Study of the Interaction Between Water and Gelidium sesquipedale (Rhodophyta): Part II: Kinetic of the Drying Process

Abstract

The study of drying of red alga (Gelidium sesquipedale, Rhodophyta), with initial sample masses varying from 1 to 10 g, was carried at different temperatures 30 -80 °C. The experimental drying curves show a slight effect of the initial mass. Two types of curves are obtained: those at temperatures below 50 °C are fitted into straight line according to an interfacial progression process in cylindrical symmetry. Those of high-temperature drying (50 < θ < 80 °C), are perfectly parabolic and show that the kinetic regime is controlled by the three-dimensional diffusion according to the Jander equation. The two types of water molecules identified were also highlighted during the drying kinetics process. The apparent activation energy of the strongly bounded water (20%) is about 36.25 kJ·mol -1 , and that of the wetting water is in the range of 47.68 kJ·mol -1 .

Drying of Gelidium sesquipedale (Rhodophyta) Under Microwave Irradiation: Study of Thermal and Kinetic Aspects of the Drying Process

“…The comparison of these results with those obtained during drying by conventional thermally conducted at atmospheric pressure at different temperatures ranging from 30 to 80 °C with different initial sample masses (Hnini et al, 2014) shows that:  The drying time by conventional heating is greater than the drying time under microwave irradiation which corresponds to a gain in energy.  During the conventional heating, the initial sample mass has a significant effect on the kinetic as well as on the duration of the drying process.…”

“…Thermal aspect under microwave irradiation of a sample of Gelidium sesquipedale. Curves of temperature changes for a sample of initial mass m 0 = 10 g As described in our previous work (Hnini et al, 2014), the variation of rate of progress α with time follows a differential law of the form:…”

“…To determine the kinetic regime that controls the drying process under microwave irradiation, we use kinetic functions which are widely used in heterogeneous kinetic processes for the determination of isothermal and non-isothermal reaction mechanisms (Hnini et al, 2014). Indeed, two approaches were discussed to describe the shapes of the experimental curves.…”

“…Figure 3 illustrates the variation of the rate of progress of drying as a function of time for initial masses ranging from 10 to 25 g. The rate progress α is defined as the ratio of the mass of water desorbed at time t and that desorbed at the end of drying (Hnini et al, 2014):…”