No abstract available

No abstract available

[en] Highlights: • Water confined between a spherical tip and a plate was theoretically studied. • Lattice gas Monte Carlo simulation on the dewetting transition of confined water. • Atomic scale roughness significantly affects the dewetting transition. Using lattice gas Monte Carlo simulations, we studied the dewetting transition of water confined between a spherical tip and a plate, which is relevant to atomic force microscopy measurements conducted in water. The dewetting transition was investigated by varying the tip-plate distance, tip size, and the pressure of water. With introduction of an atomic scale roughness (1 < nm) in the tip and the plate, the dewetting transition significantly increased in range and yielded an enhanced hydrophobic force between the tip and the plate. This finding is in agreement with the experimental results previously reported by Singh et al.

[en] Electrochemical characteristics of nitrite ion were investigated at a poly(methylene blue)-modified glassy carbon electrode by cyclic voltammetry and differential pulse voltammetry. The poly(methylene blue)- modified glassy carbon electrode exhibited enhanced anodic signals for nitrite. The effects of key parameters on the detection of nitrite were evaluated at the modified electrode, such as pH, accumulation time, and scan rate. Under optimum condition, the chemically modified electrode can detect nitrite in the concentration range 2.0 x 10^-6 to 5.0 x 10^-4 M with the detection limit of 2.0 x 10^-6 M and a correlation coefficient of 0.999. The detection of nitrite using the chemically modified electrode was not affected by common ions such as Na⁺, K⁺, Ca²⁺, Cl^-, HPO₄^2- and H₂PO₄^-. The modified electrode showed good stability and reproducibility. The practical application of the present method was successfully applied to the determination of nitrite ion in cabbage samples

[en] Electrochemical characteristics of nitrite ion were investigated at a poly(methylene blue)-modified glassy carbon electrode by cyclic voltammetry and differential pulse voltammetry. The poly(methylene blue)- modified glassy carbon electrode exhibited enhanced anodic signals for nitrite. The effects of key parameters on the detection of nitrite were evaluated at the modified electrode, such as pH, accumulation time, and scan rate. Under optimum condition, the chemically modified electrode can detect nitrite in the concentration range 2.0 x 10^-6 to 5.0 x 10^-4 M with the detection limit of 2.0 x 10^-6 M and a correlation coefficient of 0.999. The detection of nitrite using the chemically modified electrode was not affected by common ions such as Na⁺, K⁺, Ca²⁺, Cl^-, HPO₄^2- and H₂PO₄^-. The modified electrode showed good stability and reproducibility. The practical application of the present method was successfully applied to the determination of nitrite ion in cabbage samples

[en] Highlights: • Thermal performance is experimentally studied for wet cooling tower with axial fan. • Forced ventilation improves the inlet air uniformity under crosswind condition. • Water temperature drop enhances by 6.46–13.35% at forced ventilation pattern. • Merkel number enhances by 0.69–5.62% at forced ventilation pattern. -- Abstract: In this paper, an axial fan was introduced for thermal performance improvement of super-large natural daft wet cooling towers (S-NDWCTs), and the model experiment was performed to study the thermal performance of S-NDWCTs installed with an axial fan under windless and crosswind conditions. The experimental results manifested that, compared with traditional natural ventilation pattern, the thermal performance of forced ventilation is outstanding by analyzing the inlet air uniformity coefficient, cooling water temperature drop, Merkel number, etc. Moreover, the cooling water temperature drop is proportional to fan power under windless condition, and it enhances approximately by 12.06% at 3.77 W fan power, compared with natural ventilation pattern. Under crosswind conditions, the inlet air uniformity coefficient (ψ) and the water temperature difference on the water basin surface at forced ventilation pattern are more uniform than those of natural ventilation pattern, and ψ at 2.67 W condition increases by 8.08% compared with natural ventilation pattern while the crosswind velocity reaches to 0.6 m/s. Additionally, the cooling water temperature drop and Merkel number at forced ventilation pattern are also higher than those of natural ventilation pattern. Compared with natural ventilation pattern, these two parameters enhance by 6.46–13.35% and 0.69–5.62%, respectively within the experimental crosswind velocity ranges (0–0.6 m/s).

[en] Highlights: • Field tests of the NDWCT were implemented before and after structural improvement. • The effects of structural improvements on the NDWCT were analyzed. • Structural improvements enhanced the ventilation and thermal performance of NDWCT. • The Merkel number increased significantly after structural improvement. -- Abstract: In order to improve the operating performance of the natural draft wet cooling towers (NDWCTs), some structural improvement measures, including adding air-deflectors, using non-uniform fillings, and adding air-ducts, were taken in one large-scale NDWCT in China. The effects of structural improvement on the ventilation and thermal performance were researched based on the field test method. Field test results showed that, in the crosswind velocity range of 1.15–3.2 m/s (test condition), the thermal and ventilation performance decrease gradually with the rising of crosswind velocity, but the structural improvement weakens the adverse influence of crosswind. Compared with before structural improvement, the intake air uniformity coefficient, the ratio factor of ventilation rate, the temperature uniformity coefficient, and the ratio factor of Merkel number increase by about 36.6%, 15.5%, 5.5%, and, 14.5%, respectively. It manifested that the structural improvement for the NDWCT can improve the thermal and ventilation performance to a great extent.

[en] Highlights: • A novel and effective suppression method of runaway current based on magnetic energy transfer (MET) is presented in this paper. • A series of experimental experiments are carried out to verify the proposed method. • The MET can reduce the toroidal electric field, which is favor for the runaway suppression. • The MET provides a new idea to transfer the magnetic energy and to suppress runaway current for disruption mitigation in future devices. For disruptions without mitigation, a large amount of thermal energy and poloidal magnetic energy will be dissipated inside the vacuum vessel (VV). A slow current quench may be accompanied by a large halo current, while a fast current quench often causes large eddy current, which will result in electromagnetic force. At the same time, fast current quench will induce strong toroidal electric field, which will result in a large fraction of runaway current and the hitting of runaway beam on first wall. The disruption mitigation is essential for large scale tokamak. The existing methods to mitigate disruptions, such as massive gas injection and resonant magnetic perturbations, are aimed at increasing the runaway generation threshold or the lose rate of runaway electrons. It may not work for ITER with I_p = 15 MA operation. The root of runaway generation is the large toroidal electric field induced by fast current quench and the large avalanche factor with high plasma current. The reduction of toroidal electric field is favor for the runaway suppression. The magnetic energy transfer (MET) based on electromagnetic coupling for disruption mitigation has been proposed on J-TEXT. It has the advantage of transferring the magnetic energy to outside of vessel by the electromagnetic coupling. It accelerates the current quench (CQ) rate and reduces the toroidal electric field at the same time. The runaway current has been suppressed by the MET system on J-TEXT. The experimental results show that the MET can reduce the energy dissipated in the VV by 20 % through transferring of energy to outside of VV. The MET can increase the CQ rate about 50.7 % and decrease the loop voltage about 35.3 %. The MET provides a new idea to transfer the magnetic energy and to suppress runaway current for disruption mitigation in future devices.

[en] Highlights: • A novel and effective control method of runaway electrons based on magnetic energy transfer is presented in this paper. • A series of experimental tests are carried out to verify the proposed method. • The different critical MET coil current can be found under different discharge parameters. • The proposed method can be also applied in the plasma displacement control when no runaway electrons are produced. -- Abstract: During disruptions runaway electrons (REs) often drift from high field side to low field side in J-TEXT. It may cause severe damage to the plasma facing components when REs strike them with high energies. In order to mitigate the damage, a novel method called magnetic energy transfer (MET) based on electromagnetic coupling is proposed. A set of extra coils with a high coupling coefficient with plasma are installed on the high field side of the device, and a toroidal current can be induced in the coils during disruptions which can transfer the plasma poloidal magnetic energy out of vacuum vessel. Flowing in the same direction as the runaway current, the induced current can attract the runaway current to high field side, control the displacement of the RE beams and prolong runaway current plateau. Experiments are carried out on J-TEXT to verify the mitigation method, and the influence of different induced current on REs horizontal displacement is studied by changing the electrical parameters of energy absorbing unit. The experiment results show that the increase rate of RE beams’ horizontal displacement can be significantly slowed. The runaway current plateau can be prolonged by 4–5 ms and the control effect becomes better as the induced current in the MET coils increases. Moreover, MET also has a good effect on displacement control of plasma during disruption when no RE beams are produced.

[en] Highlights: • All-atom molecular dynamics simulation of water deposited on a pillared surface. • Surface wettability studied by varying the shape of pillars. • Mechanism of the transition between the Wenzel and Cassie-Baxter states revealed. • Reentrant pillars give the superior resistance to the wetting of a surface. Using all-atom molecular dynamics (MD) simulation, we investigate the wettability of a surface patterned with the trapezoidal nanopillars. The dewetting and wetting of the gap between pillars are, respectively, related to the Cassie-Baxter (CB) and Wenzel (WZ) states of a macroscopic water deposited on the pillared surface. We examine the (de)wetting transition by varying the pore structure between the pillars from an open (inverted trapezoid) to closed (trapezoid) geometry. The molecular structures and relative stabilities of various intermediate states existing between the WZ and CB states are uncovered. By identifying the transition states, we estimated the free energy barriers for the wetting and dewetting transitions. The reentrant pillars enhance the resistance to the wetting transition while facilitating the reverse transition, qualifying as the best geometry to be used for a superhydrophobic surface.