热虹吸窄矩形流道内多元非理想物系流动沸腾传热

以乙醇－水、正丙醇－水、乙醇－正丙醇－水以及乙醇－苯－水作为工质,在热虹吸矩形流道内研究了多元物系流动沸腾传热。使用校正的渐进模型关联式,结合Thome核沸腾传质阻力效应校正,构造出多元物系流动沸腾传热计算方法。     

倾斜窄矩形通道内弹状流特性的实验研究

以空气和水为工质,应用高速摄影仪,对3.25 mm×43 mm的竖直和倾斜窄矩形通道的弹状流进行了可视化研究。按分液相雷诺数将流动分为层流区(Relo3000)和湍流区(Relo≥3000)。实验结果表明,在层流区,气弹上升速度随倾斜角度的增加而增大;在湍流区,倾斜角度对气弹上升速度的影响不明显。基于湍流区拟合得到的分布参数C0和班可夫系数CA分别为1.151和0.788,与实验数据具有较好的一致性。对于空泡份额Jones-Zuber模型和Ishii模型,在湍流区两者预测结果与实验基本一致,但在层流区,Jones-Zuber模型预测效果较好而Ishii模型偏差较大。     

Experimental Study of Fibrin Embolization Under Shear Flow

Arterial thrombi consist mainly of platelets and fibrin, the biopolymer produced in the final step of the coagulation cascade. Thrombus fragmentation may result in occlusion of smaller distal vessels (embolization), a serious and often fatal event. The objective of this study is to investigate the role of the fibrin polymer network on the resistance of a clot to fragmentation under shear flow. For that purpose, a fibrin clot model representative of native clots is submitted to a shear flow that reproduces the pathophysiological range of shear stress.

The adhesion force due to specific fibrin/fibrin interactions is determined from the measurement of the shear stress producing 50% detachment of model particles of blood platelets embedded in the clot. This force was found to be several orders higher than the nonspecific colloidal forces between surfaces, which can, thus, be neglected. Influence of the number of fibrin monolayers in the clot model on adhesion force is investigated.     

Experimental Study of Fibrin Embolization Under Shear Flow

Arterial thrombi consist mainly of platelets and fibrin, the biopolymer produced in the final step of the coagulation cascade. Thrombus fragmentation may result in occlusion of smaller distal vessels (embolization), a serious and often fatal event. The objective of this study is to investigate the role of the fibrin polymer network on the resistance of a clot to fragmentation under shear flow. For that purpose, a fibrin clot model representative of native clots is submitted to a shear flow that reproduces the pathophysiological range of shear stress.

The adhesion force due to specific fibrin/fibrin interactions is determined from the measurement of the shear stress producing 50% detachment of model particles of blood platelets embedded in the clot. This force was found to be several orders higher than the nonspecific colloidal forces between surfaces, which can, thus, be neglected. Influence of the number of fibrin monolayers in the clot model on adhesion force is investigated.     

Detachment of Droplets in a Fully Developed Turbulent Channel Flow

Liquid aerosols deform and detach from solid surfaces under an external force. It is a familiar phenomenon in many engineering applications. This article experimentally investigates the deformation and detachment of liquid droplets on three different solid surfaces in a fully developed turbulent channel flow. It is shown that the droplets either are compressed or elongate under the turbulent flow. The elongation of the droplet due to the turbulent flow is measured and presented. When the friction velocity of the flow exceeds a critical value, the droplets slide along the surface. The critical friction velocity is found empirically to be inversely proportional to the square root of the contact diameter. The sliding velocity after detachment is also reported. It has been observed by many researchers that, when the external force is gravity or a simple shear flow, the retention force of the droplet is proportional to the difference between the cosines of the receding and advancing contact angles. As the shape of a deformed droplet is much more complex under a turbulent flow, this article discusses the applicability of the same relation to the turbulent channel flow.

Copyright 2014 American Association for Aerosol Research     

研究剪切流动下共混物相行为规律的实验方法

从实验原理、仪器设备、分析方法等方面,介绍了在开展剪切流动对共混物相行为影响研究中应用的实验方法,并着重介绍了包括应用最广泛的二维小角激光散射流变法在内的实时测试的各种实验方法,为不断改进和完善此类研究的实验手段提供了参考。     

Investigations of Performance Characteristics Including Limitations Due to Flow Instabilities in Continuous SPLITT Fractionation

Abstract

An investigation of SPLITT fractionation is conducted to improve its overall performance. Particular attention is devoted to factors which degrade separation resolution in the thin SPLITT channels, including the development of instabilities due to unstable stratification of density. The presence of these instabilities is quantified using the Richardson number (Ri) and the flow-rate ratio [Vdot] (a)/[Vdot] (a′), where [Vdot](a) and [Vdot] (a′) are volumetric flow rates at the top outlet substream and the top inlet feed substream, respectively. The stability boundary separating the stable and unstable flow domains is identified in terms of these parameters. Based on these criteria, the region most suitable for operation of SPLITT fractionation corresponds to [Vdot] (a)/[Vdot] (a′) ≥ 8, and Ri in the range of 0.001 to 0.0055, depending upon the value of [Vdot] (a)/[Vdot] (a′) Experimental verification is provided by the successful separation of a sample of glass bead particles using a multistage fractionation system.     

水平一上倾圆管水滴运移数值模拟研究

运用VOF模型对爬坡圆管油水两相三维流场进行了数值模拟,对油水分层波浪流产生的水滴的运移规律进行了研究.模拟研究表明,油水界面波是水滴产生的直接原因.对界面波动的相关参数与产生水滴的频率和体积的关系进行了研究,同时对所产生的水滴的几何参数(几何形状、长度、截面积等)、产生时间、间隔时间和出口流速也进行了讨论.     

Penetration of Shear Flow Into an Array of Rods Aligned With the Flow

Shear flow over a square array of widely‐spaced rods aligned with the flow is investigated using singularity methods to solve Stokes equation. The flow field is determined for various arrays occupying a fraction of a Couette channel, for solid volume fractions from 0.001 to 0.1. Flow penetration into an array is quantified by the slip velocity at the array edge. This velocity is much greater than when the flow is across the array but still less than the value predicted by the use of Brinkman's equation.     

Role of Different Parameters in the Optimization of Hydrodynamic Cavitation

Low pressure setups (up to 150 psi) for creating hydrodynamic cavitation are investigated in this study. The decomposition of chloroform in water is used as a model reaction. The effects of upstream pressure, fluid velocity, Cavitation number, C_v, and β₀ on the conversion are compared with regard to the effectiveness (conversion per pass) with changing flow conditions and scale‐up terms within three different setups. The values of C_v and β₀ are seen to be significant parameters in optimizing the hydrodynamic cavitation. Moreover, the optimal values of these parameters shift to smaller values with increasing pipe diameter. The influence of a new orifice plate specific parameter, δ, on the collapse conditions, is also described.     

液液分层流动系统速度分布及界面剪切力研究

在两平板间粘度相差较大的不互溶液液分层流动系统中轻重两相在相界面处出现近似滑脱现象 ,且剪切力在界面处不连续 ,轻相远大于重相。在速度分布模型推导过程中引入了界面剪切力参数 ,计算结果与实验数据吻合较好。     

The experimental observation and modelling of microdroplet formation within a plastic microcapillary array

This paper reports an experimental study of the formation of a two-phase liquid mixture in a circular capillary tube of 0.74 mm diameter. Organic liquid, the continuous phase, flowed through the capillary. Aqueous liquid, the dispersed phase, was injected through a hypodermic entering the side of the capillary and a stream of aqueous droplets was formed in the flowing organic liquid. The observed droplet diameters depended strongly on the ratio of the flow-rates between the dispersed and continuous phases: droplet diameters ranged between 480 and 64 μm. A simple model gave good predictions, matching the data and showing how the droplet diameter is dependant on the flow rates of the two phases. The flow geometry was similar to the T-junction configuration used for emulsion formation in microfluidic devices and was fabricated from an extruded plastic capillary array termed a microcapillary film (MCF).     

Study of Turbulent Flow in a Long Permeable Channel

Stationary liquid flow in a long (to L/d = 1440) permeable channel was studied for input Reynolds numbers from 28700 to 83000. The distributions of water pressure along the channel were obtained. Experimental data were compared with the numerical solution of equations derived from the energy equation.     

Control of Shear Dispersion by the Permeable Porous Wall of a Capillary Tube

The transfer of a neutral nonreacting mass species was studied in a capillary tube with a permeable porous wall, under the effect of combined pressure-driven and electro-osmotic flows or simply combined flows (CF). An exact expression for the shear dispersion coefficient in a tube under the influence of CF is derived, which remains constant when λ_D, inversely propotional to the permeability of the porous medium, is smaller than 1 or larger than 100 for a constant Péclet number. In addition, the equivalent one-dimensional governing equations for the concentrations of species in the tube and the permeable porous medium under the influence of CF are obtained. The proposed model is compared and verified with several existing models in the literature.     

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimented data are presented for the void fraction aud the shear stresses of stratified gas-liquid flow in a pipe, A new technique was used to measure the interface shear strew. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress prone at the gas-liquld interface. A new formula ,relatiog to the interfacial friction factor with the void fraction and superficiol gas Rcynold number, was dewloped to predict the interface shear stress. The predicted values are in good agreement with experimental data.     

催化裂化沉降器内液滴运动规律的数值模拟研究

催化裂化沉降器结焦将导致非计划停工,严重影响催化裂化装置的长周期运行.首先求取了单位时间沉降器内冷凝的油浆液滴的质量,然后利用颗粒轨道模型对液滴的运动轨迹进行模拟计算,得到液滴的停留时间、运动轨迹和分布区域.模拟计算结果表明,液滴在沉降器内的运动具有很强的随机性,不同大小的油浆液滴的停留时间不同,但大部分的液滴粘附在沉降器内壁和旋风分离器外壁上,进而缩合结焦.加强沉降器的保温可减少油气重组分的冷凝,采用"高温汽提"和"化学汽提"可减少进入沉降器的油气重组分的量,从而减少沉降器结焦.     

Application of the Electrodiffusion Method to Measure Wall Shear Stress: Integrating Theory and Practice

The electrodiffusion method has been used in fluid dynamic research for the past 50 years. It allows the measurement of wall shear stress, a crucial parameter, e.g., for the cleaning of membrane modules used in water filtration. Various authors have published articles dealing with the theory behind this technique. But no paper collects all the knowledge assembled over five decades of application. Here, comprehensive summary of the theory of steady flow, unsteady flow, and transient voltage step experiments is given. Factors influencing the accuracy of the measurements are discussed. Furthermore, a new approach to calibrate the system from voltage step experiments is introduced, and practical issues related to its application in flow measurements are discussed for an exemplary signal response to a near‐wall flow.     

非球形颗粒在矩形料斗中的流动特性(英文)

Flow behaviors of four kinds of granular particles (i.e. sphere, ellipsoid, hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern, discharge fraction, mean particle residence time and tracer concentration distribution were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere, ellipsoid and binary mixture are all parabolic shape, and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone becomes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron, sphere, binary mixture to ellipsoid. The discharge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concentration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentration of sphere in the middle is lower than that near the wall, and the contrary tendency is found for ellipsoid particles.     

高聚物熔体挤出不稳定流动的研究进展

对近年来国内外关于熔体挤出不稳定流动现象的研究进展进行了介绍。阐述了关于形成鲨鱼皮和压力振荡及其他挤出不稳定流动的相关机理，并总结了抑制挤出不稳定现象所采取的措施。