{"title":"Relative Trajectories of Contaminated, Spherical Drops in a Temperature Gradient and Gravity at Finite Stokes Numbers","authors":"Michael Rother","doi":"10.1007/s12217-024-10141-9","DOIUrl":null,"url":null,"abstract":"<div><p>This work is a theoretical investigation into the effect of finite droplet inertia on combined gravitational and thermocapillary interactions of spherical drops covered with an incompressible surfactant film. The significance of droplet inertia is indicated by the magnitude of the Stokes number <b><i>St</i></b>. Initial calculations are a continuation of previous results from <b><i>St</i></b> = 0 to finite Stokes numbers at <span>\\(\\varvec{O(1)}\\)</span> drop-to-medium viscosity and thermal conductivity ratios. Interesting outcomes, such as stable tandem motion and complex relative trajectories, are observed. At more realistic <span>\\(\\varvec{O(10)}\\)</span> ratios, the results tend to be dampened from those at lower values, although unusual behavior still occurs. Finally, interactions are determined for two physical systems, water drops in air and mercury drops in <b><i>n</i></b>-pentane. At normal gravity, two limits are usually possible. In order for the thermocapillary and gravitational contributions to be equal, the drops and their corresponding Stokes numbers must be small, while for larger drops at higher <b><i>St</i></b>, gravity is the dominant driving force. For water droplets in air with radii less than 10 <span>\\(\\varvec{\\mu }\\)</span>m, van der Waals forces control the interactions. However, drop inertia is the most important factor for droplets with radii greater than 25 <span>\\(\\varvec{\\mu }\\)</span>m. Even a small thermocapillary effect can have noticeable consequences on the relative trajectories for intermediate-sized drops. Some comments are made on the difficulty in experimentally reproducing the theoretical results, with a recommendation of centi- or milligravity conditions.</p></div>","PeriodicalId":707,"journal":{"name":"Microgravity Science and Technology","volume":"36 5","pages":""},"PeriodicalIF":1.3000,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Microgravity Science and Technology","FirstCategoryId":"5","ListUrlMain":"https://link.springer.com/article/10.1007/s12217-024-10141-9","RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENGINEERING, AEROSPACE","Score":null,"Total":0}
引用次数: 0
Abstract
This work is a theoretical investigation into the effect of finite droplet inertia on combined gravitational and thermocapillary interactions of spherical drops covered with an incompressible surfactant film. The significance of droplet inertia is indicated by the magnitude of the Stokes number St. Initial calculations are a continuation of previous results from St = 0 to finite Stokes numbers at \(\varvec{O(1)}\) drop-to-medium viscosity and thermal conductivity ratios. Interesting outcomes, such as stable tandem motion and complex relative trajectories, are observed. At more realistic \(\varvec{O(10)}\) ratios, the results tend to be dampened from those at lower values, although unusual behavior still occurs. Finally, interactions are determined for two physical systems, water drops in air and mercury drops in n-pentane. At normal gravity, two limits are usually possible. In order for the thermocapillary and gravitational contributions to be equal, the drops and their corresponding Stokes numbers must be small, while for larger drops at higher St, gravity is the dominant driving force. For water droplets in air with radii less than 10 \(\varvec{\mu }\)m, van der Waals forces control the interactions. However, drop inertia is the most important factor for droplets with radii greater than 25 \(\varvec{\mu }\)m. Even a small thermocapillary effect can have noticeable consequences on the relative trajectories for intermediate-sized drops. Some comments are made on the difficulty in experimentally reproducing the theoretical results, with a recommendation of centi- or milligravity conditions.
这项研究从理论上探讨了有限液滴惯性对覆盖着不可压缩表面活性剂薄膜的球形液滴的引力和热毛细管相互作用的影响。液滴惯性的重要性由斯托克斯数 St 的大小来表示。最初的计算延续了之前从 St = 0 到 \(\varvec{O(1)}\) 液滴与介质粘度和导热系数之比时的有限斯托克斯数的计算结果。观察到了有趣的结果,如稳定的串联运动和复杂的相对轨迹。在更现实的 \(\varvec{O(10)}\) 比值下,虽然仍会出现不寻常的行为,但结果往往会比低值下的结果有所减弱。最后,确定了两个物理系统的相互作用,即空气中的水滴和正戊烷中的汞滴。在正常重力下,通常有两个极限。为了使热毛细作用和重力作用相等,水滴及其相应的斯托克斯数必须很小,而对于较高 St 值的较大水滴,重力是主要的驱动力。对于半径小于 10 \(\varvec\{mu }\)m 的空气中的水滴,范德华力控制着相互作用。然而,对于半径大于 25 m 的水滴来说,水滴的惯性是最重要的因素。即使是很小的热毛细管效应也会对中等大小液滴的相对轨迹产生明显的影响。对于在实验中重现理论结果的困难,提出了一些意见,并建议采用厘重或毫重条件。
期刊介绍:
Microgravity Science and Technology – An International Journal for Microgravity and Space Exploration Related Research is a is a peer-reviewed scientific journal concerned with all topics, experimental as well as theoretical, related to research carried out under conditions of altered gravity.
Microgravity Science and Technology publishes papers dealing with studies performed on and prepared for platforms that provide real microgravity conditions (such as drop towers, parabolic flights, sounding rockets, reentry capsules and orbiting platforms), and on ground-based facilities aiming to simulate microgravity conditions on earth (such as levitrons, clinostats, random positioning machines, bed rest facilities, and micro-scale or neutral buoyancy facilities) or providing artificial gravity conditions (such as centrifuges).
Data from preparatory tests, hardware and instrumentation developments, lessons learnt as well as theoretical gravity-related considerations are welcome. Included science disciplines with gravity-related topics are:
− materials science
− fluid mechanics
− process engineering
− physics
− chemistry
− heat and mass transfer
− gravitational biology
− radiation biology
− exobiology and astrobiology
− human physiology