U.S. patent application number 09/756494 was filed with the patent office on 2002-08-29 for methods and apparatus for liquid densification.
Invention is credited to Lak, Tibor I., LeBlanc, John H., Lozano, Martin E., Yoshinaga, Jay K..
Application Number | 20020116931 09/756494 |
Document ID | / |
Family ID | 26893588 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020116931 |
Kind Code |
A1 |
Lak, Tibor I. ; et
al. |
August 29, 2002 |
METHODS AND APPARATUS FOR LIQUID DENSIFICATION
Abstract
An improved and simplified system for densifying a cryogenic
liquid for space vehicles is provided, which includes a heat
exchanger having heat exchange tubes therein for receiving a flow
of liquid from a storage tank, for example a liquid propellant in a
vehicle storage tank. The heat exchanger is filled around the
exchange tubes with a two-component bath, the volume of a primary
component substantially exceeding the volume of a secondary
component. The secondary component has a boiling temperature that
is lower than the boiling temperature of the primary component, and
both are lower than the boiling temperature of the cryogenic
liquid. In one example, the liquid to be densified is oxygen, the
primary component is liquid nitrogen, and a secondary component is
liquid hydrogen. The secondary component is preferably injected
into the heat exchanger in separate flows to prevent localized
freezing of the first component. A manifold having a plurality of
injectors may be used for introducing the second component to the
heat exchanger. A control system receives inputs from one or more
sensors within the heat exchanger and operates valves that control
the flow of the first and second components of the heat exchange
bath.
Inventors: |
Lak, Tibor I.; (Huntington
Beach, CA) ; LeBlanc, John H.; (Whittier, CA)
; Yoshinaga, Jay K.; (Gardena, CA) ; Lozano,
Martin E.; (Whittier, CA) |
Correspondence
Address: |
Donald E. Stout
Stout, Uxa, Buyan & Mullins, LLP
Suite 300
4 Venture
Irvine
CA
92618
US
|
Family ID: |
26893588 |
Appl. No.: |
09/756494 |
Filed: |
January 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60198228 |
Jan 10, 2000 |
|
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|
Current U.S.
Class: |
62/45.1 ;
62/50.1 |
Current CPC
Class: |
F17C 2201/056 20130101;
F17C 2270/0197 20130101; F17C 2221/011 20130101; F17C 2250/0636
20130101; B64G 5/00 20130101; F17C 2205/0397 20130101; F17C
2201/0109 20130101; F17C 2205/0323 20130101; F17C 13/083 20130101;
F17C 2260/056 20130101; F17C 2227/0341 20130101; Y02E 60/32
20130101; F17C 2221/012 20130101; F17C 13/008 20130101; F17C
2221/014 20130101; F17C 2223/0153 20130101; Y02E 60/321
20130101 |
Class at
Publication: |
62/45.1 ;
62/50.1 |
International
Class: |
F17C 001/00; F17C
011/00; F17C 007/02 |
Claims
What is claimed is:
1. A system for cooling and densifying a liquid, comprising: an
inlet supply line for supplying a liquid; a heat exchange tank
having a plurality of heat exchange tubes therein, each of the heat
exchange tubes being in fluid communication with the inlet supply
line; an outlet line in fluid communication with each of the heat
exchange tubes; a first inlet conduit connected to the heat
exchange tank for introducing a first component of a heat exchange
bath to the interior of the heat exchange tank and in contact with
the exterior of the heat exchange tubes; and a second inlet conduit
connected to the heat exchange tank for introducing a second
component of a heat exchange bath different than the first
component to the interior of the heat exchange tank and in contact
with the exterior of the heat exchange tubes.
2. The system of claim 1, further including a first flow control
valve located in the first conduit for metering introduction of the
first component to the interior of the heat exchange tank.
3. The system of claim 2, further including a second flow control
valve located in the second conduit for metering introduction of
the second component to the interior of the heat exchange tank.
4. The system of claim 3, further including at least one sensor
within the heat exchange tank and a controller connected to receive
input from the sensor, the controller being connected to operate
the first and second flow control valves based on the input
received from the sensor.
5. The system of claim 4, wherein the sensor is a fluid level
sensor.
6. The system of claim 4, wherein the sensor is a temperature
sensor.
7. The system of claim 4, wherein there is a fluid level sensor and
a temperature sensor providing input to the controller.
8. The system of claim 1, further including a mixer provided within
the heat exchange tank for mixing the heat exchange bath
therein.
9. The system of claim 1, further including a manifold in fluid
communication with the second inlet conduit and configured to
separate the flow of the second liquid into separate flow paths
into the interior of the heat exchange tank.
10. The system of claim 9, wherein the manifold is located in an
upper portion of the heat exchange tank.
11. The system of claim 10, wherein the manifold is oriented
horizontally across the heat exchange tank.
12. The system of claim 11, wherein the heat exchange tubes are
oriented horizontally within the heat exchange tank and have a
length, and the manifold is longer than the heat exchange
tubes.
13. The system of claim 9, wherein the manifold includes a
plurality of flow orifices for delivering the second liquid to the
interior of the heat exchange tank.
14. The system of claim 13, wherein the manifold is located in an
upper portion of the heat exchange tank and includes a plurality of
downwardly directed injectors, the lowermost end of each flow
injector defining the flow orifices for delivering the second
liquid to the interior of the heat exchange tank.
15. The system of claim 9, wherein the manifold is oriented
vertically within the heat exchange tank.
16. The system of claim 1, wherein the system is adapted to supply
the densified liquid to a storage tank, and further including: a
recirculation line connected between the storage tank and the inlet
supply line for returning liquid from the storage tank to the heat
exchange tubes; and a return line connected between the storage
tank and the outlet line for returning densified liquid from the
heat exchange tubes to the storage tank.
17. A method of densifying a liquid, comprising: filling a storage
tank with a liquid at a reduced temperature; circulating the liquid
propellant from the storage tank through a plurality of heat
exchange tubes within a heat exchanger; and providing a
two-component heat exchange bath in the heat exchanger for cooling
the liquid within the heat exchange tubes.
18. The method of claim 17, where the step of providing comprises
providing a first component of the heat exchange bath having a
first boiling temperature, and providing a second component of the
heat exchange bath having a second boiling temperature lower than
the first boiling temperature.
19. The method of claim 18, wherein the first and second boiling
temperatures are both lower than the boiling temperature of the
liquid to be densified.
20. The method of claim 17, further including providing a primary
component of the heat exchange bath and a secondary component of
the heat exchange bath, the volume of the primary component
substantially exceeding the volume of the secondary component.
21. The method of claim 20, wherein the primary component of the
heat exchange bath is an inert liquid.
22. The method of claim 21, wherein the liquid to be densified is
liquid oxygen and the primary component is liquid nitrogen.
23. The method of claim 22, wherein the secondary component is
liquid hydrogen.
24. The method of claim 17, where the step of providing comprises
providing a first component of the heat exchange bath and a second
component of the heat exchange bath, and introducing the second
component to the heat exchanger in more than one flow path.
25. The method of claim 24, further including introducing the
second component of the heat exchange bath through a plurality of
injectors.
26. The method of claim 25, wherein the injectors are located in an
upper portion of the heat exchange bath and oriented so that the
plurality of flows of the second component is directed
downward.
27. The method of claim 17, further including monitoring the level
and temperature of the heat exchange bath and adjusting the flows
of the two components accordingly 28. The method of claim 27,
wherein the monitoring is done with sensors within the heat
exchange tank and the adjusting is done with flow control valves,
the method including transmitting signals from the sensors to a
controller, and transmitting signals from the controller to the
flow control valves.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods and apparatus for
densifying cryogenic liquids and, more particularly, to a
simplified system for densifying liquid for long term storage, or
for use in propulsion systems as densified propellant or
reactant.
BACKGROUND OF THE INVENTION
[0002] Propulsion systems utilizing cryogenic liquid oxygen and/or
hydrogen, such as the Space Shuffle, Atlas/Centaur, Delta, etc.,
are currently filled from the facility storage tanks and
subsequently allowed to cool in the flight tanks in order to reject
the heat absorbed by the liquid as a result of environmental heat
leak, transfer line, and tank wall chill-down. The cooling of the
liquid bulk is desirable in order to increase the liquid density so
that more impulse mass can be stored in the tank, and also to
reduce the liquid vapor pressure so that the tank operating
pressure and tank weight is minimized.
[0003] The next generation of advanced reusable launch vehicle
(RLV) propulsion systems requires significant improvements in
vehicle performance and operational cost reduction in order to make
travel into space economically feasible. Recent efforts toward
achieving these goals have focused primarily on high performance
rocket engines, lightweight composite structures,
lightweight/durable thermal protection systems, and lightweight
storage tanks. Except for the use of slush hydrogen (mixture of
liquid and solid), improvements in cryogenic liquid propellant
properties have not been actively pursued.
[0004] An alternative to slush propellant has been identified that
is simple, low cost, and provides significant vehicle weight and
operational cost reductions. The concept involves the super
cooling, or densification, of liquid oxygen and hydrogen below the
present operating temperature experience. Densification of
cryogenic propellants improves fluid properties (density and vapor
pressure), which subsequently results in smaller tanks (.about.11%
LO.sub.2, and .about.7% LH.sub.2), and lower tank operating
pressures. FIG. 1 illustrates the improvement in thermo-physical
properties of liquid oxygen (LO.sub.2) as a function of sub-cooled
temperature. As is clear from the chart, lowering the temperature
of oxygen results in higher density and lower vapor pressure. The
triple point of oxygen, at approximately 98.degree. R, is
illustrated at the left, while the boiling point, at approximately
162.degree. R, is shown at the right.
[0005] These propellant attributes result in significant weight
savings for new launch vehicles or increased payload capability for
existing launchers. Vehicle sizing studies for the
single-stage-to-orbit RLV indicate a total weight reduction between
15 to 30 percent due to propellant densification. FIG. 2
illustrates the savings realized by utilizing densified liquid
oxygen and liquid hydrogen in the fuel tanks of a reusable launch
vehicle, such as the Space Shuttle. More specifically, the use of
densified fluids results in approximately a 17% reduction in
vehicle gross lift-off weight (GLOW). In addition to large vehicle
weight reduction propellant densification increases the storage
time of the cryogenic liquids without venting between 4 to 10 fold.
Also, the cost per pound of weight saved with densification is an
order of magnitude less than with other weight savings candidates
(aluminum-lithium tank, filament wound LH.sub.2 tank, composite
structure, or advanced main engines).
[0006] Because propellant densification promises large vehicle
weight reduction with low ground cooling unit investments cost,
densification has been recognized as an enabling technology for
future launch vehicle designs, or a significant performance
improvement to existing reusable or expendable launchers.
Currently, systems used to service the fuel tank of the space
shuttle require an expensive 3-stage compressor to reduce a liquid
nitrogen heat exchange bath temperature sufficiently to maintain
liquid oxygen being densified at about 120.degree. R. With larger
and more expensive compressors, the liquid oxygen temperature could
be reduced even farther, although the slush point of liquid
nitrogen at about 115.degree. R provides a lower limit.
[0007] The prior art method for generating sub-cooled cryogenic
liquid fuel is based either on directly lowering the heat exchanger
bath pressure, or lowering the bath temperature through the use of
a refrigeration system. Both of these concepts require the use of
rotating machinery and a significant external power source. The
primary disadvantages of using rotating machinery (vacuum pump,
compressor, expander, turbine, etc.) to generate low temperature
cryogens are that such densification systems tend to be complex,
they are less reliable, they require periodic maintenance/ground
check-out operation, and they are relatively expensive.
[0008] A system for densifying liquid propellant is disclosed in
USPN 5,644,920, issued to Lak et al. The '920 patent includes a
heat exchanger wherein liquid propellant is cooled and thus
densified. The heat exchanger bath is either the liquid propellant
itself, or a different liquid. For example, propellant liquid
oxygen may be cooled with even colder liquid oxygen, or with liquid
nitrogen. The heat exchanger bath fluid is cooled using a vacuum
pump or compressor that lowers the bath pressure such that it boils
at a lower temperature. The use of a vacuum pump or compressor to
cool the heat exchanger bath, however, introduces significant
complexity and cost to the densification system. For example, it is
estimated that a multi stage compressor necessary to cool a liquid
nitrogen heat exchanger bath to 120.degree. R, and having a
sufficient flow capacity for cooling liquid propellant stored in
the fuel tank of rocket, costs on the order of several million
dollars. In addition, the relatively large and complex compressors
and associated motors require constant maintenance, and checkout.
Furthermore, a relatively large power supply is required to support
the compressor. And finally, the introduction of high-voltage
machinery with rotating parts in the presence of various
propellants at a launch site introduces an inherent safety risk.
Thus, while the system disclosed in the '920 patent functions very
effectively for its intended purpose, a simpler, safer, and more
efficient approach would be desirable for cost-critical
applications.
[0009] Although densified/subcooled liquids are highly desirable
for propulsion systems to reduce launch vehicle size and operating
cost, densified liquids also benefit ground and space based storage
systems by reducing the size of the storage tank or by increasing
the storage time.
SUMMARY OF THE INVENTION
[0010] The present invention provides a liquid densification system
that is simple, inexpensive and safe. In contrast with prior
densification systems, no expensive compressor is required to
reduce the temperature of the heat exchange bath, and liquid being
cooled, within the heat exchanger. Instead, the heat exchanger
utilizes a primary, inert component and a secondary component for
the heat exchange bath. The primary component fills a majority of
space around the heat exchange tubes, while the secondary component
is colder and is injected when needed. This arrangement permits the
temperature of the liquid to be reduced in a very short time
without the need for a high-voltage power supply and maintenance
for the heat exchanger in and around the launch vehicle.
[0011] In one aspect of the present invention, a system for cooling
and densifying a liquid includes an inlet supply line and a heat
exchange tank having a plurality of heat exchange tubes therein,
each tube being in fluid communication with the inlet supply line.
An outlet line is in fluid communication with each of the heat
exchange tubes. A first inlet conduit connects to the heat exchange
tank to introduce a first component of a heat exchange bath to the
interior of the heat exchange tank, and into contact with the
exterior of heat exchange tubes. A second inlet conduit connects to
the heat exchange tank to introduce a second component of the heat
exchange bath to the interior of the heat exchange tank, and into
contact with the exterior of heat exchange tubes. The densified
liquid may be directed to a ground storage tank or vehicle tank,
such as for a space vehicle, and the liquid to be densified may be
recirculated from the tank to the heat exchange tank.
[0012] The system may include first and second flow control valves
for metering the introduction of the first and second components of
the heat exchange bath. Furthermore, the system may include at
least one sensor, such as a fluid level or temperature sensor,
within the heat exchange tank to supply input to a controller that
operates the flow control valves. A mixer may be provided within
the heat exchange tank for circulating and mixing heat exchange
bath therein. Preferably, the volume of the first component of the
heat exchange bath substantially exceeds the volume of the second
component, and the second component is introduced through a
plurality of injectors into the second component.
[0013] A further aspect of the present invention involves a method
for densifying liquid including filling a tank with a densified
liquid at a reduce temperature, circulating the liquid from the
tank to a plurality of heat exchange tubes within a heat exchanger,
and providing a two-component heat exchange bath in the heat
exchanger for cooling the liquid to be densified within the
exchange tubes. The method also preferably includes the step of
providing a first component of the heat exchange bath having a
first boiling temperature, and a second component of the exchange
bath having a second boiling temperature lower than the first
boiling temperature. Desirably, both the first and second boiling
temperatures are lower than the boiling temperature of the liquid
propellant.
[0014] In one specific embodiment, the liquid to be densified is
oxygen, the first component of the heat exchange bath is an inert
liquid, and second component has a boiling temperature that is
substantially lower than the boiling temperature of the first
component. The first component may be nitrogen, and second
component may be hydrogen. The method further may include injecting
the hydrogen along separate flow paths into the heat exchanger to
prevent localized freezing of the nitrogen.
[0015] The present invention, together with additional features and
advantages thereof, may best be understood by reference to the
following description taken in connection with the accompanying
illustrative drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a graph showing the relationship between
temperature, density, and vapor pressure of cryogenic oxygen;
[0017] FIG. 2 illustrates the difference in weight of two launch
vehicles, one utilizing liquid propellant at its normal boiling
temperature, and the other utilizing densified liquid
propellant;
[0018] FIG. 3 is a schematic diagram of a liquid densification
system of the present invention;
[0019] FIG. 4 is a schematic diagram of an alternative liquid
densification system of the present invention having a liquid
recirculation line; and
[0020] FIG. 5 is a graph of the temperature of a heat exchange bath
over time, where a second, colder liquid is gradually introduced to
a first liquid.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The present invention eliminates the need for large and
expensive compressors and associated hardware in favor of a heat
exchanger that utilizes two bath components: a first inert
component constituting the majority of the bath, and a second
component that is colder than the first component. The two
components are channeled into the heat exchanger tank as needed to
super-cool a liquid flowing through the heat exchange tubes. The
use of two components, with the primary component being inert,
enables a safe and cost-effective densification operation. One
specific example of a system to cool liquid oxygen is the use of
liquid nitrogen as the primary bath component, and liquid hydrogen
as the secondary bath component.
[0022] FIG. 3 illustrates a liquid densification system 100 of the
present invention that has improved performance and is greatly
simplified in relation to prior systems. The system 100 may be
associated with a vehicle tank 20 containing a cryogenic liquid 22
as shown, or may be used to supply densified liquid (e.g., a
propellant) to a long term storage tank in a ground- or
spaced-based storage facility. The liquid 22 originally enters the
system 100 from a main facility transfer line 24 connected to an
external source of liquid (not shown). The typical situation is
liquid oxygen as the fuel, with an initial temperature of about
120.degree. R.
[0023] An emergency relief valve 42 is typically provided on the
vehicle tank 20 for in-flight pressure relief in case of a
pressurization system failure during ascent of the vehicle. The
emergency release valve 42 is not used on the ground, however, and
is only there to protect the vehicle after lift-off.
[0024] The system 100 comprises a heat exchange tank 102 having a
plurality of the exchange coils or tubes 104 therewithin. The
liquid to be densified enters the tubes 104 through the tank wall
at inlet 106. After passing through tubes 104, the now cold and
dense liquid passes through line 50 and back to the storage tank 20
via main feed line 52.
[0025] A fluid heat exchange bath 112 within the tank 102 and
outside of heat exchange tubes 104 is maintained at a level above
the tubes using level sensor 114, controller 116, and a pair of
bath inlet valves 118 and 120. That is, controller 116 receives
input from the liquid level sensor 114 and provides output to the
control valve 118. In addition, a temperature sensor 122 in the
bath 112 provides a second input to controller 116 to regulate the
position of valve 120.
[0026] The present applicants have advantageously determined that
it is possible to eliminate expensive and high maintenance
compressors or other such equipment in favor of an innovative and
simplified two-liquid heat exchange bath 112. That is, a first
liquid enters heat exchange tank 102 via line 124, and is metered
by valve 118. The first liquid mixes with a second liquid that
enters tank 102 via line 126, the second liquid being metered by
valve 120. Preferably, the first liquid comprises the majority of
the bath 112 and is relatively inert. The first liquid may be
referred to as the primary component of bath 112. A preferred first
liquid is nitrogen, although other inert liquids, such as argon and
neon, may be contemplated. The second liquid is colder than the
first liquid, and is injected into the tank 102 only when needed to
cool the first liquid. A preferred second liquid is hydrogen,
although alternatives, such as helium or neon, may be contemplated.
The second liquid is therefore referred to as the secondary
component of bath 112.
[0027] The first liquid injected into tank 102 has a boiling
temperature that is lower than the boiling temperature of the
liquid being densified. The second liquid has a boiling temperature
that is lower than the boiling temperature of the first liquid. By
using the first liquid, which is inert, as the primary component of
cooling bath 112, the process is made relatively safe. The first
liquid is used as a vehicle for the second liquid, which is
injected to reduce the temperature of first liquid to a magnitude
sufficient to cool and density the liquid passing through tubes
104. For example, if the first liquid is liquid nitrogen with a
boiling temperature of approximately 139.3.degree. R, the bath 112
temperature can be reduced to as low as 114.degree. R (triple
point) by a metered introduction of liquid hydrogen, which has a
boiling temperature of around 36.5.degree. R.
[0028] Tests have been performed to insure that nitrogen as the
first liquid (primary component) and hydrogen as the second liquid
(secondary component) can be successfully mixed to reduce and
maintain the bath temperature to that needed to cool and densify
liquid oxygen. FIG. 5 illustrates the results of such tests, with a
bath temperature shown over a period of time after liquid hydrogen
injection into an existing, larger quantity of liquid nitrogen.
More specifically, the bath temperature is initially around
139.3.degree. R. At a time indicated on the graph as about 3500
seconds, liquid hydrogen injection commences. The bath temperature
reduces at a nearly linear rate in conformance with the constant
input flow of liquid hydrogen. At just past 5,000 seconds, the bath
temperature has been reduced to around 114.degree. R, or to the
slush temperature of liquid nitrogen. At around 6,000 seconds, the
liquid hydrogen injection is halted.
[0029] In an operating system, various temperature sensors such as
sensor 122 in FIG. 3 may be provided around the heat exchange tank
to monitor the bath temperature. If the bath temperature begins to
rise above a threshold value, the controller 116 can signal valve
120 to increase liquid hydrogen flow.
[0030] A further component of the present system 100 comprises a
mixer 130 seen in the bottom right portion of the tank 102 in FIG.
3. The mixer 130 may be employed to help circulate the bath 112 and
thoroughly mix the two bath liquids. Furthermore, the mixer 130 may
be used to facilitate heat transfer between the tubes 104 and bath
112. That is, in prior systems the bath 112 comprised liquid at its
boiling temperature. This liquid state is highly efficient for
transferring heat to and from heat exchange coils or tubes. The
present invention utilizes a liquid bath 112 that is below the
boiling temperature, and thus the mixer 130 may be desirable to
improve the heat exchange efficiency and reduce heat exchanger
size.
[0031] The injected second liquid rapidly warms and vaporizes. The
gaseous byproduct exits the heat exchange tank 102 through vent
line 134, and ultimately enters vent line 40. Some of the first
liquid may be entrained within the gaseous byproduct from boiling
of the second liquid, and thus must be replenished. Liquid level
sensor 114 is monitored by controller 116, and additional first
liquid is added by actuating valve 118.
[0032] Various arrangements are possible for introducing the first
and second liquids comprising the heat exchange bath 112. It is
believed that an arrangement in which the second, colder liquid is
split into a plurality of flow paths prior to coming into contact
with the first liquid is preferred. This, in turn, helps prevent
localized freezing of the second liquid. For example, if nitrogen
is used as the first liquid, and hydrogen as the second liquid, the
hydrogen is approximately 100.degree. R colder than the nitrogen,
and well below the slush temperature of nitrogen. Therefore,
splitting the flow of hydrogen into a plurality of paths reduces
the magnitude of localized cooling at the points at which the
hydrogen mixes with the nitrogen. Stated another way, for any one
of the separate flows of hydrogen, the heat of the surrounding
nitrogen is sufficient to prevent localized freezing.
[0033] The injection of the second flow may be accomplished in a
variety of ways. For example, one piping arrangement for injecting
the second, colder liquid into the bath may be used with a heat
exchanger that has an inner tank (preferably tubular) surrounded by
an outer tank, with the heat exchange tubes arranged longitudinally
within the inner tank. A second bath liquid inlet pipe communicates
with a second liquid inlet manifold and is disposed horizontally
across the upper portion of the inner tank. A plurality of
downwardly directed injectors are in flow communication with the
interior of the inlet manifold. The injectors are desirably evenly
spaced along the manifold, and along a length that is greater than
the length of the heat exchange tubes. In operation, the first bath
liquid is cause to flow into the inner tank until the level of the
first bath liquid exceeds the lower most ends of the injectors, and
preferably just below the manifold. After the liquid to be
densified is flowing through the heat exchange tubes, the second
bath liquid is introduced into contact with the first bath liquid
via the manifold and injectors. Second bath liquid passes through
the manifold and into the inner tank through outlet orifices at the
lower most end of the injectors Because of the separated flow paths
of the second bath liquid, localized freezing will be deterred.
Furthermore, the downwardly directed injectors help prevent
clogging because any freezing of the first liquid which may occur
around the injectors will be less likely to agglomerate on the
injectors. That is, in contrast to an upwardly directed pipe,
frozen particles of first liquid cannot fall by gravity into the
injectors.
[0034] Alternatively, the second liquid flow may be injected
through the bottom, through the side, or from the top of the heat
exchanger. For example, the tank could be oriented vertically with
the second liquid inlet manifold also being oriented vertically,
the liquid entering through the bottom of the manifold.
[0035] FIG. 4 illustrates an alternative densification system 100'
of the present invention that is in many ways similar to the system
100 of FIG. 3, and as such, like elements will be numbered the same
with a prime (') designation. As before, the system 100' comprises
a heat exchange tank 102' having a plurality of the exchange coils
or tubes 104' therewithin. The liquid to be densified enters the
tubes 104' through the tank wall at inlet 106'.
[0036] In the alternative embodiment, the liquid is recirculated
through the heat exchange tank 102' and the storage tank 20'. In
this embodiment, the liquid originates at a manifold 34 positioned
at the top of the storage tank 20' and travels through a
recirculation line 36, to a pump 108. A pump valve 110 may be
provided in line 36 to shut off flow to the pump 108. After passing
through tubes 104, the now cold and dense liquid passes through
recirculation line 50' and back to the storage tank 20' via main
feed line 52'.
[0037] A ground vent valve 30 remains open during loading of the
vehicle tank 20' to accommodate the boil off generated as a result
of filling the warmer tank, which gives off heat to the liquid 22'.
This heat absorption creates a boil off of the liquid 22' that
generates, gas 32 in the upper portion of the tank 20'. Prior to
the liquid level reaching a recirculation manifold 34, the gas 32
passes through apertures in the manifold, and through a
recirculation line 36 to the open vent valve 30. The vented gas
continues through a vent line 38 to a facility line 40 where it can
be recaptured in the facility or dumped.
[0038] Removal of the vent valve from vehicle tank 20' and placing
it on the ground is one of the primary benefits of the prior and
current densification systems. Namely, because the vent valve is on
the ground and not on the vehicle, the weight of the vehicle is
greatly reduced. Again, an emergency relief valve 42' is provided
on the vehicle tank 20' for in-flight pressure relief in case of a
pressurization system failure during ascent of the vehicle. The
emergency release valve 42' is not used on the ground, however, and
is only there to protect the vehicle after lift-off.
[0039] When the liquid 22' rises above the recirculation manifold
34, flow in the recirculation line 36 transitions from gaseous to
liquid. At this point, the ground vent valve 30 is closed, and the
densification system, denoted within dotted line 100', is primed.
Flow into the tank 20' via main feed line 52' continues to fill
both the tank and densification system 100'.
[0040] The initial temperature of the liquid 22' may have risen
above a desired level from the tank filling process and attendant
warming. Therefore, the liquid 22' must be recirculated through a
heat exchanger of the densification system 100' adjacent the launch
vehicle to reduce the-temperature once again.
[0041] A fluid heat exchange bath 112' within the tank 102' and
outside of heat exchange tubes 104' is maintained at a level above
the tubes using level sensor 114', controller 116', and a pair of
bath inlet valves 118' and 120'. That is, controller 116' receives
input from the liquid level sensor 114' and provides output to the
control valve 118'. In addition, a temperature sensor 122' in the
bath 112' provides a second input to controller 116' to further
regulate the positions of valve 120'.
[0042] A first liquid enters heat exchange tank 102' via line 124',
and is metered by valve 118'. The first liquid mixes with a second
liquid that enters tank 102' via line 126', the second liquid being
metered by valve 120'.
[0043] Again, the first liquid comprises the majority of the bath
112' and is relatively inert, being referred to as the primary
component of bath. A preferred first liquid is nitrogen, and a
preferred second liquid is hydrogen. The second liquid is therefore
referred to as the secondary component of bath 112'.
[0044] A further component of the present system 100' comprises a
mixer 130' seen in the bottom right portion of the tank 102' in
FIG. 4. The mixer 130' may be employed to help circulate the bath
112' and thoroughly mix the two bath liquids. Further more, the
mixer 130' may be used to facilitate heat transfer between the
tubes 104' and bath 112'. That is, in prior systems the bath 112'
comprised liquid at its boiling temperature. This liquid state is
highly efficient for transferring heat to and from heat exchange
coils or tubes. The present invention utilizes a liquid bath 112'
that is below the boiling temperature, and thus the mixer 130' may
be desirable to improve the heat exchange efficiency and reduce
heat exchanger size.
[0045] The injected second liquid rapidly warms and vaporizes. The
gaseous byproduct exits the heat exchange tank 102' through vent
line 134', and ultimately enters vent line 40'. Some of the first
liquid may be entrained within the gaseous byproduct from boiling
of the second liquid, and thus must be replenished. Liquid level
sensor 114' is monitored by controller 116', and additional first
liquid is added by actuating valve 118'.
[0046] As before, the injection of the second flow may be
accomplished in a variety of ways. The second flow may be injected
through the bottom, through the side, or from the top of the heat
exchanger.
[0047] While this invention has been described with respect to
various specific examples and embodiments, it is to be understood
that the invention is not limited thereto and that it can be
variously practiced within the scope of the following claims.
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