环形狭缝通道内气液两相环状流流动特性

建立了环形狭缝通道内气液两相环状流的理论模型 ,该模型计及环状流气芯流动的可压缩性、气液两相间的相滑移、气相对液滴的夹带作用等因素 .考察了两相流质量流量和干度对压降、液滴速度相对变化和狭缝喉部气芯通流面积的影响 .用建立的理论模型对空气 -水两相环状流通过环形狭缝的两相压降进行预测 ,预测值和试验值吻合良好     

大流量下倾斜管气液两相流实验研究

在较高的气液范围内,以水和空气为实验介质,在多相流实验平台上进行了倾斜向上的高产量气液两相流模拟实验研究。实验采用内径为40 mm、长8 m的透明有机玻璃管,并利用高速摄像仪记录实验过程中的流型。对实验流型进行分析,发现了倾斜管中低气流速下的一种新的流型-振荡冲击流,并研究了表观气、液流速和倾斜角对气液两相流动中压降的影响,建立气/液膜流动模型来分析表观气、液流速对压降梯度的影响作用,实验研究结果表明:在高气液量范围内,倾斜管中观察到的气液两相流型主要为振荡冲击流、过渡流和环状流,并且倾角对流型转变边界的影响不显著;振荡冲击流压降随气流速的增加而降低,环状流压降随气流速的增加而增加,过渡流压降梯度最小;倾斜管压降梯度随着倾斜角度的增加而增大。     

水平管路水环输送稠油减阻模拟实验

随着石油开采的增加，黏度较大的稠油输送受到越来越多的关注。基于自主设计的两相流水环输送稠油实验系统，模拟并开展了水环输送稠油实验。拍摄了水环发生器在不同间隙尺寸下的流动流型，分析了不同实验条件下的水环输送稠油减阻效果。结果表明：水环输送可以大大降低管道输送过程中压降；结合实验和模拟，水环发生器间隙尺寸在0.9～1.4 mm时，水环的减阻效果最好；流速增加会增大单位管道上的压降，降低水环输送的减阻效果。     

Thermal performance and entropy generation for nanofluid jet injection on a ribbed microchannel with oscillating heat flux: Investigation of the first and second laws of thermodynamics

In current numerical study, forced flow and heat transfer of water/NDG (Nitrogen-doped graphene) nanofluid in nanoparticles mass fractions (φ) of 0, 2% and 4% at Reynolds numbers (Re) of 10, 50, 100 and 150 are simulated in steady states. Studied geometry is a two-dimensional microchannel under the influence of nanofluid jet injection. Temperature of inlet fluid equals with T_c=293 K and hot source of microchannel is under the influence of oscillating heat flux. Also, in this research, the effect of the variations of attack angle of triangular rib (15°, 30°, 45° and 60°) on laminar nanofluid flow behavior inside the studied rectangular geometry with the ratio of L/H=28 and nanofluid jet injection is investigated. Obtained results indicate that the increase of Reynolds number, nanoparticles mass fraction and attack angle of rib leads to the increase of pressure drop. By increasing fluid viscosity, momentum depreciation of fluid in collusion with microchannel surfaces enhances. Also, the increase of attack angle of rib at higher Reynolds numbers has a great effect on this coefficient. At low Reynolds numbers, due to slow motion of fluid, variations of attack angle of rib, especially in angles of 30°, 45° and 60° are almost similar. By increasing fluid velocity, the effect of the variations of attack angle on pressure drop becomes significant and pressure drop figures act differently. In general, by using heat transfer enhancement methods in studied geometry, heat transfer increases almost 25%.     

Effects of Extrusion Rate,Temperature, and Die Diameter on Melt Flow Properties During Capillary Flow of Low-Density-Polyethylene

The melt flow properties of a low-density polyethylene were measured at test temperatures varying from 140 to 170°C and in a wide range of extrusion rates by means of a capillary rheometer, to identify the influence of extrusion conditions (such as temperature, shear rate, and die diameter) on the melt flow behavior in the present paper. The results showed that the entry pressure drop increased nonlinearly with an increase of the piston speeds, and it decreased with an addition of the die diameter. The melt shear flow obeyed roughly the power law and the melt shear viscosity decreased approximately linearly with an increase of the true shear rates in a bi-logarithmic coordinate system. The dependence of the melt shear viscosity on temperature accorded approximately the Arrhenius expression. Under these experimental conditions, the entrance pressure drop increases as an exponential function with an addition of the channel contraction ratio.     

油田含聚污水过滤工艺因素及臭氧处理效果评价

油田含聚污水随着聚合物驱的应用而黏度增加,水相含油能力强,分离难度大,对处理方式的要求越来越严格。过滤法作为常用方法,其污水处理性能受工艺因素的影响,处理效果不稳定;同时,臭氧作为快速、高效的污水处理方式日益受到关注。本文研究了不同滤料厚度比例、进水流速、滤床压降及污水pH对污水浊度等过滤参数的影响,结果表明核桃壳、石英砂厚度比为9∶13时过滤效果最优,提高进水流速、增加滤床压降和降低污水碱性有利于过滤的进行。探究了臭氧对含油含聚污水的处理效果,结果表明臭氧可通过降解聚合物以显著降低含聚污水黏度,同时污水的浊度和含油量也会显著下降。测定了臭氧降黏的有效消耗量,结果表明5mg臭氧可把500mL的含聚污水黏度从2.6mPa·s降低到1mPa·s以下。最后提出了采用臭氧对过滤污水预处理及处理过滤装置中的板结滤料、提高过滤效率的建议。     

Heat transfer and pressure drop performance of alumina–water nanofluid in a flat vertical tube of a radiator

This work presents experimental investigation on the effects of nanofluid inlet temperature (40–90°C), Reynolds number (12,000–30,000), particle concentration (0–1 vol.%), and air velocity (0.25–0.55?m/s) on thermal and flow characteristics of water-based alumina nanofluids in a flat vertical tube of a radiator. The specific heat capacity, viscosity, density, and thermal conductivity were measured experimentally. The heat transfer coefficient enhanced (up to 31%) with an increase in fluid inlet temperature, particle volume concentration, Reynolds number as well as air inlet velocity. The pressure drop increased with an increase in the particle volume concentration and Reynolds number, while it decreased slightly with an increase in the fluid inlet temperature. The friction factor and pumping power increased with particle concentration. The friction factor decreased, while the pumping power increased with sn increase in fluid flow rate.     

微通道内低沸点工质流动沸腾压降特性

在压力为0.5～1.7 MPa,质量流量为381～2291 kg·m^-2·s^-1,干度为0～1.0的工况范围内试验研究微尺度通道内低沸点混合工质R32/R134a的流动沸腾压降性能,同时对两相流流型进行可视化观察。微尺度通道内径为1.92 mm,0.86 mm和0.5 mm相似文献   

Geometrical dependence of viscosity of polymethylmethacrylate melt in capillary flow

The shear viscosity of polymethylmethacrylate (PMMA) melt is particularly investigated by using a twin‐bore capillary rheometer at four temperatures of 210, 225, 240, and 255°C with different capillary dies. Experimental results show that the geometrical dependence of shear viscosity is significantly dependent on melt pressure as well as melt temperature. The measured shear viscosity increases with the decrease of die diameter at lower temperatures (210 and 225°C) but decreases with the decrease of die diameter at higher temperatures (240 and 255°C). Based on the deviation of shear viscosity curves and Mooney method, negative slip velocity is obtained at low temperatures and positive slip velocity is obtained at high temperatures, respectively. Geometrical dependence and pressure sensitivity of shear viscosity as well as temperature effect are emphasized for this viscosity deviation. Moreover, shear viscosity curve at 210°C deviates from the power law model above a critical pressure and then becomes less thinning. Mechanisms of the negative slip velocity at low temperatures are explored through Doolittle viscosity model and Barus equation, in which the pressure drop is used to obtain the pressure coefficient by curve fitting. Dependence of pressure coefficient on melt temperature suggests that the pressure sensitivity of shear viscosity is significantly affected by temperature. Geometrical dependence of shear viscosity can be somewhat weakened by increasing melt temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3384–3394, 2013     

Very-viscous-oil/water/air flow through horizontal pipes: Pressure drop measurement and prediction

Core annular flow pattern, where a low viscosity liquid surrounds a very-viscous one, may be very interesting for heavy oil transportation. However, in oil production, oil and water rarely flow alone and gas is usually present. Despite several publications on liquid-liquid core annular flow, no much work has been done towards a proper characterization of the effect of gas on pressure drop. The aim of this paper is twofold: to provide a new data base on three-phase (very-viscous-oil/water/air) flow, and to propose a simple model for the determination of pressure drop.     

Transfert de matière et chute de pression lors d'un écoulement tourbillonnaire annulaire non-entretenu induit par une entrée tangentielle

This work is devoted to an experimental study of overall mass transfer and pressure in decaying swirlng annular flow induced by means of a tangential inlet. Overall mass transfer coefficients, obtained using an electrochemcal method, are found to be greater on the outer cylinder that on the inner core of the annulus, and remains largely greater than that obtained in fully developed axial flow on both cylinders. This enhancement in mass transfer rate is coupled with an increase in pressure drop, mainly due to the tangential inlet of the fluid. Nevertheless, an energetic correlation of overall mass transfer on both cylinders of the annular cell shows that decaying swirling flow induced by a single tangential inlet allows an important increase in mass transfer coefficients for a given energy consumption, compared with a fully developed annular axial flow.     

大输量多相混输管路气液两相流实验研究

为了研究大输量条件下多相混输管路的流动特性,以水和空气为实验介质,在长江大学多相流实验平台上进行了水平状态的高气液量两相流模拟实验研究。实验采用内径为60 mm、长9.4 m的透明有机玻璃管,并利用高速摄像仪记录实验过程中的流型。通过对实验流型进行整理,将水平管内的气液两相流流型划分为分层流、泡状流、段塞流和环状流,并与典型的Mandhane流型图进行对比分析。另外,对实验范围内的几种典型流型下的压降梯度变化规律进行了研究,泡状流区域压降梯度随气流速的增大而减小,段塞流区域压降梯度随气流速的增大而缓慢增大,环状流区域压降梯度随气流速的增加而继续增大。     

基于抛物线形气-液界面的超疏水微通道减阻特性

针对超疏水表面微通道中的流动减阻特性,基于抛物线形气-液界面假设,采用VOF模型模拟了微通道中的二维层流流动,分析了流动和结构参数对减阻效果的影响。结果表明,含矩形微坑的超疏水表面微通道具有显著减阻作用,fRe随Reynolds数增大而略有提高,量纲1压降比随入口速度增大而略有下降。当增大微坑面积比或减小微通道高度时,fRe减小,量纲1压降比增大;且微通道高度越小,微坑面积比对fRe的影响越显著。随抛物线形高度增加,压降比和滑移长度均线性减小,而fRe则线性增加。当微坑深度大于其宽度的40%时,压降比和滑移长度趋于定值。微坑形状对减阻效果的影响依次是燕尾形、矩形、梯形和三角形。     

水平横槽纹管内氨沸腾换热及压降特性实验研究

对水平横槽纹管内氨沸腾换热及其压降特性进行了实验研究，获得了不同热流密度、不同质量流速和不同局部蒸汽干度下沸腾换热和压降的实验数据。实验结果表明，在本实验的参数范围内，与光滑管相比，横槽纹管在压降增加不大的情况下可使管内沸腾换热系数提高３０％～１５０％，横槽纹管的节距减小对传热强化的作用明显，而对槽深的影响不大。还给出了横槽纹管内氨局部沸腾换热和压降的无因次准则关系式。     

不同倾角放置螺旋管汽波两相摩擦阻力特性

在宽广的参数范围内试验研究了螺旋管在不同倾角放置时的单相及汽液两相摩擦阻力特性,获得了螺旋管放置方向及各主要系统参数对汽液两相摩擦阻力特性的影响规律。在对试验结果及前人研究结果进行详细分析的基础上,获得了第一个能适用于不同倾角放置螺旋管的单相及汽液两相摩擦阻力计算式,从而为汽液两相摩擦阻力及螺旋管的进一步研究和应用提供了依据。     

蒸发式冷凝器在空气流动下优化设计数值模拟

利用FLUENT软件对3种常用的管形蒸发式冷凝器在空气流动状态下进行了优化设计的数值模拟,比较分析了在不同入口风速下的压降变化规律;对来流速度大小与来流角进行了优化设计,得到最适宜的来流速度在2.4—3.3 m/s,入口来流角θ范围为-15°—15°;在不同空气流量下管排的纵向间距与横向间距之比(S/L)模拟结果表明,在一定空气流量下,不同管形管排的S/L存在着一个最佳值,使得单位压降下换热盘管的平均表面传热系数最大,而且随着流量的增加,最佳的比值呈减小趋势。为蒸发式冷凝器的优化设计提供了重要依据。     

Correlation between entry pressure losses and elongation viscosity of polyethylene melts

The correlation between the entry pressure drop and elongation viscosity during entry converging flow of polymer melts was discussed in this article. The entry pressure drop during extrusion of a low density polyethylene (LDPE) melt and a linear low density polyethylene (LLDPE) melt was measured by means of a capillary rheometer under test conditions with temperature of 170 °C and shear rate varying from 10 to 300 s⁻¹. The results showed that the entry pressure drop increased nonlinearly with an increase of the shear stain rate, and the variation of entry pressure drop of the two melts was close to each other. The melt elongation viscosity of the two resins was estimated using Cogswell equation from the measured entry pressure drop data, and the predictions were compared with the melt extension viscosity measured by using a melt spinning technique published in literature. It was found that the melt extension viscosity from entry converging flow was slightly lower than that from melt spinning technique under the same temperature and extension strain rate.     

流体物性对壳侧不互溶双组分两相流动特性的影响

选用空气-水和空气-柴油2种不互溶双组分两相混合物物系,实验研究了液相物性对管壳式换热器壳侧两相流流型及其转变和两相流动特性的影响.研究表明,液相物性对间歇流向环状流的转变有显著影响,对于向泡状流转变的影响则不如在管内流动明显.研究还表明,液相物性特别是粘度和表面张力对截面含气率和两相摩擦压降有显著影响.     

流体物性对壳侧不互溶双组分两相流动特性的影响

选用空气-水和空气-柴油2种不互溶双组分两相混合物物系,实验研究了液相物性对管壳式换热器壳侧两相流流型及其转变和两相流动特性的影响.研究表明,液相物性对间歇流向环状流的转变有显著影响,对于向泡状流转变的影响则不如在管内流动明显.研究还表明,液相物性特别是粘度和表面张力对截面含气率和两相摩擦压降有显著影响.     

Effervescent atomization under sub-sonic and choked conditions—a theoretical approach

Spray formation of a bi-component mixture under sub- and choked-flow conditions has been studied. Special attention has been drawn to the processes inside the atomizer, i.e., the expansion chamber and two orifices. The relevant processes, which include the pressure drop at the inlet orifice, nuclei formation, bubble growth inside the expansion chamber, pressure drop at the discharge orifice, the velocity slip between the bubbles and the liquid bulk, and the flow regime (sub- and choked-flow) at the discharge orifice, have been analyzed by using a one-dimensional model approach.Three different operating regions have been identified. In the 1st, when the inlet to discharge orifices' diameter ratio is small, subsonic flow is anticipated, and no noticeable slip between the bubbles and the bulk liquid is expected. As the orifices' diameter ratio increases, the slip becomes more and more significant (2nd region). When the pressure at the expansion chamber exceeds the critical pressure, the flow chokes, and the slip maximizes. Further increase results in maximum slip (3rd region).The two main roles of the expansion chamber were described: (a) to provide the required time for the bubbles to grow till one bubble touches the other, and (b) to provide the discharge orifice with a well-mixed mixture to allow dominant flashing enhanced by shear stress disintegration. Optimized operation conditions for best atomization, optimized expansion chamber volume, and optimized orifices' diameter ratio are proposed in terms of the thermodynamic properties of the mixture.