U.S. patent application number 10/755165 was filed with the patent office on 2005-07-14 for double-tube apparatus for use in a heat exchanger and method of using the same.
Invention is credited to Nadig, Ranga.
Application Number | 20050150640 10/755165 |
Document ID | / |
Family ID | 34739522 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050150640 |
Kind Code |
A1 |
Nadig, Ranga |
July 14, 2005 |
Double-tube apparatus for use in a heat exchanger and method of
using the same
Abstract
An apparatus, system, and method for facilitating the transfer
of heat between two fluids where preventing the mixing of the two
fluids is imperative. In one aspect the invention is an apparatus
for use in a heat exchanger system comprising at least one outer
tube having an inner tube extending through the at least one outer
tube so as to form an interstitial space between each inner tube
and each outer tube; and a ridge located in each interstitial space
and contacting the inner tube and outer tube so as to form a fluid
passageway through each interstitial space. Preferably, the ridge
is helical in shape and extends the entire length of the
interstitial space. In other aspects, the invention is a heat
exchanger system incorporating the apparatus and a method of using
the apparatus.
Inventors: |
Nadig, Ranga; (Cherry Hill,
NJ) |
Correspondence
Address: |
COZEN O'CONNOR, P.C.
1900 MARKET STREET
PHILADELPHIA
PA
19103-3508
US
|
Family ID: |
34739522 |
Appl. No.: |
10/755165 |
Filed: |
January 9, 2004 |
Current U.S.
Class: |
165/141 |
Current CPC
Class: |
F28D 7/103 20130101;
F28F 1/36 20130101 |
Class at
Publication: |
165/141 |
International
Class: |
F28D 007/10 |
Claims
What is claimed is:
1. An apparatus for use in a heat exchanger system comprising: an
outer tube, an inner tube extending through the outer tube so as to
form an interstitial space between the inner tube and the outer
tube; and a ridge located in the interstitial space and contacting
the inner tube and the outer tube so as to form a fluid passageway
through the interstitial space.
2. The apparatus of claim 1 wherein the inner tube extends through
at least the entire length of the outer tube.
3. The apparatus of claim 1 wherein the ridge extends at least the
entire length of the interstitial space.
4. The apparatus of claim 1 wherein the ridge is helical in
shape.
5. The apparatus of claim 4 further comprising a second helical
ridge located in the interstitial space and contacting the inner
tube and the outer tube so as to form a second fluid passageway
through the interstitial space.
6. The apparatus of claim 1 wherein the ridge is formed into an
outside surface of the inner tube.
7. The apparatus of claim 1 wherein the ridge is formed into an
inside surface of the outer tube.
8. The apparatus of claim 1 wherein the outer tube is constructed
of a metal.
9. The apparatus of claim 1 wherein the inner tube is constructed
of a metal.
10. The apparatus of claim 1 wherein the ridges is constructed of a
metal.
11. A heat exchanger system comprising: a shell forming a chamber;
an inner tube positioned within the chamber; an outer tube
surrounding at least a portion of the inner tube so as to form an
interstitial space between the inner tube and the outer tube; a
ridge located in the interstitial space and contacting the inner
tube and the outer tube so as to form a fluid passageway through
the interstitial space; the shell having openings for supplying and
discharging a tubeside fluid through the inner tubes; the shell
having openings for supplying and discharging an inert fluid to the
interstitial space; and the shell having openings for supplying and
discharging a shellside fluid through the chamber so that the
shellside fluid contacts an outside surface of the outer tube.
12. The system of claim 11 further comprising means to supply the
inert fluid through the interstitial space at a pressure higher
than pressures of the tubeside fluid and the shellside fluid.
13. The system of claim 12 further comprising means to detect
pressure within the interstitial space.
14. The system of claim 13 further comprising a controller coupled
to the pressure detection means, the controller programmed to
trigger an alarm upon receiving a pressure drop signal from the
pressure detection means.
15. The system of claim 11 further comprising outer tube sheets for
supporting the inner tube within the chamber, the outer tube sheets
located in the chamber of the shell so as to allow only the
tubeside fluid to flow into the inner tube.
16. The system of claim 15 further comprising inner tube sheets for
supporting the outer tube, the inner tube sheets located in the
chamber between the outer tube sheets and positioned so as to allow
only the inert fluid to flow into the interstitial space.
17. The system of claim 16 further comprising a plurality of
baffles located in the shell chamber between the inner tube
sheets.
18. The system of claim 11 wherein the inner tube extends through
at least the entire length of the outer tube.
19. The system of claim 11 wherein the ridge extends at least the
entire length of the interstitial space.
20. The system of claim 11 wherein the ridge is helical in
shape.
21. The system of claim 20 further comprising a second helical
ridge located in the interstitial space and contacting the inner
tube and the outer tube so as to form a second fluid passageway
through the interstitial space.
22. The system of claim 11 wherein the ridge is formed into an
outside surface of the inner tube.
23. The system of claim 11 wherein the ridge is formed into an
inside surface of the outer tube.
24. The system of claim 11 comprising a plurality of the outer
tubes, each outer tube surrounding at least a portion of an inner
tube so as to form an interstitial space between each inner tube
and each outer tube, and a ridge located in each interstitial space
that contacts the respective inner tube and outer tube so as to
form fluid passageways through each respective interstitial
space.
25. A method of cooling or heating fluids comprising: providing an
apparatus comprising an outer tube, an inner tube extending through
the outer tube so as to form an interstitial space, and a ridge
located in the interstitial space and contacting the inner tube and
the outer tube so as to form a fluid passageway through the
interstitial space; flowing a tubeside fluid through the inner
tube; supplying an inert fluid to the interstitial space; and
flowing a shellside fluid over an outside surface of the outer
tube.
26. The method of claim 25 wherein the ridge is helical in shape
and extends along at least the entire interstitial space.
27. The method of claim 25 wherein the inert fluid is flowing
through the passageway of the interstitial space at a pressure
higher than pressures of the tubeside fluid and the shellside
fluid.
28. The method of claim 27 further comprising the step of
monitoring the pressure of the inert fluid for a pressure drop.
29. The method of claim 28 further comprising the step of upon
detecting a pressure drop, signaling the pressure drop to an
operator or control system.
30. The method of claim 25 wherein the ridge is formed into an
outside surface of the inner tube.
31. The method of claim 25 wherein the ridge is formed into an
inside surface of the outer tube.
32. The method of claim 25 wherein the inert fluid is non-reactive
with the shellside fluid and the tubeside fluid.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of heat
exchangers and specifically to heat exchangers having concentric
tubular members for preventing mixing between fluids involved in
the heat exchange.
BACKGROUND OF THE INVENTION
[0002] A simple heat exchanger consists of a shell containing a
large number of tubes with fluid flowing inside and outside the
tubes. The fluid flowing inside the tubes is known as tube-side
fluid whereas the fluid flowing outside the tubes is known as the
shellside fluid. During normal operation, heat will be transferred
from the hotter fluid, through the walls of the tube, and into the
cooler fluid. Depending on the relative temperatures of the fluids
and the desired result, heat can be transferred either to or from
the tube-side fluid flow.
[0003] In certain industrial applications, mixing between the
shellside and tubeside fluid leads to violent and/or hazardous
chemical reactions and/or the creation of toxic or flammable
fluids. In such application mixing between the tubeside and
shellside fluids must be prevented. Double-tube heat exchangers
have been developed to protect against this danger. In a
double-tube heat exchanger, the shellside fluid flows outside an
outer tube. The tubeside fluid flows inside the inner tube. The
inner tube is positioned within and concentric to the outer tube so
that an interstitial space exists between the inner tube and the
outer tube. The interstitial space is usually filled with an inert
fluid. The inert fluid can be stagnant or designed to flow through
the interstitial space. In the event of a leakage, the inert fluid
flows into the shellside or the tubeside thereby preventing mixing
between the shellside and tubeside fluids. An example of such a
double-tube heat exchanger is disclosed in U.S. Pat. No. 4,538,674,
Schluderberg, which is hereby incorporated by reference in its
entirety.
[0004] While existing double-tube heat exchangers help protect
against the mixing of the tube-side fluid and the shell-side fluid,
a major problem of such heat exchangers has been the ability to
properly support the inner tube within the outer tube. In existing
systems, the inner tubes are either not properly supported within
the outer tube or are supported in such a way that fluid flow of
the inert fluid though the interstitial space is impeded.
Additionally, existing systems are very complicated, difficult and
expensive to manufacture. Thus, a need exists for a double-tube
apparatus for use in heat exchanger system that properly supports
the inner tube within the outer tube without seriously impeding the
ability of the inert fluid to flow through the interstitial
space.
[0005] An additional problem with existing double-tube heat
exchangers is that impeded flow of fluid through the interstitial
space reduces the ability to transfer heat between the tubeside
fluid and the shellside fluid. Thus, there is a further need for a
double tube apparatus for use in a heat exchanger system that
improves heat transfer capabilities.
DISCLOSURE OF THE INVENTION
[0006] These and other problems are solved by the present invention
which in one aspect is an apparatus for use in a heat exchanger
system comprising: an inner and outer tube, the inner tube
extending through the outer tube so as to form an interstitial
space; and a ridge located between an outside surface of the inner
tube and an inside surface of the outer tube, the ridge contacting
the inside surface and the outside surface at specified locations
so as to form a fluid passageway through the interstitial space.
The ridge contact points are designed to eliminate flow induced
vibration. The ridge is preferably helical in shape and extends the
entire length of the interstitial space formed between the outer
and the inner tube. The ridge can be installed on the outside
surface of the inner tube or the inside surface of the outer
tube.
[0007] By providing contact between the inner and outer tubes
within the interstitial space, the ridge helps support the inner
tube within the outer tube while still maintaining a fluid flow
passageway through the interstitial space. As such, the inner tube
is more robustly supported within the outer tube without seriously
impacting the flow of fluids through the interstitial space,
thereby improving heat transfer capabilities. When the ridge is
helical in shape, the ridge will further improve heat transfer
capabilities of the double tube apparatus. The helical ridge forces
the fluid through the interstitial space along a helical
passageway, increasing the amount of time the fluid is in surface
contact with the outside surface of the inner tubular member. The
amount of heat transferred to the fluid in the interstitial space
is thereby increased.
[0008] It is further preferable that the inner tube extend through
at least the entire length of the outer tube. In an alternative
embodiment, the apparatus can further include a second helical
ridge located between the outside surface of the inner tube and the
inside surface of the outer tube. As with the first ridge, the
second helical ridge will contact both the inside surface of the
outer tube and the outside surface of the inner tube so as to form
a second fluid passageway through the interstitial space. This
second helical ridge will add further support for the inner tube
and provide a greater area of contact between the inner and outer
tube, thereby further increasing heat transfer through
conduction.
[0009] The selection of the inner and outer tube material is based
on the fluid/tube material compatibility. The inner and outer tubes
can be constructed of a variety of heat exchanger tube materials
including but not limited to steel, copper, brass, iron, aluminum,
titanium and zirconium. In such an embodiment, the ridge should
also be constructed of a metal that is compatible with the tubeside
fluid and the shellside fluid and can be attached to either the
inner or outer tube.
[0010] In another aspect, the invention is a heat exchanger system
incorporating the above described double-tube apparatus.
Specifically, in this aspect, the invention is a heat exchanger
system comprising: a shell containing an outer tube, an inner tube
positioned within the outer tube so as to form an interstitial
space between the inner tube and the outer tube; a ridge located
between an outside surface of the inner tube and an inside surface
of the outer tube, the ridge contacting the inside surface of the
outer tube and the outside surface of the inner tube so as to form
a fluid passageway through the interstitial space. The shell has
openings for supplying and discharging a shellside fluid that flows
outside the outer tubes, an annular ring having openings for
supplying and discharging an inert fluid to the interstitial space,
and a channel/bonnet having openings for supplying and discharging
a tubeside fluid that flows through the inner tube.
[0011] In order to prevent mixing between the tubeside fluid
flowing through the inner tube and the shellside fluid flowing
outside the outer tube, the system will preferably include means to
supply the inert fluid to the interstitial space at a pressure
higher than the pressures of the tubeside and shellside fluids. As
such, if a leak develops in the inner or outer tubes, the inert
fluid will flow outward from the interstitial space, reducing the
possibility that the tubeside and shellside fluids will come into
contact with one another. In order to detect the presence of a leak
in the system, the system preferably comprises a means to monitor
the pressure within the interstitial space, such as a pressure
sensor. In this embodiment, a controller is preferably coupled to
the pressure detection means and an alarm. The controller is
programmed to trigger an alarm upon receiving a signal indicating a
pressure drop within the interstitial space from the sensor.
[0012] The system also preferably includes outer tube sheets for
supporting the inner tubes. These outer tube sheets are designed so
as to allow only the tubeside fluid to flow through the inner
tubes. Inner tube sheets are also preferably provided for
supporting the outer tubes. These inner sheet are located adjacent
to and between the outer tube sheets and are positioned so as to
allow only the inert fluid to flow into the interstitial space
between the outer and inner tubes. A plurality of baffles can be
provided in the shell between the inner tube sheets. A single
system will preferably incorporate a plurality of the double-tube
apparatus within a single shell. The specific preferred
characteristics of the double-tube apparatus discussed above can be
incorporated into the system.
[0013] In yet another aspect, the invention is a method for cooling
or heating fluids comprising: an apparatus comprising an outer
tube, an inner tube extending through the outer tube so as to form
an interstitial space, a ridge located between an outside surface
of the inner tube and the inside surface of the outer tube, the
ridge contacting the inside surface of the inner tube and the
outside surface of the inner tube so as to form a fluid passageway
through the interstitial space; the tubeside fluid flowing through
the inner tube; the shellside fluid flowing outside the outer tube,
an inert fluid supplied to the interstitial space. The inert fluid
can be flowing through the interstitial space or stagnant
therein.
[0014] The inert or interstitial fluid must be compatible with the
tubeside and shellside fluids and the inner and outer tube
materials. The inert fluid is application and material
sensitive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side view of a heat exchanger according to an
embodiment of the present invention.
[0016] FIG. 2 is a cross-sectional view of the heat exchanger of
FIG. 1 showing a concentric tube apparatus according to an
embodiment of the present invention positioned therein.
[0017] FIG. 3 is a perspective view of a section of the concentric
tube apparatus shown in FIG. 2.
[0018] FIG. 4 is a top view of a section of an embodiment of the
inner tube of the concentric tube apparatus of FIG. 3.
[0019] FIG. 5 is a cross sectional view of the concentric tube
apparatus of FIG. 3 taken along line V-V.
MODES FOR CARRYING OUT THE INVENTION
[0020] Referring first to FIG. 1, heat exchanger 10 is illustrated
according to an embodiment of the present invention. Heat exchanger
10 comprises a cylindrical shell 11 having flanges 12 at its ends.
End covers 13 are secured to flanges 12 to form a tubeside chamber
14 (FIG. 2). End covers 13 can be secured to flanges 12 by welding,
bolting, or any other means known in the art. Alternatively, shell
11 can be formed so as to have end covers 13 integrally formed.
However, it is preferable that covers 13 be removable from shell 11
for access into tubeside chamber 14 (FIG. 2) for repair or
replacement of the parts therein. Shell 11 and covers 13 should be
made from a material that is resistant to the tubeside fluid being
used.
[0021] Heat exchanger 10 has a number of outlets and inlets 15-20.
Outlets and inlets 15-20 form passageways through shell 11 so that
fluids can pass into or out of different constituent chambers of
tubeside chamber 14 (FIG. 2). More specifically, heat exchanger 10
includes tube-side fluid inlet 17, tube-side fluid outlet 20,
shell-side fluid inlet 16, shell-side fluid outlet 18, interstitial
fluid inlet 15, and interstitial fluid outlet 19. As used herein,
the term fluid includes both liquids, gases, and combinations of
the two.
[0022] Referring now to FIG. 2, shell 11 is divided into numerous
chambers along its length These chambers include tube-side fluid
spaces 21, intermediate fluid spaces 22, and shell-side fluid space
23. Tube-side fluid spaces 21 are hermetically separated from the
rest of the spaces by outer tube sheets 24. Intermediate fluid
spaces 22 are formed between, and hermetically separated from the
rest of the spaces by outer tube sheets 24 and inner tube sheets
25. Inner tube sheets 25 form shell-side fluid space 23. A
plurality of baffles 26 are provided within shell-side fluid space
23. Concentric tube apparatus 40 is positioned within the shell 11.
Concentric tube apparatus 40 comprises inner tube 41 and outer tube
42. Inner tube 41 extends through outer tube 42 forming an
interstitial space 43 therebetween.
[0023] Referring now to FIGS. 3 and 4, concentric tube apparatus 40
comprises inner tube 41 and outer tube 42. Inner tube 41 extends
through outer tube 42 forming an interstitial space 43 there
between. Outer tube 42 has opening 45 extending through its entire
length. Outer tube 42 has a smooth outside surface 48 and smooth
inside surface 49 (FIG. 5). Inner tube 41 has opening 46 extending
through its entire length. A helical ridge 44 is formed onto the
outside surface 47 of inner tube 41. Inner tube 41 and helical
ridge 44 are sized so that inner tube 41 can fit within and extend
through opening 45 of outer tube 42.
[0024] Referring now to FIGS. 3 and 5, when inner tube 41 is
positioned within and extends through opening 45 of outer tube 42,
an interstitial space is formed between the outside surface 47 of
inner tube 41 and the inside surface 49 of outer tube 42.
Interstitial space 43 extends the entire length of outer tube 42.
Inner tube 41 and helical ridge 44 are sized so that helical ridge
44 contacts inside surface 49 of outer tube 42 along the top
surface of the helical ridge 44 when assembled. When inner tube 41
extends through the opening 45 of outer tube 42, helical ridges 44
forms a helical passageway through the interstitial space that
allows fluid to pass through the entire length of interstitial
space 43. In addition to forming a helical passageway through
interstitial space 43, helical ridge 44 acts to support inner tube
41 within outer tube 42 and acts to maintain the existence of
interstitial space 43.
[0025] While the ridge 44 on the outside surface 47 of inner tube
41 is illustrated as a single helix, the invention is not so
limited. The ridge can take on any shape, including a plurality of
straight ridges or a plurality of semi-circular ridges spaced along
the length of the inner tube. Additionally, a second helical ridge
can be added to form a second helical passageway through the
interstitial space. Moreover, it is not necessary to form the ridge
onto the outside surface of the inner tube. Alternatively, the
ridge can be a separate piece or formed onto the inside surface of
the outer tube. By ensuring that the ridge contacts both the inside
surface of the outer tube and the outside surface of the inner
tube, heat can be transferred between the two tubes through
conduction. Preferably, the ridge is welded or brazed to the
surfaces. Increasing the contact area of the ridge with the
surfaces of the inner and outer tubes will increase heat transfer
by conduction.
[0026] Finally, the helical ridge is not limited to any specific
pitch. The pitch of the helical shape can be varied depending on
system requirements. Inner tube 41 can be constructed of a material
compatible with the tubeside fluid, shellside fluid and
interstitial fluid. The ridge is made from material that is
compatible with the tubeside fluid, the shellside fluid, and the
inner and outer tubesheet materials.
[0027] Referring again to FIG. 2, concentric tube apparatus 40 is
positioned in chamber 14 of shell 11. Specifically, outer tube
sheets 24 support inner tube 41 in a center portion of chamber 14.
Inner tube 41 extends through the entire length of outer tube 42.
The ends of inner tube 41 are connected to outer tube sheets 40 so
as to form a hermetically sealed fluid passageway between tube-side
fluid spaces 21 through opening 46 of inner tube 41. As such,
tubeside fluid 50 can flow into tube-side fluid inlet 17, through
opening 46 of inner tube 41, and out through tube-side fluid outlet
20. It is a common practice to put the hazardous or toxic fluid
through the inner tubes.
[0028] Outer tube 42 is supported within chamber 14 by inner tube
sheets 25. The ends of outer tube 42 are connected to inner tube
sheets 25 so as to form a fluid passageway between intermediate
fluid spaces 22 through interstitial space 43. Interstitial space
43 forms a fluid passageway between intermediate fluid spaces 22.
As such, inert fluid 51 flows into interstitial fluid inlet 52,
through interstitial space 43 (along the helical passageway formed
by helical ridge 44), and out through interstitial fluid outlet
19.
[0029] Baffles 26 are provided in shell-side fluid space 23.
Preferably, the helical ridge 44 (FIG. 3) extends along the entire
length of interstitial space 43 formed between inner tube 41 and
outer tube 42. This helps support the inner tube 41 within the
outer tube 42 while still allowing the inert fluid 51 to pass
through the interstitial space with minimal obstruction.
[0030] Shell-side inlet 52 is used to permit the flow of shellside
fluid 52 into shell-side fluid space 23. Upon entering shell-side
fluid space 23, the shellside fluid 52 will contact the outside
surface 48 (FIG. 5) of the outer tube 42. The shellside fluid 52
exits the shell-side fluid space 23 through shell-side fluid outlet
18. The shellside fluid 52 is usually the non-hazardous, non toxic
fluid intended to cool or heat the tubeside fluid. Depending on the
requirements of the system, heat will be either transferred to the
shellside fluid 52 from the tubeside fluid 50 or vice versa.
[0031] Finally, it is preferable that the inert fluid 51 flowing
through the interstitial space be at a pressure greater than the
pressures of the tubeside and shellside fluids 50, 52. This can be
done using a pump and/or valving system. Providing the inert fluid
51 at a higher pressure than the tubeside and shellside fluids 50,
52 helps prohibit the mixing of the tubeside and shellside fluids
50, 52 in the event of a leak. If a leak occurs in either inner
tube 41 or outer tube 42, inert fluid 51 will respectively flow
either into inner tube 41 or into shellside fluid space 23. The
increased pressure will prohibit tubeside and shellside fluids 50,
52 from flowing into interstitial space 43. As a safety feature,
pressure sensor 60 (generically illustrated as a rectangle in FIG.
2) is provided within intermediate fluid space 22. Alternatively,
pressure sensor 60 can be provided within interstitial space 43
itself. Pressure sensor 60 measures the pressure within
intermediate fluid space 22 (which is the same as the pressure in
interstitial space 43) and transmits a data signal indicating the
pressure reading to a properly programmed processor (not
illustrated). The processor analyzes the data and compares the
measurement to a pre-programmed set value. If the pressure reading
is below the pre-programmed critical value, as would be the case if
there was a leak, the processor will send a signal to an alarm that
will be activated, informing an operator that there is a problem.
Optionally, the processor can be programmed to shut down the heat
exchanger 10 in a safe fashion.
[0032] While the invention has been described and illustrated in
sufficient detail that those skilled in this art can readily make
and use it, various alternatives, modifications, and improvements
should become readily apparent without departing from the spirit
and scope of the invention.
* * * * *