U.S. patent application number 11/738456 was filed with the patent office on 2007-10-25 for flow distribution channels to control flow in process channels.
This patent application is currently assigned to Velocys Inc.. Invention is credited to Ravi Arora, David Kilanowski, Anna Lee Tonkovich.
Application Number | 20070246106 11/738456 |
Document ID | / |
Family ID | 38524694 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070246106 |
Kind Code |
A1 |
Tonkovich; Anna Lee ; et
al. |
October 25, 2007 |
Flow Distribution Channels To Control Flow in Process Channels
Abstract
The invention describes features that can be used to control
flow to an array of microchannels. The invention also describes
methods in which a process stream is distributed to plural
microchannels.
Inventors: |
Tonkovich; Anna Lee;
(Dublin, OH) ; Arora; Ravi; (New Albany, OH)
; Kilanowski; David; (Dublin, OH) |
Correspondence
Address: |
FRANK ROSENBERG
P.O. BOX 29230
SAN FRANCISCO
CA
94129-0230
US
|
Assignee: |
Velocys Inc.
Plain City
OH
|
Family ID: |
38524694 |
Appl. No.: |
11/738456 |
Filed: |
April 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60745614 |
Apr 25, 2006 |
|
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|
Current U.S.
Class: |
137/561A |
Current CPC
Class: |
B01J 2219/00891
20130101; Y10T 137/87571 20150401; F28D 1/0341 20130101; B01J
2219/0086 20130101; Y10T 137/0329 20150401; F28F 2260/02 20130101;
B01F 5/0646 20130101; F28F 1/022 20130101; Y10T 137/87652 20150401;
B01J 19/0093 20130101; B01F 5/0655 20130101; B01F 13/0074 20130101;
B01J 2219/00873 20130101; B01F 5/0475 20130101; B01F 5/0647
20130101; Y10T 137/0318 20150401; B01F 3/0807 20130101; F28F 3/04
20130101; F28F 9/0275 20130101; Y10T 137/85938 20150401; B01F
13/0059 20130101; F28D 1/0316 20130101; B01J 2219/00835 20130101;
Y10T 137/6579 20150401; B01J 2219/00869 20130101; B01J 2219/00783
20130101; B01J 2219/00889 20130101; B01F 13/0064 20130101 |
Class at
Publication: |
137/561.00A |
International
Class: |
F16L 41/00 20060101
F16L041/00 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] This invention was made with Government support under
contract DE-FE36-04GO14271 awarded by the United States Department
of Energy. The government has certain rights in the invention.
Claims
1. A method of fluid processing, comprising: passing a process
stream into a manifold; wherein the manifold is connected to at
least a first flow distribution channel (FDC) and a second FDC;
wherein each FDC comprises a series of turns, comprising at least
four turns that are 90.degree. or less, or comprising at least two
turns that are greater than 90.degree.; and wherein the first FDC
channel connects the manifold to a first process channel; wherein
the second FDC channel connects the manifold to a second process
channel; and wherein the portion of the process stream that flows
through the first FDC connects with only one process channel and
does not connect with any other FDC so that all of the portion of
the process stream that enters the first FDC flows into the first
process channel; and conducting a unit operation in the first and
second process channels.
2. The method of claim 1 wherein each FDC comprises at least three
turns and each of said three turns has an angle of at least
135.degree..
3. The method of claim 1 comprising conducting a step of partially
boiling the process stream as it passes through the first process
channel.
4. The method of claim 3 where 0.5 to 50% of the process stream
entering the first process channel undergoes boiling in the first
process channel.
5. The method of claim 1 wherein the process stream in the process
channel comprises an emulsion, a dispersion, or a non-Newtonian
fluid.
6. The method of claim 5 wherein the first process channel has
channel walls that comprise orifices, and wherein the first process
channel comprises a first fluid comprising a first phase and a
second fluid, which is immiscible in the first fluid, passes
through the orifices into the first fluid to form an emulsion.
7. The method of claim 5 wherein flow in the first FDC is Newtonian
and wherein flow in the first process channel is non-Newtonian.
8. The method of claim 1 wherein the first and second FDCs have the
same length.
9. A method of distributing flow from a manifold into plural
process channels, comprising: passing a process stream into a
manifold; wherein the manifold is connected to at least a first FDC
and a second FDC; wherein each FDC comprises a series of turns,
comprising at least four turns that are 90.degree. or less, or
comprising at least two turns that are greater than 90.degree.; and
wherein the first FDC channel connects the manifold to a first
process channel; wherein the second FDC channel connects the
manifold to a second process channel; and wherein the first FDC
channel is on the same plane as the first process channel, and
wherein the first FDC has a cross-sectional area and the
cross-sectional area of the FDC at all points is less than the
cross-sectional area of the first process channel.
10. The method of claim 9 wherein the first FDC channel is on the
same plane as the first process channel and the manifold.
11. A microchannel device, comprising: a manifold; wherein the
manifold is connected to at least a first FDC and a second FDC;
wherein each FDC comprises a series of turns, comprising at least
four turns that are 90.degree. or less, or comprising at least two
turns that are greater than 90.degree.; and wherein the first FDC
channel connects the manifold to a first process channel; wherein
the second FDC channel connects the manifold to a second process
channel; and wherein the first FDC connects with only one process
channel and does not connect with any other FDC so that all of the
portion of the process stream that enters the first FDC flows into
the first process channel.
12. A microchannel device, comprising: a manifold; wherein the
manifold is connected to at least a first FDC and a second FDC;
wherein each FDC comprises a series of turns, comprising at least
four turns that are 90.degree. or less, or comprising at least two
turns that are greater than 90.degree.; and wherein the first FDC
channel connects the manifold to a first process channel; wherein
the second FDC channel connects the manifold to a second process
channel; and wherein the first FDC channel is on the same plane as
the first process channel.
13. A process of combining fluids, comprising: passing a first
fluid through a process channel; passing a second fluid through a
FDC and into the process channel where the first and second fluids
combine, where the FDC comprises a series of turns, comprising at
least four turns that are 90.degree. or less, or comprising at
least two turns that are greater than 90.degree.; wherein the first
and second fluids are different.
14. The process of claim 13 wherein the mass flow rate of the first
fluid into the process channel is 5% or less than the flow rate of
the second fluid in the process channel.
15. The process of claim 13 wherein the FDC comprises at least two
turns that have different angles.
16. The process of claim 13 where the process channel is straight
and wherein flow in the process channel is non-Newtonian.
17. Apparatus for combining fluids, comprising: a process channel;
an added fluid channel; a FDC connecting the added fluid channel to
the process channel, where the FDC comprises a series of turns,
comprising at least four turns that are 90.degree. or less, or
comprising at least two turns that are greater than 90.degree..
18. The apparatus of claim 17 comprising plural process channels
connected to one added fluid channel via plural FDCs, wherein each
FDC comprises a series of turns, comprising at least four turns
that are 90.degree. or less, or comprising at least two turns that
are greater than 90.degree..
19. A method of fluid processing, comprising: passing a process
stream into a manifold; wherein the manifold is connected to at
least a first flow distribution channel (FDC) and a second FDC;
wherein the first FDC comprises a first portion having a single
channel, a second portion that is connected to the first portion at
one end and a first process channel at another end, and a third
portion that is connected to the first portion at one end and a
second process channel at another end; wherein the second FDC
comprises a first channel portion having a single flow path, a
second channel portion that is connected to the first channel
portion at one end and a third process channel at another end, and
a third channel portion that is connected to the first channel
portion at one end and a fourth process channel at another end;
wherein each FDC portion comprises a series of turns, comprising at
least four turns that are 90.degree. or less, or comprising at
least two turns that are greater than 90.degree.; and conducting a
unit operation in the first, second, third and fourth process
channels.
Description
RELATED APPLICATIONS
[0001] In accordance with 35 U.S.C. sect. 119(e), this application
claims priority to provisional patent application Ser. No.
60/745,614 filed 25 Apr. 2006.
FIELD OF THE INVENTION
[0003] This invention relates to flow control in microchannel
devices.
INTRODUCTION
[0004] Many microchannel devices contain numerous planar, parallel
process microchannels. Controlling flow from a manifold or
manifolds into these parallel process microchannels has been a
major challenge of scaling up microchannel devices. Examples of
techniques to control flow (and typically to equalize flow) in
parallel process microchannels have been described by Fitzgerald et
al. in U.S. Published Patent Application Nos. 2005/0087767 and
2006/0275185, both of which applications are incorporated herein as
if reproduced in full below. Although these publications provide
very useful techniques for controlling flow, there remain some
instances in which simpler devices or devices suitable for use with
greater manufacturing tolerances or greater operability under a
range of conditions may be desired.
[0005] The prior art includes numerous examples of mixing devices
that divide and reunite flows through microchannels; for example,
U.S. Pat. No. 6,845,787. These patents do not provide suitable
means for controlling flow from a manifold in to an array of
parallel process channels.
SUMMARY OF THE INVENTION
[0006] Flow distribution in microchannel reactors, separators, and
other unit operations may require sufficiently uniform flow
distribution for many tens, or hundreds, or thousands of channels.
To achieve this sufficiently uniform flow distribution, that is
typically characterized by a quality index less than 30%, or less
than 20%, or more preferably less than 10%, or most preferably less
than 5 or even 1% or less, flow distribution features (also called
flow distribution channels (FDCs)) are used to distribute flow. In
some flow distribution features, frictional losses can be the
primary cause of pressure drop (for example, more than 50%,
preferably 70%, more than 90% of losses through the features can be
frictional losses). In this invention, orifices and porous plugs
are not flow distribution features. Flow distribution channels are
introduced either upstream or downstream, but preferably upstream,
of connecting microchannels where a unit operation is performed.
The flow distribution channels utilize a pressure drop that is
higher than the pressure drop in the connecting channels (that is,
over the entire length of the connecting channels), preferably by
at least 25%, or 50%, or more preferably 2.times. or 4.times. or
higher. The instability in time and/or variation in pressure drop
in the connecting channels where the unit operation is occurring is
mitigated from affecting the overall flow distribution to many
parallel microchannels.
[0007] In this invention the pressure drop through the flow
distribution features is preferably greater than through the
connecting channels. In contrast, flow through orifices is
controlled by expansion and contraction (not primarily frictional
losses). The invention includes both methods of controlling flow as
well as apparatus and/or designs of apparatus (preferably the
apparatus is microchannel apparatus where each connecting (i.e.,
process) channel has at least one internal dimension of 1 cm or
less, preferably 2 mm or less). A set of connecting channels
comprises at least 2, preferably at least 5, more preferably at
least 10 parallel channels connected to a common header and/or
footer.
[0008] In one aspect, the invention provides a method of fluid
processing, comprising: passing a process stream into a manifold
and a process stream. Flow distribution channels FDCs connect the
manifold and process channels. The manifold is connected to at
least a first flow distribution channel (FDC) and a second FDC.
Each of these FDCs comprises a series of turns, comprising at least
four turns that are 90.degree. or less, or comprising at least two
turns that are greater than 90.degree.. The first FDC channel
connects the manifold to a first process channel; and the second
FDC channel connects the manifold to a second process channel. The
portion of the process stream that flows through the first FDC
connects with only one process channel and does not connect with
any other FDC so that all of the portion of the process stream that
enters the first FDC flows into the first process channel. A unit
operation (which can be the same or different) is conducted in the
first and second process channels.
[0009] In a further aspect, the invention provides a microchannel
device, comprising: a manifold; wherein the manifold is connected
to at least a first FDC and a second FDC; wherein each FDC
comprises a series of turns, comprising at least four turns that
are 90.degree. or less, or comprising at least two turns that are
greater than 90.degree.; and wherein the first FDC channel connects
the manifold to a first process channel; wherein the second FDC
channel connects the manifold to a second process channel; and
wherein the first FDC connects with only one process channel and
does not connect with any other FDC so that all of the portion of
the process stream that enters the first FDC flows into the first
process channel.
[0010] In another aspect, the invention provides a method of
distributing flow from a manifold into plural process channels,
comprising: passing a process stream into a manifold; wherein the
manifold is connected to at least a first FDC and a second FDC;
wherein each FDC comprises a series of turns, comprising at least
four turns that are 90.degree. or less, or comprising at least two
turns that are greater than 90.degree.; wherein the first FDC
channel connects the manifold to a first process channel; and
wherein the second FDC channel connects the manifold to a second
process channel. In this aspect, the first FDC channel is on the
same plane as the first process channel, and the first FDC has a
cross-sectional area which, at all points, is less than the
cross-sectional area of the first process channel. "On the same
plane" means that process stream remains within the same layer in
both the FDCs and the process channels--it does not flow out of the
layer and then back into the layer. Cross-sectional area is
measured perpendicular to bulk flow. In a preferred embodiment, the
first FDC channel is on the same plane as the first process channel
and the manifold.
[0011] Similarly, the invention provides a microchannel device,
comprising: a manifold; wherein the manifold is connected to at
least a first FDC and a second FDC; wherein each FDC comprises a
series of turns, comprising at least four turns that are 90.degree.
or less, or comprising at least two turns that are greater than
90.degree.; wherein the first FDC channel connects the manifold to
a first process channel; wherein the second FDC channel connects
the manifold to a second process channel; and wherein the first FDC
channel is on the same plane as the first process channel. "On the
same plane" means that process stream remains within the same
layer--it does not flow out of the layer and then back into the
layer. The invention also includes a prebonded (or post-bonded)
assembly that comprises a stack of sheets with this
configuration.
[0012] In a further aspect, the invention provides a process of
combining fluids, comprising: passing a first fluid through a
process channel; passing a second fluid through a FDC and into the
process channel where the first and second fluids combine, where
the FDC comprises a series of turns, comprising at least four turns
that are 90.degree. or less, or comprising at least two turns that
are greater than 90.degree.. In this aspect, the first and second
fluids are different. In a preferred embodiment the mass flow rate
of the first fluid into the process channel is 5% or less (in some
embodiments 1% or less, or 0.1% or less) than the flow rate of the
second fluid in the process channel. In some preferred embodiments,
a layer comprising an array of parallel process channels are
connected to one or more added fluid channels by a plurality of
FDCs. An array of added fluid channels can be in a parallel layer.
For example, using this process, emulsions can be formed by passing
a continuous phase through process channels in a first layer and
dispersed phase through a second layer. In some embodiments, the
numbers of process channels are 5.times., 10.times., 20.times.,
100.times. greater than the number of channels for the added
fluid.
[0013] In a related aspect, the invention provides apparatus for
combining fluids, comprising: a process channel; an added fluid
channel; and a FDC connecting the added fluid channel to the
process channel, where the FDC comprises a series of turns,
comprising at least four turns that are 90.degree. or less, or
comprising at least two turns that are greater than 90.degree..
[0014] In a further aspect, the invention provides a method of
fluid processing, comprising: passing a process stream into a
manifold; wherein the manifold is connected to at least a first
flow distribution channel (FDC) and a second FDC; wherein the first
FDC comprises a first portion having a single channel, a second
portion that is connected to the first portion at one end and a
first process channel at another end, and a third portion that is
connected to the first portion at one end and a second process
channel at another end; wherein the second FDC comprises a first
channel portion having a single flow path, a second channel portion
that is connected to the first channel portion at one end and a
third process channel at another end, and a third channel portion
that is connected to the first channel portion at one end and a
fourth process channel at another end; wherein each FDC portion
comprises a series of turns, comprising at least four turns that
are 90.degree. or less, or comprising at least two turns that are
greater than 90.degree.; and conducting a unit operation in the
first, second, third and fourth process channels.
[0015] In preferred embodiments of any of the methods or apparatus
described herein, the FDCs can have a serpentine shape with, for
example, an angle of at least 135.degree.. In another preferred
embodiment, the process stream is partially boiled as it passes
through one or more of the process channels. For example, 0.5 to
50% of fluid in a process channel can boil. The inventive methods
are especially useful for applications in which the process stream
in the process channel comprises an emulsion, a dispersion, or a
non-Newtonian fluid. For example, in the method described above,
the first process channel may have channel walls with orifices and
a first fluid comprising a first phase passes through the first
process channel and a second fluid, which is immiscible in the
first fluid, passes through the orifices into the first fluid to
form an emulsion. The second fluid could pass through a FDC for
controlled flow into the process stream. The inventive methods are
especially useful for applications in which flow through the FDCs
is Newtonian and flow in (preferably straight) process channels is
non-Newtonian. In some embodiments, plural FDCs, that connect a
manifold with plural parallel process channels, have the same
length and/or same number of turns. The manifold can be a header or
footer. In some preferred embodiments, the FDCs can be planar and
can be formed, for example, by etching or stamping patterns (such
as serpentine patterns) in a sheet. Preferably, pressure drop in
the FDCs is greater than through the process channels. In some
preferred embodiments, a FDC comprises at least 4 or at least 8
turns. In some embodiments, one FDC has only one connection to a
manifold and one connection to a process channel. It is also
possible for a FDC to branch into separate sub-FDCs; for purposes
of the present invention, these are termed FDC portions. The fluids
are not limited, in some embodiments, liquids, gases or both are
processed. The FDCs can have turns of the same angle or turns of
varying angles within the same FDC.
[0016] Any of the apparatus described herein may alternatively be
described in terms of pre- or post-bonded assemblies of sheets; or
chemical systems comprising apparatus with fluid streams in the
apparatus.
[0017] An important advantage of various aspects of the invention
are the compact devices that are achievable. Preferably, the
distance from a manifold to a process channel is less than length
of process channel; more preferably, the length of a process
channel is at least 2.times., 4.times., or 10.times.greater than
the distance from the manifold to the process channel. In some
embodiments, the width of a process channel is at least 3.times.
greater than its height and the FDC or FDCs connected to the
process channel (and preferably also the connected manifold) share
a plane in the width direction. Preferably, the area of FDCs on a
device (or volume of FDCs in a device) is less than the area (or
volume) of process channels; preferably at least 10 times less. In
some embodiments, the cross-section of plural (or all) FDCs
connected to a manifold or within a layer are the same.
[0018] Some nonlimiting examples of applications for the invention
include: phase change, such as boiling or condensation either in
full or part, multiphase mixing applications, reactions comprising
oxidations, hydrogenations, sulfonations, nitrations, reforming, or
any other reactions, formation of emulsions or dispersions, or
other mixing applications, separations including distillation,
absorption, adsorption, phase separation, among others. This novel
approach may be used to manifold heat transfer fluids to any unit
operation, including those that only include heat transfer.
[0019] The inventive features can also serve to reduce the volume
in the headers and or footers of a system. By this manner they
serve to reduce the dead volume for applications that require fast
transient response such as adsorption or others that are required
to respond to transient changes in input parameters in a fast
manner. The features also serve to reduce dead volume that may act
to increase dispersion in a process such as that which broadens a
residence time distribution for the formation of products from
selective reactions including oxidations, nitrations,
hydrogenations, solids forming reactions, emulsion formation
devices and others.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 illustrates examples of turns.
[0021] FIG. 2 illustrates examples of simultaneous turns forming
flow distribution features.
[0022] FIG. 3 shows combinations of turns.
[0023] FIG. 4 illustrates fluid zones and flow exchange in surface
features.
[0024] FIG. 5 illustrates the location of some flow distribution
features.
[0025] FIG. 6 shows examples of flow distribution feature
shapes.
[0026] FIG. 7 shows flow distribution feature dimensions in Example
1.
[0027] FIG. 8 illustrates the effect of flow distribution feature
length on Q factor.
[0028] FIG. 9 is a schematic of the first layer of the repeating
unit of the device of Example 3.
[0029] FIG. 10 shows feature dimensions for Example 3.
[0030] FIG. 11 is a schematic of the third layer of the repeating
unit of the device of Example 3
[0031] FIG. 12 shows flow distribution feature dimensions in for
dispersed phase distribution in Example 3.
[0032] FIG. 13 shows an assembled unit for an emulsion forming
microchannel device.
[0033] FIG. 14 shows continuous phase flow distribution.
[0034] FIG. 15 shows the dispersed phase distribution.
[0035] FIG. 16 shows flow distribution feature dimensions in
Example 4.
[0036] FIG. 17 shows the Loss coefficient at Re=951 in Example
4.
[0037] FIG. 18 shows the Loss coefficient at Re=12172 in Example
4.
[0038] FIG. 19 shows the Loss coefficient at Re=36517in Example
4.
[0039] FIG. 20 shows the Loss Coefficient K as Function of Re from
CFD in Example 4.
[0040] FIG. 21 is a schematic of the device modeled in Example
5.
[0041] FIG. 22 is a plot of density vs. pressure for Example 5.
[0042] FIG. 23 shows the number of turns in flow distribution
features in Example 5.
[0043] FIG. 24 shows the predicted flow distribution in
microchannels in Example 5.
[0044] FIG. 25 shows the channel pressure drop variation for the
design sensitivity analysis in Example 5.
[0045] FIG. 26 shows the mass flow distribution for design
sensitivity analysis for Example 5.
[0046] FIG. 27 is a schematic of flow distribution manifold and
flow distribution features in Example 6.
[0047] FIG. 28 shows flow distribution features with sharp corner
and rounded corner from Example 6.
[0048] FIG. 29 shows a quality factor comparison with and without
flow distribution features.
GLOSSARY
[0049] As is standard patent terminology, "comprising" means
"including" and neither of these terms exclude the presence of
additional or plural components. For example, where a device
comprises a lamina, a sheet, etc., it should be understood that the
inventive device may include multiple laminae, sheets, etc. [0050]
A "header" is a manifold arranged to deliver fluid to connecting
channels. [0051] A "height" is a direction perpendicular to length.
In a laminated device, height is the stacking direction. [0052] A
"hydraulic diameter" of a channel is defined as four times the
cross-sectional area of the channel divided by the length of the
channel's wetted perimeter. [0053] A "laminated device" is a device
made from laminae that is capable of performing a unit operation on
a process stream that flows through the device. [0054] A "length"
refers to the distance in the direction of a channel's (or
manifold's) axis, which is in the direction of flow. [0055] A
"microchannel" is a channel having at least one internal dimension
(wall-to-wall, not counting catalyst if present) of 10 mm or less
(preferably 2.0 mm or less) and greater than 1 .mu.m (preferably
greater than 10 .mu.m), and in some embodiments 50 to 500 .mu.m.
Microchannels are also defined by the presence of at least one
inlet that is distinct from at least one outlet. [0056]
Microchannels are not merely channels through zeolites or
mesoporous materials. The length of a microchannel corresponds to
the direction of flow through the microchannel. Microchannel height
and width are substantially perpendicular to the direction of flow
of through the channel. In the case of a laminated device where a
microchannel has two major surfaces (for example, surfaces formed
by stacked and bonded sheets), the height is the distance from
major surface to major surface and width is perpendicular to
height. [0057] A "turn" is defined as a fluid pathway with length
greater than the hydraulic diameter of the channel, which leads to
a change in the direction of fluid flow by more than
10.degree.(more preferably by at least 90.degree., more preferably
by at least 135.degree., and in some embodiments by about
180.degree.), using the initial direction of flow as the reference.
FIG. 1 shows examples of a turn. An angle of the turn is defined as
the angle subtended between the fluid flow direction at the inlet
of the turn and at the outlet of the turn. The subtended angle is
preferably less than or equal to 180.degree.. FIG. 1(a) shows a
turn with an angle of 180.degree.. FIG. 1(b) shows a turn with a
subtended angle of 90.degree.. FIG. 1(c) also shows a turn with
subtended angle of 90.degree..
[0058] FIG. 2 shows examples of multiple turns joined together to
form a fluid path way for a flow distribution feature. FIG. 2(a)
shows an example of four turns in series, each turn subtending an
angle of 180.degree. to form a flow distribution feature. FIG. 2(b)
shows four turns, each turn subtending 180.degree. but are
separated by straight sections. FIG. 2(c) also shows 7 turns in
series, each turn subtending an angle of 90.degree.. The change in
the direction of fluid flow between two turns is not counted as a
turn because the length of the turn is less than the hydraulic
diameter of the channel. Also, for a curve segment to be a "turn"
it must a change in the derivative of slope, such as illustrated in
FIG. 2(c); a semi-circle constitutes only one 180.degree. turn, not
an arbitrary number of smaller turns.
[0059] FIG. 3 shows an example where two turns can be combined to
call as a single turn for simplicity. In FIG. 3, if dimension "a"
is two times of more than dimension "b", the turn 3 and turn 4 can
be combined together to form one turn.
[0060] Preferred embodiments of the invention comprise at least 3
turns, in some embodiments at least 6 turns, and in some
embodiments 3 to 15 turns. In some embodiments, turns are
configured to have a serpentine shape.
[0061] Turns may also be accomplished by a change in direction
within a single shim or by changing direction from shim to shim.
For example, a flow path may proceed for a certain distance in one
shim and then move to a new layer, constituting a 90.degree. turn,
and continue within the second shim at substantially the same angle
as the initial shim or at a new angle. "Unit operation" means
chemical reaction, vaporization, compression, chemical separation,
distillation, condensation, mixing (including forming emulsions),
heating, or cooling. A "unit operation" does not mean merely fluid
transport, although transport frequently occurs along with unit
operations. In some preferred embodiments, a unit operation is not
merely mixing.
DETAILED DESCRIPTION OF THE INVENTION
[0062] The flow distribution channels may be any physical geometry
and orientation but are preferably characterized by at least one
dimension (and preferably a hydraulic diameter) that is smaller
than the connecting channels (in this application, the term
"connecting channels" is synonymous with "process channels") such
that the pressure drop for a given flow rate is higher in the
distribution channels than in the connecting channels. One example
geometry of the distribution channels is an array of serpentine
features connected to an array of connecting channels. The
serpentine features may have a channel gap equal to either the
thickness of a shim (for example, stamped or etched-through
features in a sheet), or a channel gap (also called channel height,
because it is in the stacking direction of a laminated device) that
is less than the shim thickness in the case of partially etched
features. The width or span of the flow distribution features may
be less than the width or span of the connecting channel. The
distribution channels in one embodiment may be serpentine so as to
increase their effective length of the flow passage while
minimizing the volume of the manifold region overall relative to
the volume of the connecting channels. In some embodiments, it is
preferred to have a manifold within a microcomponent that has a
volume less than 100% of the volume of the set of connecting
channels, and more preferably less than 20% of the volume of the
connecting channels.
[0063] The serpentine features can be in a single shim; that is, a
single plane. Other embodiments of the flow distribution features,
including serpentine or other shaped features, may traverse
multiple layers in a manner that moves the flow back and forth from
layer to layer in a laminated device. For this embodiment, more
than one shim is required. The connecting channels can be in a
single shim or plural shims. Unlike gates and grates that have
previously described in examples of an earlier disclosure, in this
case pressure drop through the features traversing plural sheets
preferably is greater than the pressure drop through the connecting
channels.
[0064] A flow distribution feature preferably have heights of 50 mm
or less, more preferably 10 mm or less, more preferably 5 mm or
less, in some embodiments heights in the range from 0.005 to 10 mm,
in some embodiments at least 0.05 mm, and widths preferably of 2 mm
or less, in some embodiments in the range from 0.05 to 1 mm, and in
some embodiments 0.25 mm or less. The heights and widths are
typically perpendicular to flow of fluid in the channels. In some
embodiments, the cross-sectional area of the flow distribution
features is about 100 times smaller than the cross-sectional area
of processing channel. In some embodiments the cross-sectional are
of the flow distribution features is at least 2, or at least 10, or
at least 50 times smaller than the cross-sectional area of
processing channel.
[0065] The flow distribution features are different than what are
termed "surface features" in the patent literature. Surface
features are depressions or protrusions on the channel wall. A
channel with surface features has two fluid zones: fluid zone
inside the surface features and fluid zone outside the surface
feature which can also be termed as main channel zone as shown in
FIG. 4. FIG. 4 shows the cross-sectional view of a channel with
surface features. The flow between these fluid zones is
substantially exchanged in a channel with surface feature. The
fluid in the main channel enters and exits the surface channel
fluid zone from the same plane as shown in FIG. 4. However in flow
distribution features, there is generally only one fluid zone. If
other fluid zones are created, e.g. recirculation zones at the
corners, the fluid is not substantially exchanged between the
recirculation zones. The fluid enters the flow distribution feature
at one plane and exits the flow distribution feature from another
plane.
[0066] Flow distribution channels can be planar (i.e., in a single
layer) or can have a three dimensionally tortuous path through
multiple layers that preferably creates a resistance to flow that
is greater than the resistance in the connecting channels where the
unit operation is occurring.
[0067] The flow distribution channels may be constructed using any
method for constructing microchannel devices described in the art.
One embodiment includes etching or cutting of thin sheets of
material, which are stacked and joined. The invention also includes
the assemblies of stacked sheets (i.e., prebonded or bonded stacks
of sheets).
[0068] The use of distribution channels ameliorates the uncertainty
in flow that may occur from variations in the final dimensions of
the connecting channel where the unit operation occurs. Variations
may result from the introduction of a catalyst, the performance of
a catalyst, multiphase mixtures, the formation of non-Newtonian
mixtures, the formation of bubbles or any phase transformation.
Multiphase contacting including reactions may also be particularly
advantaged by this approach, where the pressure drop for either of
the phases, gas-liquid, or liquid-liquid may be hard to predict or
transient in nature or other non regular mechanisms. The use of
distribution features is also useful for embodiments where the same
apparatus is used for multiple processes or to make multiple
products.
[0069] The use of distribution features is especially useful for
processes where the fluid physical properties change significantly
(more than 20%, preferably more than 50%) along the length of the
connecting channel or process channel. Examples of fluid physical
properties that can change along the length of the process channel
include the fraction of one immiscible phase in another phase (e.g.
liquid-liquid processes, liquid-gas processes, liquid-solid
processes, and the like), changes in viscosity, changes in fluid
density, and other physical property changes.
[0070] The flow distribution features desirably create a pressure
drop between the fluid and wall that are higher (for example,
>2.times., >5.times., or even >10.times.) than the
pressure drop of the process channel. As such, the restriction in
the flow distribution features maintains a nearly uniform flow
distribution between all the channels, where the quality index
(defined below) is less than 30%, or more preferably less than 15%,
and more preferably less than 10%, more preferably less than 5%,
and most preferably 1% or less. In some embodiments, the pressure
drop in the process channels is on the order of 0.01 psi to 1 psi
for flow lengths in the range of 1 to 50 cm for a residence time
from 0.1 sec to 10 seconds. In some embodiments, the pressure drop
in the flow distribution features is on the order of 0.1 to 10 psi.
In some embodiments, the pressure drop in the flow distribution
features is on the order of 1 to 100 psi. Q = m . max - m . min m .
max .times. 100 ##EQU1## Where {dot over (m)}.sub.max=Maximum mass
flow rate in the channel, kg/s
[0071] {dot over (m)}.sub.min=Minimum mass flow rate in the
channel, kg/s
[0072] Q=Quality index
[0073] Partial boiling is one application that is particularly
advantaged by the use of distribution channels, where the high
pressure drop is achieved with a single phase fluid that is
subcooled from the boiling temperature. As boiling is initiated,
the pressure drop in the connecting microchannel may vary locally
from channel to channel with the onset of boiling and as such a
means for regulating flow to each channel is preferred.
[0074] It may also be preferred to tailor the flow distribution
within an array of channels, such that more flow is preferentially
metered to the top of the reactor where the heat load or flux is
the highest and minimized near the end of the reactor.
[0075] The distribution channels may be used for single phase unit
operations or for multiphase unit operations or any combination
therein. The distribution channels may be used to precisely meter
reactants that are used to form particles in connecting
channels.
[0076] The distribution channels are particularly useful when there
is a non-Newtonian fluid flowing through the connecting channels,
because the flow distribution features mitigate the effect of the
fluid changing apparent viscosity with changing conditions. For
example, the connecting channels may involve a changing apparent
viscosity of the flowing fluid due to polymerization, formation of
an emulsion, formation of solids, changing temperature, pressure,
local velocity, etc. through changes in the microchannel
configuration or materials used in the channel. The flow
distribution features provide a robust design for mitigating the
effect of these variations on flow distribution. Preferably,
non-Newtonian flow is restricted to flow through straight channels.
In a preferred embodiment, a fluid stream flowing through the flow
distribution features is Newtonian, and then becomes non-Newtonian
in the connecting channels (for example, due to a composition
change). This could occur, for example, where flow is occurring in
a process channel and a second phase enters the process channel
through orifices.
[0077] The flow distribution features may also be used to tailor
the addition of one reactant into a second reactant, such as in a
selective oxidation. The features could be used to provide
sufficient restriction to an oxidant or other reactant such that
the flow is metered in an even, or alternatively, a tailored,
fashion along the length of a reactor as desired. In this manner,
the metering function, namely the flow distribution channels, may
be separate from an inlet within a reactor such that an application
of a coating such as a catalyst will be less likely to plug or foul
when the coating is applied.
[0078] The distribution channels may be preferentially disposed
within a manifold section of a device such that once the fluid
enters the flow distribution channels it may only exit to one
process channel and not undergo additional redistribution. As an
example, one flow distribution channel could create a conduit that
feeds a single channel an oxidant (or other reactant or fluid) to a
single introduction point within a single microchannel, while a
second and perhaps third or more distribution channels feeds an
oxidant (or other reactant or fluid) to second or third or more
introduction points along the length of a microchannel reactor or
other unit operation. The distribution function in the form of the
distribution channels is removed or physically separated from the
unit operation.
[0079] Distribution channels may also be used for small scale or
large scale applications. The distribution channels may be helpful
to meter flows for a variety of applications including fuel cells,
including low power fuel cells or fuel processors, microfluidics,
blood or fluid analysis or other applications where metering flows
is especially challenging. Distribution channels may be used to
meter flows for any microchannel or microfluidics application.
[0080] One advantage of the use of distribution channels is for
improving flow distribution not only for a fixed condition or
design point, but also during turn up and turn down of a unit
operation or process. Specifically, the flow distribution may vary
less than 20%, or less than 10% or less than 5% in the absolute
overall quality index factor when the flow is turned down by 50% or
turned up by 20% over a selected design point. In an alternative
embodiment, the distribution features allow the turn up and turn
down of a device to vary up to +50% to -80%. In a third embodiment
the novel distribution features allow for a turn down of -95% and a
turn up of 200% over the nominal operating design point for a
multichannel unit operation that includes more than 10 channels
operating in parallel to achieve a target capacity.
[0081] In an alternative embodiment, a first set of distribution
channels may be used upstream of the connecting channels while a
second set of distribution channels may be used downstream or
alternatively at any point in between to tailor both the magnitude
of the mass flowrate in any given channel and the absolute pressure
in the channel. This approach may be particularly advantageous for
tailoring flowrate and the temperature for an application where
partial boiling may create temperatures that are different at
different axial locations along the length of the reactor.
[0082] In some preferred embodiments, flow distribution features
are used to distribute fluids (including gases) at flow rates
exceeding 1 mL/min per flow distribution channel. Alternate
examples for the use of the inventive distribution channels are for
lab on a chip or microfluidic applications, where low flows are
metered to at least two or more channels or to at least two or more
locations along the length of a channel. Metering low flowrates is
particularly challenging to control, especially with very modest
changes in channel dimensions from normal manufacturing
tolerances.
[0083] Another example application is for the production of
hydrogen peroxide that may include a catalytic reaction, such as
hydrogenation, and/or a non-catalytic reaction, such as oxidation,
where two streams must be metered into each other at preferred
ratios. There may be strict requirements for the local
concentration of the at least two or more reactants at any location
in the reactor. The reaction may not be catalyzed in one reaction,
such as the oxidation of an anthraquinone-based working solution
used in the production of hydrogen peroxide.
[0084] An alternate embodiment for this invention is the metering
of a small flow-through flow distribution features into a large
flow, such as the use of a promoter, additive, fluid catalyst,
active ingredient, pigment, preservative, fragrance, or other
species that comprises less than 20% or in some embodiments less
than 5% or less than 0.01%, and/or at least 0.001% of the mass of
the larger flow stream.
[0085] An alternate embodiment for this invention is for
micromixers of two or more fluid streams, including gas/gas,
gas/liquid, liquid/liquid, gas or liquid into a fluid that
comprises a solid or biphasic mixture. In other preferred
embodiments, the flow distribution features are used for unit
operations other than mixing, such as heat exchange. In some
embodiments, a serpentine flow distribution feature does not mix
fluids. In some preferred embodiments, the length of connecting
channels is at least 3 times, preferably 5.times. and in some
embodiments at least ten times longer than the flow distribution
features to which the channels are connected.
Flow Distribution Feature Designs
[0086] The manifold for the processes having small pressure drop in
the connecting microchannels (less than or equal to pressure drop
in the main manifold section) could be challenging. A small change
in the manifold pressure profile can lead to large mal-distribution
in the connecting microchannels. Generally the size of the manifold
for such processes would be large for a uniform flow distribution.
A common method of reducing the manifold dimensions while achieving
uniform flow distribution for such a process is by using orifices
between the manifold and the connecting microchannels. However the
pressure drop through an orifice varies as (Velocity).sup.n, where
n>1. Therefore a design with orifices for connecting
microchannels with small pressure drop is sensitive to the manifold
flow rates and may not provide a good flow distribution if the flow
rate is changed. The flow mal-distribution may cause poor
performance of the microchannel device. In summary, the manifold
may not provide uniform distribution at scale up and scale down
flow conditions.
[0087] A flow distribution feature is preferably a micro-dimension
channel (having at least one dimension of 1 cm or less, more
preferably at least one dimension of 2 mm or less) connecting main
manifold section to the connecting (process) microchannel as shown
in FIG. 5. The dimensions of a flow distribution feature, flow
cross-sectional area and length, are preferably smaller than the
main manifold section or the connecting microchannel. The
dimensions of the flow distribution features are preferably chosen
such that the pressure drop in the flow distribution feature is at
least 2 times the pressure drop in the connecting channels. The
flow distribution features increases the overall connecting channel
pressure and can thus make the requirement for manifold size for
flow distribution small. Furthermore the flow in distribution
features is preferably laminar. The pressure drop through the flow
distribution feature will vary as (Velocity).sup.n, where n=1. The
manifold designed with flow distribution features will be less
sensitive to the scale up and scale down flow conditions.
[0088] Flow distribution can be used for connecting channels with
small or large pressure drop (greater than pressure drop in the
main manifold section).
[0089] The process channels are preferably microchannels. In some
preferred embodiments, the manifolds to which the FDCs connect have
microchannel dimensions.
[0090] FIG. 6 illustrates a few designs for flow distribution
features shapes. FIG. 6a shows 8 turns. The features can be in a
2-dimensional plane or in three dimensions.
[0091] All of the following examples are calculated examples.
EXAMPLE 1
Flow Distribution With Flow Distribution Features
[0092] A case study was done to see the improvement in the flow
distribution using flow distribution features. The general
schematic of the device is shown in FIG. 5 but with a bottom
manifold. The top and bottom main manifold sections were 12.7
mm.times.2.54 mm in cross-section. The connecting channels were
5.08 mm.times.0.76 mm in dimensions. The length of connecting
channels was 127 mm. The connecting channels were separated by
0.508 mm wall. The number of connecting channels was 19. FIG. 4
shows the dimensions of the flow distribution features. The flow
distribution features were in serpentine shape. The cross-section
of the flow distribution channel was 0.76 mm.times.0.38 mm. The
manifold, flow distribution channels and connecting (process)
channels were in a common plane.
[0093] The fluid used was ethylene at 230 psig and -30.degree. C.
The total flow rate entering the main manifold section was 0.487
kg/hr. The performance of flow distribution was defined by quality
factor as defined below: Q = m . max - m . min m . max .times. 100
##EQU2## Where {dot over (m)}.sub.min=Maximum mass flow rate in the
channel, kg/s
[0094] {dot over (m)}.sub.min=Minimum mass flow rate in the
channel, kg/s
[0095] Q=Quality index
[0096] The pressure drop in the top main manifold section was
0.0005 psi and the pressure drop in the connecting channel was
0.0002 psi. The pressure drop in the flow distribution features was
0.009 psi. For the flow distribution feature design shown in FIG.
7, the Q factor was estimated to be 3.0%. A parametric study was
done to see the effect length of flow distribution features on flow
distribution. The designed flow distribution features had 12 bends
as shown in FIG. 7. To reduce the length of flow distribution
feature, the number of bends was decreased in steps and flow
distribution was estimated. FIG. 8 shows the effect of number of
turns in the flow distribution feature on Q factor.
[0097] The pressure drop in connecting channel is of the same order
of magnitude as the manifold. As we can see from FIG. 8, as the
number of turns in the flow distribution feature increases, flow
distribution is improved.
EXAMPLE 2
Flow Distribution Features Provide Uniform Flow Distribution Over a
Wide Range of Turn-up and Turn-down Flow Rates From Nominal
[0098] A geometry the same as in Example 1 was used to show that
the flow distribution features provide relatively uniform flow
distribution for turn-up and turn-down flow rates. The flow
distribution results were compared to the flow distribution
obtained in the same geometry but without flow distribution
features. The fluid, temperature and outlet pressure conditions
were kept for both the cases: with flow distribution feature and
without flow distribution features. The fluid used was ethylene at
230 psig and -30.degree. C. The nominal total flow rate entering
the main manifold section was 0.487 kg/hr.
[0099] FIG. 29 shows the quality factors with different turn-up and
turn-down factors from nominal flow rates for design with flow
distribution features and without flow distribution features. A
turn-up/turn-down ratio of 0.8 means 80% of nominal flow rate. A
turn-up/turn-down ratio of 1.3 means 130% of nominal flow rate.
[0100] As shown in FIG. 29, the flow mal-distribution increases as
the flow rate increased above nominal flow rate for case without
flow distribution features. The flow distribution remains the same
or improves as the flow rate is increased above the nominal flow
rate for the case with flow distribution features. The example
shows that the flow distribution features provide robustness to the
design for turn -up and turn-down flow rates
EXAMPLE 3
Flow Distribution for Emulsion
[0101] An emulsion is formed by mixing continuous phase liquid with
dispersed phase liquid through a porous medium. It is desired for
manufacturing that the porous medium through which continuous and
dispersed phases are mixed should be replaceable preferably with
mixing of the continuous and dispersed phases while flowing in
cross-flow direction. However depending upon the requirement, the
continuous and dispersed phases can be mixed while flowing
co-current or counter-current to each other.
[0102] In this example, only a repeating unit was modeled to
describe the performance of the device. The repeating unit has
three layers stacked together. The continuous phase enters the
first layer as shown in the schematic in the FIG. 9. The flow
enters the inlet manifold section. The cross-section of the
manifold was 25.4 mm wide.times.5.08 mm depth. The connecting
channel dimensions were 12.7 mm wide.times.2.03 mm depth.times.305
mm length. There were total 16 connecting channels. The rib between
the connecting channels was 1.27 mm. The inlet manifold is
connected to the connecting (process) channels through flow
distribution features. The flow distribution channel dimensions are
shown in FIG. 10. In the connecting channels, the dispersed phase
is added to the continuous phase to form an emulsion. The emulsion
leaves the repeating unit through the outlet manifold as shown in
FIG. 9.
[0103] The second layer of the repeating unit was porous medium.
The porous medium used in this example was Mott Corporation Wicking
structure with Media Grade=0.2. The permeability coefficient
(K.sub.L*) was 140 and the liquid pressure drop through the medium
is given by: Liquid: Pressure Drop, psid=(K.sub.L*)(Flux,
gpm/ft)(Visc, cp)(Thck, in)
[0104] The size of the porous medium was chosen to cover area
occupied by the connecting channels in the first layer. The
thickness of the porous medium was 0.039''. The material
specifications for the porous medium as listed below: [0105]
Material Specifications [0106] Bubble Point, in. of Hg: 5.0-6.9
[0107] Tensile Strength, kpsi: 30.0 [0108] Yield Strength, kpsi:
26.0
[0109] The dispersed phase enters the third layer of the repeating
unit as shown in the FIG. 11. The dispersed phase flow enters into
the inlet manifold. The cross-section of the manifold was 12.7 mm
wide.times.5.08 mm depth. The connecting channel dimensions were
42.42 mm wide.times.1.27 mm depth.times.222.25 mm long. There were
total 7 connecting channels. The rib between the connecting
channels was 1.27 mm. The inlet manifold is connected to the
connecting channels through flow distribution features. The flow
distribution feature dimensions are shown in the FIG. 12. The
schematic of assembly of layers of the repeating unit is shown in
FIG. 13.
[0110] The flow rate of continuous flow rate 1 L/min/connecting
channel while the total flow rate of the dispersed phase was 20% of
the total flow rate of the continuous phase flow rate. The density
and viscosity of continuous phase was 1000 kg/m.sup.3 and 1 cP
respectively. The density and viscosity of dispersed phase was 850
kg/m.sup.3 and 10 cP respectively. The flow uniformity was
estimated in continuous phase connecting channels and dispersed
phase connecting channels at locations 1, 2 and 3 as shown in FIG.
9 and 11 respectively (see FIGS. 14 and 15). The flow distribution
in continuous phase channel was at location 1 was 0.54% while the
flow distribution in dispersed phase channel was at location 1 was
0.03%. Table 1 shows the comparison of performance in flow
distribution with and without flow distribution features
TABLE-US-00001 With flow Without flow Performance parameter
distribution feature distribution feature Dispersed phase flow
0.03% 0.04% distribution quality (%) Continuous phase flow 0.54%
7.3% distribution quality (%) Total pressure drop in 633 psi 605
psi continuous phase (psi) Total pressure drop in 54 psi 4.0 psi
dispersed phase (psi)
[0111] As we can see from the above table, the flow distribution
features do not affect the flow distribution of the dispersed
phase. However the flow distribution features improve the flow
distribution in the continuous channel which will results in
increased uniform emulsion quality. 5 For cases where the changing
viscosity as a function of shear rate of a non-Newtonian fluid is
considered, the flow maldistribution without the use of flow
distribution features is expected to be higher than those described
in this example where a shear rate independent viscosity was
assumed.
EXAMPLE 4
Loss Coefficient in Flow Distribution Channels
[0112] A Computational Fluid Dynamics model was developed in
Fluent.TM. V6.2.16 to simulate a flow distribution feature and
estimate the loss coefficient. The fluid used wasethylene vapor.
The flow rate was varied such that the Reynolds numbers ranged from
laminar to turbulent regimes. The viscosity was assumed to be
constant and uniform inlet flow profile was assumed. The flow
properties are listed in Table 1. Geometry is as shown in FIG. 16.
The cross section of flow distribution feature was 0.38
mm.times.0.38 mm. The overall width of the feature was 3.56 mm and
the smallest distance between two consecutive turns was 1.78 mm.
For turbulent flow model, default k-.epsilon. model in Fluent.TM.
was used.
[0113] This was compared to a literature correlation by Sprenger,
H., Druckverluste in 90 o Krummern fur rechteckrohre, Schweiz.
Bauztg, Vol. 87, no. 13, pp.223-231, 1969.
[0114] It was found that the loss coefficient K decreases as Re is
increased from laminar flow to turbulent and turns to an asymptotic
value 1.41. It was also found that the first turn always has higher
pressure drop (>3.0).
Assumptions and References
[0115] A Computational Fluid Dynamics model was developed in Fluent
V6.2.16 to simulate a flow distribution feature. The viscosity was
assumed to be constant and uniform inlet flow profile was assumed.
Geometry is as shown in FIG. 1. The cross section of flow
distribution feature was 0.015''.times.0.0.015''. The overall width
of the feature was 0.14 mm and the smallest distance between two
consecutive turns was 0.07'': The purpose of the study was to
estimate the static pressure loss in a turn of a flow distribution
feature. Total number of turns defined was 12. The pressure loss
was defined as: .DELTA. .times. .times. P = K loss .times. .rho.
.times. .times. v 2 2 ##EQU3##
[0116] Where k.sub.loss is known as the loss coefficient
TABLE-US-00002 TABLE 1 Properties of the fluid used for CFD model
Ethylene Vapor Density, kg/m.sup.3 33 Viscosity, kg/m-s 9.2E-6
The CFD model was run for different Reynolds number at the inlet.
FIGS. 17-19 are examples of one of the few Reynolds numbers that
were simulated using CFD model using ethylene vapor as the fluid.
FIGS. 17-19 shows the loss coefficient at each turn. The loss
coefficient at the first turn was significantly higher than the
loss coefficient of subsequent turns. This may be attributed to
entrance effect. An average loss coefficient was estimated by
excluding the turns that exhibited entrance effect and simple
averaging the loss coefficient of the remaining turns.
[0117] FIG. 20 shows the average turn loss coefficient as a
function of Reynolds number. As the Reynolds number is increased,
the loss coefficient K.sub.loss decreases. In Reynolds number range
of turbulent flow (defined as in straight tube), K.sub.loss value
approaches an asymptotic number 1.41. This finding can be very
helpful in designing a flow distribution system using flow
distribution features.
EXAMPLE 5
Calculated Flow Distribution in a Large Scale Phase Separation
Device
[0118] Pressure drop in the flow distribution feature (shown in
Example 4) was estimated from a CFD model using Fluent. The
dimensions of the flow distribution feature was same as discussed
in Example 4.
[0119] A schematic of the internal manifold consisted of
sub-manifolds and flow distribution features is shown in FIG. 21.
Every micro-channel is connected to a sub-manifold by a flow
distribution feature. For simplicity, flow distribution features
are represented by straight lines in the figure. The uniformity in
flow distribution is achieved by designing the flow distribution
features appropriately.
[0120] The connecting channel pressure drop was assumed to be an
average pressure drop of 1 psi. Expansion losses from FDF to
connecting channel using conventional sudden expansion correlation
as shown below: .DELTA. .times. .times. P exp = [ ( 1 - A s A l ) 2
- 1 ] .times. G s 2 2 .times. .rho. + G l 2 2 .times. .rho.
##EQU4## The following assumptions were used in the calculations:
only the header is modeled (no footer); Constant outlet
pressure=230 psig; inlet fluid is 75.5% ethylene, 24.5% ethane
gaseous mixture; properties calculated at 245 psig and
-26.8.degree. C.; losses at the inlet of the submanifold; no heat
transfer in manifold section. Assumptions in 1-D model: total 100
microchannels; constant viscosity; density estimated by
curve-fitting density predictions from ChemCAD using SRK
equilibrium correlation as shown in FIG. 22.
[0121] A numerical model was developed to simulate the flow through
the geometry as shown in FIG. 21. The model was based on flow
resistances connected in series and parallel. Total number of
sub-manifolds in the geometry was 5. Each sub-manifold was
connected to 20 microchannels by flow distribution features. The
dimensions and number of sub-manifold were arbitrary chosen to show
that the flow distribution can be controlled by number of the turns
in the flow distribution features. The table below summarizes the
dimensions used in the numerical model. TABLE-US-00003 Geometry
Feature Dimensions Sub-manifolds Sub-manifold 1 20.32 mm .times.
0.381 mm Sub-manifold 2 20.32 mm .times. 0.381 mm Sub-manifold 3
33.02 .times. 0.381 mm Sub-manifold 4 33.02 mm .times. 0.381 mm
Sub-manifold 5 38.1 mm .times. 0.381 mm Flow Distribution Feature
Cross-section 0.76 mm .times. 0.381 mm Number of turns Variable
Microchannel Cross-section 5.08 mm .times. 0.38 mm Length N/A
(Nominal pressure drop of 1 psi was assumed)
[0122] The model was used to estimate number of turns in every flow
distribution feature. FIG. 23 shows the requirement for number of
turns for flow distribution features. The designed number of turns
for flow distribution feature as shown in FIG. 23 gave a Q=4.5% for
microchannel. When the definition of Quality Index Factor was
applied to flow distribution in sub-manifolds, the Q was 2.3%. The
total pressure was estimated to be 5.9 psi. The channel-to-channel
flow rate is shown in FIG. 24.
[0123] Many times due to irregularities in the channel geometry,
for the same flow rate through the microchannel, the channel
pressure drop may vary. The variation in channel pressure drop
would lead to mal-distribution. A study was done to see the effect
of pressure drop variation in the channel on flow distribution. A
.+-.5% variation in the channel pressure drop was applied in the
model. The applied channel pressure drop profile is shown in FIG.
25.
[0124] The Quality Index Factor for microchannel was 6.2% which is
very close to flow distribution without channel pressure drop
variation. The overall pressure drop was 5.8 psi. The Quality Index
Factor for sub-manifold was 4.9%. FIG. 26 shows the mass flow
distribution across the microchannels.
[0125] The model was run for four more random variation of channel
pressure drop with +/-5% variation with average pressure drop of 1
psi. The table below lists the overall Q-factor, sub-manifold
Q-factor and overall pressure drop obtained. TABLE-US-00004 Run
Overall Q- Sub-manifold Q- Overall Pressure No factor (%) factor
(%) drop (psi) 1 6.2% 4.9% 5.8 psi 2 6.2% 4.9% 5.8 psi 3 6.0% 4.9%
5.8 psi 4 6.5% 5.0% 5.8 psi
The example shows the robustness of the flow distribution design
with flow distribution features to pressure variations in the
connecting channels.
EXAMPLE 6
Application of Flow Distribution Feature for Partial Boiling in
Process Channels
[0126] A schematic of the flow distribution geometry is shown in
FIG. 27. The flow enters the main header which is 19.05
mm.times.12.7 mm. From the main manifold, the flow is distributed
into secondary header. The cross-sectional dimension of the
secondary header was 1.78 mm.times.5.08 mm. The total number of
secondary headers was 44. Each secondary header distributes the
flow to three connecting coolant channels through flow distribution
features. For simple representation, flow distribution feature are
shown by straight pathways and are referred as "FDF" in the figure.
The connecting channel dimensions were 2.54 mm.times.0.51
mm.times.190.5 mm. The cross-section of the flow distribution
feature was 0.76 mm.times.0.25 mm.
[0127] The fluid is water. The total volumetric flow rate entering
the main manifold was 2.2 L/min. The temperature of the coolant in
the main header, secondary manifold and flow distribution features
is 228.degree. C. The pressure at the outlet of coolant channels
was such that water at the inlet of coolant channel is at saturated
conditions. On the walls of the coolant channels, a varying heat
flux is applied. In each secondary header, the center coolant
channel, has the heat flux applied to all four walls while the
outlet coolant channels have heat flux applied to only one wall.
Heat flux profile varies linearly from 1.0 W/cm2 (near flow
distribution feature) to 0.25 W/cm2 (near outlet). The heat causes
partial boiling in the coolant channel. Two different types of flow
distribution features were considered as shown in FIG. 28. The flow
distribution feature in FIG. 28(a) was referred as "sharp corner
flow distribution feature and the flow distribution features in
FIG. 28(b) was referred as "round corner flow distribution
features". A CFD was built to determine the loss coefficient as a
function of Reynolds number.
[0128] The loss coefficient correlation for sharp corner flow
distribution feature and round corner flow distribution features as
a function of Reynolds number and width of the flow distribution
feature is shown below: K DP , rounded = ( 0.9115814 + 17.246946
.times. W FDF - 0.00048750521 .times. .times. Re FDF + 5.8078157
.times. 10 - 8 .times. Re FDF 2 ) .times. ( 1 - 8.9274612 .times. W
FDF - 0.00025069524 .times. .times. Re FDF + 2.9785762 .times. 10 -
8 .times. Re FDF 2 ) ##EQU5## K DP , sharp = ( 8.2902919 - 291.3301
.times. W FDF - 0.00088695604 .times. .times. Re FDF + 4705.144
.times. W FDF 2 + 2.894361110 - 8 .times. Re FDF 2 + 0.018871653
.times. W FDF .times. Re FDF ) ##EQU5.2##
[0129] The Table below summarizes the flow distribution performance
without flow distribution feature and with flow distribution
features. TABLE-US-00005 TABLE Flow distribution performance with
partial boiling in the coolant channels Quality Factor (%) Number
of Rounded flow Sharp flow turns in flow distribution distribution
distribution features feature feature <2 16.5% 14.6% 4 10.0%
8.4% 6 7.1% 5.9% 8 5.5% 4.6% 10 4.5% 3.7%
We can see from the table that the addition of flow distribution
features helped improving the flow distribution.
* * * * *