Inertia Effects on the Flow of Bingham Plastics Through Sudden Contractions in a Pipe

The present numerical study concentrates on the effects of moderate and high Reynolds numbers on the laminar flow of a non-Newtonian rigid viscoplastic (Bingham) fluid through a sudden contraction in a pipe. The flow is assumed to be steady, incompressible, and isothermal. Results are presented for a wide range of the governing Reynolds and yield numbers and the significant effects of these two parameters both on the integral and local kinematic properties of the flow field are established. Low yield numbers result in the disappearance of the recirculating flow region at the corner replacing it with a region of very low rates of deformation. The evolution of the centerline velocity in the vicinity of the contraction plane is shown to be independent of the yield number and dependent on the Reynolds number, while the concavities in the streamwise velocity profiles appearing at high Reynolds numbers are independent of the yield number. The pressure losses through the contraction increase with yield number with the effect being more pronounced at lower Reynolds numbers.     

The effect of the macroscopic local inertial term on the non-Newtonian fluid flow in channels filled with porous medium

The transient hydrodynamics behavior of the non-Newtonian fluid flow in horizontal parallel-plate channels filled with porous medium is investigated numerically. The role of the macroscopic local inertial term in the porous domain momentum equation is studied. It is found that the macroscopic local inertial term has insignificant effect on the channel hydrodynamics behavior for all non-Newtonian fluids having power law index less than 0.5 and over the entire range of Darcy and Forchheimer numbers. However, the macroscopic local inertial term has significant effect when the power law index is greater than 1 over a wide range of Darcy and Forchheimer numbers especially for relatively high values of Darcy and low values of Forchheimer numbers. It is found that the effect of the macroscopic local inertial term is very sensitive to the Forchheimer number at high values of Darcy numbers and power law index. Also, there is an upper limit for n beyond which changing the power law index has insignificant effect on the local inertial term.     

Hot-pressurized fluid extraction of flavonoids and phenolic acids from Brazilian propolis and their cytotoxic assay in vitro

This work has examined the hot-pressurized fluid extraction of seven flavonoids, caffeic acid phenethyl ester and four phenolic acids from Brazilian propolis lumps generating, during the process, fat- and water-soluble extracts. The solid content of water-soluble extract obtained by hot-pressurized water in the presence of 29% natural surfactant was 35.2 mg/mL and was 44% greater than that obtained without natural surfactant. Furthermore the amount of the seven flavonoids and caffeic acid phenethyl ester in the fat-soluble extract exceeded those in the water-soluble sample while, on the other hand, the amount of the four phenolic acids in the water-soluble extract was more than those in the fat-soluble extract. Our findings show that the total solid content and the amount of these 12 active compounds produced by the emulsified hot-pressurized water are 36% and 7% higher, respectively, than those produced by emulsified water at atmospheric pressure. The EC₅₀ value of the free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl of the emulsified hot-pressurized water extract was the lowest, and presented the strongest anti-oxidation ability among all the extracts. In vitro cytotoxicity indicated that the water-soluble extract strongly suppressed the growth of leukemia (HL-60, U937), lung cancer (A549, CH27) and liver cancer (Hep G2, Hep 3B) cells in a concentration-dependent behavior.     

Using CFD to predict the behavior of power law fluids near axial-flow impellers operating in the transitional flow regime

A computational fluid dynamics (CFD) model of flow in a mixing tank with a single axial-flow impeller was developed with the Fluent^TM software. The model consists of an unstructured hexagonal mesh (158,000 total cells), dense in the region from the surface of the impeller. The flow was modeled as laminar and a multiple reference frame approach was used to solve the discretized equations of motion in one-quarter of a baffled tank. A solution of 0.1% Carbopol in water, a shear-thinning fluid, was found to be clear enough to measure impeller discharge angles using laser Doppler velocimetry. This is the first time that impeller discharge angles have been reported in the literature for a shear-thinning fluid with a hydrofoil impeller. Rheological measurements indicated that the Carbopol solution can be characterized by the power law (K=9,n=0.2) under the range of shear conditions (0.1- expected near the impeller in the mixing tank. The CFD model accurately predicted the dependence of power number and discharge angle on Reynolds number (as predicted by Metzner and Otto), for an A200 (pitched blade turbine or PBT) and an A315 (Hydrofoil) impeller operating in the transitional flow regime (Reynolds numbers: 25-400) with glycerin and 0.1% Carbopol solutions. Subsequently, the results of a systematic CFD study with power law fluids indicated that the power number and discharge angle of an axial-flow impeller in the transitional flow regime depends not only on the Reynolds number (as determined by Metzner and Otto's method) but also on the flow behavior index n. Consequently, an alternative to Metzner and Otto's method was pursued. The results of converged CFD simulations indicate that the near-impeller “average shear rate” increases not only with increasing RPM (as proposed by Metzner and Otto), but also with decreasing flow behavior index (n) and discharge angle in the transitional flow regime. Considering this result, an improved method of estimating the power number and discharge angle for power law fluids in the transitional flow regime is proposed.     

Nonhomogeneous flow of micellar solutions: A kinetic—network theory approach

The rheological behavior of micellar solutions is analyzed under nonhomogeneous velocity and stress flow conditions. The framework is based on the extended irreversible thermodynamics and the transient network formulation coupled to the underlying kinetics embodying two relevant processes: formation of wormlike chains from a free micellar solution through a thermally activated process and their flow induced degradation. The second kinetic process consists in the formation of entanglements from the free wormlike chains and their flow‐induced breakage. These processes are modeled in a coupled kinetic scheme constituted by a set of reversible kinetic equations describing the evolution in average of the three microstates (free short rod‐like micelles, free wormlike chains, and entangled wormlike chains) that reflect the complexity of macromolecular interactions. The predictions of the shear stress and first normal stress difference as a function of shear‐rate under banded flow are in good agreement with experimental data. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2277–2292, 2018     

新型纳米活性流体协同改变油湿性砂岩表面润湿性的机理

以带正电的碳酸钙纳米颗粒和阳-非离子双子表面活性剂为原料，制备了一种纳米活性流体。通过Zeta电位、红外光谱（IR）、石英晶体微天平（QCM）、接触角测量和自发渗吸实验等方法研究了制得纳米活性流体中碳酸钙纳米颗粒和阳-非离子双子表面活性剂协同改变油湿性砂岩表面润湿性的机理。结果表明，纳米活性流体处理后的油湿性砂岩表面红外光谱中，原油的羰基吸收峰强度低于阳-非离子双子表面活性剂处理后的砂岩表面羰基吸收峰强度；当阳-非离子双子表活剂质量分数均较高时（>0.003%），纳米活性流体中的碳酸钙颗粒促进了双子表面活性剂和原油羧基离子对的形成和解吸附过程，使得纳米活性流体处理过的砂岩表面共振频率变化量（Δf）比阳-非离子双子表面活性剂处理过的砂岩表面Δf小；接触角测定结果进一步确认，纳米活性流体改变油湿性砂岩表面润湿性的效果比单一阳-非离子双子表面活性剂和碳酸钙纳米颗粒效果更好，纳米活性流体中的两种组分起到协同效应。     

太阳能驱动有机朗肯循环的工质比较

针对太阳能热水和其它低品位热能的动力利用,研究了工作在100℃供热温度和30℃冷凝温度之间的有机朗肯循环工质的优化选择,以满足较高的循环效率、较大的机械能输出、较小的排气量需求等要求。工质模型采用RKS状态方程,针对R22在-30～95℃温度区间内,计算结果与ASHRAE20-2005数据比较,除液相密度外,其它的热力学参数计算绝对误差小于5%,满足工程模拟要求。利用RKS模型,文中分析了19种有机工质的动力循环参数,发现工质R11的热力学性能系数最高。结合GWP和ODP环境指标,发现R142b、Rc318与R600适合于低温朗肯循环。     

Effects of different simulated fluids on anticorrosion biometallic materials

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硬脂酸铝液润滑下的GCr15/45副的电摩擦性能

通过辅助电极 ,考察了不同极性、不同幅值的电压对 0 4%硬脂酸铝液润滑下的GCr15 /4 5副的电摩擦性能。结果表明 :工作电极上施加负电压时 ,系统的摩擦系数显著升高。随着负电压幅值增高 ,摩擦系数的增加幅度也相应加大 ;而施加正电压对摩擦系数没有影响。随着外加电压幅值增加 ,GCr15钢球的磨痕直径增大 ;正电压作用下 ,磨痕直径比同幅值下负电压作用时的小。用电化学反应所生成的皂化膜的吸附特性解释了系统的电摩擦性能。     

磁流变双筒式液压减振器设计及磁路仿真研究

介绍了某装甲车辆用被动式双筒式液压减振器的基本结构,基于这种结构提出了两种磁流变双筒式液压减振器的结构设计方案.为了确定最优的设计方案,利用Ansofi工程电磁场有限元分析软件对两种不同结构的MRF双筒式液压减振器的磁路进行了有限元分析.使用车载电源,在相同的工作电流下仿真得到两种结构该型MRF双筒式液压减振器的磁感应强度矢量和磁场强度分布,为其在车辆悬挂系统半主动控制中的应用奠定了基础.