Intercomparisons of Experimental Convective Heat Transfer Coefficients and Mass Transfer Coefficients of Urban Surfaces

Abstract

The convective heat transfer coefficient (CHTC) of an urban canopy is a crucial parameter for estimating the turbulent heat flux in an urban area. We compared recent experimental research on the CHTC and the mass transfer coefficient (MTC) of urban surfaces in the field and in wind tunnels. Our findings are summarised as follows.(1) In full-scale measurements on horizontal building roofs, the CHTC is sensitive to the height of the reference wind speed for heights below 1. 5 m but is relatively independent of roof size.(2) In full-scale measurements of vertical building walls, the dependence of the CHTC on wind speed is significantly influenced by the choice of the measurement position and wall size. The CHTC of the edge of the building wall is much higher than that near the centre. (3) In spite of differences of the measurement methods, wind-tunnel experiments of the MTC give similar relations between the ratio of street width to canopy height in the urban canopy. Moreover, this relationship is consistent with known properties of the flow regime of an urban canopy. (4) Full-scale measurements on roofs result in a non-dimensional CHTC several tens of times greater than that in scale-model experiments with the same Reynolds number. Although there is some agreement in the measured values, our overall understanding of the CHTC remains too low for accurate modelling of urban climate.

Progress in Urban Meteorology :A Review

“…1). Surface albedo for infinite twodimensional street canyons (Arnfield 1982;Sievers and Zdunkowski 1985;Sakakibara 1996;Masson 2000;Kusaka et al 2001;Martilli Table 1 Reviews on urban meteorology published after 2000 Reference Topic Roth (2000) atmospheric turbulence over cities Jauregui (2000) tropical urban climatology Fernando et al (2001) air circulation and dispersion in cities Arnfield (2003) comprehensive review of urban climate, 1980climate, -2003climate, Shepherd (2005 urban-induced rainfall, Hagishima et al (2005 transfer coefficients of urban surfaces Oke (2006) scientific communication in urban climates Grimmond (2006) measuring and observing the urban atmosphere Masson (2006) urban surface modeling Kanda (2006b) physical scale modeling of the urban climate Mills (2006) sustainable settlements Best (2006a) weather forecasts for city dwellers Li et al (2006) CFD of flow and dispersion in street canyons Fig. 1.…”

“…Parameterization of local transfer coefficients for momentum and scalars between surfaces (e.g., roof, street, walls) and a reference height requires more than a one-dimensional approximation. However, a compilation of experimental data suggests that such coefficients largely differ case by case and thus are difficult to arrange in a simple formulation (see Hagishima et al 2005 for review).…”

A coupled energy transport and hydrological model for urban canopies evaluated using a wireless sensor network

“…Unlike their natural counterparts (bare soils or vegetation), hydrological models for urban pavements or impervious roofs should be capable of resolving the water-holding capacity of impervious media, which regulates the evaporation for the major fraction of urban surfaces (Yamanaka et al, 1997;Andersen et al, 1999;Hagishima et al, 2005;Borselli and Torri, 2010;Nakayama and Fujita, 2010;Abahri et al, 2011). Therefore, urban hydrological models, in addition, need to incorporate the unique feature of evaporation arising from surfaces with engineered materials.…”

Convective heat transfer coefficients for exterior building surfaces: Existing correlations and CFD modelling

“…A clear overview of the different experimental techniques to determine these CHTCs and their limitations was given by Hagishima et al [9]. CHTCs were also determined for greenhouses of which a concise review can be found in Roy et al [10].…”

“…A recent and extensive review on CHTC correlations for applications towards solar collectors was provided by Palyvos [8]. Hagishima et al [9] and Roy et al [10] included a more concise overview of CHTC correlations in their work, from the viewpoint of urban canopy modelling and the greenhouse climate, respectively. In the overview in this paper, primarily additional information to existing reviews will be presented, while for other information, reference will be made to these earlier reviews.…”