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BACKGROUND OF THE INVENTION
A portable, self heating container has important uses. For example,
programs for exploration of the planets have required that precautions be
taken to prevent any potentially hazardous organisms from contaminating
the Earth between the time when the sample is brought to the Earth on a
space vehicle and the time when the sample is brought to a control
laboratory on the Earth. A container is required whose outer surface is
sterilized at some point prior to entering the Earth's atmosphere, but
without administering excessive heat to the contents of the container that
would damage the enclosed specimen. Such a container must be efficient, of
low weight, simple, and pose no hazard to the spacecraft. A similar type
of container would be useful in passing a container into or out of a
biologically hazardous laboratory (such as where recombinant DNA
experiments are conducted).
A container which can heat the inside walls of the container and/or the
contents therein, is also useful in a variety of situations, as in
providing sterilizing facilities for field hospitals and other emergency
situations, where a lightweight device is necessary which can rapidly
apply high sterilizing temperatures.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the invention, a container is provided
which can apply considerable heat, and yet which is of low weight and
simple design. The container includes a layer of a combustible charge such
as thermit type pyrotechnic which is held between a pair of container
walls that can withstand at least moderately high temperatures, and with
the combustible material extending around substantially the entire
container in a thin layer. When the combustible material is ignited, it
generates considerable heat, which can sterilize the outside of the
container, the inside of the container, or the contents of the container,
depending on the construction of the container.
In one container structure wherein the outside of the container must be
sterilized without excessively heating the contents of the container, the
thermit-type charge lies between a thin outer casing and a thicker
structural and buffer layer, and an insulative layer is provided within
the structural layer. The thickness of the thermit-type layer is chosen so
that it produces sufficient heat to heat the thin casing to a moderately
high temperature, so that all outer surface portions are heated to at
least 230.degree. C. to assure destruction of all potential
microorganisms, and yet to not create so much heat as to melt the thin
outer casing. The structural layer lying within the thermit-type charge is
thick enough to absorb considerable amounts of heat to avoid reaching a
very high temperature, and the insulator serves to minimize the transfer
of heat to the contents of the container so that the inner walls of the
container are maintained at a temperature below 100.degree. C.
In another container, the thermit-type layer lies near a thin inside casing
or wall of the container to heat it, so as to sterilize the inside of the
container and/or heat the contents of the container.
The novel features of the invention are set forth with particularity in the
appended claims. The invention will be best understood from the following
description when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a container constructed in accordance with
one embodiment of the present invention.
FIG. 2 is an enlarged view of the area 2--2 of FIG. 1.
FIG. 3 is a view taken on the line 3--3 of FIG. 1.
FIG. 4 is a sectional side view of a container constructed in accordance
with another embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cannister or container 10 which is designed to hold a
specimen or other goods G, and to sterilize its exterior surface without
excessively heating the goods. The particular container is designed to
avoid contamination of the Earth by any microorganisms on the container,
when it is used to bring a specimen from another planet to the Earth and
then to a secured laboratory where the container can be opened and the
specimen examined. The outside of the container must be heated to a
considerable temperature such as above 230.degree. C. at every location of
the outside surface, without heating the goods to 100.degree. C.
The container includes two similar parts 10A, 10B that are bolted together
by fasteners 12. Each container half includes a substantially uniformly
thin layer of combustible material 14 such as thermit-type pyrotechnic
which can react and self-sustainedly create heat without the need for
additional oxygen or the like. A thin casing 16 surrounds the thermit
layer and forms the outside of the container. A structural-buffer member
or layer 18 in the form of a container lies within the thermit-type
material 14, and an insulator 20 lies within the structural layer. An
electrical squib igniter 22 is utilized to ignite a small quantity of
pyrotechnic powder 24, which secondarily ignites the thermit-type layer
14.
As the combustible layer 14 reacts, it creates heat which is transferred to
the casing 16 and structural layer 18 that lie on opposite sides of the
combustible layer. The heat raises the temperature of all portions of the
casing surface 16s to a moderately high temperature such as above
230.degree. C. for all surface areas of the casing for a short period of
time, typically several minutes, to destroy any microorganisms on the
casing surface. The thickness of the combustible layer 14, in relation to
the heat capacity of the casing 16, is chosen so that the casing 16 will
be heated to the required temperature, but not to such a high temperature
that it will melt. Of course, about half of the heat generated by the
ignited combustible layer 14 will be applied to the structural layer 18 to
raise its temperature. However, the structural layer 18 is designed to
have a greater heat capacity than the thin casing 16, so that the
structural layer 18 will not be heated to as high a temperature as the
casing. The insulator layer 20 is also provided to minimize the amount of
heat transfer from the structural layer 18 to the inner surface 20s of the
container and the goods G within the container. Instead, after the
combustible layer 14 has been fully combusted to raise the temperature of
the casing 16, and after the temperature of the casing 16 then drops, much
of the heat from the structural layer 18 will be transferred into the
interior of the cannister. The thin casing will soon drop in temperature
after having been raised to the sterilizing temperature, so that heat from
inner parts of the container can be conducted out to the environment.
Thus, the amount of the heating of the inside of the container is
minimized by conducting heat away from the cannister and by distributing
the limited amount of heat generated by the combustible layer to the large
heat capacity structure formed by the structural member 18 and the
insulator 20.
In order to facilitate the opening and closing of the container, the casing
16 is provided with a pair of flanges 26 which can be bolted together.
Each of the flanges is formed with a groove 28 that is filled with the
combustible charge 14, to heat the flange and the fastener 12 thereon to
assure sufficient heating of the flanges to raise them to the required
temperature. The two halves 10A, 10B of the container can be identical,
with both of them formed to receive a squib 22 and with the two squibs
being initiated simultaneously.
A container of the type shown in FIG. 1 can be constructed using aluminum
for the casing 16 and structural layer 18, to minimize the weight of the
container. The container was designed with an aluminum casing 16 of
one-eighth inch thickness, a combustible layer 14 of thermit (a mixture of
finely divided metallic zirconium and one or more oxides such as barium
chromate or iron oxide) of a substantially uniform thickness of about two
millimeters or about 0.080 inch, an aluminum structural layer 18 of
one-quarter inch thickness, and a Teflon (or rubber, formed plastic,
glass, etc. ) insulative layer 20 of one-quarter inch thickness. The
outside diameter of the container was about four inches and the height was
about one foot so that the combustible portion at the end of the container
had a diameter or length and width of much more than ten times its
thickness (actually, about fifty times its thickness). The combustible
layer portion 14w at the side walls of the container, had a
circumferential length of about one foot, which is also much more than ten
times the thickness of the layer.
The container can be formed using aluminum tubing, and the thermit-type
powder can be poured into the container space between the casing 16 and
structural layer 18 and compacted using an arc-shaped tamper just slightly
thinner than the annular space. The ends of the cylindrical container can
be formed by merely laying layers of the material on one another and
welding them to the cylindrical container portions, the flanges 26 being
similarly welded in place.
The combustible layer 14 is preferably constructed of a composition which
reacts without the significant release of gas, so that no venting is
required. A propagation speed of the ignition will be on the order of 0.2
to 1.0 centimeters per second. It is estimated that the powder reacts in
the temperature range of 800.degree.-1,000.degree. C. The pyrotechnic
column 24 which connects the electrical squib to the thermit can be formed
of a boron based pyrotechnic powder.
In many applications, heating of a container surface is necessary at the
inside of the container rather than the outside. For example the inside of
a container intended to carry a material which must not be contaminated
may have to be first sterilized. Also, there are applications where the
contents of a container must be heated, such as to sterilize instruments
in a field hospital or to begin the operation of a fuel cell that must
start at a high temperature. FIG. 4 illustrates a container 30 constructed
in accordance with another embodiment of the invention, which can provide
in-the-field heating at the inside of a portable container. The container
30 includes a combustible layer 32 of a thermit-type material which is
trapped between a casing 34 forming the innner wall of the container, and
a structural buffer layer 36 surrounding the combustible layer. An
insulator layer 38 can be provided around the structural layer 36, and a
protective outer layer 40 can be provided around the insulator. When the
combustible layer 32 is ignited as by an electrically ignitible squib 22
and pyrotechnic column 24, the combustible layer creates heat which heats
the inner casing 34. The heat can sterilize the inner casing where this is
desired, and can heat goods lying within the inner casing where this is
desired. Where only the casing needs to be heated, a thin thermit layer
can be utilized. Where goods within the inner casing 32 must be heated,
such as implements to be sterilized or a quantity of water to be turned
into steam, a somewhat thicker layer of thermit-type material may be
utilized. The casing 34 may be constructed of a very high
temperature-resistant material such as stainless steel, to enable
considerable heat transfer without melting. The surrounding structural
layer 36 serves as a structure to hold the container together and as a
heat-isolating buffer for absorbing heat from the thermit layer to
minimize the temperature at which it and the insulating layer 38 is
raised. The insulating layer 38 prevents the outside of the container from
reaching a very high temperature.
The container 30 can be constructed with a cylindrical portion 30A and an
end portion 30B, which can be easily assembled and disassembled. In many
applications, the combustible layer 32 extends around substantially the
entire container to completely sterilize the outer or inner surface
thereof. However, where it is desired only to heat goods within the
container, it is possible to utilize the thermit layer so it extends
around only a portion of the container.
Thus, the invention provides a container of relatively simple design, and
which can be highly portable, which can heat its outside or inside.
Uniform distributed heating can be obtained by a thin layer of a
combustible material such as a thermit-type pyrotechnic which can be held
at one side by a casing that is to be heated by the thermit type charge
layer. The thickness of the casing and of the thermit layer are chosen so
that the casing is heated to the desired temperature but is not
overheated. The casing is preferably constructed of a highly thermally
conductive material such as aluminum or copper, so that a large portion of
the heat generated by the combusted thermit type material is absorbed by
the casing. Although a casing of steel can be utilized, a material of
higher thermal conductivity than steel, such as aluminum or copper
provides more effective transference of heat to the casing. The side of
the combustible layer opposite the casing, can be formed of a thick layer
of material which can withstand high temperatures, so that this layer will
not be raised to as high a temperature as the casing. An insulative layer
can lie on a side of the thick isolating layer which is opposite the
thermit, so that the side (inside or outside) of the container opposite
the casing is not excessively heated.
Although particular embodiments of the invention have been described and
illustrated herein, it is recognized that modifications and variations may
readily occur to those skilled in the art, and consequently it is intended
that the claims be interpreted to cover such modifications and
equivalents.
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