油气输送管线中液滴的湍流扩散特性研究

在对气核中液滴运动进行详细分析的基础上,通过考虑剪切气流中液滴所受升力作用对液滴终端沉降速度的影响,首次在理论上实现了在液滴扩散特性计算中计及剪切升力的作用,同时在所建立的计算模型中还综合考虑了液滴和其携带流体间的局部滑移以及液膜表面粗糙度的影响,应用该模型对油气输送条件下液滴扩散特性计算的平均计算误差从 28. 2%降低到 16. 8%。     

The entry length for slurries in horizontal pipeline flow

The entry length for horizontal slurry pipeline flows has been determined experimentally using a pipeline of diameter 50 mm. Concentration and velocity distributions have been measured in the vertical direction at positions 6, 50 and 185 diameters downstream of the entrance. The measurements show that the entry length is of the order of 50 pipe diameters for sand slurries. High particle settling velocities give somewhat shorter lengths than intermediate settling velocities. With lower density polystyrene particles for which dispersive effects are important, the entry length is significantly greater than 50 diameters. The velocity distributions show that the velocity profiles develop concurrently with the concentration profiles. For sand slurries, a two-dimensional simulation gives a satisfactory representation of the developing concentration profiles.     

Verification of the near-wall model for slurry flow

For a number of years, an analytical model of particulate slurry flow has been under development at GIW Industries, USA, while large bodies of experimental data, including concentration profiles, were obtained at the Saskatchewan Research Council, Canada, and other laboratories. The present paper amalgamates information from these sources, showing that the analytic predictions match the observed concentration profiles.     

Dispersive-force modelling of turbulent suspension in heterogeneous slurry flow

The force-balance model, originally developed for coarse-particle slurries, has now been extended to slurries of finer particles susceptible to turbulent suspension. The analysis involves a turbulent dispersive force — an equivalent body force between the fluid and solid phases. The use of this force, together with the intergranular stresses for contact-load particles, allows the calculation of concentration and velocity profiles which vary continuously with height. The calculated profiles are found to be in generally good agreement with experimental data from the Saskatchewan Research Council.     

Friction factor for gas-non-newtonian liquid flow in horizontal bends

Experimental investigations have been carried out to evaluate the two-phase pressure drop data across different types of horizontal bends for gas-non-Newtonian liquid flow. The non-Newtonian liquids used were different concentrations of the sodium salt of carboxymethyl cellulose (SCMC) which behaved like pseudoplastic fluids. Correlations have been developed to predict the gas-non-Newtonian liquid two-phase friction factor as a function of various physical and dynamic parameters of the system. Statistical analysis of the correlations suggests that the correlations are of acceptable accuracy.     

油水混合物在水平管中的二相流动特性研究

对内径40mm的钢管和有机玻璃管内油水二相水平流动时的流型、摩擦压降特性进行了详细的实验研究,结果表明:油包水向水包油的转变发生在含水体积分数约0. 4时。随含水体积分数的增大,油水二相流的摩擦压降先是急剧减小,其后在含水体积分数大于0. 4时压降变化趋于平缓。油水二相流的摩擦压降受含水体积分数、管壁润湿特性、管壁粗糙度以及混合物流速的影响,当二相流体处于水包油状态时,钢管内的摩擦压降比有机玻璃管内的大;而当处于油包水时,有机玻璃管内的摩擦压降则比钢管内的摩擦压降大。     

The hydrodynamics of ejector-Venturi scrubbers and their modelling by an annular flow/boundary layer model

The performance of ejector-Venturi scrubbers has been studied experimentally. Data have been obtained on overall pressure drop, axial pressure profiles and droplet sizes. The effect of throat diameter, length and spray angle was investigated. Empirical models for pressure drop across Venturis have been tested against the data. Only when the model is tuned to the experimental data they are successful. The model of Azzopardi et al. which incorporates all the important physical mechanisms, has been successfully adapted to handle ejector-Venturi. It has been found to give accurate predictions.     

水平同心型料管道输送的数学模型

在假设条件下,参照管道水力学理论,分别引入运动型料表面和静止管道壁面的摩阻系数,建立水平同心型料管道流的简易数学模型。该模型较好地描述了型料管道的流动特性,能快速计算型料管道输送参数,其计算值和实验测试值非常吻合,适用于型料管道输送原理的研究和管道工程系统的设计。     

On a turbulence model for slurry flow in pipelines

In this paper, the possibility of extending the Kolmogoroff's model of multi-scale turbulence structure to dense slurry flows in pipelines is explored. The analysis is based on experimental data of slurry behavior as a Newtonian liquid with some equivalent density and viscosity. A connection is made between the turbulence structure and the head losses in the pipeline that can be calculated by the known engineering methods. The latter, the total loss, is considered as comprising of viscous and turbulent components, and the turbulent component is associated with the turbulence structure. In this paper, the lower turbulence scale for the dense slurries is estimated. For the simulation of turbulence in stratified flows, a modified application of the known two-layer model of slurry flow is proposed.     

Adiabatic two-phase flow in narrow channels between two flat plates

Adiabatic cocurrent flow of air and water through a narrow passage between two flat plates 240 mm long and 99mm wide with gap-widths of 0.778 mm and 1.465 mm was investigated for six different orientations: Vertically upward and downward, 45^° inclined upward and downward, and horizontal flows between horizontal plates and between vertical plates. Except for horizontal flow between vertical plates, the effects of gap width and flow channel orientation on flow pattern, void fraction and friction pressure drop were found to be small in narrow channels. The void fraction and two-phase friction multiplier data could also be reasonably correlated in terms of the Martinelli parameter. For horizontal flow between vertical plates, both the void fraction and friction multiplier data showed strong mass velocity effects. Several friction pressure drop correlations were tested for applicability to the narrow channels including a separated flow model proposed in this work.     

An experimental study of energy-saving pneumatic conveying system in a horizontal pipeline with dune model

In order to reduce power consumption and conveying velocity, a pneumatic conveying system where a dune model is mounted in a pipeline is proposed in this paper. The experimental study focuses on the effect of the mounted dune model in the horizontal pneumatic conveying system in terms of pressure drop, power consumption and conveying velocity. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80 mm and a length of about 5 m. Polyethylene spherical particles with a density of 952 kg/m³ and diameters of 2.3 and 3.3 mm are used as conveying materials. The mean air velocity is varied from 9 to 16 m/s, and the solid mass flow rate is from 0.25 to 0.45 kg/s. Firstly, the effect of the dune model location on pneumatic conveying is experimentally studied. It is found that in the lower air velocity range, the pressure drop of the pneumatic conveying with a mounted dune model is lower than that of a conventional pneumatic conveying system. A lower conveying velocity and energy-saving conveying can be realized by installing a dune model in the conveying pipe. Especially the case of fixing the dune model on the bottom of the pipe at the inlet of particle feed is more effective. The particle flow patterns also show that the dune model reduces the deposition of particles. Then, the effect of different surface materials of the dune model is examined. By using a surface material of the dune model with a large coefficient of restitution, the pressure drop of conveying large particles is the lowest. When conveying relatively small particles, however, the pressure drop becomes the lowest by a small coefficient of restitution. The maximum reduction rates of the minimum velocity and power consumption by the dune model are about 19% and 34%, respectively.     

上升管内环状流含液体积分数与压降预测模型

对垂直上升管中气液二相环状流的含液体积分数及压降预测进行了研究,在充分考虑了环状流的流型特征以及合理假设的前提下,以二相流动力学理论和Wallis有关经验式为基础,推导出了环状流的数学模型。通过求解力学方程,获得了含液体积分数及压降预测的新模型,将新模型及已有模型与实验数据进行对比,结果表明,新模型不仅与实验结果符合良好,还具有计算速度快的特点,从而为垂直上升管内气液二相环状流含液体积分数与压降的预测提供了一种新的有效方法。     

A new technique for the visualization of the concentration boundary layer in an electrodialysis cell

A new method for the visualization of the concentration boundary layer is described. The technique involves the use of a dilute solution of an indicator which reacts with H⁺ formed on the membrane surface to form a coloured trace when the electrodialysis cell is operating above the limiting current density. The thickness of the concentration boundary layer determined by the visualization method agrees well with results obtained from limiting current density measurements and theoretical predictions. The visualization method proposed in this work can be used for understanding the transport taking place between a solid wall and a liquid in steady and unsteady flow processes.     

Experimental test of a model for laminar slurry flow with sedimentation

The ability of a flow-sedimentation model to simulate the flow of a slowly-settling suspension being transported in the laminar regime through a pipeline with a constant overall pressure drop imposed on it was assessed using experimental scaled-down pipeline data. Comparison of predicted volumetric flow rate versus time profiles to those observed suggested that the blockage process took place in two steps. Initially, a sediment grew on the lower pipe wall and the flow gradually lessened, as was modelled. As the flow slowed down, ultimately a plug, which enclosed the full cross-section of the pipe, formed and lead to the rapid blockage of the pipe. It was envisioned that the granular properties of the concentrated suspension became dominant during the final blockage process. A deposit velocity criterion was also developed from the flow-sedimentation model and was used to generate a deposit velocity versus pipe diameter plot. Results from the plot indicate that the laminar pipeline flow of a slowly-settling suspension is possible in small diameter pipes.     

An improved falling-film reactor for viscous liquids

This paper presents the design of a sulfonation reactor that is intended for enhanced performance when the viscosity of the liquid phase increases, thus reducing gas-liquid transfer rates. The proposed design allows adequate transfer rates to be maintained by progressively increasing the shear stress exerted by the gas over the liquid film. The effectiveness of the design has been tested in runs in which dodecylbenzene and lauryl alcohol 1.80E are sulfonated/sulfated.     

An ultrasonic interface layer model for bond evaluation

An interface layer model for adhesive bonding weakness evaluation is described to assist in ultrasonic oblique incidence analysis of waves traveling across the interface. This model assumes that the interface between the substrate and adhesive can be treated from a wave propagation point of view as a homogenous isotropic interface layer. The interface bonding quality can then be estimated by predetermined properties of the interface layer. The smooth bond can be formed by a thin nonviscous liquid layer between the two solid media. Numerical results show a frequency dependence of the reflection factors as well as a direct influence of the interface layer properties on reflection. Experiments on bonded structures were conducted to confirm the theoretical prediction. Experiments on smooth bond simulation structures showed the same trends as the theoretical curves of longitudinal wave reflection vs. frequency. Higher sensitivities of shear waves at oblique incidence for bonding weakness detection were found compared with longitudinal waves at normal incidence.     

Comparison of experimental pressure gradient and experimental relationships for the low density spherical capsule train with slurry flow relationships

In the experimental part of this study, pressure drops that occur in the flow of a low density spherical capsule train conveyed by water in a horizontal pipe were found to be 5-30% of the capsule transport concentrations. The developed experimental relations were compared with well-known relations used for slurry flow. Experimental variables (i.e. bulk velocity, diameter of particle or capsule, diameter of pipe, concentration of particle, density of particle, etc.) were applied to the pressure gradient expressions developed for the slurry flow (asymmetric suspension flow), so that the pressure gradients calculated for a concentration by 5% and 10% were compared with the experimental findings and with the developed mathematical model. It was observed that the pressure gradient expressions of the slurry flow did not simulate the experimental results of the capsule flow. However, a comparison of the empirical expression developed for the pressure drops of the spherical capsule train flow in region (2.5 × 10⁴ < Re < 1.5 × 10⁵) with the experimental findings revealed an average deviation of 3.37%.     

Pressure drop in two phase cocurrent upward flow in packed beds: Air/non-newtonian liquid systems

New data on the two phase pressure drop for the concurrent upflow of air-liquid (Newtonian and non-Newtonian) mixtures through packed beds of spherical and non-spherical particles are presented. The results for single phase flows and for the air-Newtonian liquid mixtures have been used both to gauge the overall accuracy of the present experimental methods and to evaluate the validity of the predictive expressions available in the literature. The two phase pressure drop has been measured as a function of the liquid and gas flow rates, column diameter and the power law model constants. Depending upon a suitable combination of the gas and liquid fluxes and the power law index, the two phase pressure drop may be less than its value for the flow of liquid alone. A simple expression is proposed which correlates the present set of experiments (nearly 500 data points) with satisfactory levels of accuracy over the following ranges of conditions: 0.54 ≤ n ≤ 1; 0.001 ≤ Re_L^* ≤ 50; 3.7 ≤ Re_G ≤ 177 and 0.9 ≤χ (Lockhart-Martinelli parameter) ≤ 104.     

The surface renewal model of wall turbulence for boundary layer flow with transpiration

The object of this paper is to develop and evaluate the basic surface renewal modeling approach for transpired turbulent boundary layer flows. Using a simple form of the surface renewal model in conjunction with the standard mixing length representation of the turbulent core, calculations are established for the dimensionless burst frequency s⁺, and distributions in velocity u⁺ within the inner region as a function of transpiration rate v⁺ and pressure gradient P⁺.     

Two layer heat transfer model for supercritical fluid flow in a vertical tube

Experimental heat transfer data in a supercritical vertical upward CO₂ flow were analyzed, based on the relationship between the wall heat flux and mass flux, buoyancy and flow acceleration effects, and specific heat variation across the turbulent boundary layer. These analyses indicated that the flow acceleration and significant specific heat variation in the boundary layer greatly influenced the heat transfer phenomena under the tested experimental conditions. A two layer heat-transfer model that sufficiently reflects both the effects of flow acceleration and specific heat variation was proposed to quantify the heat-transfer characteristics of supercritical fluids. This model was based on the thermal resistance behavior in the viscous sub-layer and the buffer layer. In our assessment of this model, the Nusselt number calculated from various experiments agreed with our data within a margin of error of ±30%. Also, the location of the peak inner wall temperature from experimental data almost coincided with the peak maximum thermal resistance in the viscous sub-layer, calculated using the proposed model.