ISS: Dynamic Manipulation of Multi-Phase Flow Using Light-Responsive Surfactants for Phase-Change Applications

沸腾传热在广泛的地面应用中起着关键作用，包括在美国产生大部分电力的发电厂，建筑物的加热和冷却，海水淡化和蒸馏。沸腾传热性能与沸腾过程中气泡的去除率直接相关。然而，在大多数地面应用中，气泡的离开是由浮力自然驱动的；气泡偏离的大小和频率难以控制。一种能够主动控制气泡运动且调节范围大的简单方法是非常可取的，因为它将大大扩大可实现的沸腾换热率范围，具有提高电厂效率和降低建筑热管理能耗的潜力。该项目旨在开发一种控制气泡和液滴的新方法，通过利用表面张力可以随光改变的液体。微重力环境消除了浮力的干扰，使我们能够纯粹地观察和理解这种光驱动的流体运动。这种方法可以推广到控制多相流体的冷凝过程和应用，包括3D打印、生物医学和光学应用的芯片实验室微流体的精确控制。本研究的总体目标是利用光和光响应表面活性剂实现多相流体运动的动态控制，并将其应用于提高沸腾传热。光响应表面活性剂在光照下可以可逆地改变其分子构象，从而产生动态可调和空间可重构的表面张力，从而驱动多相流体运动（光-马兰戈尼效应）。该项目的任务包括：(i)实验测试水滴和气泡在光控制下的脱壳标准和迁移速度，（ii）开发光-马兰戈尼效应的第一个建模框架，以及最终（iii）通过控制光学“挤压”气泡来促进沸腾过程中的气泡偏离以增强热传输。微重力的使用对于实现超过地球上典型毛细长度的大长度尺度以及气泡/液滴离开的长时间尺度至关重要，这大大降低了微观和高速可视化的要求。微重力还将允许直接实验观察提出的光控运动，没有浮力和自然对流，这确保了准确的基本理解和与理论的比较。这种光调谐方法将作为一个有效而简单的动态流体和热传递操作的新平台。该平台将大大有助于开发新的研究能力和激发热传递以外的新应用，例如基于液滴的生化分析，动态图案和制造的新方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Boiling heat transfer plays a key role in a wide range of terrestrial applications, including power plants that produce the majority of electricity in the US, heating and cooling of buildings, desalination and distillation. The boiling heat transfer performance is directly related to the removal rate of bubbles generated during boiling. However, in most terrestrial applications, bubble departure is naturally driven by buoyancy; it is difficult to control the bubble departure size and frequency. A simple method that can actively control bubble motion with large tuning range is highly desirable, since it would significantly expand the range of achievable boiling heat transfer rate, with the potential to improve the efficiency of power plants and reduce energy consumption in building thermal management. This project aims to develop a new method to control bubbles and droplets, by exploiting liquids whose surface tension can be changed with light. The microgravity environment eliminates the interference of buoyancy, which allows us to purely observe and understand this light-driven fluid motion. This method can be generalized to manipulate multi-phase fluid for condensation processes and applications including precision control in 3D printing, lab-on-a-chip microfluidics for biomedical and optical applications. The overarching goal of this research is to achieve dynamic manipulation of multi-phase fluid motion using light and photo-responsive surfactants, and apply it to enhance boiling heat transfer. Photo-responsive surfactants can reversibly switch their molecular conformation when illuminated with light, resulting in a dynamically tunable and spatially reconfigurable surface tension that can drive multi-phase fluid motion (the photo-Marangoni effect). The project tasks include: (i) experimentally test the depinning criteria and migration velocity of droplets and bubbles controlled by light, (ii) develop the first modeling framework for the photo-Marangoni effect, and ultimately (iii) promote bubble departures during boiling to enhance thermal transport by optically “pinching off” bubbles with control. The use of microgravity is essential to enable large length scales exceeding the typical capillary lengths on earth, as well as long time scales for bubble/droplet departure, which greatly reduces the requirements of microscopic and high-speed visualization. Microgravity will also allow direct experimental observation of the proposed light-controlled motion without buoyancy and natural convection, which ensures accurate fundamental understanding and comparison to theory. This light-tuning method will serve as an effective yet simple new platform for dynamic fluid and heat transfer manipulation. This platform will significantly contribute to developing new research capabilities and inspiring new applications beyond heat transfer, such as novel approaches to droplet-based biochemical assays, dynamic patterning and manufacturing.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.