In many engineering projects, like cooling electronics or designing rooms, heat moves in a closed space. This happens through two ways: “Natural Convection” (moving air) and “Radiation” (heat waves). Understanding how these two work together is hard. To study this, engineers use Heat Transfer in an Enclosure CFD simulation. The most important factor here is “Emissivity,” which is how well a surface radiates heat. A black surface has high emissivity, while a shiny mirror has low emissivity.

This project is a Heat Transfer in an Enclosure fluent tutorial. We will teach you how to model this using the S2S Radiation fluent simulation method. We use ANSYS Fluent to visualize how changing the surface properties changes the airflow. By performing this Radiation in enclosure simulation, we can see how heat fills a room. For more lessons on thermal modeling, please visit our Radiation tutorials. The geometry is based on the research by Saravanan and Raja [1].

• Reference [1]: Saravanan, S., and N. Raja. “Coupled radiative and convective heat transfer in enclosures: effect of inner heater–enclosure wall emissivity contrast.” Physics of Fluids 32.9 (2020).

Figure 1: The physical setup of the 2D square enclosure with a heater at the bottom. [1].

Simulation Process: S2S Radiation and Emissivity Setup

To start this Heat Transfer in an Enclosure ANSYS fluent analysis, we built a simple 2D square box. Inside, there is a heater on the bottom floor. We filled the box with a “Structured Grid” to make the calculation accurate. The most critical part of the setup is the Surface-to-Surface (S2S) Radiation model. This model calculates how heat jumps from one wall to another through the air.

We created two different cases to compare the physics.

1. Positive Contrast: The heater is a strong radiator (Emissivity = 0.8), but the walls are shiny and reflective (Emissivity = 0.1).
2. Negative Contrast: The heater is weak (Emissivity = 0.1), but the walls are strong absorbers (Emissivity = 0.8). We want to see how these settings change the S2S Radiation results.

Post-processing: Analysis of Radiation and Convection

To truly understand the success of this Heat Transfer in an Enclosure CFD simulation, we must look at the Cause and Effect story. The cause is the Radiation. In the “Positive Contrast” case (right side of Figure 2), the heater has high emissivity (0.8). It shoots heat out powerfully into the room. Because the walls have low emissivity (0.1), they reflect this heat back into the air. This traps the energy inside. The Temperature Contour shows the result clearly: the entire enclosure is filled with warm, green-colored air. The average temperature here reaches approximately 306 K. The heat is spread out widely.

In the “Negative Contrast” case (left side of Figure 2), the story is different. The heater has low emissivity (0.1), so it struggles to release heat. The walls have high emissivity (0.8), so they quickly absorb any heat that hits them. They do not reflect it back. The result is a much cooler room. The contour is mostly blue, indicating a lower temperature of around 300 K. This proves that if you want to heat a room, you need a high-emissivity heater and reflective walls.

Figure 2: Temperature fields showing the warm Positive Contrast (306 K) and cool Negative Contrast (300 K).

The final effect is on the Airflow (Natural Convection). Heat makes air light, causing it to rise. In the Positive Case (hotter), the strong heat creates a powerful “Plume” of air rising from the center. Figure 3 shows complex, chaotic swirls because the energy is so high. In the Negative Case (cooler), the heat is weak. The air rises slowly and forms a simple “Two-Cell” circulation pattern. This S2S Radiation fluent simulation proves that simply changing the surface finish (emissivity) completely changes both the temperature and the wind inside the box.

Figure 3: Velocity streamlines showing complex plumes vs simple circulation cells.

Key Takeaways & FAQ

• Q: What is the S2S Radiation model?
  • A: S2S stands for Surface-to-Surface. It calculates how surfaces exchange heat based on their “View Factors” in this Heat Transfer in an Enclosure CFD simulation.
• Q: How does emissivity affect temperature?
  • A: High emissivity on the heater (0.8) creates a warmer room (306 K). Low emissivity on the heater (0.1) leads to a cooler room (300 K).
• Q: Does radiation change the airflow?
  • A: Yes. Higher radiation creates more heat, which creates stronger buoyancy forces. This leads to more complex airflow patterns in the Heat Transfer in an Enclosure ANSYS fluent result.