Patent Publication Number: US-2010120351-A1

Title: Frost reduction by air curtain

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&#39;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  12 C at the horizontal plenum  214  of the distributing channel  210 . 
     Referring to  FIG. 3 , at the top of the cabinet  12 C, 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  12 A 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&#39;s length along the bottom surface  12 A 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  16 A and a second door  16 B, 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  16 A and  16 B. The output from the middle plenum  616  and top horizontal plenum  614  would be switched according to the opening of the doors  16 A and  16 B. Therefore, if the second door  16 A 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  16 A and  16 B. 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  16 A 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.