also be incorporated
in these
various aspects as well. These refinements and additional features may exist
individually or in
any combination. For instance, various features discussed below in relation to
one or more of
the illustrated embodiments may be incorporated into any of the above-
described aspects of
the present disclosure alone or in any combination. Again, the brief summary
presented
above is intended only to familiarize the reader with certain aspects and
contexts of some
embodiments without limitation to the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other features, aspects, and advantages of certain
embodiments will
become better understood when the following detailed description is read with
reference to
the accompanying drawings in which like characters represent like parts
throughout the
drawings, wherein:
[0016] FIG. 1A illustrates schematically a heat pump in heating mode.
[0017] FIG. 1B illustrates schematically a heat pump in cooling mode.
[0018] FIG. 2 illustrates schematically a cross section of a coaxial heat
exchanger according to
one embodiment.
[0019] FIG. 3 illustrates schematically a coaxial heat exchanger according to
one
embodiment.
[0020] FIG. 4 illustrates schematically a portion of a coaxial heat exchanger
utilizing projecting
structures according to one embodiment.
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[0021] FIG. 5 illustrates schematically a coaxial heat exchanger according to
one
embodiment.
[0022] FIG. 6 illustrates schematically a coaxial heat exchanger according to
one
embodiment.
[0023] FIG. 7 illustrates schematically a folded fin material according to one
embodiment.
[0024] FIG. 8 illustrates schematically a coaxial heat exchanger according to
one
embodiment.
[0025] FIG. 9 illustrates schematically a coaxial heat exchanger according to
one
embodiment.
[0026] FIG. 10 illustrates a data plot comparing the water side differential
pressure of two
coaxial heat exchangers
[0027] FIG. 11 illustrates a data plot comparing the heat transfer of two
coaxial heat
exchangers
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0028] One or more specific embodiments of the present disclosure will be
described below.
In an effort to provide a concise description of these embodiments, all
features of an actual
implementation may not be described. It should be appreciated that in the
development of
any such actual implementation, as in any engineering or design project,
numerous
implementation-specific decisions must be made to achieve the developers'
specific goals,
such as compliance with system-related and business-related constraints, which
may vary
from one implementation to another. Moreover, it should be appreciated that
such a
development effort might be complex and time consuming, but would nevertheless
be a
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routine undertaking of design, fabrication, and manufacture for those of
ordinary skill having
the benefit of this disclosure.
[0029] When introducing elements of various embodiments, the articles "a,"
"an," "the," and
"said" are intended to mean that there are one or more of the elements. The
terms
"comprising," "including," and "having" are intended to be inclusive and mean
that there may
be additional elements other than the listed elements.
[0030] Turning to the figures, FIG. 1A and FIG 1B each illustrate
schematically a heat pump.
A heat pump operates on the principal that heat moves from a warmer material
to a cooler
material. A coil that is cooler than its surroundings will absorb head, and a
coil that is warmer
that its surroundings will release heat.
[0031] FIG. 1A illustrates a heat pump 100 in heating mode. In heating mode,
the outdoor
heat exchanger 110 serves as an evaporator and absorbs heat from its
surroundings.
Conversely, the indoor heat exchanger 120 serves as a condenser and releases
heat to its
surroundings. Low-pressure liquid refrigerant or a liquid-vapor mixture enters
the outdoor
heat exchanger 110, absorbs heat from the surrounding environment, and
vaporizes. The low-
pressure refrigerant vapor then enters the compressor 130 where it is
compressed to a high-
temperature and high-pressure vapor. The high-temperature, high-pressure vapor
then
enters the indoor heat exchanger 120 where it releases heat to the surrounding
environment
and condenses to a high-pressure liquid. The high-pressure liquid passes
through a metering
device 140, such as thermal expansion valve or a capillary tube, where it
becomes a low-
pressure liquid or liquid-vapor mixture and enters the outdoor heat exchanger
and then
repeats the process. It will be appreciated that the "indoor" heat exchanger
is not required
to be physically indoors. In certain HVAC applications, the indoor heat
exchanger may be in
communication with the indoor air, a water loop, or another system that
communicates heat,
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directly or indirectly, to the area to be climate controlled. It will
similarly be appreciated that
the "outdoor" heat exchanger is not required to be physically outdoors. In
certain HVAC
applications, the outdoor heat exchanger may be in communication with a water
loop or
other system that communicates heat, directly or indirectly, to the outside
environment.
[0032] FIG. 1B illustrates a heat pump 101 in cooling mode. In cooling mode,
the heat pump
operates on the same underlying principal, but the outdoor heat exchanger 111
serves as a
condenser and releases heat to its surroundings. Conversely, the indoor heat
exchanger 121
serves as an evaporator and absorbs heat from its surroundings. The flow of
refrigerant may
be reversed when the reversing valve 151 changes position.
[0033] In water source heat pumps (WSHPs) the refrigerant transfers heat to
and/or from a
flowing stream of water or water-antifreeze mixture. This transfer of heat is
typically
performed using a coaxial heat exchanger. The water to refrigerant heat
exchanger is
generally referred to as the outdoor heat exchanger although it will be
appreciated that the
outdoor heat exchanger may be positioned indoors.
[0034] FIG. 2 schematically illustrates a cross section of coaxial heat
exchanger 200 according
to one embodiment. The inner tube 210 of the heat exchanger 200 is configured
to allow
water to flow through the inner tube. In some embodiments, the interior
surface of the inner
tube 210 is rifled, knurled, patterned, or otherwise textured in order to
increase the heat
transfer between water flowing through the inner tube and the material of the
inner tube
itself. In some embodiments, the inner tube 210 is engineered tubing or tech
tube. In some
embodiments, the inner tube 210 comprises copper, copper-nickel allow,
titanium, and/or
stainless steel. In some embodiments, the inner tube is an evaporator tube
such as, for
example, B4 or B5 tubes. In some embodiments, the inner tube is a condenser
tube such as,
for example, C+LW or C5 tubes.
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[0035] Coaxial heat exchanger 200 also includes an intermediate member 220
positioned
outboard of the inner tube 210. The intermediate member 220 may be a
configured as a
sleeve with projecting members, folded fins, or a combination of the two. In
some
embodiments, a folded fin intermediate member may be arranged as a ruffled
folded fin,
plain folded fin, and/or a lanced and offset folded fin. In some embodiments,
the projecting
structures and/or fins of the intermediate tubing member may be textured,
twisted, and/or
axially rifled. In some embodiments, these surface features increase the
mixing and/or
turbulence of a flowing fluid, thereby enhancing the degree of heat
transferred between the
intermediate tubing member and the fluid.
[0036] As shown in FIG. 2, when intermediate member 220 is configured as a
folded fin,
portions of the folded fin are in contact with the inner tube 210, thereby
allowing heat
transfer from the inner tube 210 to the intermediate member 220. The increased
surface
area created by intermediate member allows for increased heat transfer.
[0037] In some embodiments, intermediate member 220 is initially in a
generally planar
configuration and is wrapped around the inner tube 210 to form a tubular
intermediate
member. In some embodiments, the intermediate member is brazed to itself to
maintain a
tubular configuration rather than a planar form. Depending on the respective
length of the
inner tube and the intermediate member, in some embodiments, multiple
intermediate
members sections may be wrapped around the inner tube or positioned axially
around the
inner tube. In some embodiments, an intermediate member section is between 4
to 6 inches
long. In some embodiments, an intermediate member 220 may comprise one or more
than
one intermediate member sections. In some embodiments, the intermediate member
sections may be in contact with each other. In some embodiments, the
intermediate member
sections are separated by a gap. In some embodiments, the gap between
intermediate
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member sections is smaller at the first or last portion of the heat exchanger
as compared to
the middle portion of the heat exchanger. In some embodiments, an intermediate
member
comprises a plurality of rings axially aligned around the inner tube. In such
embodiments,
one or more than one of the rings includes axially projecting structures.
[0038] The intermediate member 220 is positioned within an outer jacket 230.
The outer
jacket 230 is outboard of the intermediate member 220 and the inner tube 210.
In some
embodiments, the outer jacket 230 is rigid. In some embodiments, the outer
jacket 230
contains metal, such as, for example, steel, stainless steel, copper, or
aluminum. The outer
jacket 230 is sufficiently strong to resist deformation at the appropriate
working pressures
such as, for example, refrigerant pressures.
[0039] The volume contained within the interior of the inner tube 210 is
referred to as the
inner volume 240. The volume between the interior of the outer jacket 230 and
the exterior
of the inner tube 210 is referred to as the outer volume 250.
[0040] In some embodiments, the coaxial heat exchanger 200 allows a first
fluid to flow
through the inner volume 240 while a second fluid flows through the outer
volume 250. Heat
is exchanged between the first and second fluids through the inner tube 210
and the
intermediate member 220. In some embodiments, the first fluid is water and the
second fluid
is a refrigerant which undergoes a phase change as heat is exchanged between
the water and
refrigerant.
[0041] In some embodiments, in order to create and/or increase contact between
the inner
tube 210 and the intermediate member 220, the inner tube is expanded or
otherwise
deformed. The inner tube 210 may be expanded using pressure, such as, for
example,
hydrostatic pressure, or using mechanical expansion processing. In some
embodiments, it is
advantageous to expand the inner tube 210 using hydrostatic pressure in order
to avoid
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crushing or significantly deforming the texture and/or rifling on the interior
surface of the
inner tube 210.
[0042] In some embodiments, before the inner tube 210 is expanded, the inner
tube 210 is
annealed. The inner tube 210 is annealed by heating it to a predetermined
temperature and
allowing the inner tube 210 to cool at a controlled rate. Once the inner tube
210 is annealed,
the inner tube material is generally softer and may be more easily expanded.
[0043] In some embodiments, the inner tube 210 is optimized to transfer heat
between a
water solution in the inner volume 240 and a refrigerant in the outer volume
250 when the
refrigerant is in a two-phase mixture or is in the process of changing phases
(either
evaporation or condensation). In some embodiments, the exterior of the inner
tube contains
ridges that are optimized to promote the evaporation of refrigerant by
facilitating the
formation of bubbles when the refrigerant evaporates. In some embodiments, the
exterior
of the inner tube contains ridges that are optimized to promote the
condensation of
refrigerant by facilitating the formation of droplets when the refrigerant
condenses. It will be
appreciated that embodiments that are optimized to facilitate evaporation of
the refrigerant
will also promote condensation of the refrigerant when compared to an inner
tube with a
generally smooth exterior surface.
[0044] In some embodiments, the first and/or last portions of a condenser or
evaporator
generally contain more single-phase refrigerant while the middle portion
contains more
liquid-vapor mixture. Accordingly, in some embodiments, engineered tubing with
an
enhanced textured exterior surface may be used for the middle portion of the
inner tube and
tubing with a smooth or otherwise unenhanced exterior surface may be used for
the first
and/or last portion of the inner tube. In some embodiments, regardless of the
state of the
exterior surface of the inner tube, the interior surface of the inner tube
will contain an
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engineered textured surface to take advantage of the increased turbulence and
heat transfer
with the liquid water solution flowing through the interior of the inner tube.
[0045] In some embodiments, the intermediate member increases the surface area
in contact
with a refrigerant, whether the refrigerant is in a single-phase (liquid or
vapor) or in a two-
phase mixture. In some embodiments, the intermediate member facilitates
greater heat
transfer when the refrigerant is in a single phrase as compared to when the
refrigerant is in a
two-phase mixture. In some embodiments, the intermediate member is only
present at the
first and last portions of the coaxial heat exchanger. In some embodiments,
the intermediate
member is not included in the portions of the heat exchanger that are expected
to contain
significantly two-phase mixtures of refrigerant. In some embodiments, the
intermediate
member is made of multiple intermediate member sections. In some embodiments,
there is
a gap between each intermediate member section. In some embodiments, the gap
between
intermediate member sections is larger in the middle portion of the coaxial
heat exchanger
as compared to the end portions of the heat exchanger. In some embodiments,
the gap
between intermediate member sections is larger in the four feet middle section
of a ten feet
long heat exchanger than in the three feet sections at either end of the ten
feet long heat
exchanger.
[0046] In some embodiments, the linear length of a coaxial heat exchanger is
about ten feet.
In some embodiments, about three-foot long sections closest to the ends of the
heat
exchanger contain inner tube members with a generally smooth or otherwise
unenhanced
exterior surface while the middle about four-foot section contains enhanced
engineered
inner tube with an exterior surface designed to promote evaporation or
condensation of the
refrigerant..
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[0047] FIG. 3 schematically illustrates a coaxial heat exchanger 300 according
to one
embodiment. Heat exchanger 300 includes a copper innertube 310, an
intermediate member
320 configured in a folded fin design, and a steel outer jacket 330. FIG. 3
also illustrates fluid
inlet 340 that allows a second fluid to flow into the outer volume 360 to
exchange heat with
a first fluid in the inner volume 350. Not shown in FIG. 3 is an analogous
fluid outlet that
allows the second fluid to exit the outer volume of the coaxial heat exchanger
300.
[0048] FIG. 4 schematically illustrates a coaxial heat exchanger 400 according
to one
embodiment. FIG. 4 illustrates an inner tube 410 and an intermediate member
420. For
clarity, FIG. 4 does not show an outer jacket. In some embodiments, inner tube
400 comprises
copper and has a textured or rifled interior surface. In some embodiments, the
outer surface
of inner tube 410 is generally smooth. In some embodiments, intermediate
member 420
comprises extruded aluminum such as, for example, a single piece of extruded
aluminum.
Aluminum may be extruded to form particular cross-sectional designs. As shown
in FIG. 4,
intermediate member 420 may include a generally circular interior surface 423
with
projecting structures 425 radiating therefrom. The generally circular interior
surface 423 of
intermediate tubing member 420 allows for a high degree of contact between the
intermediate member 420 and the inner tube 410.
[0049] In some embodiments, contact between the inner tube 410 and the
intermediate
tubing member 420 is increased by annealing the inner tube, then axially
inserting the
annealed inner tube into the intermediate tubing member and hydrostatically
expanding the
annealed inner tube within the intermediate tubing member. This process
creates an
increased degree of contact and facilitates heat transfer between the inner
tube 410 and the
intermediate tubing member 420. This arrangement allows the intermediate
tubing member
420 to transfer heat between the first fluid, flowing within the inner volume
within the inner
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tube 410 to or from a second fluid flowing in the outer volume between the
intermediate
tubing member 420 and the outer jacket (not shown) without the intermediate
tubing
member 420 being in contact with the first fluid. In some embodiments, the
first fluid
contains water and the second fluid contains a refrigerant such as, for
example, R410A, R32,
R454B, DR-55, R134a, R513A, R515A, R515B, HFO refrigerants such as HF0-1234ze,
HFO-
1233zd, or HF0-1234yf, or any number of combinations thereof. Expanding the
annealed
inner tube within the intermediate tubing member increases contact between the
inner tube
and intermediate member thereby facilitating thermal transfer. In some
embodiments,
expanding the inner tube within the intermediate member creates a press fit.
This
arrangement prevents the material of the intermediate tubing member from
contacting the
first fluid within the inner tube. This arrangement allows the intermediate
member to contain
materials that may not be suitable for sustained contact with the first fluid.
Expanding the
annealed inner tube using hydrostatic pressure allows the use of pre-existing
engineered
tubing or tech tube that has a rifled interior surface to be used with an
extruded aluminum
intermediate tubing member.
[0050] FIG. 5 schematically illustrates a coaxial heat exchanger 500 according
to one
embodiment. FIG. 5 illustrates an inner tube 510 and an intermediate member
520.
Intermediate member 520 is an extruded member. In some embodiments, the
extruded tube
member 520 includes a generally circular inner surface 523 and a generally
circular outer
surface 525 with a plurality of channels 527 passing through the length of the
tube member
520. This arrangement allows the tube member to form a high degree of contact
and thermal
transfer between the tube member and the inner tube, thereby facilitating a
high degree of
thermal transfer between the first fluid flowing through the inner tube and
the second fluid
flowing through the channels 527 of the tube member 520. In some embodiments,
the outer
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surface 525 of the tube member 520 is connected to a coupling 550. Fluid inlet
540 allows
fluid to enter the volume between the coupling 550 and the inner tube 510.
This volume is
in fluid communication with the channels 527 that pass through the tube member
520. The
tube member 520 is positioned axially outboard of the inner tube 510. A
coupling 550 seals
the outer volume, causing the second fluid to flow through the fluid
inlet/outlet 540 in order
to pass through the outer volume. In some embodiments, no separate outer
jacket is required
as the second fluid is contained within the volume defined by the channels of
the extruded
tube member and the coupling 550.
[0051] In some embodiments, the coupling 550 is also in contact with the
exterior surface of
the inner tube 510. In some embodiments, the coupling is sealed, adhered,
and/or brazed to
the exterior surface of the inner tube 510 and exterior surface of the tube
member 520 to
prevent leakage of the second fluid. In such embodiments, no outer jacket is
required.
[0052] FIG. 6 schematically illustrates a coaxial heat exchanger 600 according
to one
embodiment. In some embodiments, the intermediate member 620 includes a fin
portion
623 and a non-fin portion 625. In some embodiments, the intermediate member is
formed
as an aluminum extrusion with fins or other projecting structures along the
length of the
intermediate member. In some embodiments, the fins or projecting structures
are machined
off or otherwise removed from the intermediate member, thereby forming the non-
fin
portion of the intermediate member.
[0053] In some embodiments, the intermediate member serves as a double wall
construction
around the inner tube 610. This double wall construction prevents any mixing
of the first and
second fluids in the event that either the inner tube 610 or the intermediate
member 620
corrodes or otherwise becomes damaged, resulting in a leak. In some
embodiments, the
outer jacket 630 is sealed around the non-fin portion 625 of the intermediate
member 620.
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In some embodiments, the outer jacket 630 is arranged so that no separate
coupling is
required. As shown in FIG. 6, in some embodiments, the fluid inlet/outlet may
be
incorporated into the outer jacket 630, allowing fluid to flow into or out of
the outer volume
between the outer jacket 630 and the intermediate member 620.
[0054] In some embodiments, the outer jacket 630 is brazed to the intermediate
member
620 and any space between the intermediate member and inner tube is left open
to the
atmosphere. In such embodiments, if the intermediate member becomes damaged,
any
refrigerant flowing through the outer zone is released into the atmosphere
rather than
contaminating the circulating water solution within the inner tube. It will be
appreciated that
any space between the inner tube and intermediate member is very small and
does not
significantly reduce the thermal transfer between the first and second fluids.
[0055] FIG. 7 illustrates a folded fin structure 700 in a planar or flat form
according to one
embodiment. In some embodiments of the heat exchanger, the folded fin
structure 700 is
wrapped, rolled, or otherwise positioned around an inner tube to form the
intermediate
member.
[0056] FIG. 8 illustrates a heat exchanger 800 according to one embodiment. It
will be
appreciated that the components of heat exchanger 800 have been positioned for
clarity.
Engineered inner tube 810 includes a textured interior surface and a textured
exterior
surface. Intermediate member 820 is configured as a folded fin. Intermediate
member 820
is positioned axially outboard of the engineered inner tube 810. In some
embodiments,
intermediate member 820 is initially a substantially flat or planar member and
is wrapped
around inner tube 810. The innertube 810 and intermediate member 820 are
positioned
within outer jacket 830.
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[0057] In some embodiments, the intermediate member is configured to create an
axial gap
portion 840. The exterior surface of the inner tube is generally not covered
by the
intermediate member in the axial gap portion. In some embodiments, the heat
exchanger is
coiled after it is assembled. In some embodiments, the axial gap portion
allows the heat
exchanger to be coiled while reducing the amount of crimping or crushing of
the intermediate
member. If the intermediate member were significantly crimped or crushed, the
damaged
portion of the intermediate member could restrict the flow of fluid through
the volume
between the inner tube and outer jacket. In some embodiments, the axial gap
portion is
positioned at the interior radius of the coiled coaxial heat exchanger.
[0058] In some embodiments, a spacer (not shown) may be positioned axially to
the inner
tube. In some embodiments, the spacer may be positioned in the axial gap
portion. In some
embodiments, the spacer comprises a flexible material that allows fluid to
pass through the
spacer such as, for example, copper wool.
[0059] FIG. 9 illustrates a heat exchanger 900 according to one embodiment.
The inner tube
910 includes a rifled interior surface and a textured exterior surface.
Intermediate member
920 is in contact with both the inner tube 910 and the outer jacket 930. In
some
embodiments, inner tube 910 has been hydrostatically expanded in order to
increase contact
between the inner tube 910 and the intermediate member 920 without deforming
the
texture on either the interior or exterior surfaces of the inner tube 910. In
some
embodiments, the outer jacket 930 or intermediate member 920 may be shrunk
once the
inner tube 910 is positioned within the outer jacket 930 or intermediate
member 920 in order
to create a press fit or otherwise increase contact between the intermediate
member 920
and the inner tube 910.
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[0060] FIG. 10 illustrates a data plot comparing the water side pressure drop
of an example
embodiment of the coaxial heat exchanger described herein (square data points)
and a
commercially available fluted tube coaxial heat exchanger (diamond data
points). When
water is pumped into a coaxial heat exchanger the water enters the heat
exchanger at a
higher pressure than the water exits the heat exchanger. This drop in pressure
is due to liquid
friction and turbulence created within the heat exchanger. The greater the
drop in pressure,
the more energy must be used to pump water into the heat exchanger.
[0061] As shown in FIG. 10, the coaxial heat exchanger according to one
embodiment
described herein had a lower water side pressure drop than the commercially
available fluted
tube heat exchanger at all flow rates. The difference in waterside pressure
drop increases as
the flow rate increases.
[0062] FIG. 11 illustrates a data plot comparing the heat transfer of an
example embodiment
of the coaxial heat exchanger described herein (square data points) and a
commercially
available fluted tube coaxial heat exchanger (diamond data points). As can be
seen in FIG. 11,
the coaxial heat exchanger according to one embodiment described herein had a
greater heat
transfer than the commercially available fluted tube heat exchanger at all
flow rates. The
difference in heat transfer increases as the flow rate increases.
[0063] While the aspects of the present disclosure may be susceptible to
various
modifications and alternative forms, specific embodiments have been shown by
way of
example in the drawings and have been described in detail herein. But it
should be
understood that the invention is not intended to be limited to the particular
forms disclosed.
Rather, the invention is to cover all modifications, equivalents, and
alternatives falling within
the spirit and scope of the invention as defined by the following appended
claims.
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