828,566 research outputs found

    Cfd investigation of spacer-filled channels for membrane distillation

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    The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ranging from ~200 to ~800. A good qualitative agreement between simulations and experiments can be observed for the areal distribution of the normalized heat transfer coefficient. Trends of the average heat transfer coefficient are reported as functions of Re for the geometries investigated, thus providing the basis for CFD-based correlations to be used in higher-scale process models

    Separator for alkaline electric batteries and method of making

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    Battery separator membranes of high electrolytic conductivity comprising a cellulose ether and a compatible metallic salt of water soluble aliphatic acids and their hydroxy derivatives are described. It was found that methyl cellulose can be modified by another class of materials, nonpolymeric in nature, to form battery separator membranes of low electrolytic resistance but which have the flexibility of membranes made of unmodified methyl cellulose, and which in many cases enhance flexibility over membranes made with unmodified methyl cellulose. Separator membranes for electrochemical cells comprising a cellulose ether and a modified selected from the group consisting of metallic salts of water soluble alphatic acids and their hydroxy derivatives and to electrochemical cells utilizing said membranes are described

    Fixed-Connectivity Membranes

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    The statistical mechanics of flexible surfaces with internal elasticity and shape fluctuations is summarized. Phantom and self-avoiding isotropic and anisotropic membranes are discussed, with emphasis on the universal negative Poisson ratio common to the low-temperature phase of phantom membranes and all strictly self-avoiding membranes in the absence of attractive interactions. The study of crystalline order on the frozen surface of spherical membranes is also treated.Comment: Chapter 11 in "Statistical mechanics of Membranes and Surfaces", ed. by D.R. Nelson, T. Piran and S. Weinberg (World Scientific, Singapore, 2004); 25 pages with 26 figures (high resolution figures available from author

    Polyelectrolyte multilayer films as backflushable nanofiltration membranes with tunable hydrophilicity and surface charge

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    A diverse set of supported polyelectrolyte multilayer (PEM) membranes with controllable surface charge, hydrophilicity, and permeability to water and salt was designed by choosing constituent polyelectrolytes and by adjusting conditions of their deposition. The membranes were characterized in terms of their water and MgSO4 permeabilities and resistance to colloidal fouling. The commercial nanofiltration membrane (NF270) was used as a comparative basis. Highly hydrophilic and charged PEMs could be designed. For all membranes, MgSO4 permeability coefficients of NF270 and all PEM membranes exhibited a power law dependence on concentration: Ps [is proportional to] C-[tau], 0.19 < [tau] < 0.83. PEM membranes were highly selective and capable of nearly complete intrinsic rejection of MgSO4 at sufficiently high fluxes. With the deposition of colloids onto the PEM surface, the separation properties of one type of polyelectrolyte membrane showed similar rejection and superior flux properties compared to NF270 membranes. We hypothesize that a PEM-colloid nanocomposite was formed as a result of colloidal fouling of these PEM films. The feasibility of regenerating the PEM membranes fouled by colloids was also demonstrated. In summary, the PEM-based approach to membrane preparation was shown to enable the design of membranes with the unique combination of desirable ion separation characteristics and regenerability of the separation layer

    Synthesis and textural properties of unsupported and supported rutile (TiO2) membranes

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    Two approaches were postulated for improving the stability of porous texture of titania membranes: (1) retarding the phase transformation and grain growth; (2) avoiding the phase transformation. Based on the second approach, rutile membranes were made directly from a rutile sol, prepared by the precipitation of titania on SnO2 nuclei. The rutile membranes were stable up to 800 °C, with a porosity of ca. 40%, whereas normal titania membranes (starting with anatase) show very little porosity above 600 °C. Alumina substitution retards grain growth and pore growth at 850 °C for unsupported as well as supported membranes. \u

    Lateral phase separation of confined membranes

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    We consider membranes interacting via short, intermediate and long stickers. The effects of the intermediate stickers on the lateral phase separation of the membranes are studied via mean-field approximation. The critical potential depth of the stickers increases in the presence of the intermediate sticker. The lateral phase separation of the membrane thus suppressed by the intermediate stickers. Considering membranes interacting with short and long stickers, the effect of confinement on the phase behavior of the membranes is also investigated analytically

    The preparation and characterization of alumina membranes with ultra-fine pores : Part 4. Ultrafiltration and hyperfiltration experiments

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    The rejection characteristics of three types of alumina membranes for polyethylene glycol (PEG) polymers and dextrans soluted in water have been investigated. If the temperature at which the membranes are treated is increased, the pore size increases and as a result the cut-off value also increases. The Al2O3-400 membrane (i.e., the membrane treated at 400°C) exhibits a cut-off value of 2,000 for PEG while that of an Al2O3-800 membrane is about 20,000. Both Al2O3-500 and Al2O3-800 membranes show rejections higher than 80% for the dextrans investigated. The rejection behaviour is compared with literature data on Nuclepore membranes. The performance of the alumina membranes is compared with that of other inorganic membranes. Low molecular weight solutes show only small rejection values solar, although high values are reported in the literature for Vycor glass membranes with pores of similar size
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