Analysis of convective heat and mass transfer at the vertical walls of a street canyon

The combined effects of urbanization and global climate warming give rise to increased temperatures in urbanized areas, a phenomenon called the urban heat island effect. The higher air temperatures have a negative impact on the energy demand for cooling and on the comfort and health of the people residing in urban areas. One way to mitigate the excess heat in urban areas is to make use of evaporative cooling, for example from ponds, from surfaces wetted by wind-driven rain, or from vegetated surfaces. Therefore understanding the interaction between the urban microclimate and evaporation processes is of interest. In the current paper, a two-step methodology for the simulation of drying processes is proposed and subsequently applied to study the drying behavior of both vertical walls of a square-shaped street canyon. Simulation results reveal the importance of using location-dependent convective heat and mass transfer coefficients (CHTC and CMTC) to capture the spatially non-uniform drying behavior of the wall. Whether the CMTC is obtained via Computational Fluid Dynamics simulations or via a simplified method based on the Chilton–Colburn analogy only slightly affects the drying behavior. The potential for evaporative cooling of wet walls in a hot climate is demonstrated in a final example.