U.S. patent application number 10/973629 was filed with the patent office on 2005-04-21 for heat exchanger.
Invention is credited to Kaellis, Joseph.
Application Number | 20050082047 10/973629 |
Document ID | / |
Family ID | 33161772 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050082047 |
Kind Code |
A1 |
Kaellis, Joseph |
April 21, 2005 |
Heat exchanger
Abstract
The invention is a shell and tube type heat exchanger that
provides a greater heat transfer coefficient to pressure drop
ratio. The invention includes a mini-vortex generator on the
surface of tubes within the tube bundle in the shell of the heat
exchanger. The mini-vortex generator increases the heat transfer
coefficient for grid baffle type heat exchangers having a
longitudinal shell fluid flow without resulting in a significant
increase in pressure drop. The invention also includes a
sinuous-type grid baffle which permits a greater tube packing
density and reduced pressure drop in a heat exchanger having
longitudinal shell fluid flow. The invention also encompasses a
shell and tube heat exchanger having mini-vortex generators and
sinuous baffles.
Inventors: |
Kaellis, Joseph; (Tarzana,
CA) |
Correspondence
Address: |
SHELDON & MAK, INC
225 SOUTH LAKE AVENUE
9TH FLOOR
PASADENA
CA
91101
US
|
Family ID: |
33161772 |
Appl. No.: |
10/973629 |
Filed: |
October 25, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10973629 |
Oct 25, 2004 |
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09680387 |
Oct 4, 2000 |
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6808017 |
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60157880 |
Oct 5, 1999 |
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Current U.S.
Class: |
165/159 |
Current CPC
Class: |
F28F 9/0132 20130101;
F28F 9/22 20130101; F28F 13/12 20130101; F28F 1/34 20130101 |
Class at
Publication: |
165/159 |
International
Class: |
F28D 007/00 |
Claims
1-16. (canceled)
17. A heat exchanger comprising: (a) a shell; (b) a tube bundle
inside the shell, the tube bundle comprising a plurality of
substantially parallel tubes for passage of a first fluid, each
tube having a base diameter of between about 0.5" and about 1", at
least a portion of the tubes having on their exterior surface
mini-vortex generators comprising two or more ridge members that
encircle at least a portion of the exterior surface of a tube, the
height of each ridge member being between about 0.2 mm and about
1.0 mm, the spacing between any two ridge members being between
about 2 mm and about 40 mm; (c) a grid baffle for supporting the
tubes; (d) a tube inlet for passage of the first fluid into the
tubes and a tube outlet for passage of the first fluid out of the
tubes; (e) a shell inlet for passage of a second fluid into the
shell and exterior of the tubes and a shell outlet for withdrawing
a second fluid from the shell, wherein the first and second fluid
are passed either countercurrent, co-current, or in multi-pass
substantially parallel flow, and when the fluids are at different
temperatures, a transfer of heat occurs between the fluids.
18. The heat exchanger of claim 17 wherein the ridge members have a
flow blocking surface that disrupts the longitudinal flow of the
second fluid proximal to the exterior surface of the tubes.
19. The heat exchanger of claim 18 wherein the ridge members
further comprise a sloped surface disposed downstream of the flow
blocking surface.
20. The heat exchanger of claim 17 wherein the spacing between any
two ridge members is between 2.6 mm and about 13 mm.
21. The heat exchanger of claim 17 wherein the spacing between any
two ridge members is between about 10 times and about 15 times the
height of the ridge members.
22. The heat exchanger of claim 17 wherein the ridge members are
integral with the tubes.
23. The heat exchanger of claim 17 wherein: the tubes are oriented
along a longitudinal axis; and the ridge members are disposed
perpendicular to the longitudinal axis of the tubes.
24. The heat exchanger of claim 17 wherein the ridge members are
annular rings protruding from the external surface of the
tubes.
25. The heat exchanger of claim 17 wherein: the tubes are oriented
along a longitudinal axis; and the ridge members are spiral shaped
and wind around the external surface of the tubes along the
longitudinal axis.
26. A method of exchanging heat between two fluids comprising:
obtaining a heat exchanger according to claim 17; pumping a first
fluid through the tubes in the tube bundle; and pumping a second
fluid through the shell to transfer heat between the first fluid
and the second fluid.
Description
RELATED APPLICATIONS
[0001] This invention is a continuation-in-part of U.S. Provisional
Patent Application 60/157,880, filed Nov. 5, 1999 entitled "Heat
Exchanger with Vortex Generator and Slat Baffles", which is hereby
incorporated by reference in it's entirety.
FIELD OF THE INVENTION
[0002] This invention relates generally to shell and tube heat
exchangers, and, more specifically to mini-vortex generators and
sinuous baffles used in shell and tube-type heat exchangers.
BACKGROUND OF THE INVENTION
[0003] Heat transfer is an important engineering concern for many
process. Heat exchangers are a well known apparatus for
transferring heat from one medium to another. There are many types
of heat exchangers, including for example shell and tube designs,
double pipe type shell and tube designs, plate and frame designs,
plate-fin designs, and others. These heat exchangers are used in
many industries, including those engaged in generating energy,
producing chemicals, refining petroleum products, and air
conditioning. All of these industries would stand to benefit from a
more efficient heat exchanger design.
[0004] A common goal in the design of shell and tube-type heat
exchangers is to enhance heat transfer while trying to keep the
associated pressure drop low, or in other words to maximize the
ratio of the heat transfer coefficient to the pressure drop. The
higher the pressure drop, the more energy must be expended to pump
the fluids through heat exchanger.
[0005] A problem with existing shell and tube type heat exchanger
designs is a failure to maximize the heat transfer coefficient
while keeping the pressure drop to a minimum. This is evidenced in
shell and tube exchangers utilizing segment type baffles, which
generate flow perpendicular to the tube bundle, which is otherwise
known as crossflow. These baffles have a high heat transfer
coefficient but also have a high pressure drop resulting from the
crossflow. Alternatively, current commercial designs utilizing grid
baffles with flow parallel to the tube bundle, have a low pressure
drop but have a less favorable heat transfer coefficient.
Consequently the overall efficiency, as measure by the ratio of the
heat transfer coefficient to pressure drop, is not maximized in
current shell and tube type heat exchangers.
[0006] What is needed is a shell and tube type heat exchanger that
improves upon the heat transfer coefficient to pressure drop ratio
of current shell and tube heat exchangers utilizing grid type
baffles.
SUMMARY
[0007] The invention satisfies this need. The invention is a shell
and tube type heat exchanger that provides a greater heat transfer
coefficient to pressure drop ratio and is thus more efficient.
[0008] The heat exchanger has a shell and a tube bundle inside the
shell. The tube bundle includes a plurality of substantially
parallel tubes for passage of a first fluid. At least a portion of
the tubes have a mini-vortex generator on their exterior surface.
The heat exchanger further includes a grid baffle between the
tubes, a tube inlet for passage of the first fluid into the tubes,
and a tube outlet for passage of the first fluid out of the tube.
The shell has a shell outlet for passage of a second fluid into the
shell and exterior to the tubes and a shell outlet for withdrawing
a second fluid from the shell.
[0009] In another embodiment, the heat exchanger has a shell and a
tube bundle inside the shell. The tube bundle includes a plurality
of substantially parallel tubes for passage of a first fluid. In
this embodiment, the heat exchanger has sinuous baffles for
supporting the tubes. Each sinuous baffle includes a plurality of
wiggle bar tube support members disposed between the tubes. The
heat exchanger further includes a tube inlet for passage of the
first fluid into the tubes and a tube outlet for passage of the
first fluid out of the tube. The shell has a shell outlet for
passage of a second fluid into the shell and exterior to the tubes
and a shell outlet for withdrawing the second fluid from the
shell.
[0010] In another embodiment, the heat exchanger has sinuous
baffles and at least a portion of the tubes of the heat exchanger
have a mini-vortex generator on their exterior surface.
[0011] In operation, when the first and second fluid are passed
countercurrent, co-current, or in multi-pass substantially parallel
flow, and when the fluids are at different temperatures, a transfer
of heat occurs between the fluids.
DRAWINGS
[0012] These features, aspects and advantages of the present
invention will become better understood with regard to the
following description, appended claims and accompanying figures
where:
[0013] FIG. 1 is a cross-sectional side view of a heat exchanger
having features of the invention;
[0014] FIG. 2 is a perspective view of a heat exchanger tube,
including an enlarged scale view of a mini-vortex generator having
features of the invention;
[0015] FIG. 3 is a side elevation in partial coss-section of the
heat exchanger illustrated in FIG. 1, taken along line 3-3;
[0016] FIG. 4 is a coss-sectional view of the heat exchanger
illustrated in FIG. 1, taken along line 4-4;
[0017] FIG. 5 is a coss-sectional view of the heat exchanger
illustrated in FIG. 1, taken along line 5-5; and
[0018] FIG. 6 is a coss-sectional view of the heat exchanger
illustrated in FIG. 1, taken along line 6-6.
DETAILED DESCRIPTION
[0019] The following discussion describes in detail one embodiment
of the invention and several variations of that embodiment. This
discussion should not be construed, however, as limiting the
invention to those particular embodiments. Practitioners skilled in
the art will recognize numerous other embodiments as well.
[0020] The invention is a heat exchanger 10 having a shell 12, a
tube bundle 14 having a plurality of tubes 16 within the shell 12,
and a grid baffle 18 between the tubes 16.
[0021] The shell 12 encloses the tube bundle 14 and holds the shell
fluid 20 as it passes against the exterior of the tubes 16. The
shell 12 typically has two outlets, a first shell outlet 22 for
passage of the shell fluid 20 (otherwise referred to herein as the
second fluid) into the shell 12 and a second shell outlet 24 for
withdrawing the shell fluid 20 from the shell 12 and out of the
heat exchanger 10. The outlets are typically configured as nozzles.
As illustrated in the embodiments in the Figures, the shell 12 is
typically a pipe, rolled cylinder, or similar such cylindrical
tank-like structure. The diameter of the shell 12 is typically
between about 8" and about 30", or other sizes as needed. More
typically, the diameter of the shell 12 is between about 12" and
about 25". The length of the shell 12 is typically between about 10
feet and about 45 feet.
[0022] As illustrated in the embodiment in FIG. 1, the tube bundle
14 comprises two tube sheets 26 that are affixed to the shell 12.
The tube sheets 26 separate the tube fluid 28 (otherwise referred
to herein as the first fluid 28) from the shell fluid 20 and
support the end portions of the tubes 16 within the shell 12. The
tube sheets 26 have tube holes 30 through which the tubes 16
protrude. The tubes 16 are typically welded directly to the tube
hole 30 of the tube sheet 26, or expanded by rolling to give a
leak-proof fit. The tube sheet 26 is typically a metal such as
steel, aluminum, admiralty metal, or others.
[0023] In another embodiment (not shown), one tube sheet 26 is
affixed to the shell 12 and the other tube sheet 26 is floating and
is not affixed to the shell 12. This design permits the tubes
bundle 14 to be removable. In still another embodiment (not shown),
the tube bundle 14 comprises one tube sheet 26 with U-tubes.
[0024] As illustrated in FIG. 1 and FIGS. 4-6, the tube bundle 14
is comprised of a plurality of tubes 16 that are disposed
substantially parallel to each other and parallel to the
longitudinal axis of shell 12. As illustrated in FIG. 1, the heat
exchanger 10 has a tube inlet 32 for passage of tube fluid 28
through a first header 33a into the tubes 16 and a tube outlet 34
for passage of the tube fluid 28 from the tubes 16 into a second
header 33b and out of the heat exchanger 10. As illustrated, the
tube inlet 32 and the tube outlet 34 are disposed on opposite ends
of the heat exchanger 10. However, in multi-pass units (not shown)
the tube inlet 32 and tube outlet 34 are disposed at the same end
of the heat exchanger 10. The tubes 16 are typically formed of a
metal, such as steel, copper, aluminum, or admiralty metal. The
diameter of the tubes 16 is typically between about 1/2 and about
2". More typically, the diameter of the tubes 16 is between about
5/8" and 1".
[0025] In the embodiment illustrated in FIG. 2 and FIG. 3, at least
a portion of the tubes 16 have a mini-vortex generator 36 on their
exterior surface. The function of the mini-vortex generator 36 is
to abruptly interrupt the flow of the shell fluid 20 proximal to
the exterior surface of the tube 16. Preferably, the mini-vortex
generators 36 comprise small protrusions on the external surface of
the tubes 16 which interrupt the longitudinal flow of the shell
fluid 20 proximal to the tubes 16 exterior surface. This
interruption in fluid flow by the mini-vortex generators 36 results
in a shell fluid 20 flow which can be described as recirculating,
separated, or a vortex flow. The result is a disruption of the
shell fluid 20 laminar sub-layer which exist in turbulent flow
conditions and is proximal to the tube 16, and a corresponding
disruption in the temperature profile close to the tube 16 wall.
The vortex fluid flow process results in a decrease in resistance
close to the exterior of the tube 16 wall and an increase in the
heat transfer rate. The heat transfer benefit of the invention is
generally greatest for fluids having a high or moderate Prandtl
number where heat transfer occurs to a large extent by a movement
of the fluid mass which contains the heat, as opposed to heat
transfer in fluids with a low Prandtl number where heat is
transferred predominantly by conduction.
[0026] In a preferred embodiment, the mini-vortex generators 36 are
comprised of ridge members 36a that encircle at least a portion of
the exterior surface of the tubes 16. Preferably, the ridge members
36a are integral with the tubes 16. In a preferred embodiments, the
ridge members 36a have a flow blocking surface 38 that disrupts the
longitudinal flow of the shell fluid 20 proximal to the exterior
surface of the tubes 16. As illustrated in the embodiment in FIG.
2, the ridge members 36a are disposed generally perpendicular to
the longitudinal axis of the tubes 16, and each ridge member 36a
disrupts the shell fluid 20 flow predominantly upstream of itself.
In a preferred embodiment (not shown), the ridge members 36a are
configured as annular rings 36a that protrude from the external
surface of the tubes 16.
[0027] In the embodiment illustrated in FIG. 2, the ridge members
36a have a sloped surface 40 that is disposed rearward of the flow
blocking surface 38 such that the fluid vortex is created upstream
of the flow blocking surface 38 and the surrounding shell fluid 20
passes by the slopped surface 40 after it encounters the flow
blocking surface 38.
[0028] In other embodiments (not shown), the ridge member 36a has
an alternative configuration in cross-section such as for example
square, rectangular, beveled rectangular, or curved. In another
embodiment (not shown), the mini-vortex generator 36 comprises
spiral-like ridges 36b that wind around the exterior surface of the
tubes 16. In still other embodiments (not shown), the mini-vortex
generator 36 comprises alternative protrusions or alterations on
the exterior surface of the tubes 16.
[0029] Preferably, the height of the ridge member 36a from the
exterior tube 16 surface is between about 0.2 mm and about 1.0 mm
on a tube 16 having a base diameter of between about 5/8" and about
1". Accordingly, the diameter of the portion of the tube 16 having
a ridge member 36a is preferably greater than the base diameter by
about 0.4 mm to about 2.0 mm. In other embodiments, the height of
the ridge members 36a is greater. For example, a heat exchanger 10
using a shell fluid 20 that is high fouling or which tends to form
deposits on the tubes 16 should utilize ridge members 36a of
between about 1 mm and about 3 mm to offset deposit formation on
the tubes 16 caused by the shell fluid 20. In still other
embodiments, the height of the ridge members 36a is greater than 3
mm.
[0030] As illustrated in FIG. 2 and FIG. 3, there are typically a
plurality of ridge members 36a disposed along the longitudinal axis
of each tube 16. Preferably, the spacing between ridge members 36a,
otherwise known as the pitch, is between about 2 mm and about 15
mm. Further preferable, the pitch of the ridge members 36a is
between about 2.6 mm and about 13 mm. However, in other embodiments
the pitch is between about 2 mm and about 40 mm. Generally, the
pitch of the ridge members 36a increases in relation to their
height. Typically, the pitch of the ridge members 36a is between
about 10 times and about 15 times the height of the ridge members
36a. Preferably, the height of the ridge members 36a is selected to
minimize the pressure drop of the shell fluid 20 while maximizing
heat transfer. The width of each ridge member 36a is typically
between about 0.2 mm and about 1.0 mm, and is variable when one or
more surface of the ridge member 36a is sloped, beveled, curved, or
otherwise non-rectangular in cross-section.
[0031] Baffles in a heat exchanger 10 function to support the tubes
16 and to direct the flow of the shell fluid 20. In the heat
exchanger 10 illustrated in FIG. 1, there are a plurality of
grid-type baffles 18. The term grid baffle 18 as use herein refers
to a baffle that permits longitudinal shell fluid 20 flow (parallel
to the longitudinal axis of the shell 12). In contrast, heat
exchangers 10 utilizing segmented baffles generate a shell fluid 20
crossflow (perpendicular to the tube bundle 14) as opposed to a
longitudinal flow (parallel to the tube bundle 14).
[0032] Each grid baffle 18 comprises a plurality of tube support
members 42. Typically, each tube support member 42 is elongate and
spans at least a portion of the shell 12 in a plane perpendicular
to the longitudinal axis of the shell 12. Preferably, each tube
support member 42 has opposed ends that are attached to a baffle
hoop 44 that is disposed within the shell 12 in a plane
substantially perpendicular to the tube bundle 14. The spacing of
grid baffles 18 within the shell 12 depend on the tube 16 diameter.
Tubes 16 having a 1" diameter are typically supported every 60"
along the tubes 16 longitudinal axis, tubes 16 having a 3/4"
diameter are typically supported every 45", and tubes 16 having a
1/2" diameter are typically supported every 30". The tubes 16 can
be supported by baffles 18 at a shorter distance, however the
Tubular Exchangers Manufactures Association (TEMA) calls for the
spacing not to exceed these distances. Accordingly, since each grid
baffle 18 may furnish only partial support for the tube 16, the
baffle spacing generally does not exceed an integer fraction of 60,
45, or 30".
[0033] In the embodiment illustrated in FIG. 1 and FIGS. 4-6, the
heat exchanger 10 comprises sinuous baffles 18a (referred to as
slat baffles in related application No. 60/157,880), which are a
type of grid baffle 18. As illustrated in these Figures, each
sinuous baffle 18a has a plurality of tube support members 42 which
are referred to herein as wiggle bars 42a. The wiggle bars 42a have
a sinusoidal or wave-like configuration about a elongate axis that
spans the baffle hoop 44, and the wiggle bars 42a are disposed
between the tubes 16 to provide support for the tubes 16. A tube 16
can also be supported directly by the baffle hoop 44 on one side to
maximize the tube 16 packing.
[0034] In a preferred embodiment, the heat exchanger 10 comprises
groups of three sinuous baffles 18a whereby the elongated axis of
the wiggle bars 42a of each sinuous baffle 18a are oriented at
60.degree. relative to the nearest sinuous baffle. For example, in
a heat exchanger 10 having tubes 16 with a 1" diameter the tubes 16
are supported by a sinuous type baffle every 20" or less (60
divided by the integer 3) and each baffle is rotationally disposed
60.degree. relative to the nearest sinuous baffle. Tube support
members 42 in a grid baffle 18 produce resistance to the
longitudinal flow of the shell fluid 20. However this series of
three sinuous baffles 18a allows maximal flow area at each sinuous
baffle 18a, thus minimizing the resistance to the longitudinal flow
of the shell fluid 20 while still providing tube 16 support.
[0035] In a preferred embodiment, the depth (dimension parallel to
the longitudinal tube axis) of the wiggle bar 42a is between about
1/4" and about 1/2". The spacing between tube centers, otherwise
known as the tube 16 pitch, is typically 11/4times the tube
diameter as required by TEMA. The width of the wiggle bar 42a, the
distance between the exterior surface of two adjacent tubes 16, is
thus typically 1/4 times the tube 16 diameter. The width of a
wiggle bar 42a for a heat exchanger 10 utilizing tubes 16 with 3/4"
diameter is typically about {fraction (3/16)}". The width of a
wiggle bar 42a for a heat exchanger 10 utilizing tubes 16 with a 1"
diameter is typically about 1/4". The tube 16 pitch and wiggle bar
42a width may vary in alternative embodiments. In a heat exchanger
10 utilizing mini-vortex generators 36 and sinuous baffles 18a, the
width of the wiggle bars 42a may be slightly less than 1/4 times
the tube 16 diameter in order to allow clearance for the
mini-vortex generators 36.
[0036] Pitch to diameter ratios larger than required by TEMA give a
less compact tube packing density. The advantage of sinuous baffles
18a is that they allow the tubes 16 to be oriented with a
triangular pitch and with a tube to pitch ratio which does not
exceed TEMA's requirements. A triangular pitch, as opposed to a
square pitch permits a greater tube 16 packing density with about
151/2% more tubes in the same diameter tube bundle 14.
[0037] In embodiments having multipass flow (not shown), the heat
exchanger 10 typically further comprises one or more blocking bars
integral with or attached to the baffles 18 at the pass section of
the shell 12 to prevent shell fluid 20 bypass. Tube bundles 14 are,
preferably packed as fully as possible with tubes 16 to eliminate
large fluid passageways on the periphery of the tube bundle 14
which permit shell fluid 20 to bypass the tube bundle 14.
Passageways which still remain are preferably blocked by attaching
nodules or protrusions on the baffle hoop 44.
[0038] In the embodiment illustrated in FIGS. 4-6, for every
sinuous baffle 18a each tube 16 is in contact and is supported by
two wiggle bars 42a, with the exception of some tubes 16 disposed
proximal to the baffle hoop 44. Preferably, each wiggle bar 42a is
in contact with a portion of the circumference of external surface
of each tube 16 defined by an arc (corresponding to an angle of a
portion of the circular tube 16) of between about 30.degree. and
about 180.degree.. Further preferable, each wiggle bar 42a is in
contact with a portion of the circumference of each tube 16 defined
by an arc (corresponding to an angle of a portion of the circular
tube 16) of between about 45.degree. and about 75.degree..
[0039] With reference to the first sinuous baffle 18a in a
repeating series of three illustrated in FIGS. 4-6, a tube 16
contacts one wiggle bar 42a on one side of the tube 16 along about
a 60.degree. arc and the same tube 16 contacts another wiggle bar
42a along about a 60.degree. arc on the opposing side of the tube
16. Accordingly, for each sinuous baffle 18a most tubes 16 are in
supporting contact with a wiggle bar 42a over a total arc
circumference corresponding to a combined angle of about
120.degree.. The second sinuous baffle 18a in a series contacts the
same tube 16 at two opposing arcs rotationally displaced about
60.degree. from the first sinuous baffle, and the third sinuous
baffle 18a in series contacts the same tube at two opposing arcs
rotationally displaced about 60.degree. from the second sinuous
baffle. After three sinuous baffles 16, the tube 16 has been
contacted three times at three adjacent sections of the tube 16
circumference, each contact being 120.degree., or a total of
360.degree., with depth of the contact surface being equivalent to
the depth of the wiggle bar 42a. The tube 16 has now been
contacted, and is supported around its entire periphery. The next
sinuous baffle 18a begins a new series of three.
[0040] The invention further includes a method of heat exchange
between fluids comprising utilizing the heat exchanger 10 described
herein. In operation, the first and second fluid are passed either
countercurrent, co-current, or in multi-pass with substantially
parallel flow. Preferably, the first and second fluid are passed in
substantially counter-current directions (in opposite directions)
or in multi-pass flow, and parallel to the longitudinal axis of
shell 12. A transfer of heat occurs between the fluids when the
first fluid and second fluid are at different temperatures.
[0041] Having thus described the invention, it should be apparent
that numerous structural modifications and adaptations may be
resorted to without departing from the scope and fair meaning of
the instant invention as set forth hereinabove and as described
hereinbelow by the claims.
* * * * *