Note: Descriptions are shown in the official language in which they were submitted.
1
M1CROCHANNEL HEAT EXCHANGER
TECHNICAL FIELD
This disclosure relates generally to a heating, ventilation, and air
conditioning
(HVAC) system. More specifically, this disclosure relates to an improved
microchannel heat exchanger.
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BACKGROUND
HVAC systems can be used to regulate the environment within an enclosed
space. Various types of HVAC systems, such as residential and commercial, may
be
used to provide cool air, for example during hot times of the year, and/or
provide heat,
for example, during cooler times of the year. Providing heating and/or cooling
may
be important for user comfort levels. If adequate heating and/or cooling is
not
provided, a user may be uncomfortable in the enclosed space. In HVAC systems,
a
condenser cools refrigerant by heat exchange with ambient air drawn or blow
across a
condenser coil by a fan. Microchannel heat exchangers may be used within the
condenser to sufficiently cool the refrigerant. Current microchannel heat
exchanger
designs are limited.
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SUMMARY
In certain embodiments, a microchannel heat exchanger includes at least one
manifold and at least one a microchannel tube. The microchannel tube includes
a
plurality of ports, and the microchannel tube extends from the at least one
manifold.
The plurality of ports each have a width and a height. The microchannel heat
exchanger further includes at least one fin extending from the at least one
manifold.
The fins are arranged between the at least one microchannel tube and a second
microchannel tube. The microchannel heat exchanger further includes a
refrigerant
arranged to flow through the microchannel tube. At least one port of the
plurality of
ports has a cross-section area less than 0.35 millimeters squared.
In some embodiments, a condenser includes an enclosure and a microchannel
heat exchanger enclosed within the enclosure. The microchannel heat exchanger
includes at least one manifold and at least one a microchannel tube. The
microchannel tube includes a plurality of ports, and the microchannel tube
extends
from the at least one manifold. The plurality of ports each have a width and a
height.
The microchannel heat exchanger further includes at least one fin extending
from the
at least one manifold. The fins are arranged between the at least one
microchannel
tube and a second microchannel tube. The microchannel heat exchanger further
includes a refrigerant arranged to flow through the microchannel tube. At
least one
port of the plurality of ports has a cross-section area less than 0.35
millimeters
squared.
In certain embodiments, a heating, ventilation, and air conditioning (HVAC)
system includes a condenser and a microchannel heat exchanger. The
microchannel
heat exchanger includes at least one manifold and at least one a microchannel
tube.
The microchannel tube includes a plurality of ports, and the microchannel tube
extends from the at least one manifold. The plurality of ports each have a
width and a
height. The microchannel heat exchanger further includes at least one fin
extending
from the at least one manifold. The fins are arranged between the at least one
microchannel tube and a second microchannel tube. The microchannel heat
exchanger further includes a refrigerant arranged to flow through the
microchannel
tube. At least one port of the plurality of ports has a cross-section area
less than 0.35
millimeters squared.
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Certain embodiments of the present disclosure may provide one or more
technical advantages. For example, increasing the aspect ratio of ports of a
microchannel tube increases the tubeside heat transfer coefficient, and
provides for
better cooling for a refrigerant with low global warming potential (low-GWP
refrigerant).
In certain embodiments where the aspect ratios is close to one, the decrease
in
the cross-section area increases the heat transfer rate due to higher
refrigerant
velocities.
In some embodiments, reducing the cross-section area of the ports results in
increased heat transfer rates, which are beneficial for low-GWP refrigerants
and may
reduce the width of the condenser tubes.
As another example, reducing the port width compared to convention
microchannel tubes, and maintaining fixed port height ( as shown in FIGURE
3B),
may allow a low-GWP refrigerant flowing through a microchannel tube to
transfer as
much or more heat than a conventional refrigerant flowing through a
conventional
microchannel tube (e.g., in FIGURE 3A). Consequently, a condenser with the
same or
lower size and weight can be used for applications involving the use of low
GWP
refrigerants.
As additional example, reducing both the height and the width of the ports of
microchannel tubes (e.g., FIGURE 3C) reduces the cross-section area of the
port, and
the refrigerant velocity increases, which increases the tubeside heat transfer
coefficient. Another advantage of this embodiment is the reduction in airside
pressure
drop due to the reduced tube height, resulting in reduced fan power
consumption. This
embodiment may allow for increased condenser heat rejection per unit area.
As another example, using smaller ports for microchannel tubes allows a
microchannel heat exchanger with a low-GWP refrigerant to maintain the
effectiveness of a microchannel heat exchanger with a conventional
refrigerant,
without increasing the size, weight, cost, or complexity of the microchannel
heat
exchanger.
Certain embodiments of the disclosure may include none, some, or all of the
above technical advantages. One or more other technical advantages may be
readily
apparent to one skilled in the art from the figures, descriptions, and claims
included
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herein. Moreover, while specific advantages have been enumerated above,
various
embodiments may include all, some, or none of the enumerated advantages.
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BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present disclosure, reference is now
made to the following description, taken in conjunction with the accompanying
drawings, in which:
FIGURE 1 is a diagram illustrating an example microchannel heat exchanger,
according to some embodiments;
FIGURE 2 is a diagram illustrating an example microchannel heat exchanger,
according to some embodiments;
FIGURES 3A, 3B, and 3C illustrate example microchannel tubes, according
to some embodiments; and
FIGURE 4 is a diagram illustrating outdoor an HVAC unit comprising a
=
microchannel heat exchanger.
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DETAILED DESCRIPTION
Microcharmel heat exchangers may consist of several tubes, with each tube
containing multiple ports that the refrigerant may flow through.
Traditionally,
microchannel heat exchangers have been used with a conventional refrigerant
(e.g.,
hydrofluorocarbons such as R-410A), which have significant global warming
potential (GWP) when released into the atmosphere. As companies continue to
emphasize global warming mitigation, new refrigerants with low global warming
potential (low-GWP refrigerants) are being integrated into existing HVAC
systems.
HVAC systems may use microchannel heat exchangers as condensers. Due to the
poor condensing heat transfer characteristics of low GWP refrigerants, it may
be
necessary to increase the surface area of the heat exchangers. For example,
low-GWP
refrigerants may have lower specific heat, lower enthalpy, and/or lower
evaporation/condensation heat transfer coefficients. Further, current
microchannel
heat exchangers have a narrow range of port sizes that are not well suited to
these
new, low-GWP refrigerants. Thus, heat transfer occurs at a reduced rate in
these low-
GWP refrigerants. Increasing the size of the microchannel heat exchanger using
a low
GWP refrigerant, may provide the same system performance as with a
conventional
refrigerant. However increasing the size further increases cost, expense, and
space
required to house the microchannel heat exchanger, while further requiring
additional
fan power consumption, thus reducing the system efficiency. Thus, there is a
need for
a microchannel heat exchanger design that increases the tubeside heat transfer
coefficient, to compensate for the poor thermal properties associated with low-
GWP
refrigerant.
This disclosure recognizes that an improved microchannel heat exchanger
using refrigerants with poor thermal properties may include an increased
number of
ports in a microchannel tube, a reduced port hydraulic diameter, a reduced
port cross-
section area, and an increased aspect ratio of the ports due to reduction in
the width.
This improved microchannel heat exchanger may facilitate increasing the heat
transfer
coefficient of the microchannel heat exchanger, in some embodiments. This
improvement creates a more compact and efficient microchannel heat exchanger
for
low-GWP refrigerants.
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Embodiments of the present disclosure and its advantages are best understood
by referring to FIGURES 1 through 4 of the drawings, like numerals being used
for
like and corresponding parts of the various drawings.
FIGURE 1 is a diagram illustrating example microchannel heat exchanger 101
according to some embodiments. Microchannel heat exchanger 101 comprises
manifolds 140, a plurality of microchannel tubes 110, and a plurality of fins
120.
Microchannel heat exchanger 101 comprises manifold 140 and 141.
Manifolds 140 and 141 may be in communication with the overall air-
conditioning
system. Manifold 140 introduces refrigerant to microchannel heat exchanger 101
through inlet tubing (e.g., flow 191) and releases refrigerant from
microchannel heat
exchanger 101 through outlet tubing (e.g., flow 194). Although manifolds 140
and
141 are shown of a cylindrical configuration, they may be of a rectangular,
half of a
cylinder or any other shape, as well as have a single chamber or multi-chamber
design, depending on the refrigerant path arrangement.
Microchannel tubes 110 are generally elongated and substantially flat, and
extend from one or more manifolds 140, providing a path for refrigerant to
flow.
Each microchannel tube 110 has a first end mounted to manifold 140 and a
second
end mounted to manifold 141, and at least one flow channel extending
longitudinally,
thereby providing a flow path between manifold 140 and manifold 141.
Microchannel tubes 110 generally extend in a horizontal direction between
manifolds
140, providing a plurality of parallel refrigerant flow paths between
manifolds 140.
Each microchannel tube 110 may include any number of ports within. In some
embodiments, microchannel tubes may be made of aluminum. The heat exchanger
refrigerant pass arrangement may be of a multi-pass configuration, such as
depicted in
FIGURE 1, or of a single-pass configuration, depending on particular
application
requirements.
A plurality of fins 120 may be arranged between microchannel tubes 110, and
parallel to each other. Fins 120 extend from microchannel tubes 110 such that
the
surface area is increased and configured to transfer heat efficiently. Fins
120 may be
straight or angled. Fins 140 may have flat, wavy, corrugated or louvered
design and
typically form triangular, rectangular, offset or trapezoidal airflow
passages. In
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operation, air may below across fins 120 in order to remove heat from
refrigerant
flowing through microchannel tubes 110.
In operation, a refrigerant flows through microchannel tubes 110 in various
directions. Refrigerant may be introduced to microchannel heat exchanger 101
at
manifold 140 through flow 191. The refrigerant may split such that a portion
flows
through one or more microchannel tubes 110 until it reaches manifold 140 at
flow
192. As it flows through microchannel tubes 110, fins 120 facilitate a heat
transfer
such that the refrigerant is cooled. The refrigerant continues to flow 193 in
manifold
141 where the refrigerant again may split such that a portion flows through
one or
more microchannel tubes 110 from flow 193 to flow 194 at manifold 140. At flow
194, refrigerant then exits microchannel heat exchanger 101. After completing
its
flow through microchannel heat exchanger 101 at flow 194, refrigerant may be
cooled
to a lower temperature than when it entered microchannel heat exchanger 101 at
flow
191.
Modifications, additions, or omissions may be made to the systems described
herein without departing from the scope of the disclosure. For example,
microchannel
heat exchanger 101 may include any number of manifolds 140, microchannel tubes
110, and fins 120. The components may be integrated or separated. Moreover,
the
operations may be performed by more, fewer, or other components. FIGURE 2 is a
diagram illustrating example microchannel heat exchanger 201, according to
some
embodiments. In some embodiments, manifolds 240 and 241 operate as manifolds
140 and 141 of FIGURE 1. In some embodiments, microchannel tubes 210 and fins
220 operate as microchannel tubes 110 and fins 120 of FIGURE 1. Ports 230 may
be
individual channels of microchannel tube 210, providing a path for refrigerant
to flow
through microchannel tube 210 from manifold 240 to manifold 241. Microchannel
tubes 210 may include any number of ports 230. As the size of ports 230
varies, the
size of microchannel tubes 210 may increase or decrease, thus affecting the
number of
required microchannel tubes 210 in a microchannel heat exchanger (e.g.,
microchannel heat exchanger 101 of FIGURE 1), in order to sufficiently cool
the
refrigerant.
FIGURES 3A, 3B, and 3C illustrate example microchannel tubes 310a, 310b,
and 310c, according to some embodiments. In some embodiments, microchannel
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tubes 310a-c may be similar to microchannel tubes 110 and 210 of FIGURE 1 and
FIGURE 2, respectively. For example, refrigerant may flow through microchannel
tubes 310a-c using ports 330a-c from one manifold to another in order to
transfer heat
from the refrigerant.
5 In FIGURE 3A, microchannel tube 310a represents an embodiment used
in a
microchannel heat exchanger with conventional refrigerant. Port 330a has
height
331a and width 33 lb. The aspect ratio of port 330a is height 331a divided by
width
331b. For example, the aspect ratio of port 330 may range from 0.4-1.8, with
width
33 I b ranging from 0.50 mm-1.9 mm, height 331a ranging from 0.50 mm-1.40 mm,
10 and cross-section areas ranging from 0.35 mm2-1.4 mrn2.
This disclosure recognizes that an improved microchannel heat exchanger may
alter the microchannel ports to provide a more efficient heat transfer. The
improved
microchannel heat exchanger of this disclosure may reduce the width, height,
port
cross-section area (i.e. width times height), and/or increased aspect ratio of
the ports.
In some embodiments, the width of a port may be reduced. In certain
embodiments,
the height of the port may be reduced. In some embodiments, both the width and
the
height of the ports may be reduced. Reducing the width, height, or both the
width and
the height of the ports (e.g., compared to a convention microchannel heat
exchanger)
creates a smaller cross-section area of the port. This improved microchannel
heat
exchanger may facilitate increasing the heat transfer coefficient of the
microchannel
heat exchanger, in some embodiments. This improvement creates a more compact
and efficient microchannel heat exchanger for low-GWP refrigerants.
Reducing the cross-section area of the port in a traditional microchannel heat
exchanger would not provide similar benefits when using traditional
refrigerants.
Microchannel heat exchangers may be air-cooled and therefore may have a high
airside thermal resistance. The overall heat transfer coefficient of the
microchannel
heat exchanger is a function of the airside convection coefficient, which is
usually the
lowest, the effective conduction heat transfer coefficient, which is typically
the
highest, and the refrigerant side heat transfer coefficient. Specifically, the
heat transfer
coefficient for traditional refrigerants is high enough, such that further
reduction in
the cross-section area of the port would not significantly increase the
overall heat
transfer coefficient of the traditional microchannel heat exchanger. Further,
creating a
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smaller cross-section area would create a pressure drop, such that the
compressor
requires more power, and the system efficiency decreases.
The improved
microchannel heat exchanger of this disclosure uses a refrigerant with low
thermal
properties and a low heat transfer coefficient. Thus, reducing the cross-
section area of
the port would provide a significant increase in the heat transfer
coefficient, thus
resulting in a more compact condenser and providing a more efficient system
because
the airside pressure drop across the coil is lower, which may reduce the fan
power
required. FIGURES 3B and 3C illustrate improved microchannel heat exchangers,
according to some embodiments. These embodiments are illustrative rather than
limiting in nature, and a wide range of variations, modifications, changes,
and
substitutions may be contemplated.
In FIGURE 3B, microchannel tube 310b may be an embodiment of the present
disclosure, where the width of ports may be reduced to compensate for the low-
GWP
refrigerant's poor thermal qualities. In some embodiments, microchannel tube
310b
includes ports 330b. Port 330b may have width 332b ranging from 0.3mm-0.6mm
and height 331b ranging from 0.3mm-0.6mm. Port 330b may include any
combination of width 332 and height 331 b. In some embodiments, port 330b has
a
smaller width 332b than width 332a of port 330a, thus creating a more
rectangular
shape for port 330b than port 330a. For example, port 330b may have width 331b
of
0.3mm, 0.4mm, or 0.5 mm. In this example, height 331b may remain the same or
lesser than the height shown in 331a (e.g., 0.50 mm-1.4mm). Creating thinner
ports
330b increases the number of ports 330b that may fit within microchannel tube
310b.
Also, reducing width 33 lb may increase the aspect ratio of port 330b. In some
embodiments, the port cross-section areas are lower than 330a. For example,
the
aspect ratio of port 330b may be 1.0-1.80 or higher and areas may range
between 0.09
mm2 and 0.25 mm2. Reducing the cross-section areas of ports 330b may reduce
the
hydraulic diameter of port 330b, which may increase the tubeside heat transfer
coefficient, and provide for better heat transfer with a low-GWP refrigerant.
Thus, by
reducing width 331b, a low-GWP refrigerant flowing through microchannel tube
310b may transfer as much heat as a conventional refrigerant flowing through
microchannel tube 310a.
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In FIGURE 3C, microchannel tube 310c may be an embodiment of the present
disclosure, where the width and height of ports may be reduced to compensate
for the
low-GWP refrigerant's poor thermal qualities. In some embodiments,
microchannel
tube 310b includes ports 330b. Port 330b may have width 332b ranging from 0.3
mm-0.6 mm and height 331b ranging from 0.3 mm-0.6 mm. Port 330b may include
any combination of width 332 and height 33 lb. In some embodiments, port 330c
has
a smaller width 332c than width 332a of port 330a and a smaller height 331e
than
height 331a of port 330a. By reducing both height 331c and width 332a of port
330c,
the velocity of the refrigerant increases, which may also increase the heat
transfer
coefficient, and allow the low-GWP refrigerant to cool more quickly. Also, by
reducing both height 331c and width 332a of port 330c, additional ports 330c
may be
included in microchannel tube 310c than microchannel tube 310a. In some
embodiments, even when reducing both height 331c and width 332a, port 330c may
remain close to a square shape, (e.g., 0.5 mm by 0.5 mm, 0.55 mm by 0.45 mm,
0.29
mm by 0.31 mm), and the aspect ratio of port 330c may remain approximately 1.0
(e.g., 0.8 - 1.2). By reducing the cross-section area, the velocity of the
refrigerant
increases, which increases the heat transfer coefficient, and allows the low-
GWP
refrigerant to cool more quickly. The smaller ports (e.g., ports 330b-c) allow
a
microchannel heat exchanger with a low-GWP refrigerant to maintain the same
effectiveness as a microchannel heat exchanger with a conventional refrigerant
without increasing the size, weight, cost, or complexity. In some embodiments,
arranging ports 330b and 330c as described in this disclosure would have
limited
impact on the tubeside resistance of a microchannel heat exchanger using
conventional refrigerant. The change in size of ports 330b and 330c from 330a
may
only increase the heat transfer coefficient of a conventional refrigerant by a
nominal
amount. In general, air-cooled condensers have a higher heat transfer
resistance on
the airside. In air-cooled condensers using conventional refrigerants the
tubeside
resistance is lower, and the air side resistance is dominant, so even if the
heat transfer
coefficient of the refrigerant is increased slightly, the air cannot absorb
enough heat to
affect the actual cooling of the conventional refrigerant. However, with low-
GWP
refrigerants, the tubeside resistance is higher and an increase in the
tubeside heat
transfer coefficient may greatly impact the actual cooling of the low-GWP
refrigerant.
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Thus, providing ports with higher aspect ratios (e.g., ports 330b), or smaller
ports with
aspect ratios close to 1.0 (e.g., ports 330c), low-GWP refrigerants may
perform
cooling as effectively as a conventional refrigerant in the same type and size
of
microchannel heat exchanger.
In some embodiments, ports 330c are a smaller size (e.g., compared to ports
330a) such that microchannel tube 310c may also be reduced in height (e.g.,
compared to the height of microchannel tube 310a). By reducing the height of
microchannel tube 310c, microchannel heat exchanger (e.g., microchannel heat
exchanger 101 of FIGURE 1) may be made with fewer materials, thus conserving
resources and expense. By reducing the height of microchannel tube 310c,
microchannel heat exchanger (e.g., microchannel heat exchanger 101 of FIGURE
1),
may include fins (e.g., fins 120 of FIGURE 1) with an increased height. Larger
fins
may increase the surface area on which air is blowing, thus increasing the
heat
transfer and providing better cooling for the low-GWP refrigerant. Also, by
reducing
the height of microchannel tube 310c, microchannel heat exchanger (e.g.,
microchannel heat exchanger 101 of FIGURE 1) may include additional tubes
(e.g.,
tubes 110) to create additional pathways for the low-GWP refrigerant to flow
through,
and thus increasing the amount heat transfer.
FIGURE 4 is a diagram illustrating outdoor HVAC unit or condenser 401
comprising a microchannel heat exchanger 101 of FIGURE 1. Outdoor unit 401 may
encase microchannel heat exchanger 101 in an enclosure such that it is
protected from
an external environment. In some embodiments, outdoor unit 401 may further
comprise fan 405. Fan 405 may direct a flow of air across microchannel heat
exchanger. Fan 405 provides air flow to microchannel heat exchanger 101 to
facilitate cooling the refrigerant flowing through microchannel heat exchanger
101.
Any number of fans may be included.
In some embodiments, microchannel heat exchanger 101 may incorporate
ports 330b and/or 330c from FIGURE 3. By incorporating smaller ports 330b
and/or
330c than ports 330a, heat is transferred from the low-GWP refrigerant more
efficiently. Thus, fan 405 may consume less power for a given air flow. With
fan
405 consuming less power, outdoor HVAC unit 401 operates more efficiently, and
conserves resources.
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Modifications, additions, or omissions may be made to the systems,
apparatuses, and methods described herein without departing from the scope of
the
disclosure. The components of the systems and apparatuses may be integrated or
separated. Moreover, the operations of the systems and apparatuses may be
performed by more, fewer, or other components. For example, microchannel heat
exchanger 101 may include any number of microchannel tubes 110, fins 120,
manifolds 140 and 141, and so on, as performance demands dictate. One skilled
in
the art will also understand that microchannel heat exchanger 101 and outdoor
HVAC
unit 401 can include other components that are not illustrated but are
typically
included with HVAC systems.
Although this disclosure has been described in terms of certain embodiments,
alterations and permutations of the embodiments will be apparent to those
skilled in
the art, and it is intended that the present disclosure encompass such
changes,
variations, alterations, transformations, and modifications as fall within the
scope of
the appended claims. Accordingly, the above description of the embodiments
does
not constrain this disclosure. Other changes, substitutions, and alterations
are possible
without departing from the spirit and scope of this disclosure.
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