Title: Convective Heat and Mass Transfer at Exterior Building Surfaces (Convectief warmte- en massatransport op gebouwoppervlakken)
Other Titles: Convective Heat and Mass Transfer at Exterior Building Surfaces
Authors: Defraeye, Thijs
Issue Date: 27-Jan-2011
Abstract: This thesis aims on establishing more accurate and detailed predictionsof convective heat and mass transfer at exterior building surfaces. A first part of this work focuses on fluid-side convective heat transfer atsurfaces of buildings for forced-convective high-Reynolds number flow in the atmospheric boundary layer. The convective heat transfer coefficient (CHTC) is analysed with computational fluid dynamics (CFD), by using validated steady Reynolds-averaged Navier-Stokes simulations, combined with low-Reynolds number modelling (LRNM) to resolve the boundary-layer region. The heat transport in the boundary layer, the spatial distribution of the CHTC over the building surfaces, its correlation with the wind speed and the influence of wind direction and buoyancy on the CHTC are investigated. Furthermore, several approaches to enhance numerical modelling of CHTCs with CFD are developed, such as an improved temperature wall function and the use of low wind speeds to determine CHTC-wind speed correlations for LRNM purposes, based on Reynolds number independence of the flow field. In addition, a methodology is proposed to determine the temporally-averaged CHTC for a building surface over a long time span, with which a significant dependency of this CHTC on the building surface orientation and the local wind climate is identified. In order to account simultaneously for heat and mass transport in the air flow and in porous materials, a conjugate heat and mass transfer model is developed in asecond part of this work, which does not require a-priori knowledge of convective transfer coefficients (CTCs), where they can be determined a-posteriori. Conjugate modelling of convective drying of a porous material identifies a distinct spatial and temporal variability of these CTCs, where also the validity of the heat and mass transfer analogy is verified. Conjugate modelling thereby shows significant advantages regarding convective transfer assessment, compared to the use of CTCs. Furthermore, a conjugate convective drying experiment is performed and compared with numerical simulations, indicating the need for detailed conjugate experiments for validation of conjugate models as well as porous-material models. Moreover, the propagation of uncertainties in material properties onthe porous-material modelling results for convective drying is investigated by stochastic analysis, which identifies a distinct sensitivity of the drying behaviour to these material transport properties.
ISBN: ISBN 978-94-6018-315-7
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Building Physics Section
Structural Mechanics Section
Division of Mechatronics, Biostatistics and Sensors (MeBioS)

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