Purpose

The purpose of this study is to perform a detailed review on the numerical modeling of multiphase and multicomponent flows in microfluidic system using phase-field method. The phase-field method is of emerging importance in numerical computation of transport phenomena involving multiple phases and/or components. This method is not only used to model interfacial phenomena typical to multiphase flows encountered in engineering and nature but also turns out to be a promising tool in modeling the dynamics of complex fluid-fluid interfaces encountered in physiological systems such as dynamics of vesicles and red blood cells). Intrinsically, a priori unknown topological evolution of interfaces offers to be the most concerning challenge toward accurate modeling of moving boundary problems. However, the numerical difficulties can be tackled simultaneously with numerical convenience and thermodynamic rigor in the paradigm of the phase field method.

Design/methodology/approach

The phase-field method replaces the macroscopically sharp interfaces separating the fluids by a diffuse transition layer where the interfacial forces are smoothly distributed. As against the moving mesh methods (Lagrangian) for the explicit tracking of interfaces, the phase-field method implicitly captures the same through the evolution of a phase-field function (Eulerian). In contrast to the deployment of an artificially smoothing function for the interface as used in the volume of a fluid or level set method, however, the phase-field method uses mixing free energy for describing the interface. This needs the consideration of an additional equation for an order parameter. The dynamic evolution of the system (equation for order parameter) can be described by Allen–Cahn or Cahn–Hilliard formulation, which couples with the Navier–Stokes equation with the aid of a forcing function that depends on the chemical potential and the gradient of the order parameter.

Findings

In this review, first, the authors discuss the broad motivation and the fundamental theoretical foundation associated with phase-field modeling from the perspective of computational microfluidics. They subsequently pinpoint the outstanding numerical challenges, including estimations of the model-free parameters. They outline some numerical examples, including electrohydrodynamic flows, to demonstrate the efficacy of the method. Finally, they pinpoint various emerging issues and futuristic perspectives connecting the phase-field method and computational microfluidics.

Originality/value

This paper gives unique perspectives to future directions of research on this topic.

中文翻译：

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微流体系统中多组分和多相流的相场建模：综述

目的

本研究的目的是使用相场法对微流体系统中多相和多组分流动的数值建模进行详细审查。相场方法在涉及多相和/或分量的输运现象的数值计算中具有新兴的重要性。这种方法不仅用于模拟工程和自然中遇到的多相流典型的界面现象，而且被证明是模拟生理系统中遇到的复杂流体-流体界面的动力学的有前途的工具，例如囊泡和红血的动力学细胞）。本质上，先验界面的未知拓扑演化是移动边界问题精确建模的最令人关注的挑战。然而，在相场方法的范式中，数值困难可以通过数值方便和热力学严谨性同时解决。

设计/方法/方法

相场法用扩散过渡层代替了宏观上分离流体的尖锐界面，其中界面力平滑分布。与用于显式跟踪界面的移动网格方法（拉格朗日）相比，相场方法通过相场函数（欧拉）的演化隐式地捕捉到相同的情况。然而，与在流体体积或水平集方法中使用的界面人为平滑函数的部署相反，相场方法使用混合自由能来描述界面。这需要考虑阶参数的附加方程。系统的动态演化（阶参数方程）可以用 Allen – Cahn 或 Cahn –来描述Hilliard 公式，在依赖于化学势和顺序参数梯度的强迫函数的帮助下与 Navier-Stokes 方程耦合。

发现

在这篇综述中，首先，作者从计算微流体的角度讨论了与相场建模相关的广泛动机和基本理论基础。随后，他们指出了突出的数值挑战，包括无模型参数的估计。他们概述了一些数值示例，包括电流体动力学流，以证明该方法的有效性。最后，他们指出了连接相场方法和计算微流体的各种新兴问题和未来观点。

原创性/价值

本文为该主题的未来研究方向提供了独特的视角。