Steam Methane Reforming (SMR) is the most common industrial method for Hydrogen production. In this chemical process, Methane (CH4) reacts with Steam (H2O) inside a reactor. With the help of a catalyst, they transform into Hydrogen (H2) and Carbon Monoxide (CO). This reaction is endothermic, which means it absorbs a massive amount of heat to work. Industries rely on this process for oil refining and manufacturing electronics.

In this Steam Methane Reforming CFD simulation, we perform a numerical validation study. We aim to replicate the results of a specific scientific paper by Lao et al. (2016). By using ANSYS Fluent, we validate the physics of the reactor to ensure our settings match real-world data. This tutorial demonstrates how to model complex chemical reactions using advanced CFD techniques.

CH4 + H2O → CO + 3H2

• Reference [1]: Lao, Liangfeng, et al. “CFD modeling and control of a steam methane reforming reactor.” Chemical Engineering Science148 (2016): 78-92.

SMR Simulation Setup: Mesh, UDF, and Physics in ANSYS Fluent

To begin this CFD validation study, we first prepared the geometry in ANSYS Design Modeler. We created a 2D rectangular domain with dimensions of 12.5 meters by 0.063 meters. Although the drawing is 2D, we set the solver to “axisymmetric.” This is a crucial step because it allows the software to simulate a cylindrical combustion chamber efficiently without creating a heavy 3D model. Next, we focused on the grid generation in ANSYS Meshing. A high-quality mesh is essential for capturing chemical reactions. We generated a structured grid containing exactly 64,000 cells. As shown in Figure 1, the mesh is fine and uniform, which helps in calculating the gradients of temperature and species accurately.

Figure 1- Close-up view of the structured mesh grid (64,000 cells) generated for the SMR combustion chamber.

For the physics setup in ANSYS Fluent, we selected the k-epsilon turbulence model combined with “Enhanced Wall Treatment.” This ensures the flow near the reactor walls is calculated correctly. Because the SMR reaction involves high temperatures, radiation plays a major role. Therefore, we activated the Discrete Ordinates (DO) radiation model. To simulate the chemistry, we used the Species Transport model. However, the standard Arrhenius kinetic model was not sufficient for this specific case. To solve this, we wrote and compiled a User-Defined Function (UDF) to control the volume reaction rate precisely. Finally, we enabled the Porous Media module to simulate the resistance of the catalyst bed inside the chamber.

SMR CFD Post-Processing: Thermal Analysis and Hydrogen Yield Validation

In this section, we analyze the results of the Steam Methane Reforming CFD. We examine the chemical behavior and thermal distribution to confirm the accuracy of our UDF and boundary conditions. First, we analyze the production of Carbon Monoxide (CO), which indicates the reaction progress. The Mass Fraction contour (Figure 2) reveals the reaction zone. When the Methane enters the inlet, it does not react immediately. We can observe a clear entry length where the Methane mixes with the Water Vapor. Once the mixing is sufficient, the reaction ignites, and CO is produced. The contour shows that the reaction stabilizes further down the tube. This visual evidence confirms that our UDF is correctly controlling the reaction kinetics, as the delay matches the physical expectations of mixing time.

Furthermore, the temperature distribution is critical for this endothermic reaction. The Temperature Contour (Figure 3) depicts the thermal field inside the combustion chamber. The reference paper specified a particular temperature gradient for the upper wall, which we applied using an expression. The results show a temperature range between 837 K and 1130 K. The software reports an average chamber temperature of 1122 K. This high average temperature proves that the heat transfer is effective. Moreover, it justifies our use of the Discrete Ordinates (DO) model, as ignoring radiation at these temperatures would lead to significant errors in the energy balance.

Finally, we validate our CFD analysis by comparing our quantitative data with Table 5 from the reference paper. The key performance indicator is the Mole Fraction of Hydrogen (H2) at the outlet. The reference paper reports a value of 0.4645. Our ANSYS Fluent simulation achieved a value of 0.4605. Comparing these two numbers reveals an error of only 0.86%. This exceptionally low error rate confirms that the combination of the UDF, the Porous Media model, and the structured mesh has resulted in a highly accurate and validated model.

Figure 2- Mass fraction contour of Carbon Monoxide (CO) showing the reaction ignition zone.

Figure 3 – Temperature distribution contour showing the thermal gradient (837K – 1130K) across the reactor.

Key Takeaways & FAQ

• Q: What is Steam Methane Reforming (SMR)?
  • A: SMR is a process used in industries to make Hydrogen. It mixes Methane and Steam over a catalyst to create Hydrogen and Carbon Monoxide.
• Q: Why use a User-Defined Function (UDF) in this simulation?
  • A: We use a UDF because the specific chemical reaction rate in this study does not follow the standard library models in ANSYS Fluent. The code tells the software exactly how fast the reaction should happen.
• Q: Why is the Discrete Ordinates (DO) model important here?
  • A: The reactor operates at very high temperatures (up to 1130 K). At this level, heat radiation is very strong. The DO model accurately calculates this radiation, ensuring the temperature results are correct.