Abstract:
An impingement plate atomizer apparatus includes a longitudinal member having an upper surface sized and shaped to receive a liquid cryogen thereon, a lower surface opposite to the upper surface, and at least one hole extending through the longitudinal member; and an ultrasonic transducer in contact with the longitudinal member for providing ultrasonic energy thereto for atomizing the liquid cryogen at the upper surface into a cryogen fog.

Description:
BACKGROUND 
       [0001]    The present embodiments relate to freezer apparatus used to cause heat transfer to objects, such as for example food products, by the application of a cryogen to same. 
         [0002]    In a cryogenic food freezing system, nitrogen liquid, for example, is sprayed into a freezing chamber to provide refrigeration for the system process. It is desirable to spray the liquid nitrogen onto the warm surface of the incoming food product so that a phase change (heat of vaporization) occurs on the surface of the food product. This evaporative cooling effect creates extremely high heat transfer coefficients. Until now, it has been very difficult if not impossible to direct a high portion of the liquid spray onto the food product, as the spray is injected through nozzles that are positioned in a freezing chamber above a belt upon which the products travel for processing. Although a portion of the liquid nitrogen is deposited onto the surface of the product, another portion of the nitrogen travels to and through the belt without contacting the product. This results in an inefficient use of the liquid cryogen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which: 
           [0004]      FIG. 1  shows an ultrasonic impingement plate atomizer apparatus embodiment of the present invention; and 
           [0005]      FIG. 2  shows an enlarged portion of the embodiment in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0006]    As discussed below with respect to the present invention, when liquid nitrogen (N 2 ) is atomized, the atomized droplets provide for a faster or higher heat transfer rate when the nitrogen spray is deposited onto the food product, thereby maximizing overall evaporative heat transfer at the product and use of the nitrogen. This is because the atomization of liquid nitrogen produces very small size droplets. As a result of the small droplet size, the volume of liquid nitrogen, now in an atomized state, has a very high surface area. These small droplets with high surface area produce extremely high evaporative heat transfer rates when introduced for direct contact with a warm product such as for example a food product. 
         [0007]    The liquid nitrogen is disposed on an impingement plate and then atomized by an ultrasonic transducer coacting with the plate to therefore effectively replace cryogen nozzles in a freezing process. 
         [0008]    Referring to  FIGS. 1 and 2 , the ultrasonic impingement plate atomizer apparatus shown generally at  10  includes an impingement plate  12  positioned above a conveyor  11  for transporting a food product  14  to be frozen. The plate  12  may be constructed of stainless steel, aluminum, plastics including UHMW (ultra high weight molecular) or Teflon and holds or retains a quantity of liquid cryogen, such as for example liquid nitrogen  16 . This is accomplished by the plate  12  having an upper surface  18  and an edge  20  extending upward therefrom to retain a select amount of the liquid nitrogen  16  on the upper surface  18 . As shown in  FIG. 1 , the edge  20  extends along an outer perimeter or periphery of the plate  12 , but can also be constructed to extend along the plate at another area thereof where necessary to retain the liquid nitrogen. 
         [0009]    The plate  12  is formed with at least one or a plurality of holes  22  or apertures therethrough, each one of the holes  22  having an edge  24  turned upward away from the conveyor belt  11  to facilitate the flow of gas as described below. The holes  22  can be arranged in a myriad of different patterns at the plate  12 . The raised or elevated surface area  24  extends around each one of the holes  22  to prevent the liquid nitrogen  16  from pouring or seeping through the holes  22  before the nitrogen has been atomized. The raised surface area  24  functions as a dam and can be formed on the upper surface  18  by for example either pressing the plate  12  to have the upper surface  18  between the raised surface areas  24  in relief as compared to the areas  24  with same extending above the upper surface  18  as shown in  FIG. 2 , or by providing a wall of material to extend upward around the edges  24  of the holes  22 . The raised surface area  24  may be formed integral with the plate  12 . Although the holes  22  are shown having a circular shape, other shapes for the holes may be used. The liquid nitrogen  16  may be provided to the upper surface  18  from a pipe  19  having a first end connected to a cryogen source (not shown) and a second outlet end  23  proximate the upper surface for providing the liquid cryogen to the upper surface  18  to maintain a constant level of nitrogen at said surface of the plate. 
         [0010]    At least one ultrasonic transducer  26  is mounted to the upper surface  18  of the impingement plate  12 . The at least one ultrasonic transducer  26  may also be mounted (as at  26 A) to another area of the impingement plate  12 , such as a lower surface  34  of the plate depending upon the amount of space and operational environment available in which to use the apparatus  10 . The ultrasonic transducer  26  provides high frequency vibration to the impingement plate  12  as represented by arrow “V”. The transducers  26 , 26 A can be provided at both the upper surface  18  and/or the lower surface  34  of the impingement plate  12  to provide ultrasonic energy to the plate. 
         [0011]    The high frequency vibration “V” will cause the liquid nitrogen  16  disposed on the plate  12  to break-up into small atomized droplets  28 . High velocity gas jets  30  are created by a flow of atomized nitrogen gas  28  through the holes  22  of the impingement plate  12  by internal fans (not shown). The nitrogen droplets  28  are entrained in the gas jets  30  and forced through the holes  22 . 
         [0012]    Alternatively, and referring to  FIG. 2 , the edge  24  can be turned downward as shown by the broken line  25  toward the food product  14  to facilitate the flow of the gas jets  30  through the holes  22 . If the edge  25  is used, a raised or elevated surface area  27  would extend around each one of the holes  22  to prevent the liquid nitrogen  16  from pouring or seeping through the holes  22  before the nitrogen has been atomized. The raised surface area  27  functions as a dam and can be formed on the upper surface  18  by for example pressing the plate  12  to have the upper surface  18  between the raised surface areas  27  in relief. The raised surface area  27  may also be formed integral with the plate  12 . 
         [0013]    Although the holes  22  are shown having a circular shape, other shapes for the holes may be used. A nitrogen injection system (not shown) may also be used to provide a constant level of nitrogen at the surface  18  of the plate  12 . 
         [0014]    The droplets  28  are discharged from the holes  22  to be deposited on the product  14 . The food product  14  is positioned closest to the discharge of the holes  22  by being transported upon the conveyor  11 , such as a belt, as shown in  FIG. 2 . The ultrasonic energy transferred to the impingement plate  12  creates the droplets  28  to be of such a small size that the entrainment of the droplets  28  in the gas jets  30  provides for an atomized nitrogen fog  32  to be deposited upon the food product transported on the conveyor  11 . The fog  32  is very effective for covering or blanketing the exposed surface of the food product  14  as it is deposited thereon, instead of being deposited on the conveyor  11  or passing through the conveyor. 
         [0015]    The embodiment  10  can be constructed and arranged in a new freezer, or retrofit to an existing freezer. 
         [0016]    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.