U.S. patent number 3,717,201 [Application Number 05/139,057] was granted by the patent office on 1973-02-20 for cryogenic thermal switch.
This patent grant is currently assigned to Cryogenic Technology, Inc.. Invention is credited to Thomas P. Hosmer, John F. Peterson.
United States Patent |
3,717,201 |
Hosmer , et al. |
February 20, 1973 |
CRYOGENIC THERMAL SWITCH
Abstract
A thermal switch for linking a source of cryogenic refrigeration
to a load. A copper plunger operating in a pressurized helium
atmosphere provides a thermal link between a heavy-walled copper
heat station cooled by a refrigeration source and one or more
successive thick walled copper heat stations thermally separated by
thin-walled stainless steel sections. Movement of the plunger can
be used to control the temperature of the successive heat stations
and the load associated with them. The thermal switch and its
linear driving mechanism may be located within different physical
environments and the switch itself is adapted to cross barriers
defining different physical environments.
Inventors: |
Hosmer; Thomas P. (Concord,
MA), Peterson; John F. (Lynnfield, MA) |
Assignee: |
Cryogenic Technology, Inc.
(Waltham, MA)
|
Family
ID: |
22484919 |
Appl.
No.: |
05/139,057 |
Filed: |
April 30, 1971 |
Current U.S.
Class: |
165/96; 62/383;
165/DIG.133; 165/287 |
Current CPC
Class: |
F25D
3/10 (20130101); F02G 1/0445 (20130101); F25B
9/14 (20130101); F25D 19/006 (20130101); Y10S
165/133 (20130101) |
Current International
Class: |
F25D
19/00 (20060101); F25D 3/10 (20060101); F02G
1/00 (20060101); F02G 1/044 (20060101); F25B
9/14 (20060101); F28f 027/00 () |
Field of
Search: |
;62/383 ;165/32,96 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Broome; Harold
Claims
We claim:
1. A thermal switch adapted to effect a thermal linkage between a
source of refrigeration and a thermal load, comprising in
combination
a. a fluid-tight cylindrical housing, the wall of which is
alternately formed of relatively thick-walled sections of a first
material having relatively high thermal conductivity and high heat
capacity at cryogenic temperatures and of relatively thin-walled
sections of a second material having relatively low thermal
conductivity and low heat capacity at cryogenic temperatures, said
housing terminating with one of said thick-walled sections sealed
with an end member of said first material;
b. a plunger free from any permanent connection with said housing
and movable within said housing, said plunger being formed of a
material having relatively high thermal conductivity and high heat
capacity at cryogenic temperatures, and defining with the wall of
said housing a narrow annular spacing;
c. helium filling the void volume within said housing;
d. means to move said plunger connected to said plunger and
including means external of said housing which are adapted to
effect the movement of said plunger within said housing;
e. thermal connection means adapted to thermally link a source of
refrigeration with that thick-walled section most remote from said
thick-walled section sealed with an end member.
2. A thermal switch in accordance with claim 1 wherein said first
material is copper and said second material is stainless steel.
3. A thermal switch in accordance with claim 1 wherein said plunger
is formed of copper.
4. A thermal switch in accordance with claim 1 wherein there are at
least three of said thick-walled sections, the sections between
said thick-walled section sealed with an end member and said
thick-walled section most remote therefrom having means adapted to
thermally link them to refrigeration loads.
5. A thermal switch in accordance with claim 1 wherein said means
to move said plunger comprises, in combination
1. bellows means affixed to said housing means and forming a part
thereof,
2. driving rod means attached to said plunger and in axial
alignment therewith located within said housing means, and
3. means external of said housing for effecting linear motion of
said driving rod means and of compressing and extending said
bellows means.
6. A thermal switch in accordance with claim 5 wherein said means
for effecting linear motion of said driving rod means comprises, in
combination
1. a calibrated barrel surrounding said bellows means,
2. a rotatable operating knob adapted for linear motion along said
barrel, and
3. mechanical linking means connecting said knob with said driving
rod and said bellows and including means to prevent twisting of
said bellows as said operating knob is rotated.
7. A thermal switch in accordance with claim 1 wherein said means
to move said plunger comprises, in combination
1. rack means affixed to one end of said plunger,
2. pinion means engageable with said rack means, and
3. means to rotate said pinion.
8. A thermal switch in accordance with claim 1 wherein there are
two thick-walled sections of said housing and said means to move
said plunger comprises, in combination
1. a nonmagnetic sheath tube forming an extension of said
housing,
2. first and second coil means adapted to generate first and second
magnetic fields, said coils means surrounding said sheath tube and
being separated by a spacing essentially equal to the thin-walled
section of said housing separating said thick-walled sections,
3. a driving rod attached to and in axial alignment with said
plunger,
4. a magnetic mass attached to said driving rod, and
5. means to selectively energize either said first or second coil
means to position said magnetic mass in said first or second
magnetic field and thereby to position said plunger within one or
the other of said thick-walled sections.
9. A thermal switch in accordance with claim 1 wherein said thermal
connection means comprises a copper plate thermally bonded to said
thick-walled section and means adapted to form a thermal bond
between said plate and the heat station of a source of
refrigeration.
10. A thermal switch in accordance with claim 1 wherein said
thermal connection means comprises a copper strap bent to be
thermally bonded around a portion of the outer wall of said
thickwalled section and adapted for attachment to the heat station
of a refrigeration source.
11. A thermal switch in accordance with claim 1 wherein said
thermal connection is a copper block configured on one surface to
form a thermal bond with a portion of the outer wall of said
thick-walled section and adapted to be contacted on another surface
by a liquid cryogen.
Description
This invention relates to thermal switches and more particularly to
devices designed to controllably connect and disconnect one or more
thermal loads to a source of refrigeration.
In the use of cryogenic refrigeration to cool such thermal loads as
cryopumping panels, detecting devices such as ir detectors, and
specimens to be examined in one manner or another, it is sometimes
necessary to be able to effect rapid cooldown of such loads.
Because cryogenic refrigeration devices require a relatively long
cooldown time, it is desirable to have the cryogenic refrigeration
continuously available and to use a flow path or thermal switching
means which may be controllably connected to the load for rapid
cooling and precise temperature control. Such thermal switching
means should be able to control the flow of thermal energy between
two bodies at different temperatures and/or to vary the temperature
of the refrigeration load. When the switch is completely engaged it
should be of a kind which maintains a minimum temperature
difference between the refrigeration source and thermal load; and
when it is completely disengaged to break the thermal link between
the load and refrigeration source it should be designed so that no
drain of thermal energy is impressed on the refrigeration source
other than the minimal leak to its surroundings.
The thermal switch of this invention comprises a fluidtight
cylindrical housing, the wall of which is alternately formed of
relatively thick copper sections (or other high heat conductivity,
high heat capacity material) and relatively thin stainless steel
sections (or other low heat conductivity, low heat capacity
material). A plunger of copper is moved within the fluidtight
cylinder to serve as a thermal link between the thick-walled copper
sections. Helium fills the void volume within the housing, and
means are provided to move the plunger and to thermally connect one
of the thick copper sections to a refrigeration source and the
remaining copper section or sections to thermal loads.
It is therefore a primary object of this invention to provide an
improved thermal switch capable of providing a controllable heat
flow path between a refrigeration source and one or more thermal
loads. It is another object to provide a switch of the character
described which can be manipulated accurately to control and vary
the temperature of one or more thermal loads. It is yet another
object of this invention to provide an improved thermal switch
which can be engaged to deliver refrigeration from a continuous
source to a load to effect rapid cooling of the load. It is still
another object to provide a thermal switch which is of a design
which makes it easy to cross physical barriers separating two
different physical states such as two chambers maintained at two
different pressure levels. Other objects of the invention will in
part be obvious and will in part be apparent hereinafter.
The invention accordingly comprises the features of construction,
combinations of elements, and arrangements of parts which will be
exemplified in the constructions hereinafter set forth, and the
scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the
invention, reference should be had to the following detailed
description taken in connection with the accompanying drawings in
which
FIG. 1 is a longitudinal cross section of one embodiment of the
switch of this invention which is thermally linked to a cryogenic
refrigerator;
FIG. 2 is a cross section of the switch of FIG. 1, taken along line
2--2 of FIG. 1, showing one means by which the switch may be
thermally linked to the refrigerator;
FIG. 3 is a longitudinal cross section of a portion of another
embodiment of the switch of this invention designed to be thermally
linked to two separate and distinct thermal loads;
FIG. 4 is a cross section of the switch of FIG. 3, taken along line
4--4 of FIG. 3, showing another means by which the switch may be
thermally linked to a refrigerator;
FIG. 5 is a longitudinal cross section of yet another embodiment of
the switch of this invention which is thermally linked to a
reservoir of cryogenic fluid serving as the source of
refrigeration;
FIG. 6 is a cross section of the switch of FIG. 5, taken along line
6--6 of FIG. 5, showing a means by which the switch may be
thermally linked to the fluid reservoir; and
FIG. 7 illustrates, partly in cross section, a switch of this
invention having magnetic means to turn it on and off.
The thermal switch illustrated in FIGS. 1 and 2 is suitable for
connecting a thermal load to a cryogenic refrigerator in a manner
to be able to accurately vary and control the temperature of the
load. Such a load may typically be an ir detector or a sample to be
physically examined, e.g., to have its ir absorption determined. In
the following description those parts of the apparatus which are
formed of a metal which exhibits relatively high thermal
conductivity and relatively high heat capacity at cryogenic
temperatures will, for convenience, be referred to as copper.
However, it is meant to include any metal which possesses these
desired characteristics including, but not limited to, silver and
aluminum. Likewise those parts of the apparatus which are formed of
a metal which exhibits low thermal conductivity and low heat
capacity while retaining sufficient structural strength will be
referred to as stainless steel; but it is meant to include any
metal which possesses these desired characteristics including, but
not limited to, beryllium copper, constantan, silicon bronze and
alloys of iron and nickel.
The thermal switch of FIG. 1 is formed of a cylindrical housing
member 10 fluid-tightly sealed on the refrigeration delivery ends
by means of a copper cap 11 which in itself may form a heat station
to which the load to be refrigerated is thermally bonded. The term
"heat station" is used hereinafter to designate a high heat
conductivity mass which connects a refrigeration source such as an
expanding fluid or evaporating cryogen to some object to be
refrigerated or to an auxiliary refrigeration transfer means such
as a heat transfer path to a Joule-Thomson loop or a thermal link
to some refrigeration load.
The cylindrical housing 10 is fluid-tightly sealed within the
linear moving mechanism generally indicated at 14 and described in
detail below. The cylindrical housing is formed of a thin-walled
stainless steel section 15 which extends into linear moving
mechanism 14, a first thick-walled copper section 16 which is
thermally linked to the refrigeration source, another thin-walled
stainless steel section 17 and a second thick-walled copper section
18 which is sealed by copper cap 11. A solid copper plunger 19,
mounted on a rod 20 formed of a low conductivity material such as
stainless steel, micarta or polytetrafluoroethylene, is positioned
for movement within chamber 21 defined within the fluid-tight
cylindrical housing. The void volume of chamber 21 is filled with
helium, preferably above one atmosphere, e.g., up to about 5
atmospheres. It is preferable that the annular spacing 22 between
the plunger 29 and inner wall of the housing be kept at a minimum,
e.g., about 0.0002 inch, at least for the thick-walled copper
sections. In such an arrangement, thick-walled copper section 16
and thick-walled copper section 18 along with cap 11 are heat
stations.
The refrigeration source, partially shown in FIG. 1, is a staged
cryogenic refrigerator 23 having a heat station 24 associated with
its coldest end. Such a refrigerator is described in U.S. Pat. No.
2,966,035 and a preferred type of heat station is described in a
copending application Ser. No. 807,606 filed Mar. 17, 1969, in the
names of Fred F. Chellis and James A. O'and assigned to the same
assignee as the present application. It is, of course, within the
scope of this invention to use other types of cryogenic apparatus
such as that described, for example, in U.S. Pat. Nos. 2,906,101,
2,657,553, and 1,275,507. It is also within the scope of this
invention to use a circulating fluid cryogen as the source of
refrigeration as illustrated in FIGS. 5 and 6. A copper disk 25 is
thermally bonded to the end of heat station 24 which is cooled by
the fluid within a refrigeration chamber surrounded by the heat
station. A copper plate 26 is thermally bonded to the first
thick-walled copper section 16 of the cylindrical housing and the
copper disk 25 and plate 26 are thermally bonded to each other
through an indium shim 27 under the force of screw 28. This
provides the final thermal link between the refrigerator and the
thermal switch.
Although the housing 10, plunger 19 and rod 20 are referred to as
"cylindrical" and shown to be circular in cross section in the
drawings, the term "cylindrical" is to be understood as being used
in its broadest sense to encompass housings and rods of any
suitable cross section including, but not limited to, oval,
triangular, square and polygonal.
The thermal switch of FIG. 1 is designed to attain variable and
accurately controlled temperature of the load associated with cap
11 serving in the role of a heat station. This, in turn, requires a
accurately controllable linear moving mechanism, that shown in FIG.
1 representing one example of such a mechanism. It is necessary to
move rod 20 up and down and to be able to determine the position of
plunger 19 and relate its position to a predetermined load
temperature for any one switch and refrigeration source. Rod 20
(typically of Micarta) is attached through an aligning member 30 to
a stainless steel driving rod 31 which is encased partially in
housing section 15 and partially in a bellows 32. The bellows 32
are fluid-tightly sealed to an upper cylindrical block 33, through
which driving rod 31 moves, and to a lower cylindrical block 34.
(It will be appreciated that "upper" and "lower" as used in
describing the components of this switch are merely relative and
are employed for convenience in describing the particular
orientation illustrated in the drawings. The switch of this
invention may be oriented in any desired manner.) Block 33 is
affixed to a threaded collar 35 to form a pressure-tight seal, and
collar 35 is in turn welded to the bottom end of the stainless
steel section 15. Collar 35 is adapted to have a sealing means such
as O-ring 36 associated with it to make a seal with an apertured
mounting member 37 such as a barrier which can isolate the volume
in which the switch itself is located from the volume in which the
linear moving mechanism 14 may be located. The lower block 34 is
fastened to a rod 38 which has a keyway 39 engageable by a pin 40
mounted in a ring 41 which in turn is affixed to the main barrel 42
of the linear moving mechanism. This main barrel 42 may contain
calibrations such as external line markings 43 for position
read-out in .degree.K, similar to a micrometer. Driving rod 31 is
advanced or withdrawn by turning operating knob 44 which is
threaded along its internal wall to engage threads in the bottom
section 45 of the main barrel 42. A pivot block 46, located within
the knob 44 against ring 47 and affixed to rod 38, permits rotation
of knob 44 while the pin and keyway system prevents rotation or
twisting of bellows 32. An end member 48 provides a cover for the
operating knob 44 and serves to retain pivot block 46 by clamping
it against ring 47. The fluid-tight domain which is filled with
helium ends with the chamber 49 defined within the bellows.
In the operation of the thermal switch of FIGS. 1 and 2, the copper
plunger 19 is moved within the housing to control the amount of
refrigeration delivered to, and hence the temperature of, a thermal
load associated with cap 11. If no refrigeration is to be delivered
to such a load, then copper plunger 19 is withdrawn, by turning
knob 44, preferably to a position such that the top of plunger 19
is essentially on the same level as the top of the thick-walled
copper section 16 connected to the refrigerator. During those times
when no refrigeration is delivered to a load the top of the plunger
19 may occupy a position anywhere between this preferred position
and just below the lower level of the next thick-walled copper
section 18. However, as the copper plunger approaches the lower
level of the thick-walled copper section 18 some cooling of this
wall section will be effected. The purpose of the helium gas is to
provide conduction across the narrow annular gap 22 between plunger
19 and the copper heat stations 16 and 18. Thus when the switch is
disengaged, the distance between plunger 19 and copper wall section
18 is wide, conduction is poor and essentially no refrigeration is
delivered to cap 11 and to a thermal load associated with it. When
refrigeration of the cap and its associated thermal load is desired
the knob 44 is turned to advance copper plunger 19 into the
thick-walled section 18. When plunger 19 enters the thick-walled
section 18 to define the narrow gap 22 between the outer surface of
plunger 19 and the inner wall of section 18, the length of gap 22
determines the temperature of cap 11 and its associated load. The
further the plunger is moved upwardly to lenghten this gap, the
lower is the temperature of cap 11. Minimum temperature is reached
when plunger 19 contacts cap 11. The position of knob 44 relative
to the calibrated lines 43 on barrel 42 may therefore be calibrated
for any one refrigeration source-switch combination to read
directly in .degree.K of stabilized load temperature. As an example
of the performance of the thermal switch of FIGS. 1 and 2, if the
fluid in the refrigeration chamber in refrigerator 23 which is used
to cool heat station 24 is at 20.degree.K, then it is possible to
cool a one-watt load thermally linked to cap 11 to 22.degree.K.
Depending upon the load and the refrigeration source it is possible
to achieve cooling over a range from about 15.degree.K to
200.degree.K.
The thermal switch of this invention is readily adaptable for use
within two different physical domains since it can be installed to
intersect a barrier between such domains in addition to barrier 37
which separates the switch from the linear drive mechanism 14. The
switch can be mounted so that the barrier is intersected by the
thin-walled stainless steel section 17 which can be further
thermally insulated from the barrier if desired. As an example, a
portion of the switch along with the refrigeration source may be
located within an evacuated chamber while the remaining portion of
the switch and its associated thermal load may be located in a
controlled atmosphere, the pressure of which may be greater or less
than that of the chamber in which the refrigerator is located.
FIGS. 3 and 4, in which like reference numerals are used to refer
to identical components of FIGS. 1 and 2, show a thermal switch
adapted to refrigerate two separate loads and a modification of the
means by which a heat station of a refrigerator may be thermally
linked to the switch. The housing 10 of the thermal switch of FIG.
3 is constructed to have an additional thin-walled stainless steel
section 51 and an additional thickwalled copper section 52 between
copper section 16 to which the refrigerator is linked and copper
section 18 which is linked to the load. The thick-walled copper
section 52 may be thermally linked to a load, for example the
thin-walled, high-surface area ring 53. Exemplary of the use of the
thermal switch of FIG. 3 is the cooling of an ir detector. The
thin, high-surface ring 53 may serve as a cryopumping surface to
condense and adsorb moisture from the environment in which the
detector is located prior to the cooling of the detector itself
which would be mounted for cooling on cap 11. The copper plunger
is, in such an instance, moved first so that its top is at
essentially the same level as the top of the thick-walled section
52. By maintaining the clearance passage 54 between the outer wall
of the plunger 19 and the inner wall of thick-walled section 52 at
a minimum, e.g., about 0.0002 inch, heat transfer may be effected
across the helium within this clearance passage. Therefore, as
plunger 19 is moved upwardly to enter that portion of chamber 21
defined by wall section 52, refrigeration is delivered to wall
section 52 and hence to load ring 53. As the plunger is moved
upwardly, the ring 53 becomes colder, finally reaching a
temperature only a few degrees higher than heat station 24.
Continuing the example of cooling an ir detector, after the ring 53
has been cooled for a time sufficient to condense and adsorb the
moisture in the atmosphere surrounding the detector, the plunger is
moved upwardly again into the thick-walled section 18 and into
contact with the inner surface of cap 11, if desired, to obtain a
predetermined temperature of the detector which is cooled and
remains free of any condensed moisture.
The thermal switch of FIGS. 3 and 4 is linked to the heat station
24 of the refrigerator by means of a flexible copper strap 55 which
is fastened to copper disk 25 by means of a screw 56 or the like
and is curved around the outer surface of thick-walled section 16
to make thermal contact with it. It will be appreciated that the
thermal linking systems shown in FIGS. 2 and 4 are readily
interchangeable.
In the modification of the thermal switch of this invention shown
in FIGS. 5 and 6, a liquid cryogen is used as the source of
refrigeration, a different driving system is used to move the
copper plunger and the housing is modified. The basic concept of
the switch and its operation are however the same as that for the
switches of FIGS. 1-4. In the thermal switch of FIGS. 5 and 6, the
cylindrical housing 65 is formed of a plurality of sections,
designated from right to left as a rack housing 66, a T-joint
section 67 providing communication with another cylinder to be
described, a thin-walled stainless steel section 68, a thick-walled
copper section 69, a second thin-walled stainless steel section 70,
and a second thick-walled copper section 71 terminating in a solid
copper plug 72. The copper plunger 19 is attached to a rack 73,
preferably formed of a material exhibiting low thermal conductivity
and having a low heat capacity. The width of the narrow annular
spacing 74 between the plunger and the internal wall of the housing
remains constant throughout in this embodiment.
A second fluid-tight cylinder 75 is connected with cylinder 65
through a fluid-tight T-joint 76. This cylinder 75 is formed of a
tubing 77 which in turn is connected to a heavy tubing member 78. A
pinion rod 79 connects pinion 80 with a hand-actuated knob 81 and
it is encased in a rod casing 82 which, through sealing means not
shown, makes a fluid-tight seal with heavy tubing member 78. Rod
casing 82 and the inner wall of cylinder 75 define an annular
spacing 83 which is connected through a valve-controlled conduit 84
to a source of high-pressure helium (not shown) and to the annular
spacing 74 within cylinder 65.
In the embodiment illustrated in FIGS. 5 and 6, a cryogenic fluid,
e.g., liquid helium, furnishes the required refrigeration. A vessel
90 is provided to contain liquid helium 91, or other cryogen; and a
copper mass 92 designed to fit around at least a portion of copper
section 69 (see FIG. 6) defines at least a part of the bottom of
vessel 90 to serve as a heat station. A valve-controlled insulated
conduit 93 provides fluid communication between a source of liquid
helium (not shown) and the interior of vessel 90. A conduit 94
having a one-way, pressure-controlled valve 95 provides for the
discharge of vaporized helium from vessel 90. Around the liquid
helium vessel 90 is an annularly-shaped vessel 96 for containing a
liquid cryogen 97 such as nitrogen to serve as a radiation
shielding for the helium vessel. The liquid nitrogen is introduced
into vessel 96 through a valve-controlled conduit 98 and vaporized
nitrogen gas is removed through conduit 99 having a one-way,
pressure-controlled valve 100. In accordance with accepted practice
in handling cryogenic refrigeration sources, an effective
insulation means such as an evacuated chamber (not shown) will be
used to surround the refrigeration source whether it is a
refrigerator or a supply of a liquid cryogen.
In some uses of the thermal switch, it may not be necessary to be
able to vary the temperature of the load over a range, but just
operate it in "on" and "off" modes. For such cooling applications
the switch may have a simple means for moving the copper plunger
between two limits of travel. Such a simple means, magnetically
operated, is shown somewhat schematically in FIG. 7 wherein like
reference numerals are used to refer to like components of FIG. 1.
In FIG. 7, the normal stainless steel housing (e.g., 15 of FIG. 1)
is replaced by a nonmagnetic sheath tube 110 sealed at the bottom
by cover 111. Around the sheath tube 110 are positioned two sets of
coils 112 and 113 spaced apart a distance essentially corresponding
to the distance between the two thick-walled copper sections 16 and
18. Each set of coils is contained within proper sheathings 114 and
115, respectively, and is connected to a suitable power source 116,
through connection leads 117 and 118 for coils 112 and connection
leads 119 and 120 for coils 113. A three-way switch 121 makes it
possible to alternately connect coils 112 or 113 to the power
source to cause the rod 20, which has a slug of magnetic material
122 affixed to its end, to move to its lowermost position to turn
the thermal switch off or to move to an uppermost position within
the magnetic field generated by coils 113 to turn it on.
The thermal switch of this invention is particularly suited for use
in cryopumping devices, for cooling samples for physical analysis,
and for cooling ir detectors and the like. It can also be
incorporated in very small delicate instruments such as those used
in cryosurgery.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
constructions without departing from the scope of the invention, it
is intended that all matter contained in the above description or
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
* * * * *