Decomposition of MgO with Argon Gas for Magnesium Particle Production, ANSYS Fluent Training

Introduction

Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic, as heat is required to break chemical bonds in the compound undergoing decomposition. According to the following equation, the decomposition reaction of magnesium oxide is endothermic, and this process is done by preheating through argon gas.

MgO(s)→Mg(s)+O2(g)

This project involves a Computational Fluid Dynamics (CFD) simulation of a magnesium-oxygen (Mg-O) heat reaction using ANSYS Fluent. The study aims to investigate the complex interactions between fluid flow, heat transfer, and chemical reactions in a specialized reactor geometry. Understanding these processes is crucial for optimizing the design and operation of Mg-O-based energy systems, which have potential applications in clean energy production and storage.

The simulation was conducted using ANSYS Fluent, a powerful CFD software package. The geometry was designed in ANSYS Design Modeler and meshed using ANSYS Meshing, resulting in a structured grid with 53,760 elements. This level of mesh refinement ensures a good balance between computational accuracy and efficiency.

Methodology

A steady-state, pressure-based solver was employed with the SST k-omega turbulence model.

The Species Transport model with Eddy-Dissipation Turbulence-Chemistry Interaction was used for reaction modeling.

The Discrete Phase Model (DPM) was activated to simulate particle behavior, with droplet-type particles evaporating from MgO-particle to MgO-fluid.

Boundary conditions included Argon gas and MgO particle injection from the right inlet and Argon gas from the left inlet boundary.

Conclusion

The CFD simulation of the Mg-O heat reaction provides valuable insights into the complex processes occurring within the reactor. Key findings include:

1. Static Pressure: The pressure distribution (-1.893 to 2.994 Pa) shows higher pressures near walls and lower in the central region, promoting reactant mixing.
2. Temperature: The range of 300-700 K, with highest temperatures in the lower chamber and outlet, indicates the primary reaction zone.
3. Velocity: Magnitudes range from 0 to 2.199 m/s, with complex flow patterns and recirculation zones enhancing mixing and reaction rates.
4. Species Distribution:
   • Mg mass fraction (0-0.06) is highest in the lower chamber, correlating with high-temperature regions.
   • MgO-f mass fraction (0-0.1) peaks in the central chamber, showing product formation and transport.
   • O2 mass fraction (0-0.039) is inversely correlated with Mg concentration, confirming reaction progress.

These results demonstrate the interplay between fluid dynamics, heat transfer, and chemical reactions. The reaction is most intense in the lower chamber, with significant recirculation enhancing mixing. The formation and distribution of MgO-f are clearly observed.