Convective heat transfer at an annular jet impingement on a flat blockage

The experimental results on heat transfer of an annular impinging jet have been. The Reynolds numbers $\rm Re = (1.2$–$3.6) \times 10^4$, the distance $S$ from the nozzle to a blockage, $S/d_0 = 2, 4, 6$, and the circular slit height $d_2/d_0 = 0.51$ and $0.71$, where $d_0$ and $d_2$ are the internal and external nozzle diameters, have been varied. It is been shown that at the same air mass flow rate, replacement of a round nozzle with an annular one results in heat-transfer intensification (up to $70\%$ at the stagnation point). The maximum heat transfer gain occurs at a small nozzle–wall distance $(S/d_0 = 2)$. The heat-transfer increase is accompanied by an increase in the thermal pulsation intensity. The degree of intensification of the heat exchange depends on the height of the circular slit and the nozzle–wall distance.