Local mass transfer coefficients over idealised two-dimensional urban street canyons

In view of the large number of urban inhabitants, ventilation and pollutant transport in urban areas are major research problems for several decades. This paper focuses on the studies of the correlation between the ventilation and pollutant removal over idealised two-dimensional urban street canyons using wind tunnel experiments in the Department of Mechanical Engineering, The University of Hong Kong. To construct street canyon models of different building-height-to-street-width (aspect) ratios, movable rectangular aluminium blocks were placed in the test section of the wind tunnel. Water evaporation method was used throughout the experiments, in which soaked filter papers were applied on the model, simulating a uniform mass concentration on the building facades and ground surface. The variations of the average mass transfer coefficients over a wider range of aspect ratios were examined. Scaling effect, which occurs even if the kinematic similarity is fully complied with, is observed so a more in-depth data analysis and another extensive comparison with our mathematical modelling results are required.