Adsorptive solar powered ice maker: experiments and model

A solar adsorptive ice maker model is presented and experimentally validated. In order to determine the model parameters, the identification procedure is carried out employing an experimental data base obtained from tests carried out on two adsorptive solar-powered ice-makers using a methanol/carbon pair. The packaged component, the collector–condenser, represents the main new feature of these units. The prediction is compared with results of correlations. This allows a comparison of the collector–condenser behavior in the two units since the collector–condenser of one of these units is equipped with a radiation shield. The model is then used to study daily ice production sensitivity vis-à-vis critical physical parameters of the unit and to estimate the limits of the collector–condenser technology with flat plate collectors.     

Municipal solid waste compost application improves productivity, polyphenol content, and antioxidant capacity of Mesembryanthemum edule

Organic wastes were successfully used as soil amendment to improve agrosystems productivity. Yet, the effectiveness of this practice to enhance plant antioxidant capacities has received little attention. Here, we assess the effect of municipal solid waste (MSW) compost (at 40 t ha(-1)) on growth, polyphenol contents and antioxidant activities of Mesembryanthemum edule. MSW compost application significantly increased the soil contents of carbon, nitrogen, calcium, phosphorus and potassium. This was associated with higher nutrient (N, P, and K) uptake, which likely led to the significant improvement of the plant biomass and relative growth rate (RGR) (+93% on average) as compared to the control. In the same way, the fertilizing effect of the added organic matter significantly enhanced the antioxidant potential M. edule, assessed by radical scavenging activity, iron reducing power and β-carotene bleaching capacity. This was associated with significantly higher antioxidant contents, mainly total phenols and flavonoids. Heavy metal (Pb, Cd, Cu, and Zn) concentrations were slightly increased upon compost application, but remained lower than phytotoxic values. Overall, our results point out that short-term MSW compost application at 40 t ha(-1) is efficient in enhancing the productivity together with the antioxidant potentiality of M. edule without any adverse environmental impact.     

Antibacterial activity of quaternary ammonium salt grafted cotton

Cotton having good antibacterial activity can be obtained without the need for a binding chemical as a cross linker or the need for chemically pre-treated antibacterial agent. The procedure of synthesis consists in grafting an alkali-cellulose fibre by a quaternary ammonium salt: Epoxy propyltrimethylammonium chloride (EPTMAC). The characterization of grafted cotton (EPTMAC-Cotton) has been targeted on the nitrogen and the methyl group in the ammonium graft structure, by using some analytical techniques, such as infrared, NMR spectroscopy, and volumetric measurement. The antibacterial activity of EPTMAC-Cotton has been studied using four kinds of bacterial stains (Escherichia coli 25922, Pseudomonas aeruginosa 27853, Staphylococcus aureus 259223 and Salmonella LT2DT104 typhimirium). An optimization of conditions of culture medium has been carried out for the bacterial strain for which the modified cotton presents the best antibacterial activity. This optimization is achieved while varying the most important parameters influencing the bacterial growth. We have chosen the pH and the sodium chloride concentration as variable parameters, and we have applied an experiment plant, in order to consider all possible combinations of experiments, and therefore, to estimate the effect of each factor, as well as the effect of their interaction. It has been noticed that a quaternary ammonium salt (EPTMAC) is an efficient antibacterial agent, especially against salmonella in alkaline medium slightly concentrated in salt, and its action depends, in some manner, on the whitening procedure of cotton.     

Impact of aging conditions on mechanical properties of thermoplastic polyurethane

In this study, impact of environmental aging conditions on the mechanical properties of thermoplastic polyurethane (TPU) was investigated. Especially, effect of temperature on water diffusion has been studied. Water-sorption experiments, tensile test and dynamic mechanical thermal analysis (DMTA) were performed after immersion in distilled water at different temperatures (25, 70 and 90 °C). The sorption process was analyzed by gravimetric measurements at different temperatures. Also, diffusion coefficients of solvent molecules in the TPU samples were identified. Therefore the activation energy and the mixing enthalpy were deduced. The aging impact on some mechanical properties of this material has been investigated after various aging cycles. Degradation of mechanical properties was observed. In fact, elastic modulus and stress at 200% of strain were decreased. It was also shown that such degradation largely depends on both aging temperature and aging immersion duration. The storage modulus (E′) was also affected by the hygrothermal (HT) environment. The modification of mechanical properties seems to be well correlated to structural observations obtained from scanning electron microscopy (SEM) photographs. Finally, through thermal aging experiments, it was deduced that the combination of temperature with water seems to be a major factor of TPU degradation.     

Energetic Performance and Permeate Flux Investigation of Direct-Contact Membrane Distillation for Seawater Desalination

The performance of the direct-contact membrane distillation (DCMD) process in desalting Mediterranean seawater was investigated. Theoretical and experimental optimization of various operating parameters was conducted. The effects of temperature differences, feed velocity, and membrane characteristics were studied. When using commercial polyvinylidene fluoride membranes, the vapor transfer throughout the membrane pores is dominated by the Knudsen-molecular diffusion model. Maximum permeate flux was obtained when increasing temperature, feed velocity, membrane pore size, and porosity and decreasing membrane tortuosity and thickness. Thermal efficiency, gained output ratio, and specific thermal energy consumption were improved when increasing feed temperature. By application of the DCMD process to Mediterranean seawater, a high water quality was obtained.     

Thermodynamic and economic analysis of the performance of a direct evaporative cooler working under extreme summer weather conditions

Journal of Mechanical Science and Technology - Riyadh is a desert region characterized by large daily and seasonal ambient temperature variations. Air cooling using mechanical vapor compression...     

Investigations on hygrothermal aging of thermoplastic polyurethane material

In this investigation, the absorption and diffusion of water in thermoplastic polyurethane (TPU) was studied. Water-sorption experiments, physical and mechanical property tests were performed after immersion in water at a set temperature of 70 °C for up to 6 months. Emphasis was given to the effect of immersion aging on thermal, mechanical and tribological properties. Fickian diffusion behaviour was found during the initial immersion time followed by saturation stage as time progressed. The use of differential scanning calorimetry (DSC) analysis showed that the glass transition temperature (Tg) was sensitive to the effect of hygrothermal aging and it decreased with increasing water uptake.More significantly, the mechanical properties in bulk material, obtained from tensile test, were affected by aging. Elastic modulus and stress at 200% of strain of the studied TPU were decreased after sufficient exposure to moisture. On the other hand, the mechanical properties of the material surface were equally investigated with the help of an abrasive wear test. A decrease in wear resistance of the aged TPU was discerned. The reversibility of mechanical and physical properties after moisture exposure was also assessed in this study. The polymer degradation was found as irreversible phenomenon.Finally, the evolution of the mechanical properties seems to be well correlated to structural modifications obtained from Fourier transform infrared spectroscopy (FTIR) characterization.     

Poly(2-hydroxyethylmethacrylate-graft-folic acid), synthesis,solubility enhancement,and release dynamic of folic acid

A series of poly (2-hydroxyethylmethacrylate-graft-folic acid) (FAHEMA) systems are synthesized by grafting of folic acid (FA) into poly (2–hydroxyethylmethacrylate) via an esterification reaction. The structure of these copolymers is confirmed by NMR and CHN analyses. The thermal behavior of these materials is characterized by DSC and TGA analyses. The surface morphology of FAHEMA films before and after the release process is examined by the SEM method. The cumulative FA released in different pH media from FAHEMA materials occurred via a retro-esterification reaction at body temperature during 72 h in which the influence of the swelling degree of PHEMA, the FA content and pH media on the dynamic release is widely investigated. The results obtained revealed that the solubility of FA in water deduced from the release process is widely improved compared with literature reports. It is also revealed that the diffusion of water in different pH media through the PHEMA matrix and that of FA through FAHEMA materials perfectly obeyed the Fickian models. It was deduced from the kinetic study that the release performance is obtained with the copolymers containing initially 10 and 20 wt% of FA contents.     

Robust direct power control based on the Lyapunov theory of a grid-connected brushless doubly fed induction generator

This paper deals with robust direct power control of a grid-connected brushless doubly-fed induction generator(BDFIG). Using a nonlinear feedback linearization strategy, an attempt is made to improve the desired performances by controlling the generated stator active and reactive power in a linear and decoupled manner. Therefore, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability. Thus, an optimal operation of the BDFIG in sub-synchronous operation is obtained as well as the stator power flows with the possibility of keeping stator power factor at a unity. The proposed method is tested with the Matlab/Simulink software. Simulation results illustrate the performances and the feasibility of the designed control.