U.S. patent application number 10/437655 was filed with the patent office on 2004-11-18 for cryogenic freezer.
Invention is credited to Brooks, Jeff.
Application Number | 20040226956 10/437655 |
Document ID | / |
Family ID | 33029796 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040226956 |
Kind Code |
A1 |
Brooks, Jeff |
November 18, 2004 |
Cryogenic freezer
Abstract
A rectangular double walled cryogenic freezer has a vacuum space
filled with alternating layers of flexible insulating material and
a reflective material. A support structure is also positioned in
the vacuum space. The support structure is open-celled and provides
structural support for the freezer walls to prevent wall
deformation when a vacuum is drawn. The support structure may be
open-cell rigid foam or a support grid sandwiched between two
layers of rigid insulation material.
Inventors: |
Brooks, Jeff; (Jasper,
GA) |
Correspondence
Address: |
R. Blake Johnston, Esq.
PIPER RUDNICK
P.O. Box 64807
Chicago
IL
60664-0807
US
|
Family ID: |
33029796 |
Appl. No.: |
10/437655 |
Filed: |
May 14, 2003 |
Current U.S.
Class: |
220/592.02 |
Current CPC
Class: |
F25D 2201/124 20130101;
F25D 3/10 20130101; F25D 23/06 20130101; F25D 2201/1282 20130101;
F25D 2201/14 20130101; F25D 2201/1262 20130101 |
Class at
Publication: |
220/592.02 |
International
Class: |
F25D 023/00 |
Claims
What is claimed is:
1. A cryogenic freezer for storing materials at temperatures
deviating greatly from ambient comprising: a) an inner container,
said inner container comprising four walls and a bottom; b) an
outer container enclosing the inner container and defining a vacuum
space therebetween, said outer container comprising four walls and
a bottom, said inner container being connected to the outer
container at the top of said walls to seal said vacuum space; c) a
plurality alternating layers of reflective material and flexible
insulating material; and d) a support structure positioned in the
sealed vacuum space with one side positioned adjacent to the
plurality of alternating layers, said support structure
substantially reducing deflection of the walls when air is
evacuated from the vacuum space.
2. The cryogenic freezer of claim 1 wherein said support structure
is a support grid.
3. The cryogenic freezer of claim 2 wherein the support grid
includes a first set of parallel strip members oriented
perpendicular to a second set of parallel strip members so that a
plurality of cells are formed.
4. The cryogenic freezer of claim 3 wherein openings are provided
in said parallel strip members so that the cells are open.
5. The cryogenic freezer of claim 4 where the support grid is
sandwiched between layers of rigid insulation material.
6. The cryogenic freezer of claim 2 wherein the support grid is
sandwiched between layers of rigid insulation material.
7. The cryogenic freezer of claim 6 wherein the rigid insulation
material is fiberglass sheeting.
8. The cryogenic freezer of claim 1 where in the support structure
is open-cell foam.
9. The cryogenic freezer of claim 1 wherein the vacuum space also
includes a molecular sieve for absorbing gases therein.
10. The cryogenic freezer of claim 1 wherein the flexible
insulation material is insulation paper.
11. The cryogenic freezer of claim 1 wherein the reflective
material is reflective foil.
12. The cryogenic freezer of claim 1 further comprising a sealable
vacuum port formed in the outer container.
13. The cryogenic freezer of claim 1 wherein the plurality of
alternating layers are adjacent to the inner container and the
support structure is adjacent to the outer container.
14. A method for assembling a doubled walled vacuum insulated
cryogenic freezer for storing materials at temperatures deviating
greatly from ambient comprising the steps of: a) providing an inner
container with four walls and a bottom; b) positioning a plurality
of alternating layers of reflective material and flexible
insulating material adjacent to the inner container; c) positioning
a support structure adjacent to the plurality of alternating layers
for preventing deflection of the walls and bottom surface when a
vacuum is drawn; d) positioning the inner container in an outer
container, the outer container having four walls and a bottom, to
define a vacuum space therebetween; e) connecting the inner
container to the outer container at the top walls to seal the
vacuum space; and f) evacuating air from the vacuum space.
15. The method of claim 14 further comprising the step of
sandwiching the support structure between two layers of rigid
insulation material.
16. The method of claim 15 wherein the rigid insulation material is
fiberglass sheets.
17. The method of claim 14 wherein the flexible insulation material
is insulation paper.
18. The method of claim 14 wherein the reflective material is
reflective foil.
19. The method of claim 14 wherein the support structure is a
support grid.
20. The method of claim 14 wherein the support structure is
open-cell foam.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to cryogenic freezers, and, more
particularly, to a vacuum insulated cryogenic freezer that provides
increased storage capacity and improved insulation performance.
[0002] Cryogenic freezers have a wide variety of industrial
applications, including but not limited to, storing biological
materials such as blood, bone marrow, and micro-organic cultures.
These biological materials must be maintained at low temperatures
in order to be stored for an extended period without
deteriorating.
[0003] Cryogenic freezers typically are double walled, vacuum
insulated containers partially filled with a cryogenic liquid such
as liquid nitrogen for establishing an extremely cold storage
environment. Liquid nitrogen has a low boiling point of 77.4 K
(-320.4.degree. F.). Since cryogenic liquids have a low boiling
point and, thus, a low heat of vaporization, heat inflow from the
ambient can cause significant losses of cryogen due to the
evaporation.
[0004] In order to minimize the amount of cryogen lost due to
evaporation, the cryogenic freezer requires thermal and radiant
barriers such as insulation and a high vacuum between the container
walls. The vacuum space can also be filled with multiple layers of
insulation to reduce heat transfer.
[0005] An example of multi-layered insulation is a low conductive
sheet material comprised of fibers for reducing heat transfer by
conduction. Also, the insulation can comprise radiation layers that
are combined with the fiber layers. The radiation layer reduces the
transmission of radiant heat in the freezer see, for example, U.S.
Pat. No. 5,542,255 to Preston et al. and U.S. Pat. No. 5,404,918 to
Gustafson.
[0006] The insulation and vacuum chambers of prior cryogenic
freezers address the heat transfer problems due to the low boiling
point of the cryogen. But, the characteristics of the insulation
materials pose limitations to the physical design of the cryogenic
freezers.
[0007] Containers have been designed with the vacuum space capable
of maintaining a low pressure of 0.1 microns when the container is
holding a cryogen. Such containers, however, typically feature a
round, oval, or cylindrical shape. Such shapes provide the
structural strength required by the walls of the container when
such a high vacuum is drawn. If these cryogenic freezers were
rectangular, the walls would collapse or deform when the vacuum is
drawn due to insufficient structural support. Typically, the
insulation materials disposed in the vacuum space of flat panel
freezers fail to provide enough structural support for the
container walls. Thus, the shape of the container is limited to
cylindrical shapes.
[0008] Accordingly, it is desirable to provide a cryogenic freezer
with optimum storage capacity such as a cube or rectangular
enclosure which enables the walls of the freezer to maintain their
shape when a high vacuum is drawn.
[0009] A rectangular cryogenic freezer that addresses the above
issues is disclosed in U.S. Pat. No. 6,230,500 to Mao et al. The
Mao et al. '500 patent discloses a rectangular freezer with a
vacuum space that is filled with alternating layers of reflective
material and three dimensional geometric grid support structure
material. The reflective material is comprised of pieces of
reflective foil surrounding an insulating material, such as
SUPERGEL foam, manufactured by the Cabot Corporation of Boston,
Mass. While effective, a disadvantage of the freezer of the Mao et
al. '500 patent is the added costs and manufacturing complexity of
using multiple support structure layers. In addition, the three
dimensional geometric grid material and reflective material of the
Mao et al. '500 are expensive to construct.
[0010] Accordingly, it is an object of the present invention to
provide a cryogenic freezer that offers maximum storage capability
at a low cost with flat interior and exterior walls.
[0011] It is another object of the present invention to provide a
cryogenic freezer with reduced thermal conductivity and radiant
energy transfer.
[0012] It is another object of the present invention to provide a
cryogenic freezer that is economical to construct.
SUMMARY OF THE INVENTION
[0013] The present invention is a cryogenic freezer for storing
materials at temperatures deviating greatly from ambient. The
freezer includes inner and outer containers, each having four walls
and a bottom. The inner container is positioned within the outer
container and the tops of their walls are sealed so that a vacuum
space is defined therebetween. A plurality of alternating layers of
reflective material and a flexible insulating material are
positioned in the vacuum space adjacent the walls of the inner
container. A support structure is positioned in the sealed vacuum
space with one side positioned adjacent to the plurality of
alternating layers and the other side adjacent to the walls of the
outer container. The support structure substantially reduces
deflection of the walls when air is evacuated from the vacuum
space.
[0014] The support structure may be a support grid sandwiched
between two layers of rigid insulating material. The support grid
includes a first set of parallel strip members oriented
perpendicular to a second set of parallel strip members so that a
plurality of cells are formed. Openings are provided in the
parallel strip members so that the cells are open. Alternatively,
the support structure may be an open-cell foam material. The vacuum
space also includes a molecular sieve for absorbing gases therein.
A sealable vacuum port is formed in the outer container and is in
communication with the vacuum space so that a vacuum may be pulled
on the vacuum space.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side elevation view showing a section of a first
embodiment of the cryogenic freezer of the present invention;
[0016] FIG. 2 is an enlarged sectional view taken along line 2-2 of
FIG. 2 showing the support grid and the reflective material that
are inserted between the inner and outer container;
[0017] FIG. 3 is a perspective view of the support grid of the
cryogenic freezer of FIGS. 1 and 2;
[0018] FIG. 4 is a top view of the support grid of FIG. 3;
[0019] FIG. 5 is a side elevation view showing a section of a
second embodiment of the cryogenic freezer of the present
invention;
[0020] FIG. 6 is an enlarged sectional view taken along line 6-6 of
FIG. 5 showing the support foam and the reflective material that
are inserted between the inner and outer container.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] With reference to FIG. 1, a first embodiment of the
cryogenic freezer of the present invention is indicated generally
at 10. The cryogenic freezer 10 features an inner container 12, an
outer container 14, and a vacuum space 16 therebetween. The inner
container 12 and outer container 14 are preferably constructed from
stainless steel. Typical freezer dimensions are
27".times.27".times.35" (L.times.W.times.H).
[0022] The freezer 10 is cubic or box-shaped and the inner
container 12 and the outer container 14 each have four square or
rectangular side walls and a square or rectangular bottom. A top 15
is pivotally connected to the top edge of the freezer. The
rectangular freezer takes up the same amount of floor space as
cylindrical shaped cryogenic freezers commonly known in the art.
The larger volume of the rectangular design, however, provides
additional storage space in the freezer.
[0023] As illustrated in FIG. 2, the vacuum space 16 contains
alternating layers of a reflective material 18 and a flexible
insulating material 20 adjacent to inner container 12. A support
structure in the form of a support grid 22 sandwiched between two
layers of rigid insulation material 26a and 26b is positioned
between the outer container 14 and the alternating reflective and
flexible insulating material layers.
[0024] As illustrated in FIG. 1, the vacuum space includes a
molecular sieve 24. The molecular sieve 24 can be, but is not
limited to, a carbon or ceramic based material. The molecular sieve
24 is preferably laid on the outside bottom surface of the inner
container 12 during assembly. The molecular sieve 24 addresses the
problem of out-gassing and chemically absorbs gas remaining after a
vacuum is drawn.
[0025] Alternatively, getters, commonly known in the art, can be
placed at the bottom of the freezer in the vacuum space. The
getters also address the problem of out-gassing. The getters
chemically absorb the gas remaining after a vacuum is drawn.
[0026] Turning to FIG. 2, the reflective material 18 is preferably
comprised of sheets of reflective foil. An example of a suitable
flexible insulating material 20 is insulation paper such as
CRYOTHERM 243 insulating paper from the Lydall Corporation of
Manchester, Conn. At least one layer of the flexible insulating
material 20 is placed on either side of the reflective foil 18. The
air between the reflective and flexible insulating material layers
is evacuated as the vacuum space 16 is evacuated. The reflective
foil reduces the radiant energy that is transmitted through the
vacuum space 16 between the inner container 12 and the outer
container 14. The flexible insulating material 20 provides a
thermal barrier between each layer of reflective foil.
[0027] FIG. 3 illustrates, in general at 22, a perspective view of
the support grid. The support grid 22 features a first set of
parallel strip members 23 that are oriented in perpendicular
fashion to a second set of parallel strip members 24. As a result,
as illustrated in FIG. 4, a number of cells 25 are formed. As
illustrated in FIGS. 1, 2 and 3, the portions of the strip members
23 and 24 defining the walls of each cell 25 are provided with
openings 27. As a result, the support grid 22 features an open-cell
configuration to allow air to be evacuated out of the vacuum space
16 to form the vacuum. The open-cell grid structure also enables
the molecular sieve 24 to absorb residual moisture and gas in the
vacuum space to insure long vacuum life.
[0028] The support grid preferably is constructed from a composite,
plastic, or ceramic material. The support grid 22 material should
be selected to limit the thermal conductivity and control
out-gassing in the vacuum space. A list of appropriate materials
for the support grid 22 includes, but is not limited to, T304
stainlesss steel, polyurethane, Ryton R4, Vectra LCP, Vectra E130,
Noryl GFN-3-801, Ultem 2300, Valox 420, Profax PP701N,
polypropylene and Nylon 66.
[0029] The support grid 22 provides physical support to the walls
of the inner and outer containers 12 and 14 of the cryogenic
freezer so that when a vacuum is drawn in vacuum space 16, they do
not collapse. The support grid 22 can withstand the maximum
pressure at full vacuum because of its grid structure. The support
grid 22 uniformly distributes the load on the walls of the inner
and outer containers 12 and 14. Thus, the thickness of the walls of
the inner and outer containers 12 and 14, respectively, can be
reduced.
[0030] The low heat transfer coefficient of the support grid 22
minimizes the heat conducted from the outer container 14 to the
inner container 12. The support grid 22 also reduces heat
conductivity by maximizing the open space and minimizing direct
contact between the support grid 22 and the layers of rigid
insulation material 26a and 26b (FIG. 2).
[0031] As stated above and illustrated in FIG. 2, the support grid
22 is sandwiched between two layers of rigid insulation material
26a and 26b. The rigid insulation material preferably is G-11
fiberglass sheeting. The rigid insulation material provides
additional thermal insulation between the support grid 22 and the
outer container 14 as well as between the support grid and the
alternating layers of reflective material 18 and flexible
insulation material 20. In addition, rigid insulation material 26a
prevents the edges of support grid 22 from tearing the reflective
and flexible insulation materials 18 and 20.
[0032] The cryogenic freezer 10 is assembled by placing the
molecular sieve 24 on the outside bottom surface of the inner
container 12. Alternating layers of the reflective material 18 and
flexible insulation 20 are layered in the vacuum space such that
the first and last layer placed are flexible insulation 20. The
number of layers is preferably thirty or less. This is followed by
the rigid insulation material 26a, then the support grid 22 and
then the rigid insulation material 26b which abuts the inside
surface of the outer container 14. After the inner container 12 is
positioned within the outer container 14, the annular opening
between the two at the top of the freezer is closed with a
ring-shaped top plate, illustrated at 30 in FIG. 1. The top plate
30 is welded to the top edges of the inner container 12 and the
outer container 14 to seal the space between them, that is, vacuum
space 16.
[0033] A vacuum is drawn in space 16 to increase the insulation
value of the freezer. The cryogenic freezer 10 includes a port 28
(FIG. 1) in the outer container 14 for that purpose. The port 28
may be located at the rim of the top or on the bottom of the
freezer. (A vacuum pump is connected to the port 28 to evacuate the
air in the vacuum space 16. Thereafter the port is sealed.
[0034] A second embodiment of the cryogenic freezer of the present
invention is indicated in general at 110 in FIG. 5. As with the
embodiment of FIGS. 1-4, the freezer includes an inner container
112 and an outer container 114 with a vacuum space 116
therebetween. The inner and outer containers each include four
rectangular or square side walls and a square or rectangular bottom
so that the freezer is cubic or box-shaped. In addition, as with
the embodiment of FIGS. 1-4, a molecular sieve 124 or a getter is
positioned within the vacuum space 116 to absorb gas therein. A top
115 is pivotally connected to the top edge of the freezer.
[0035] As illustrated in FIG. 6, the vacuum space 116 is filled
with a foam support structure 122 and, as with the embodiment of
FIGS. 1-4, alternating layers of reflective material 118 and
flexible insulation 120. The reflective material 118 and flexible
insulation 120 may be constructed of the same materials recited
above with reference to reflective material 18 and flexible
insulation 20 in FIG. 2.
[0036] The foam support structure 122 replaces the support grid and
rigid insulation layers (22, 26a and 26b, respectively, in FIG. 2)
of the embodiment of FIGS. 1-4. The rigid open cell foam support
122 may be, but is not limited to, plastic, metallic or ceramic
open cell foam. The foam material should be selected to limit the
thermal conductivity and control out-gassing in the vacuum space.
For example, the support foam material may be, but is not limited
to, stainless steel, polyurethane or polystyrene.
[0037] The support foam provides physical support to the walls
inner and outer containers 112 and 114 so that when a vacuum is
drawn on vacuum space 116, they do not collapse. The support foam
122 can withstand the maximum pressure at full vacuum because of
its cellular structure. The support foam 122 uniformly distributes
the load on the walls of the inner and outer containers 112 and
114. As a result, the thickness of the walls may be reduced.
[0038] The support foam 122 is configured with an open-cell
structure to allow air to be evacuated out of the vacuum space 116
to form the vacuum. The open-cell foam structure enables the
molecular sieve 124 to absorb residual moisture and gas in the
vacuum space 116 to ensure long vacuum life for the freezer. As
with the embodiment of FIGS. 1-4, the low heat transfer coefficient
of the support foam 122 minimizes the heat conducted from the outer
container 114 to the inner container 112. The support foam 122 also
reduces heat conductivity by maximizing the open space.
[0039] The cryogenic freezer 110 is assembled by placing the
molecular sieve 124 on the outside surface of the bottom of the
inner container 112. Alternating layers of the reflective material
118 and the flexible insulation 120 are then placed in the vacuum
space 116 such that the first layer placed against the inner wall
112 is flexible insulation material. Preferably up to 30 layers are
formed with the last sheet being a sheet of flexible insulation
material. The support foam 122 is next positioned so as to rest
between the layers and the walls of outer container 114 when the
freezer is assembled. Once the inner container 112 is properly
positioned within the outer container 114, the resulting open
annular top is closed, and the vacuum space 116 sealed, by a
ring-shaped top plate 130 that is welded to the top edges of the
walls of inner container 112 and outer container 114 (FIG. 5).
[0040] As with the embodiment of FIGS. 1-4, a vacuum is drawn in
space 16 to increase the insulation value of the freezer. The
cryogenic freezer 110 includes a sealable port 128 (FIG. 5) in the
outer container 114 that connects to a vacuum pump for that
purpose.
[0041] While the preferred embodiments of the invention have been
shown and described, it will be apparent to those skilled in the
art that changes and modifications may be made therein without
departing from the spirit of the invention, the scope of which is
defined by the appended claims.
* * * * *