Impingement of an impact jet onto a spherical cavity. Flow structure and heat transfer

An experimental study of flow characteristics and heat transfer for jet impingement cooling of obstacles in the form of single spherical cavities is reported. The distributions of flow velocities between the nozzle and the obstacle, and also the fields of pressure and heat-transfer coefficients inside the cavity were measured. It is found that, at a value of depth the cavity generates the large-scale toroidal vortex, essentially influencing on the heat transfer. The cavity flow becomes unstable, exhibiting low-frequency pulsations of local heat fluxes. In the examined ranges of Reynolds numbers, Re = (1.2–5.8)104, and cavity depths (equal to or smaller than 0.5Dc) the local heat-transfer intensity in the cavity is lower than that on a flat obstacle; yet, this reduction is almost fully compensated by increased area of the heat-exchanging surface.