The steady thermocapillary flow of nonvolatile layers, nonuniformly heated from below, is examined. The interactions among viscous forces, thermocapillarity, and hydrostatic effects give rise to the steady-state dimpling of the interface. The steady dimpling of nonuniformly heated silicone-oil layers with mean thicknesses ranging from 0.125 to 1.684 mm is studied experimentally. The temperature distribution in the substrate is monitored by thermocouples and the interface shapes by a mechanical impedance probe. Measured steady shapes and theoretical predictions agree within 20% for moderate heating when the film is not close to rupture. When the heating rate causes the film to "dry out" above the hottest point on the substrate, the long-wave theory delivers a parametric index, involving thermocapillary and hydrostatic effects, which is an excellent predictor of rupture. Nonlinear long-wave theories of the type discussed here have never been tested experimentally, until now. The confirmation of this thermocapillary theory is suggestive of the validity of the previous long-wave analysis [Phys. Fluids A 2, 313 (1990)] of unsteady, evaporating/condensing liquid layers.
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