[Paper Review] Computational modelling of gas-liquid-solid multiphase free surface flow with and without evaporation

Huihuang Xia, Marc Kamlah|arXiv (Cornell University)|Jul 18, 2023

Fluid Dynamics and Heat TransferEngineering3 citations

TL;DR

This paper presents an improved resolved CFD-DEM framework for simulating gas-liquid-solid multiphase free surface flows with and without evaporation, incorporating a refined capillary force model for partially floating particles. The model accurately predicts fluid-solid interactions and particle trajectories, validated through benchmark cases and demonstrated in evaporation-driven particle transport and accumulation scenarios.

ABSTRACT

Gas-liquid-solid multiphase systems are ubiquitous in engineering applications, e.g. inkjet printing, spray drying and coating. Developing a numerical framework for modelling these multiphase systems is of great significance. An improved, resolved CFD-DEM framework is developed to model the multiphase free surface flow with and without evaporation. An improved capillary force model is developed to compute the capillary interactions for partially floating particles at a free surface. Two well-known benchmark cases, namely drag coefficient calculation and the single sphere settling, are conducted to validate the resolved CFD-DEM model. It turns out that the resolved CFD-DEM model developed in this paper can accurately calculate the fluid-solid interactions and predict the trajectory of solid particles interacting with the liquid phase. Numerical demonstrations, namely two particles moving along a free surface when the liquid phase evaporates, and particle transport and accumulations inside an evaporating sessile droplet show the performance of the resolved model.

Motivation & Objective

• To develop a computational framework for simulating complex gas-liquid-solid multiphase free surface flows in engineering applications such as inkjet printing and spray drying.
• To address the challenge of accurately modeling capillary interactions between partially floating solid particles and a free liquid surface.
• To extend the resolved CFD-DEM approach to include evaporation effects in multiphase systems with free surfaces.
• To validate the model against established benchmarks and demonstrate its predictive capability in realistic flow scenarios involving particle transport and accumulation.

Proposed method

• An improved capillary force model is developed to compute interfacial forces acting on partially floating particles at a gas-liquid free surface.
• The resolved CFD-DEM framework couples computational fluid dynamics (CFD) with the discrete element method (DEM) to resolve fluid-particle and particle-particle interactions at the resolved scale.
• The volume of fluid (VOF) method is employed to track the free surface of the liquid phase in multiphase flows.
• Evaporation is modeled as a surface mass transfer process at the liquid-gas interface, coupled with the VOF framework.
• The model integrates fluid dynamics, particle mechanics, and interfacial forces into a monolithic solver for transient simulations.
• Benchmark cases such as drag coefficient calculation and single sphere settling are used to validate the fluid-solid interaction accuracy.

Experimental results

Research questions

• RQ1 How accurately can the resolved CFD-DEM framework predict fluid-solid interactions in free surface flows without evaporation?
• RQ2 What is the impact of the improved capillary force model on the dynamics of partially floating particles at a free surface?
• RQ3 How does the model simulate particle transport and accumulation during the evaporation of a sessile droplet?
• RQ4 Can the framework capture complex multiphase flow behaviors such as liquid bridge formation and particle migration under evaporation?
• RQ5 How well does the model reproduce established benchmark results for drag and settling in multiphase systems?

Key findings

• The resolved CFD-DEM model accurately predicts the drag coefficient and settling trajectory of a single sphere in a quiescent fluid, validating its fluid dynamics component.
• The improved capillary force model successfully captures the equilibrium position and force balance of partially floating particles at the free surface.
• In simulations of two particles moving along a free surface during evaporation, the model reproduces particle migration toward the contact line due to capillary forces.
• The model correctly simulates particle accumulation at the edge of an evaporating sessile droplet, driven by Marangoni and capillary flows.
• The framework demonstrates robustness and accuracy in simulating complex multiphase interactions involving evaporation, free surface deformation, and particle transport.