Homer Christopher J, Jiang Xingmao, Ward Timothy L, Brinker C Jeffrey, Reid Jonathan P
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS.
Phys Chem Chem Phys. 2009 Sep 28;11(36):7780-91. doi: 10.1039/b904070f. Epub 2009 Jun 3.
The evolving composition of evaporating ethanol-water droplets (initially 32.6 or 45.3 microm radius) is probed by stimulated Raman scattering over the period 0.2 to 3 ms following droplet generation and with a surrounding nitrogen gas pressure in the range 10 to 100 kPa. The dependence of the evaporation rate on the relative humidity of the surrounding gas phase is also reported. The measured data are compared with both a quasi-steady state model and with numerical simulations of the evaporation process. Results from the numerical simulations are shown to agree closely with the measurements when the stimulated signal is assumed to arise from an outer shell with a probe depth of 2.9+/-0.4% of the droplet radius, consistent with a previous determination. Further, the time-dependent measurements are shown to be sensitive to the development of concentration gradients within evaporating droplets. This represents the first direct measurement of the spatial gradients in composition that arise during the evaporation of aerosol droplets and allows the influence of liquid phase diffusion within the condensed phase on droplet evaporation to be examined.
通过受激拉曼散射，在液滴产生后的0.2至3毫秒内，以及在10至100千帕的周围氮气压力下，对正在蒸发的乙醇 - 水滴（初始半径为32.6或45.3微米）的成分演变进行探测。还报告了蒸发速率对周围气相相对湿度的依赖性。将测量数据与准稳态模型以及蒸发过程的数值模拟进行比较。当假设受激信号来自一个探针深度为液滴半径的2.9±0.4%的外壳时，数值模拟结果与测量结果显示出密切一致，这与先前的测定结果相符。此外，随时间变化的测量结果显示对蒸发液滴内浓度梯度的发展很敏感。这是对气溶胶液滴蒸发过程中出现的成分空间梯度的首次直接测量，并能够研究凝聚相内液相扩散对液滴蒸发的影响。
