Experimental study and simulation of a solar dryer for spearmint leaves (Mentha spicata)

An indirect forced convection solar dryer consisting of an air flat plate collector and a drying cabin was designed and fabricated to investigate its performance under the climate of Algiers. Drying experiments have been performed for spearmint leaves at different air flow rates in order to determine the drying velocity, the characteristic drying curve, the effective diffusion coefficient and the activation energy. A mathematical model based on thermal and mass balances over the component of the solar collector and the cabinet dryer was developed. Simulations are carried out for meteorological data of Algiers (Algeria). We analyse the effect of air mass flow rate, air temperature, products mass, collector area, air recycling rate on the drying time, the solar fraction and the efficiency of the dryer.     

Mass transfer from a contaminated fluid sphere

The unsteady mass transfer from a contaminated fluid sphere moving in an unbounded fluid is examined numerically for unsteady‐state transfer. The effect of the interface contamination and the flow regime on the concentration profiles, inside and outside a fluid sphere, is investigated for different ranges of Reynolds number (0 < Re < 200) and Peclet number (0 < Pe < 10⁵), viscosity ratio between the dispersed phase and the continuous phase (0 < κ < 10), and the stagnant‐cap angle (0° < θ_cap < 180°). It was found that the stagnant‐cap angle significantly influences the mass transfer from the sphere to a surrounding medium. For all Peclet and Reynolds numbers and κ, the contamination reduces the mass transfer flux. The average Sherwood number increases with an increase of stagnant‐cap angle and reaches a maximum equal to the average one for a clean fluid sphere at low viscosity ratio and large Peclet numbers. A predictive equation for the Sherwood number is derived from these numerical results. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Facile synthesis of CdSe nanocrystals for bulk-heterojunction solar cells

Oleic acid (OA)-capped cadmium selenide (CdSe) nanocrystals (NCs) have been synthesized via a new high-scale route. X-ray diffraction and transmission electron microscopy confirmed that rod-like hexagonal (wurtzite) CdSe NCs with an average size of 10 nm were obtained via this new route. The obtained CdSe NCs were treated individually with pyridine and tert-butylamine (t-BA) for ligand exchange. Fourier transform infrared spectra of the as-synthesized and treated CdSe NCs confirmed the removal of OA ligands from the surface of CdSe NCs after treatments with pyridine and t-BA. Bulk-heterojunction (BHJ) solar cell devices were prepared using untreated and surface treated CdSe NCs blended with poly (3-hexylthiophene-2,5-diyl) (P3HT) polymer. BHJ solar cell devices made from P3HT:(surface treated CdSe NCs) blends showed greater improvement in photovoltaic performances compared to P3HT:(untreated CdSe NCs) blend. The improvement in photovoltaic performances was due to the increase of electron mobility in P3HT:(CdSe NCs) blends after surface treatment of CdSe NCs.     

Modeling the Effects of Strand Surface Bulging and Mechanical Softreduction on the Macrosegregation Formation in Steel Continuous Casting

Positive centerline macrosegregation is an undesired casting defect that frequently occurs in the continuous casting process of steel strands. Mechanical softreduction (MSR) is a generally applied technology to avoid this casting defect in steel production. In the current paper, the mechanism of MSR is numerically examined. Therefore, two 25-m long horizontal continuous casting strand geometries of industrial scale are modeled. Both of these strand geometries have periodically bulged surfaces, but only one of them considers the cross-section reduction due to a certain MSR configuration. The macrosegregation formation inside of these strands with and without MSR is studied for a binary Fe-C-alloy based on an Eulerian multiphase model. Comparing the macrosegregation patterns obtained for different casting speed definitions allows investigating the fundamental influence of feeding, bulging and MSR mechanisms on the formation of centerline macrosegregation.     

Biodegradation of the endogenous residue of activated sludge in a membrane bioreactor with continuous or on-off aeration

The goal of this study was to determine the effect of a long sludge retention time on the biodegradation of the endogenous residue in membrane digestion units receiving a daily feed of sludge and operated under either aerobic or intermittently aerated (22 h off-2 h on) conditions. The mixed liquor for these experiments was generated in a 10.4 day sludge retention time membrane bioreactor fed with a synthetic and completely biodegradable influent with acetate as the sole carbon source. It had uniform characteristics and consisted of only two components, heterotrophic biomass X_H and endogenous residue X_E. Membrane digestion unit experiments were conducted for 80 days without any sludge wastage except for some sampling. The dynamic behaviour of generation and consumption of filtered organic digestion products was characterized in the membrane digestion unit systems using three pore filter sizes. Results from this investigation indicated that the colloidal matter with size between 0.04 μm and 0.45 μm was shown to contain a recalcitrant fraction possibly composed of polysaccharides bound to proteins which accumulated in the membrane digestion unit under both conditions. Modelling the membrane digestion unit results by considering a first-order decay of the endogenous residue allowed to determine values of the endogenous residue decay rate of 0.0065 and 0.0072 d⁻¹ under fully aerobic and intermittently aerated conditions, respectively. The effect of temperature on the endogenous decay rate was assessed for the intermittently aerated conditions in batch tests using thickened sludge from tests gave an endogenous decay rate constant of 0.0075 d⁻¹ at 20 °C and an Arrhenius temperature correction factor of 1.033.     

Interactions between PLA,organo-montmorillonite and plasticizer: Synergistic effect on the barrier and mechanical properties of PLA nanocomposites blown films

In this study, the impact of incorporating a plasticizer on the compatibility between organo-montmorillonite (OMMt) and polylactic acid (PLA) is investigated, and the resulting barrier and mechanical properties are reported. Four polymers were chosen as plasticizers to prepare the PLA nanocomposite blown films: poly(ethylene glycol), poly(ethylene oxide), polycaprolactone (PCL), and random ethylene-methyl acrylate-glycidyl methacrylate terpolymer. Firstly, 5 wt% of each plasticizer and 3 wt% of OMMt (Dellite® D43B) were mixed simultaneously with PLA in a twin-screw extruder and then introduced into the hopper of a single screw extruder to produce D43B-PLA/plasticizer nanocomposite films. The compatibilization effect was examined based on microstructure observations and thermodynamic predictions. Crystallinity was evaluated using DSC and XRD measurements. The results obtained for permeability and mechanical testing showed that the improvement of barrier and mechanical properties depends directly on the degree of compatibility between plasticizer, OMMt, and PLA. Indeed, the interfacial properties, XRD diffraction, and TEM images showed that a synergistic effect can result from high interfacial interactions between different compounds.     

Novel polyhydrazides and polyoxadiazoles based on 1,3,4-thiadiazole moiety in the main chain with high thermal stability,good solubility,and notable antimicrobial activity

Polyoxadiazoles (PODs) and polyhydrazides (PHs) have wide potential applications; however, PODs are normally insoluble in organic solvents, do not melt, and do not express glass-transition temperature (T_g), and also PHs do not have high-temperature resistance. In this work, novel PHs based on 1,3,4-thiadiazole in the polymer main chain were synthesized by low-temperature polycondensation. New PODs were then obtained by cyclodehydration of the PHs. The thermal behavior, surface morphology, and crystalline structure were studied using differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. In addition, the viscosity, solubility, UV–visible absorption, and antimicrobial activity were examined. The new polymers showed melting, T_g, high thermal stability, good solubility in polar aprotic solvents, and significant antimicrobial activities. The enhanced solubility may be attributed to the ability of thiadiazole moiety to form hydrogen bonding with the solvent molecules. Also, it can be concluded that introducing 1,3,4-thiadiazole and other bulky moieties like the oxadiazole ring into the polymer main chain encouraged more free volumes and weakened the chains packing; hence, the solubility was enhanced and T_g decreased without affecting the thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47770.     

Effect of the inflation strategy on the piezoelectric response of cellular poly(vinylidene fluoride) ferroelectret

Cellular poly(vinylidene fluoride) (PVDF)-montmorillonite (MMT)-calcium carbonate (CaCO₃) based piezoelectret films were produced using uniaxial stretching and various gas diffusion expansion (GDE) treatments followed by corona charging. The cross section micrographs revealed that a cellular structure was developed at the interface between the solid CaCO₃ particles and the polymer matrix. Sample characterization showed that the piezoelectric coefficient (d₃₃) was a function of the external gas pressure and treatment temperature, as well as the way they were applied. The results also showed that the maximum d₃₃ was obtained when the inflation pressure was increased stepwise from 3 to 5 MPa at a constant treatment temperature of 130°C for a certain period of time. Finally, the overall electromechanical performance of the cellular PVDF piezoelectrets is discussed in terms of the GDE procedure and the developed microstructures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47540.     

Chemically modified olive stone: a low-cost sorbent for heavy metals and basic dyes removal from aqueous solutions

In the present work, we have investigated the sorption efficiency of treated olive stones (TOS) towards cadmium and safranine removal from their respective aqueous solutions. TOS material was prepared by treatment of olive stones with concentrated sulfuric acid at room temperature followed up by a subsequent neutralization with 0.1 M NaOH aqueous solution. The resulting material has been thoroughly characterized by SEM, energy-dispersive X-ray (EDX), MAS (13)C NMR, FTIR and physicochemical parameters were calculated. The sorption study of TOS at the solid-liquid interface was investigated using kinetics, sorption isotherms, pH effect and thermodynamic parameters. The preliminary results indicate that TOS exhibit a better efficiency in terms of sorption capacities toward the two pollutants (128.2 and 526.3 mg/g for cadmium and safranine, respectively) than those reported so far in the literature. Moreover, the sorption process is ascertained to occur fast enough so that the equilibrium is reached in less than 15 min of contact time. The results found in the course of this study suggest that ion exchange mechanism is the most appropriate mechanism involved in cadmium and safranine removal. Finally, the sorption efficiency of TOS is compared to those of other low-cost sorbents materials yet described in the literature.