Flat plate (vapor chamber) heat pipes were made by enclosing metal wicking between two capillary grooved flat panels. These heat pipes provide a unique configuration and have good capacity and conductance capabilities in zero gravity. When these flat plate vapor chamber heat pipes are heated or cooled, the surfaces are essentially isothermal, varying only 3 to 5 C over the panel surface

Fleischman, G. L.

Marcus, B. D.

English

NASA Technical Reports Server

United States Patent 1191 
Marcus et al. 
[54] FLAT-PLATE HEAT PIPE 
1751 Inventors: Bruce D. Marcus, Los Angeles; 
George L. Fleischman, Inglewood, 
both of Calif. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
1211 Appl. NO.: 579,989 
[22] Filed: May 22, 1975 
[SI] Int. Cl.2 .............................................. F28D 15/00 
[58] Field of Search ......................................... 165/105 
[52] U.S. C I .  .................................................... 165/105 
11 11 4,046,190 
I451 Sept. 6, 1977 
I561 References Cited 
U.S. PATENT DOCUMENTS 
3,603,767 9/1971 Scicehitano ..................... 165/105 X 
3,613,778 10/1971 Feldman, Jr. ........................ 165/105 
3,734,173 5/1973 Moritz .................................. 165/105 
Primary Examiner-Albert W. Davis, Jr. 
Attorney, Agent, or Firm-John 0. Tresansky; Robert 
Kinberg; John R. Manning 
ABSTRACT [571 
Flat-plate (vapor chamber) heat pipes are made by en- 
closing metal wicking between two capillary grooved 
flat panels. These heat pipes provide a unique configura- 
tion and have good capacity and conductance capabili- 
ties in zero gravity. When these flat-plate vapor cham- 
ber heat pipes are heated or cooled, the surfaces are 
essentially isothermal, varying only 3" to 5" C over the 
panel surface. 
6 Claims, 1 Drawing Figure 
6 
https://ntrs.nasa.gov/search.jsp?R=19770025469 2020-03-20T07:44:44+00:00Z
U.S. Patent Sept. 6, 1977 4,046,190 
6 
4,046,190 
1 
FLAT-PLATE HEAT PIPE 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 U.S.C. 2457). 
BACKGROUND O F  THE INVENTION 
Heat pipes or heat pipe-type devices operate on 
closed evaporating-condensing cycles for transporting 
heat from a locale of heat addition to a locale of heat 
rejection, using a capillary structure or wick for return 
of the condensate. Such devices generally consist of a 
closed container which may be of any shape or geome- 
try. Early forms of these devices had the shape of a pipe 
or tube closed on both ends and the term "heat pipe" 
was derived from such devices. The term "heat pipe," 
as used herein however, refers to a device of any type of 
geometry designed to function as described above. 
In such a heat pipe device, air or other noncondens- 
able gases are usually removed from the internal cavity 
of the container. All interior surfaces are lined with a 
capillary structure, such as a wick. The wick is soaked 
with a fluid which will be in the liquid phase at the 
normal working temperature of the device. The free 
space of the cavity then contains only the vapor of the 
fluid at a pressure corresponding to the saturation pres- 
sure of the working fluid at the temperature of the de- 
vice. If, at any location, heat is added to the container, 
the resulting temperature rise will increase the vapor 
pressure of the working fluid, and evaporation of liquid 
will take place. The vapor that is formed, being at a 
higher pressure, will flow towards the colder regions of 
the container cavity and will condense on the cooler 
surfaces inside the container wall. Capillary effects will 
return the liquid condensate to areas of heat addition. 
Because the heat of evaporation is absorbed by the 
phase change from liquid to vapor and released when 
condensation of the vapor takes place, large amounts of 
heat can be transported with very small temperature 
gradients from areas of heat addition to areas of heat 
removal. 
SUMMARY OF THE INVENTION 
Flat-plate vapor chamber heat pipes are fabricated by 
sealing two flat plates together in parallel planes so that 
the edges are aligned normal to the surface of the plates. 
Surfaces of the plates facing each other have capillary 
grooves at right angles to each other; i.e., the capillary 
grooves in one plate are at right angles to the grooves in 
the opposing plate so the working fluid can flow in all 
directions. Metal wicking is arranged between the 
plates so as to intersect every groove on the surface of 
both plates to provide fluid flow from plate to plate and 
a vapor path to all portions of the plate. The working 
fluid is sealed between the flat grooved panels and con- 
denses at spots where the heat is removed and evapo- 
rates at places where heat is applied. 
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Heat pipes of this invention can be used as electronic 60 
cold plates for mounting high power density electronic 
equipment, substrates for integrated circuit chips, solar 
cells, or laser mirrors. 
Typical flat-plate heat pipes according to this inven- 
tion, utilizing methanol as the working fluid, can dem- 65 
onstrate a heat input flux of 2.8 watts/square centimeter 
with a 3' to 5' C temperature difference throughout the 
panel surface at zero gravity. Typical capacity of the 
2 
flat-plate heat pipe may be about 25 watt-in/in at 0.5 
inch evaporator elevation and 50 watt-in/in in zero 
gravity using methanol at 55" F. Typical conductances 
were approximately 1 watt/in2-' F at the evaporator 
and 0.3 watt/inZ-" F at the condenser. Higher values for 
all these parameters are possible with water as the 
working fluid. 
BRIEF DESCRIPTION OF THE DRAWING 
The FIGURE in the drawing is a perspective view of 
a disassembled flat-plate vapor chamber heat pipe. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
Referring to the FIGURE in the drawing, capillary 
grooves 1 are machined or etched into the facing sur- 
faces of plates 2 and 3. Spacing studs 4 are aligned at 
regular intervals to provide structural support for pan- 
els 2 and 3 as well as an anchor for metal wicking §. 
Metal wicking 5 is arranged so that they collective cross 
or intersect every groove on the faces of plates 2 and 3. 
Side bars 6 and 7 are joined at the edges of panels 2 and 
3 to provide further structural support and spacing of 
the panels, as well as a seal for the working fluid. Side 
bars 6 and 7 and spacing studs 4 are joined to panels 2 
and 3 by any suitable means, for example, soldering, 
brazing, welding, or diffusion bonding. 
Plates 2 and 3 can be made from any of the structural 
metals. Metals such as copper, brass, nickel, stainless 
steel, Monel, and titanium are a few which are suitable 
for these heat pipes. 
When choosing a metal for the heat pipe, consider- 
ation must be given to selecting a compatible working 
fluid. The working fluid must be compatible with the 
metal under all conditions to which the heat pipe will be 
exposed or corrosion will occur. It has been found that 
copper, brass, nickel, and stainless steel are compatible 
with methanol while copper, Monel, and titanium are 
compatible with water. 
Water, methanol, and ammonia are three well-known 
low temperature working fluids. Ammonia is not suit- 
able for flat plate heat pipes because it has a high vapor 
pressure at ambient conditions and would be difficult to 
contain without deformation of the flat plates. While 
high pressures in tubular heat pipes is but a minor prob- 
lem, pressurization in flat-plate heat pipes presents more 
serious considerations. Hence, in the near ambient tem- 
perature ranges, low pressure fluids such as water and 
methanol are the most suitable working fluids. Where 
higher temperature ranges are contemplated for the 
heat pipe use, other working fluids, exhibiting low 
vapor pressures at the desired operating temperatures, 
would be required. 
Capillary grooves 1, in plates 2 and 3, may be formed 
by any suitable process means. Generally, chemical 
milling or photofabrication by processes well-known in 
the art is employed to etch the capillary grooves into 
the surface of the plates. Metals which form wide shal- 
low grooves when etched, as exexemplified by stainless 
steel, are less desirable than metals which form the 
narrow grooves necessary for the capillary effect as 
examplified by copper. 
Capillary grooves 1 on panel 2 are oriented 90" to 
capillary grooves 1 on panel 3. This right angle orienta- 
tion of grooves 1 in combination with metal wicking 5 
provides a continuous liquid path from any one groove 
to any other within the enclosure. This will allow con- 
tinuous circulation of working fluid between all points 
2 
4,046,190 
J 
of the heat pipe. Nearly isothermal heat transfer ,is 
achieved by virture of a practically uniform internal 
vapor pressure and temperature in combination with 
extremely high coefficients of evaporation and conden- 
sation heat transfer from and to grooved surfaces. 5 
We claim: 
1. A heat pipe device comprising: 
i. two flat-plates in parallel planes having edges sealed 
and aligned normal to the parallel plates with capil- 
lary grooves in the facing surfaces at right angles to 10 
the grooves of the opposing plate; and 
ii. metal wicking intersecting every groove. 
2. A heat pipe device according to claim 1 wherein: 
said metal wicking is metal wire felt. 
3. A heat pipe device according to claim 1 wherein: 15 
4 
said metal wicking is porous sintered powdered 
4. A heat pipe device comprising: 
i. two equidistant flat plates having sealed aligned 
edges normal to the surfaces and capillary grooves 
in the opposing surfaces at right angles to the 
grooves of the opposing plate; 
metal. 
ii. metal wicking intersecting every groove; and 
iii. a working fluid sealed between said plates. 
5. A heat pipe device according to claim 4 wherein: 
said metal wicking is metal wire felt. 
6. A heat pipe device according to claim 4 wherein: 
said metal wicking is porous sintered powdered 
metal. * * * * *  
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65 


Flat-plate heat pipe

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