Collaborative Research: ISS: Revealing interfacial stability, thermal transport and transient effects in film evaporation in microgravity

液膜表面的蒸发是许多工业过程中的关键，包括涂层、半导体晶体生长、磁存储设备的表面纹理、造纸过程中的表面光洁度、聚合物加工和燃料电池电极制造。这些应用依赖于挥发诱导的蒸发(不施加热量)。许多其他蒸发应用包括加热固体衬底，如冷却、干燥、燃料蒸发、食品加工、化学制造和制药。蒸发还可用于颗粒的自组装和多孔结构的形态控制。许多天基热管理系统也依赖于蒸发。尽管这种现象无处不在，但目前对胶片蒸发过程的理解是不完整的。膜表面的非稳定运动和膜内液体的运动极大地影响了蒸发速率和换热，特别是在瞬时或非稳定蒸发过程中。本研究的主要目的是通过在正常和微重力条件下对蒸发膜进行详细的实验和数值分析来探索这些复杂现象的基本机制。这一努力对蒸发过程的更好理解可能会在许多实际应用中产生广泛的影响。该项目将利用国际空间站进行长时间微重力测试的独特能力，通过揭示通常在陆地条件下被掩盖的物理机制，来更全面地了解蒸发薄膜的行为。具体的科学目标包括确定：(I)蒸发薄膜中长波和短波表面不稳定性之间的转变，(Ii)对流结构从蒸发开始到稳定状态的演变，以及(Iii)对热传输的相应影响。蒸发率将通过外部加热量和脉冲改变系统压力的组合进行控制。诊断技术包括超声膜厚度测量、光学成像以及热和压力测量。蒸发膜的稳定性将通过线性稳定性分析和回归量化分析来检验。后者是一种相对较新的诊断技术，它提供了诸如测量界面膜状态及其持续时间的重现的速率和捕获时间之类的度量。电影事件的这些定量特征的提取可以作为“预警系统”的触发器，以预测和控制突发的电影行为。这项调查产生的新的、详细的信息将是变革性的，因为它将导致对影响液膜行为和蒸发膜中的热传递速率的复杂机制的起源和性质的基本了解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Evaporation at the surface of a liquid film is critical to many industrial processes including coatings, semiconductor crystal growth, surface texturing in magnetic storage devices, surface finish during paper production, polymer processing, and electrode manufacturing for fuel cells. These applications depend on volatility-induced evaporation (no applied heat). Many other evaporation applications involve heating a solid substrate such as cooling, drying, fuel vaporization, food processing, chemical manufacturing and pharmaceuticals. Evaporation is also used for self-assembly of particles and morphological control of porous structures. Many space-based thermal management systems also depend on evaporation. Despite this ubiquity, the current understanding of film-evaporation processes is incomplete. The unsteady motion at the film surface and the motion of the liquid within the films drastically affect evaporation rates and heat transfer, particularly during transient, or unsteady, evaporation. The overarching goal of this research is to probe the fundamental mechanisms of these complex phenomena by conducting detailed experiments and numerical analysis of evaporating films in both normal- and microgravity conditions. The improved understanding of evaporation processes resulting from this effort may have broad impact in numerous practical applications. This project will use the unique capabilities of the ISS for long-duration microgravity testing to develop a more complete understanding of the behavior of evaporating films by revealing physical mechanisms normally masked under terrestrial conditions. Specific scientific objectives include determining: (i) the transitions between long-wave and short-wave surface instabilities in evaporating films, (ii) the evolution of the convective structures from the onset of evaporation to steady-state, and (iii) the corresponding impacts on thermal transport. Evaporation rates will be controlled using a combination of external heat addition and impulsively changing the system pressure. Diagnostic techniques include ultrasonic film thickness measurements, optical imaging, and thermal and pressure measurements. The stability of evaporating films will be examined by linear stability analysis and Recurrence Quantification Analysis. The latter is a relatively new diagnostic technique that provides metrics such as the rates and trapping-times that measure the recurrence of interfacial film states and their duration. The extraction of these quantitative signatures of film events can serve as triggers for “early warning systems” to predict and control emergent film behavior. The new, detailed information resulting from this investigation will be transformative in that it will lead to fundamental understanding of the origins and nature of the complex mechanisms that impact the liquid film behavior and the rate of heat transfer in evaporating films.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.