US20100120351A1

US20100120351A1 - Frost reduction by air curtain

Info

Publication number: US20100120351A1
Application number: US12/570,202
Authority: US
Inventors: Wendell Morris; Dennis H. Smith
Original assignee: Thermo Fisher Scientific Asheville LLC
Current assignee: Thermo Fisher Scientific Asheville LLC
Priority date: 2008-11-10
Filing date: 2009-09-30
Publication date: 2010-05-13

Abstract

An ultra-low temperature freezer, including a cabinet with a freezer compartment maintained within a certain temperature range, a door providing a seal with the cabinet when engaged with the cabinet, a catch basin at the bottom of the cabinet for collecting air, and a distribution channel fluidly connected to the catch basin, for recirculating the air collected from the catch basin to the top of the cabinet, the distribution channel at the top of the cabinet pushing compressed air across the front of the cabinet and forming an air curtain and thermal barrier to incoming warmer air.

Description

The present application claims the filing benefit of U.S. Provisional Application Ser. No. 61/112,904, filed Nov. 10, 2008, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a method and system of frost reduction in freezers. More particularly, the present invention relates to a system and method of reducing frost in ultralow temperature freezers by an air curtain.

BACKGROUND OF THE INVENTION

There has been a rapid increased demand for refrigeration systems that can attain a very low temperature range. One type of system that can reach such temperatures is called an ultra-low refrigeration system or called an ultra-low freezer, which can maintain a very low range of temperatures. The ultra-low temperature refrigeration systems can be used to store and protect a variety of objects including critical biological samples so that they are safely and securely stored for extended periods of time. However, with the low storage temperatures involved and the need to periodically insert and remove particular samples from the freezer compartment, various problems may arise.
Generally, in refrigeration systems, a refrigerant gas is compressed in a compressor unit. Heat generated by the compression is then removed generally by passing the compressed gas through a water or air cooled condenser coil. The cooled, condensed gas is then allowed to rapidly expand into an evaporating coil surrounding a refrigerator or freezer compartment where the gas becomes much colder, thus cooling the coil and the compartment of the refrigeration system or freezer around which the coil is placed.
Ultra-low and cryogenic temperatures ranging from approximately −95 degrees Celsius to −150 degrees Celsius have been achieved in refrigeration systems using a single circuit vapor compressor or dual circuit vapor compressors. The single circuit systems typically use a single compressor to pump a mixture of four or five chlorofluorocarbon (CFC) containing refrigerants to reach an evaporative temperature of as low as −160 degrees Celsius.
During normal operation, freezers accumulate frost as a result of humid air entering the freezer. This problem is especially critical in ultra-low temperature freezers as the samples stored in such freezers can be particularly sensitive to changes in the environment within the freezer. The frost that is developed, even in the smallest amounts, can affect the environment of some or all of the individual samples within the freezer compartment and, therefore, contribute to serious problems. There is a need for having greater control of the environment within such a freezer, especially a control of the frost conditions that can develop with everyday use of such a freezer.

SUMMARY OF THE INVENTION

The foregoing needs are met, to a great extent, by the present invention, wherein, in one aspect, an apparatus and technique is provided for reducing the accumulation of frost in the sample compartment of the freezer apparatus.
In accordance with one aspect of the invention, an ultra-low temperature freezer, includes a cabinet with a freezer compartment maintained within a certain temperature range, a door providing a seal with the cabinet when engaged with the cabinet, a catch basin at the bottom of the cabinet for collecting air, and a distribution channel fluidly connected to the catch basin, for recirculating the air collected from the catch basin to the top of the cabinet, the distribution channel at the top of the cabinet pushing compressed air across the front of the cabinet and forming an air curtain and thermal barrier to incoming warmer air.
The freezer can also include the distribution channel disposed exterior to the cabinet. The freezer can also include nozzles disposed on the distribution channel at the top of the cabinet for outputting the compressed air. Additionally, there can be at least two plates with an opening in between, on the distribution channel at the top portion of the cabinet for forming the air curtain. Moreover, the distribution channel can be disposed between insulation and an evaporator.
Alternatively, the distribution channel can include a tortured path from a front of the freezer to the back of the freezer and back to the front of the freezer, where the front of the freezer is the plane where the door seals the cabinet. Furthermore, the distribution channel can include a middle portion between the door and a second door connected to the cabinet, providing an air curtain from the middle portion to the catch basin.
In another aspect of the present disclosure, an ultra-low temperature refrigeration apparatus, includes a cabinet with a freezer compartment maintained within a certain temperature range, a door providing a seal with the cabinet when engaged with the cabinet, a collection means at the bottom of the cabinet for collecting gas, and a distribution means fluidly connected to the collection means, for recirculating the gas collected from the collection means to the top of the cabinet, the distribution means at the top of the cabinet pushing compressed gas across the front of the cabinet and forming a curtain and thermal barrier to warmer outside environment.
In yet another aspect of the present disclosure, a method of an ultra-low temperature freezer, includes collecting air at a catch basin at the bottom of a freezer cabinet when opening a door of the freezer, compressing and distributing the air collected from the catch basin to the top of the cabinet via a distribution channel, and outputting the compressed air across the front of the cabinet from the top of the cabinet to the bottom of the cabinet toward the catch basin and forming an air curtain and thermal barrier to incoming warmer air.
This disclosure describes certain embodiments of the invention in order that the detailed description may be better understood, and in order that the present contribution to the art may be better appreciated. Additional embodiments of the invention are described below or will be apparent from this description to one skilled in the art and do not limit the subject matter of the invention as set forth in the claims.
The invention includes embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.

FIG. 1 illustrates a front view of one embodiment of a freezer.

FIG. 2 is a side view of the freezer of FIG. 1 with an air curtain unit.

FIG. 3 is a partial view of the freezer of FIG. 1, showing the distribution channel forming the air curtain.

FIG. 4 is a detailed view of the air curtain unit.

FIGS. 4A and 4B are diagrammatic views of alternative embodiments of distribution channels.

FIG. 5 illustrates another embodiment with a tortured path for the distribution channel.

FIG. 6 illustrates another embodiment with a selectively reduced area for the air curtain.

FIG. 7 illustrates yet another embodiment with the distribution channel embedded within the freezer.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with reference to the figures, in which like reference numerals refer to like parts throughout.
Frost accumulates during routine operation of ultra-low temperature freezers through humid air entering the freezer. Sources for air entry in the freezers are, for example, a door opening to remove and/or replace experiment samples. Humid air can also enter through a faulty seal in the storage chamber of the freezer or in the door that seals the chamber. Humid air can also enter, as described below, during the pressure equalization process that occurs after the door is resealed if warmer (less dense) air has entered the freezer compartment while the door was open.
As seen in FIG. 1, the ultra-low temperature freezer 10 can include an outer frame 14, with insulated walls of the cabinet 12 of the freezer 10 providing a storage chamber or freezer compartment 24 to contain materials being cooled and maintained at low temperatures in a desired range (e.g., −80° C. to −160° C. or −95° C. to −150° C., for biological laboratory samples). The storage chamber or freezer compartment 24 can be subdivided further into a plurality of compartments (not shown). The freezer 10 also includes a door 16 that is attached to the frame or outer housing 14 and provides a seal of the freezer 10, including the freezer compartment 24, when closed. FIG. 1 shows the door 16 in the open position, in which humid air can be transferred from outside of the freezer 10 into the compartment 24.
Over a period of time, especially as the freezer door 16 is opened to insert new samples or remove samples, frost will build up due to condensation of humidity from the admitted air onto surfaces of the freezer compartment 24 and surfaces of the samples. During the door 16 opening, the very dense cold air (−90° C.) quickly falls out of the bottom of the cabinet 12 and is replaced by ambient air. Since the ambient air typically has higher moisture content than the cold air, moisture condenses quickly on all cold areas inside the cabinet 12. Over a prolonged period of time, this causes an increase in ice formation build-up. Over time, this frost can impede operation and will have to be removed by the user. The removal of frost can be accomplished by defrosting the freezer 10 or “chipping” the frost away. Neither of these methods is easily accomplished. A defrost requires the freezer compartment or chamber 24 to be empty and samples stored in the freezer 10 are not allowed to defrost. Manually removing the frost is cumbersome and can result in damage to the freezer 10 interior and possible damage to stored samples. Both methods are time consuming and add no value to the user's process. Additionally, any automated defrosting method will also require time and there is a danger of affecting the materials stored in the freezer 10 within the freezer compartment 24, especially when the stored materials are hyper-sensitive to even the slightest of temperature fluctuations.
However, the freezer 10 of the present disclosure does include an air curtain unit 100 that will reduce the frost. The air curtain unit 100 has a catch basin 200 positioned below the area where the door 16 closes with the outer frame 14 of the freezer 10. The catch basin 200 receives air or other type of gas and avoids contact with the door 16. The air curtain unit 100 also includes a continuous distributing channel 210 that moves the air received at the catch basin 200 and distributes the air or other type of gas to another location on the freezer 10 in order to create an air curtain. The freezer 10 of the present disclosure would reduce the amount of cold and warm air exchange that takes place during a door 16 opening of an ultra-low temperature freezer 10 with the air curtain unit 100.
Referring to FIGS. 1 and 2, the catch basin 200 is just below the door 16 and is fluidly connected to the distributing channel 210. The distributing channel 210 can include a vertical plenum 212 and horizontal plenum 214 being fluidly connected in a single continuous unit. Other configurations of the distributing channel can be made as long as the air or gas collected from the catch basin 200 is redistributed to a different area of the cabinet 12 for generating the air curtain. The distributing channel 210 compresses the air received from the catch basin 100 and forwards the air from the vertical plenum 212 to the horizontal plenum 214 for outputting the air curtain across the front of the cabinet 12.
Referring to FIGS. 1 through 4, the process of reducing frost by an air curtain is shown in more detail as follows. As soon as the door 16 opens, the denser air falls into a catch basin 200 at the bottom of the cabinet 12. The air is collected at the catch basin 200 and recirculated through a distributing channel 210 from the catch basin 200 through the vertical plenum 212 and finally to the top part of the cabinet 12C at the horizontal plenum 214 of the distributing channel 210.
Referring to FIG. 3, at the top of the cabinet 12C, the air would be pushed out across the front of the cabinet 12 through the distributing channel 210 forming an air curtain and thermal barrier to incoming warmer air. The use of this cold air for the air curtain would reduce the frost formation, as well as provide quicker temperature recovery of the storage chamber 24 of the cabinet 12 since the air falling to the bottom of the cabinet 12 would be replaced with cold recycled chamber air.
Referring to FIG. 4, the air drops to the catch basin 200 when the door 16 is opened, and the air is actively pushed by a motor 230 (i.e., motor for a fan, blower or other means for actively pushing the air) through the distribution channel 210 from the catch basin 200. Other types of gases can also be used or mixed in with the air. The distribution channel 210 can have a smaller cross-sectional area for the flow of air than the catch basin 200 in order to compress the air. The compressed air goes through the vertical plenum 212 and pushes up to the horizontal plenum 214. On the horizontal plenum 214, the compressed air is pushed out through outlets 216 on the bottom side of the horizontal plenum 214 of the distribution channel 210. The outlets 216 can be, for example, nozzles 218 as shown in FIG. 4A or plates 220 with an opening space 222 in between as shown in FIG. 4B to allow the air or other type of gas to release. The airflow 400 pushes down to the catch basin 200 and recirculates.
The location of the distribution channel 210 of FIG. 4 accommodates after-market installation of the freezer 10. As seen in FIGS. 1-3, the distribution channel 210 is positioned toward the front of the freezer 10 and accommodates an efficient installation with minimal steps. The after-market installation thus avoids being limited to installation in the original manufacture of the freezer 10 and avoids expensive installation or expensive changes in the assembly line.
Alternatively, instead of including the motor 230 to push the air and be compressed in the distribution channel 210, a compressed air source (not shown) can be added. Additionally, a cold air filter (not shown) can be included in the distribution channel 210 in order to separate out any foreign particles that may fall into the catch basin through the grills and thereby prevent the obstruction of the distribution channel 210. The air can alternatively be pushed across horizontally from the vertical plenum 212 of the distribution channel 210. The distribution channel 210 can be a cylindrical shape hose construction, rectangular construction or other configurations.
Referring to FIG. 4, the catch basin 200 can be configured in a variety of configurations. The catch basin 200 can be extended a certain distance from the cabinet 12 on a plane parallel with the ground and toward the bottom portion of the freezer 10 and below the cabinet 12 as seen in FIG. 2. Other configurations can be used, including where the location of the catch basin 200 can be closer to the ground or can be restricted to being below the cabinet 12 and above the refrigeration deck 300 or at the top portion of the refrigeration deck 300. The refrigeration deck 300 includes, for example, the compressor for the freezer 10. The catch basin 12 can extend along the length of the bottom portion of the cabinet 12 and just below the door 16, accommodating the closing of the door 16 with the cabinet 12. Alternatively, the catch basin 200 can extend around only a portion of the bottom surface 12A of the cabinet 12. Alternatively, the catch basin 200 can be a variety of shapes including a rectangular shape along the length of the cabinet 12. The catch basin 200 can be longer than the cabinet's length along the bottom surface 12A of the cabinet 12.
Referring to FIG. 5, in another embodiment, the distribution channel 510 can have a more tortured path than the path seen in FIG. 1. The catch basin 200 is connected to the distribution channel 510 that is embedded within the refrigeration deck 300 and feeds along toward the back portion of the freezer 10, then up toward the top portion of the freezer 10 and finally toward the front of the freezer cabinet 12 that is attached to the door 16. Other configurations of even more tortured path can be used. The increased path of the distribution channel allows the air a greater path in which to be compressed and thus providing greater pressure in the air curtain.
The air curtain can be alternatively formed in the horizontal direction as mentioned above, with an alternate configuration of the distribution channel accommodating recirculation of the air (not shown). The air curtain unit 100 can also be split into two sections, where two air curtain units 100 of FIG. 3 are arranged independently on both sides of the cabinet 12.
Referring to FIG. 6, in another embodiment, a smaller space for the air curtain can be configured. For example, if the freezer 10 includes a first door 16A and a second door 16B, then the air curtain would only run across the space of the door 16 that is open. The distribution channel 610 would include a path not only on the top portion of the cabinet 12, but also in between the first and second doors 16A and 16B. The output from the middle plenum 616 and top horizontal plenum 614 would be switched according to the opening of the doors 16A and 16B. Therefore, if the second door 16A is opened, then only the open space is configured with an air curtain as the air is outputted through the middle plenum 616 to the catch basin 200. The pressure of the air can also be lower than if it was to cover the larger space. Additionally, the air curtain unit can collect the air failing through spaces between the inner doors 16A and 16B. Additionally, the circulation path can be shortened. Above the middle plenum 616 there can be a second catch basin 202 that can shorten the circulation path when the first door 16A is opened. The distribution channel 610 can include valves or other means (not shown) to accommodate the shortened circulation or an alternate configuration. The catch basins 200 and 202 are fluidly connected with the distribution channel 610. The blower within the air curtain unit can include a smaller fan when the air curtain is reduced as in FIG. 6.
In another embodiment, the cold air is pulled in and compressed to form an air curtain as mentioned above. Rather than using the distribution channel to compress the air, the air can be already compressed through an active compressing device (not shown).
In FIGS. 1-4, an illustration is made showing the recirculation or distributing channel 210 going on the outside of the cold space. However, referring to FIG. 7, a cross sectional view of a freezer includes another embodiment. Rather than being placed external to the frame 14 of the freezer 10 in FIG. 1, the distributing channel 210 in FIG. 7 is embedded between the insulation 702 and the evaporator 704 and within the frame 14 of the freezer 700. In this embodiment, the distributing channel 210 may have a more tortured path as shown in connection with the embodiment of FIG. 5. The location of the distributing channel 210 being placed between the insulation 702 and evaporator 704, and its possible long tortured path, would allow the air that forms the air curtain to be at the same or similar temperature as the evaporator 704. The reduction of warm moist air that enters the cabinet during a door opening will reduce the amount of frost that forms and extend the time span between defrosts or user removal of frost build-up.
The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. An ultra-low temperature freezer, comprising:

a cabinet with a freezer compartment maintained within a certain temperature range;

a door providing a seal with the cabinet when engaged with the cabinet;

a catch basin at the bottom of the cabinet for collecting air; and

a distribution channel fluidly connected to the catch basin, for recirculating the air collected from the catch basin to the top of the cabinet, the distribution channel at the top of the cabinet pushing compressed air across the front of the cabinet and forming an air curtain and thermal barrier to incoming warmer air.

2. The apparatus of claim 1, wherein the distribution channel is disposed exterior to the cabinet and configured to compress the air.

3. The apparatus of claim 1, further comprising nozzles disposed on the distribution channel at the top of the cabinet for outputting the compressed air.

4. The apparatus of claim 1, further comprising at least two plates with an opening in between, on the distribution channel at the top portion of the cabinet for forming the air curtain.

5. The apparatus of claim 1, wherein the distribution channel is disposed between insulation and an evaporator.

6. The apparatus of claim 1, wherein the distribution channel includes a tortured path from a front of the freezer to the back of the freezer and back to the front of the freezer, where the front of the freezer is the plane where the door seals the cabinet.

7. The apparatus of claim 1, wherein the distribution channel includes a middle portion between the door and a second door connected to the cabinet, providing an air curtain from the middle portion to the catch basin.

8. An ultra-low temperature refrigeration apparatus, comprising:

a door providing a seal with the cabinet when engaged with the cabinet;

a collection means at the bottom of the cabinet for collecting gas; and

a distribution means fluidly connected to the collection means, for recirculating the gas collected from the collection means to the top of the cabinet, the distribution means at the top of the cabinet pushing compressed gas across the front of the cabinet and forming a curtain and thermal barrier to warmer outside environment.

9. The apparatus of claim 8, wherein the distribution means is disposed exterior to the cabinet.

10. The apparatus of claim 8, further comprising nozzles disposed on the distribution means at the top of the cabinet for outputting the compressed gas.

11. The apparatus of claim 8, further comprising at least two plates with an opening in between, on the distribution means at the top portion of the cabinet for forming the curtain.

12. The apparatus of claim 8, wherein the distribution means is disposed between insulation and an evaporator.

13. The apparatus of claim 8, wherein the distribution means includes a tortured path from a front of the apparatus to the back of the apparatus and back to the front of the apparatus, where the front of the apparatus is the plane where the door seals the cabinet.

14. The apparatus of claim 8, wherein the distribution means includes a middle portion between the door and a second door connected to the cabinet, providing the curtain from the middle portion to the collection means.

15. A method of an ultra-low temperature freezer, comprising:

collecting air at a catch basin at the bottom of a freezer cabinet when opening a door of the freezer;

compressing and distributing the air collected from the catch basin to the top of the cabinet via a distribution channel; and

outputting the compressed air across the front of the cabinet from the top of the cabinet to the bottom of the cabinet toward the catch basin and forming an air curtain and thermal barrier to incoming warmer air.

16. The method of claim 15, further comprising of recirculating the air outputted across the front of the cabinet and into the catch basin via a distributing channel.

17. The method of claim 15, further comprising cooling the air through the distribution channel disposed adjacent to an evaporator.

18. The method of claim 15, further comprising of actively cooling and compressing the air circulating through the distribution channel.