Hybrid formulation and solution for transient conjugated conduction–external convection

This work presents a hybrid numerical–analytical solution for transient laminar forced convection over flat plates of non-negligible thickness, subjected to arbitrary time variations of applied wall heat flux at the fluid–solid interface. This conjugated conduction–convection problem is first reformulated through the employment of the coupled integral equations approach (CIEA) to simplify the heat conduction problem on the plate by averaging the related energy equation in the transversal direction. As a result, an improved lumped partial differential formulation for the transversally averaged wall temperature is obtained, while a third kind boundary condition is achieved for the fluid from the heat balance at the solid–fluid interface. From the available steady velocity distributions, a hybrid numerical–analytical solution based on the generalized integral transform technique (GITT), under its partial transformation mode, is then proposed, combined with the method of lines implemented in the Mathematica 5.2 routine NDSolve. The interface heat flux partitions and heat transfer coefficients are readily determined from the wall temperature distributions, as well as the temperature values at any desired point within the fluid. A few test cases for different materials and wall thicknesses are defined to allow for a physical interpretation of the wall participation effect in contrast with the simplified model without conjugation.Indisponível

Mechanical and thermal characterization of a beet pulp-starch composite for building applications

This work shows the making of a new bio-based material for building insulation from sugar beet pulp and potato starch. The material is both lightweight and ecofriendly. The influence of starch/ sugar beet pulp ratio (S/BP) is studied. Four binder mass dosages are considered, 10, 20, 30 and 40% (relative to the beet pulp). Samples are characterized in terms of absolute and bulk density, compressive and flexural strength, as well as thermal properties (thermal conductivity and thermal inertia). The compressive strength increases linearly with the S/BP mass ratio to reach 0.52 MPa and the compressive strain is 30%. The thermal conductivity is to around 0.070 W/m. K. The results obtained shows that increasing starch amount tends to decrease composite porosity but increases thermal conductivity and mechanical properties. Depending on the starch content, beet pulp composites have a good thermal and can be used as building materials

Etude des interactions thermiques fluide-structure par un couplage de codes de calcul

Dans cette thèse, nous présentons le couplage thermique entre un code Navier-Stokes de type volumes finis avec un code de conduction de type éléments finis. Ce couplage a été réalisé au moyen de la bibliothèque informatique MpCCI. Le couplage entre les deux codes est effectué à l'interface par l'intermédiaire de conditions de raccord ou conditions aux limites thermiques. Ces conditions font intervenir des coefficients de couplage à l'interface et associés au milieu fluide et au milieu solide. Dans le cadre du couplage thermique en régime permanent, l'étude de la stabilité des conditions de raccord permet de définir les coefficients de couplage optimaux en terme de stabilité et de convergence. La méthode de couplage a été validée sur un cas élémentaire et sur des configurations industrielles. La deuxième partie est consacrée à l'étude du couplage en régime transitoire. Un algorithme de couplage original a été mis en oeuvre et répond à un certain nombre de besoins industriels. Cet algorithme consiste à filtrer les hautes fréquences, ce qui revient à considérer le fluide comme stationnaire à chaque instant de couplage. L'algorithme instationnaire a été validé expérimentalement sur le cas d'un écoulement sur une plaque plane.In this thesis, a conjugate heat transfer procedure between a finite-volume Navier-Stokes solver and a finite-element conduction solver is presented. The coupling has been performed through the MpCCI library and thermal boundary conditions, on the coupling surfaces. These conditions define two coupling coefficients connecting both the fluid and the solid domain. The first part describes the fluid-solid thermal steady state coupling. The stability analysis of the boundary conditions highlights the most efficient coefficients in terms of stability and convergence. As a consequence, a steady state algorithm has been implemented. It corresponds to an iterative procedure between the Navier-Stokes solver and the heat conduction solver. Thanks to the MpCCI library, the thermal quantities (heat flux, temperature) are exchanged between each solver until the thermal steady state is reached in both the fluid and the solid domains. This coupling method has been validated on a simple case, namely a flat plate, and two industrial cases, a flow around a turbine blade and an effusion cooling system. The second part of this thesis is dedicated to the fluid-solid thermal transient coupling. An original coupling algorithm applied to industrial problems is described. This algorithm corresponds to an iterative procedure between a steady state fluid description and a transient solid description. The experimental setup consists of an interaction between a steady flowfield and a transient heat conduction in a flat plate.REIMS-BU Sciences (514542101) / SudocSudocFranceF

The Mechanical Fracture of a Railway Bogie under Cyclic Loading by Ansys

The main objective this study has been to modeling a train bogie in order to highlight some flaws. Indeed, during the operation, premature deterioration of the bogie axles was observed. The purpose of this model is to present a numerical model to predict the mechanical behavior under different cyclic form of stress. The numeric and geometric model will be directed by Ansys software

Effects of humidification process on thermal performance of floor heating systems: An experimental study

International audienc

Experimental and numerical investigation of the thermal inertia of sugar-beet-pulp/starch based bricks enhanced with phase change materials

Due to environmental concerns, bio-based materials are being increasingly investigated and used in buildings. In general, the density of these materials, and thus their thermal inertia, is low. Thermal inertia can be beneficial for reducing the energy use of buildings by damping indoor temperature fluctuations or by reducing and delaying incoming (solar) heat through the façade.This study explores the thermal inertia of regular-sized bricks made of a sugar-beet-pulp/starch mixture (BP/S), and with 17 circular holes inside. The holes were filled either with the BP/S mixture, with air, with a stabilised phase change material (PCM) gel or with a salt-hydrate based PCM. The brick was insulated on all sides but one. Two series of experimental measurements were performed: 1.) a heating film placed at the back (insulated) side of the brick heated the brick until steady-state conditions were reached; 2.) the heated brick was then passively cooled down to ambient temperature by cutting the power to the heating film. Numerical simulations of these experimental measurements were also modelled using the COMSOL Multiphysics® software. In addition, simulations were run to study the thermal inertia of a full brick wall made out of 1 layer and of 4 layers of the BP/S brick with and without PCM, exposed to a combination of a sinusoidal outdoor air temperature fluctuation with an imposed radiation flux on the outdoor surface, representing summer conditions.The results show that the brick in which the holes were filled with phase change material had a slower temperature response and thus higher thermal inertia than the bricks in which the holes were filled with BP/S or with air. The salt-hydrate based PCM with the higher latent heat of fusion led to the slowest temperature response and highest thermal inertia. Furthermore, the calculated simulations could accurately reproduce the experimental measurements. Applying PCM in thick walls (40 cm) made of BP/S bricks however hardly affects the temperature amplitude damping and time delay of the complete wall. The addition of PCM therefore is only effective for thinner walls (10 cm)

TRANSIENT CONJUGATED CONDUCTION -EXTERNAL CONVECTION WITH FRONT FACE IMPOSED WALL HEAT FLUX

ABSTRACT This work presents hybrid numerical-analytical solutions for transient laminar forced convection over flat plates of non-negligible thickness, subjected to arbitrary time variations of applied wall heat flux at the interface fluid-solid wall. This conjugated conduction-convection problem is first simplified through the employment of the Coupled Integral Equations Approach (CIEA) to reformulate the heat conduction problem on the plate by averaging the related energy equation in the transversal direction. As a result, a partial differential formulation for the average wall temperature is obtained, while a third kind boundary condition is achieved for the fluid in the heat balance at the solid-fluid interface. From the available velocity distributions, the solution method is then proposed for the coupled partial differential equations, based on the Generalized Integral Transform Technique (GITT) under its partial transformation mode, combined with the method of lines implemented in the Mathematica 5.2 routine NDSolve. INTRODUCTION New perspectives in convective heat transfer analysis have been opened by hybrid numerical-analytical approaches that attempt to incorporate the advantages associated with the classical analytical approaches, while offering sufficient flexibility for dealing with more than just model equations, and aiming at providing a feasible alternative to the purely discrete approaches in a significant range of applications. One such hybrid approach is the so-called Generalized Integral Transform Technique (GITT) [1][2][3][4][5], which extends the classical integral transform analytical approach towards the hybrid analysis of linear and nonlinear diffusion and convectiondiffusion problems, and has been applied to a number o

Sunspot analysis under varying conditions climate: Distributed radiation on cooling floor and its effect on dynamic thermal behaviour

International audienc

Experimental study on the effects of a moving sun patch on heating radiant slabs: The issue of occupants’ thermal comfort

International audienc

Determination des diffusivites thermiques des materiaux composites par methode flash bidirectionnelle

SIGLEINIST T 76567 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc