Katre Pallavi, Balusamy Saravanan, Banerjee Sayak, Sahu Kirti Chandra
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India.
Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India.
Langmuir. 2022 Apr 19;38(15):4722-4735. doi: 10.1021/acs.langmuir.2c00306. Epub 2022 Apr 4.
We experimentally investigate the evaporation of water-ethanol binary sessile droplets loaded with alumina nanoparticles on a critically inclined heated surface and compare it to the no-loading condition. In contrast to a droplet of pure fluids, several distinct and interesting phenomena observed in a binary-nanofluid droplet on a critically inclined substrate are reported for the first time. The critical angle at which a droplet begins to slide increases for ethanol-rich binary droplets up to 0.6 wt % nanoparticle loading. The critical angle for binary droplets also increases as the substrate temperature increases and as the ethanol concentration decreases for modest loading conditions. It is observed that the advancing side of a binary droplet is pinned in both the loading and no-loading scenarios, whereas the receding side is pinned in the loading case but shrinks continuously in the no-loading case. The pinning effect caused by nanoparticles results in a larger perimeter and surface area for the nanoparticle-laden droplets, enhancing the evaporation rates and significantly decreasing the lifetime of the nanoparticle-containing droplets compared to the no-loading case. Increasing the ethanol percentage in the binary droplet placed on an inclined substrate produces complex thermosolutal Marangoni convection, which becomes more affluent in the case of nanoparticles loading than the no-loading condition. The radial symmetry of the circular coffee ring structure observed on a horizontal surface is shattered in the inclined case because the droplet elongates and preferentially deposits toward the advancing side of the triple line due to the action of the body force. Despite its fundamental nature, the present study can contribute to understanding many practical applications.
我们通过实验研究了在临界倾斜加热表面上负载氧化铝纳米颗粒的水 - 乙醇二元 sessile 液滴的蒸发情况，并将其与无负载条件进行比较。与纯流体液滴不同，首次报道了在临界倾斜基底上的二元纳米流体液滴中观察到的几种独特且有趣的现象。对于富含乙醇的二元液滴，在纳米颗粒负载量高达 0.6 wt%时，液滴开始滑动的临界角会增大。在适度负载条件下，二元液滴的临界角也会随着基底温度的升高和乙醇浓度的降低而增大。可以观察到，在负载和无负载情况下，二元液滴的前进侧都被固定，而在负载情况下后退侧被固定，但在无负载情况下会持续收缩。与无负载情况相比，纳米颗粒引起的固定效应导致负载纳米颗粒的液滴具有更大的周长和表面积，提高了蒸发速率并显著缩短了含纳米颗粒液滴的寿命。增加放置在倾斜基底上的二元液滴中的乙醇百分比会产生复杂的热溶质马兰戈尼对流，在纳米颗粒负载情况下比无负载条件下更为丰富。在倾斜情况下，水平表面上观察到的圆形咖啡环结构的径向对称性被打破，因为液滴由于体力的作用而伸长并优先沉积在三相线的前进侧。尽管本研究具有基础性质，但它有助于理解许多实际应用。
