Abstract
The present invention is a high-performance ultra-low temperature chest freezer capable of reaching temperatures as low as 160 C. within several hours with the capability to automatically and continually defrost and dehumidify its payload bay before, during, and after a door open event without needing to cease freezing operations or raise the setpoint.
Claims
1. An ultra-low temperature chest freezer, comprising: a payload bay; a lid attached to the payload bay; an evaporator housing attached on an underside of the lid, such that the evaporator housing is within the payload bay when the lid is closed and is coupled to an atmosphere within the payload bay; one or more evaporators within the evaporator housing thermally coupled to one or more coolant tubes; a liquid nitrogen inlet and an exhaust outlet attached to the one or more coolant tubes to allow nitrogen flow into the liquid nitrogen inlet through the one or more coolant tubes, and out the exhaust outlet; one or more cryogenic solenoid valves and one or more check valves that control nitrogen flow within the one or more coolant tubes; and one or more purge inlet valves within the payload bay that allow nitrogen flow from the one or more coolant tubes directly into the payload bay.
2. The freezer of claim 1, wherein the payload bay and lid comprise insulation to substantially reduce heat gain from an outside environment.
3. The freezer of claim 1, wherein the evaporator housing is coupled to the atmosphere within the payload bay with one or more interstitial holes, one or more staggered holes, and a screen.
4. The freezer of claim 1, wherein the payload bay and lid, when shut, are airtight and prevent airflow within the payload bay.
5. The freezer of claim 1, wherein the one or more coolant tubes are placed in series or in parallel.
6. The freezer of claim 1, wherein the one or more check valves restrict air flow from the one or more coolant tubes into the payload bay through one or more over-pressurization relief valves.
7. The freezer of claim 1, comprising an oxygen source coupled to one or more purge inlet valves to mix oxygen with nitrogen prior to entering the payload bay.
8. The freezer of claim 7, wherein the one or more check valves restrict oxygen from entering the one or more coolant tubes.
9. The freezer of claim 1, wherein liquid nitrogen is evaporated to gaseous nitrogen within the one or more coolant tubes and directed to one or more purge inlet valves by one or more cryogenic solenoid valves.
10. The freezer of claim 1, wherein the one or more purge inlet valves release gaseous nitrogen into the payload bay to over-pressurize the payload bay immediately prior to a door-open event to prevent airflow into the payload bay.
11. The freezer of claim 1, wherein the one or more purge inlet valves release gaseous nitrogen into the payload bay during a door-open event to prevent moisture from entering the payload bay.
12. The freezer of claim 1, wherein the one or more purge inlet valves release gaseous nitrogen into the payload bay while the payload bay is sealed to dehumidify and defrost the payload bay.
13. The freezer of claim 12, wherein the gaseous nitrogen in the payload bay exits through the one or more over-pressurization relief valves.
14. The freezer of claim 1, comprising one or more over-pressurization relief valves within the payload bay to allow air flow from the payload bay to the exhaust outlet.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is an exemplary perspective view of one embodiment of the present invention with one possible iteration of the evaporator housing.
[0025] FIG. 2 is an exemplary top view of one embodiment of the present invention demonstrating the one or more purge inlet valves and one or more over-pressurization relief valves.
[0026] FIG. 3 is an exemplary perspective cutaway view of the lid to demonstrate the one or more evaporators and the one or more coolant tubes.
[0027] FIG. 4 is an exemplary section view of the payload bay of one embodiment of the present invention demonstrating the airflow within the payload bay compared to prior art.
[0028] FIG. 5 is a chart showing the actual temperature profile of one embodiment of the present invention.
[0029] FIG. 6 is a chart showing a detailed portion of the actual temperature profile of one embodiment of the present invention, highlighting its temperature homogeneity.
[0030] FIG. 7 is a chart showing the actual temperature profile of a prior art chest freezer.
[0031] FIG. 8 is a chart showing a detailed portion of the actual temperature profile of a prior art chest freezer, highlighting its temperature homogeneity.
[0032] FIG. 9 is a chart showing a detailed portion of the actual temperature profile of a prior art chest freezer, highlighting its temperature homogeneity at a different setpoint than that of FIG. 8.
[0033] FIG. 10 has several exemplary section views of the evaporator housing using different methods of being atmospherically coupled to the payload bay.
[0034] FIG. 11 is a progression diagram demonstrating airflow into the payload bay of prior art chest freezers.
[0035] FIG. 12 is a progression diagram demonstrating the pressurization of the payload bay of one embodiment of the present invention to prevent moisture inflow.
[0036] FIG. 13 is a progression diagram demonstrating moisture saturation of the atmosphere of the payload bay of prior art chest freezers during an open-door event.
[0037] FIG. 14 is a progression diagram demonstrating the over-pressurization of the payload bay of one embodiment of the present invention to prevent moisture inflow during an open-door event.
[0038] FIG. 15 is a progression diagram demonstrating the stripping of frost within the payload bay of one embodiment of the present invention.
[0039] FIG. 16 is a plumbing diagram of one embodiment of the present invention.
DESCRIPTION
[0040] A detailed description of embodiments of the present invention is provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art how to employ the present invention in virtually any appropriately detailed system.
[0041] Referring to FIGS. 1-3, a high-performance ultra-low temperature chest freezer 100 is composed of a payload bay 101, one or more linear actuators 102, and a lid 103. An evaporator housing 104 is attached to the lid 103 in such a way as to cover the majority of the surface area above the payload bay 101 when the lid 103 is closed. Within the evaporator housing 104 are one or more evaporators 105. One or more coolant tubes 106 are thermally coupled to the one or more evaporators 105. The evaporator housing 104 is designed such that the one or more evaporators 105 are atmospherically coupled to the payload bay 101. A liquid nitrogen inlet 109 is coupled to the one or more coolant tubes 106 and can attach to a liquid nitrogen source. An exhaust outlet 110 is coupled to the one or more coolant tubes 106 in such a way as to cause liquid nitrogen to flow from the liquid nitrogen inlet 109, through the one or more coolant tubes 106 and out the exhaust outlet 110. One or more cryogenic solenoid valves 111 control the flow of liquid nitrogen within the one or more coolant tubes 106. The liquid nitrogen phase changes to gaseous nitrogen within the one or more coolant tubes 106 as they absorb thermal energy. One or more purge inlet valves 107 are coupled to the one or more coolant tubes 106 in such a way as to allow gaseous nitrogen to exit the one or more coolant tubes 106 and enter the payload bay 101 through the one or more purge inlet valves 107. One or more over-pressurization relief valves 108 are coupled to the one or more coolant tubes 106 in such a way as to only allow flow from the payload bay 101 to the exhaust outlet 110 without any possibility of flow coming the opposite way. The one or more linear actuators 102 lift the lid 103.
[0042] Now referring to FIG. 4, one embodiment is composed of the payload bay 101, the lid 103, the evaporator housing 104, the one or more coolant tubes 106, the one or more evaporators 105, the one or more purge inlet valves 107, and the one or more over-pressurization relief valves 108. One embodiment is the high-performance ultra-low temperature chest freezer 100 from FIGS. 1-3 and operates as such. Two forms of prior art chest freezers are considered, one with a heat exchanger 201 arranged vertically on the first prior art payload bay 202 and another with an air circulator 200 that circulates chilled air through the second prior art payload bay 203.
[0043] The cooling means, or the one or more evaporators 105, are directly above the payload bay 101 of one embodiment of the present invention. As the air within the payload bay 101 is cooled, the individual particles of air lose some of their kinetic energy. This cooling occurs as thermal energy is transferred across the temperature gradient of the warmer air of the payload bay 101 and the colder one or more evaporators 105. In other words, air is cooled as it comes into contact with the one or more evaporators 105. Air particles with lower kinetic energies drop beneath similar air particles with higher kinetic energies because they cannot resist the gravitational force acting on them as much as the air particles with higher kinetic energies. This results in cold air dropping from around the one or more evaporators 105 to the bottom of the payload bay 101. Warmer air, or air with relatively greater kinetic energies, will rise above the colder air, or air with relatively lesser kinetic energies. As the one or more evaporators 105 cover a significant portion of the surface area of the top of the payload bay 101, cold air drops across the entire top face of the payload bay 101. This doesn't allow for specific channels of warmer air to rise within the payload bay 101 to the one or more evaporators 105. Thus, there is homogeneity in the temperature throughout the payload bay 101 if one were to sample temperatures throughout a horizontal slice of the atmosphere within the payload bay 101. This results in complete mixing and extremely even cooling of the payload bay.
[0044] In contrast, referring to prior art #1 of FIG. 4, when the cooling means, or the heat exchanger 201, is placed within the walls of the first prior art payload bay 202, heat transfer occurs from the air within the first prior art payload bay 202 immediately adjacent to the walls and in no other location. This results in cold air falling only along the walls of the first prior art payload bay 202. This cold air will pool along the bottom of the first prior art payload bay 202. Warmer air will rise within all available volume not already taken up by falling cold air, which is the bulk of the area of first prior art payload bay 202 not immediately adjacent to a wall. This causes a cyclic action of dropping along a wall and rising in the middle. This does not lead to even temperatures as the individual air particles even their kinetic energies out over time as they collide with each other, or in other words the cold air warms up as it goes throughout the cycle. Modest temperature homogeneity is the best typical prior art using this method can expect.
[0045] Furthermore, referring to prior art #2 of FIG. 4, when the cooling means, or the air circulator 200, expels cold air within the second prior art payload bay 203, a similar cyclic action occurs except the cold air drops away from the air circulator 200 and rises away from it, depending on the configuration. Regardless, unless intricate configurations are used, this method can only provide modest temperature homogeneity at best.
[0046] Comparing the present system to prior art #1 and prior art #2, the present system is capable of much tighter and more even temperature homogeneity.
[0047] Now referring to FIGS. 5-6, the actual temperature profile of one embodiment of the present invention is shown. Eighteen thermocouples were placed within the payload bay equally spaced out from each other and their temperatures shown. The difference between the warmest and coldest thermocouple at each datapoint is also shown.
[0048] One embodiment reached 120 C. in approximately one hour. During the test, the liquid nitrogen supply was switched to a lower pressure at around the one-hour mark. This was done because small Dewar's were used as the liquid nitrogen source and one had run out, requiring a switch. This second Dewar was at a substantially lower pressure which resulted in a slower cooling rate. Had the embodiment continued to utilize the higher pressure, it would have reached 160 C. in approximately two hours.
[0049] One embodiment was held at 160 C. for approximately five hours, during which the greatest temperature difference between internal thermocouples was just over 2 C. and the greatest difference from 160 C. any individual thermocouple showed was just over 3 C. At times, the greatest difference from 160 C. any individual thermocouple showed was below 1 C. while simultaneously the greatest temperature difference between internal thermocouples was under 2 C. Those familiar with the art of ULT freezers know that the cooling means of an ULT freezer is turned on and off cyclically, maintaining a temperature within a few degrees of the setpoint. As an ULT freezer's cooling cycle turns off, cold air drops to the bottom of the ULT freezer because there is nothing mixing it. It is because of this cold air dropping that the embodiment had temperature differences larger than the minimum. This shows that the embodiment is capable of extremely tight temperature tolerances and temperature homogeneity. Greater variation in the testing data is due to the cyclic cooling those skilled in the art of chest freezers would recognize.
[0050] It is notable that the above system held impressive temperature homogeneity during warm-up, between the twelve-hour mark and the eighteen-hour mark.
[0051] Now referring to FIGS. 7-9, the actual temperature profile of a prior art chest freezer is shown. The prior art chest freezer utilized cooling tubes within its side walls. Eighteen thermocouples were placed within the payload bay equally spaced out from each other and their temperatures are shown. The difference between the warmest and coldest thermocouple at each datapoint is also shown.
[0052] One embodiment was used to cool down the prior art chest freezer up until the eight-hour mark. This was done in order to rapidly cool down the prior art chest freezer to save time. Prior art was used in the prior art chest freezer after the eight-hour mark. The prior art chest freezer was held at 160 C. for approximately nine hours, during which the greatest temperature difference between internal thermocouples was over 15 C. and the greatest difference from 160 C. any individual thermocouple showed was around 14 C. At times, the greatest difference between internal thermocouples was approximately 12 C. with a corresponding 7 C. for the greatest difference from 160 C. for the thermocouples. Comparing this with the embodiment from FIGS. 5-6, the system was approximately seven times more precise and uniform over conventional chest freezer.
[0053] Additionally, the prior art chest freezer was held at 80 C. for over ten hours, during which the greatest temperature difference between internal thermocouples was around 5 C. and the greatest difference from 80 C. any individual thermocouple showed was just over 4 C. At its best, the prior art chest freezer had a temperature difference between internal thermocouples just over 4 C. and a difference from 80 C. at just over 2 C. during this time. Again, comparing this data with the data from the embodiment of FIGS. 5-6, the design was over twice as precise and uniform when compared to the conventional chest freezer, despite the higher temperature of the prior art chest freezer. Tighter temperature homogeneity and uniformness should have occurred at the warmer temperature. This demonstrates the great capability of one embodiment of the present invention.
[0054] Now referring to FIG. 10, the evaporator housing 104 encloses the one or more evaporators 105 with a method of atmospherically coupling the atmosphere within the evaporator housing 104 with the atmosphere beneath it. The methods include, but are not limited to, one or more interstitial holes 300, one or more staggered holes 301, and a screen 302.
[0055] As previously discussed, colder air drops when compared to warmer air. When one or more interstitial holes 300 are placed on the bottom of the evaporator housing 104, cold air is allowed to fall through them. Cold air will bunch up on the spaces around the one or more interstitial holes 300, which can reduce the air flow. When one or more staggered holes 301 are placed on the bottom of the evaporator housing 104 such that the one or more evaporators 105 within the evaporator housing 104 cannot be seen, cold air falls within the one or more staggered holes 301. Additionally, when the area around the one or more staggered holes 301 is slanted, as shown in FIG. 10, air is allowed to drop more readily with the assistance of gravity. When the screen 302 is placed on the bottom of the evaporator housing 104, cold air is allowed to fall through it, but the screen 302 hampers the air flow slightly.
[0056] With the one or more interstitial holes 300, it can be seen that the air flow is significantly hampered by the flat portions. In other words, the arrows simulating airflow are significantly turned from pointing downward. With the one or more staggered holes 301, it can be seen that the slanted area between the one or more staggered holes 301 hampers airflow, but not as much as with the one or more interstitial holes 300. The screen 302 doesn't alter the directionality of the airflow whatsoever, but it does reduce the airflow slightly.
[0057] Now referring to FIG. 11, the payload bay 101 is sealed shut by the lid 103. Step One shows a sealed prior art chest freezer at room temperature. Air particles are simulated by circles. Step Two shows the same prior art chest freezer but at its colder setpoint. The air particles within it are colder, and as such have become less dense, which is demonstrated by the more tightly packed circles. The empty area simulates a vacuum, which causes a sucking force, demonstrated by two arrows. This sucking force will cause ambient air at warmer temperatures to enter the payload bay 101. Step Three simulates the warmer air within the payload bay 101.
[0058] The warmer ambient air that enters the payload bay 101 brings humidity with it, which will freeze on the walls of the payload bay 101.
[0059] Now referring to FIG. 12, the payload bay 101, is sealed shut by the lid 103. One or more purge inlet valves 107 and one or more over-pressurization relief valves 108 are placed within the payload bay 101. Step One shows the sealed present invention at room temperature. Air particles are simulated by circles. Step Two shows one embodiment at a colder setpoint. The original air within it is colder and denser, as simulated by the tightly packed circles. The one or more purge inlet valves 107 are expelling gaseous nitrogen into the payload bay 101 and is being used to pressurize the payload bay 101. This gaseous nitrogen is simulated by two arrows. No external air is entering into the payload bay 101. Step Three shows the embodiment completely full of air at its setpoint. Should the pressure within this embodiment exceed that deemed safe, the one or more over-pressurization relief valves 108 allow air to flow into them to equalize the pressure of the payload bay 101.
[0060] No external air enters the payload bay 101 which means that no additional moisture enters within the payload bay 101, reducing frost. One embodiment can reach its setpoint with the payload bay 101 safely pressurized and without moisture.
[0061] Now referring to FIG. 13, the payload bay 101 is exposed directly to ambient air. Air originally within the freezer is simulated with circles while humid air is simulated by triangles. Step One shows a prior art chest freezer immediately after a door-open event. The air within it is at the setpoint at which it was set prior to the door-open event, simulated by the close spacing of the circles. Step Two simulates the same prior art chest freezer sometime after a door-open event has started. The air within the payload bay 101 is warming up, shown by the greater spacing between circles, and moist ambient air is slowly entering, simulated by the triangles entering the payload bay 101. Step Three simulates the same prior art chest freezer some more time after a door-open event has started. The moist air, or triangles, have completely intermixed with the original air, or circles. Moisture from the moist air has accumulated and frosted onto the interior walls of the payload bay 101, as simulated by the triangles directly adjacent to the walls of the payload bay 101.
[0062] Now referring to FIG. 14, the payload bay 101 is exposed directly to ambient air. One or more purge inlet valves 107 are within the payload bay 101. Step One shows one embodiment immediately after a door-open event. The air within it is at the setpoint at which it was set prior to the door-open event, simulated by the close spacing of the circles. Step Two simulates the embodiment sometime after a door-open event has started. The air within the payload bay 101 is warming up, shown by the greater spacing between circles. The one or more purge inlet valves 107 allow gaseous nitrogen at a cold temperature to enter the bottom of the payload bay 101. This colder, denser air settles at the bottom of the payload bay 101 and slowly expands as it warms up. This causes the air within the payload bay to spill upward and outward, holding the moist, ambient air at bay, which is simulated by triangles. Step Three simulates the embodiment some more time after a door-open event has started. The airflow within the payload bay 101 has reached equilibrium. The cold, gaseous nitrogen entering the payload bay 101 through the one or more purge inlet valves 107 slowly expands and causes air to spill out of the payload bay, holding off any moisture from entering the payload bay 101 and even purging any moisture already within the payload bay 101.
[0063] Now referring to FIG. 15, the payload bay 101 is sealed shut by the lid 103. One or more purge inlet valves 107 and one or more over-pressurization relief valves 108 are within the payload bay 101. Step One shows one embodiment at its setpoint. Frost lines the interior surfaces of the payload bay 101. Step Two shows the embodiment sometime after Step One. The one or more purge inlet valves 107 allow gaseous nitrogen to enter the payload bay 101. This gaseous nitrogen is completely dry and causes the atmosphere of the payload bay 101 to increase. The one or more over-pressurization relief valves 108 allow the air from within the payload bay 101 to escape once it reaches above a certain pressure. As previously explained, solidified water will sublimate to reach its partial pressure. As the payload bay 101 is over-pressurized and de-pressurized in turn, dry air enters the payload bay 101 and then the air within the payload bay 101 leaves, decreasing the ice partial pressure. This causes the ice to sublimate to reach its partial pressure. The continual lowering of the ice partial pressure, or rather the continual atmospheric renewal with dry air, causes the ice to sublimate constantly. Thus, the system constantly defrosts and dehumidifies itself.
[0064] Now referring to FIG. 16, the liquid nitrogen inlet 109 is attached to one or more coolant tubes 106. One or more cryogenic solenoid valves 111 control the flow of nitrogen through the one or more coolant tubes 106. One or more check valves 112 help control the direction of liquid nitrogen flow. The one or more coolant tubes 106 enter the payload bay 101. The nitrogen exits the one or more coolant tubes 106 at the exhaust outlet 110. A safety valve 113 is used to ensure that the pressure within the one or more coolant tubes 106 remain within safe levels. One or more over-pressurization relief valves 108 are used to allow air to flow from the payload bay 101 to the exhaust outlet 110. One or more purge inlet valves 107 are used to allow nitrogen flow into the payload bay 101.
[0065] It is dangerous for systems to release gas into air breathed by humans. One embodiment therefore utilizes an oxygen source 114 that mixes with the nitrogen going into the payload bay 101 through the one or more purge inlet valves 107. This eliminates possibility of suffocation.
[0066] While there have been shown what are presently considered to be preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope and spirit of the invention.
