Patent Application
20130125562
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 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.
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, 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.
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.
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 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
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 26A) 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 26,26A 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.
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.
Alternatively, and referring to
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.
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
The embodiment 10 can be constructed and arranged in a new freezer, or retrofit to an existing freezer.
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.
