Sainte-Foy-lès-Lyon, France
Sainte-Foy-lès-Lyon, France
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Rouchier S.,CETHIL | Rouchier S.,INSA Lyon | Janssen H.,Catholic University of Leuven | Rode C.,Technical University of Denmark | And 4 more authors.
Construction and Building Materials | Year: 2012

Several years after their installation, building materials such as concrete present signs of ageing in the form of fractures covering a wide range of sizes, from microscopic to macroscopic cracks. All sizes of fractures can have a strong influence on heat and moisture flow in the building envelope, but their distribution is difficult to predict due to the variety of environmental factors which cause them. This paper aims at applying experimental non-destructive techniques for the observation of fracture patterns and of fluid flow in fractures, in order to provide this data to models for fluid transfer in fractured porous media. Digital Image Correlation was performed during the fracturing of concrete samples, in which moisture uptake was then monitored using X-ray radiography. Finite-element simulations were then performed based on the measurements of the fracture patterns, in order to recreate the measured moisture concentration profiles. Digital Image Correlation was found suitable as a mean to obtain a complete mapping of the deformations at the surface of the samples, and a first step was made towards the use of non-destructive fracture characterization for the purpose of moisture transfer modelling. © 2012 Elsevier Ltd. All rights reserved.

David D.,CETHIL | David D.,University of Lyon | David D.,INSA Lyon | Kuznik F.,CETHIL | And 5 more authors.
Applied Thermal Engineering | Year: 2011

In construction, the use of Phase Change Materials (PCM) allows the storage/release of energy from solar radiation and internal loads. The application of such materials for lightweight construction (e.g., a wood house) makes it possible to improve thermal comfort and reduce energy consumption. The heat transfer process between the wall and the indoor air is convection. In this paper, we have developed a numerical model to evaluate several convective heat transfer correlations from the literature for natural, mixed and forced convection flows. The results show that the convective heat transfer highly influences the storage/release process in case of PCM walls. For the natural convection, the numerical results are highly dependent on the correlation used and the results may vary up to 200%. In the case of mixed and forced convection flows, the higher is the velocity, the more important is the storage capacity. © 2011 Elsevier Ltd.

Kuznik F.,CETHIL | Kuznik F.,INSA Lyon | Catalina T.,Technical University of Civil Engineering Bucharest | Gauzere L.,Électricité de France | And 4 more authors.
Applied Thermal Engineering | Year: 2011

The present paper presents a numerical modelling of a double skin faade (DSF). The model developed includes a zonal model approach for the mass transfer based on the pressure difference in the DSF. The radiative and convective heat transfers are also taken into account to obtain a global coupling between the different phenomena. A full-scale DSF has been experimentally studied in summer configuration with different airflow rates through the air channels of the faade and for different angles of the solar shading devices. First the numerical modelling has been validated using the experimental data. Then, the model has been used to study the influence of airflow rates and blades angles (Venetian blind) on heat transfer in DSF. © 2011 Elsevier Ltd. All rights reserved.

Rouchier S.,CETHIL | Monikawoloszyn M.,University of Savoy | Foray G.,INSA Lyon | Roux J.-J.,CETHIL
Proceedings of BS 2013: 13th Conference of the International Building Performance Simulation Association | Year: 2013

Moisture transfer in porous construction materials carries many causes for their degradation: mould development and freeze-thaw damage are favoured by the accumulation of water, and chemicals such as chloride ions and carbon dioxide may accelerate the fracturing of cementitious composites. Over time, microscopic and macroscopic cracks progressively develop under the effects of mechanical loading and sorption/desorption cycles: their influence is to be accounted for in long-term hygrothermal performance assessments of the building envelope. Current simulation codes for heat and moisture transfer modelling in building facades do not allow accounting for the presence of cracks and defects in the material layers. The present work aims at integrating such effects of damage in simulations at the scale of building facades. Experimental measurements of crack patterns were integrated into a newly developed numerical model predicting coupled heat and moisture transfer in multi-layered components. The consequences of fractures on the hygrothermal performance of these components were then investigated by comparing damaged and undamaged materials in a series of simulation cases. Cracks were found to accentuate the amplitude of daily sorption/desorption cycles and moisture accumulation in the walls, particularly in case of impacting rain. Their impact on the overall thermal performance is small, although not negligible in case of water infiltration towards an insulation layer. Copyright © 2011 by IPAC'11/EPS-AG.

David D.,University Claude Bernard Lyon 1 | Kuznik F.,CETHIL | Kuznik F.,INSA Lyon | Johannes K.,University Claude Bernard Lyon 1 | And 2 more authors.
Computers and Fluids | Year: 2015

This paper is the continuity of Guo's work (2009) about a lattice Boltzmann model for axis-symmetric flows. This is a radius weighted LBM model: all the moments are proportional to the radial coordinate r. A Taylor series analysis is performed on the discrete Boltzmann model in order to assess the consistency. The truncation error terms do not indicate any error increase along the radial direction, but they contain a spurious term ur/r which considerably reduces the model accuracy when radial velocity is non-null: simulation results highlight a reductions of the order of accuracy (from second to first). A new axis boundary condition was created to improve the model accuracy and to cope with the spurious error term. It was assessed though several test cases. © 2015 Elsevier Ltd.

Ollier E.,CEA Grenoble | Soupremanien U.,CEA Grenoble | Remondiere V.,CEA Grenoble | Dijon J.,CEA Grenoble | And 12 more authors.
Microelectronic Engineering | Year: 2014

As the power of electronic systems is increasing, thermal fluxes are getting higher, up to more than 100 W/cm2 in the more critical cases. They result in hot spots with various consequences, especially performance reduction and reliability issues. Most of the prior research has been focused on active liquid cooling and on reducing hot spots by the implementation of thermal interface materials (TIMs) and spreading solutions. The approach presented here is based on the implementation in silicon of nanocomposite structures including carbon nanotubes (CNTs) and phase change materials (PCMs). The simulation model presented here shows how the composite CNTs/PCM structure efficiently reduces the temperature excursion at the silicon surface compared to the implementation of PCM only or a thicker silicon. A fabrication process flow is presented with a special focus on the assembly of silicon top and bottom parts with CNTs. Process conditions are explored to insure mechanical adhesion and thermal contact quality. This thermal interposer concept provides a new solution for thermal management and reliability improvement of devices. It is of great interest for electronic and optical devices, MEMS and 3D integration. © 2014 Elsevier B.V. All rights reserved.

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