U.S. patent application number 15/699766 was filed with the patent office on 2018-03-15 for double-wall heat exchanger.
The applicant listed for this patent is Climate Master, Inc.. Invention is credited to Michael F. Taras, Steven A. Trimble.
Application Number | 20180073811 15/699766 |
Document ID | / |
Family ID | 61559745 |
Filed Date | 2018-03-15 |
United States Patent
Application |
20180073811 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
March 15, 2018 |
DOUBLE-WALL HEAT EXCHANGER
Abstract
An improved double-wall heat exchanger in which the safety
"leak" space between heat exchange surfaces forming channels for
the fluids exchanging heat is filled with a heat transfer medium
with improved thermal conductivity in comparison to air. Pressure
responsive rupture points allow release of the heat transfer medium
and the heat exchange fluid in the event of failure of one of the
containment surfaces. Metal-to-metal heat transfer points are
dispersed in the gap to further enhance heat transfer between the
hot and cold heat exchange fluid streams.
Inventors: |
Taras; Michael F.; (Oklahoma
City, OK) ; Trimble; Steven A.; (Broken Arrow,
OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Climate Master, Inc. |
Oklahoma City |
OK |
US |
|
|
Family ID: |
61559745 |
Appl. No.: |
15/699766 |
Filed: |
September 8, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62393404 |
Sep 12, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 3/046 20130101;
F28D 7/103 20130101; F28F 2265/06 20130101; F28F 3/02 20130101;
F28F 1/003 20130101; F28D 9/0012 20130101; F28F 2265/16 20130101;
F28D 15/00 20130101; F28F 23/00 20130101; F28D 9/00 20130101; F28F
3/005 20130101; F28D 15/02 20130101; F28D 9/005 20130101 |
International
Class: |
F28D 9/00 20060101
F28D009/00; F28F 3/04 20060101 F28F003/04; F28F 3/00 20060101
F28F003/00 |
Claims
1. A double-wall heat exchanger comprising: a first conduit for a
first heat exchange fluid and having a heat transfer surface; a
second conduit for a second heat exchange fluid and having a heat
transfer surface; wherein the heat transfer surface of the first
conduit and the heat transfer surface of the second conduit
together define a heat transfer space bounded by a perimeter; and
wherein the heat transfer space is occupied by a thermally
conductive medium.
2. The double-wall heat exchanger of claim 1 wherein the heat
exchanger is a plate heat exchanger.
3. The double-wall heat exchanger of claim 1 wherein the heat
exchanger is a tube-in-tube heat exchanger.
4. The double-wall heat exchanger of claim 1 wherein the perimeter
of the heat transfer space includes a rupture point configured to
permit release of thermally conductive medium if the internal
pressure of the heat transfer space exceeds a predetermined
level.
5. The double-wall heat exchanger of claim 4 wherein the heat
exchanger comprises a plurality of solid heat transfer contacts
providing surface-to-surface heat transfer connections between the
heat transfer surface of the first conduit and the heat transfer
surface of the second conduit.
6. The double-wall heat exchanger of claim 1 wherein the thermal
conductivity of the thermally conductive medium exceeds 0.134 W/(m
K) at 288K temperature.
7. The double-wall heat exchanger of claim 1 wherein the heat
exchanger comprises a plurality of solid heat transfer contacts
providing surface-to-surface heat transfer connections between the
heat transfer surface of the first conduit and the heat transfer
surface of the second conduit.
8. The double-wall heat exchanger of claim 7 wherein the solid heat
transfer contacts are formed of wire mesh or foam filling the heat
transfer space.
9. The double-wall heat exchanger of claim 1 wherein the thermally
conductive medium is a single phase medium.
10. The double-wall heat exchanger of claim 1 wherein the thermally
conductive medium is a phase change medium.
11. The double-wall heat exchanger of claim 1 wherein the thermally
conductive medium comprises a nano-fluid.
12. The double-wall heat exchanger of claim 11 wherein the
nanoparticles in the nano-fluid include metal particles having a
thermal conductivity greater than 6.6 W/(m K) at 288K temperature.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/393,404, filed Sep. 12, 2016, which is
incorporated by reference herein in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
[0002] [NOT APPLICABLE]
FIELD OF THE INVENTION
[0003] The present invention relates generally to heat exchangers
used in heating, ventilation, and air conditioning systems and,
more particularly but without limitation, to double-wall heat
exchangers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate one or more
embodiments of the present invention and, together with this
description, serve to explain the principles of the invention. The
drawings merely illustrate preferred embodiments of the invention
and are not to be construed as limiting the scope of the
invention.
[0005] FIG. 1 is a schematic diagram of a section of a double-wall
plate heat exchanger made in accordance with a preferred embodiment
of the present invention.
[0006] FIG. 2 is schematic diagram of a section of a double-wall
tube-in-tube heat exchanger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0007] Sustainability initiatives and regulations in the heating,
ventilation, air conditioning, and refrigeration (HVAC&R)
industry drive an increase in the system efficiency and heat
exchanger effectiveness thresholds. At the same time, safety
standards and building codes require enhanced rigidity and
durability in the heat exchanger designs providing an improved
protection to the end user. These trends are contradictory and
steer the heat exchanger design to one end of the spectrum or the
other. Consequently, such competing objectives have led the
industry to design larger heat exchangers that in turn increase the
overall footprint and cost of the HVAC&R system.
[0008] Double-wall heat exchangers are an example of this ongoing
struggle. Double-wall designs for brazed plate and tube-in-tube
heat exchangers include a space or gap between the cooling and
heating media. This gap is designed to prevent direct leakage from
the high pressure side to a low pressure side, which in turn leads
to the system over-pressurization and fluid cross-contamination.
While the double-wall construction improves safety, the space
between the heat exchange fluids significantly increases thermal
resistance thereby reducing the effectiveness of the heat
exchanger.
[0009] The present invention provides a double-wall heat exchanger
that accommodates the goals of safety and improved efficiency. In
accordance with the invention, the space between the double-walls
is filled with thermally conductive heat transfer media.
Additionally, intentional weak points or rupture points in the
walls forming the boundaries of the gap may be designed to rupture
and release pressure in the event of leakage to prevent
over-pressurization. Still further, heat transfer may be enhanced
by increasing a number of solid thermally conductive contact points
between the surfaces forming the gap.
[0010] The present invention is applicable to any double-wall heat
exchanger design, including without limitation brazed plate heat
exchangers and tube-in-tube heat exchangers. As the specific
designs of the various types of heat exchanger are well known, the
entire heat exchangers will not be shown or described in detail
herein. By way of example only, one double-wall brazed plate heat
exchanger is shown and described in U.S. Pat. No. 9,163,882,
entitled "Plate Heat Exchanger with Channels for `Leaking Fluid`"
issued Oct. 20, 2015, and is incorporated herein by reference.
[0011] Turning now to the drawings and to FIG. 1 in particular,
there is shown therein a diagrammatic illustration of a section of
a plate heat exchanger and designated generally at 100. The heat
exchanger comprises plates "P" with grooves or ribs that are
aligned to form flow passages for heat exchange fluids. Typically,
but not always, the flow passages direct a first heat exchange
fluid in one direction and a second heat exchange fluid in an
opposite direct. It will be understood that assembled heat
exchanger comprises multiple plates that form multiple flow paths
in each direction, typically in an alternating manner. As used
herein, "first conduit" refers to the collective flow paths in the
first direction, and "second conduit" refers to the collective flow
paths in the second, opposite direction.
[0012] By way of example, as illustrated in FIG. 1, the plates P1
and P2 form flow passage A, Plates P3 and P4 form flow passage B,
plates P5 and P6 form flow passage C, and plates P7 and P8 form
flow passage D. As indicated by the arrows, flow passages A and C
direct fluid in the first direction (upward as viewed in the
drawings), and flow passages B and D direct fluid in the opposite
direction (downward as viewed in the drawing). Thus, the flow
passages A and C collectively comprise the first conduit for a
first heat exchange fluid, and flow passages B and D collectively
comprise the second conduit for the second heat exchange fluid.
[0013] With continued reference to FIG. 1 and as previously
indicated, the heat exchanger 100 is designed as a double-wall heat
exchanger. To that end, the plates P1-P8 are configured to form a
gap or space between opposing flow passages, which space is
referred to herein as a heat transfer space. More specifically, the
external surfaces of the plates, that is, the surfaces that are
outside of the flow passages and that oppose each other define the
heat transfer space. Thus, the heat transfer space S1 is formed by
the heat transfer surface T1 of plate P2 and the heat transfer
surface T2 of plate P3, the heat transfer space S2 is formed by the
heat transfer surface T3 of plate P4 and the heat transfer surface
T4 of plate P5, and the heat transfer space S3 is formed by the
heat transfer surface T5 of plate P6 and the heat transfer surface
T6 of plate P7. The periphery of the plates is sealed in a known
manner, such as by brazing, welding, or soldering, and this
provides a closed perimeter 102 for the heat transfer spaces. This
perimeter 102 is indicated only diagrammatically in the
drawings.
[0014] In conventional double-wall heat exchangers, the gap may be
occupied by air. However, in accordance with a preferred embodiment
of the present invention, the heat transfer spaces S1-S3 are filled
by a thermally conductive medium M. As used herein, "thermally
conductive medium" denotes a medium that is more conductive than
air. Preferably, the thermal conductivity of the thermally
conductive medium exceeds about 0.134 W/(m K) at 288K temperature.
More preferably, the thermal conductivity of the thermally
conductive medium exceeds about 0.182 W/(m K) at 288K temperature,
and most preferably, the thermal conductivity of the thermally
conductive medium is at least about 0.200 W/(m K) at 288K
temperature. Suitable heat transfer media include, without
limitation, water, propylene glycol, ethylene glycol, HVAC&R
refrigerants, nano-fluids containing aluminum oxide, copper oxide,
or titanium oxide.
[0015] The thermally conductive medium M may be a gas, a liquid, a
solid such as a wire mesh or porous foam, a gel, a slurry, a
suspension, a colloidal dispersion, or a phase change medium. The
medium M may be a single phase medium, such as a water.
Alternately, the medium M may be a phase change medium, such as a
refrigerant. In one embodiment of the invention, the medium M
comprises a nano-fluid in which the nano-particles include metal
particles of any size, form and shape having a thermal conductivity
greater than about 6.6 W/(m K) at 288K temperature. More
preferably, the thermal conductivity of the nanoparticles exceeds
about 13.2 W/(m K) at 288K temperature, and, most preferably, the
thermal conductivity of the nanoparticles is at least about 19.8
W/(m K) at 288K temperature.
[0016] Referring still to FIG. 1, conductivity of the heat transfer
spaces S1-S4 may be enhanced by introducing at least one extra and
preferably a plurality solid heat transfer contact points,
designated generally as "CP," that provide direct
surface-to-surface heat transfer connections between the heat
transfer surfaces of the first conduit and the heat transfer
surfaces of the second conduit. The size, number, and position of
these contacts CP may vary. These contacts may be made of metal and
most preferably will be formed of a relatively heat conductive
metal. Such metals may include copper, aluminum, titanium, and
stainless steel and may take the form of a solid or a porous
surface. These contacts CP may be formed by any suitable process.
For example, metal beads may be positioned in the space S to
provide separate metal-to-metal contact to improve heat transfer
between the hot and cold heat exchange fluids. Alternately, the
contacts CP may be formed by soldering, brazing, welding or a
combination of these techniques. Still further, the heat transfer
contacts CP may be used alone, that is, without the thermally
conductive medium M, or in conjunction with the medium.
[0017] In the event of a failure of one of the plates that results
in heat exchange fluid leaking into the a heat transfer space, the
heat exchanger 100 may include at least one rupture point "R" in
the perimeter for each of the heat transfer spaces S1-S3. These
rupture points R will be designed to burst and permit release of
thermally conductive medium M if the internal pressure of the heat
transfer space exceeds a predetermined level.
[0018] Turning now to FIG. 2, various features of the present
invention will be explained as applied to a tube-in-tube heat
exchanger designated generally at 200. In this type of heat
exchanger (also called concentric tube or double-pipe type heat
exchangers), opposing flow paths are formed by concentric tubes.
Thus, in the exemplary form shown, the heat exchanger 200 comprises
an innermost tube 202, an outermost tube 204, and an intermediate
tube 206. The innermost tube 202 forms a flow passage A for a first
heat exchange fluid to flow in a first direction (downward as
viewed in the drawings). The annulus formed by the outer diameter
of the tube 206 and the inner diameter of the tube 204 forms a flow
passage B that directs a second heat exchange fluid in the opposite
direction (upward as viewed in the drawing). Thus, the flow passage
A comprises the first conduit for a first heat exchange fluid, and
the flow passage B comprises the second conduit for the second heat
exchange fluid. It will be understood that in some embodiments not
depicted in the drawings, the flow in the passages A and B may be
parallel or in the same direction, rather than in opposite
directions.
[0019] With continued reference to FIG. 2, the heat transfer space
S is the annular space between the outer diameter of the inmost
tube 202 and inner diameter of the intermediate tube 206. Thus, the
heat transfer space S is formed by the heat transfer surface T1 of
tube 206 and the heat transfer surface T2 of the tube 202. The
periphery of the tubes, that is, the ends of the tubes 202, 204,
and 206, are sealed in a known manner, such as by soldering,
brazing, welding, or a combination of these techniques, and this
provides a closed perimeter 208 for the heat transfer space S. This
perimeter 208 is indicated only diagrammatically in the
drawings.
[0020] As in the previous embodiment, thermally conductive medium M
preferably occupies the heat transfer space S, and the heat
exchanger 200 may include at least one rupture point "R" in the
perimeter 208 for allowing release of the medium in the event of
failure of one of the tubes. Additionally, a plurality of solid
heat transfer contacts CP may be included to provide direct
surface-to-surface heat transfer connections as previously
explained.
[0021] Now it will be appreciated that the use of the heat transfer
medium as a filler in the heat transfer space as well as the
placement of heat transfer contact points CP increase the
effectiveness of the heat exchanger and provide improved system
performance. The improved performance permits the size of the heat
exchanger to be reduced which in turns allows the size of the
overall footprint of the entire HVAC&R system to be
reduced.
[0022] The embodiments shown and described above are exemplary.
Many details are often found in the art and, therefore, many such
details are neither shown nor described herein. It is not claimed
that all of the details, parts, elements, or steps described and
shown were invented herein. Even though numerous characteristics
and advantages of the present invention have been described in the
drawings and accompanying text, the description is illustrative
only. Changes may be made in the details, especially in matters of
shape, size, materials, and arrangement of the parts within the
principles of the invention to the full extent indicated by the
broad meaning of the terms of the attached claims. The description
and drawings of the specific embodiments herein do not point out
what an infringement of this patent would be, but rather provide an
example of how to use and make the invention. Likewise, the
abstract is neither intended to define the invention, which is
measured by the claims, nor is it intended to be limiting as to the
scope of the invention in any way. Rather, the limits of the
invention and the bounds of the patent protection are measured by
and defined in the following claims.
* * * * *