Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-04-03
2001-02-13
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S400000, C126S020000, C239S498000, C239S504000
Reexamination Certificate
active
06188045
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable.)
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
(Not Applicable.)
BACKGROUND OF THE INVENTION
The present invention relates to cooking ovens, and in particular, to combination ovens and steamers.
Combination ovens provide the ability to cook foods using steam, hot air or a combination of both. A motor driven fan is used to circulate air within a cooking chamber past electrical heating elements or gas fired heat exchange tubes. Combination ovens can be designed with or without a boiler. To produce steam within the cooking chamber, a water line feeds water into the cooking chamber near the heating elements to vaporize the water.
It is well known that the rate of thermal heat transfer increases in proportion to the surface over which the heating occurs. Thus, combination ovens typically feed the water within the inner diameter of the fan so that the water is drawn through the fan. Contact of the water with the fan blades separates the water into small droplets having an effective large surface area which can be vaporized more efficiently. To further improve thermal efficiency, some prior art combination ovens include an atomization element at the hub of the fan which is rotated by the motor. The atomization element which acts to break up the water before it is further reduced by the fan blades. This two stage atomization process produces a fine mist of water surrounding the heating elements.
One type of two stage atomizer is disclosed in U.S. Pat. No. 5,014,679, wherein the atomizer element is a cylindrical drum forming a trough with an open end into which the water is fed. As the drum is rotated, centrifugal force directs the water to pass through the open end where it is broken up by shear forces at the circular edge. The broken up water is then directed radially outward to a fan. A variation on this design includes a perforated cylindrical drum with centrifugal force directing the water out of the perforations. The water is broken up more finely in this design due to increased shearing of the water by the perforations.
An alternative design is disclosed in U.S. Pat. No. 5,530,223. This patent discloses a combination oven in which the water is directed at an outer surface of a pre-atomizer as it is rotated. The pre-atomizer is a sphere, a hemisphere or a plate having no openings. The contact of the water with the outer surface of the rotating atomizer element preliminarily breaks up the water before it is drawn into the fan. However, in this design, there is relatively little shear forces acting on the impinging water, compared to the perforated drum, such that the water is not as finely broken up.
Accordingly, a combination steam and convection oven is desired that provides improved atomization of water.
SUMMARY OF THE INVENTION
The present invention provides a combination steam and convection oven for preparing food having a three stage atomizer providing highly energy efficient steaming operation. An atomizer cup preliminarily breaks up impinging water at inner surfaces before it is sheared through opening in the walls and drawn into and through a fan.
Specifically, the atomizer includes a fan rotating about an axis to dispel air radially outward. The fan has an open face providing access to a fan interior. Heating elements surround the fan in the path of the dispelled air. A cup is attached to the fan along the axis within the fan interior to rotate with the fan. The cup has an open face providing access to a cup interior defined by axially extending cup walls, which receives water from a water line. The cup walls vary in distance from the axis as a function of an angle about the axis. At least one cup wall includes an opening through which the water in the cup interior passes. In this way, the cup walls provide impact surfaces striking and atomizing water introduced through the open face of the cup to the cup interior. The edges of the opening causes shearing of the water so as to further break up the water passing through the opening before contacting blades of the fan.
In one aspect of the invention, the cup can include a plurality of openings. The openings can be perforations, preferably however, the openings are slots disposed along the union of adjacent walls.
In another aspect of the invention, the atomizer cup has rectilinear walls defining a rectangular cross-sections. The walls may, however, have an N-sided cross-section where N is between 3 and 10. In this way, the walls can be configured to extend radially outward so that adjacent walls define water receiving pockets. The walls can also be curved to define concave inward pockets for receiving water. In either case, water feed into the cup interior is impacted and agitated by the cup walls, particularly at their edges, before the water exits the openings.
In one preferred form, the present invention provides a convection food oven having improved steam generating capabilities. The oven includes an oven enclosure containing a water line and at least one heating element. A motor-driven radial fan, positioned near the heating element, rotates about a rotation axis. An atomizer cup is attached to a hub of the fan and has a plurality of rectilinear walls with slotted edges. As such, water from the water line is atomized in three stages. In the first stage, impinging water is broken up by contact with the inside surfaces of the of walls. In the second stage, the water is sheared by passing through the slots. And, in the third stage, the water is further atomized by contacting the fan blades.
These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow.
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Hansen William J.
Raghavan Jembu K.
Alto-Shaam, Inc.
Pelham Joseph
Quarles & Brady LLP
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