Field of the Invention
!0002] This disclosure relates generally to a thermal energy storage cooling
system that is useful to cool systems that output bursts of heat. In particular, the system may
include a thermal energy storage system that uses a salt hydrate as a phase change material to
cool bursts of heat from a directed energy weapons system.
Description of the Related Art
!0003] Conventional vapor compressiOn systems may be efficient at cooling
environmental loads, such as rooms or systems with relatively slovv gains in heat However,
these systems alone do not generally provide the rapid cooling features necessary to cool a
system that outputs bursts of heat. A vapor compression system may take up to a minute, or
in some cases more time, to reach full capacity and usually several minutes or longer to
provide cooling to the target heat load. However, once these vapor compression systems are
running they can be efficient in cooling a target heat load to a specific temperature.
[0004J Thermal energy storage systems have been used to level a cooling load by
substituting coolmg capacity and at times reduce costs in many environments. Many different
types of matenals have been used as phase change materials within thermal energy storage
systems, mcluding inorganic systems such as salt and salt hydrates, organic compounds such
as paraffins or fatty acids. Polymeric materials, such as poly(ethylene glycol) have also been
used as phase change materials. In addition chilled water and ice systems, have been used.
These chilled water systems are reliable but also heavy and bulky as they rely only on the
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heat capacity of water. Ice storage systems are more compact and lighter than chilled water
due to the phase change energy of 1ce to water, but heat transfer problems for rapid melting
and freezing of ice as required for burst cooling, along with the requirement to recharge at
temperatures below 0°C even if the cooling temperature is around 20°C, proved
disadvant:1geous. Paraffins have been used as phase change matenal in pnor systems,
although they were not found to be advantageous for cooling rapid bursts of heat In use, a
cooling system reduces the temperature to induce a phase change to solidify the paraffin wax
to a solid form within a tank that is part of the thermal energy storage system. A heat transfer
fluid is then circulated through the tank so that the solid wax absorbs heat from the heat
transfer fluid and melts.
[0005] 1Jnfortunately, several properties of paraffin wax, such as its heat transfer
properties and melting dynamics resulted in it being a poor choice for applications designed
to rapidly cool systems which output bursts of heat.
SlJJ\1"MARY
[0006] The embodiments disclosed herein each have several aspects no single one
of vvhich is solely responsible for the disclosure's desirable attributes. \Vithout limiting the
scope of this disclosure, its more prominent features will novv be brief1y discussed. After
considering this discussion, and particularly after reading the section entitled "Detailed
Description," one will understand how the features of the embodiments described herein
provide advantages over existing systerns, devices and methods.
[0007] One embodiment is a thermal energy cooling system for a high-energy
laser. In this embodiment the system mcludes: a thermal energy storage systern comprising
phase change rnaterial having a transition temperature of between 10°C and 20°C, a phase
change material energy density of at least 200kJ/kg, a phase change material density of at
least lg/cc and a phase change material thermal conductivity of at least 0.5W/mK; a cooling
loop comprising a heat transfer fluid connected to the thermal energy storage system and a
heat exchanger m thermal communication with the lugh-energy laser; and a control system
programmed to read sensor data and determine when to initiate burst mode cooling to mitiate
discharge of the thermal energy storage system, wherein the burst mode cooling comprises
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pumping the heat transfer t1uid through the cooling loop including the thermal energy storage
system that is capable of dischargmg over a period of less than five minutes.
[0008] Another embodiment 1s a method of cooling a high-energy laser using a
thermal energy storage system. The method includes providing a thermal energy storage
system comprising phase change material having a transition temperature of between 10°C
and 20°C, a phase change material energy density of at least 200kJ/kg, a phase change
material density of at least 1 glee and a phase change material thermal conductivity of at least
0.5'W/mK; reading sensor data to determine when to initiate burst mode cooling and
discharge of the thermal energy storage system; and upon determining that it's time to initiate
a burst mode cooling and the discharge, pumping heat transfer t1uid through a cooling loop
connected to the thermal energy storage system and a heat exchanger in thermal
communication with the high-energy laser, wherein the thermal energy storage system is
capable of discharging over a period of less than five minutes.
BRIEF DESCRIPTION OF THE DRA \:V1NGS
[0009] The foregoing and other features of the present disclosure will become
more fully apparent from the following description and appended claims, taken in
conjunction with the accompanying drawings. Understanding that these drawings depict
only several embodiments in accordance with the disclosure and are not to be considered
lirniting of its scope, the disclosure will be described with additional specificity and detail
through use of the accompanying drawings. In the following detailed description, reference
is made to the accompanying drawings, which form a part hereof In the drawings, similar
symbols typically identif-Y similar components, unless context dictates otherwise. The
illustrative embodiments described in the detailed descnption, drawings, and claims are not
meant to be limiting. Other embodiments may be utilized, and other changes may be made,
without departing from the spirit or scope of the subject matter presented here. It will be
readily understood that the aspects of the present disclosure, as generally described herein,
and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide
vanei)' of different configurations, all of which are explicitly contemplated and make part of
this disclosure.
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[0010] FIG l is a schematic illustration of an embodiment of a thermal energy
cooling system having a storage system and a vapor compressiOn system according to one
embodiment.
[OOHJ FIG. 2 1s a schematic illustration of the cross section of a thermal energy
storage system of FIG. 1, according to one embodiment.
[0012J FIG. 3 is a block diagram of an embodiment of a control system that 1s
part of the thermal energy cooling system of Figure l.
[0013J FIG. 4 is a flow diagram of one embodiment of operating a thermal energy
cooling system.
DETAILED DESCRIP110N
[0014] Thermal energy cooling systems and methods are disclosed for rapidly
cooling products, devices or other heat loads. Such systems use a thermal energy storage
system configured to rapidly cool bursts of heat, such as from a high-energy laser directed
energy weapon system. The thermal energy storage system can act as a sink to absorb heat
being generated by the directed energy >veapons system. In one embodiment, the thermal
energy storage system comprises a salt hydrate, such as a potassium fluoride tetra hydrate as
the phase change material that is used to store heat.
[0015] In one embodiment, the thermal energy cooling system pumps a heat
transfer tluid from a heat exchanger in thermal contact vvith a directed energy >veapons
system through a thermal energy storage system to rapidly of-1-load the absorbed heat. The
heat transfer tluid may be ethylene glycol water or a phase change refrigerant. In this
embodiment, they systern may be configured to maintain the fiber amplifiers and other
critical system components of the laser weapon system between about l Y'C - 35°C, 20°C -
30'-'C or 22°C - 28°C or similar temperature ranges.
[0016J Thermal energy storage systems that are applicable for use with the abovementioned
high-energy laser cooling system may be configured to undergo a solid-hquid
phase change with a phase transition temperature between about 1 0°C and about 2Y'C. Tlus
range may be between about 15°C and 2Y'C assuming that a heat transfer i1uid (coolant)
flow to the laser is has a temperature in the range of about 20°C to 30°C. Others had
previously discussed using 1ce as a phase change material due to its high phase change
energy of 333kJ/kg. Given that the phase transition temperature of water to ice is at 0°C and
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accounting for subcooling and heat transfer, the temperature of a heat transfer fluid needed to
freeze 1ce should be around -6°C to -1 0°C. Thus, storing thermal energy in ice for an
application that only requires to be cooled to around 20°C is very energy inefficient. The
vapor compression equipment required to cool the heat transfer fluid down to -6°C to -1 0°C
will consume a lot of power and needs to be sized for undue large capacity to accomplish fast
freezing for such low fluid temperatures.
[0017] Phase change material with a more appropriate phase transition
temperature between about l CY)C and 20°C have lower phase change energies, with some
paraffins and hydrated salts having a material energy density of around 200kJikg or slightly
above. Thus, one embodiment of the invention is a system that uses a phase change material
with a phase change material energy density of above 200kJikg of latent heat. This yields a
system of reasonable energy density. To achieve compactness the phase change material
should also have a relatively high material density. Ice has a material density of roughly 1
glee. Paraffins have material densities of less than 1 glee often only 0.8 to 0.85 glee:. In
contrast, hydrated salt complexes usually have densities of significantly above 1 glee thus
making energy storage systems of a given mass of phase change material volumetrically
more compact. In one embodiment, the material density of the phase change material used
within embodiments of the invention is above l.lglcc, 12 glee, L3glcc, 1.4g/cc, or more
making the phase change material very volume effective.
[0018] Another property to consider in addition to the size and weight of the
thermal energy storage system is the thermal conductivity of the phase change material. As
the thermal energy has to travel from the heat transfer surface throughout the phase change
material to facilitate the phase change, a lugher thermal conductivity correlates to a faster
thennal energy propagation and the thicker the phase change material layer can be for a
given time period to propagate. A tlucker layer of phase change material rneans there is more
material per heat transfer surface area that can be applied. This minirnizes the amount of heat
transfer hardware needed and thereby minimizes the we1ght and size of the overall thermal
energy storage system. In some embodiments, the thermal conductivity of the phase change
matenal is above 0. 6 W /mK and preferably closer to or above 1 \V /mK or greater.
[0019] While several hydrates and paraffins have phase change energies at or
above 200 kJ/kg, suitable paraffins with phase transition temperatures between 1 0°C and
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25°C, i.e. typically 14, 15 or 16 carbon chain paraffins, fall short in the other thermodynamic
properties exhibiting thermal conductivities of often less than 0.2 W /mK and matenal
densities well below l g/cc, often below 0. 9g/cc. Paraffins, as well as morganic hydrates,
both exhibit noticeable subcooling during the freezing process, wh1ch can be somewhat
mitigated with additives for inorgamc hydrates. Another disadvant:'lge of orgamc paraffins is
the fact that they do not show crystallization propagation as experienced with most hydrates,
wherein the crystallization propagation through the material improves the temperature
distribution throughout the material from the subcooled liquid state.
[0020] In one embodiment the thermal energy storage system uses a potassium
fluoride-based phase change material. The properties of potassium t1uoride, and particularly
potassium fluoride tetra hydrate allow the thermal energy storage system to rapidly absorb
relatively large bursts of heat coming from a system such as a directed energy weapons
system. In particular, this salt hydrate was found to have a ve1y good crystal growih
propagation that spreads throughout the phase change material and aids thermal distribution
into the phase change material. This material also has a high thermal conductivity, vvhich
helps minimize thermal gradients. Also, the material density of potassium f1uoride
tetrahydrate is 144 glee, which is 70%) higher than the 16 C-chain paraffin of similar
transition temperature. Therefore, the potassium fluoride tetrahydrate was found to have a
70?.'0 higher volumetric density than the similar paraffin. \Vhen taking into account the 4 to 5
titnes lugher thermal conductivity and the crystallization propagation ability allowing for a
much higher phase change rnaterial to heat transfer hardware mass and volume ratio, such
potassium nuoride tetrahydrate based systems can be designed to be nmch lighter and more
than twice as compact when compared to for example an n-hexadecane paraffin systern of
sunilar rnel ting temperature and phase change energy.
[ 0021 J The operating conditions for a laser weapon cooling system in which the
phase change materials are used as a thermal energy storage system call for much more rapid
melt and freeze periods than traditionally required for seasonal or diurnal thermal energy
storage. System discharge (melting) of the phase change material in the thermal energy
storage system often has to occur in less than five minutes and more frequently even in less
than three, or even two minutes. The time to charge (re-freeze) the phase change material is
also much shorter, typically in less than 20 minutes, and often less than 10, 8, 6, 5 or 4
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minutes. In some embodiments, once the phase change material in the thermal energy
storage system 1s frozen, so that the storage system charged, the phase change material needs
to be maintained m its frozen state. To maintain the phase change material m a frozen state, a
vapor compresswn system may be activated at particular time intervals such that any phase
change material which transitioned into a liquid state is cooled back mto a frozen state and/or
maint:1ined in the frozen state.
[0022] During use, the laser weapon may be activated for a total firing period of
1, 2 or 3 or even 5 minutes. Since the firing period usually occurs in pulses of several
seconds for each target, as short as 2 or 3 seconds and as long as about 10 to 15 seconds, the
total discharge period of 1, 2 or 3 or even 5 minutes can occur over periods of 5 to 30
minutes. Depending on the target occurrence, or lack thereof, the system may also be
recharged before it is completely depleted. The thermal management system including the
thermal energy storage system, however, usually has a design requirement to be able to
operate under a worst case scenario of continuous lasing of 1, 2 or 3 or even 5 minutes,
vvhich likely vvill never occur. Accordingly, the thermal energy cooling system preferably has
the capacity to discharge the thermal energy storage system and cool the laser over this entire
continuous time period. Of course, the tot.al activation period, including pauses betvveen
firing, may be longer, depending on the particular need. In addition, the system preferably
can recharge (re-freeze) the phase change media in the thermal energy storage system fairly
rapidly once the activation time has ended, for example in less than 20, 10, 8, 6, 5, or 4
minutes so that the thermal energy cooling system can be ready to etTectively cool the laser
weapon for additional activation periods.
[0023J One objective of a thermal energy storage system m the laser weapon
thennal management is to reduce nmss and volume, for what is often referred to SWaP (size
weight and power) in the military, compared to not having a thermal energy storage system.
In order to facilitate size and weight advanta.ges a thennal energy storage system is expected
to complete the phase change process for well above 50~o, preferably above 75% or above
90% of the phase change material withm the time constraints g1ven above of typically m less
than 25 minutes, and often less than 10, 8, 6, 5 or 4 minutes of freeze time and less than 5
minutes and often 3 mmutes or 2 minutes of melt time.
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[0024] In one embodiment, the thermal energy storage system compnses an
enclosure or tank comprising a system of heat transfer tubes runnmg throughout the tank.
Depending on design, the phase change material may be located either mside or outside the
heat transfer tubes and the heat transfer fluid on the other side. Alternative designs to these
tubular systems are plate-type configurations with the phase change material in between plate
heat exchangers. Both types of systems, particularly the tubular configurations, may have
fins on the phase change medium side for mcreased heat transfer between the heat transfer
media and the phase change material, e.g. potassium fluoride.
[0025] In one embodiment, the thermal energy storage system may be made out
of one or more modules, each module having a plurality of heat transfer tubes with phase
change material inside the heat transfer tubes and heat transfer fluid flowing on the outside of
the heat transfer tubes and within the tank. Such a plurality of heat transfer tubes may be in
multiple planar levels or in one or more bundles. An example tube diameter may be 0. 5 inch,
but embodiments may include heat transfer tubes with an outer diameter between about ~~4
inch or about 1" depending on system response time requirements, fin heat transfer
enhancements, additive heat transfer enhancements or the effectiveness of any crystallization
additives used within the phase change material to reduce subcooling. Examples of such
crystallization additives include pumice, a textured volcanic glass, which reduces the
subcooling during the freezing process.
[0026] In one ernbodiment, a vapor cornpress10n system is used to cool the
thermal energy storage system pnor to use. Typical subcoolmg for potassiurn fluoride tetra
hydrate phase change medium 1s 10'-'C to 15°C below its transition temperature of l8°C.
Once solidification and freezing of the phase change material has sta.rted the heat transfer
fluid, cooled by the vapor compression system, can be adjusted to a temperature closer to the
transition ternperature to complete the freezing process, provided an adequate differential
ternperature for rapid freezing is maintamed. Tlus may call for an operating strategy in
which a relatively small amount of cooling energy is transferred from the vapor compression
system to the thermal storage system at a temperature of about Y'C to initiate the nucleation
of the phase change material with the remainder of the cooling energy provided with heat
transfer fluid that is much closer to the phase change temperature of the potassium fluoride
tetra hydrate material. By cooling the phase change material with heat transfer i1uid at a
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relatively higher temperature, the cooling system capacity and energy efficiency is much
higher because the vapor compression system does not require as much energy to provide the
cooling energy to the heat transfer fluid at a higher temperature and offers a higher cooling
capacity.
[0027] In one embodiment, the system 1s operated to ret:1in a reserve of frozen
phase change material to prevent the phase change matenal from completely melting.
Because the required heat transfer fluid temperature required to initiate crystallization of the
phase change material is relatively high, the system may be more energy efficient by keeping
a reserve of crystallized frozen phase change material within the thermal energy storage unit.
For example, each sub-containment portion of the thermal energy storage system (e.g. tube,
channel, space between plates) may retain a minimum percentage of frozen, crystalized phase
change material. For example, the retained minimum percentage may be 1 ~o, 2%, 3%, 4~~,
5%, 6%, 7%, 8%, 9%1, 10%, 15% or more of the total frozen phase change material. The
retained portion may be 2%1-S%, 4%-8%1, or 5%-10%1, 5%-15%1 10%-15%, or 15%-20% of
total volume of phase change material in the thermal energy storage system. Higher
percentages of total frozen phase change material will of course also avoid the need for initial
nucleation and crystallization.
[0028] If the system retains a minimum amount of frozen phase change material,
the temperature of the heat transfer f1uid required to freeze the thermal energy storage system
can be, for example, between 8°C and 16°C. If the phase change material 1s allowed to fully
melt, the temperature of the heat transfer fluid may need to be 5°C or colder to initiate
crystallization and freezing of the phase change matenal. Accordingly, in one embodiment
it is more energy dricient to maintain the retained minimum portion of crystalized, frozen
phase change nmterial during cooling operations and prevent the phase change nmterial from
completely melting.
[0029] In one embodiment, the control systern monitors the temperature of the
phase change material or the heat transfer i1uid temperatures entenng and exiting the thermal
energy storage system along with the flow rate of the heat transfer fluid. From these data, the
control system may calculate or estimate the amount of frozen phase change matenal
remaining m the thermal energy storage system. The thermal energy storage system may be
made of hundreds of separate tubes, channels or plates. ln case of tubes, each tube may have
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more or less frozen phase change material located within it. Measuring the actual amount of
frozen phase change matenal m each individual tube may not be practical, so estimating the
amount of frozen phase change material by measuring the overall temperature of the phase
change material and heat transfer fluid flows may be more practical.
[0030] If the control system determines that the amount of remaining frozen
phase change matenal is below a predetermined threshold, the control system may initiate the
vapor compression system to start circulating heat transfer fluid and freezing the phase
change material. In addition, the control system may prevent the system from being able to
initiate additional cooling operations using the thermal energy storage system until the vapor
compression system has had time to freeze more of the phase change material in the thermal
energy storage system. In one embodiment, the system may only allow the system to
perform additional cooling cycles if, after such a cooling cycle, the remaining frozen phase
change material would remain above the minimum set threshold. To ensure that every tube,
or almost every tube, within the thermal energy storage system is very likely to contain at
least some frozen phase change material, the system may choose a minimum set threshold
value that is higher than what is needed in any particular tube. For example, the system may
set the threshold at 15~o, such that 'vvhen the control system determines that only 15% of the
total volume of phase change material remains frozen it will activate the vapor control
system to start freezing the phase change material. By choosing a minimum value of 15%,
this may ensure that each tube within the thermal energy storage system has at least sorne
frozen phase change material to sta.rt an efficient cooling cycle. Of course, depending on the
system design, it may require the minimum threshold to be set at Y'l(,, 1 m'IJ, 15~'0 or even 20%
to ensure that each tube within the system contains some amount of frozen phase change
material. Selecting a higher percentage is of course always an option, however, the higher the
percentage of left over frozen material, the lower the thermal energy storage system capacity
will be.
!0031J In one embodiment, the thermal energy cooling system acts as a burst
mode cooling system to remove the heat generated from each firing event of a directed
energy weapons system, such as a laser weapons system. Dunng each finng cycle, the
system transfers thermal energy from the weapon to the cooling and thermal energy storage
system. In one embodiment this can be accomplished by using a set of heat transfer tubes
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running through the thermal storage system and contaming a thermal heat transfer fluid such
as glycol/water or refrigerant. Alternatively, the fluid can run outside the heat transfer tubes
with the phase change material in the heat transfer tubes. It is also possible, although not
always preferred, that refrigerant or thermal heat transfer i1uid coming from directed energy
weapons system may be routed through a vapor compression system to perform initial
cooling on the heated thermal transfer t1uid, followed by c1rcttlation through the thermal
energy storage system.
!0032] In another embodiment, the vapor compresswn system 1s used to
supplement the cooling capacity of the thermal energy storage system as the directed energy
weapons system is being fired. Accordingly, during a firing event, the vapor compression
system and thermal energy storage system may all act in concert to provide cooling capacity
to remove heat from the directed energy weapons system. In one embodiment, the control
system for the vapor compression system is a vector drive controller that is used to increase
efficiency of the overall system.
[OfB3] In other embodiments, the system compnses a heater configured to
increase the temperature of the heat transfer f1uid in order to bring the components of the
system up to their operating temperature. For example, the components of a laser weapon,
such as the laser diode amplifiers and diodes, may be designed to function most reliably at
temperatures of between 15°C and 35°C If the ambient temperature is 5°C, then the system
may activate a heater connected to a heat transfer Huid loop within the system to begin
circulating warmed heat transfer fluid to the laser components. Sirnilarly, the components of
the hotel load may also need to be warmed up to their operating temperature if they are in a
relatively cold ambient environment. Thus, the heater may also be connected through valves
to the heat transfer fluid loop that runs through the hotel loads connected to the system. The
heater may be heated through waste heat from a generator, or by combustion of fuel, or be an
electric resistance heater in some embodiments. In one embodiment, the heater 1s connected
to the controller and a series of temperature sensors in order to mamtain each of the system
components within their operational temperature range, whether that requires heating, or
cooling, of the component.
[0034] Directed energy weapons systems may also include additional ancillary
mechamcal or electncal equipment or components that need to be cooled in order to operate
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the weapons system efficiently. Such additional equipment, also termed a "hotel load" may
include sensors, radar systems, battenes, power modules, generators, pumps, motors,
computers, electronics and other equipment that is ancillary to the mam weapons system. ln
particularly warm environments, such as the desert, these additional components may work
more efficiently by being cooled pnor to use. Thus, in one embodiment, the thermal energy
cooling system includes a vapor compression system that acts as an ancillary cooling system
configured to cool these additional components (as well as the laser diode amplifiers) to a
predetermined temperature, or within a temperature range, so that they operate efficiently in
warmer environments.
!0035] In some embodiments, the directed energy weapons system and hotel
loads are located on a single platform. The platform may include a variety of different
sensors to monitor and to send signals to components of the directed energy weapons system
and the hotel loads. These sensors are used to generate sensor data that is read by the
weapon system including the thermal energy cooling system controller in order to determine
the proper time to activate the weapon system including the burst mode cooling cycle and
discharge the thermal energy storage system. In some embodiments, the controller also
receives sensor data from sensors and systems that are not located on the platform, and the
controller may use this external sensor data to help determine the correct time to activate the
vveapon system and the burst mode cooling event.
[0036] The vapor compressu:m system may be composed of multiple
compressors, some dedicated to freeze and rnaintam frozen phase change material, such as
potassium nuoride tetra hydrate, in the thermal energy storage system, and some configured
to cool the hotel load. However, given a control signal that there is a need to charge the
thennal energy storage system, all compressors may be activated to charge the thermal
energy storage system if the hotel load is determined to be able to afford a temporary lack of
coohng. This detennination may be based on whether the individual components of the hotel
load are detected to be at or below their individual component design temperature. The
compressors, some or all, may also be used to cool the high-energy laser in parallel to use of
the thermal energy storage system bemg discharged. In some embodiments, the vapor
compression system has a capacity of about lkW to 50kW, 51kW to lOOkW, or up to several
hundred kilowatts of cooling power or more.
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[0037] In some embodiments, the vapor compression system comprises a vapor
compresswn system with a vanable speed compressor that is controlled to vary the output
capacity of the vapor compression system. The vapor compression system may be controlled
by a Vector Control System (VCS) that is configured to optim1ze the eiTiciency of the vapor
compression system by varying the torque placed on the compressor.
[0038J Embodiments of the Vector Control System (VCS) described herein
expand the one-dimenswnal speed control of the vapor compression system into a two
dimensional speed and torque control system. Incorporating torque control into the vapor
compression system allows for optimal use of the compressor motor to increase the overall
system efficiency. The VCS usually controls multiple motors within the vapor compression
system, such as the compressor motor, as well as fan and blower motors are all optimized
with respect to speed and resulting torque operating conditions. A VCS optimization process
can take into account characteristics of the compressor motor's performance as a function of
speed, compression ratio and absolute pressures. The VCS may also take into account other
system motor characteristics in the system to improve the efficiency of condenser fan(s) and
in some cases evaporator fans or blowers or f1uid pump motors in cases vvhere the evaporator
cools a heat transfer f1uid. Vector Drive control constitutes a t\.vo dimensional energy
efficiency optimization incorporating refrigerant flow as vvell as high side (condenser) air
f1ovv and, in some instances low side (evaporator) air flow or pumped t1uid t1ovv, deriving the
best system energy eiTi.ciency obtainable at any given load and temperature condition. As
will be recognized, fluid pumps are generally controlled by a motor and the term "pump" as
used herein may include the motor that drives the pmnp. The motor may be part of the pump
as a hermetic systern or connected to the pump via a gear, belt or pulley, as known to those
skilled in the art.
[0039J In one example, a vapor compress1on operating condition that
conventionally calls for a certain predeternuned compressor speed at a set condition is
improved by operating the compressor at a lower torque setting while usmg the same
refrigerant flow. Although the system would be using less torque the resultant cooling
capacity would remain the same because the refrigerant flow through the vapor compression
circuit doesn't change. The lower compressor torque could be achieved by increasing the
airflow of a condenser fan. This increased airflow would lower the condenser temperature
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and pressure which may decrease the torque required by the compressor to compress the
refngerant. Depending on the compressor motor and condenser fan characteristics, the
additional energy required to increase the fan speed could be less than the energy saved by
reducing the torque on the compressor. Thus, in this embodiment, the VCS would evaluate
the energy required to increase the condenser fan speed and balance that against the energy
saved by lowering the torque on the compressor. If the energy saved by reducing the torque
on the compressor was greater than the energy reqmred to increase the fan speed, then the
VCS would increase the condenser fan to save energy overall.
[0040] In other embodiments, reducing the compressor torque may reduce the
overall efficiency if the energy required to increase the speed of the condenser fan is more
than the energy required to operate the compressor at a higher torque. Thus, the VCS system
can va1y different components in different components within the vapor compression circuit
to increase the overall system efficiency by modulating the torque placed on different motors
and by adjusting the speed of the various motors to give the optimum energy efficiency.
[0041] The use of a vector control system may reduce the overall electrical
energy requirements of a directed energy vveapon system by reducing the povver requirements
for the cooling system. This may be important for directed energy >veapons systems that are
transportable and powered by portable generator systems using fossil fuels. In these
transportable systems, the directed energy weapons system, portable generator, and cooling
systems may be located on one or more mobile platforms. Since the energy required to
operate the directed energy weapons system is being provided by a portable generator, any
savings m electrical energy can translate into a fuel savings. By saving the fuel, the
transportable system may be able to remam active for a longer period of time before needing
to be refueled.
[0042J One embodirnent of the invention is a cooling system that mcludes a
thennal energy storage system that is controlled by a vector control system as described
above for the vapor compression system. In this embodiment, the vector control system
controls the speed and torque of a pump connected to the cooling loop of the thermal energy
storage system. The pump may be configured to move a phase change fluid, such as
refrigerant, through a cooling loop of the thermal energy storage system and to a heat
exchanger connected to the thermal load in need of cooling and the evaporator of the vapor
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compression system for system charge and maintenance. The torque imposed on the pump is
proportional to the pressure drop of the phase change i1uid flowing through the heat
exchanger and thus a function of the flow rate and the vapor quality, i.e. the ratio of gas to
liquid. Adjusting the speed of the pump motor will adjust the speed of the phase change fluid
moving through the cooling loop. Because the phase change fluid 1s present in both liquid
and gaseous states, the speed of the pump motor may also affect the quality (liquid/gas ratio)
of the phase change fluid. Monitormg the torque placed on the pump motor may allow the
vector control system to monitor and control the pressure drop of the phase change i1uid as it
passes through the pump via the vector control system adjusting the speed of the pump and
thus the quality of the phase change fluid to meet a desired target leveL In one embodiment,
the vector control system is activated while the thermal energy storage system is being
charged by the vapor compression system. In another embodiment, the thermal energy
storage system is activated during discharge of cooling from the thermal energy storage
system. It should be realized that the vector control system may be used any time the thermal
energy storage system pump motor is operated regardless of charge, discharge or
maintenance cooling status of the thermal energy storage system.
[0043] The thermal energy storage system may vvork by freezing potassium
fluoride tetra hydrate, \Vithin a tank or vvithin heat transfer tubes or between fins or plates.
For example, the vapor compression system may cool a heat transfer liquid, such as
propylene glycol or ethylene glycol and water that 1s run through the thermal energy system
in a series of heat transfer channels, heat transfer tubes, plates or other heat exchanger. The
heat exchangers may be within a containment, which also houses potassium fluoride tetra
hydrate and cool the pota.ssium fluoride tetra hydrate so that it changes from a liquid into a
solid. In another embodiment, the thennal energy storage system includes a series of heat
transfer tubes filled with phase change material, and the heat transfer t1uid runs into the tank
and surround the filled heat transfer tubes. When the system needs to offload heat from a
finng event, heat transfer i1uid (refrigerant or a pumped thermal heat transfer liquid)
circulates into the thermal energy storage system and melts the potassium fluoride tetra
hydrate into a liquid phase, thereby offloading heat
[0044] It should be realized that thermal energy storage systems are not only
made from potassium fluoride tetra hydrate, but also from other salt hydrates such as calcium
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chloride hydrates, calcium chloride/calcium bromide mixture hydrates, sodium based
hydrates, lithium based hydrates, such as lithium chlorate tn-hydrate, etc. In some
embodiments, the salt hydrate iS the 4 hydrate of potassium fluoride.
!0045J In some embodiments, the thermal energy storage system has its own
pump connected to route thermal heat transfer i1uid through the thermal energy storage
system cooling loop. If the thermal heat transfer i1uid is a liquid such as ethylene or
propylene glycol water, the pump may be a pump that is controlled by a variable speed
motor. If the thermal heat transfer t1uid is phase change refrigerant, the pump motor may be
connected to a vector control system (VCS) as the pressure drop (constituting torque) is now
adjustable via the flow rate and the resulting degree of phase change of the refrigerant, also
called the quality of the refrigerant. This is the ratio of liquid and gas components of the
refrigerant. For example, at a relatively low flow rate with low pressure drop the quality of
the refrigerant may go from 90% liquid to 50~o liquid and at a high flow rate it may go from
80% liquid to 20 % liquid. The vector control system may be programmed to optimize
efficiency of the thermal energy storage system pump between the best amount of heat
transfer and the resulting pressure drop of the refrigerant, which equates to energy
consumption by the pump motor.
[0046] The vapor compression system may normally act to cool or heat the hotel
load from the ancillary equipment that is adjacent to the directed energy weapons system.
However, in some circumstances the vapor compression system may be used to rapidly cool
and freeze the phase change material within the thermal energy storage system, and during
other times, especially during peak operations times the vapor compresswn system is also
cooling the laser load. Thus, in advance of using the directed energy weapons system, the
vapor compresswn system may be activated to freeze and mamtain the phase change material
in a frozen or partially frozen state within the thennal energy storage systern.
[0047] A control system monitors the ternperatures of the vanous systems,
including the directed energy weapons system, the ancillary components, the thermal energy
system and the vapor compression system. The control system uses stored logic and
programming to determine the appropnate use of each component. If the system is idle, and
the temperature of the thermal energy storage system iS lugh or mdicates a partial melt, the
control system may activate the vapor compresswn system to begin re-freezmg the thermal
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energy storage system. However, if the control system also determines that the ancillary
components are too hot, the control system may prioritize having the vapor compression
system cool the ancillary components so they don't become damaged before having the
vapor compression system re-freeze the phase change material m the thermal energy storage
system. The flex1bility of the system allows for the control system to work towards bemg as
efficient as possible to cool the components of the system and maintain the system m a state
of readiness for the next activation of the directed energy weapons system.
!0048] In some embodiments, the hotel load of the directed energy weapons
system may need to be within a predetermined temperature range for the thermal energy
storage system to efficiently provide rapid cooling. The ancillary cooling system may be
configured to maintain the thermal load or related environment at a predetermined
temperature to help maximize the efficiency of rapidly cooling the directed energy weapons
system with the burst mode cooling process.
!0049] It should be realized that the ancillary cooling/heating system may not be
directly in thermal contact with the hotel load but may instead be used to cool or heat the
environment or equipment directly and/or indirectly relating to the hotel load. For example,
the hotel load may be part of a larger system with pumps, motors, and other heat generating
equipment The vapor compression system may be configured to cool this related
environment or related equipment By heating or cooling the equipment adjacent the thermal
load, this may help keep the thermal load at a predetermined temperature.
[0050J It should also be realized that there rnay be many different components of
the hotel load that each need to be cooled (or heated) by the vapor compression system,
either serially or in parallel. In one ernbodiment, the vapor compresswn system serially cools
a set of hotel load components by running a heat transfer fluid from relatively cool
components to hotter components. For example, the vapor compression system may have a
fluid line carrying thermal heat transfer fluid to a first heat exchanger adjacent or connected
to a first component that 1s operating at 40°C. As the thermal heat transfer fluid leaves the
first heat exchanger it may cool the first component to 35"C and be warmed to near 30°C.
The fluid line may then enter a second heat exchanger that is adjacent to or mtegrated in a
second hotel load component that is operating at 50°C. If the thermal heat transfer fluid still
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has capacity to absorb additional heat, it can also cool the second component from 5CY'C to
45°C temperature.
[0051] In a second embodiment, the vapor compression system may connect in
parallel to one of more of the components within the hotel load, such that each component
has a heat exchanger tied to fluid cooled coming directly from the evaporator of the vapor
compresswn system.
[0052] In one embodiment, the hotel load may be a hotel load of a vehicle. In one
embodiment, the hotel load is the thermal load caused by all systems on a vehicle other than
propulsion. For example, a hotel load of a military transportation vehicle may be the thermal
loads caused by radar equipment, inverters, electronics, batteries, cabin loads and the
warfighter. Embodiments of the vapor compression system may be configured to thermally
regulate these hotel loads to keep them at a predetermined temperature.
[0053] The control system may be configured in many ways to activate a burst
mode cooling cycle of the system. In one embodiment, the controller is any electronic device
or apparatus that activates, modulates, or deactivates the t1ovv of refrigerant or heat transfer
fluids in the system. The control system may include any electronic device or apparatus that
controls a pump, fan, or valve which moves heat transfer fluid throughout the system.
[0054] In one embodiment, the control system is linked to one or more
temperature sensors and activates a burst mode cooling cycle \vhen a temperature sensor near
the directed energy weapons system reaches a predetermined target temperature. The
temperature sensor may be thermally linked to the directed energy weapons systern so when
that thermal load reaches the predetermined target temperature, a burst tnode cooling cycle is
begun. Alternatively, the control system may be electronically linked to an activation signal
that triggers a burst mode coolmg cycle. The activation signal may be controlled by a
predictive process that senses a variety of data, including mtelligent signaling of approaching
target(s) and then predict when to activate a cooling cycle. For example, the control system
may sense the present temperature of the thermal load, the time since the last activation, and
the state of other equipment of devices linked to the directed energy weapons system. Using
this data, the system may activate a burst mode cooling cycle just before the directed energy
weapons system starts to heat In some embodiments, the control system may activate a
cooling cycle 1, 2, 3, 4, 5, 6, or 10 seconds in advance of a determmed cooling event.
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A. System
[0055] Figure 1 shows one exemplary thermal energy cooling system 100 that has
a vapor compressiOn system 115 that is designed to provide burst mode cooling to rapidly cool a directed energy weapons system 140 during the first few seconds of operation by
movmg heat transfer i1uid from a heat exchanger 130 adjacent and connected to the directed
energy weapons system 140 to a thermal energy storage system 110.
!0056] The vapor compression system 115 connects to output control valves 125
which control output of thermal heat transfer fluid from the vapor compression system 115 to
the heat exchanger 130 that is in thermal communication with a directed energy weapons
system 140. The heat exchanger 130 then connects to a pump 147 which communicates with
a set of input control valves 120 to form a vapor compression cooling loop from the vapor
compression system 115 to the directed energy weapons system 140 and back again.
[0057] As sho>vn in Figure 1, the pump 147 and input control valves 120 also
connect to the thermal energy storage system 110. The thermal energy storage system 11 0
may include frozen or partially frozen phase change material, such as potassium fluoride tetra
hydrate, that is used to cool the directed energy weapons system while active. The thermal
energy storage system is connected to the output control valves 125 which connect the
thermal energy storage system to the directed energy weapons system heat exchanger 130.
The directed energy weapons system heat exchanger 130 connects to the pump 147 wluch
can return heated thermal heat transfer fluid from the directed energy weapons systern heat
exchanger 130 to the input control valves 120 and back to the thermal energy storage system
110 in a thermal energy storage system cooling loop. It should be reahzed that in one
embodiment the vapor cornpression loop and the thennal energy storage system cooling loop
may use the same refrigerant or thermal heat transfer fluid and thereby share some of the
same piping, valves and pumps to commumcate within the system 100. Alternatively, the
system 100 may include parallel cooling loops from the vapor compressiOn system and the
thermal energy storage system where they do not share the same refrigerant, thermal heat
transfer i1uid, piping, valves and pumps, and therefore thermally communicate through the
same or different heat exchangers with the directed energy weapons system.
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[0058] In one embodiment, the vapor compression system 115 is designed to
form a vapor compressiOn cooling loop to the hotel load heat exchanger in order to cool the
components of the system 100 that make up the hotel load. As shown, the output control
valves 125 may route the thermal heat transfer i1uid from the vapor compression system to
the hotel load heat exchanger 135 that is adjacent to the hotel load 145. The pump 147 then
may recirculate the thermal heat transfer fluid coming from the hotel load heat exchanger 13 5
back though the mput control valves 120 to the vapor compressiOn system 115, forming a
loop.
[0059] As shown in Figure 1, the vapor compresswn system 115 is also
connected to the thermal energy storage system 110 through pipes 147 running heat transfer
i1uid through into the thermal energy storage system 110. In use, the vapor compression
system may be used to cool and charge the thermal energy storage system. It should be
realized that the thermal energy storage system 110 may comprise a series of heat transfer
tubes or heat transfer plates which act as heat exchangers to transfer heat from heat transfer
f1uid to the frozen phase change material \Vithin the thermal energy storage system 110.
[0060] As mentioned above, the thermal energy storage system 110 and vapor
compression system 115 are connected to the set of input control valves 120 and output
control valves 125. These valves control the f1ovv of thermal heat transfer fluid or two phase
refrigerant through the system 100 and into and out of each component As sho\vn, a control
system 127 is in electrical cormnunication with the vapor compression system 11 5, input
control valves 120 and output control valves 125. By opening and closing the electrically
controllable valves witlun the input control valves 120 and output control valves 125 the
control system may control which component of the system is c1rculating thermal heat
transfer fluid or refngerant at any particular time during operation.
[ 0061 J The output control valves 125 connect to a directed energy system heat
exchanger that is in thennal connnunication with a directed energy weapons system 140.
The directed energy weapons system 140 is shown as being thermally connected to the heat
exchanger 130. In the case that two phase refrigerant 1s bemg circulated within the system
100, it should be realized that the heat exchanger may be an evaporator configured to change
or partially change the phase of the refrigerant 1n the case that a thermal heat transfer fluid
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or media such as glycol-water is being circulated, the heat exchangers may be heat transfer
tubes, coils or plates configured to absorb heat into the thermal heat transfer fluid.
[0062] In one embodiment, the directed energy weapons system may be a highenergy
laser, and the directed energy system heat exchanger 130 may be in thermal
commmucation with the laser diodes and diode amplifiers of that system which generate the
bulk of heat bursts while the system is activated. A lugh-energy laser may mclude lasers that
are 3, 5, 10, 15, 30, 50, 75, l 00, 125, 150, 250, or 500 kilowatt or higher energy lasers.
!0063] The output control valves 125 also connect to the one or more hotel loads
heat exchangers 135 that are in thermal communication with the hotel load 145 adjacent to
the directed energy weapons system 140. As discussed above, the hotel load 145 may
include the batteries, motors, radar, communications and other equipment that is ancillary to
the directed energy weapons system. As mentioned above, in the circumstance where
thermal transfer media such as glycol-water is used instead of refrigerant, the hotel load heat
exchangers may be replaced with a thermal transfer system configured to transfer heat to the
thermal transfer media.
[0064] The pump 147 is connected to the outputs of the directed energy vveapons
system heat exchanger 130 and hotel load heat exchanger 135 and used to move thermal heat
transfer f1uid or refrigerant into the input control valves 120 so the system may recirculate
these f1uids into the thermal energy storage system 11 0 or vapor compression system 115.
[0065] It should be realized that the system 100 may include more than the one
pump 147 and that additional pumps, fans, valves and motors may be included within the
system to operate as described herein. For example, additional purnps may be included
adjacent to the output control valves 125 to move thermal heat transfer fluid to the heat
exchangers 130, 135. Fans may be disposed adjacent to the directed energy system heat
exchanger 130 or hotel load heat exchanger 135 to move heated or cooled air across the heat
exchangers.
!0066] The system 1 00 is flexible m that during the use the system may route
heated fluid from the directed energy weapons system heat exchanger 130 into either or both
of the vapor compression system and thermal energy storage system. Depending on the
temperature of the heat transfer fluid, and the predicted cooling needs of the system, the heat
transfer fluid may be routed to only the thermal energy storage system for cooling. However,
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m some embodiments, the heat transfer i1uid may be routed m parallel or sequentially
through the thermal storage system and the vapor compression system.
[0067] Figure 2 shows a cross-sectional view of the thermal energy storage
system 110. As shown the thermal energy storage system 110 contains a tank or enclosure
200, filled with a heat transfer fluid 202, and having a series of heat transfer tubes 205 which
are filled with phase change material and which are disposed withm a set of support brackets
or cavities withm the tank 200. The size and number of heat transfer tubes deposited within
the tank 200 can be chosen to maximize the thermal transfer of heat from the heat transfer
fluid 202 circulating in the tank into the phase change material within the heat transfer tubes
205. In this embodiment, the tubes have an outer diameter of 0. 5", but they could be any
dimension between 1;'4" and 1" and functionally similar. Each tank may have 25, 50, 1 00,
200, 300, 400, 500, 1000, 2000, 3000, 4000, 5000 or more heat transfer tubes depending on
the specific architecture of the thermal energy storage system. In one embodiment, the tank
200 includes about 300 heat transfer tubes that are 0.5'' in outer diameter and about 60 inches
in length.
[0068] Figure 3 sho>vs an illustration of the control system 127, vvhich is
programmed with instructions to control operations of the system 100. The control system
127 includes a processor 310 vvhich may be any type of weH-knovvn microprocessor or
microcontroller that is capable of managing the valves, fans and other components of the
system 1 00. The processor 310 is connected to a memory 312 for stonng programs and
commands for operating the system.
[0069] The processor 31 0 is connected to a directed energy module 325 wluch
includes instructions for activating a cooling cycle in response to the directed energy
weapons systern being activated by firing. In one embodiment, the directed energy module
325 is prograrnmed to activate the burst mode cooling cycle from the vapor cornpression
system and begin to rapidly cool the thermal load when a predetermined signal is received by
control system 127. The signal may be an activation signal from a firing system connected to
the directed energy weapons system. With each firing event the weapon system may interface
with a vapor compression control module 345 to trigger the burst cooling mode of the system
100 in order to reduce the temperature of the weapon system.
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[0070] In one embodiment, the directed energy module 325 communicates with a
temperature sensor which monitors the temperature of the directed energy thermal load. In
one embodiment, the directed energy module 325 activates a burst cooling cycle by
interfacing with the vapor compression control module 345 when the temperature of the
directed energy load reaches a predetermined temperature. For example, when the
temperature of the directed energy system 1s above 30"C, then the directed energy module
325 instructs the vapor compression control module 345 to begm rapidly circulating heat
transfer fluid to the directed energy weapons system heat exchanger and through the thermal
energy storage system. When the temperature is below 15°C a heating system is activated to
bring up the temperature. In some embodiments, the vapor compression control module may
be activated when the temperature of the directed energy load is above 25°C or above 35°C.
In some embodiments a heating system m.ay be activated when the temperature of the
directed energy system is below 1 O"C or below 20°C.
!0071] Of course, embodiments are not limited to performing only a single burst
cooling procedure. During activation, the thermal load, or an attached weapons system, may
request multiple burst mode cooling operations to maintain the temperature of the thermal
load below a certain target temperature.
[0072] ·while burst mode cooling can be performed by operating the vapor
compression system or the vapor compression system and the thermal energy storage system,
in some embodiments, the system performs a burst mode cooling cycle by only
communicating with the thermal energy storage system. For example, as shown m Fig. 3, the
thennal energy storage module 340 may also be activated by the directed energy module 325
to begin a cooling cycle m response to the directed energy weapons system being discharged.
For exarnple, following a discharge the directed energy module rnay mstruct the thermal
energy storage module 340 to begin a cooling cycle. The thermal energy storage rnodule 340
would then adjust the input control valves and output control valves so that thermal heat
transfer fluid runnmg through the thermal energy storage system begms circulating in a
thermal energy cooling loop though the heat exchanger adjacent to the directed energy
weapons system.
[0073] The vapor compresswn control module 345 may include instructions for
managing the motor, valve and pump functions of the vapor compresswn system discussed
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above. For example, the vapor compression control module may control the input valves and
output valves, along with valves routing thermal heat transfer fluid mto and out from the
thermal energy storage system. By manipulating these valves, the vapor compression control
module may route thermal heat transfer fluid to the particular components of the system 1 00
as needed to efficiently operate the system.
!0074J As shown the vapor compression control module may also include a
vector control system 347 that is configured as discussed above to provide etTic1ent control of
the vapor compression system compressor and torque. For example, the vector control
system 347 may monitor the torque placed on a compressor within the vapor compression
system and adjust the speed of one or more fans or blowers to alter the pressure within the
system to increase, or decrease, the torque placed on the compressor to increase the vapor
compression system efficiency.
[0075] After the burst mode cooling requests have subsided, the control system
127 the thermal energy storage module 340 may communicate with a temperature sensor
vvithin the thermal energy storage system and activate the vapor compression system to start
cooling the thermal energy storage system back down to its target temperature and freeze the
phase change material.
[0076] As shown, the control system 127 also includes a hotel load control
module 315 for controlling cooling of the hotel loads within the system 100. The hotel load
control module 315 may include instructions for reading data from temperature or other
environmental sensors and determining the proper parameters for cooling or heating the hotel
load or adjacent systems of the directed energy weapons systern. For example, if the hotel
load control module 315 receives data showing that the hotel load is above 40°C it may
activate the vapor cornpression systern to begin a cooling cycle to reduce the ternperature of
the hotel load back down to a target temperature. Similarly, if the hotel load control module
315 deternunes that the thermal load is below, for example, Y'C it may initiate a heating
cycle of the vapor compression system or an auxiliary heater to increase the temperature of
the thermal load up to a target temperature.
!0077J In one embodiment, the hotel load control module 315 mmntams the
temperature of the hotel load or ancillary eqmpment withm the range of 25°C to 50°C. ln
another embodiment, the hotel load control module 315 maint:'lins the temperature of the
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hotel load or ancillary eqmpment within the range of 20°C to 30°C. However, embodiments
are not limited to only these temperature ranges. The hotel load control module 315 may be
designed to mamtain the temperature of the thermal load or ancillary equipment to be above
its minimum equipment design operating temperature m cold climates for an efficient startup.
Similarly, the hotel load control module 315 may be des1gned to cool the hotel load or
ancillary eqmpment to be below the equipment's maximum des1gn operating temperature at
any ambient temperature if the equipment generates heat This allows the eqmpment to be
placed in relatively hot ambient environments, such as the desert, where the ambient
conditions alone may require cooling of the equipment to be within the range of, for
example, 5°C to 40°C.
[0078] Other embodiments include a hotel load control module 315 that maintains
the temperature of the hotel load or ancillmy equipment in order for efficient cooling of the
thermal load to occur. Of course, the system is not limited to only managing thermal loads at
these temperature parameters. The hotel load control module 315 may detect when
temperatures of a thermal load is above 5°C, 10°C, l5°C, 20°C, 2SOC, 30°C, 35°C, 40°C or
more before activating the vapor compression system. In some embodiments the hotel load
control module 315 is also configured to maintain operating temperatures of equipment that
is a subsystem, of linked system to the thermal load. For example, the thermal load may be
adjacent to, or electronically linked with, electronic subsystems, such as radar, electronic or
power inverters, generators, high-capacity batteries, cabin/enclosures and warfighter cooling
systems. The hotel load control module 315 rnay be designed to maintain the operating
ternperatures of each of these ancillary dev1ces or systems in addition to maintaming the
operating tern perature of the thermal load and adjacent equipment.
[0079] The hotel load control module 315 may also gather data frotn other
sources, such as through a network connection to determine the predicted environmental
ternperature for the day. For example, the hotel load control module 315 may receive the
predicted daytime high temperature from a weather service across a network and use that
dat:'l to ensure that the thermal load or other ancillary components of the target system remam
cool to a predetermined target temperature.
[0080] It should be realized that aspects of the control system may manage the
vanable speed operation of various pumps and fans within the system based on the
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temperature of the thermal load. For example, as the temperature of the thermal load, or
surrounding env1romnent, increases the speed of pumps and fans within the system may also
mcrease. Similarly, as the temperature of the thermal load, or surrounding environment
decreases, the controller may slow the speed of the pumps and/or fans.
B. O~eration
[0081] In operation, a cycle may be activated when a directed energy weapons
system is first begun to be powered up for use. While the below operation is described for
circulating refrigerant to the hotel load and directed energy system coil, it should be realized
that the system is not limited to using phase change refrigerant, and thermal heat transfer
fluids may also work similarly within the system.
!0082] As can be realized, these systems include ancillary equipment that may
need to be cooled before the system becomes fully operational. For example, the ancillary
equipment may be powered on along with the vapor compression system. The control
system may therefore activate the output control valves such that the refrigerant output of the
vapor compression system is routed to the various components of the hotel load heat
exchanger, the input control valves are set to recirculate the refrigerant from the hotel load
heat exchanger back to the vapor compression system, and the pump is activated to move the
refrigerant in a cooling loop to begin removing heat from the hotel load.
[0083] The control system may detect the temperature of the thermal energy
storage system using a temperature sensor, and determine if the thennal energy storage
system is cooled to a target temperatures so that it may act as a heat capacitor to absorb
excess heat frmn the system once the system becornes operational. If the control system
determines that the temperature of the thermal energy storage system is above a
predetennined threshold it may begin routing thermal heat transfer f1uid or refrigerant that
has been cooled by the vapor compression system into the thermal energy storage system.
The control system may mclude programming to balance the cooling requirements of the
hotel load against the necessity to also cool the thermal energy storage system, and determine
the priority for each system based on their current temperature and how soon the system may
need to use the thermal energy storage system.
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[0084] Once the system 1s ready to fire, the vapor compression system may be put
into a standby mode where it is ready to begin burst mode cooling as soon as a firing event 1s
detected or a control signal indicates 1mmediate firing to be initiated. Once a finng event is
signaled or detected the system will enter a burst mode cooling cycle. The control system
will activate the thermal energy storage system loop so that heated thermal heat transfer fluid
from the directed energy system heat exchanger is routed into the thermal energy storage
system.
!0085] As the directed energy system heat exchanger continues to detect firing
events and transfers heat from the heat exchanger to the thermal energy storage system for
burst cooling, the control system may monitor each component to ensure that the flexible
system is operating efficiently. For example, in one embodiment in the first 5, 10, 15, 20, 25,
30 or more seconds following activation the heated thermal heat transfer fluid from the
directed energy system heat exchanger may not be routed to the vapor compression system
because the cooling requirement during that firing event may be handled sufficiently by the
thermal energy storage system. However, as the firing events continue and the thermal load
of the directed energy weapons system maintains or increases, the control system may route a
portion of the refrigerant coming from the directed energy weapons system heat exchanger
directly to the vapor compression system.
[0086] It should be realized that in some embodiments the vapor compression
cooling system is used to supplement the cooling provided by the thermal energy storage
system. Thus, following activation, the thermal energy storage system may provide rapid
burst tnode cooling for the first seconds after the weapon's activation. Then, or even
simultaneously, the vapor compression system may be activated to provide a secondary
coohng loop to the directed energy weapons system heat exchanger and provide additional
cooling capacity above that provided by the thermal energy storage system.
[0087] Figure 4 describes one process 400 for cooling a laser weapon. The
process 400 begms at a sta.rt state 402 and then moves to a decision state 404 wherein a
determination is made whether a laser finng event has been detected by the control system.
If a laser firing event is not detected the process 400 moves to state 406 and enters a
mamtenance mode. In the maintenance mode the system continues to mamtain the hotel load
at a target operational temperature so that the system is ready to operate once a firing event
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has been detected. During the maintenance mode the vapor compression system may be used
to recharge the phase chance material or media housed within the thermal energy storage
system so that the thermal energy storage system is prepared to deliver cooling power to the
system when needed.
[0088] If a deternunation is made at the decision state 404 that a laser finng event
has been detected, then the process 400 moves to a state 408 wherein the thermal energy
storage system is mitiated to quickly absorb a burst of heat, for example 10, 25, 50, 100, 150,
200 or more kilowatts of heat energy from the laser system. After activating of the burst
mode cooling system at the state 408, the process 400 moves to a state 412 wherein a cooling
loop from the vapor compression system is activated to provide additional cooling power to
the laser weapon. Because the vapor compression system may take additional time to absorb
heat, it may be used as an ancillary cooling supply to the more rapid cooling provided in the
first few seconds after a firing event by the thermal energy storage system.
!0089] After the cooling loop from the thermal energy storage system has been
initiated, the process 400 moves to a decision state 418 \vherein a determination is made
whether the laser weapons system is at its target temperature. Typically, this target
temperature may be bet\veen l5°C and 30°C. If the laser weapons system is not at the target
temperature then the process 400 moves to a state 420 wherein the tlow rate of the cooling
loop from the thermal energy storage system may be increased to help move additional heat
away from the laser weapons system. Additionally, a vapor compression system may also be
brought online to add additional cooling power to the overall system and help reduce the
ternperature of the laser weapons system.
[ 0090J If a determination is made that the laser is at the target temperature, then
the process 400 moves to a state 425 wherein a determination is made whether the laser firing
process has been completed. If the process has not been completed, then the process 400
returns to the decision state 404 in order to wait for additional firing events. If a
deternunation is made at the decisions state 425 that the laser firing has been completed then
the process 400 moves to a state 430 wherem the vapor compresswn system may begin
recharging the phase change material within the thermal energy storage system so it can be
ready to provide additional cooling for future firing events. The process 400 then moves to
an end state 450 and terminates.
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Example
[0091] A thermal energy storage system is made that 1s capable of cooling a laser
weapon that outputs 1 OOkW of heat. In this example, the laser outputs bursts of energy over
a 120 second period and then stays deactivated for 280 seconds. The thermal energy storage
system uses an enclosure that contains heat transfer tubes of potassium i1uoride tetrahydrate
as the phase change material. A 100 kW heat load from a laser that is active over a 120
second period generates 12,000 kJ of heat energy that needs to be dissipated. Potassium
i1uoride tetrahydrate is able to store 230 kJ/kg of material, thus the thermal energy storage
system is made from 52.2 kg of potassium tluoride tetrahydrate to absorb 12,000 kJ of heat
energy.
!0092] The material density of potassium fluoride tetrahydrate is 1455 kg/ m3 so
that 52.1 kg of material requires a volume of 0.0359 m3 of space within the heat transfer
tubes located inside the thermal energy storage system enclosure.
[0093] A vapor compression system 'vvith a cooling capacity of at least 20 kW,
preferably 25 kW or more vvith phase change refrigerant is thermally connected to the
thermal energy storage system to recharge the system in less than 10 minutes follo\ving
discharge by cooling the laser weapon.
[0094] Headings are included herein for reference and to aid m locating various
sections. These headings are not intended to limit the scope of the concepts described with
respect thereto. Such concepts may have applicability throughout the entire specification.
[0095J The prevwus descnption of the disclosed implementations is provided to
enable any person skilled in the art to make or use the present invention. Various
modifications to these implementations will be readily apparent to those skilled in the art,
and the generic principles defined herein rnay be apphed to other implernentations without
departing from the spirit or scope of the invention. Thus, the present invention is not
intended to be limited to the implementations shown herem but is to be accorded the widest
scope consistent with the principles and novel features disclosed herein.
[0096] While the above description has pointed out novel features of the
invention as applied to vanous embodiments, the skilled person will understand that various
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om1sswns, substitutions, and changes in the form and details of the device or process
illustrated may be made without departing from the scope of the invention.

vVHAT lS CLAiMED lS:
l. A thermal energy cooling system for a high-energy laser, comprising:
a thermal energy storage system comprising phase change matenal havmg a
transition temperature of between 1 0°C and 20°C, a phase change matenal energy
density of at least 200kJ/kg, a phase change matenal density of at least lg/cc and a
phase change material thermal conductivity of at least 0. 5W /mK;
a cooling loop comprising a heat transfer fluid connected to the thermal
energy storage system and a heat exchanger in thermal communication with the highenergy
laser; and
a control system programmed to read sensor data and determine when to
initiate burst mode cooling to initiate discharge of the thermal energy storage system,
wherein the burst mode cooling comprises pumping the heat transfer fluid through the
cooling loop including the thermal energy storage system that is capable of
discharging over a period of less than five minutes.
2. The thermal energy cooling system of claim 1, vvherein the system further
comprises a vapor compression system configured to recharge the phase change material in
the thermal energy storage system in a recharge period of less than 25 minutes.
3. The thermal energy cooling system of claim 2, wherein the vapor compression
system initially provides fluid at a temperature of below 1 0°C to the thermal energy storage
system to initiate a crystalhzation process of the phase change nmterial, and followmg such
initialization, then provides i-1uid at a temperature at or above 1 0°C to continue freezing the
phase change material while optimizing energy efficiency of the thermal energy cooling
system.
4. The thermal energy coolmg system of claims 2 or 3, wherein the recharge period
is less than 1 0 minutes.
5. The thermal energy cooling system of any of claims 2-4, wherein the recharge
period is less than 5 mmutes.
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6. The thermal energy cooling system of any of claims 2-5, wherein pumice is used
as a nucleation agent to reduce subcooling in the recharge process.
7. The thermal energy cooling system of any of claims 2-5, wherein the vapor
compresswn system is configured to cool ancillary equipment connected to the high-energy
laser system.
8. The thermal energy cooling system of any of claims 1-7, wherein the discharge
period is less than three minutes.
9. The thermal energy cooling system of any of claims l-8, wherein the heat transfer
fluid to the directed energy weapon system is cooled to between 20°C and 30°C during the
discharge period.
10. The thermal energy cooling system of any of claims 1-9, wherein the discharge of
the thermal energy storage system results in a phase change of at least 50% of the phase
change material.
11. The thermal energy cooling system of any of claims 1-1 0, wherein the discharge
of the thermal energy storage system results in a phase change of at least 75%) of the phase
change material.
12. The thermal energy cooling system of any of claims 1-11, wherein the discharge
of the thermal energy storage system results in a phase change of at least 90~.-Q of the phase
change material.
13. The thermal energy coohng system of any of clairns 1-12, wherem the phase
change material is a hydrated salt complex.
14. The thermal energy cooling system of claim 11, wherein the hydrated salt
complex is potassium fluoride tetrahydrate.
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15. The thermal energy cooling system of any of claims l-14, wherein the thermal
energy storage system comprises an enclosure and a plurality of heat transfer tubes, and the
phase change material is positioned inside the heat transfer tubes.
16. The thermal energy cooling system of claim 13, wherein the heat transfer tubes
have an outer diameter of between 114 mch and 1 mch.
l 7. The thermal energy cooling system of any of claims 1-14, wherein the thermal
energy storage system comprises an enclosure and a plurality of heat transfer tubes, and the
phase change material is positioned outside the heat transfer tubes.
18. The thermal energy cooling system of any of claims l-14, wherein the thermal
energy storage system comprises an enclosure and a plurality of heat transfer plates, wherein
the phase change material is positioned between heat transfer plates.
19. The thermal energy cooling system of any of claims 1-14, wherein the thermal
energy storage system comprises an enclosure and a series of grooves, wherein the phase
change material is positioned in the grooves.
20. The thermal energy cooling system of any of claims 1-19, \vherein the heat
transfer fluid is a glycol/water mixture.
21. The thermal energy cooling system of any of clairns 1-20, wherein the heat
transfer fluid is a phase change refrigerant
22. The thermal energy cooling system of any of claims 1-21, wherein the control
system for the f-1uid flow through the thermal energy storage systern compnses a vector
control systern that accounts for f-luid How and pressure drop while controlling a purnp.
23. The thermal energy cooling system of any of claims 1-22, wherem the sensor data
comprises temperature sensor data, operating status s1gnals, or detection signals from one or
more sensors.
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24. The thermal energy cooling system of claim 21, wherein the thermal energy
cooling system, the high-energy laser system, and the one or more sensors are located on a
platform.
25. The thermal energy cooling system of claun 21, wherem the thermal energy
cooling system and the high-energy laser are located on a platform, and the one or more
sensors are not located on the platform.
26. The thermal energy cooling system of claim 21, wherein the thermal energy
cooling system and the high-energy laser are located on a platform, and one or more signals
are received from locations not located on the platform.
27. The thermal energy cooling system of any of claims 1-26, wherein the control
system monitors the amount of frozen phase change material in the thermal energy storage
system, and prevents additional melting and/or initiates additional freezing of the phase
change material, if the amount of frozen phase change material is belovv a predetermined
threshold.
28. The thermal energy cooling system of claim 25, vvherein the predetermined
threshold is a value between 2~'iJ and 5% of a total volume of phase change material.
29. The thermal energy storage system of claim 25, wherein the predetermined
threshold is a value between 5 1~-'IJ and 15% of a total volume of phase change rnaterial.
30. The thermal energy storage system of claim 25, wherein the predetermined
threshold is above 15?-o of a total volume of phase change material.