U.S. patent application number 10/817171 was filed with the patent office on 2005-10-06 for compact counterflow heat exchanger.
Invention is credited to Kudija, Charles T. JR..
Application Number | 20050217837 10/817171 |
Document ID | / |
Family ID | 35053006 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050217837 |
Kind Code |
A1 |
Kudija, Charles T. JR. |
October 6, 2005 |
Compact counterflow heat exchanger
Abstract
A geometric arrangement of components in a compact counter-flow
heat exchanger that allows for either an increase in effectiveness
at a set mass, or a reduction in heat exchanger mass at a set
effectiveness, or a combination of the two. The geometric
arrangement can be achieved by either tube bending at the level of
piece part manufacture and subsequent care during the tube stacking
process, or by elastic deformation of the tube stack at the time of
bonding.
Inventors: |
Kudija, Charles T. JR.;
(Chicago, IL) |
Correspondence
Address: |
Tyrone Davis
c/o Davis & Kendall, PC
Suite 1245
205 West Randolph
Chicago
IL
60606
US
|
Family ID: |
35053006 |
Appl. No.: |
10/817171 |
Filed: |
April 2, 2004 |
Current U.S.
Class: |
165/165 |
Current CPC
Class: |
F28D 7/0008 20130101;
F28F 2009/0287 20130101 |
Class at
Publication: |
165/165 |
International
Class: |
F28F 007/00 |
Claims
What is claimed is:
1. A compact counterflow heat exchanger comprising: a plurality of
longitudinally extending and parallel fluid carrying tubes arranged
in thermal contact with one another, each tube having at least one
bend congruent to a bend in an immediately adjacent tube; and a
first heat exchange fluid flowing through any one tube in a
direction opposite to a flow direction of a second heat exchange
fluid flowing through an immediately adjacent tube, thereby
establishing a counter-flow heat exchange relation between the
first and second heat exchange fluids.
2. The heat exchange system of claim 1, wherein the fluid carrying
tubes comprise stainless steel.
3. A microchannel recuperator including a core mass, comprising
multiple layers in a vertical plane of multiple fluid carrying tube
arranged adjacent to each together and a substrate layer disposed
in a horizontal plane, alternating tubes having a longitudinal
offset bend equal to at least the width of a tube, and fluid
carrying counter-flow channels comprising alternate tube layers
communicating across the entire horizontal plane thereof, whereby
the fluid carrying tubes of the core mass are directly adjacent to
the fluid carrying counter-flow channels.
4. The microchannel recuperator of claim 3, wherein the offset bend
in each tube is at least equal to 1/2 a dimension of any tube.
5. The microchannel recuperator of claim 4, wherein the tubes
comprise stainless steel.
6. A method of making a heat exchanger comprising the steps of:
preparing a substrate layer of multiple square metal tubes arranged
adjacent and physically attached to each other in a horizontal
plane, each tube having a longitudinally extending offset bend;
configuring multiple layers in a vertical plane of multiple square
metal tubes arranged adjacent to each other and the substrate layer
in a horizontal plane and having interposed between each layer or
multiple metal tubes Physically and communicating therewith a braze
alloy thus forming a heat exchange core causing the braze alloy
within the core to bond the multiple layers of multiple square
metal tubes forming a core mass comprising in a vertical plane,
multiple layers of multiple square metal tubes arranged adjacent
and physically attached to each other and the substrate layer;
forming in alternate tube layers counter-flow fluid channels
communicating across the entire horizontal plane thereof; providing
the core mass with side containment shells 10 and manifolds in
communication with the multiple square metal tube core mass and the
counterflow counterflow channels; and brazing the heat exchanger to
bond parts thereof together.
7. A method of thermal transfer comprising the steps of: providing
adjacent first and second fluid carrying tubes in heat exchange
contact one with another; forming an offset bend in each tube; and
flowing a first thermal transfer fluid through the first fluid
carrying tubes, and flowing a second thermal transfer fluid through
the second fluid carrying tubes, respectively.
8. The method of claim 7, further comprising the step of forming
the offset bend in a distance equal to at least 1/2 a dimension of
the first or second fluid carrying tube.
9. The method of claim 8, further comprising the step of forming
the first and second fluid carrying tubes of stainless steel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to heat exchangers,
particularly, high-efficiency compact counter-flow heat
exchangers.
[0003] 2. Discussion of the Related Art
[0004] In the art of heat exchangers, it is generally acknowledged
that fin effectiveness takes on values between zero and one, as
constrained by conservation of energy principles. More
specifically, the value of the fin effectiveness is always less
than one for common engineering materials because of their finite
thermal diffusivity.
[0005] However, a premium is placed on system mass for aerospace
design because of the energy expense of achieving and maintaining
flight. Under ordinary conditions, each flight system performs a
variety of functions to successfully complete its mission. A common
function necessary to aerospace system operation is the power
conversion function. To the extent that a given power conversion
function can be accomplished more effectively by a given component
of given mass, energy costs per unit payload can be decreased, or
to the extent that a given power conversion function can be
accomplished by a component of lesser mass, payload can be
increased. Heat exchange is one such energy conversion function
that finds common use in aerospace dynamic power systems.
Production of compact micro-channel heat exchangers 10 using
micro-channel flow passages has yielded somewhat unreliable results
because conventional fabrication methods cannot be controlled
sufficiently well to yield consistent flow passage dimensions.
Compact gas-gas heat exchangers are usually of the plate-fin type
and are fabricated from thin sheets of material or plates to which
are bonded, such as by furnace brazing, the fins. The fins are
usually fabricated from strips of the same material used for the
plates, forming a braze assembly. The fins and a sheet of braze
foil are tack welded together prior to firing the assembly in a
braze furnace. Alternatively, tack welding is used and welding of
the many hundreds of fins is usually done by hand, which can be
costly. Manifolds are usually welded to pre-inserted weld stubs
which are included with the braze assembly.
[0006] When the assembly of very small flow passage heat exchangers
attempted however, distortion of the thin sheet-metal fins, weld
splatter, arid braze drop-through often form significant and
uncontrollable flow path obstructions. The present invention avoids
the problems associated with conventional plate-fin construction by
providing a pre-machined microchannel counterflow path in the form
of a square tube having a particularly advantageous geometry.
Opportunities for weld-splatter, braze drop-through and part
distortion are restricted to the latter stages of the total
assembly process which are finished by a reliable final machining
operation, such as laser machining, water jet machining, electrical
discharge machining, or conventional machining, resulting in
consistent and controllable flow passage dimensions. Hence, a
compact microchannel heat exchanger is produced having a plurality
of parallel tubes for carrying a working fluid a header and a tank
assembly at each end of the tubes for directing working fluid
through the tubes in a desired flow path. The compact counter-flow
heat exchanger according to the present invention allows for an
increase in heat exchange efficiency and effectiveness at a set
mass, a reduction of heat exchanger mass at a set effectiveness, or
a combination of the two. Such compact counter-flow heat exchanger
offers a power designer system conversion more freedom for
innovation on any given heat exchanger system.
SUMMARY OF THE INVENTION
[0007] A novel aspect of the present invention is a heat exchange
system comprising a plurality of longitudinally extending and
parallel fluid carrying tubes arranged in thermal contact with one
another, each tube having at least one bend congruent to a bend in
an immediately adjacent tube; and a first heat exchange fluid
flowing through any one tube in a direction opposite to a direction
of a second heat exchange fluid flowing through an immediately
adjacent tube, thereby establishing a counter-flow heat exchange
relation between the first and second heat exchange fluids.
[0008] Another novel aspect of the present invention is a
micro-channel recuperator including a core mass comprising multiple
layers in a vertical plane of multiple fluid carrying tubes
arranged adjacent to each together and a substrate layer disposed
in a horizontal plane, alternating tubes having a longitudinal
offset bend equal to at least the width of a tube, and fluid
carrying counter-flow channels comprising alternate tube layers
communicating across the entire horizontal plane thereof, whereby
the fluid carrying tubes of the core mass are directly adjacent to
the fluid carrying counter-flow channels.
[0009] Another novel aspect of the present invention is a method of
making a heat exchanger comprising the steps of preparing a
substrate layer of multiple square metal tubes arranged adjacent
and physically attached to each other in a horizontal plane, each
tube having a longitudinally extending offset bend; configuring
multiple layers in a vertical plane of multiple square metal tubes
arranged adjacent to each other and the substrate layer in a
horizontal plane and having interposed between each layer of
multiple metal tubes physically and communicating therewith a braze
alloy thus forming a heat exchange core; causing the braze alloy
within the core to bond the multiple layers of multiple square
metal tubes forming a core mass comprising in a vertical plane,
multiple layers of multiple square metal tubes arranged adjacent
and physically attached to each other and the substrate layer;
forming in alternate tube layers counter-flow fluid channels
communicating across the entire horizontal plane thereof; providing
the core mass with side containment shells and manifolds in
communication with the multiple square metal tube core mass and the
counter-flow channels; and brazing the heat exchanger to bond parts
thereof together
[0010] Another novel aspect of the present invention is method of
thermal transfer comprising the steps of providing adjacent first
and second fluid carrying tubes in heat exchange contact one with
another; forming an offset bend in each tube; and flowing a first
thermal transfer fluid through the first fluid carrying tubes, and
flowing a second thermal transfer fluid through the second fluid
carrying tubes, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a typical baseline heat transfer
arrangement;
[0012] FIG. 2 shows a heat transfer arrangement for a set or fluid
channels according to the present invention; and
[0013] FIG. 3 shows the counterflow fluid flow streams according a
typical baseline transfer arrangement.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0014] FIG. 1 shows a typical baseline heat transfer arrangement
comprising a heat exchange core assembly 10 of square-formed
seamless channels 16, and an identical square formed seamless
counterflow channel 18. The channels 16, 18 each have multiple
square tubes 12 of equal dimensions, 10 and arranged in parallel
configuration.
[0015] Onto the substrate layer 22 are added seriatim multiple
layers of the tubes 12, each provided with a particular geometric
feature. The tubes 12 are stacked in a vertical plane and arranged
adjacent to each other and the substrate layer 22. In other words,
tube 12 comprising the channel 16, 18 or the assembly 10 are
arranged, or "stacked", in ascending and descending column-like
channels, both above and below one another, in an alternating
checkerboard pattern, as shown in section A-A.
[0016] In preparing the core assembly 10, each one of the tubes 12
forming channels 16, 18 is made of a suitable material having
desired heat transfer characteristics, such as type 304 stainless
steel. The tubes 12 are assembled by brazing, using for example, a
high temperature braze alloy (90/10 Ag/Pb), as discussed below.
[0017] Manufacture of the core assembly 10 comprises preparing a
substrate layer 22 of multiple tubes 12 arranged adjacent and
physically attached to one another in a horizontal plane. Although
tubes 12 are shown in FIG. 1 and discussed herein as having a
square internal cross-section, any suitable internal
cross-sectional shape having desirable heat transfer
characteristics would be useful in the present invention.
[0018] Interposed between each layer of tubes 12 is a layer of
brazing material or alloy 24 such as 90/10 Ag/Pb alloy activated to
effect bonding of the individual tubes 12, such as by furnace
brazing or any other well-known brazing technique. Upon completion
of formation of the core assembly 10, headers and manifolds 20 are
attached, also such as by brazing, to the core assembly 10.
[0019] FIG. 2 shows that alternating ascending columns of tubes 13
of the present invention and are provided with a longitudinal
offset bend that "jogs", or slightly deflected in the vertical
plane. Each of the respective tubes 13 are offset, or jogged, in
parallel and congruent fashion, upwards through a distance equal to
the width of a tube 13.
[0020] The longitudinal offset bend, or jog, in each tube 13
improves heat transfer between any two sets of tubes 13, so that a
maximum surface area each tube 13 is in contact with material of
type 304 stainless steel with which a silver base alloy is used for
brazing. Moreover, with proper tooling table design, the heat
exchange core assembly 11 can be formed with elastic tube
deformation brazed in place. Any material other than stainless
steel having desirable heat transfer structural and convection
characteristics would be equally as useful in the present
invention.
[0021] FIG. 3 shows that the heat exchanger core assembly 11 is
provided with a pair of headers or side containment shells 14. Each
header or shell 14, which are positioned at opposing ends of the
assembly 11 is configured to function not only with the tubes 13,
but cooperatively also with the alternating counter-flow channels
16, 18, which are cut parallel to the horizontal plane of the core
assembly 11. Engaging the headers or side containment shells 14 are
manifolds 20 which communicate with a cooling fluid source. The
cooling fluid source supplies circulating cooling fluid to the heat
exchanger in flow directions depicted by the arrows.
[0022] The heat exchanger of the present invention functions in the
following manner. Fluid streams "A", and "B" of different
temperatures are introduced to the heat exchanger in the directions
shown by the arrows in FIG. 4. The inlet for stream "A" directs
fluid flow into tube 13, via respective manifolds 20. The inlet for
stream "B." directs fluid flow into counter-flow channels 18 via
respective manifold 20.
[0023] Once introduced into the heat exchanger, streams "A" and "B"
flow in opposing directions to each other. The hotter stream losses
heat to the colder stream, thereby effecting an exchange of heat
energy. The amount of heat gained in the colder stream and the
amount of heat lost from the hotter stream are easily computed by
conventional heat exchange analysis methods.
[0024] Thus, the longitudinal bend, or jog, of the heat exchanger
tubes 11, according to the present invention ensures that the
entire surface of one fluid carrying tube 13 is directly adjacent
on all sides to the tube surface of the other fluid, thereby
creating an increase in the direct contact surface area at the
interior of the tube stack where each fluid carrying tube 13 is
surrounded on all sides by tubes 13 carrying the complementary
counterflow fluid. However, there are compensating effects at the
external surface of the heat exchange core where some of the tubes
13 do not have a corresponding adjacent contact surface.
Nevertheless, in most common heat transfers situations, where there
are many parallel tubes 13, the majority of the tubes will be in
interior tubes and 13 while demonstrate a net improvement in heat
exchanger effectiveness.
[0025] In addition to being useful in aerospace power conversion
systems, the heat exchanger of the present invention is useful in
such apparatus and systems as engine combusters, heat sinks, and
recuperators, including microchannel recuperators.
[0026] Accordingly, the description for the present invention is to
be construed as illustrative only and is for the purpose of
teaching those skilled in the art the best mode of carrying out the
invention. The details may be varied substantially without
departing from the spirit of the invention, and the exclusive use
of all modifications with are within the scope of the appended
claims is reserved.
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