Comparisons of various experimental results on the convective heat transfer coefficient of urban surfaces

The convective heat transfer coefficient (CHTC) of an urban canopy is a crucial parameter for estimating the turbulent heat flux in an urban area. However, the features of the CHTC remain unclear. After describing the measurement methods of CHTC, we review recent experimental researches on CHTC of urban surfaces in the field, laboratory, and in wind tunnels. Our findings are summarized as follows. 1) The relationships between CHTC and the wind speed based on the Full-scale measurements vary from site to site and are particularly variable for the vertical walls of buildings. This variability is due to variations in building shape, the distance of the referential wind speed, and thermal stability. 2) The relations between mass transfer coefficient (MTC) of 2D urban-like canopy and the shape of canopy based on the two wind tunnel experiments are similar in spite of the differences of the measurement method. The relationships MTC vs. W/H of these works are consistent with the knowledge on the flow regime of urban canopy. 3) The relations between Nusselt number and Reynolds number based on the full-scale measurement does not agree with those based on the scale model experiments.