United States Patent
[I51
3,700,028
Noren
[45]
Oct. 24, 1972
[54] HEAT PIPES
[72] Inventor: Don W. Nor-en, Redwood City,
Calif.
[73] Assignee: Noren Products, Inc., Redwood
City, Calif.
[22] Filed:
Dec. 10, 1970
[21] Appl. No.: 96,836
[52]
US. Cl .................................... ..165/32, 165/105
[51]
[58]
Int. Cl ............................................. ..F28d 15/00
Field of Search ............................... ..l65/32, 105
[56]
ments of heat pipe structures arranged to readily con
duct heat in one direction and conduct only a limited
amount of heat in the opposite direction. In both em
bodiments, the heat pipe is shown as comprising a ho]
low, sealed tube having wick material positioned in
engagement with selected portions of the inner sur
face. A vaporizable ?uid is placed in the tube in an
amount sufficient to wet the wick. In one embodi
ment, the wick extends over and is in engagement with
only those portions of the wall surface from which it is
desired to transfer heat. The other portions of the wall
surface are bare. Consequently, ?uid in the wick can
be vaporized and flow to the bare wall portion for
condensation. However, if the bare wall portions are
References Cited
at a higher temperature, heat cannot be transferred to
UNITED STATES PATENTS
tube wall. In the second embodiment, the entire inner
3,613,774
10/1971
Bliss ..................... ..165/105 X
3,587,725
’ 6/1971
Basiulis ................ ..l65/105 X
Primary Examiner-—Albert W. Davis, Jr.
Att0rney—Fay, Sharpe & Mulholland
the wicked portion except by conduction through the
surface is covered by a wick but in certain areas, the
wick is spaced from the surface. The spaced areas
function in the manner of the bare areas of the ?rst
embodiment but allow the unit to be used in any
ABSTRACT
orientation since droplet formation in the spaced wick
areas permit the droplets to engage the spaced wick
for capillary ?ow to the heated wick portion.
The speci?cation and drawings disclose two embodi
4 Claims, 5 Drawing Figures
[57]
38
4053175 50
3.700.028
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ATTORNEYS
3,700,028
2
1
HEAT PIPES
The present invention is directed toward the heat
transfer art and, more particularly to improved heat
pipes which provide controlled heat flow charac
teristics.
The functioning of the device is readily apparent.
Note that heat applied to the wick engage area will
cause vaporization of the fluid and the vapor will travel
- to the cooler, non-wicked areas and condense. How
ever, if the high heat level occurs at a non-wicked area,
The invention will be described with reference to_
certain preferred embodiments formed from speci?ed
any liquid on these areas will be vaporized and passed
materials; however, as will become apparent, the heat
pipes constructed in accordance with the invention
could have many different structural arrangements and
to the wicked areas. Further heat conduction cannot
take place since liquid in the wicked areas cannot
return to the non-wicked areas. Thus, any heat transfer
from the non-wicked areas can only take place by con
be made from many different materials or combination
of materials.
duction through the heat pipe wall. This can, of course,
be controlled by making the body or portions thereof
Inthe past few‘years, heat pipes have become an im . from insulating material or material having a low con
portant method of transferring heat. Their high effi
ductivity.
ciency and capacity have made them ideal for use in 15 In accordance with another aspect of the invention,
cooling electronic components and the like. Further,
the wick extends over all inner surfaces of the wall.
since orientation and presence or absence of gravity
have no effect on a heat pipe’s ability to function, they
are particularly suited for outer space applications.
However, in those areas from which it is not desired to
have heat transfer,’ the wick is spaced outwardly from
the surface a distance substantially equal to the droplet
forming capabilities of the liquid. Thus, the wick can
The typical heat pipe comprises a hollow, ?uid im‘
pervious tube with a tubular wick member positioned
not conduct ?uid to the wall in the portion in the areas
in its interior closely in engagement with the inner wall
where it is outwardly spaced. It can, however, conduct
surface. A vaporizable ?uid is placed in the tube in an
liquid from the spaced wall back to the wall surfaces
amount generally slightly in excess of that required to 25
with which it engages. Note that as droplets are formed,
completely wet the wick. Thereafter, the tube is par
they will build up to a size where they can engage the
tially evacuated and sealed.
The operation of a heat pipe is relatively simple.
spaced wick.
‘
.
' As can be appreciated, this form of the invention can
When the tube is subjected to uneven heat conditions,
liquid in the wick at the hot points is vaporized. The 30 operate in any orientation. Further, heat pipes can be
formed with controlled transfer characteristics so that
vapor moves to cooler points on the tube and conden~
heat will be conducted equally from several spaced
ses giving up its latent heat of vaporization. The con
points while intermediate points can only receive heat.
densed liquid then moves back to the hot points by
Accordingly, the primary object of the invention is
capillary action in the wick.
As can be appreciated, since the latent heat of 35 the provision of a simple heat pipe structure wherein
selected areas of the pipe can have different heat
vaporization is carried by movement of vapor from the
transfer characteristics.
point of vaporization to the point of condensation, heat
Another object is the provision of a heat pipe with
is transferred down the pipe with little or no tempera- '
selective
heat transfer characteristics which is simple to
ture drop along the length of the pipe. Further, heat
construct.
’
can be transferred in either direction along the pipe.
40
Still
another
object
is
the provision of a heat pipe of
Generally, the fact that heat is transferred in either
the
general
type
described
which can control the
direction is a decided advantage. However, in certain
direction of heat ?ow without complicated internal
installations, it would be much more preferable to have
valving or other moving parts.
a heat pipe which is effective to conduct heat only in
A still further object of the invention is the provision
one direction. For example, when it is desired to main 45
of a heat pipe structure that can have substantially any
tain a component at a high temperature, it would be
desirable to use heat pipes which would not conduct
desired heat transfer characteristics.
The above and other objects and advantages will
become
apparent from the following description when
the heat source is disconnected.
The subject invention provides a heat pipe structure 50 read‘ in conjunction with the accompanying drawings
wherein:
in which heat ?ow can take place predominately only
heat away fromv the component during periods when
FIG. 1 is a longitudinal cross-sectional view through
a heat pipe formed in accordance with the invention;
in one direction. Although some heat can flow in the
other direction, it must take place primarily by conduc
FIGS. 2 and 3 are cross-sectional views taken on
tion through the outer wall of the tube. In accordance
with the invention, the heat pipe comprises a hollow, 55 lines 2-2 and 3—3 of FIG. 1, respectively;
FIG. 4 is a longitudinal cross-section through a
?uid impervious body having a relatively thin wall.
second
embodiment of heat pipe formed in accordance
Wick material is positioned in engagement with the
with the invention; and,
inner surface of the wall throughout only a portion of p
FIG. 5 is a cross-sectional view taken on line 5-5 of
the wall’s total inner surface. The portions engaged
constitute those areas from which it is desired to con
duct heat. The remaining portions of the inner wall sur
face are spaced from the wick material and constitute
areas to which it is desired to conduct heat but from
60
FIG. 4.
.
7
Referring more particularly to FIG. 1, the overall ar
rangement of the inventive heat pipe is shown as com
prising a tubular outer body 10 formed from any
which it is desired to impede the ?ow of heat. Addi 65' desired ?uid impervious material such as hard copper
tubing, stainless steel tubing, or the like. The opposite
tionally, a vaporizable ?uid is placed in the body in an
ends of the tubing are sealed in any convenient manner
amount preferably slightly greater than that required to
such as through the use of metallic discs 12 and 14 sol
fully wet the wick.
3,700,028
3
A
dered or bonded into the ends of the tube W. Posi
Although the FIGS. ll through 3 embodiment is
limited to orientations in which the unwicked portions
tioned within the tube and closely in engagement with
the inner wall 16 throughout a selected portion of the
tube 10, is a cylindrical wick member 13. The wick
member 18, in the embodiment under consideration, is
formed from a ?ne wire screen (shown diagramatically
in a somewhat larger than actual size). It should be ap
preciated that any desired type of wicking material can
be used and, for example, metal felt, fiber glass and the
like is often used.
As is customary, a vaporizable fluid is placed within
are at an elevation slightly above the wicked end, the
embodiment of H68. it and 5 shows how the same
general principals can be utilized to provide a heat pipe
which permits flow of heat substantially in only one
direction but is not limited by orientation. As shown in
FIGS. 4i and 5, the heat pipe includes an outer tubular
body or housing member 30 which can be formed from
any desired type of ?uid impervious material having
characteristics required. The opposite ends of the tube
the tube in an amount sufficient to slightly more than
30 are closed and sealed by end plates 32 and 34 sol
wet the entire wick 1%. Additionally, the interior of the
tube is evacuated and/or ?lled with a non-condensible
gas to provide selected heat transmitting characteristics
dered or otherwise bonded therein. Positioned within
the tube 36 is a Wick member 36 having a ?rst portion
38 which engages the inner wall 40 of tube 30. The
in the resulting tube.
According to the invention, the inner wick member
is arranged so that it engages only those portions of the
remaining portion 42 of the wick 36 is spaced inwardly
of the wall surface 40 a predetermined distance. In this
embodiment, the wick portions 38 and 42 are continu
tube wall which are desired to function as heat trans 20 ous and join through a tapered section 44; however, as
will become apparent hereafter, the wick could have
mitting or conducting portions, That is, only those
many shapes and con?gurations and be formed from a
areas of the tube from which it is desired to conduct
plurality of different materials and in independent sec
heat are covered by the wick. As shown in FIG. l, the
tions merely connected by some capillary portion to
wick extends approximately half way up the tube from
provide
a ?ow path between them. It is important that
the end 14. The inner surface of the end 14 is likewise
the tapered section 44 between the wick sections have
covered with wick material.
openings of other means for permitting vapor flow
The FIG. 1 form of the invention is adapted to func
between the annular space 51 and the inner space 53'.
tion primarily when the end 12 is at an elevation higher
As previously mentioned, portions of the wick are
than end llél. To appreciate the operation of the FIG. 1
spaced
inwardly from the inner wall 40 of the tube. The
embodiment, assume that the end coated with wicking
particular
areas which are spaced inwardly can be
material is at a higher temperature level than the op
located as desired. Those areas to which heat is to be
posite end. The fluid in the wick i8 is thus caused to
conducted, but from which heat is not to be conducted,
evaporate and moves to the opposite end where it will
condense giving up its heat of vaporization. The con 35 should have a substantial spacing from the wall. For ex
ample, in the FIG. 4 embodiment, the tube is arranged
densed liquid will form droplets and ?ow back to the
so that heat can be conducted from area A to area B.
wick material for conduction to the particular spots at
which vaporization is taking place. It should be ap
To explain, assume that the wick has been saturated
with the desired vaporizable ?uid and the assembly is
preciated that the area covered by wick soon becomes
subjected
to heating along area A. The liquid within the
relatively uniform in temperature in the manner of a 40
wick
portion
3% is quickly vaporized and travels to the
conventional heat pipe. Likewise, the heat flow to the
cooler wall of the tube 10 in area B where it condenses.
opposite end is rapid as is the case with a standard heat
As shown, the fluid will tend to form droplets, for ex
pipe. However, if the unwicked end should become
ample, droplets S?, on the inner wall of the tube. When
warmer than the wicked end, very little heat can ?ow to
the droplets have formed to a relatively large size, they
the wicked end. Note that the unwicked end cannot 45
will contact the wick portion 42 and be conducted by
maintain a supply of ?uid in engagement with the walls.
capillary action back to the heated area of the tube.
if any moisture droplets remain on the walls, they will
be quickly vaporized and condensed on the wick por
tion. The lack of wick in the higher temperature end
Note that this action will take place irrespective of the
orientation of the tube. For example, assume that the
end 32 is at an elevation higher than the end 34. The
droplets or the condensed fluid will either ?ow by
gravity along the wall to the wick portion 38 or, al
thus prevents the return of the fluid to the hotter por
tion of the tube. If any heat is to be transferred from the
unwicked to the wicked end, it travels by conduction
ternately, they will engage the spaced wick portion 42
through the walls of tube it). Thus, the rate of heat flow
and be conducted back to wick portion 38 by capillary
from the unwicked end to the wicked end is extremely 55 action.
low when compared to heat flow in the opposite
Assume however, that the tube is heated to a higher
direction.
level at some point on portion B. In such case, the fluid
llt should be appreciated that many variations could
which happens to be on the inner wall 40 will be
be made in the arrangement of the internal wick sur
vaporized and will pass to the wick or cooler wall por
faces. For example, the central section of the tube 60 tion in area A. Quickly, however, all the fluid on the
could be provided with wick and both ends left bare so
wall in the portion of area B will be vaporized.
that heat could only flow from the center of the tube to
Thereafter, no further fluid is available for vaporization
the outer ends. Additionally, since the only heat flow
and heat can only be conducted to area A by conduc
which can take place from the unwicked end to the
tion through the wall of the tube 30. A substantial in
65
wicked end is through conduction, intermediate insu
crease in temperature would be required to cause any
lating rings could be inserted to reduce this heat flow if
desired.
vaporization of the fluid in the wick in portion 42.
Thus, the heat pipe can readily conduct heat from por
5
3,700,028
6
tion A to portion B but substantially no heat is con
ducted from B to A.
As can be appreciated, the heat pipe of FIGS. 4 and 5 '
can have any desired configuration and the internal
wick can be spaced at whatever location is desired to
be a non-heat transmitting portion. Further, the inter
of said wick in close engagement with the interior
surfaces of said inner walls and the remaining por
tion being spaced from said wall a distance such
that ?uid condensing on the wall adjacent said
spaced portion will not engage the spaced wick
until it has formed substantial sized droplets.
nal wick arrangement can vary widely.
2. The heat pipe as de?ned in claim 1 wherein said
wick member is substantially continuous throughout
the interior of said body and spaced from the inner wall
The invention has been described in great detail suf- -
?cient to enable one of ordinary skill in the heat
transfer art to make and use the same. Obviously,
of said body throughout an extent of greater than 10%
of the internal wall surface.
ment will occur to others upon 'a reading and un- v
3. A heat pipe as de?ned in claim 1 wherein said
derstanding of the speci?cation and it is my intention to
body comprises a ?rst sealed tubular member and
include all such modi?cations and alterations as part of
wherein said wick member comprises a second tubular
my invention insofar as they come within the scope of 15
member having portions of at least two different outer
the appended claims.
diameters
including a ?rst outer diameter to closely en
What is claimed is:
gage the interior surface of said body and a second
l. A heat pipe assembly adapted to transmit heat
outer diameter to be spaced from interior surface of
primarily in one direction comprising:
'said body.
a sealed, ?uid impervious body having a hollow in
4. A heat pipe as de?ned in claim it wherein said
terior;
modi?cations and alterations of the preferred embodi
body is formed from metal having a relatively thin wall.
a wick member adapted to conduct ?uid by capillary
'
action positioned within said body with a portion
'
25
30
35
45
55
60
65
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