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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:518100 |
| Date | January 2010 |
| Creators | Smith, James O. |
| Contributors | Hammond, Geoffrey |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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