M. Kouhila

DRYING KINETICS OF PRICKLY PEAR FRUIT (OPUNTIA FICUS INDICA)

Abstract The present work examines the effect of drying air conditions on drying kinetics of the prickly pear fruit in a convective solar drier operating with an auxiliary heating system under air controlled conditions. Moreover, the prickly pear fruits are sufficiently dried in the ranges between 32 and 36 °C of ambient air temperature, 50–60 °C of drying air temperature, 23–34% of relative humidity, 0.0277–0.0833 m3/s of drying air flow rate and 200–950 W/m2 of solar radiation. The results verified with good reproducibility that drying air temperature is the main factor in controlling the drying rate and the experimental drying curves show only a falling rate period. The expression of the drying rate equation is determined empirically from the characteristic drying curve. Eight different thin layer drying models were compared according to their coefficients of determination to estimate solar drying curves. The two-term model was found to satisfactorily describe the solar drying curves of prickly pear fruit with a correlation coefficient (r) of 0.9999. The constants and coefficients of this model could be explained by the effect of drying air temperature with a correlation coefficient (r) of 1.0000.

EXPERIMENTAL STUDY OF SORPTION ISOTHERMS AND DRYING KINETICS OF MOROCCAN EUCALYPTUS GLOBULUS

ABSTRACT The paper deals with sorption isotherms and drying kinetics of Eucalyptus globulus. The sorption isotherms have been determined using a static gravimetric method and then fitted by GAB equation at T = 30, 40, and 50°C over a range of relative humidity from 0.05 to 0.9. The drying kinetics in a solar dryer with an auxiliary heating system are determined. The results show with good reproducibility that temperature is the main factor in controlling the drying rate. The drying rate equation is determined empirically from the characteristic curve of drying.

Moisture adsorption–desorption isotherms of prickly pear cladode (Opuntia ficus indica) at different temperatures

Abstract The equilibrium moisture contents of cladode of Opuntia ficus indica were determined using the gravimetric static method at 30, 40 and 50 °C over a range of relative humidity (Rh) from 0.05 to 0.9. The sorption capacity of cladode decreased with increase in temperature at constant Rh. The experimental sorption curves are then described by the GAB, Henderson’s and BET models. The BET model was found to be the most suitable for describing the sorption curves. The monolayer moisture content values for the sorption at different temperatures are calculated.

Experimental study of drying kinetics by forced convection of aromatic plants

This paper has the objectives to determine the isotherms of sorption and the drying kinetics of verbena, which is the most consumed aromatic plant in Morocco. The experiments undertaken consist of examining the effects of drying air velocity, temperature of drying air and air moisture content on the drying kinetics of verbena in a laboratory drying tunnel working by forced convection. The results verified, with good reproducibility, that temperature is the main factor in controlling the rate of drying. The expression of the drying rate is determined empirically from the characteristic curve of drying.

Experimental determination of the sorption isotherms of mint (Mentha viridis), sage (Salvia officinalis) and verbena (Lippia citriodora)

Abstract Mint (Mentha viridis), verbena (Lippia citriodora) and sage (Salvia officinalis) are the most produced and consumed aromatic herbs in Morocco. The sorption isotherms of the three plants were determined within the range of 10–90% relative air humidity at three different temperatures (25°C, 40°C and 50°C), using saturated salt solutions method. Hendersons equation was fitted to the experimental data and the agreement between experimental and calculated values was satisfactory. The comparison between the sorption isotherms of mint, verbena and sage is studied.

Adsorption-desorption isotherms and heat of sorption of prickly pear fruit (Opuntia ficus indica)

Abstract The equilibrium moisture contents were determined for prickly pear fruit using the gravimetric static method at t=30, 40 and 50 °C over a range of relative humidities from 0.05 to 0.9. The sorption curves of prickly pear fruit decreased with increase in temperature at constant relative humidity. The hysteresis effect was observed. The GAB, modified Halsey, modified Chung-Pfost, modified Oswin and modified Henderson models were tested to fit the experimental data. The GAB model was found to be the most suitable for describing the sorption curves. The monolayer moisture content values for the sorption at different temperatures are calculated using a modified BET equation. The isosteric heats of desorption and adsorption of water were determined from the equilibrium data at different temperatures.

Experimental study and modelling of adsorption and desorption isotherms of prickly pear peel (Opuntia ficus indica)

Abstract Moisture equilibrium data for adsorption and desorption of water from prickly pear peel ( Opuntia ficus indica ) were investigated at temperatures in the range of 30–50 °C and water activity ranging from 0.05 to 0.9. The experimental procedure used was based on the gravimetric static method. The experimental curves of sorption are then described by GAB, Henderson’s and BET models. The BET and Henderson models were found to be the most suitable for describing the sorption curves. The monolayer moisture content values for the sorption at different temperature are calculated.

SORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF POWDERED MILK

Moisture sorption isotherms of powdered milk were obtained using the gravimetric static method at 30°, 40°, and 50°C. Peleg and Enderby equations were found to be the most suitable models for describing the sorption curves among six well-known tested equations. Thermodynamic properties such as differential enthalpy and entropy of sorption were determined from moisture adsorption and desorption data, using the Clausius-Clapeyron equation. The experimental data showed that enthalpy-entropy compensation theory was applicable to the moisture sorption behavior of powdered milk.

Experimental study and modelling of isotherms of sorption of humid natural phosphate

Abstract Morocco has the most important deposits of phosphate in the world. The present paper aims to determine experimentally the isotherms of sorption of humid natural phosphate using the saturated salt method. The experiments are conducted at five temperatures which are: T =30°C, 40°C, 50°C, 60°C and 70°C. The experimental curves of sorption are then described by Henderson’s, Guggenheim, Anderson, and Boer’s and Brunauer, Emmet and Teiler’s models. The isotherms of sorption calculated by the three models are compared.

SINGLE-LAYER DRYING BEHAVIOR OF MEXICAN TEA LEAVES (CHENOPODIUM AMBROSIOIDES) IN A CONVECTIVE SOLAR DRYER AND MATHEMATICAL MODELING

Single-layer solar drying experiments were conducted for Mexican tea leaves (Chenopodium ambrosioides) grown in Marrakech. An indirect forced convection solar dryer was used in drying the Mexican tea leaves at different conditions such as ambient air temperature (21° to 35°C), drying air temperature (45° to 60°C) with relative humidity (29 to 53%), airflow rate (0.0277 to 0.0556 m 3/s), and solar radiation (150–920 W/m2). The experimental drying curves showed only a falling rate period. In order to select the suitable form of drying curves, 14 mathematical models were applied to the experimental data and compared according to their statistical parameters. The main factor in controlling the drying rate was found to be the temperature. The drying rate equation was determined empirically from the characteristic drying curve. The diffusion coefficient of the Chenopodium ambrosioides leaves was estimated and varied between 1.0209 × 10−9 and 1.0440 × 10−8 m 2·s−1.The activation energy was found to be 89.1486 kJ·mol−1.