U.S. patent number 3,913,665 [Application Number 05/402,655] was granted by the patent office on 1975-10-21 for external tube artery flexible heat pipe.
This patent grant is currently assigned to The Boeing Company. Invention is credited to James L. Franklin, John T. Pogson.
United States Patent |
3,913,665 |
Franklin , et al. |
October 21, 1975 |
External tube artery flexible heat pipe
Abstract
A flexible heat pipe employing external tube arteries in the
adiabatic region to transfer the heat pipe working fluid from the
wick contained in the condenser portion to the wick contained in
the evaporator section.
Inventors: |
Franklin; James L. (Bellevue,
WA), Pogson; John T. (Seattle, WA) |
Assignee: |
The Boeing Company (Seattle,
WA)
|
Family
ID: |
23592804 |
Appl.
No.: |
05/402,655 |
Filed: |
October 1, 1973 |
Current U.S.
Class: |
165/104.26;
122/366 |
Current CPC
Class: |
F28D
15/0241 (20130101); F28F 2280/105 (20130101) |
Current International
Class: |
F28D
15/02 (20060101); F28D 015/00 () |
Field of
Search: |
;165/105 ;122/366 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Davis, Jr.; Albert W.
Attorney, Agent or Firm: Streck; Donald A.
Claims
What is claimed is:
1. A heat pipe containing a quantity of fluid and being an airtight
enclosure composite structure comprising in combination:
a. first enclosure means defining a first space and a second space,
said first space containing first internal conductor means for
containing and transporting the fluid therethrough as a liquid,
said second space being a passageway for containing and
transporting the fluid therethrough as a vapor;
b. second enclosure means operatively connected to said first
enclosure means and having a flexible passageway disposed adjacent
to said second space of said first enclosure means so as to allow
the fluid to move from said second space of said first enclosure
means into said second enclosure means as a vapor;
c. third enclosure means comprising a third space and a fourth
space operatively connected to said second enclosure means, said
third space containing second internal conductor means for
containing and transporting the fluid therethrough as a liquid,
said fourth space being a passageway disposed adjacent to said
second enclosure means so as to allow the fluid to move from said
second enclosure means into said fourth space of said third
enclosure means as a vapor; and,
d. flexible external capillary conduit means operatively connected
to said first enclosure means and to said third enclosure means,
said flexible external capillary conduit means having its ends
disposed adjacent to said first internal conductor means and said
second internal conductor means so as to allow the fluid to move
from said second internal conductor means to said first internal
conductor means through said flexible external capillary conduit
means, a portion of said flexible external capillary conduit means
being in the shape of a helix, said flexible passageway of said
second enclosure means being disposed within the coils of said
helix.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heat conductive devices and more
particularly to heat pipes wherein a wick is employed to transfer a
fluid in an evaporative/condensation cycle through capillary
action.
2. Description of the Prior Art
A heat pipe is a closed environment containing a fluid which
constantly undergoes an evaporative/condensation cycle. A
continuous wick transfers the condensed fluid from the cold portion
or condenser to the hot portion or evaporator where the fluid
returns to the vapor state. The vapor then moves through the closed
environment in that portion not occupied by the wick base to the
condenser where it returns to the fluid state. If the heat pipe is
to remain operative, the integrity of the cycle must be maintained.
Loss of fluid continuity in the wick is the critical item in the
cycle. Typically the wick is constructed of a material or by a
process which will yield a porous structure comprising a series of
intermeshed capillaries. As the fluid in the evaporator enters the
gaseous state a high meniscus is formed in these capillaries. The
fluid is drawn toward the evaporator by the surface tension of the
meniscus. If a dry spot should form across the wick the continuity
of this fluid flow may be lost and the cycle broken. Likewise if
the "prime" of the wick is lost, the cycle may not begin when heat
is applied to the evaporator section of a heat pipe in the static
condition.
The foregoing is particularly important when it is desired to
incorporate a flexible portion within the heat pipe as may be
required in many applications particularly where vibration or body
forces i.e. gravity may be a factor. The environmental enclosure of
the heat pipe can be made flexible through the use of common
materials such as flexible tubing. Providing a flexible wick with
adequate performance characteristics which will resist forming
discontinuities or changes in performance characteristics is
another matter.
The use of helical capillary passages contained within a bellows
has been advocated but is limited by surface tension pumping
capabilities. Consequently, the total energy that can be dissipated
by the heat pipe in a gravity environment is small. Likewise, a
wire mesh cut on the bias has been used to bridge the discontinuity
in the wick across the flexible portion. In this case the fluid
flow capacity of the wire mesh is adequate but the screen wick
tends to pull away from the tube wall causing an inefficiency and
loss of lifting capacity where the condensor is located above the
evaporator.
Another feature which would be desirable in a heat pipe is the
ability to provide a simple on/off or "diode" capability. An
external artery conducting the working fluid can provide such
control. If the capillary is heated, causing the liquid to vaporize
within the capillary, the cycle will stop. When the capillary is
cooled, vaporization within the artery cannot take place and the
cycle will continue.
Therefore, it is an object of the present invention to provide a
high performance flexible heat pipe of low flow resistance, high
resistivity to loss of prime, and high flow capacity.
It is another object of the present invention to provide a high
performance flexible heat pipe which can be constructed of
non-special materials.
It is yet another object of the present invention to provide a high
performance flexible heat pipe which allows for the cooling or
heating of any external arteries contained in the structure.
It is a further object of the present invention to provide a
flexible heat pipe that is self priming.
It is a final object of the present invention to provide a flexible
heat pipe that eliminates the need for continuous wicks and permits
the use of composite wick concepts.
Other objects and advantages of the present invention will become
apparent from the figures and specifications which follow.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a heat pipe employing a flexible section as disclosed by
the present invention wherein a felt metal wick is employed.
FIG. 2 is a heat pipe employing a flexible section as disclosed by
the present invention wherein a slab artery with spirally grooved
walls is employed.
FIG. 3 is a cross sectional view of FIG. 1 at 3--3.
FIG. 4 is a heat pipe of a slab configuration employing a flexible
joint as disclosed by the present invention between a solid
evaporator and solid condenser. In this example the capillary
arteries connecting the wicks are of a tortion bar configuration as
where minimal flexure is anticipated.
FIG. 5 is an optional configuration for an interconnecting
capillary artery for use with slab heat pipes as in FIG. 4 allowing
greater flexure with less resistance.
FIG. 6 is a partial cross section through a slab heat pipe as shown
in FIG. 4 wherein the two slabs are sealed and the flexure
interconnection is replaced with a hinge means. In this
configuration, both the wicks and vapor paths are interconnected
with capillary arteries.
FIG. 7 is a partial cross section at 7--7 in FIG. 6 showing the
staggering of the capillary arteries to interface with the wick and
vapor space.
FIG. 8 is a temperature profile for a methanol flexible heat pipe
0.5 inches in diameter and 1.5 feet in length.
Note that in FIGS. 1 through 7 like functioning elements are
numerically the same even though sometimes differently shaped so as
to easily interrelate the various species of heat pipe employing
the present invention.
DESCRIPTION AND OPERATION OF THE INVENTION
The basic heat pipe assembly 10 comprises an evaporator section 12,
an adiabatic region 14, and a condenser section 16 as shown in FIG.
1, FIG. 2, and FIG. 4. A liquid (not shown) circulates throughout
the assembly 10 carrying heat from the evaporator section 12 to the
condenser section 16 as vapor and returning to the evaporator
section 12 as a liquid. While the shape of the heat pipe may vary
for differing applications as will be described hereinafter, the
basic configuration and operation of the present invention will be
described in relation to a cylindrical heat pipe as shown in FIG.
1.
Referring to FIG. 1, the rigid portions of the heat pipe are formed
by outer enclosures 18. The outer enclosures 18 are completely
closed except where they interface with a flexible conduit 20 which
interconnects the outer enclosures 18 to form a closed environment
assembly 21. Within the outer enclosures 18 and adjacent to the
periphery thereof is a porous wick 22 as more clearly shown in FIG.
3. In the preferred embodiment as tested to date the wick 22 is
constructed of metal felt. The wick 22 is contained only in the
outer enclosures 18 and terminates at the interfaces with the
flexible conduit 20. The space remaining within the closed
environment assembly 22 provides a vapor path 24 for liquid vapor
(not shown) to flow from the evaporator section 12 to the condenser
section 16 while the wick 22 provides a path for the return of the
liquid (not shown) from the condenser section 16 to the evaporator
section 12.
The present invention provides a means for bridging the
discontinuity in the liquid flow path as hereinbefore described due
to the absence of the wick 22 in the flexible conduit 20. Capillary
artery tubes 26 are operably connected through the outer enclosures
18 to provide a path for liquid flow from the wick 22 in the
evaporator section 12 to the wick 22 in the condenser section 16.
In the preferred embodiment, as depicted in detail in FIG. 3, an
artery structure 28 is contained between the wick 22 and the outer
enclosure 18 to provide a path for the dispersal of the liquid and
reduce pressure loss. The artery structure 28 extends both
longitudinally and circumferally for optimal liquid transfer. In a
cylindrical heat pipe as shown in FIG. 1 the capillary artery tubes
26 are positioned helically about the flexible conduit 20 to
provide flexibility with minimal single point flexure in the
capillary artery tubes 26. The material of the capillary artery
tubes 26 is determined as is the material of the entire outer
enclosure 18 by the physical requirements of containing the liquid
used in the heat pipe. The size is determined by the application
and is a function of the number of capillary artery tubes 26 and
the pressure differential across the flexible conduit 20. Various
configurations employing the present invention are described
hereinafter.
Referring to FIG. 2, a heat pipe assembly 10 is shown in a
cylindrical form as that of FIG. 1. FIG. 2 demonstrates the
interfacing technique to be employed where a composite wick
structure is used such that there is a poor transfer potential
between the wick and the capillaries at their juncture. As shown in
FIG. 2 a slab artery with spirally grooved walls 30 replaces the
conventional wick. In this case an interfacing wick 32 of metal
felt is provided to connect the slab artery 30 to the capillary
artery 26. The interfacing wick 32 provides a buffer to contain the
liquid and allow transfer between the slab artery 30 and the
capillary artery 26 in the optimal manner for each. The interfacing
wick 32 incorporates an artery structure 28 as described in
conjunction with FIG. 1 herein before.
Referring to FIG. 4, a heat pipe assembly 10 is shown in a slab
form with the flexible conduit 20 in the form of a bellows as in an
accordion. In the configuration as shown, the capillary arteries 26
are shaped to provide a tortion bar effect providing stiffness and
limited flexibility. By incorporating capillary arteries 26 as
shown in FIG. 5, the same slab heat pipe would be more flexible and
less stiff.
Referring finally to FIG. 6 and FIG. 7, there is depicted a portion
of a slab heat pipe in which there are two distinct outer
enclosures 18. The flexible conduit 20 of FIGS. 1, 2, and 4 is
replaced with hinge means 34. In such an arrangement, if the
capillary arteries 26 are of a stiff tortion configuration as shown
in FIG. 4, one slab can be folded and latched in place for
subsequent automatic deployment when unlatched. Since the
continuity of the vapor path 24 is lost, vapor arteries 36 would
have to be provided to interconnect the vapor paths 24 as shown in
FIG. 6 and FIG. 7. To prevent condensation within the vapor
arteries 36 they would have to be surrounded with insulation 38 and
of sufficient number and size to provide full vapor flow. The same
configuration would, of course, work if the hinge means 34 were
removed and the two slabs were physically separated.
* * * * *