One-dimensional modelling of mixing, dispersion and segregation of multiphase fluids flowing in pipelines

The flow of immiscible liquids in pipelines has been studied in this work in order to formulate a one-dimensional model for the computer analysis of two-phase liquid-liquid flow in horizontal pipes. The model simplifies the number of flow patterns commonly encountered in liquid-liquid flow to stratified flow, fully dispersed flow and partial dispersion with the formation of one or two different emulsions. The model is based on the solution of continuity equations for dispersed and continuous phase; correlations available in the literature are used for the calculation of the maximum and mean dispersed phase drop diameter, the emulsion viscosity, the phase inversion point, the liquid-wall friction factors, liquid-liquid friction factors at interface and the slip velocity between the phases. In absence of validated models for entrainment and deposition in liquid-liquid flow, two entrainment rate correlations and two deposition models originally developed for gas-liquid flow have been adapted to liquid-liquid flow. The model was applied to the flow of oil and water; the predicted flow regimes have been presented as a function of the input water fraction and mixture velocity and compared with experimental results, showing an overall good agreement between calculation and experiments. Calculated values of oil-in-water and water-in-oil dispersed fractions were compared against experimental data for different oil and water superficial velocities, input water fractions and mixture velocities. Pressure losses calculated in the full developed flow region of the pipe, a crucial quantity in industrial applications, are reasonably close to measured values. Discrepancies and possible improvements of the model are also discussed. The model for two-phase flow was extended to three-phase liquid-liquid-gas flow within the framework of the two-fluid model. The two liquid phases were treated as a unique liquid phase with properly averaged properties. The model for three-phase flow thus developed was implemented in an existing research code for the simulation of three-phase slug flow with the formation of emulsions in the liquid phase and phase inversion phenomena. Comparisons with experimental data are presented

Effect of partial wetting on liquid/solid mass transfer in trickle bed reactors

The wetting efficiency of liquid trickle flow over a fixed bed reactor has been measured for a wide range of parameters including operating conditions, bed structure and physico-chemistry of liquid/solid phases. This data bank has been used to develop a new correlation for averaged wetting efficiency based on five different non-dimensional numbers. Finally liquid/solid mass transfer has been determined in partial wetting conditions to analyse what are the respective effects of wetting and liquid/gas flow turbulence. These effects appear to be separated: wetting being acting on liquid/solid interfacial area while the liquid/solid mass transfer coefficient is mainly connected to flow turbulence through the interstitial liquid velocity. A correlation has been proposed for liquid/solid mass transfer coefficient at very low liquid flow rate

Flow conveying and diagnosis with carbon nanotube arrays

Dense arrays of aligned carbon nanotubes are designed into strips, nanowicks, as a miniature wicking element for liquid delivery and potential microfluidic chemical analysis devices. Liquid wicks away along the nanowicks spontaneously. This delivery function of nanowicks enables novel fluid transport devices to run without any power input, moving parts or external pump. Flow around the opaque nanotubes can be detected either directly or indirectly. Direct signals of the flow come out of dyed liquid or from the liquid–air interface; indirect signals are detected through observing surface-tension-induced deformation and dislocation of the nanotubes. Here we show that flow progression around and inside nanowicks is sensitive to liquid properties. Different flow progression leaves different traces of liquid. These traces not only allow liquid diagnosis any time after sampling, but also enable analysis of flow at a nanoscale resolution with scanning electron microscopy

Investigation and prediction of slug flow characteristics in highly viscous liquid and gas flows in horizontal pipes

Slug flow characteristics in highly viscous liquid and gas flow are studied experimentally in a horizontal pipe with 0.074 m ID and 17 m length. Results of flow regime map, liquid holdup and pressure gradient are discussed and liquid viscosity effects are investigated. Applicable correlations which are developed to predict liquid holdup in slug body for low viscosity flow are assessed with high viscosity liquids. Furthermore, a mechanistic model is developed for predicting the characteristics of slug flows of highly viscous liquid in horizontal pipes. A control volume is drawn around the slug body and slug film in a slug unit. Momentum equations with a momentum source term representing the significant momentum exchange between film zone and slug body are applied. Liquid viscosity effects are considered in closure relations. The mechanistic model is validated by comparing available pressure gradient and mean slug liquid holdup data produced in the present study and those obtained from literature, showing satisfactory capabilities over a large range of liquid viscosity

Direct numerical simulation of the near-field dynamics of annular gas-liquid two-phase jets

Copyright © 2009 American Institute of Physics.Direct numerical simulation has been used to examine the near-field dynamics of annular gas-liquid two-phase jets. Based on an Eulerian approach with mixed fluid treatment, combined with an adapted volume of fluid method and a continuum surface force model, a mathematical formulation for the flow system is presented. The swirl introduced at the jet nozzle exit is based on analytical inflow conditions. Highly accurate numerical methods have been utilized for the solution of the compressible, unsteady, Navier–Stokes equations. Two computational cases of gas-liquid two-phase jets including swirling and nonswirling cases have been performed to investigate the effects of swirl on the flow field. In both cases the flow is more vortical at the downstream locations. The swirling motion enhances both the flow instability resulting in a larger liquid spatial dispersion and the mixing resulting in a more homogeneous flow field with more evenly distributed vorticity at the downstream locations. In the annular nonswirling case, a geometrical recirculation zone adjacent to the jet nozzle exit was observed. It was identified that the swirling motion is responsible for the development of a central recirculation zone, and the geometrical recirculation zone can be overwhelmed by the central recirculation zone leading to the presence of the central recirculation region only in the swirling gas-liquid case. Results from a swirling gas jet simulation were also included to examine the effect of the liquid sheet on the flow physics. The swirling gas jet developed a central recirculation region, but it did not develop a precessing vortex core as the swirling gas-liquid two-phase jet. The results indicate that a precessing vortex core can exist at relatively low swirl numbers in the gas-liquid two-phase flow. It was established that the liquid greatly affects the precession and the swirl number alone is an insufficient criterion for the development of a precessing vortex core.EPSR

Bubble simulations with an interface tracking technique based on a partitioned fluid-structure interaction algorithm

Numerical techniques frequently used for the simulation of one bubble can be classified as interface tracking techniques and interface capturing techniques. Most of these techniques calculate both the flow around the bubble and the shape of the interface between the gas and the liquid with one code. In this paper, a rising axisymmetric bubble is simulated with an interface tracking technique that uses separate codes to determine the position of the gas-liquid interface and to calculate the flow around the bubble. The grid converged results correspond well with experimental data. The gas-liquid interface is conceived as a zero-mass, zero-thickness structure whose position is determined by the liquid forces, a uniform gas pressure and surface tension. Iterations between the two codes are necessary to obtain the coupled solution of both problems and these iterations are stabilized with a fluid-structure interaction (FSI) algorithm. The flow around the bubble is calculated on a moving mesh in a reference frame that rises at the same speed as the bubble. The flow solver first updates the mesh throughout the liquid domain given a position of the gas-liquid interface and then calculates the flow around the bubble. It is considered as a black box with the position of the gas-liquid interface as input and the liquid forces on the interface as output. During the iterations, a reduced-order model of the flow solver is generated from the inputs and outputs of the solver. The solver that calculates the interface position uses this model to adapt the liquid forces on the gas-liquid interface during the calculation of the interface position

An ultrasonic system for profiling bubblers in water

Multi-phase flow occurs as two or more discrete phases flow in a closed pipe or a vessel. Examples of phases include gas, liquid or solid and also different immiscible liquids or solids[1]. Two phase flow of fluids (e.g. gas/liquid, liquid/liquid, etc.) is an important phenomenon in which two immiscible phases coexist in a thermodynamic equilibrium. As a two phase flow regime, bubbly flow column are intensively used as multiphase contactors and reactors in chemical, biochemical and petrochemical industries. Investigation of design parameters characterizing the operation and transport phenomena of bubble columns have led to better understanding of the hydrodynamic properties, heat and mass transfer mechanisms and flow regime characteristics ongoing during the operation[2, 3]. Due to the stringent regulations on precise flow control especially in the case of two phase fluid flow,, there has always been a necessity for developing an easier to use, yet more precise approaches or instrumentation. Accordingly, tomographic measurement is more significant and attractable especially in today's industrial process .

Control of Initiation, Rate, and Routing of Spontaneous Capillary-Driven Flow of Liquid Droplets through Microfluidic Channels on SlipChip

This Article describes the use of capillary pressure to initiate and control the rate of spontaneous liquid–liquid flow through microfluidic channels. In contrast to flow driven by external pressure, flow driven by capillary pressure is dominated by interfacial phenomena and is exquisitely sensitive to the chemical composition and geometry of the fluids and channels. A stepwise change in capillary force was initiated on a hydrophobic SlipChip by slipping a shallow channel containing an aqueous droplet into contact with a slightly deeper channel filled with immiscible oil. This action induced spontaneous flow of the droplet into the deeper channel. A model predicting the rate of spontaneous flow was developed on the basis of the balance of net capillary force with viscous flow resistance, using as inputs the liquid–liquid surface tension, the advancing and receding contact angles at the three-phase aqueous–oil–surface contact line, and the geometry of the devices. The impact of contact angle hysteresis, the presence or absence of a lubricating oil layer, and adsorption of surface-active compounds at liquid–liquid or liquid–solid interfaces were quantified. Two regimes of flow spanning a 104-fold range of flow rates were obtained and modeled quantitatively, with faster (mm/s) flow obtained when oil could escape through connected channels as it was displaced by flowing aqueous solution, and slower (micrometer/s) flow obtained when oil escape was mostly restricted to a micrometer-scale gap between the plates of the SlipChip (“dead-end flow”). Rupture of the lubricating oil layer (reminiscent of a Cassie–Wenzel transition) was proposed as a cause of discrepancy between the model and the experiment. Both dilute salt solutions and complex biological solutions such as human blood plasma could be flowed using this approach. We anticipate that flow driven by capillary pressure will be useful for the design and operation of flow in microfluidic applications that do not require external power, valves, or pumps, including on SlipChip and other droplet- or plug-based microfluidic devices. In addition, this approach may be used as a sensitive method of evaluating interfacial tension, contact angles, and wetting phenomena on chip