Determination of optimal operating conditions for a polymer electrolyte membrane fuel cell stack: optimal operating condition based on multiple criteria

A methodology for optimal control of the polymer electrolyte membrane fuel cell (PEMFC) with multiple criteria is presented here. In this regard, thermoelectric objectives and thermoeconomic objective are considered, simultaneously. The proposed fuel cell is a 1200 W Ballard PEMFC namely Nexa? power module. The net power density and exergetic efficiency of the PEMFC are maximized, and the unit cost of the generated power is minimized in a multi‐objective optimization procedure using the NSGA‐II (non‐dominated sorting genetic algorithm). Operating temperature and pressure, air stoichiometric coefficient at the cathode and the current density are considered as controlling parameters in order to acquire optimal performance of the PEMFC. A set of optimal solution namely the Pareto frontier is obtained, and a final optimal solution is selected from available solutions located on the Pareto frontier using the fuzzy decision‐making process based on the Bellman–Zadeh approach. Results are compared with corresponding results obtained previously in single objective optimization scenarios. It has been shown that the optimal operating condition obtained based on the multiple criteria approach has least deviation from the ideal features of the fuel cell in comparison to the corresponding optimal solution obtained in conventional single‐objective optimization approaches. Copyright © 2013 John Wiley & Sons, Ltd.     

STUDY OF CAPTURING EMITTED CO2 IN THE FORM OF HYDRATES IN A TUBULAR REACTOR

Stabilizing atmospheric CO₂ concentration requires the development of novel methods for capturing it in the form of permanent reservoirs. Among the proposed methods is CO₂ storage in the form of hydrate. In this study a method was established for CO₂ conversion to hydrate. This method can be applied to bioethanol plants, which produce CO₂ as a by-product of ethanol fermentation. In this regard, a tubular recirculating flow reactor was developed for the study of CO₂ hydrate formation. The experiments were carried out at 279 K and 3.5–5 MPa to determine the rate of CO₂ hydrate formation. Further, a model was developed for prediction of the rate of hydrate formation based on the mass transfer, crystallization, and thermodynamic concepts. The predicted hydrate formation rate was compared to the experimental data in order to validate the model prediction. The predicted results were in good agreement with the experimental data at different operating conditions.     

Experimental and theoretical study of gas hydrate formation in a high‐pressure flow loop

A set of mathematical models are developed based on thermodynamics, mass transfer, and crystallisation concepts to predict hydrate formation rate and the aqueous phase composition in the flow loop. In order to validate the model, experimental study is carried out in a 10 m loop with the inside diameter of 10.6 mm using gas mixture of 73% methane and 27% propane to measure the hydrate formation rate. The experimental conditions include temperature from 4 to 5°C and pressures between 2 and 3 MPa. Good agreements are noticed when the experimental and theoretical hydrate formation rates are compared at different operating conditions.     

Mathematical modeling and simulation of pigging operation in gas and liquid pipelines

The pigging operation is a common practice in the petroleum and gas industry. Pigging flow lines is employed for many reasons including cleaning deposits such as wax layers, the removal of liquids and condensate, the separation of products pumped one after the other in the same pipeline, measurement, and control and flow line inspection. In this paper, the mathematical modeling of the transient motion of a pig through liquid and gas pipelines is presented. For this purpose, the fluid flow equations were combined with a linear momentum equation for the pig. The nonlinear equations are solved under an unsteady state condition by the method of characteristics (MOC) with a regular rectangular grid through the pipeline under appropriate initial and boundary conditions. From this simulation, the pig position, optimum flow rate in upstream flow and the time that the pig reaches the end of the pipeline are obtained. Comparison of the simulation results with the field data of liquid flow through the pipeline from KG to AG located in Iran show that the derived mathematical models are effective for the prediction of position and pig velocity under the given operational conditions of a pipeline. Similar results are also obtained for gas flow through the pipeline from Nar-1 to Nar-2 located in Iran, in comparison with the field data.     

La-Si-O-N glasses: Part II: Vickers hardness and refractive index

Vickers hardness and refractive index have been determined for a series of La-Si-O-N oxy-nitride glasses containing 30–62 e/o of La and 9–68 e/o of N. The hardness varies between 7.7 and 11.5 GPa at a load of 1 kg and is dependent of the N content, while the La content does not influence it significantly. The increase of the hardness with N content is, contrary to reported findings for other oxy-nitride glasses, found not to be linear over the whole compositional range. The refractive index varies between 1.8 and 2.3 and increases non-linearly with increasing N content. The compositional variations of hardness and refractive index are compared with previously published results.     

Solubility Calculation of Oil‐Conta‐minated Drill Cuttings in Supercritical Carbon Dioxide Using Statistical Associating Fluid Theory (PC‐SAFT)

Supercritical fluid extraction is a new technology that could be effectively used to treat oil‐contaminated drill cuttings generated during drilling for oil and gas. In this work, the solubility of oil‐contaminated drill cuttings in supercritical carbon dioxide is obtained by an experimental flow type apparatus. The solubility was measured at 200 bar pressure, over a temperature range of 55–79.5 °C. The measured solubility and experimental data for oil in drill cuttings were correlated using the PC‐SAFT, PR and SRK EOS models, without any adjustable parameters. Average absolute derivations of less than 15.1 %, 98.7 %, and 99.3 % are achieved between predicted and experimental values for the PC‐SAFT, PR and SRK EOS models, respectively, over a wide range of temperatures.     

An experimental study of drag reduction by nanofluids in slug two-phase flow of air and water through horizontal pipes☆

This study investigates the effect of injecting nanofluids containing nano-SiO2 as drag reducing agents (DRA) at different concentrations on the pressure drop of air–water flow through horizontal pipe....     

Spark plasma sintering of B4C ceramics: The effects of milling medium and TiB2 addition

Boron carbide (B₄C) ceramics, with a relative density up to 98.4% and limited grain growth, were prepared at 1600-1800 °C by spark plasma sintering (SPS) technique. The effects of powder milling medium (water and 2-propanol) on the powders' surface characteristics and TiB₂ addition on the sintering densification were investigated. The ball milling processing of B₄C powders in water can promote the sintering of B₄C ceramics. A B₂O₃ layer on B₄C particle surface is concluded to promote the densification of the B₄C ceramics at an early sintering stage. This B₂O₃ layer, which normally inhibits the densification process at the final stage of the sintering, can be reduced through reaction with TiB₂ particles, resulting in further densification of the B₄C ceramics.     

Effect of Natural Extracted Antioxidants from Eriobotrya japonica (Lindl.) Fruit Skin on Thermo Oxidative Stability of Soybean Oil During Deep Frying

The effects of ultrasound-assisted, supercritical CO₂ and solvent extraction techniques on antioxidant activity of Eriobotrya japonica (Lindl.) skin extracts were investigated using 2, 2-diphenyl-1-picrylhydrazyl, β-carotene, and Rancimat assays. Solvent extract of skin at 400 ppm had the highest antioxidant activity. Solvent extraction was the most effective method on extraction of phenols and tocopherols. Protective effects of extracts in stabilization of soybean oil during frying were determined by measuring its peroxide value, total polar compounds, carbonyl value, free fatty acids, conjugated dienes, and trienes. Results indicated that solvent extract of skin at 400 ppm exhibited stronger antioxidant activity in oil than tertiary butylhydroquinone.     

Antioxidant Activity of Loquat (Eriobotrya japonica Lindl.) Fruit Peel and Pulp Extracts in Stabilization of Soybean Oil During Storage Conditions

The antioxidation activities of Eriobotrya japonica (Lindl.) fruit peel and pulp extracts were determined using DPPH, β-carotene, and Rancimat methods. Results showed that ethanol-water extract of peel and ethanol extract of pulp had the highest antioxidant activity. Protective effects of extracts in stabilization of soybean oil were tested and compared to tert-butyl hydroquinone by measuring peroxide values, free fatty acids, thiobarbituric acid, oxidative stability, and conjugated dienes and trienes values during storage (65 days at 25°C). Results showed that the ethanol-water extract of peel at 400 ppm exhibited stronger antioxidant activity, but the highest effect was observed in tert-butyl hydroquinone.