A review on methanol crossover in direct methanol fuel cells: challenges and achievements

Direct methanol fuel cells have the potential to power future microelectronic and portable electronic devices because of their high energy density. One of the major obstacles that currently prevent the widespread applications of direct methanol fuel cells is the methanol crossover through the polymer‐electrolyte membrane. Methanol crossover is closely related to several factors including membrane structure and morphology, membrane thickness, and fuel cell operating conditions such as temperature, pressure, and methanol feed concentration. This work presents a comprehensive overview of the state‐of‐the‐art technology for the most important factors, affecting methanol crossover in direct methanol fuel cells. In addition, the current and future directions of the research and development activities, aiming to reduce the methanol crossover are reviewed and discussed in order to improve the performance of direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Computational fluid dynamics modeling of gas dispersion in multi impeller bioreactor

In the present study, experiments have been carried out to identify various flow regimes in a dual Rushton turbines stirred bioreactor for different gas flow rates and impeller speeds. The hydrodynamic parameters like fractional gas hold-up, power consumption and mixing time have been measured. A two fluid model along with MUSIG model to handle polydispersed gas flow has been implemented to predict the various flow regimes and hydrodynamic parameters in the dual turbines stirred bioreactor. The computational model has been mapped on commercial solver ANSYS CFX. The flow regimes predicted by numerical simulations are validated with the experimental results. The present model has successfully captured the flow regimes as observed during experiments. The measured gross flow characteristics like fractional gas hold-up, and mixing time have been compared with numerical simulations. Also the effect of gas flow rate and impeller speed on gas hold-up and power consumption have been investigated.     

Feature subset selection using differential evolution and a statistical repair mechanism

One of the fundamental motivations for feature selection is to overcome the curse of dimensionality problem. This paper presents a novel feature selection method utilizing a combination of differential evolution (DE) optimization method and a proposed repair mechanism based on feature distribution measures. The new method, abbreviated as DEFS, utilizes the DE float number optimizer in the combinatorial optimization problem of feature selection. In order to make the solutions generated by the float-optimizer suitable for feature selection, a roulette wheel structure is constructed and supplied with the probabilities of features distribution. These probabilities are constructed during iterations by identifying the features that contribute to the most promising solutions. The proposed DEFS is used to search for optimal subsets of features in datasets with varying dimensionality. It is then utilized to aid in the selection of Wavelet Packet Transform (WPT) best basis for classification problems, thus acting as a part of a feature extraction process. Practical results indicate the significance of the proposed method in comparison with other feature selection methods.     

Effects of Acidity and Method of Preparation on Nucleate Pool Boiling of Nanofluids

Past research has shown contradicting trends in the rate of heat transfer during pool boiling of nanofluids, which could be attributed either to their stability or to their method of preparation or to both. An experimental study has been conducted to investigate the effects of electrostatic stabilization and preparation method of nanofluids on their pool boiling rate of heat transfer. Nanofluids made from water and alumina nanoparticles at 0.1 vol% concentration were used. The effect of electrostatic stabilization was investigated by changing the pH value from 6.5, neutral, to 5, acidic. The effect of preparation method has been investigated by using nanofluids prepared from dry particles and from ready-made suspensions. Compared with water, all nanofluids investigated resulted in deterioration in the rate of heat transfer during pool boiling. Neutral nanofluids made from ready-made suspensions and from dry particles resulted into almost the same deterioration in the rate of heat transfer of 49% and 45%, respectively, with respect to that of pure water. The most significant effect of electrostatic stabilization was found in the case of acidic nanofluids made from dry particles, which resulted in deterioration in the rate of heat transfer of 31%. However, acidic nanofluids made from ready-made suspensions resulted in a deterioration of 46%, which is almost the same as that of suspension-made and dry particles-made nanofluids. These results indicate that electrostatic stabilization using acid addition is most effective with nanofluids made from dry particles.     

A Behavioral Model of MEMS Convective Accelerometers for the Evaluation of Design and Calibration Strategies at System Level

This paper presents a behavioral model that can be used to improve the manufacturability of systems based on MEMS convective sensors. This model permits to handle faults related to process scattering, taking into account not only the electrical and lateral geometrical parameters but also the influence of the cavity depth. Moreover correlations between conductive and convective phenomena are included. The model is validated with respect to FEM simulations and a very good agreement is obtained between the behavioral model and FEM results. The proposed model can then be used in system-level simulations, for instance to evaluate the impact of process scattering on the performances of the sensing part and/or to investigate different design and calibration strategies with respect to the system robustness.     

The Effect of Temperature on the Tribological Behavior of RBD Palm Stearin

The wide use of petroleum-based oils raises concerns with regard to pollution, and the rising of awareness of greenhouse gases has created a demand for the use of environmentally friendly and biodegradable lubricants for industrial applications. Vegetable oils are one of the bio-oils that have been promoted as a replacement for petroleum products, in part due to their environmentally friendly characteristics; they are nontoxic, biodegradable, and easy to dispose of. Many researchers have performed studies on sunflower oil, corn oil, and soy oil, but few have studied palm oil as a lubricant. Palm oil produced in a high-throughput manner could fulfill the demand for bio-based lubricants. In this study, the influence of temperature on friction and wear performance for refined, bleached, and deodorized (RBD) palm stearin and additive-free paraffinic mineral oil is presented. The experiments were conducted using a four-ball tribotester. Test temperatures of 55, 65, 75, and 85°C were used. The sliding speeds were set to 1,200 rpm. Experiments were run for 1 h under a 392.4 N load. The results of RBD palm stearin were compared with those of paraffinic mineral oil. The experimental results showed that the RBD palm stearin had better performance compared to paraffinic mineral oil in terms of reducing frictional constraints.     

Synthesis of novel dyestuffs containing sulphonamido moieties and their application on wool and polyamide fibres

A new series of azo disperse dyestuffs were prepared by the reaction of sulphanilamidodiazonium chloride derivatives with indan-1,3-dione. Application of these dyes on wool and nylon 6.6 gave excellent results. The synthesised compounds show good biological activity towards different microorganisms.     

Electrochemical hydrodehalogenation of polychloromethanes at silver and carbon electrodes

The reductive dehalogenation of CCl₄, CHCl₃, CH₂Cl₂ and CH₃Cl has been investigated by cyclic voltammetry and controlled-potential electrolysis at Ag, glassy carbon (GC) and graphite electrodes in dimethylformamide (DMF) + 0.1 M Et₄NClO₄ in the absence and presence of a proton donor. In particular, the study was focused in the evaluation of the intermediates and final products of the reduction process and how their distribution could be affected by tuning relevant chemical and electrochemical parameters. In general, depending on the value of the applied potential, all polychloromethanes (PCMs) can be partially or completely dechlorinated, methane being exclusively formed in the latter case. The nature of the electrode material and the proton availability of the medium affect drastically the distribution of reduction products. The results point out that at both types of electrode, reduction of PCMs takes place through two competing reaction pathways both leading to methane. One reaction route involves a sequence of reductive dehalogenation steps, with the removal of one chlorine atom at a time, whereas the other is based on hydrogenolysis of carbenes and bypasses the intermediacy of partially dechlorinated PCMs. The presence of a proton source affects substantially the hydrodehalogenation efficiency, enhancing the concentration of intermediate PCMs and the final yield of methane. The silver electrode exhibits an extraordinary electrocatalytic effect resulting in remarkable positive shifts of the reduction potentials of all PCMs with respect to GC. The Ag surface strongly affects the kinetics of the dissociative electron transfer to CH_nCl_(4−n) (n = 0–3) as well as the reactivity of the intermediate radicals, carbanions and carbenes.