• Membrane Journal
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• v.8 no.3
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• pp.148-156
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• 1998

Diffusion dialysis is a membrane process driven by concentration difference using ion-exchange membranes and has been employed for many years for the acid recovery from acidic waste generated in steel, metal-refining and dectro-plating industries. Theoretically acid flux increases in propomon to the acid concentration difference. At acid concentrations higher than 3 N HCl, however, the acid flux had not increased linearly with the concentration difference. In this paper the effects of acid concentrations on diffusion dialysis for hydrochloric acid recovery and the acid transport mechanism in an anion exchange membrane were studied by membrane sorption tests and diffusion clialysis cell tests. The experimental results showed that the molecular diffusion was a major transport mechanism in a low acid concentration range and the proton leakage through an anion exchange membrane played an important role at higher acid concentrations. Also osmotic water transport and membrane dehydration retarded the transport of protons and caused the permeate flux to decrease.

• Asian Journal of Atmospheric Environment
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• v.2 no.2
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• pp.81-89
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• 2008

The numerical simulation of wind and ozone ($O_3$) transport in mountainous regions was performed with a computational fluid dynamics technique. A dry deposition model for $O_3$ was designed to estimate $O_3$ deposition in complex terrain, and the qualitative validity of the predicted $O_3$ concentration field was confirmed by comparison with observed data collected with passive samplers. The simulation revealed that wind velocity increases around ridge lines and peaks of mountains. The areas with strong wind corresponded well with the sites of tree decline at high altitudes, suggesting that it is an important factor in the localization of tree/forest decline. On the other hand, there is no direct relationship between forest decline and $O_3$ concentration. The $O_3$ concentration, however, tends to increase as wind velocity becomes higher, thus the $O_3$ concentration itself may be a potential secondary factor in the localized decline phenomena. While the diffusion flux of $O_3$ is not related to localized tree decline, the pattern of advection flux is related to those of high wind velocity and localized tree decline. These results suggest that strong wind with large advection flux of $O_3$ may play a key role in the promotion of tree/forest decline at high mountain ridges and peaks.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.988-1004
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• 1996

The characteristics of flow and oxygen concentration are numerically studied in Czochralski 8" silicon crystal growing process considering radiative heat transfer. The analysis of net radiative heat flux on all relevant surfaces shows growing crystal affects the heater power. Furthermore, the variation of the radiative heat flux along the crystal surface in the growing direction is confirmed and should be a cause of thermal stress and defect of the crystal. The calculated distributions of temperature and, heat flux along the wall boundaries including melt/crystal interface, free surface and crucible wall indicate that the frequently used assumption of the thermal boundary conditions of insulated crucible bottom and constant temperature at crucible side wall is not suitable to meet the real physical boundary conditions. It is necessary, therefore, to calculate radiative heat transfer simultaneously with the melt flow in order to simulate the real CZ crystal growth. If only natural convection is considered, the oxygen concentration on the melt/crystal interface decreases and becomes uniform by the application of a cusp magnetic filed. The heater power needed also increases with increasing the magnetic field. For the case of counter rotation of the crystal and crucible, the magnetic field suppresses azimutal flow produced by the crucible rotation, which results in the higher oxygen concentration near the interface.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.950-955
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• 1998

The objective of this study was to investigate the effect of running time, operating pressure, feed concentration and circulation rate on the permeation flux and the rejection rate in cross-flow ultrafiltration of polyethylene glycol(PEG) solution of molecular weight($M_w$) 8000 and 20000. The membranes used for this study were MWCO(Molecular Weight Cut-off) of 6 K and 20 K. The experiments were performed at the operating pressures of 7, 14 and 28 psi, the circulation rates of 1000 mL/min and 2000 mL/min, and the feed concentration of 100 mg/L and 1000 mg/L. At a constant pressure, the permeation flux and the observed rejection($R_o$) appeared to be approximately constant within the range of running time, 0~480 min. The permeation flux increased with increasing the operating pressure, and it increased with decreasing the feed concentration and decreasing Mw of PEG at a given pressure. On the other hand, $R_o$ decreased slightly with increasing the operating pressure. However, $R_o$ increased with increasing the feed concentration and increasing of $M_w$ of PEG at a given pressure. The variation in circulation rates did not cause any significant influence on the permeation flux. Increasing of circulation rate caused the increase of $R_o$, and $\alpha$ was increased substantially with the decrease of $M_w$ of PEG. The dimensionless parameter. permeability ratio($\alpha$), which was used to investigate flux-pressure behavior, was increased with the increase in circulation rate and operating presure. The value of $\alpha$ was less than 1 in all cases. The estimated intrinsic rejection(R). which was obtained from mass transfer coefficient, was decreased with the increase of operating pressure. However R increased with the increase of linear velocity of feed and $M_w$ of PEG.

• Membrane Journal
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• v.24 no.6
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• pp.453-462
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• 2014

Thin film composite (TFC) polyamide (PA) membranes were prepared on polyester (PET) nonwoven reinforced polysulfone supports for forward osmosis (FO) processes. PSF (polysulfone) supports were prepared via the phase inversion process from PSF casting solutions in dimethyl formamide (DMF) solvents (19 wt%) by using a PET nonwoven (thickness of $100{\mu}m$) as a mechanical reinforcing material for reverse osmosis (RO) membrane. The PSF support from 19 wt% of DMF/PSF casting solution showed sponge-like morphology and asymmetric internal structure. To reduce the internal concentration polarization in FO operation, thin ($20{\mu}m$ of thickness) nonwoven-supported PSF supports were prepared by using PSF/DMF casting solution (9~19 wt%). A desirable support structure with a highly porous sponge-like morphology were achieved from the thin nonwoven-supported PSF layer prepared with 9~12 wt% casting solution. A crosslinked aromatic polyamide layer was fabricated on top of each support to form a TFC PA membrane. The tested sample from 12 wt% of DMF/PSF casting solution presented outstanding FO performance, almost 5.5 times higher water flux (24.3 LMH) with low reverse salt flux (RDF, 1.5 GMH) compared to a thick nonwoven rainforced membrane (4.5 LMH of flux and 3.47 GMH of RSF). By reducing the thickness of the nonwoven and optimizing PSF concentration of casting solution, the morphology of the prepared membranes were changed from a dense structure to a porous sponge structure in the boundary area between nonwoven and PET support layer.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.5
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• pp.281-288
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• 2002

Recombinant Escherichia coli strain harboring the ${\lambda}$pR-pL promotor and heterologus poly-${\beta}$-hydroxybutyrate (PHB) biosynthesis genes was used to investigate the effect of culture conditions on the efficient PHB production. The expression of phb genes was induced by a temperature upshift from $33^{\circ}C\;to\;38^{\circ}C$. The protein expression levels were measured by using two-dimensional electrophoresis, and the enzyme activities were also measured to understand the effect of culture temperature, carbon sources, and the dissolved oxygen (DO) concentration on the metabolic regulations. AcetylCoA is an important branch point for PHB production. The decrease in DO concentration lowers the citrate synthase activity, thus limit the flux toward the TCA cycle, and increase the flux for PHB production. Since NADPH is required for PHB production, the PHB production does not continue leading the overproduction of acetate and lac-tate. Based on these observations, a new operation was considered where DO concentration was changed periodically, and it was verified its usefulness for the efficient PHB production by experiments.

• Membrane and Water Treatment
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• v.2 no.3
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• pp.147-158
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• 2011

Membrane distillation process was used for desalination of hot (333 K) geothermal water, which was applied in the plant producing heating water. The investigated water contained 120 g salts/$dm^3$, mainly NaCl. The mineral composition was studied using an ion chromatography method. The obtained rejection of solutes was closed to 100%, but the small amounts of $NH_3$ also diffused through the membrane together with water vapour. However, the composition of obtained distillate allowed to use it as a makeup water in the heating water system. The geothermal water under study was concentrated from 120 to 286 g NaCl/$dm^3$. This increase in the solution concentration caused the permeate flux decline by a 10-20%. The geothermal water contained sulphates, which was subjected to two-fold concentration to achieve the concentration 2.4-2.6 g $SO{_4}{^{2-}}/dm^3$ and the sulphates then crystallized in the form of calcium sulphate. As a results, an intensive membranes scaling and the permeate flux decline was observed. The XRD analysis indicated that beside the gypsum also the NaCl crystallites were deposited on the membrane surfaces. The fresh geothermal water dissolved the mixed $CaSO_4$ and NaCl deposit from the membrane surface. This property can be utilized for self-cleaning of MD modules. Using a batch feeding of MD installation, the concentration of geothermal water was carried out over 800 h, without significant performance losses.

• Membrane Journal
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• v.19 no.3
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• pp.212-221
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• 2009

This study focuses on preparation of PVDF/PDMS composite membranes to effectively separate butanol from water-butanol mixture using pervaporation. We prepared various composite membranes by changing PVDF concentration of support layer and PDMS cross-linking condition of active layer. Pervaporation performance was tested by measuring butanol flux and separation factor with various cases of butanol concentration, temperature, and flow rate of feed. As results, performance of our novel PVDF/PDMS membranes surpasses that of PVDF/POMS membrane, manufactured by GKSS (Germany), in term of butanol flux, permeate concentration, and separation factor.

• Membrane Journal
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• v.2 no.1
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• pp.59-66
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• 1992

The experimental studies were carried out on ultrafiltration of PEG #6000 and dextran 70T macromole¬cules. using an asymmetric cellulose acetate membrane in a cross flow plane type cell. Effects of pressure difference. feed concentration were studied on permeate flux and observed rejection for both the macromole¬cules. and the concentration polarization layer resistance $R_{b1}$ on permeate flux was analysed. The concentration polarization layer resistance $R_{b1}$ was correlated with the average macromolecule concen¬tration $C_{b1}$ in polarization layer. The resulting dimensionless correlation was expressed as : $\frac{R_{b1}}{{R_m}}=\alpha[\frac{\rho_{b1}}{C_{b1}}]^\beta$

• Environmental Engineering Research
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• v.23 no.3
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• pp.316-322
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• 2018

In this study, the effects of polymer concentration and additive in the formation of asymmetric nanofiltration (NF) membrane were evaluated. The membrane fabrication was carried out via dry/wet phase inversion technique. A new formulation of dope solution with polymer concentration ranging between 17 wt% to 21 wt% and the present of additive was developed. The results show that the permeate flux gradually decreases as polymer concentration increased, until $2.5969L/m^2h$ and increased the rejection up to 98.7%. Addition of additive, polyethylene glycol 600 increased dyes rejection up to 99.8% and decreased the permeate flux to $3.6501L/m^2h$. This indicates that the addition of polyethylene glycol additive led towards better membrane performance. The morphological characteristics of NF membrane were analysed using a Scanning Electron Microscopy.