Empty Channels Research Articles

Modelling temperature and salt concentration distribution in membrane distillation feed channel

The method of Ilias and Govind for modeling ultrafiltration was modified to model a flat sheet air gap membrane distillation module with empty channels. In the membrane distillation process, there is mutual dependence of the momentum and heat transport processes. It complicates the solution of the governing equations and often leads to using simplifications. The developed method allows solving hydrodynamic and heat transport equations without additional assumptions for decoupling the equations with permeation taken into account. Velocity and temperature distributions inside the membrane feed channel were obtained, as well as the concentration profiles of a sparingly soluble salt (barium sulfate). Severe temperature polarization, occurring under poor mixing conditions, has been shown. Supersaturation profiles of barium sulfate are shown to be dependent on the inlet temperature of the membrane channel, and at certain conditions a maximum value of the barium sulfate concentration lies in the bulk of the channel, rather than at membrane surface.

Effects of net-type spacers on heat and mass transfer in direct contact membrane distillation and comparison with ultrafiltration studies

The study of heat and mass transfer enhancement in direct contact membrane distillation (DCMD) by the net-type spacers was intended to develop the heat transfer correlation for the spacer-filled channels. DCMD experiments performed with 20 spacers different in voidages and hydrodynamic angles were used to determine the spacer performance in heat and mass transfer enhancement. The effect of high mass transfer rates on heat and mass transfer coefficients was also investigated to explain the experimental results compared with ultrafiltration (UF) with the spacers. The results showed that spacers enhanced mass fluxes up to 60% and increased heat transfer coefficients by approximately two times over the empty channels. The optimum spacer geometry was found at the voidage and hydrodynamic angle of 0.6 and 90°, respectively. The heat transfer correlation for spacer-filled channel was obtained. The analysis of high mass transfer rate convection showed that the effect of high mass transfer rates on mass transfer coefficients was remarkable for ultrafiltration but was insignificant for membrane distillation.

Magnetically Induced Large Mesoporous Single‐Domain Monoliths Using a Mineral Liquid Crystal as a Template

AbstractIn this paper, we report on how the properties of the suspensions of a lyotropic nematic mineral liquid crystal (MLC) based on V2O5 ribbons are exploited to synthesize single‐domain mesostructured inorganic–inorganic composites, aligned at the centimeter length scale by application of a relatively small magnetic field (0.85 T). In addition, the removal of the mineral template from the inorganic matrix leaves aligned empty channels, fingerprints of the V2O5 ribbons. Large colorless and birefringent mesoporous material is obtained where the orientational order of the channel director has retain the magnetic‐field alignment of its mineral template up to the centimeter length scale within the porous macroscopic silica matrix. A representative material exhibits slit‐like pores with cross‐sectional dimensions of 2 × 20 nm over 600 nm, and has a specific surface area of 207 m2 g–1.

Optimization of commercial net spacers in spiral wound membrane modules

CFD simulations have been used to determine mass transfer coefficients and power consumption of commercial net spacers. The simulations show transversal and longitudinal vortices, vortex shedding and instationary flow behavior leading to the enhanced mass transfer in spacer filled-channels compared to empty channels. The results of the simulations were validated with experiments and compared with data reported in literature, showing satisfactory agreement. Furthermore, CFD simulations were used to optimize the geometry of commercial net spacers in terms of mass transfer and power consumption. The performance of these optimized spacer geometries will be used as reference for future work on the development of new high-performance spacer shapes.

Computational fluid dynamics modelling of flow and permeation for pressure-driven membrane processes

While models of membrane systems with varying degrees of complexity have been developed since the early 1960s, reports of the use of computational fluid dynamics to provide in-depth insights into the separation phenomenon have only recently appeared in the literature. This paper describes the validation and application of a computational fluid dynamics model of pressure-driven membrane processes involving selective removal of components in the feed channel and their transfer to the permeate channel. The effects of changes in rejection, wall permeation rates and solution properties on velocity and concentration profiles are presented for empty channels and channels with eddy promoters. For high polarisation applications typically encountered in conventional ultrafiltration applications, the results demonstrate the need for very fine meshes near the membrane wall, together with high order numerical schemes and accurate modelling of rejection and physical property variations in order to obtain accurate and reliable predictions of the polarisation and flow phenomenon.

Synthesis, structure and metamagnetic behaviour of a three-dimensional Fe(II) carboxyethylphosphonate: [Fe3(OH)2(H2O)4(O3P(CH2)2CO2H)2] or MIL-38

Abstract [FeII3(OH)2(H2O)4(O3P(CH2)2CO2H)2] labelled MIL-38 was hydrothermally synthesized (170 °C, 48 h, autogeneous pressure). Its three-dimensional open structure was solved by single crystal X-ray diffraction (monoclinic, space group P21/c (No. 14), a=4.6308(5), b=10.4322(10), c=17.711(2) A, β=96.051(2)°, Z=2, V=850.8(2) A3). It is built up from linear trimers of edge-sharing iron(II) octahedra linked by organic moieties thus delimiting empty channels along [1 0 0] . This new compound was characterized by 57Fe Mossbauer spectrometry and magnetic measurements: it adopts a metamagnetic behaviour below 10 K, antiferromagnetic at low fields and ferromagnetic above 1.5 T.

Gas and liquid phase mass transfer within KATAPAK-S ® structures studied using CFD simulations

The gas phase mass transfer in the empty channels, and the liquid phase mass transfer within the catalyst-packed channels, of the criss-crossing sandwich structures of KATAPAK-S have been studied using computational fluid dynamics. Due to the “upheaval” caused by the flow splitting at the cross-overs, the mass transfer coefficient is significantly larger than that for fully developed flow in a single tube.

Electron cryo-microscopy and image reconstruction of adeno-associated virus type 2 empty capsids.

Adeno-associated virus type 2 empty capsids are composed of three proteins, VP1, VP2 and VP3, which have relative molecular masses of 87, 72 and 62 kDa, respectively, and differ in their N-terminal amino acid sequences. They have a likely molar ratio of 1:1:8 and occupy symmetrical equivalent positions in an icosahedrally arranged protein shell. We have investigated empty capsids of adeno-associated virus type 2 by electron cryo-microscopy and icosahedral image reconstruction. The three-dimensional map at 1.05 nm resolution showed sets of three elongated spikes surrounding the three-fold symmetry axes and narrow empty channels at the five-fold axes. The inside of the capsid superimposed with the previously determined structure of the canine parvovirus (Q. Xie and M.S. Chapman, 1996, J. Mol. Biol., 264, 497-520), whereas the outer surface showed clear discrepancies. Globular structures at the inner surface of the capsid at the two-fold symmetry axes were identified as possible positions for the N-terminal extensions of VP1 and VP2.

Solid–gas reactions of complex oxides inside an environmental high-resolution transmission electron microscope

In a gas reaction cell (GRC), installed in a high-resolution transmission electron microscope (HRTEM) (JEOL 4000EX), samples can be manipulated in an ambient atmosphere (p<50 mbar). This experimental setup permits not only the observation of solid–gas reactions in situ at close to the atomic level but also the induction of structural modifications under the influence of a plasma, generated by the ionization of gas particles by an intense electron beam. Solid state reactions of non-stoichiometric niobium oxides and niobium tungsten oxides with different gases (O 2, H 2 and He) have been carried out inside this controlled environment transmission electron microscope (CETEM), and this has led to reaction products with novel structures which are not accessible by conventional solid state synthesis methods. Monoclinic and orthorhombic Nb 12O 29 crystallize in block structures comprising [3×4] blocks. The oxidation of the monoclinic phase occurs via a three step mechanism: firstly, a lamellar defect of composition Nb 11O 27 is formed. Empty rectangular channels in this defect provide the diffusion paths in the subsequent oxidation. In the second step, microdomains of the Nb 22O 54 phase are generated as an intermediate state of the oxidation process. The structure of the final product Nb 10O 25, which consists of [3×3] blocks and tetrahedral coordinated sites, is isostructural to PNb 9O 25. Microdomains of this apparently metastable phase appear as a product of the Nb 22O 54 oxidation. The oxidation reaction of Nb 12O 29 was found to be a reversible process: the reduction of the oxidation product with H 2 results in the formation of the starting Nb 12O 29 structure. On the other hand, the block structure of Nb 12O 29 has been destroyed by a direct treatment of the sample with H 2 while NbO in a cubic rock salt structure is produced. This in situ technique has also been applied to niobium tungsten oxides which constitute the solid solution series Nb 8− n W 9+ n O 47 with 0≤ n≤4. All of these phases crystallize in the threefold tetragonal tungsten bronze (TTB) superstructure of Nb 8W 9O 47 ( n=0). In the main reaction, these phases decompose in a gas plasma (O 2, H 2 or He, p=20 mbar) into WO 3− x , which evaporates and solidifies again near the irradiated crystallite, and (Nb,W) 24O 64, which crystallizes in a 2 a superstructure of the TTB type observed here for the first time in the system Nb–W–O. Nb 8W 9O 47, Nb 7W 10O 47 and Nb 6W 11O 47 always react in this way, independent of the applied gas. On the other hand, the treatment of Nb 5W 12O 47 ( n=3) and Nb 4W 13O 47 ( n=4) in an oxygen atmosphere often caused a different reaction: these phases have been oxidized and a heavily disordered bronze-type structure has been formed. The oxygen excess in these products is largely accommodated in segregated domains of WO 3.

Crystal Chemistry of Defective Intermetallics with Empty Triangular Metalloid Channels: The New Phosphide Zr6Cr60P39

The ternary compound ZrCr60P39has been synthesized by the tin flux method. It presents a hexagonal crystal structure [a=21.413(2) Å,c=3.354(1) Å], space groupP63/m, with one formula per unit cell. The X-ray structure has been refined from three-dimensional single-crystal intensity data to a finalRvalue of 0.053 (Rw=0.056) for 451 reflections [I>2σ(I)]. The resulting structure is of a new type and exhibits empty triangular phosphorus channels. This structure belongs to a new series of hexagonal defective compounds named direct series with a metal/nonmetal ratio slightly lower than 2, the first members of which are the compounds Cr12P7and Zr2Cr30P19. The structural relationships with the reverse series, including the ternariesR2Co12P7(R=rare earth element), Yb6Co30P19, UCo5Si3, U6Co30Si19, and U10Co51Si33, are discussed in terms of metal vacancies and coordination polyhedra. Finally, a general crystal chemical rule has been established that permits prediction of the different members for the two series and their definition structurally in terms of lattice parameters and theoretical X-ray diffraction patterns. Moreover this rule gives for each member the number of empty triangular metalloid channels as well as the distribution of the different polyhedra occupied by the metal atoms (trigonal prisms, pyramids, tetrahedra).

An organic channel structure formed by the supramolecular assembly of trithiocyanuric acid and 4,4′‐bipyridyl

Trithiocyanuric acid (TCA) and 4,4′-bipyridyl (BP) form hydrogen-bonded co-crystals with aromatic compounds such as benzene, toluene, p-xylene and anthracene. The TCA–BP co-crystal is composed of cavities formed by the N–H…N hydrogen bonds between the two molecules, and the three-dimensional structure contains channels of approximately 10 A where aromatic molecules are accommodated. The molar ratios of TCA, BP and the aromatic compound in the co-crystals are 2∶1∶1 or 2∶1∶0.5. Benzene, toluene and p-xylene are removed from the channels around 190, 183 and 170 °C respectively, and these aromatic guests can be reintroduced into the empty channels of the apo-hosts. The apo-hosts with empty channels have reasonable thermal stability and exhibit shape selectivity in that the empty channels accommodate p-xylene but not m- or o-xylene or mesitylene.

Salt Crystal Growth as Weathering Mechanism of Porous Stone on Historic Masonry

It is well known that in porous stones, NaCl precipitation on and beneath a surface depends on the solution supply and the evaporation rate according to the microclimate and the effective pore structure. In the present work, the study of salt crystal growth mechanisms in large heterogeneous systems like porous stone masonries is attempted. The historic masonries of the Medieval City of Rhodes act as a pilot, due to the intense marine environment and the climatic conditions in favour of NaCl crystallization into the highly porous stones. Weathered monument samples from various depths on masonries exposed to the sea are examined systematically under SEM and EPMA. The obtained results permit the differentiation of crystal growth patterns occurring during distinguished phases of the evaporation process within the porous stone masonry in depth. In the first phase, salt crystals grow favourably in the larger pores, connecting with the empty evaporation channels, and being supplied by solution from the next smaller pores. The isometric crystal habits attaining an equilibrium form correspond to those growing immersed in the solution, when a granular crust is formed. In a second phase, the crystals already exceed the pore size and overlap other smaller pores. As the rate of evaporation exceeds the solution supply, the solution retires and the substrate dries out, the area where the crystal contacts the solution is reduced, and consequently, columnar crystals grow. The pressure exerted by crystallization against the pore walls, when the crystals filling entirely the coarse pores continue growing, leads to disruption.

Crystalloid Inclusions in Brain Macrophages and Hemopoietic Tissue in GFAP-IL3 Mice Resemble Inclusions Identified in Multiple Sclerosis

Crystalloid inclusions or "pole bodies" observed in brain macrophages in human demyelinating disease represent a morphological enigma. Similar inclusions were detected in brain macrophages from the GFAP-IL3 mouse, a transgenic murine model for macrophage mediated demyelination. Mice also showed inclusions in hematopoietic tissue. They appear to be related to phagocytosis and secretion, respectively, as evidenced by the fact that in phagocytosing cells they often merged with lysozomes and that affected cells showed empty channels open to the interstitium. Based on ultrastructural and immunolocalization studies using chaperonin-10, lysozyme, and cathepsin the authors suggest that these inclusions are consistent with phagocytosis-related secretory products. This study may provide insight into the nature and significance of similar macrophage inclusions recently identified in multiple sclerosis.

Spectroscopic examination of the Na/Si(111)-(3×1) surface structure

We have examined a recently proposed experimental model for the alkali-metal induced Si(111)-$(3\ifmmode\times\else\texttimes\fi{}1)$ surface structure, based on density-functional theory calculations and their comparison with experiments on the structural and electronic properties of Na/Si(111)-(3$\ifmmode\times\else\texttimes\fi{}$1). This model, characterized by the alkali-metal adsorption in empty channels and the resulting honeycomblike substrate reconstruction, is energetically favored and reproduces well the experimental scanning-tunneling-microscope images, surface-state band structure, and Si 2$p$ surface core-level spectra, which together provide a convincing theoretical demonstration that the employed model is acceptable both in energetics and in spectroscopic examination.

Some aspects of flow in granular materials in hoppers

The main part of the paper is devoted to the description of the localized deformation zones in plane (slow) flow of granular materials from hoppers. Specifically, two types of zones are discussed i...

Nonlinear optical properties of semiconductor quantum wires

Nonlinear optical transmission at discrete frequencies (bleaching bands) has been observed in CdSe and GaAs quantum wires crystallized in chrysotile asbestos nanotubes with average diameter ≈ 6 nm and in nanocrystals of CdS (crystallized in the transparent molecular filter—mica with empty channels of designed diameter). The induced decrease of absorption in quantum wires has been explained by filling of the size-quantized energy bands with nonequilibrium carriers (saturation effect) and by the phase-space filling of excitons.

Forced Convective Heat Transfer Through Horizontal Annular Porous Channel.(Dept.M)

In present work, the forced convective heat transfer through horizontal annular porous channel is theoretically and experimentally studied in the experimental work, annular channel with aspect ratio of 1.85 is designed such that one can study the effect of various parameters controlling the behaviour of the flow. Heat flux of 12.6 Kw/m2 to 16.9 Kw/m2 is applied to examine the effect of heat flux on heat transfer process. Porous media of diameters 3 mm and 5 mm stainless steel spherical beads are used to examine the effect of porosity on flow. Water, as a test-liquid, is used with mass flow rates of 40,50,60 and 70kg/hr. Using the obtained experimental data, the value of local and average heat transfer coefficients and Nusselt number are calculated. In the theoretical work, the govering equations describing the problem are approximated to a set of linear algebraic equations using finite divided difference technique. Computer programs are designed to solve this mathematical model. The agreement between experimental and theoretical results is fairly good in all examined conditions, especially, in case of 5 mm bead diameter medium. The results show that, higher value of heat transfer coefficient can be obtained using porous medium compared with empty channels.

Synthesis and crystal structure of Cu6[Ge6O18] · 6H2O, a dioptase-type cyclo-germanate

AbstractCu

The Role of Cultured Schwann Cell Grafts in the Repair of Gaps within the Peripheral Nervous System of Primates

With recent advances in cell culture techniques it is possible to isolate human SCs from adult peripheral nerves, expand and purify their number in cell culture, and construct a cellular prosthesis from the cultured cells. The current study was designed to ascertain whether these techniques could be used to repair nonhuman primate nerve injuries. In 12 adult femalecynomologousmonkeys, the musculocutaneous (msk) nerve was divided and prevented from regenerating and the brachioradialis nerve (brach) was exposed bilaterally (n=24 nerves) and injured so that a 15-mm gap existed within the nerve. The brach nerves were either repaired with sural nerve autografts (n=6), guidance channels which contained monkey SCs (120×106cells/ml;n=6), or guidance channels without SCs (n=6). The remaining brach nerves (n=6) had either no injury or an injury to the nerve without a repair. Autologous expanded primate SCs were increased in number at least 10-fold over a 2-week period at which time the SC purity exceeded 99.9%. Monkeys in each group, including the control group, regained some degree of elbow flexion after 3 months despite sectioning both the mask nerve and the brach nerve; therefore, we were unable to determine simply on clinical grounds which repair was the most effective in promoting functional recovery. Brach nerves repaired with sural nerve grafts were superior to both the channels which contained SCs and empty channels in regards to the number of myelinated axons proximal, within, and distal to the repair site (P<0.05). Electrophysiologic results closely paralleled the histologic data with evidence of reinnervation of the brachioradialis muscle based on the compound muscle action potential in both sural nerve graft and monkey SC channel repair groups.

Sorption of Ammonia, Methylamine and Methanol by the P3 Polymorph of Gossypol. Synthesis of Unsymmetrical Monoamine Derivatives of Gossypol by a Solid-state Reaction

The P3 polymorph of gossypol has wide, empty channels andstrongly absorbs linear amines. One of the two gossypol aldehydegroups is located near the channel wall. This situation allowsreaction of the amines with half of a gossypol molecule,yielding unsymmetric monoaminoderivatives of gossypol in highyield and by a simple, solid-state method.