JP7288117B2 - cryogenic refrigerator - Google Patents

Description

Application of Section 30, Paragraph 2 of the Patent Act Publication date: May 9, 2017 to May 12, 2017; Publication location: M5J 1A6, Toronto, Ontario, Canada, Harbor Square 1, Westin Harbor Castle Hotel 2017 ISBER Annual Meeting

The present invention relates generally to refrigerators or dewars for storing materials at low temperatures, and more particularly to cryogenic refrigeration using mechanical refrigeration systems in combination with cryogenic fluid reservoirs for cooling. Regarding the machine.

When storing biological material in a cryogenic refrigerator, there is a requirement to maintain the sample at a single, controlled temperature. In addition to being a single temperature, the desired temperature itself will vary with the type of material being stored and the intended 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 transplanted tissue, -50°C is required. Cryogenic refrigerators have been deployed in two separate routes to meet the various demands of storage. Cooling by liquid nitrogen (or "LN2") and mechanical cooling.

A conventional LN2 cryogenic dewar is indicated schematically by 10 in FIG. 1 and features an outer shell 12 containing an inner tank 14 . The outer shell and inner tank are separated by a vacuum insulated space 16 and a removable insulated lid or flag 18 allows access to the interior of the inner tank. Several stainless steel storage racks (one of which is shown at 22) hold boxes containing biological samples and are positioned inside the dewar. The racks rest on a circular rotating tray platform 26 . To access storage rack 22 , the user rotates tray 26 using handle 28 . At the bottom of the dewar is a reservoir 32 of liquid nitrogen (-196°C) to keep the biological sample in the dewar cool.

In the dewar 10 of FIG. 1, the racks are not in direct contact with the liquid nitrogen, but are in the vapor space above the liquid. The temperature of the rack therefore varies with the distance from the liquid nitrogen. More specifically, the lowest temperature is near the bottom of the rack, closest to the nitrogen pool, while the highest temperature is at the top of the rack, furthest from the pool. In the early days of such storage dewars, it was not uncommon for the temperature difference to be 100° C. from top to bottom of the dewar.

More recent dewars use thermally conductive materials in the racks to minimize this temperature stratification within the dewar structure, approximating the temperature of a liquid nitrogen pool from top to bottom. Examples of such dewars are presented in US Pat. No. 6,393,847, generally owned by Brooks et al. The Brooks et al. '847 patent discloses a dewar having a turntable or rotatable tray featuring a bottom liquid cryogen reservoir and a cylindrical sleeve. A cylindrical sleeve features a skirt that extends into a pool of liquid cryogen to transport heat from the biological samples stored on the tray. While such a pairing method works, the temperature of the dewar tends to be close to liquid nitrogen temperatures, making such dewars best suited for long term storage applications.

Mechanical refrigerators work in a similar manner to household refrigerators. An electrically driven refrigeration system cools the insulated container. Some refrigeration systems 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 -40°C to -100°C temperature range.

The greatest drawback exhibited by mechanical refrigerators is their dependence on electricity for operation. If power is lost or the refrigeration system fails, the refrigerator warms up in a short period of time (2 days). In liquid nitrogen refrigerators, if power is lost or the level control fails, the pool of nitrogen at the bottom of the dewar typically provides one month of refrigeration. For this reason, the refrigeration market tends to favor the use of liquid nitrogen refrigeration in low temperature storage or situations where expensive materials are to be cooled. Mechanical refrigerators are used in situations that do not require extremely low temperatures or to cool easily replaceable contents.

Conventional liquid nitrogen refrigerators have two inherent problems in maintaining a single and selective temperature. First, as mentioned above, liquid nitrogen refrigerant is stored in the bottom of the refrigerator. Since cold gases are denser than warm gases, refrigerators with bottom nitrogen reservoirs naturally tend to have temperature stratification. All the heat that enters inside the refrigerator warms the steam, which becomes less dense and 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 stratification problem.

Second, since liquid nitrogen is stored at atmospheric pressure, its temperature is always around -196°C. As a result, if the stratification in the dewar were eliminated, the temperature inside would be approximately -196°C.

Additionally, liquid nitrogen refrigerators require a system to refill the liquid nitrogen when it is consumed. This increases the cost of installation (ie capital cost of piping and tanks) and the cost of liquid nitrogen consumed is also very high.

1 is a cross-sectional side view of a prior art cryogenic dewar; FIG.

1 is a perspective view of one embodiment of a cryogenic refrigerator of the present disclosure; FIG.

Figure 3 is a front top perspective view of the top of the refrigerator of Figure 2 with the shroud removed;

4 is a rear perspective view of the upper portion of FIG. 3; FIG.

Figure 5 is a side sectional view of the refrigerator of Figures 2-4;

Figure 6 is an enlarged side cross-sectional view of the refrigeration module of Figure 5;

Figure 7 is a perspective view of a portion of the cryocooler and housing bottom or floor panel of the refrigerator of Figures 2-6;

Figure 7 is a flow chart of the procedure performed by the system controller of the refrigerator of Figures 2-6;

FIG. 7 is a graph of storage temperature, reservoir pressure and cryocooler current versus rack insertion inside the dewar of the refrigerators of FIGS. 2-6. FIG.

FIG. 7 is a graph of reservoir temperature versus time with the cryocooler turned off for the refrigerators of FIGS. 2-6. FIG.

2 is a side cross-sectional view of a second embodiment of a cryogenic refrigerator of the present disclosure; FIG.

12 is an enlarged side cross-sectional view of the upper portion of the dewar of the refrigerator of FIG. 11; FIG.

One embodiment of the cryogenic refrigerator of the present disclosure is indicated generally by 40 in FIG. The refrigerator includes a storage dewar 42 . Although a cylindrically shaped dewar is shown, the dewar may have another shape. As is known in the art, a dewar comprises an outer wall/outer sleeve and an inner wall/inner jacket with an evacuated space between the two to provide vacuum insulation. An access neck 44 is located at the top of the dewar and defines an access opening through which the internal storage space of the dewar can be accessed. A lid 46 covers the access opening. A shroud 48 is also located on top of the dewar and provides an opening through which a control panel 52 with touch screen and display can be accessed and viewed. By way of example only, shroud 48 may be molded from plastic. Stairs 54 allow user access to access neck 44 and control panel 52 .

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 in FIGS. 2 and 3, the control panel 52 is mounted on the front wall 58 of the housing. The housing also preferably includes a removable side panel or cover plate 62 attached by screws 64 (although other attachments may be used). As illustrated in FIG. 4, the rear panel 66 of the housing includes cooling slots 68 whose functionality will be described below. The housing is preferably constructed of metal, although other materials may be used.

FIG. 5 provides a cross-sectional view of refrigerator 40 (with the shroud of FIG. 2 removed). An internal storage space 72 is defined by the dewar 42 and comprises a carousel or turntable with a partition 74 . Each septum is provided with a handle 76 so that the carousel or turntable can be rotated so as to access the biological samples or other materials stored in the compartments of the rack.

A cylindrical reservoir 78 is centrally located in the storage space 72 and defines a storage interior 80 having a headspace above the cryogenic liquid to hold the cryogenic liquid 82 . The reservoir interior space 80 is sealed to the dewar's reservoir space 72 (i.e., there is no fluid communication between the two), but the reservoir space passes through walls of the reservoir preferably constructed of a metallic material. cooled by heat transfer. Merely by way of example, the cryogenic liquid can be liquid nitrogen (LN2). Carousel or turntable bulkheads 74 are provided with cutouts 84 so that they rotate about the reservoir when the rack is rotated via handle 76 .

A cylindrical reservoir neck 86 extends up from the reservoir 78 and has a lower end that is in fluid communication with the headspace (with the remainder of the reservoir interior space 80). The upper end of reservoir neck 86 receives the cold finger and cold tip 88 of the cold head, generally indicated at 90 , of refrigeration module 60 .

An enlarged view of the refrigeration module is provided in FIG. Refrigeration module 60 employs a mechanical refrigeration system that uses a cryogenic fluid as a coolant to cool cold tip 88, and is hereinafter referred to as a "cryogenic refrigerator." 6 and 7, a cryocooler is indicated generally at 92 and is located within housing 56 as illustrated in FIG. By way of example only, the cryocooler may use an acoustic Stirling (“pulse tube”) refrigeration cycle and may be a QDRIVE cryocooler available from Chart Industries, Inc. of Ball Ground, Georgia.

As illustrated in FIGS. 6 and 7, the cryocooler 92 may include a pressure wave generator 94 connected to a heat isolation core 96 via a transport line 98 . A cold head, generally indicated at 90 , includes a cold finger 100 extending downwardly from a heat shield core 96 and terminating within cold tip 88 . A pair of heat sinks 102a, 102b are located on opposite sides of the heat isolation core 96 and include electric fans 104a, 104b. Compliance tank 106 includes a coiled inertance tube that is also connected to cold head 90 . In operation, pulse width generator 94 , which includes an electric reciprocating linear motor, applies pressure waves or pulses of helium gas to thermal isolation core 96 . Cooling is through cooling of the gas in the thermal isolation core (heat is drawn through the heat sinks 102a, 102b) and expansion of the gas in the cold head 90 via a virtual piston effect in the inertance tube (in the compliance tank 106). is applied to the cold tip 88 .

Further details of embodiments of the cryogenic refrigerator 92 described above are provided 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. can be found in

Another type of mechanical refrigeration system using another refrigeration cycle known in the art may be used in place of cryocooler 92 of FIGS. 5-7.

As illustrated in FIG. 5, lower tube 108 is connected to the bottom of cryogenic reservoir 78 and leads to fill valve 112, FIG. 4, which is also connected to the LN2 fill port/connection. The upper tube, illustrated at 114 in FIG. 5, includes the reservoir headspace, the reservoir exhaust valve (116 in FIG. 4), the safety jet or burst valve (118 in FIG. 4), and the ambient pressure lead (120 in FIG. 4). connect to. During refilling of the cryogenic reservoir 78, the LN2 source is connected to the fill port/connection and the fill valve (112 in FIG. 4) and reservoir vent valve (116 in FIG. 4) are opened. As a result, the reservoir fills with LN2 from the bottom through the bottom tube 108 . When reservoir 78 is filled to the proper level of LN2, the valve is closed and the LN2 source is disconnected.

Referring to FIG. 6, electronics 122 are also located within housing 56 of refrigeration module 60 and include absolute pressure sensors, differential pressure sensors, and system controls. A system controller is a microprocessor or electronically programmable device that is connected to the absolute and differential pressure sensors to receive signals from the two pressure sensors. An absolute pressure sensor is connected to the upper tube 114 (FIG. 5) and measures the absolute pressure in the reservoir 78, i.e. the pressure in the headspace of the reservoir 78 minus the ambient pressure from the ambient pressure lead 120 in FIG. Determine pressure.

A differential pressure sensor in electronics 122 connects to lower tube 108 and upper tube 114 and uses the received reservoir headspace and (liquid) bottom pressure to calculate the liquid level in the reservoir. Such differential pressure level sensors are known in the art. If the system controller detects, via the differential pressure sensor, that the cryogenic liquid level in reservoir 78 has fallen below a predetermined level, the reservoir needs to be refilled. An alarm is sounded to indicate to the user that.

Additionally, a temperature sensor may be placed within the storage space of the dewar and connected to the system control (which also leads to the control panel 52 of FIGS. 2 and 3) such that the temperature within the storage space is displayed on the control panel. Additional temperature sensors may be placed within the storage space and may provide connections for external equipment or systems.

The remaining functionality of the system control is now described.

Control method

The purpose of the operational control performed by the system controller (part of the electronics of FIG. 6), referring to FIG. It responds with a corresponding level of heat extraction or cooling/refrigeration response by the cryocooler 92 through the reservoir 78, thereby providing little to no reduction of reservoir contents with minimal temperature change in the reservoir space. to maintain a low temperature in the storage space.

To accomplish the above, the system controller performs the process illustrated in FIG. As indicated by block 132 in FIG. 8, the system controller first measures the condition of the fluid in the reservoir (78 in FIG. 5). The reservoir contains primarily liquid, but also vapor in the headspace above it. Since the reservoir is closed and substantially at saturation equilibrium within the closed vessel, the laws of physics relate temperature and pressure such that one measurement appropriately indicates the other. When heat is applied to the storage space through normal leaks through insulation, openings in access necks, or insertion of material warmer than the storage space, the heat is absorbed by the cryogenic liquid in the reservoir. This slightly increases the temperature and pressure of the vapor associated with LN2 in the reservoir. Similarly (although not normally), if an object is inserted that has a lower initial temperature than the rest of the storage space, the cooling effect cools the reservoir, slightly reducing its temperature and pressure. Inexpensive pressure sensors are much more accurate and reliable than inexpensive temperature sensors, so it is generally preferred to measure changes in conditions within the reservoir as changes in pressure.

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

Increased pressure in the reservoir means that some of the liquid therein boils to vapor, but the contents of the reservoir are not lost under normal conditions. A reservoir to allow vapor to escape in emergency situations (such as insulation failure) where an abnormal amount of heat could overwhelm the cryocooler, or in the event of an extended, untreated freezer failure is fitted with a safety release device (safety blow or burst valve 118 in FIG. 4). However, under normal operating conditions, the normal target pressure is substantially below the safe discharge pressure. For example, the refrigerator target operating pressure may be set at about 25 psig with a safe discharge of 40 psig. A difference of 15 psi 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 the glass transition temperature of ice, about 136 K (-137°C). This is still well below the generally accepted safe long-term storage temperature for biological materials. In another example, the refrigerator may have a set point of 22 psig and a safe pressure release setting of 50 psig.

The proportionality constant of the control algorithm is preferably set to bring the refrigerator to full (maximum) capacity with a deviation range of about 5 psi. This maximum cooling capacity is approximately twice the steady state heat leakage. Thus, in normal operation, the refrigerator has more than enough capacity to restore normal conditions after heat is applied (by the introduction of new material) without exceeding safe pressure limits.

A graph of reservoir temperature, reservoir pressure, cryocooler current (in response to applied voltage) for two warm rack insertions is shown in FIG. 9 to illustrate the function and performance of the control system. ing.

Notable advantages of this control system include:

(1) No consumption or replacement of refrigerant is required under normal operating conditions.

(2) Power consumption (to operate the cryocooler) is met, thereby minimizing start-stop cycles and total energy usage.

(3) regulated cooling rather than start-stop cooling minimizes heat excursions in the stored material and extends its usable life by minimizing freezer burn effects;

(4) insulation, power supply, storage in case of refrigerator failure, as the liquid must first rise to a safe discharge pressure and then boil completely and be vented before any significant temperature rise occurs; It is safe for the substances tested. This is illustrated by monitoring the reservoir temperature when the refrigerator is turned off, as illustrated in the graph provided in FIG.

Process for changing refrigeration modules

As mentioned above, the refrigerator embodiment consists of a vacuum insulated vessel (dewar) with a central reservoir for the cryogenic fluid (typically liquid nitrogen or oxygen) and a a refrigeration module for processing and cooling the contents of the reservoir. The refrigeration module 60 with reservoir (78 in FIG. 5) and its interface are unique and novel with advantages in the manufacture, use and field repair of refrigerators.

In operation, the refrigerator of the present disclosure stores highly valuable (and often irreplaceable) biological materials that are degraded or destroyed by even brief exposure to temperatures above about 135K. used to In the event of refrigeration failure in prior art refrigerators, transfer such material from the failed refrigerator to another (if sufficient It needs to be moved quickly (if space is available). This is a dangerous process, cumbersome and risky for both materials and workers, and not always successful.

The refrigerator of FIGS. 2-6 and its unique refrigeration module 60 allow repair and restoration of full cooling without contacting or even moving stored material. The flow of such repair is as follows.

(1) Freezing fails (mechanical or electrical failure)

(2) an alarm signal warns the user of the problem; User requests replacement.

(3) As heat leakage through the reservoir insulation continues, the pressure in the reservoir begins to rise slowly.

(4) A new refrigeration module arrives on site.

(5) Power is disconnected from the module.

(6) The reservoir release valve (116 in FIG. 4) is manually opened to vent the reservoir to atmospheric pressure. (There is some loss of refrigerant, but the cooling effect of the exhaust minimizes losses to a small amount, eg, 7-12% depending on initial pressure between 22 and 50 psig.)

(7) The cover plate (62 in FIGS. 3 and 4) is removed from the refrigeration module housing (56 in FIGS. 3 and 4) to expose the fixtures that attach the cryocooler to the dewar.

(8) The screws are removed from the cryocooler-dewar attachment in both the reservoir cold finger flange (142 in FIG. 6) and the refrigeration module support bracket (144 in FIG. 6). Fasteners other than screws may of course be used in other embodiments.

(9) The failed refrigeration module is removed from the dewar and laid aside for off-site repair.

(10) The reservoir continues to vent steam through the open neck flange with the cold finger removed. This evacuation prevents air and moisture from entering the reservoir while the now unsealed reservoir is open.

(11) A new module is put in place with a new gasket on the flange of the cold finger.

(12) The screw for sealing the cold finger to the reservoir and module to support the bracket is replaced.

(13) Power is reapplied and refrigerator operation is started and verified.

(14) The module cover (panel 62 in FIGS. 3 and 4) is replaced.

The reservoir release valve (116 in FIG. 4) is closed.

(15) If necessary, lost cryogenic liquid is replaced. (In some cases, this can be done later, for example, if the downtime is less than 3-5 days.)

(16) The freezer is returned to user operation without handling or significant temperature rise of the samples in the freezer.

(17) The failed module is packaged for shipment to the repair shop.

By comparison, prior art mechanical refrigerators, in the event of a mechanical or electrical failure, require extensive disassembly, including removal and rearrangement of stored material, and removal and recharging of refrigerant. do. In addition to the hazards to stored materials, such transportation requires careful coordination of alternate locations by the user, keeping records of each material involved, moving these materials, returning them later, and the process. requires a considerable amount of time to assume that the maximum temperature limit is not exceeded through In particular, such failures typically occur in conventional mechanical refrigerators every few years.

Advantages of the upper enclosure against noise and electromagnetic interference

As noted above, the refrigerator embodiments of the present disclosure use the enclosure to deal with noise and electromagnetic interference (EMI) radiation (such radiation is typical of all electromechanical devices). may include an upper housing having two layers of

More specifically, as first described above and illustrated in FIGS. is enclosed within a housing 56 constructed by The housing reduces EMI radiation. As shown in FIG. 4 and described above, the rear panel 66 of the housing includes cooling slots 68 for cooling the airflow. A baffle wall, indicated by 148 in FIG. 6, is disposed within the housing 56 and faces the cooling slots in an obtrusive manner to reduce noise and EMI radiation passing through the slots. It should be noted that other air vent configurations may be substituted for cooling slots 68 .

A second outer layer of the housing is provided by shroud 48 in FIG. The shroud 48 is preferably formed of a polymeric material and has the effect of enveloping and reflecting the acoustic emissions of the cryocooler and fan internally. The shroud also provides an aesthetic enhancement.

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 indicated at 152 in Figures 5-7. As shown in FIG. 7, a pair of air intake holes 154a, 154b are positioned below the cryocooler heat sinks 102a, 102b. The heat sink fans 104a, 104b are configured such that, during operation, air is drawn into the housing interior through the air intake holes 154a, 154b, as indicated by arrows 156a, 156b.

Referring to FIG. 6, bulkhead 162 extends from floor to ceiling and from wall to wall within the housing. A motorized fan, indicated at 164 in FIG. 6, is mounted within the bulkhead and directs air from the front chamber 166 toward the rear chamber 168, as indicated by arrow 172 in FIG. (FIG. 4) configured to blow out. As a result, cooling gas flows over electronics 122 . In addition, the partition prevents recirculation of air from the back chamber 168 of the housing back to the front chamber 166, reducing the transfer of noise from the cryogenic refrigerator pulse generator motor 94 to the front of the refrigerator. Bulkhead 162 preferably includes a layer of foam having recesses and openings to accommodate fan 164 .

Anti-icing characteristics

The refrigerator embodiments described above differ from prior art refrigerators that use a similar vacuum insulated dewar construction (typically cooled by the loss of liquid nitrogen in an open pool at the bottom of the storage space). , in the absence of such nitrogen vapor, the storage space is filled with normal air containing moisture as indicated by humidity. Furthermore, during operation of the refrigerator, new air and additional moisture can be introduced into the storage space of the dewar through the respective access openings. Due to the low temperatures in the storage space, such moisture freezes quickly and over time can build up in excessive amounts, interfering with handling of the stored material. The refrigerator may optionally include mitigation features to deal with icing.

Referring to FIG. 5 and as previously described, lid 46 seals the access opening of access neck 44 . Lid 46 includes a cylindrical top plate 174 to which plug 176 is attached. By way of example only, lid top 174 may be constructed from plastic and plug 176 may be constructed from foam or cork. In some embodiments, the plug may be sized to engage the inner surface of access neck 44 .

An annular rim is formed on the lower surface of top plate 174 and surrounds the upper end of plug 176, and a gasket ring, indicated at 182 in FIG. 5, is positioned below the annular rim. A gasket ring 182 engages the upper edge of the side wall of the access neck when the lid is in the closed position. The neck may also be provided with a gasket in the form of a sleeve (rubber or silicone tubular) that folds over the top sidewall of the access neck 44 all around. Additionally, the lid 46 and access neck 44 may be provided with a latch that pulls the gasket ring down against the upper edge of the side wall of the access neck to ensure a plug-neck connection upon closure, thereby allowing the dewar to close. Blocks the flow of air and moisture to the storage space when closed.

Given that ice is most likely to form on the inside of the access neck when the plug is removed (the first cold surface encountered by the incoming air), the neck is a cylindrical, sleeve-like, flexible silicone-like material. Alternatively, it may be lined (covering at least a portion of the inner surface of the access neck) formed by an ice-phobic material. Ice will still form there, but periodically, the sleeve (formed as an extension and part of sealing the gasket at the top of the side wall of the access neck as described above) will lift with the ice. , can be bent like a home ice maker to release ice from the dewar and replaced in the neck without ice.

Additionally, the turntables within the storage space may be lightly lined that hang from the top of the turntable bulkhead (74 in FIG. 5), containing spaces in which the material stored in each compartment is placed. A possible bag-like element may be provided. Again, periodically, these lined bags can be removed and replaced with new, dry or original once dried. One variation of such a liner concept is to provide a liner with a silicone outer surface that separates from the turntable but has an inner surface that is infused with a moisture barrier that attracts and traps water vapor therein.

Referring to FIG. 7, the coldest part of the cold finger is the cold tip 88 (i.e., the bottom of the cold finger) and the warmest part of the cold finger is the top, thereby creating a temperature gradient across the cold finger 100 . exist. In the refrigerator embodiment illustrated in FIG. 5, the cold finger is located within the reservoir neck 86 . As a result, the warmest portion of the cold finger is located inside the reservoir neck 86, providing additional heat leakage to the reservoir and dewar storage spaces. In another refrigerator embodiment, shown generally at 200 in FIG. 11, a steam branch 202 is in fluid communication with a reservoir neck 203 of the refrigerator and a vacuum is applied at the top of the dewar (also shown in FIG. 12). It passes through space 204 . As a result, the cold finger 206 of the cryocooler is surrounded by a vacuum space 204 with only the cold tip 208 positioned within the steam branch 202, as illustrated in FIG. As a result, heat transport from the warmest portion of cold finger 206 to the reservoir and dewar storage space is virtually eliminated, which increases refrigerator efficiency. Other details and elements of the refrigerator of FIGS. 11 and 12 are the same or similar to those described above for the FIG. 5 embodiment.

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 disclosure, and the scope of the present disclosure covers the following patents: defined by the claims.

Claims (21)

a dewar defining a storage space;
located within or adjacent to said storage space and having a headspace above a cryogenic liquid within a reservoir interior space configured to be sealed to said storage space a reservoir configured to contain a cryogenic liquid such that
a refrigeration module in heat exchange relationship with the headspace of the reservoir;
a sensor configured to determine the temperature or pressure within the reservoir;
connected to the sensor and the refrigeration module and configured to control the amount of cooling of the reservoir to the headspace from a steady state operating level when pressure or temperature in the headspace increases; a system controller comprising
the refrigeration module includes a cold tip in heat exchange relationship with the headspace of the reservoir ;
the reservoir is secured within the dewar by a reservoir neck in fluid communication with the headspace of the reservoir, the cold tip positioned within the reservoir neck;
The system controller is configured to enhance cooling of the cold tip in heat exchange relationship with the headspace of the reservoir when pressure or temperature within the headspace rises above a set point. and wherein enhanced cooling of the cold tip recondenses vapor in the headspace and the resulting liquid returns to the liquid pool of the reservoir below. 2. The cryogenic refrigerator of claim 1, wherein the refrigeration module is removably mounted on the dewar. The dewar includes a vacuum insulated space and further comprises a steam branch in fluid communication with the headspace of the reservoir through the vacuum insulated space, the cold tip being located within an upper portion of the steam branch. A cryogenic refrigerator according to claim 1. 2. The cryogenic refrigerator of claim 1, wherein said refrigeration module uses an acoustic Stirling refrigeration cycle. 5. The cryogenic refrigerator of claim 4, wherein said refrigeration module includes a housing. 6. The cryogenic refrigerator of claim 5, wherein the housing includes a partition for separating the interior of the housing into a forward chamber containing the system controls and a rear chamber containing the motor of the refrigeration module. The housing includes an air intake hole located within the front chamber, an air discharge hole located within the rear chamber, and further comprising a fan located within the bulkhead for drawing cool air into the housing through the air intake hole, and 7. The cryogenic refrigerator of claim 6, configured to expel air out of the housing through an exhaust port. 8. The cryogenic refrigerator of claim 7, further comprising a baffle wall located within said rear chamber of said housing and opposite said exhaust port. 8. The cryogenic refrigerator of claim 7, wherein said refrigeration module includes a heat sink adjacent said air intake. 10. The cryogenic refrigerator of claim 9, further comprising a fan attached to the heat sink and configured to draw air over the heat sink through the air inlet. 8. The cryogenic refrigerator of claim 7, wherein the vent includes a cooling slot located in a rear panel of the housing. 6. The cryogenic refrigerator of claim 5, further comprising a shroud mounted on said dewar and covering most of said housing. 2. The cryogenic refrigerator of claim 1, wherein the cold tip is removed from the reservoir neck when the refrigeration module housing is removed from the dewar. 2. The cryogenic refrigerator of claim 1, wherein said dewar includes an inner wall surrounded by an outer wall with a vacuum insulating space therebetween. 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 closing the lid. 2. The cryogenic refrigerator of claim 1, wherein said plug engages said access neck to seal said access opening when said plug is received in said access opening for cooling. 16. The cryogenic refrigerator of claim 15, wherein the access neck includes a gasket sleeve engaged by the gasket ring when the lid is in the closed configuration. 17. The cryogenic refrigerator of claim 16, wherein said gasket sleeve extends along an inner surface of said access neck and is removable to allow icing to be removed from said dewar. transferring a cryogenic liquid into an interior space of a reservoir located within the storage space such that the storage space of the dewar is cooled by the reservoir, said interior space of said reservoir relative to said storage space of said dewar; is sealed with
A headspace of the reservoir above the cryogenic liquid is cooled by a cold tip of a refrigeration module, the cold tip being in heat exchange relationship with the headspace, and the reservoir being the headspace of the reservoir. secured within said dewar by a reservoir neck in fluid communication with said cold tip located within said reservoir neck; and
A system controller causes cooling of the headspace of the reservoir to be increased from steady state operating levels when the temperature or pressure of the reservoir increases , the increased cooling recondensing vapor in the headspace. and, in response to said enhanced cooling, the resulting liquid returns to the liquid pool of said reservoir below. Increasing the cooling of the headspace of the reservoir from a steady state operating level when the temperature or pressure of the reservoir increases when the temperature or pressure in the reservoir rises above a set point. 19. The method of claim 18, comprising enhancing cooling of the headspace to. 20. The method of claim 19, wherein cooling the headspace of the reservoir above the cryogenic liquid is accomplished using an acoustic Stirling refrigeration cycle. 20. The method of claim 19, further comprising venting the reservoir when pressure or temperature within the reservoir exceeds a predetermined level.

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