Molecular Simulations of Supercritical Fluid Permeation through Disordered Microporous Carbons

International audienceFluid transport through microporous carbon-based materials is inherent in numerous applications, ranging from gas separation by carbon molecular sieves to natural gas production from coal seams and gas shales. The present study investigates the steady-state permeation of supercritical methane in response to a constant cross-membrane pressure drop. We performed dual control volume grand canonical molecular dynamics (DCV-GCMD) simulations to mimic the conditions of actual permeation experiments. To overcome arbitrary assumptions regarding the investigated porous structures, the membranes were modeled after the CS1000a and CS1000 molecular models, which are representative of real microporous carbon materials. When adsorption-induced molecular trapping (AIMT) mechanisms are negligible, we show that the permeability of the microporous material, although not significantly sensitive to the pressure gradient, monotonically decreases with temperature and reservoir pressures, consistent with diffusion theory. However, when AIMT occurs, the permeability increases with temperature in agreement with experimental data found in the literature

Evaluating socio-economic and environmental sustainability of the sheep farming activity in Greece: a whole-farm mathematical programming approach

Ruminant livestock farming is an important agricultural activity, mainly located in less favoured areas. Furthermore, ruminants have been identi fi ed as a signi fi cant source of GHG emissions. In this study, a whole-farm optimization model is used to assess the socio-economic and environmental performance of the dairy sheep farming activity in Greece. The analysis is undertaken in two sheep farms that represent the extensive and the semi-intensive farming systems. Gross margin and labour are regarded as socio-economic indicators and GHG emissions as environmental indicators. The issue of the marginal abatement cost is also addressed. The results indicate that the semi-intensive system yields a higher gross margin/ewe (179 €) than the extensive system (117 €) and requires less labour. The extensive system causes higher emissions/kg of milk than the semi-intensive system (5.45 and 2.99 kg of CO2 equivalents, respectively). In both production systems, abatement is achieved primarily via reduction of the fl ock size and switch to cash crops. However, the marginal abatement cost is much higher in the case of the semi-intensive farms, due to their high productivity

Influence du froid, du vent et de la pluie sur les dépenses énergétiques et la thermorégulation de sept types génétiques de brebis

International audienc

Understanding the unsteady pressure field inside combustion chambers of compression-ignited engines using a computational fluid dynamics approach

[EN] In this article, a numerical methodology for assessing combustion noise in compression ignition engines is described with the specific purpose of analysing the unsteady pressure field inside the combustion chamber. The numerical results show consistent agreement with experimental measurements in both the time and frequency domains. Nonetheless, an exhaustive analysis of the calculation convergence is needed to guarantee an independent solution. These results contribute to the understanding of in-cylinder unsteady processes, especially of those related to combustion chamber resonances, and their effects on the radiated noise levels. The method was applied to different combustion system configurations by modifying the spray angle of the injector, evidencing that controlling the ignition location through this design parameter, it is possible to decrease the combustion noise by minimizing the resonance contribution. Important efficiency losses were, however, observed due to the injector/bowl matching worsening which compromises the performance and emissions levels.The authors want to express their gratitude to CONVERGENT SCIENCE Inc. and Convergent Science GmbH for their kind support for performing the CFD calculations using CONVERGE software.Torregrosa, AJ.; Broatch, A.; Margot, X.; Gómez-Soriano, J. (2018). Understanding the unsteady pressure field inside combustion chambers of compression-ignited engines using a computational fluid dynamics approach. International Journal of Engine Research. 1-13. https://doi.org/10.1177/1468087418803030S113Benajes, J., Novella, R., De Lima, D., & Tribotté, P. (2014). Analysis of combustion concepts in a newly designed two-stroke high-speed direct injection compression ignition engine. International Journal of Engine Research, 16(1), 52-67. doi:10.1177/1468087414562867Costa, M., Bianchi, G. M., Forte, C., & Cazzoli, G. (2014). A Numerical Methodology for the Multi-objective Optimization of the DI Diesel Engine Combustion. Energy Procedia, 45, 711-720. doi:10.1016/j.egypro.2014.01.076Navid, A., Khalilarya, S., & Taghavifar, H. (2016). Comparing multi-objective non-evolutionary NLPQL and evolutionary genetic algorithm optimization of a DI diesel engine: DoE estimation and creating surrogate model. Energy Conversion and Management, 126, 385-399. doi:10.1016/j.enconman.2016.08.014Benajes, J., García, A., Pastor, J. M., & Monsalve-Serrano, J. (2016). Effects of piston bowl geometry on Reactivity Controlled Compression Ignition heat transfer and combustion losses at different engine loads. Energy, 98, 64-77. doi:10.1016/j.energy.2016.01.014Masterton, B., Heffner, H., & Ravizza, R. (1969). The Evolution of Human Hearing. The Journal of the Acoustical Society of America, 45(4), 966-985. doi:10.1121/1.1911574Strahle, W. C. (1978). Combustion noise. Progress in Energy and Combustion Science, 4(3), 157-176. doi:10.1016/0360-1285(78)90002-3Flemming, F., Sadiki, A., & Janicka, J. (2007). Investigation of combustion noise using a LES/CAA hybrid approach. Proceedings of the Combustion Institute, 31(2), 3189-3196. doi:10.1016/j.proci.2006.07.060Klos, D., & Kokjohn, S. L. (2014). Investigation of the sources of combustion instability in low-temperature combustion engines using response surface models. International Journal of Engine Research, 16(3), 419-440. doi:10.1177/1468087414556135Cyclic dispersion in engine combustion—Introduction by the special issue editors. (2015). International Journal of Engine Research, 16(3), 255-259. doi:10.1177/1468087415572740Hickling, R., Feldmaier, D. A., & Sung, S. H. (1979). Knock‐induced cavity resonances in open chamber diesel engines. The Journal of the Acoustical Society of America, 65(6), 1474-1479. doi:10.1121/1.382910Torregrosa, A. J., Broatch, A., Margot, X., Marant, V., & Beauge, Y. (2004). Combustion chamber resonances in direct injection automotive diesel engines: A numerical approach. International Journal of Engine Research, 5(1), 83-91. doi:10.1243/146808704772914264Broatch, A., Margot, X., Gil, A., & Christian Donayre, (José). (2007). Computational study of the sensitivity to ignition characteristics of the resonance in DI diesel engine combustion chambers. Engineering Computations, 24(1), 77-96. doi:10.1108/02644400710718583Eriksson, L. J. (1980). Higher order mode effects in circular ducts and expansion chambers. The Journal of the Acoustical Society of America, 68(2), 545-550. doi:10.1121/1.384768Broatch, A., Margot, X., Novella, R., & Gomez-Soriano, J. (2017). Impact of the injector design on the combustion noise of gasoline partially premixed combustion in a 2-stroke engine. Applied Thermal Engineering, 119, 530-540. doi:10.1016/j.applthermaleng.2017.03.081Tutak, W., & Jamrozik, A. (2016). Validation and optimization of the thermal cycle for a diesel engine by computational fluid dynamics modeling. Applied Mathematical Modelling, 40(13-14), 6293-6309. doi:10.1016/j.apm.2016.02.021Payri, F., Benajes, J., Margot, X., & Gil, A. (2004). CFD modeling of the in-cylinder flow in direct-injection Diesel engines. Computers & Fluids, 33(8), 995-1021. doi:10.1016/j.compfluid.2003.09.003Benajes, J., Novella, R., De Lima, D., & Thein, K. (2017). Impact of injection settings operating with the gasoline Partially Premixed Combustion concept in a 2-stroke HSDI compression ignition engine. Applied Energy, 193, 515-530. doi:10.1016/j.apenergy.2017.02.044Lesieur, M., Métais, O., & Comte, P. (2005). Large-Eddy Simulations of Turbulence. doi:10.1017/cbo9780511755507Pope, S. B. (2004). Ten questions concerning the large-eddy simulation of turbulent flows. New Journal of Physics, 6, 35-35. doi:10.1088/1367-2630/6/1/035Silva, C. F., Leyko, M., Nicoud, F., & Moreau, S. (2013). Assessment of combustion noise in a premixed swirled combustor via Large-Eddy Simulation. Computers & Fluids, 78, 1-9. doi:10.1016/j.compfluid.2010.09.034Jamrozik, A., Tutak, W., Kociszewski, A., & Sosnowski, M. (2013). Numerical simulation of two-stage combustion in SI engine with prechamber. Applied Mathematical Modelling, 37(5), 2961-2982. doi:10.1016/j.apm.2012.07.040Qin, W., Xie, M., Jia, M., Wang, T., & Liu, D. (2014). Large eddy simulation of in-cylinder turbulent flows in a DISI gasoline engine. Applied Mathematical Modelling, 38(24), 5967-5985. doi:10.1016/j.apm.2014.05.004Broatch, A., Margot, X., Novella, R., & Gomez-Soriano, J. (2016). Combustion noise analysis of partially premixed combustion concept using gasoline fuel in a 2-stroke engine. Energy, 107, 612-624. doi:10.1016/j.energy.2016.04.045Torregrosa, A. J., Broatch, A., Martín, J., & Monelletta, L. (2007). Combustion noise level assessment in direct injection Diesel engines by means of in-cylinder pressure components. Measurement Science and Technology, 18(7), 2131-2142. doi:10.1088/0957-0233/18/7/045Payri, F., Broatch, A., Margot, X., & Monelletta, L. (2008). Sound quality assessment of Diesel combustion noise using in-cylinder pressure components. Measurement Science and Technology, 20(1), 015107. doi:10.1088/0957-0233/20/1/015107Ihlenburg, F. (2003). The Medium-Frequency Range in Computational Acoustics: Practical and Numerical Aspects. Journal of Computational Acoustics, 11(02), 175-193. doi:10.1142/s0218396x03001900Lapuerta, M., Armas, O., & Hernández, J. J. (1999). Diagnosis of DI Diesel combustion from in-cylinder pressure signal by estimation of mean thermodynamic properties of the gas. Applied Thermal Engineering, 19(5), 513-529. doi:10.1016/s1359-4311(98)00075-1Payri, F., Olmeda, P., Martín, J., & García, A. (2011). A complete 0D thermodynamic predictive model for direct injection diesel engines. Applied Energy, 88(12), 4632-4641. doi:10.1016/j.apenergy.2011.06.005Payri, F., Broatch, A., Tormos, B., & Marant, V. (2005). New methodology for in-cylinder pressure analysis in direct injection diesel engines—application to combustion noise. Measurement Science and Technology, 16(2), 540-547. doi:10.1088/0957-0233/16/2/029Shahlari, A. J., Hocking, C., Kurtz, E., & Ghandhi, J. (2013). Comparison of Compression Ignition Engine Noise Metrics in Low-Temperature Combustion Regimes. SAE International Journal of Engines, 6(1), 541-552. doi:10.4271/2013-01-1659Yakhot, V., & Orszag, S. A. (1986). Renormalization group analysis of turbulence. I. Basic theory. Journal of Scientific Computing, 1(1), 3-51. doi:10.1007/bf01061452Redlich, O., & Kwong, J. N. S. (1949). On the Thermodynamics of Solutions. V. An Equation of State. Fugacities of Gaseous Solutions. 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Assessment of flamelet versus multi-zone combustion modeling approaches for stratified-charge compression ignition engines. International Journal of Engine Research, 17(3), 280-290. doi:10.1177/1468087415571006Torregrosa, A. J., Broatch, A., Gil, A., & Gomez-Soriano, J. (2018). Numerical approach for assessing combustion noise in compression-ignited Diesel engines. Applied Acoustics, 135, 91-100. doi:10.1016/j.apacoust.2018.02.006Torregrosa, A., Olmeda, P., Degraeuwe, B., & Reyes, M. (2006). A concise wall temperature model for DI Diesel engines. Applied Thermal Engineering, 26(11-12), 1320-1327. doi:10.1016/j.applthermaleng.2005.10.021Broatch, A., Javier Lopez, J., García-Tíscar, J., & Gomez-Soriano, J. (2018). Experimental Analysis of Cyclical Dispersion in Compression-Ignited Versus Spark-Ignited Engines and Its Significance for Combustion Noise Numerical Modeling. Journal of Engineering for Gas Turbines and Power, 140(10). doi:10.1115/1.4040287Molina, S., García, A., Pastor, J. 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Anaerobic degradation of 2-propanol: Laboratory and pilot-scale studies

The anaerobic degradation of 2-propanol, an important industrial solvent, was scaled-up from batch assays to a pilot expanded granular sludge bed (EGSB) reactor at 25 °C. Batch studies indicated that 2-propanol followed Haldane kinetics, with a maximum rate at 10 g COD L−1. Concentrations as high as 25 g COD L−1 did not inhibit the degradation of ethanol, a common co-solvent. Similar specific methanogenic activities (SMA) were obtained for water-solvent and water-brewery sludges (88 and 77 ml CH4 g-VS−1 d−1 at 5 g COD L−1). Continuous degradation showed a lag-phase of three weeks with water-brewery sludge. Increases in 2-propanol load from 0.05 to 0.18 kg COD kg-VS−1 d−1 caused a shift from the consumption of soluble matter to methane production, indicating polyhydroxybutyrates (PHB) accumulation. Conversely, smooth increases of up to 0.29 kg COD kg-VS−1 d−1 allowed 2-propanol degradation without PHB accumulation. The slowdown rate of 2-propanol-oxidizer and acetate-utilizing methanogen bacteria below 20 °C adversely impacted both removal and CH4 yield

A combined numerical and experimental study of the 3D tumble structure and piston boundary layer development during the intake stroke of a gasoline engine

Due to its positive effect on flame propagation in the case of a well-defined breakdown, the formation of a large-scale tumble motion is an important goal in engine development. Cycle-to-cycle variations (CCV) in the tumble position and strength however lead to a fluctuating tumble breakdown in space and time and therefore to combustion variations, indicated by CCV of the peak pressure. This work aims at a detailed investigation of the large-scale tumble motion and its interaction with the piston boundary layer during the intake stroke in a state-of-the-art gasoline engine. To allow the validation of the flow near the piston surface obtained by simulation, a new measurement technique called “Flying PIV” is applied. A detailed comparison between experimental and simulation results is carried out as well as an analysis of the obtained flow field. The large-scale tumble motion is investigated based on numerical data of multiple highly resolved intake strokes obtained using scale-resolving simulations. A method to detect the tumble center position within a 3D flow field, as an extension of previously developed 2D and 3D algorithms, is presented and applied. It is then used to investigate the phase-averaged tumble structure, its characteristics in terms of angular velocity and the CCV between the individual intake strokes. Finally, an analysis is presented of the piston boundary layer and how it is influenced by the tumble motion during the final phase of the intake stroke

Vivienne Westwood and the ethics of consuming fashion

Our paper examines ethical consumption using the case study of Vivienne Westwood, the fashion designer, and her eponymous firm, and shows how consumers of fashion might be considered ethical. The fashion industry has figured prominently in ethical debates, notably its role in encouraging overconsumption of resources and promoting an idealised lifestyle that is often neither materially nor psychically sustainable for consumers (Buchholz, 1998). We acknowledge this, yet suggest the purchase and use of clothing carries with it the potential to be ethical insofar as customers find themselves personally implicated with and caring for a designers' work

Irregular breakfast eating and health status among adolescents in Taiwan

BACKGROUND: Regular breakfast eating (RBE) is an important contributor to a healthy lifestyle and health status. The aims of the present study were to evaluate the relationships among irregular breakfast eating (IRBE), health status, and health promoting behavior (HPB) for Taiwanese adolescents. METHODS: A cross-sectional, descriptive design was used to investigate a cluster sample of 1609 (7(th )-12(th )grade) adolescents located in the metropolitan Tao-Yuan area during the 2005 academic year. The main variables comprised breakfast eating pattern, body weight, and health promoting behaviors. Data were collected by a self-administered questionnaire. RESULTS: A total of 1609 participants were studied, 64.1% in junior high school and 35.9% in high school, boys (47.1%) and girls (52.9%) ranging in age from 12–20 years. Of the total participant population, 28.8% were overweight and nearly one quarter (23.6%) reported eating breakfast irregularly during schooldays. The findings indicated that adolescents with RBE had a lower risk of overweight (OR for IRBE vs. RBE = 1.51, 95% CI: 1.12, 2.04), and that the odds of becoming overweight were 51% greater for IRBE than for RBE even after controlling for demographical and HPB variables. IRBE also was a strong indicator for HPB. However, the profile of the high-risk IRBE group was predominantly junior high schoolchildren and/or children living without both parents. CONCLUSION: This study provides valuable information about irregular breakfast eating among adolescents, which is associated with being overweight and with a low frequency of health promoting behavior. School and family health promotion strategies should be used to encourage all adolescents to eat breakfast regularly