Convective Nucleate Boiling on a Heated Surface Cooled by an Impinging, Planar Jet of Water

Convective nucleate boiling has been studied on a flat, upward facing, constant heat flux surface cooled by a planar, impinging water jet. Surface temperature distributions are presented for jet velocities between 1.8 and 4.5 m/s, fluid temperatures of 30, 40, and 50°C, and heat fluxes between 0.25 and 2.5 MW/m². Although the critical Reynolds number, Re_x*,c, is independent of heat flux for q” < q”_ONB, boiling incipience strongly affects the transition to a turbulent boundary layer. As the heat flux increases, vapor bubbles of 1 mm diameter first appear at the point of maximum surface temperature, which also marks the onset of boundary layer turbulence. The leading edge of these bubbles moves toward the stagnation line and Re_x*,c decreases with further increases in heat flux. Acceleration in the stagnation region stabilizes the flow, however, so that boundary layer turbulence is restricted to x/w_j ≳ 1.6. With increasing heat flux, vigorous nucleate boiling covers more of the heater and surface temperature variations decrease.