U.S. patent application number 12/831824 was filed with the patent office on 2011-01-13 for aluminum porous media.
This patent application is currently assigned to Firestar Engineering, LLC. Invention is credited to Gregory S. Mungas, Gregory H. Peters, Jon Anthony Smith.
Application Number | 20110005195 12/831824 |
Document ID | / |
Family ID | 43426386 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110005195 |
Kind Code |
A1 |
Mungas; Gregory S. ; et
al. |
January 13, 2011 |
ALUMINUM POROUS MEDIA
Abstract
Disclosed are materials of variable density or tiered porosity
micro-fluidic porous media structures of sintered metal or other
materials, and methods of making same. An embodiment discloses an
aluminum porous media element of variable density having a tiered
porosity micro-fluidic media structure. A method of making the
aluminum porous media element disclosed herein includes mixing a
binding agent with a metal powder to generate a first mixture,
heating the first mixture to a sub metal sintering temperature to
get a homogeneous composite of the metal powder and heating the
homogeneous composite to a metal sintering temperature to
sinter-bond the metal powder to get a porous media of first
porosity.
Inventors: |
Mungas; Gregory S.; (Mojave,
CA) ; Peters; Gregory H.; (Palmdale, CA) ;
Smith; Jon Anthony; (Rancho Cordova, CA) |
Correspondence
Address: |
HENSLEY KIM & HOLZER, LLC
1660 LINCOLN STREET, SUITE 3000
DENVER
CO
80264
US
|
Assignee: |
Firestar Engineering, LLC
Mojave
CA
|
Family ID: |
43426386 |
Appl. No.: |
12/831824 |
Filed: |
July 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61223611 |
Jul 7, 2009 |
|
|
|
Current U.S.
Class: |
60/257 ;
156/272.8; 156/60; 216/33; 419/2 |
Current CPC
Class: |
Y10T 156/10 20150115;
F23D 14/82 20130101; F16K 17/366 20130101; Y10T 29/49 20150115;
F02K 9/566 20130101; F16K 17/40 20130101 |
Class at
Publication: |
60/257 ; 419/2;
156/272.8; 156/60; 216/33 |
International
Class: |
F02K 9/42 20060101
F02K009/42; B22F 3/11 20060101 B22F003/11; B32B 38/00 20060101
B32B038/00; B32B 37/02 20060101 B32B037/02; B32B 38/10 20060101
B32B038/10 |
Claims
1. A method of producing sintered media element, the method
comprising: mixing a binding agent with a metal powder to generate
a first mixture; heating the first mixture to a sub metal sintering
temperature to get a homogeneous composite of the metal powder;
heating the homogeneous composite to a metal sintering temperature
to sinter-bond the metal powder to get a porous media of first
porosity; and treating the porous media of first porosity to remove
an oxide patina from the porous media of first porosity.
2. The method of claim 1, further comprising pressing the
homogeneous composite while heating it to the metal sintering
temperature.
3. The method of claim 1, wherein the metal powder is aluminum
powder.
4. The method of claim 1, wherein removing the oxide layer of the
porous media of first porosity further comprises bathing the porous
media of first porosity in an oxide removing acid.
5. The method of claim 4, further comprising exposing the porous
media of first porosity to a jet of an inert gas.
6. The method of claim 5, wherein the inert gas is at least one of
argon and helium.
7. The method of claim 4, wherein the oxide removing acid is
muriatic acid.
8. The method of claim 1, further comprising: adding at least one
of silicon beads and silicon dioxide beads to the mixture; and
dissolving the at least one of silicon beads and silicon dioxide
beads using an etching agent.
9. A method of creating a tiered porosity media structure, the
method comprising: generating a porous media structure of the first
porosity according to the method of claim 1; generating a porous
media structure of a second porosity according to the method of
claim 1, wherein the second porosity is different than the first
porosity; and merging the porous media structure of the first
porosity with the porous media structure of the second
porosity.
10. The method of claim 9, wherein the merging comprises pressing
the porous media structure of the first porosity with the porous
media structure of the second porosity.
11. The method of claim 9, further comprising striking-off a first
layer of a porous media structure of the first porosity before
merging the porous media structure of the first porosity with the
porous media structure of the second porosity.
12. The method of claim 11, wherein striking-off a first layer of a
porous media structure of the first porosity further comprises
striking-off a first layer of a porous media structure of the first
porosity using an electrical discharge machining wire.
13. The method of claim 11, wherein striking-off a first layer of a
porous media structure of the first porosity further comprises
striking-off a first layer of a porous media structure of the first
porosity using an electrical discharge machining plunge.
14. The method of claim 9, wherein the merging comprises: stacking
pressing the porous media structure of the first porosity with the
porous media structure of the second porosity; and heating and
pressing the porous media structure of the first porosity with the
porous media structure of the second porosity.
15. The method of claim 1, further comprising evacuating oxygen
from the porous media of first porosity.
16. The method of claim 9, further comprising exposing the porous
media structure of the first porosity with the porous media
structure of the second porosity to detonation wave of weak but
increasing strength.
17. A method of creating a layered micro-fluidic porous media
element, the method comprising: fabricating a plurality of
micro-fluidic porous media slices, comprising: coating a thin film
with a photoresist coating; covering the coated thin film with a
mask; exposing the covered thin film to electromagnetic energy to
develop the mask; etching the exposed thin film; and removing the
mask; registering each of the plurality of micro-fluidic porous
media slices; and bonding one or more of the plurality of
micro-fluidic porous media slices.
18. The method of claim 17, wherein registering each of the
plurality of micro-fluidic porous media slices further comprises:
placing the plurality of micro-fluidic porous media slices on top
of each other; aligning the plurality of micro-fluidic porous media
slices with their fiducial marks; rotating one or more of the
plurality of micro-fluidic porous media slices by a pre-determined
amount; and bonding the plurality of micro-fluidic porous media
slices.
19. The method of claim 17, wherein rotating one or more of the
plurality of micro-fluidic porous media slices by a pre-determined
amount further comprises rotating one or more of the plurality of
micro-fluidic porous media slices so that each opening in two
adjacent micro-fluidic porous media slices are imperfectly aligned
with each other.
20. A method of creating a tiered porous media, comprising:
generating a plurality of metal foils with an array of micro-sized
pores; and bonding the plurality of metal foils with an array of
micro-sized pores.
21. The method of claim 20, wherein generating the plurality of
metal foils further comprises: passing the laser source through a
microlens array; and ablating a metal foil with the laser source
passed through the microlens array.
22. The method of claim 20, further comprising removing an oxide
layer from each of the plurality of metal foils before bonding the
plurality of metal foils.
23. The method of claim 22, wherein removing the oxide layer of the
metal foils further comprises bathing the metal foils in an oxide
removing acid.
24. The method of claim 23, further comprising exposing the metal
foils to a jet of an inert gas.
25. A monopropellant system, comprising: a monopropellant tank with
an internal surface made of an aluminum porous media element; a
monopropellant delivery apparatus with an internal surface made of
an aluminum porous media element; and a flashback arresting device
having a microfluidic porous element adapted to deliver the
monopropellant to an ignition device; wherein the internal surface
of the monopropellant tank and the internal surface of the
monopropellant delivery apparatus are bonded together.
26. The monopropellant system of claim 25, wherein the porosity of
the internal surface of the monopropellant tank is different from
the porosity of the internal surface of the monopropellant delivery
apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims benefit of priority to U.S.
Provisional Patent Application No. 61/223,611, entitled "Propulsion
Systems and Components Thereof" and filed on Jul. 7, 2009, which is
specifically incorporated by reference herein for all that it
discloses or teaches. Further, the present application is related
to U.S. patent application Ser. No. 11/950,174, entitled
"Spark-Integrated Propellant Injector Head With Flashback Barrier",
filed on Dec. 4, 2007 and to U.S. patent application Ser. No.
12/633,770 entitled "Regeneratively Cooled Porous Media Jacket"
filed on Dec. 8, 2009. Further, the present application is related
to: U.S. patent application Ser. No. ______, entitled "Tiered
Porosity Flashback Suppressing Elements For Monopropellant Or
Pre-Mixed Bipropellant Systems" (Attorney Docket No. 488-011-USP1),
U.S. patent application Ser. No. 12/831,767, entitled "Flashback
Shut-off" (Attorney Docket No. 488-011-USP3), and U.S. patent
application Ser. No. 12/831,703, entitled "Detonation Wave
Arrestor" (Attorney Docket No. 488-011-USP2), all three of which
are filed on Jul. 7, 2010, which are also specifically incorporated
by reference herein for all they disclose or teach.
BACKGROUND
[0002] A monopropellant is a single liquid that serves as both fuel
and oxidizer. A monopropellant decomposes into a hot gas in the
presence of an appropriate catalyst, upon introduction of a
high-energy spark, or upon introduction of similar point source
ignition mechanism. Monopropellants, for example, can be used in a
liquid-propellant rocket engine. A common example of a
monopropellant is hydrazine, often used in spacecraft-attitude
control jets. Another example is HAN (hydroxylammonium
nitrate).
[0003] Another form of propellant is called a bipropellant, which
consists of two substances usually stored separately: the fuel and
the oxidizer. Anytime a combustion process is employed, pre-mixing
of combustion components may be desirable. Examples of fuels which
can benefit from pre-mixing prior to combustion include, without
limitation, natural gas, gasoline, diesel, kerosene, ethane,
ethylene, ethanol, methanol, methane, acetylene, and nitro methane.
Examples of oxidizers that can be pre-mixed with said fuels
include, without limitation, air, oxygen/inert gas mixes, oxygen,
nitrous oxide, and hydrogen peroxide. Fuel components can be mixed
with oxidizing components in many different ratios to make a
pre-mixed bipropellant and thus obtain a desired combustion
reaction. The flashback arrestor element described herein is
specifically relevant to any situation where the combustion
components are mixed prior to entering a combustion chamber.
[0004] Chemically reacting monopropellants and pre-mixed
bipropellants contain constituents that liberate chemical energy
through thermal decomposition and/or combustion. The chemical
energy release is initiated by a mechanism designed within the
chemical reaction chamber (where the majority of chemical energy
release occurs). Commonly, this initiation mechanism is
incorporated in the vicinity of a chemical reaction chamber's
injector head.
[0005] Deflagration is a common form of combustion where the flame
speed travels at velocities less than the speed of sound.
Deflagration combustion is commonly associated with low pressures.
However, contained or pressurized combustion may result in the more
powerful detonation phenomenon.
[0006] A detonation is a phenomenon characterized by supersonic
flame front propagation. Usually associated with detonation waves
are pressure/temperature spikes and shock waves. The physics and
corresponding reaction phenomenon are sufficiently different from a
deflagration to warrant separate designations and analysis. The
aforementioned conditions can result in a transient phenomenon
containing immense power that can be used for destructive or
carefully controlled constructive purposes.
[0007] An ignition source is any energy mechanism that causes a
chemical combustion process to initiate. In combustion reactions,
the reactants are at a higher energy state than the products
following combustion. However, to release the energy stored within
the chemical bonds of the reactants, a certain quantity of energy
(activation energy) must first be provided. The sources of the
initiation energy in a combustion process are referred to as
ignition sources. Many ignition sources exist including, without
limitation, electrical sparks, catalysts (substances which lower
the activation energy by providing a surface which increases a
reaction's chemical kinetics), heat sources, impact loads,
compression, or any combination thereof.
[0008] If an ignition source exists downstream of a detonable
mixture/detonable single component, in particular monopropellants
and premixed bipropellants, flames can propagate (also known as
"flashback"), through a feed line and into a storage container
causing catastrophic system failure An ignition source downstream
of a detonable mixture can cause a detonation to propagate
upstream.
[0009] Rocket engines commonly operate with monopropellants that
can have very high gas and/or liquid densities as compared to more
conventional air/fuel mixtures or low-pressure fuel and oxidizer
mixtures. Flashback at these much higher monopropellant energy
densities is not readily controlled. As a result, high energy
density monopropellants that have small quenching distances (e.g.,
fluid gap, pore, and/or effective fluid passageway diameters small
enough such that flames cannot propagate through the passageway)
have been traditionally avoided because of the flashback failure
mechanism that is very difficult to control.
SUMMARY
[0010] A tiered porosity flashback-suppressing element intended to
advance safety in the use of highly combustible gases and liquids,
particularly at high propellant densities (high gas pressure or
liquid phase), in a tubing flow path is described herein. Such a
flashback arrestor may be used, for example, in spacecraft
propulsion, energy generation, work producing cycles, and general
combustion reactions employing monopropellants and pre-mixed
bipropellants. Accordingly, disclosed herein are materials, methods
and devices relating to various components of such propulsion and
work producing systems including, without limitation, micro-fluidic
porous media elements, injector heads, flashback arrestors and
shut-off valves in the field of rocket propulsion or other
applications wherein combustible materials may be subject to
flashback. The materials are variable density micro-fluidic porous
media elements of sintered metal or other materials, and methods of
making same. The flashback arrestors comprise such porous media
elements and other elements to provide a flashback arrestor or
shut-off valve for use with high temperature and pressure
propellants in feed lines.
[0011] Disclosed are materials of variable density or tiered
porosity micro-fluidic porous media structures of sintered metal or
other materials, and methods of making same. While micro-fluidic
materials may be used in filters, heat exchangers, catalyst beds,
and lightweight structural materials, the disclosed tiered porosity
materials and the corresponding processes for making these
disclosed materials find particular use in components of rocket
propulsion systems, such as injector heads, flashback arrestors and
shut-off valves, and in similar components in other work producing
systems where a detonation-susceptible fluid propellant or such
energetic materials must be safely fed from a storage container to
a chemical reaction chamber, a combustion chamber or the like where
work is extracted from the resulting of heat of reaction.
[0012] Generally speaking, work extracting cycles that can
implement the flashback arrestor element may include without
limitation gas turbine cycles (e.g., Brayton similar cycles,) Otto
cycles, diesel cycles, and constant pressure expansions of
combusted products (e.g., similar to pneumatic machines).
Accordingly, it should be understood that materials, devices, and
methods described herein may have other applications in addition to
rocket propulsion.
[0013] In an embodiment, the method of producing aluminum porous
media disclosed herein comprises mixing a binding agent with
aluminum powder to generate a first mixture, heating the first
mixture to a sub aluminum sintering temperature to get a
homogeneous composite of the metal powder, heating the homogeneous
composite to an aluminum sintering temperature to sinter-bond the
aluminum powder to get aluminum porous media of first porosity, and
treating the aluminum porous media of first porosity to remove an
oxide patina from the porous media of first porosity.
[0014] In an alternate embodiment, removing the oxide layer of the
aluminum porous media of first porosity further comprises bathing
the aluminum porous media of first porosity in an oxide removing
acid such as muriatic acid. In yet another embodiment, the aluminum
porous media bathed into the oxide removing acid is exposed to a
jet of an inert gas such as argon, helium, etc. In yet alternate
embodiment, at least one of silicon beads and silicon dioxide beads
are added to the mixture and subsequently the at least one of
silicon beads and silicon dioxide beads are dissolved using an
etching process.
[0015] In an embodiment, an aluminum porous media of a first
porosity and aluminum porous media of a second porosity are merged
together to create an aluminum porous media of varying porosity,
wherein the first porosity is different than the second porosity.
The merging may comprise pressing the aluminum porous media of the
first porosity with the aluminum porous media of the second
porosity. In an alternate embodiment, the method of creating an
aluminum porous media of a first porosity may further comprise
striking-off a first layer of aluminum porous media of the first
porosity before merging the aluminum porous media of the first
porosity with the aluminum porous media of the second porosity.
[0016] An alternate embodiment of the method disclosed herein
provides creating a layered micro-fluidic porous media element, the
method comprising fabricating a plurality of micro-fluidic porous
media slices, registering each of the plurality of micro-fluidic
porous media slices, and bonding one or more of the plurality of
micro-fluidic porous media slices, wherein fabricating a plurality
of micro-fluidic porous media slices further comprises coating a
thin film with a photoresist coating, covering the coated thin film
with a mask, exposing the covered thin film to electromagnetic
energy to develop the mask, etching the exposed thin film, and
removing the mask.
[0017] An alternate embodiment of the method disclosed herein
provides generating a plurality of metal foils with an array of
micro-sized pores, and bonding the plurality of metal foils with an
array of micro-sized pores. In an implementation of such a method,
generating the plurality of metal foils may further comprise
passing the laser source through a microlens array, and ablating a
metal foil with the laser source passed through the microlens
array. A yet alternate implementation may further comprise removing
an oxide layer from each of the plurality of metal foils before
bonding the plurality of metal foils.
[0018] In an implementation, the aluminum porous media may be used
in a monopropellant system comprising, a monopropellant tank with
an internal surface made of an aluminum porous media element, a
monopropellant delivery apparatus with an internal surface made of
an aluminum porous media element, and a flashback arresting device
having a microfluidic porous element adapted to deliver the
monopropellant to an ignition device, wherein the internal surface
of the monopropellant tank and the internal surface of the
monopropellant delivery apparatus are bonded together. In an
embodiment of such a monopropellant system, the porosity of the
internal surface of the monopropellant tank is different from the
porosity of the internal surface of the monopropellant delivery
apparatus.
[0019] Other implementations are also described and recited
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective schematic view of an orbital or
space craft with several attitude or apogee thrusters using the
presently disclosed flashback-arresting devices.
[0021] FIG. 1A is an enlarged schematic cross section of an example
monopropellant propulsion system in the orbital vehicle using
flashback-arresting devices according to the presently disclosed
technology.
[0022] FIG. 2 illustrates an example flowchart for monopropellant
or bipropellant systems using detonation-arresting devices for
propulsion systems, working fluid production systems, and/or
electricity generation systems.
[0023] FIG. 3 illustrates an example embodiment of a detonation
wave arrestor with a disk-shaped tiered porosity
flashback-suppressing element.
[0024] FIG. 4 illustrates an alternate implementation of a
flashback arrestor with a conical-shaped tiered porosity
flashback-suppressing element.
[0025] FIG. 5 illustrates yet another alternate implementation of a
flashback arrestor with a hemispherical-shaped tiered porosity
flashback-suppressing element.
[0026] FIG. 6 illustrates yet another alternate implementation of a
flashback arrestor with a cup-shaped tiered porosity
flashback-suppressing element.
[0027] FIG. 7 illustrates the microfluidic porous element of
various shapes.
[0028] FIG. 8 demonstrates an example combustible mixture quenching
curve generated for a nitrous oxide blended fuel mixture.
[0029] FIG. 9 demonstrates example micro-fluidic porous media
pressure drop vs. mass flow data for a 10-micron porous metal media
element.
[0030] FIG. 10 illustrates an example of a fabrication process for
a tiered porosity micro-fluidic porous medium wherein the metal
powders are mixed with a binding agent.
[0031] FIG. 11 illustrates an example process for laying up a very
thin micro-fluidic porous media membrane that can be subsequently
bonded onto other structures.
[0032] FIG. 12 illustrates another example process for
manufacturing a thin micro-fluidic porous media element or membrane
that involves electrical discharge machining (EDM) machining thin
slice of micro-fluidic porous media from a larger block
[0033] FIG. 13 illustrates another example process for
manufacturing a tiered porosity micro-fluidic porous medium that
involves EDM removal (either wire or plunge EDM) of material from a
micro-fluidic porous media pre-bonded onto a lower pressure drop
substrate.
[0034] FIG. 14 illustrates another example process for
manufacturing a micro-fluidic porous media element or membrane that
involves stacking and rotating foils with predrilled micro-fluidic
passageways.
[0035] FIG. 15 illustrates an exemplary process for manufacturing
an aluminum micro-fluidic porous media element comprised of
aluminum metal films that first go through an oxidation-reduction
process before being diffusion bonded together in an inert
atmosphere.
[0036] FIG. 16 illustrates an example process for increasing a
micro-fluidic porous media element's rating on detonation wave
strength by exposing the element to weak but progressively
increasing strength detonation waves in the fabrication.
[0037] FIG. 17 illustrates a tiered porosity micro-fluidic porous
medium that incorporates multiple small porosity micro-fluidic
porous thin elements embedded in larger porous media structure to
provide redundancy to flashback embedded in a single structure.
[0038] FIG. 18 illustrates a flowchart depicting a process for
creating porous media element of variable porosity.
[0039] FIG. 19 illustrates a method that leverages some advances in
laser etching, but used here to make precisely ablated porous
sheets or foils.
[0040] FIG. 20 illustrates bonding together of processed foils to
form the region of small mean pore diameter of a tiered porosity
flashback suppressing member.
DETAILED DESCRIPTION
[0041] In the following description, for the purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. It will
be apparent, however, to one skilled in the art that the present
invention may be practiced without some of these specific details.
For example, while various features are ascribed to particular
embodiments, it should be appreciated that the features described
with respect to one embodiment may be incorporated with other
embodiments as well. Similarly, however, no single feature or
features of any described embodiment should be considered essential
to the invention, as other embodiments of the invention may omit
such features.
[0042] Equation 1 below covers gases and liquids, it uses the mass
flux moving through the structure rather than the fluid velocity as
there is no ambiguity in terms of what velocity you are speaking of
when using "fluid velocity". All combustion reactions (from which
detonations could be derived) are most commonly based on mass or
molar flow rates of constituents rather than fluid velocities.
P s = - C .rho. m ''2 - .mu. .rho. K m '' ##EQU00001##
[0043] Wherein dP/ds--Pressure change along a fluid streamline
moving through the element, K--micro-fluid porous media
permeability coefficient, C--micro-fluidic porous media Form
coefficient, .mu.--Fluid dynamic viscosity, .rho.--fluid density,
{dot over (m)}''--mass flux of fluid moving through micro-fluidic
porous media element.
[0044] The special case of further derivation of Equation 2 below,
for ideal gases flowing through a structure of thickness, L (this
equation is consistent with our FIG. 2 data):
( P 1 2 - P 2 2 ) = ( 2 RTL ) ( C ) ( m '' ) 2 + ( 2 RTL ) ( .mu. )
( 1 K ) ( m '' ) ##EQU00002##
[0045] Wherein, P.sub.1--Pressure immediately upstream of
micro-fluidic porous media element, P.sub.2--Pressure immediately
downstream of micro-fluidic porous media element, L--micro-fluidic
porous media element thickness, K--micro-fluid porous media
permeability coefficient, C--micro-fluidic porous media Form
coefficient, R--gas constant, T--gas temperature in micro-fluidic
porous media element, .mu.--Fluid dynamic viscosity, .rho.--fluid
density, {dot over (m)}''--mass flux of fluid moving through
micro-fluidic porous media element.
[0046] FIG. 1 is a perspective schematic view of an orbital or
space craft 100 with several attitude or apogee thrusters using the
presently disclosed flashback-arresting devices. The thrusters 110
may use a monopropellant propulsion system 110 that is described
below in further detail in FIG. 1A.
[0047] FIG. 1A illustrates a cross-sectional view of an example
monopropellant propulsion system 110 that may be using
flashback-arresting devices 102, 104, 106 according to the
presently disclosed technology. The example monopropellant
propulsion system 110 includes a monopropellant tank 112. An
ignition interface 106 is located between the rocket body 110 and a
combustion chamber 114, which feeds into an expansion nozzle 116.
In the illustration, the rocket would be propelled from left to
right.
[0048] Propellant from the monopropellant tank 112 is fed to the
combustion chamber 114 via monopropellant lines 118.
Flashback-arresting shut-off valve 102 may shut off the fuel in the
event of the flashback. A flashback arrestor 104 diverts the energy
caused by a flashback away from the lines 118 and tank 112.
Flashback-arresting ignition interface 106 may contain a
micro-fluidic porous media structure of sintered metal or other
heat resistance materials. Further, the shut-off valve 102 and/or
the flashback arrestor 104 may also contain a micro-fluidic porous
media structure. Note that while the flashback arresting devices
102, 104, 106 are disclosed in FIG. 1 with respect to a rocket,
such devices may also be used in other propellant and/or power
generation systems.
[0049] In an embodiment of the space craft 100, substantial, or
all, parts of the monopropellant propulsion system 110 may be made
of aluminum porous media disclosed herein. Specifically, in such an
embodiment, various components of the monopropellant propulsion
system 110, such as the monopropellant tank 112, the lines 118, the
combustion chamber 114, the nozzle 116, etc., may be made of the
aluminum porous media disclosed herein. In an embodiment, the
aluminum porous media may be made of variable density and the
density of the aluminum porous media in each component of the
monopropellant propulsion system 110 may be different from the
density in other components. Moreover, the gradient of the density
of the aluminum porous media may also be different in different
components of the monopropellant propulsion system 110.
[0050] Thus, in an embodiment of the monopropellant propulsion
system 110, various components, such as the monopropellant tank
112, the lines 118, the combustion chamber 114, the nozzle 116,
etc., may be made of aluminum porous media in a manner so that
there are no transition joints between the various components of
the monopropellant propulsion system 110 between dissimilar
materials.
[0051] Because aluminum is a very light-weight material, using
aluminum porous media in one or more components of the
monopropellant propulsion system 110 allows reducing overall weight
of the monopropellant propulsion system 110. Similarly aluminum
porous media may also be used in other engines, resulting in
reduced mass of the engine. In one embodiment, the gradient of
porosity of aluminum porous media used in various components of the
vehicle 100, or components of other engines, may be determined
based on the gradient of the temperatures that may affect one or
more of such components. In yet another embodiment, one or more
components of the monopropellant propulsion system 110, or
components of other engines, may be constructed using
regeneratively cooled micro-fluidic porous arrays of aluminum.
These could include powerplant heat exchangers, generators, and
piston engines requiring heat dissipation.
[0052] Moreover, one or more of these components include one or
more micro-fluidic porous media structures, in particular one or
more tiered porosity flashback suppressing elements made of
materials and using methods as will be detailed below. It should be
understood that while it is preferred to incorporate such tiered
porosity elements into valve structures, blast deflector structures
and the like, in some situations and with some monopropellants or
pre-mixed bipropellants, it may be possible or even desirable to
interpose such elements alone in the propellant flow path.
[0053] FIG. 2 illustrates an example flowchart 200 for
monopropellant or bipropellant systems using flashback-arresting
devices for flashback protection in propulsion systems (e.g.,
thruster 220), working fluid production systems (e.g., gas
generator 222), and/or electricity generation systems (e.g., power
plant 224). In a first depicted implementation, monopropellant tank
226 is the fuel/oxidizer source for a power generation system 220,
222, or 224. Flashback valve 228, flashback arrestor 236, and/or
regulator 232 contain flashback-arresting technology as presently
disclosed. The flashback arresting technology prevents or stops
detonation waves from propagating upstream and causing catastrophic
system failure in monopropellant feed lines and/or monopropellant
tank 226. Further, the presently disclosed flashback arresting
technology (e.g., flashback arrestor 236) may also divert energy of
the detonation waves away from the feed lines and/or monopropellant
tank 226.
[0054] In a second depicted implementation, bipropellant tanks
(i.e., fuel tank 228 and oxidizer tank 230) are premixed before
injection into the power generation system 220, 222, or 224.
Example fuels for such systems include, without limitation, natural
gas, gasoline, diesel, kerosene, ethane, ethylene, ethanol,
methanol, methane, acetylene, and nitro methane. Example oxidizers
for such systems include, without limitation, air, oxygen/inert gas
mixtures, oxygen, nitrous oxide, and hydrogen peroxide. Fuel
components can be mixed with oxidizing components in many different
ratios to obtain a desired combustion reaction.
[0055] Flashback valve 234, flashback arrestor 236, and/or the
regulator 232 may contain flashback-arresting or suppressing
technology as presently disclosed. The flashback arresting
technology prevents or stops detonation waves from propagating
upstream towards the tanks 226, 228, 230 and causing catastrophic
system failure in feed lines downstream of where fuel is premixed
with oxidizer. Further, the presently disclosed flashback arresting
technology (e.g., flashback arrestor 236) may also include
detonation wave arrestor/diverter to divert energy of the
detonation waves away from the feed lines and/or fuel tank 228 and
oxidizer tank 230.
[0056] Further, FIG. 2 illustrates three alternative power
generation systems (i.e., thruster 220, gas generator 222, or power
plant 224), each with a corresponding injector head 238. Other
power generation systems are also contemplated herein. For example,
various work-extracting cycles may implement the flashback
arresting technology (e.g., gas turbine (Brayton) cycles, Otto
cycles, diesel cycles, and constant pressure cycles). The injectors
238 may also be equipped with the aforementioned flashback
arresting technology that prevents or stops detonation waves from
propagating upstream of the injectors 238 and causing catastrophic
system failure. The implementations shown in FIG. 2 demonstrates
the flashback arrestor 236 implemented to protect single ignition
source, that is one flashback arrestor for protecting tank 226, and
one flashback arrestor 236 to protect the tanks 228, 230. However,
in an alternate embodiment, a single flashback arrestor may be
implemented to protect multiple sources of combustible mixture.
Moreover, the flashback arrestors 236 may be implemented at any
point between an ignition source and a container of combustible
mixture.
[0057] In an embodiment of the components illustrated in flowchart
200, one or more of the components may be made of the aluminum
porous media disclosed herein. For example, in an embodiment, the
monopropellant tank 226, the injectors 238, and one or more
sections of the regulator 232 and the flashback diverter 230 may be
made of the aluminum porous media disclosed herein. In yet
alternate embodiment, each of these components may be made of the
aluminum porous media disclosed herein having porosity different
from each other.
[0058] FIG. 3 illustrates an example geometry and composition of an
assembly of components of an embodiment of a flashback arrestor
assembly 300. The flashback arrestor assembly 300 may include a
detonation wave deflector 302, a cap 304, a flame arrestor
structure 306, a burst membrane 308, a bottom compression fitting
310, and a top compression fitting 312. A number of screws or other
mechanisms may hold together the flashback arrestor assembly 300.
For example, in the illustrated embodiment, the cap 304 and the
flame arrestor structure 306 have threads 320 for screws that hold
together the detonation wave deflector 302 and the burst membrane
308 between the cap 304 and the flame arrestor structure 306. The
cap 304 has an opening 322 along its central axis and the flame
arrestor structure 306 has an opening 324 along its central axis.
In an alternate embodiment, each of the openings 322 and 324 may be
located in a direction perpendicular to, or any other direction,
the central axis of the cap 304 and the flame arrestor structure
306. In the example implementation of the flashback arrestor 300,
the bottom compression fitting 310 connects with the flame arrestor
structure 306 via the opening 324 and the top compression fitting
312 connects with the cap 304 via the opening 322.
[0059] Each of the bottom compression fitting 310 and the top
compression fitting 312 provides a path for propellant fluids
(gases, liquids, or a combination thereof) through cavities in
their bodies. The bottom compression fitting 310 may be designed so
that it may be connected to tubes, pipes or other mechanism
designed for transporting such fluids towards the bottom
compression fitting 310 from the tanks 226, 228, 230. Similarly,
the top compression fitting 312 may be designed so that it may be
connected to tubes, pipes or other mechanism designed for
transporting a fluid away from the bottom compression fitting 312
towards the injectors 238. The flame arrestor structure 306 may be
designed to incorporate a receptor 326 on one of its surface to
hold a tiered porosity element 330. Note that while in the
embodiment illustrated in FIG. 3, the receptor 326 is shown to have
a flat structure, as will be discussed below, receptor 326 may have
various alternate geometrical structures. In such alternate
embodiments, the porous media element 330 may also have a
geometrical structure that is not flat. The detailed designs of the
various components of the flashback arrestor assembly 300 are
illustrated in further detail below.
[0060] The flashback arrestor assembly 300 is configured to be
positioned in the path of fluid from a fluid reservoir such as the
tanks 226, 228, 230 to the injectors 238. Thus, the fluid from a
tank may travel through a connecting pipe, tube, or other mechanism
towards the bottom compression fitting 310. The bottom compression
fitting 310 is connected to the flame arrestor structure 306 in a
manner so that the fluid from the bottom compression fitting 310
travels towards the receptor 326 containing the porous media
element 330. As discussed above, the porous media element 330
allows the fluid to pass through it, but is structured to resist a
flame front from progressing through it, as will be detailed below.
Moreover, the fluid may also travel in the direction of the surface
of the receptor 326 and thus, perpendicular to the flow of the
fluid through the porous media. In FIG. 3, a directional arrow 332
denotes the path of the fluid along the surface of the receptor
326, whereas a directional arrow 334 denotes the path of fluid
through the porous media 330.
[0061] The bottom surface of the detonation wave deflector 302 is
designed so that it deflects the fluid travelling thorough the
porous media element 330 towards the periphery of the detonation
wave deflector 302. Moreover, the side surface of the detonation
wave deflector 302 is designed in a manner so that when the burst
membrane 308 is fitted around the detonation wave deflector 302, a
number of flow paths are formed along the side surface of the
detonation wave deflector 302. The fluid coming from the porous
media element 330 and the fluid traveling along the surface of the
receptor 326 may travel through such flow paths formed between the
detonation wave deflector 302 and the burst membrane 308 towards
the cap 304. Directional arrows 336 denote such path of fluid flow
between the detonation wave deflector 302 and the burst membrane
308.
[0062] The outer surface of the detonation wave deflector 302 that
is designed to be adjacent to the cap 304 may also be designed in a
manner so as to form a number of flow paths 338 between the
detonation wave deflector 302 and the cap 304. The fluid traveling
between the detonation wave deflector 302 and the burst membrane
308 along paths 336 may flow though the path 338 towards the
central opening in the body of the cap 304. Subsequently, the fluid
may flow through the opening in the cap 304 towards the top
compression fitting 312 and from there towards a pipe, tube, or
other mechanism connecting the top compression fitting to the
injector 238.
[0063] In an alternate embodiment, the tiered porosity
flashback-suppressing element can be incorporated, either alone or
in an arrestor assembly as described above, into a shut-off valve.
For example, a shut-off valve may be placed adjacent to the
receptor 326 and attached to the burst membrane 308 so that in the
case of a flashback, the shutoff valve closes off the flow of fluid
from the tank 226, 228, 230 to the injector 238. As discussed
below, such a shut-off valve may be attached to the burst membrane
308 in a manner to trigger a shut-off in case of a bursting of the
burst membrane 308.
[0064] An alternate implementation may provide a propellant
shut-off assembly for isolating a propellant source in the event of
a flashback, wherein the propellant shut-off assembly may include a
burst membrane configured to fail in presence of the flashback and
a biased closed shut-off valve attached to the burst membrane. Such
a shut-off valve may be held open by the burst membrane while the
burst member is intact. Yet another implementation may provide a
method of isolating a propellant source in the event a flashback.
In such an embodiment, while propellant moves through the
propellant shut-off assembly in a propellant flow direction, the
propellant shut-off assembly may experience a flashback. As a
result, a burst membrane within the propellant shut-off assembly
may be fractured to failure because of the flashback. Such a
failure of the burst membrane causes the propellant shut-off
assembly to close and isolate a propellant source from any
components of the propellant delivery system that have failed as a
result of the flashback.
[0065] In case of an incident causing flashback, the porous element
330 operates as a thermal sponge that absorbs combustion energy at
rates higher than the rate at which a detonation wave can release
combustion energy. As a result, the porous media element 330
provides a detonation quenching. However, because in the normal
operation, the porous media element 330 is also providing a path
for combustible fluid, the porous media element 330's effective
microchannel diameter sizing and surface area are strategically
chosen for each particular application based on combustible fluid
mass flow rate requirements and allowable pressure drop. While the
quenching distance of the porous media element 330 may be
sufficient to arrest a primary detonation wave, the energy release
from a line flashback can cause secondary ignitions through
mechanical failures and/or heat transport through solid material.
This conductive heat transport can produce hot spots in direct
contact with un-combusted combustible fluid sufficient to ignite a
propellant upstream of the flashback arrestor assembly 300.
[0066] However, the detonation wave deflector 302 together with the
burst membrane 308 provides additional protection to the sources of
combustible fluids from the potential harm caused by such
additional detonation wave. Specifically, the detonation wave
deflector 302, together with the burst membrane 308, allows the
detonation products travelling from the opening in the top
compression fitting 312 to be vented before they reach the porous
media element 330 or at least in the immediate vicinity of the
porous media element 330. Moreover, the detonation wave deflector
302, when hit by a combustion wave, disperses the shock wave away
from the porous media element 330. Specifically, the detonation
wave deflector 302 directs the shock wave energy towards the burst
membrane 308.
[0067] FIG. 4 illustrates an alternate implementation of a
flashback arrestor assembly 400 and various components thereof.
Specifically, the flashback arrestor assembly 400 is shown to have
a detonation wave deflector 402 and a flame arrestor structure 404.
The bottom surface of the detonation wave deflector 402 is designed
to have a cone shape. The cone shaped bottom surface 408 may
include a number of circular steps 410 as well as a number of
grooves 412 expanding outwards from the center of the detonation
wave deflector 402. Similarly, the flame arrestor structure 404 may
have a cone shaped protruding surface 414 and a number of circular
steps on the cone shaped protruding surface 414 around its central
axis. A porous media element 406 that is shaped in the form of a
cone may be positioned between the cone shaped bottom surface of
the detonation wave deflector 402 and the cone shaped protruding
surface 414 of the flame arrestor structure 404.
[0068] FIG. 5 illustrates an alternate implementation of a
flashback arrestor assembly 500 and various components thereof.
Specifically, the flashback arrestor assembly 500 is shown to have
a detonation wave deflector 502 and a flame arrestor structure 504.
The bottom surface of the detonation wave deflector 502 is designed
to have a hemi-spherical shape. The hemi-sphere shaped bottom
surface 508 may include a number of circular steps 510 as well as a
number of grooves 512 expanding outwards from the center of the
detonation wave deflector 502. Similarly, the flame arrestor
structure 504 may have a hemi-sphere shaped protruding surface 514
and a number of circular steps on the hemi-sphere shaped protruding
surface 514 around its central axis. A porous media element 506
that is shaped in the form of a hemi-sphere may be positioned
between the hemi-sphere shaped bottom surface of the detonation
wave deflector 502 and the hemi-sphere shaped protruding surface
514 of the flame arrestor structure 504.
[0069] FIG. 6 illustrates an alternate implementation of a
flashback arrestor assembly 600 and various components thereof.
Specifically, the flashback arrestor assembly 600 is shown to have
a detonation wave deflector 602 and a flame arrestor structure 604.
The bottom surface of the detonation wave deflector 602 is designed
to have an inverted cup shape. Similarly, the flame arrestor
structure 604 may have a protruding surface 606. A porous media
element 608 that is shaped in the form of a cup may be positioned
between the cup shaped bottom surface of the detonation wave
deflector 602 and the cup shaped protruding surface 606 of the
flame arrestor structure 604. A cap 608 may be provided to fit on
top of the flashback arrestor assembly 600.
[0070] FIG. 7 illustrates various shapes for the microfluidic
porous element. For example, the microfluidic porous element may be
provided in the shape of a thin disk 702, a cone 704, hemisphere
706, a cup 708, etc. Each of the shapes 702-708 provides one or
more advantages compared to the other shapes and may be more or
less suitable for different applications. Moreover, other
components of a flashback arrestor assembly 300, 400, 500, 600 may
have to be changed for them to properly function with the
microfluidic porous elements of shapes 702-708.
[0071] FIG. 8 demonstrates an example combustible mixture quenching
curve 800 generated for a nitrous oxide blended fuel mixture. The
detonation wave generated from a volume filled with a combustible
fluid density can effectively be quenched by a micro-fluidic porous
media element such as an aluminum porous media element. The ability
of a micro-fluidic porous media element to quench said wave is
dependent on the lowest flow-resistant path through the structure.
In general the smaller the effective flow passageway diameter
(corresponds to pore diameter in a sintered particle element) and
or the more tortuous path, the higher the probability that a
detonation wave will be quenched. Design of good micro-fluidic
porous media elements will require very high product reliabilities
for mitigating a detonation wave that could potentially be
generated for a given propellant and propellant density.
Micro-fluidic porous media should therefore be tested and rated for
a given application. Because a detonation wave's interaction(s)
with a complex micro-fluidic structure is an inherently complex
process, this phenomenon can be more accurately evaluated
experimentally rather than analytically. To explore this phenomenon
experimentally, one can fill a test fixture with a combustible
mixture and intentionally ignite the mixture within a contained
volume. If the element is sealed such that the only path for fluid
flow is through the porous element, the flame propagation
phenomenon through said element can be explored. In this
implementation, it is critical that volumes are entirely "sealed"
from one another by a porous element. Live data monitoring during
the ignition, or post inspection of the porous element can indicate
if the flame has propagated through the porous element. When this
process is repeated over a range of porous media elements and fluid
densities of the same combustible mixture, curves can be fit to the
data. These curves are useful in specification of a porous element
for specific uses. As shown in graph 800 of FIG. 8, as the
propellant density increases, the quenching distance and therefore
corresponding pore size necessary to prevent flashback decreases.
In FIG. 8, the pass points 802 are represented by diamonds and they
generally lie to the left of and below the curve 800. On the other
hand, fail points 804 are represented by circles.
[0072] FIG. 9 demonstrates example graph 900 for micro-fluidic
porous media (gas) flow data for a 10 micron porous metal media
element. In addition to the quenching characteristics of a porous
element, the flow characteristics must meet the requirements for
the intended application. This data can be extracted from a
micro-fluidic porous media element experimentally. The data can
then be post processed to accurately size the surface area of the
micro-fluidic porous media element for the intended application's
mass flow rates. In general, the smaller the pore size in a porous
media, the larger the pressure drop through the medium by changes
in the porous media's flow coefficients (typically larger C and
smaller K values shown in Eq. 1 and Eq. 2).
[0073] For ideal detonation wave quenching, the micro-fluidic
porous media must consist of sufficiently small fluid channel
diameters and/or tortuous paths to quench effectively back
propagation of a flame front. At the same time, the micro-fluidic
porous media must be made sufficiently thin to avoid excessive
pressure drop during normal operation (i.e., it permits the flow of
propellant into the combustion chamber). To quench a flame, typical
flame propagation into a medium is on the order of 1's to 100's of
quenching diameters into the medium. For example, for a combustible
fluid that requires 10 micron pores to quench a flame, the
thickness of the membrane necessary to quench the flame may be as
small as .about.100 microns. However, the combustion process may
generate combustion pressures that drive the preferred membrane
thickness to be significantly greater in order to provide
mechanical strength during a combustion event. If the micro-fluidic
porous media is nominally designed for both small quenching
distances and very large thicknesses to accommodate the combustion
pressures, very large fluid pressure drops may ensue when flowing a
combustible fluid through the micro-fluidic porous media structure,
i.e., a thick membrane of small pore size will interfere with the
normal flow of propellant into the combustion chamber.
[0074] Therefore, a more optimal design for a flashback arrestor is
one in which the pore diameters of the micro-fluidic porous media
varies through the thickness of the micro-fluidic porous media.
Near the front surface of the micro-fluidic porous media where the
combustion event may be initiated (e.g., on the combustion chamber
side of the flashback arrestor), the effective pore diameters
should be much smaller than the much thicker porous structure which
lies below (e.g., on the propellant tank side of the flashback
arrestor). This micro-fluidic porous media structure transfers
mechanical loads from near the surface where the combustion event
has occurred and ensures that the overall structure does not
mechanically fail. Therefore, the process for creating variable
density micro-fluidic porous media should meet the requirements for
preventing flashback with much lower pressure drops than
micro-fluidic porous media structures that have uniform pore
structures throughout.
[0075] The goal is to provide a porous media element that prevents
flashback with minimum propellant flow pressure drop through the
micro-fluidic porous media. This element may be composed of metal
or other materials. In one embodiment, the membrane is composed of
metal or other materials that are ductile, highly thermally
conductive to dissipate heat, and can take many thermal cycles
without cracking. The pores are approximately within a range of 10
nanometers to 100 microns in diameter.
[0076] One method for providing such characteristics with a very
thin micro-fluidic porous media membrane to minimize fluid pressure
drop through the membrane utilizes one or more of the fabrication
processes disclosed below.
[0077] FIG. 10 illustrates an example system 1000 used for a
fabrication process for a variable density or tiered porosity
micro-fluidic element.
[0078] In one embodiment, in order to create very thin sintered
metal membranes with reproducible thicknesses, a process is used in
which a binding agent or other fluid medium is mixed with metal
powders in a batch process. The binder (for example, a mixture of
paraffin based waxes) has physical properties such that at slightly
elevated temperatures, it will melt and become fluid, thus allowing
conventional mixing with selected metal powders to create a
homogenous blended composite. The system 1000 exemplifies one
embodiment in which the mixing of the binder 1002 with the powder
1004 may be done by mechanical mixing apparatus 1006. At ambient or
room temperature, the binder/metal mixture will remain in a plastic
such as for example, clay-like, state. At this stage, the
plasticity of the mix provides amenability to placement on a
molding surface or substrate to form the composite material to a
prescribed thicknesses and shape. Very thin structures may be
reproducibly made using this method. For example, in one embodiment
a structure of approximately 0.020 inches thickness may be made by
using the method described above. Subsequently, the mixture may be
heated at a temperature lower than that of the metal-sintering
temperature, initially to melt out binding agent leaving a porous
part of the prescribed thickness and shape. The part may then be
subjected to higher temperatures to become sinter-bonded. A
pressing mechanism may also be deployed at the time of sintering
that will apply a force to the part for consolidation and
strengthening.
[0079] Oxidation Reduction: Micro-fluidic porous media structures
made of metals such as aluminum may be treated by an additional
chemical process in which the aluminum oxide patina is at least
partially reduced back to aluminum metal. An oxide patina reduces
the particle to particle bond strength, which will compromise the
strength of the micro-fluidic porous media structure. Reducing
agents may be used to reduce the aluminum oxide patina during the
mixing and/or sintering processes. Liquid reductants (i.e. ammonia
and ammonia based compounds, oxalic acid, muriatic acid, formic
acid, dilute nitric acid, sodium mercury amalgams, dilute
hydrochloric acid containing amalgams), metal reductants (i.e.
zinc, tin, magnesium), hydride reductants (i.e. LiAlH, NaBH,
BiH.sub.3) powders or suspensions of powdered reductants may be
mixed in prior to sintering. A releasing agent such as alkyl
stearates or stearic acid may be used in order to release the
micro-fluidic porous media structure from the mold.
[0080] Dissolvable pore space occupiers: Silicon or silicon dioxide
beads may be mixed into the homogenous batch process shown in FIG.
10 and subsequently dissolved with an etchant such a KOH, NaOH, HF,
or Buffered Oxide Etch (BOE). Once the silicon or silicon dioxide
beads have been dissolved, the micro-fluidic porous media structure
and the bead cavities remain. To fabricate variable density porous
injector head components, a plastic state mould process (PSMP) may
be used to create very thin elements that may be pre-sintered as
thin membranes and subsequently merged with other pre-sintered
elements in a process termed merging. One embodiment is shown in
steps A-D of FIG. 11. Merging is a process whereby a pre-molded
porous element made of materials with one pore size, is pressed
onto another pre-molded element, made material of second
(different, and often smaller, pore size). Merging may also include
stacking more than two pre-molded elements into multiple layers of
elements with varying densities. The stack of elements is
subsequently heated and pressed to create variable porous layering
within a single part, as shown as step D in FIG. 12. The
sintering/pressing process may also include a method for evacuating
or displacing the oxygen from the process at sintering temperatures
to avoid oxidation decomposition of the part. The equivalent of
pressing may also be done by heating the part under fixed
constraints that don't expand as much as the part such that a large
internal pressure is applied throughout the part.
[0081] For aluminum fabrication using PSMP, reduction
oxidation-reduction agents are used to reduce the surface oxidation
of the particles and performed in an inert, non-oxidizing
environment.
[0082] FIG. 11 illustrates one embodiment for the procedure 1100
for fabricating tiered porosity flashback suppressing elements.
Step A 1102 shows a cross sectional view illustrating the operation
of "striking-off" a first layer 1104 of a plastic state mould
process (PSMP) produced composite within a mold. Step B 1106 shows
a second mold 1108 being placed atop the first 1104. Step C 1110
shows the striking-off of the second layer 1108 of material onto a
surface of the first layer 1104. Step D 1112 shows how sintering
heat and force are used to consolidate the layers into a single
variable density element having tiered pore sizes. While FIG. 11
shows a flat or disk shaped element, it should be understood that
other shapes having tiered porosity may be made using this
process.
[0083] The process illustrated in FIG. 11 is specifically important
when the first layer 1104 and the second layer 1104 are made of
aluminum porous media. Because aluminum porous media is susceptible
to oxidation reduction, it is possible that it will be covered by a
patina on its surface. Such patina makes it difficult for one layer
of aluminum porous media to create bonds with another layer of
aluminum porous media. Striking-off a thin layer from the first
layer 1104 before mold pressing the second layer 1104 allows better
and more robust bonds to be created between the two layers.
[0084] FIG. 12 illustrates one embodiment for an apparatus 1200 for
fabricating tiered porosity flashback suppressing elements using
electrical discharge machining (EDM). Specifically, in using the
apparatus 1200, an EDM wire 1202 is used to slice a preformed
micro-fluidic porous media plug 1204 to produce a very thin slice
of micro-fluidic porous media element. For example, in one
embodiment, a slice with a thickness of less than 0.030 inches may
be produced using the apparatus 1200. The small pored structure
generated in this manner can go through an oxidation reduction
process as required and a merging process to combine a thin sliced
micro-fluidic porous media element generated in this manner to
another mechanical structure that provides sufficient mechanical
backing and fluid wetting on the upstream (the propellant side) of
the thin element.
[0085] FIG. 13 illustrates one embodiment for a procedure 1300 for
fabricating tiered porosity flashback suppressing elements using
electrical discharge machining (EDM) on pre-bonded elements. In
this process, a micro-fluidic porous media element is diffusion
bonded using, for example, an oxidation-reduction process (as
necessary) and merging process. For example, 1302 illustrates a
micro-fluidic porous media element having higher porosity.
Subsequently, 1304 illustrates a micro-fluidic porous media element
having medium porosity being diffusion bonded on top of the
micro-fluidic porous media element having higher porosity.
Similarly, 1306 illustrates a micro-fluidic porous media element
having lower porosity being diffusion bonded on top of the
micro-fluidic porous media element having medium porosity. An EDM
wire or plunge EDM 1310 is used to remove excess micro-fluidic
porous media material until only a very thin portion remains
pre-bonded to a low pressure drop porous media.
[0086] FIG. 14 shows an alternate example embodiment of a method
1400 of fabricating a tortuous path micro-fluidic porous media.
Specifically, the method 1400 comprises using integrated circuit
processing methods to form aluminum micro-fluidic porous media.
This uses the standard masking process. A thin aluminum film is
coated with a photoresist coating. The coated film is covered by a
mask and exposed to UV or other electromagnetic energy/light to
develop the mask. Subsequently, the film is acid etched. The mask
is removed, and the wafer or film is released as a thin layer.
Several micro-fluidic porous media elements may be fabricated on a
single large aluminum foil or film. The micro-fluidic porous media
elements may be masked again, and etched away from the wafer
structure or cut away with more conventional mechanical shearing
processes, leaving the separate micro-fluidic porous media
elements. The individual slices are then bonded using a method such
as anodic bonding, annealing or fusing, or similar method. During
bonding, each slice is registered, a process by which one slice is
placed atop another by aligning key reference points in the films
previously created during the etching process, and placed during
fabrication.
[0087] The process of registering each slice is shown in FIG. 14.
Drawings 1400 shows how the use of rotation of one element slice
with respect to another may define small, definable-size paths. The
size of the paths, given appropriate fabrication, will vary
continuously from fully open to submicron sizes depending on the
degree of rotation of each micro-fluidic porous media slice. This
alignment allows for different pore sizes without necessarily
requiring a new mask and processing for each pore size desired.
This process may also be used to accomplish a continuous, smoothly
curved or a jagged path, depending on the desired tortuousity. For
example, in an embodiment, each micro-fluidic porous media slice is
rotated by a pre-determined amount from around its central axis to
provide a smoothly curved path of desired tortuousity.
Specifically, FIG. 14 is a top down view of the embodiment of the
method using integrated circuit processing methods to produce a
micro-fluidic porous structures comprising three stacked
micro-fluidic porous media elements. The diagrams show the overlap
of each layer with the registration of A, relative to B, relative
to C.
[0088] FIG. 15 illustrates an aluminum foil assembly process 1500.
For aluminum structures with simple or complex microfluidic pores,
the integrated circuit (IC) process may be applied to foils 1502 to
create geometric pore configurations, however the oxide layers of
each foil must be reduced prior to diffusion bonding processes.
After the IC process, the oxide patina on each foil 1502 may be
reduced by bathing the foils in a solution of 8-10% HCl (Muriatic
Acid) 1504, followed by exposing each foil 1502 to an argon or
helium jet 1506 to blow off excess solution and then stacking the
foils in a prearranged order and orientation 1508. The entire
process must take place in a non-oxidizing environment facilitated
by a glove box or similar enclosure with a positive pressure purge
of argon or helium.
[0089] Mechanical alteration to an existing porous element can
minimize flow alteration while increasing the element's flashback
resistance. A number of post manufacturing processes may
effectively achieve the same result of reduction in mean pore
diameter. These post manufacturing processes may include, without
limitation, cold pressing, water hammering, ball peening, or
detonation "burn in" of a first porosity medium to form a layer of
having a second, preferably smaller porosity. In one embodiment,
the method of detonation burn in has produced desirable results. In
this process, a detonable fluid is loaded within a fixture to a
density below the predicted flashback failure point of the porous
element and the fluid is intentionally detonated. If this process
is repeated with progressively higher combustible fluid density,
mechanical alteration particularly near the surface structure on
the combustion side of a porous element can be achieved to
effectively decrease the pore size of the membrane near this
surface. In addition to mechanical alteration of the structure,
this process can be used to validate a flashback arresting device's
characteristics prior to use as a flashback arresting device.
[0090] FIG. 16 illustrates an example process for increasing a
micro-fluidic porous media element's rating on detonation wave
strength by exposing the element to weak but progressively
increasing strength detonation waves in the fabrication.
[0091] Specifically, FIG. 16 illustrates graph 1600 with test data
of a burn in alteration of a porous element. Both the unaltered
element's flashback arresting points as well as the flashback
failure points are shown. The example burnt-in micro-fluidic porous
media repeatably failed at densities over .about.30% higher than
the unaltered porous elements, as shown by the distance between the
two dotted vertical lines in graph 1600. This test data indicates
that burn-in alteration of a porous element can increase the
flashback resistance of said element.
[0092] Therefore, in an embodiment, micro-fluidic porous media
elements are repeatedly exposed to detonation waves of weak but
progressively increasing strength. Thus, for example, a
micro-fluidic porous media element may be first exposed to a
detonation wave of 0.015 g/cc detonation wave. If the exposure does
not result in the failure, it may be subsequently exposed to a
detonation wave of 0.016 g/cc, etc. Based on the characteristics of
the micro-fluidic porous media element, it may be empirically
decided as to what point the exposure to detonation wave of
increasing strength should stop.
[0093] Not only must the micro-fluidic porous media element be able
to quench the detonation wave by dissipating heat in the
micro-fluidic structure at a higher rate than it is being
chemically released, but the structure must also be designed to
tolerate the high transient combustion wave (e.g. detonation)
pressures that ultimately will be incident on the micro-fluidic
porous media element. This structural requirement can be met
through a number of design means including, without limitation,
working with geometries that minimize exposure of the micro-fluidic
porous media elements to maximum strength combustion waves, and
providing sufficient material of a given type to dissipate the
energy of the combustion wave without causing material failure or
alteration of the micro-fluidic structure.
[0094] For example, it is possible simply to increase the thickness
of a micro-fluidic porous media element in order to effectively
dissipate the detonation wave shock energy without mechanically
failing. However, this method would also increase the pressure drop
through the micro porous element. As discussed above, any design
must balance the needs of desired flow of propellants to the
combustion chamber with the ability to provide flashback protection
characteristics. However, if the issues of pressure drop and the
scale of the element can be overcome, there are valid methods by
which to increase the mechanical strength of the micro porous
element.
[0095] To achieve this end, mechanical backing reinforcement may be
placed in strategic locations to increase the micro-fluidic porous
media element's (and backing structure's) tolerance to shock energy
without mechanically failing. In this configuration, a very thin
membrane-like structure that quenches the combustion wave is bonded
onto a stronger mechanical substrate that is also permeable and/or
contains fluid passageways to the thinner micro-fluidic porous
media element. This backing structure could be, for example, a
higher permeability porous media element bonded to the much thinner
micro-fluidic porous media element. Alternatively, the
micro-fluidic porous media element's permeability may be designed
to vary continuously. In another configuration, the very thin
membrane and/or a variable density micro-fluidic porous media
element can be placed on a solid backing structure that allows high
load transfer without micro-fluidic porous media element failure
and simultaneously contains fluid passageways to distribute fluid
across the micro-fluidic porous media element. To achieve this end,
mechanical reinforcement should be placed in strategic locations to
minimize the internal stresses, yet maximize the porous element's
fluid throughput. Such backing structures are shown as integrally
formed in flame arrestor structure 306 as described above.
[0096] Another method by which to mitigate the mechanical failure
is to utilize structural design of the micro-fluidic porous media
elements that can handle much higher compressive pressure loads.
Such structures may consist without limitation geometries such as a
cone or hemisphere. The bulk of these shapes may have a porosity
with relatively high propellant fluid flow, but likely inadequate
to suppress flashback in that fluid, while the first or outer
surface of such shapes have been made or treated to have the
requisite mean porosity to dependably suppress such a flashback.
The first or outer surface would be facing "downstream" i.e., away
from the propellant storage vessel or vessels and towards the
ignition source i.e., combustion chamber of a rocket engine, gas
generator or power plant.
[0097] FIG. 17 illustrates a tiered porosity element 1700
comprising multiple small porosity thin elements 1702, 1704 into
larger porous media regions 1706, 1708 to provide redundancy to
flashback suppression. Specifically, FIG. 17 illustrates a tiered
porosity micro-fluidic porous medium 1700 that incorporates
multiple small porosity micro-fluidic porous thin elements 1702,
1704 embedded in larger porous media regions 1706, 1708 to provide
redundancy to flashback embedded in a single structure tiered
porosity micro-fluidic porous medium 1700.
[0098] FIG. 18 illustrates a flowchart 1800 depicting a process for
creating porous media element of variable porosity. Specifically,
the flowchart 1800 illustrates one or more steps for creating
aluminum porous media element of variable porosity. Note that while
the steps of the flowchart 1800 depict a particular order, in an
alternate embodiment, these steps may be performed in a different
order. Moreover, not all the steps of the flowchart 1800 may be
necessary in every implementation of creating porous media element
of variable porosity.
[0099] At step 1802, a binding agent such as wax is mixed with a
metal powder such as aluminum. Such mixing is illustrated in
further detail in FIG. 10 above. At step 1804, the mixture of the
binding agent and the metal powder is heated to a sub-metal
sintering temperature to remove all the binding agents from the
resulting composite. At step 1806, the composite is heated to a
metal sintering temperature to create sinter-bonds among the metal
molecules. Subsequently at a step 1808, the composite is pressed to
strengthen the sinter-bonds. In an alternate embodiment, the
composite may be pressed concurrently with the heating of the
mixture and the composite at steps 1804 and 1806.
[0100] A porous media element created in the above manner may have
a surface patina created due to an oxidation-reduction. At step
1810, the porous media element may be treated to remove the patina
surface. Such removal of patina may include, for example, treating
the porous media element with a reducing agents to reduce the
aluminum oxide patina during the mixing and/or sintering processes.
Again, treating the porous media element with reducing agent may be
done concurrently with one of the steps 1804-1808. Subsequently, at
a step 1812, an EDM wire or plunge may be used to strike-off a
layer of material from the porous media element.
[0101] At step 1814, one or more films of porous media element may
be merged together. Such merging is disclosed in further detail in
FIG. 11 above. In one embodiment of the flowchart 1800, the merged
porous media element may be exposed to a series of weak detonation
waves of increasing strength in a manner discussed above with
respect to FIG. 15.
[0102] The tiered porosity flashback suppressing elements can be
thought of crudely as a thermal sponge that absorbs the combustion
energy at rates higher than the detonation wave can release. The
rate of energy absorption of a micro-fluidic porous media element
increases with smaller flow passage effective diameter and to some
extent the tortuosity and geometry of the fluid path. It should be
noted that supersonic detonation wave quenching distances can
typically be significantly smaller than the subsonic deflagration
wave quenching distances given the dramatically different rates of
thermal release associated with the speed of the wave. Many high
energy density propellants have submicron to 100-micron detonation
wave quenching distances. The disclosed elements, created by
sintering pre-sorted metal media, can effectively create flow paths
as small as 0.1 micron and can conceivably eventually be
manufactured down into nanometer scales. The described flashback
arrestor creates sufficiently small flow paths to quench
high-pressure closed line detonations preventing ignition past said
flashback arrestor.
[0103] Preferably, then, the porous elements of whatever shape can
be made of a precursor particles or sheets and should be of a
material that is physically robust, has a high thermal conductivity
and thermal diffusivity, and can be bonded to form a porous body
having a controllable mean pore diameter. Such materials should
also be chemically inert with regard to the propellant flowing
therethrough. Alternatively, some reactive or catalytic but
otherwise desirable precursor materials can be made inert by
isolating the surfaces of the elements with an inert coating.
Without limitation, inert coatings for a particular propellant
(e.g. MgO, Al.sub.2O.sub.3, and Yttria) may be applied to allow use
of materials that may be catalytic with the propellant.
[0104] FIG. 19 illustrates a method 1900 that leverages some
advances in laser etching, but used here to make precisely ablated
porous sheets or foils 1902. These precisely processed foils 1902
are bonded together to form the region of small mean pore diameter
of a tiered porosity flashback suppressing member 2002 shown in
FIG. 20. Referring to FIG. 19, a laser source 1904 of appropriate
power and wavelength produces a highly collimated beam 1906 that
passes through a microlens array 1908. This array is of known type
in the microelectronics industry and produces a precise array of
closely packed, precisely focused beams. The combination of laser
source and lens array ablates a layer of material, preferably the
metal foil 1902 to form a corresponding array of micron-sized pores
by ablating the foil 1902. These pores are of precise, repeatable
size and shape, preferably having an hourglass or double cone
shape, by taking advantage of the shape of the focused beams
emitting from the microlens array. The laser ablation process is
repeated many times to create ablated foils. As shown in FIG. 20,
these foils are subsequently bonded together is a precise,
repeatable manner to form a microporous medium which, when bonded
to a robust porous layer, can provide a tiered porous member 2000
having the desired flow and flame arresting characteristics
discussed above.
[0105] In an embodiment, the bathing and bonding process described
above with respect to FIG. 15 may be applied to the sheets of foils
1902 disclosed in FIGS. 19 and 20.
[0106] The above specification, examples, and data provide a
complete description of the structure and use of example
embodiments of the invention. Since many embodiments of the
invention can be made without departing from the spirit and scope
of the invention, the invention resides in the claims hereinafter
appended. Furthermore, structural features of the different
embodiments may be combined in yet another embodiment without
departing from the recited claims.
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