3,148 research outputs found
Analysis of coupled heat and moisture transfer in masonry structures
Evaluation of effective or macroscopic coefficients of thermal conductivity
under coupled heat and moisture transfer is presented. The paper first gives a
detailed summary on the solution of a simple steady state heat conduction
problem with an emphasis on various types of boundary conditions applied to the
representative volume element -- a periodic unit cell. Since the results
essentially suggest no superiority of any type of boundary conditions, the
paper proceeds with the coupled nonlinear heat and moisture problem subjecting
the selected representative volume element to the prescribed macroscopically
uniform heat flux. This allows for a direct use of the academic or commercially
available codes. Here, the presented results are derived with the help of the
SIFEL (SIimple Finite Elements) system.Comment: 23 pages, 11 figure
Uncertainty Updating in the Description of Coupled Heat and Moisture Transport in Heterogeneous Materials
To assess the durability of structures, heat and moisture transport need to
be analyzed. To provide a reliable estimation of heat and moisture distribution
in a certain structure, one needs to include all available information about
the loading conditions and material parameters. Moreover, the information
should be accompanied by a corresponding evaluation of its credibility. Here,
the Bayesian inference is applied to combine different sources of information,
so as to provide a more accurate estimation of heat and moisture fields [1].
The procedure is demonstrated on the probabilistic description of heterogeneous
material where the uncertainties consist of a particular value of individual
material characteristic and spatial fluctuations. As for the heat and moisture
transfer, it is modelled in coupled setting [2]
Modelling cavity ventilation behind brick veneer cladding : how reliable are the common assumptions?
Throughout the years, different numerical HAM-simulation tools have been developed to assess and predict the heat, air and moisture response of building components. But, though commercially available and commonly applied in building practice, still, several simplifications and shortcomings exist in the common models. Probably the most important one, is the fact that most tools neglect or strongly simplify air transport, focusing only on heat and moisture transport. Especially for the analysis of wood frame constructions, these simplified models may cause a large discrepancy between simulation results and real performance. This study aims at a comparison of the outcomes of numerical HAM -simulations for wood frame constructions with experimental data of real test cases. In particular, the focus of this paper is on cavity ventilation behind brick veneer. Therefore, a simplified version of a wood frame wall with brick veneer cladding is studied in this paper. Different common modelling assumptions are compared. Furthermore, a detailed measuring campaign has been conducted at the VLIET test building of the KU Leuven to validate the different modelling approaches. By verifying the results of the numerical simulations by the data of real test cases, the reliability of the modelling assumptions can be analysed. The results of this study clearly show that simplified assumptions on cavity ventilation in HAM-models might cause large discrepancies between simulation results and in-situ measurements
Selected topics in homogenization of transport processes in historical masonry structures
The paper reviews several topics associated with the homogenization of
transport processed in historical masonry structures. Since these often
experience an irregular or random pattern, we open the subject by summarizing
essential steps in the formulation of a suitable computational model in the
form of Statistically Equivalent Periodic Unit Cell (SEPUC). Accepting SEPUC as
a reliable representative volume element is supported by application of the
Fast Fourier Transform to both the SEPUC and large binary sample of real
masonry in search for effective thermal conductivities limited here to a steady
state heat conduction problem. Fully coupled non-stationary heat and moisture
transport is addressed next in the framework of two-scale first-order
homogenization approach with emphases on the application of boundary and
initial conditions on the meso-scale.Comment: 19 pages, 13 figures, 2 table
Modelling of heat and moisture transfer in concrete at high temperature
Moisture diffusion and related fluid pressures play a key role in cracking and spalling of concrete subject to high temperatures. This paper describes recent developments of a mode for moisture and heat transfer in porous materials, to be combined with an existing and well tested meso-mechanical model for concrete. Liquid and gas flows are formulated separately, yet later they can be combined in terms of s single variable, Pv. The material pore distribution curve is taken as the basis for developing a new physically-based desorption isotherm alternative to the traditional Bazant & Thonguthai’s model. A simple academic example for temperatures between 27 and 800ºC is presented to show the behaviour of the model
Analysis of different frost indexes and their potential to assess frost based on HAM simulations
To reach the climate goals of 2020 our buildings have to become a lot more energy-efficient. This challenge rests mainly on the shoulders of the renovation sector because new buildings are only a small part of our building stock. Old buildings mainly cannot get insulated on the outside because the facade is historically valuable or because of urban planning restrictions. In those cases interior insulation or - if possible - cavity insulation are the only options. However, these renovation strategies may induce severe risks for the existing structure. One of the main risks is frost damage: the interior insulation lowers the temperature of the exterior facade and decreases the drying potential to the inside which leads to an increased risk of frost damage. Most of the studies that assess the risk of frost damage struggle with the dependency of the highly variable material properties of the façade
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