An approach to design and fabrication of a piezo-actuated microdroplet generator

In this research, a piezo-actuated microdroplet printing device for drop on demand (DOD) is studied. Microdroplet devices are used in applications such as inkjet printing, rapid prototyping, and production of metal powder. An experimental device is designed and manufactured, in which the fluctuation of a flexible diaphragm–by a piezoelectric element–pushes the liquid out of the nozzle and produces droplets. The deflection of diaphragm due to different voltages is investigated by analytical and experimental study. In experiments, beside deflection voltage, the effect of suction and compression time and nozzle diameter on droplet size, droplet velocity, satellite droplets, and cutoff length is also investigated. High-speed camera is used to take photo of the formation of droplets. In order to calculate droplet diameter and velocity, outputs of high-speed camera are processed by MATLAB R2008a. Results obtained by analytical and experimental are in good agreement with each other and could be used to control droplet properties. It is shown that the device is able to produce droplet of diameter from 450 to 1,000 μm. Velocity of droplet can be also controlled in a range of about 0.2 to 1.4 m/s. The repeatability is investigated by ink printing on a paper attached to a rotary table.     

A multi-dimensional approach to the assessment of tunnel excavation methods

Selection of tunnel excavation method in rock calls for an exact assessment of engineering geology as well as geotechnical conditions of the tunnel strike. Moreover, uncertainties related to properties of engineering geology of rock often trigger complexity. In order to select the best possible excavation technique, one needs to take into account numerous operational, economic, environmental factors, and so forth. Using a hybrid methodology, including multiple attributes decision-making techniques and fuzzy set theory, the present study aims to evaluate the excavation methods of tunnels. The proposed approach is based on fuzzy-AHP and TOPSIS methods where the fuzzy-AHP determines weights of the criteria by decision makers in uncertain environment and TOPSIS concludes rankings of the excavation methods. Finally, a case study of Ghomroud project in Iran is presented to demonstrate the result of the proposed methodology.     

Thermodynamic analyses of adsorption-enhanced steam reforming of glycerol for hydrogen production

A non-stoichiometric thermodynamic analysis is performed on the adsorption-enhanced steam reforming of glycerol for hydrogen production based on the principle of minimising the Gibbs free energy. The effects of temperature (600–1000 K), pressure (1–4 bar), water to glycerol feed ratio (3:1–12:1), percentage of CO₂ adsorption (0–99%) and molar ratio of carrier gas to feed reactants (1:1–5:1) on the reforming reactions and carbon formation are examined. The results show that the use of a CO₂ adsorbent enhances glycerol conversion to hydrogen and the maximum number of moles of hydrogen produced per mole of glycerol can be increased from 6 to 7 due to the CO₂ adsorption. The analyses suggest that the most favourable temperature for steam–glycerol reforming is between 800 and 850 K in the presence of a CO₂ adsorbent, which is about 100 K lower than that for reforming without CO₂ adsorption. Although high pressures are favourable for CO₂ adsorption, a lower operating pressure gives a higher overall hydrogen conversion. The most favourable water to glycerol feed ratio is found to be 9.0 above which the benefit becomes marginal. Carbon formation could occur at low water to glycerol feed ratios, and the use of a CO₂ adsorbent can suppress the formation reaction and substantially reduce the lower limit of the water to glycerol feed ratio for carbon formation.     

Influence of Concentrations of KOH and Na_2SiO_3 Electrolytes on the Electrochemical Behavior of Ceramic Coatings on 6061 Al Alloy Processed by Plasma Electrolytic Oxidation

In this study,ceramic coatings were deposited on 6061 Al alloy using a plasma electrolytic oxidation(PEO)technique,and the effect of concentrations of KOH and Na_2SiO_3 as electrolytes for PEO process was studied on microstructure,chemical composition,and electrochemical behavior of PEO coatings formed on the 6061 Al alloy.The results indicated that the increase in concentration of KOH led to rise in electrical conductivity of electrolyte.Consequently,the breakdown voltage reduced,which in turn improved the surface quality and the corrosion behavior.Moreover,the increase in concentration of Na_2SiO_3 resulted in the increase in incorporation of Si in the coating,which led to a higher corrosion potential in the concentration of 4 g L~(-1).According to this investigation,the best protection behavior of coatings can be obtained when the KOH and Na_2SiO_3 concentrations in PEO electrolyte are equal to 4 g L~(-1).     

A Fully Discretized Nonlinear Finite Strip Formulation for Pre-Buckling and Buckling Analyses of Viscoelastic Plates Subjected to Time-Dependent Loading

A semi-analytical fully discretized finite strip method is developed to investigate the pre-buckling and local buckling of viscoelastic plates with different boundary conditions subjected to time-dependent loading. The mechanical properties of the material are considered to be linear viscoelastic by expressing the relaxation modulus in terms of Prony series. The fully discretized finite strip equations are developed using a two-point recurrence formulation, which leads to a computationally superior formulation. Time history of maximum deflection of plates with different end conditions is calculated. The effects of thickness, length of plate, and transverse loading on critical buckling load are also studied.     

Probiotics as potential detoxification tools for mitigation of pesticides: a mini review

Pesticides play a key role in agriculture and food production by controlling the insects, weeds, plant pathogens and microbial contaminations. Although they are useful in some aspects, their inappropriate application can induce health problems including carcinogenicity, reproductive toxicity, neurodegenerative diseases and disruption of endocrine system. In this respect, efficient strategies should be applied to reduce pesticide residue in foodstuffs. Several methods have been proposed in food processing for reduction of pesticides residue. Recently, detoxification via microorganisms such as lactic acid bacteria and probiotics has been extensively studied and degradation of pesticides through hydrolytic enzymes has been introduced as the possible mechanism and it has been highlighted that some probiotics harbour pesticide-degrading genes. The aim of this review is to evaluate the efficacy of probiotics in detoxification of pesticides.     

Electrolyzer-fuel cell combination for grid peak load management in a geothermal power plant: Power to hydrogen and hydrogen to power conversion

This study provides comprehensive energy, exergy, and economic evaluations and optimizations of a novel integrated fuel cell/geothermal-based energy system simultaneously generating cooling and electricity. The system is empowered by geothermal energy and the electricity is mainly produced by a dual organic cycle. A proton exchange membrane electrolyzer is employed to generate the oxygen and hydrogen consumed by a proton exchange membrane fuel cell utilized to support the network during consumption peak periods. This fuel cell can be also used for supplying the electricity demanded by the network to satisfy the loads at different times. All the simulations are conducted using Engineering Equation Solver software. To optimize the system, a multi-objective optimization method based on genetic algorithm is applied in MATLAB software. The objective functions are minimized cost rate and maximized exergy efficiency. The optimum values of exergy efficiency and cost rate are found to be 62.19% and 18.55$/h, respectively. Additionally, the results reveal that combining a fuel cell and an electrolyzer can be an effective solution when it comes to electricity consumption management during peak load and low load periods.     

Phenol biodegradation in a bioreactor considering different geometries and process parameters

In this study, a three-dimensional coupled lattice Boltzmann model and cellular automata platform was developed to simulate biofilm growth and phenol biodegradation as an effective and sustainable way to remove phenolic contaminants in aquatic systems. Two three-dimensional bioreactors with cubic or spherical obstacles at varying inlet phenol concentrations and flow velocities were examined. The results showed that the cubic-bioreactor had higher phenol reduction than the spheric-bioreactor due to the greater effects of cubic obstacles on flow patterns. The biofilm concentration in bioreactors decreased up to 36.4% as inlet velocity increased and in the spheric-bioreactor at the same inlet phenol concentration. The cubic-bioreactor had the highest normalized reduction rate of 1.194 at the lowest inlet phenol concentration, while the spheric-bioreactor had the lowest one of 0.871 at the highest inlet phenol concentration. The results proved the accuracy of the model to assess the performance of wastewater treatment bioreactors under different conditions.