U.S. patent application number 12/925584 was filed with the patent office on 2012-04-26 for methods for improving pool boiling and apparatuses thereof.
This patent application is currently assigned to Rochester Institute of Technology. Invention is credited to Satish G. Kandlikar.
Application Number | 20120097373 12/925584 |
Document ID | / |
Family ID | 45971976 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120097373 |
Kind Code |
A1 |
Kandlikar; Satish G. |
April 26, 2012 |
Methods for improving pool boiling and apparatuses thereof
Abstract
A method and apparatus for pool boiling includes introducing a
fluid into a chamber of a housing which has one or more protruding
features. One or more diverters extend at least partially across
the one or more protruding features in the chamber. One or more
bubbles are formed in the fluid in the chamber as a result of
bubble nucleation. At least one of growth and motion of the one or
more of the bubbles are diverted with the one or more diverters to
generate additional localized motion of the fluid along at least
one of the one or more protruding features and other surfaces in
the chamber of the housing to at least one of transfer additional
heat to the liquid and increase the critical heat flux limit.
Inventors: |
Kandlikar; Satish G.;
(Rochester, NY) |
Assignee: |
Rochester Institute of
Technology
Rochester
NY
|
Family ID: |
45971976 |
Appl. No.: |
12/925584 |
Filed: |
October 25, 2010 |
Current U.S.
Class: |
165/104.29 ;
165/185 |
Current CPC
Class: |
F28F 3/02 20130101; F28F
3/022 20130101; F28F 13/187 20130101; F28D 15/0266 20130101; F28F
13/06 20130101 |
Class at
Publication: |
165/104.29 ;
165/185 |
International
Class: |
F28D 15/00 20060101
F28D015/00; F28F 7/00 20060101 F28F007/00 |
Claims
1. A method for pool boiling, the method comprising: introducing a
liquid into a chamber of a housing which has one or more protruding
features and one or more diverters extending at least partially
across the one or more features in the chamber; forming one or more
bubbles in the liquid in the chamber as a result of bubble
nucleation; and diverting one or more of the bubbles from the
boiling with the one or more diverters which are arranged to
generate additional localized motion of the liquid along at least
one of the one or more protruding features and other surfaces in
the chamber of the housing to at least one of transfer additional
heat to the liquid and increase the critical heat flux limit.
2. The method as set forth in claim 1 further comprising arranging
the one or more diverters to divert at least one of growth and
motion of one or more of the bubbles in a selected direction to
facilitate heat transfer.
3. The method as set forth in claim 1 wherein at least one of the
one or more diverters comprises an asymmetric shaped structure with
at least one loped surface arranged to divert at least one of
growth and motion of one or more of the bubbles in a selected
direction to facilitate heat transfer.
4. The method as set forth in claim 1 wherein at least one of the
one or more diverters comprises a structure with at least a
partially triangular shape configured to divert at least one of
growth and motion of one or more of the bubbles in a selected
direction to facilitate heat transfer.
5. The method as set forth in claim 1 wherein at least one of the
one or more diverters comprises a structure with at least a
partially rounded shape configured to divert at least one of growth
and motion of one or more of the bubbles in a selected direction to
facilitate heat transfer.
6. The method as set forth in claim 1 wherein at least one of the
one or more diverters comprises a structure with at least a
quadrilateral shape configured to divert at least one of growth and
motion of one or more of the bubbles in a selected direction to
facilitate heat transfer
7. The method as set forth in claim 1 wherein the one or more
protruding features comprise one or more fins.
8. The method as set forth in claim 7 wherein the one or more fins
are in an offset arrangement in the chamber.
9. The method as set forth in claim 1 wherein the one or more
protruding features comprise one or more pins.
10. The method as set forth in claim 1 wherein the forming one or
more bubbles further comprises triggering the bubble nucleation in
the chamber of the housing to form the one or more bubbles.
11. A pool boiling apparatus comprising: a housing with a chamber;
one or more protruding features in the chamber of the housing; one
or more diverters extending at least partially across the one or
more protruding features in the chamber, the chamber of the housing
with the one or more protruding features and the one or more
diverters configured to form one or more bubbles as a result of
bubble nucleation to transfer heat and to divert one or more of the
bubbles with the one or more diverters to generate additional
localized motion of the liquid along at least one of the one or
more protruding features and other surfaces in the chamber of the
housing to at least one of transfer additional heat to the liquid
and increase the critical heat flux limit.
12. The apparatus as set forth in claim 11 wherein the one or more
diverters are arranged to divert at least one of growth and motion
of one or more of the bubbles in a selected direction to facilitate
heat transfer.
13. The apparatus as set forth in claim 11 wherein at least one of
the one or more diverters comprises an asymmetric shaped structure
with at least one loped surface arranged to divert at least one of
growth and motion of one or more of the bubbles in a selected
direction to facilitate heat transfer.
14. The apparatus as set forth in claim 11 wherein at least one of
the one or more diverters comprises a structure with at least a
partially triangular shape configured to divert at least one of
growth and motion of one or more of the bubbles in a selected
direction to facilitate heat transfer.
15. The apparatus as set forth in claim 11 wherein at least one of
the one or more diverters comprises a structure with at least a
partially rounded shape configured to divert at least one of growth
and motion of one or more of the bubbles in a selected direction to
facilitate heat transfer.
16. The apparatus as set forth in claim 11 wherein at least one of
the one or more diverters comprises a structure with at least a
quadrilateral shape configured to divert at least one of growth and
motion of one or more of the bubbles in a selected direction to
facilitate heat transfer
17. The apparatus as set forth in claim 11 wherein the one or more
protruding features comprise one or more fins.
18. The apparatus as set forth in claim 17 wherein the one or more
fins are in an offset arrangement in the chamber.
19. The apparatus as set forth in claim 11 wherein the one or more
protruding features comprise one or more pins.
20. The apparatus as set forth in claim 11 wherein at least one of
the chamber of the housing with the one or more protruding features
and the one or more diverters configured to is configured to
trigger the bubble nucleation in the chamber of the housing to form
the one or more bubbles.
Description
FIELD
[0001] This technology generally relates to methods and device for
improving pool boiling and, more particularly, methods for at least
one of improving heat transfer and increasing critical heat flux in
pool boiling and apparatuses thereof.
BACKGROUND
[0002] In a cooling system with a network of multiple flow passages
a fluid used for cooling is introduced. The fluid may be
single-phase liquid, gas or a two-phase liquid-vapor mixture. As
the fluid flows through the network, heat transfer is by convection
from the heated walls. The heat transfer rate to the fluid from the
heated walls is characterized by the heat transfer coefficient.
Higher heat transfer coefficients are desired for higher heat
dissipation rates. Additionally, providing smaller channel internal
dimensions leads to higher single phase heat transfer
performance.
[0003] Employing liquid as the introduced fluid results in a higher
heat transfer rate than with gas for the same flow conditions due
to the higher thermal conductivity of liquids as compared to gases.
To further improve this heat transfer rate and take advantage of
the large latent heat of vaporizations compared to the sensible
heat transfer with a few degrees temperature change, flow boiling
can be employed. Heat transfer by flow boiling occurs when the
liquid is forced to flow in the passages and boiling of the liquid
occurs. This flow requires an external mechanism, such as a pump,
to drive the liquid and vapor mixture through the passages. Due to
the confined nature of the flow boiling system, sometimes backflow
occurs in one or more channels causing the liquid to flow in a
backward direction. This condition can lead to a critical heat flux
condition at relatively low heat fluxes.
[0004] Pressure drop through a cooling system with flow boiling is
also often a concern. As a result, efforts are made to reduce the
pressure drop and/or external pumping power to achieve a desired
cooling performance. Pressure drop also affects the saturation
temperature of the liquid as it flows through the cooling system.
Short passage lengths are desirable to reduce the pressure drop in
a flow boiling system. However, reducing the passage length
requires large number of inlets and outlets. As a result, the
header design for flow boiling cooling systems can become quite
complex.
[0005] In contrast, heat transfer by pool boiling occurs without
any external pumping when a heated surface, which presents no
enclosed channels to contain the liquid, is cooled by the liquid
and boiling of the liquid occurs. When the bulk of the liquid is at
its saturation temperature corresponding to the existing pressure
in the liquid and boiling occurs on the heated surface, heat
transfer is by saturated pool boiling mode. When the bulk of the
liquid is at a temperature below the saturation temperature
corresponding to the existing pressure in the liquid and boiling
occurs over the heated surface, heat transfer is by subcooled pool
boiling. Pool boiling covers both subcooled and saturated pool
boiling. Boiling covers both pool and flow boiling.
[0006] Pool boiling can occur when nucleating bubbles are generated
over the heated surface in a liquid environment when the liquid
superheat exceeds the nucleation criterion. Another method of
generating nucleating bubbles is to provide localized microheaters
in conjunction with a natural or artificial nucleation cavity. The
heating of liquid around the cavity above the liquid saturation
temperature leads to bubble nucleation when the nucleation
criterion for the cavity is satisfied.
[0007] In addition to a natural convection mechanism over the
portion of the heater surface that is unaffected by the nucleation
activity, heat transfer in pool boiling generally occurs as a
result of three mechanisms: microconvection caused by convection
currents induced by a bubble; transient conduction caused by the
transient heat transfer to the fresh liquid that displaces the
heated liquid over the heated surface in the region of nucleating
bubbles; and microlayer evaporation caused by the evaporation of a
thin liquid layer that appears underneath the nucleating bubble. A
significant portion of the heat transfer during pool boiling occurs
due to microconvection and transient conduction modes. The heat
transfer by all these mechanisms aid in transferring heat from the
heater surface and evaporating liquid into the growing vapor
bubbles.
[0008] Another method of heat transfer involves introducing gas
bubbles (not resulting from boiling) that grow and depart in the
liquid in the vicinity of a heated surface and create motion at the
liquid-gas interface. However, evaporation is not the primary
mechanism in this case as the temperatures are generally below the
saturation temperature of the liquid at the system pressure. The
absence of evaporation in these systems with introduced gas bubbles
results in considerably lower heat transfer rates as compared to
pool boiling. Nevertheless, the heat transfer rate in such systems
is still higher than that in systems with stagnant liquids.
[0009] To enhance pool boiling, surface features protruding from a
base, such as pin fins of various cross sections, offset strip fins
with rectangular pin fins arranged in staggered fashion, and other
fin configurations, can be employed to enhance pool boiling.
Additionally, to enhance pool boiling heat transfer fins, porous
surfaces and active nucleation sites formed on the heated surface
can be employed.
[0010] The maximum heat that can be dissipated with boiling without
causing excessive temperature rise is limited by the Critical Heat
Flux (CHF). It is desirable to increase the CHF limit during
boiling. This limit is also an important consideration in the
design of a boiling system.
[0011] The CHF limit can be increased by changing the contact angle
of the liquid-vapor interface of a growing bubble. Increasing
wettability of a surface by reducing the contact angle leads to
enhancement of CHF. Reducing the wettability leads to a decrease in
CHF.
SUMMARY
[0012] A method for pool boiling includes introducing a liquid into
a chamber of a housing which has one or more protruding features.
One or more diverters extend at least partially across the one or
more protruding features in the chamber. One or more bubbles are
formed in the liquid in the chamber as a result of bubble
nucleation. One or more of the bubbles resulting from nucleation
are diverted with the one or more diverters to generate additional
localized motion of the liquid along at least one of the one or
more protruding features and other surfaces in the chamber of the
housing to at least one of transfer additional heat to the liquid
and increase the critical heat flux limit. The motion of liquid and
vapor created by the one or more diverters may increase the
critical heat flux limit by allowing removal of vapor and access of
liquid to regions previously occupied by vapor.
[0013] A pool boiling apparatus includes a housing with a chamber,
one or more protruding features in the chamber of the housing, and
one or more diverters extending at least partially across the one
or more protruding features in the chamber. The chamber of the
housing with the one or more protruding features and the one or
more diverters is configured to form one or more bubbles as a
result of boiling to transfer heat. Additionally, the chamber of
the housing is configured to divert one or more of the bubbles as a
result of bubble nucleation with the one or more diverters to
generate additional localized motion of the liquid along at least
one of the one or more protruding features and other surfaces in
the chamber of the housing to at least one of transfer additional
heat to the liquid and increase the critical heat flux limit. The
motion of liquid and vapor created by the one or more diverters can
increase the critical heat flux limit by allowing removal of vapor
and access of liquid to regions previously occupied by vapor.
[0014] This technology provides more efficient and effective
methods and apparatuses for at least one of improving heat transfer
performance and increase critical heat flux in pool boiling. With
this technology, heat can be removed more effectively from heated
surfaces than with prior pool boiling systems. Additionally, this
technology is superior to prior flow boiling cooling techniques
because it does not require an external pumping device or a
complicated input and/or exit header design to remove heat from the
heat transfer surfaces. Instead, this technology utilizes
nucleating bubbles and one or multiple cover element devices to
control and divert the localized motion of the bubbles and liquid
through the passageways formed by the surface features for
effective heat transfer in the region affected by the nucleating
bubbles and in a more compact and simpler heat transfer apparatus.
The localized motion of liquid and vapor created by the diverters
can also improve the critical heat flux limit.
[0015] This technology incorporates one or multiple diverters
positioned over a chamber and features to divert liquid around one
or more nucleating bubbles over the surfaces of the chamber and/or
features to provide enhanced heat transfer. With this technology,
fresh liquid for additional heat transfer is introduced in the
regions or passageways where the diversion occurred with little
resistance as a result of the diverted fluid. The diverters are
designed to introduce very little resistance to fluid flow in the
regions or passageways which helps in bringing the liquid into the
regions or passageways especially at high heat fluxes, thereby
improving Critical Heat Flux. In addition to facilitating fresh
liquid entering the regions or passageways with little resistance,
this technology ensures the surfaces of the one or more features
and other surfaces in the chamber of the housing do not dry out or
remain under dry conditions for extended time, and increase the
critical heat flux. The neighboring diverters can be designed to
interact with each other in directing liquid and vapor in specific
directions to allow for more efficient flow of fluids through the
passageways, vapor out of the passageways and liquid into the
passageways. The diverters could also be designed to control vapor
and liquid motion in all three dimensions by providing different
shapes and profiles.
[0016] With this technology, the diverted growth and/or motion of
one or more bubbles also causes enhanced microconvection over the
one or more and other surfaces in the chamber of the housing and/or
other features. This enhanced microconvection over the one or more
and other surfaces in the chamber of the housing and/or other
features leads to enhanced heat transfer. The enhanced
microconvection may lead to increase of the heat transfer by other
modes of heat transfer during boiling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a top view of an exemplary pool boiling assembly
with diverters and fasteners removed;
[0018] FIG. 1B is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 1A;
[0019] FIG. 1C is a top view of an exemplary pool boiling assembly
shown in FIG. 1A with the diverters and fasteners;
[0020] FIG. 1D is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 1C;
[0021] FIG. 2A is a top view of another exemplary pool boiling
assembly with diverters and fasteners removed;
[0022] FIG. 2B is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 2A;
[0023] FIG. 2C is a top view of an exemplary pool boiling assembly
shown in FIG. 2A with the diverters and fasteners;
[0024] FIG. 2D is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 2C;
[0025] FIG. 3A is a top view of yet another exemplary pool boiling
assembly with diverters and fasteners removed;
[0026] FIG. 3B is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 3A;
[0027] FIG. 3C is a top view of an exemplary pool boiling assembly
shown in FIG. 3A with the diverters and fasteners;
[0028] FIG. 3D is a side, cross-sectional view of the exemplary
pool boiling assembly shown in FIG. 3C;
[0029] FIG. 4 are side cross-sectional views of different exemplary
diverters;
[0030] FIGS. 5A-5C are partial, side cross-sectional views of fluid
flow induced by bubble growth in an exemplary pool boiling
assembly; and
[0031] FIGS. 6A-6B are partial, side cross-sectional views of fluid
flow induced by bubble growth in another exemplary pool boiling
assembly with asymmetric diverters.
DETAILED DESCRIPTION
[0032] An exemplary pool boiling assembly 12(1) is illustrated in
FIGS. 1A-1D. The exemplary pool boiling assembly 12(1) includes a
chamber 14(1) which has a plurality of fins 16(1) which define a
plurality of regions 18(1) creating passageways to receive a
cooling fluid, although the apparatus could comprise other numbers
and types of systems, devices, components and other elements in
other configurations. This technology provides more efficient and
effective methods and apparatuses for at least one of improving
heat transfer performance and increase critical heat flux in pool
boiling.
[0033] Referring more specifically to FIGS. 1A-1D, the exemplary
pool boiling assembly 12(1) is illustrated. The pool boiling
assembly 12(1) defines an internal chamber 14(1) having a
rectangular shape, although the pool boiling assembly can have
other numbers and types of chambers or other openings with other
shapes.
[0034] The plurality of strip fins 16(1) are located in the chamber
14(1) of the pool boiling assembly 12(1), although the chamber of
the pool boiling assembly could have other numbers and types of
features. (For ease of illustration only one of the plurality of
strip fins in FIGS. 1A-1D is shown with a reference numeral). In
this example, the plurality of strip fins 16(1) are arranged in an
aligned parallel pattern in the chamber 14(1) of the pool boiling
assembly 12(1), although the plurality of strip fins could have
other arrangements. The plurality of strip fins 16(1) define a
plurality of regions 18(1) between the strip fins 16(1) which can
receive the cooling liquid or other fluid and where boiling can
occur, although the chamber of the pool boiling assembly could have
other numbers and types of regions with other shapes and in other
directions.
[0035] The surfaces of the chamber 14(1) of the pool boiling
assembly 12(1) and the plurality of strip fins 16(1) are formed
with natural and/or artificial cavities to promote nucleation to
start bubble formation, although other manners for promoting bubble
formation can be used. The bubbles resulting from this nucleation
induce localized movement of a liquid in the chamber 14(1) of the
pool boiling assembly 12(1) without an external pumping device,
although other manners for promoting pool boiling bubble formation
can be used.
[0036] Six diverters 32(1) are spaced apart and extend across the
chamber 14(1) of the pool boiling assembly 12(1), although other
types and numbers of diverters can be used. Each end of the six
diverters 32(1) is secured to the pool boiling assembly 12(1),
although other manners for securing the diverters can be used. In
this example, each of the diverters 32(1) has a rectangular
cross-sectional shape, although the diverters could have other
types of shapes and configurations as illustrated with exemplary
diverters 32(4)-32(12) in FIG. 4, such as circular, concave,
convex, open triangular, closed triangular, angled triangular,
asymmetric and funnel shapes by way of example only. Each of the
different cross-sectional shapes for the diverters 32(1) can
interact with the formed bubbles differently to facilitate a
different type of localized motion of the liquid. Additionally,
diverters 32(1) with different cross-sectional shapes as well as
other types, numbers and combinations of diverters can be used with
the pool boiling assembly 12(1) to further enhance localized motion
and heat transfer.
[0037] Additionally, three optional fasteners 34(1) are spaced
apart, extend at least partially across, and are secured to each of
the diverters 32(1) to secure the position of each of the
diverters, although other types and numbers of fastening mechanisms
could be used. Openings to the chamber 14(1) are defined between
the diverters 32(1) and fasteners 34(1), although other types of
arrangements could be used. Although not illustrated, the pool
boiling assembly 12(1) could also have a containment cover spaced
from and seated over the chamber 14(1) and the diverters 32(1) and
fasteners 34(1) to retain the cooling liquid, in particular the
vaporized liquid, in the pool boiling assembly 12(1). Additionally
and also not illustrated, the pool boiling assembly 12(1) could
include a condensation system to capture, condense and return any
vaporized liquid to the regions 18(1) in the chamber 14(1).
Additionally and also not illustrated, the pool boiling assembly
12(1) could include a means to circulate the cooling liquid into
and out of the volume formed by the containment cover and the
chamber 14(1). The loop could include an external heat exchanger to
remove heat from the cooling fluid and to condense any vapor that
leaves the volume. As discussed earlier, the cooling fluid may be
single-phase liquid, gas or a two-phase liquid-vapor mixture,
although other types of fluids could be used.
[0038] Referring to FIGS. 2A-2D, an example of another pool boiling
assembly 12(2) is illustrated. The pool boiling assembly 12(2)
defines another internal chamber 14(2) having a rectangular shape,
although the housing can have other numbers and types of chambers
or other openings with other shapes.
[0039] A plurality of strip fins 16(2) are located in the chamber
14(2) of the pool boiling assembly 12(2), although the chamber of
the pool boiling assembly could have other numbers and types of
features. (For ease of illustration only one of the plurality of
strip fins 16(2) in FIGS. 3A-3D is shown with a reference numeral).
The plurality of strip fins 16(2) are in an offset arrangement in
the chamber 14(2) of the pool boiling assembly 12(2), although the
plurality of strip fins could have other arrangements. The
plurality of strip fins 16(2) define a plurality of parallel
regions 18(2) creating passageways between the strip fins 16(2)
which can receive the cooling liquid or other fluid and where
boiling can occur, although the chamber of the pool boiling
assembly could have other numbers and types of regions with other
shapes and in other directions. The pitch and spacing in both
directions, shape, width and length of the fins could remain same
or vary in the chamber 14(2).
[0040] The surfaces of the chamber 14(2) of the pool boiling
assembly 12(2) and the plurality of strip fins 16(2) are formed
with natural and/or artificial cavities to promote nucleation to
start bubble formation, although other manners for promoting bubble
formation can be used. The bubbles resulting from this nucleation
induce localized movement of a liquid in the chamber 14(2) of the
pool boiling assembly 12(2) without an external pumping mechanism,
although other manners for promoting bubble formation can be
used.
[0041] Six diverters 32(2) are spaced apart and extend across the
chamber 14(2) of the pool boiling assembly 12(2), although other
types and numbers of diverters can be used. Each end of the six
diverters 32(2) is secured to the pool boiling assembly 12(2),
although other manners for securing the diverters can be used. In
this example, each of the diverters 32(2) has a rectangular
cross-sectional shape, although the diverters could have other
types of shapes and configurations as illustrated with exemplary
diverters 32(4)-32(12) in FIG. 4, such as circular, concave,
convex, open triangular, closed triangular, angled triangular,
asymmetric and funnel shapes by way of example only. Each of the
different cross-sectional shapes for the diverters 32(2) can
interact with the formed bubbles differently to facilitate a
different type of localized motion of the liquid in the
passageways. Additionally, diverters 32(2) with different
cross-sectional shapes can be used with the pool boiling assembly
12(2) to further enhance localized motion and heat transfer.
[0042] Additionally, three optional fasteners 34(2) are spaced
apart, extend at least partially across, and are secured to each of
the diverters 32(2) to secure the position of each of the
diverters, although other types and numbers of fastening mechanisms
could be used. Openings to the chamber 14(2) are defined between
the diverters 32(2) and fasteners 34(2), although other types of
arrangements could be used. Although not illustrated, the pool
boiling assembly 12(2) could also have a containment cover spaced
from and seated over the chamber 14(2) and the diverters 32(2) and
fasteners 34(2) to retain the cooling liquid, in particular the
vaporized liquid, in the pool boiling assembly 12(2). Additionally
and also not illustrated, the pool boiling assembly 12(2) could
include a condensation system to capture, condense and return any
vaporized liquid to the regions 18(2) in the chamber 14(2).
Additionally and also not illustrated, the pool boiling assembly
12(2) could include a means to circulate the cooling liquid into
and out of the volume formed by the containment cover and the
chamber 14(2). The loop could include an external heat exchanger to
remove heat from the cooling fluid and to condense any vapor that
leaves the volume.
[0043] Referring to FIGS. 3A-3D, an example of yet another pool
boiling assembly 12(3) is illustrated. The pool boiling assembly
12(3) defines another internal chamber 14(3) having a rectangular
shape, although the housing can have other numbers and types of
chambers or other openings with other shapes.
[0044] A plurality of pins 16(3) are located in the chamber 14(3)
of the pool boiling assembly 12(3), although the chamber of the
pool boiling assembly could have other numbers and types of
features. The fin shown is circular in cross section, although fins
could be of any constant or variable cross sections. (For ease of
illustration only one of the plurality of pins in FIG. 3A is shown
with a reference numeral). The plurality of pins 16(3) are in an
offset arrangement in the chamber 14(3) of the pool boiling
assembly 12(3), although the plurality of pins 16(3) could have
other arrangements. The plurality of pins 16(3) define a plurality
of regions 18(3) creating passageways between the pins 16(3) which
can receive the cooling liquid or other fluid and where boiling can
occur, although the chamber 14(3) of the pool boiling assembly
12(3) could have other numbers and types of regions with other
shapes and in other directions.
[0045] The surfaces of the chamber 14(3) of the pool boiling
assembly 12(3) and the plurality of pins 16(3) are formed with
natural and/or artificial cavities to promote nucleation to start
bubble formation, although other manners for promoting bubble
formation can be used. The bubbles resulting from this nucleation
induce localized movement of a liquid in the chamber 14(3) of the
pool boiling assembly 12(3) without an external pumping device,
although other manners for promoting pool boiling bubble formation
can be used.
[0046] Four diverters 32(3) are spaced apart and extend across the
chamber 14(3) of the pool boiling assembly 12(3), although other
types and numbers of diverters can be used. Each end of the four
diverters 32(3) is secured to the pool boiling assembly 12(3),
although other manners for securing the diverters can be used. In
this example, each of the diverters 32(3) has a rectangular
cross-sectional shape, although the diverters could have other
types of shapes and configurations as illustrated with exemplary
diverters 32(4)-32(12) in FIG. 4, such as circular, concave,
convex, open triangular, closed triangular, angled triangular,
asymmetric and funnel shapes by way of example only. Each of the
different cross-sectional shapes for the diverters 32(3) can
interact with the formed bubbles differently to facilitate a
different type of localized motion of the liquid. Additionally,
diverters 32(3) with different cross-sectional shapes can be used
with the pool boiling assembly 12(3) to further enhance localized
motion and heat transfer.
[0047] Additionally, one optional fastener 34(3) extends at least
partially across and is secured to each of the diverters 32(3) to
secure the position of each of the diverters 32(3), although other
types and numbers of fastening mechanisms could be used. Openings
to the chamber 14(3) are defined between the diverters 32(3) and
fastener 34(3), although other types of arrangements could be used.
Although not illustrated, the pool boiling assembly 12(3) could
also have a containment cover spaced from and seated over the
chamber 14(3) and the diverters 32(3) and fastener 34(3) to retain
the cooling liquid, in particular the vaporized liquid, in the pool
boiling assembly 12(3). Additionally and also not illustrated, the
pool boiling assembly 12(3) could include a condensation system to
capture, condense and return any vaporized liquid to the regions
18(3) in the chamber 14(3). Additionally and also not illustrated,
the pool boiling assembly 12(2) could include a means to circulate
the cooling liquid into and out of the volume formed by the
containment cover and the chamber 14(2). The loop could include an
external heat exchanger to remove heat from the cooling fluid and
to condense any vapor that leaves the volume.
[0048] A method for transferring heat with pool boiling assembly
12(1) will now be described with reference to FIG. 1 and FIGS.
5A-5C. For ease of illustration, the plurality of strip fins 16(1)
are not illustrated in the side cross-sectional views of FIGS.
5A-5C. The method for transferring heat with the heat transfer
assemblies 12(2)-12(3) is the same as for pool boiling assembly
12(1), except as illustrated and/or described herein.
[0049] A liquid or liquid vapor mixture is initially introduced
into regions 18(1) of the chamber 14(1) of the pool boiling
assembly 12(1). The liquid contacts surfaces of the plurality of
strip fins 16(1) and other surfaces of the chamber 14(1) to
transfer heat from the pool boiling assembly 12(1). At least
portions of the surfaces of the plurality of strip fins 16(1)
and/or the chamber 14(1) of the pool boiling assembly 12(1) are
formed with natural and/or artificial cavities to promote
nucleation. The heated surfaces of the chamber 14(1) and/or
plurality of strip fins 16(1) along with the cavities trigger
nucleation to start the formation of bubbles to induce localized
movement of the liquid in the chamber 14(1) of the pool boiling
assembly 12(1).
[0050] For example, as the introduced liquid engages with natural
and/or artificial cavities in a heated surface of the pool boiling
assembly 12(1) and/or the plurality of strip fins nucleation may be
triggered. When nucleation is triggered, one or more bubbles, such
as a bubble B shown in FIG. 5A, may be formed, although other
manners for forming bubbles could be used.
[0051] As the bubble B grows as shown in FIG. 5B, liquid in the
regions 18(1) is induced to move locally in one or multiple
directions without an external pumping mechanism. This localized
movement of the liquid causes more interaction and heat transfer
between the liquid and surfaces of the pool boiling assembly 12(1)
and/or the plurality of strip fins 16(1). In this example, heat
transfer from this boiling occurs as a result of microconvection,
transient conduction, and microlayer evaporation.
[0052] As shown in FIG. 5C, as the bubble B engages with one or
more of the diverters 32(1) which diverts the vapor bubble to grow
and/or travel in certain directions. The bubble may escape from the
opening in the diverter or may break the initial bubble B into
three new bubbles B that leave the passageways and induce liquid
movement in the passageways and further induce fresh liquid to
enter the passageways, although other manners for generating other
numbers of bubbles and liquid movement within the passageways could
be used. Additionally, the diverters may redirect the growth and
path of the bubbles without breaking the bubbles. In this example,
the diverters 32(1) have a rectangular cross-sectional shape,
although the diverters 32(1) could have other cross-sectional
shapes that provide further enhancement to the heat transfer. The
movement of the original bubble and generation of these three new
bubbles B by the diverters 32(1) creates additional localized
motion of the liquid. This additional localized movement of the
liquid causes additional interaction and further enhanced heat
transfer between the liquid and surfaces of the pool boiling
assembly 12(1) and/or the plurality of strip fins 16(1) without the
need for an external pumping device or complicated header design.
In this example, the additional heat transfer occurs as a result of
micro convection, transient conduction, and microlayer
evaporation.
[0053] Another method for transferring heat with pool boiling
assembly 12(1) with asymmetric diverters 32(12) will now be
described with reference to FIG. 1, 4 and FIGS. 6A-6B. For ease of
illustration, the plurality of strip fins 16(1) are not illustrated
in the side cross-sectional views of FIGS. 6A-6B. This exemplary
method for transferring heat with pool boiling assembly 12(1) with
diverters 32(12) is the same as described earlier with reference to
FIGS. 6A-6B, except as illustrated and described herein.
Additionally, this exemplary method for pool boiling assembly 12(1)
is the same for the heat transfer assemblies 12(2)-12(3), except as
illustrated and/or described herein.
[0054] When nucleation is triggered, one or more bubbles as shown
in FIG. 6A, may be formed, although other manners for forming
bubbles could be used. As the bubble B grows as shown in FIG. 5B,
liquid in the regions 18(1) is pushed out of the passageway and
fresh liquid is drawn in with little resistance without an external
pumping mechanism. The shape and positioning of the asymmetric
diverter 32(12) enhances and controls the direction of the
diversion of bubble growth providing further enhancement and
control of heat transfer in the pool boiling assembly 12(1),
although other types, numbers and combinations of diverters could
be used to generate and control other types of localized flows.
Accordingly, with this technology heat transfer can be optimized by
the particular selection of geometry and configurations of
diverters and surface features for a given fluid and operating
conditions.
[0055] As described earlier, this localized movement of the liquid
causes more interaction and heat transfer between the liquid and
surfaces of the pool boiling assembly 12(1) and/or the plurality of
strip fins 16(1). In this example, heat transfer from this boiling
occurs as a result of microconvection, transient conduction, and
microlayer evaporation.
[0056] Accordingly, as illustrated and described with reference to
the examples herein, this technology provides a more efficient and
effective method and apparatus for transferring heat with pool
boiling from a heated surface to an introduced fluid. With this
technology, heat can be removed more effectively from heated
surfaces than with prior pool boiling systems. Additionally, this
technology is superior to prior flow boiling cooling techniques
because it does not require an external fluid pumping device or
complicated fluid input header designs. Instead, this technology
utilizes nucleating bubbles and one or multiple cover element
devices to control and divert the localized motion of the bubbles,
liquid-vapor interfaces and liquid through the passageways for
effective heat transfer and in a more compact and simpler heat
transfer apparatus. The efficient movement of vapor and liquid
allows for dissipating larger heat fluxes and enhances the heat
transfer rate for a given wall superheat and also increases the
critical heat flux as compared to prior pool boiling and flow
boiling systems.
[0057] Having thus described the basic concept of the invention, it
will be rather apparent to those skilled in the art that the
foregoing detailed disclosure is intended to be presented by way of
example only, and is not limiting. Various alterations,
improvements, and modifications will occur and are intended to
those skilled in the art, though not expressly stated herein. These
alterations, improvements, and modifications are intended to be
suggested hereby, and are within the spirit and scope of the
invention. Additionally, the recited order of processing elements
or sequences, or the use of numbers, letters, or other designations
therefore, is not intended to limit the claimed processes to any
order except as may be specified in the claims. Accordingly, the
invention is limited only by the following claims and equivalents
thereto.
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