Abstract:
A cryogenic fog generator is provided which includes a container having an interior in which liquid cryogen is disposed; an opening in the container from which the liquid cryogen can flow from the interior out of the container; a surface area upon which the flow of liquid cryogen is received; an ultrasonic transducer disposed proximate the opening for coacting with the surface area to transmit ultrasonic energy to the surface area and the liquid cryogen for providing a cryogenic fog. A method of producing a cryogenic fog is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present embodiments relate to chilling atmospheres in freezers. 
         [0002]    A problem with conventional cryogenic sprays for freezers is that the sprays are heavier than gas present in the freezer atmosphere and therefore, the sprays tend to fall onto a specific area of a conveyor belt in the freezer, thereby creating localized, instead of uniform, areas of high heat transfer. In addition, known cryogen spray nozzles produce large liquid droplets which are not as effective at providing high evaporative heat transfer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]    For a more complete understanding of the present embodiments, reference may be had to the following drawing figure taken in conjunction with the description of the embodiments, of which: 
           [0004]    The Figure shows a nitrogen fog generator embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0005]    There is currently no known method for creating a nitrogen fog or more specifically, a finely atomized liquid nitrogen spray which appears gaseous in nature, but is actually composed of very small droplets of liquid nitrogen. 
         [0006]    With a nitrogen fog, a larger amount of freezing surface area can be covered effectively, efficiently and more uniformly. The fog can populate an entire freezing zone, if so desired, resulting in uniform, extremely high heat transfer rates throughout the freezing zone and production process. 
         [0007]    Referring to the figure, a nitrogen fog generator embodiment is shown generally at  10  for use in a freezer (not shown), such as for example a cryogenic freezer. The fog generator  10  can also be used with mechanical freezers (not shown), such as for example by being disposed at a front end or a rear end of a mechanical freezer system. The fog generator  10  is used to increase or augment the heat transfer effect of an existing freezer, such as for example a nitrogen freezer. 
         [0008]    The fog generator  10  includes a container  12  or vessel which can be vacuum jacketed. The container includes sidewalls  14 , a top  16 , a bottom  18  and an internal chamber  20  to which liquid nitrogen  22  can be introduced and contained. 
         [0009]    A pressure transducer  24  is mounted to the top  16  for sensing pressure in the space  26  of the chamber  20  above a surface of the liquid cryogen  22 . An exhaust pipe  28  or vent is in communication with the space  26  such that excess pressure in the space  26  can be vented through the pipe  28  in the direction of arrow  30 . The space  26  includes gaseous pressure resulting from the phase change of liquid nitrogen in the chamber  20 . A valve  32 , such as a solenoid valve, is disposed in the exhaust pipe  28 . Communication between the pressure transducer  24  and the solenoid valve  32  for actuation is through a wire  34  interconnecting the transducer  24  with the valve  32 . 
         [0010]    A pipe  36 , which may be vacuum jacketed, is connected to the container  12  for communication with the internal chamber  20  for introducing the liquid cryogen  22 , such as nitrogen, into the chamber  20 . The pipe  36  is connected to a remote source of cryogen (not shown), which can provide the liquid cryogen under a pressure higher than atmospheric, as indicated by arrow  38  directed to the chamber  20 . 
         [0011]    The bottom  18  of the container  12  is constructed and arranged to provide a nozzle  40  in communication with the chamber  20  and through which the liquid cryogen  22  is directed under the effect of gravity in a flow shown generally at  42  for further application. 
         [0012]    Disposed beneath the container  12  is a collection or capture plate  44  or pan constructed to collect the cryogen flow  42  emitted from the nozzle  40 . A plurality of rods  46  or stanchions are provided in a number sufficient to support the container  12  above the pan  44  and in registration therewith so that the cryogen flow  42  emitted from the nozzle  40  is collected in the pan  44 . The rods  46  provide for a sufficient amount or volume of space  48  between the bottom  18  of the container and an upper surface  50  of the pan  44 . 
         [0013]    Upon exposure of the liquid nitrogen  22  to the atmosphere of the space  48 , the nitrogen liquid is disposed evenly onto the surface  50  of the pan  44  forming a reservoir  51  or pool of liquid nitrogen. 
         [0014]    An ultrasonic transducer  54  is disposed beneath and in contact with the pan  44 . Electrical leads  56  provide power from a remote source, such as a power generator (not shown), to actuate the transducer  54 . The transducer may operate from between 10-45 kHz. The power generator (not shown) provides from 100 watts to 2 kilowatts (kW) of power. An alternative embodiment has the pan  44  constructed as an integral part of the transducer  54 . 
         [0015]    The upper surface  50  of the pan  44  is constructed to distribute the liquid nitrogen flow  42  so as to maximize surface area of the pool  51  of liquid nitrogen when being collected in the pan. As the liquid nitrogen comes into contact with the pan which is vibrated at a very high frequency by the transducer  54 , the liquid nitrogen is atomized and dispersed away from the pan  54  as a nitrogen fog  52  to provide increased heat transfer effect in the freezing atmosphere for the product (not shown), which can be for example food products. 
         [0016]    In the present embodiments, the liquid nitrogen  22  is delivered via the vacuum jacketed piping  36  to the chamber  20  of the vacuum jacketed container  12  with a venting system  24 , 28 , 32 , 34 . The container  12  collects the liquid nitrogen  22  and lowers its pressure to atmospheric pressure. The pressure transducer  24  or a similar device mounted to the chamber  20  inside the container, senses pressure and subsequently actuates solenoid valve  32  to vent nitrogen gas and maintain a constant pressure in the chamber. The low pressure liquid nitrogen is discharged through the nozzle  40  onto the pan  44  which is in contact with the ultrasonic transducer  54 . The pan  44  is designed to distribute the liquid nitrogen flow  42  to form the pool  51  in such as way as to maximize surface area coverage so that the pool  51  can be easily and uniformly atomized by the ultrasonic transducer  54 . The nozzle  52  is sized so that the flow  42  into the pan  44  can be controlled. As the liquid nitrogen comes into contact with the pan  44  it is vibrated at very high frequency, atomized and then flows away from the device as a nitrogen fog  52 . The transducer  54  is controlled by the power generator (not shown) which sets the correct power and frequency of the transducer. 
         [0017]    The fog generator embodiment  10  or a plurality of same can be installed directly into a freezing zone of a cryogenic freezer. 
         [0018]    It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.