Showing papers by "Raymond Viskanta published in 1992"

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

Abstract: 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, Rex*,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 Rex*,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/wj ≳ 1.6. With increasing heat flux, vigorous nucleate boiling covers more of the heater and surface temperature variations decrease.

A laminar boundary layer model of heat transfer due to a nonuniform planar jet impinging on a moving plate

Abstract: A theoretical model is developed of planar jet impingement heat transfer on a moving plate. Boundary layer equations in their integral forms are used in order to include, both near and away from the stagnation line, the effects of surface motion directed perpendicular to the jet plane, an arbitrary surface temperature variation, and nonuniform jet discharge velocity profiles. The validity and accuracy of the approximate solution is assessed by comparison to an exact solution restricted to regions near the stagnation line. Results indicate that the influence of a nonuniform jet discharge velocity decreases with distance from the stagnation line. Surface motion affects heat transfer at regions away from the stagnation line, but has little influence near the stagnation line when the surface temperature is constant.