A loose nanofiltration (NF) membrane with excellent dye rejection and high permeation of inorganic salt is required to fractionate dye/salt mixture in dye wastewater treatment. In this study, we fabricated the loose NF membrane by using the electrospray interfacial polymerization (EIP) method. It is a novel and facile interfacial polymerization method, which controls the thickness of the poly(piperazine-amide) (PPA) layer in nanometers (1 nm/min) and changes cross-linking degree of PPA layer and pore size by varying the electrospray time; consequently, water permeance and dye/salt rejection ratio can be handled. The fabricated EIP membrane with an optimized fabrication condition (M30, electrospray time was 30 min) possessed excellent pure water permeance (20.2 LMH/bar), high dye rejection (e.g., 99.6% for congo red (CR)), and low salt rejection (e.g., 6.3% for NaCl). Moreover, the EIP membrane exhibited enhanced antifouling property than commercial NF membrane (NF90) with a high flux recovery rate (FRR) of 87.1% and low irreversible fouling (R ir ) of 12.9% after fouled by bovine serum albumin (BSA) due to its great smooth surface (average roughness (R a ) is 12.2 nm), hydrophilicity property, enhanced zeta potential, and low protein adsorption. The results indicate that the EIP loose NF membrane had a high potential for dye wastewater treatment.
Membrane
deformation is a significant problem in osmotically driven
membrane processes, as it restricts practical operating conditions
and reduces overall process performance due to unfavorable alteration
of membrane permeation characteristics. In this respect, a spacer
plays a crucial role, as it dictates the form and extent of membrane
deformation in association with concentration polarization (CP), which
is also influenced by spacer-induced hydrodynamic behavior near the
membrane surface. These two roles of spacers on membrane permeation
characteristics are inherently inseparable with the coexistence of
hydraulic and osmotic pressures. Here, we suggest a novel analytical
method to differentially quantify the proportions of effective osmotic
pressure drop caused by membrane deformation and CP. Furthermore,
we tested two different FO membranes with three different spacer configurations
to define and discuss different forms of membrane deformation and
their effects on membrane permeation characteristics. The differential
analysis revealed the effect of spacer configuration on effective
osmotic pressure drop in membrane deformation (up to ∼201%
of variation) is much greater than that in CP (up to ∼20.1%
of variation). In addition, a combined configuration of a feed spacer
and tricot spacer demonstrated its ability of mitigating membrane
deformation with lower selectivity loss and channel pressure drop
under pressurization.
We report an ultra-low resistance superconducting joint using unreacted multifilament MgB2 wires produced by tailoring the powder compaction pressure within the joint with heat treatment conditions. The joint demonstrated an ultra-low resistance of 5.48 10 -15 and critical current (Ic) of 91.3 A at 20 K in self-field. The microstructural and composition studies of the joint revealed cracks and a high amount of MgO, respectively. These two features reduced the Ic of the joint to some extent; nevertheless, the joint resistance was not affected by it. Our tailored joining process will play a pivotal role in superconducting joint development.
A superconducting
joint architecture to join unreacted carbon-doped
multifilament magnesium diboride (MgB2) wires with the
functionality to screen external magnetic fields for magnetic resonance
imaging (MRI) magnet applications is proposed. The intrinsic diamagnetic
property of a superconducting MgB2 bulk was exploited to
produce a magnetic field screening effect around the current transfer
path within the joint. Unprecedentedly, the joint fabricated using
this novel architecture was able to screen magnetic fields up to 1.5
T at 20 K and up to 2 T at 15 K and thereby almost nullified the effect
of the applied magnetic field by maintaining a constant critical current
(I
c). The joint showed an I
c of 30.8 A in 1.5 T at 20 K and an ultralow resistance
of about 3.32 × 10–14 Ω at 20 K in a
self-field. The magnetic field screening effect shown by the MgB2 joint is expected to be extremely valuable for MRI magnet
applications, where the I
c of the joints
is lower than the I
c of the connected
MgB2 wires in a given magnetic field and temperature.
Persistent-mode operation is a key feature of magnetic resonance image systems to improve the required field stability. The superconducting joint is known to be beneficial for reducing all the resistant components in an electrically closed-circuit. The joint technique of magnesium diboride (MgB2) multifilamentary wire, however, is the main obstacle to the use of magnet in practical applications. In response, herein, we designed and developed a unique configuration of superconducting joint to further enhance the interconnection of exposed cores between two 18-multifilamentary wires. It was confirmed that developed joint samples achieved high critical current similar to a non-jointed wire. The proposed joint technique was directly applied to the MgB2 single-turn coil and MgB2 magnet for estimating a joint property through persistent-mode operation. This work provides fundamental insights into the design of persistent-mode MgB2 magnets to boost magnetic resonance image systems.
Understanding the DC breakdown characteristics of polymeric insulators is essential for stable operation of high-capacity DC electrical equipment. To predict the breakdown characteristics of lowdensity polyethylene (LDPE), we propose a numerical methodology with a new critical index in which the internal current varying with temperature, thickness, and injection barrier height. To evaluate this currentbased index, we applied the fully coupled bipolar charge transport (BCT) and molecular chain displacement (MCD) models to analyze the influence of each variable on breakdown phenomena. The results of this analysis revealed that the amount of space charge accumulation within the insulator has a maximum value at approximately 50 ℃, which corresponds to the known morphological transition temperature of LDPE. The breakdown strength calculated using this numerical model was found to decrease with increasing temperature and thickness. Although injection barrier height at the electrode was found to be negatively correlated with breakdown strength, its effect was not as significant as that of the other variables. The breakdown strength values obtained using this numerical method were found to be in close agreement with values reported in the literature. Based on these results, we newly suggest the physical quantity to predict the breakdown strength, the current relaxation speed, which is the slope of the Boltzmann sigmoid function, as a positively correlated index. Finally, we determined that the breakdown phenomena are initiated when the amount of impact accumulated in the insulator changes discontinuously and analyzed the contribution of factors affecting the breakdown using the Pearson correlation coefficient and the Sobol sensitivity index.
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