On the basis of the icing-delay performance and ice adhesion strength, the anti-icing potential of the superhydrophobic surface has been well-investigated in the past few years. The present work ...mainly emphasized the investigations of ice nucleation and growth to fully explore the anti-icing potential of the superhydrophobic surface. We took the various surfaces ranging from hydrophilic to superhydrophobic as the research objects and, combining the classical nucleation theory, discussed the ice nucleation behaviors of the water droplets on these sample surfaces under the condition of supercooling. Meanwhile, the macroscopical growth processes of ice on these surfaces were analyzed on the basis of the growth mechanism of the ice nucleus. It was found that the superhydrophobic surface could greatly reduce the solid–liquid interface nucleation rate, owing to the extremely low actual solid–liquid contact area caused by the composite micro–nanoscale hierarchical structures trapping air pockets, leading to the bulk nucleation dominating the entire ice nucleation at the lower temperatures. Furthermore, ice on the superhydrophobic surface possessed a lower macroscopical growth velocity as a result of the less ice nucleation rate and the insulating action of the trapped air pockets.
Multilevel PWM rectifiers are featured with low-voltage stress of switching devices, low harmonic content and suitable for high-voltage high-power applications. This paper presents a novel ...single-phase five-level PWM rectifier based on coupled inductor. In order to improve the dynamic response of the system and reduce the current harmonic content of the grid side, a sliding mode proportional integral resonance (PIR) control algorithm was proposed. Firstly, the circuit topology and working principle of the new single-phase five-level PWM rectifier were analysed. A mathematical model of the rectifier in d–q axis synchronous rotating reference frame was derived and analysed its voltage outer loop sliding mode and current inner loop PIR control algorithm. Compared with the traditional PI current control algorithm based on d–q axis, the proposed sliding mode PIR control algorithm has a faster dynamic response speed and a lower current harmonic content on the grid side. Finally, a simulation model based on MATLAB/Simulink and a hardware-in-the-loop real-time simulation experiment platform based on RT-lab were built up, and the proposed sliding mode PIR and the traditional PI current control algorithm based on d–q axis were compared. Simulation and experimental results have verified the correctness and feasibility of the proposed algorithm.
•We designed nanotube, nanowire or nanomesh on features of microscale Ti6Al4V pits.•Secondary nanostructures significantly improved superhydrophobicity.•The effects of nanostructures on ...superhydrophobicity were investigated in detail.•The surface with microscale pits and nanowire owned strong superhydrophobicity.
Micro-nanostructures were successfully synthesized on a Ti6Al4V alloy and then coated with a monolayer of hydrophobic groups to obtain the superhydrophobic surfaces. The effect of secondary nanostructures (nanotube, nanowire and nanomesh) on superhydrophobic performance was investigated by the characterization of contact process of a falling water droplet onto the superhydrophobic surface via a high-speed camera. Meanwhile, the apparent contact angle and sliding angle of the water droplet were measured by a contact angle analyzer. The results indicated that the superhydrophobic surface with micro-nanostructures (microscale pits and nanowire) exhibited robust superhydrophobic properties (apparent contact angle 161° and sliding angle approximately 3°) due to the large amount of flowing air being trapped underneath the droplet. Moreover, it was observed that once the impacting droplet contacted with the superhydrophobic surface, it spread uniformly before retracting and finally lifted off the surface within 13ms.
The present paper investigates the ceiling maximum smoke temperature and longitudinal decay in tunnel fires using a horseshoe shaped 1:3.7 scale-model tunnel constructed by concrete and a full-scale ...model tunnel established by SIMTEC for the first time. The maximum smoke temperature beneath the ceiling and the longitudinal temperature profiles were obtained and analyzed. The major conclusions are summarized as follows: The ceiling maximum smoke temperature rise right above the fire source is directly proportional to the terms of Q2/3/Hf5/3 and the ceiling maximum smoke temperature decreases as a sum function of two exponential equations of horizontal distance. Modified equations are proposed for maximum smoke temperature rise beneath the ceiling and longitudinal temperature decay, and the predictions show a good agreement with the values measured by experiments and numerical simulations. The results obtained by numerical simulations agree well with experimental results, and SIMTEC is reasonable to simulate the tunnel fires to predict the temperature profiles. The results are of important significance for tunnel fire safety and personnel evacuation. Keywords: Ceiling maximum temperature, Longitudinal temperature decay, Horseshoe shaped tunnel, Tunnel fires
The DC/DC converter is the core part of the two-stage electric vehicle Onboard Charger. At present, the phase-shifted full-bridge soft-switching DC/DC converter has problems such as difficulty in ...commutation of the lagging leg, voltage fluctuation on the secondary side of the transformer, and low efficiency. A full-bridge DC/DC converter with two clamp diodes and synchronous rectification is proposed in this paper. Clamping diodes are used to suppress the voltage oscillation of the secondary side of the transformer and provide the commutating energy of the lagging leg. Synchronous rectification reduces the loss of the switching device. The operating principle and control method of the DC/DC converter are analyzed, and the switching device loss is calculated. The simulation and experimental results show that, compared with the traditional DC/DC converter, the voltage impulse of the secondary side of the transformer is smaller, the efficiency is higher, and the soft switch can be realized in a wide load range, which satisfies the requirement of fast charging of vehicle-mounted batteries.
The effects of diluents, thermodynamic interactions, different quenching conditions and coarsening on the morphology of poly(vinylidene fluoride) (PVDF) membranes via thermally induced phase ...separation were investigated. Scanning electron microscopy indicated that an interconnected spherulitic structure was obtained in the PVDF–DMP system, while the PVDF–DMP–DOS and PVDF–DMP–DOA systems showed a jagged and sharp-edged spherulitic structure. As the interactions decreased, the spherulitic structure was increasingly non-discernable and the value of porosity increased in the order of PVDF–DMP, PVDF–DMP–DOA, PVDF–DBP and PVDF–DMP–DOS. When quenching in 353 K and 368 K, the spherulities became more discernable, and the size of spherulity increased. When quenching in different conditions, the discernible spherulitic structure was obtained in ice water, a greater spherulitic size was obtained in a water bath at 303 K, and PVDF crystallized much slower and improved in an air bath.
A robust fractional-order linear super-twisting sliding mode observer (LSTSMO) for an induction motor speed sensorless system is proposed in this study to solve the problem of balance between sliding ...mode chattering and estimation accuracy. First, the stability of the linear super-twisting algorithm is proven with the Lyapunov function, and the convergence and gain coefficient range of the algorithm are analyzed. Next, the fractional integral sliding mode surface based on the stator current error term is established, and the linear super-twisting algorithm is introduced to design the fractional LSTSMO. In addition, a flux correction link is added to enhance the robust performance of the observer. The results of the simulations and experiments verify that the observer has high flux linkage estimation accuracy, which can enhance transient performance rapidity and chattering suppression ability simultaneously, thereby improving robustness against parameter drifts. Moreover, the designed observer improves the dynamic and steady state performance of the motor in the full-speed range.
Vehicle charging power supply is widely used because of its small size and portability. Aiming at the problems of slow dynamic response, subharmonic, oscillation and limited soft-switching range of ...phase-shifted full-bridge DC/DC converter, the paper proposed a modified PSFB converter by introducing clamp diodes at the primary side of the transformer to suppress voltage oscillation of the transformer’s secondary side. Also, digital peak current phase-shifting control and slope compensation are introduced to avoid subharmonic oscillation. Dynamic dead-time control technology introduced adjust the dead-time in different load ranges through the dead-time adjustment subroutine. Finally, an experimental platform of on-board charging phase-shifted full-bridge DC/DC converter is established. The experimental results show that the power supply eliminates subharmonic oscillation, achieves a wide range of soft-switching, improves the dynamic performance and antiinterference ability of the system, and optimizes the power efficiency.
The Cu2ZnSnS4 (CZTS) was firstly wrapped uniformly throughout the surface of TiO2 nanowire arrays (NWs) via in-situ solvothermal method. It was found that the shape of time-dependent CZTS evolved ...from nanoparticles to nanosheets, and the size and deposition amount of CZTS could be controlled by adjusting the reactant concentration. Then, the CZTS/TiO2 NWs heterostructure electrodes were prepared and characterized respectively by photoelectrochemical response measurements, optical measurements, and electrochemical impedance spectroscopy (EIS). The results showed that the optimized CZTS/TiO2 NWs sample exhibited enhanced photoelectrochemical performance, with the photocurrent density being 23.2 times as high as that of the pure TiO2 NWs electrode and the efficiency for hydrogen generation reaching 1.1%.
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•CZTS/TiO2 NWs was fabricated via in-situ solvothermal method.•The formation mechanism of CZTS/TiO2 NWs heterostructure was proposed.•The heterostructure films show a response to visible light.•CZTS/TiO2 NWs film exhibited enhanced photoelectrochemical performance.
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