Kabi Prasenjit, Bahal Simrandeep, Tiwari Manish K, Barbosa Dos Anjos Emerson, Naveira-Cotta Carolina Palma, Cotta Renato Machado
Nanoengineered Systems Laboratory, Mechanical Engineering, University College London, London WC1E 7JE, UK.
UCL Hawkes Institute, University College London, London W1W 7TS, UK.
Philos Trans A Math Phys Eng Sci. 2025 Jul 17;383(2301):20240363. doi: 10.1098/rsta.2024.0363.
The physics and modelling of cooling and freezing of droplets in contact with a colder substrate are of interest in various engineering applications. This work provides experimental results of this process employing infrared thermography for temperature measurements at the droplet's surface. Also, a high-speed camera is employed to observe the recalescence period and measure the freezing front movement and the droplet shape change. Three substrates are prepared with distinct wettability ranges, i.e. one hydrophilic and two hydrophobic surfaces. From the experimental observation of a solidification front parallel to the substrate plane, a mixed lumped-differential model of the heat transfer process based on the Coupled Integral Equations Approach is proposed, reformulating the two-dimensional partial differential formulation in cylindrical coordinates into a one-dimensional transient energy equation for the droplet external surface temperature. Direct comparisons of the experimental and theoretical results for the supercooling period show excellent agreement for the droplet surface temperatures at different heights and for different values of the substrate-droplet contact angle. It is also shown that the classical partial lumped system analysis does not provide adequate predictions in the present problem. Finally, the dynamics of the recalescence and freezing stages are experimentally evaluated and physically interpreted.This article is part of the theme issue 'Heat and mass transfer in frost and ice'.
与较冷基底接触的液滴冷却和冻结的物理过程及建模在各种工程应用中都备受关注。本研究通过红外热成像技术对液滴表面温度进行测量，给出了该过程的实验结果。此外，还使用高速摄像机观察再辉光期，测量凝固前沿的移动以及液滴形状的变化。制备了三种具有不同润湿性范围的基底，即一个亲水表面和两个疏水表面。基于凝固前沿与基底平面平行的实验观察，提出了一种基于耦合积分方程法的传热过程混合集总 - 微分模型，将圆柱坐标系下的二维偏微分方程转化为液滴外表面温度的一维瞬态能量方程。过冷期实验结果与理论结果的直接对比表明，在不同高度以及不同基底 - 液滴接触角的情况下，液滴表面温度的实验值与理论值吻合良好。研究还表明，经典的部分集总系统分析在当前问题中无法给出充分的预测结果。最后，对再辉光和冻结阶段的动力学进行了实验评估和物理解释。本文是主题专辑“霜与冰中的传热传质”的一部分。
