Intercomparisons of Experimental Convective Heat Transfer Coefficients and Mass Transfer Coefficients of Urban Surfaces |
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Authors: | Email author" target="_blank">Aya?HagishimaEmail author Jun?Tanimoto Ken-ich?Narita |
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Institution: | 1.Interdisciplinary Graduate School of Engineering Sciences,Kyushu University,Fukuoka,Japan;2.Department of Engineering,Nippon Institute of Technology,Japan |
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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.
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(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.
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(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.
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(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.
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Although there is some agreement in the measured values, our overall understanding of the CHTC remains too low for accurate
modelling of urban climate. |
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Keywords: | |
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