U.S. patent application number 12/210274 was filed with the patent office on 2009-03-19 for cooling system for high power vacuum tubes.
This patent application is currently assigned to Raytheon Company. Invention is credited to Richard M. Weber.
Application Number | 20090071630 12/210274 |
Document ID | / |
Family ID | 40453223 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090071630 |
Kind Code |
A1 |
Weber; Richard M. |
March 19, 2009 |
Cooling System for High Power Vacuum Tubes
Abstract
According to one embodiment, a two-phase cooling system includes
a condensing heat exchanger fluidly coupled to an evaporator
assembly and a pressure controller. The condensing heat exchanger
condenses a coolant from a vapor phase to a liquid phase by
removing heat from the coolant. The evaporator assembly is
thermally coupled to a vacuum tube and operable to receive liquid
coolant from the condensing heat exchanger, cool the vacuum tube by
evaporating the coolant from the liquid phase to the vapor phase,
and transporting the evaporated coolant to the condensing heat
exchanger. The pressure controller maintains the pressure of the
coolant in the evaporator assembly at a sub-ambient pressure to
lower the boiling point of the coolant for reducing the operating
temperature of the vacuum tube.
Inventors: |
Weber; Richard M.; (Prosper,
TX) |
Correspondence
Address: |
BAKER BOTTS L.L.P.
2001 ROSS AVENUE, SUITE 600
DALLAS
TX
75201-2980
US
|
Assignee: |
Raytheon Company
Waltham
MA
|
Family ID: |
40453223 |
Appl. No.: |
12/210274 |
Filed: |
September 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60972960 |
Sep 17, 2007 |
|
|
|
Current U.S.
Class: |
165/104.21 |
Current CPC
Class: |
H01J 23/005 20130101;
H01J 19/36 20130101; H01J 23/033 20130101; H01J 17/28 20130101 |
Class at
Publication: |
165/104.21 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Claims
1. A two-phase cooling system for a vacuum tube comprising: a
condensing heat exchanger that is operable to condense water from a
vapor phase to a liquid phase by removing thermal energy from the
water; an evaporator assembly having an inlet and an outlet that
are fluidly coupled to the condensing heat exchanger, the
evaporator assembly in thermal communication with a vacuum tube and
operable to: receive, through the inlet, the water in the liquid
phase from the condensing heat exchanger; cool the vacuum tube by
transferring thermal energy from the vacuum tube to the water, the
transfer of thermal energy causing the water in the liquid phase to
boil and vaporize; and transport, using a pump, the vaporized water
to the condensing heat exchanger through the outlet; and a pressure
controller operable to maintain the pressure of the water in the
evaporator assembly and the condensing heat exchanger at a
sub-ambient pressure of less than three
pounds-per-square-inch-absolute.
2. A two-phase cooling system for a vacuum tube comprising: a
condensing heat exchanger that is operable to condense a coolant
from a vapor phase to a liquid phase by removing thermal energy
from the coolant; an evaporator assembly having an inlet and an
outlet that are fluidly coupled to the condensing heat exchanger,
the evaporator assembly in thermal communication with a vacuum tube
and operable to: receive, through the inlet, the coolant in the
liquid phase from the condensing heat exchanger; cool the vacuum
tube by transferring thermal energy from the vacuum tube to the
coolant, the transfer of thermal energy causing the coolant in the
liquid phase to boil and vaporize; and moving the vaporized coolant
to the condensing heat exchanger through the outlet; and a pressure
controller operable to maintain the pressure of the coolant in the
evaporator assembly at a sub-ambient pressure.
3. The two-phase cooling system of claim 2, wherein the evaporator
assembly is operable to cool the vacuum tube using a pool boiling
technique.
4. The two-phase cooling system of claim 2, wherein the evaporator
assembly is operable to cool the vacuum tube using a spray/jet
impingement cooling technique.
5. The two-phase cooling system of claim 2, wherein the coolant
comprises water.
6. The two-phase cooling system of claim 2, wherein the coolant
comprises water and one or more antifreeze agents.
7. The two-phase cooling system of claim 2, wherein the coolant
comprises a perfluorocarbon.
8. The two-phase cooling system of claim 2, further comprising a
pump fluidly coupled between the condensing heat exchanger and the
evaporator assembly, the pump operable to transport the coolant
from the condensing heat exchanger to the inlet of the evaporator
assembly.
9. The two-phase cooling system of claim 2, further comprising an
air removal system coupled to the condensing heat exchanger, the
air removal system operable to remove air from the condensing heat
exchanger and the evaporator assembly.
10. The two-phase cooling system of claim 2, wherein the coolant
comprises water and the sub-ambient pressure is less than three
pounds-per-square-inch-absolute.
11. The two-phase cooling system of claim 2, wherein the pressure
controller is operable to maintain the pressure of the coolant in
the condensing heat exchanger at the sub-ambient pressure.
12. A method for cooling a vacuum tube comprising: receiving a
coolant in a liquid phase from a condensing heat exchanger, the
condensing heat exchanger operable to condense the coolant from a
vapor phase to the liquid phase by removing thermal energy from the
coolant; cooling the vacuum tube by transferring thermal energy
from the vacuum tube to the coolant, the transfer of thermal energy
causing the coolant in the liquid phase to boil and vaporize;
moving the vaporized coolant to the condensing heat exchanger; and
maintaining the coolant at a sub-ambient pressure.
13. The method of claim 12, wherein receiving the coolant in the
liquid phase comprises receiving water in the liquid phase.
14. The method of claim 12, wherein receiving the coolant in the
liquid phase comprises receiving water and one or more antifreeze
agents in the liquid phase.
15. The method of claim 12, receiving the coolant in the liquid
phase comprises receiving perfluorocarbon in the liquid phase.
16. The method of claim 12, wherein receiving the coolant from the
condensing heat exchanger comprises pumping the coolant from the
condensing heat exchanger using a pump.
17. The method of claim 12, further comprising removing air from
the condensing heat exchanger and the evaporator assembly using an
air removal system.
18. The method of claim 12, wherein cooling the vacuum tube by
boiling and vaporizing the coolant from the liquid phase to the
vapor phase comprises cooling the vacuum tube by boiling and
vaporizing the coolant from the liquid phase to the vapor phase
using a pool boiling technique.
19. The method of claim 12, wherein cooling the vacuum tube by
boiling and vaporizing the coolant from the liquid phase to the
vapor phase comprises cooling the vacuum tube by boiling and
vaporizing the coolant from the liquid phase to the vapor phase
using a spray/jet impingement cooling technique.
20. The method of claim 12, wherein maintaining the coolant at the
sub-ambient pressure comprises maintaining the coolant at less than
three pounds-per-square-inch-absolute.
21. The method of claim 12, further comprising maintaining the
pressure of the coolant in the condensing heat exchanger at the
sub-ambient pressure.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 60/972,960, entitled "COOLING SYSTEM FOR HIGH
POWER VACUUM TUBES," which was filed on Sep. 17, 2007.
TECHNICAL FIELD OF THE DISCLOSURE
[0002] This disclosure generally relates to the field of cooling
systems, and more particularly, to a system for cooling vacuum
tubes using a coolant that operates at a sub-ambient pressure to
lower the boiling point of the coolant.
BACKGROUND OF THE DISCLOSURE
[0003] A variety of different types of structures can generate heat
or thermal energy in operation. To prevent such structures from
over heating and to provide stable operating conditions, a variety
of different types of cooling systems may be utilized to dissipate
the thermal energy, including two-phase systems in which their
constituent coolants change phase from a liquid state to a vapor
state or a solid state to a liquid state.
SUMMARY OF THE DISCLOSURE
[0004] According to one embodiment, a two-phase cooling system
includes a condensing heat exchanger fluidly coupled to an
evaporator assembly and a pressure controller. The condensing heat
exchanger condenses a coolant from a vapor phase to a liquid phase
by removing heat from the coolant. The evaporator assembly is
thermally coupled to a vacuum tube and operable to receive liquid
coolant from the condensing heat exchanger, cool the vacuum tube by
evaporating the coolant from the liquid phase to the vapor phase,
and transporting the evaporated coolant to the condensing heat
exchanger. The pressure controller maintains the pressure of the
coolant in the evaporator assembly at a sub-ambient pressure to
lower the boiling point of the coolant for reducing the operating
temperature of the vacuum tube.
[0005] Certain embodiments of the disclosure may provide numerous
technical advantages. For example, a technical advantage of one
embodiment may include an enhanced cooling of high-power, vapor
cooled vacuum tubes (such as those configured to power radio
frequency heating equipment and for high power transmission of
radio frequency signals) by lowering the vacuum tube's operating
temperatures. A technical advantage of another embodiment may
include use of a pressure controller that maintains a suitable
coolant (such as water) at a sub-ambient pressure, allowing a
reduction of the coolant's effective boiling point. This reduced
effective boiling point, in turn, may allow the operating
temperature of high-power, vapor cooled vacuum tubes to be reduced
for enhanced performance in some embodiments.
[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] A more complete understanding of embodiments of the
disclosure will be apparent from the detailed 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
disclosed herein;
[0009] FIG. 2 is a block diagram of another embodiment of a cooling
system that may be utilized in conjunction with other embodiments
disclosed herein;
[0010] FIG. 3 shows one embodiment of a cooling system, according
to an embodiment of the present disclosure;
[0011] FIG. 4 shows another embodiment of a cooling system for a
vapor cooled vacuum tube, according to an embodiment of the
disclosure; and
[0012] FIG. 5 is a flowchart showing one embodiment of a series of
actions that may be performed by the embodiments of FIGS. 1 through
4 to cool a vacuum tube according to the teachings of the present
disclosure.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE
[0013] It should be understood at the outset that although example
embodiments of the present disclosure are illustrated below, the
present disclosure may be implemented using any quantity of
techniques, whether currently known or in existence. The present
disclosure 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] High power vacuum tubes may be used for various purposes,
such as radio frequency (RF) commercial broadcast, exciters for
nuclear research, and high power short wave communications. Known
cooling systems for these high power vacuum tubes have typically
incorporated water as a coolant where some configurations of these
high power vacuum tubes are cooled using water that changes phase
from a liquid state to a vapor state as heat energy is absorbed. At
normal ambient pressure, the resulting vacuum tube component
temperatures are generally limited by the temperature of the water
phase change that occurs at 100 degrees Celsius. For these types of
vacuum tubes to operate at lower temperatures, the boiling point of
the water should be lowered. Lowering the boiling point of the
water used to cool vapor cooled vacuum tubes, however, has not been
possible using known cooling systems.
[0015] FIG. 1 is a block diagram of one embodiment of a cooling
system 10 that may be utilized in conjunction with other
embodiments disclosed herein, namely the embodiments described with
reference to FIGS. 3 and 4. 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 disclosure, including the cooling system 100,
described with reference to FIG. 2.
[0016] 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 suitable structure for which dissipation of heat is
needed or desired. In one embodiment, structure 12 is a vacuum
tube. Because a structure 12 such as a vacuum tube can vary
greatly, the details of structure 12 are not illustrated and
described. Cooling system 10 includes a vapor line 14, a liquid
line 16, one or more evaporator assemblies 18a and 18b, a pump 20,
one or more inlet orifices 22a and 22b, a condenser heat exchanger
24, an expansion reservoir 26, and a pressure controller 28.
[0017] Structure 12 may be arranged and designed to conduct heat or
thermal energy to evaporator assemblies 18a and 18b. To receive
this thermal energy or heat, evaporator assemblies 18a and 18b may
be disposed on an edge of structure 12 (e.g., as a thermosyphon,
heat pipe, or other device) or may extend through portions of
structure 12, for example, through a thermal plane of structure 12.
In particular embodiments, evaporator assemblies 18a and 18b may
extend up to the components of structure 12, directly receiving
thermal energy from the components. Although two evaporator
assemblies 18a and 18b are shown in cooling system 10, one
evaporator assembly or more than two evaporator assemblies may be
used to cool structure 12 in other cooling systems.
[0018] In operation, a fluid coolant flows through each of the
evaporator assemblies 18a and 18b. As described later, this fluid
coolant may be a two-phase fluid coolant, which enters inlet
conduits 32 of evaporator assemblies 18a and 18b in liquid form.
Absorption of heat from 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 34 of evaporator assemblies
18a and 18b in a vapor phase. To facilitate such absorption or
transfer of thermal energy, evaporator assemblies 18a and 18b may
be lined with pin fins or other similar devices which, among other
things, increase surface contact between the fluid coolant and
walls of evaporator assemblies 18a and 18b. In particular
embodiments, the fluid coolant may be forced or sprayed into the
evaporator assemblies 18a and 18b to ensure fluid contact between
the fluid coolant and the walls of evaporator assemblies 18a and
18b.
[0019] The fluid coolant departs exit conduits 34 and flows through
vapor line 14, condenser heat exchanger 24, expansion reservoir 26,
pump 20, liquid line 16, and a respective one of two inlet orifices
22a and 22b, in order to again reach the inlet conduits 32 of
evaporator assemblies 18a and 18b. Pump 20 transports fluid through
evaporator assemblies 18a and 18b. In particular embodiments, pump
20 may use magnetic drives such that no shaft seals are
implemented, which can wear or leak with time. Although vapor line
14 uses the term "vapor," it may contain some liquid.
[0020] Inlet orifices 22a and 22b in particular embodiments may
facilitate proper partitioning of the fluid coolant among the
evaporator assemblies 18a and 18b, and may also help to create a
desired pressure drop between the output of pump 20 and evaporator
assemblies 18a and 18b. Inlet orifices 22a and 22b may have the
same size, or may have different sizes in order to partition the
coolant in a proportional manner to facilitate the removal of
different levels of heat from different evaporator assemblies 18a
and 18b.
[0021] A flow 38 of fluid (either a gas such as air or liquid) may
be forced to flow through condenser heat exchanger 24, for example
by a fan (not shown) or other suitable device. In particular
embodiments, the flow 38 of fluid may be ambient air that cools the
coolant in condenser heat exchanger 24 using convection currents.
The condenser heat exchanger 24 transfers heat from the coolant
that may be in the vapor state to the flow 38 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 40 may be provided for liquid fluid
coolant that either may have exited the evaporator assemblies 18a
and 18b or that may have condensed from vapor fluid coolant during
travel to the condenser heat exchanger 24. In particular
embodiments, the condenser heat exchanger 24 may be a cooling
tower.
[0022] The liquid fluid coolant exiting the condenser heat
exchanger 24 may be fluidly coupled to expansion reservoir 26.
Since fluids typically take up more volume in their vapor phase
than in their liquid phase, the expansion reservoir 26 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
produced by structure 12 may vary over time, as structure 12 system
operates in various operational modes.
[0023] Turning now in more detail to the fluid coolant, one
relatively 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 mass 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 mass of liquid that is vaporized.
[0024] The fluid coolant used in the embodiment of FIG. 1 may
include, but is not limited to, mixtures of antifreeze and water or
water, alone. In particular embodiments, the antifreeze may be
ethylene glycol, propylene glycol, methanol, or other suitable
antifreeze formulations. In other embodiments, the liquid may be a
perfluorocarbon, such as octafluoropropane, perfluorohexane, or
perfluorodecalin. These perfluorocarbons are relatively inert and
generally electrically insulative making them well suited for use
around vacuum tubes.
[0025] At a typical ambient pressure of 14.7
pounds-per-square-inch-absolute, water boils at a temperature of
100.degree. C. In particular embodiments, the fluid coolant's
boiling temperature may be reduced to between 55 to 65.degree. C.
by subjecting the fluid coolant to a sub-ambient pressure in the
range of approximately 2 to 3 pounds-per-square-inch-absolute.
Thus, inlet orifices 22a and 22b may permit the pressure of the
fluid coolant downstream from them to be substantially less than
the fluid coolant pressure between the pump 20 and inlet orifices
22a and 22b, which in this embodiment is shown as approximately 12
pounds-per-square-inch-absolute. Pressure controller 28 maintains
the coolant at a pressure of approximately 2 to 3
pounds-per-square-inch-absolute along the portion of the loop which
extends from the outlet of inlet orifices 22a and 22b to the inlet
of pump 20, in particular through evaporator assemblies 23 and 24,
condenser heat exchanger 24, and expansion reservoir 26. In
particular embodiments, a metal bellows may be used in the
expansion reservoir 26 and coupled to the loop using any suitable
approach, such as with brazed joints. In particular embodiments,
pressure controller 28 may control loop pressure using a motor
driven linear actuator coupled to the metal bellows or by using a
small gear pump that evacuates the loop to the desired pressure
level. The fluid coolant removed may be stored in the metal
bellows. In other configurations, pressure controller 28 may
utilize other suitable devices capable of controlling pressure.
[0026] In particular embodiments, the fluid coolant flowing from
pump 20 to inlet orifices 22a and 22b through liquid line 16 may
have a temperature of approximately 55.degree. C. to 60.degree. C.
and a pressure of approximately 12 pounds-per-square-inch-absolute
as referenced above. After passing through inlet orifices 22a and
22b, the fluid coolant may still have a temperature of
approximately 55.degree. C. to 60.degree. C., but may also have a
lower pressure in the range of approximately 2 to 3
pounds-per-square-inch-absolute. Due to this reduced pressure,
fluid coolant in the liquid state can absorb heat by boiling within
evaporator assemblies 18a and 18b where the boiling occurs at a
temperature less than 100 degrees Celsius.
[0027] After leaving exit conduits 34 of evaporator assemblies 18a
and 18b, the sub-ambient coolant vapor travels through vapor line
14 to condenser heat exchanger 24 where heat or thermal energy can
be transferred from the coolant vapor to the flow 38 of fluid. The
flow 38 of fluid in particular embodiments may have any temperature
less than the temperature of the fluid coolant, such as 50.degree.
C. or 40.degree. C. As heat is removed from the fluid coolant, any
portion of the fluid coolant that is in its vapor phase will
condense such that all or most of the coolant will be in liquid
form when it exits condenser heat exchanger 24. At this point, the
fluid coolant may have a temperature of approximately 55.degree. C.
to 60.degree. C. and a sub-ambient pressure of approximately 2 to 3
pounds-per-square-inch-absolute. The liquid coolant may then flow
to pump 20, which in particular embodiments may increase the
pressure of the fluid coolant to a value in the range of
approximately 12 pounds-per-square-inch-absolute. There may be a
fluid connection to an expansion reservoir 26 which, when used in
conjunction with the pressure controller 28, controls the pressure
within the cooling loop.
[0028] It will be noted that the embodiment of FIG. 1 operates
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 structure 12.
[0029] FIG. 2 is a block diagram of another embodiment of a cooling
system 100 that may be utilized in conjunction with other
embodiments disclosed herein, namely the embodiments described with
reference to FIGS. 3 and 4. Cooling system 100 may operates
generally similar to cooling system 10 of FIG. 1; however, cooling
system 100 of FIG. 2 also incorporates an air removal system 190.
For a variety of reasons, unintended air may be introduced into
cooling system 100. For example, in embodiments operating at
sub-ambient pressure, outside ambient air may leak into the
sub-ambient system due to a leak in the system. Accordingly,
cooling system 100 may utilize air removal system 190 to remove
this unwanted air from cooling system 100. Air removal system 190
in the embodiment of FIG. 2 includes an air pump 192, a reclamation
heat exchanger 194, coolant reservoir 196, and a reclamation fill
valve 198.
[0030] With reference to FIG. 2, the cooling loop of cooling system
100 including an evaporator 118, a pump 120, a liquid line 116, a
vapor line 114, an expansion reservoir 126, a pressure controller
128, and a condenser heat exchanger 124 is similar to the cooling
loop for cooling system 10 of FIG. 1. Fluid or air leaks 102 may
enter the cooling loop at evaporator assembly 118 or other location
and travel in vapor line 114 to the condenser heat exchanger 124.
At condenser heat exchanger 124, vaporized coolant will condense to
a liquid while the leaked air that cannot condense will accumulate
in areas of condenser heat exchanger 124 where the velocity of the
air is greatly reduced. Accumulated leakage air and any associated
vapor coolant that may be present in the form of humidity may be
pumped using air pump 192 to reclamation heat exchanger 194.
Reclamation heat exchanger 194 cools the air/vapor coolant
combination, which condenses the vapor from the air stream being
removed from the bottom of the condenser heat exchanger 124.
Condensed coolant separates from the air in coolant reservoir 196
while the air exits through vent 195. A level switch 197 may be in
communication with a reclamation fill valve 198 to allow the
reclamation fill valve 198 to open when recovered coolant is
present. The recovered coolant may be reintroduced to the cooling
loop through reclamation fill valve 198 and a conduit in
communication with pump 120.
[0031] Although one example of an air removal system 190 has been
shown with reference to FIG. 2, other air removal systems may be
used in other embodiments of the disclosure with more, less, or
alternative component parts. Additionally, although components of
embodiments of cooling system 10 and 100 have been shown in FIGS. 1
and 2, it should be understood that other embodiments of the
cooling system 10 can include more, fewer, or different component
parts. For example, although specific temperatures and pressures
have been described for such one embodiment of cooling systems 10
and 100, other embodiments of cooling system 10 and 100 may operate
at different pressures and temperatures.
[0032] FIG. 3 shows one embodiment of a cooling system 200 that is
retrofitted from a known cooling system that is used to cool a
vacuum tube 202. Cooling system 200 of the present disclosure
differs from known cooling system in that cooling system 200 may be
operable to cool vacuum tubes 202 at temperatures below 100 degrees
Celsius. For example, cooling system 200 of FIG. 3 incorporates a
fluid coolant that operates at a sub-ambient pressure in the range
of 1 to 3 pounds-per-square-inch-absolute such that the boiling
point of its water coolant cools vacuum tube 202 to between 40 to
60 degrees Celsius.
[0033] Although the system 200 of FIG. 3 is retrofitted from a
known cooling system, it should be understood that other
embodiments may retrofit other known cooling systems to provide
sub-ambient cooling. In other embodiments, some, none, or all of
the components of known cooling systems may be utilized. With this
embodiment and other embodiments described herein, any of a variety
of methods that keep water as an insulator may be utilized. Such
methods are common practice with vapor and water cooled vacuum
tubes.
[0034] In the embodiment of FIG. 3, cooling system 200 has
components similar to the cooling systems 10 and 100 of FIGS. 1 and
2. For example, cooling system 200 has a vapor line 214, a liquid
line 216, an evaporating heat exchanger 218, a condensing heat
exchanger 224, an expansion reservoir 226, a pressure controller
228, and a liquid bypass and an equalization line 240. Each of
these components may operate in a similar or different manner than
the respective components described with reference to FIGS. 1 and
2. Evaporating heat exchanger 218 of this type is generally
referred to as a "pool boiling mechanism."
[0035] Cooling system 200 also includes a control box 242, a
solenoid valve 244, and a make-up reservoir 246 that form a portion
of the known cooling system. Control box 242 may be provided to
control various aspects of cooling system 200 including operating
pressures and/or flow rate of fluid coolant. Solenoid valve 244
operates with make-up reservoir 246 to store additional fluid
coolant and provides this additional fluid coolant to cooling
system 200 on an as needed basis. In other embodiments, more less
or different components of a known cooling system may be used for
retrofitting cooling system 200.
[0036] In this disclosure, the term "subambient pressure" generally
refers to a pressure of fluid coolant that is less than normal
ambient pressure of approximately 14.7 pounds-per-square-inch. In
particular embodiments, cooling system 200 may provide an advantage
over known cooling systems in that the sub-ambient pressure of the
fluid coolant may cool vacuum tube 202 at a relatively lower
temperature than provided by known cooling systems. In a particular
embodiment in which the coolant is water, cooling system 200 may
enable vaporization of water receiving thermal energy from vacuum
tube 202 at temperatures below 100 degrees Celsius that my result
in lower vacuum tube anode and seal temperatures than if the water
has boiled at 100 degrees Celsius.
[0037] FIG. 4 shows another embodiment of a cooling system 300 for
a vacuum tube 302, according to an embodiment of the disclosure.
Cooling system 300 has several components that are similar to
cooling systems 10, 100, 300 of FIGS. 1, 2 and 3. For example,
cooling system 300 has a vapor line 314, a liquid line 316, a
condensing heat exchanger 324, an expansion reservoir 326, a
pressure controller 328, a liquid bypass and equalization line 340,
a solenoid valve 344, a make-up reservoir 346, an evaporating heat
exchanger 318, and a pump 320. Cooling system 300 differs, however,
in that it includes a sump reservoir 348 with an associated sump
line 350, and spray jets 352.
[0038] Pump 320 operates in a generally similar manner to pumps 20
and 120 of FIGS. 1 and 2, respectively. Sump line 350 transfers
liquid water in evaporator assembly 318 to the sump reservoir 348
for circulation back through the pump 320. Spray jets 352 direct a
spray and/or spays of water directly onto the tube's anode to
enhance the efficiency of the thermal contact between the boiling
coolant and the surfaces from which heat energy is removed.
[0039] While spray cooling has been shown in this embodiment, in
other embodiments, other enhancement techniques may be utilized to
enhance cooling of the anode, including, but not limited to, using
either forced cross flow boiling or jet impingement cooling
techniques. Such techniques may be used in conjunction with surface
enhancing configurations (e.g., pin fin configurations). Some of
such configurations are described in United States patent
application Ser. No. 11/420,184, which is hereby incorporated by
reference.
[0040] Particular embodiments of evaporating heat exchanger 318 may
provide an advantage in that spray or jet impingement of coolant
may have a better heat transfer coefficient than pool boiling as
described with regard to cooling system 200 of FIG. 3. Spray or jet
impingement of coolant may also provide certain advantages in that
cooling fins configured on the vacuum tube 302 may be made
relatively smaller while realizing a relatively higher heat
transfer coefficient than obtained with pool boiling with larger
fins.
[0041] FIG. 5 is a flowchart showing one embodiment of a series of
actions that may be performed to cool vacuum tubes using a fluid
coolant operated at a sub-ambient temperature. In act 400, the
process is initiated.
[0042] In act 402, evaporator assembly 18, 118, 218, or 318
receives fluid coolant in liquid form from condensing heat
exchanger 24, 124, 224, or 324. The fluid coolant may be
transported through evaporator assembly 18, 118, 218, or 318 and
condensing heat exchanger 24, 124, 224, or 324 using any suitable
approach. In one embodiment, fluid coolant is pumped using a pump
20, 120, or 320. In other embodiments, fluid coolant may be moved
through evaporator assembly 18, 118, 218, or 318 and condensing
heat exchanger 24, 124, 224, or 324 using convection flow of fluid
coolant.
[0043] In act 404, the pressure of fluid coolant in evaporator
assembly 18, 118, 218, or 318 is maintained at a sub-ambient
pressure level. In a particular embodiment, the fluid coolant
includes water. To control the operating pressure of the water,
pressure controller 28, 128, 228, or 328 operates in conjunction
with expansion reservoir 26, 126, 226, or 326 to alternatively
expand or contract the volume within cooling system to maintain the
pressure of the water at a sub-ambient level. A pump 20, 120, or
320 configured upstream of evaporator assembly 18, 118, 218, or 318
may cause the pressure at inlet conduits 32 to exceed a desired
sub-ambient level. The pressure of water provided by pump 20, 120,
or 320 may be reduced by inlet orifices 22 that restrict the flow
of the water and thereby reducing its pressure. In other
embodiments as described with reference to FIG. 3, control of the
pressure of the water may be controlled by control box 220.
[0044] In act 406, the fluid coolant is evaporated in evaporator
assembly 18, 118, 218, or 318 to vacuum tube 202 or 302. Evaporator
assembly is thermally coupled to vacuum tube 202 or 302 using any
suitable approach. In one embodiment, evaporator assembly 18, 118,
218, or 318 using a pool boiling mechanism that causes fluid
coolant to flow in relatively close proximity to the anode of
vacuum tube 202 or 302. In another embodiment, evaporator assembly
18, 118, 218, or 318 uses a spray/jet impingement cooling technique
that sprays fluid coolant onto a surface that is thermally coupled
to the anode of vacuum tube 202 or 302. In other embodiments,
evaporator assembly 18, 118, 218, or 318 may include other surface
enhancing configurations, such as a pin fin configuration.
[0045] In act 408, the evaporated fluid coolant is moved to
condensing heat exchanger 24, 124, 224, or 324 where it is
condensed back to it liquid phase. Once condensed, the fluid
coolant may again be pumped to evaporator assembly 18, 118, 218, or
318 for further cooling of vacuum tube 202 or 302.
[0046] In act 410, air is optionally removed from the cooling
system 10, 100, 200, or 300. In certain cases, unwanted air from
the environment may leak into cooling system 10, 100, 200, or 300
due to sub-ambient pressures maintained inside. Air introduced into
cooling system 10, 100, 200, or 300 may not evaporate in a manner
similar to fluid coolant and thus may reduce the efficiency of
cooling system 10, 100, 200, or 300 in certain embodiments. Air may
be removed from cooling system 10, 100, 200, or 300 by pumping
uncondensed mixture of vapor coolant and air to a reclamation heat
exchanger 194 that condenses the vapor coolant for separation of
the air. Once separated, the air may be released from the system
through a vent 195.
[0047] The fluid coolant may be re-circulated through cooling
system 10, 100, 200, or 300 for continued cooling of vacuum tube
202 or 302. When cooling of vacuum tube 202 or 302 is no longer
needed or desired, the process ends in act 412.
[0048] Modifications, additions, or omissions may be made to the
previously described method without departing from the scope of the
disclosure. The method may include more, fewer, or other acts. For
example, a portion of fluid coolant exiting evaporator assembly 18,
118, 218, or 318 as liquid may bypass condensing heat exchanger 24,
124, 224, or 324 by flowing through a bypass and equalization line
40, 240, or 340. Thus, cooling system 10, 100, 200, or 300 may be
configured to handle process variations, such as variations in
thermal loading of vacuum tube 202 or 302 that may cause a
corresponding variations in the evaporation rate of its fluid
coolant.
[0049] Although the present disclosure 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 disclosure
encompass such changes, variations, alterations, transformation,
and modifications as they fall within the scope of the appended
claims.
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