U.S. patent number 3,802,211 [Application Number 05/308,409] was granted by the patent office on 1974-04-09 for temperature-staged cryogenic apparatus of stepped configuration with adjustable piston stroke.
This patent grant is currently assigned to Cryogenic Technology, Inc.. Invention is credited to James A. 0'Neil, Walter H. Bamberg.
United States Patent |
3,802,211 |
Bamberg , et al. |
April 9, 1974 |
TEMPERATURE-STAGED CRYOGENIC APPARATUS OF STEPPED CONFIGURATION
WITH ADJUSTABLE PISTON STROKE
Abstract
A temperature-staged cryogenic refrigeration apparatus of
stepped configuration wherein a high-pressure fluid is introduced
into and then exhausted as low-pressure fluid from two or more
variable-volume refrigeration chambers defined by moving pistons.
The refrigeration chambers are of decreasing diameter and deliver
refrigeration at decreasing temperature levels. One or more of the
pistons defining the variable-volume refrigeration chambers is
linked to its adjacent piston through variable piston linkage means
so that the stroke length of the piston as well as its diameter may
be used to adjust the ratios of maximum volumes between the
refrigeration chambers.
Inventors: |
Bamberg; Walter H. (Stoughton,
MA), 0'Neil; James A. (Bedford, MA) |
Assignee: |
Cryogenic Technology, Inc.
(Waltham, MA)
|
Family
ID: |
23193877 |
Appl.
No.: |
05/308,409 |
Filed: |
November 21, 1972 |
Current U.S.
Class: |
62/6; 60/521 |
Current CPC
Class: |
F25B
9/14 (20130101); F02G 1/0445 (20130101); F25B
2309/003 (20130101); F02G 2250/18 (20130101) |
Current International
Class: |
F25B
9/14 (20060101); F02G 1/044 (20060101); F02G
1/00 (20060101); F25b 009/00 () |
Field of
Search: |
;62/6 ;60/24 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wye; William J.
Attorney, Agent or Firm: Lepper; Bessie A.
Claims
We claim:
1. In a temperature-staged cryogenic apparatus wherein at least two
directly connectable pistons of different diameters reciprocate
within a fluid-tight housing of stepped configuration to define at
least two refrigeration chambers of different diameters capable of
delivering refrigeration at different temperature levels, wherein
said refrigeration chambers are connected by a fluid flow path and
wherein the largest-diameter piston is connected to external
driving means, the improvement comprising variable piston linkage
means adapted to provide engagement between said pistons and
arranged to cause said largest-diameter piston to impart reciprocal
motion to at least one of the other of said pistons through a
stroke length less than that experienced by said largest diameter
piston.
2. A cryogenic apparatus in accordance with claim 1 wherein said
variable piston linkage means comprise
a. flange means affixed to the engaging end of one of said pistons;
and
b. lip means, adapted to engage said flange means, affixed to the
engaging end of another of said pistons.
3. A cryogenic apparatus in accordance with claim 2 wherein said
flange means are affixed to said largest-diameter piston and said
lip means to said other of said pistons.
4. A cryogenic apparatus in accordance with claim 2 wherein said
lip means are affixed to said largest-diameter piston and said
flange means to said other of said pistons.
5. A cryogenic apparatus in accordance with claim 2 including
spring means adapted to maintain said flange means in engagement
with said lip means during those times in the operation of said
apparatus when the volume of the largest-diameter refrigeration
chamber is increasing and while it remains at maximum.
6. A cryogenic apparatus in accordance with claim 1 wherein said
variable piston linkage means comprise
a. flange means affixed to the engaging end of said other of said
pistons; and
b. a cavity within said largest-diameter piston providing a
contacting surface and having an opening into the largest-diameter
refrigeration chamber, said opening having inwardly directed lip
means adapted to enge said flange, said cavity being sized to
permit therein the motion of said other of said pistons
engaged.
7. A cryogenic apparatus in accordance with claim 1 wherein said
variable piston linkage means comprise
a. lip means terminating the engaging end of said other of said
pistons;
b. a cavity within said largest-diameter piston providing a
contacting surface, having an opening into the largest-diameter
refrigeration chamber and being sized to permit therein the motion
of said other of said pistons engaged; and
c. flanged post means adapted to engage said lip means, affixed to
said contacting surface and extending into said cavity.
8. A cryogenic apparatus in accordance with claim 1 wherein said
variable piston linkage means comprise
a. post means affixed to that portion of the wall of said housing
which defines the end of the smallest-diameter refrigeration
chamber, said post means terminating in flange means;
b. a cavity within said other of said pistons which in its motion
defines said smallest-diameter refrigeration chamber, said cavity
providing an engagement surface and opening into said
smallest-diameter refrigeration chamber to provide an inwardly
directed lip means adapted to engage said flange; and
c. spring means adapted to maintain said flange means in engagement
with said lip means during those times in the operation of said
apparatus when the volume of said smallest diameter refrigeration
chamber is increasing and while it remains at maximum.
9. In a temperature-staged cryogenic apparatus wherein at least two
directly connectable pistons of different diameters reciprocate
within a fluid-tight housing of stepped configuration to define at
least two refrigeration chambers of different diameters capable of
delivering refrigeration at different temperature levels, wherein
said refrigeration chambers are connected by a fluid flow path
which includes heat storage means located within said pistons and
wherein the largest-diameter piston is connected to external
driving means, the improvement comprising variable piston linkage
means adapted to provide engagement between said pistons and
arranged to cause said largest-diameter piston to impart reciprocal
motion to at least one of the other of said pistons through a
stroke length less than that experienced by said largest-diameter
piston.
10. A cryogenic apparatus in accordance with claim 9 wherein said
variable piston linkage means comprise
a. flange means affixed to the engaging end of one of said pistons;
and
b. lip means, adapted to engage said flange means, affixed to the
engaging end of another of said pistons.
11. A cryogenic apparatus in accordance with claim 10 wherein said
flange means are affixed to said largest-diameter piston and said
lip means to said other of said pistons.
12. A cryogenic apparatus in accordance with claim 10 wherein said
lip means are affixed to said largest-diameter piston and said
flange means to said other of said pistons.
13. A cryogenic apparatus in accordance with claim 9 wherein said
variable piston linkage means comprise
a. first cap means affixed to the engaging end of said other of
said pistons, said cap means terminating in a flange and being
arranged to provide fluid communication into the heat storage means
located within said other of said pistons; and
b. second cap means affixed to said largest-diameter piston, said
second cap means providing a contacting surface and having an
opening into the largest-diameter refrigeration chamber, said
opening having inwardly directed lip means adapted to engage said
flange, said cavity being sized to permit therein the motion of
said other of said pistons engaged and providing fluid
communication means between said cavity and the heat storage means
located within said largest-diameter piston.
14. A cryogenic apparatus in accordance with claim 13 including
spring means adapted to maintain said flange in engagement with
said lip means during those times in the operation of said
apparatus when the volume of said largest-diameter refrigeration
chamber is increasing and while it remains at maximum.
15. A temperature-staged cryogenic apparatus for delivering
refrigeration at at least two temperature levels, comprising in
combination
a. housing means formed of at least two cylindrical sections of
different diameters to provide a fluid-tight enclosure of stepped
configuration;
b. at least two directly connectable pistons of different diameters
adapted to move within an associated section of said housing means
and in their motion to define at least two variable-volume
refrigeration chambers of different diameter and different maximum
volume, the temperatures attainable in said chambers decreasing
with decreasing chamber diameter;
c. fluid flow path means providing fluid communication between said
refrigeration chambers and incorporating heat storage means;
d. external driving means associated with the largest-diameter
piston and adapted to control its motion within said housing;
and
e. variable piston linking means providing engagement between said
pistons and arranged to cause said largest-diameter piston to
impart motion to the other of said pistons, at least one of which
is caused to experience a stroke length less than that experienced
by said largest-diameter piston.
16. A cryogenic apparatus in accordance with claim 15 wherein said
variable piston linkage means comprise
a. flange means affixed to the engaging end of one of said pistons;
and
b. lip means, adapted to engage said flange means, affixed to the
engaging end of another of said pistons.
17. A cryogenic apparatus in accordance with claim 16 wherein said
flange means are affixed to said largest-diameter piston and said
lip means to said other of said pistons.
18. A cryogenic apparatus in accordance with claim 16 wherein said
lip means are affixed to said largest-diameter piston and said
flange means to said other of said pistons.
19. A cryogenic apparatus in accordance with claim 16 including
spring means adapted to maintain said flange means in engagement
with said lip means during those times in the operation of said
apparatus when the volume of said largest-diameter refrigeration
chamber is increasing and while it remains at maximum.
20. A cryogenic apparatus in accordance with claim 15 wherein said
variable piston linking means comprise
a. flange means affixed to the engaging end of said other of said
pistons; and
b. a cavity within said largest-diameter piston providing a
contacting surface and having an opening into the largest-diameter
refrigeration chamber, said opening having lip means adapted to
engage said flange, said cavity being sized to permit therein the
motion of said other of said pistons engaged.
21. A cryogenic apparatus in accordance with claim 15 wherein said
variable piston linkage means comprise
a. post means affixed to that portion of the wall of said housing
which defines the end of the smallest-diameter refrigeration
chamber, said post means terminating in flange means;
b. a cavity within said other of said pistons which in its motion
defines said smallest-diameter refrigeration chamber said cavity
providing an engagement surface and opening into said
smallest-diameter refrigeration chamber to provide an inwardly
directed lip means adapted to engage said flange; and
c. spring means adapted to maintain said flange means in engagement
with said lip means during those times in the operation of said
apparatus when the volume of said smallest-diameter refrigeration
chamber is increasing and while it remains at maximum.
22. An apparatus in accordance with claim 15 wherein said heat
storage means are located within said pistons and said variable
piston linkage means comprise
a. first cap means affixed to the engaging end of said other of
said pistons, said cap means terminating in a flange and being
arranged to provide fluid communication means into the heat storage
means located within said other of said pistons; and
b. second cap means affixed to said largest-diameter piston, said
second cap means providing a contacting surface and having an
opening into the largest-diameter refrigeration chamber, said
opening having inwardly directed lip means adapted to engage said
flange, said cavity being sized to permit therein the motion of
said other of said pistons engaged and providing fluid
communication means between said cavity and the heat storage means
located within largest-diameter.
23. An apparatus in accordance with claim 15 wherein said
largest-diameter piston in its motion also defines an additional
chamber of variable volume which is in fluid communication through
said fluid flow path with said refrigeration chambers.
24. An apparatus in accordance with claim 15 including
a. a high-pressure fluid source; and
b. a low-pressure fluid reservoir.
25. An apparatus in accordance with claim 24 wherein said
high-pressure fluid source and said low-pressure fluid reservoir
are located externally of said housing and wherein said apparatus
includes valved conduit means providing fluid communication between
said high-pressure fluid source and said low-pressure fluid
reservoir and said refrigeration chambers.
26. An apparatus in accordance with claim 25 wherein said
high-pressure fluid source and said low-pressure fluid reservoir
are combined in a compressor.
27. An apparatus in accordance with claim 24 including within said
housing means an additional piston operable to define a
variable-volume compression chamber adapted to serve as said
high-pressure fluid source and as said low-pressure fluid
reservoir.
28. An apparatus in accordance with claim 24 including within said
housing means displacer means defining high-temperature and
intermediate-temperature chambers of variable volumes in fluid
communication through heat storage means, said high-temperature and
intermediate-temperature chambers in combination being adapted to
serve as said high-pressure fluid source and said low-pressure
fluid reservoir.
29. An apparatus in accordance with claim 15 wherein said housing
is formed of three cylindrical sections and three pistons move
within said housing, at least one of the other of said pistons
being caused to experience a stroke length less than that
experienced by said largest-diameter piston.
30. An apparatus in accordance with claim 15 wherein said housing
is formed of three cylindrical sections and wherein the piston
moving within the intermediate-diameter section of said housing is
linked through said variable piston linking means to said
largest-diameter piston and the piston moving within the
smallest-diameter section of said housing is linked through said
variable piston linking means to said intermediate-diameter piston,
whereby the length of the stroke of said intermediate-diameter
piston is less than that of said largest-diameter piston and the
length of the stroke of said smallest-diameter piston is less than
that of said intermediate diameter piston.
31. An apparatus in accordance with claim 29 including
a. an external high-pressure fluid source;
b. an external low-pressure fluid reservoir; and
c. valve-controlled fluid conduit means arranged to provide fluid
communication between said chambers and said external high-pressure
fluid source and said low-pressure fluid reservoir.
32. An apparatus in accordance with claim 15 including stroke
adjusting means associated with said variable piston linkage means
adapted to control the length of the stroke of said other of said
pistons.
33. A temperature-staged cryogenic apparatus adapted to liquefy a
gas comprising in combination
a. housing means formed of three cylindrical sections of different
diameters to provide a fluid-tight enclosure of stepped
configuration;
b. three directly connectable pistons of different diameters
adapted to move within associated sections of said housing means
and in their motion to define three variable-volume refrigeration
chambers of different diameter and different maximum volume, the
temperatures attainable in said chambers decreasing with decreasing
chamber diameter;
c. fluid flow path means providing fluid communication between said
refrigeration chambers and incorporating heat storage means;
d. a first high-pressure fluid source;
e. a first low-pressure fluid reservoir;
f. external driving means associated with the largest-diameter
piston and adapted to control its motion within said housing;
g. variable piston linking means providing engagement between said
pistons and arranged to cause said largest-diameter piston to
impart motion to the other two of said pistons, at least one of
which is caused to experience a stroke length less than that
experienced by said largest-diameter piston;
h. heat station means associated with each of said refrigeration
chambers and being adapted to deliver refrigeration through
out-of-contact heat exchange with fluid in said refrigeration
chambers at three decreasing temperature levels;
i. a second high-pressure fluid source external of said housing
means;
j. a second low-pressure fluid reservoir external of said housing
means;
k. liquefaction means adapted to expand and at least partially
liquefy high-pressure fluid from said second high-pressure fluid
source;
l. vessel means adapted to receive the liquefied fluid and to
provide a source of cold low-pressure fluid;
m. heat exchange means incorporating said heat station means at
said three temperature levels adapted to effect out-of-contact heat
exchange between fluid from said second high-pressure fluid source
delivered to said liquefaction means and said cold low-pressure
fluid delivered from said vessel means to said second low-pressure
fluid reservoir.
34. An apparatus in accordance with claim 33 wherein said first and
second high-pressure fluid sources are combined as one and said
first and second low-pressure fluid reservoirs are combined as one,
and further including valve-controlled fluid conduit means adapted
to provide fluid communication between the combined high-pressure
fluid source and the combined low-pressure fluid reservoir and said
fluid flow path means.
35. An apparatus in accordance with claim 34 wherein said
low-pressure fluid reservoir and said high-pressure fluid source
are combined in a compressor.
36. An apparatus in accordance with claim 33 including within said
housing means an additional piston operable to define a
variable-volume compression chamber adapted to serve as said first
high-pressure fluid source and as said first low-pressure fluid
reservoir.
37. An apparatus in accordance with claim 33 including within said
housing means displacer means defining high-temperature and
intermediate-temperature chambers of variable volumes in fluid
communication through heat storage means, said high-temperature and
intermediate-temperatures in combination being adapted to serve as
said first high-pressure fluid source and said first low-pressure
fluid reservoir.
Description
This invention relates to temperature-staged cryogenic
refrigerators and more particularly to temperature-staged cryogenic
refrigerators of a stepped configuration adapted to deliver
refrigeration at more than one temperature level. The basic
apparatus principles are applicable to cryogenic refrigerators
operating on the cycle described in U.S. Pat. No. 2,906,101 and
more particularly to the form of that cycle described in U.S. Pat.
No. 2,966,035. The invention is also applicable to apparatus for
developing refrigeration through the use of the Stirling and the
Vuilleumier cycles.
In constructing a temperature-staged cryogenic refrigerator having
two or more refrigeration chambers it is of course necessary
because of mass flow considerations to construct each refrigeration
chamber to have a smaller volume than that delivering refrigeration
at the next higher temperature level. Superimposed upon this
requirement for decreasing refrigeration chamber volumes are such
considerations as the achievement of simplicity of construction,
the attainment of maximum regenerator efficiency and the
minimization of heat losses, particularly those due to heat leaks
brought about through conduction and piston motion. The most
satisfactory design which meets these requirements is a stepped
configuration, that is a refrigerator having a housing which is
constructed in the form of hollow cylindrical sections of
decreasing diameters suitably sealed to define a fluid-tight
enclosure and rigidly joined pistons of varying diameter adapted to
experience reciprocal motion in the housing sections. The pistons
through their motion define refrigeration chambers of decreasing
diameter thereby providing the decreasing refrigeration chamber
volumes desired. Thus in this widely used stepped configuration,
since the pistons are rigidly linked and all undergo the same
length of stroke, the chamber diameter is the only design parameter
which may be changed to control the volume ratio of the two or more
refrigerations chambers.
It is not feasible, however, to arbitrarily vary the diameter of
the colder refrigeration chambers without regard to several
limiting factors. For example, in a stepped-configuration
refrigerator wherein the regenerators are located within the
pistons (and this is generally the case) the regenerator pressure
drop and the thermal performance of the regenerator is at least in
part determined by the regenerator diameter (and hence the piston
diameter) as well as the length of the regenerator. This fact in
turn places relatively rigorous limitations on the extent to which
the pistons defining the lower-temperature refrigeration chambers
may be reduced in diameter. This then leaves as an alternative to
decreasing piston diameter, the control of the stroke length for
those pistons defining the volumes of the lower-temperature
refrigeration chambers. Since there is provided a single driving
means for these piston sections formed of decreasing diameters, the
previously used rigid mechanical linkages between piston sections
is not suitable to vary the piston stroke lengths.
The apparatus of this invention makes possible the adjustment of
piston stroke length by providing linking means for the piston
sections which permit engagement between the piston sections in
series and thereby causes the largest diameter piston to impart
reciprocal motion to one or more smaller diameters pistons through
a stroke length less than that experienced by the largest diameter
piston. It has been found that by varying the ratio of stroke
lengths it is possible to vary the temperature and refrigeration
capacity for each stage within certain limits, to optimize overall
refrigerator performance by adjusting relative piston
displacements, and to decrease the losses associated with the
lower-temperature regenerators while still obtaining the benefits
of previously determined optimal design considerations such as
minimum conduction and motional heat leak losses and simplicity of
overall construction.
It is therefore a primary object of this invention to provide an
improved temperature-staged cryogenic refrigerator of stepped
configuration. It is another object to provide a refrigerator of
the character described wherein the volume of the refrigeration
chambers operating at the lower temperature levels may be readily
optimized by changing the length of stroke of the reciprocating
piston section defining the volume. It is yet another object to
provide a cryogenic refrigerator which is capable of attaining
lower temperatures than one of equal size and configuration
constructed with a stepped piston, the sections of which are
rigidly linked. This invention has for a further object the
provision of a stepped, temperature-staged cryogenic refrigerator
in which the mass flow may be optimized for each stage, the
regenerator efficiency may be increased, and the PV diagram for any
stage optimized for a desired performance. Other objects of the
invention will in part be obvious and will in part be apparent
hereinafter.
The cryogenic apparatus which achieves the objects of this
invention is one which is adapted to introduce a high-pressure
expansible fluid from a high pressure fluid source into two or more
refrigeration chambers of variable volumes operating at different
temperature levels and to discharge expanded low-pressure fluid
therefrom to a low-pressure reservoir. The fluid is conveyed to the
refrigeration chambers through a fluid flow path incorporating
regenerators and is returned from the chambers back through the
same flow path. The refrigeration chambers have diameters which
decrease with decreasing temperature levels and their variable
volumes are defined by reciprocating pistons which are so linked as
to provide engagement between the pistons in series such that the
largest diameter piston imparts reciprocal motion to the other
piston or pistons through predetermined and controlled stroke
lengths, these stroke lengths being less than that experienced by
the largest diameter piston.
The apparatus of this invention is applicable to devices designed
to operate on the cycles of U.S. Pat. Nos. 2,906,101 and 2,966,035
wherein the high-pressure fluid source and low-pressure fluid
reservoirs are external of the refrigerator and are connected
through valved-controlled lines, as well as on the Stirling cycle
such as illustrated by U.S. Pat. Nos. 2,657,553 and on the
Vuilleumier cycle such as disclosed in U.S. Pat. Nos.
1,275,507.
The use of a variable linkage between pistons has been applied to
in-line refrigerators wherein each piston moves within its own
separate concencentric housing that extends up into the warm end of
the refrigerator. (See U.S. Pat. No. 3,673,809.) This makes it
possible to use seals only on the warm end. The apparatus of U.S.
Pat. No. 3,673,809 is suitable for refrigerators where some overall
efficiency can be sacrificed for ease of construction; and it is
particularly suitable for constructing larger refrigerators where
relatively large heat losses can be tolerated.
In the apparatus of U.S. Pat. No. 3,673,809 the pistons are all of
essentially of the same diameter, a fact which means that stroke
length is the only design parameter which can be adjusted to
achieve desired ratios between the refrigeration chamber volumes.
Therefore the construction and operation of a small inline
refrigerator such as described in U.S. Pat. No. 3,673,809 designed
to attain very low temperatures and relatively high efficiencies
present almost insurmountable problems. This is due to the fact
that since the diameters of the lower-temperature refrigeration
chambers must be essentially as large as that of the refrigeration
chamber at the highest temperature, the stroke lengths of the
piston defining the lower-temperature chambers must be extremely
short, a fact which presents adjustment and control problems.
Moreover, high thermal losses due to excessive conduction through
the extended chamber surface and to large motional heat leaks
through the extended piston surfaces materially detract from the
realization of an efficient cryogenic refrigerator, particularly in
small sizes, capable of delivering refrigeration at low
temperatures, e.g., below 15.degree.K.
The apparatus of this invention makes it possible to balance the
factors of piston and cylinder diameters with piston stroke lengths
to obtain optimum operational performance for any sized
refrigerators and particularly those delivering up to about 20
watts refrigeration at 10.degree.K or lower.
The invention accordingly comprises the features of construction,
combination 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 somewhat simplified longitudinal cross section of a
two-staged refrigerator, constructed in accordance with this
invention to operate on the cycle of U.S. Pat. No. 2,966,035, along
with its attendant components;
FIG. 2 is a modification of the refrigerator of FIG. 1 wherein the
regenerators are located external of the refrigerator housing;
FIG. 3 is a somewhat simplified longitudinal cross section of a
three-staged refrigerator constructed in accordance with this
invention to operate on the cycle of U.S. Pat. No. 2,966,035 along
with the components of a Joule-Thomson loop adapted to use the
refrigeration developed to liquefy helium;
FIG. 4-7 are detailed cross sections of four embodiments of
variable linkage means between pistons usable in the refrigerators
of FIGS. 1-3;
FIGS. 8-11 illustrate the steps involved in the operation of the
variable linkage of FIGS. 4 and 5;
FIG. 12 illustrates a variation in the last step of operation when
the variable linkage embodiment of FIG. 7 is used.
FIG. 13 is a PV diagram for a typical cryogenic refrigerator
operating on the cycle of U.S. Pat. No. 2,966,035 and incorporating
early cutoff of the supply of high-pressure fluid into the
refrigerator;
FIG. 14 is a PV diagram for the colder refrigeration chamber of a
two-staged refrigerator constructed in accordance with this
invention and using the linkage of FIG. 4 or 5;
FIG. 15 is a PV diagram for the colder refrigerator chamber of
two-staged refrigerator constructed in accordance with this
invention and using the linkage of FIG. 7;
FIG. 16 is a detailed cross section of an embodiment of this
invention wherein the variable linkage between pistons is a
combination of surface engagement and restraining means affixed to
the refrigerator housing;
FIGS. 17-19 illustrate the steps involved in the operation of the
refrigerator embodiment of FIG. 16;
FIG. 20 is a PV diagram for the colder refrigerator chamber of a
two-staged refrigerator constructed in accordance with this
invention and using the linkage of FIG. 16;
FIG. 21 is a somewhat simplified longitudinal cross section of a
two-staged refrigerator constructed in accordance with this
invention to operate on the cycle of U.S. Pat. No. 2,906,101;
FIG. 22 is a somewhat simplified longitudinal cross section of a
two-staged refrigerator constructed in accordance with this
invention to operate on the Stirling cycle; and
FIG. 23 is a somewhat simplified longitudinal cross section of a
two-staged refrigerator constructed in accordance with this
invention to operate on the Vuilleumier cycle of U.S. Pat. No.
1,275,507.
It should be noted in the following description of the apparatus of
this invention such words as "warm" and "cold" are relative, and
the use of "up" and "down" are for convenience in describing one
exemplary orientation of the apparatus since the devices under
consideration may generally be operated in any orientation. To
simplify the discussion and to make the description of the
apparatus applicable to apparatus formed in two, three or more
stages, the terms "largest-diameter", "smallest-diameter" etc. as
applied to pistons, displacers and refrigeration chambers will
generally be used even through only two stages are involved. It
will also be convenient to refer to the movable body as a "piston"
in general discussions and to use the term in its broadest sense in
order to include a displacer within its meaning. Thus the term
"piston" includes all sliding bodies moving within a cylindrical
vessel whether or not they experience pressure differentials on
their surfaces; while the term "displacer" is reserved for sliding
bodies which experience essentially no pressure differential on
their surfaces.
The apparatus of FIG. 1 is a two-staged refrigerator which operates
on the so-called no-work cycle of U.S. Pat. No. 2,966,035. This
refrigerator has a stepped fluid-tight housing 10 formed of a
larger diameter section 11 and a smaller diameter section 12 joined
through annular shoulder 13. Within housing section 11 the larger
diameter displacer 14 defines in its motion a variable-volume warm
chambers 15 and a first variable-volume refrigeration chamber 16.
Within housing section 12 the smaller diameter displacer 17 defines
a second, lower-temperature refrigeration chamber 18. Displacer 14
is mechanically linked to a driving means 19 through driving rod 20
and to the smaller diameter displacer 17 through a variable linkage
25 shown in somewhat simplified form to comprise an annular flange
26 on the upper or warmer end of displacer 17 and a
flange-engageable ring in the form of a lip 27 extending inwardly
within an open cavity 28 located in the bottom or colder end of
displacer 14 and sized to permit the upper flanged end of displacer
17 to reciprocate therein with a small clearance. Exemplary
constructions of this variable linkage and modifications thereon
are shown in detail in FIGS. 4-7 and described below. Suitable
seals 21 and 22 (either of the active or passive type) are provided
for the two displacers 14 and 17, respectively, and if required,
some form of shock-absorbing means such as a leather washer 23 may
be affixed to the colder end of displacer 17 or to the internal end
wall of housing section 12.
Displacer 14 has a regenerator 30, and displacer 17 a regenerator
31. The basic fluid flow path within the refrigerator comprises
warm chamber 15, one or more fluid conduits 32 providing fluid
communication between chamber 15 and regenerator 30, the clearances
around flange 26 and lip 27 connecting regenerator 30 with the
first refrigeration chamber 16, regenerator 31 which is in direct
fluid communication through cavity 28 with regenerator 30, one or
more fluid conduits 33 providing fluid communication between
regenerator 31 and the second colder refrigeration chamber 18 and
refrigeration chamber 18.
High-pressure fluid is supplied by a high-pressure fluid source,
e.g., the discharge side of compressor 34 through line 35 and valve
36 and low-pressure fluid is exhausted into a low pressure
reservoir, e.g., the inlet side of compressor 34 through line 37
and valve 38. This fluid loop of a typical closed cycle also has a
suitable fluid clean-up system shown at 39. Alternatively, in an
open cycle the high-pressure supply 40 (e.g., a pressurized gas
source) need not be connected with the low-pressure reservoir 41
(e.g., the atmosphere). FIG. 1 illustrates a mechanical driving
means. It is also within the scope of this invention to use
pneumatic driving means such as shown, for example, in U.S. Pat.
Nos. 3,045,436 and 3,188,819.
Refrigeration is delivered at two temperature levels at a higher
temperature level (typically 30.degree. to 120.degree.K) from the
fluid in refrigeration chamber 16 through a heat station 42 and at
a lower temperature level (typically 8.degree. to 25.degree.K) from
the fluid in refrigeration chamber 18 through a heat station
43.
The apparatus of FIG. 2, wherein like reference numerals are used
to identify like components in FIG. 1, exemplifies a modification
of the apparatus of FIG. 1 in that the regenerators 48 and 49 are
located externally of the housing 10 and the fluid flow path
comprises, in addition to regenerators 48 and 49, fluid conduits
50-53. The displacers 54 and 55, shown in cross hatching for
convenience of identification, may be solid or hollow.
The three-staged refrigerator of FIG. 3 is constructed to have
Although housing 60 formed of three different diameter housing
sections 61, 62 and 63 and to have three displacers 64, 65 and 66
operable therein and sealed with seals 67, 68 and 69. Regenerators
70, 71 and 72 are located within their respective displacers.
Variable linkage 73 provides the driving means for displacer 65 and
linkage 74 for displacer 66. The displacers in their motion define
variable volume refrigeration chambers 75, 76 and 77 which have
associated therewith heat stations 78, 79 and 80, respectively. The
flow path within the refrigerator is identical with that of FIG. 1
with an additional regenerator and refrigerator chamber and fluid
conduit 59. ALthough the three-stage refrigerator of FIG. 3 is
shown to have intermediate-diameter displacer 64 connected to the
displacer 65 and smallest-diameter displacer 66 connected to
intermediate-diameter displacer 65 through variable linkage means,
it is also within the scope of this invention to use only one
variable linkage in a refrigerator having three or more stages, the
variable linkage being employed between any two of the
displacers.
The refrigerator of FIG. 3 is also shown to have a Joule-Thomson
loop making it possible, if desired, to liquefy a gas. In keeping
with known apparatus design, this Joule-Thomson loop comprises
three heat exchangers 81, 82 and 83 adapted to effect refrigeration
of the high-pressure fluid in the loop through out-of-contact heat
exchange between high-pressure fluid in line 84 and returning
low-pressure fluid in line 85. The high-pressure fluid is also
refrigerated at appropriate temperature levels by out-of-contact
heat exchange with the fluid within the refrigeration chambers
through heat stations 78, 79 and 80 in heat exchangers 86, 87 and
88. A final Joule-Thomson heat exchanger 89 and expansion valve 90
are provided. Liquefied gas is collected in vessel 91 from which
the low-pressure gas is returned through the loop in line 85.
FIGS. 4-7 illustrate three exemplary embodiments of the variable
linkage, e.g., linkage 25 of FIGS. 1 and 2 and linkages 73 and 74
of FIG. 3. The refrigerator of FIG. 1 will be used as exemplary and
the same reference numerals will be used in FIGS. 4-7 to identify
the same apparatus components.
In the embodiment of the linkage shown in FIG. 4 the flow path
provides for direct connection between the two regenerators 30 and
31. The flange 26 for the upper end of the smaller diameter
displacer 17 is formed as a threaded cap 100 adapted to engage
threads in the internal wall 101 of displacer 17. Cap 100 has a
central opening 102 providing a fluid port into regenerator 31
which is shown to comprise stacked screens 103. The engageable lip
27 is conveniently provided as a part of a threaded cap 104 adapted
to engage threads in the internal wall 105 of displacer 14. When
cap 104 is screwed in place, its outer flange 106 rests flush with
a lower edge of displacer outer wall 107 to form a smooth end wall.
Regenerator 31 terminates in a perforated disk 108 which engages
the upper edge of cap 104 and which serves to retain the lead
balls, screens or other filling providing the regenerative material
in place within the regenerator. The under side of perforated disk
108 provides a contacting surface 109 which makes physical contact
with the upper surface of lip 26 to drive displacer 17 downwardly.
During upward movement the engagement is, of course, between flange
26 and lip 27.
It may be desirable to be able to vary the extent to which the
stroke lengths of the two displacers differ, i.e., to control the
length of travel of displacer 14 before engagement with displacer
17. This may conveniently be done by inserting an optional washer
99 into cap 104 to effectively raise the height of lip 27. It is,
of course, within the scope of this invention to replace flange 26
with a series of two or more equally spaced pins extending radially
outwardly from the top of cap 100 or to use any other suitable
engaging means capable of linking the smallest-diameter piston to
the largest-diameter piston as the latter experiences motion in a
direction to effect an increase in volume of its associated
refrigeration chamber.
In the embodment of FIG. 5, the variable linkage is modified to
accomodate a fluid flow path of the basic type described in U.S.
Pat. No. 3,218,815. The end cap 110 of displacer 17 is solid and
fluid ports 111 through the displacer wall are spaced at intervals
to provide a fluid passage into regenerator 31. Displacer 14 is
configured to have a lower section 112 of somewhat smaller diameter
than the remaining part of the displacer thereby to define an
annular fluid flow passage 113 which opens into a number of radial
passages, two of which are shown at 114, which in turn lead into
regenerator 31 which terminates in an impervious bottom wall 115.
The surface 116 of cavity 28 serves as the contacting face for the
engagement of the displacer during downward movement. The flow of
high-pressure fluid is shown by arrows. It is, of course, reversed
for the returning low-pressure fluid. The fluid flow path of the
embodiment of FIG. 5 offers thermal advantages, but these may in
part be offset by a somewhat higher pressure drop because of the
indirect flow path.
FIG. 6 shows a modification of the variable linkage of FIG. 4
wherein an engaging post 117 is affixed to the perforated disk 108
of displacer 14 to provide a flange 118 which is sized to engage an
inwardly extending lip 119 around the opening of a cavity 28a in
the engaging end of displacer 17. A foraminous plate 108a is shown
as a cover for regenerator 31. It will be apparent that the
operation of the apparatus of FIG. 6 is identical to that of the
apparatus of FIG. 4.
The variable linkages of FIGS. 4-6 rely upon seal friction against
pressure drop to keep the smaller diameter displacers in place
until engaged. However, it may be desirable in some cases to
provide positive means for ensuring that displacer 17 does not
experience unwanted motion. Such means are provided in the form of
a spring 116 in compression as shown in FIG. 7. The effect of the
use of such a spring will be described in the discussion of FIGS.
8-15 which follows.
The use of the variable linkage in the stepped, staged refrigerator
of this invention has important thermodynamic significance which
can best be explained with reference to FIGS. 8-15. FIGS. 8-11
detail the operation of the linkage of the apparatus of this
invention as it is illustrated in the embodiment of FIG. 1 using
the linkage detailed in FIGS. 4-6. No attempt has been made to
detail the apparatus components in these FIGS. 8-11 and the larger-
and smaller-diameter displacers are cross hatched for ease of
identification.
It may be assumed in this description of the operation of this
apparatus that a cycle begins with the complete exhaustion of
essentially all of the low-pressure cold fluid (except that in void
volumes) from all of the refrigeration chambers, i.e., chambers 16
and 18. This necessitates the closing of low-pressure valve 38 and
the opening of high-pressure valve 36. With the introduction of
high-pressure fluid into the system, the upper, larger-diameter
displacer is moved upwardly (FIG. 9) thus defining a first
refrigeration chamber 16 of increasing volume while displacer 17
remains in its lowermost position by virtue of the seal friction of
seal 22 (FIG. 1), After displacer 14 has experienced a
predetermined portion of its total stroke length, the variable
linkage causes displacer 14 to engage displacer 17 through flange
26 and lip 27 and to raise it. In a preferred embodiment of this
cycle, the high-pressure fluid is cut off before refrigeration
chambers 16 and 18 attain their full volume (early cutoff). As the
larger-diameter displacer 14 continues to be moved upwardly the
volume of refrigeration chamber 18 increases. At the end of this
upward movement the stroke length of displacer 14 is l.sub.14 while
that of displacer 17 is l.sub.17 ; and so the ratio of the final
volumes of refrigeration chambers 16 and 18 is a function of
l.sub.14 /l.sub.17 as well as of the diameters of displacers 14 and
17.
With the attainment of maximum volume (FIG. 10) the exhaust valve
is opened. Seal friction is sufficient to hold displacer 17 in the
position shown in FIG. 10 even though the highpressure gas
exhausting from chamber 18 through regenerator 31 results in a net
force on displacer 17 in the upward direction. Displacer 14 is
moved downwardly until contacting surface 109 engages flange 26 of
the smaller diameter displacer (FIG. 11). This downward motion of
both displacers then effects the final exhaustion of the fluid from
the refrigerator to return it to the condition required to begin
another cycle (FIG. 8).
The effect of the variable linkage on the PV diagrams for the
refrigerator is clearly seen in FIGS. 13 and 14. FIG. 13 is a PV
diagram for the first or larger diameter refrigeration chamber 16
and it follows a typical PV curve for the cycle with early cut-off.
(Volumes in these PV diagrams are expressed in terms of aribtrary
units of stroke length of the displacer which defines the volume.)
By restricting the motion and stroke length of displacer 17 the
lower-temperature refrigeration chamber 18 has the PV diagram of
FIG. 14 which is essentially the right-hand portion of the PV
diagram of FIG. 13. One result of the attainment of these two
different PV diagrams for the two refrigeration chambers is the
realization of a fuller PV diagram for the larger volume
refrigeration chamber which in turn means that the fluid in this
chamber is colder by several degrees K. This in turn, coupled with
the attainment of a larger displacement ratio (e.g., ratio of the
volume of the larger-diameter chamber to the volume of the
smaller-diameter chamber) results in decreased regenerator losses;
for the colder the fluid is in the first larger refrigerator
chamber the smaller is the .DELTA.T across the regenerator. This in
turn means that the fluid in the refrigeration chamber at the
lowest temperature level reaches a lower temperature or is capable
of delivering more refrigeration at a fixed temperature. Moreover,
the regenerator associated with the colder refrigeration chamber
(e.g., regenerator 31 of FIG. 1) is normally formed of a mass of
lead balls since lead has a high heat capacity at these low
temperatures. However, lead has a relatively low specific heat, Cp,
at these temperatures. By reducing the mass flow through the lead
(brought about by decreasing the temperature in the larger-diameter
refrigeration chamber and curtailing the volume of the smaller
diameter refrigeration chamber) the lead experiences a smaller
temperature swing, .DELTA.T, and thereby becomes a more efficient
heat transfer means.
The use of spring 116 in the embodiment of FIG. 7 alters the end of
the stroke as shown in FIG. 12 which is equivalent to the same
point in the cycle illustrated in FIG. 11 for a variable linkage
without the positive holding action of the spring. It will be seen
that the spring force tends to hold displacer 17 in spaced relation
with displacer 14, and as a result displacer 17 is moved downwardly
at the time displacer 14 starts its downward motion. This in turn
gives rise to a somewhat modified PV diagram for chamber 18 as
illustrated in FIG. 15. However, the overall results of colder
temperatures, decreased mass flow into refrigeration chamber 18 and
decreased regenerator losses are essentially the same.
FIG. 16 illustrates an embodiment of the apparatus of this
invention wherein the variable linkage between the displacers is a
combination of surface engagement between the displacers and
actuating/restraining means associated with the smaller diameter
displacer only. The lower portion of the refrigerator illustrated
is of the same two-staged type of FIG. 1 and like reference
numerals are used to refer to like components. In the apparatus
embodiment of this invention of FIG. 16, the larger-diameter
displacer 120 (having regenerator 121 and fluid conduits 122) is
not linked to the smaller diameter displacer 123 (having
regenerator 124) by any mechanical linkage; but displacer 120 does
impart downward motion to displacer 124 when the bottom driving
surface 125 of displacer 120 makes contact with the upper surface
126 of the perforated disk 127 serving as the ported cover for
regenerator 124.
Because of the lack of any separate mechanical linkage between
displacers 120 and 123, some means must be provided to control the
upward motion of displacer 123 and adjust its stroke length. This
means is provided in the form shown in detail in FIG. 16. A post
130, having an engaging flange 131, is affixed such as by screw
132, to the bottom 133 of housing 12, and the colder end of
displacer 123 is modified to provide a flange-engaging lip 134
extending inwardly from the mouth of cavity 135 which is sized to
permit a predetermined length of stroke of displacer 123 before lip
134 engages flange 131. A spring 136 in compression maintains
displacer 123 in its upwardmost position during those periods in
the cycle when displacer 120 is not exerting a downward force on
displacer 123. The fluid flow path between regenerator 124 and
refrigeration chamber 18 is essentially that of U.S. Pat. No.
3,218,815 and includes radial passage 137 and annular passage
138.
The operation of the embodiment of FIG. 16 is illustrated in FIGS.
17-20. From FIGS. 17 it will be seen that the same conditions apply
at startup as were noted in FIG. 8 for the apparatus embodiment of
FIG. 1. However, when high-pressure fluid begins to be introduced
into the refrigerator a portion thereof immediately enters chamber
18, the volume of which begins to increase immediately and is
finally limited by the length of post 130. Chamber 16 continues to
experience increasing volume after maximum volume is attained in
chamber 18. This is different from the embodiment of FIG. 1 as will
be clear from a comparison between FIGS. 18 and 19 with FIGS. 9 and
10. However, the downward strokes of the two apparatus are
identical in their results. FIG. 20, which is a PV diagram for the
colder refrigeration chamber 18 of the refrigerator of FIG. 16,
shows that it is essentially equivalent to the left-hand side of
the PV diagram for the larger-diameter refrigeration chamber as
shown in FIG. 13.
Apparatus may be constructed according to this invention to operate
on the cycle of U.S. Pat. No. 2,906,101 as shown in FIG. 21. The
apparatus of FIG. 21 differs from that of FIG. 1 in that the warm
chamber 15 is not present. In accordance with the difference of the
two cycles involved, the cycle of FIG. 21 delivers some external
mechanical energy in place of the thermal energy delivered by the
refrigerator of FIG. 1 operating on the no-work cycle.
In FIG. 21 like reference numerals are used to refer to like
elements shown in FIG. 1. As indicated above, fluid-tight stepped
housing 10 is open at the top and the upper section 140 is
preferably constructed to have a thicker wall than the remaining
portion of housing 10. Some modification is required in section 140
of the housing inasmuch as the high-pressure fluid must be
introduced directly into and low-pressure fluid exhausted directly
from regenerator 30. This modification in FIG. 21 takes the form of
a multiplicity of slots 141 in wall 140. High-pressure fluid is
brought into the system and low-pressure fluid exhausted from it
through line 142 which is, of course, equivalent to line 35 and 37
of FIG. 1. This external conduit is in fluid communication with the
regenerator through slots 141, an outer annular passage 143, an
annular passage 144 cut into the side of the displacer wall and a
series of radial passages 145 leading into regenerator 30. The
fluid flow path between chambers 16 and 18 by way of regenerators
30 and 31 may be identical to that described above for FIGS. 4 and
5. Sealing rings 146 and 147 are provided so that displacer 14 may
make fluid-tight contact with the inner wall housing section
140.
The advantages realized in the apparatus of FIG. 21 are essentially
the same as those described for the apparatus of FIG. 1. The
modifications in fluid flow path, the use of a spring as shown in
FIG. 7 and the embodiment of the variable linkage illustrated in
FIG. 16 are all applicable to the apparatus of FIG. 21.
FIG. 22 illustrates the application of this invention to one
embodiment of a Stirling engine which may briefly be described as
an apparatus which includes an additional compressor piston
operable within the housing to define a compressor chamber of
variable volume to alternately serve as a source of high-pressure
fluid and as a low-pressure fluid reservoir. In the embodiment of
the Stirling engine illustrated in FIG. 22 the
expansion-refrigeration portion of the housing 150 is of a stepped
configuration separated from the compressor housing 151. However,
the compressor chamber may be located in the same housing as the
expansion chamber and the housings may be considered as a single
housing means. In FIG. 22 the two housing parts are joined by a
suitable fluid conduit 152 having a aftercooler 153 incorporated in
it. Conduit means 154 is provided to circulate a cooling fluid
through the aftercooler. Compression of the fluid within the engine
takes place in chamber 156 and is effected by means of a piston 157
driven by rod 158 from a suitable driving means 159. In keeping
with this invention the expansion is accomplished in two expansion
chambers 160 and 161 through the movement of a larger-diameter
piston 162 mechanically linked through rod 163 with driving means
159 and a smaller-diameter piston 164 operable within stepped
housing 150 formed of a larger diameter section 165 and a
smaller-diameter section 166. Pistons 162 and 164 are variably
linked as described in detail in FIGS. 4-6 and regenerators 167 and
168 are located internally of pistons 162 and 164,
respectively.
Within housing 150 large diameter piston 162 moves to define
refrigeration chamber 160 and an intermediate-temperature chamber
170. The flow path within the expansion portion of the apparatus
will be seen to be comprised of a passage 173 drilled in the header
174, intermediate-temperature chamber 170, passage 175, regenerator
167, the first larger volume expansion chamber 160, regenerator
168, and the second smaller volume refrigeration chamber 161.
Inasmuch as the Stirling cycle is well known, it will not be
further detailed here. Since the staged Stirling cycle involves the
delivery of refrigeration at two temperature levels, the use of
regenerators, and considerations of mass flow similar to those of
the cycle on which the apparatus of FIG. 1 operates, it follows
that essentially the same advantages of lower temperatures and/or
greater refrigeration capacity are to be gained by adjusting the
refrigeration chamber volumes by the combination of diameter and
stroke length control.
FIG. 23 illustrates the application of this invention to a
refrigeration apparatus designed to operate on the Vuilleumier
cycle. The operation of this cycle requires that there be provided
a hot chamber and a chamber of intermediate-temperature and one or
more cold expansion chambers, these terms being relative for any
one system. Thus the basic apparatus for carrying out the
Vuilleumier cycle includes, in addition to one or more displacers
for defining variable-volume refrigeration chambers, additional
displacer means to define a high-temperature variable-volume
chamber and an intermediate-temperature variable-volume chamber
which in combination serve as a source of high-pressure fluid and a
reservoir for low-pressure fluid. The Vuilleumier cycle is a
completely closed cycle and the flow path which joins these
chambers includes heat storage means such as regenerators. In the
apparatus of FIG. 23 the expansion chambers along with a portion of
the intermediate-temperature chamber are found in stepped housing
180 formed of a larger-diameter section 181 and a smaller diameter
section 182; and the hot chamber along with the remaining portion
of the intermediate-temperature is found in a housing 183. Within
housing 183 is located a warm (or hot) chamber 184. The
intermediate-temperature chamber is made up of a combination of
chambers 185 located within housing 183 and chamber 186 located in
housing 180. These are joined through a conduit 187 which has
associated with it a heat exchanger 188. Conduit 187 passes down
through the header 189 which serves as one end of housing 180.
Within housing 183 is a piston 190 containing a regenerator 191. It
is, of course, within the scope of this invention and in the
operation of the cycle to locate the regenerator external of the
housing if this is desired. Piston 190 is driven by means of a
suitable driving means such as a crank 192 to which the piston rod
193 is mechanically linked. Inasmuch as the operation of this cycle
requires that heat (thermal energy for compression) be introduced
into the system in the fluid in the hot chamber 184, there is
provided coils 194 which are in thermal contact with the outer wall
of housing 783 and through which a heating fluid may be passed.
Alternatively, if the temperature of the refrigerator is such that
the heat put into the fluid in chamber 184 is at room temperature,
the coils may be replaced with heat transfer fins.
Within stepped housing 180, there are defined two expansion
chambers, the first 195 which is at an intermediate low-temperature
and the second 196 which is at the coldest temperature of the
refrigerator. These are defined through the movement of
larger-diameter pistons 197 and smaller-diameter piston 198 which
are joined through a variable linkage 199 such as that detailed in
FIGS. 4-7. Suitable sealing means, shown as O-ring seals 200 and
201, are provided to isolate the refrigeration chambers.
Displacers 197 is driven by a piston rod 202 which is also attached
to crank 192. Generally, rods 193 and 202 will be about 90 degrees
out of phase; however, this may be varied and may easily be
determined for any set of conditions by one skilled in the art.
The fluid flow path within the apparatus will be seen to comprise
(reading from chamber 184 to chamber 196) the passages 203,
regenerator 191, passages 204, chamber 185, conduit 187, chamber
186, passage 215, regenerator 205 in piston 197, chamber 195,
regenerator 206, in displacer 198, and chamber 196.
Inasmuch as the cycle itself is not part of this invention, it need
not be described in detail. A complete description of the cycle on
which this apparatus operates can be found in U.S. Pat. No.
1,275,507. It will be apparent that the apparatus of FIG. 23
realizes the same operational advantages as that of FIGS. 1, 20 and
21.
It will, of course, be apparent to those skilled in the art that
the apparatus of FIGS. 21-23 may be constructed to have more than
two refrigeration stages and that the pistons associated with one
or more stages may be joined by variable linkages as described for
the apparatus of FIG. 3. Moreover, such modifications as the fluid
flow path of FIG. 5, the spring of FIG. 1, the linking means of
FIG. 16 and pneumatic driving means may be applied to the apparatus
of FIGS. 21-23.
The apparatus of this invention therefore provides a means whereby
the volumes of those refrigeration chambers in a multistaged
cryogenic refrigerator which are maintained at the lower levels may
be adjusted by using an optimum combination of chamber diameter and
the length of the stroke of the piston defining the chambers in a
housing.
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.
* * * * *