Cryogenic freezer

Abstract

To provide a cryogenic freezer using a mechanical freezing system combined with a cryogenic fluid storage part for cooling, in a freezer or dewar for storing substances at a low temperature.SOLUTION: A cryogenic refrigerator 40 is characterized by a dewar 42 that defines a storage space 72. The reservoir 78 is located within the storage space 72 and is configured to contain a cryogenic liquid with a headspace above the cryogenic liquid within a reservoir interior space that is sealed with respect to the storage space 72. Refrigeration module 60 is in a heat exchange relationship with the headspace of reservoir 78. The sensor is configured to determine temperature or pressure within the reservoir 78. A system controller is coupled to the sensor and the refrigeration module and is configured so that the refrigeration module is adjusted to provide additional cooling to the headspace of the reservoir when the pressure or temperature in the headspace increases.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention generally relates to a refrigerator or a dewar for storing substances at low temperatures, and particularly to a cryogenic refrigerator that uses a mechanical refrigeration system combined with a cryogenic fluid reservoir for cooling.

Background Art

[0002] When storing biological materials in a cryogenic refrigerator, there is a requirement to maintain the sample at a single, controlled temperature. In addition to the temperature being single, the desired temperature itself varies depending on the type of material being stored and the purpose of use. For example, for long-term storage of biological cells, it is desirable to keep the temperature below -160°C. For short-term storage of plasma or transplant tissue, -50°C is required. To meet the various requirements of storage, cryogenic refrigerators have been developed in two separate ways. Cooling by liquid nitrogen (or "LN2") and mechanical cooling.

[0003] A conventional LN2 cryogenic dewar is schematically shown by 10 in FIG. 1 and is characterized by an outer shell 12 that houses an inner tank 14. The outer shell and the inner tank are separated by a vacuum insulation space 16, and a removable insulation lid or plug 18 allows access to the inside of the inner tank. Several stainless steel storage racks (one of which is shown at 22) hold boxes that contain biological samples and are placed inside the dewar. The racks are placed on a circular rotating tray platform 26. To access the storage rack 22, the user rotates the tray 26 using a handle 28. At the bottom of the dewar is a pool 32 of liquid nitrogen (-196°C) that keeps the biological samples inside the dewar at a low temperature.

[0004] In the dewar 10 of FIG. 1, the rack is not in direct contact with the liquid nitrogen and is in the vapor space above the liquid. Therefore, the temperature of the rack varies depending on the distance from the liquid nitrogen. More specifically, the temperature is lowest near the bottom of the rack, which is closest to the nitrogen pool, while the temperature is highest at the top of the rack, which is farthest from the pool. In such an initial storage dewar, it is not uncommon for the temperature difference from the top to the bottom of the dewar to reach 100 °C.

[0005] More recent dewars use a heat-conducting material in the rack to minimize such temperature stratification within the dewar structure and bring the temperature closer to that of the liquid nitrogen pool from the top to the bottom. An example of such a dewar is generally represented in U.S. Patent No. 6,393,847 owned by Brooks et al. The Brooks et al.'847 patent discloses a dewar having a bottom liquid coolant pool and a turntable or rotatable tray featuring a cylindrical sleeve. The cylindrical sleeve features a skirt that extends into the liquid coolant pool to transport heat away from the biological samples stored on the tray. Such a counter-stratification method works, but the temperature of the dewar tends to approach the liquid nitrogen temperature, making such dewars most suitable for long-term storage applications.

[0006] Mechanical refrigerators operate in a similar manner to household refrigerators. The insulated container is cooled by an electrically driven refrigeration system. There are also refrigeration systems that use cryogenic liquids as refrigerants. However, mechanical refrigerators are limited to the temperatures achieved by the insulation of the refrigerator and the efficiency of the refrigeration system. They tend to operate in the temperature range of -40 °C to -100 °C.

[0007] The greatest drawback exhibited by mechanical refrigerators is that their operation depends on electricity. When power is lost or the refrigeration system malfunctions, the refrigerator warms up within a short period (two days). In the case of a liquid nitrogen refrigerator, when power fails or the liquid level control unit malfunctions, the nitrogen accumulation at the bottom of the dewar typically provides refrigeration for about a month. For this reason, the refrigerator market tends to prefer the use of liquid nitrogen refrigerators in situations where storage at low temperatures or cooling of expensive materials is involved. Mechanical refrigerators are used in situations that do not require extremely low temperatures or where the contents can be easily replaced.

[0008] Conventional liquid nitrogen refrigerators have two inherent problems in maintaining a single, and furthermore, selectable temperature. First, as described above, the liquid nitrogen refrigerant is stored at the bottom of the refrigerator. Since cold gas is denser than warm gas, a refrigerator with a nitrogen accumulation at the bottom naturally tends to have temperature stratification. All the heat entering the interior of the refrigerator warms the vapor, the density of the vapor decreases, and it rises to the top. Since most liquid nitrogen refrigerators have a top opening, most of the heat entering the refrigerator first reaches the top and is not efficiently absorbed by the liquid at the bottom. This adds to the problem of stratification.

[0009] Second, since liquid nitrogen is stored at atmospheric pressure, its temperature is always approximately -196°C. As a result, if the stratification within the dewar is removed, the temperature inside will be approximately -196°C.

[0010] Furthermore, liquid nitrogen refrigerators require a system to refill when the liquid nitrogen is consumed. This increases the cost of introduction (i.e., the capital cost of piping and tanks), and the cost of the liquid nitrogen consumed is also very high.

Brief Description of the Drawings

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Best Mode for Carrying Out the Invention

[0023] One embodiment of the cryogenic refrigerator of the present disclosure is shown generally at 40 in FIG. 2. The refrigerator includes a storage dewar 42. Although a cylindrical dewar is shown, the dewar may have another shape. As is known in the art, the dewar includes an outer wall / outer sleeve and an inner wall / inner jacket, with a space between the two from which air has been removed to provide vacuum insulation. An access neck 44 is located at the top of the dewar and defines an access opening through which the interior storage space of the dewar can be accessed. A lid 46 covers the access opening. A shroud 48 is also disposed at the top of the dewar and includes an opening through which a control panel 52 having a touch screen and a display can be accessed and viewed. By way of example only, the shroud 48 can be molded from plastic. A staircase 54 enables a user to access the access neck 44 and the control panel 52.

[0024] As shown in FIGS. 3 and 4 with the shroud removed, a refrigeration module, generally indicated at 60, includes a housing, generally indicated at 56. As can be seen from FIGS. 2 and 3, the control panel 52 is mounted on the front wall 58 of the housing. The housing also includes a removable side panel or cover plate 62, preferably (although other fixtures can also be used) attached by screws 64. As shown in FIG. 4, the rear panel 66 of the housing includes cooling slots 68, the functionality of which is described below. The housing is preferably constructed of metal, although other materials can also be used.

[0025] FIG. 5 provides a cross-sectional view of the refrigerator 40 (with the shroud of FIG. 2 removed). The internal storage space 72 is defined by the dewar 42 and includes a rotating rack or turntable having a partition 74. Each partition includes a handle 76 so that the rotating rack or turntable can be rotated to provide access to biological samples or other materials stored within the compartments of the rack.

[0026] The cylindrical storage section 78 is located at the center of the storage space 72, has a head space above the cryogenic liquid, and defines a storage internal space 80 that holds the cryogenic liquid 82. The storage internal space 80 is sealed with respect to the storage space 72 of the dewar (i.e., there is no fluid communication between the two), but the storage space is cooled by heat transfer through the wall of the storage section preferably made of a metallic material. By way of example only, the cryogenic liquid can be liquid nitrogen (LN2). The partition walls 74 of the rotary rack or turntable are provided with cutouts 84 such that they rotate around the storage section when the rack is rotated via the handle 76.

[0027] The cylindrical storage section neck 86 extends upward from the storage section 78 and has a lower end in fluid communication with the head space and (the rest of the storage section internal space 80). The upper end of the storage section neck 86 receives the cryogenic finger and the cryogenic tip 88 of the cryogenic head of the refrigeration module 60, which is generally indicated at 90.

[0028] An enlarged view of the refrigeration module is given in FIG. 6. The refrigeration module 60 uses a mechanical refrigeration device that uses a cryogenic fluid as a refrigerant to cool the cryogenic tip 88 and is hereinafter referred to as a "cryogenic refrigerator". In FIGS. 6 and 7, the cryogenic refrigerator is generally indicated at 92 and is located within the housing 56 as shown in FIG. 6. By way of example only, the cryogenic refrigerator can use an acoustic Stirling ("pulse tube") refrigeration cycle and can be a QDRIVE cryogenic refrigerator available from Chart Industries, Incorporated of Ball Ground, Georgia.

[0029] As shown in FIGS. 6 and 7, the cryogenic refrigerator 92 may include a pressure wave generator 94 connected to the thermal isolation core 96 via a transport line 98. The cryogenic head, generally designated 90, includes a cryogenic finger 100 that extends downwardly from the thermal isolation core 96 and terminates within the cryogenic tip 88. A set of heat sinks 102a, 102b are located on opposite sides of the thermal isolation core 96 and include electric fans 104a, 104b. The compliance tank 106 also includes a coiled inertia tube connected to the cryogenic head 90. In operation, a pulse width generator 94, which includes an electric reciprocating linear motor, applies a pressure wave or pulse of helium gas to the thermal isolation core 96. Cooling is provided to the cryogenic tip 88 through cooling of the gas within the thermal isolation core (where heat is drawn through the heat sinks 102a, 102b) and expansion of the gas within the cryogenic head 90 via a virtual piston effect within the inertia tube (within the compliance tank 106).

[0030] Further details of the above-described embodiments of the cryogenic refrigerator 92 can be found in U.S. Patent No. 7,628,022 to Spoor et al. and U.S. Patent Application Publication No. 2015 / 0033767 to Corey et al., which are hereby incorporated by reference in their entirety.

[0031] Another type of mechanical refrigeration device that uses another refrigeration cycle known in the art may be used in place of the cryogenic refrigerator 92 of FIGS. 5 - 7.

[0032] As shown in FIG. 5, the lower tube 108 is connected to the bottom of the cryogenic storage 78 and also leads to the fill valve 112 of FIG. 4, which is also connected to the LN2 fill port / connection. The upper tube, illustrated as 114 in FIG. 5, connects to the headspace of the storage, the storage exhaust valve (116 of FIG. 4), the safety ejection or burst valve (118 of FIG. 4), and the ambient pressure lead (120 of FIG. 4). During refilling of the cryogenic storage 78, the LN2 source is connected to the fill port / connection and the fill valve (112 of FIG. 4) and the storage exhaust valve (116 of FIG. 4) are opened. As a result, the storage is filled with LN2 from the bottom via the lower tube 108. When the storage 78 is filled to the appropriate liquid level of LN2, the valves are closed and the connection to the LN2 source is removed.

[0033] Referring to FIG. 6, the electronic device 122 is also disposed within the housing 56 of the refrigeration module 60 and includes an absolute pressure sensor, a differential pressure sensor, and a system control unit. The system control unit is a microprocessor or an electronically programmable device and is connected to the absolute pressure sensor and the differential pressure sensor to receive signals from the two pressure sensors. The absolute pressure sensor is connected to the upper pipe 114 (FIG. 5) and determines the absolute pressure within the reservoir 78, i.e., the pressure obtained by subtracting the ambient pressure from the peripheral pressure lead 120 in FIG. 4 from the pressure within the headspace of the reservoir 78.

[0034] The differential pressure sensor of the electronic device 122 is connected to the lower pipe 108 and the upper pipe 114 and calculates the liquid level within the reservoir using the received pressures of the reservoir headspace and the (liquid) bottom. Such differential pressure level sensors are known in the art. If the system control unit detects via the differential pressure sensor that the liquid level of the cryogenic liquid within the reservoir 78 has dropped below a predetermined liquid level, an alarm is sounded to indicate to the user that the reservoir needs to be refilled.

[0035] Furthermore, a temperature sensor may be disposed within the storage space of the dewar and connected to the system control unit (which also communicates with the control panel 52 in FIGS. 2 and 3) such that the temperature within the storage space is displayed on the control panel. Additional temperature sensors may be disposed within the storage space and may provide connections for external equipment or systems.

[0036] The remaining functionality of the system control unit is described herein.

[0037] Control Method

[0038] The purpose of the operation control executed by the system control unit (a part of the electronic device in FIG. 6) is, with reference to FIG. 5, to respond to the changing heat load in the storage space 72 of the dewar 42 by the corresponding heat extraction or cooling / freezing level by the cryogenic refrigerator 92 through the liquid reservoir 78 therebetween, thereby maintaining the low temperature in the storage space with a minimum temperature change in the storage space and reducing the reduction of the contents of the reservoir from a small amount to none.

[0039] To achieve the above, the system control unit executes the process illustrated in FIG. 8. As shown by block 132 in FIG. 8, the system control unit first measures the state of the fluid in the reservoir (78 in FIG. 5). The reservoir mainly contains liquid, but also contains vapor in the headspace above it. Since the reservoir is sealed and in substantially saturated equilibrium within the sealed container, physical laws relate temperature and pressure such that one measurement appropriately indicates the other. When heat is added to the storage space through normal leakage through insulation, the opening of the access neck, or the insertion of a material warmer than the storage space, the heat is absorbed by the cryogenic liquid in the reservoir. This slightly raises the temperature and pressure of the vapor associated with the LN2 in the reservoir. Similarly (although not normally), if an object with an initial temperature lower than the rest of the storage space is inserted, the cooling effect cools the reservoir and slightly reduces its temperature and pressure. Since the accuracy and reliability of an inexpensive pressure sensor are much greater than those of an inexpensive temperature sensor, it is generally preferred to measure the change in the state in the reservoir as a change in pressure.

[0040] The reading of the absolute pressure sensor is provided to a system control unit that compares it to a preselected setpoint temperature (block 134 in FIG. 8) desired for the storage space. To account for steady-state heat leakage through the storage space from external peripherals to the reservoir, a small statistical difference can be defined. The difference between the reading of the reservoir and the setpoint, taking into account the intended difference, is input into a conventional proportional-integral control algorithm (well known in the art), and as shown in block 136 of FIG. 8, a voltage is output to the motor of a cryogenic refrigerator (92 in FIGS. 5-7) that adjusts the power of the motor and thereby the cooling capacity of the refrigerator to reduce and eliminate the deviation. That is, when the heat added, absorbed by the liquid, raises the pressure in the reservoir, the refrigerator receives a voltage greater than its steady-state operating level, and the voltage remains higher than normal until the previous steady state is restored.

[0041] The increased pressure in the reservoir means that some of the liquid there has boiled into vapor, but the contents of the reservoir are not normally lost. In the event of an emergency where an abnormal amount of heating (such as a failure of insulation) overwhelms the cryogenic refrigerator, or in the case of an extended, unprocessed refrigerator failure, the reservoir is equipped with a safety release device (safety ejection or burst valve 118 in FIG. 4) to vent the vapor. However, in normal operating conditions, the normal target pressure is substantially lower than the safety release pressure. For example, the target operating pressure of the refrigerator can be set at about 25 psig with a safety release of 40 psig. The 15 psi difference corresponds to an increase in the saturation temperature of oxygen (the preferred species in the reservoir) from 90 to 97 K (-183°C to -176°C), which is still well below the generally safe long-term storage temperature for biological materials, which is about 136 K (-137°C), the glass transition point of ice. In another example, the refrigerator can have a setpoint of 22 psig and a safety pressure release setting of 50 psig.

[0042] The proportionality constant of the control algorithm is preferably set to bring the refrigerator to full (maximum) capacity within a deviation range of about 5 psi. This maximum cooling capacity is about twice the steady-state heat leakage. Thus, in normal operation, the refrigerator has sufficient capacity to return to normal conditions without exceeding the safe pressure limit after heat is added (by the introduction of new material).

[0043] Graphs of the temperature of the storage section, the pressure in the storage section, and the current (responding to the applied voltage) of the cryogenic refrigerator for the insertion of two warm racks are shown in FIG. 9, illustrating the function and performance of the control system.

[0044] Notable advantages of this control system include the following.

[0045] (1) There is no need for refrigerant consumption or replacement in normal operating conditions.

[0046] (2) The power consumption (to operate the cryogenic refrigerator) is in line with requirements, thereby minimizing start-stop cycles and total energy usage.

[0047] (3) Controlled cooling rather than start-stop cooling minimizes heat deviation in the stored material and extends its usable life by minimizing the freezer burn effect.

[0048] (4) It is safe for the stored material in case of insulation, power supply, or refrigerator failure because the liquid must first rise to the safe release pressure and then fully boil and be vented before a significant temperature rise occurs. This is shown by monitoring the temperature of the storage section when the refrigerator power is turned off, as illustrated in the graph given in FIG. 10.

[0049] Steps for changing the refrigeration module

[0050] As described above, an embodiment of the refrigerator includes a vacuum-insulated container (Dewar) having a central storage container for cryogenic fluids (typically liquid nitrogen or oxygen), and a refrigeration module 60 shown at 60 in FIGS. 3-6 that processes and cools the contents of the storage section. The refrigeration module 60 having a storage section (78 in FIG. 5) and its interface have advantages in the manufacture, use, and on-site repair of the refrigerator, and are unique and novel.

[0051] During operation, the refrigerator of the present disclosure is used to store very valuable (and often irreplaceable) biological materials that are degraded or destroyed even by short-term exposure to temperatures higher than about 135K. If there is a failure in refrigeration in a prior art refrigerator, in order to minimize icing in the released air and avoid damage to the material, it is necessary to quickly transfer such a material from the failed refrigerator to another one (if sufficient space is available). This is a risky process, cumbersome and risky for both the material and the worker, and not always successful.

[0052] With the refrigerator of FIGS. 2-6 and its unique refrigeration module 60, repair and complete recovery of cooling are possible without even contacting or moving the stored material. Such a repair process is as follows.

[0053] (1) Refrigeration fails (mechanical or electrical failure)

[0054] (2) An alarm signal warns the user of the problem. The user requests a replacement.

[0055] (3) Due to continued heat leakage through the insulation of the storage section, the pressure in the storage section begins to slowly rise.

[0056] (4) A new refrigeration module arrives on site.

[0057] (5) The power connection is disconnected from the module.

[0058] (6) The storage release valve (116 in Fig. 4) is manually opened to exhaust the storage section to atmospheric pressure. (Although some refrigerant is lost, the cooling effect due to the exhaust minimizes the loss to a small amount, e.g., 7 - 12% depending on the initial pressure between 22 and 50 psig.)

[0059] (7) The cover plate (62 in Figs. 3 and 4) is removed from the housing of the refrigeration module (56 in Figs. 3 and 4), exposing the fixture for attaching the cryogenic refrigerator to the dewar.

[0060] (8) Screws are removed from the attachment of the cryogenic refrigerator - dewar at both the flange of the low - temperature finger of the storage section (142 in Fig. 6) and the refrigeration module support bracket (144 in Fig. 6). Of course, fixtures other than screws can be used in other embodiments.

[0061] (9) The failed refrigeration module is removed from the dewar and placed horizontally for off - site repair.

[0062] (10) The storage section continues to discharge vapor from the neck flange where the low - temperature finger has been removed and opened. This exhaust prevents air and moisture from entering the storage section while the now - unsealed storage section is open.

[0063] (11) A new module is installed in position with a new gasket on the flange of the low - temperature finger.

[0064] (12) Screws for sealing the low - temperature finger to the storage section and the module to support the bracket are returned to their original positions.

[0065] (13) The power supply is reinstalled, the operation of the refrigerator is started and verified.

[0066] (14) The cover of the module (panel 62 in Figs. 3 and 4) is returned to its original position.

[0067] The release valve of the storage section (116 in Fig. 4) is closed.

[0068] (15) If necessary, the lost cryogenic liquid is restored. (In some cases, this can be done later, for example, if the interruption time is less than 3 to 5 days.)

[0069] (16) The refrigerator is returned to the user's operation without handling the sample inside the refrigerator or a significant temperature rise.

[0070] (17) The failed module is packaged for transportation to the repair factory.

[0071] In comparison, when a mechanical or electrical failure occurs in a prior art mechanical refrigerator, it requires a wide range of disassembly including removal and rearrangement of the stored materials and removal and refilling of the refrigerant. In addition to the danger to the stored materials, such transportation requires the user to carefully arrange an alternative location, record each of the relevant materials, move these materials, return them later, and the time to be spent assuming that the maximum temperature limit cannot be exceeded throughout the process. In particular, such failures typically occur in conventional mechanical refrigerators every few years.

[0072] Advantages of the upper housing against noise and electromagnetic interference

[0073] As described above, an embodiment of the refrigerator of the present disclosure may include an upper housing having two layers of the housing to handle noise and electromagnetic interference (EMI) radiation (such radiation is typical in all electromechanical devices).

[0074] More specifically, first, as described above and illustrated in FIGS. 5 and 6, the components of the refrigerator including the cryogenic refrigerator, the heat exchanger associated with the system control unit, and the fan are preferably enclosed within a housing 56 made of metal. The housing reduces EMI radiation. As shown in FIG. 4 and described above, the rear panel 66 of the housing is provided with cooling slots 68 for cooling the air flow. The baffle wall shown by 148 in FIG. 6 is disposed within the housing 56 and faces the cooling slots so as to block the cooling slots to reduce the noise and EMI radiation passing through the slots. It should be noted that another configuration of the air exhaust holes can be substituted for the cooling slots 68.

[0075] The second outer layer of the housing is provided by the shroud 48 in FIG. 2. The shroud 48 is preferably formed of a polymeric material and has the effect of enclosing and reverberating the acoustic radiation of the cryogenic refrigerator and the fan inside. The shroud also provides an improvement in aesthetics.

[0076] The cooling air flowing through the housing 56 is discharged from the back of the housing away from the user, thereby further reducing the level of noise experienced by the user. More specifically, the housing includes a floor panel shown as 152 in FIGS. 5 - 7. As shown in FIG. 7, a set of intake holes 154a, 154b are disposed below the heat sinks 102a, 102b of the cryogenic refrigerator. The fans 104a, 104b of the heat sinks are configured such that during operation, air is drawn into the housing through the intake holes 154a, 154b as shown by the arrows 156a, 156b.

[0077] Referring to FIG. 6, the partition wall 162 extends from the floor to the ceiling and from wall to wall within the housing. An electric fan, indicated at 164 in FIG. 6, is installed within the partition wall and is configured to blow air from the front chamber 166 toward the rear chamber 168 and ultimately out of the cooling slots 68 (FIG. 4) of the housing as indicated by arrow 172 in FIG. 6. As a result, the cooling gas flows over the electronic device 122. Further, the partition wall prevents recirculation of air returning from the rear chamber 168 of the housing to the front chamber 166 and reduces the movement of noise from the pulse wave generation motor 94 of the cryogenic refrigerator to in front of the refrigerator. The partition wall 162 preferably includes a layer of foam having a recess and an opening for housing the fan 164.

[0078] Opposed ice characteristics

[0079] The cryogenic refrigerator embodiments described above differ from prior art cryogenic refrigerators that use a similar vacuum insulated dewar structure (typically cooled by loss of liquid nitrogen in an open sump at the bottom of the storage space) in that there is no such nitrogen vapor and the storage space is filled with normal air containing moisture as indicated by the humidity. Further, during operation of the cryogenic refrigerator, fresh air and additional moisture can be introduced into the storage space of the dewar through each access opening. Due to the low temperature within the storage space, such moisture rapidly freezes and over time can accumulate in excessive amounts, interfering with the handling of the stored material. The cryogenic refrigerator may optionally include a mitigation function for dealing with icing.

[0080] Referring to FIG. 5 and as previously described, the lid 46 seals the access opening of the access neck 44. The lid 46 includes a cylindrical top plate 174 to which a plug 176 is attached. By way of example only, the top plate 174 of the lid may be constructed of plastic and the plug 176 may be constructed of foam or cork. There are also embodiments where the plug may be sized to engage the inner surface of the access neck 44.

[0081] An annular edge is formed on the lower surface of the top plate 174, surrounding the upper end of the plug 176, and the gasket ring, shown at 182 in FIG. 5, is disposed below the annular rim. When the lid is in the closed position, the gasket ring 182 engages the upper end of the side wall of the access neck. The neck may also be provided with a gasket in the form of a (rubber or silicone) sleeve whose entire circumference overlaps the upper end of the side wall of the access neck 44. Further, the lid 46 and the access neck 44 may be provided with a latch that pulls the gasket ring downward against the upper end of the side wall of the access neck to ensure the plug-neck connection when closed, thereby blocking the flow of air and moisture into the storage space when the dewar is closed.

[0082] If ice is most likely to form inside the access neck when the plug is removed (the first cold surface encountered by the incoming air), the neck can be lined with a flexible, ice-repellent material such as silicone in the form of a cylindrical sleeve-like liner (covering at least a portion of the inner surface of the access neck). Ice will still form there, but periodically, the sleeve (which is part of the gasket that seals at the upper part of the side wall of the access neck as described above and is formed as an extension) is lifted with the ice, bent like a household ice maker, and released from the dewar and returned to its original position inside the neck without ice.

[0083] Furthermore, the turntable in the storage space can be lined with a lightweight liner suspended from the upper part of the partition wall of the turntable (74 in FIG. 5), providing an element such as a removable bag that includes a space in which the materials stored in each compartment are placed. Again, periodically, these lined bags can be removed and replaced with new, dry ones, or the original ones once dried. One variation of such a lining concept is to provide a lining with an outer surface of silicone that is remote from the turntable but has an inner surface infused with a moisture absorbent that draws in and captures water vapor.

[0084] Referring to FIG. 7, since the coldest part of the cold finger is the cold tip 88 (i.e., the lower end of the cold finger) and the warmest part of the cold finger is the upper end, there is a temperature gradient in the cold finger 100. In the embodiment of the refrigerator shown in FIG. 5, the cold finger is located within the reservoir neck 86. As a result, the warmest part of the cold finger is located inside the reservoir neck 86, providing further heat leakage to the reservoir and the storage space of the dewar. In another embodiment of the refrigerator, shown generally at 200 in FIG. 11, the vapor branch tube 202 is in fluid communication with the reservoir neck 203 of the refrigerator and passes through the vacuum space 204 at the upper part of the dewar (also shown in FIG. 12). As a result, as shown in FIG. 12, only the cold tip 208 of the cryogenic refrigerator's cold finger 206 is disposed within the vapor branch tube 202 and surrounded by the vacuum space 204. As a result, heat transport from the warmest part of the cold finger 206 to the reservoir and the storage space of the dewar is virtually eliminated, which increases the efficiency of the refrigerator. Other details and elements of the refrigerators of FIGS. 11 and 12 are the same as or similar to the above description for the embodiment of FIG. 5.

[0085] While the preferred embodiments of the present disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications can be made therein without departing from the spirit of the present disclosure, and the scope of the present disclosure is defined by the following claims.

Claims

1. A dewar that defines the storage space, a reservoir configured to contain a cryogenic liquid located within or adjacent to the storage space and secured within the storage space of the dewar by a reservoir neck, the reservoir having a headspace above the cryogenic liquid and the reservoir neck receiving a cryotip, the cryotip being in heat exchange relationship with the reservoir headspace, the cryotip being located within the headspace above the cryogenic liquid and within the reservoir neck securing the reservoir to the dewar; a cryo-module in heat exchange with the headspace of the reservoir, the cryo-module comprising the cold tip; 1. A cryogenic refrigerator comprising: a system control unit connected to the refrigeration module and configured to control the amount of cooling of the head space of the reservoir by adjusting power supplied to the refrigeration module, the adjustment including: (1) variably increasing the power supplied to the refrigeration module when the pressure or temperature of the head space increases; and (2) variably decreasing the power supplied to the refrigeration module when the pressure or temperature of the head space decreases.

2. 2. The cryogenic refrigerator of claim 1, wherein said refrigeration module is removably mounted in said dewar.

3. 2. The cryogenic refrigerator of claim 1, wherein the dewar includes a vacuum insulated space and further comprises a vapor manifold that passes through the vacuum insulated space and is in fluid communication with the headspace of the reservoir, the cold tip being located within an upper portion of the vapor manifold.

4. 10. The cryogenic refrigerator of claim 1, wherein the refrigeration module uses an acoustic Stirling refrigeration cycle.

5. The cryogenic refrigerator of claim 4 , wherein the refrigeration module includes a housing.

6. 6. The cryogenic refrigerator of claim 5, wherein the housing includes a partition for separating an interior of the housing into a front chamber including the system control unit and a rear chamber including a motor of the refrigeration module.

7. 7. The cryogenic refrigerator of claim 6, wherein the housing includes an intake hole located inside the front chamber and an exhaust hole located inside the rear chamber, and further includes a fan located in the partition wall and configured to draw cool air into the housing through the intake hole and expel air outside the housing through the exhaust hole.

8. The cryogenic refrigerator of claim 7 , further comprising a baffle wall located within the rear chamber of the housing and facing the exhaust hole.

9. The cryogenic refrigerator of claim 7 , wherein the refrigeration module includes a heat sink adjacent the air inlet.

10. The cryogenic refrigerator of claim 9 , further comprising a fan attached to the heat sink and configured to draw air through the intake vent and past the heat sink.

11. The cryogenic refrigerator of claim 7 , wherein the exhaust comprises a cooling slot located in a rear panel of the housing.

12. The cryogenic refrigerator of claim 5 , further comprising a shroud mounted to said dewar and covering most of said housing.

13. 6. The cryogenic refrigerator of claim 5, wherein the cold tip is removed from the neck of the reservoir when the housing of the refrigerator module is removed from the dewar.

14. 10. The cryogenic refrigerator of claim 1, wherein the dewar includes an inner wall surrounded by an outer wall with a vacuum insulated space therebetween.

15. 2. The cryogenic refrigerator of claim 1, wherein the dewar includes an access neck defining an access opening with a lid removably covering the access opening, the lid including a top plate, a plug, and a gasket ring, the gasket ring engaging the access neck to seal the access opening when the plug is received in the access opening to close the lid.

16. The cryogenic refrigerator of claim 15 , wherein the access neck includes a gasket sleeve that is engaged by the gasket ring when the lid is in a closed configuration.

17. 17. The cryogenic refrigerator of claim 16, wherein the gasket sleeve extends along an inner surface of the access neck and is removable to allow ice buildup to be removed from the dewar.

18. transferring a cryogenic liquid to a reservoir located within or adjacent to a storage space of a dewar such that the storage space is cooled by the reservoir and secured within the dewar by a reservoir neck; cooling a headspace of the reservoir above the cryogenic liquid with a cold tip of a refrigeration module, the cold tip being located within the reservoir neck of the reservoir in the headspace above the cryogenic liquid and in heat exchange relationship with the headspace; 16. A method of cooling a storage space of a dewar, comprising regulating cooling of said cryo-tip in heat exchange relationship with said headspace of said reservoir by variably increasing and decreasing power supplied to said refrigeration module by a system control.

19. 20. The method of claim 18, wherein augmenting cooling of the cold tip comprises augmenting cooling of the cold tip when a temperature or pressure in the reservoir rises above a set point.

20. 20. The method of claim 19, wherein cooling of the cold tip is accomplished using an acoustic Stirling refrigeration cycle.

21. 20. The method of claim 18, further comprising evacuating the reservoir when a pressure or temperature within the reservoir exceeds a predetermined level.

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