Stéphane Lassue

Study of solar walls — validating a simulation model

The aim of this article is to present the results of a comparative study of four different types of solar wall. These results have been obtained using a numerical simulation model. In order to validate the model, an extensive experimental study has been conducted on a composite solar wall. The first part of the article is devoted to the particular features of the four solar wall configurations, followed by a description of the experimental installation, the measurements and study of the various modes of thermal transfer necessary for the model to be validated. The third section begins with a brief presentation of the principle used to develop this model, continuing with the validation phase. The model is then used to study the energy efficiency of solar walls in different locations and under different climatic conditions. This is followed by an analysis of the way in which they release the energy supply, and their performance during the summer period. The results of this study are fundamental in helping architects or project managers to choose the best suited configuration for each type of building.

A numerical study of the melting of phase change material heated from a vertical wall of a rectangular enclosure

This article presents the first research effort of our group to formulate, implement and validate a numerical method in order to optimise the design of solar passive walls involving phase change materials (PCMs). The fusion of ice, gallium and the commercially available PCM 27 (hydrated salt), engineered by Cristopia and later embedded within an experiment unit, was studied. Comparisons against other prediction methods and experimental data for the fusion of gallium were carried out with good agreement of the solutions. The proposed enthalpy-based method is found to be excellent to predict the fusion, but still fails to reproduce adequately the exact solidification pattern measured for the PCM 27. Further research is going on to improve the model.

Non-destructive testing of a building wall by studying natural thermal signals

Abstract The behaviour of civil engineering works (structures, buildings, dams, etc.) in time is a current problem which is the subject of deep consideration and numerous research projects. These studies — which are aimed at adopting a better approach to repair, maintenance and reinforcement operations — have revealed a significant need for the development of means to diagnose and monitor structures. Many non-destructive testing techniques already exist but a major difficulty in applying them arises from the fact that they are not universal. It is therefore necessary to analyse their limits and define fields of application. Choosing a suitable technique is always a delicate process. In addition, the results obtained are generally affected by a considerable degree of uncertainty; cross tests using different techniques make it possible to improve the quality of the diagnosis. Thermal approaches are currently emerging and being developed quickly. They are typically based on infrared thermography measurements. These techniques involve a contact-free analysis and provide overall information on the structure. They are adapted to a qualitative type of research in which the prime objective is to highlight anomalies. However, it is generally complicated and difficult to make a quantitative interpretation of the results [1] . This article presents a new thermal method based on the concept of thermal impedance, which can be measured at the surface of a structure. It is adapted to a local quantitative analysis and should be used as a complement to the overall measurements taken by infrared thermography to quantify and refine the analysis.

An overview of phase change materials and their implication on power demand

Latent heat storage systems involving phase change materials (PCMs) are becoming more and more attractive for space heating and cooling in buildings, solar applications, off-peak energy storage, and heat exchanger improvements. This paper presents an introduction to previous works on thermal energy storage with respect to these applications. It focuses mostly on applications involving a reduction of electric power consumption. It is therefore more likely to be appreciated by those who would like an introduction to the topic rather than pin-point information on novel aspect of the subject.

A Consistent Interpolation Function for the Solution of Radiative Transfer on Triangular Meshes, II—Validation

This article presents selected problems used to assess the validity and usefulness of a first-order skew, positive coefficient, upwind scheme (SPCUS) applied to radiative transfer. This particular procedure could be incorporated in several discretization methods such as finite-volume, finite-element, or control-volume finite-element methods for the prediction of radiative transfer in participating media. The suggested scheme has been validated by application to several basic two-dimensional test problems, acknowledged by the radiative heat transfer community, and its performance has proven to be good.

A skew upwinding scheme for numerical radiative transfer

This paper exhaustively presents a skewed upwinding procedure for application to finite volume methods (FVMs), finite element methods (FEMs) or control volume finite element methods (CVFEMs) in the context of radiative heat transfer problems involving participating media. The proposed scheme is based on the application of sound physical arguments. Through its basis of development, this scheme: (1) yields fast convergence of the algorithm; (2) inherently precludes the possibility of computing negative coefficients to the discretized algebraic equations; (3) reduces false scattering (diffusion); (4) is relatively insensitive to grid orientation; and (5) produces solutions completely free from undesirable oscillations. Theses attributes renders the scheme attractive, especially in the context of combined modes of heat transfer and fluid flow problems for which CPU time is a major concern. The suggested first-order skew upwind (SU) scheme has been validated by application to several basic two-dimensional test problems, acknowledged by the radiative heat transfer community: its performance has proven to be excellent. However, the validation is discussed for a few problems only to avoid making this contribution overly lengthy. NOMENCLATURE w f f , ,   Weighting functions m n G Geometric quantity, [sr]  J  Flux of  (radiative) per unit solid angle, [W∙m∙sr] M Midpoints of element edges N Number of panels defining a control volume, Node of an element n  Unit vector normal to a surface O Centroid of an element p Control volume surface (panel)  S Rate of volumetric generation of  I S Source of radiative intensity Greek symbols  Dependent variable Subscripts b Blackbody B Boundary l Element edge n Control volume surface (panel) P Node of reference r Radiation or Reference point  Integer function: n n  ) (  , n  = 1, 2, 3; and 3 ) (   n n  , n  = 4, 5 Superscripts → Vectorial quantity ′ Incoming direction m Discrete direction

Numerical Method Approach to Calculate Earth-Energy of Earth-Pipe-Air Heat-Exchanger for Winter Heating

A numerical method is proposed to calculate earth-energy of earth-air-pipe heat exchanger during winter heating. The proposed method is based on using numerical computation developed on Scilab a free open source software. Authors showed the comparison between their simple numerical model called Heatground with the well-known Amitrano results. The comparison is given for different parameters as the airflow, the pipe length, the depth of buried pipe, the pipe diameter.

TURBULENT FORCED CONVECTION IN A HORIZONTAL CHANNEL WITH RECTANGULAR OBSTACLE

This paper presents a numerical investigation of turbulent forced convective f low in a horizontal channel filled with rectangular obstacles located on the lower surface. An exchanger isothermal test plate is embedded in the lower wall, in the fully developed region of the flow. Immediately above this plate, on the upper surface, a black coated isothermally heating resistance facing downwards is installed. This perfectly absorbing surface provides a controlled radiative heat flux on the lower test plate. In this study, custom-built tangential gradient fluxmeters (TGFM) are used to provide local measurements of convective heat transfer so as to validate the numerical predictions. Then, parametric studies are carried out. The profiles for the heat flux densities are presented for different Reynolds numbers in the flow direction along the cold isothermal lower plate. The influence of the presence of an obstacle on the heat flux densities is also investigated. All numerical predictions are carried out with Fluent, previously calibrated against benchmark problems and experimental measurements. In the paper, special emphasis is given in the systematic comparison between experimental and numerical results.

Simulation of a Composite Solar Wall with the Finite Difference Method

The passive solar walls use the solar energy to heat the buildings. The composite wall solar collector system consists of a glazing, a massive wall and an insulating wall. Thanks to the big thermal resistance of the insulating wall, there is little inverse thermal flux that crosses from the interior to the exterior. In this paper, the thermal performances of a composite Trombe-Michel wall are studied. The simulation is developed with the finite difference method (FDM). The model of this simulation was validated by experimentation. The parameters of the composite wall are based on a previous experimental study. The meteorological data are one of Carpentras in France for 10 days from February 26 to March 7. The results of the simulation show that the composite wall has a good performance in cold and/or cloudy climate