Nucleate boiling on downward-facing heaispherical surfaces

摘要

Quenching experiments were conducted to investigate effects of azimuthal angle and wall material properties on nucleate boiling heat transfer from downward-facing,hemispherical stainless-steel and aluminum surfaces.The test sections had a diameter of 0.150 m and wall thickness of 0.020 m.Temperature measurements at eleven locations near the boiling surface (approx 0.5 mm) provided a time dependent boundary condition for 2-D numerical calculations of transient6 temperature field within the wall.The local pool boiling heat fluxes for both stainless steel and aluminum surfaces showed parabolic dependence on azimuthal angle.They decreased as azimuthal angle increased from theta =0 deg (the lowermost position) to theta = 45 deg (reaching a minimum),then increased with increased azimuthal angle on the surface.Nucleate boiling heat flux values for aluminum were about 4 approx 6 times higher than those for stainless steel at higher wall superheats (20 K< DELTA T < 30 K).However,the differnece between the nucleate boiling heat fluxes for the two materials diminished as the wall superheats decreased.