Concentric air delivery and return oven

Electric heating – Heating devices – Combined with container – enclosure – or support for material...

Reexamination Certificate

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Details

C219S388000, C126S21400R, C034S223000, C034S232000

Reexamination Certificate

active

06259064

ABSTRACT:

TECHNICAL FIELD
The invention disclosed herein relates to impingement heat transfer apparatus for preparing food.
BACKGROUND OF INVENTION
Pizzas and other fast food products are generally cooked in ovens to bake the crust and to bake, heat, and melt the toppings. One style of pizza oven is a deck oven that uses radiant and conductive heat for cooking. Typically, the required baking time in a deck oven would be in a range between about 15 and 25 minutes.
An impingement oven uses mostly convection to heat the pizza, as well as some heat of conduction. The newer pizza ovens typically are impingement ovens which move the pizzas through the oven on conveyors while others are equipped with rotating turntables for moving the pizza relative to air streams that impinge the pizza.
An impingement oven is described in U.S. Pat. No. 4,679,542 to Don Paul Smith. These ovens, which are a special type of forced convection oven using columnated heated air to impact the pizza, have increased heat transfer capabilities and therefore have reduced the bake time of pizza and other foods significantly.
Impingement ovens have achieved wide acceptance among pizza restaurants, and pizza delivery systems, especially those which deal with high volume and fast service. The typical bake time for the commercially available impingement ovens is in the range of about 5 to 9 minutes. However, by using partially pre-baked crust in an impingement oven at a relatively high temperature, the final cooking time may be reduced to a little over one minute.
U.S. Pat. No. 4,965,435 discloses a jet impingement oven in which spent air from jets formed by tubes is drawn toward the front wall of the oven. U.S. Pat. No. 5,310,978 discloses an oven in which spent is drawn toward opposite sides of the oven for returning the spent air to a fan. U.S. Pat. No. 5,510,601 discloses an air impingement oven wherein air is delivered by a fan into hollow fingers for forming columns of heated air that are projected through tubes. After the columns of air impinge against the surface of the food product, the spent air is drawn toward the back wall of the oven.
Pellicane U.S. Pat. No. 4,960,100 discloses a plurality of spaced discrete nozzles, each nozzle defining a slot orifice disposed transverse to the path of travel of a conveyor. The nozzles are spaced along the path of travel so that the surface of the product to be cooked which is impinged upon by air flowing through the nozzles will pass from an area of high velocity to an area of low velocity between the slot orifices.
Moshonas U.S. Pat. No. 5,671,660 discloses a blower which draws air from a baking chamber through apertures into a suction chamber extending between air distributors which dispense air back into the baking chamber.
In each of the patents referred to above, after the jets impinge upon the surface of the product, the spent air is drawn around or through jets of air that have not yet impinged against the surface of the product. This tends to disrupt or “wash out” the collimated jets of air.
SUMMARY OF INVENTION
The impingement heat transfer device disclosed herein transfers heat between a stream of temperature controlled air and a product wherein an air supply duct and an air return duct have a common wall. A pattern of tubes, where each tube has one end communicating with the inside of the air supply duct and another end extending through an opening in the air return duct. Air is circulated by a fan to reduce pressure in the air return duct and increase pressure in the air supply duct such that a stream of air flows through and out of the tubes and spent air is drawn through the opening encircling each tube into the air return duct.
A preferred method of transferring heat between a stream of temperature controlled air and a product in an impingement heat transfer device includes the step of directing a plurality of streams of air to impinge against a plurality of splash areas spaced over the surface of the product such that heat is transferred between each stream of air and the splash area against which it impinges. Each stream, after impinging on the product, is diffused transversely away from the stream to form a volume of spent air.
Each volume of spent air is drawn transversely toward the stream of air that was diffused to form the spent volume such that spent air from each of the plurality of streams does not influence the flow of air toward the product in any other stream.
Each volume of spent air is collected adjacent the stream of air that was diffused to form the spent volume.
Imparting relative movement between the product and the plurality of streams, wherein the splash areas move across the surface of the product, causes heat to be transferred substantially uniformly over the surface of the product.
Steps of directing a plurality of streams of air to impinge against a plurality of splash areas spaced over the surface of the product and for drawing each volume of spent air transversely toward the stream of air that was diffused to form the spent volume are preferably accomplished by providing an air supply duct and an air return duct having a common wall wherein a tube has one end communicating with the inside of the air supply duct and another end extending through an opening in the air return duct The opening in the air return duct has an inside diameter and the tube has an outside diameter, the outside diameter of the tube being less than the inside diameter of the opening in the air return duct to form an inlet into the air return duct encircling the tube. A stream of air flows through and out of the tube and spent air is drawn through the opening encircling the tube into the air return duct.
This process produces a plurality of areas of low pressure, at least one of the areas of low pressure being adjacent to and encircling each of the plurality of tubes and spaced from the outlet of each tube wherein spent air is drawn toward the area of low pressure encircling the tube after the stream impinges the product and before the spent air flows to influence the flow of air toward the product in any other stream. Air from each tube has an independent air return path and adjacent air streams do not influence air flow from another tube. Air flow from each tube is balanced and does not disturb the integrity of other air streams.
An impingement heat transfer device for accomplishing the transfer of heat between a stream of temperature controlled air and a food product generally includes a cabinet and fan or blower for directing a plurality of streams of air to impinge against a plurality of splash areas spaced over the surface of the product such that heat is transferred between each stream of air and the splash area against which it impinges. Each stream is diffused transversely away from the stream to form a volume of spent air.
Spent air collectors are provided in the cabinet for drawing each volume of spent air transversely relative to the direction of flow of the stream toward the stream of air that was diffused to form the spent volume. Thus, spent air from each of the plurality of streams does not influence the flow of air toward the product in any other stream and each volume of spent air is collected adjacent the stream of air that was diffused to form the spent volume. Spent air from each stream of air is concentrically balanced with the volume of air in the original air stream.
The product may be carried on a conveyor or turntable for imparting relative movement between the product and the plurality of streams or in the alternative the apparatus forming the streams may move to impart movement of the splash areas across the surface of the product such that heat is transferred substantially uniformly over the surface of the product.
Fingers in the cabinet form and direct a plurality of streams of air to impinge against a plurality of splash areas spaced over the surface of the product such that heat is transferred between each stream of air and the splash area against which it impinges.
The fingers serve the dual function of forming collectors between a

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