One-dimensional Raman spectroscopy and shadowgraphy for the analysis of the evaporation behavior of acetone/water drops

This paper reports – for ambient conditions – experimentally determined surface regression rates of acoustically levitated acetone/water drops as a function of the mixture composition at the drop boundary. The fluid levitated as a drop was a mixture of acetone and water with vapor pressures of 24.5 kPa and 3.17 kPa, respectively, at ambient conditions. As expected the acetone evaporated faster from the acetone/water drop than water. Already small quantities of acetone in the mixture significantly increased the surface regression rate of the drop. Temporally and spatially resolved composition profiles were measured along a line through the drops using one-dimensional Raman spectroscopy. Shadowgraphs of the evaporating drops were acquired, from which the drop shrinkage was derived. Due to the good spatial (120 μm) and temporal (1 s) resolution of the one-dimensional Raman experiment the evolution of the radial composition profiles through the drop could be followed showing that the diffusion-process inside the drop plays an important role in the binary evaporation process.