U.S. patent application number 12/674971 was filed with the patent office on 2011-05-26 for heat exchanger for shedding water.
Invention is credited to Allen C. Kirkwood.
Application Number | 20110120177 12/674971 |
Document ID | / |
Family ID | 40795806 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110120177 |
Kind Code |
A1 |
Kirkwood; Allen C. |
May 26, 2011 |
HEAT EXCHANGER FOR SHEDDING WATER
Abstract
A microchannel heat exchanger includes a two headers and tubes
that extend between the headers. Each tube has an elongated
cross-section, the cross-section having a first end and an opposing
second end. In one example, each tube is angled such that a line
defined between the ends of each tube is angled relative to the
horizontal. As the tubes are angled, water that collects on the
tubes is directed away from the tubes. In another example, a plate
fin directs water away from the tubes. The plate fin includes
openings, and a louver including parallel vertical slots is located
between each of the openings. Each tube is interference fit in one
of the openings of the plate fin, positioning a louver between each
tube.
Inventors: |
Kirkwood; Allen C.;
(Brownsburg, IN) |
Family ID: |
40795806 |
Appl. No.: |
12/674971 |
Filed: |
December 18, 2007 |
PCT Filed: |
December 18, 2007 |
PCT NO: |
PCT/US2007/087901 |
371 Date: |
February 24, 2010 |
Current U.S.
Class: |
62/498 ;
165/173 |
Current CPC
Class: |
F28F 2260/02 20130101;
F28F 1/325 20130101; F28D 2001/0266 20130101; F28D 1/05383
20130101; F25B 39/022 20130101 |
Class at
Publication: |
62/498 ;
165/173 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F28F 9/02 20060101 F28F009/02 |
Claims
1. A heat exchanger comprising: a first header and a second header;
and a plurality of tubes extending along an axis between the first
header and the second header, wherein each of the plurality of
tubes has an elongated cross-section taken substantially
perpendicular to the axis, a first end and an opposing second end,
and each of the plurality of tubes are angled relative to a
horizontal such that the first end is higher than the opposing
second end.
2. The heat exchanger as recited in claim 1 wherein the heat
exchanger is an evaporator.
3. The heat exchanger as recited in claim 1 wherein the heat
exchanger is a microchannel heat exchanger.
4. The heat exchanger as recited in claim 1 wherein each of the
plurality of tubes includes an outer surface having a flattened
portion.
5. The heat exchanger as recited in claim 1 wherein the first
header and the second header are substantially vertical, each of
the plurality of tubes are substantially horizontal, refrigerant
flows through a plurality of channels in the plurality of tubes,
and air flows over the plurality of tubes in a direction
substantially perpendicular to a flow of the refrigerant through
the plurality of tubes.
6. The heat exchanger as recited in claim 1 further including a
plate fin including a plurality of collars each defining an
opening, and each of the plurality of tubes is received in one of
the plurality of openings.
7. The heat exchanger as recited in claim 6 wherein the plate fin
includes a louver located between each of the plurality of
openings, each of the louvers is located between two of the
plurality of tubes, and each of the louvers includes a plurality of
parallel vertical slots.
8. The heat exchanger as recited in claim 6 wherein each of the
plurality of collars includes a v-shaped channel that surrounds
each of the plurality of openings.
9. A refrigeration system comprising: a compressor for compressing
a refrigerant; a condenser for cooling a refrigerant; an expansion
device for expanding the refrigeration; and an evaporator for
heating the refrigerant, wherein the evaporator includes a first
header and a second header and a plurality of tubes extending along
an axis between the first header and the second header, wherein
each of the plurality of tubes have an elongated cross-section
taken substantially perpendicular to the axis, a first end and an
opposing second end, each of the plurality of tubes include a
plurality of channels, and each of the plurality of tubes are
angled relative to a horizontal such that the first end is higher
than the opposing second end.
10. The refrigeration system as recited in claim 9 wherein each of
the plurality of tubes includes an outer surface having a flattened
portion.
11. The refrigeration system as recited in claim 9 wherein the
first header and the second header are substantially vertical, each
of the plurality of tubes are substantially horizontal, refrigerant
flows through a plurality of channels in the plurality of tubes,
and air flows over the plurality of tubes in a direction
substantially perpendicular to a flow of the refrigerant through
the plurality of tubes.
12. The refrigeration system as recited in claim 9 further
including a plate fin including a plurality of collars each
defining an opening, and each of the plurality of tubes is received
in one of the plurality of openings.
13. The refrigeration system as recited in claim 9 wherein the
plate fin includes a louver located between each of the plurality
of openings, each of the louvers is located between two of the
plurality of tubes, and each of the louvers includes a plurality of
parallel vertical slots.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to a microchannel heat
exchanger that improves water shedding from a surface of tubes.
[0002] Microchannel heat exchangers (MCHX) can be used as a
condenser in a refrigeration system. The microchannel heat
exchanger includes horizontal tubes with a flattened surface that
extend between two vertical headers. The flattened surface of the
tubes is substantially horizontal, and water does not shed from
fins effectively. Water sits on the tubes, decreasing heat transfer
performance, causing an increase in pressure drop, and allowing the
gradual build up of ice under frosting conditions. For this reason,
microchannel heat exchangers have not been widely applied as
evaporators or as outdoor coils for heat pumps.
[0003] In another prior microchannel heat exchanger, the tubes are
oriented vertically to prevent the accumulation of water on the
tubes. Any condensate that forms gradually drains through louvers
in the fins of the microchannel heat exchanger. However, this is
not optimal as the louvers are blocked by the water, reducing heat
transfer performance. Additionally, for a residential heat pump
application, the length of the horizontal headers could be eight
feet in length and must be bent several times to fit into a
chassis. This creates manufacturing difficulties and reliability
concerns and is more expensive than the vertical header/horizontal
tube configuration.
SUMMARY OF THE INVENTION
[0004] A heat exchanger includes a two headers and tubes that
extend between the headers. Channels are defined in each of the
tubes. Refrigerant flows through the channels of the tubes, and air
that passes over the tubes exchanges heat with the refrigerant. In
one example, the heat exchanger is a microchannel evaporator. Each
tube has an elongated cross-section taken perpendicular to a length
of the tubes, the cross-section of the tubes having a first end and
an opposing second end.
[0005] In one example, each tube is angled relative to the
horizontal such that a line defined between the ends of each tube
is angled relative to the horizontal. As the tubes are angled,
water that collects on the tubes is directed away from the
tubes.
[0006] In another example, a plate fin directs water away from the
tubes. The plate fin includes openings, and a louver including
parallel vertical slots is located between each opening. Each tube
is interference fit in one of the openings of the plate fin,
positioning a louver between each of the tubes.
[0007] These and other features of the present invention will be
best understood from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The various features and advantages of the invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows:
[0009] FIG. 1 illustrates a prior art refrigeration system;
[0010] FIG. 2 illustrates a microchannel heat exchanger;
[0011] FIG. 3 illustrates a cross-section of a tube of the
microchannel heat exchanger;
[0012] FIG. 4 illustrates a header of the microchannel heat
exchanger;
[0013] FIG. 5 illustrates a plate fin of the microchannel heat
exchanger;
[0014] FIG. 6 illustrates a cross-sectional view of a portion of
the plate fin of FIG. 5 showing a louver and a v-shaped
channel;
[0015] FIG. 7 illustrates an alternate plate fin of the
microchannel heat exchanger;
[0016] FIG. 8 illustrates a cross-sectional view of the
microchannel heat exchanger; and
[0017] FIG. 9 illustrates a cross-sectional view of another
configuration of the microchannel heat exchanger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] FIG. 1 illustrates a refrigeration system 20 including a
compressor 22, a first heat exchanger 24, an expansion device 26,
and a second heat exchanger 28. Refrigerant circulates through the
closed circuit refrigeration system 20.
[0019] When the refrigeration system 20 is operating in a cooling
mode, the refrigerant exits the compressor 22 at a high pressure
and a high enthalpy and flows through the first heat exchanger 24,
which acts as a condenser. In the first heat exchanger 24, the
refrigerant rejects heat to air and is condensed into a liquid that
exits the first heat exchanger 24 at a low enthalpy and a high
pressure. A fan 30 directs the air through the first heat exchanger
24. The cooled refrigerant then passes through the expansion device
26, expanding the refrigerant to a low pressure. After expansion,
the refrigerant flows through the second heat exchanger 28, which
acts as an evaporator. In the second heat exchanger 28, the
refrigerant accepts heat from air, exiting the second heat
exchanger 28 at a high enthalpy and a low pressure. A fan 32 blows
air through the second heat exchanger 28. The refrigerant then
flows to the compressor 22, completing the cycle.
[0020] When the refrigeration system 20 is operating in a heating
mode, the flow of the refrigerant is reversed with a four-way valve
34. The first heat exchanger 24 accepts heat from the air and
functions as an evaporator, and the second heat exchanger 28
rejects heat to the air and functions as a condenser.
[0021] The heat exchangers 24 and 28 are microchannel heat
exchangers 38. The microchannel heat exchanger 38 can be part of a
refrigeration system 20 used with a microdevice or an automobile
air conditioner.
[0022] FIG. 2 shows the microchannel heat exchanger 38. The
microchannel heat exchanger 38 includes two headers 40 and 42 that
extend along an axis Y, and tubes 44 having a length that extend
between the two headers 40 and 42 along an axis X. The tubes 44
include channels or openings 46 (shown in FIG. 3). The headers 40
and 42 are substantially vertical, and the tubes 44 extend
substantially horizontally between the headers 40 and 42. The
refrigerant flows through the tubes 44 and exchanges heat with the
air that flows over the tubes 44. The openings 46 can be
substantially circular, rectangular, or have any shape or
geometry.
[0023] In one example, as shown in FIG. 3, a cross-section of the
tubes 44 taken perpendicular to the axis X has an elongated shape,
such as a rectangle or oval. For example, the tubes 44 can include
an outer surface 36 with a flattened portion. Each tube 44 include
a first end 48 and an opposing second end 50, and a line A extends
between the ends 48 and 50.
[0024] The line A defined between the ends 48 and 50 of the tubes
44 extends at an angle B.degree. relative to the horizontal. The
first end 48 is a distance S from the ground G, and the opposing
second end 50 is a distance R from the ground G. That is, the first
end 48 is farther from the ground G than the opposing second end 50
is from the ground G (the first end 48 is higher than the second
end 50). The tubes 44 are optimally angled to balance the competing
effects of shedding water and airside pressure drop.
[0025] FIG. 4 shows the header 40. Although only the header 40 is
illustrated and described, the header 42 also includes the same
features. The tubes 44 extend into and out of the page along the
axis X.
[0026] FIG. 5 shows a plate fin 52 including c-shaped collars 54
that each define an opening 64. The collars 54 create various
different fin densities required for different applications. The
collars 54 include a V-shaped channel 68 (shown in FIG. 6) that
surrounds and defines the opening 64. The openings 64 and the
collars 54 extend at the angle B.degree. relative to the
horizontal.
[0027] The plate fin 52 includes a first edge 70 and a second edge
72 that extend along the axis Y. The first edge 70 is continuous,
and the second edge 72 is interrupted by the openings 64. An
elongated surface 74 is defined between the first edge 70 and the
openings 64. In one example, the elongated surface 74 is located on
the side 70 near the second end 50 of the tubes 44 (the lower end
of the tubes 44).
[0028] The plate fin 52 also includes at least one louver 56 having
parallel slots 58. In one example, the parallel slots 58 are
vertical and extend along the axis Y. A louver 56 is located
between each of the openings 64 and extend at the angle B.degree.
relative to the horizontal. That is, the louvers 56 and the
openings 64 alternate along the axis Y.
[0029] In another example plate fin 52 shown in FIG. 7, the second
edge 72 is continuous and not interrupted by the openings 64. In
this example, the material of the plate fin 52 completely surrounds
the openings 64, and the collars 54 can have an oval or rectangular
shape. The tubes 44 are laced in the openings 64 and received in
the openings 64 with an interference fit. The tubes 44 are then
brazed to the plate fin 52.
[0030] In the example shown in FIGS. 8 and 9, the louvers 56 extend
upwardly relative to the first edge 70. In another example shown in
FIG. 8, the louvers 56 extend downwardly relative to the first edge
70.
[0031] Each tube 44 is received in one of the openings 64 of the
plate fin 52 with an interference fit, positioning a louver 56
between adjacent tubes 44 to improve heat transfer. The plate fin
52 is then brazed to the tubes 44.
[0032] As refrigerant flows through the openings 46 in the tubes
44, it exchanges heat with the air that flows over the tubes 44. If
the refrigerant is accepting heat from the air, the microchannel
heat exchanger 38 is acting as an evaporator, and condensate can
form on the surface of the tubes 44. As the tubes 44 are angled
relative to the horizontal, water sheds from the tubes 44 and does
not collect on the tubes 44. The collars 54 and the v-shaped
channels 68 allow the water to flow towards the first edge 70 and
then downwardly towards the bottom of the microchannel heat
exchanger 38 along the elongated surface 74. The parallel slots 58
also direct water downwardly. Shedding water or condensate from the
surface of the tubes 44 increases heat performance, does not cause
an increase in pressure drop, and prevents the accumulation of
ice.
[0033] The foregoing description is only exemplary of the
principles of the invention. Many modifications and variations of
the present invention are possible in light of the above teachings.
The preferred embodiments of this invention have been disclosed,
however, so that one of ordinary skill in the art would recognize
that certain modifications would come within the scope of this
invention. It is, therefore, to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of
this invention.
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