Transient Response of Particle Distribution in a Chamber to Transient Particle Injection

We inject a large number of newly created nano‐particle aggregates into a chamber for the purpose of removing harmful contents in an indoor environment. This study is to experimentally and numerically investigate transient response of particle distributions to particle injections. A room‐sized chamber of 4 m × 2.1 m × 2.4 m is connected to a specially designed particle‐injection system, with two Optical Particle Counters used to simultaneously measure particle‐number densities with the size range from 0.3 μm to 10 μm at the inlet and in the chamber. A velocity probe measures the flow that is up to 1 m/s. An Euler‐type particulate‐phase‐transport model is developed and validated by comparing with experimental data. The study shows that the transient behavior of particle distributions is determined by many factors, including particle size, particle settling speed, sampling location, and velocity distribution. Particle number densities decrease in time more quickly for large particles than for small particles, and locations farther downstream in the chamber correlate more weakly with the inlet injection.     

Spontaneous Formation of Antiferromagnetic Vortex Lattice in a Fast Rotating BEC with Dipole Interactions

When a Bose-Einstein condensate is set to rotate,superfluid vortices will be formed,which finally condense into a vortex lattice as the rotation frequency further increases.We show that the dipole-dipole interactions renormalize the short-range interaction strength and result in a distinction between interactions of parallel-polarized atoms and interactions of antiparallel-polarized atoms.This effect may lead to a spontaneous breakdown of the rapidly rotating Bose condensate into a novel anti-ferromagnetic-like vortex lattice.The upward-polarized Bose condensate forms a vortex lattice,which is staggered against a downward-polarized vortex lattice.A phase diagram related to the coupling strength is obtained.     

The Effects of Wettability on Primary Vortex and Secondary Flow in Three-Dimensional Rotating Fluid

The secondary flow driven by the primary vortex in a cylinder,generating the so called "tea leaf paradox",is fundamental for understanding many natural phenomena,industrial applications and scientific researches.In this work,the effect of wettability on the primary vortex and secondary flow is investigated by the three-dimensional multiphase lattice Boltzmann method based on a chemical potential.We find that the surface wettability strongly affects the shape of the primary vortex.With the increase of the contact angle of the cylinder,the sectional plane of the primary vortex gradually changes from a steep valley into a saddle with two raised parts.Because the surface friction is reduced correspondingly,the core of the secondary vortex moves to the centerline of the cylinder and the vortex intensity also increases.The stirring force has stronger effects to enhance the secondary flow and push the vortex up than the surface wettability.Interestingly,a small secondary vortex is discovered near the three-phase contact line when the surface has a moderate wettability,owing to the interaction between the secondary flow and the curved gas/liquid interface.     

Simulation of Vortex Convection in a Compressible Viscous Flow with Dynamic Mesh Adaptation

In this work, vortex convection is simulated using a dynamic mesh adaptation procedure. In each adaptation period, the mesh is refined in the regions where the phenomena evolve and is coarsened in the regions where the phenomena deviate since the last adaptation. A simple indicator of mesh adaptation that accounts for the solution progression is defined. The generation of dynamic adaptive meshes is based on multilevel refinement/coarsening. The efficiency and accuracy of the present procedure are validated by simulating vortex convection in a uniform flow. Two unsteady compressible turbulent flows involving blade-vortex interactions are investigated to demonstrate further the applicability of the procedure. Computed results agree well with the published experimental data or numerical results.     

圆管管翅散热器肋侧主流方向绝对涡通量研究

本文以圆管管翅式散热器为研究对象,采用数值模拟的方法对圆管管翅式散热器肋侧空气通道主流方向绝对涡通量的特性进行了探讨。给出了肋侧空气通道主流方向绝对涡通量无量纲化参数,二次流雷诺数;横向管间距、肋侧空气流动雷诺数对二次流雷诺数及努塞尔数的影响。     

Thermally Radiative Rotating Magneto-Nanofluid Flow over an Exponential Sheet with Heat Generation and Viscous Dissipation:A Comparative Study

This article examines a mathematical model to analyze the rotating flow of three-dimensional water based nanofluid over a convectively heated exponentially stretching sheet in the presence of transverse magnetic field with additional effects of thermal radiation,Joule heating and viscous dissipation.Silver(Ag),copper(Cu),copper oxide(Cu O),aluminum oxide(Al_2O_3)and titanium dioxide(Ti O_2)have been taken under consideration as the nanoparticles and water(H_2O)as the base fluid.Using suitable similarity transformations,the governing partial differential equations(PDEs)of the modeled problem are transformed to the ordinary differential equations(ODEs).These ODEs are then solved numerically by applying the shooting method.For the particular situation,the results are compared with the available literature.The effects of different nanoparticles on the temperature distribution are also discussed graphically and numerically.It is witnessed that the skin friction coefficient is maximum for silver based nanofluid.Also,the velocity profile is found to diminish for the increasing values of the magnetic parameter.     

Statistical Assessment of Counter-Flow Vortex Tube Performance for Different Nozzle Numbers,Cold Mass Fractions,and Inlet Pressures Via Taguchi Method

Abstract

In this article, the effect and optimization of process parameters in a counter-flow vortex tube on temperature difference were investigated through the Taguchi method. The experiments were planned as per Taguchi's L27 orthogonal array with each experiment performed under different conditions of inlet pressure, nozzle number, and cold mass fraction. By means of analysis of variance and regression analysis, the effects of factors and their interactions on temperature difference were determined and modeled with a correlation coefficient of 93.5%. Accordingly, it was observed that temperature difference goes up with the increase in inlet pressure, and the cold mass fraction and decreases with the increase in nozzle number. In addition, the optimum settings of process parameters maximizing the temperature difference are an inlet pressure of 650 kPa, a nozzle number of 2, and a cold mass fraction of 0.7. Finally, confirmation tests verified that the Taguchi method was successful in the assessment of vortex tube parameters for temperature difference.     

改进粒子水平集法及其应用

针对传统粒子水平集方法的缺陷提出一种虚拟粒子对距离函数的修正方法.改进算法针对虚拟粒子与待修正网格点的各种相对位置进行误差修正,可以避免虚拟粒子在非界面法线方向移动而产生的误差.数值求解涡旋流场问题显示:改进算法的界面捕捉性能得到显著提高.在此基础上,结合投影法求解Navier-Stokes方程组,数值模拟存在高密度比(10³量级)及粘性比(10²量级)的不可压缩两相流问题(气泡上升及自由面不稳定性问题).计算结果与已有结果吻合良好,详细分析主要控制参数对瑞利-泰勒不稳定性现象的影响.     

滴形颗粒在通道中沉降的格子Boltzmann-虚拟区域方法模拟

采用格子Boltzmann-虚拟区域方法对滴形颗粒在垂直通道中的沉降过程进行直接数值模拟.通过格子Boltzmann方法求解N-S方程,流体与固体之间的相互作用通过虚拟区域方法描述.研究雷诺数在10^-2到100范围内颗粒形状因子对其摩擦系数和阻力系数的影响.为便于比较,给出了圆形颗粒沉降的结果.结果发现,当雷诺数小于1的时候,颗粒的摩擦系数始终保持常数,而当雷诺数大于1时摩擦系数随雷诺数的增大而增大.此外,当雷诺数小于约30时圆形颗粒的摩擦系数和阻力系数均小于滴形颗粒,而当雷诺数大于30时情况正好相反.颗粒周围的压力分布证明了这一结论.     

Eigenvalue Spectrum of a Dirac Particle in Static and Spherical Complex Potential

It has been observed that a quantum theory need not be Hermitian to have a real spectrum. We study the non-Hermitian relativistic quantum theories for many complex potentials, and obtain the real relativistic energy eigenvalues and corresponding eigenfunctions of a Dirac-charged particle in complex statically and spherically symmetric potentials. Complex Dirac–Eckart, complex Dirac–Rosen–Morse II, complex Dirac–Scarf and complex Dirac–Poschl–Teller potential are investigated.     

Experimental Investigation of the Effect of Purge Flow and Main Flow Interaction in a Low-Speed Turbine Cascade Passage

In order to protect the vulnerable turbine components from extreme high temperature, coolant flow is introduced from the compressor to the disk cavity, inevitably interacting with the main flow. This paper describes an experimental investigation of the interaction between the main flow and the purge flow in a low-speed turbine cascade with three purge flow rates, Cm = 0, Cm = 1%, and Cm = 2%. In order to study the effect of the interaction between the main flow and the purge flow on the secondary flows, a Rortex method developed by Liu Chaoquan is introduced to identify the vortex in the flow field. In the meantime, a method to calculate the mean entropy production rate based on the particle image velocimetry (PIV) result is adopted to investigate the flow loss. The PIV result indicates that the purge flow has a prominent impact on the flow field of the cascade passage, changing the velocity distribution that induces a local blockage area. The results of vortex identification show that the purge flow promotes the generation of the passage vortex near the suction side. In addition, the purge flow makes the passage vortex migrate to the tip wall direction, enlarging the region affected by the secondary flow. The mean entropy production (MEP) result shows that the flow loss is mainly caused by the passage vortex. The coincidence of the high-MEP region and the location of the passage vortex indicates that the purge flow increases the secondary flow loss by affecting the formation and the migration of the passage vortex.     

自旋为1粒子在旋转磁场中的几何相位和动力学相位(英文)

文章研究了自旋为1的粒子在旋转磁场中的几何相位和动力学相位.推导出如何计算自旋为1的粒子在绝热和非绝热演化中的几何相位和动力学相位公式,并利用这些公式计算其相位.最后我们讨论了三种情况下的Berry相位,当考虑ω1<<ω时,系统处于绝热近似,此时,几何相位就是Berry相位.     

Comparisons of Performances of a Flat Tube Bank Fin Model Mounted Vortex Generators and the Real Heat Exchanger

Abstract

In this article, we compared the model results obtained by the naphthalene sublimation method with the results obtained by experiments with the real heat exchanger based on the model used in the naphthalene sublimation experiment. The results reveal that in the Reynolds number region studied in the present article, the experimental results obtained by naphthalene sublimation agree with the experimental data of the real heat exchanger under the working conditions within a 10% deviation. The heat/mass transfer coefficient obtained with an isothermal condition using naphthalene sublimation can be applied to the mixed thermal boundary condition. The effects of mounted and punched vortex generators on thermal-hydraulic performances are limited to the configuration studied in this article.     

全尺度方法对颗粒与流体之间相交换量研究

本文采用了内嵌边界多重直接力算法全尺度计算研究了三维空间中颗粒群在重力作用下沉降时,颗粒群与流体之间的相互作用过程。结合多相流的欧拉-欧拉双流体模型方法中对颗粒群与流体之间相互作用力的处理方式,分析了颗粒与流体之间的相交换量。并把全尺度计算得到的颗粒群与流体之间的相交换量与本文中提到的单颗粒受力模型(SPM)和颗粒群受力模型(GPM)对相互作用力进行了比较分析。     

离心压气机叶排间涡脱落及气流脉动行为研究

对某一带叶片扩压器跨声速离心压气机内部三维非定常流场进行了数值模拟,依据计算结果描述了叶轮叶片尾缘尾迹涡脱落行为,给出了叶轮尾缘脉动压力频谱特性图和叶轮出口位置脉动速度动能分布图。研究结果表明,主叶片与分流叶片尾缘尾迹涡脱落过程交替进行;转静干涉和转子叶片尾缘的涡脱落行为是造成叶轮尾缘气流脉动行为的主要原因,随着时间的...     

Subcooled Flow Boiling Heat Transfer to Water and Ethylene Glycol/Water Mixtures in a Bottom-heated Tube

Subcooled flow boiling heat transfer experiments were performed with water and ethylene glycol/water mixtures at five flow velocities and four fluid inlet temperatures. Both turbulent flow and laminar flow were tested in a special test facility with its experimental test section heated from the bottom surface only. Boiling curves and subcooled flow boiling heat transfer coefficients of the tested fluids were determined from the experimental measurements. Predictive correlations of the subcooled flow boiling heat transfer coefficients were developed based on the experimental data. Comparisons are presented of wall temperatures between the experimental measurements and the correlation predictions.     

Locally Resolving Measurements of PSD,Particle Concentration and Particle Velocity by Means of TFS with Dual Beams

Transmission fluctuation spectrometry with spatial correlation (TFS‐SC) is based on transmitting two beams of radiation through a flowing suspension, whereby the distance of the beam centers is varied. Thus, the spatial correlation of the transmission fluctuations of the two beams is determined as a function of the beam distance. By numerical modeling, the transition functions of the correlation are found as a function of beam distance, beam diameters, particle diameter and beam intersection angle. Experimentally determined spatial correlation spectra can be inverted to obtain the particle concentration and particle size distribution by using the theoretical transition functions for mono‐sized particles. In addition, time correlations can be used to extract information on particle velocity. Some experimental results obtained by TFS‐SC are presented and discussed. This method appears promising for application in the local resolving of measurements of PSD, particle concentration and particle velocity in two‐phase flows, both in the laboratory and in process control.     

微粗糙面上方球形粒子的光散射及其散射截面的计算

基于互易定理研究了光波入射时微粗糙面与其上方球形粒子复合模型的光散射。根据粗糙表面电流积分方程并利用表面微扰展开，得到了微粗糙面表面极化电流的迭代解，给出了耦合电场的计算方法。结合散射耦合场散射矩阵和已有的微粗糙面及球形粒子的散射矩阵，给出了复合模型散射截面的计算公式，数值计算了复合模型的后向散射截面并进行了详细讨论。     

Interaction Between Isoquercitrin and Bovine Serum Albumin by a Multispectroscopic Method

ABSTRACT

The interaction of isoquercitrin and bovine serum albumin (BSA) was investigated by means of fluorescence spectroscopy (FS), resonance light scattering spectroscopy (RLS), and ultraviolet spectroscopy (UV). The apparent binding constants (K _a) between isoquercitrin and BSA were 5.37 × 10⁵ L mol^?1 (293.15 K) and 2.34 × 10⁵ L mol^?1 (303.15 K), and the binding site values (n) were 1.18 ± 0.03. According to the Förster theory of non-radiation energy transfer, the binding distances (r) between isoquercitrin and BSA were 1.94 and 1.95 nm at 293.15 K and 303.15 K, respectively. The experimental results showed that the isoquercitrin could be inserted into the BSA, quenching the inner fluorescence by forming the isoquercitrin–BSA complex. The addition of increasing isoquercitrin to BSA solution leads to the gradual enhancement in RLS intensity, exhibiting the formation of the aggregate in solution. It was found that both static quenching and non-radiation energy transfer were the main reasons for the fluorescence quenching. The entropy change and enthalpy change were negative, which indicated that the interaction of isoquercitrin and BSA was driven mainly by van der Waals interactions and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative.