Performance analysis of a tubular solid oxide fuel cell with an indirect internal reformer

A 2‐D steady‐state mathematical model of a tubular solid oxide fuel cell with indirect internal reforming (IIR‐SOFC) has been developed to examine the chemical and electrochemical processes and the effect of different operating parameters on the cell performance. The conservation equations for energy, mass, momentum as well as the electrochemical equations are solved simultaneously employing numerical techniques. A co‐flow configuration is considered for gas streams in the air and fuel channels. The heat radiation between the preheater and reformer surface is incorporated into the model and local heat transfer coefficients are determined throughout the channels. The model predictions have been compared with the data available in the literature. The model was used to study the effect of various operating conditions on the cell performance. Numerical results indicate that as the cell operating pressure increases, the reforming reaction extends to a larger portion of the cell and the maximum temperature move away from the cell inlet. As a result, a more uniform temperature prevails in the solid structure which reduces thermal stresses. Also, at higher excess air, the rate of heat transfer to the air stream is augmented and the average cell temperature is decreased. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental and numerical investigation of thermal loads in Inocnel 718 machining

Inducing high thermal loads in machining of difficult-to-cut materials changes the mechanical properties of a machined surface/subsurface. In particular, a thermally affected layer leads to tensile residual stresses and microstructure changes. Nickel-based alloys are hard materials and frequently used in different industries. Since the generation of thermal loads in machining Inconel 718 is evident, in this paper an experimental and numerical investigation were performed to evaluate thermal loads and the depth of the affected layer in the machining of Inconel 718 superalloy. First, the effect of cutting parameters was studied on the average machined surface temperature by experimental tests. Then, the results of experiments were used to validate a 3D numerical model. Using the calibration strategy, the heat transfer coefficient at the chip–tool interface was found to be dependent on the cutting conditions. Next, the effect of the initial workpiece hardness and tool geometry, including tool nose radius and edge radius, was evaluated on thermal loads and the depth of the recrystallized layer. The critical strain criterion was used to estimate the depth of the recrystallized layer and then, the numerical results were compared with experimentally measured depth of the affected layer at different machining parameters.     

Development of an intelligent model to optimize heat-affected zone,kerf, and roughness in 309 stainless steel plasma cutting by using experimental results

Plasma cutting is an effective way to cut hard metals. In this process, three output parameters cutting width (kerf), surface roughness (Ra) and heat-affected zone (HAZ) are critical factors which affect the quality and efficiency of the cutting. In this paper, an experimental study was conducted to investigate the cutting quality in terms of kerf, Ra, and HAZ for the 309 stainless steel plasma cutting. First, the research tested the effect of input parameters including current, gas pressure, and cutting speed on the process outputs. Then, the results were used to develop three predictive models by intelligent systems based on genetic algorithm (GA) and artificial neural network (ANN). Finally, a hybrid technique of genetically optimized neural network systems (GONNs) was designed and employed to simultaneously optimize the process outputs. The results show that the implemented strategy is an effective method for optimizing the output parameters in the plasma cutting process.     

Electrochemical study on the semiconductor properties and fractal dimension of poly ortho aminophenol modified graphite electrode in contact with different aqueous electrolytes

The fractal dimension of poly ortho aminophenol (POAP) films in the presence of different counter ions was investigated. The POAP films were deposited on graphite electrode by cyclic voltammetry. The deposited films were also characterized by electrochemical impedance spectroscopy (EIS) in wide frequency range. The length scale, the distances between two nearest points that the anions somehow sense (by yardstick of the size of their jump-length), were also derived. The resulting Mott-Schottky plot of the polymer capacitance describes the reduced polymer as a p-type semiconductor with a flat band potential of about 200 mV vs. SCE. The discussion shows that the nature of the anion plays a major role on the electrochemical behavior of the polymer.     

A vision of UMTS/IMT-2000 evolution

A vision is presented for a fully IP-based mobile network which goes beyond UMTS/IMT-2000. A top-to-bottom design approach is introduced that is capable of offering new and innovative services and applications to both fixed and mobile users efficiently, cost effectively and in a user-friendly manner. Some issues and examples in the design steps following this new approach are discussed. It is clearly shown that the convergence of mobile and fixed networks will be achieved naturally through the use of an `all IP' based solution for both access and core networks     

Kinetics and electrocatalytic behavior of nanocrystalline CoNiFe alloy in hydrogen evolution reaction

Electrocatalytic activity of electrodeposited nanocrystalline CoNiFe alloy in hydrogen evolution reaction (HER) was studied in 1 M NaOH solution. The steady-state polarization measurement and electrochemical impedance spectroscopy were used to determine the Tafel slope, the exchange current density and the activation energy. The simulation of the data obtained from these two methods, using a nonlinear fitting procedure, allowed us to determine the surface coverage and the rate constants associated with the mentioned reaction. The ac-impedance spectra measured at various overpotentials in the HER region exhibited three semicircles in the complex plane plots. The high-frequency semicircle was attributed to the electrode geometry, whereas the intermediate and low frequency semicircles were due to the electrode kinetics. The results also demonstrated that CoNiFe alloy possessed slightly higher specific electrocatalytic activity than Ni itself. Nevertheless, the contribution of high specific surface area of nanocrystalline alloy in hydrogen evolution was by far more significant. The effects of temperature and poisoning on the electrochemical parameters were also studied.     

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.     

Impact of Silicon Foliar Application on the Growth and Physiological Traits of Carthamus tinctorius L. Exposed to Salt Stress

Silicon - Althought safflower is a tolerant crop against many environmental stresses, but its yield and performance reduce under stress. The aim of this experiment was to investigate the effect of...