Non-newtonian liquid flow through globe and gate valves

Experimental data on the pressure drop across 1/2-in. globe and gate valves in the horizontal plane for non-Newtonian pseudoplastic fluids in laminar flow are presented. Generalized correlations in terms of the various physical and dynamic variables of the system have been developed for prediction of the frictional pressure drop for each valve. Statistical analysis of the correlations suggest that they are of acceptable accuracy.     

Vertical upward flow of gas-solid two-phase mixtures through monolith channels

This paper reports some recent experimental observations of both gas and gas-solid two-phase flows through small monolith channels. For gas flows, the laminar-to-turbulent transition in monolith channels was observed to occur at a Reynolds number of ∼620, much lower than the conventional transition criterion of 2200 for large pipes. Surface roughness of and non-uniform distribution of gas in monolith channels were proposed to be possible reasons. For gas-solid two-phase flows, both pressure drop and solids hold-up were measured. It was found that the pressure drop of gas-solid two-phase flows through monolith channels was significantly lower than that through packed particle beds with even lower surface area per unit bed volume. Reprocessing of the pressure drop data in terms of the dimensionless groups showed that the Euler number depended approximately linearly on the solids-to-gas mass flux ratio for a given superficial gas velocity, and suspended particle size imposed little effect under the conditions of this study. Measurements of the solids hold-up showed that the hold-up in monolith channels increased with a decrease in both the gas velocity and the suspended particle size. The pressure drop results were also compared with semi-theories developed for pneumatic conveying. An overprediction was observed, an indication of the need for more controlled experiments for fundamental understanding of the hydrodynamics in monolith channels.The work reported here on gas-solid two-phase flows through monolith channels represents the first attempt in this area as no previously studies have been found in the literature.     

Non-newtonian flow modeling in the mixing section of a single-screw extruder with flow analysis network method

The flow of non-Newtonian fluids obeying the power-law relation through the mixing sections of a single-screw extruder is analyzed with a modified flow analysis network (FAN) method. Three types of mixing elements, the Maddock, the dulmage, and the blister ring elements, are studied. The Maddock and the blister ring elements are dispersive type elements. They generate high pressure drop, and yield a negative pressure gradient which indicates poor pumping capability. The flow fields are rather regular in these elements. On the other hand, the dulmage element is a distributive type element. It generates a low pressure drop, and yields a positive pressure gradient at low extrusion rate which indicates better pumping capability than the dispersive type elements. Extensive flow splitting and reorientation is observed in this element. The power-law exponent has significant effect on pumping characteristics. However, the overall flow patterns of Newtonian fluids and power-law fluids in these mixing elements are quite similar.     

Non-newtonian two-phase circulation in bubble columns

Gas-liquid and gas-slurry bubble columns are widely used in the mineral and engineering industries, particularly for aeration (oxidation), synthesis of oil and flotation of mineral fines. Even though gas may be introduced into a bubble column evenly through a distributor plate over the whole column floor, undesirable circulation patterns generally develop in the column. This paper extends a force balance approach (originally used for turbulent systems) to predict circulation in non-Newtonian gas-liquid mixtures and demonstrates how the rheological properties will affect a single circulation pattern in a column.     

Friction factor-Reynolds number relationship for laminar flow of non-Newtonian fluids in open channels of different cross-sectional shapes

The effect of channel shape on the friction factor-Reynolds number relationship for laminar, open channel flow of three non-Newtonian fluids was investigated. For each channel shape, the data can be described by a general relationship, f=K/Re where f is the Fanning friction factor and Re is the appropriate Haldenwang et al. (2002) Reynolds number corresponding to the flow curve model used to describe the non-Newtonian behaviour exhibited by the test fluid. The K values were found to be 14.6 for triangular channels with a vertex angle of 90°, 16.2 for semi-circular channels, 16.4 for rectangular channels and 17.6 for trapezoidal channels with 60° sides. These K values were found to be in line with those reported by Straub et al. (1958) and Chow (1959) for open channel flow of Newtonian fluids as opposed to the assumption made by Haldenwang et al., 2002, Haldenwang et al., 2004 of using a constant value of 16 based on the pipe flow paradigm for all channel shapes.     

Flow through regular polygonal channels

A general method for analyzing viscous flow through regular polygonal channels is presented, based upon the assumption that the flow rate through regular polygonal sections equals that through circular sections of the same area. In addition we offer alternatives which apply specifically to equilaterial triangles and to squares.     

Two-phase gas-liquid flow in rectangular channels

The results of investigation of hydraulics in a two-phase gas—liquid flow in vertical and horizontal rectangular channels have been presented in the paper.Flow regime maps have been worked out and a method for calculating the pressure drop in a two-phase mixture flow has been proposed.The methods applied in a two-phase flow in pipes have been used to describe the results of investigations, after adopting the correction for the difference between the flow in rectangular channels and that in pipes.     

Geometric parameters for some flow channels

A method was proposed earlier⁽¹⁾ for prediction of the average velocity or pressure drop in the flow of non- Newtonian fluids in conduits of arbitrary cross section. The method requires only a knowledge of two geometric parameters which characterize the flow geometry, and the fluid model equation. In this paper, evaluations of geometric parameters are presented for infinite and finite (enclosed)square and triangular arrays of cylinders, and for regular polygonal and star-shaped conduits. With these parameters, predictions of the average velocity or related variables for the Zlow of any arbitrary non-Newtonian fluid can now be made. Comparisons are made with recent analytical solutions and experimental data pertaining to non-Newtonian flow in concentric annuli, and equilateral and right isosceles triangular ducts, which give additional support to the reliability of the proposed method.     

复杂流道结构料仓的下料流率预测

在实验室搭建的有机玻璃料仓下料平台上,分别以自由流动粉体玻璃微珠和黏附性粉体煤粉和聚氯乙烯为实验介质,针对无改流体(No-In)、封闭改流体(Con-In)和开放改流体(Ucon-In)三种情况所形成的不同流道结构,开展了粉体料仓下料及其流率建模研究,定量分析了改流体对粉体下料流率的促进作用,对比给出了玻璃微珠、煤粉和聚氯乙烯在不同流道结构料仓内的下料特性。研究表明,改流体的引入有利于提高料仓下料流率,Con-In促进流动效果最明显,对于流动性弱的煤粉,下料流率提升幅度达到最大的58%。基于剪切摩擦区的概念,提出流率校正因子F对最小能量理论方程进行了修正,将理想的料仓下料模型拓展至实际下料过程。进一步,对于Con-In,根据流道结构特征结合对粉体的受力分析,修正了模型中的锥角项;对于Ucon-In,基于粉体下料流动竞争机制,提出分阶段下料模式并关联了内层和夹层的下料流率,最终建立了复杂流道结构料仓的下料流率预测模型。该模型综合考虑了粉体物性、下料流型和流道结构的影响,可有效预测自由流动粉体和黏附性粉体流经传统料仓(No-In)和改流体料仓(包括Con-In和Ucon-In)的粉体下料流...     

微小三角形槽道内电渗流动特性分析

提出了微小三角形槽道内电渗流动理论计算方法,通过Galerkin法计算并分析了其内部的电势及速度分布,获得了温度、槽道尺寸、外加电势的电场强度、ζ电势以及电解质浓度对微小三角形槽道内电渗流动的影响规律。计算结果表明：微小三角形槽道内液体的质量流量随ζ电势、电场强度、流体温度及电解质浓度的增加而增加,随微小三角形槽道尺寸的增加先增加后减小。     

锌溴液流电池通道的计算流体力学模拟

针对不同类型的锌溴液流电池通道,利用流体力学计算软件 FLUENT对流体的流动状态进行了模拟。结果表明,在相同流速条件下,直角通道和弯角通道流体的局部流速最大值都出现边壁突变处;在液流电池反应区,流体的局部流速和湍流程度的分布存在不均匀现象。通过改变进出反应区的分流通道数量和结构,可以使电解液在反应区流动均匀,改进整个流动体系的传质性能,进而使锌溴液流电池电堆的充放电性能得到提高。     

Hydrodynamic and mass transfer in inertial gas–liquid flow regimes through straight and meandering millimetric square channels

Heat-exchanger reactors are an important part of process intensification technology. For plate geometries, one solution for intensifying transfer and increasing residence times is to construct two-dimensional meandering channels. Supported by this scientific context, the present work aims at characterising gas–liquid mass transfer in the same square millimetric meandering channel, as in Anxionnaz (2009), this constituted the preliminary step required for performing exothermic gas–liquid reactions. Firstly, the gas–liquid hydrodynamics were characterised for a water/air system. When compared to a straight channel of identical compactness and sectional-area (2×2 mm²), the meandering channel induced (i) a delay in the transition from Taylor to annular-slug regimes, (ii) a rise of 10–20% in bubble lengths while conserving almost identical slug lengths, (iii) higher deformations of bubble nose and rear due to centrifugal forces (bends). Secondly, an original method for verifying the relevancy of the plug flow model and accurately determining k_la was used (measurements of concentrations in dissolved oxygen along the channel length). For the Taylor flow regime, k_la increased coherently when increasing j_g, and the meandering geometry had a small influence. On the contrary, this effect was found no more negligible for the slug-annular flow regime. Whatever the channels, the NTU_l remained low, thus showing that, even if millimetric channels allowed to intensify k_la, a special attention should be paid for generating sufficient residence times. At identical compactness, the meandering channel was found to be the most competitive. Finally, results on gas–liquid interfacial areas and mass transfer coefficients were confronted and discussed with respect to the predictions issued from the model developed by Van Baten and Krishna (2004).     

平板膜组件内部流体流动状态的可视化

自行设计了透明的有机玻璃膜组件,用于直接观测组件内部流体流动状态。分别测定了空流道和含有料液隔网流道的压力损失,并根据摩擦因子f随Re值的变化曲线确定了临界Reynolds数（Re_c）的范围。结果表明,含有料液隔网流道的Re_c相比空流道大大减小。利用注射颜料的方法对流体流动情况进行观测,验证了上述结果。随后测定了表面粗糙度、隔网排布形式、孔隙率对流体流动情况的影响。最后,自制小型卷式膜进行测试,结果与平板膜的压力损失情况相符,表明平板膜的实验结果可以用于预测卷式膜的行为。