Session: 10-03-02: CFD Applications - II

Paper Number: 95717

95717 - Simulation for Optimization of a Filter Cake System 

The goal of this project is to simulate a simple filtration system using Ansys Fluent. The simulation will demonstrate the flow of water through a filter cake, providing a relationship between the velocity of the water and the pressure drop through the filter cake. Simulation is planned to take place in three steps— a microscale direct simulation, a full-scale static-geometry simulation, and a full-scale dynamic-geometry simulation. The microscale simulation will demonstrate a small section of the flow of water around the filter cake particles directly; the two full-scale simulations will be modeled with porous media to show the overall patterns of flow through the filter cake. The system is composed of pure water flowing through a filter cake of rice hull ash (RHA), a porous and highly permeable byproduct of other processes performed at the Agrilectric Power plant. To demonstrate the flow, a simple theoretical two-dimensional simulation was created using ANSYS Fluent. Calculations based on the Darcy’s Law equation were used to verify the simulation results. Other calculations such as the Reynold’s number, viscous resistance, and porosity were used to calibrate the results of the initial simulation.

Following this, a three-dimensional simulation was created to better represent a real system and understand flow patterns within the filter cake. This simulation was augmented to show the process of a filter cake forming over a period of time. In reality, the RHA cake would form by being filtered out of a slurry of water and RHA that is sent through the system; the RHA would collect and form a cake on a piece of filter cloth. As the filter cake thickness increases, the pressure drop across the filter cake will increase. To model this in Fluent, a named expression was created to control the viscous resistance of the filter cake cell zone to simulate the viscous resistance of the cake as it increases in height. The relationship between the flow rate, concentration of RHA in the slurry, and the rate of thickness increase in the filter cake was determined.

In the study, a dynamically filter cake build up were simulated.The local viscous resistence is used to represent the presence of the filter cake, and is updated at every time step based on the flow and slurry loads at every time step. User-defined functions were used to implment these calculations into FLUENT solvers. An Euler-Euler two phase flow model is used for the simulation. The flow and pressure results were compared with experimental measurement for validation, and the agreement is reasonaly well. 

Presenting Author: Ning Zhang McNeese State University

Presenting Author Biography: Professor of Mechanical Engineering<br/>McNeese State University<br/>Ph.D. Kansas State University

Authors:

Alyssa Johnson McNeese State University
Allison Lebleu McNeese State University
Ning Zhang McNeese State University