Key words: Stratified fluid layers; Salt–gradient pond; Hydrodynamic, heat and mass transfer; Numerical simulation; Finite–volume method; Transient regime.

Abstract: In this paper, we studied numerically the effect of thermal Rayleigh number and the buoyancy ratio on the transient fluid flow, heat and mass transfer in a salt–gradient pond (SGP) wherein the layers of fluid are stratified. The objective of this numerical work is to give a fine knowledge of the hydrodynamic, thermal and solute characteristics during the storage of thermal energy in a SGP. The pond is filled with a mixture of salt and water to constitute three zones with different salinities: Upper Convective Zone (UCZ), Non–Convective Zone (NCZ) and Lower Convective Zone (LCZ). Water is heated by a heat serpentine covered the bottom of the pond. The transport equations for continuity, momentum, thermal energy and mass transfer are solved by a finite–volume method to provide
the fields of temperature, concentration and velocities in a SGP in transient regime. Simulations are performed for several values of both the thermal Rayleigh number in the range between 104 and 107, and the buoyancy ratio in the range between 0 and 10, whose influence on the temporal evolution of velocities, temperature and concentration distributions in a SGP are analyzed and discussed. The flow structure shows the generation of convective cells in the lower and upper zones of the pond, and permits to explain the slight increase of temperature in the UCZ and the important rise of temperature in the LCZ. In addition, this work shows the importance of the buoyancy ratio to preserve the high temperature in the bottom of the pond and to reduce the phenomena of heat and mass transfer across the NCZ.

Key words: Thermal conductivity, liquids, coaxial cylinders method.

Abstract: Thermal conductivity is an important thermophysical property; its value is required in all heat transfer calculations. This study deals with the elaboration of theoretical principles of measurement and with the  realization of an apparatus based on the coaxial cylinders method allowing us to obtain, simply, the thermal conductivity of liquids. In this work, we have measured the variation of thermal conductivity versus temperature of some liquids like ethanol and ethylene glycol. Thermal conductivities of some other liquids are measured at 25°C. The obtained results have been compared with literature data and they present a good agreement with them.

Key words: CFD modeling, fire source, smoke.

Abstract: In this study, the spread of fire smoke in a room that contains a heat source is simulated numerically using the CFD code Fluent. We’re studying essentially the heat transfer between two fluids of different densities, typically hot and cold air in a space containing a heat source. A simple geometry is adopted, consisting of a room with a door that plays the role of inlet-outlet for the fluid. A volumetric heat source was placed at the centre of the room. As the flow is turbulent and buoyant we used the standard k-e model together with the Boussinesq approximation. The results of the mathematical model are validated with available  experimental data. These results give a detailed description of the flow studied; the distribution of velocity and temperature are reasonably predicted. Following this conclusion, the mathematical model adopted can provide a knowledge base for the evaluation of thermal and dynamic parameters in the case of a fire in the studied configuration, and can be extended to a more complex geometry. It is concluded that this work illustrates the ability of the CFD approach in the study of heat transfer between tow fluids of different densities, however it would be extended and improved by studying the effect of various geometric parameters and thermal diffusion of the heat in a confined environment.

Key words: Numerical method, Entropy generation, porous media, mixed convection.

Abstract: The numerical analysis of two-dimensional laminar mixed convection flow through a channel filled with saturated porous media under thermal gradient is investigated. The Darcy-Brinkman model is employed. The conservation equations are solved using a Control Volume Finite Element Method. Total entropy generation is investigated at global and local levels by varying the porosity from 1 to 0.2 at fixed values of Ra= 10⁴, Re =10, Br*=10^-3. Results show the existence of dissipative structures.

Key words: Fluid-structure, finite element, modal reduction, double panel, sound transmission.

Abstract: This paper presents a finite element model for sound transmission analysis through a double panel inserted in an infinite baffle. The proposed model is derived from a multi-field variational principle involving structural displacement and acoustic pressure inside the fluid cavity. To solve the vibro-acoustic problem, the plate displacements are expanded as a modal summation of the plate's eigenfunctions in vacuo. Similarly, the cavity pressure is expanded as a summation of the modes of the cavity with rigid boundaries. Then, an appropriate reduced-order model is introduced. The structure is excited by a plane wave at the source side. The radiated sound power is calculated by means of a discrete solution of the Rayleigh Integral. Fluid loading is neglected. An example of the normal
sound transmission loss of a double aluminum panel is shown. This example illustrates the accuracy and the versatility of the proposed reduced order model, especially in terms of prediction of sound transmission.