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

Abstract 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.

[1]  Chun-Ho Liu,et al.  Large-Eddy Simulation of Flow and Scalar Transport in a Modeled Street Canyon , 2002 .

[2]  Vice President,et al.  AMERICAN SOCIETY OF HEATING, REFRIGERATION AND AIR CONDITIONING ENGINEERS INC. , 2007 .

[3]  Nathan Mendes,et al.  New external convective heat transfer coefficient correlations for isolated low-rise buildings , 2007 .

[4]  Michael Schatzmann,et al.  Quality assurance and improvement of micro-scale meteorological models , 2011 .

[5]  A. Colburn,et al.  Mass Transfer (Absorption) Coefficients Prediction from Data on Heat Transfer and Fluid Friction , 1934 .

[6]  Bert Blocken,et al.  CFD evaluation of wind speed conditions in passages between parallel buildings : effect of wall-function roughness modifications for the atmospheric boundary layer flow , 2007 .

[7]  Jon Wieringa,et al.  Updating the Davenport roughness classification , 1992 .

[8]  Sandrine Anquetin,et al.  Pollutant dispersion and thermal effects in urban street canyons , 1996 .

[9]  Jörg Franke,et al.  The COST 732 Best Practice Guideline for CFD simulation of flows in the urban environment: a summary , 2011 .

[10]  Thijs Defraeye,et al.  Convective Heat and Mass Transfer at Exterior Building Surfaces (Convectief warmte- en massatransport op gebouwoppervlakken) , 2011 .

[11]  J. Palyvos.  A survey of wind convection coefficient correlations for building envelope energy systems’ modeling , 2008 .

[12]  Jan Carmeliet,et al.  CONSERVATIVE MODELLING OF THE MOISTURE AND HEAT TRANSFER IN BUILDING COMPONENTS UNDER ATMOSPHERIC EXCITATION , 2007 .

[13]  M. S. Sodha,et al.  A review—Cooling by water evaporation over roof , 1982 .

[14]  David Pearlmutter,et al.  The effect of urban evaporation on building energy demand in an arid environment , 2008 .

[15]  E. Erell,et al.  Experimental studies on a novel roof pond configuration for the cooling of buildings , 2003 .

[16]  D. Asimakopoulos.  Energy and Climate in the Urban Built Environment , 2001 .

[17]  P. Richards,et al.  Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model , 1993 .

[18]  Refrigerating.  ASHRAE handbook and product directory /published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc , 1977 .

[19]  Dominique Derome,et al.  High-resolution CFD simulations for forced convective heat transfer coefficients at the facade of a low-rise building , 2009 .

[20]  Bje Bert Blocken,et al.  A combined CFD–HAM approach for wind-driven rain on building facades , 2007 .

[21]  Jan Carmeliet,et al.  CFD analysis of convective heat transfer at the surfaces of a cube immersed in a turbulent boundary layer , 2010 .

[22]  P. Jones,et al.  Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates , 2008 .

[23]  T. Stathopoulos,et al.  CFD simulation of the atmospheric boundary layer: wall function problems , 2007 .

[24]  Janet F. Barlow,et al.  Dispersion and transfer of passive scalars in and above street canyons—Large-eddy simulations , 2008 .

[25]  J. Carmeliet,et al.  Convective heat transfer coefficients for exterior building surfaces: Existing correlations and CFD modelling , 2011 .