EAGER: Experimental Determination of Non-Evaporating Film Thickness in Pool Boiling

cbet - 1445946marooboil用于家庭和工业应用，从住宅制冷系统到发电系统，如沸水反应堆。例如，在美国，大约90%的发电是通过使用蒸汽轮机，其中很大一部分系统使用锅炉产生蒸汽。由于其广泛的适用性，沸腾已经被研究了50多年，以了解气泡动力学和增强传热；然而，对气泡生长现象的完整认识仍然缺乏。其中一个关键的缺失部分是纳米尺度的不蒸发液体膜（也被称为“吸附”膜），它被广泛地理论认为存在于气泡的底部。这种薄膜在气泡动力学中是至关重要的，因为它可以承受降低/负的液体压力，导致液体流向表面蒸发和气泡生长。由于非蒸发膜在湍流沸腾过程中具有纳米级厚度和流体性质的复杂性，尚未在池沸实验中直接测量；提出的研究旨在克服这一缺点。本研究的目的是通过使用一种新的跨学科方法：在水的池沸腾实验中应用两种独立的自由空间光学技术，光谱反射法和迈克尔逊干涉法，对池沸腾过程中纳米尺度非蒸发膜厚度进行原位测量。这些高分辨率技术将能够测量非蒸发膜厚度及其在低热通量隔离气泡状态下气泡生命周期中的变化。研究了热通量和表面温度的增加对膜厚的影响。与目前的数值模拟相比，非蒸发膜厚度的实验测定将有助于准确地表示微层（膜存在的区域）的蒸发特性及其对气泡生长的贡献，而目前的数值模拟将膜视为具有恒定厚度的边界条件。这项工作也可以作为通过新的表面改性和其他旨在改变非蒸发膜和接触线区域的技术来增强池沸腾传热的基础。拟议的研究将使新的课程材料和实验室演示给学生提供跨学科可视化技术的第一手经验。本科生也将积极参与拟进行的研究。

CBET-1445946MarooBoiling is used in domestic and industrial applications, ranging from residential refrigeration systems to power generation systems such as boiling water reactors. For example, about 90% of all electricity generation in the United States is by the use of steam turbines, where a large percentage of systems generate the steam using boilers. Due to its wide applicability, boiling has been researched for over five decades to understand bubble dynamics and attain enhancements in heat transfer; however, a complete knowledge of the bubble growth phenomenon is still lacking. One of the key missing pieces is the nanoscale non-evaporating liquid film (also known as the "adsorbed" film) widely theorized to exist at the base of a bubble. This film is of critical importance in bubble dynamics as it can sustain reduced/negative liquid pressure causing liquid to flow to the surface for evaporation and bubble growth. The non-evaporating film has not yet been directly measured in pool boiling experiments due to complexities associated with its nanoscale thickness and fluidic nature in the turbulent boiling process; the proposed research aims to overcome this shortcoming.The objective of the proposed research is to perform in-situ measurements of the nanoscale non-evaporating film thickness in pool boiling through the use of a novel interdisciplinary approach: application of two independent free-space optical techniques, spectral reflectometry and Michelson-interferometry, in pool boiling experiments of water. These high resolution techniques will enable measurement of the non-evaporating film thickness and its variation during a bubble's life-cycle in the isolated bubble regime at low heat fluxes. The effect of increasing heat flux and surface temperature on the film thickness will also be investigated. The experimental determination of the non-evaporating film thickness will facilitate accurate representation of the evaporation characteristics of the microlayer (region where the film is present) and its contribution to bubble growth, compared to current numerical simulations where the film is treated as a boundary condition with an assumed constant thickness. This work can also act as a basis for enhancing pool boiling heat transfer via novel surface modifications and other techniques aimed at altering the non-evaporating film and contact line region. The proposed research will enable new course materials and lab demonstrations to give students first-hand experience in interdisciplinary visualization techniques. Undergraduate students will also be actively engaged in the proposed research.