Flow transitions in evaporating saline droplets: interplay between Rayleigh convection and Marangoni effects

IF 4.3 2区工程技术 Q2 ENGINEERING, CHEMICAL

Chemical Engineering Science Pub Date : 2025-10-04 DOI:10.1016/j.ces.2025.122721

Lingfeng Wang, Zhengtao Li, Zhijie Yuan, Xuehua Ruan, Wu Xiao, Xuemei Wu, Gaohong He, Xiaobin Jiang

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Abstract

Saline droplet evaporation constitutes a fundamental physicochemical phenomenon with critical applications in separation technologies, desalination processes, and crystal engineering. This investigation elucidates circulation mechanisms during saline droplet evaporation through systematic examination of various geometrical configurations and thermal conditions. A computational fluid dynamics approach validated through optical visualization and infrared thermal imaging revealed distinct circulation regimes governed by the interplay between Rayleigh convection and Marangoni effects. At ambient conditions, droplets exhibited predominantly Rayleigh-driven convection, with contact angles below 90° generating peripheral deposition patterns while angles exceeding 90° produced centralized crystal accumulation due to non-uniform evaporation flux distribution. Temperature modulation induced substantial flow pattern transitions at specific critical thresholds, with thermal Marangoni effects overriding Rayleigh convection when temperature differences exceeded 0.94 K for droplets with 120° contact angles. Circulation transitions manifested more prominently in droplets with larger contact angles, characterized by progressive transformation from Rayleigh-driven clockwise flows to thermal Marangoni-driven counterclockwise patterns. Interfacial heat transfer coefficients exhibited deterministic influence on circulation dominance, with values below 10 W/m²·K maintaining Rayleigh-dominated flow and values between 100–1000 W/m²·K establishing thermal Marangoni dominance. A comprehensive phase diagram correlating dimensionless Rayleigh and Marangoni numbers to circulation patterns was developed, providing predictive capability for flow regime transitions under varying evaporation conditions. The established quantitative relationships between thermal parameters and circulation mechanisms enable precise control of crystal deposition morphologies through interfacial thermal regulation.

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蒸发盐滴中的流动转变：瑞利对流和马兰戈尼效应之间的相互作用

盐滴蒸发是一种基本的物理化学现象，在分离技术、海水淡化工艺和晶体工程中有着重要的应用。这项研究阐明了循环机制在生理盐水液滴蒸发通过系统检查各种几何构型和热条件。通过光学可视化和红外热成像验证的计算流体动力学方法揭示了由瑞利对流和马兰戈尼效应相互作用控制的独特环流模式。在环境条件下，液滴主要表现为瑞利驱动的对流，接触角小于90°时形成外围沉积模式，接触角大于90°时由于蒸发通量分布不均匀而形成集中结晶积聚。温度调制在特定的临界阈值下诱导了大量的流型转变，当温度差异超过0.94 K时，120°接触角液滴的热马兰戈尼效应超过瑞利对流。在接触角较大的液滴中，环流转变更为明显，其特征是由瑞利驱动的顺时针流逐渐转变为马兰戈尼驱动的逆时针流。界面换热系数对循环优势表现出确定性影响，低于10 W/m2·K维持瑞利优势流动，100-1000 W/m2·K维持热马兰戈尼优势流动。开发了将无量纲瑞利数和马兰戈尼数与环流模式相关联的综合相图，为不同蒸发条件下的流态转变提供了预测能力。热参数与循环机制之间建立的定量关系使得通过界面热调节来精确控制晶体沉积形态成为可能。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Chemical Engineering Science 工程技术-工程：化工

CiteScore

7.50

自引率

8.50%

发文量

1025

审稿时长

50 days

期刊介绍： Chemical engineering enables the transformation of natural resources and energy into useful products for society. It draws on and applies natural sciences, mathematics and economics, and has developed fundamental engineering science that underpins the discipline. Chemical Engineering Science (CES) has been publishing papers on the fundamentals of chemical engineering since 1951. CES is the platform where the most significant advances in the discipline have ever since been published. Chemical Engineering Science has accompanied and sustained chemical engineering through its development into the vibrant and broad scientific discipline it is today.