Kinetics and Mechanism of Low-Grade Manganese Ore Reduction by Natural Gas

Metallurgical and Materials Transactions B - The calcination and the reduction behaviors of a low-grade manganese ore by methane was studied at 973 K to 1273 K by several techniques. The onset...     

An experimental study of the synergistic effects of BMIM-BF_4,BMIM-DCA and TEACI aqueous solutions on methane hydrate formation

In this work, the effects of three ionic liquids(ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium dicyanamide and tetraethyl-ammonium chloride, on methane hydrate formation and dissociation kinetic parameters were studied. The kinetic parameters including the initial rate of hydrate formation, hydrate stability at atmospheric pressure and hydrate storage capacity were evaluated. The experimental measurements were performed in an initial pressure range of 3.5-7.1 MPa. It was found that both of ILs with imidazolium-based cation increase the initial methane hydrate formation rate while the IL with ammonium-based cation leads to a decrease in the initial methane hydrate formation rate. It was also interpreted from the results that all of the three studied ILs decrease methane hydrate stability at atmospheric pressure and increase methane hydrate storage capacity. Finally, both of ILs with imidazolium-based cations were found to have higher impacts on decreasing hydrate stability at atmospheric pressure and increasing the methane hydrate storage capacity than the applied IL with ammonium-based cation.     

Improving Deep Attractor Network by BGRU and GMM for Speech Separation

Deep Attractor Network (DANet) is the state-of-the-art technique in speech separation field, which uses Bidirectional Long Short-Term Memory (BLSTM), but the complexity of the DANet model is very high. In this paper, a simplified and powerful DANet model is proposed using Bidirectional Gated neural network (BGRU) instead of BLSTM. The Gaussian Mixture Model (GMM) other than the k-means was applied in DANet as a clustering algorithm to reduce the complexity and increase the learning speed and accuracy. The metrics used in this paper are Signal to Distortion Ratio (SDR), Signal to Interference Ratio (SIR), Signal to Artifact Ratio (SAR), and Perceptual Evaluation Speech Quality (PESQ) score. Two speaker mixture datasets from TIMIT corpus were prepared to evaluate the proposed model, and the system achieved 12.3 dB and 2.94 for SDR and PESQ scores respectively, which were better than the original DANet model. Other improvements were 20.7% and 17.9% in the number of parameters and time training respectively. The model was applied on mixed Arabic speech signals and the results were better than that in English.     

CFD and artificial neural network modeling of two-phase flow pressure drop

A large number of experiments in a 2 cm diameter and 6 m length tube were carried out in order to study the two-phase flow regimes and pressure drops in it. The two-phase flow in the experimental tube was modeled using commercial CFD code, Fluent 6.2. An Artificial Neural Network (ANN) with three inputs including gas and liquid velocities and tube slope was designed and trained to predict average pressure drop across the tube. The comparison between CFD and ANN predictions of pressure drops with experimental measurements shows that the CFD results are more accurate than the ANN evaluations for new conditions.     

Effect of process variables on product yield distribution in thermal catalytic cracking of naphtha to light olefins over Fe/HZSM-5

The effect of temperature, WHSV and Fe loading over HZSM-5 catalyst in thermal-catalytic cracking (TCC) of naphtha for the production of light olefins has been studied. The response surface defined by three most significant parameters is obtained from Box-Behnken design method and the optimal parameter set is found. The results show that ethylene increases with temperature, while propylene shows an optimum at 650 °C. Moderate WHSV is favorable for maximum production of light olefins. Addition of Fe to HZSM-5 has a favorable effect on the production of light olefins up to 6% of loading. Excess amount of loading decreases the conversion of naphtha, which leads to a drop in light olefin yields. The yield of light olefins (ethylene and propylene) at 670 °C, 44 hr⁻¹ and 6 wt% Fe has been increased to 5.43 wt% compared to the unmodified HZSM-5 and reaches to 42.47 wt%.     

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na₂O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na₂O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na₂B₂O₄) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na₂O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas.     

High-voltage portable pulsed power supply fed by low voltage source

This article proposes a new structure of voltage multiplier for portable pulsed power applications. In this configuration, which is based on capacitor-diode voltage multiplier, the capacitors are charged by low AC input voltage and discharge through the load in series during pulse generation mode. The proposed topology is achieved by integrating of solid-state switches with conventional voltage multiplier, which can increase the low input voltage step by step and generate high-voltage high-frequency pulsed power across the load. After some discussion, simulations and experimental results are provided to verify the effectiveness of the proposed topology.     

Antioxidant Capacity and Phenolic Content of the Aqueous Extract of Commonly Consumed Cucurbits

The antioxidant capacity of commonly consumed cucurbits vegetable was determined by the DPPH, FRAP, Fe³⁺ reducing power, and hydrogen peroxide scavenging assay. The aqueous extract of Luffa cylindrica showed the highest value of phenolic content and antioxidant capacity based on FRAP, Fe³⁺ reducing power, and hydrogen peroxide scavenging assay. However, Laginaria siceraria extract showed the highest flavonoid and DPPH scavenging activities among all three cucurbits used in this study. Phenolic content in aqueous extracts of Luffa cylindrica and Laginaria siceraria was almost equal. Cucurbita maxima exhibited the lowest phenolic, flavonoid content, and exhibited the lowest power of antioxidant scavenging. The antioxidant capacity of cucurbits was significantly correlated (P < 0.05) with the phenolic content of their extracts. The antioxidant capacity of Luffa cylindrica and Laginaria siceraria have also shown a significant correlation (P < 0.05).