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The multi-size group (MUSIG) model is employed in this paper to simulate the gas–liquid two-phase flow in pump as turbine (PAT) since the traditional Eulerian–Eulerian two-fluid model is unable to take into account the phenomena of breakup and coalescence of bubbles. First, the simulation of gas–liquid two-phase flow in a square column is compared with the experiment to verify the accuracy of the MUSIG model. Then, the results of gas–liquid two-phase flow in PAT simulated by the MUSIG model are compared with those by the conventional uniform bubble (UB) model and find that the MUSIG model is more favorable to capture the flow pattern at high gas content compared to the UB model. Based on the MUSIG model, the internal flow characteristics, pressure fluctuation, and bubble size distribution of the PAT are analyzed. The rotation of the blades breaks a part of big bubbles into small bubbles in the volute, resulting in a smaller diameter of the bubbles entering the impeller. As the gas content increases, the number and size of vortices in the impeller flow channel increase. The vortex is formed at locations where the gas phase distribution in the impeller flow channel is concentrated. The outlet of the impeller is more prone to bubble consolidation under high gas content conditions. In conclusion, the MUSIG model can well predict the complex flow characteristics of gas–liquid two-phase inside the PAT and identify the key influencing factors of energy acquisition, which can provide support for improving the performance of the PAT design. [ABSTRACT FROM AUTHOR]

High-power microwave-induced low-pressure discharges seriously threaten the reliability of space payload systems. Under extremely low-pressure conditions, the evolution of ionized and secondary electrons at the initial stage of discharge is crucial to figure out the discharge process. Therefore, this paper investigates the development of multiple electrons in the discharge process under a highly low-pressure environment using numerical simulation. A three-dimensional simulation model based on the Monte Carlo algorithm is established by considering various electron-gas collisions and secondary electron emissions from different material surfaces. The evolution characteristics of various electrons' populations, energy, and distribution patterns during the discharge process are analyzed. In addition, the influence of the critical conditions at different air pressures on the electron evolution during the discharge process and the intrinsic causes are also investigated. This study is significant in revealing the transition characteristics between multipactor and low-pressure discharge and exploring their inherent mechanisms. [ABSTRACT FROM AUTHOR]

An improved optimization algorithm, namely, multi-strategy-sparrow search algorithm (MSSSA), is proposed to solve highly non-linear optimization problems. In MSSSA, a circle map is utilized to improve the quality of the population. Moreover, the adaptive survival escape strategy (ASES) is proposed to enhance the survival ability of sparrows. In the producer stage, the craziness factor integrated with ASES is introduced to enhance the search accuracy and survival ability. In the scout stage, the ASES facilitates sparrows successful escape from danger. Besides, opposition-based learning or Gaussian–Chachy variation helps optimal individuals escape from local solutions. The performance of the MSSSA is investigated on the well-known 23 basic functions and CEC2014 test suite. Furthermore, the MSSSA is applied to optimize the real-life engineering optimization problems. The results show that the algorithm presents excellent feasibility and practicality compared with other state-of-the-art optimization algorithms. [ABSTRACT FROM AUTHOR]

Treatment of ZnO films in a supercritical fluid (SCF) has been reported to improve the performance of devices in which the treated ZnO films are incorporated; however, the mechanism of this improvement remains unclear. In this paper, we study the transformation of the surface morphologies and emission properties of ZnO films before and after SCF treatment, establishing the relationship between the treated and untreated structures and thereby enabling tuning of the catalytic or opto-electronic performance of ZnO films or ZnO-film-based devices. Both undoped and N-doped ZnO nanostructures generated by SCF treatment of films are investigated using techniques to characterize their surface morphology (scanning electron microscopy (SEM) and atomic force microscopy (AFM)) as well as room-temperature photoluminescence (RT-PL) spectroscopy. The water-mixed supercritical CO2 (W-SCCO2) technology was found to form nanostructures in ZnO films through a self-catalyzed process enabled by the Zn-rich conditions in the ZnO films. The W-SCCO2 was also found to promote the inhibition of defect luminescence by introducing -OH groups onto the films. Two models are proposed to explain the effects of the treatment with W-SCCO2. This work demonstrates that the W-SCCO2 technology can be used as an effective tool for the nanodesign and property enhancement of functional metal oxides. [ABSTRACT FROM AUTHOR]