U.S. patent number 3,656,240 [Application Number 05/037,975] was granted by the patent office on 1972-04-18 for freeze-dryer.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Nicolaas Antonie Van Dijk.
United States Patent |
3,656,240 |
Van Dijk |
April 18, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
FREEZE-DRYER
Abstract
The invention provides a freeze-dryer of a simple construction
in which the freeze-drying temperature of the vacuum chamber and
the temperature of the condenser chamber which is at a lower level
are adjusted by means of a liquid conducted along the cold head of
a cold-gas refrigerator. This liquid is also advantageously used
for defrosting the ice mass formed in the condenser chamber in a
very short period of time, after the freeze-drying process.
Inventors: |
Van Dijk; Nicolaas Antonie (Van
Houtenlaan, NL) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
|
Family
ID: |
19807069 |
Appl.
No.: |
05/037,975 |
Filed: |
May 18, 1970 |
Foreign Application Priority Data
|
|
|
|
|
May 30, 1969 [NL] |
|
|
6908334 |
|
Current U.S.
Class: |
34/92 |
Current CPC
Class: |
F26B
5/06 (20130101) |
Current International
Class: |
F26B
5/06 (20060101); F26B 5/04 (20060101); F26b
013/30 () |
Field of
Search: |
;34/5,15,92
;165/61,100,107 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matteson; Frederick L.
Assistant Examiner: Anderson; W. C.
Claims
What is claimed is:
1. In a freeze-dryer apparatus including a vacuum freeze-drying
chamber and a condensor chamber and vacuum pump means in
communication with both chambers, and a cold-gas refrigerator for
producing cold, the apparatus further comprising first, second, and
third heat-exchanger means for heat exchange respectively with said
refrigerator, the condensor chamber, and the freeze-drying chamber,
first closed duct system which includes said first and second heat
exchangers and first pump means, second closed duct system which
includes said third heat exchanger and a portion of the first duct
system, second pump means, and heating means, liquid circulated in
both of said duct systems by said corresponding pump means, a
by-pass duct in said second duct system for by-passing said portion
of the first duct system within said second duct system, control
means for controlling liquid flow in said first and second duct
systems and in said by-pass duct, whereby said circulated liquid
cools said chambers and said liquid when heated in the second duct
system also defrosts ice formed in the condensor chamber.
2. A freeze-dryer according to claim 1, further comprising a liquid
expansion container, in which a gaseous medium is present above the
liquid under such a pressure that, at any operating temperature of
the liquid, boiling of said liquid is prevented, and at least one
of said duct systems communicates with said container.
3. A freeze-dryer as claimed in claim 2 in which the operating
temperature of the vacuum chamber is controlled within the range of
from approximately -30.degree. C. to approximately +30.degree. C.
and the operating temperature of the condenser chamber is
approximately -80.degree. C., characterized in that the liquid is
R11 (trichlore monofluoro-metane -CCl.sub.3 F).
Description
The invention relates to a freeze-dryer comprising at least one
vacuum freeze-drying chamber communicating with a condenser chamber
in which a lower temperature prevails during operation than in the
vacuum chamber; a cold-producing device for supplying cold to the
chambers, including a heating device is present for controlling the
operating temperature of the vacuum chamber.
In a known freeze-dryer the cold producing device is formed by an
evaporation-condensation refrigerator in which a gas is compressed
to a high pressure by one or more compressors, is then condensed in
a condenser and expanded in one or more throttle devices. On the
one hand, liquid medium is supplied to a vaporizer arranged in the
condenser chamber where it evaporates by the withdrawal of heat
from the condense chamber and flows back to the compressor. On the
other hand, liquid medium is conducted to a second vaporizer which
is in a heat exchanging contact with a liquid present in a closed
system of ducts, supplies its cold to said liquid and flows back to
the compressor again in the gaseous phase. By means of a pumping
device incorporated in the closed system of ducts, the liquid can
circulate and again supply cold taken up from the second vaporizer
in one part of the system of ducts, to the vacuum chamber which is
in heat exchanging contact with another part of the system of
ducts. Furthermore a heating device is present in the closed system
of ducts by means of which the temperature of the cooled liquid and
hence the temperature of the vacuum chamber can be controlled. The
vacuum chamber is evacuated by means of a vacuum pumping device
communicating with the condenser chamber.
The operation of this known freeze dryer is further described as
follows: aqueous preparations which have been frozen at -50.degree.
C., for example outside the freeze-dryer, are placed in the vacuum
chamber which has previously been cooled, to -30.degree. C., for
example. The vacuum chamber is then evacuated and it is ensured, by
supplying thermal energy to the vacuum chamber via the liquid in
the closed system of ducts, that the ice present in the
preparations sublimes to water vapor. This water vapor is drawn off
to the condenser chamber cooled at a lower temperature, condenses
therein and freezes to the cold surface of the condenser
chamber.
After a few batches of preparations have thus been freeze-dried, a
large quantity of ice has deposited in the condenser chamber which
necessitates the defrosting of this chamber before the
freeze-drying process can be repeated. The cooling of the condenser
chamber generally occurs to temperatures of approximately
-80.degree. while the temperature of the vacuum chamber is
controlled from +30.degree. C. to -30.degree. to -40.degree. C.
This known freeze dryer has a few drawbacks. The dryer is
comparatively complicated, which is due to the fact, that in order
to be able to reach cooling temperatures to -80.degree. C., at
least one low-pressure compressor and one high pressure compressor
are required to obtain a high compression/expansion pressure ratio
of the gas. An additional difficulty is that special precautions
are necessary to return lubricating oil originating from the
compressors and taken along by the compressed gas to said
compressors.
Furthermore this freeze-dryer is complicated due to the fact that a
separate liquid-filled (for example, glycol) system of auxiliary
ducts is necessary to be able to control the temperature of the
vacuum chamber. Owing to the above-mentioned temperature
requirements, only a small number of gases is to be considered for
use in the evaporation-condensation refrigerator. The choice is
furthermore restricted by the properties of the compressors which
in connection with their dimensions require a given minimum suction
pressure. The sucked gas originates from the vaporizers in which
the liquefied gas evaporates. It is also desirable that the
refrigerator condenser can be cooled with cooling water which means
a further restriction in the choice of the gas.
A further drawback is that the gases which can be used, for
example, the medium known as Freon 22, have a vapour pressure which
is lower than 1 atm. at comparatively low temperatures. This means
that, since the gas pressure in the system of ducts is hence lower
than the atmospheric pressure, air can easily leak in with all the
detrimental consequences of this (reduction in efficiency,
pollution, corrosion).
In addition, with the known freeze dryer the time necessary to
defrost the ice formed in the condenser chamber is very long. This
is caused by the fact that the defrosting should be carried out at
comparatively low temperatures since otherwise the gas pressure in
the system of ducts would become inadmissibly high. In practice the
defrosting is carried out by means of water of, for example,
40.degree. C. The condition, whereby the water can transfer its
heat only to the outside of the ice mass (the ice surrounds the
vaporizer arranged in the condenser chamber for The greater part)
results in a further unfavorable influencing of the defrosting
time.
It is the object of the invention to provide a freeze-dryer of a
considerably simplified construction with which the said drawbacks
are avoided. For that purpose, the freeze-dryer according to the
invention is characterized in that the cold-producing device is
formed by a cold gas refrigerator, a first closed system of ducts
being present which comprises a first heat exchanger for exchanging
heat with the cold-gas refrigerator, and also comprises a second
heat exchanger arranged in the condenser chamber, a liquid and a
first pumping device being present in said system, a system of
ducts being furthermore present which communicates on either side
of the first heat exchanger with the first system of ducts and in
which a third heat exchanger is present arranged in the vacuum
chamber, the same liquid being present in the second system of
ducts and a bypass duct being present which communicates on either
side of the third heat-exchanger with the second system of ducts, a
second pumping device being present which, together with the
heating device, is incorporated in one part of the second system of
ducts which is situated between the two connection places of the
bypass duct with said system and which part also comprises the
third heat exchanger, one or more control cocks being present in
the second system of ducts and the bypass duct, respectively, for
controlling the flow of liquid through said system and said duct,
respectively, the first system of ducts being furthermore
constructed so that in a position of the said control cocks in
which the bypass duct is substantially entirely closes and when
only the second pumping device is in operation, the liquid mainly
flows through the second system of ducts and the part of the first
system of ducts which is situated between the connection places of
the second system of ducts hereto and which part comprises the
second heat-exchanger.
In this manner a freeze-dryer is obtained which presents great
advantage as compared with the known freeze-dryer.
By using the cold-gas refrigerator in combination with liquid in
the systems of ducts it is possible to bring both the vacuum
chamber and the condenser chamber each at their desirable
temperatures in a simple, rapid and reliable manner.
For circulating the liquid in the system of the ducts, simple
circulating pumps will do. The systems of ducts and heat exchangers
cannot be polluted by lubricating oil, since the lubricating oil
circuit forms no part of the independently operating cold-gas
refrigerator. By using liquid in the systems of ducts, the danger
of air inleak is no longer present and a good heat transfer is
ensured between said liquid and the cold and warm places
respectively, along which it is conducted.
Whereas in the known device a separate system of auxiliary ducts
with liquid is necessary which can be used only for controlling the
temperature of the vacuum chamber by heating the liquid circulating
in said system, the liquid present in the freeze-dryer according to
the invention can also be used for defrosting the condenser
chamber. By conducting the liquid, after heating in the second
system of ducts, through the second-heat-exchanger, a considerable
reduction of the defrosting time of the ice deposited in the
condenser chamber is obtained. Actually, the temperature of the
liquid, suitably chosen for that purpose, is the systems of ducts
may now be high without the danger of too high a pressure in the
ducts. The ice mass is now defrosted from within. In addition it is
possible to use water of likewise a high temperature to defrost the
ice mass again from the outside.
By choosing a second heat-exchanger which has a considerably lower
resistance to flow than the first heat exchanger, or by closing,
for example, cocks incorporated in the two sections of the first
system of ducts situated between the first heat-exchanger and the
connection places of the second system of ducts, it is achieved
that upon defrosting the condenser chamber, when the warm flow of
liquid is circulated by the second pumping device, said flow of
liquid flows substantially entirely or entirely through the second
heat exchanger or does substantially not flow or does not flow at
all through the first heat exchanger. The overall flow of liquid
hence is available for the defrosting process which owing to a
maximum heat transport through the liquid, is favorable for a rapid
defrosting. Since warm liquid does not pass the cold place of the
cold-gas refrigerator, the additional advantage is obtained that
unnecessary heating of the cold-gas refrigerator is prevented. So
during the defrosting period the freeze-dryer obtains its low
operating temperature and remains ready for operation.
In a favorable embodiment of the freeze-dryer according to the
invention at least one of the systems of ducts communicates with a
liquid expansion container in which a gaseous medium is present
above the liquid under such a pressure that, at any operating
temperature of the liquid, boiling of said liquid is prevented. As
a result of this strong evaporation of an formation of vapor
bubbles in the liquid in the systems of ducts is prevented, os that
a good heat transfer between the liquid and the heat exchangers
remains ensured. By choosing the pressure of the gaseous medium in
the expansion container to be sufficiently high, it is possible to
produce an increase of the boiling point of the liquid which is of
advantage upon defrosting the condenser chamber. The liquid can
then be heated to an extra high temperature by the heating device
without the danger of boiling phenomena occurring.
A further favorable embodiment of the freeze-dryer according to the
invention in which the operating temperature of the vacuum chamber
is controlled within the range of from approximately -30.degree. to
++.degree. C. and the operating temperature of the condenser
chamber is approximately -80.degree. C. is characterized in that
the liquid is R11 (trichlormonofluoromethane-CC1.sub.3 F.). The use
of this known liquid presents various advantages. First of all the
viscosity of said liquid (boiling point 23.8.degree. C.) in the
operative temperature range is rather constant. This means that in
the temperature range considered a good heat transfer is maintained
between the liquid and the heat exchangers. Actually, the danger
that the normally turbulant flow of liquid in the systems of ducts
decreases at comparatively low temperatures of the liquid owing to
the increased viscosity and changes into a laminar flow is absent
here.
Owing to the comparatively low viscosity a small pumping action is
sufficient while the pumps are always subjected to a substantially
constant load as a result of the fact that the viscosity remains
substantially constant in the active temperature range. All this
enables the use of small, comparatively cheap pumps in which the
constant load favorably influences the lifetime.
The use of R11 also makes it possible to heat the liquid to
comparatively high temperatures upon defrosting the moisture
receiving chamber while at the same time the pressure in the
expansion container and the systems of ducts can be comparatively
low so that thin-walled and low-weight ducts can be used. It is
possible, for example, to heat R11, at a pressure of 2.5
atmospheres in the systems of ducts, to 60.degree. C. without the
danger of boiling occuring.
BRIEF DESCRIPTION OF THE DRAWING
In order that the invention may be readily carried into effect, it
will now be described in greater detail, by way of example, with
reference to the accompanying diagrammatic drawing.
FIG. 1a shows not to scale an embodiment of the freeze dryer.
FIGS 1b and 1c shows a slightly different embodiment of the part of
the freeze-dryer shown in FIG. 1a on the right hand side of the
lines I--I.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference numeral 1 in FIG. 1a denotes a first closed system of
ducts in which a heat-exchanger 2 is incorporated which is in a
heat exchanging contact with the cold head 3 of a cold-gas
refrigerator 4, and in which a heat exchanger 5 is arranged in a
condense chamber 6. The condenser chamber communicates via a duct 7
with a vacuum freeze-drying chamber 8, and communicates via a duct
9 with a vacuum pumping device 10. It furthermore comprises a water
inlet 6' and a water outlet 6". At the places A and B, a second
system of ducts 11 communicates with the first system of ducts 1;
the second system of ducts a heat exchanger 12 is incorporated
which is arranged in the vacuum freeze-drying chamber 8.
At the places C and D a bypass duct 13 with controllable cock 14
communicates with the second system of ducts 11. A pumping device
15 is present in the first system of ducts 1, while in the second
system of ducts a controllable cock 16, a heating device 17 and a
pumping device 18 are incorporated. At the place E an expansion
container 19 comprising a valve 20 communicates with the first
system of ducts 1.
The systems of ducts are filled with a liquid which may be, for
example, R11. Above the liquid in the expansion container 19 a gas
under pressure, for example, nitrogen, is present. The heat
exchanger 2 has a resistance to flow which is considerably larger
than that of the heat exchanger 5.
The operation of this device is as follows: Cooling of the
condenser chamber 6 takes place by circulating liquid in the system
of ducts 1 by means of the pumping device 15 in the direction
denoted by the solid-line arrows. Cold absorbed by the liquid at
the cold head 3 of the refrigerator 4 in the heat exchanger 2 is
delivered again to the condenser chamber in the heat exchanger 5.
For cooling the vacuum freeze-drying chamber 8, a part of the flow
of liquid which is conducted along the cold-gas refrigerator is
tapped at A and conducted, by the pumping device 18, through the
second system of ducts 11 and heat exchanger 12 in the direction
likewise denoted by the solid-line arrows. In this heat exchanger
12 the liquid supplies its cold to the vacuum freeze-drying chamber
8. During cooling of the vacuum freeze-drying chamber 8, the
heating device 17 is not in operation and the cock 14 is fully or
partly opened. A part of the flow of liquid originating from the
heat exchanger 12 will then enter the bypass duct 13 at the point D
and mix at the point c with the cold flow of liquid passed by the
cock 16 so that there a mixed temperature of the liquid is
obtained. The remaining part of the flow of liquid originating from
the heat exchanger 12, flows to B and is mixed there with the flow
of liquid originating from the heat exchanger 5. By controlling the
passage of the cocks 16 and 14, respectively, the vacuum
freeze-drying chamber can be brought to the desirable temperature,
a temperature which is higher than that so which the condenser
chamber is adjusted. If it is desired that much cold be supplied to
the heat exchanger 12, the cock 14 can be closed so that the
overall quantity of liquid displaced by the pumping device 18 flows
to point B and then to the heat exchanger 2.
After the vacuum freeze-drying chamber 8 and the condenser chamber
6 have each reached their operating temperatures, said chambers are
evacuated by means of the vacuum pump device connected thereto and
the actual freeze-drying of the preparations can take place. For
that purpose, the heating device 17 is switched on and supplies as
much thermal energy to the flow of liquid flowing to the heat
exchanger 12 as is necessary to sublime the ice present in the
preparations in the vacuum freeze-drying chamber to water vapor,
which water vapor condenses and freezes in the condenser chamber 6
kept at a lower temperature. After a few batches of preparations
have thus been freeze-dried, a large quantity of ice has deposited
in the condenser chamber, mainly on the outside of the heat
exchanger 5. The defrosting of the condenser chamber can now be
effected in a simple and rapid manner a follows: the pumping device
15 is switched off. The cock 14 is closed and the cock 16 is fully
opened. The liquid which is heated to a comparatively high
temperature by the heating device 17 is now circulated by the
pumping device 18, along the path denoted by the broken-line
arrows. The warm liquid supplies its thermal energy in the heat
exchanger 5 to the ice in the condenser chamber. As compared with
the process during the cooling, there are tow striking differences.
First of all, the flow of liquid during the heating process flows
through the pumping device 15 and the heat exchanger 5 in a
direction which is opposite to that during the cooling process. By
the use of circulation pumps this is no problem. Secondly, the flow
of liquid substantially does not flow through or does not flow at
all through the heat exchanger 2. This is caused by the fact
already mentioned above that the resistance to flow of the heat
exchanger 2 is considerably larger than that of the heat exchanger
5 so that the flow of liquid chooses the easiest way through the
last-mentioned heat exchanger. Of course it is also possible to
prevent the flow of liquid through the heat exchanger 2 by means of
cocks incorporated in the sections of the ducts situated between
the heat exchanger 2 and the points A and E.
Since substantially little or no liquid flows through the first
heat exchanger, the whole flow of liquid is available for the heat
transport from the heating device 17 to the condenser chamber 6
which is in favor of a rapid defrosting. The liquid is heated to a
comparatively high temperature, as gas under pressure for example,
nitrogen, present in the expansion container 19 above the liquid
ensuring that the liquid does not start boiling. When the operating
temperature of the vacuum chamber is approximately in the
temperature range of from -30.degree. to +30.degree. C., and when
the operating temperating temperature of the condenser chamber is
from -70.degree. to -80.degree. C. the liquid, when R11 is used,
can be heated without boiling to 60.degree. C. at a pressure of 2.5
atmospheres in the expansion container and the systems of ducts.
During normal operation of the freeze-dryer, the pressure may vary
between 1 and 1.5 atmospheres. Should, during operation, the
pressure in the system of ducts increase too strongly by some
cause, the valve 20 opens. Since a large flow of liquid of high
temperature is conducted through the heat exchanger 5, the ice mass
deposited on it is rapidly defrosted from within. In addition, said
mass can be defrosted from without by conducting water of a high
temperature in the condenser chamber via the inlet 6'. Melting
water can flow away out of the condenser chamber via the outlet 6".
During the defrosting process the warm liquid does not pass the
cold place of the cold-gas refrigerator, so the cold supplied by
said machine is not lost. Whereas in FIG. 1a two cocks 16 and 14
are present in the duct 11 and the bypass duct 13, respectively,
FIGS. 1b and 1c show that it is also possible to use a mixing valve
21 and a distributing valve 22, respectively. For the rest the
operation remains equal to that of the freeze-dryer shown in FIG.
1a. It will be obvious from the above that the invention provides a
simple and readily operating freeze-dryer.
* * * * *