Papers by thouraya ghnimi
Journal of Applied Phycology, Mar 15, 2019
The current study deals with an innovation in the hot air convective drying process consisting of... more The current study deals with an innovation in the hot air convective drying process consisting of the application of two consecutive drying steps. Temperatures ranging between 60 and 80 C for times between 200 and 600 s were applied for the first stage, and from 40 to 80 C for the second stage. Salvia officinalis, an aromatic, medicinal Mediterranean plant with remarkable antioxidant properties, was selected for this study. A management of the process regarding the antioxidant capacity of S. officinalis extracts and energy consumption was carried out: (i) artificial neural networks were applied to model the evolution of the antioxidant capacity and moisture content of the product in the drying process; (ii) a genetic algorithm and a multiobjective genetic algorithm were selected to optimize the drying process, considering the antioxidant capacity and/or the energy consumption in the objective function. The results showed that the optimum values depended, logically, on the controllable variables values (hot air temperatures and drying times), but also on the uncontrollable variable values (room air temperature and relative humidity and the product's initial mass and moisture content).
Heat and Mass Transfer, Sep 5, 2018
The aim of this work was to investigate the energy efficiency of infrared radiation drying (label... more The aim of this work was to investigate the energy efficiency of infrared radiation drying (labeled IR) and hot air drying (labeled HA) of spirulina assisted by capillary drainage (labeled DC). Capillary drainage effect was introduced by a porous material (filter paper) placed under a thin layer of spirulina biomass of 3 mm thickness. Infrared drying experiments were performed using a laboratory IR-30 moisture analyzer while convective drying experiments were realized in a pilot-scale drying tunnel. The spirulina was dried at two initial moisture contents on dry basis; 5 kg/kg and 7 kg/kg. For both infrared and convective processes, the drying temperature range was 50 to 80°C and the air velocity was 0.5 m/s. The air humidity was not controlled but calculated for each temperature from the dry and wet bulb temperatures. The drying kinetic coefficients were identified by fitting the falling rate drying period data by Lewis semi-empirical model. According to our results, the capillary drainage provided a real possibility to dry faster and thus reduces the energy consumption for both infrared and convective drying processes. The time reduction percentage, averaged over the range of the operating conditions, was around 60% for infrared drying and 40% for convective drying. Moreover, the mean maximum drying rate was much higher for IR-DC drying (2.091.10 −3 kg/kg s −1) than HA-DC drying (1.115.10 −3 kg/kg.s −1). As concerns, the kinetic drying coefficient, this parameter was significantly increased by the presence of the porous material essentially for infrared drying.
Heat and Mass Transfer, 2018
The aim of this work was to investigate the energy efficiency of infrared radiation drying (label... more The aim of this work was to investigate the energy efficiency of infrared radiation drying (labeled IR) and hot air drying (labeled HA) of spirulina assisted by capillary drainage (labeled DC). Capillary drainage effect was introduced by a porous material (filter paper) placed under a thin layer of spirulina biomass of 3 mm thickness. Infrared drying experiments were performed using a laboratory IR-30 moisture analyzer while convective drying experiments were realized in a pilot-scale drying tunnel. The spirulina was dried at two initial moisture contents on dry basis; 5 kg/kg and 7 kg/kg. For both infrared and convective processes, the drying temperature range was 50 to 80°C and the air velocity was 0.5 m/s. The air humidity was not controlled but calculated for each temperature from the dry and wet bulb temperatures. The drying kinetic coefficients were identified by fitting the falling rate drying period data by Lewis semi-empirical model. According to our results, the capillary drainage provided a real possibility to dry faster and thus reduces the energy consumption for both infrared and convective drying processes. The time reduction percentage, averaged over the range of the operating conditions, was around 60% for infrared drying and 40% for convective drying. Moreover, the mean maximum drying rate was much higher for IR-DC drying (2.091.10 −3 kg/kg s −1) than HA-DC drying (1.115.10 −3 kg/kg.s −1). As concerns, the kinetic drying coefficient, this parameter was significantly increased by the presence of the porous material essentially for infrared drying.
Journal of Applied Phycology, 2019
The current study deals with an innovation in the hot air convective drying process consisting of... more The current study deals with an innovation in the hot air convective drying process consisting of the application of two consecutive drying steps. Temperatures ranging between 60 and 80 C for times between 200 and 600 s were applied for the first stage, and from 40 to 80 C for the second stage. Salvia officinalis, an aromatic, medicinal Mediterranean plant with remarkable antioxidant properties, was selected for this study. A management of the process regarding the antioxidant capacity of S. officinalis extracts and energy consumption was carried out: (i) artificial neural networks were applied to model the evolution of the antioxidant capacity and moisture content of the product in the drying process; (ii) a genetic algorithm and a multiobjective genetic algorithm were selected to optimize the drying process, considering the antioxidant capacity and/or the energy consumption in the objective function. The results showed that the optimum values depended, logically, on the controllable variables values (hot air temperatures and drying times), but also on the uncontrollable variable values (room air temperature and relative humidity and the product's initial mass and moisture content).
Heat and Mass Transfer, 2016
The aim of this work is to determine the desorption isotherms and the drying kinetics of bay laur... more The aim of this work is to determine the desorption isotherms and the drying kinetics of bay laurel leaves (Laurus Nobilis L.). The desorption isotherms were performed at three temperature levels: 50, 60 and 70 °C and at water activity ranging from 0.057 to 0.88 using the statistic gravimetric method. Five sorption models were used to fit desorption experimental isotherm data. It was found that Kuhn model offers the best fitting of experimental moisture isotherms in the mentioned investigated ranges of temperature and water activity. The Net isosteric heat of water desorption was evaluated using The Clausius–Clapeyron equation and was then best correlated to equilibrium moisture content by the empirical Tsami’s equation. Thin layer convective drying curves of bay laurel leaves were obtained for temperatures of 45, 50, 60 and 70 °C, relative humidity of 5, 15, 30 and 45 % and air velocities of 1, 1.5 and 2 m/s. A non linear regression procedure of Levenberg–Marquardt was used to fit drying curves with five semi empirical mathematical models available in the literature, The R2 and χ2 were used to evaluate the goodness of fit of models to data. Based on the experimental drying curves the drying characteristic curve (DCC) has been established and fitted with a third degree polynomial function. It was found that the Midilli Kucuk model was the best semi-empirical model describing thin layer drying kinetics of bay laurel leaves. The bay laurel leaves effective moisture diffusivity and activation energy were also identified.
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Papers by thouraya ghnimi