液滴冲击流动液膜的格子Boltzmann模拟

采用单相格子Boltzmann方法模拟了二维液滴冲击流动液膜的含自由面的流动过程。由定义的质量与密度的比例系数来追踪气液自由面的变化。表面张力通过计算界面格点处作用在流体上的汽液相间作用力加入到模型中。数值模拟了速度比(液膜流动速度与液滴撞击速度的比值)和液膜相对厚度(液膜实际厚度与液滴直径的比值)不同时,液滴冲击流动液膜的过程。与液滴冲击静止液膜时的计算结果和理论分析结果进行对比,分析了液滴冲击流动液膜后产生的流动现象及其内在机理,产生的水花的铺展半径和溅起高度随时间的变化规律,并讨论了飞溅产生条件。     

稠油碱驱中液滴流提高采收率机理

利用微观可视化实验和岩心驱替实验,研究了碱驱提高稠油采收率的驱油机理。微观实验结果表明,在稠油碱驱过程中,碱液能够渗入原油中,形成外面包含一层油膜的“水柱”和“小水滴”,出现液滴流现象。依靠液滴流的高黏度和产生的贾敏效应,可以有效抑制驱替液的指进,从而增大了波及系数,且随着碱浓度的上升,液滴流现象越明显,波及系数就越大。岩心驱替实验结果表明,随着碱浓度增加,采收率增值和压力降均上升,这与微观实验得出波及系数随碱浓度的上升而增大规律相吻合。因此,碱驱液滴流增大波及系数是提高稠油采收率的主要作用机理。     

油/聚合物溶液体系动态界面扩张模量的测量

以十二烷为油相,以HPAMMo 4000(M=2.0×107,HD=24%)在0.5%NaCl盐水中的溶液为水相,用法国ITConcept公司的Tracker型全自动液滴界面张力仪在30℃测定了油水界面的动态扩张模量E。结果表明,初始滴体积V对E～t曲线无明显影响;固定V=20μL,E达到动态平衡值所需时间(振荡周期λ=10s)随水相聚合物浓度CP增大而缩短,E平衡值随CP增大而增大,随λ增大而略有减小,因此V,t,λ等测量参数均需采用实验方法确定。根据纯水表面张力测量值,此方法的实验误差为0.7%。介绍了测量原理。用此法测定胜利孤岛原油(70℃粘度52.9mPa·s)与0.75、1.0、1.5g/LMo 4000溶液间的E值,分别为16.4、17.8、21.4mN/m。图3表2参7。     

Effects of liquid viscosity on inception of disturbance waves and droplets in gas–liquid annular two‐phase flow

The structure of gas–liquid two‐phase flow is investigated in order to establish a reliable criterion for the development of disturbance waves and droplets considering the effects of liquid viscosity. The structure of the gas–liquid interface and the flow rate of droplets entrained in gas are measured simultaneously at five kinematic viscosities (1.0, 3.2, 9.9, 30, 70 mm²/s). The time‐series traces of liquid film thickness measured by five holdup probes reveal that the inception of disturbance waves occurs at a liquid Reynolds number of 200 or a non‐dimensional liquid film thickness of 6.5. It is also shown that droplets are generated before the inception of disturbance waves with increasing liquid kinematic viscosity at a liquid velocity of 0.02 to 0.03 m/s. As previously published criteria for the inception of droplets are found to be unsatisfactory, a new critical condition for droplet generation balancing the interfacial shear stress $τi$ with the wave height h and surface tension σ is proposed: $τih/σ=0.025$. This relation describes the action of shear force and surface tension on wave crests, and is notably independent of liquid viscosity. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 529–541, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20176     

用格子Boltzmann方法模拟液滴合并过程

用格子Boltzmann方法中的伪势模型对两个液滴的合并过程进行了数值模拟。详细研究了两液滴能否合并临界尺寸和液滴合并过程中液桥的形成与演化的关系，并研究了表面张力对合并速度的影响。研究结果发现当两个液滴之间距离小于2倍界面厚度时，两个液滴在不受外力的作用下能够自动合并；液桥的宽度与演化时间有一定的指数关系；表面张力越大，合并速度越快，这个结果与前人的理论预测和实验结果一致。     

空心静叶栅沉积水滴的去除方法和(火用)分析

基于利用控制容积法求解Reynolds时均的N-S方程、k-ε模型和Lagrange方法等模型,分析了空心静叶栅内部的二维湿蒸汽汽液两相流场和不同粒径的水滴沉积规律、沉积位置,同时在沉积位置开2种宽度、3个方向和不同数量的缝隙分别分析了抽吸和吹除两种方法的去湿效果,并且根据计算的结果对各工况进行了效率分析。通过流场分析结果表明:开缝隙方向尽量要和当地的流速方向一致且缝隙宽度不能太大,这样缝隙内就较好的流场,且吹除方法可以有效地减少水滴的沉积,但通过效率分析抽吸方法比吹除方法效率高,从减少水滴沉积和能量损失两方面考虑,抽吸方法更好一些。图3表3参6     

粒径对庚烷液雾爆炸场影响的数值模拟

为了研究液雾索特直径(D_(32))对爆炸参数的影响,以庚烷为对象,控制液雾总浓度不变(80 g·m~(-3)),改变液雾粒径,数值模拟了爆炸容器内庚烷(C_7H_(16))液雾粒径对爆炸参数的影响。结果表明:庚烷液雾场索特直径D_(32)为0~18.1μm时,最大爆炸压力p_(max)随D_(32)增加逐渐减小,最大值为1.01 MPa,最小值为0.9015 MPa。最大爆炸压力上升速率随D_(32)增大整体呈下降趋势,在0处达到最大值0.37571 MPa·ms~(-1),在18.1μm处达到最小值0.18439 MPa·ms~(-1),但在6.81~12μm发生反向突变,在10.1μm处达到极大值0.34217 MPa·ms~(-1),随后恢复下降趋势。液雾的径向火焰传播速度在径向距离15 cm附近突然增加,在16 cm之后剧烈下降。最大火焰速度随液雾场D_(32)不同而变化,D_(32)=10.1,12.9,18.1,6.81,0μm条件下液雾场的最大火焰速度依次降低,最大值为5.714 m·s~(-1),其后依次为1.737,1.36,1.34,1.27 m·s~(-1)。     

Inner flow behavior in an oscillating liquid droplet

A numerical simulation was conducted to investigate the inner flow in an oscillating liquid droplet. A 2D model was proposed to describe the interfacial and inner flow of oscillating droplets with shear stress induced by outside air flow. The 2D inner flow field was reconstructed to explore the liquid flow velocity and pressure profile and better understand the oscillating mechanisms. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20274     

On‐line acoustic attenuation spectroscopy of emulsions stabilized by vinyl alcohol–vinyl acetate copolymers: a model system for the suspension polymerization of vinyl chloride

BACKGROUND: Poly[(vinyl alcohol)‐co‐(vinyl acetate)] (PVA) copolymers obtained by partial hydrolysis of poly(vinyl acetate) are currently used as industrial stabilizers in the suspension polymerization of vinyl chloride monomer (VCM). Their molecular characteristics, mainly the average degree of hydrolysis (DH ) and average degree of polymerization (DPw ), have a major influence on the monomer droplet size and the properties of the final poly(vinyl chloride) resin. RESULTS: The average droplet size and size distribution of chlorobutane/water emulsions, as a model system for VCM/water emulsions, were studied using acoustic attenuation spectroscopy on‐line with an agitated laboratory reactor. The emulsions were stabilized by PVA with DH values between 73 and 88 mol% and DPw values between 450 and 2500. The effects of agitation speed, stirring time and concentration of the PVA copolymers were investigated. An attempt was made to correlate the interfacial tension and the droplet size. CONCLUSION: On‐line acoustic spectroscopy appears to be a suitable technique for the real‐time control of the droplet size of monomer suspensions. The advantages and limitations of the technique are outlined. The validity and the application limits of the commonly cited correlation between the droplet size and the Weber number are established for polymeric surfactant‐stabilized emulsions. Copyright © 2009 Society of Chemical Industry