U.S. patent application number 12/854285 was filed with the patent office on 2012-02-16 for method of controlling tube temperatures to prevent freezing of fluids in cross counterflow shell and tube heat exchanger.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. Invention is credited to JOE BORGHESE.
Application Number | 20120037347 12/854285 |
Document ID | / |
Family ID | 45563952 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120037347 |
Kind Code |
A1 |
BORGHESE; JOE |
February 16, 2012 |
METHOD OF CONTROLLING TUBE TEMPERATURES TO PREVENT FREEZING OF
FLUIDS IN CROSS COUNTERFLOW SHELL AND TUBE HEAT EXCHANGER
Abstract
Methods and apparatus for controlling tube temperatures may
prevent freezing of fluids in cross counterflow shell and tube heat
exchangers. Cold gas may flow inside the tubes of the heat changer
and warm liquid may flow outside the tubes. The tube diameter and
tube spacing may be varied through the tube passes through the heat
exchanger in order to provide a hot side conductance to cold side
conductance ratio which results in the tube temperature being
safely above the liquid freezing point. The heat exchanger may be
used in, for example, the aerospace industry as a fuel oil cooler
or as a preconditioner for reactants in a spacecraft propulsion
system.
Inventors: |
BORGHESE; JOE; (Yucca
Valley, CA) |
Assignee: |
HONEYWELL INTERNATIONAL
INC.
MORRISTOWN
NJ
|
Family ID: |
45563952 |
Appl. No.: |
12/854285 |
Filed: |
August 11, 2010 |
Current U.S.
Class: |
165/165 ;
165/177 |
Current CPC
Class: |
F28D 7/1646 20130101;
F28D 2021/0033 20130101 |
Class at
Publication: |
165/165 ;
165/177 |
International
Class: |
F28D 7/00 20060101
F28D007/00; F28F 1/00 20060101 F28F001/00 |
Claims
1. A heat exchanger comprising: a first pass of tubes carrying a
first fluid at a first temperature through the heat exchanger; a
second pass of tubes carrying the first temperature fluid from the
first pass of tubes, through the heat exchanger; a second fluid at
a second temperature passing over the second pass of tubes and then
the first pass of tubes, wherein tubes of the second pass of tubes
have at least one of a decreased diameter and an increased tube
spacing, relative to tubes of the first pass of tubes.
2. The heat exchanger of claim 1, wherein the first temperature is
colder than the second temperature.
3. The heat exchanger of claim 1, wherein tubes of the second pass
of tubes have both a decreased diameter and an increased tube
spacing, relative to tubes of the first pass of tubes.
4. The heat exchanger of claim 1, further comprising a third pass
of tubes, wherein tubes of the third pass of tubes have at least
one of a decreased diameter and an increased tube spacing, relative
to tubes of the second pass of tubes.
5. The heat exchanger of claim 4, further comprising a fourth pass
of tubes, wherein tubes of the fourth pass of tubes have at least
one of a decreased diameter and an increased tube spacing, relative
to tubes of the third pass of tubes.
6. The heat exchanger of claim 1, wherein the heat exchanger is a
cross counterflow shell and tube heat exchanger.
7. The heat exchanger of claim 6, further comprising baffles to
provide structural support of the tubes.
8. The heat exchanger of claim 1, wherein a gas flow area of the
first pass of tubes is greater than a gas flow area of the second
pass of tubes.
9. The heat exchanger of claim 2, wherein the first fluid is a cold
gas and the second fluid is a warm liquid.
10. The heat exchanger of claim 9, wherein the cold gas has a
temperature of about -100.degree. F. and the warm liquid is a warm
liquid having a freezing point of about 12.degree. F.
11. A cross counterflow shell and tube heat exchanger comprising: a
cold fluid inlet delivering a cold gas to a first pass of tubes; a
second pass of tubes receiving the cold gas from the first pass of
tubes; and a warm liquid passing across the second pass of tubes
and then the first pass of tubes, wherein tubes of the second pass
of tubes have at least one of a decreased diameter and an increased
tube spacing, relative to tubes of the first pass of tubes, and
wherein the warm liquid remains in a liquid state as it passes
through the heat exchanger.
12. The heat exchanger of claim 11, wherein tubes of the second
pass of tubes have both a decreased diameter and an increased tube
spacing, relative to tubes of the first pass of tubes.
13. The heat exchanger of claim 11, further comprising a third pass
of tubes, wherein tubes of the third pass of tubes have at least
one of a decreased diameter and an increased tube spacing, relative
to tubes of the second pass of tubes.
14. The heat exchanger of claim 11, further comprising a fourth
pass of tubes, wherein tubes of the fourth pass of tubes have at
least one of a decreased diameter and an increased tube spacing,
relative to tubes of the third pass of tubes.
15. A method of heat exchange between a warm liquid and a cold gas
without freezing the warm liquid, the method comprising: passing
the cold gas through a first pass of tubes through the heat
exchanger; and passing the cold gas from the first pass of tubes
through a second pass of tubes, wherein tubes of the second pass of
tubes have at least one of a decreased diameter and an increased
tube spacing, relative to tubes of the first pass of tubes, and
wherein the warm liquid remains in a liquid state as it passes
through the heat exchanger.
16. The method of claim 15, wherein the warm liquid passes over the
tubes in a cross counterflow arrangement.
17. The method of claim 15, further comprising passing the cold gas
from the second pass of tubes through a third pass of tubes,
wherein tubes of the third pass of tubes have at least one of a
decreased diameter and an increased tube spacing, relative to tubes
of the second pass of tubes.
18. The method of claim 17, further comprising passing the cold gas
from the third pass of tubes through a fourth pass of tubes,
wherein tubes of the fourth pass of tubes have at least one of a
decreased diameter and an increased tube spacing, relative to tubes
of the third pass of tubes.
19. The method of claim 15, wherein the pressure drop across the
second set of tubes is less than the pressure drop across the first
set of tubes.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to apparatus and methods for
controlling temperatures in heat exchanger fluids and, more
particularly, to apparatus and methods for controlling tube
temperatures in cross counterflow shell and tube heat exchangers to
prevent freezing of fluids therein.
[0002] Generally, a heat exchanger is a device that may be used for
efficient heat transfer between multiple mediums. For example, a
heat exchanger may take in a first medium at a low temperature and
a second medium at a high temperature. Within the body of the heat
exchanger, the first and second mediums may come into contact,
either directly or indirectly via a solid wall. When the two
mediums come into contact, the high temperature of the second
medium may cause the first medium to raise its temperature, while
the low temperature of the first medium may also cause the second
medium to lower its temperature. In other words, heat is exchanged
between the two mediums, causing the first medium to increase in
temperature and the second medium to decrease in temperature.
[0003] A cross counterflow tubular heat exchanger is used to heat a
cold gas (for example, -100.degree. F.) using a liquid with a
freezing point at roughly 12.degree. F. In the last pass of the
heat exchanger, the cold inlet gas at -100.degree. F. (inside the
tubes) transfers heat to the warm liquid which has already been
cooled somewhat in the previous passes. The wall temperature must
be kept above the freezing point of the liquid to prevent the
liquid from freezing on the tubes. Freezing of the liquid must be
prevented so flow on the liquid side is not reduced due to the
frozen blockage and no frozen liquid can be allowed to spill off
and migrate downstream. Performance of the overall system will be
impaired if any freezing occurs.
[0004] As can be seen, there is a need for a heat exchanger
apparatus and heat exchange methods that may prevent freezing of
the heat exchange media.
SUMMARY OF THE INVENTION
[0005] In one aspect of the present invention, a heat exchanger
comprises a first pass of tubes carrying a cold fluid through the
heat exchanger; a second pass of tubes carrying the cold fluid from
the first pass of tubes, a warm fluid passing first over the second
pass of tubes and then the first pass of tubes, wherein tubes of
the second pass of tubes have at least one of a decreased diameter
and an increased tube spacing, relative to tubes of the first pass
of tubes.
[0006] In another aspect of the present invention, a cross
counterflow shell and tube heat exchanger comprises a cold fluid
inlet delivering a cold gas to a first pass of tubes; a second pass
of tubes receiving the cold gas from the first pass of tubes; a
warm liquid passing across the second pass of tubes and then the
first pass of tubes, wherein tubes of the second pass of tubes have
at least one of a decreased diameter and an increased tube spacing,
relative to tubes of the first pass of tubes, and wherein the warm
liquid remains in a liquid state as it passes through the heat
exchanger.
[0007] In a further aspect of the present invention, a method of
heat exchange between a warm liquid and a cold gas without freezing
the warm liquid comprises passing the cold gas through a first pass
of tubes through the heat exchanger; and passing the cold gas from
the first pass of tubes through a second pass of tubes, wherein
tubes of the second pass of tubes have at least one of a decreased
diameter and an increased tube spacing, relative to tubes of the
first pass of tubes, and wherein the warm liquid remains in a
liquid state as it passes through the heat exchanger.
[0008] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following drawings, description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is cross-sectional view of a heat exchanger according
to an embodiment of the present invention;
[0010] FIG. 2 is a cross-section view taken along line 2-2 of FIG.
1; and
[0011] FIG. 3 is a flow chart describing a method for preventing
freezing in a heat exchanger according to an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The following detailed description is of the best currently
contemplated modes of carrying out exemplary embodiments of the
invention. The description is not to be taken in a limiting sense,
but is made merely for the purpose of illustrating the general
principles of the invention, since the scope of the invention is
best defined by the appended claims.
[0013] Various inventive features are described below that can each
be used independently of one another or in combination with other
features.
[0014] Broadly, embodiments of the present invention provide
methods and apparatus for controlling tube temperatures to prevent
freezing of fluids in cross counterflow shell and tube heat
exchangers. Cold gas may flow inside the tubes of the heat changer
and warm liquid may flow outside the tubes. The tube diameter and
tube spacing may be varied through the tube passes through the heat
exchanger in order to provide a hot side conductance to cold side
conductance ratio which results in the tube temperature being
safely above the liquid freezing point. The heat exchanger may be
used in, for example, the aerospace industry as a fuel oil cooler
or as a preconditioner for reactants in spacecraft propulsion
systems.
[0015] As used herein, the modifier "cold", as used to refer to a
cold gas or a cold fluid, is a not meant to refer to any particular
temperature, but as a temperature relative to a "warm fluid" or a
"warm liquid". Consequently, as used herein, the modifier "warm",
as used to refer to a warm fluid or a warm liquid, is a not meant
to refer to any particular temperature, but as a temperature
relative to a "cold fluid" or a "cold gas".
[0016] Referring to FIG. 1, a cross counterflow shell and tube heat
exchanger 10 may receive a cold fluid, such as a cold gas, through
a cold fluid inlet 12. The cold gas may be between about
-80.degree. F. to about -120.degree. F., typically about
-100.degree. F. The cold gas may flow from the cold fluid inlet 12
to tubes 14 of a first cold fluid pass 16. The cold gas may flow
from the first cold fluid pass 16 to a second cold fluid pass 18.
The cold gas may flow from the second cold fluid pass 18, through a
third cold fluid pass 20 and a fourth cold fluid pass 22 before
exiting out a cold fluid outlet 24. While FIGS. 1 and 2 show four
cold fluid passes 16, 18, 20, 22, the heat exchanger 10 may include
at least two cold fluid passes and may include more than four cold
fluid passes.
[0017] The heat exchanger 10 may receive a warm fluid, such as a
warm liquid, through a warm fluid inlet 26. The warm liquid may
have a freezing point above the temperature of the cold gas flowing
through the tubes 14. For example, the warm liquid may have a
freezing point from about 0.degree. F. to about 20.degree. F. In
one embodiment, the warm liquid may have a freezing point of about
12.degree. F. The warm fluid may pass in a cross counterflow
arrangement through the heat exchanger 10. Baffles 28 may be
present inside the heat exchanger 10 to provide structural support
of the tubes. While the heat exchanger 10 is shown as a cross
counterflow heat exchanger, the tube design according to an
exemplary embodiment of the present invention, as described in
greater detail below, may be applied to other heat exchanger
designs, such as cross parallel flow heat exchangers.
[0018] Referring now to FIG. 2, as the cold gas enters the first
cold fluid pass 16, the number of tubes 14 and tube diameter is
such that the inside gas side 32 heat transfer is low relative to
the liquid side 34. The tube spacing in the first cold fluid pass
16 may be tighter (as compared to subsequent passes) so that the
outside liquid side 34 heat transfer is high relative to the inside
cold gas side 32. As used herein the tube spacing refers to the
non-dimensionalized tube spacing and may be defined as the center
to center spacing (between adjacent tubes) divided by the diameter
of the tubes.
[0019] In the second cold fluid pass 18, after the cold gas within
the tubes 14 has warmed some, the tube diameter can be decreased to
improve the heat transfer on the inside gas side 32. The tube
spacing in the second cold fluid pass 18 may be increased relative
to the first cold fluid pass 16. In optional subsequent passes on
the liquid side (such as third cold fluid pass 20 and fourth cold
fluid pass 22), the tube spacing can be increased in order to
reduce the liquid side pressure drop. Using this tube diameter and
spacing design, the wall temperature of the tubes 14 may be
controlled to prevent freezing of the liquid on the tubes 14. In
addition, the tube diameter and spacing design, in a cross
counterflow arrangement, can be used to reduce the overall size of
the heat exchanger, relative to conventional cross parallel flow
arrangements.
[0020] Referring to FIG. 3, a method 40 for preventing liquid from
freezing in a heat exchanger (e.g., heat exchanger 10) may include
a first step 42 of passing the cold gas through a first pass of
tubes through the heat exchanger. The first tube diameter and the
first tube spacing may be designed such that the gas flow area is
large (relative to subsequent tube passes through the heat
exchanger). Such a design may provide a low heat transfer
coefficient between a cold gas in the tubes and a warm liquid
outside of the tubes. A second step 44 may include passing the cold
gas from the first pass of tubes through a second pass of tubes,
wherein tubes of the second pass of tubes have at least one of a
decreased diameter and an increased tube spacing, relative to tubes
of the first pass of tubes, and wherein the warm liquid remains in
a liquid state as it passes through the heat exchanger. Optional
third and fourth passes of tubes, as shown in steps 46 and 48, may
have at least one of a decreased diameter and an increased tube
spacing, relative to the immediately preceding tube pass. The
increased tube spacing may help limit the pressure drop on the
liquid side of the heat exchanger.
[0021] It should be understood, of course, that the foregoing
relates to exemplary embodiments of the invention and that
modifications may be made without departing from the spirit and
scope of the invention as set forth in the following claims.
* * * * *