An improved semi-empirical friction model for gas-liquid two-phase flow in horizontal and near horizontal pipes

Pressure drop and liquid hold-up are two very important fluid flow parameters in design and control of multiphase flow pipelines. Friction factors play an important role in the accurate calculation of pressure drop. Various empirical and semi-empirical closure relations exist in the literature to calculate the liquid-wall, gas-wall and interfacial friction in two-phase pipe flow.However most of them are empirical correlations found under special experimental conditions. In this paper by modification of a friction model available in the literature, an improved semiempirical model is proposed. The proposed model is incorporated in the two-fluid correlations under equilibrium conditions and solved. Pressure gradient and velocity profiles are validated against experimental data. Using the improved model, the pressure gradient deviation from experiments diminishes by about 3%; the no-slip condition at the interface is satisfied and the velocity profile is predicted in better agreement with the experimental data.     

稳定分层湍流中逆梯度输运的关联分析研究

本文采用关联分析方法研究了稳定温度分层湍流中的结构特性、输运特性，以及热量、动量逆梯度输运现象的尺度效应及其参数演化．首先采用大涡模拟方法对稳定分层湍流中的结构特性和输运特性进行了分析，将逆梯度输运发生的时间尺度作为已知条件，结合关联量分析方法在波数空间中的解析解，对逆梯度输运现象的尺度效应进行了分析研究．结果发现，稳定分层强度较大的流动中发生垂向热量及动量逆梯度输运现象，发生的结构尺度与关联分析所发现垂向热量、动量逆梯度输运的波数形成了呼应．随着分层强度增加，热量、动量的输运强度均受抑制，与逆梯度输运关联的流场结构尺度减小，同样的效应也发生在流场结构向下游演化的过程中．     

Nano-sized local magnetic field induced by circular motion of ions and molecules in a nanotorus under gigahertz rotating electric fields

Recently, we reported molecular dynamics simulations of stable cyclotron motions of ions and water molecules in a carbon nanotorus, induced by different rotating electric fields (EFs). This study is devoted to the calculation and characterisation of the magnetic field (MF) induced by these cyclotron motions. Results show that carbon nanotorus containing ions or water molecules acts as an EF-to-MF transducer. Components of the instantaneous induced MF show large-scale oscillations superimposed by strong fluctuations arising respectively from overall circular motion and random collisions of moving species. Analysis of the space-dependencies of the induced MF components shows that the induced MF is maximum at the centre of the nanotorus. The MF induced by cyclotron motion of ions follows the orders B(Ca²⁺)?>?B(Na⁺)?≈?B(K⁺) at E?=?1.0?V/nm and B(E?=?1.0?V/nm)?>?B(E?=?0.5?V/nm)?>?B(E?=?0.1?V/nm). The time-averaged induced MF of the cyclotron motion of 81 water molecules is almost 10² times stronger than that of ions. The induced MF strength is decreased with increasing distance from nanotorus and decays effectively at about 17.3–18.1 and 15.9–18.2?nm along the z-axis of the nanotorus for ions and water molecules, respectively. The magnitude of the MF induced by cyclotron motions of water molecules and ions, respectively, decreases and increases in the nanotorus with freed carbon atoms.     

分子模拟实验课程建设的探索与实践

We put forward the idea of building a molecular simulation experiment course. After two-year teaching practice, we write the experiment textbook which not only covers the classic experimental projects, but also includes the frontier hot issues, and open exploration experiment. This article summarizes the teaching requirements, basic content, assessment methods, the initial achievements made so far and the prospects for the future.     

染料敏化太阳能电池载流子传输的数值模拟

由于在染料敏化太阳能电池(dye-sensitized solar cell, DSSC)中存在染料弛豫、半导体薄膜中电子与氧化态染料分子发生反应和电子在电解质中与氧化态离子复合等不利反应,利用一个更完善的DSSC载流子传输模型对电池的光电性能进行模拟就显得非常重要。为此,本文基于由多重俘获理论建立的DSSC中的包括电子、染料阳离子、碘化物和三碘化物在内的载流子传输模型,数值模拟得到了不同TiO₂薄膜厚度、不同入射光强度与不同染料分子吸收系数下DSSC的J-V曲线。结果表明,随着TiO₂薄膜厚度的增加,太阳能电池的短路电流密度增大,开路电压减小,光电转换效率先增大后减小。当DSSC的TiO₂薄膜厚度为20 μm时,光电转换效率达到最大值7.41%,同时光电转换效率随入射光强度与染料分子吸收系数的增大均有一定程度提高,其中在吸收系数为4 500 cm^-1时,光电转换效率为6.73%。以上结果可以为改进DSSC的光电性能提供理论指导。     

Experimental and molecular simulating study on promoting electrolyte-immersed mechanical properties of cellulose/lignin separator for lithium-ion battery

Lithium-ion batteries have been developing intensively and earn an unprecedented reputation, yet advanced performance and safety issue still require considerable investigation. Separator is vital to comprehensive properties of batteries, where the mechanical properties are key to breaking through of new-type separator. Unfortunately, electrolyte submersion has caused damage to strength of cellulose separator. Whereupon, in this work, cellulose separator is optimized by introducing lignin particles to promote electrolyte-immersed mechanical strength. Experiments are conducted concerning surface morphology, contact angle, porosity, electrolyte uptake, mechanical properties and electrochemical performance. Molecular simulation is implemented to explore the mechanism of tensile behavior of cellulose and lignin subjected to electrolyte solvents. Experimental results confirm positive effect of lignin addition in improving mechanical properties and simultaneously maintaining impressive electrochemical performance of the cellulose/lignin composites separators. Besides, lignin addition amount of 2.5% and 5% is recommended to achieve promising overall properties. Molecular simulation has successfully unveiled that weakening of cellulose separator submerged in electrolyte is resulted by the deformed cellulose amorphous region and the promoting effect of adding lignin is contributed from the new hydrogen bonds generated between cellulose and lignin molecules. Hopefully, this work provides novel insight on preparing remarkable separator and mechanism of materials behavior.     

Kinetic study of hydrogen sulfide decomposition on Pt(111) surface

In this work, kinetic of H₂S conversion to H₂ molecule on the surface of Pt(111) is studied using kinetic Monte Carlo simulation. The results of simulation were fitted to the experimental temperature-programed desorption spectra. The good agreement between the empirical and the simulated data confirms the proposed mechanism and kinetic data (activated energies and pre-exponential factors). The influence of variables such as temperature and concentrations of H₂S and H₂ on the overall results of hydrogen production is studied. The condition is proposed in which the best yield of reaction at minimum temperature is obtained. Results show that platinum is a perfect catalyst for converting H₂S to H₂ and it has a perfect performance (98%) after 5 μs at low temperature of 227°C.     

Simultispin: A versatile graphical user interface for the simulation of solid-state continuous wave EPR spectra

Solid-state continuous wave (cw) electronic paramagnetic resonance (EPR) spectroscopy is particularly suitable for metal complex analysis. Extracting magnetic parameters by simulation is often necessary to describe the electronic structure of the studied molecular compounds that can have various electronic spin states and characterized by different parameters like g-values, hyperfine coupling or zero field splitting values. Easyspin toolbox on MATLAB is a powerful tool, but for the user, it requires spending time with coding and could discourage nonexperts. Facing this context, we have developed a graphical user interface called Simultispin, dedicated to solid-state cw-EPR spectra simulation. Some examples of experimental spectra of metal complexes (mixture of low spin and high spin Fe^III complexes, dynamic disorder of a Cu^II complex, photogeneration of a Mn^III complex), highlighting specific solid-state functions, are described and analyzed based on simulations performed with Simultispin. We hope that its ergonomy and the ease to set up a complete set of parameters to get reliable simulations could help a large EPR community to improve the efficiency of their interpretations.     

具有复合幂函数和共存吸引子的新混沌系统的动力学分析与电路仿真

构造一个具有复合幂函数的三维连续自治混沌系统。系统的状态方程仅有5项，其中一项是指数小于1的复合幂函数。该系统具有结构简单、非双曲平衡点、吸引子共存的性质，展现出了复杂的动力学行为。首先，对系统的动力学行为进行分析，包括李雅普诺夫（Lyapunov）指数谱、分岔图以及庞加莱映射等，结果表明此系统具有混沌特性。然后进行混沌系统的电路设计，电路仿真结果验证了理论分析的正确性。