In the summer of 2007, the number of people living in the world’s urban areas
exceeded that of those living in the countryside. Such urbanisation tends to
modify the climates of towns and cities as a result of a number of factors which
together form the ‘urban heat island’ effect. In order to better design buildings
and urban areas to cope with these effects, it is first necessary to understand the
heat transfer mechanisms which are taking place. The aim of the current
research has therefore been to provide convective heat transfer data appropriate
for low-rise urban environments by investigating the effects of wind speed,
direction and street geometry.
The research has employed the naphthalene sublimation technique which has
been extended in several fundamental areas including development of a novel
approach to measure the rate of sublimation from wind tunnel models. This
technique has permitted measurements to be made over an array of discrete
locations, revealing the variation across building surfaces. The uncertainty in the
convective heat transfer coefficients obtained was calculated to be approximately
±6%. Tests were conducted in the BRE wind tunnel with an atmospheric
boundary layer simulation appropriate to inner city areas. Cube models were
arranged so as to form long rows of flat-roofed buildings referred to as ‘street
canyons’.
A series of correlations have been derived from the experimental results from
which the rate of convection occurring from each building surface may be
obtained with respect to wind speed. The greatest rates of convective heat
transfer have been shown to occur at the top of the windward wall and leading
edge of the roof, the lowest rates from the leeward wall of a building. Convection
was found to be reduced in narrow street canyons. In wider street canyons, the
convective coefficients on the exposed windward and roof surfaces of buildings
were higher, but the values on the leeward wall are lessened due to the
distancing of the downstream windward vortex. The effect of wind direction was
found to be relatively small and therefore it is proposed that the convective heat
transfer relationships presented may be applied irrespective of wind direction.
Date of Award | 1 Mar 2010 |
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Original language | English |
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Awarding Institution | |
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Supervisor | Geoff Hammond (Supervisor) |
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- convective heat transfer
- urban heat islands
- buildings
Determination of the convective heat transfer coefficients from the
surfaces of buildings within urban street canyons
Smith, J. (Author). 1 Mar 2010
Student thesis: Doctoral Thesis › PhD