Abstract:
A combination convection and steam oven having a three stage atomizer for breaking up supply water prior to vaporization. The atomizer includes a motor-driven fan having an atomizer cup at its hub which revolves with the fan about an axis of rotation. The atomizer cup has rectilinear or concave walls defining pockets having lengthwise slots at their corners. As the atomizer cup is rotated, supply water is fed into the cup so as to impact the inner surfaces and shear as it exits through the slots under centrifugal force, which directs the water through the fan blades. The supply water thereby is broken up by three separate actions prior to vaporization.

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an atomizer of the present invention and a drive unit and water feed within a combination convection and steam oven, the drive unit and water feed shown schematically; 
     FIG. 2 is an enlarged perspective view of an atomizer cup, fan, a water line and heating elements of the atomizer of FIG. 1; 
     FIG. 3 is a side view of the atomizer of FIG. 2, shown with one set of heating elements removed; 
     FIG. 4 is front view of the atomizer; 
     FIG. 5 is an enlarged front view of an alternate embodiment of the atomizer cup; and 
     FIG. 6 is an enlarged front view of another embodiment of the atomizer cup. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a combination convention and steam cooking oven  10  includes an enclosure  12  defining a cooking chamber  14  for containing foodstuffs. The cooking chamber also includes heating elements  16  as well as an atomizer  18  comprising a motor-operated fan  20  and an atomizer cup  22  at one side of the cooking chamber  14 . The heating elements  16  are conduits of a metallic material through which gas heated by the oven burners (not shown) circulates. Preferably, the heating elements  16  include two sets of three conduits extending in close proximity to the outer diameter of the fan  20 , preferably at each side, in front of and behind the fan  20 . Alternatively, the heating elements  16  may be suitable solid resistive heating elements. The heating elements  16 , fan  20  and atomizer cup  22  are located adjacent to a partition  24  separating the cooking chamber  14  from an electronics area  26 . 
     The fan  20  is a squirrel cage design having a plurality of inwardly cupped blades  28  attached at a fixed end  30  to parallel circular rims  32 . The blades  28  are oriented to draw air in through an open side  34  and expel air radially outward toward the heating elements  16  when rotated clockwise. Opposite the open side  34 , the fan  20  includes a wall  36  having a concentric opening  38  for suitably mounting the fan  20  to a motor shaft  40  positioned along a rotation axis  42 . 
     The motor shaft  40  also extends through an opening  44  in the partition  24  back to the electronics area  26  in which a suitable electric motor  46  is disposed. Preferably, the motor  46  is mounted by suitable bracketry (not shown) to the partition  24 . The motor  46  is coupled to a control module (not shown) having a suitable keypad user interface (not shown) viewable from the front exterior of the enclosure  12  for setting cooking time and temperature. 
     The motor shaft  40  also mounts the atomizer cup  22  at the center of the fan  20 . In a preferred embodiment, the atomizer cup  22  includes a plurality of rectilinear walls  48  joined at edges  50  defining a cup volume  52  having an open side  54  and an opposite walled side  56 . The walled side  56  includes an opening  58  through which the motor shaft  40  is inserted. The atomizer cup  22  can be mounted to the motor shaft  40  by any suitable connection, such as a press-fit, threaded fastener or slot pin and connection. In one preferred embodiment, the atomizer cup  22  includes four walls  48  joined at right angles. Preferably, the walls  48  have lengthwise slots  60  at the edges and an inwardly tapered lip  62  at the opening sides  54  to provide a trough for presenting water at the inner surfaces of the walls  48  from exiting out the open side  54  of the atomizer cup  22 . The slots  60  are preferably sized large enough so as not be easily clogged by buildup of calcium deposits from the water. The walls  48  are preferably made of a material resistant to the affects of heat and corrosion, such as stainless steel. 
     A water line  64  of suitable tubing extends from a fitting  66  within the electronics area  26  of the enclosure  12  at which a water supply line (not shown) is attached to a flow control valve  68 , such as a solenoid, coupled to the electronic control module (not shown). From the control valve  68 , the water line  64  continues through an opening  69  (see FIG. 1) in the partition  24  into the cooking chamber  14  in a suitable path to avoid interfering with the fan  20 . The water line  64  terminates at an open end  70  within the cup volume  52  of the atomizer cup  22 . 
     The combination oven  10  can be used solely for convection cooking. In this case, the flow control valve  68  remains dosed so that no water is fed to the atomizer  18 . The motor  46  rotates the fan  20  to pick up and circulate heat radiating from the energized heating elements  16 . When steam cooking is desired, the flow control valve  68  is operated to allow supply water to flow through the water line  64  to the atomizer  18 . The flow control valve  68  can be controlled to provide intermittent or steady stream flow of water through the water line  64 . In either case, the flow rate is controlled to provide only the volume of water that can be immediately vaporized by the heating elements  16  so that overflowing water does not accumulate at the bottom of the cooking chamber  14 . 
     As the atomizer cup  22  and fan  20  are rotated, the impinging water is broken up and directed past the heating elements  16 . The atomizer cup  22  and fan  20  act to break up the water in three stages. First, water leaving the water line  64  impinges on the inside surface of the atomizer cup walls  48 . The rotating rectilinear walls  48  disrupt and agitate the impinging water to a greater extent than smooth curvilinear surfaces. Second, the centrifugal force generated by rotation directs the water within the cup volume  52  radially outward to the edge slots  60 . As the water passes through the slots  60  it is sheared by its edges. Third, the fan  20  draws this water into contact with the revolving blades  28 , which further shears the water. The water is broken up to increase its surface area as it passes by the heating elements  16 . According to known heat transfer principles, increasing surface area of a body increases the rate at which heat is transferred to that body. Here, the water flowing from the water line  64  will be more efficiently vaporized to steam by the heating elements  16  due to the atomization of the water. Thus, the heating elements will consume less energy while generating a given amount of steam. 
     FIG. 5 shows an alternate embodiment of the oven  10 A with an atomizer cup  22 A having six rectilinear walls  48 A joined at their edges  50 A at alternating obtuse and acute included angles. The walls separated by the acute included angles define pockets  80  in which the impinging water can be captured and agitated before it is directed out edgewise slots  60 A to the fan  20 . This embodiment provides additional edges and surfaces for contacting and breaking up the impinging water prior to exiting through the slots  60 . 
     FIG. 6 shows another embodiment of an atomizer cup  22 B having four arcuate walls  48 B joined at their edges  50 B. The arcuate walls  48 B define in concave interior pockets  80 B, which capture and agitate water fed into the atomizer cup  22 B before it is directed out slots  60 B. This embodiment, as well as that shown in FIG. 5, preferably includes an inwardly directed rim (not shown) at the open side of the atomizer cup for retaining water. 
     The present invention may include other aspects not specifically delineated in the aforementioned preferred embodiments. For example, the atomizer cup may have more or less walls of the same or different sizes to provide other suitable configurations. Thus, the above in no way is intended to limit the scope of the invention. Accordingly, in order to apprise the public of the full scope of the present invention, reference must be made to the following claims.