Ventilated Brick Wall Using DPM CFD Simulation, ANSYS Fluent Training

A ventilated brick wall, as explored by Buratti et al. (2018) [1], is a building envelope design incorporating an air gap between the external brick layer and the inner insulation. This cavity facilitates natural or mechanically-driven airflow, enhancing thermal performance by reducing heat transfer during both heating and cooling seasons. The external brick layer, exposed to solar radiation, heats the air within the cavity. This warmed air then rises and vents out through openings at the top, drawing cooler air in from the bottom, creating a continuous airflow. This process minimizes heat transfer to the inner wall, improving insulation effectiveness and reducing energy consumption for climate control. The study by Buratti et al. specifically focuses on optimizing the size and placement of these ventilation openings using Computational Fluid Dynamics (CFD) to maximize airflow and thermal efficiency while maintaining structural integrity, particularly important when the external brick layer is solely supported by a steel anchorage system. So in the current study, we benefit from the reference papers called “Development and optimization of a new ventilated brick wall: CFD analysis and experimental validation”[1] and also “The effects of ventilation and floor heating systems on the dispersion and deposition of fine particles in an enclosed environment” [2].

• Reference [1]: Buratti, Cinzia, et al. “Development and optimization of a new ventilated brick wall: CFD analysis and experimental validation.” Energy and Buildings168 (2018): 284-297.
• Reference [2]: Zhou, Yu, et al. “The effects of ventilation and floor heating systems on the dispersion and deposition of fine particles in an enclosed environment.” Building and Environment125 (2017): 192-205.

Figure 1: Prototype of constructed ventilated brick wall in the laboratory [1]

Simulation Process

The ventilated brick wall inside the room is designed primarily. It then discretized by 753048 tetrahedral cells using ANSYS Meshing. The current multiphase model consist of air flow and dust particles are solved considering Eulerian-Lagrangian approach. The dust dispersed phase which is tracked by Lagrangian approach, is modeled using Two-way Discrete Phase Model (DPM). Due to variety of dust diameters, rosin-rammler diameter distribution model is employed. Given their small size, the Thermophoretic and Two-way turbulence coupling may play an effective role. However, just to assure their disruptive impact on walls, the Erosion/Accretion sub model is also activated, despite it is not our main target. Last but not the least, the sun radiation is taken into the account by Discrete Ordinates (DO) radiation model.

Post-processing

The particle residence time within the dust separator, as visualized by the particle tracks, demonstrates the effectiveness of the design in trapping dust particles. Along the particle tracks, the color variation shows how long each particle stays in the separator. Warmer colors (red and orange) show longer residence times. The fact that these warmer colors are mostly found in the lower part of the separator supports what was meant to happen: once dust particles are introduced, they tend to stay in the designated collection zone at the bottom. This longer stay time lets gravity help the separation process even more, making sure that dust particles are effectively removed from the airflow. The different stay times also point to a complicated flow pattern inside the separator, which is affected by things like the speed of the particles coming in, their size, and the shape of the device itself.

Figure 2: Dust particles residence time inside the room

The velocity magnitude contours and streamlines provide further insight into the flow dynamics that facilitate dust separation. The fastest speeds (shown by red and orange areas) can be seen near the entrance and along the top of the separator, which shows the main flow path. The speed of the airflow slows down a lot in the lower part, where the dust particles gather, as it moves through the internal structure. This slowing down is important for particle trapping because it lowers the upward drag forces that could move the settled dust again. The streamlines make the flow pattern very clear. They show how the design directs the airflow downhill, which helps the particles settle and reduces re-entrainment. Additionally, the longer particle residence times and controlled flow behavior help the dust divider remove particulate matter from the airstream more effectively.

Figure 3: Discrete phase velocity magnitude (dust particles)