U.S. patent application number 10/861801 was filed with the patent office on 2005-12-08 for heat transfer apparatus with enhanced micro-channel heat transfer tubing.
This patent application is currently assigned to American Standard International, Inc.. Invention is credited to Hancock, Stephen S..
Application Number | 20050269069 10/861801 |
Document ID | / |
Family ID | 35446416 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050269069 |
Kind Code |
A1 |
Hancock, Stephen S. |
December 8, 2005 |
Heat transfer apparatus with enhanced micro-channel heat transfer
tubing
Abstract
Heat exchange apparatus includes elliptical cross section heat
exchange tubing provided with a partition dividing the interior of
the tubing into at least two parallel flow passages. The flow
passages are delimited by inwardly projecting fins formed on the
tubing wall and on the partition, the fins extending parallel to
each other and having a height less than the anticipated thickness
of the velocity boundary layer of heat exchange fluid flowing
through the tubing passages. The tubing may be arranged in
serpentine or coiled arrangements of the heat exchange apparatus or
parallel tubes extending between heat exchanger header tanks. The
heat exchange apparatus is particularly adapted for use in HVAC
systems.
Inventors: |
Hancock, Stephen S.; (Flint,
TX) |
Correspondence
Address: |
MICHAEL E. MARTIN
THE TRANE COMPANY
PATENT DEPARTMENT - 12-1
3600 PAMMEL CREEK ROAD
LA CROSSE
WI
54601
US
|
Assignee: |
American Standard International,
Inc.
NEW YORK
NY
|
Family ID: |
35446416 |
Appl. No.: |
10/861801 |
Filed: |
June 4, 2004 |
Current U.S.
Class: |
165/179 |
Current CPC
Class: |
F28F 1/40 20130101; F28D
1/0478 20130101; F22B 37/12 20130101; F28D 1/0473 20130101; F28F
1/36 20130101; F22B 37/101 20130101; F28F 1/022 20130101; F28F
2260/02 20130101 |
Class at
Publication: |
165/179 |
International
Class: |
F28D 007/12 |
Claims
What is claimed is:
1. Apparatus for transferring heat between fluids comprising:
micro-channel tubing having a generally curved cross sectional
shape to be presented to a heat transfer fluid flowing thereover,
said cross sectional shape being defined by a wall of said tubing;
said tubing including partition means dividing an interior space of
said tubing into parallel longitudinal flow passages; and generally
parallel, longitudinal, spaced apart fins extending from said wall
and said partition means into said flow passages, respectively, to
provide enhanced heat transfer between fluids flowing over the
exterior of said tubing and within said flow passages,
respectively.
2. The apparatus set forth in claim 1 wherein: said partition means
comprises a partition extending along and substantially parallel to
an axis of said cross sectional shape of said tubing.
3. The apparatus set forth in claim 2 wherein: said axis is a minor
axis of an ellipse.
4. The apparatus set forth in claim 3 wherein: said ellipse defines
said cross sectional shape of said tubing and said ellipse has a
major axis which is approximately twice the length of said minor
axis.
5. The apparatus set forth in said claim 4 wherein: said apparatus
is arranged to provide for flow of a heat exchange fluid over the
exterior of said tubing generally normal to a minor axis of said
elliptical cross section.
6. The apparatus set forth in claim 1 wherein: the cross sectional
shape of said tubing is substantially elliptical.
7. The apparatus set forth in claim 6 wherein: said apparatus is
formed as a serpentine coil of said tubing and said tubing is bent
in reverse bends about an axis substantially parallel to a major
axis of said elliptical cross sectional shape.
8. The apparatus set forth in claim 6 wherein: said apparatus is
formed in a continuous helical coil of said tubing which is bent
about an axis substantially parallel to a major axis of said
elliptical cross sectional shape.
9. The apparatus set forth in claim 1 wherein: said fins have a
substantially trapezoidal cross sectional shape.
10. The apparatus set forth in claim 1 wherein: the height of said
fins is less than the thickness of a velocity boundary layer of
fluid flowing through said flow passages, respectively.
11. The apparatus set forth in claim 10 wherein: the height of said
fins is determined from the equation
e=2.multidot.R.sup.7.multidot.A/P where e=height of said fins, R is
a variable having a value of from about 0.60 to 0.95, A is the
cross sectional area of one of said flow passages and P is the
perimeter length of said one flow passage.
12. The apparatus set forth in claim 1 wherein: the thickness of
said wall is in a range of about 70% to 80% of the thickness of
said partition means.
13. Apparatus for transferring heat between fluids comprising:
micro-channel tubing having a generally elliptical cross sectional
shape to be presented to a heat transfer fluid flowing thereover,
said cross sectional shape being defined by a wall of said tubing;
said tubing including a partition extending along and substantially
parallel to an axis of said cross sectional shape of said tubing
and dividing an interior space of said tubing into parallel
longitudinal flow passages; and generally parallel, longitudinal,
spaced apart fins extending from said wall and said partition into
said flow passages, respectively, said fins having a height less
than the thickness of a velocity boundary layer of a fluid flowing
through said flow passages to provide enhanced heat transfer
between fluids flowing over the exterior of said tubing and within
said flow passages, respectively.
14. The apparatus set forth in claim 13 wherein: said axis is a
minor axis of said elliptical cross sectional shape of said
tubing.
15. The apparatus set forth in claim 14 wherein: said elliptical
cross sectional shape of said tubing has a major axis which is
approximately twice the length of said minor axis.
16. The apparatus set forth in claim 13 wherein: said fins have a
substantially trapezoidal cross sectional shape.
17. The apparatus set forth in claim 13 wherein: said apparatus is
formed as a serpentine coil of said tubing and said tubing is bent
in reverse bends about an axis substantially parallel to a major
axis of said elliptical cross sectional shape.
18. The apparatus set forth in claim 13 wherein: said apparatus is
formed in a continuous helical coil of said tubing which is bent
about an axis substantially parallel to a major axis of said
elliptical cross sectional shape.
19. Micro-channel tubing for transferring heat between fluids and
having a generally curved cross sectional shape to be presented to
a heat transfer fluid flowing thereover, said cross sectional shape
being defined by a wall of said tubing; said tubing including at
least one partition dividing an interior space of said tubing into
parallel longitudinal flow passages; and generally parallel,
longitudinal, spaced apart fins extending from said wall and said
partition, respectively, into said flow passages, respectively, to
provide enhanced heat transfer between fluids flowing over the
exterior of said tubing and within said flow passages,
respectively, said fins having a substantially trapezoidal cross
sectional shape and a height less than the thickness of a velocity
boundary layer of fluid flowing through said flow passages.
20. The tubing set forth in claim 19 wherein: said cross sectional
shape of said tubing is elliptical and includes a major axis and a
minor axis and said partition is coincident with said minor
axis.
21. The tubing set forth in claim 20 wherein: the length of said
major axis is about twice the length of said minor axis.
22. The tubing set forth in claim 19 wherein: the height of said
fins is determined from the equation
e=2.multidot.R.sup.7.multidot.A/P where e=height of said fins, R is
a variable having a value of from about 0.60 to 0.95, A is the
cross sectional area of one of said flow passages and P is the
perimeter length of said one flow passage.
23. Micro-channel tubing for transferring heat between fluids and
having a generally curved cross sectional shape to be presented to
a heat transfer fluid flowing thereover, said cross sectional shape
being defined by a wall of said tubing; said tubing including at
least one partition dividing an interior space of said tubing into
parallel longitudinal flow passages; and generally parallel,
longitudinal, spaced apart fins extending from said wall and said
partition, respectively, into said flow passages, respectively, to
provide enhanced heat transfer between fluids flowing over the
exterior of said tubing and within said flow passages,
respectively, said fins having a height determined from the
equation e=2.multidot.R.sup.7.multidot.A/P where e=height of said
fins, R is a variable having a value of from about 0.60 to 0.95, A
is the cross sectional area of one of said flow passages and P is
the perimeter length of said one flow passage.
24. The tubing set forth in claim 23 wherein: R has a value of
about 0.87.
Description
BACKGROUND OF THE INVENTION
[0001] Apparatus requiring heat transfer from one fluid to another
is ubiquitous. For example, heating, ventilating and air
conditioning (HVAC) equipment using heat transfer fluids is quite
widely used and there is an ever-present need to provide more
efficient heat transfer and to reduce the requirements for size and
weight of heat transfer equipment as well as the volume of heat
transfer fluid required to achieve a particular performance
classification. Moreover, in residential and commercial HVAC
systems, for example, there is a continuing desire to provide for
greater heat transfer and a more compact equipment package to
reduce the volume of refrigerant fluid used in the system for
environmental and economic reasons.
[0002] To achieve the above-mentioned desires, heat transfer
apparatus using so called micro-channel heat transfer tubing has
been developed. The external dimensions of the heat transfer tubing
are relatively small, the tubing is relatively thin walled and a
dense, continuous tube type apparatus is provided or a large number
of closely spaced apart tubes are provided in the heat exchange
apparatus to achieve more efficient heat transfer between a working
fluid, such as a vaporizable refrigerant, and ambient air, for
example.
[0003] One improvement in heat transfer tubing has been to provide
the tubing with an arcuate, preferably elliptical, cross section
which improves the efficiency of a heat exchanger using such tubing
by reducing the resistance to flow of fluid over the external
surfaces of the tubing. Outdoor heat exchangers, such as air
conditioning condenser units or heat pump heat exchanger units, for
example, enjoy the benefits of elliptical shaped heat exchanger
tubing. Other applications of heat exchanger apparatus using
elliptical tubing may also benefit from this improvement.
[0004] However, in the pursuit of greater efficiencies and heat
transfer capacity for a given size of heat exchanger or heat
transfer apparatus, there has been a continuing desire to provide
heat transfer tubing which has an even greater capacity for heat
transfer while retaining mechanical strength and durability. It is
to these ends that the present invention has been developed.
SUMMARY OF THE INVENTION
[0005] The present invention provides an improved heat exchange
apparatus including multi-ported heat exchanger tubing with
improved heat transfer characteristics. The present invention also
provides an improved heat exchanger apparatus utilizing, in
particular, multi-ported or multi-passageway heat transfer tubing
having a substantially arcuate or curved cross section, either
circular or elliptical, for example.
[0006] In accordance with one aspect of the present invention, a
substantially elliptical cross section heat transfer tube, having
relatively small dimensions and being of the so-called
micro-channel type, is provided with at least two internal
longitudinal parallel flow passages which are separated by a
partition, preferably extending along and coincident with the minor
axis of the elliptical cross section of the tubing. The wall
surfaces of the respective parallel flow passages are provided with
heat transfer fins extending longitudinally along the flow passages
and being disposed substantially over the entire surface of the
tubing wall which defines the flow passages. The fins are of a
geometry such that the fin height with respect to the nominal wall
surface is less than the thickness of the velocity boundary layer
of the fluid flowing through the passages so as to minimize fluid
pressure losses of fluid flowing through the passages. The fin
height is also defined by an equation disclosed herein and in
accordance with the invention. Fins also extend along the surfaces
of the wall or partition which defines the multiple flow passages
within the tubing.
[0007] In accordance with another aspect of the present invention,
there is provided a heat transfer apparatus comprising a
continuous, elliptical cross section, tubing with multiple flow
passages and internal finning in accordance with the invention and
wherein the heat transfer apparatus comprises such continuous
tubing disposed in a selected geometric pattern. Alternatively, a
heat transfer apparatus in accordance with the invention is
provided with multiple elliptical cross section heat exchanger
tubes in accordance with the invention arranged to extend between
manifolds or header tanks such that there is substantial parallel
fluid flow through parallel side-by-side arranged heat exchanger
tubes.
[0008] Heat transfer tubing in accordance with the invention enjoys
improved heat transfer performance without materially increasing
resistance to fluid flow through the tubing. The combination of the
multiple parallel passage, elliptical cross section tubing with
heat transfer fins extending in the direction of flow within
parallel tubing passages provides an economical heat transfer
device with an improved heat transfer performance
characteristic.
[0009] Those skilled in the art will further appreciate the
advantages and superior features of the invention together with
other important aspects thereof upon reading the detailed
description which follows in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of an improved heat transfer
tube in accordance with the present invention;
[0011] FIG. 2 is a transverse section view of a heat transfer tube
in accordance with the invention;
[0012] FIG. 3 is a detail view showing a preferred geometry of the
heat transfer fins which extend within the internal flow passages
of the heat transfer tube shown in FIGS. 1 and 2;
[0013] FIG. 4 is a side elevation of one preferred embodiment of a
heat transfer apparatus utilizing a continuous heat transfer tube
in accordance with the invention;
[0014] FIG. 5 is an end view taken from the line 5-5 of FIG. 4
showing the arrangement of the heat transfer tubing in the
apparatus of FIG. 4;
[0015] FIG. 6 is plan view of another preferred embodiment of a
heat transfer apparatus in accordance with the invention;
[0016] FIG. 7 is side elevation detail view of the heat transfer
apparatus shown in FIG. 6;
[0017] FIG. 8 is a side elevation of another embodiment of a heat
transfer apparatus in accordance with the invention; and
[0018] FIG. 9 is a detail section view taken from the line 9-9 of
FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In the description which follows, like parts are marked
throughout the specification and drawings with the same reference
numerals, respectively. The drawing figures are not necessarily to
scale and certain features may be shown exaggerated in scale or in
somewhat generalized or schematic form in the interest of clarity
and conciseness.
[0020] Referring to FIG. 1, there is illustrated a heat exchanger
or heat transfer tube in accordance with the present invention and
generally designated by the numeral 10. The heat transfer tube 10
is preferably of an arcuate, and more preferably elliptical, cross
sectional shape and is provided with plural, elongated, parallel,
internal flow passages 12 and 14 which are formed in part by a
centrally disposed divider or partition 16. The tube 10 also,
preferably, includes a continuous outer wall 18 integrally formed
with the partition 16, the wall 18 being of substantially constant
cross section thickness and the partition 16 being of essentially
the same or greater cross section thickness as the wall 18. The
tube wall 18 has an outer surface 20 which is essentially
uninterrupted but may be provided with heat transfer finning of
various types and is shown, by way of example, to have a preferred
form of heat transfer finning applied thereto as will be described
further herein.
[0021] The inner wall surface 21 of the wall 18, as well as the
opposed surfaces of the partition 16, is provided with
longitudinally extending, closely spaced heat transfer fins,
generally designated by the numeral 22 in FIGS. 1 and 2. The tube
10 may be of the so-called micro-channel type wherein the nominal
external and internal dimensions of the tube are relatively small,
an example of which will be described further herein. Moreover, the
fins 22 are preferably integrally formed with the wall 16 and 18
and may also be of a predetermined preferred geometry to be
described further herein. The tube 10 may be formed by extrusion
processes and may be formed of suitable metals, such as aluminum,
or other metals having suitable engineering characteristics with
respect to extrusion processes, heat transfer, corrosion resistance
and, possibly, the need to be compatible with additional
fabrication processes and components contiguous with the tube.
[0022] A preferred form of external heat transfer finning is shown
for the tube 10 in FIG. 1 as comprising so-called spine finning
wherein a strip of heat conductive, continuous, flexible spine fin
24 is applied to the exterior surface 20 of the tube 10 in a known
manner and as described further in U.S. Pat. No. 4,535,838 to Gray
et al. and U.S. Pat. No. 5,967,228 to Bergman et al., both assigned
to the assignee of the present invention. U.S. Pat. Nos. 4,535,838
and 5,967,228 are incorporated herein by reference. Multiple
integral spines 26 extend from a side edge strip 28 of the spine
finning 24, substantially perpendicular to the outer surface 20 of
the tube 10. The spine finning 24 may be secured to the tube 10 in
a known manner and as described in the above-referenced patents.
The spine finning 24 is preferably helically wrapped tightly around
the surface of the tube 10 and in this regard, the elliptical cross
section of the tube 10 is suitable for wrapping the spine finning
24 thereon.
[0023] Referring now to FIG. 2, a preferred cross sectional
geometry of the tube 10 is illustrated. The partition 16 is
preferably disposed along and centered on the minor axis 17 of a
preferred elliptical cross section geometry of the tube 10. The
major axis 19 is, of course, normal to the minor axis 17.
[0024] As further shown in FIG. 2, a preferred geometry of the
cross section of the tube 10 is such that the width of the tube "a"
comprising the extent of the major axis of the elliptical cross
section is about twice the height "b" of the tube which is the
extent of the minor axis 17. Ratios of width to height, or length
of major axis to length minor axis may be of selected values.
However, a ratio of a/b of 2:1 is indicated to be satisfactory. The
wall thickness "c" of the wall 18 is preferably about equal to or
less than the wall thickness "d" of the partition 16 and may be
about 75% to 80% of the wall thickness of the partition. As shown
in FIG. 2, the interior surface 21 of the wall 18, and the opposed
surfaces of the partition 16 which separate the parallel fluid flow
passages 12 and 14, are substantially continuously provided with
parallel spaced apart inwardly projecting fins 22. The fins 22 are
preferably of a height less than the anticipated velocity boundary
layer thickness of the fluid flowing through the passages 12 and 14
so as to minimize fluid pressure losses while optimizing heat
transfer capacity of tube 10. The height of the fins 22 is
preferably determined by the equation:
e=2.multidot.R.sup.7.multidot.A/P (1)
[0025] wherein e=the fin height, A=cross sectional area of passage
12 or 14, respectively (excluding the fins), P is the cross
sectional perimeter length of the passage 12 or 14, respectively,
(including the fins) and R is a variable having a value of from 0.6
to 0.95. The value of R is preferably about 0.87.
[0026] Referring also to FIG. 3, the detail illustration of the
fins 22 indicates that the fins preferably have a trapezoidal shape
leaving passage portions 13 between adjacent fins, also having a
trapezoidal shape. FIG. 3 indicates that fins 22 of height "e",
have a thickness or width at their peaks "f", a width "g" at their
base, and a spacing "h" between adjacent side edges as illustrated
in FIG. 3. For a heat transfer apparatus for use with conventional
refrigerant fluids used in commercial and residential HVAC systems,
micro-channel tubing, such as the tube 10, may have the following
dimensions: a=10.0 mm, b=5.0 mm, c=0.47 mm, d=0.60 mm, e=0.33 mm,
f=0.05 mm, g=0.23 mm, and h=0.284 mm. Specific geometries and
dimensions given above are for one preferred embodiment of the
invention. Those skilled in the art will recognize that these
dimensions may be varied somewhat, but for typical heat exchanger
tubing of the micro-channel type in accordance with the invention,
the dimensions given herein are preferred and advantageous,
including the determination of fin height "e" from equation
(1).
[0027] The enhanced heat exchange tube 10 may be provided in heat
transfer apparatus having various configurations. For example,
referring to FIG. 4, there is illustrated a heat exchanger 30
characterized by a serpentine arrangement of the tube 10 wherein
parallel runs of the tube 10 are indicated at 32. The heat
exchanger 30 is formed by bending the tube 10, with or without
spine finning 24 applied thereto, to have reverse bends 34. Heat
exchanger 30 is typically arranged such that a heat transfer fluid
flows through the heat exchanger 30 and over the exterior of tube
10 in the direction of arrow 36, see FIG. 5. The direction of flow
of heat exchange fluid, such as ambient air, indicated by arrow 36,
is normal to the minor axis 17 of the tube 10 and meets a reduced
resistance to fluid flow across the heat exchanger 30. One
advantage of the finned partition 16 is that the tube 10 may be
bent about radii having respective axes 37, see FIG. 5, parallel to
axis 19, without a tendency to collapse the tube and thus reduce
the cross sectional area of flow passages 12 and 14.
[0028] FIGS. 6 and 7 illustrate another embodiment of a heat
exchanger or heat transfer apparatus, generally designated by the
numeral 40, having a continuous tube 10 wound in a spiral fashion
and arranged such that heat exchange fluid flows through the heat
exchanger in the direction of the arrows 36 in FIG. 7. Continuous
convolutions 42 are formed in a spiral manner as illustrated in
FIG. 7, in particular. The tube 10 may be bent about an axis 37a
parallel to axis 17 so as to present a reduced tube cross section
to airflow in the direction of arrows 36 in FIG. 7. Alternatively,
the tube 10 may be bent about an axis parallel to axis 19 to form
the spiral convolutions. The general configurations of the heat
exchangers 30 and 40 are also described, together with the
advantages thereof, in U.S. Pat. No. 5,967,228.
[0029] Referring to FIGS. 8 and 9, the tube 10, with or without
finning 24, (the tube is shown without), may be provided in a heat
exchanger 50. Heat exchanger 50 includes opposed manifolds or
header tanks 52 and 54 together with a heat exchange fluid inlet 53
and an outlet 55. Heat exchange tubes 10 are arranged as
illustrated in FIG. 9 extending between and joined to header tanks
52 and 54. Airflow through the heat exchanger 50 is preferably in
the direction of arrow 36 or, of course, in the opposite direction
and, normal to the minor axis of the heat exchange tubes 10.
[0030] Those skilled in the art will appreciate the advantages and
superior features of the invention from the foregoing description.
Construction and applications of the heat exchange tube 10, as well
as the heat exchangers 30, 40 and 50, may be carried out using
conventional engineering practices and materials used for heat
exchanger apparatus. Although preferred embodiments of the
invention have been described in detail herein, those skilled in
the art will also recognize that various substitutions and
modifications may be provided without departing from the scope and
spirit of the appended claims.
* * * * *