U.S. patent application number 09/997491 was filed with the patent office on 2003-05-22 for fluid flow control freeze/thaw valve for narrow bore capillaries or microfluidic devices.
Invention is credited to Bouvier, Edouard S. P., Dourdeville, Theodore, Gerhardt, Geoff C..
Application Number | 20030094206 09/997491 |
Document ID | / |
Family ID | 25544088 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030094206 |
Kind Code |
A1 |
Gerhardt, Geoff C. ; et
al. |
May 22, 2003 |
FLUID FLOW CONTROL FREEZE/THAW VALVE FOR NARROW BORE CAPILLARIES OR
MICROFLUIDIC DEVICES
Abstract
Methods and devices for the management of fluid flow within
nanoscale analytical systems, comprising a freeze thaw valve having
differing geomentries to constrict a frozen plug within the freeze
thaw segment. The freeze thaw valve is directed to use in
high-pressure analytical systems. The geometry of an inner diameter
of a channel or tube within a freeze thaw segment is configured to
cause constriction of a freeze plug when axial force is applied.
The constriction is used in the flow-path of a freeze thaw valve to
prevent movement of the frozen plug at high pressures to avoid
valve leakage.
Inventors: |
Gerhardt, Geoff C.;
(Milbury, MA) ; Bouvier, Edouard S. P.; (Stow,
MA) ; Dourdeville, Theodore; (Marion, MA) |
Correspondence
Address: |
Anthony J. Janiuk, Esq.
WATERS CORPORATION
34 Maple Street
Milford
MA
01757
US
|
Family ID: |
25544088 |
Appl. No.: |
09/997491 |
Filed: |
November 19, 2001 |
Current U.S.
Class: |
137/828 |
Current CPC
Class: |
G01N 30/20 20130101;
G01N 2030/3038 20130101; G01N 2035/00267 20130101; B01L 2400/0677
20130101; Y10T 137/0391 20150401; G01N 30/6065 20130101; Y10T
137/4643 20150401; Y10T 137/2196 20150401; G01N 30/30 20130101;
B01L 3/502738 20130101; F16L 55/103 20130101; G01N 30/20 20130101;
G01N 30/6004 20130101; G01N 2030/6008 20130101; F16K 13/10
20130101 |
Class at
Publication: |
137/828 |
International
Class: |
F16K 049/00 |
Claims
What is claimed is:
1. A method for managing liquid flow through tubing or channels by
freezing and thawing the liquid within a segment of capillary
tubing or channels comprising the steps of: configuring a
constriction segment of an interior passage of said tubing or
channels to have a constrictive geometry; freezing the constriction
segment to stop the passage of fluids; and thawing the constriction
segment to allow the passage of fluids.
2. The method of claim 1 wherein said interior passage is contained
within a capillary tubing.
3. The method of claim 1 wherein said interior passage is a
micro-channel.
4. The method of claim 1 wherein said liquid flow is under high
pressure greater than 20,000 p.s.i.
5. The method of claim 1 wherein said freezing of said segment is
by the use of carbon dioxide.
6. The method of claim 1 wherein said freezing of said segment is
by the use of a heat pump.
7. The method of claim 1 wherein said constrictive geometry is
tapered.
8. The method of claim 1 wherein said constrictive geometry is
bulbous.
9. The method of claim 1 wherein said constrictive geometry has a
first diameter and a second diameter and said first diameter is
greater than said second diameter.
10. The method of claim 1 wherein said geometry is a degree
bend.
11. An apparatus for managing liquid flow through tubing or
channels by freezing and thawing the liquid within a segment of
capillary tubing or channels comprising: a valve segment having an
interior diameter for fluid flow; a constriction geometry within
said interior diameter; a means for freezing said fluid within said
valve segment forming a frozen plug; wherein said frozen plug stops
fluid flow and is held in place by constrictive forces created by
said constriction geometry; and a means for thawing said fluid
within said valve segment to allow fluid flow.
12. The apparatus of claim 11 wherein said liquid flow is under
high pressure greater than 20,000 p.s.i.
13. The apparatus of claim 11 wherein said means for freezing said
segment is by the use of carbon dioxide.
14. The apparatus of claim 11 wherein said means for freezing said
segment is by the use of a heat pump.
15. The apparatus of claim 11 wherein said geometry is tapered.
16. The apparatus of claim 11 wherein said geometry is bulbous.
17. The apparatus of claim 11 wherein said geometry has a first
diameter and a second diameter and said first diameter is greater
than said second diameter.
18. The apparatus of claim 11 wherein said geometry is a bend.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to a method and apparatus
for controlling liquid flow through nanoscale capillary tubing and
channels, by freezing the liquid or thawing the frozen liquid in a
segment of the tube or channel.
BACKGROUND OF THE INVENTION
[0002] The management of the flow of liquids within small diameter
channels presents challenges as the scale of the channels and
volumes of the liquids are reduced. One significant constraint is
the configuration of traditional valve technology. Nanoliter
volume-scale fluid management is severely negatively affected by
poorly-swept or "dead" volume that is inherent within traditional
valving methods. The method of using a fluid within these nanoscale
capillaries and channels to act as its own on/off valve by freezing
and thawing that liquid is known in the art, see for example U.S.
Pat. Nos. 6,159,744 and 5,795,788. It has been found that the flow
of liquids can be diverted to a further channel or chamber by
merely freezing and thawing the liquid contained within a segment
of tubing or channel. This flow-switching device, that is commonly
referred to as "freeze thaw valving", requires no moving parts and
most importantly contributes substantially no dead volume within
the analytical system.
[0003] Prior art freeze thaw valves rely on the resistance to
shearing motion that is obtained between a resulting frozen plug
and the channel wall to restrict fluid flow during the valve closed
state. While this method of fluid management has been successful in
analytical systems involving low pressure, experience with these
valves at high pressures (e.g. greater than 20,000 p.s.i) reveals
that the frozen plug can be displaced from the valving segment
resulting in low-level flow or leakage. As the frozen plug is
extruded out of the valving segment, new fluid entering the valving
segment is solidified maintaining an incomplete valve closure.
Unfortunately, this low-level leakage is unacceptable when these
freeze thaw valves are used for capillary chromatography and other
nanoscale analytical systems where fluid flow rates as low as a few
nanoliters per minute and high delivery pressures are used.
SUMMARY OF THE INVENTION
[0004] The invention provides methods and devices for the
management of fluid flow within high pressure nanoscale analytical
systems. The device comprises freeze thaw valves implemented by
fluid conduits having differing geometries to restrain the motion
of frozen plugs. The freeze thaw valve contemplated by the
invention is directed to use in high-pressure analytical systems.
The geometry of a fluid conduit within a freeze thaw segment of the
valve is configured to cause constriction of at least a portion of
a freeze plug, when a hydraulic load is applied to the upstream
side of the plug. This geometry is used in the flow path of the
freeze thaw valve segment to prevent movement of the frozen plug at
high pressures to substantially avoid leakage. The configuration of
the freeze thaw segment can be a variety of geometries that cause
the constriction of the freeze plug when a hydraulic load is
applied.
[0005] The fluid conduits contemplated within the invention have
transverse dimensions (normal to the flow axis) on the order of
approximately 2 .mu.m to 500 .mu.m, and more typically 25-100
.mu.m. The pressures within the analytical systems utilizing the
freeze thaw segments contemplated within the invention are on the
order of approximately 20,000 PSIG or greater.
[0006] Means for freezing the liquid phase within the freeze thaw
segment, in an illustrative embodiment, is a finely directed jet of
cooling gas. The cooling gas can be provided from a liquefied
source of gas under pressure, such as liquid carbon dioxide.
Alternative means for freezing the liquid phase, within the freeze
thaw segment, include the use of a cryogenic liquid such as liquid
nitrogen, or a thermoelectric method such as a Peltier-based heat
pump. It is contemplated within the invention, that a warming means
for thawing the frozen plug, within the freeze thaw segment, can be
a directed jet of warm air or other gas, an electrical resistance
heating element, or the ambient air within the analytical
environment. The temperature of the freeze thaw segment may be
monitored by conventional means known to those skilled in the art
such as a thermocouple incorporated into the freeze thaw segment.
Further, the cooling means may be applied continuously during the
time required to maintain the limiting frozen plug and interrupted
by alternative heating means when fluid flow is desired.
[0007] Advantages of the invention include provision of a simple
and low cost mechanism for implementing freeze thaw valving in high
pressure contexts. Migration of the frozen plug and leakage are
substantially avoided. The present invention provides methods and
apparatus for the management of fluid flow within a nanoscale high
pressure analytical system while avoiding introduction of
poorly-swept or dead volumes.
BRIEF DESCRIPTION OF DRAWINGS
[0008] These and other features and advantages of the present
invention will become apparent from the following detailed
description taken in conjunction with the accompanying drawings
which illustrate the exemplary embodiments of the method and
apparatus for freeze thaw valving of the present invention.
[0009] FIGS. 1A, 1B, and 1C depict prior art freeze thaw
valving;
[0010] FIGS. 2A and 2B depict configurations used to constrict a
freeze plug;
[0011] FIG. 3 depicts a porous frit bonded to a capillary wall to
constrict a freeze plug;
[0012] FIG. 4 depicts capillaries having different diameter to
constrict a freeze plug;
[0013] FIG. 5 depicts chemical modification of capillary walls to
impart surface roughness; and
[0014] FIG. 6 depicts a bend in a capillary tube used to constrict
a freeze plug.
DETAILED DESCRIPTION
[0015] In typical freeze thaw valves a resistance to shearing
motion exists between the frozen liquid plug and capillary walls;
that resistance is sufficient to restrict fluid flow. However, this
method of valving has been found to be problematic as pressures are
increased, such as within a high pressure analytical system.
Referring to FIGS. 1A and 1B, a typical freeze thaw valve is
depicted. In the typical freeze thaw valve a solid plug 101 is
formed within a segment of capillary tubing 104 by directing a
refrigerant 103 such as carbon dioxide to a selected segment 102 of
capillary tubing 104 or channel. As shown in FIG. 1B, the frozen
plug 101 is formed causing fluid flow within the selected segment
102 to cease. Turning to FIG. 1C, a high pressure analytical system
(e.g. 20,000 p.s.i or greater) is depicted. Within this high
pressure analytical system, fluid pressure within the capillary
tubing 104 or channel produces an axial force on the frozen plug,
which creates a shear stress at the interface between the formed
frozen plug 101 and capillary wall 105. A sufficiently high applied
fluid pressure will cause the frozen plug 101 to move. The movement
of the frozen plug 101 results in valve leakage. While a subsequent
frozen plug 106 is formed, the movement of the original frozen plug
101 can be problematic for the downstream analysis.
[0016] Turning to FIG. 2A, the interior geometry of a capillary
tubing is changed to provide a freeze thaw valve that not only
relies on the resistance to shearing motion obtained between a
frozen plug 202 and the corresponding capillary walls, but also
uses a region of convergent geometry within the fluid channel to
prevent the frozen plug from moving and causing leakage. A taper
201 is formed within the interior of the capillary to allow
constriction of the frozen plug 202 in the presence of an applied
hydraulic load, preventing failure and migration of the freeze thaw
plug in analytical systems that involve fluid pressures in excess
of 20,000 p.s.i. The altered geometry of the freeze thaw segment is
formed by tapering the internal dimensions of the capillary tubing
or channel to form a convergent region. For example, the capillary
internal diameter can be tapered inwardly approximately one-half
the normal capillary interior diameter over a length of
approximately one times the normal capillary interior diameter
(e.g. for a 100 .mu.m capillary a taper to 50 .mu.m over a length
of 100 .mu.m) in order to facilitate the constriction feature or
mechanism.
[0017] As shown in FIG. 2B, an illustrative alternative embodiment
has a freeze thaw segment 301 having an interior channel 302 with a
geometry that is bulbous in configuration, including a divergent
region followed by a convergent region. As in the above inventive
freeze thaw valves, the geometry of this embodiment imparts, in
addition to the resistance to shearing motion utilized in prior art
valves, constriction forces that allow its use in high pressure
analytical systems. In this embodiment the capillary interior
diameter is increased to approximately one and one-half times the
normal capillary interior diameter over a length of three times the
normal capillary interior diameter to form the constriction
mechanism.
[0018] Turning to FIG. 3, a further illustrative alternative
embodiment is shown. In this alternative embodiment, a porous frit
401 is bonded to a capillary wall 402 forming a freeze thaw valve
segment 403. As in the above inventive freeze thaw valves, the
configuration of this embodiment provides a frozen plug 404 within
the freeze thaw segment with not only a resistance to shearing
motion between the plug and the capillary wall, but also
constriction forces that allow the use of this embodiment in high
pressure analytical systems. In this illustrative embodiment the
frit 401 is formed by polymerizing sodium silicate in situ over a
length of approximately two times the capillary interior diameter.
The frit 401 prepared in this way forms covalent linkages to the
capillary wall thereby maintaining a stationary position. The frit
401 has a pore size of approximately 0.5 .mu.m. Within this porous
frit 401, the fluid pathways or interstitial spaces include
repeated instances where convergent geometry is obtained.
[0019] As shown in FIG. 4, an additional illustrative alternative
embodiment has a freeze thaw segment 501 that has a proximal
capillary 502 having a first interior diameter 504 and a distal
capillary 503 having a second interior diameter 505. The proximal
capillary 502 is joined with the distal capillary 503 forming the
freeze thaw segment 501. The first interior diameter 504 is larger
than the second interior diameter 505. The difference in the
diameter of the first interior and the second interior diameters
imparts to the freeze thaw segment 501 a configuration that allows
a frozen plug 506 to be held in place by not only the resistance to
shearing motion obtained at the interface between the plug and the
capillary wall, but constrictive forces that are caused by the
differing diameters.
[0020] As illustrated in FIG. 5, a further alternative embodiment
provides a freeze thaw segment having changes to its interior
capillary walls 601. Chemical modifications of the interior
capillary wall, by methods known to those skilled in the art, such
as filling a capillary with IN NaOH for approximately 24 hours at
25.degree. C., produces a capillary wall that is rough in texture.
This rough surface allows a frozen plug 602 to be held in place by
not only resistance to shearing motion obtained at the interface
between the plug and the capillary wall, but also constrictive
forces that are created where regions of divergent geometry are
followed by regions of convergent geometry.
[0021] In FIG. 6, yet a further alternative embodiment having a
freeze thaw segment 703 containing a bend 701 in a capillary tubing
702 or channel. This bend 701, within the freeze thaw segment 703,
imparts constrictive forces that allow a frozen plug to be held in
place by not only resistance to shearing motion obtained between
the plug and the capillary wall, but also constrictive forces that
are caused by the non-linear shape of the freeze thaw segment
703.
[0022] The freeze thaw valves according to the invention can be
manufactured by methods known to those skilled in the art.
Capillary or channel composition will be a function of structural
requirements, manufacturing processes, and reagent
compatibility/chemical resistance properties. The choice of
materials will depend on a number of factors such as ease in
manufacturing and inertness to fluids that will flow through the
nanoscale channels or capillary tubing, as is known to those
skilled in the art. Specifically, capillary tubing and channels are
provided that are made from inorganic crystalline or amorphous
materials, e.g. silicon, silica, quartz, inert metals, or from
organic materials such as plastics, for example, poly(methyl
methacrylate) (PMMA), acetonitrile-butadiene-styrene (ABS),
polycarbonate, polyethylene, polystyrene, polyolefins,
polypropylene, polyphenylene sulphide (PPS), PEEK, and metallocene.
Capillary tubing and channels according to the invention can be
fabricated from thermoplastics such as polyethylene, polypropylene,
methylmethacrylates, polycarbonates, and certain Teflons, among
others, due to their ease of molding, stamping and milling.
Alternatively, capillary tubing and channels can be made of silica,
glass, quartz or inert metal.
[0023] Although the present disclosure is described in detail with
respect to chromatographic applications and specifically capillary
chromatography where flow rates as low as 5 nanoliters per minute
are used, it is contemplated that embodiments of the present
invention can also be directed to industrial and process control
applications as well.
[0024] Although the inventive freeze thaw valve is discussed in
terms of nanoscale applications, it should be appreciated that the
configurations disclosed herein can be adapted to much larger scale
channels or tubes where liquids under high pressure are used.
Although specific geometries have been set forth in the above
illustrative embodiments, it should be appreciated that the
configurations disclosed herein are not an exhaustive illustration
of geometries or configurations that can be used. It should be
further appreciated that any of various configuration that impart
compressive or constrictive forces to a freeze plug within a freeze
thaw segment, in the presence of an applied hydraulic load, can be
utilized.
[0025] Various other changes, omissions and additions in the form
and detail of the present invention may be made therein without
departing from the spirit and scope of the invention. Therefore,
the above description should not be construed as limiting, but
merely as exemplification of the various embodiments.
* * * * *