Diffusion characteristics of air pollutants across building floorsunder thermal plume effect

Taking a 6-storey building with single-side ventilation as the research object, considering the coupling effect of horizontal flow and near-wall thermal plume caused by solar radiation, this study conducts the wind tunnel experiment and numerical simulation to investigate the heat flux movement on the building wall, the temperature distribution and the diffusion and transmission characteristics of pollutants across building floors in the vertical direction under different Ri. The results show that when Ri≤5.64, the horizontal wind is dominant, and there is obvious downwind and bilateral flow on the windward wall below 2/3 of the building height. The pollutants released from the first floor have almost no effect on the floors above the second floor, and the normalized net escape velocity NEV*remains basically unchanged. When Ri>5.64, the effect of wall thermal buoyancy cannot be ignored, and NEV*increases obviously with the increase of Ri, which indicates that more pollutants will diffuse from the first floor, and the heat flux moving upwind along the windward wall has an impact on the upper floors, resulting in increasing risk of pollutant cross-floor transmission.