Rached Ben Younes

Modeling of Unsteady Turbulent Flow in a Buried Co-Axial Exchanger—The Use of Green's Functions Theory

This work presents an analytical and numerical investigation of the heat transfer problem of turbulent flow under forced convection in a buried co-axial exchanger. A hybrid model consisting of a finite element method at the boundary (BEM) for the heat transfer problem on the boundary, and a finite volume method (FVM) to solve the turbulent flow inside solves this complicated problem. The development of the BEM method is based on Greens functions theory. The mathematical model employed makes a scientific contribution to a similar practical situation. The results can be of great interest for industrial processes requiring the estimation of the heating time necessary to obtain steady states. Essentially, the axial evolution of the heat transfer coefficient versus Reynolds number and transfer duration is treated here. The temperature field and the heat flux density at the wall are also investigated.

H2-broadening, shifting and mixing coefficients of the doublets in the ν2 and ν4 bands of PH3 at room temperature

ABSTRACT The broadening, shifting and mixing coefficients of the doublet spectral lines in the ν2 and ν4 bands of PH3 perturbed by H2 have been determined at room temperature. Indeed, the collisional spectroscopic parameters: intensities, line widths, line shifts and line mixing parameters, are all grouped together in the collisional relaxation matrix. To analyse the collisional process and physical effects on spectra of phosphine (PH3), we have used the measurements carried out using a tunable diode-laser spectrometer in the ν2 and ν4 bands of PH3 perturbed by hydrogen (H2) at room temperature. The recorded spectra are fitted by the Voigt profile and the speed-dependent uncorrelated hard collision model of Rautian and Sobelman. These profiles are developed in the studies of isolated lines and are modified to account for the line mixing effects in the overlapping lines. The line widths, line shifts and line mixing parameters are given for six A1 and A2 doublet lines with quantum numbers K = 3n, (n = 1, 2, …) and overlapped by collisional broadening at pressures of less than 50 mbar.

Optimization of thermal conductivity in composites loaded with the solid-solid phase-change materials

Abstract This work focuses on identifying the thermal conductivity of composites loaded with phase-change materials (PCMs). Three configurations are studied: (1) the PCMs are divided into identical spherical inclusions arranged in one plane, (2) the PCMs are inserted into the matrix as a plate on the level of the same plane of arrangement, and (3) the PCMs are divided into identical spherical inclusions arranged periodically in the whole matrix. The percentage PCM/matrix is fixed for all cases. A comparison among the various situations is made for the first time, thus providing a new idea on how to insert PCMs into composite matrices. The results show that the composite conductivity is the most important consideration in the first case, precisely when the arrangement plane is parallel with the flux and diagonal to the entry face. In the present work, we are interested in exploring the solid-solid PCMs. The PCM polyurethane and a wood matrix are particularly studied.