Experimental Research on Salt-out Particle Motion and Concentration Distribution in a Vortex Pump Volute

The vortex pump is suitable for salt solution transportation. But the salt-out flow mechanism in the pump has not been understood fully. Salt-out layer formation and growth rate are closely related to crystal particle motion and concentration distribution. Study on the particle hydrodynamic characteristics in the pump volute becomes a key problem, because the crystal particles are mainly distributing in this zone after they enter the pump. Phase Doppler particle analyzer(PDPA) is used to measure the two-phase flow field in a model pump volute to get more understanding about the salt-out phenomenon. The crystal particle velocities are obtained in all three peripheral, radial and axial directions. Particle size and particle number density(PND) measurements are also performed in the experiment. Results are presented and discussed along the radial direction under different pump operating conditions, as well as various axial measurement positions. It is found that particle velocity gradient of peripheral component varies with the pump discharge. There is a turning point of relation between peripheral velocity component and discharge. Radial flow velocity curves look like a saddle shape and velocity magnitudes are changing greatly with the discharge. The non-equilibrium velocity feature between liquid and solid phase on this direction is also remarkable. Particles flow into the impeller at radial position R1, and the axial velocity component increases in this region. The particle size curve shows an open-up parabola distribution. The largest particles are distributing near the casing peripheral wall. As flow rate increases, accordingly PND increases. It also grows up in the axial-outward direction towards the suction cover. Crystal particle aggregation phenomenon can be revealed from the analysis of particle size and PND distribution, and the aggregation region is determined as well. Research results are helpful for optimal design of this kind of pump preventing salt-out.     

ECT measurement and CFD–DEM simulation of particle distribution in a down-flow fluidized bed

In the present study, a combined model of computational fluid dynamics and the discrete element method (CFD–DEM) was used to simulate the particle distributions in a down-flow fluidized bed (DFB) with a newly designed particle–air distributor. In the simulation model, particle motion is calculated by solving Newton’s equations and the flow field of air is predicted by the Navier–Stokes equations. The calculation was made for the same geometric and operating conditions as the experiment which was carried out for comparison with the simulation using electrical capacitance tomography (ECT). The numerical predictions for the axial and radial profiles of the particle distribution agreed well with the experimental results.     

Effect of a diffuser on gas-solid behavior in CFB riser for CO2 capture

Gas-solid fluidized beds have been used in CO₂ capture processes because of their high mixing characteristic and heat and mass transfer. Sufficient residence time of solid particles in a reactor is required to capture CO₂. However, a fraction of solid particles pass through a reactor without capturing CO₂ due to normal reaction characteristics. Therefore, the objective of the present study was to increase the sorbent residence time using a diffuser in a reactor for CO₂ capture. An Eulerian-Eulerian model in a commercial CFD program was employed to simulate gas-solid flow in the reactor. First, sensitivity analysis depending on operating conditions was conducted to predict the residence time of solid particles. The diffuser was located in the middle of the reactor and the angle of the diffuser was changed. Solid particles dispersed in the radial direction because of gas characteristics in the diffuser and increased the residence time. The results showed that the diffuser increased the sorbent residence time, so that the probabilities of gas-solid reaction would be also improved.

     

Hydrodynamics and particle mixing/segregation measurements in an industrial gas phase olefin polymerization reactor using image processing technique and CFD-PBM model

Particle size distribution (PSD) has a significant impact on the performance of fluidized bed reactors due to uneven distribution in the segregation and mixing phenomena. This paper develops a new method of digital image processing that investigates the hydrodynamics of an industrial gas phase olefin polymerization reactor and studies the fluidization structure of a wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD-PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the applied parameter assumptions and closure laws were appropriately chosen to satisfactorily predict the available operational data in terms of pressure drop and bed height. The transient CFD-PBM/DQMOM coupled model and image analysis technique are then implemented extensively to analyze bubble fluidization structure and segregation phenomena at different velocities. The particle segregation indicates that the small bubbles present in the bed are unable to induce vigorous mixing at low superficial gas velocity while particle mixing improves at a velocity above the minimum fluidization velocity. Further, the predicted results show higher axial segregation phenomena when compared to the radial direction.     

Multidepth, multiparticle tracking for active microrheology using a smart camera

The quantitative measurement of particle motion in optical tweezers is an important tool in the study of microrheology and can be used in a variety of scientific and industrial applications. Active microheology, in which the response of optically trapped particles to external driving forces is measured, is particularly useful in probing nonlinear viscoelastic behavior in complex fluids. Currently such experiments typically require independent measurements of the driving force and the trapped particle's response to be carefully synchronized, and therefore the experiments normally require analog equipment. In this paper we describe both a specialized camera and an imaging technique which make high-speed video microscopy a suitable tool for performing such measurements, without the need for separate measurement systems and synchronization. The use of a high-speed tracking camera based on a field programmable gate array to simultaneously track multiple particles is reported. By using this camera to simultaneously track one microsphere fixed to the wall of a driven sample chamber and another held in an optical trap, we demonstrate simultaneous optical measurement of the driving motion and the trapped probe particle response using a single instrument. Our technique is verified experimentally by active viscosity measurements on water-ethylene glycol mixtures using a phase-shift technique.     

Multi‐Functional Particle Detection with Embedded Optical Fibers in a Poly(dimethylsiloxane) Chip

Abstract

This paper describes a polydimethylsiloxane microfluidic chip with embedded optical fibers for particle detection. It consists of a microchannel for sample delivery, two pairs of fibers for multi‐functional particle detection, and electrodes for high voltage supply to generate electrokinetic particle motion. A small size semiconductor laser and a Si‐PIN detector are used for optical detection. The detection system allows easy switch between two‐fiber detection mode and one‐fiber detection mode, and is capable of counting particles, measuring particle velocity, and identifying particle sizes in a single polydimethylsiloxane chip. The technique described here is potentially applicable to a range of particulate diagnostic systems.     

The μPIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (μPIV) and optical tweezers (OT). This instrument, the μPIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (～70 pN μm(-1) for a 20 μm polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R(2) = 0.988, RMS error = 13.04 μm s(-1)). Interaction between both techniques is shown to be negligible for 15 μm to 35 μm diameter trapped particles subjected to fluid velocities from 50 μm s(-1) to 500 μm s(-1) even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle-particle hydrodynamics.     

Direct evidence of radial and tangential morphology of high-modulus aromatic polyamide fibres

Previous work, at foreign laboratories, essentially based on electron microscopy of longitudinal sections, has suggested a radial morphology for the aromatic poly-amide high modulus fibres; the present paper gives direct evidence of such a morphology, thanks to a special preparation technique which allows a great improvement in the quality of the cross-sections of these fibres. This is demonstrated for both a commercial ‘Du Pont de Nemours’ yarn sample ‘Kevlar 29’, and an experimental high modulus aramid RPT (Rhǒne Poulenc Textile) yarn. In the first case, Ag₂S insertion technique was used and permitted one to see, on the cross-sections, an alternation of dark and clear radial bands, again with a tendency towards tangential splitting. In the second case the fibres were included into an amorphous polymer, a sample preparation technique which greatly enhances the quality of the cross-sections; optical microscopy showed the radial morphology fairly well; dark-field transmission electron microscopy—using the equatorial doublet of the electron diffraction pattern—allowed satisfactory resolution: both the radial, and occasionally the tangential, splitting, and the size of the cross-sectioned crystallites were easily revealed: these crystallites appear as isodiametric bright particles c. 15 nm in lateral size.     

Vibration sensitivity of the scanning near-field optical microscope with a tapered optical fiber probe

In this paper the Rayleigh-Ritz method was used to study the scanning near-field optical microscope (SNOM) with a tapered optical fiber probe's flexural and axial sensitivity to vibration. Not only the contact stiffness but also the geometric parameters of the probe can influence the flexural and axial sensitivity to vibration. According to the analysis, the lateral and axial contact stiffness had a significant effect on the sensitivity of vibration of the SNOM's probe, each mode had a different level of sensitivity and in the first mode the tapered optical fiber probe was the most acceptive to higher levels of flexural and axial vibration. Generally, when the contact stiffness was lower, the tapered probe was more sensitive to higher levels of both axial and flexural vibration than the uniform probe. However, the situation was reversed when the contact stiffness was larger. Furthermore, the effect that the probe's length and its tapered angle had on the SNOM's probe axial and flexural vibration were significant and these two conditions should be incorporated into the design of new SNOM probes.     

Measurement of axial neutral density profiles in a microwave discharge ion thruster by laser absorption spectroscopy with optical fiber probes

In order to reveal the physical processes taking place within the "μ10" microwave discharge ion thruster, internal plasma diagnosis is indispensable. However, the ability of metallic probes to access microwave plasmas biased at a high voltage is limited from the standpoints of the disturbance created in the electric field and electrical isolation. In this study, the axial density profiles of excited neutral xenon were successfully measured under ion beam acceleration by using a novel laser absorption spectroscopy system. The target of the measurement was metastable Xe I 5p(5)((2)P(0) (3/2))6s[3/2](0) (2) which absorbed a wavelength of 823.16 nm. Signals from laser absorption spectroscopy that swept a single-mode optical fiber probe along the line of sight were differentiated and converted into axial number densities of the metastable neutral particles in the plasma source. These measurements revealed a 10(18) m(-3) order of metastable neutral particles situated in the waveguide, which caused two different modes during the operation of the μ10 thruster. This paper reports a novel spectroscopic measurement system with axial resolution for microwave plasma sources utilizing optical fiber probes.     

CFD-DEM simulation on the complex gas-solid flow in a closed chamber with particle groups

There is a complex gas-solid flow in the cylindrical closed chamber during the interior ballistic process in a modular-charge gun launch. The motion and the distribution of particles in the flow have significant effects on the combustion stability in the interior ballistic process. Therefore, the solid particle-scale details of the gas-solid flow in the closed chamber with hollow-cylindrical particle groups were numerically simulated by using the computational fluid dynamics combined with the discrete element method (CFD-DEM). The results show that the particle final distribution is composed of a gentle-slope accumulation, a horizontal accumulation, and a steep-slope accumulation. Thereinto, the voidage of the steep-slope accumulation is decreased with the axial position far away from modules. With the increase of the initial spacing between two particle groups, the axial length of the steep-slope accumulation is increased exponentially, whereas the tangent value of the inclined angle is decreased exponentially.

     

Heat transfer and gas-solid behaviors in pneumatic transport reactor used of carbon capture system

A pneumatic transport reactor can be used for continuous carbon capture processes using a dry sorbent because it can handle large quantities of flue gas. To design efficient reactors, it is necessary to understand the internal characteristics of a reactor with a complicated gas-solid flow. Computational fluid dynamics using an Eulerian-Eulerian approach was adopted to simulate gas-solid two-phase flow to better understand the gas-solid behaviors and heat transfer characteristics in a pneumatic transport reactor. Numerical simulations were used to analyze the pressure difference, solid mass flux, and heat transfer coefficient. The results showed that the gas-solid behavior was unstable and that localized particle flow affects the heat transfer characteristics. The degree of particle mixing near the solid return inlet was lower than that at greater heights within the reactor; in the inlet region, the heat transfer coefficient is not uniform in accordance with the non-uniformity of solid particle behavior.     

旋风分离器内颗粒浓度分布特性的数值分析

采用改进的雷诺应力模型和分散的颗粒随机轨道模型,并利用单元内颗粒源法对旋风分离器内的颗粒浓度分布进行数值模拟,与试验结果对比表明两者吻合较好,有较高的预报精度。数值模拟结果表明,旋风分离器外壁的颗粒浓度呈螺旋带状分布,且螺旋灰带以一定的频率上下窜动,在环形空间和灰斗的顶板下方存在顶灰环,且顶灰环不均匀,具有显著的非对称性;在分离空间下部排尘口附近有明显的颗粒返混,范围在排尘口上方约1.5 D (筒体直径)以内,排尘口上方的强旋流动对颗粒有显著的二次分离作用。讨论粒径(3～23 μm)、工作温度(20～ 1 000 ℃)、入口含尘浓度(0.03～10 kg/m3)和进气速度(12～30 m/s)对颗粒浓度分布特性的影响规律。     

水力旋流器细粒分离效率优化与数值模拟

水力旋流器内流体质点的切向速度、径向速度和轴向速度的分布规律及其流体动力学机理对于细粒分级粒径和效率具有决定性作用,并且受旋流器的结构参数、操作参数和物性参数等因素的影响。选用耐磨耐腐蚀的聚氨酯材料制造的不同规格固液分离水力旋流器,综合考虑分割粒径、处理流量、沉砂产率3项分离效率指标,通过多指标正交试验优化得到分离钙土的工作参数如下:旋流器直径50 mm,底流口直径10 mm,溢流口直径8 mm,并且在0.30 MPa给料压力下可达到分割粒径1.78μm,处理流量为2.39 m3/h的分离效率。同时针对优化后的旋流器工作参数,利用适用于旋流器湍流场的雷诺应力模型,运用FLUENT软件计算不同直径颗粒的亲水性固体在水动力中的速度场,得到分离介质的滞留时间为1.8×10 2s,反向轴速度最大可达3.08 m/s,最大切向速度半径为0.046 m,使得分离效率达到78.6%;从压力场的数值模拟结果看出,径向压强梯度从762.5 kPa/m增大到6 822.2 kPa/m,实现分割粒径达到1.78μm的效果。根据旋流器中压力场、速度场分布特征以及分离介质轨迹等数值模拟结果,提出延长分离介质的滞留时间、提高进料压力、降...     

Fiber-coupled laser-driven flyer plates system

A system for the launch of hypervelocity flyer plates has been developed and characterized. Laser-driven flyers were launched from the substrate backed aluminum-alumina-aluminum sandwiched films. A laser-induced plasma is used to drive flyers with typical thickness of 5.5 μm and diameters of less than 1 mm, to achieve velocities of a few km/s. These flyer plates have many applications, from micrometeorite simulation to laser ignition. The flyer plates considered here have up to three layers: an ablation layer, to form plasma; an insulating layer; and a final, thicker layer that forms the final flyer plates. This technique was developed aiming at improving the energy efficiency of the system. The kinetic energy of flyers launched with the additional layer was found to be enhanced by a factor of near 2 (up to 30%). The optical fiber delivery system governs the output spatial profile of the laser spot and power capacity. Moreover, a technique for coupling high-power laser pulses into an optical fiber has been developed. This fiber optic system has been successfully used to launch flyer plates, and the surface finishing quality of the fiber was found to be an important factor. Importantly, measurements of the flyer performance including the mean velocities and planarity were made by an optical time-of-arrival technique using an optical fiber array probe, demonstrating the good planarity of the flyer and the achievable average velocity of 1.7 km/s with approaching 1 mm diameter. Finally, the relationship between flyer velocities and incident laser pulses energy was also investigated.     

Fibreoptical spatial filter velocimeter for measurement of local liquid velocity

The spatial filtering velocimetry is the basis of the new optical hydrometric measuring probe. Like a laser Doppler velocimeter, the hydrometric probe determines the velocity of tracer particles in the liquid flow. Essential parts of the hydrometric probe are a differential fibreoptical spatial filter and an illumination source. The tracer particles are imaged onto the spatial filter by a shadow projection with a parallel light beam. The hydrometric probe can be used for velocity and flow measurements in pipes and river flows. The technique permits the design of robust and low cost optical hydrometric probe which can be used for different hydrometric applications.     

The Influence of Speed,Grease Type,and Temperature on Radial Contaminant Particle Migration in a Double Restriction Seal

Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile.

In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication.     

利用光压差分技术筛选细胞的影响参数

本文采用有限体积法建立了交叉型细胞分离模型,提出了一种基于光压差分的细胞筛选仿真方法,分析微流体中细胞筛选的影响因素。基于层流、流体流动粒子追踪、波动光学理论,利用有限元分析法建立了一种交叉型光学颗粒分离模型,研究了利用光压差分技术分离细胞的各种影响因素,其中包括微粒直径,激光功率、温度、光纤直径,分析了微粒在流体中因光辐射压力作用下的偏移距离。实验结果表明:在微流体中,激光功率、细胞直径、温度(20℃)和偏移距离大体上成正比关系,光纤直径和细胞直径在大小相当的情况下光辐射压力能够达到最大值,当激光通过光纤作用于直径分别为3,8和20μm的微粒时,光纤直径为7μm或8μm时光辐射压力最大,所以选用直径为8μm的单模光纤作为一个重要的实验光学器件。所得结论为深入研究细胞筛选影响因素的数值仿真精度提供了参考与借鉴。     

Laser dispersion and ignition of metal fuel particles

The development of a laser-shock technique for dispersing Al metal fuel particles at velocities approaching those expected in a detonating explosive is discussed. The technique is described in detail by quantifying how air drag affects the temporal variation of the velocity of the dispersed particle plume. The effect of particle size is incorporated by examining various poly-dispersed commercial Al powders at different dispersion velocities (390-630 m/s). The technique is finally tested within a preliminary study of particle ignition delay and burn time, where the effect of velocity is highlighted for different particle sizes. It was found that plume velocity exhibits a modified exponential temporal profile, where smaller particles are more susceptible to air drag than larger ones. Moreover, larger particles exhibit longer ignition delays and burn times than smaller ones. The velocity of a particle was found to significantly affect its ignition delay, burn time, and combustion temperature, especially for particles in the diffusion-controlled regime. Shorter ignition delays and burn times and lower temperatures were observed at higher particle velocities. The utility of this technique as a combustion screening test for future, novel fuels is discussed.     

基于流态化技术的振动流化床气固两相流动分析

在对基于流态化技术的振动流化床气固两相流动的欧拉（Euler）方法的双流体模型研究的基础上,利用专业流体力学分析软件Fluent对褐煤颗粒床层进行数值模拟．研究振动、风速、褐煤颗粒粒度等参数对振动流化床床层中褐煤颗粒均匀流化的影响．实验结果表明：振动及气流的交互作用,可有效抑制褐煤颗粒在床层中的返混现象,使得振动流化床褐煤颗粒干燥均匀;选择双流体模型,将Fluent用于振动流化床气固两相流动数值模拟,是一种行之有效的数值模拟方法．