| To filter the imported air into residential buildings while maintaining sufficient ventilation, a breathing wall seems a good alternative to replace the traditional well-sealed wall. The breathing wall is composed of solar radiation absorption panel, zigzag flow channel, and porous media unit. Although the classic filtration theory can well predict the filtration performance in porous media unit, whether it is suit for breathing wall has to be validated. Moreover, few studies focus on particle deposition in low velocity and curved channel as in Breathing Wall.Primarily, a breathing wall test-bed in winter case is built to measure particle filtration efficiency of breathing wall.5cm thick quartz sands are filled in. According to the measurement from a portable particle counter, it seems that most particles are captured by porous media unit, which filtration efficiency is stable (<5%). In addition, it obviously shows that particles, which are larger than5μm, are hard to pass the channel.Based on the measurement, particle deposition in zigzag flow channel and porous media unit are modeled separately. For zigzag flow channel, a trajectory analysis method (TAM) is organized to track particles, where the collision between particle and wall is solved by a hard sphere model. RNG k-s model is adopted to simulate the air flow of breathing wall with a volume averaging method for porous media. It seems the difference between simulation and experiment is no more than5%. On the other hand, it is proved that the filtration performance of porous media unit can be predicted by classical filtration theory with less than5%deviation.Furthermore, the performance of particle deposition in breathing wall is discussed. In the porous media unit, particles (<0.1-0.3μm) are filtered by diffusion and interception, particles (>5-7μm) are captured by inertial effect and interception, and the other size of particles are easy to pass the unit. On the other side, the zigzag flow channel is segmented into vertical straight channel,90°band and180°band. As the simulation from TAM, almost do airborne particles deposit in the vertical straight channel, the180°upward band and the outlet part of90°band. Moreover, the deposition efficiency is depended on the other segments. The deposition efficiency of zigzag flow channel is mainly impacted by air flow rate and the size of the zigzag flow channel. In addition, higher deposition efficiency comes from lower air flow rate and wider flow channel. |
