[en] Highlight• Flow of reflux condensation in air-cooled condenser tube is studied numerically. • A model-based approach to determine the condensation length is proposed. • Effect of varying vapor/air operations on reflux condensation is considered. • Dynamic behavior relating to complete and countercurrent condensation is visualized. A numerical simulation was presented to investigate and visualize the flow characteristics of reflux condensation in core tube related to air-cooled condenser. The simulation had been performed in a flat tube under a saturation pressures of 13 kPa. The sensitivity of condensation length, condensate thickness and interfacial shear was examined with varying the vapor mass flux and cooling air Reynolds number. In addition, the condensate-void and vapor-absence corresponding to complete condensation were visualized in a transient simulation. Interfacial rivulets, film climbing and liquid entrainment corresponding to flow-through condensation were identified by contours of liquid void fraction and further explained by the cross-sectional velocity profiles. Meanwhile, several recommendations to experiment and operation on upflow finned tubes were proposed based on numerical results.

[en] This work presents the preparation of hydrophilic graphene/graphene oxide nanosheets by liquid-shear-exfoliation using graphite oxide as an additive. And the as-prepared graphene/graphene oxide nanosheets are applied to the synthesis of the three-dimensional graphene/polyaniline composites that are applied as supercapacitor electrodes directly. A variety of influencing factors on the concentration of graphene/graphene oxide nanosheets are systematically explored, indicating that this method is easy to scale up. A series of characterizations prove that the graphene can be successfully exfoliated with the help of graphite oxide, and graphene can effectively combine with graphene oxide. The composites exhibit better electrochemical properties (gravimetric capacitance of 483 F g⁻¹ at 1 A g⁻¹) than materials built with the mixture of graphene, graphene oxide, and polyaniline as precursors. In addition, the symmetric supercapacitor which is assembled from the composites demonstrates a high energy density of 17.9 Wh kg⁻¹ at a power density of 500 W kg⁻¹. These results show that graphene/graphene oxide nanosheets have a good application in supercapacitors.

[en] Highlights: • Interference-free localised electrochemical impedance spectroscopy diagnostic system. • Segment gas diffusion layer does not be needed in a localised impedance measurement. • Anode inlet gas relative humidity is essential in the increase of catalyst utilisation. • The optimum reaction site shifts as the current density increases. • Cathode outlet suffers mass transport problem even at a medium current density. -- Abstract: Polymer electrolyte membrane fuel cells are promising power sources for vehicle and other portable applications due to their high energy efficiency and zero pollution emission during operation. To improve the performance and reliability of polymer electrolyte membrane fuel cells, effective and accurate diagnostic tools are urgently needed for polymer electrolyte membrane fuel cells practical applications. Different from the previous diagnostic methods that may damage the fuel cell structure, a novel interference-free diagnostic system based on the printed circuit board is proposed in this study. Fuel cell localised electrochemical impedance spectroscopy at different current density is observed. It is found that the activation impedance near inlet decreases sharply when current density increase. In addition, it is also found the flooding problem and the mass transport problem can occur at a medium current density due to the non-uniform behaviour of the polymer electrolyte membrane fuel cells. The proposed diagnostic system is demonstrated to be an effective tool to improve efficiency and robust of polymer electrolyte membrane fuel cells.

[en] In wireless network planning, large-scale MIMO can be applied to beam forming technology, which can ensure the continuous signal of user receiver without interruption. When the user moves, beamforming technology requires beamswitching to reposition the user, which increases unnecessary overhead. In this paper, the user azimuth beam tracking algorithm based on Kalman filtering decomposed the user’s trajectory in the actual scene, and used Kalman filtering algorithm to track the decomposed user’s trajectory, so that the beam can be adjusted to point to the user in real time. Through experimental verification, Kalman filtering is relatively accurate in predicting the position of mobile users relative to the Angle information of base station, and the predicted beam can ensure the stability of users’ connection, and at the same time achieve the purpose of reducing the number of beam-to-beam switching, reducing the overhead, improving the beam tracking efficiency, and making the connection more stable. (paper)