DEVICE FOR DEEP-FREEZING PORTIONS OF ORGANIC MATERIAL

The present invention relates to an apparatus for freezing and storage of portions of organic material.

BACKGROUND

In order to successfully preserve biomolecules, cells and biological tissue for extended periods of time, storage below -80° C is generally required. However, both shelf life and the ability to recover living cells are dramatically improved at even lower temperatures down to about -196° C, which is the boiling point of liquid nitrogen. Therefore, liquid nitrogen is often used as a cooling agent for preservation of organic material, although due care must be taken when handling it in order to avoid frost-bites, also from the nitrogen that vaporizes due to the large temperature difference between the liquid gas and the surrounding air.

Freezers operating at such low temperatures are generally known as cryogenic freezers, and the organic material stored therein is said to be cryo-preserved. There are different opinions on the upper temperature limit below which the term cryogenics should be applied to temperatures. The American National Institute of Standards and Technology has suggested an upper limit of -150° C, while some scientists regard the boiling point of oxygen (-183° C) as the upper limit. However, it is generally agreed, that a freezer refers to a storage device that operates from about -5° C to -20° C, an ultra low freezer operates from about -50° C to -90° C, and a cryogenic freezer operates from about -140° C to -196° C.

Hospitals, laboratories and other research institutes all over the world experience an ever increasing need to be able to cryo-preserve, store and handle different types of organic material, and many hospitals have storage systems for frozen and cryo- preserved material spread around in many different departments. Such use of a

number of relatively small storage systems is not very effective, neither when it comes to the space occupied by the many systems, nor when regarding the energy consumed to keep the stored materials at sufficiently low temperatures.

Especially, when storage systems are arranged as ordinary laboratory freezer compartments, where containers are normally stored in front of and on top of each other in order to maximize the use of the available space within the freezer, the freezer door often is required to be kept open for an extended period of time while the desired sample container is found, and the interior temperature of the storage system increases temporarily. Not only is it energy consuming to bring back the interior temperature to a desired level, but the samples of material housed near the door of the storage system may degrade rapidly due to repeated thawing and refreezing as the temperature raises and decreases again every time the door is opened.

Therefore, since space is often in short supply in hospitals, liquid nitrogen is a very expensive substance and it is important to avoid thawing of stored material, increasingly large, more energy efficient and automated storage systems have been constructed.

International Patent Application WO 91/02202 discloses a low-temperature freezing and storage apparatus comprising a housing with a plurality of chambers kept at different temperatures, through which chambers a common conveyor supporting a number of specimen-containing receptacles run. An access door in the insulated shell enables deposition and removal of a selected one of the receptacles from the housing, the selected receptacle being brought to a position just inside the access door by a computerized system controlling the movements of the conveyor. Some drawbacks of the disclosed system is that the samples experience varying temperatures as they are transported through the different chambers of the housing by the conveyor, that the interior temperature of at least one whole chamber is raised when the access door

is opened, and that the capacity of the storage system (for instance measured as volume of organic material stored per unit volume of the system) is not very high.

The refrigeration storage system disclosed in International Patent Application WO 01/88446 is better optimized with respect to the utilization of the space inside the system. In this system, however, the access opening opens up to the whole of the interior of the storage system, thus exposing all stored samples to a raise in temperature, when the access opening is opened.

U.S. Patent Application US 2004/0154322 discloses an automated storage and retrieval apparatus for freezers comprising a climate-controlled chamber on a side wall for deposition of samples into the system and removal of samples from the system. The apparatus, which operates at ultra low temperatures, is confined to very small samples that are suitable for being stored in the wells of microplates. The system is far from being optimized with regard to utilization of space. Furthermore, all samples are kept in one chamber meaning that a raise in temperature will affect all samples stored in the system.

An objective of the present invention is to provide a large-scale apparatus for cryo- preservation of portions of organic material overcoming the problems and drawbacks of systems known in the art as described above.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to an apparatus for freezing and storage of portions of organic material, said apparatus comprising an internal conveyor system for transportation of stored portions of organic material inside said apparatus, an insulated shell and a primary door in said shell. Said apparatus further comprises at least two secondary doors in said shell, each of which secondary doors opens only to a limited number of said stored portions of organic material, and said primary door

and said secondary doors are arranged so that portions of organic material can be deposited into or removed from said apparatus when said primary door and at least one of said secondary doors are open at the same time.

A system where at least two doors need to be open at the same time in order to get access to the cold interior of the apparatus, of which one or more secondary doors only open to a limited number of stored portions of organic material, is advantageous for at least two reasons, since a raise of temperature only occurs among the portions of organic material to which the one or more secondary doors open. Firstly, the problems of thawing and refreezing of stored material are also limited to the same limited number of portions of organic material. Secondly, the amount of energy needed to regain the desired temperature of the interior of the apparatus is also reduced, because only a part of the interior is affected by the temperature raise.

In a preferred embodiment of the invention, the primary door constitutes a part of the insulated shell. Therefore, the primary door is well insulated and the secondary doors can be made without any substantial amount of insulation, thus making it possible to open and close the secondary doors quickly and reduce the amount of time in which at least a part of the interior system is open to the environment. In particular, if sliding doors are used as secondary doors, they can be made very thin if they do not need to be insulated.

Is should be noticed, that by the term "portion" is meant any given quantity or amount of organic material to be frozen and stored within the apparatus. Examples of portions of organic material could be a small tissue sample, such as a biopsy or a scrap of skin stored for later analysis, or half a liter of human blood stored for use in connection with a surgical operation or the like.

According to the present invention, said one or more secondary doors may be hinged. In a preferred embodiment of the invention, however, said one or more secondary doors comprise one or more sliding doors.

The use of sliding doors is preferred because they require much less space to open and close than hinged doors, thus leaving more space for storage inside the apparatus.

It should be noticed that the term "door" does also include doors comprising two or more parts that open together, the openings behind which doors form a common opening through the insulated shell.

In a preferred embodiment of the invention, the apparatus further comprises a plurality of cassettes arranged each to be able to comprise a plurality of said portions of organic material.

The use of cassettes is advantageous in that it enables the users of the system to organize and arrange different stored portions of organic material that are related to each other in one way or another and should advantageously be stored together. Also, the use of cassettes enables storage of portions of organic material of different sizes and dimensions by adapting cassettes to contain different formats of the portions of organic material.

Furthermore, the use of cassettes enables for easy access to storage space deep inside the system, which would otherwise have been difficult to reach, and cassettes can be packed tightly, thus optimizing the utilization of the space for storage inside the apparatus, and at the same time facilitates the organization of the stored portions of organic material.

In a preferred embodiment of the invention, said cassettes each comprises one or more lids arranged to be able to be opened for access to material stored inside the cassette.

In order for the stored material not to fall out of the cassettes when the internal conveyor system of the apparatus is moving, which can very well imply that the cassettes are turned upside down, it is advantageous if the cassettes are equipped with one or more lids.

In a further preferred embodiment of the invention, said cassettes each further comprises a first locking mechanism arranged to be positioned in one of at least two different positions, in a first position of which first locking mechanism said one or more lids can be opened and closed, and in a second position of which first locking mechanism said one or more lids are locked in a closed position.

Advantageously, the lids of the cassettes are equipped with a locking mechanism in order to prevent the lids from opening when it is not desired.

In an embodiment of the invention, said cassettes each are arranged to be deposited into or removed from said apparatus as a unity.

Preferably, the cassettes can be deposited into and removed from the system as unities for at least three reasons. Firstly, if a cassette were to be opened and one or more portions were picked up from it or deposited into it while the cassette was still inside the apparatus, the two doors would have to be open for an extended period of time causing an excessive amount of energy to be lost. Secondly, too much space that could otherwise have been used for storage would be required inside the apparatus for handling the cassettes without first removing them from the apparatus. Thirdly, if the portions of organic material stored in a cassette are related to each

other and should be used together, it is advantageous if they could be removed from the apparatus in a single operation.

In a preferred embodiment of the invention, the widths of said secondary doors correspond to the widths of said cassettes.

If the widths of the secondary doors correspond to the widths of the cassettes, the opening into the cold interior is as small as possible while still enabling a cassette to be deposited or removed, thus reducing to a minimum the energy loss during the opening period.

In another preferred embodiment of the invention, the widths of said secondary doors correspond to the widths of said cassettes plus between 0 cm and 8 cm, preferably between 0.5 cm and 5 cm, said secondary doors are shifted by half a cassette width with relation to said cassettes, and neighboring secondary doors overlap each other.

By shifting the secondary doors by half a cassette width and opening two secondary doors at a time, more space for depositing or removing a cassette is obtained. Furthermore, with such a construction, it is possible to make the secondary doors overlap each other and seal the secondary doors in an appropriate manner. Still, on each side of the cassette, there will be half a cassette width minus the overlap and possibly some space for sealing, when the two secondary doors are opened.

Also within the scope of the present invention are embodiments including secondary doors with smaller widths than the cassettes, in which embodiments it is necessary to open a set of doors comprising two or more secondary doors in order to deposit or remove a cassette.

In a preferred embodiment of the invention, the apparatus further comprises a plurality of boxes each suitable for storage of a plurality of said portions of organic material.

Arranging the stored material in a number of boxes is an efficient and practical way of organizing the material and, furthermore, boxes can be packed very tightly, thus optimizing the utilization of the space for storage inside the apparatus. Also, the use of boxes enables usage of different types and sizes of cassettes by adapting boxes to contain different formats of cassettes.

In a further preferred embodiment of the invention, said boxes are arranged each to be able to comprise at least one of said cassettes.

In yet a further preferred embodiment of the invention, said boxes are arranged each to be able to comprise a plurality of said cassettes arranged in one or more rows.

Combining the use of boxes and cassettes, the latter being preferably arranged in one or more rows, optimizes the utilization of the space for storage inside the apparatus and facilitates the organization of the stored material.

In a preferred embodiment of the invention, the width of said primary door corresponds to the length of said one or more rows.

If the length of the primary door corresponds to the length of the one or more rows of cassettes, the opening is as small as possible while still enabling any particular cassette to be deposited or removed by opening the relevant secondary door(s), thus reducing to a minimum the energy loss during the opening period.

In a preferred embodiment of the invention, said boxes are connected together to form a closed loop chain, i.e. an endless chain, at least partly constituting said internal conveyor system.

The tightest packing of the boxes and, thus, the most efficient utilization of the space for storage inside the apparatus is obtained, if the boxes are connected together and, themselves, constitute at least a part of the internal conveyor system.

In a preferred embodiment of the invention, said internal conveyor system is of the paternoster type.

The term "paternoster" ("Our Father" in Latin, the beginning of the Lord's Prayer) refers to a series of compartments moving along a looped circuit, probably due to the similarity with rosary beads (prayer beads).

A series of compartments (in the present case represented by boxes) moving along a looped circuit is a very efficient way of transporting things, when a particular item should always be able to be transported to a given position (in the present case: to the system of primary and secondary doors in the insulated shell) in a relatively short time.

In a preferred embodiment of the invention, said cassettes each further comprises a second locking mechanism arranged to be positioned in one of at least two different positions, in a first position of which second locking mechanism the cassette can be deposited into or removed from said apparatus, and in a second position of which second locking mechanism the cassette is locked directly or indirectly to said conveyor system.

In order to prevent the cassettes from being shaken unnecessarily and tumble around when the internal conveyor system of the apparatus is moving, it is advantageous if the cassettes can be locked to the conveyor system.

In yet a preferred embodiment of the invention, in said second position of said second locking mechanism the cassette is locked to one of said boxes comprising the cassette.

If the cassettes are stored in boxes, the simplest and easiest solution is to lock the cassettes directly to the boxes in which they are stored.

In a further preferred embodiment of the invention, said second locking mechanism is automatically positioned in said second position, if it is not already positioned there, when said internal conveyor system starts moving.

This is a very advantageous feature ensuring that the cassettes are locked to the conveyor system when moving, even if the operator should forget to lock the cassette after depositing it into the apparatus.

In a preferred embodiment of the invention, said first locking mechanism and said second locking mechanism both are integrated in a single combined locking mechanism.

Advantageously, the two locking mechanism are integrated in one mechanism for easy handling of the cassettes. Also, combining the two mechanisms into one mechanism saves space inside the apparatus.

In a preferred embodiment of the invention, said insulated shell comprises at least an inner part and an outer part.

Constructing the insulated shell as multipart insulation comprising at least two parts is advantageous for obtaining a very efficient insulating function of the shell.

According to the present invention, any suitable material, such as a plastic material may be used for the insulated shell. In a preferred embodiment of the invention, however, said inner part comprises at least one layer of vacuum panels enclosed by at least one layer of fibrous material, such as fiberglass.

In a preferred embodiment of the invention, said outer part comprises at least one layer of vacuum panels enclosed by at least one layer (typical a double layer) of fibrous material, such as fiberglass.

Constructing the inner part and the outer part of the insulated shell using vacuum panel assures a very good insulation effect, since vacuum panels range between the most efficient types of insulating materials on the market.

In a further preferred embodiment, a mean space between said inner part and said outer part contains insulating foam, such as polystyrene foam.

Placing insulating foam between the inner part and the outer part of the insulated shell further improves the insulating function of the shell.

In a preferred embodiment of the invention, the air pressure in a mean space between said inner part and said outer part is higher than the air pressure outside said insulated shell.

In yet a preferred embodiment of the invention, the air pressure in the inner space of said apparatus is higher than the air pressure outside said insulated shell

Keeping the air pressures between the two parts of the insulated shell and inside the shell, i.e. inside the apparatus, higher than the air pressure outside the shell significantly reduces the amount of air at ambient temperature that enters the interior of the apparatus and, thus, the temperature raise within the apparatus, when the doors are opened.

In a preferred embodiment of the invention, a cooling tank containing a cooling agent is arranged in a position, where it is at least partly surrounded by said internal conveyor system.

Placing a cooling tank inside the system is advantageous because it provides the system with an operational reliability even if the external supply of cooling agent should fail for a shorter period of time,

Placing the tank in the center of the apparatus, i.e. within the internal conveyor system, is advantageous because this space could not be utilized for storage of any portions of organic material anyway. Furthermore, when the tank is placed within the insulated shell of the system, the requirements for insulating the tank itself is dramatically reduced compared to the requirements of a tank placed outside the system. Finally, a central position of the cooling tank is optimal because the energy absorbed by vaporization of the cooling agent is used for cooling the system.

In a preferred embodiment of the invention, said portions of organic material are individually contained in sample containers.

Depending on the type of organic material, the portions are advantageously contained in sample containers in order to avoid contamination of the organic material and for hygienic reasons.

In a preferred embodiment of the invention, said portions of organic material comprise a liquid and said sample containers comprise one or more liquid containers.

It should be understood that the expression "liquid" refers to a material that is liquid at normal room temperatures. Like most other materials, such a material will be in a solid (frozen) state at cryogenic temperatures like the ones inside an operating apparatus according to the present invention.

In a preferred embodiment of the invention, the apparatus is cooled by vaporization of liquid nitrogen.

According to the invention, the apparatus can be arranged for operating at different temperatures within the ultra low as well as within the cryogenic temperature ranges as defined above. In a preferred embodiment of the invention, however, the apparatus is arranged for operating at cryogenic temperatures about -170° C.

Both shelf life and the ability to recover living cells that have been frozen are dramatically improved, if they have been frozen at cryogenic temperatures like -170° C, which can, advantageously, be obtained by cooling the apparatus by vaporization of liquid nitrogen.

In a preferred embodiment, the apparatus is constructed and manufactured in one or more assembly modules arranged to be combined with each other to form the complete apparatus on the site in which the apparatus is supposed to be placed and operated, each of which modules has dimensions small enough to let the module be transported through the opening of a standard door opening.

By the term "a standard door opening" is meant the dimensions of a door that could be expected to be found in a hospital, such as a door of height 2200 mm and width 800 mm or 1000 mm.

Manufacturing the apparatus in assembly modules within the above mentioned dimensions is advantageous, because this makes it possible to install the apparatus in existing buildings without having to rebuild or modify the buildings.

In a preferred embodiment, the apparatus is combined with computer means facilitating registration of portions of organic material to be stored within the apparatus and automating storage, search of and/or access to individual portions of organic material stored within the apparatus.

Modern computer means are ideal both for registration of the portions of organic material stored within the apparatus and for controlling the operation and movement of the internal conveyor system.

In a preferred aspect of the invention, it is used for freezing and storage of portions of blood.

Among other utilizations, the invention is intended to be used for storage of blood portions, typically about half a liter each, for use in connection with surgical operations or the like, which portions are advantageously contained in liquid containers.

It is a general purpose of the present invention to provide a very compact system in order to minimize the amount of space and energy used for cooling and storage and, thus, obtain a high energy efficiency compared to systems known in the art.

BRIEF DESCRIPTION OF THE FIGURES

A preferred embodiment of the invention will be described in the following with reference to the figures in which

fig. 1 illustrates a cross-sectional view of an apparatus according to a preferred embodiment of the present invention,

fig. 2 shows a partly cut-away perspective view of the same apparatus as shown in fig. 1,

fig. 3 shows a perspective view of a cassette for storage of portions of organic material,

fig. 4 shows a perspective view of the locking mechanism of a cassette for storage of portions of organic material,

fig. 5 shows a perspective view of two boxes for storage of portions of organic material,

fig. 6 shows a perspective view of the connection of neighbouring boxes,

fig. 7 shows a perspective view of a pair of pulling wheels mounted on a pulling wheel axle,

fig. 8 shows a perspective view of the interaction between a pulling wheel and a number of box wheel axles,

fig. 9a shows a perspective view of a cooling tank,

fig. 9b shows a perspective view of the same cooling tank as shown in fig. 9a, only without the top cover,

fig. 10 shows a perspective view of the chassis of the apparatus,

fig. 11 illustrates a cross-sectional view of a part of the insulated shell,

fig. 12 illustrates the principle of the cooling system,

fig. 13 illustrates the opening of the insulated shell and

fig. 14 shows a partly cut-away perspective view of the insulated shell.

The appended figures are provided for illustrative purposes only and are not intended to limit the scope of protection as defined by the claims in any way.

DETAILED DESCRIPTION

In the following is disclosed a preferred embodiment of the present invention.

Fig.1 illustrates a cross-sectional view of an apparatus 1 for freezing and storage of portions of organic material according to a preferred embodiment of the present invention. The apparatus 1 is encased in an insulated shell 2 in which a primary door 3 is positioned for providing access to the interior of the apparatus 1. If desired, the door 1 can be equipped with an air lock system (not shown) as described above.

A plurality of boxes 4 for storage of portions of organic material are connected together to form a closed loop chain, i.e. an endless chain, constituting at least a part of an internal conveyor system 5. The conveyor system 5, which is driven by two sets of pulling wheels 6, is used for transporting the stored portions of organic material around inside the apparatus 1.

A cooling tank 7 containing a cooling agent is placed in the centre of the apparatus 1 , i.e. inside the conveyor system 5, where it does not occupy any space that could

otherwise have been used for storage of portions of organic material. In order to keep the stored portions of organic material at a cryogenic temperature of about -170° C, liquid nitrogen, having its boiling point at -196° C, is preferably used as cooling agent.

As can be seen from the figure, such a conveyor system 5, comprising a chain of boxes 4, works like a paternoster system, enabling a very efficient utilization of the space available for storage of portions of organic material. The packing of the boxes 4 is very compact at the linear parts of the system, while some space is wasted between the outer parts of the boxes 4 at the ends. Thus, the longer the conveyor system 5, the better the utilization of space, since the wasted space at the ends does not dependent on the length of the linear parts of the conveyor system 5.

In fig. 2, the same apparatus is shown in a partly cut-away perspective view. This figure illustrates how access through the insulated shell 2 is obtained by opening the primary door 3. Furthermore, it is indicated how each of the boxes 4 contains a row of cassettes 8 for storage of portions of organic material, and how the dimensions of the opening of the primary door 3 correspond to the dimensions of the end parts of a row of cassettes 8.

It is also seen how one pair of pulling wheels 6 is driven by an external motor 9 through a self-braking worm gear 10 and a drive axle 11. Preferably, both the motor 9 and the worm gear 10 are placed outside the insulated shell 2, but in other embodiments of the invention, the worm gear 10 might be placed in a space between two layers of the insulated shell 2.

The invention is meant to be installed in ordinary rooms without any or at least with a minimum of special installations or reinforcements. Therefore, the construction consists primarily of lightweight materials in order to minimize the load on the supporting foundation of the place of installation.

All interior parts of the apparatus 1 must be produced from materials that are stable at cryogenic temperatures at least down to about -170° C.

The construction is meant to be easy to clean and maintain. Therefore, all parts are supposed to last during the full lifetime of the apparatus 1, and the moving parts are not supposed to be lubricated.

The apparatus 1 is assembled from a number of assembly modules, each of which has dimensions small enough to pass through a normal door opening of height 2200 mm and width 800 mm or 1000 mm.

The underside of the insulated shell 2 is placed directly on the floor, and the apparatus 1 can be operated by a person standing on the floor in an ergonomic correct way, especially with regards to opening of doors and heavy lifts.

Fig. 3 shows a perspective view of a cassette 8 for storage of portions of organic material. The cassette 8 has two lids 12 of which one is shown closed and the other one is shown open. A number of sample containers 13 for storage of portions of organic material are placed within the cassette 8. In the shown embodiment, the cassette is designed to be able to contain up to 16 sample containers 13, each consisting of a carton comprising a bag of blood. Since normally there is about half a liter of blood in a portion, the cassette 8 illustrated in fig. 3 is able to contain about 8 liters of blood, when it is filled up with sample containers 13.

Preferably, the cassettes 8 are made from thin plastic, which is cheap and at the same time a stable material that is easy to process and handle. Furthermore, by producing the cassettes 8 in thin plastic, the amount of heat energy transported in and out of the system when a cassette 8 is deposited or removed, respectively, is reduced due to the relatively low heat capacity of most plastic materials.

Each cassette 8 is equipped with its own identification code (not shown), preferably a machine-readable code such as a bar code, a Radio Frequency Identification (RFID) or a 3D code, for addressing and recognition of individual cassettes 8.

At the one end of the cassette, there is a locking mechanism 14, which serves at least three purposes, namely locking the lids 12 of the cassette 8 in a closed position, locking the cassette 8 to the box 4 and providing a handle 15 to be used for depositing and removing the cassette 8 from the apparatus 1 and for handling the cassette 8, when it is not in the apparatus 1.

In fig. 4, a perspective view of the locking mechanism 14 of a cassette 8 for storage of portions of organic material is shown. When the handle 15 is in an upright position with respect to the cassette 8 as illustrated in the figure, the locking mechanism 14 secures the two lids 12 in the closed position. At the same time, a locking pin 16 engages a slot 17 in the box 4 containing the cassette 8, thus locking the cassette 8 to the box 4.

By rotating the locking mechanism 14, the locking pin 16 can be made to disengage from the slot 17, and the cassette 8 can be removed from the box 4 and from the apparatus 1.

When the handle 15 is rotated about 45° with respect to the locked position, an opening (not shown) in the locking mechanism 14 will enable for opening and closure of the lids 12 of the cassette 8.

The apparatus 1 is equipped with a safety mechanism consisting basically of guides

(not shown) that automatically engage with the handles 15 and rotate the locking mechanisms 14 to an angle deviating not more than 10° from the upright position, if the handles 15 are not already in this position, when the internal conveyor system 5

starts moving. This safety mechanism, thus, ensures that a cassette 8 is locked to the box 4, even if the operator should forget to do so when depositing the cassette 8 into the apparatus 1.

Fig. 5 shows a perspective view of two boxes 4 for storage of portions of organic material, each box 4 being divided into seven compartments for cassettes 8. The dividing walls 18 between the individual compartments serve two purposes. Apart from separating the compartments from each other, thus facilitating the deposition and removal of cassettes 8, the dividing walls 18 also play a role in reinforcing the construction of the box 4. The figure further illustrates that there is a slot 17 for a locking pin 16 in the box wall within each compartment.

The boxes 4, which are, preferably, made from stainless steel or aluminum, are connected together to form an endless chain constituting the main part of the internal conveyor system 5.

The connection between neighboring boxes 4 is provided by a box wheel axle 19 and three flanges 20 related to each box 4. At both ends of each box wheel axle 19, a box wheel 21, preferably made from a plastic material such as Murflor, is placed for supporting the box 4 when moving around with the internal conveyor system 5.

The connection of flanges 20 and box wheel axles 19 is illustrated in further detail in fig. 6. Here, it is also indicated how the box wheel axles 19 are fixated in the axial direction by means of washers 22 and locking rings (not shown) placed adjacent to the flanges 20.

Fig. 7 shows a perspective view of a pair of pulling wheels 6 for the internal conveyor system 5 mounted on a pulling wheel axle 23. The figure further illustrates how the pulling wheels 6 are toothed, the width of each tooth 24 corresponding to the distance between two neighboring box wheel axles 19 in the chain of connected boxes 4.

The internal conveyor system 5 comprises two pairs of pulling wheels 6, each pair mounted on a pulling wheel axle 23. One of the pulling wheel axles 23 is connected to the drive axle 11, which is driven by the motor 9 and the worm gear 10 through a coupling (not shown). The other pulling wheel axle 23 is not driven but simply follows the motion of the conveyor system 5.

The interaction between a pulling wheel 6 and a number of box wheel axles 19 is illustrated in fig. 8. It is seen how the pulling wheel 6 engages the box wheel axles 19 between the box wheels 21 and the flanges 20. The drive works like a roller chain being driven by a sprocket wheel, each box wheel axle 19 acting as a roller joint.

Fig. 9a shows a perspective view of a cooling tank 7, constructed to contain the cooling agent, preferably liquid nitrogen. The tank 7, which is preferably made from aluminum, comprises six mounting flanges 25 for mounting the tank 7 to the chassis 26 (see fig. 10) of the apparatus 1.

Furthermore, the cooling tank 7 is equipped with two inspection holes 27 for maintenance purposes and a pair of guide rails 28 for the boxes 4. Preferably, the guide rails 28 consist of aluminum rails, welded onto the top cover 29 of the cooling tank 7, supporting a pair of plastic rails (not shown) made from a material with a low-friction surface such as PEHD-500, which is also used for slide bearings. The centre flange 20 of each box 4 is supposed to slide between the two guide rails 28, thus preventing the box wheels 21 from being pressed against the side frames 30 of the chassis 26 (see fig. 10).

A perspective view of the cooling tank 7 without the top cover 29 is shown in fig. 9b. The illustrated tank 7 comprises three reinforcement walls 31, each with a pair of through-going circulation holes 32 for circulation of the cooling agent within the tank 7.

A perspective view of the chassis 26 of the apparatus 1 is shown in fig. 10. The main parts of the chassis 26 are two side frames 30 between which the cooling tank 7 as well as the two pulling wheel axles 23 are mounted. In the preferred embodiment of the invention, the side frames 30 are made from aluminum, stainless steel or plastic.

The figure further illustrates that there is a tensioning system 33 (not shown in detail) for keeping the chain of flanges 20 constituting the main part of the internal conveyor system 5 tight at any time. An axle pin 34 for connecting the drive axle 11 to one of the pulling wheel axles 23 is also shown in the figure.

Fig. 11 illustrates a cross-sectional view of a part of the insulated shell, which consists of an inner part 35 and an outer part 36 between which there is a mean space 39. The inner part 35 comprises two layers of fiberglass 37 between which are arranged two layers of vacuum panels 38. Likewise, the outer part 36 comprises one or more layers of fiberglass 37 between which are arranged one or more layers of vacuum panels 38. In order to be able to gain access to the interior of the apparatus 1, both the inner part 35 and the outer part 36 are preferably divided in an upper part and a bottom part (not shown), which are bolted together.

Insulating foam, preferably polystyrene, is placed in the mean space 39 between the inner part 35 and the outer part 36.

The principle of a preferred embodiment of the cooling system is illustrated in fig. 12.

Cryogens like liquid nitrogen have very high expansion rates, typically around 700:1, when they vaporize. Therefore, it is necessary to have some kind of outlet for the gas in order to avoid very high pressures and, eventually, explosions.

In the preferred embodiment of the present invention, the liquid nitrogen in the cooling tank 7 vaporizes in a vaporizing system (not shown) and fills the inner space 41 of the apparatus 1. By this vaporization, heat is absorbed form the system. The cold gas 42 is lead from the inner space 41 to the mean space 39 of the insulated shell 2, where it is circulated to cool down the insulated shell 2 from the inside, before it exits to the exterior as indicated by the arrows of the figure. In this way, the cooling capability of the nitrogen is optimally utilized.

Another possibility is to use the cooling capacity of the nitrogen on its way out of the system to establish an air lock by cooling down some air, compress the air in order to extract moisture from it and dry it as much as possible, and lead the cold and dry air past the opening into the system. In this way, hot and humid air can be prevented from entering the system, and nitrogen gas can be prevented from leaving the system, when the doors are opened.

In a simple embodiment of the invention, the gaseous nitrogen may exit directly from the interior to the exterior of the system without circulating between different layers of the insulate shell.

Higher air pressures in the mean space 39 between the two parts of the insulated shell 2 and in the inner space 41 of the apparatus 1 than outside the shell 2 assures that the gaseous nitrogen 42 flows in the right direction and significantly reduces the amount of air at ambient temperature that enters the inner space 41 of the apparatus 1 and, thus, the temperature raise within the apparatus 1, when the doors 3, 43 are opened.

Fig. 13 illustrates the opening of the insulated shell 2 with a primary door 3 and a secondary door 43, the latter being preferably constructed as a sliding door made from a plastic material such as polyacryl. As is indicated in the figure, the primary door 3 has a gas-cooled mean space 39 just like the rest of the insulated shell 2.

When the larger primary door 3 is opened, the secondary door 43 is still closed. The secondary doors 43 are opened manually, and each of them opens only to a single cassette 8 for depositing or removing the cassette 8. When the primary door 3 is closed, the secondary doors 43 close automatically.

A partly cut-away perspective view of the insulated shell 2 is shown in fig. 14. Apart from the already discussed features of the shell 2, the figure illustrates that there is a number of safety tracks 44 placed inside the bottom part of the shell 2. If, by accident, a cassette 8 should be loosened from a box 4, the handle 15 will be caught between the safety tracks 44, and the cassette 8 will be drawn along the upper side of the tracks 44, whereby it can be transported to the opening 3, 43 through which it can be removed for reparation.

Furthermore, a side frame rail 45 is illustrated. There is such a rail 45 in each side of the shell 2 for supporting the side frames 30 of the chassis 26.

REFERENCE LIST

In the drawings the reference numbers refer to:

1. Apparatus for freezing and storage of portions of organic material

2. Insulated shell

3. Primary door

4. Box for storage of portions of organic material

5. Internal conveyor system 6. Pulling wheel for internal conveyor system

7. Cooling tank

8. Cassette for storage of portions of organic material

9. Motor for pulling the internal conveyor system

10. Self-braking worm gear 11. Drive axle for internal conveyor system

12. Lid for cassette

13. Sample container for storage of portions of organic material

14. Locking mechanism for cassette

15. Handle for locking mechanism 16. Locking pin for cassette

17. Slot for locking pin

18. Dividing wall between box compartments for cassettes

19. Box wheel axle

20. Flange for box 21. Box wheel

22. Washer for box wheel axle

23. Pulling wheel axle for internal conveyor system

24. Tooth on pulling wheel

25. Mounting flange for cooling tank 26. Chassis

27. Inspection hole for cooling tank

28. Guide rail for boxes

29. Top cover for cooling tank

30. Side frame for chassis 31. Reinforcement walls for cooling tank

32. Circulation hole for cooling tank

33. Tensioning system for internal conveyor system

34. Axle pin for connecting the drive axle to a pulling wheel axle 35. Inner part of insulated shell 36. Outer part of insulated shell

37. Fiberglass layer for insulated shell

38. Vacuum panel for insulated shell

39. Mean space between inner and outer parts of insulated shell

40. Foam inside the mean space of the insulated shell 41. Inner space of apparatus

42. Gaseous nitrogen

43. Secondary door

44. Safety track for cassettes

45. Side frame rail