Heat transfer and flow structure of a multichannel impinging jet

High speed particle image velocimetry and infrared thermography were used to investigate the behavior of hot jets with specific injections. A jet exiting from a round nozzle, a jet resulting from a nozzle with a straight-lined structure (Sw = 0) and a jet resulting from a nozzle with a curved structure (Sw = 0.26) have been studied for nozzle-to-plate distances from one injection diameter to 6 and for three mass flow rates (corresponding to injection Reynolds number from 23,000 to 33,000). For small nozzle-to-plate distances, the presence of a structure (straight-lined or curved in the injection tube) modifies the flow and increases the Nusselt number values in comparison with classical round jet flows. These modifications tend to disappear with increasing nozzle-to-plate distance. Moreover, the swirling effect principally affects ambient air entrainment into the jet and consequently effectiveness.