Transient heat transfer characteristics of small jet impingement on high-temperature flat plate

Numerical studies on the transient heat transfer characteristics of small-air-jet impingement under the condition of a large temperature difference between the nozzle and the plate are presented. The Reynolds number (Re) varied from 20,000 to 60,000 which is based on the hydraulic diameter of the circular jet. The nondimensional jet-to-plate distance (H/D) with nozzle diameter (D) of 5 mm is varied from 0.2 to 2. Variations in the stagnation point and boundary point Nusselt numbers with cooling times are discussed. It was found that with the decrease of jet-to-plate distance the heat transfer near stagnation point is enhanced, while it is decreased near boundary point. The velocity field is proposed as an explanation for the observed transient heat transfer.