The use of impingement heating apparatus for thermally treating food products has previously been disclosed. These conventional apparatus typically employ columnated jets of temperature-controlled gas which impinge against the surface of a food product moving relative thereto. Such devices are disclosed, for example, in U.S. Pat. Nos. 3,884,213; 4,154,861; 4,289,792; and 4,338,911. When used for heating purposes, these devices can also be employed in combination with microwave generators.
In conventional conveyorized ovens which utilize impingement heating, high velocity jets of a temperature-controlled gas are directed against the surface of food products transported through the apparatus on a conveyor. The temperature-controlled gas is discharged by a blower into a plenum that directs the flow of gas into a series of spaced-apart tapered ducts extending transversely across the conveyor. These ducts are in turn adapted to direct the flow of gas into columnating orifices which cause the gas jets to impinge against the surface of the food products.
In the past, those working with such ovens have encountered difficulty in balancing the gas flow across the plenum and into the various ducts, especially those farthest removed from the point at which the gas is discharged from the blower. Plenums utilized in the conventional, commercially available impingement ovens have generally employed a substantially vertical, planar front wall having a plurality of spaced apart, rectangular ports disposed therein for providing fluid communication with the outwardly extending ducts. The blower is typically disposed inside a shroud at the rear of the plenum. Attempts have previously been made to balance the flow of gas into the ducts farthest removed from the blower by tapering the rear wall of the plenum toward the front wall as it extends laterally outward from the blower. Attempts have also been made to balance the flow within the ducts by tapering the wall opposite the columnating orifices. However, even when the plenum and ducts are designed and constructed in this manner, the gas entering the inlet ports of the remote ducts is likely to overshoot the columnating orifices nearest the inlet ports. Also, it has been found that the flat surfaces between the inlet ports on the front wall of the plenum cause turbulence which further disrupts the flow of gas and hinders the even distribution of the gas to adjacent ducts.
In view of these and other disadvantages that have been encountered in using the conventional, commercially available devices, an improved apparatus is needed that will facilitate even distribution of the gas throughout a plurality of ducts while simultaneously reducing the overall turbulence inside the plenum.