An experimental investigation of the effect of surface-tension variation around air and vapor bubbles on a downward-facing heated surface is reported. For air bubbles, and vapor bubbles at moderate heat fluxes, regimes of flow where surface-tension forces and buoyancy forces respectively dominate are defined. For boiling at heat fluxes near the burnout limit, flow driven by surface-tension forces appears to play a large role in cooling the heated surface. It is shown that small amounts of surfactant added to the liquid result in dramatic changes in the boiling mechanism, and at high heat fluxes a substantial improvement in the heat transfer. Most of the experiments were conducted with the liquid at temperatures less than the saturation temperature.

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