An empirical correlation for the outside convective air-film coefficient for horizontal roofs

Clear, RD; Gartland, Lisa Mummery; Winkelmann, F.C.

doi:10.1016/s0378-7788(02)00240-2

Cited by 63 publications

(33 citation statements)

References 3 publications

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“…This agreement suggests that the CHTC is relatively independent of roof size, but is inconsistent with the former remarks based on indoor experiments (e.g., Cole and Sturrock, 1977). In addition, this tendency is also inconsistent with the modelling of the local Nusselt number of a flat roof by Clear et al (2003). The effect of the parapets around the target roofs is a possible factor.…”

Section: Horizontal Roofmentioning

confidence: 59%

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

Hagishima

Tanimoto

Narita

2005

Boundary-Layer Meteorol

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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.

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Section: Horizontal Roofmentioning

confidence: 59%

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

Hagishima

Tanimoto

Narita

2005

Boundary-Layer Meteorol

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“…In [2,[3][4][5][6][7][8][9][10][11][12][13][14][15][16] it is shown that the average CHTC on the windward façade is not very sensitive to wind direction so that a wind direction of 45° from the normal can represent a wide range of wind directions between 0° and 60°.…”

Section: Cfd Numerical Modelmentioning

confidence: 99%

CFD Analysis of Convective Heat Transfer Coefficient on External Surfaces of Buildings

2015

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Convective heat transfer coefficients for external building surfaces are essential in building energy simulation (BES) to calculate convective heat gains and losses from building facades and roofs to the environment. These coefficients are complex functions of: building geometry, building surroundings, local air flow patterns and temperature differences. A microclimatic analysis in a typical urban configuration, has been carried out using Ansys Fluent Version 14.0, an urban street canyon, with a given H/W ratio, has been considered to simulate a three-dimensional flow field and to calculate the thermal fluid dynamics parameters that characterize the street canyon. In this paper, the convective heat transfer coefficient values on the windward external façade of the canyon and on the windward and leeward inner walls are analyzed and a comparison with values from experimental and numerical correlations is carried out.

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“…The need for more accurate and truthful estimates of CHTCs for buildings led to an extensive amount of field measurements for building facades [15][16][17][18][19][20][21][22][23][24][25][26], for roofs [24,27,28] and to study the effect of glazing framework on the CHTC [29][30][31]. A clear overview of the different experimental techniques to determine these CHTCs and their limitations was given by Hagishima et al [9].…”

Section: Full-scale Experimentsmentioning

confidence: 99%

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

Defraeye

Blocken

Carmeliet

2011

Energy Conversion and Management

221

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Convective heat transfer at exterior building surfaces has an impact on the design and performance of building components such as double-skin facades, solar collectors, solar chimneys, ventilated photovoltaic arrays, etc. and also affects the thermal climate and cooling load in urban areas. In this study, an overview is given of existing correlations of the exterior convective heat transfer coefficient (CHTC) with the wind speed, indicating significant differences between these correlations. As an alternative to using existing correlations, the applicability of CFD to obtain forced CHTC correlations is evaluated, by considering a cubic building in an atmospheric boundary layer. Steady Reynolds-Averaged Navier-Stokes simulations are performed and, instead of the commonly used wall functions, low-Reynolds number modelling (LRNM) is used to model the boundary-layer region for reasons of improved accuracy. The flow field is found to become quasi independent of the Reynolds number at Reynolds numbers of about 10 5 . This allows limiting the wind speed at which the CHTC is evaluated and thus the grid resolution in the near-wall region, which significantly reduces the computational expense. The distribution of the power-law CHTC-U 10 correlation over the windward and leeward surfaces is presented (U 10 = reference wind speed at 10 m height). It is shown that these correlations can be accurately determined by simulations with relatively low wind speed values, which avoids the use of excessively fine grids for LRNM, and by using only two or three discrete wind speed values, which limits the required number of CFD simulations.

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An empirical correlation for the outside convective air-film coefficient for horizontal roofs

Cited by 63 publications

References 3 publications

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

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

CFD Analysis of Convective Heat Transfer Coefficient on External Surfaces of Buildings

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

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