U.S. patent application number 09/992574 was filed with the patent office on 2002-03-28 for loop heat pipe for equipment cooling.
Invention is credited to Eastman, G. Yale.
Application Number | 20020036076 09/992574 |
Document ID | / |
Family ID | 23912365 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020036076 |
Kind Code |
A1 |
Eastman, G. Yale |
March 28, 2002 |
Loop heat pipe for equipment cooling
Abstract
The apparatus is a loop heat pipe with the heat input above the
heat output, so that the loop heat pipe is used to cool a
transformer or equipment enclosure above ground with the condenser
located and the heat being dissipated in the ground below the
location at which the heat is being generated. One embodiment uses
a coiled pipe for a condenser and buries it in the ground encased
in concrete. Another embodiment of the invention is used to cool a
diesel electric locomotive by placing the condenser below the
engine and attaching multiple cooling fins to it.
Inventors: |
Eastman, G. Yale;
(Lancaster, PA) |
Correspondence
Address: |
Samuel W. Apicelli
Duane Morris LLP
305 N. Front Street
P.O. Box 1003
Harrisburg
PA
17108-1003
US
|
Family ID: |
23912365 |
Appl. No.: |
09/992574 |
Filed: |
November 6, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09992574 |
Nov 6, 2001 |
|
|
|
09481546 |
Jan 10, 2000 |
|
|
|
Current U.S.
Class: |
165/45 ;
165/104.21 |
Current CPC
Class: |
F28D 15/0266 20130101;
Y02E 60/142 20130101; F28D 20/0052 20130101; Y02E 60/14
20130101 |
Class at
Publication: |
165/45 ;
165/104.21 |
International
Class: |
F28D 001/00; F28D
015/00 |
Claims
What is claimed as new and for which Letters Patent of the United
States are desired to be secured is:
1. A loop heat pipe for cooling a heat generating device
comprising: a capillary pump located in proximity to and heated by
a heat generating device, with the capillary pump including a
liquid input and a vapor output; a condenser section which is
constructed of pipe, located below the capillary pump, and
installed underground; a vapor pipe interconnecting the condenser
section to the vapor output of the capillary pump; a liquid return
pipe interconnecting the condenser section to the liquid input of
the capillary pump; and a heat dissipating means in contact with
and cooling the condenser section.
2. The loop heat pipe of claim 1 wherein the condenser section is
formed as a helix.
3. The loop heat pipe of claim 1 wherein the condenser section is
formed into a serpentine configuration.
4. The loop heat pipe of claim 1 wherein the heat dissipating means
is soil surrounding the condenser section.
5. The loop heat pipe of claim 1 wherein the heat dissipating means
is a concrete body formed around the condenser section.
6. The loop heat pipe of claim 1 wherein the heat dissipating means
is a concrete body formed around the condenser section, and the
concrete body is located underground surrounded by soil.
7. The loop heat pipe of claim 1 wherein the heat dissipating means
is a concrete body formed around the condenser section, and the
concrete body is part of a building.
8. The loop heat pipe of claim 1 wherein the condenser section is
installed underground and below the frost line.
9. The loop heat pipe of claim 1 wherein the heat generating device
is electrical equipment.
10. The loop heat pipe of claim 1 wherein the heat generating
device is electrical equipment installed within a building.
11. A loop heat pipe for cooling a heat generating device
comprising: a capillary pump located in proximity to and heated by
a heat generating device, with the capillary pump including a
liquid input and a vapor output; a condenser section which is
constructed of pipe, located below the capillary pump, and
installed aboard a locomotive; a vapor pipe interconnecting the
condenser section to the vapor output of the capillary pump; a
liquid return pipe interconnecting the condenser section to the
liquid input of the capillary pump; and a heat dissipating means in
contact with and cooling the condenser section.
12. The loop heat pipe of claim 1 wherein the loop heat pipe is
installed aboard a locomotive, the capillary pump is installed
within the locomotive, and the condenser section is installed below
the undercarriage of the locomotive.
13. The loop heat pipe of claim 1 wherein the loop heat pipe is
installed aboard a locomotive, the condenser section is installed
below the undercarriage of the locomotive, and the heat dissipating
means is a group of cooling fins attached to the condenser section.
Description
BACKGROUND OF THE INVENTION
[0001] This invention deals generally with cooling electrical
equipment, and more specifically with a loop heat pipe arranged for
cooling heat generating devices for which it is impractical to
install cooling systems at the same height as or above the heat
source.
[0002] At the same time that heat generation from electrical
devices is increasing because of significant increases in the
electrical power being used, environmental concerns are making it
more difficult to cool many electrical devices in the traditional
manner.
[0003] For example, the typical means for cooling a building which
holds telephone switching or radio transmitting equipment is to
mount a heat exchanger or air conditioner condenser in a
window-like opening in the building and to use a high volume, high
speed fan to expel the heat into the atmosphere around the
building. That is all very well when the building is located on an
isolated site remote from any people, but it is becoming
increasingly necessary to locate such buildings in or near
population centers. When people or other buildings are nearby, the
noise and heat produced by such cooling systems are at least an
annoyance, and may also be illegal.
[0004] For high power electrical transformers, the type commonly
seen in electrical substations, the problem is similar. Such
transformers have previously been cooled by natural convection or
by small, relatively quiet fans, but the trend is to increase the
power rating of such transformers, and thus the heat load is
becoming more difficult to handle. In fact, to avoid unsightly
surface installations the trend is to install such transformers
underground, sometimes in or below building basements, and that
creates a significant heat disposal problem.
[0005] A somewhat different situation arises in the cooling of
diesel electric locomotives. In that case, short term heavy loads,
such as those caused by moving up a steep grade, make it necessary
to store heat until the heavy load is reduced and the cooling
system can dispose of the stored heat. It would be very desirable
to dissipate the extra heat load rather than store it, but there is
simply no available space in the typical locomotive to expose a
heat dissipating radiator to external air.
SUMMARY OF THE INVENTION
[0006] Each of the cooling problems discussed above can be solved
by the use of a loop heat pipe constructed with the heat
dissipating condenser at a level below that of the heat generating
component. For the cooling of electrical equipment buildings and
transformers, loop heat pipes transfer the generated heat directly
from the heat generating device to the soil below the site, and for
increased heat transfer to the soil the condenser of the loop heat
pipe is embedded in a concrete body. Such a concrete structure can
actually be part of the foundation of the building in which the
heat generating device is located. The advantage of loop heat pipes
is their ability to transfer heat against gravity, and to deliver
heat to a large extended surface, such as an underground structure,
without the use of any external power.
[0007] Loop heat pipes are well known in the art of heat transfer.
Superficially they appear to be a simple closed loop of pipe with a
larger diameter section at the heat input point. They are used for
transferring heat because they enable the heat transfer system to
operate without the external power required for operating
mechanical pumps to circulate the heat transfer fluid. In a loop
heat pipe the heat input into the system is the only power needed
to circulate the heat transfer fluid, so that loop heat pipes have
been particularly valuable where electrical power for mechanical
pumps is unavailable or difficult to access. For example, loop heat
pipes have been used in spacecraft where the power consumption of a
conventional pump motor is too high.
[0008] Loop heat pipes operate somewhat similarly to a conventional
still. Liquid entering the pump is vaporized by heat applied to it
at an evaporator section, and the vapor then moves out of the pump
to a cooler location in the system. At the cooler location, which
is the condenser, the vapor condenses and the liquid condensate is
either returned to the pump or to a liquid reservoir which feeds
the pump. It is the differences in vapor pressure throughout the
system which move both the vapor and the liquid.
[0009] There are, however, significant differences between a loop
heat pipe and a simple still, the major one being that the loop
heat pipe includes a capillary pump and a pressure differential to
return the condensed liquid to the heat input region to be
evaporated again. A porous wick separates the liquid inlet of the
capillary pump from its vapor outlet and, unlike a still, in which
heat is applied directly to the liquid, the input heat to drive the
capillary pump, which is usually supplied from a device which is
being cooled, is applied to this separating wick. The heat applied
to the wick causes liquid, which has been moved into the wick by
capillary action, to be vaporized and to move out of the wick and
along pipes in the system to the condenser where the vapor is
condensed. Such capillary pumps are often mounted adjacent and
parallel to other capillary pumps on a cooling plate upon which are
mounted heat producing components which are being cooled.
[0010] A typical capillary pump is built as a cylindrical
configuration so that heat can be applied to the outside of the
cylinder. In such a configuration, the liquid enters into the
center of the cylinder from one end, and the capillary wick forms
the outer cylindrical boundary of the liquid chamber, which is
closed off at the liquid chamber end remote from the liquid entry
pipe by a simple plug. An annular vapor chamber surrounds the
capillary wick, with the outer casing of the pump forming the
outermost boundary of the annular vapor chamber, and the outer
casing extends longitudinally beyond the capillary wick where it
essentially becomes a hollow pipe which can be connected to other
pipes to transport the vapor to the condenser. Thus the typical
capillary pump essentially has liquid entering one end of a heated
cylinder and has vapor leaving the other end.
[0011] In order for the external heat to be more effectively
transferred to the wick through the annular vapor chamber, the
vapor chamber is usually constructed as a group of longitudinal
channels within the inner wall of the casing or the outer surface
of the wick, with the side walls of the channels actually
contacting the adjacent capillary wick or casing. This structure
with longitudinal grooves permits the external heat to be conducted
directly to the wick through the sidewalls of the grooves, and to
evaporate the liquid which is in the wick, yet it provides space
within the grooves for the vapor to escape from the wick.
[0012] To aid movement of the condensed liquid from the condenser
back to the evaporator of the capillary pump, the prior art loop
heat pipes typically are constructed with the condenser at the same
height or higher than the capillary pump. This orientation then
uses gravity to help the movement of the liquid back to the
capillary wick of the capillary pump. Although the structure of
such loop heat pipes is conventional, the subtle limitation of such
a structure is that the source of heat is almost always located at
a lower level than the cooling condenser. However, such devices are
not taking full advantage of the capability of a loop heat pipe.
With a properly designed loop heat pipe, the condenser of the loop
heat pipe can be placed well below the evaporator, and differences
in internal pressure in the loop heat pipe move the liquid back to
the capillary pump evaporator wick. Experimental operation has
demonstrated that a condenser ten to thirty feet below the
evaporator is quite practical.
[0013] The present invention is therefore a loop heat pipe with the
condenser located below the capillary pump evaporator, and a heat
sink designed to take full advantage of the heat transfer of the
loop heat pipe. It has two important applications.
[0014] The first is for cooling electrical equipment enclosures and
transformers. In such applications the capillary pump is located at
the heat generating source, the electrical equipment or the
transformers, and the condenser is located lower than the capillary
pump, underground where the heat can be dissipated into the soil.
However, the heat conductivity of soil is rather poor, and it
limits the effective distance of heat transfer to only a foot or so
from the condenser pipe of the loop heat pipe. To counteract this
limitation, the condenser is constructed as a helix or some other
layout for which the length of the total structure is significantly
shorter than the length of the pipe from which it is constructed.
Such a structure greatly increases the surface area of the pipe and
the heat transfer area for the condenser, and the increased heat
transfer area facilitates heat transfer into the soil even though
soil has a relatively poor heat conductivity.
[0015] To further improve the heat transfer, the helix is embedded
in a solid concrete body poured around the condenser in the ground.
Although concrete is not a good heat conductor relative to metals,
it is significantly better than the typical soil, so that the solid
concrete body acts as both a heat storage body and a means of
increasing the soil surface area to which the heat is
transferred.
[0016] The second application for the invention is cooling of
diesel electric locomotives. The advantage in this application is
the ability to locate an air cooled radiator below the engine, in
an otherwise unused location, which is, however, exposed to outside
air. Thus, the capillary pump evaporator is located at the engine
component to be cooled, and the loop condenser is located under the
engine, between the wheels. In that location, a conventional heat
exchanger, such as an assembly of fins, is attached to the
condenser section of the loop heat pipe, and the heat exchanger is
exposed to the air flowing below the locomotive. A layout of the
condenser pipe as multiple parallel paths or a single serpentine
layout can be used to increase the heat transfer area available to
the outside air.
[0017] The invention thereby furnishes improved and environmentally
friendly cooling for two applications for which cooling has
previously been difficult.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a simplified schematic drawing of the invention
installed in a manner to cool an electrical equipment
enclosure.
[0019] FIG. 2 is a simplified schematic drawing of an alternate
embodiment of the invention installed to cool components in a
locomotive.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 is a simplified schematic drawing of loop heat pipe
10 of the invention installed in a manner to cool an electrical
equipment enclosure 12 within a building 14.
[0021] The evaporator of loop heat pipe 10 is included within
capillary pump 16 in the conventional construction of a loop heat
pipe, and is connected to condenser section 18, which is a simple
length of pipe, by pipes 20 and 22, either of which could be the
vapor pipe or the liquid return, depending upon the orientation of
capillary pump 16. For the present invention, condenser section 18
is located below capillary pump 16.
[0022] Capillary pump 16 is built conventionally as a cylindrical
configuration so that heat can be applied to the outside of the
cylinder. In such a configuration, the liquid enters into the
center of the cylinder from, for example, pipe 20 at one end, and a
capillary wick forms an outer cylindrical boundary of a liquid
chamber, with the liquid chamber closed off at the end remote from
liquid entry pipe 20. An annular vapor chamber surrounds the
capillary wick and the liquid chamber, with the outer casing of the
pump forming the outermost boundary of the annular vapor chamber.
The outer casing extends longitudinally beyond the capillary wick
where it essentially becomes a hollow pipe which is connected to
vapor pipe 22 which transports the vapor generated in capillary
pump 16 to condenser 18.
[0023] In the preferred embodiment of the present invention, loop
heat pipe 10 is installed with a substantial portion of it, at
least entire condenser section 18, below ground level 24 and below
the frost line 25. This permits the soil to act as a heat sink to
cool condenser section 18 which condenses the vapor within loop
heat pipe 10. To take full advantage of the relatively constant 55
degree Fahrenheit temperature of the soil below frost line 25,
condenser section 18 is installed below ground level 24 by a
distance A which should be a minimum of 24 inches.
[0024] For loop heat pipe 10, condenser 18 is constructed as a
helix to increase the surface area of the pipe relative to the
space occupied by the entire structure and to simplify
installation. However, the invention also functions satisfactorily
when the condenser is constructed as a straight length of pipe or
some other geometry such as a serpentine configuration.
[0025] Since soil is a relatively poor conductor of heat, the
operation of the invention can also be improved by encasing
condenser section 18 in concrete which is a better heat conductor
than most soils. Concrete body 26 is therefore shown in FIG. 1
completely encasing condenser section 18. With such a structure,
concrete body 26 not only withdraws heat from condenser section 18,
but acts as a heat storage medium, and since it provides a much
larger surface area than the area of the pipes of condenser section
18, it aids in conducting heat to the surrounding soil. It also can
be very advantageous to install condenser section 18 within part of
a structure of a building, such as foundation 27.
[0026] Typical dimensions for the structure of loop heat pipe 10
can be up to a total length of 20 to 30 feet, with a typical tubing
size of 1/4 to 1.0 inch internal diameter, and copper, stainless
steel, or low carbon steel used as the material of the loop heat
pipe. Condenser 18 has 6 to 12 turns with the helix 12 to 18 inches
in outer diameter, and 2 to 3-1/2 feet long depending upon the
power being transferred. Capillary pump 16 has an O.D. of 1 to 2
inches and a length of 4 to 8 inches. Its casing is constructed of
the same material as the rest of the loop heat pipe, and its
internal capillary wick is constructed of sintered metal powder. In
the preferred embodiment, the top of condenser section 18 is
installed below frost line 25. Concrete body 26 is constructed of
conventional concrete and is 18 to 24 inches in diameter and 2 to 4
feet long.
[0027] Such a structure can dissipate 10 to 100 watts into the soil
with a typical temperature difference of 5 to 20 degrees centigrade
between the heat input to capillary pump 16 and the soil
temperature.
[0028] FIG. 2 is a simplified schematic drawing of an alternate
embodiment of the invention with loop heat pipe 30 installed to
cool component 32 of locomotive 34. Loop heat pipe 30 has capillary
pump 36 located in proximity to heat generating component 32, and
has condenser section 38 located outside locomotive 34, below the
undercarriage of locomotive 34, and lower than capillary pump
36.
[0029] Condenser section 38 is constructed in a serpentine
configuration with assemblies of multiple cooling fins 40 attached
to the pipe segments of condenser section 38. Each pipe segment is
oriented across the width of locomotive 34 so that each fin 40 is
oriented parallel to the direction of the air stream flowing past
the engine. Thus, loop heat pipe 30 furnishes additional cooling
for the locomotive and utilizes space which is not otherwise
utilized.
[0030] The present invention thereby furnishes a means for cooling
equipment which is extremely simple to install and operate. The
invention requires no electrical or mechanical interconnection to
operate a pump or fan and produces no noise. The invention actually
operates with no moving parts, which minimizes maintenance
requirements, and the underground embodiment does not dissipate
heat into the surrounding air.
[0031] It is to be understood that the form of this invention as
shown is merely a preferred embodiment. Various changes may be made
in the function and arrangement of parts; equivalent means may be
substituted for those illustrated and described; and certain
features may be used independently from others without departing
from the spirit and scope of the invention as defined in the
following claims.
* * * * *