Simulation of abrasive flow machining process for 2D and 3D mixture models

Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a Newtonian fluid and the flow laminar with no wall slip.     

Kinetics of phase transfer catalyzed reduction of nitrochlorobenzenes by aqueous ammonium sulfide: Utilization of hydrotreater off-gas for the production of value-added chemicals

The reduction of nitrochlorobenzenes (NCBs) was carried out in an organic solvent, toluene, under liquid–liquid mode with phase transfer catalyst, tetrabutylammonium bromide (TBAB). The selectivity of chloroanilines (CANs) was found to be 100%. The reaction rate of m-nitrochlorobenzene (MNCB) was found to be highest among the three NCBs followed by o- and p-nitrochlorobenzene (ONCB and PNCB). The reactions were found to be kinetically controlled with apparent activation energies of 22.8, 19.6 and 9.4 kcal/mol for ONCB, PNCB and MNCB, respectively. The effects of different parameters such as TBAB concentration, NCB concentration, sulfide concentration, ammonia concentration, and elemental sulfur loading on the conversion and reaction rate of NCBs were studied to establish the mechanism of the reaction. The rate of reaction of NCBs was found to be proportional to the concentrations of the catalyst and NCBs and to the cube of the concentration of sulfide. A generalized empirical kinetic model was developed to correlate the experimentally obtained conversion versus time data for the three NCBs.     

Removal of mercury by foam fractionation using surfactin, a biosurfactant

The separation of mercury ions from artificially contaminated water by the foam fractionation process using a biosurfactant (surfactin) and chemical surfactants (SDS and Tween-80) was investigated in this study. Parameters such as surfactant and mercury concentration, pH, foam volume, and digestion time were varied and their effects on the efficiency of mercury removal were investigated. The recovery efficiency of mercury ions was highly sensitive to the concentration of the surfactant. The highest mercury ion recovery by surfactin was obtained using a surfactin concentration of 10 × CMC, while recovery using SDS required < 10 × CMC and Tween-80 >10 × CMC. However, the enrichment of mercury ions in the foam was superior with surfactin, the mercury enrichment value corresponding to the highest metal recovery (10.4%) by surfactin being 1.53. Dilute solutions (2-mg L(-1) Hg(2+)) resulted in better separation (36.4%), while concentrated solutions (100 mg L(-1)) enabled only a 2.3% recovery using surfactin. An increase in the digestion time of the metal solution with surfactin yielded better separation as compared with a freshly-prepared solution, and an increase in the airflow rate increased bubble production, resulting in higher metal recovery but low enrichment. Basic solutions yielded higher mercury separation as compared with acidic solutions due to the precipitation of surfactin under acidic conditions.     

Electricity Generation and Wastewater Treatment of Oil Refinery in Microbial Fuel Cells Using Pseudomonas putida

Microbial fuel cells (MFCs) represent a novel platform for treating wastewater and at the same time generating electricity. Using Pseudomonas putida (BCRC 1059), a wild-type bacterium, we demonstrated that the refinery wastewater could be treated and also generate electric current in an air-cathode chamber over four-batch cycles for 63 cumulative days. Our study indicated that the oil refinery wastewater containing 2213 mg/L (ppm) chemical oxygen demand (COD) could be used as a substrate for electricity generation in the reactor of the MFC. A maximum voltage of 355 mV was obtained with the highest power density of 0.005 mW/cm² in the third cycle with a maximum current density of 0.015 mA/cm² in regard to the external resistor of 1000 Ω. A maximum coulombic efficiency of 6 × 10⁻²% was obtained in the fourth cycle. The removal efficiency of the COD reached 30% as a function of time. Electron transfer mechanism was studied using cyclic voltammetry, which indicated the presence of a soluble electron shuttle in the reactor. Our study demonstrated that oil refinery wastewater could be used as a substrate for electricity generation.     

Numerical and experimental study on the three-dimensional extrusion of square section from square billet through a polynomial shaped curved die

The geometry of die profile plays a major role in reducing the extrusion pressure and ensuring the smooth flow of material. In general, the extrusion process is mostly affected by billet geometry, die geometry, and interface frictional force at the die billet geometry. In the present investigation, an analysis using three-dimensional upper bound method using fifth-order die profile function has been carried out for extrusion of square sections from square billet. The extrusion pressure and optimum die length have been computed by multivariable optimization technique. The present die shape profile is found to be superior to many other profiles. The results obtained will help in design of optimum die profile and investigation of its performance.     

Experimental investigations and comparison of various MPPT techniques for photovoltaic system

This paper deals with Matlab/Simulink and experimental investigations of various maximum power point tracking (MPPT) techniques namely incremental conductance (Inc), perturb and observation (P&O), constant voltage control (CVC) method, and introduction of a novel reference power (Pref) method for extracting the maximum power from the solar photovoltaic (PV) system. The complete system model along with these MPPT methods are developed in Matlab/Simulink and simulation results are obtained during sudden increase in irradiation of 1000 W/m², and verified experimentally. These MPPT methods are also implemented on Inverse-Sepic converter, which claims to extract maximum power from the PV system. Various experimental observations are taken to access the performance of these MPPT techniques such as settling time of the full load current under sudden exposure of irradiation level of 1000 W/m², performance during step increase in irradiation level (from 500 W/m² to 1000 W/m²) and vice versa. Extensive results are taken to compare these methods. The proposed Pref method is found to have lowest settling time to stabilize the load current as 520 ms, whereas, Inc method takes 1.24 s. Further, the efficiency of Inverse-Sepic converter with Pref method achieves the highest efficiency of 95.26%, whereas, it extracts lowest efficiency on same input as 90.77% with P&O method. The overall performance of the proposed Pref method is found to be superior as compared to other discussed MPPT methods as verified by experimental results.     

One-pot fabrication and magnetic studies of Mn-doped TiO(2) nanocrystals with an encapsulating carbon layer

Mn-doped TiO(2) nanocrystals encapsulated in a carbon layer (Ti(1-x)Mn(x)O(2)@C) were synthesized by the one-pot RAPET (reaction under autogenic pressure at elevated temperature) technique. Manganese was doped into the body-centered tetragonal TiO(2) anatase phase to give a Mn:Ti atomic ratio of 1%, 5% and 10%. The surface modification by carbon was achieved in order to make the cubic/tetragonal nanocrystals non-toxic and biocompatible. Electron paramagnetic resonance (EPR) studies revealed a broad resonance (centered at g = 1.9977 due to the interacting spins in the oxide matrix) with increased dopant concentration and the resonance due to carbon. Manganese is mainly present as +II or +III oxidation states. The magnetic behavior was found to be very dependent on the manganese concentration with a ferromagnetic behavior of the 1% doped sample due to the coupling between carriers and manganese spins. A predominant paramagnetic behavior was observed for the higher Mn-doped samples. This study opens up a new dimension for the carbon encapsulation of room-temperature ferromagnetic diluted magnetic semiconductor (DMS) nanomaterials.     

Comparative analysis of storage modules under different dispatch strategies for an optimum decentralized hybrid energy solution: a case study of a remote Indian village

India has a large poor population in spite of having a steady economic growth. Supply of centralized grid power to remote villages of India is not feasible due to adverse topography and poor economic condition of the villagers. To supply the reliable power at a minimum cost including penalty due to carbon dioxide emission, a suitable decentralized energy combination using locally available resources may be a better sustainable solution. The economy of such a hybrid energy supply system significantly depends on storage devices and dispatch strategies. Therefore, selection of appropriate storage devices and dispatch strategy need to be optimized based on available local resources. In this study, the comparative analysis of techno-economic factors for five different storage devices (lead acid battery, lithium-ion battery, vanadium redox battery, zinc bromide battery and pumped hydro energy storage) are studied under two different dispatch strategies, i.e., Load Following and Cycle Charging. The estimated cost of energy and net present cost of the recommended optimum combined energy system are in the range of US$0.197/kWh–US$0.453/kWh and US$3,62,384–US$5,76,369, respectively. The cost of energy, net present cost and carbon dioxide emission for the selected energy generators combination with the zinc bromide battery is 48.964–56.512%, 24.149–32.147% and 43.419–55.865% lower than other storage-based energy systems, respectively. The abovementioned economic and environmental factors are lower by 34.113, 10.489 and 31.094%, respectively, under Load Following dispatch strategy with respect to the Cycle Charging dispatch strategy for the optimum energy combination with zinc bromide battery.

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Application of response surface methodology with a Box–Behnken design for struvite precipitation

Struvite crystals were precipitated by the reaction of magnesium chloride hexahydrate and ammonium dihydrogen phosphate using different concentrations of citric acid as the additive (100, 300, and 500 ppm). The structure, morphology, functional groups and particle size of the crystals were evaluated experimentally by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and particle size analysis. The experimental results demonstrated that citric acid exerted a significant influence on the struvite precipitation and the crystal morphology changed from rod-like to tubular shaped with a larger size and hollow bodies. The average particle size changed from 17.60 to 33.60 μm with increasing citric acid concentration. The results of FTIR suggested that the citric acid adsorbed on the crystal surface. Following the characterization of the crystals prepared using different concentrations of citric acid, the response surface methodology coupled with Box-Behnken design were applied as a statistical tool to determine the effects of the key parameters affecting the precipitation process (temperature, pH and additive concentration) on the responses (namely, particle size and specific cake resistance of struvite). Second-order polynomial equations for both responses were improved to correlate the parameters. Analysis of variance (ANOVA) showed a significant quadratic regression model with high coefficients of the determination values. The optimum conditions for particle size were found to be 60 °C, pH 8 and 500 ppm additive concentration.     

Strategic Fast Induction Heating to Combat Hysteresis Barriers in a Flexible MOF for Rapid CO2 Desorption in Biogas Upgrading

A major challenge in Cyclic Swing Separation using flexible adsorbents that have high equilibrium CO₂ adsorption capacity is their very low-pressure hysteresis that hinders efficient desorption. Mg-Gallate MOF is such a flexible adsorbent that only begins to release CO₂ at its pore closing pressure at 0.08 bar and 30 °C, showing very slow and inefficient desorption in pressure or temperature swing. Therefore, a novel strategy is presented that combines state of art technique Magnetic Induction Heating with a vacuum swing for fast and efficient CO₂ desorption from flexible adsorbents at a moderately elevated temperature (70 °C).