Abstract The evaporation of a binary sessile ethanol-water droplet on an inclined substrate is studied experimentally just below the critical sliding angles for different substrate temperatures. A customized goniometer equipped with a CMOS camera and an infrared (IR) camera is used. The droplet is observed to remain pinned in the advancing side during the evaporation process, while the receding side contracts. The asymmetry in the advancing and receding contact angles of the droplet on inclined substrate results in complex thermo-solutal Marangoni convection that is captured through IR images. The droplet exhibits two distinct oscillatory water-rich cold regions around the advancing contact line during the early stage of evaporation, while the more volatile and lighter ethanol creates a hotter and rapidly evaporating cell near the receding side. As ethanol evaporates away, the ethanol rich cells collapse producing thermal pulsations along the incline. Subsequently, the thermal patterns become similar to that of the pure-water droplet. It is also observed that the thermo-solutal driven oscillatory convection increases with increasing substrate temperature. Despite the complexity in convection dynamics, the evaporation rate exhibits a universal behavior in the normalized time at different substrate temperatures which can be represented by piecewise linear fits at the early and late stages of evaporation.

中文翻译：

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临界倾斜加热表面上无柄乙醇-水滴的蒸发

摘要 通过实验研究了在不同基底温度下临界滑动角以下的倾斜基底上的二元固着乙醇-水滴的蒸发。使用配备有 CMOS 摄像头和红外 (IR) 摄像头的定制测角仪。观察到液滴在蒸发过程中保持固定在前进侧，而后退侧收缩。倾斜基板上液滴的前进和后退接触角的不对称性导致复杂的热溶质 Marangoni 对流，该对流通过红外图像捕获。在蒸发的早期阶段，液滴在前进的接触线周围表现出两个不同的振荡富水冷区，而更易挥发和更轻的乙醇在后退侧附近形成一个更热且蒸发速度更快的细胞。随着乙醇蒸发掉，富含乙醇的细胞坍塌，沿着斜坡产生热脉动。随后，热模式变得类似于纯水滴的热模式。还观察到热溶质驱动的振荡对流随着衬底温度的增加而增加。尽管对流动力学很复杂，但蒸发速率在不同基板温度下的归一化时间内表现出普遍行为，这可以通过蒸发早期和晚期阶段的分段线性拟合来表示。还观察到热溶质驱动的振荡对流随着衬底温度的增加而增加。尽管对流动力学很复杂，但蒸发速率在不同基板温度下的归一化时间内表现出普遍行为，这可以通过蒸发早期和晚期阶段的分段线性拟合来表示。还观察到热溶质驱动的振荡对流随着衬底温度的增加而增加。尽管对流动力学很复杂，但蒸发速率在不同基板温度下的归一化时间内表现出普遍行为，这可以通过蒸发早期和晚期阶段的分段线性拟合来表示。