U.S. patent application number 11/465372 was filed with the patent office on 2007-05-31 for system and method for boiling heat transfer using self-induced coolant transport and impingements.
This patent application is currently assigned to Raytheon Company. Invention is credited to Albert P. Payton, Kerrin A. Rummel, Richard M. Weber.
Application Number | 20070119572 11/465372 |
Document ID | / |
Family ID | 38780774 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070119572 |
Kind Code |
A1 |
Weber; Richard M. ; et
al. |
May 31, 2007 |
System and Method for Boiling Heat Transfer Using Self-Induced
Coolant Transport and Impingements
Abstract
According to one embodiment of the invention, a cooling system
for a heat-generating structure comprises a chamber and structure
disposed within the chamber. The chamber has an inlet and an
outlet. The inlet receives fluid coolant into the chamber
substantially in the form of a liquid. The outlet dispenses the
fluid coolant out of the chamber at least partially in the form of
a vapor. The structure disposed within the chamber receive thermal
energy from the heat generating structure and transfers at least a
portion of the thermal energy to the fluid coolant. The thermal
energy from the heat-generating structure causes at least a portion
of the fluid coolant substantially in the form of a liquid to boil
and effuse vapor upon contact with a portion of the structure. The
effusion of vapor creates a self-induced flow in the chamber. The
self-induced flow distributes non-vaporized fluid coolant
substantially in the form of a liquid to other portions of the
structure.
Inventors: |
Weber; Richard M.; (Prosper,
TX) ; Rummel; Kerrin A.; (Richardson, TX) ;
Payton; Albert P.; (Sachse, TX) |
Correspondence
Address: |
BAKER BOTTS LLP
2001 ROSS AVENUE
6TH FLOOR
DALLAS
TX
75201
US
|
Assignee: |
Raytheon Company
Waltham
MA
|
Family ID: |
38780774 |
Appl. No.: |
11/465372 |
Filed: |
August 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11290065 |
Nov 30, 2005 |
|
|
|
11465372 |
Aug 17, 2006 |
|
|
|
Current U.S.
Class: |
165/80.4 ;
257/E23.088; 257/E23.105; 361/699 |
Current CPC
Class: |
H01L 23/4735 20130101;
F28F 3/022 20130101; H01L 23/3677 20130101; F28F 3/12 20130101;
H01L 23/427 20130101; F28D 15/0266 20130101; H01L 2924/0002
20130101; H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/080.4 ;
361/699 |
International
Class: |
H05K 7/20 20060101
H05K007/20 |
Claims
1. A cooling system for a heat-generating structure, the cooling
system comprising: a fluid coolant; a chamber having an inlet and
an outlet, the inlet operable to receive a fluid coolant into the
chamber substantially in the form of a liquid, the outlet operable
to dispense of the fluid coolant out of the chamber at least
partially in the form of a vapor; a structure which directs a flow
of the fluid coolant substantially in the form of a liquid into the
chamber through the inlet; a structure disposed in the chamber, the
structure operable to receive thermal energy from the heat
generating structure and transfer at least a portion of the thermal
energy to the fluid coolant, the thermal energy from the
heat-generating structure causing at least a portion of the fluid
coolant substantially in the form of a liquid to boil and effuse
vapor upon contact with a portion of the structure; and wherein the
effusion of vapor creates a self-induced flow in the chamber, the
self-induced flow distributing non-vaporized fluid coolant
substantially in the form of a liquid to other portions of the
structure.
2. The cooling system of claim 1, wherein the flow of the fluid
coolant substantially in the form of a liquid into the chamber
through the inlet is less than double the amount of flow necessary
to absorb thermal energy with one hundred percent conversion.
3. The cooling system of claim 2, wherein the flow of the fluid
coolant substantially in the form of a liquid into the chamber
through the inlet is less than thirty percent more than the amount
of flow necessary to absorb thermal energy with one hundred percent
conversion.
4. The cooling system of claim 1, wherein the self-induced flow is
chaotic.
5. The cooling system of claim 1, wherein the structure is a
plurality of pin fins.
6. The cooling system of claim 1, further comprising: a structure
which reduces a pressure of the fluid coolant to a subambient
pressure at which the fluid coolant has a boiling temperature less
than a temperature of the heat-generating structure.
7. A cooling system for a heat-generating structure, the cooling
system comprising: a chamber having an inlet and an outlet, the
inlet operable to receive a fluid coolant into the chamber
substantially in the form of a liquid, the outlet operable to
dispense of the fluid coolant out of the chamber at least partially
in the form of a vapor; a structure disposed in the chamber, the
structure operable to receive thermal energy from the heat
generating structure and transfer at least a portion of the thermal
energy to the fluid coolant, the thermal energy from the
heat-generating structure causing at least a portion of the fluid
coolant substantially in the form of a liquid to boil and effuse
vapor upon contact with a portion of the structure; wherein the
effusion of vapor creates a self-induced flow in the chamber, the
self-induced flow distributing non-vaporized fluid coolant
substantially in the form of a liquid to other portions of the
structure.
8. The cooling system of claim 7, wherein the self-induced flow is
chaotic.
9. The cooling system of claim 7, wherein the structure is a
plurality of pin fins.
10. The cooling system of claim 9, wherein the self-induced flow
includes globs of fluid coolant substantially in the form of a
liquid thrown against pin fins.
11. The cooling system of claim 7, wherein the system creates a
maximum temperature differential between different portions of the
structure disposed in the chamber less than two degrees
Celsius.
12. The cooling system of claim 7, wherein a flow of fluid coolant
into the chamber is gravity fed.
13. The cooling system of claim 7, wherein a portion of the system
operates as a thermal siphon to circulate fluid through the
system.
14. The cooling system of claim 7, wherein structure is a plurality
of pin fins.
15. The cooling system of claim 7, wherein a flow of fluid coolant
substantially in the form of a liquid into the chamber through the
inlet is less than double the amount of flow necessary to absorb
thermal energy with one hundred percent conversion.
16. The cooling system of claim 14, wherein the flow of the fluid
coolant substantially in the form of a liquid into the chamber
through the inlet is less than thirty percent more than the amount
of flow necessary to absorb thermal energy with one hundred percent
conversion.
17. The cooling system of claim 7, further comprising: a structure
which reduces a pressure of the fluid coolant to a subambient
pressure at which the fluid coolant has a boiling temperature less
than a temperature of the heat-generating structure.
18. A method for cooling a heat-generating structure, the method
comprising: transferring thermal energy from a heat generating
structure to a structure disposed in a chamber; introducing a fluid
coolant into the chamber; exposing the fluid coolant to at least a
portion of the structure disposed in the chamber, thereby causing
at least a portion of the fluid coolant substantially in the form
of a liquid to boil and effuse vapor, the effused vapor creating a
self-induced flow in the chamber; distributing non-vaporized fluid
coolant substantially in the form of a liquid to other portions of
the structure using the self-induced flow; and transferring at
least a portion of the thermal energy from the structure disposed
in the chamber to the fluid coolant.
19. The method of claim 18, wherein the introduction of fluid
coolant into the chamber has a flow that is less than double the
amount of flow necessary to absorb thermal energy with one hundred
percent conversion.
20. The method of claim 18, further comprising: reducing a pressure
of the fluid coolant to a subambient pressure at which the fluid
coolant has a boiling temperature less than a temperature of the
heat-generating structure.
Description
RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of U.S. patent
application Ser. No. 11/290,065 filed on Nov. 30, 2005.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates generally to the field of cooling
systems and, more particularly, to a system and method of boiling
heat transfer using self-induced coolant transport and
impingements.
BACKGROUND OF THE INVENTION
[0003] A variety of different types of structures can generate heat
or thermal energy in operation. To prevent such structures from
over heating, a variety of different types of cooling systems may
be utilized to dissipate the thermal energy. To facilitate the
dissipation of such thermal energy in such cooling systems, a
variety of different types of coolants may be utilized.
SUMMARY OF THE INVENTION
[0004] According to one embodiment of the invention, a cooling
system for a heat-generating structure comprises a chamber and
structure disposed within the chamber. The chamber has an inlet and
an outlet. The inlet receives fluid coolant into the chamber
substantially in the form of a liquid. The outlet dispenses the
fluid coolant out of the chamber at least partially in the form of
a vapor. The structure disposed within the chamber receive thermal
energy from the heat generating structure and transfers at least a
portion of the thermal energy to the fluid coolant. The thermal
energy from the heat-generating structure causes at least a portion
of the fluid coolant substantially in the form of a liquid to boil
and effuse vapor upon contact with a portion of the structure. The
effusion of vapor creates a self-induced flow in the chamber. The
self-induced flow distributes non-vaporized fluid coolant
substantially in the form of a liquid to other portions of the
structure.
[0005] Certain embodiments of the invention may provide numerous
technical advantages. For example, a technical advantage of one
embodiment may include the capability to enhance heat transfer in a
coolant stream. Other technical advantages of other embodiments may
include the capability to utilize pin fin configurations to alter
the heat transfer phenomenology and thereby enhance the transfer of
thermal energy. Yet other technical advantages of other embodiments
may include the capability to reduce a flow requirement into a
chamber utilized for heat transfer.
[0006] Although specific advantages have been enumerated above,
various embodiments may include all, some, or none of the
enumerated advantages. Additionally, other technical advantages may
become readily apparent to one of ordinary skill in the art after
review of the following figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of example embodiments of
the present invention and its advantages, reference is now made to
the following description, taken in conjunction with the
accompanying drawings, in which:
[0008] FIG. 1 is a block diagram of an embodiment of a cooling
system that may be utilized in conjunction with other
embodiments;
[0009] FIGS. 2A-2C illustrate conventional coldplate
configurations;
[0010] FIG. 3A is an isolated perspective view of a pin fin
configuration and FIG. 3B is a side cross-sectional view of a pin
fin configuration that may be utilized in embodiments of the
invention;
[0011] FIGS. 4A, 4B, 4C, and 4D show pin fin configurations,
according to embodiments of the invention; and
[0012] FIGS. 5A-6C show a comparison of two heat load test
articles.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION
[0013] It should be understood at the outset that although example
embodiments of the present invention are illustrated below, the
present invention may be implemented using any number of
techniques, whether currently known or in existence. The present
invention should in no way be limited to the example embodiments,
drawings, and techniques illustrated below, including the
embodiments and implementation illustrated and described herein.
Additionally, the drawings are not necessarily drawn to scale.
[0014] FIG. 1 is a block diagram of an embodiment of a cooling
system 10 that may be utilized in conjunction with other
embodiments disclosed herein, namely surface enhancement
embodiments described with reference to FIGS. 3A-4D and FIGS.
6A-6C. Although the details of one cooling system will be described
below, it should be expressly understood that other cooling systems
may be used in conjunction with embodiments of the invention.
[0015] The cooling system 10 of FIG. 1 is shown cooling a structure
12 that is exposed to or generates thermal energy. The structure 12
may be any of a variety of structures, including, but not limited
to, electronic components, modules, and circuits. Because the
structure 12 can vary greatly, the details of structure 12 are not
illustrated and described. The cooling system 10 of FIG. 1 includes
channels 23 and 24, pump 46, inlet orifices 47 and 48, a condenser
heat exchanger 41, an expansion reservoir 42, and a pressure
controller 51.
[0016] The structure 12 may be arranged and designed to conduct
heat or thermal energy to the channels 23, 24. To receive this
thermal energy or heat, the channels 23, 24 may be disposed on an
edge of the structure 12 or may extend through portions of the
structure 12, for example, through a thermal plane of structure 12.
In particular embodiments, the channels 23, 24 may extend up to the
components of the structure 12, directly receiving thermal energy
from the components. Further, in particular embodiments the
channels 23, 24 may be cold walls. Although two channels 23, 24 are
shown in the cooling system 10 of FIG. 1, one channel or more than
two channels may be used to cool the structure 12 in other cooling
systems.
[0017] In operation, a fluid coolant flows through each of the
channels 23, 24. As discussed later, this fluid coolant may be a
two-phase fluid coolant, which enters inlet conduits 25 of channels
23, 24 in liquid form. Absorption of heat from the structure 12
causes part or all of the liquid coolant to boil and vaporize such
that some or all of the fluid coolant leaves the exit conduits 27
of channels 23, 24 in a vapor phase. To facilitate such absorption
or transfer of thermal energy, the channels 23, 24 may be lined
with pin fins or other similar surface enhancement devices which,
among other things, increase surface contact between the fluid
coolant and walls of the channels 23, 24. Further details of the
surface enhancement configurations, namely pin fin configurations,
are described below with reference to FIGS. 3A-4D and FIGS.
6A-6C.
[0018] The fluid coolant departs the exit conduits 27 and flows
through the condenser heat exchanger 41, the expansion reservoir
42, a pump 46, and a respective one of two orifices 47 and 48, in
order to again to reach the inlet conduits 25 of the channels 23,
24. The pump 46 may cause the fluid coolant to circulate around the
loop shown in FIG. 1. In particular embodiments, the pump 46 may
use magnetic drives so there are no shaft seals that can wear or
leak with time.
[0019] The orifices 47 and 48 in particular embodiments may
facilitate proper partitioning of the fluid coolant among the
respective channels 23, 24, and may also help to create a large
pressure drop between the output of the pump 46 and the channels
23, 24 in which the fluid coolant vaporizes. The orifices 47 and 48
may have the same size, or may have different sizes in order to
partition the coolant in a proportional manner which facilitates a
desired cooling profile.
[0020] A flow 56 of fluid (either gas or liquid) may be forced to
flow through the condenser heat exchanger 41, for example by a fan
(not shown) or other suitable device. In particular embodiments,
the flow 56 of fluid may be ambient fluid. The condenser heat
exchanger 41 transfers heat from the fluid coolant to the flow 56
of ambient fluid, thereby causing any portion of the fluid coolant
which is in the vapor phase to condense back into a liquid phase.
In particular embodiments, a liquid bypass 49 may be provided for
liquid fluid coolant that either may have exited the channels 23,
24 or that may have condensed from vapor fluid coolant during
travel to the condenser heat exchanger 41.
[0021] The liquid fluid coolant exiting the condenser heat
exchanger 41 may be supplied to the expansion reservoir 42. Since
fluids typically take up more volume in their vapor phase than in
their liquid phase, the expansion reservoir 42 may be provided in
order to take up the volume of liquid fluid coolant that is
displaced when some or all of the coolant in the system changes
from its liquid phase to its vapor phase. The amount of the fluid
coolant which is in its vapor phase can vary over time, due in part
to the fact that the amount of heat or thermal energy being
produced by the structure 12 will vary over time, as the structure
12 system operates in various operational modes.
[0022] Turning now in more detail to the fluid coolant, one highly
efficient technique for removing heat from a surface is to boil and
vaporize a liquid which is in contact with a surface. As the liquid
vaporizes in this process, it inherently absorbs heat to effectuate
such vaporization. The amount of heat that can be absorbed per unit
volume of a liquid is commonly known as the latent heat of
vaporization of the liquid. The higher the latent heat of
vaporization, the larger the amount of heat that can be absorbed
per unit volume of liquid being vaporized.
[0023] The fluid coolant used in the embodiment of FIG. 1 may
include, but is not limited to mixtures of antifreeze and water. In
particular embodiments, the antifreeze may be ethylene glycol,
propylene glycol, methanol, or other suitable antifreeze. In other
embodiments, the mixture may also include fluoroinert. In
particular embodiments, the fluid coolant may absorb a substantial
amount of heat as it vaporizes, and thus may have a very high
latent heat of vaporization.
[0024] Water boils at a temperature of approximately 100.degree. C.
at an atmospheric pressure of 14.7 pounds per square inch absolute
(psia). In particular embodiments, the fluid coolant's boiling
temperature may be reduced to between 55-65.degree. C. by
subjecting the fluid coolant to a subambient pressure of about 2-3
psia. Thus, in the cooling system 10 of FIG. 1, the orifices 47 and
48 may permit the pressure of the fluid coolant downstream from
them to be substantially less than the fluid coolant pressure
between the pump 46 and the orifices 47 and 48, which in this
embodiment is shown as approximately 12 psia. The pressure
controller 51 maintains the coolant at a pressure of approximately
2-3 psia along the portion of the loop which extends from the
orifices 47 and 48 to the pump 46, in particular through the
channels 23 and 24, the condenser heat exchanger 41, and the
expansion reservoir 42. In particular embodiments, a metal bellows
may be used in the expansion reservoir 42, connected to the loop
using brazed joints. In particular embodiments, the pressure
controller 51 may control loop pressure by using a motor driven
linear actuator that is part of the metal bellows of the expansion
reservoir 42 or by using small gear pump to evacuate the loop to
the desired pressure level. The fluid coolant removed may be stored
in the metal bellows whose fluid connects are brazed. In other
configurations, the pressure controller 51 may utilize other
suitable devices capable of controlling pressure.
[0025] In particular embodiments, the fluid coolant flowing from
the pump 46 to the orifices 47 and 48 may have a temperature of
approximately 55.degree. C. to 65.degree. C. and a pressure of
approximately 12 psia as referenced above. After passing through
the orifices 47 and 48, the fluid coolant may still have a
temperature of approximately 55.degree. C. to 65.degree. C., but
may also have a lower pressure in the range about 2 psia to 3 psia.
Due to this reduced pressure, some or all of the fluid coolant will
boil or vaporize as it passes through and absorbs heat from the
channels 23 and 24.
[0026] After exiting the exits ports 27 of the channels 23, 24, the
subambient coolant vapor travels to the condenser heat exchanger 41
where heat or thermal energy can be transferred from the subambient
fluid coolant to the flow 56 of fluid. The flow 56 of fluid in
particular embodiments may have a temperature of less than
50.degree. C. In other embodiments, the flow 56 may have a
temperature of less than 40.degree. C. As heat is removed from the
fluid coolant, any portion of the fluid which is in its vapor phase
will condense such that substantially all of the fluid coolant will
be in liquid form when it exits the condenser heat exchanger 41. At
this point, the fluid coolant may have a temperature of
approximately 55.degree. C. to 65.degree. C. and a subambient
pressure of approximately 2 psia to 3 psia. The fluid coolant may
then flow to pump 46, which in particular embodiments 46 may
increase the pressure of the fluid coolant to a value in the range
of approximately 12 psia, as mentioned earlier. Prior to the pump
46, there may be a fluid connection to an expansion reservoir 42
which, when used in conjunction with the pressure controller 51,
can control the pressure within the cooling loop.
[0027] It will be noted that the embodiment of FIG. 1 may operate
without a refrigeration system. In the context of electronic
circuitry, such as may be utilized in the structure 12, the absence
of a refrigeration system can result in a significant reduction in
the size, weight, and power consumption of the structure provided
to cool the circuit components of the structure 12.
[0028] Although components of one embodiment of a cooling system 10
have been shown in FIG. 1, it should be understood that other
embodiments of the cooling system 10 can include more, less, or
different component parts. For example, although specific
temperatures and pressures have been described for one embodiment
of the cooling system, other embodiments of the cooling system 10
may operate at different pressures and temperatures. Additionally,
in some embodiments a coolant fill port and/or a coolant bleed port
may be utilized with metal-to-metal caps to seal them. Further, in
some embodiments, all or a portion of the joints between various
components may be brazed, soldered or welded using metal-to-metal
seal caps.
[0029] In boiling heat transfer, there are four general ways in
which a fluid interacts with a surface: (1) pool boiling, (2) flow
boiling, (3) jet impingement cooling, and (4) spray cooling. With
pool boiling, a volume of coolant comes in contact with a heated
surface and the coolant is not forced to flow over the surface
using a pump or other forcible method. Rather, gravity feeds
coolant to the heated surface to replenish the coolant that has
turned to vapor. Pool boiling reaches a limit when the effusing
vapor does not allow for adequate coolant replenishment. When this
happens, a film of vapor develops between the heated surface and
the body of coolant as the boiling action transitions to film
boiling. As a result, a higher temperature of the heated surface is
required to drive the heat through the vapor film for boiling to
happen at the vapor-liquid interface. When this happens the heat
transfer coefficient drops significantly resulting in poor transfer
of heat.
[0030] With flow boiling, coolant is forced to flow across the
heated surface. As a result, vapor bubbles are washed away allowing
for liquid coolant to replenish the coolant that has vaporized.
This approach, in general, supports higher heat fluxes and yields
higher heat transfer coefficients than pool boiling. Flow boiling
has a limit at which there can be so much vapor produced that even
a forced flow of coolant can not ensure adequate wetting of the
heated surface. Flow boiling can also transition to film boiling,
but generally at significantly higher heat fluxes than pool
boiling.
[0031] With jet impingement cooling, coolant is forced to impinge
the heated surface due to the momentum of the coolant coming out of
a jet. The coolant forcibly passes through any vapor bubbles or a
vapor film to wet the heated surface and pushes the vapor bubbles
outward along the heated surface. Once the coolant flow is away
from the area of impingement, the coolant flow behaves like flow
boiling as there is no more impingement action to penetrate a
volume of bubbles or a vapor film.
[0032] Spray cooling creates a mist or stream of coolant drops that
impact the heated surface. In this case a thin liquid film of
coolant is "painted" on the surface. As the coolant vaporizes, it
is replenished by a continuing stream of mist from the spay head.
Because spray nozzles for spray cooling are typically positioned at
an appreciable distance from the heated surface, spray cooling is
unsuitable for particular applications, namely densely packaged
electronics.
[0033] FIGS. 2A-2C illustrate conventional coldplate
configurations. FIG. 2A shows straight fin stock 90A that can be
used in a coldplate; FIG. 2B shows wavy fin stock 90A that can be
used in a coldplate; and FIG. 2C shows a cross sectional view of a
coldplate 80 with straight fin stock 90A. With reference to FIG.
2C, thermal energy or heat from a structure is transferred to the
coldplate 80, then to the straight fin stock 90A, and then to a
cross-flowing coolant stream (illustrated by arrow 82) within the
coldplate 80. To facilitate this flow, the coldplate 80 may include
features such as an inlet 84, an inlet passage 86, a porous foam
header 87, a chamber 85, and an outlet 88. In operation, coolant
generally flows parallel to the coldplate surface through the
chamber 85 and through channels created by the walls of the
straight fin stock 90A.
[0034] For conventional two-phase coldplates to be efficient,
coolant typically flows in excess of that needed for energy balance
to ensure wetting of the surfaces by forcing the removal of created
vapor--thereby preventing surfaces from transitioning to film
boiling. In an energy balance, a flow rate of "1.times." is the
amount of flow necessary to absorb thermal energy with 100%
conversion--that is, one unit of liquid is put in that totally goes
to vapor and takes out all the heat. For coldplates that require
low temperature gradients, the required flow rate can be many times
that needed for energy balance (1.times.)--that is, flow rates on
the order of 3.times., 4.times., 5.times., or 6.times.. This is due
to the confining action of the walls of the fin stock, which create
channels that allow the effusing vapor to hold the liquid off the
walls thus preventing wetting. Thus, such conventional
configurations need very high flow rates to allow the momentum of
the liquid stream to overcome the ability of the effusing vapor to
hold the liquid trapped in the vapor stream.
[0035] To overcome the action of the vapor that prevents wetting of
the walls, the above-referenced jet impingement cooling or spray
cooling may be utilized. Although jet impingement and spray cooling
work well, they are more complex and may not be able to be used due
to packaging limitations. Accordingly, teaching of some embodiments
of the invention recognize that pin fins configurations can be
utilized to alter the heat transfer phenomenology and thereby
enhance heat transfer. In some of such embodiments, when a small
amount of liquid enters a field of pin fins, a violent, exploding,
and chaotic reaction occurs as liquid vaporizes. This reaction
disperses the unvaporized liquid as globs amongst the pin fins in a
Brownian motion-like or stochastic-like manner. This dispersion can
create jet impingement-like and spray-like qualities with a low
flow rate.
[0036] FIG. 3A is an isolated perspective view of a pin fin
configuration 110A and FIG. 3B is a side cross-sectional view of a
pin fin configuration 110B that may be utilized in embodiments of
the invention. In particular embodiments, the pin fin
configurations 110A, 110B may be disposed within the channels 23,
24 described with reference to FIG. 1. In other embodiments, the
pin fin configurations 110A, 110B may be disposed in other heat
transfer structures. For purposes of illustration, the pin fin
configurations 110A, 110B will be described as being disposed in a
channel operable to receive fluid. The pin fin configurations 110A,
110B of FIGS. 2A and 2B are examples of surface enhancements that
may be utilized to enhance the transfer of thermal energy from a
heat generating structure to a fluid. Other types of surface
enhancements that may be utilized with other embodiments of the
invention include, but are not limited to, conductive foam and
conductive fibers.
[0037] With reference to FIGS. 3A and 3B, a plurality of pin fins
113, 115 protrude from channel walls 125 and are arranged in pin
fin configurations 110A, 110B. Pin fin configuration 110A shows a
staggered arrangement and pin fin configuration 110B shows an
inline arrangement. FIG. 3B additionally shows a channel 120 with a
fluid flow towards the pin fin configuration 110B, indicated by
arrow 132, and a fluid flow away from the pin fin configuration
110B, indicated by arrow 134. In operation, thermal energy is
transferred to the pin fins 113, 115 (e.g., from the channel wall
125 to the pin fins 113, 115) and to a fluid traveling through the
channel, for example, channel 120. In particular embodiments, the
pin fin configurations 110A, 110B may be utilized to enhance
boiling heat transfer. In such embodiments, liquid fluid coolant
(e.g., traveling in direction of arrow 132 towards the pin fins
113, 115) comes in contact with the pin fins 113, 115 and is boiled
and vaporized. The vaporized fluid coolant (e.g., traveling away
from the pin fins in direction of arrow 134) inherently contains
the thermal energy transferred from the pin fins 113, 115 to the
fluid coolant during vaporization. As described in further details
below, the fluid flow in particular embodiments may be relatively
slow, allowing a reduction in components that are used to create
the fluid flow (e.g., pumps, conduits, etc.). Further, in
particular embodiments, components may not be necessary to create a
fluid flow, for example, in gravity-fed embodiments.
[0038] In particular embodiments, pin fins 113, 115, may be used
inside a coldplate, allowing the coolant to move in multiple
directions since there are no confining walls. At high heat fluxes,
the effusing vapor creates a violent and near chaotic flow with
liquid entrained in the vapor. Because the effusing vapor is
confined to the core of the coldplate, its motion is internal to
the core thus forcing it over the pin fins 113, 115. As the vapor
effuses, it transports unvaporized liquid coolant in a near chaotic
swirl, which results in the pin fins being impinged with liquid
coolant. The vapor produced at all sites of the pin fins 113, 115
collectively energizes the swirl of vapor with liquid embedded in
it. Additionally, globs of liquid coolant (e.g., formed from the
vaporization of other liquid coolant) are thrown against downstream
pin fins 113, 115--creating a spray cooling-like quality.
Accordingly, the pin fin configurations 110A, 110B allow a cross
flowing coolant to be used while taking advantage of the attributes
of jet impingement and spray cooling, which are provided by the
chaotic cross flowing liquid impacting the pin fins 113, 115. Such
a phenomenology in particular embodiments may result in a need for
less coolant flow rate because the effusing vapor self induces the
flow of coolant and creates a form of spray cooling or jet
impingement cooling as the liquid impinges the pins. In other
words, the spraying effect in particular embodiments is
self-induced by the effusing vapor--that is, the energizing means
for the spraying effect is the effusing vapor itself.
[0039] As referenced above, in particular embodiments relatively
small flow rates may be used with pin fin configurations. In some
of such embodiments, reduced pumping requirements, reduced sizes of
flow lines, and the like may be achieved. Generally, a flow rate of
"1.times." is the amount of flow necessary to absorb thermal energy
with 100% conversion--that is, one unit of liquid is put in that
totally goes to vapor and takes out all the heat. To ensure proper
wetting, for example in conventional configurations described
above, flow rates must typically be on the order of 3.times.,
4.times., 5.times., or 6.times.. Such flow rates provide excessive
amount of liquids. In particular embodiments, such conventional
configurations can be contrasted with pin fin configurations in
which the chaotic action reduces the flow rate towards 1.times..
For example, in particular embodiments, flow rate requirements for
pin fin configurations can be 1.1.times., 1.2.times., or
1.3.times.. Thus, a dribble of liquid can be provided at the
opening of the chamber housing the pin fins. Upon the liquid
contacting the pin fins, the chaotic reaction occurs dispersing the
liquid in a Brownian motion-like manner amongst all pin fins in the
chamber.
[0040] A further benefit of the above referenced distribution in
particular embodiments is small temperature differentials amongst
the pin fins. Because the chaotic reaction creates Brownian
motion-like distributions, the--result is a near-equal energy
transfer distribution amongst pin fins--that is, each of the pins
fins is allowed to transfer its thermal energy to the fluid in more
equal-like manner. Thus, the chaos of the effusing action creates
order in the thermal energy transfer. In particular embodiments,
temperature differentials amongst pin fins can be on the order of
one degrees Celsius.
[0041] A yet further benefit of the above referenced distribution
in particular embodiments is prevention of excess fluid. Excess
fluid is created by either excess flows or spray nozzles that spray
outside of an effective thermal transfer area. In particular
embodiments, fluid slightly above that needed for energy balance
(1.times.) may be placed in the chamber of pin fins and the chaotic
action will equally distribute the fluid amongst the pin fins.
[0042] In particular embodiments, no powering mechanism (e.g., a
pump or the like) is needed to create a flow in the system. Rather,
flow may be gravity fed to the pins fins where the liquid is
vaporized. The vaporized liquid travels away from the pin fins,
condenses in a separate area of the system and then is gravity fed
back to the pin fins. Systems similar to this are sometimes
referred to as thermal siphons.
[0043] The pin fins 113, 115 may be made of a variety of materials
and may take on a variety of sizes and shapes. In this embodiment,
the pin fins are made of a nickel plated copper and vary in size
from 0.04 inches high to 0.1675 inches high. The pin fins 113, 115
are shown with a columnar shape. In other embodiments, the pin fins
113, 115 may be made of other materials, may have heights less than
0.04 inches, may have heights greater than 0.1675 inches, and may
have shapes other than columnar shapes. Additionally, in other
embodiments the pin fins 113, 115 may be arranged in configurations
other than inline or staggered configurations. Further, in
particular embodiments, the pin fins may be made of a conductive
foam or conductive fiber.
[0044] FIGS. 4A, 4B, 4C, and 4D show pin fin configurations 110A,
110B, 110C, and 110D, according to embodiments of the invention.
Pin fin configuration 110A of FIG. 4A is an inline configuration,
pin fin configuration 110B of FIG. 4B is an inline configuration,
pin fin configuration 110C of FIG. 4C is an inline configuration
with square columns, and pin fin configuration 110D of FIG. 4D is
an inline configuration with long tubular columns. The pin fin
configurations 110A, 110B, 110C, and 110D of FIGS. 4A, 4B, 4C, and
4D illustrate only some of the many configurations that may be
utilized, according to embodiments of the invention.
[0045] FIGS. 5A-6C show a comparison of two heat load test
articles. FIGS. 5A, 5B, and 5C illustrate a conventional forced
flow configuration 130 and it associated parameters. FIGS. 6A, 6B,
and 6C illustrate a pin fin configuration 140 and its associated
parameters. The forced flow configuration 130 shown in FIGS. 5A and
5B uses a forced flow of cross-flowing coolant that is supplied to
each of sixteen heated blocks 135. FIG. 5A shows one side of the
test assembly and FIG. 5B shows the opposite side of the test
assembly.
[0046] The pin fin configuration 140 of FIGS. 6A and 6B show pin
fins on each of sixteen heated blocks 145. The pin fins create the
chaotic reaction referenced above. In comparing the parameters
associated with each as shown in FIGS. 5C and 6C, the assembly of
FIGS. 6A and 6B has almost 82% less coolant (140 ml/min versus 800
ml/min) for the 800 Watt heat load. Further, the maximum
temperature differentials of the transmit/receive (TR) sites is 2.8
degrees Celsius in the FIG. 5C and 1.9 degrees Celsius in the FIG.
5C for the 800 Watt heat load. Thus, in particular embodiments, the
assembly of FIGS. 6A and 6B would be preferred over the assembly of
FIGS. 5A and 5B.
[0047] The embodiments of pin fin configurations may be utilized in
a variety of configurations including but not limited to: [0048] 1)
High Power Phased Arrays--for high powered phase arrays to cool the
transmit-receive (TR) functions and power supplies. [0049] 2)
Cooling of Electronic Chassis--for removing heat from the cold
walls of electronic chassis. [0050] 3) Micro Channel Cooling--Micro
channel cooling may be used to cool single electronic chips, small
circuit assemblies, and device die. [0051] 4) Heat
Exchangers--There are two-phase heat exchangers built using
straight and wavy fin stock. Some of these may perform better and
be less expensive if built using pin fins.
[0052] Although the present invention has been described with
several embodiments, a myriad of changes, variations, alterations,
transformations, and modifications may be suggested to one skilled
in the art, and it is intended that the present invention encompass
such changes, variations, alterations, transformation, and
modifications as they fall within the scope of the appended
claims.
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