U.S. patent application number 12/197925 was filed with the patent office on 2008-12-18 for multiple temperature sensitive devices using two heat pipes.
Invention is credited to G. Yale Eastman, Scott D. Garner.
Application Number | 20080308259 12/197925 |
Document ID | / |
Family ID | 28452478 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080308259 |
Kind Code |
A1 |
Garner; Scott D. ; et
al. |
December 18, 2008 |
MULTIPLE TEMPERATURE SENSITIVE DEVICES USING TWO HEAT PIPES
Abstract
A heat pipe assembly comprises a first heat pipe having a
condenser and a working fluid. A reservoir communicates with the
condenser of the first heat pipe and contains a non-condensable gas
which variably permits access of the working fluid to the condenser
of the first heat pipe, depending on a pressure of the working
fluid. A second heat pipe has an evaporator. At least a portion of
the evaporator of the second heat pipe is contained inside of the
condenser of the first heat pipe.
Inventors: |
Garner; Scott D.; (Lititz,
PA) ; Eastman; G. Yale; (Lancaster, PA) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Family ID: |
28452478 |
Appl. No.: |
12/197925 |
Filed: |
August 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10696270 |
Oct 29, 2003 |
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12197925 |
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10106277 |
Mar 26, 2002 |
6675887 |
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10696270 |
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Current U.S.
Class: |
165/104.21 |
Current CPC
Class: |
F28D 15/06 20130101;
F28D 15/0275 20130101; F28D 15/046 20130101 |
Class at
Publication: |
165/104.21 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. A heat pipe assembly, comprising: a first heat pipe having a
condenser and a working fluid; a reservoir containing a
non-condensable gas which variably permits access of the working
fluid to the condenser of the first heat pipe, depending on a
pressure of the working fluid; and a second heat pipe having an
evaporator that is in thermal contact with the first heat pipe.
2. The heat pipe assembly of claim 1, wherein the reservoir is
internal to the first heat pipe.
3. The heat pipe assembly of claim 1, wherein: the first heat pipe
has an envelope, and the second heat pipe has conductive members
connecting the evaporator of the second heat pipe to an inside of
the envelope of the first heat pipe at the condenser thereof.
4. The heat pipe assembly of claim 3, wherein the conductive
members are a plurality of radial fins.
5. The heat pipe assembly of claim 3, further comprising a heat
sink or a plurality of fins attached to the condenser of the second
heat pipe, wherein the first heat pipe has no heat sink or fins
attached directly thereto.
6. The heat pipe assembly of claim 1, further comprising an
insulator that reduces heat transfer between an envelope of the
first heat pipe and an envelope of the second heat pipe,
7. The heat pipe assembly of claim 6, wherein the envelope of the
first heat pipe has a section formed of a thermally insulating
material at the condenser of the first heat pipe.
8. The heat pipe assembly of claim 7, wherein the evaporator of the
second heat pipe is located within the section formed of the
thermally insulating material.
9. The heat pipe assembly of claim 7, wherein the non-condensable
gas has a moving front with a range of motion within the section
formed of the thermally insulating material.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/696,270, filed Oct. 29, 2003, which is a
divisional of U.S. patent application Ser. No. 10/106,277, filed
Mar. 26, 2002, now U.S. Pat. No. 6,675,887, issued Jan. 13,
2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to heat transfer
devices and, more particularly, to variable conductance heat
pipes.
[0004] 2. Description of Related Art
[0005] The reliability of electronic components decreases
significantly as a result of high temperature extremes or large
temperature swings, especially in circumstances where these swings
or cycles are frequent. Causes of these temperature cycles include,
for example, electronic loading or environmental temperature
differences.
[0006] A heat pipe is a widely used device for transferring high
rates of heat flow across large distances with negligible
temperature drop. It generally includes a closed pressure vessel
containing a working fluid (liquid and vapor) in saturated thermal
equilibrium. External heat from a heat generating source is input
to an evaporator section, and heat is rejected to and dissipated by
an external heat sink from a condenser section. The evaporator
section and condenser section are connected by a vapor flow volume
and an internal capillary wick. A working fluid, such as ammonia,
evaporates in the evaporator section, and the vapor flows to the
condenser section and condenses, giving up its heat of vaporization
to the heat pipe wall. The working fluid then returns in liquid
form to the evaporator section via capillary pumping action within
the wick.
[0007] The conventional heat pipe is effective in transferring a
large amount of heat where a temperature difference between two
places is small, but such a heat pipe can not execute a temperature
control function. A Variable Conductance Heat Pipe (VCHP) is a
device which provides better temperature control, i.e., maintains a
heat source at a stable temperature within a few degrees of a set
point, in situations where, for example, electronics equipment can
either dissipate at different power levels, or the condenser or
heat sink is exposed to varying environmental temperatures. With a
VCHP, the amount of heat transferred is usually controlled by
blocking part of the condenser area with a non-condensable gas. The
non-condensable gas, which is stored in a gas reservoir fluidly
connected to the condenser of the VCHP, displaces a controlled
portion of the working fluid vapor in the condenser, rendering that
portion of the condenser containing the non-condensable gas
thermally inactive by blocking the interior condenser surface. Heat
transfer is inhibited because the working fluid vapor must diffuse
through the non-condensable gas in order to reach the condenser
surface. Increasing condenser blockage effectively closes the heat
pipe, reducing the area available for heat transfer. As the heat
load from a heat generating source is increased, the vapor pressure
of the working fluid increases causing the non-condensable gas to
compress and expose more of the condenser area, resulting in a
passively controlled heat transfer device.
[0008] Not only does a VCHP work to maintain a relatively constant
temperature despite varying heat input from heat generating sources
at the evaporator end of the VCHP, but it also is effective at
maintaining the heat generating source at a relatively constant
temperature where there is great variation in heat sink temperature
due to varying environmental conditions.
[0009] FIG. 5 shows a typical prior art variable conductance heat
pipe 400 having an evaporator end 405 and a condenser end 410. The
VCHP 400 comprises a hollow envelope 420, a wick 430 a working
fluid (not shown), a gas reservoir 440 containing a non-condensable
gas 442, and fins 450. A heat generating source, such as an
electronic device 300 is in thermal contact with the evaporator end
405 of the VCHP 400.
[0010] The sensitivity or control level of the VCHP 300 is driven
by the ratio of reservoir volume to condenser volume. As shown in
FIG. 5, in a typical VCHP, the gas front range 444 must swing over
a relatively large distance to block or expose the entire condenser
area and transfer heat to all of the fins 450. This results in the
requirement of a large volume reservoir to achieve a certain
desired level of control.
[0011] An improved VHCP is desired.
SUMMARY OF THE INVENTION
[0012] The present invention is a heat pipe assembly comprising a
first heat pipe having a condenser and a working fluid. A reservoir
contains a non-condensable gas which variably permits access of the
working fluid to the condenser of the first heat pipe, depending on
a pressure of the working fluid. A second heat pipe has an
evaporator that is in thermal contact with the first heat pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional view of a heat pipe assembly of
the present invention.
[0014] FIG. 2 is a cross-sectional view of a variation of the heat
pipe assembly of FIG. 1.
[0015] FIG. 3 is a cross-sectional view of another embodiment of
the heat pipe assembly of the present invention.
[0016] FIG. 4 is a cross-sectional view of another variation of the
heat pipe assembly of FIG. 1.
[0017] FIG. 5 is a cross-sectional view of a prior art variable
conductance heat pipe.
[0018] It will be understood that the drawings are not scale
drawings. One of ordinary skill in the art can readily select
appropriate dimensions for a specific cooling application.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] In the description below, the terms top, bottom, left and
right are understood to refer to the directions appropriate when
the device is oriented in the manner shown in the figures. Such
terms do not limit the possible orientations of the device, and it
is understood that the device can be oriented in any manner, and
such relational terms as top, bottom, left and right would
automatically be changed.
[0020] In the various drawings, parts identified by the same
reference numeral are the same.
[0021] Referring to FIG. 1, a heat pipe assembly 101 according to
one embodiment of the invention comprises a variable conductance
heat pipe (VCHP) 100 and a second heat pipe 200. The exemplary
second heat pipe 200 provides an extremely stiff heat sink or
condenser area of the first heat pipe 100. This provides
significant improvement in the temperature control of the first
VHCP 100.
[0022] VCHP 100 has an evaporator end 105 and a condenser end 110.
VCHP includes a hollow envelope 120, a wick 130, a working fluid
(not shown) and a gas reservoir 140, which may be external to the
VHCP (as shown in FIG. 1) or integral (as shown by 540 in FIG. 4).
Gas reservoir 140 contains non-condensable gas 142. Envelope 120 is
typically comprised of a metal such as copper or aluminum, and is
typically selected based on compatibility with the selected working
fluid. The structure and composition of wick 130 may vary depending
on the application and may include such structures known to those
of ordinary skill in the art such as groove, screen, cable/fiber,
or sintered powder metal. Likewise, the working fluid may vary
depending on the application and temperature range, and may include
water, ammonia or freon, for example. Suitable non-condensable
gases 142 include inert gases such as nitrogen, argon, helium, neon
and mixtures thereof.
[0023] In the exemplary embodiment of FIG. 1, fins are not included
on the condenser 110 of the first heat pipe 100. Rather, heat from
the first heat pipe is dissipated to the environment by way of the
second heat pipe 200. Second heat pipe 200 has an evaporator end
205 and a condenser end 210. Second heat pipe 200 comprises a
hollow envelope 220, a wick (not shown) and a working fluid (not
shown). Second heat pipe 200 may further include a heat sink 240
attached to condenser end 210. Heat sink 240 may be in the form of
fins as shown in FIGS. 1-3. Second heat pipe 200 may be a
conventional heat pipe or alternatively, second heat pipe 200 may
itself be a variable conductance heat pipe.
[0024] Envelope 220, like envelope 120, is typically comprised of a
metal such as copper or aluminum. The structure and composition of
the wick of the second heat pipe 200 and the composition of the
working fluid, again, may vary depending on the application and may
include any structure or composition known to those of ordinary
skill in the art. Preferably, the envelope of second heat pipe 200
is made of the same material as the envelope of first heat pipe
100, and the working fluids are the same.
[0025] The exemplary assembly of FIG. 1 is assembled in the
following manner. As shown in FIG. 1, wick 130 of VCHP 100 lines an
inside surface of envelope 120. The envelope 120 is evacuated. A
sufficient amount of the working fluid (in liquid form) is added so
as to saturate the wick 130. When the working fluid reaches thermal
equilibrium, the working fluid (in liquid and gas states)
substantially fills envelope 120. Gas reservoir 140 is mechanically
and fluidly connected to the condenser end 110 of VCHP 100 via
tubing 144. Non-condensable gas 142 is variably contained within
the gas reservoir 140, tubing 144 and condenser end 110 of VCHP
100.
[0026] Evaporator end 205 of second heat pipe 200 is mechanically
attached and sealed to condenser end 110 of VCHP and at least a
portion of evaporator end 205 of second heat pipe 200 is contained
inside of condenser end 110 of VCHP 100. Evaporator end 205 of
second heat pipe 200 could be in thermal contact with the condenser
end 110 of VCHP 100. Preferably, hear sink 240 or a plurality of
individual fins are attached to an outside surface of envelope 210
of second heat pipe 200.
[0027] The embodiment of FIG. 1 operates in the following manner.
In the embodiment of FIG. 1, an outside surface of the envelope] 20
at the evaporator end 105 of VCHP 100 is in thermal contact with an
external heat generating source or sources, such as electronic
devices 300. At a low end of the operating temperature range (at
low operating power for electronics devices), the gas charge in the
gas reservoir 140 is at such a pressure that the gas blankets the
condenser end 110 of the VCHP 100.
[0028] A variable gas front 145 marks the separation point between
the working fluid vapor and the non-condensable gas 142. The
non-condensable gas 142 has a moving front 145 with a range of
motion 146 within the condenser 110 of the first heat pipe 100. The
non-condensable gas 142 variably permits access of the working
fluid to the condenser 110 and evaporator 205. When the moving
front 145 is at a first (right in FIG. 1) boundary of the range of
motion 146, the working fluid does not access a portion of the
condenser 110 in which the evaporator 205 of the second heat pipe
200 is located. When the moving front 145 is at a second (left in
FIG. 1) boundary of the range of motion 146, the working fluid
accesses a portion of the condenser 110 in which the evaporator 205
of the second heat pipe 200 is located. When the gas front 145
moves to the towards the right in FIG. 1, the condensable gas front
is to the right of the evaporator end 205 of heat pipe 200 and the
blockage of the condenser end 110 by the non-condensable gas 142
prevents efficient heat transfer to condenser end 110 (and thus
prevents heat transfer to the evaporator 205 of second heat pipe
200 and to heat sink 240). This allows the heat source(s) 300 to
remain at a relatively constant temperature. As heat generated by
the heat source(s) 300 heats the evaporator end 105 of VCHP 100,
the working fluid is vaporized and the vapor begins to flow toward
the condenser end 110 of VCHP 100, which is at a lower temperature.
This vapor pressure causes the non-condensable gas to compress, and
moves the gas front 145 further away from the evaporator end, thus
exposing more of the condenser end (the "active condenser'") to the
hot working fluid vapor.
[0029] In prior art VCHP's, as shown in FIG. 5, the gas front range
444 must swing over a relatively large distance (i.e., the length
of the finstack 450) to block or expose the entire condenser area.
This results in the necessity of a large volume reservoir to
achieve a given level of control. In the embodiment of FIG. 1, the
incorporation of a second heat pipe 200 as the heat sink for the
VCHP 100 allows the heat pipe assembly 101 to absorb the entire
heat load with very little surface area of condenser end 110
exposed to the condensing vapor.
[0030] In FIG. 1, the range of motion 146 is substantially shorter
in the longitudinal direction than the condenser 110 of the first
heat pipe 100, and substantially shorter in the longitudinal
direction than the condenser 210 of the second heat pipe 200. For
example, the range of motion may be less than 0.2 times as long as
the condenser of the first heat pipe, or in some embodiments,
between 0.07 and 0.2 times as long as the condenser of the first
heat pipe. Similarly, the range of motion may be less than or equal
to about 0.2 times as long as the condenser 210 of the second heat
pipe 200, or the length of the finstack 240. This reduces the size
of the reservoir and condenser area needed achieve the desired
controlled heat transfer.
[0031] As soon as the gas front 145 touches the evaporator 205 of
the second heat pipe 200, heat pipe 200 transfers the heat load to
the heat sink 140, from which the heat is dissipated. This in turn
decreases the vapor pressure of the evaporator end 105 of the VCHP
100 causing the gas front to move back towards the evaporator end
105. This expansion of the non-condensable gas 142 again blocks
access to the condenser end 110 of VCHP 100 and second heat pipe
200. In this state almost no heat can be rejected and the pressure
will begin to increase where the heat source is generating heat.
With this improved heat pipe assembly, as shown in FIG. 1, the
distance the gas front 145 must move (the "gas front range" 146),
to go from "full on" to "full off" is very small compared to the
prior art VCHP's as shown in FIG. 5, while still allowing the
temperature of the heat source(s) to remain stable within a few
degrees.
[0032] Referring to FIG. 2, there is shown a variation of the heat
pipe assembly 201 containing a further improvement. Heat pipe
assembly 201 includes a VCHP 100' and a second heat pipe 200'.
[0033] VCHP 100' in the variation of FIG. 2 is the same as VCHP 100
in FIG. 1. VCHP 100' has an evaporator end 105' and a condenser end
110', VCHP 100' includes a hollow envelope 120', a wick 130', a
working fluid (not shown) and a gas reservoir 140'. Gas reservoir
140' contains non-condensable gas 142'.
[0034] Second heat pipe 200' has an evaporator end 205' and a
condenser end 210'. Second heat pipe 200' includes a hollow
envelope 220', a wick (not shown), a working fluid (not shown) and
evaporator fins 250. Second heat pipe 200' may further include a
heat sink 240' attached to condenser end 210'. Such heat sink 240'
may be in the form of fins as shown in FIGS. 1-3. Second heat pipe
200' may be a conventional heat pipe or alternatively, second heat
pipe 200' may itself be a variable conductance heat pipe.
Evaporator fins 250' are preferably comprised of metal such as
aluminum, copper or steel.
[0035] In the embodiment as shown in FIG. 2, the distance from
"full off" to "full on" is further reduced by the addition of
conductive members, such as radial evaporator fins 250' to the
evaporator end 205' of second heat pipe 200'. These conductive
members 250' add surface area to the evaporator end 205' of second
heat pipe 200' to further enhance heat transfer from the VCHP 100'
to second heat pipe 200'. The result is an even more sensitive heat
transfer device.
[0036] In the assembly 20] shown in FIG. 2 including the evaporator
fins 250', evaporator fins 250' are mechanically and conductively
coupled to evaporator end 205' of second heat pipe 200' to increase
the evaporator surface area of (and heat transfer to) the
evaporator end 205' of the second heat pipe 200' for enhancing heat
transfer from VCHP 100' to the second heat pipe 200', The
evaporator fins 250' are contained within the condenser end 110' of
the VCHP 100'.
[0037] Although the exemplary conductive members are fins 250',
other shapes of conductive members may be used. For example, the
conductive members may be radial columns or pins having a variety
of shapes. Preferably, a shape that does not create significant
resistance to movement of the vaporized working fluid is used.
[0038] Referring to FIG. 3, there is shown another embodiment of
the heat pipe assembly 301 of the present invention containing a
further improvement. Heat pipe assembly 301 includes a VCHP 100''
and a second heat pipe 200''.
[0039] VCHP 100'' has an evaporator end 105'' and a condenser end
110''. VCHP 100'' includes a hollow envelope 120'', a wick 130'', a
working fluid (not shown) a gas reservoir 140'', and an insulator
150''. Gas reservoir 140'' contains non-condensable gas 142''.
Insulator 150'' is preferably comprised of a ceramic material, but
may be comprised of any thermally insulating material, such as a
low conductivity metal.
[0040] In the first heat pipe 100'', the envelope 120'' has a
section 150'' formed of a thermally insulating material at the
condenser 110'', Insulating section 150'' provides continuity in
the vapor seal of envelope 120'', while substantially reducing or
eliminating the conductive couplings between the evaporator end
105'' of the envelope 120'' and the evaporator 205'' of second heat
pipe 200''. Wick 130'' extends in the section between the thermally
conductive portions of envelope 120'', and abuts the inside surface
of insulator 150''. With an insulating section 150'' in the
envelope 120'', heat transfer from the evaporator 105'' to the
evaporator 205'' is essentially by way of the vaporized working
fluid contacting the evaporator 205''.
[0041] The second heat pipe 200'' of FIG. 3 is the same as that
shown in FIG. 1. Second heat pipe 200'' has an evaporator end 205''
and a condenser end 210''. Second heat pipe 200'' includes a hollow
envelope 220'', a wick 230'', and a working fluid (not shown).
Second heat pipe 200'' may further include a heat sink 240''
attached to condenser end 210''. Heat sink 240'' may be in the form
of fins. Second heat pipe 200'' may be a conventional heat pipe or
alternatively, second heat pipe 200'' may itself be a variable
conductance heat pipe. The evaporator 205'' of the second heat pipe
200'' is located within the section fanned of the thermally
insulating material.
[0042] The heat pipe assembly 301 shown in FIG. 3 improves the
control sensitivity of the heat exchange system. In a typical VCHP,
as well as in the improved VCHP's of FIGS. 1 and 2, heat can be
conducted from the metal envelope 120 at the evaporator end 105 of
VCHP 100 to the condenser end 110 and to the evaporator of the
second heat pipe 200. This conductive heat path decreases the
control sensitivity of the system. In an ideal system, the two heat
pipes would be completely thermally isolated except for heat
transfer by condensing working fluid vapor from the VCHP to the
evaporator of the second heat pipe. The incorporation of insulator
150'' into the envelope 120'' of VCHP 100'' minimizes this
alternative heat flow path, thus reducing any decrease in control
sensitivity of the system.
[0043] FIG. 4 shows another variation of the heat pipe assembly. In
assembly 501, the reservoir 540 is completely internal to the first
heat pipe 100'''. VCHP 100''' has an evaporator end 105''' and a
condenser end 110''', a hollow envelope 120''', a wick 130''', and
a working fluid (not shown). Gas reservoir 540 contains
non-condensable gas 542. Second heat pipe 200''' has an evaporator
end 205''', a condenser end 210''', a hollow envelope 220''', a
heat sink 240''', a wick (not shown) and a working fluid (not
shown).
[0044] The improved heat pipe assemblies 101, 201 or 301 of FIGS.
1-4 will be useful wherever temperature control of a device
dissipating heat is desired. One application is for outdoor
telecommunications equipment where the life of the electronic
devices as well as their optimum performance can be improved by
maintaining a relatively narrow operating temperature. Outdoor
ambient temperatures can range from -45.degree. C. to 50.degree. C.
Electronics cooled by traditional fixed conductance heat sinks will
have a similarly large fluctuation in operating temperatures. Use
of conventional VCHP's can shrink that range, and use of the
improved heat pipe assemblies of the exemplary embodiments can
shrink that range even further to an almost isothermal operating
environment.
[0045] Another application for the heat pipe assemblies of FIGS.
1-4 is in situations where there are multiple heat sources or a
single source with a varying heat load. With a fixed conductance
heat sink the temperature will be linear with the amount of power
dissipated. In order to have relatively fixed operating
temperatures with varying loads requires an active feed back
control to the heat sink. This active control might undesirably
increase fan speed, liquid flow or compressor capacity in a
refrigerated system.
[0046] The proposed system can be used to couple multiple devices
to an over-capacity heat sink operating at a constant temperature.
The device operating temperatures will be maintained at a
relatively constant temperature regardless of how many devices are
operating at a given time.
[0047] Although the invention has been described in terms of
exemplary embodiments, it is not limited thereto. Rather, the
appended claims should be construed broadly, to include other
variants and embodiments of the invention, which may be made by
those skilled in the art without departing from the scope and range
of equivalents of the invention.
* * * * *