Fabrication of microporous membranes from melt extruded polypropylene precursor films via stretching: Effect of annealing

In this work, the effects of annealing conditions on the microstructure of polypropylene(PP) precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.     

Determination of acoustic impedances of multi matching layers for narrowband ultrasonic airborne transducers at frequencies <2.5 MHz - Application of a genetic algorithm

The effective ultrasonic energy radiation into the air of piezoelectric transducers requires using multilayer matching systems with accurately selected acoustic impedances and the thickness of particular layers. One major problem of ultrasonic transducers, radiating acoustic energy into air, is to find the proper acoustic impedances of one or more matching layers. This work aims at developing an original solution to the acoustic impedance mismatch between transducer and air. If the acoustic impedance defences between transducer and air be more, then finding best matching layer(s) is harder. Therefore we consider PZT (lead zirconate titanate piezo electric) transducer and air that has huge acoustic impedance deference. The vibration source energy (PZT), which is used to generate the incident wave, consumes a part of the mechanical energy and converts it to an electrical one in theoretical calculation. After calculating matching layers, we consider the energy source as layer to design a transducer. However, this part of the mechanical energy will be neglected during the mathematical work. This approximation is correct only if the transducer is open-circuit. Since the possibilities of choosing material with required acoustic impedance are limited (the counted values cannot always be realized and applied in practice) it is necessary to correct the differences between theoretical values and the possibilities of practical application of given acoustic impedances. Such a correction can be done by manipulating other parameters of matching layers (e.g. by changing their thickness). The efficiency of the energy transmission from the piezoceramic transducer through different layers with different thickness and different attenuation enabling a compensation of non-ideal real values by changing their thickness was computer analyzed (base on genetic algorithm). Firstly, three theoretical solutions were investigated. Namely, Chebyshev, Desilets and Souquet theories. However, the obtained acoustic impedances do not necessarily correspond to a nowadays available material. Consequently, the values of the acoustic impedances are switched to the nearest values in a large material database. The switched values of the acoustic impedances do not generally give efficient transmission coefficients. Therefore, we proposed, in a second step, the use of a genetic algorithm (GA) to select the best acoustic impedances for matching layers from the material database for a narrow band ultrasonic transducer that work at frequency below the 2.5 MHz by considering attenuation. However this bank is rich, the results get better. So the accuracy of the propose method increase by using a lot of materials with exact data for acoustic impedance and their attenuation, especially in high frequency. This yields highly more efficient transmission coefficient. In fact by using increasing number of layer we can increase our chance to find the best sets of materials with valuable both in acoustic impedance and low attenuation. Precisely, the transmission coefficient is almost equal to unity for the all studied cases. Finally the effect of thickness on transmission coefficient is investigated for different layers. The results showed that the transmission coefficient for air media is a function of thickness and sensitive to it even for small variation in thickness. In fact, the sensitivity increases when the differences of acoustic impedances to be high (difference between PZT and air).     

Turbulence modulation for gas - particle flow in vertical tube and horizontal channel using four-way Eulerian-Lagrangian approach

Turbulence modulation of gas-solid flow in vertical tube and horizontal channel in dilute and moderately dense suspensions is investigated numerically using a four way Eulerian-Lagrangian approach. Low Reynolds number k-l model is used for analyzing the fluid phase motion. A new model is presented based on a source-term formulation, which can predict fluid phase turbulence augmentation due to the presence of large particles and damping of turbulence due to small particles in the core of the channel and tube. Particle-particle and particle-wall collisions are simulated based on a deterministic approach, and coupling terms representing the fluid-particle interactions are also taken into account. The predicted fluid mean velocity and turbulence intensity profiles are in good agreement with the available experimental data. Additional numerical simulation results for variation of the eddy viscosity, turbulence production and dissipation are also presented for different values of loading ratios.     

Synthesis of novel ZnAl2O4/Al2O3 nanocomposite by sol–gel method and its application as adsorbent

Journal of Sol-Gel Science and Technology - In this research, ZnAl2O4/Al2O3 nanocomposites with different ZnAl2O4 (30, 50, and 70?wt.%) were successfully prepared in one step by sol–gel...     

Ultrasound-assisted handling force reduction during the solar silicon wafers production

Surface adhesion between wet wafers poses great challenges for silicon wafer handling. It has been shown that both the shear and normal handling forces of the solar silicon wafers can be dramatically reduced by using the ultrasound energy. Approximately 20 and 5 times reduction in horizontal and vertical forces were achieved by as low power as 10 W, and a good agreement was found between the measured values and the predictions of a simple model for the effect of longitudinal vibration we developed.     

Vibration amplitude and induced temperature limitation of high power air-borne ultrasonic transducers

The acoustic impedances of matching layers, their internal loss and vibration amplitude are the most important and influential parameters in the performance of high power airborne ultrasonic transducers. In this paper, the optimum acoustic impedances of the transducer matching layers were determined by using a genetic algorithm, the powerful tool for optimizating domain. The analytical results showed that the vibration amplitude increases significantly for low acoustic impedance matching layers. This enhancement is maximum and approximately 200 times higher for the last matching layer where it has the same interface with the air than the vibration amplitude of the source, lead zirconate titanate-pizo electric while transferring the 1 kW is desirable. This large amplitude increases both mechanical failure and temperature of the matching layers due to the internal loss of the matching layers. It has analytically shown that the temperature in last matching layer with having the maximum vibration amplitude is high enough to melt or burn the matching layers. To verify suggested approach, the effect of the amplitude of vibration on the induced temperature has been investigated experimentally. The experimental results displayed good agreement with the theoretical predictions.     

Induced super hydrophilicity due to surface modification of polypropylene membrane treated by O2 plasma

Radio frequency (RF) plasma offers a unique route for the surface modification of polymer. The influence of the plasma treatment on the basic properties of the porous membranes such as effective void volume and the flow rate were investigated. It was shown that the polymer ablation significantly alters the hydrophilicity leading to the enhancement of the water flux. Here, the polypropylene membrane was tested by O₂ plasma to emphasize that the contact angle nonlinearly decreases with the treatment time. The XPS surface sensitive technique was applied to confirm the drastic skin change of the oxygen content showing that membrane becomes super hydrophilic due to the significant O₂ implant.     

Synthesis of the novel CuAl2O4–Al2O3–SiO2 nanocomposites for the removal of pollutant dye and antibacterial applications

Research on Chemical Intermediates - CuAl2O4–Al2O3–SiO2 nanocomposites with different amounts of CuAl2O4 (40, 50, 60 and 70 wt. %) were synthesized by the sol–gel method and...     

Temperature measurement of a premixed radially symmetric methane flame jet using the Mach-Zehnder Interferometry

The temperature field of a premixed methane symmetric laminar flame jet is visualized by studying the interferograms of the flame, using the Mach-Zehnder Interferometry. Two kinds of oxidizers are chosen for combustion: industrially pure oxygen and oxygen-enriched air. The flame is chosen to be both lean, and rich. For the lean oxygen-enriched combustion (OEC), the equivalence ratio was held constant at 0.5, and the oxygen enrichment was adjusted to 0.5 and 0.6, and for rich OEC, equivalence ratio is chosen to be 1.2 while the oxygen enrichment was 0.7 and 0.8. For methane/oxygen combustion, the equivalence ratio varied from 0.35 to 0.55 for the lean flame, and 1.3 and 1.7 for the rich flame. Attempt was made to keep the Reynolds number unchanged at 500, for OEC, and 1000, for methane/oxygen flame. In the present study a non-contact method is successfully developed to measure the temperature field of a premixed radially symmetric laminar methane flame jet. The effect of oxygen enrichment and equivalence ratio on temperature field is also investigated and depicted.