Jalila Sghaier

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.

Low-Pressure Superheated Steam Drying of a Porous Media

The present study aimed at developing a theoretical model to simulate the drying process of a porous particle in low-pressure superheated steam drying (LPSSD). Spherical and porous particles of ceramic and coal are used as the model material in this work. Experimental data for ceramic and coal particles reported in the literature were used for the model validation. The effect of particle thermophysical properties and operating variables is tested. Results showed that a decrease in pressure and an increase in the fluid temperature during drying lead to an elevation of mass flux during the constant rate period (CRP) and the falling rate period (FRP) of the drying process. Moreover, this increase in mass flux is more significant for particles with the highest effective porosity. Thus, we conclude that decreasing pressure and increasing the drying fluid temperature reduce the mass flow.

Low-Pressure Superheated Steam Drying—Vacuum Drying of a Porous Media and the Inversion Temperature

This article deals with comparative study of low-pressure superheated steam drying (LPSSD) and vacuum drying using coal particles as model material. The focus is made on the inversion temperature, which means that the drying rate in the two drying processes becomes equal. This temperature is of great importance because it allows the choice of drying agent for given operating conditions. The effect of external and internal parameters on the drying kinetics and the inversion temperature were investigated. Several studies have shown discrepancies of inversion temperature values basing on the constant rate period (CRP) and the falling rate period (FRP). This work points out gaps in these temperature values using the two calculation methods.

In-Line Monitoring of Drying Kinetics of a Fixed Bed Using an Electrical Imaging Technique

The main objective of this study is to determine the drying kinetics of a fixed bed composed of porous particles using the electrical capacitance tomography (ECT) technique. This technique is an imaging modality in which the permittivity distribution inside an object is computed using capacitive measurements from the boundary of the object and mathematical algorithms. An experimental convective drying device equipped with an electrical tomography system is built. An existing relationship between the average moisture content and the dielectric permittivity of the product is determined experimentally from a calibration of the moisture content during the drying process. The tomograms of normalized permittivity distribution are presented. As a result, the distribution of the moisture content of the packed bed is then determined. The drying kinetics of the silica gel is drawn, and the various stages of the drying process are identified. The thermal behavior during the drying process at different levels of the granular bed has been established. The results show the efficiency of electrical tomography technique. This technique can be used to find other parameters such as the evolution of the porosity of the medium during drying as well as other parameters.

Determination of porosity from shrinkage curves during sintering of granular materials

ABSTRACT This paper investigates the implementation of an analytical model to determine the porosity of a granular material during reactive and nonreactive sintering. A graphical interpretation of this model is proposed to calculate the porosity by comparing the experimental shrinkage curve with the ideal one. For the nonreactive sintering, some examples have been taken from the literature to illustrate the application of this method for two granular materials (alumina and zircon). In the case of reactive sintering, we have used our experiments to study the sintering behavior of magnesium hydroxide. The shrinkage curve was determined by dilatometer and the porosity was measured by helium pycnometer. The comparison revealed that the porosity calculated from the model is fully consistent with the porosity measurements in the both cases.

FINITE ELEMENT SIMULATION OF TEMPERATURE AND CURRENT DISTRIBUTIONS DURING SPARK PLASMA SINTERING (SPS).

Souhir Mankai 1 , Jamel Madiouli 1,2 and Jalila Sghaier 1 . 1. Department of Energy Engineering, National Engineering School of Monastir, University of Monastir, 5019 Monastir, Tunisia. 2. Mechanical Engineering Department, Faculty of Engineering, King Khalid university, Abha, KSA. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Falling Film in a Heated Micro-channel

The main objective of this work is to study experimentally and numerically a falling film in a micro-channel. The experimental section involves in creating a temperature gradient within the liquid, while monitoring the temperature using an infrared camera. A numerical model is established and solved by a semi-analytical method called the thermal quadrupole method. Finally, we conclude with a comparison between the experiments and the numerical study.

Experimental study of the convective heat transfer coefficient in a packed bed at low Reynolds numbers

An experimental study to evaluate the convective heat transfer coefficient in a cylindrical packed bed of spherical porous alumina particles is investigated. The task consists in proposing a semi-empirical model to avoid excessive instrumentation and time consumption. The measurement of the bed temperature associated to a simple energy balances led to calculate the gas to particle heat transfer coefficient using a logarithmic mean temperature difference method. These experiments were performed at atmospheric pressure. The operating fluid is humid air. The gas velocity and temperature ranged from 1.7-3 m/s and 120-158 degrees C, respectively. The data obtained was compared with the correlations reported in the literature. It is shown that the proposed model is in reasonable agreement with the correlation of Ranz and Marshall. Despite, many researches on experimental investigations of heat transfer coefficient in packed beds at low and average temperature are proposed, few studies presented calculation of convective heat transfer coefficient at high temperature (above 120 degrees C). A possible application of the proposed model is drying and combustion.