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.
In a cryogenic food freezing system, nitrogen liquid, for example, is sprayed into the freezing chamber to provide refrigeration for the 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.
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:
As discussed below with respect to the present invention, when liquid nitrogen (N2) is atomized, surfaces of the atomized droplets are charged by exposure to an electrostatic field. The product, such as for example a food product to be chilled or frozen, can be grounded or provided with an opposite charge which will attract the charged, atomized nitrogen droplets, allowing for a much greater proportion of the nitrogen spray being deposited onto the food product, thereby maximizing overall evaporative heat transfer at the product and use of the nitrogen.
The liquid nitrogen is disposed on an impingement plate and then atomized by an ultrasonic transducer. The impingement plate is charged such that it provides a charge directly to the atomized nitrogen gas, the charged atomized liquid nitrogen droplets are entrained directly into the flow of nitrogen gas as a fog passing through the impingement plate. This process provides more even distribution of the charged nitrogen fog and can therefore effectively replace cryogen nozzles in a freezing process.
Referring to
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 downward as shown at 25 toward the product 14 to facilitate the flow of gas as discussed below. A raised or elevated surface area 27 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 electrostatically charged and atomized. The raised surface area 27 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 27 in relief as compared to the areas 27 with same extending above the upper surface 18 as shown in
At least one ultrasonic transducer 26 is mounted to the upper surface 18 of the impingement plate 12. The ultrasonic transducer 26 vibrates the charged impingement plate 12 at high frequencies. The transducer 26 can also be mounted to a lower surface 34 of the impingement plate 12, as shown for example in
The high frequency vibration will cause the liquid nitrogen 16 disposed on the plate 12 to break-up into small atomized droplets 28. In addition, there are high velocity gas jets 30 created by a flow of nitrogen gas 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. The droplets 28 become charged by direct contact with the impingement plate 12.
The droplets 28 are discharged from the impingement holes 22 and seek the closest grounded or oppositely charged object, which will be the food product 14. The food product 14 is positioned closest to the discharge at the holes 22 by being transported upon the conveyor 11, such as a belt, as shown in
The embodiment 10 can be constructed and arranged in a new freezer system, or retrofit to an existing freezer system.
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.