Multi-Phase Tank Filling System CFD Analysis - ANSYS Fluent Simulation

Project Overview

This computational fluid dynamics investigation examines multi-phase tank filling operations using ANSYS Fluent software, focusing on the complex interactions between three distinct phases: water, alcohol, and air. The simulation addresses critical industrial applications in chemical processing where component separation and pure substance extraction from multi-component mixtures are essential operational objectives.

Industrial Significance

Tank filling systems with multiple fluid phases represent fundamental operations in chemical industry applications, particularly in separation processes where different fluid components must be isolated based on their physical properties. Understanding the interface dynamics and phase interactions enables optimization of separation efficiency and process design.

Multi-Phase Flow Analysis

The simulation employs the Volume of Fluid (VOF) methodology to investigate the complex three-phase interactions during the filling process. Surface tension effects between phase boundaries are incorporated through applied surface stresses, providing realistic representation of interfacial phenomena that govern phase separation behavior.

System Configuration and Operational Parameters

Tank Geometry and Inlet Configuration

The computational domain consists of a cubic container with 1-meter side dimensions, providing adequate volume for comprehensive phase interaction analysis. Water injection occurs through a square valve measuring 10 cm on each side, positioned within the tank wall to facilitate controlled fluid entry at 1 m/s velocity.

Initial Fluid Distribution

The initial configuration establishes 40 cm of alcohol in the bottom portion of the container, creating a stratified system that allows investigation of density-driven phase separation and interface stability during the water injection process.

Geometric Design and Computational Grid

Three-Dimensional Model Development

The computational domain was designed using Design Modeler software, incorporating realistic tank dimensions and inlet valve geometry to simulate industrial filling operations. The cubic configuration facilitates analysis of three-dimensional flow patterns and phase distribution throughout the filling process.

Structured Mesh Implementation

Grid generation utilized ANSYS Meshing software with structured mesh topology containing approximately 421,000 computational elements. The structured approach provides enhanced accuracy for capturing regular geometric features and ensures efficient computational performance for the complex three-phase transient simulation.

CFD Simulation Configuration

Fundamental Modeling Assumptions

The simulation employs a pressure-based solver approach suitable for incompressible flow conditions with constant fluid properties. The analysis is conducted in transient mode to capture temporal evolution of phase interactions and interface dynamics. Gravitational acceleration of -9.81 m/s² along the negative y-axis drives density-stratified flow behavior and phase separation mechanisms.

Multi-Phase Flow Modeling

The Volume of Fluid homogeneous model governs the three-phase flow field equations for water, alcohol, and air phases. Sharp interface modeling ensures accurate tracking of phase boundaries throughout the filling operation. The explicit formulation provides computational efficiency while maintaining solution accuracy for the complex multi-phase system.

Surface Tension Implementation

Phase interaction modeling incorporates surface tension coefficients to accurately represent interfacial forces between different fluid pairs. The water-air interface utilizes a surface tension coefficient of 0.072 N/m, representing the strong interfacial tension typical of water-gas systems. The alcohol-water interface employs 0.043 N/m, reflecting the moderate interfacial tension between these miscible liquids. The air-alcohol interface uses 0.022 N/m, corresponding to the relatively weak interfacial forces between alcohol vapor and air.

Material Properties

Water properties are defined with density of 998.2 kg/m³, representing standard liquid water conditions. Alcohol properties utilize density of 790 kg/m³, typical of ethanol at standard conditions. Air properties employ density of 1.225 kg/m³, corresponding to standard atmospheric conditions. All thermodynamic properties are maintained constant throughout the simulation for simplified analysis.

Turbulence Modeling

The realizable k-epsilon turbulence model with standard wall functions captures turbulent flow effects during the injection and mixing processes. This approach provides accurate representation of turbulent energy dissipation and momentum transfer while maintaining computational efficiency for the multi-phase application.

Boundary Condition Specifications

The water inlet is configured as a velocity inlet with 1 m/s magnitude to provide controlled fluid injection. The tank outlet employs pressure outlet boundary conditions with zero gauge pressure to maintain atmospheric pressure communication. The cell zone condition specifies a mixture fluid type to accommodate the three-phase system throughout the computational domain.

Numerical Solution Methods

Pressure-velocity coupling utilizes the SIMPLE algorithm for iterative solution convergence in multi-phase applications. Pressure discretization employs the PRESTO scheme, optimized for complex geometries with significant density variations. Momentum equations use second-order upwind discretization for enhanced accuracy, while turbulent kinetic energy and dissipation rate equations employ first-order upwind discretization for numerical stability. Volume fraction transport utilizes the Geo-Reconstruct scheme to maintain sharp interface definition and accurate phase boundary tracking.

Results and Engineering Analysis

Phase Interaction Dynamics

The simulation results demonstrate the complex three-phase interactions as water injection displaces the existing alcohol and air phases. Velocity contours at 1 and 15 seconds reveal the temporal evolution of flow patterns and phase redistribution throughout the filling process.

Density-Driven Stratification

The analysis shows how density differences between phases drive natural stratification, with the denser water phase settling toward the bottom and displacing the lighter alcohol phase upward. This behavior demonstrates the fundamental principles governing gravity-driven phase separation in industrial applications.

Interface Tracking and Separation Potential

The VOF model successfully captures the non-mixing behavior between water and alcohol phases, maintaining distinct phase boundaries throughout the filling process. This characteristic enables potential separation operations through strategically placed drainage valves at the tank bottom, as demonstrated by the clear phase stratification results.

Engineering Applications

The simulation provides valuable insights for designing industrial separation systems, including optimal injection velocities, tank geometries, and drainage configurations. The three-phase analysis enables assessment of separation efficiency and process optimization for chemical industry applications requiring component isolation from multi-phase mixtures.

Temporal Evolution Analysis

The velocity field evolution demonstrates how injection momentum affects phase distribution and mixing patterns, providing guidance for controlling separation effectiveness through operational parameter adjustment in industrial tank filling systems.