Habib Sammouda

A Method for Determination of Porosity Change from Shrinkage Curves of Deformable Materials

Among the numerous models developed to predict the shrinkage of materials during drying, the model developed by Katekawa and Silva [1] gives a general relationship between shrinkage and porosity with a limited number of parameters such as initial density of the wet product, true density of the solid phase, and true density of the liquid phase. A graphical interpretation of this model is proposed to visualize the changes of porosity by comparing the experimental shrinkage curve with an ideal one. Four examples are given to illustrate the applicability of the model using different materials (carrot, banana, xerogel, and sludge), two types of the solvent (water, isopropanol), and two drying technologies (convective drying, freeze drying). Porosity calculations were found to be very consistent and complementary with porosity measurements.

Non-contact Measurement of the Shrinkage and Calculation of Porosity During the Drying of Banana

A novel non-intrusive technique (stereo-correlation) was used to determine the apparent volume of a banana in convective drying condition. The volume was calculated using the 3D Digital Image Correlation method (3D-DIC), which provides the 3D shape of the banana during drying. The combination of this technique and mass measurement allows the calculation of the porosity using the model of Katekawa and Silva[ 1 ] and the graphical interpretation presented by Madiouli et al.[ 2 ] The banana shows an ideal shrinkage at the beginning of drying but stops shrinking at low moisture content, thus increasing the porosity up to 30–35%. The comparison of the experimental shrinkage and the calculated porosity with the experiments deduced from the literature enables us to conclude the effectiveness of the 3D-DIC technique as well as the porosity calculation model.

Effect of Surface Radiation on the Natural-Convection Stability in a Two-Dimensional Enclosure with Diffusely Emitting Boundary Walls

A transient interaction of natural convection with thermal radiation of gray surfaces of a square cavity filled with air is investigated numerically. The effect of radiation on the flow field, temperature distribution, and onset of oscillatory instability of flow is predicted. A complete study of stability of some value of Rayleigh number is performed for emissivity ε varying from 0 to 1. The finite-element and the fractional step time methods are used to solve the two-dimensional time-dependent Navier-Stokes and energy equations. The results are reduced in terms of the time-series averages Nusselt number and velocity component near vertical walls and at the center of the cavity. The Grashof number is varied up to 5 × 10 7 to determine the new critical values of regime flow for different values of emissivity.

Poiseuille Rayleigh-Benard problem in a horizontal duct of finite length in streamwise direction: stability analysis

This paper deals with mixed convection within a rectangular duct heated from below, which is named Poiseuille-Rayleigh-Benard (PRB) problem. In particular, we study the transition towards transverse 2D-rolls appearing at low Reynolds. The effect of longitudinal confinement on the PRB stability problem and to numerically highlight the effect of the existing of thermal input area before the settling of the transverse 2D-rolls. The supercritical Rayleigh for the onset of convection is predicted numerically, based on the linear stability analysis. Since the flow is confined, the aspect ratio effect is taken into account and analysed. It is demonstrated that, the critical Rayleigh number depends on the Peclet number and the length of the domain and tends toward the classical natural convection critical Rayleigh value ad infinitum.

Effect of acetylation and additive on the tensile properties of wood fiber–high-density polyethylene composite:

The wood plastic composites studied in this work are composed of high-density polyethylene matrix and Pinus pinaster wood fibers. Despite some interesting intrinsic properties, this wood plastic composite has limited mechanical properties because of the incompatibility between the polar hydrophilic fibers and the non-polar hydrophobic matrix. In this study, the effects of maleic anhydride-modified polyethylene additive, of carbon chains grafted by acetylation and of wood fiber contents on the tensile mechanical properties of the wood plastic composite were studied. Tensile tests were carried out using digital image correlation as an intrusiveness and robust method for strain measurements. Results showed first that the addition of wood fibers made the wood plastic composite stiffer but less flexible. Acetylation improved the interfacial adhesion properties: the Young modulus was increased and a lower strain at failure was reported. The coupling agent also increased the compatibility but mainly in the case where there was no grafted chain. With regard to the carbon chains, the number of grafts improved the elastic properties while their length did not appear to have any influence. Finally, a scanning electron microscope was used to characterize the post-mortem morphology of the fracture surfaces, the results of which supported the observations obtained from the tensile mechanical properties.

Analytical and Numerical Solutions for Natural Convection in a Shallow Cavity Filled with Two Immiscible Fluids: Shear Stress Action

A shallow horizontal cavity filled with two layers of nonmiscible fluids, is studied both analytically and numerically. The upper free surface of the layer is subject to a shear stress. The analytical solution, based on the parallel flow approximation, is found to be in good agreement with a numerical solution. The existence of both natural and antinatural flows is demonstrated. Indeed, the critical Rayleigh number for the onset of motion is dependent on the side heating intensity. Multiple steady state solutions are possible in a range of the rate of fluids dynamics viscosity that depends strongly on the upper fluid one.

Natural convection in shallow cavity filled with nanofluids taking into account the Soret effect

Natural convection, in a shallow horizontal cavity filled with nanofluids, is studied both numerically and analytically. The horizontal surface of the enclosure are submitted to heat on the bottom and cooled on the upper. The vertical walls are subject to variable heat fluxes. The nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration. The analytical solution, based on the parallel flow approximation, is found to be in good agreement with a numerical solution. The existence of both natural and antinatural flows is demonstrated. Indeed, the critical Rayleigh number for the onset of motion is dependent on the concentration of nanoparticles and their nature.

Performance comparison between commercial mono-crystalline and poly-crystalline PV modules under LCPV conditions

In this work, a theoretical study is presented in the aim to evaluate the performance of two different types of silicon PV modules under Low Concentration Photovoltaic LCPV conditions. For this purpose, this paper describes a mathematical LCPV model implanted in MATLAB/Simulink® software. Based on the numerical results, we demonstrate and compare the limitation of using commercial mono-crystalline and poly-crystalline PV modules. We perceive from the characteristic parameters variation, the necessity of using a cooling system to improve the PV modules efficiency.

Simulation and comparison of P&O and fuzzy logic MPPT techniques at different irradiation conditions

In the last decades, photovoltaic technology has become more employed by the industry, labs and universities, due its many benefits such as the exploitation and increasing of the solar energy conversion efficiency. In this paper, we will study and compare the performances of MPPT techniques control system consisting a PV system under different conditions of irradiation in the order to minimize the loss of energy provided by the PV module and to improve energy efficiency. This control is carried out by implementing of the MPPT based on Perturb and Observe algorithm (P&O) and Fuzzy Logic algorithm (FL) under MATLAB/Simulink® environment. Results of simulation showed that the FL controller exhibits a much better behavior than P&O controller.

Performance comparison of silicon PV module between standard test and real test conditions

The purpose of the work was to evaluate and compare the performances of silicon PV module under standard test and real test conditions. This paper provides a detailed analytical model for characterizing the electrical performance of silicon photovoltaic module. The simulation results have been performed in MATLAB/Simulink® environment. We proved that difference between the standard test and real test conditions, is attributed to various factors including effect of temperature variations and consequently some adjustments should be considered in electrical parameters to improve the PV module efficiency.