Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds

Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid velocities during stable liquid–gas flow of water and SF₆ within a packing of 5 mm spheres contained within columns of diameter 40 and 27 mm; images being acquired using ¹H and ¹⁹F observation for the water and SF₆, respectively. Liquid and gas flow rates calculated from the velocity images are in agreement with macroscopic flow rate measurements to within 7% and 5%, respectively. In addition to the information obtained directly from these images, the ability to measure liquid and gas flow fields within the same sample environment will enable us to explore the validity of assumptions used in numerical modelling of two-phase flows.     

Evaluation of micro-bubble size and gas hold-up in two-phase gas-liquid columns via scattered light measurements

In this paper, potential use of an elliptically polarized light scattering (EPLS) method to monitor both bubble size and gas hold-up in a bubble-laden medium is explored. It is shown that with the use of the new EPLS system, normalized scattering matrix elements (M_ij's) measured at different side and back-scattering angles can be used to obtain the desired correlations between the bubble sizes and input flow parameters for a gas-liquid (GL) column, including gas flow rate and surfactant concentrations. The bubble size distributions were first evaluated experimentally using a digital image processing system for different gas flows and surfactant concentrations. These images showed that the bubbles were not necessarily spherical. We investigated the possibility of modeling the bubbles as effective spheres. The scattering matrix elements were calculated using the Lorenz-Mie theory and the results were compared against the experimentally determined values. It was observed that the change in the bubble size yields significant changes in M₁₁, M₃₃, M₄₄, and M₃₄ profiles. An optimum single measurement angle of θ=120^° was determined for a gas velocity range of 0.04-0.35 cm/s (). The choice of the optimum angle depends on frit pore size, column diameter, gas pressure, and surfactant concentration. These results suggest that a simplified version of the present EPLS system can effectively be used as a two-phase flow sensor to monitor bubble size and liquid hold-up in industrial systems.     

对流梯形微通道内气液两相流动的数值研究

采用VOF方法,对梯形微通道内不可压缩气液两相流动进行了数值模拟研究,详细分析了气泡形成过程,以及当量直径、截面形状、液体表面张力和粘度等对气泡液柱形成过程和长度的影响,拟合出微通道气泡液柱长度计算公式。结果表明:气泡液柱的长度受表观气速和表观液速的影响较大;表面张力对气泡尺寸的影响较小,当液体粘度增加为水粘度的10倍时,形成的气泡形状不规则。增大表面张力,形成气泡的时间增加;增大粘度,形成气泡的时间减小。     

液氢加注系统低温管道中的两相流仿真与分析

在液氢加注输送过程中,由于其具有低温和高压的特性,极易产生气液两相流,而使管道发生过压故障.因此,对液氢管道的仿真研究有着重要作用.文中对裸态和防护后的液氢管道进行建模计算,并通过AMESim软件的两相流库对氢物理属性和管道模型进行仿真分析,然后对系统的对液氢输送管道进行了应用改进与分析.仿真结果表明:液氢在裸管道中输...     

基于分形多孔介质三维网络模型的非混溶两相流驱替数值模拟

提出了一个描述多孔介质孔隙尺寸分布的三维分形网络模型,利用该模型对多孔介质中的非混溶两相流驱替进行了数值模拟,研究了孔隙尺寸分布分维D_f和两相流黏滞比M对驱替前沿指进型的影响,结果表明指进型容量维数D_h随着孔隙尺寸分布分维D_f以及黏滞比M的增大而减少,并通过曲线拟合得到了它们之间的定量关系. 关键词： 多孔介质 三维网络 黏滞指进 非混溶两相流     

Direct pore-level modeling of incompressible fluid flow in porous media

We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier–Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid–solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 μm resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate.     

Three-phase compressible flow in porous media: Total Differential Compatible interpolation of relative permeabilities

We describe the construction of Total Differential (TD) three-phase data for the implementation of the exact global pressure formulation for the modeling of three-phase compressible flow in porous media. This global formulation is preferred since it reduces the coupling between the pressure and saturation equations, compared to phase or weighted formulations. It simplifies the numerical analysis of the problem and boosts its computational efficiency. However, this global pressure approach exists only for three-phase data (relative permeabilities, capillary pressures) which satisfy a TD condition. Such TD three-phase data are determined by the choice of a global capillary pressure function and a global mobility function, which take both saturations and global pressure level as argument. Boundary conditions for global capillary pressure and global mobility are given such that the corresponding three-phase data are consistent with a given set of three two-phase data. The numerical construction of global capillary pressure and global mobility functions by C¹${\text{C}}^1$ and C⁰${\text{C}}^0$ finite element is then performed using bi-Laplacian and Laplacian interpolation. Examples of the corresponding TD three-phase data are given for a compressible and an incompressible case.     

The effects of porosity and permeability on fluid flow and heat transfer of multi walled carbon nano-tubes suspended in oil (MWCNT/Oil nano-fluid) in a microchannel filled with a porous medium

The forced convection heat transfer and laminar flow in a two-dimensional microchannel filled with a porous medium is numerically investigated. The nano-particles which have been used are multi walled carbon nano-tubes (MWCNT) suspended in oil as the based fluid. The assumption of no-slip condition between the base fluid and nano-particles as well as the thermal equilibrium between them allows us to study the nanofluid in a single phase. The nanofluid flow through the microchannel has been modeled using the Darcy–Forchheimer equation. It is also assumed that there is a thermal equilibrium between the solid phase and the nanofluid for energy transfer. The walls of the microchannel are under the influence of a fluctuating heat flux. Also, the slip velocity boundary condition has been assumed along the walls. The effects of Darcy number, porosity and slip coefficients and Reynolds number on the velocity and temperature profiles and Nusselt number will be studied in this research.     

E-Elman神经网络在冰蓄冷空调系统建模中的应用

冰蓄冷技术能够为空调系统带来显著的节能效果, 已广泛地应用在现代建筑当中, 准确的监测数据预测值有利于系统合理地运行; 针对实际冰蓄冷空调工程中的能源管理控制系统（energy management and control system, EMCS）数据采样周期较长所导致在系统制冰与融冰阶段数据不足的问题, 提出了一种改进的机组运行状况预测模型; 模型算法以数据变化趋势为依据, 在传统Elman中引入评价层以约束网络输出值, 增加计算针对性, 从而提高模型输出的准确性; 仿真结果表明, 此种建模方法解决了系统融冰与制冰阶段的数据突变及网络输出值局部最优解等问题, 与传统Elman网络结构相比, 其输出值更为接近测量值, 有效地提高了模型输出的真实性; 通过关联函数, 设计的模型对冷水机组的能源消耗也可起到预测作用, 进一步说明了其实用性。     

Monitoring acoustic emission (AE) energy of abrasive particle impacts in a slurry flow loop using a statistical distribution model

Slurry erosion has been recognized as a serious problem in many industrial applications. In slurry flows, the estimation of the amount of incident kinetic energy that transmits from particles suspended in the fluid to the containment structures is a key aspect in evaluating its abrasive potential. This work represents a systematic investigation of particle impact energy measurement using acoustic emission (AE), as indicated by a sensor mounted on the outer surface of a sharp bend, in an arrangement that had been pre-calibrated using controlled single and multiple impacts. Particle size, free stream velocity, and nominal particle concentration were varied, and the amount of energy dissipated in the carbon steel bend was assessed using a slurry impingement flow loop test rig. Silica sand particles of mean particle size 225–650 μm were used for impingement on the bend with particle nominal concentrations between 1 and 5% while the free stream velocity was changed between 4.2 and 14 ms⁻¹.     

Computational (MP2 and DFT) modeling of the substrate/inhibitor interaction with the LDH active pocket in the gas phase and aqueous solution: bimolecular charged (pyruvate/oxamate–guanidinium cation) and neutral adducts (pyruvic/oxamic acids–guanidine)

Two types of bimolecular adducts were studied for the substrate and inhibitor of lactate dehydrogenase (LDH), one type of adducts between ionic species, α‐keto‐carboxylates (pyruvate and oxamate) and the guanidinium cation, and the other type of adducts between neutral species, α‐ketocarboxylic (pyruvic and oxamic) acids and guanidine. Calculations were performed in the gas phase and aqueous solution using the MP2 and PCM methods and the 6‐31++G** basis set. Application of the DFT(B3LYP) and PCM methods led to similar results. A change of the adducts' preference was observed when proceeding from the gas phase to aqueous solution. This change is in good agreement with the acidity–basicity scales in both phases. Formation constant (K_HB) for adduct between neutral species is greater for pyruvic than for oxamic acid in the gas phase, whereas a reverse situation takes place in aqueous solution, where the K_HB value for adduct between ionic species is smaller for pyruvate than for oxamate. The water molecules favor interactions of more polar oxamate with the guanidinium cation. Stronger interaction with this cation, a model of the arginine fragment of the LDH pocket, suggests that oxamate (inhibitor of LDH) has stronger binding properties in aqueous solution than pyruvate (substrate of LDH). Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of transpiration on unsteady MHD flow of an upper convected Maxwell （UCM） fluid passing through a stretching surface in the presence of a first order chemical reaction

The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell （UCM） model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration （suction） and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration （suction） and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case.     

The role of Bi2O3 as a network modifier and a network former in xBi2O3 · (1 − x)LiBO2 glass system

The effect of Bi₂O₃ on the glass transition temperature, electrical conductivity and structure of LiBO₂ glass has been investigated. T_g vs. composition curve shows three different linear regions, while there is an overall decrease in T_g with the increase in Bi₂O₃ content. The slope of these three straight lines is in a decreasing order. These results are interpreted in terms of the increase in the number of non-bridging oxygen atoms, substitution of Bi-O bond in place of B-O bond and change in Li⁺ ion concentration. The conductivity vs. composition curve exhibits two maxima which are interpreted in terms of the structural modification effect of Bi₂O₃ on LiBO₂ network and mixed-former effect, respectively. Results obtained from the XPS studies of the samples of composition x 0.005, have shown that the number of non-bridging oxygen atoms from B-O bond increases with the increase in Bi₂O₃ content. It has a maximum value at x = 0.003 where the conductivity has also exhibited a maximum value. Further increase of Bi₂O₃ content causes decrease in it. For higher Bi₂O₃ content (x * > 0.005), O 1s spectra of Bi₂O₃ has been separated out from that of Bi₂O₃. Bismuth ions have been substituted for boron ions as network former ions.