Investigation of Thin Liquid Layer Rupture for Liquid-Protected Divertors

Abstract

The liquid surfaces of liquid-protected high heat flux plasma-facing components may be subject to large temperature gradients caused by non-uniform incident particle and heat flux. Thermocapillary flows due to such gradients can potentially cause dry-out in high-temperature regions. Experimental and numerical investigations have been conducted to determine the maximum allowable non-dimensional temperature gradient just before rupture in thin liquid films of various aspect ratios and viscosities μ. Experiments were conducted using a needle contact method to measure the liquid film height of axisymmetric silicone oil (μ = 4.8 × 10^-3 N·s/m²-9.6 × 10^-1 N·s/m²) films for aspect ratios of 0.0065 to 0.02 on a non-isothermal stainless steel surface. The experimental data were compared with predictions from both an axisymmetric asymptotic analysis for the steady-state film height for thin layers and a direct numerical simulation using the level contour reconstruction method for thicker layers. The results of this investigation will provide component designers with experimentally-validated limits on the maximum allowable temperature radients to prevent local dry spot formation and possible burnout.