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Babuty A.,ESPCI ParisTech | Joulain K.,University of Poitiers | Chapuis P.-O.,Catalan Institute of Nanoscience and Nanotechnology | Chapuis P.-O.,Lyon Center of Thermal Science | And 2 more authors.
Physical Review Letters | Year: 2013

We report local spectra of the near-field thermal emission recorded by a Fourier transform infrared spectrometer, using a tungsten tip as a local scatterer coupling the near-field thermal emission to the far field. Spectra recorded on silicon carbide and silicon dioxide exhibit temporal coherence due to thermally excited surface waves. Finally, we evaluate the ability of this spectroscopy to probe the frequency dependence of the electromagnetic local density of states. © 2013 American Physical Society.

Obrecht C.,Lyon Center of Thermal Science | Obrecht C.,Laboratoire Of Linformatique Du Paralllisme | Kuznik F.,Lyon Center of Thermal Science | Tourancheau B.,Laboratoire Of Linformatique Du Paralllisme | Roux J.-J.,Lyon Center of Thermal Science
Computers and Mathematics with Applications | Year: 2011

Emerging many-core processors, like CUDA capable nVidia GPUs, are promising platforms for regular parallel algorithms such as the Lattice Boltzmann Method (LBM). Since the global memory for graphic devices shows high latency and LBM is data intensive, the memory access pattern is an important issue for achieving good performances. Whenever possible, global memory loads and stores should be coalescent and aligned, but the propagation phase in LBM can lead to frequent misaligned memory accesses. Most previous CUDA implementations of 3D LBM addressed this problem by using low latency on chip shared memory. Instead of this, our CUDA implementation of LBM follows carefully chosen data transfer schemes in global memory. For the 3D lid-driven cavity test case, we obtained up to 86% of the global memory maximal throughput on nVidia's GT200. We show that as a consequence highly efficient implementations of LBM on GPUs are possible, even for complex models. © 2011 Elsevier Ltd. All rights reserved.

Chow T.T.,Hong Kong University of Science and Technology | Tiwari G.N.,Indian Institute of Technology Delhi | Menezo C.,Lyon Center of Thermal Science
International Journal of Photoenergy | Year: 2012

The market of solar thermal and photovoltaic electricity generation is growing rapidly. New ideas on hybrid solar technology evolve for a wide range of applications, such as in buildings, processing plants, and agriculture. In the building sector in particular, the limited building space for the accommodation of solar devices has driven a demand on the use of hybrid solar technology for the multigeneration of active power and/or passive solar devices. The importance is escalating with the worldwide trend on the development of low-carbon/zero-energy buildings. Hybrid photovoltaic/thermal (PVT) collector systems had been studied theoretically, numerically, and experimentally in depth in the past decades. Together with alternative means, a range of innovative products and systems has been put forward. The final success of the integrative technologies relies on the coexistence of robust product design/construction and reliable system operation/maintenance in the long run to satisfy the user needs. This paper gives a broad review on the published academic works, with an emphasis placed on the research and development activities in the last decade. © 2012 T. T. Chow et al.

Merabia S.,University Claude Bernard Lyon 1 | Termentzidis K.,Lyon Center of Thermal Science | Termentzidis K.,École Centrale Paris
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In this article, we compare the results of nonequilibrium (NEMD) and equilibrium (EMD) molecular dynamics methods to compute the thermal conductance at the interface between solids. We propose to probe the thermal conductance using equilibrium simulations measuring the decay of the thermally induced energy fluctuations of each solid. We also show that NEMD and EMD give generally speaking inconsistent results for the thermal conductance: Green-Kubo simulations probe the Landauer conductance between two solids which assumes phonons on both sides of the interface to be at equilibrium. On the other hand, we show that NEMD give access to the out-of-equilibrium interfacial conductance consistent with the interfacial flux describing phonon transport in each solid. The difference may be large and reaches typically a factor 5 for interfaces between usual semiconductors. We analyze finite size effects for the two determinations of the interfacial thermal conductance, and show that the equilibrium simulations suffer from severe size effects as compared to NEMD. We also compare the predictions of the two above-mentioned methods-EMD and NEMD-regarding the interfacial conductance of a series of mass mismatched Lennard-Jones solids. We show that the Kapitza conductance obtained with EMD can be well described using the classical diffuse mismatch model (DMM). On the other hand, NEMD simulation results are consistent with an out-of-equilibrium generalization of the acoustic mismatch model (AMM). These considerations are important in rationalizing previous results obtained using molecular dynamics, and help in pinpointing the physical scattering mechanisms taking place at atomically perfect interfaces between solids, which is a prerequisite to understand interfacial heat transfer across real interfaces. © 2012 American Physical Society.

Assoa Y.B.,French National Solar Energy Institute | Menezo C.,Lyon Center of Thermal Science
Solar Energy | Year: 2014

This work presents the development of a concept of solar Photovoltaic/Thermal (PV/T) hybrid air collector. This type of collector combines the preheating of air through a gap at the underside of the PV modules in addition to the ordinary function of electricity production. The cooling of PV modules by heat extraction can improve the electrical efficiency. In this paper, a simplified dynamic two-dimensional mathematical model of solar PV/T hybrid air collector with a metal absorber is presented. The validation of this numerical model with the measured data obtained with a full-scale test bench located near Lyon is proposed. Then, a numerical parametric study is undertaken to determine the effect of the air gap ventilation type on the system preheated air thermal production and electrical production. The results show that forced ventilation provides the higher value of thermal production but natural ventilation is sufficient to cool the integrated PV modules. © 2014 Elsevier Ltd.

Bouquerel M.,Électricité de France | Bouquerel M.,Lyon Center of Thermal Science | Duforestel T.,Électricité de France | Baillis D.,CNRS Contacts and Structural Mechanics Laboratory | Rusaouen G.,Lyon Center of Thermal Science
Energy and Buildings | Year: 2012

A vacuum insulation panel (VIP) is a very efficient thermal insulation system for buildings. A porous core material structure is evacuated and wrapped into a gas barrier envelope. Thanks to the low pressure, the total conductivity measured is as low as 5 mW/(m K) for best panels, six to ten times lower than conventional insulation materials. Thin insulation systems with very high thermal performance can thus be designed with VIPs. Heat transfer modeling in these panels is complex, resulting on four contributions of heat fluxes: radiative transfer, solid conduction, gaseous transfer, and envelope thermal bridge. These last years, several approaches have been investigated to estimate the contribution of each heat transfer mode. A complete first review on heat transfer modeling in vacuum insulation panels containing nanoporous silicas is conducted. Monolithic aerogel but also granular aerogels and nanoporous powders (pyrogenic and precipitated) are considered in this review. The parameters that play a key role in the total heat transfer are identified. A special emphasis is put to discuss the influence of pressure and humidity on the total conductivity. The results synthesis can be used to set up a design strategy to minimize the thermal conductivity and to understand the main aging mechanisms. © 2012 Elsevier B.V. All rights reserved.

Coquard R.,Societe Etude Conseils Calcul en Mecanique des Structures EC2MS | Baillis D.,Lyon Center of Thermal Science | Randrianalisoa J.,Grenoble Institute of Technology
International Journal of Thermal Sciences | Year: 2011

The aim of the present study is to investigate the suitability of two different continuum-based approaches for the modeling of the radiative transfer in two types of foams lying in the geometric optic regime: open cell metal foams and closed cell polymer foams. The two approaches are the commonly used Homogeneous Phase Approach (HPA) and the Multi-Phase Approach (MPA) which is rather new in the field of radiative transfer. For both approaches, the radiative properties involved in their respective frameworks are determined using newly developed Ray-Tracing methods applied to 3-D meshes representing the porous structures of open cell or closed cell foams. The 3-D meshes have been obtained from X-Ray Tomography applied to real metal and polymer foams. The radiative properties determined are used to compute the transmittances and reflectances of one-dimensional slabs of foams by the two approaches. They are compared with the results of a baseline Monte Carlo simulation in order to evaluate, for the two types of foams, the suitability of each method. It appears that both approaches are globally appropriate for predicting the radiative transfer in open cell metal foams although they are not able to match exactly the directional distribution of the transmittances and reflectances. For polymer foams, the accuracy of the HPA is demonstrated whereas the MPA provides significant differences with the reference MC simulations. © 2011 Elsevier Masson SAS. All rights reserved.

Catalina T.,Technical University of Civil Engineering Bucharest | Virgone J.,Lyon Center of Thermal Science | Blanco E.,CNRS Ampere Laboratory
Renewable Energy | Year: 2011

In this article, an original multi-criteria approach is applied to multi-source systems used for the design and the choice of the optimal alternative. The high number of alternatives and potential solutions when dealing with multi-source systems require a decision support method to be implemented and easy to use. Information data on the economic variables, energy performance and impact on the environment of the systems are presently data which analysis and quantification is difficult. To deal with this high level of complexity and uncertainty, an evaluation approach is needed. The multi-criteria decision support methodology concept is described (ELECTRE III) and then applied for a case study. The decision support algorithm has its bases on the developed models and makes the outranking of possible solutions. It is also shown that multi-criteria analysis can provide a technical-scientific decision-making support that is capable to justify the clearly rank of the alternatives in the renewable energy sector. The use of multi-criteria decision aid for assessing the multi-source systems showed encouraging results and interesting insights. © 2011 Elsevier Ltd.

Obrecht C.,Électricité de France | Obrecht C.,Lyon Center of Thermal Science | Kuznik F.,Lyon Center of Thermal Science | Tourancheau B.,Laboratoire Of Linformatique Du Parallelisme | Roux J.-J.,Lyon Center of Thermal Science
Computers and Mathematics with Applications | Year: 2013

The lattice Boltzmann method (LBM) is an increasingly popular approach for solving fluid flows in a wide range of applications. The LBM yields regular, data-parallel computations; hence, it is especially well fitted to massively parallel hardware such as graphics processing units (GPU). Up to now, though, single-GPU implementations of the LBM are of moderate practical interest since the on-board memory of GPU-based computing devices is too scarce for large scale simulations. In this paper, we present a multi-GPU LBM solver based on the well-known D3Q19 MRT model. Using appropriate hardware, we managed to run our program on six Tesla C1060 computing devices in parallel. We observed up to 2.15×109 node updates per second for the lid-driven cubic cavity test case. It is worth mentioning that such a performance is comparable to the one obtained with large high performance clusters or massively parallel supercomputers. Our solver enabled us to perform high resolution simulations for large Reynolds numbers without facing numerical instabilities. Though, we could observe symmetry breaking effects for long-extended simulations of unsteady flows. We describe the different levels of precision we implemented, showing that these effects are due to round off errors, and we discuss their relative impact on performance. © 2011 Elsevier Ltd. All rights reserved.

Sanvicente E.,Lyon Center of Thermal Science | Giroux-Julien S.,Lyon Center of Thermal Science | Menezo C.,Lyon Center of Thermal Science | Bouia H.,Électricité de France
International Journal of Thermal Sciences | Year: 2013

The work presented here is an experimental study on natural convection flows in a differentially heated open channel configuration. The applications concern the free cooling of both the photovoltaic components integrated within the building envelope (double-skin configuration) and the building itself. Particular focus is given to the identification of integration configurations favorable to both heat transfer on the rear side of components and buoyancy enhancement. The test section consists of a vertical channel with two walls composed of different heating modules. In the present investigation the thermal configuration considers one wall heated uniformly while the other is not heated. We focus on the kinematic characteristics of the flow and convective heat transfer at the heated wall. A PIV system allows investigating the mean velocity field and velocity fluctuations at different levels of the channel height. The experimental procedure allows inferring the wall surface temperature, local heat transfer coefficient and local and average Nusselt numbers. The experimental evidence shows that the flow is neither really turbulent nor purely laminar for the range of Rayleigh numbers considered. Although the average characteristics of the flow seem perfectly consistent with the results obtained, changes of behavior seem to occur intermittently. © 2012 Elsevier Masson SAS. All rights reserved.

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