Note: Descriptions are shown in the official language in which they were submitted.
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
APPARATUS AND METHOD FOR TRANSFERRING A CRYOGENIC FLUID
SPECIFICATION
BACKGROUND OF THE INVENTION
In many cryogenic fluid transfer applications, it is important that the fluid
be
transferred in a 100% liquid state, or as close to 100% as possible.
Conventionally, this.
required the fluid to be initially phase-separated and/or subcooled in a heat
exchanger
and/or vacuum jacketing the line to keep it well insulated. Otherwise, the
heat leak in the
transfer line would cause boil-off, thereby causing flow undulations in the
transfer line
and resulting in a non-steady, pulsing and generally undesirable flow. Heat
leak is
particularly a problem for long transfer lines.
The present invention addresses this first concern for cryogenic transfer
lines with
a coaxial or "tube-in-tube" geometry where a first portion of the cryogenic
fluid flows
through the inner tube while a second portion flows through an annulus between
the
inner tube and outer tube which annulus is at a lower pressure than the inside
tube. By
virtue of this pressure differential, one skilled in the art can appreciate
that the liquid in
the annulus can provide a refrigeration duty to the liquid inside the inner
tube (e.g. such
as by boiling) such that this inner liquid is cooled and stays a saturated
liquid.
Preferably, the liquid is even subcooled slightly such that a "cushion" of
refrigeration is
available to fight heat leak.
It is also important in many cryogenic fluid transfer applications that the
transfer
line be lightweight and flexible. This provides for maximum degrees of freedom
during
installation, operation and maintenance and also enables the line to withstand
repeated
bending. The present invention addresses this second concern for cryogenic
transfer
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
2
lines by making at least a portion of the line out of a flexible material (for
example a
polymeric material).
The prior art does not provide for a cryogenic fluid transfer line that
addresses
both of these important concerns.
U.S. Pat. No. 3,696,627 (Longsworth) teaches a liquid cryogen transfer system
having a rigid coaxial piping arrangement for subcooling and stabilizing
cryogen flow
during transfer. U.S. Pat. Nos. 4,296,610 (Davis), 4,336,689 (Davis),
4,715,187
(Stearns) and 5,477, 691 (White) teach similar systems.
Chang et al. teaches non-metallic, flexible cryogenic transfer lines for use
in
cryosurgical systems where the cryogen is used to cool the cryoprobe in a
cryosurgical
system ("Development of a High-Performance Multiprobe Cryosurgical Device",
Biomedical Instrumentation and Technology, Sept./Oct. 1994, pp. 383 -390). Due
to the
heat leak boil-off resulting from the design of the flexible lines in Chang,
combined with
intrinsically poor insulation, such lines must be short and fed with a
substantially
subcooled cryogenic liquid (e.g. liquid nitrogen at -214 °C) in order
to work properly.
This requires the up-stream usage of complex and expensive cryogenic storage,
supply
and control systems.
Cryogenic transfer lines are also taught for use in machining applications
where
the cryogen is used to cool the interface of the cutting tool and the
workpiece. See for
example U.S. Pat. Nos. 2,635,399 (West), 5,103,701 (Lundin), 5,509,335
(Emerson),
5,592,863 (Jaskowiak), 5,761,974 (Wagner) and 5,901,623 (Hong). Similar to
Chang,
such lines must be short and fed with a substantially subcooled cryogenic
liquid to
combat heat leak boil-off and thus requires an expensive up-stream subcooling
system.
U.S. Pat. No. 3,433,028 (Klee) discloses a coaxial system for conveying
cryogenic fluids over substantial distances in pure single phase. Using fixed-
size, inlet
orifices in the cryogenic-conveying inner line, the liquid is admitted to the
outer line
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
3
where it vaporizes when subject to an external heat leak. A thermal sensor-
based flow
control unit, mounted at the exit end of this coaxial line, chokes the flow of
the vapor in
the outer line depending on the value of temperature required, usually 50 to
100 deg. F
more than the boiling point of the liquid in the inner line. As a result, the
outer line
pressure may be near the cryogenic source pressure, and its vapor always will
be
warmer than the inner line liquid. Moreover, high heat leaks cannot be fully
countered
since the amount of liquid admitted to the outer line for evaporation is
permanently
limited by the fixed-size inlet orifices. These operating principles
necessitate the use of
high-pressure resistant, non-flexing metal tubes and a thick-wall thermal
insulation in the
construction of the line.
JP 06210105 A teaches a polymeric coaxial transfer line for non-cryogenic
degassing applications. The tube material characteristics preclude the use of
the
transfer line in cryogenic applications.
BRIEF SUMMARY OF THE INVENTION
The present invention is a method and apparatus for transferring a cryogenic
fluid. A polymeric, coaxial transfer line is utilized where a first portion of
the cryogenic
fluid flows through an inner conduit while a second portion flows through the
annulus
between the inner conduit and outer conduit which annulus is at a lower
pressure than
the inside conduit. In one embodiment, the inner conduit is substantially non-
porous and
the transfer line is preceded by a flow control means to distribute at least
part of the first
and second portions of the cryogenic fluid to the inner conduit and annulus
respectively.
In a second embodiment, a least a portion of the inner conduit is porous with
respect to
both gas permeation and liquid permeation such that both a gaseous part and a
liquid
part of the first portion permeates into the annulus to form at least a part
of the second
portion.
CA 02428777 2005-11-15
3a
The invention thus provides according to an aspect, for a transfer line for
transferring a cryogenic fluid comprising an inner conduit surrounded by an
outer
conduit wherein (a) a first portion of the cryogenic fluid flows through the
inner
conduit while a second portion flows through an annulus between the inner
conduit
and the outer conduit; (b) the first portion is at a higher pressure than the
second
portion by virtue of a means which maintains the pressure in the inner conduit
higher
than the annulus; (c) at least a portion of the transfer line is made of a
flexible
material; and (d) at least a fraction of the second portion of fluid inside
the annulus is
liquid that provides a refrigeration duty to the first portion of fluid inside
the inner
conduit.
According to another aspect, the invention provides for a method for transfer-
ring a cryogenic fluid utilizing a transfer line which comprises an inner
conduit sur-
rounded by an outer conduit. The method comprises flowing a first portion of
the
cryogenic fluid flows through the inner conduit while flowing a second portion
through an annulus between the inner conduit and the outer conduit wherein (a)
the
first portion is at a higher pressure than the second portion; (b) at least a
portion of
the transfer line is made of a flexible, polymeric material; and (c) at least
a fraction of
the second portion of fluid inside the annulus is liquid that provides a
refrigeration
duty to the first portion of fluid inside the inner conduit.
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
4
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
Figure 1 is a schematic drawing of one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention's polymeric, coaxial transfer line is best illustrated
with
respect to a general embodiment thereof such as Figure 1's embodiment where
the
transfer line 22 is preceded by a flow control box 20. Transfer line 22
comprises an
inner tube 72 surrounded by an outer tube 74 surrounded by insulation 70
surrounded by
flexible protective casing 68. A first portion of the cryogenic fluid flows
through the inner
tube while a second portion flows through the annulus between the inner tube
and outer
tube. The first portion is at a higher pressure than the second portion.
At least a portion of the transfer line is made of a flexible material, for
example a
polymeric material. In one possible embodiment, substantially all of the inner
tube and
substantially all of the outer tube are made of a flexible, polymeric
material. In another
possible embodiment, substantially all of the outer tube can be made of a
flexible
polymeric material while substantially all of the inner tube can be made of a
flexible non-
polymeric material that do not become brittle at cryogenic temperatures such
as (i)
copper and its alloys, (ii) aluminum and its alloys, (iii) nickel and its
alloys, (iv) austenitic
stainless steels, (v) dense graphite or (vi) ceramic fiber textile-woven
tubing products. In
another possible embodiment, substantially all of the inner tube and
substantially all of
the outer tube are made of a flexible non-polymeric material selected from the
group
consisting of (i) copper and its alloys, (ii) aluminum and its alloys, (iii)
nickel and its
alloys, (iv) austenitic stainless steels, (v) dense graphite or (vi) ceramic
fiber textile-
woven tubing products. In yet another embodiment, substantially all of the
outer tube
can be made of a flexible insulating material. In still another embodiment,
instead of
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
being tubes, the inner and/or outer conduits could have cross sections that
are
substantially in the shape of a rectangle, polygon, oval or other regularly
shaped
geometric figure.
The inner tube can be substantially non-porous such that little, if any, of
the
5 second portion of the fluid in the annulus is a result of permeation through
the inner tube
Or, at least a portion of the inner tube can have holes drilled into it and/or
be porous with
respect to both gas permeation and liquid permeation such that both a gaseous
part and
a liquid part of the first portion permeates into the annulus to form at least
a part of the
second portion. Or, certain sections of the inner tube, perhaps spaced equally
along
the length of the inner tube, could be of enhanced porosity.
The transfer line is advantageously preceded by a flow control means to
distribute at least part of the first and second portions of the cryogenic
fluid to the inner
tube and annulus respectively such as flow control box 20 in Figure 1. The
flow control
means would also typically integrate the means (e.g. valve) to reduce the
pressure of the
second portion of fluid that is distributed to the annulus, at least a
fraction of which
second portion of fluid is distributed into the annulus as a liquid. By virtue
of this
pressure differential, the liquid in the annulus can provide a refrigeration
duty to the fluid
inside the inner tube. In the case of an at least partially porous inner tube,
the
permeation from the inner tube into fihe annulus gas can supplement at least a
portion of
the fluid distribution performed by the flow control box. The connections and
internal
components of the flow control box include three onloff (e.g. solenoid) valves
(61, 62,
63) and a manual metering valve 64, which valves are in fluid communication
with the
inlet 30 to the flow control box and adapted to receive and pressure regulate
a flow of the
cryogenic fluid. A key internal component of flow control box 20 is 3-way
coupling 66
which introduces the first and second portions of the cryogenic fluid to the
inner tube and
annulus respectively. Thread connection 78 connects the 3-way coupling 66 to
the outer
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
6
tube 74. An optional line clamp 76 may be used to clamp the outer tube to the
thread
connection. Flow control box 20 has an insulated casing and optionally
contains
insulating filler. Pressure relief valve 84 is optional. On/off valves 62 and
63 have an
internal bypass orifice (86, 88) drilled in their internal wall or valve seat.
At least a fraction of the second portion of fluid in the annulus can be
transferred
to the transfer destination and/or cooling target along with the liquid stream
in the inner
tube. Optionally, at least a fraction of the second portion of fluid in the
annulus can be
vented away from the transfer destination/cooling target. In the former case,
this can be
accomplished via the use of a coaxial nozzle having an inner conduit in fluid
communication with the inner tube of the transfer line and an outer conduit in
fluid
communication with the annulus of the transfer line. In the latter case where
all of the
annulus fluid is vented, this would remove the constraint that the flow
direction in the
annulus be concurrent with the flow direction in the inner tube. Preferably,
any nozzle
should include thermal shrink connectors to prevent leaks between the
interface of the
transfer line and nozzle.
Examples of suitable polymeric materials for the present invention's transfer
line
include carbon based polymers, carbon-fluorine based polymers, co-polymers and
composites thereof such as TefIonT"' products. (TefIonTM is a registered
trademark of E.I.
DuPont de Nemours and Company).
Examples of cryogenic fluids that can be transferred by the present
invention's
transfer line include nitrogen, argon or mixtures thereof.
The present invention's apparatus and method for transferring a cryogenic
fluid is
particularly suitable for transfer locations and/or cooling targets that
require a relatively
low flow rate and a rapid liquid response. Examples of such transfer
destinations and/or
cooling targets for the present invention's transfer line include:
CA 02428777 2003-05-13
WO 02/40915 PCT/USO1/47516
7
(i) an environmental test chamber used for stress screening electronic
components;
(ii) a component to be shrink fitted;
(iii) a specimen holding container used in for biological storage;
(iv) a nitrogen droplet dispenser;
(v) a cutting tool and/or workpiece in a machining application; and
(vi) a cryoprobe in a cryosurgical system.
