Microporous polymers are a class of microporous materials with high free volume elements and large surface areas. Microporous polymers have received much attention for various applications in gas ...separation, gas storage, and for clean energy resources due to their easy processability for mass production, as well as microporosity for high performance. This review describes recent research trends of microporous polymers in various energy related applications, especially for gas separations and gas storages. The new classes of microporous polymers, so-called thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs), have been developed by enhancing polymer rigidity to improve microporosity with sufficient free volume sizes. Their rigidity improves separation performance and efficiency with extraordinary gas permeability. Moreover, their solubility in organic solvents allows them to have potential use in large-scale industrial applications.
In this study, a finite volume method is employed to investigate the performance of a novel parabolic trough solar collector with synthetic oil–Al2O3 nanofluid as the heat transfer fluid. An annular ...porous structure is installed inside the absorber tube to improve heat transfer. The effects of the simultaneous utilization of porous structure and nanoparticle addition on heat transfer, pressure drop, and thermal efficiency of the receiver are investigated for different values of Reynolds number, volume fraction of nanoparticle, inlet temperature and Darcy number of the porous region. The results show that as Reynolds number and volume fraction of nanoparticle increase, heat transfer coefficient, pressure drop, and thermal efficiency increase. However, the increases in inlet temperature lead to the decreases in heat transfer coefficient, pressure drop, and thermal efficiency. At Reynolds numbers higher than 30×104, simultaneous utilization of porous structure with Da = 0.3 and nanoparticles increases heat transfer coefficients nearly 7% and 20%, pressure drops up to 42.5% and 42%, thermal efficiencies up to 8% and 15%, overall efficiencies nearly 5% and 14%, and exergetic efficiencies by 7% and 15% for inlet temperature of 500 and 600 K, respectively.
•Simultaneous utilization of porous structure and nanofluid are investigated.•Nanoparticle addition and porous structure are recommended at high HTF flow rates.•HTF with lower inlet temperatures provides higher thermal efficiencies.•Installing inner porous annular structure increases thermal efficiency up to 13%.•Porous structure increases exergetic efficiency of solar collectors by about 15%.
In order to grasp the partition diffusion and pollution of respirable dust under various turbulent velocities in fully-mechanized mining face, Finite Volume Method was adopted to simulate and study ...the diffusion behavior characteristics of respirable dust of 52305-1 fully-mechanized mining face in Daliuta coal mine at different areas under full section independent negative pressure ventilation conditions based on airflow streamline, airflow vector, and dust trace. Especially the dust particle movements under the impact of turbulent inlet velocity were defined accurately. The results show that a narrow and long high-speed zone is formed between the coal shearer and corresponding hydraulic pillars due to the blocking effect of coal shearer. At the height of breathing zone, the area with maximum air velocity is performed from the variable cross section, the maximum velocity reaches up to 1.44–2.52 times over inlet air velocity, also the value decreases as the inlet air velocity increases. Average respirable dust concentration of breathing zone height decreases with the increase of inlet air velocity, however the decreasing degree is weakened gradually. With the increase of turbulent inlet velocity, the settlement range of the dust from advancing support and the transverse diffusion range of the dust from drum cutting coal is gradually reduced, also the high concentration respirable dust area with more than 1440 mg/m3 gradually disappear. When the inlet air velocity is over 2.5 m/s, the effect of dust removal by ventilation is weakened gradually.
•Full scale refined partition physical model with original proportion.•Parameters setting based on field measurement with more precise apparatus.•Partition pollution of respirable dust from different dust sources is studied.•The pollution mechanism of respirable dust under different velocity is obtained.•The maximal allowable turbulent velocity for dust removal is investigated.
Con el objetivo de determinar si la especificidad de las tareas técnico-tácticas de los entrenamientos afecta a la carga externa (CE) expuesta por los jugadores, se registraron datos de 11 jugadores ...de entre 15 y 16 años (15.55 ± 0.52) de un equipo masculino de fútbol sala durante 10 entrenamientos con acelerómetros Polar Team Pro®, analizando las aceleraciones (A) y desaceleraciones (D) de baja intensidad (m/s2): A-1 0.50 a 0.99, A-2 1.00 a 1.99, D-1 –0.50 a –0.99, D-2 –1.00 a –1.99; y de alta intensidad (m/s2): A-3 2.00 a 2.99, A-4 3.00 a 50.00, D-3 –2.00 a –2.99 y D-4 –3.00 a –50.00. Se obtuvieron posibles relaciones entre la CE y los ejercicios de nivel de aproximación III (orientación especial) en D-3 (r = .85; p = .03), D-4 (r = .98; p = <.01), A-3 (r = 1.00; p = <.01), TOTAL A-D 3 (r = .96; p = <.01) y TOTAL A-D 3-4 (r = .97; p = <.01). El análisis de regresión lineal mostró posibles causalidades entre la CE y los ejercicios de Nivel III en D-3 (R2 = .73), D-4 (R2 = .97), A-3 (R2 = .99), TOTAL A-D 3 (R2 = .93) y TOTAL A-D 3-4 (R2 = .95). Los resultados sugirieron que, en este contexto específico, los ejercicios de Nivel III provocarían un aumento en la CE de alta intensidad. Controlar estos aspectos puede ser útil para programar la carga según las demandas competitivas y las características de la plantilla.
In this work, a series of mixed matrix membranes (MMMs) consisting of Pebax® 1657 as the main polymer matrix, poly(ethylene glycol) (PEG) derivatives with low molecular weights as additives, and ...graphene oxide (GO) with different loadings as a nanofiller, were prepared for CO2/N2 separation. Changes in the amorphous and crystalline regions of Pebax®/PEG blend membranes and in the free volume of GO-embedded MMMs were estimated based on differential scanning calorimetry (DSC) thermograms. The fractional free volume and density of the Pebax®/PEG blend membranes were investigated according to additive models. Particularly, blending poly(ethylene glycol) methyl ethyl acrylate (PEG-MEA) with the Pebax® matrix significantly improved CO2 permeability without sacrificing high CO2/N2 selectivity. Incorporating GO nanosheets up to 0.3 wt% into the Pebax®/PEG-MEA matrix was found to have a considerable impact on increasing CO2/N2 selectivity, due to largely in part to an increase in the CO2 solubility coefficients. Upon a further increase in GO loading, both CO2 permeability and CO2/N2 selectivity decreased as a result of increasing tortuosity for gas diffusion and also GO aggregation at high GO loading content. More importantly, the Pebax®/PEG-MEA blend membrane with the optimized loading of GO, i.e., 0.3 wt% indicated outstanding anti-CO2 plasticization resistance up to 10 bar as well as long-term stability over 100 days without significant deterioration of CO2/N2 separation performance.
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•Graphene Oxide (GO)-embedded mixed matrix membranes (MMMs) were systematically designed with two additives.•GO-embedded MMMs show both higher CO2 permeability and CO2/N2 selectivity beyond the upper bound.•The effect of GO on transport property of MMMs was explained using solution-diffusion model.•Incorporating GO nanosheets in MMMs play a significant role against CO2-induced plasticization.
Water transport rate in network membranes is inversely correlated to thickness, thus superior permeance is achievable with ultrathin membranes prepared by complicated methods circumventing nanofilm ...weakness and defects. Conferring ultrahigh permeance to easily prepared thicker membranes remains challenging. Here, a tetrakis(hydroxymethyl) phosphonium chloride (THPC) monomer is discovered that enables straightforward modification of polyamide composite membranes. Water permeance of the modified membrane is ≈6 times improved, give rising to permeability (permeance × thickness) one magnitude higher than state‐of‐the‐art polymer nanofiltration membranes. Meanwhile, the membrane exhibits good rejection (RNa2SO4 = 98%) and antibacterial properties under crossflow conditions. THPC modification not only improves membrane hydrophilicity, but also creates additional angstrom‐scale channels in polyamide membranes for unimpeded transport of water. This unique mechanism provides a paradigm shift in facile preparation of ultrapermeable membranes with unreduced thickness for clean water and desalination.
Facile modification of polyamide composite membranes by an inexpensive phosphonium monomer featuring tetrahedral geometry is found to create additional water transport channels, improving the water purification performance without reducing film thickness. Compared with cutting‐edge ultrathin membranes, the modified membrane highlights good rejection, antibacterial properties, superior water permeability, and facile preparation.
Membranes and membrane reactors for pure hydrogen production are widely investigated not only because of the important application areas of hydrogen, but especially because mechanically and ...chemically stable membranes with high perm-selectivity towards hydrogen are available and are continuously further improved in terms of stability and hydrogen flux. Membrane reactors are (multiphase) reactors integrating catalytic reactions (generally reforming and water gas shift reactions for hydrogen production) and separation through membranes in a single unit. This combination of process steps results in a high degree of process integration/intensification, with accompanying benefits in terms of increased process or energy efficiencies and reduced reactor or catalyst volume.
The aim of this review is to highlight recent advances in hydrogen selective membranes (from palladium-based to silica and proton conductors) along with the advances for the different types of membrane reactors available (from packed bed to fluidized bed, from micro-reactors to bio-membrane reactors). In addition, the application of membrane reactors for hydrogen production from different feedstock is also discussed.
► Recent advances in hydrogen selective membranes are presented. ► Commercial membranes for hydrogen production are discussed. ► An overview of the membrane reactor concepts is highlighted. ► The application of membrane reactors to different feedstock is reported.
El desarrollo en América Latina y el Caribe debe pensarse como un problema de restricción externa, donde se han impuesto discursos que impiden cualquier proceso de convergencia con las economías ...desarrolladas. Por esto, se hace necesario cuestionar los fundamentos teóricos de tales discursos, demostrando que, en su mayoría, han sido controvertidos y declarados inconsistentes; transformando tales posturas en ideológicas y nunca coherentes. Así pues, en este artículo se busca afrontar los desafíos del desarrollo que enfrenta la región a partir de un análisis teórico alternativo que nos acerque a una concepción global de los conflictos socio-económicos del desarrollo y nos permita sostener postulados normativos para contribuir al debate por el desarrollo de nuestras naciones, abogando siempre por políticas de industrialización y de crecimiento vía demanda efectiva.
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