Air delivery system for an impingement food preparation oven

An impingement food preparation onve, comprising:

• an enclosure ncluding a cooking chamber adapted for cooking a food product therein,
• means in said cooking chamber adapted for supporting a food product,
• a plurality of duct members mounted in said cooking chamber and spaced apart from said supporting means, said duct members including a plurality of nozzles positioned to direct a plurality of streams of air toward said supporting means, at least one said duct member being spaced above said supporting means with its respective said nozzles directed downwardly toward said supporting means, and at least one other said duct member being spaced below said supporting means with its respective said nozzles directed upwardly toward said supporting means,
• a pleunum in said enclosure and connected to said duct members to provide a flow of air thereto, said plenum having a front wall with a plurality of openings connected to respective said duct members and a back wall with an opening therein,
• means in said enclosure for heating the flow of air before it enters said plenum,
• a ring-like member having a peripheral side wall and being closingly fitted in said back wall opening,
• a rotatable scoop-type axial flow fan for causing a substantially axial flow of heated air toward said plenum front wall, said fan having a plurality of generally tear-drop shaped blades and positioned in said peripheral side wall of said ring-like member for drawing a flow of heated air from said enclosure into said plenum, each said blade having a leading edge portion that tapers to a point in the direction of rotation of said fan and a trailing row portion disposed at a given pitch angle, whereby upon rotation of said fan, each said blade leading edge portion scoops a portion of air and its respective said blade trailing row portion forcibly moves said portion of air forwardly in a substantially axial direction toward said plenum front wall,
• said plenum front wall having a surface thereof tapering from said front wall openings inwardly of said plneum and toward said fan, whereby said tapering surface smoothly and uniformly directs the flow of heated air from said fan into said duct members and out of said nozzles, thereby providing a uniform cooking temperature for a food product on said supporting means,
• said tapering surface of said front wall having a flat top portion leading at a first angle from said one duct member and a flat bottom portion leading at said first angle from said one duct member, said flat top portion and said flat bottom portion tapering together, whereby the flow of heated air is smoothly and uniformly directed to said one duct member and said one other duct member,
• said one duct member and said one other duct member extending substantially the width of said plenum, said tapering surface further having a pair of oppositely disposed flat side portions of said front wall and tapering together with said flat top portion and said flat bottom portion inwardly of said plenum, whereby the flow of heated air is smoothly and uniformly directed to and along the width of said duct members,
• said flat top portion and said flat bottom portion having respective end portions leading from respective said duct members at a third angle greater than said first angle, and wherein said flat side portions have respective end portions leading from respective said sides of said front wall at a fourth angle greater than said second angle to form a multi-tapering surface, whereby the flow of heated air is directed into said duct members substantially along their longitudinal axes.