Experimental investigation of evaporation-induced convection in water using laser based measurement techniques

Recent studies have shown that the evaporation of water can induce surface tension gradients along the water surface that ultimately lead to a surface driven flow, known as Marangoni convection. To visualize and characterize the Marangoni convection in water, this study generated evaporation driven convection in pure water with a vacuum pump to control and increase the evaporation rate of water within a rectangular cuvette that was placed within a vacuum chamber, and investigated the velocity and temperature distributions of the generated convection. The investigation was performed as the vacuum chamber pressure ranged from ∼250 Pa to ∼820 Pa. The temperature field obtained from thermocouple measurements and temperature planar laser induced fluorescence (temp-PLIF) measurements indicated that no buoyancy driven motion was generated during the investigation. Velocity vector fields captured with stereo particle image velocimetry (stereo-PIV) demonstrated a convection pattern that was strong and symmetric with the centerline of the cuvette. The strength of the convection was found to be correlated with the mean evaporation rate of water. The estimated Marangoni number exceeded the critical value typically used to characterize the onset of Marangoni convection. The convection had a similar pattern as Marangoni convection observed in volatile liquids evaporated from capillary tubes. In both cases, the convection scaled with the width of the liquid container even though the sizes of the containers differ by an order of magnitude. In addition, the size of the convection in this study was much larger than the Marangoni convection in water that was observed in previous studies.

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