本文以载人航天工程中的空间应用两相系统和空间在轨流体管理，以及我国深空探测的需求为背景，旨在解决空间蒸发相变与热质传输过程强化实验中的关键科学问题，同时探索新的工程技术应用。本文以具有相变气液界面的液层和液滴为主要研究对象，通过实验和理论分析相结合的方式，深入探究了蒸发对流和纳米流体强化传热的机理及相关问题。在液层蒸发方面，通过地面实验系统，研究了热毛细对流的流动规律和蒸发相变效应。在液滴蒸发方面，开展了大尺度单元和双元液滴的地面蒸发实验，研究了组分物性、浓度等因素对蒸发过程中形貌演化和蒸发特性的影响。最后，本文利用纳米流体强化传热实验系统，探究了纳米流体的传热特性，为深化相关领域的理论研究和应用提供了一定的科学支持。
在液层研究方面，通过设计和搭建液层热毛细对流实验系统，深入研究了液层的蒸发对流现象及其转捩机制。实验发现，在0.65cSt硅油和HFE7200液层的蒸发过程中，会出现三种典型的流型：振荡多涡胞流型（OMC）、热液波（HTWs）流型和行波流型。通过对液层转捩的临界条件进行分析，我们得到不同流型转捩的临界Ma数和Bo数，并以Ma vs. Bo为坐标总结了所有实验的结果，绘制了流型转捩图。此外，本文还通过时空演化的方法对各流型的特征进行分析，发现OMC流型表现为从液池冷端向热端传播的两列交叉的行波。两列行波的波源点位于液池冷端两侧，以相同的传播角从点源发出，形成了对称传播的网状对流图案。热液波流型表现为由液池中心处的线源出发，分别沿反方向以一定角度向两侧传播的行波。两列行波的传播相互独立，互不干扰。行波表现为液池冷端处发出的一列行波。此时液池内的液体已经不足以维持液层的形状，而是类似于液膜，因此只在冷端处还存有波。最后，本研究还对蒸发效应对液层对流不稳定性的影响展开了研究，结果表明蒸发只在热液波的产生的阶段有较为重要的影响。
在液滴研究方面，本文设计并搭建了附壁液滴蒸发实验系统，从液滴形貌演化规律和蒸发特性方面对单元和双元液滴蒸发实验进行了分析。在形貌演化方面，实验发现不同实验工质（HFE7100、乙醇和异丙醇）的单元液滴蒸发过程都经历了恒定接触线阶段和混合阶段，但蒸发速率和形态变化存在差异。挥发性最强的HFE7100在极短时间内脱钉，而挥发性较弱的乙醇和异丙醇则在较长时间内仍保持着钉扎状态。对于物性相似的乙醇和异丙醇，其液滴蒸发过程的形貌演化规律相同。对于双元液滴，其形貌演化特性取决于二元混合物的初始组成和单元组分的浓度。对于组分挥发性差异较大的HFE7100-乙醇/异丙醇，其形貌演化经历两个明显的阶段，即初始的CCR阶段和后面的混合阶段。第一阶段表现为急速的下降趋势，下降的快慢并不随组分浓度的变化而改变；第二阶段则表现为相对较为缓慢的下降，下降的快慢同样也不受组分浓度的影响。对于组分差异较小的异丙醇-乙醇，其蒸发过程中的形貌演化表现出高度的一致性，可视为纯滴蒸发。在蒸发特性方面，单元液滴的蒸发速率在蒸发过程中保持不变，不受蒸发模式的影响。对于双元液滴，组分挥发性差异较大的二元液滴（HFE7100-乙醇/异丙醇），其蒸发过程中的体积变化呈现出了三个不同的阶段。第一阶段表现为液滴体积快速下降，蒸发速率恒定；第二阶段为过渡阶段，液滴蒸发速率逐渐下降；第三阶段液滴体积恢复线性下降，蒸发速率保持不变。对于挥发性差异较小的水-乙醇二元液滴，蒸发过程类似于第二阶段，只有在乙醇浓度足够高时，液滴中乙醇的蒸发速率远高于水，这时蒸发过程由乙醇主导，液滴的蒸发表现出类似于单元液滴的蒸发特征，液滴体积随时间呈线性变化。对于挥发性相近的异丙醇-乙醇二元液滴，无论组分浓度如何改变，其体积变化趋势都表现出高度的一致性，其蒸发特性与纯液滴蒸发类似。
在纳米流体强化换热研究方面，我们利用地面测试装置对纳米流体的稳定性和热物性进行了分析。实验结果表明，我们可以通过选择合适的组分浓度和搅拌方式制备稳定的纳米流体。此外，在热物性方面，我们分析了纳米流体热导率的影响因素，并基于实验数据建立了较为适用的热导率物理模型。在空间实验方面，我们发现在微重力条件下，液滴呈现出完全的球冠状形态，而在施加电场的情况下，则呈现出清晰的锥形形态。相比之下，在重力条件下，液滴的形态主要受重力影响，呈现出椭球形态。此外，我们也发现，在没有电场的微重力条件下，HFE-7100液滴的平均蒸发速率主要由蒸气扩散效应控制。值得注意的是，电场对于在常重力条件下的HFE-7100液滴平均蒸发速率并没有显著的影响。然而，在微重力条件下，有电场的平均蒸发速率明显高于无电场的平均蒸发速率，这表明电场对于液滴在微重力和重力条件下的蒸发速率产生了不同的影响。

This study focuses on the space application of two-phase systems and fluid management in manned space engineering, as well as the demand for deep space exploration in China. The objective is to address the key scientific concerns related to intensified evaporation phase change and heat transfer mechanisms, while simultaneously exploring novel engineering implementations. The main research objects of this study are liquid layers and droplets with phase change gas-liquid interfaces. A combined approach of experimental and theoretical analysis was adopted to study the characteristics of evaporation convection and nanofluid-enhanced heat transfer. Regarding the evaporation of liquid layers, the flow characteristics of thermal capillary convection and phase change effects were investigated through a ground experimental system. As for the evaporation of liquid droplets, large-scale single-component and binary droplet evaporation experiments were conducted on the ground to study the effects of factors such as component properties and concentration on the morphology evolution and evaporation characteristics during the process. Finally, the heat transfer characteristics of nanofluids were explored using a nanofluid-enhanced heat transfer experimental system, providing scientific support for the theoretical research and applications in related fields.
In the study of liquid layers, a thermal capillary convection experimental system was designed and constructed. The experiments revealed that during the evaporation process of 0.65cSt silicone oil and HFE7200 liquid layers, three typical flow patterns were observed: oscillatory multi-cellular convection (OMC), thermal liquid waves (HTWs), and traveling waves. By varying the horizontal temperature difference (Ma number), the critical Bo numbers for different flow patterns were obtained. All experimental results were summarized in a Ma vs. Bo coordinate system, and a flow pattern transition diagram was plotted. The critical conditions for the transition of liquid layer flow were analyzed. In addition, the characteristics of each flow pattern were analyzed using spatiotemporal evolution methods. It was found that the OMC pattern formed from the cold end of the liquid pool and gradually extended to the entire pool. Two crossing waves propagating towards the hot wall were formed, with wave source points located on both sides of the cold wall of the pool, emitting from the same propagation angle as a point source, forming a symmetric spreading mesh-like convection pattern. The wave pattern of the HTWs was characterized by a line source originating from the center of the liquid pool, propagating in opposite directions at a certain angle on the direction perpendicular to the temperature gradient, and in both directions from the cold end to the hot end. The propagation of the two wave columns was independent and did not interfere with each other. As the liquid layer continued to evaporate, the liquid in the pool was no longer sufficient to maintain the shape of the layer, and instead resembled a liquid film. Finally, the impact of the evaporation effect on the convective instability of the liquid layer was studied. The results showed that evaporation only had a significant impact during the generation phase of the HTWs.
In the field of droplet research, this paper analyzes the evaporation characteristics of single-component and binary-component droplets from the perspectives of droplet morphology evolution and evaporation behavior by a droplet evaporation experimental system. In terms of morphology evolution, for single-component droplets, the experiment found that the evaporation process of three experimental fluids (HFE7100, ethanol, and isopropanol) all undergoes a constant contact line (CCL) stage and a mixed stage, but with different evaporation rates and shape changes. The most volatile HFE7100 quickly detaches in a very short time, while the less volatile ethanol and isopropanol remain pinned for a longer time. In experimental fluids with similar physical properties, the flow mechanism of the droplet evaporation process is the same. For binary-component droplets, the morphology evolution characteristics during the evaporation process depend on the initial composition of the binary mixture and the concentration of the component. For binary droplets with a large difference in component volatility, the evaporation process undergoes two distinct stages, the initial CCL stage and the later mixed stage. The first stage shows a rapid downward trend, which does not change with the variation of component concentration; the second stage shows a relatively slow decline, which is also unaffected by the component concentration. For isopropanol and ethanol with small differences in composition, the evaporation process of their binary droplets exhibits a high degree of consistency and can be regarded as pure droplet evaporation. In terms of evaporation characteristics, the evaporation rate of single-component droplets remains unchanged during the evaporation process and is not affected by the evaporation mode. For binary droplets with a large difference in component volatility (HFE7100-ethanol/isopropanol), the volume change during the evaporation process exhibits three different stages. The first stage shows a rapid decrease in droplet volume with a constant evaporation rate; the second stage is a transitional stage, during which the droplet evaporation rate gradually decreases; the third stage shows a linear decrease in droplet volume with a constant evaporation rate. For binary droplets with small differences in volatility, such as isopropanol-ethanol, the volume change trend remains highly consistent regardless of the variation of component concentration, and their evaporation characteristics are similar to those of pure droplets.
In the field of nanofluid-enhanced heat transfer, an analysis of the stability and thermal properties of nanofluids was conducted using a ground-based experimental setup. The experiments identified suitable component concentrations and mixing methods for producing stable nanofluids. In terms of thermal properties, the factors affecting the thermal conductivity of nanofluids were analyzed through experiments, and a mathematical model based on the experimental data was developed to obtain a more applicable physical model of thermal conductivity. In space experiments conducted under microgravity conditions, droplets exhibited a completely spherical shape, while under an electric field, they displayed a clear conical shape. In gravity conditions, droplet morphology was mainly determined by gravity and appeared as an ellipsoid. Under microgravity conditions without an electric field, the average evaporation rate of the HFE-7100 pinned droplets appeared to be mainly controlled by vapor diffusion effects. Furthermore, the average evaporation rate under gravity conditions with an electric field was lower than that without an electric field, while the average evaporation rate under microgravity conditions with an electric field was higher than that without an electric field. This indicates that under microgravity and gravity conditions, the effect of the electric field on the evaporation rate of HFE-7100 droplets is opposite.