Mixture Velocity Research Articles

Investigation of the Gas-Liquid Two-Phase Flow and Separation Behaviors at Inclined T-Junction Pipelines.

The T-junction is a novel type of separator used in the petroleum and gas industry. It is used to achieve the gas–liquid or liquid–liquid two-phase separation. To obtain an applicative T-junction separator, in the present study, the gas–liquid two-phase separation characteristics in multiple inclined T-junctions were investigated through a series of numerical simulations and field experiments. Two representative multiphase modes, namely, the Euler model and the mixture model, were chosen for this study. Comparisons of the field experiments were made to obtain a highly accurate simulation model. The mixture model was chosen to be better suited for this study. It is used to investigate the gas–liquid two-phase flow and the separation behaviors, which include the effect of inlet flow velocity, inlet bubble diameter, and the split ratio of two outlets. The results indicate that the best flow split ratio exists when the two-phase separation reaches the best consequence, and the best flow split ratio changes when the separation demands of gas or liquid are different. Furthermore, the separation efficiency keeps decreasing as the inlet velocity is increased. Hence, the inlet mixture velocity should be reduced to improve the gas–liquid two-phase separation. More specifically, to obtain a better separation for the same throughput, the size of the T-junction should be increased. Moreover, the separation efficiency increases as the inlet bubble diameter increases. Consequently, the results can be used to design the T-junction as an industrial separator, which can then be directly used in petroleum and gas production.

Numerical study on pressure drop and heat transfer characteristics of gas-liquid Taylor flow in a microchannel based on FFR method

Two-phase Taylor flow in microchannels as a critical way to enhance heat dissipation has attracted extensive attention due to the high integration and miniaturization development of electronic devices. To further elucidate the pressure drop and development process of heat transfer characteristics in Taylor flow, a 2-D planar T-junction microchannel with a width of 1 mm was investigated numerically by using the fixed frame computational domain method. The local Nusselt number distribution is divided into four parts for analysis, and the effects of mixture velocity and void fraction on the heat transfer coefficient are also discussed. The results indicate that the injection of gas-phase leads to an increase in pressure gradient, and the flow-pattern related model has a better predictive result. Strong evidence of internal circulation was found when the shear stress in Y direction is not equal to zero in Taylor flow. The investigation of Nusselt number has shown that the mixture velocity and the void fraction affect the temperature field distribution and heat absorption capacity in the liquid slug, respectively. Together these simulation data, nearly 1.8 times higher of the Nusselt number was observed compared to pure water flow.

Evaluation of an empirical model used for deriving the fluidization velocity of binary mixtures of biomasses and sand

In a previous study, a statistical model was developed using the experimental planning technique for evaluating the influence of its variables on fluidization velocity. In this study, we investigated the Vasconcelos-statistical model (VSM) in data representation, considering fluidization with and without segregation. The methodology used was based on the simulation of the fluidization velocity of nine binary systems, comprising sand, and eight biomasses published by six authors. In addition, the results obtained using VSM were compared with those obtained using five other models, reported by different authors, but adjusted to the experimental data of these biomasses. The result obtained by the proposed models mainly indicated a discrepancy between the experimental and calculated fluidization velocities. VSM, using only three variables (particle size, particle diameter, and biomass mass fraction), yielded results of smaller discrepancy values in all simulations (2.23–12.51%), as opposed to the other comparative models, which presented more significant numbers of variables. Thus, VSM is defined as one of the most interesting models for predicting the fluidization velocity of several biomasses.

Estimation of swirl velocity of gas in Ranque-Hilsch vortex tube using a combined thermal and species separation model

ABSTRACT A Ranque-Hilsch Vortex Tube (RHVT) is a device that can cause simultaneous thermal and species separation in a compressible fluid mixture. The binary mixture is compressed and tangentially introduced into the vortex chamber of the RHVT, and two streams are withdrawn at opposite ends of the device. The RHVT acts as a centrifugal separator that separates the mixture into two streams, one enriched and the other depleted of the component with higher molecular weight. The extent of separation depends on the magnitude of swirl velocity of gas mixture inside the RHVT. Now a new combined heat and mass transfer model using heat and mass transfer analogy has been proposed by the authors to predict the species separation in a RHVT. The aim of this paper is to use this model to estimate the magnitude of swirl velocity of gas mixture inside the RHVT. The estimated values have been compared with range of experimentally as well as numerically obtained values reported in the literature. For a given configuration in published literature and values of cold mass fraction the average swirl velocity inside the RHVT was found to vary between 90 m/s and 130 m/s. It is found that for a fixed value of inlet pressure, average swirl velocity is a function of cold mass fraction. The value of average swirl velocity minimizes near cold mass fraction = 0.3 and maximizes near cold mass fraction = 0.8. Parametric studies have been carried out to understand the effect of important RHVT parameters on swirl velocity. Also relation between swirl velocity and species separation has been explored.

Flame stabilization regimes for premixed flames anchored behind cylindrical flame holders

The objective of this study is to construct a regime diagram for laminar flames stabilized behind flame holders with respect to the presence of a recirculation zone (RZ), trend of heat loss to the burner, and flow strain and flame curvature effects. This is achieved by varying the radius of the cylindrical flame holder and the mixture velocity between the flashback limit and the blow-off limit at a fixed equivalence ratio. It is found that for all flame holders, a RZ vortex is not present near the flashback limit. At flashback, flow strain is almost zero and the flame curvature is found to be the main contributor to flame stretch. With increasing mixture velocity, the heat loss to the flame holder decreases for smaller radii and a RZ does not appear till blow-off occurs. For flame holders with radii greater than twice the flame thickness, the heat loss to the flame holder first decreases with increasing mixture velocity without a RZ. A further increase in the mixture velocity does not result in blow-off but instead, a RZ appears behind the flame holder reversing the heat loss trend. In this scenario, flow strain is found to increase significantly and becomes the major contributor to flame stretch, although curvature effects are still present. With the RZ present, the blow-off limits are significantly extended and the stabilization mechanism is altered. The RZ vortex shields the flame base from intense pre-heating resulting from the increase in heat loss to the flame-holder while it provides support to the flame leading edge by recirculation of hot products. The results obtained from this study are used to construct a regime diagram, which offers a broader view of the whole flame stabilization process and its mechanisms.

Energy Analysis and Phase Inversion Modeling of Two-Phase Flow with Different Additives

Liquid-liquid flow in the pipeline transportation system can consume large energy due to high frictional drop which can be decreased by adding some chemical additives. The effect of these additives is different from type to type and most of them used only for single phase flow. This work focuses on reducing the pump energy requirements of two-phase flow (oil–water) by using three types of additives, anionic surfactant (sodium lignosulfonate (SLS)), cationic surfactant (hexadecyltrimethylammonium bromide (CTAB)) and titanium nanoparticles. An energy analysis in case of varying the type of additives, mixture velocity, and oil fraction are presented.The results showed that the power consumption is reduced significantly and maximum reduction (84%) was gained by using CTAB. The results also confirm that less value of oil fraction is required to phase inversion point after using CTAB, while SLS and nanoparticle cause an increase in the required value of oil fraction.

CFD investigation of the flow characteristics of liquid–solid slurry in a large-diameter horizontal pipe

As an efficient and environmentally friendly method of delivering solid particles, the transport of liquid–solid slurry through a pipeline has attracted considerable attention. However, the flow characteristics of the slurry in large-diameter pipes, especially multi-sized slurry, are far from fully understood. In this study, an Eulerian multiphase model is applied to investigate single- and multi-sized slurry flows in horizontal pipes. The results show that the pipe diameter has a distinct effect on the particle distribution and that the flow properties of multi-sized slurry are different from those of single-sized slurry. In the 900-mm pipe, the variations in the solid concentration and velocity distributions of single-sized slurry are significantly affected by the particle size and efflux concentration but display weak dependence on the mixture velocity. The total particle concentration profile of the multi-sized slurry becomes relatively symmetric in the upper half of the pipe and highly asymmetric in the lower half with increasing mean particle size. The pressure drop per meter of the single-sized slurry first decreases and then increases with increasing particle size, and the pressure drop of the multi-sized slurry containing coarse particles is much higher than that of the single-sized slurry under the same working conditions.

Analysis and numerical modeling of subcooled boiling in energy systems in vertical porous channel

Boiling phenomena are interested in many fields of engineering such as piping and cooling electronic systems. Usually, the phase change through the heat transfer process is avoided as it makes the fluid flow unstable and complex. In the current study, the effect of using porous media in the channel to control the thermo-hydraulic characteristics of the system is studied. To do this aim a steady-state one-dimensional system of equations is solved by numerical method. The gas and liquid Navier–Stokes equations coupled with energy equations are solved simultaneously. The developed method validated with a well-known benchmark problem and the comparison shows a good agreement. The results show that Sauter bubble diameter, forces on the cross-sectional area of fluid, Froude number, fluid wall forces, velocity of mixture, Reynolds number of vapor, fluid velocity, square root of Froude number divided by Weber number, base volume fraction, vapor volume portion, maximum vapor volume portion, critical vapor volume fraction decrease by an increase in Darcy forces, while mean root square of the applied force over the cross section of fluid and heat transported by thermal radiation increased by an increase in Darcy friction up to 1000. The porous media parameters have negligible effects on Eotvos number, speed of sound, liquid Reynolds number, bubble departure frequency, convection heat transfer coefficient, and critical pipe diameter.

CFD Investigation of Parameters Affecting Oil-Water Stratified Flow in a Channel

Stratified flow is a common occurrence for various internal flow based industrial multiphase flow patterns. This involves fully or partially well-defined interface which continuously evolve with space and time. Hence stratified flow analysis essentially involves proper interface capturing approach. The present work focuses on the numerical analysis of oil-water stratified pattern using the Coupled level set and volume of fluid method (CLSVOF) in ANSYS Fluent in a two-dimensional channel. The work involves predicting the effect of density ratio, kinematic viscosity and surface tension coefficient on the mixture velocity and total pressure changes. At outset, the final conclusions may be gainfully employed in oil transportation pipeline, chemical industries and in pipeline flow control administration, etc.

The Performance Characteristics of Electromagnetic Flowmeter in Vertical Low-Velocity Oil-Water Two-Phase Flow

Since the responses of the electromagnetic flowmeter (EMF) can be affected by the flow characteristics, the combination of the EMF and the void fraction meter is always necessary for the two-phase flow measurement. Combined with a plug-in conductance sensor array (PICSA), the measurement characteristics of the EMF in low-velocity oil-water two-phase flows are investigated in this study. In a low-velocity oil-water flow experiment, the water holdup of the oil-water flows at low velocity is measured by the PICSA. By introducing correction coefficients of the EMF under different flow patterns, the correlations between the EMF responses and the oil holdup are established to measure the water superficial velocity. Finally, the oil superficial velocity is accurately predicted by a drift flux model derived from the liquid holdup and mixture velocity. Satisfactory prediction accuracy for the oil superficial velocity can be achieved without the need to introduce oil velocity measurement as in previous studies.

Влияние физико-химических параметров на сорбционное выделение водорода из многокомпонентных смесей

The results of a study of the physicochemical parameters influence on the evolution of hydrogen from a multicomponent mixture are presented. It is shown that the search for alternative energy sources is currently one of the urgent tasks in various fields of science, industry and ecology. The most promising under the current conditions is the transition to the use of hydrogen fuel. At the same time, hydrogen is used both as a caloric additive to hydrocarbon fuel to reduce the toxicity of combustion products, and for independent use as a fuel. The relevance of the study of the problem of the use of hydrogen is associated with the possibility of obtaining a greater amount of energy than when using a similar amount of gasoline, as well as with its widespread use in the chemical, electronic, pharmaceutical industries, in the automotive industry, metallurgy, etc. The work showed that to obtain pure hydrogen from gas mixtures, mainly three main processes of hydrogen concentration are used: selective filtration through polymer membranes; short cycle adsorption; cryogenic separation. The choice of one or another method of hydrogen evolution depends, as a rule, on economic indicators and technology flexibility. In this case, the most widely used in the production of high-purity hydrogen are adsorption methods, which feature are a high degree of extraction of impurities, as well as low operating costs and comparative ease of implementation. Typical substances associated with hydrogen are nitrogen, carbon monoxide and carbon dioxide, methane. A problem in the adsorption production of hydrogen is also the high selectivity of the sorbents used to the components of mixtures of hydrogen-containing gases associated with hydrogen. Promising materials for these purposes are sorbents with a molecular sieve effect – molecular sieves and carbon molecular sieves of various production, but the choice of a specific material for this task is a very acute analytical task, since the material should have many positive characteristics. The influence of such physicochemical parameters on the process of adsorption of hydrogen from a multicomponent mixture, such as the concentration of production hydrogen, the velocity of the gas mixture in the adsorber, and the pressure at the adsorption stage, is studied.

Experimental investigation on phase inversion point and flow characteristics of heavy crude oil-water flow

The phase inversion point is of great significance for drag reduction in the flow of heavy crude oil. In this study, we used 25-mm inner diameter (ID) stainless steel pipes to investigate the oil-water flow characteristics of four heavy oils at five temperatures (90, 85, 80, 75 and 70 °C). The effects of temperature, velocity, and oil viscosity on the phase inversion point of heavy oil-water flow were studied. The viscosity of the experimental oil ranges from 358 to 4995 mPa·s. The phase inversion model of Yao and Gong (2006) was modified to fit high-viscosity oils. The proposed model was verified with pipe flow experimental data from various heavy oilfields. This study found that the effect of temperature on the phase inversion point of heavy crude oil is almost negligible. The flow pattern with the largest pressure drop during heavy oil-water flow is Int, and the flow patterns with a smaller pressure drop include semi-Anw, Anw, and DAnw. The water content at the inversion point of heavy oil-water flow is mostly between 45% and 70%. As the viscosity increases, the water fraction at the inversion point decreases. A high velocity helps the water maintain a continuous phase. The occurrence of phase inversion requires the mixture velocity to be maintained above a specific value, which should be high enough for the flow pattern to transition to semi-annular flow.

Oil–water flow splitting in eccentric annular T-junction tubes—Experimental and CFD analysis

A novel eccentric annular T-junction tube was designed for oil–water separation. The separation characteristics of the eccentric annular T-junction tube were investigated by performing experiments and numerical analyses. The Eulerian model combined with the standard k-ε turbulence model was used to numerically analyze the flow characteristics. Combining the dynamic separation principle of the T-junction tubes with the shallow pond theory, the eccentric annular T-junctions can achieve better overall separation performance than the regular T-junctions. The experimental results indicated that reducing the degree of mixing of the two-phases at the inlet improved the phase separation in the eccentric annular T-junction tubes. The flow pattern had a larger effect on the separation performance than the mixture velocity. The floating oil tube was beneficial to the oil–water separation, particularly at a low mixture velocity and high oil content. The results can be used for the design and operation of tube separators.

RETRACTED: Behavior assessment, regression analysis and support vector machine (SVM) modeling of waste tire rubberized concrete

Abstract An experimental study was undertaken to assess the properties of rubberized concrete made by recycled tire rubber. Mechanical tests were carried out and the ultrasonic technique was also used to measure the acoustic properties of the rubberized concrete, such as wave velocity, and the relationships between the mechanical properties and pulse velocity for different mixtures were investigated. Then, based on the experimental data, a thorough strength modeling was performed using regression analysis and support-vector machine (SVM) technique. To develop the predictive models for strength behavior of the recycled rubber concrete, a comprehensive regression analyses including ANOVA, t-test and F-test were conducted, and the significance of the influencing variables was determined. Then, several regression models by incorporating different combinations of the variables were developed and compared. Finally, the SVM method as a machine-learning technique was utilized to develop several models by using different kernel functions, optimization algorithms, and hyperparameters optimization to predict the compressive strength of the recycled rubber concrete. The results obtained were compared with those of regression models and it was found that SVM outperforms all the regression models assessed in this study.

On the life and habits of gas-core slugs: characterisation of an intermittent horizontal two-phase flow

Slugs are intermittent structures observed in horizontal co-current gas-liquid two-phase flow. Published data examining horizontal flow indicate the existence of intermittent sub-flow patterns. There is limited work performed on the study of this sub-categorisation. This paper presents a method, exploiting non-intrusive Electrical Capacitance Tomography (ECT) measurements, to assess and to characterise the spatial and temporal features of horizontal gas-oil flow. A logic-based algorithm is proposed to automatically identify and classify flow regimes. This algorithm uses the spatial distribution of the phases, based on measurements of the intrinsic dielectric properties of the fluids. The measurements were performed at the NEL UK national standard multiphase flow loop using a high-speed dual-plane ECT sensor array. The ECT measurements identified intermittent liquid structures with a sustained gas-core in the central region of the pipe cross-section with outer features analogous to those of liquid slugs. Assessment of the frequency and time span of the periodic structures showed that gas-core slugs are, typically, shorter than full slug structures but are more frequent for the same given time period. For both flow structures, the mixture velocity was a determinant factor, with gas-core slugs dominating the flow at higher velocities. The experimental work led to the modification of existing flow pattern transition models. The modified flow regime maps suggested in this study aim to widen the applicability of the results by enabling the prediction of gas-core slug flow for similar experimental and operating conditions. The present work comprises the initial steps towards automatic flow regime identification in multiphase flow metering. Automatic flow regime recognition has the potential to lead to better process control and improved accuracy in production allocation.

X-ray measurements of thin liquid films in gas–liquid pipe flow

This paper presents a method for reconstructing the thickness profile of the thin liquid film being present in steady, fully developed gas–liquid annular pipe flow, taking advantage of nonintrusive X-ray measurements. Experiments have been performed with low liquid loading, annular flows, in a near horizontal pipe system (inclination +2.5°), using a high-density gas (SF6) and Exxsol D60 oil. Special care was taken to ensure the flows were fully developed, and statistically steady. The superficial gas velocity was maintained at a constant value of 10 m/s, while the superficial liquid velocity was varied between 0.5 mm/s and 42 mm/s. The X-ray measurements were supplemented by gamma ray densitometer data and isokinetic data. An explicit mathematical method is presented, whereby the shape and thickness of very thin liquid films can be reconstructed if X-ray images of the flow have been obtained from two independent directions: one with a vertical view of the pipe, and another with a horizontal side view. The method can be straightforwardly applied to cases where the film volume dominates the total volume of droplets suspended in the gas phase. This condition is generally satisfied for the experiments presented in this paper, as verified by isokinetic measurements.Mean liquid hold-up values determined by gamma densitometer are in reasonable agreement with the X-ray results. It is found that the mean film thickness at any position on the pipe wall increases with the superficial liquid velocity. While the film thickness is maximal at the pipe bottom in virtually all experimental cases, its profile exhibits multiple local maxima and minima, with the smallest thickness apparently 20°–30° away from at the pipe top. The presented film reconstruction method is highly sensitive; even at extremely low liquid levels, with a superficial liquid velocity less than 0.01% of the mixture velocity, the film and its thickness profile are clearly detected. An analytical fit for the film profile as a function of perimeter angle and superficial liquid velocity is given. The fit captures the main features of the profile as derived from X-ray measurements, for thin films with maximum thickness less than 5% of the pipe diameter.

Сепарація насіння ріпаку

The issues of purification of rapeseed from heavy weeded seeds have been considered. It has been established that general purpose pneumatic separator separators, which are generally used to cleanse rapeseed seeds, remove significant amounts of weed, mineral and organic impurities, but completely remove heavyseparate seeds such as weeds such as mice, chicken millet, the submarine is fragile and the others fail. It is suggested to cleanse rapeseed from heavy impregnated impurities by throwing it into the air with a mixture of rotating particles, thus using, in addition to the aerodynamic properties during the separation, the gyrating effect and the Magnus effect. The initial flight velocity of the particles of the mixture, the angular and circumferential velocities at which the separation process at the gyratory separator is possible are calculated. The purpose of the article is to determine the basic structural-kinematic parameters of the process of separation of rapeseed on a gyratory separator with rolls located one above the other, in which the lower roll rotates at a speed greater than the upper, namely angular and circumferential speeds of the rolls, the initial speed of departure of seeds, exit and the energy intensity of the separation process. Thus, the studies made it possible to determine the structural-kinematic parameters of the process of separation of rapeseed on a gyratory separator. These parameters are: the initial velocity of the particles after passing through the rollers 3.3 m/s, the angular velocity 1650 1/s, and the circumferential velocity of 1.65 m/s. Experimental studies have established that up to 91.1 % of rapeseed can be separated from the mixture by up to 2 % at the initial 6.6 %, in one pass, ie to obtain conditioned seeds at a productivity of up to 100 kg/h for 0.2 m of roll length.

Turbulent coarse-particle suspension flow: Measurement and modelling

Solid-liquid suspension flows are widely encountered in industrial applications. In many of these flows, the carrier fluid exhibits shear-thinning behaviour and the solids have a broad size distribution. Shear-thinning suspensions can occur in laminar or weakly turbulent regimes due to their high viscosity. This paper presents a DNS-DEM model for weakly turbulent coarse-particle suspension flows. Although our interest is in shear-thinning suspensions, we aim firstly to develop a liquid-solid model in a Newtonian fluid to remove the uncertainty in particle-fluid interaction in non-Newtonian suspensions. Matching experiments were conducted for validation. The predicted mixture velocity and concentration profiles are in good agreement with experiments, and discrepancies are mostly less than 10%. The mean velocity profiles are significantly damped by coarse particles and particle phase generally exhibits a higher fluctuation. This DNS-DEM modelling approach is viable for simulating these flows and will form the basis of future work on shear-thinning suspension flow.

EFFECT OF PIPE INCLINATION ON COARSE-GRAINED PARTICLE-WATER MIXTURES FLOW

The effect of the mixture velocity, solid concentration, and pipe inclination on the coarse-grained particle–water mixtures flow behaviour, concentration distribution, and pressure drops were experimentally studied in horizontal, vertical, and inclined pipes of inner diameter D=100 mm. Graded basalt gravel was used as a solid phase. The local concentration distribution was studied with the application of a gamma-ray densitometer. The study revealed the stratified flow pattern of the coarse particle-water mixture in horizontal and inclined pipes. The particles moved principally close to the pipe invert, and particle saltation becomes the dominant mode of particle conveying for higher and moderate flow velocities. The frictional pressure droops in ascending pipe increases with increasing pipe inclination up to about 30 degrees, then gradually decreases. For the pipe inclination lower than about 30°, the effect of pipe inclination on local concentration distribution was not significant. The in-situ concentration reached higher values in the ascending than in the descending sections.

Experimental and numerical study of air-water flow characteristics in a horizontal duct

The horizontal bubbly two-phase flow is preferably used in various industrial applications because it provides high interfacial areas which enhance the heat and mass transfer. In the present research, the phase distribution of controlled air-water flow in a horizontal acrylic round pipe with 60 mm inside diameter (D) has been investigated experimentally and modeled numerically. The modeled differential pressure and the mixture velocity profile at a distance of 33D from the mixing section (fully developed region) are computed numerically and compared with those obtained experimentally from the two-phase flow system established and maintained at the National Institute of Standards (NIS-Egypt). Furthermore, the numerical and the experimental data have been compared with previous correlations and models. Reasonable quantitative agreement between all data is found. An electronic device based on Arduino Uno board was designed and used with careful data manipulation for measuring the slug bubble velocity. The results point out that the air volume fraction has a maximum value at the upper pipe wall as the gas bubbles tend to migrate to the upper wall. A new correlation was obtained for bubble migration length to the upper pipe wall which is very important in chemical industrial processes and other engineering application.