平面上液滴蒸发诱发耦合Marangoni对流失稳机制及耗散结构特征

Normal temperature gradient and tangential temperature gradient are spontaneously coupled in evaporating sessile droplet on a flat plate. The coupled Marangoni convection is thus occurred in the sessile droplet and its instability mechanism and characteristics of dissipative structure are not yet known up to date. In this proposal the possible instability models of coupled Marangoni convection and its critical conditions for the incipience of them will be determined firstly by linear stability analysis. The influences of Ma, Re, Nu, E, Pr and contact angle on them will be investigated and the stability of the coupled Marangoni will be understood clearly. Through analyzing the dynamic relationship between fluid flow, heat transfer and temperature perturbation and velocity perturbation, the instability mechanism of coupled Marangoni will be discovered clearly. Then, the energy contributions of Marangoni effect, the evaporating cooling effect, heat convection, heat diffusion and viscous dissipation on the instability will be calculated respectively by energy budget analysis. Their deeply relationship between the energy contributions and the instability models will be explained and then the physical mechanism of coupled Marangoni instability will be comprehended. Finally, by combining experiments and three-dimensional simulations, the evolution law and three-dimensional characteristics of fluid flow and heat transfer of the dissipative structure will be investigated. By comparing with BM convection instability and thermocapillary convection instability, the fundamental discrepancy between them will be understood. This study has important values not only for deeply understanding the instability of coupled Marangoni convection in evaporating sessile droplet on flat plate, but also for improving the quality of ink-jet printing of function materials and improving the DNA mapping technology and etc.

平面上液滴蒸发导致液滴内自发形成耦合的法向温度梯度和切向温度梯度，由此产生耦合Marangoni对流，其失稳机制和耗散结构特征尚不清楚。项目拟通过线性稳定性分析确定耦合对流可能的失稳模式及临界条件，分析Ma数、Re数、Nu数、蒸发数E、Pr数及接触角对它们的影响，切实了解其稳定性；分析流动和传热过程与温度扰动和速度扰动的动力学关系，阐明耦合对流的失稳机制；通过能量收支分析计算Marangoni效应、蒸发冷却、热对流、热扩散、粘性耗散对耦合对流不稳定性的能量贡献，分析它们与失稳模式的深层次关系，深入理解耦合对流失稳的物理机理；三维数值模拟结合实验观测认识耗散结构的演变规律和细微特征，与BM对流失稳和热毛细对流失稳比较，认识耦合对流失稳与它们的根本区别。研究对理解平面上液滴蒸发诱发耦合Marangoni对流不稳定性、提高功能材料喷墨打印质量、改善DNA芯片制作技术具有重要的学术价值和指导意义。

平面上液滴蒸发是自然界和生产生活中普遍存在的物理现象，由于液滴为弯曲自由面，液滴内同时存在法向温度梯度和切向温度梯度，由此导致的耦合Marangoni对流，其失稳机制和耗散结构特征不同于平液层情况，项目以此为研究目标，主要研究了：（1）液滴蒸发诱发耦合Marangoni对流的不稳定性。实验和数值模拟发现了蒸发液滴内圆弧形Bénard-Marangoni对流涡胞、纵向卷胞、热流体波等失稳现象，确定了产生这些耗散结构的临界Ma数，分析了液滴润湿半径、接触角、挥发性、液滴形态等对它们的影响。（2）液滴蒸发诱发耦合Marangoni对流的失稳机制。通过三维数值模拟蒸发液滴内流场和温度场，研究了液滴内流体流动和传热特征，结合实验结果和理论分析，揭示了它们与平液层内Marangoni对流失稳现象的根本区别，阐明了液滴内产生圆弧形BM对流涡胞、纵向卷胞、热流体波的物理机制。（3）液滴蒸发诱发耦合Marangoni对流耗散结构的特征。实验观察观察了BM对流涡胞、纵向卷胞、热流体波等失稳现象随蒸发过程的演化过程，测量了它们的波长、波数、频率、传播方向等波动特征，结合数值模拟，阐明了平面上液滴蒸发诱发耦合Marangoni对流耗散结构的特征。研究对认识蒸发液滴内耦合Marangoni对流失稳机理和耗散结构特征具有十分重要的学术价值，对喷墨打印、DNA芯片制作、喷淋冷却等工程应用具有重要的指导意义。已以第一作者或通讯作者发表期刊论文共18篇，其中SCI期刊论文14篇（含自然指数期刊论文1篇）、EI论文3篇、中文核心期刊论文1篇（含封面论文1篇）；另发表国际学术会议论文6篇（含最佳展板论文1篇）、国内学术会议论文7篇（含优秀青年论文1篇），培养博士后1名（在站），培养博士研究生6名（毕业2名）和硕士研究生11名（毕业8名），授权发明专利1项。项目超额完成了申请书所提研究目标。