Drop Flow Research Articles

Modeling of laminar flows of nanofluids between two coaxial cylinders in microfluidic devices

The laminar flow of three immiscible nanofluids between two coaxial cylinders due to a constant pressure drop at the inlet and outlet of the channel is considered. Experimental studies of the flows of different nanofluids through the tubes and channels of microfluidic devices have shown that the measured relationships between the pressure drop and volumetric flow do not correspond to the calculations of the corresponding Poiseuille flows in the same geometry due to tangential momentum transfer during diffuse scattering of nanoparticles on the wall roughness. When the characteristic roughness scale has the same order as the particle size, the scattering becomes significant in both dilute gases and suspensions of nanoparticles. Accordingly, the solution of the problem was obtained with the second order velocity slip boundary conditions at the rough walls. The presence of wall layers with a constant thickness and different viscosities is associated with the repulsion of the nanoparticles from the walls into the core of the flow. At the interfaces between the layers, the continuity conditions for velocities and tangential stresses were accepted. An analytical solution of the system for pressure and velocities of the fluids is obtained. Expressions for volumetric flow and wall stresses are calculated. It is shown that for some sets of model parameters it is possible to obtain a significant increase in the flow rate and decrease in viscous dissipation due to tangential momentum transfer at the walls. The effect could increase the efficiency of various microfluidic systems. The formula for the capillary viscometer in the case of measuring the viscosity of nanofluids was also obtained. The derived analytical solution can be used for validation of numerical codes for more complex flows (transient, turbulent) in similar geometries.

Computational fluid dynamics simulation of multi‐phase flow characteristics in an industrial‐scale randomly packed tower

AbstractA three‐dimensional (3‐D) two‐phase Eulerian–Eulerian‐based computational fluid dynamics (CFD) simulation method coupled with a porous media model was developed in this study to simulate the air–water two‐phase flow in an industrial‐scale randomly packed air cooling tower (RPACT). The authors discussed the effects of gas kinetic energy factor, liquid load, packing materials, and packed bed height on the hydrodynamic performances of the gas–liquid counter‐current flow in the proposed RPACT. The simulation results show that the pressure drop increases with the gas or liquid load increases. Liquid load influences the pressure drop, liquid holdup, and wall film flow rate sensitively. A smaller liquid load, a middle range of gas kinetic energy factor, a relatively greater porous resistance coefficient of packing material, and a higher packed bed height can achieve a more uniform liquid flow distribution in an RPACT. The optimum operating conditions for the present RPACT are determined as gas kinetic energy factor is from 1.76 to 2.11 [(m/s) (kg/m3)0.5], liquid load is in the range of 32.40–67.73 m3/h, and the plastic Cascade ring (filled in the second packing layer) with a height of 10 m. The presented CFD models are useful for engineers to design and optimize the structure and operation conditions of industrial‐scale RPACTs.

Investigation on the macro-meso fatigue damage mechanism of rock joints with multiscale asperities under pre-peak cyclic shear loading

The fatigue damage mechanical behaviours of rock joints under pre-peak cyclic shear loading are one of the key factors affecting the dynamic stability of slopes. In this study, the macro-meso fatigue damage mechanism of rock joints with multiscale asperities, when considerthe influence of the normal stress, shear rate, shear amplitude, first-order asperity angle, number of shear cycles and joint morphology, were investigated using experimental and numerical approaches under a constant normal load (CNL). The laboratory pre-peak cyclic shear experiments on the saw-tooth rock joints with different first-order asperity angles, i.e., 30°, 45° and 60°, and the same second-order asperity angle of 45°, were first conducted under different influence factors mentioned above. Six evolution stages of the shear stress with the shear displacement, i.e., initial nonlinear shear contraction deformation, approximate linear elastic shear dilation deformation, cyclic fatigue damage deformation, plastic deformation of the local compression-shear fracture, full plastic deformation of the stress brittle drop and ideal plastic flow deformation, were obtained. Additionally, the variation rules of the influence factors mentioned above with the peak (and residual) shear strengths and the cumulative shear (and normal) displacements were explored. Subsequently, the PFC2D discrete element method was used for the meso numerical simulations, in which the meso fatigue damage evolution processes of the saw-tooth and wavy rock joints were simulated considering more number of shear cycles. Meanwhile, the change rules of the meso fatigue damage crack number (and energy) with the shear displacement (and the number of cycles), and the distribution characteristics of the meso fatigue damage particles were observed. Based on the good agreement between the macro experimental results and the meso numerical observations, the macro-meso fatigue damage failure modes of rock joints can be generally summarized as three basic types, i.e., compacting – climbing failure mode, climbing – cyclic abrading – extruding – gnawing failure mode and gnawing – sliding failure mode.

Passage of surfactant-laden and particle-laden drops through a contraction

The flow of either particle-laden or surfactant-laden drops through a contraction under an imposed pressure has been investigated in a microfluidic setup. The drop deformation generates surface concentration gradients in adsorbed species, which results in surface tension gradients. Crossing of the contraction is driven by the coupling between the drop flow and surface tension gradients and can result in larger passage times for surfactant-laden drops.

Modeling the behavior of direct current electromagnetic forces acting on a drop of liquid metal during electroslag remelting

The article presents mathematical and computer modeling of the behavior of liquid electrode metal drops during the process of electroslag remelting (ESP) at a constant current source. The study of the effect of electric field created by direct current allowed us to show the deviation of the drop trajectory from the electrode axis. The flow of electrons and drops of the electrode metal are exposed to electromagnetic forces, which leads to their displacement relative to the remelted electrode axis. This effect entails destabilization of the liquid metal bath and crystal heterogeneity. In turn, the use of external influence on the flow of ESR process can make it possible to stabilize the liquid metal bath even with the use of direct current. Centrifugal forces can act as such forces. They can arise when implementing the technology with the consumable electrode rotation around its own axis. To establish the optimal parameters of rotation speed, it is necessary to estimate the magnitude of impact of the magnetic field that occurs during direct current remelting process. The modeling was carried out using the Ansys Fluent 16.0 software package on the example of remelting 12Kh18N10T steel under the flux ANF-6. The algorithm for calculating of Ansys Fluent is based on the finite element method. In this paper, the mathematical apparatus was not changed and was used in its initial form. The method of magnetic induction was used. The database of information about the ongoing process was built on a grid of finite elements with certain, but sufficient level of adequacy and quality. Each element contains information about the model at a given point, specified for this modeling process. We have revealed the change in the trajectory of the electrode metal drop by electric field from the opposite direction along which the drop flows. The average length of the path traversed by liquid metal drop from the mold axis to the inner surface is from 5 to 15 cm. The motion of an electrode metal drop without an external magnetic field was simulated. This simulation made it possible to determine (estimate) the direction of movement of electrode metal drops and the indicator of necessary external force to stabilize the liquid metal bath during ESP process at direct current equal to 0.067 N.

Pressure Drop Method as a Useful Tool for Detecting Rheological Properties of Non-Newtonian Fluids during Flow

The aim of the research was to develop a pressure drop measuring method dedicated to fluids under real flow through a pipeline. The measurement system is a set of appropriately configured flow meter and pressure sensors installed on the pipeline. The pressure drop values detected on the measuring section are sufficient to clearly determine the rheological properties of the fluid. The measuring system used for the tests consisted of a screw pump, two pressure sensors and an electromagnetic flow meter. The length of the measuring section was 4.12 m, and the internal diameter of the pipeline was 0.026 m. To calibrate of the measuring system a glycerol was used. As a model fluid, a 1% water solution of xanthan gum was used and was subjected to the flow at following shear rate conditions: 5, 11, 17, 23, 29, 35, 41, 47, 53, 59, 65 s−1. The obtained raw experimental data included the pressure drop values and flow rate and they created full information about the fluid behavior during flow. According to the momentum balance equation, the rheological parameters of Ostwald de Waele model were estimated. The estimation procedure was carried out with the help of the Marquardt-Levenberg minimisation method. The same solutions simultaneously were tested with the help of a rotational rheometer. The data obtained from the pressure drop method were consistent with the results obtained from the rotational rheometer. The use of the pressure drop allows to determine the rheological properties of the non-newtonian fluids under the process conditions directly in the pipeline. In addition, it is possible to perform full rheological characteristics based on one flow rate under laminar conditions.

Numerical investigation of API 31 cyclone separator for mechanical seal piping plan for rotating machineries

API plan 31 uses a cyclone separator that taps a small portion of discharge line process liquid for mechanical seal cooling process. Despite its simplicity, this piping plan requires comprehensive designing process to ensure its performances (flow rate to mechanical seal and pressure drop) are satisfactory. In this research, API 31 cyclone separator geometrical parameters (length cylinder, conical and vortex finder and radius overflow and underflow) effects onto pressure drop and seal flow rate are investigated using numerical method via ANSYS FLUENT software. It is found that increasing overflow and underflow radius and length of cylinder and conical decrease pressure drop by 15.94%, 24.82%, 20.30% and 11.42% respectively. Increasing vortex finder length meanwhile increases pressure drop by 7.77%. Meanwhile, increasing radius overflow and length of vortex finder increase flow rate to seal by 43.79% and 9.63% respectively. Increasing radius underflow and length of cylinder and conical reduces flow rate to seal by 71.92%, 6.41% and 8.93% respectively. It is also observed that a generalization of a particular cyclone separator geometry is not always applicable as it depends on the cyclone separator base design itself where in this case all geometrical factors are significant to pressure drop and flow to seal.

Dynamic behavior of droplet formation in dripping mode of capillary flow focusing

Experimental study on the liquid dripping in a capillary flow focusing process is performed. Due to the high-speed gas stream that drives the inner liquid co-flowing through an orifice, complex phenomena for the droplet formation in dripping regime can be found as the gas pressure drop and the liquid flow rate change. Periodic dripping mode can produce uniform droplets, and non-periodic ones can result in satellites and droplets of different diameters. The droplet-droplet coalescence in the core of co-flowing gas stream is also obtained. The size of resultant droplets is measured under different values of gas pressure drop and liquid flow rate. It can be seen that the droplet size tends to decrease as the gas pressure drop increases and keeps nearly the same as the liquid flow rate increases. The results also indicate that the dynamic behavior of droplet formation in dripping mode of capillary flow focusing is mainly dominated by the gas pressure drop, and the capillary flow focusing technique can produce droplets with high throughput even in the dripping regime. Cited as: Si, T. Dynamic behavior of droplet formation in dripping mode of capillary flow focusing. Capillarity, 2021, 4(3): 45-49, doi: 10.46690/capi.2021.03.01

Investigation of Single-Phase Flow Characteristics in an Inline Pin-Fins Complex Geometry

In this guess investigation of concerns R113 heat transfer of pressure drop flow in single-phase flow in inline on the square shape of micro-channel of pin-fins own a (5×5 mm2) cross-area segment section via of (5 mm) heightly. Therefore, the inline square micro-channel of pin-fins complex geometry additionally owning (25) numbers of the pin-fins, total pin-fins channel dimension (50 mm × 50 mm). Subsequently. The liquid has (25°C) inlet temperature for the same inlet temperature six mass flow rates were applied, ranging from (0.0025 - 0.01 kg/sec), and heat apply ranged from (40-200 Watts). Guess single-phase heat transfer coefficients, guess liquid temperatures and guess wall temperatures were reported in this investigation.

A facile approach to synthesize SSZ-13 membranes with ultrahigh N2 permeances for efficient N2/CH4 separations

Separation of inert nitrogen from natural gas by membranes is much more energy-saving than cryogenic distillation but very challenging because the size difference of both gas molecules is quite small. Herein, high-quality and N2-selective SSZ-13 membranes on α-alumina tubes were prepared using a novel synthesis approach called seeded-gel synthesis. Seeded-gel synthesis was more convenient and credible than the conventional secondary growth because a seeding step on the substrate was omitted for the former method. The effect of calcination atmosphere on the quality of membranes was also discussed. SSZ-13 membranes had the fewest defects when ozone calcination was used. The predicted values of single-component N2 and CH4 permeances by the Maxwell-Stefan equations agreed well with the experimental ones. The SSZ-13 membrane exhibited ultrahigh N2 permeance of 850 × 10−9 mol m−2 s−1 Pa−1 (equals 2500 GPU) and a high N2/CH4 selectivity of 13.5 at 298 K and 0.303 MPa feed pressure (absolute). Membrane preparation by seeded-gel method had good reproducibility. The effects of temperature, pressure drop and feed flow rate on membrane performances were investigated for N2/CH4 mixture separations. The membrane also displayed good separation performance in N2/CH4 system either at 2.6 MPa feed pressure or under humid conditions. The continuous SSZ-13 thin membranes prepared by the simple seeded-gel synthesis showed great potentials for energy-efficient N2 removal from unconventional gases.

Evaluating voltage drop snapshot and time motor starting study methodologies—An offshore platform case study

This paper presents a comparison between static (Snapshot) and dynamic (Time Study) motor starting study methodologies in terms of buses voltage drop and power flow, using a case study of an offshore platform. For this purpose, the Power Tools for Windows (PTW) software and the real-time digital simulator (RTDS) were used to performing the analysis of the Snapshot and Time-Domain methodologies, respectively. The investigation has focused on differences in the parameter requirements necessary for each methodology, with a special application in a complex isolated system, such as the case of an offshore platform typical composed of synchronous generators and the large induction motors. The advantages and disadvantages of each methodology will be analyzed according to the strict operating and handling requirements of an actual offshore platform. Simulation results demonstrated that a motor starting study in the time domain contributes better information than the static one, even more for this type of particular system. This work reveals the need that selection criterias between the two methodologies must be defined in the IEEE 3002.7–2018 standard and for isolated systems is highly recommended to perform an analysis in the time domain.

Динамические характеристики скорости истечения жидкости из форсунок в струйных газопромывателях целлюлозного производства

It is shown that the modern development of pulp production technology is associated with the development of gas-liquid systems equipment. Such equipment provides the main technological processes of pulp cooking and regeneration of chemical reagents. Furthermore, this equipment, designed to recover chemical reagents and reduce their emissions into the environment, is part of the technological process. The use of scrubbers in pulp production has an advantage over many other industries, since it uses a closed liquor regeneration cycle. Currently, studies of the processes occurring in scrubbers of different types are becoming more numerous and fundamental. This paper is devoted to the development of jet scrubbers. These devices have a number of properties that do not have scrubbers of other types. They do not create resistance to the gas flow in the flue; they have a gravitational property due to ejection. Only jet scrubbers create the necessary conditions for the stability of the gas flow and have a jet effect that allows to significantly increase the efficiency of emissions cleaning. To implement the jet effect and intensify the technological equipment operation it is required to describe transfer processes in jet scrubbers with regard to polydisperse structure of drop flow and features of liquid splitting up into drops by centrifugal-jet nozzles. Scientific works devoted to the problem of realization of the jet effect showed the need to study the dynamics of liquid splitting in centrifugal-jet nozzles, which create a drop-filled jet with a large opening angle. The research purpose is to study the speed of the initial movement of drops in the area immediately after the splitting section of the continuous jet of liquid flowing from the nozzle. A photographic technique with two spark lamps was used for the experiment. At the same time, the distribution of irrigation density was controlled. The results of measuring the distributions of absolute speed of drops and irrigation density were compared with each other and the function of liquid speed distribution in the cross section of the gas-liquid jet of the jet scrubber was determined. Based on the obtained data, a theoretical model was developed to determine the initial speed of drops of centrifugal jet nozzles, an indicator required for the development of new jet scrubbers. The results can be applied to improve the technological processes of pulp production.

Effect of visco-plastic and shear-thickening/thinning characteristics on non-Newtonian flow through a pipe bend

This study investigates the influence of the rheological parameters on the unyielded zone, pressure drop, and secondary flow pattern of non-Newtonian fluid like fresh cement mortar through a pipe bend with different curvatures. The regularized Herschel–Bulkley model is employed in the framework of lattice Boltzmann method to model the effects of the visco-plastic and shear-thickening/thinning characteristics with variations on the yielding stress σ0 and the power-law index n. The sharper curvature, higher power-law index contributes to a smaller and more asymmetric unyielded zone and even vanishes for curvature radius Rc=1D and n = 1.4, as the width and distribution of plug region are governed by the comparison between yielding stress and shear stress. The increased yielding stress and power-law index lead to an increase in the total pressure drop and additional pressure loss; however, their variations with respect to the curvature radius display an opposite trend. The intensity of the helical secondary flow in the elbow, primarily governed by the competition between the centrifugal and viscous force, is reduced to about one quarter when σ0 and n increase from 0 Pa and 0.6 to 50 Pa and 1.4.

Effect of artery curvature on the coronary fractional flow reserve

Understanding the effect of the artery curvature on the pressure drop inside the arteries is of great importance due to the existence of several curved portions inside the coronary arterial system. In this paper, an experimental model is developed to account for the effect of the curvature of the coronary arteries on the pressure drop and Fractional Flow Reserve (FFR). FFR is an index for the evaluation of the functional significance of coronary stenosis and is defined as the ratio of the coronary pressure downstream of the stenosis to its upstream value. To measure the pressure drop and FFR across curved artery models, three-dimensional-printed curved artery models are fabricated and installed in the test section of the experimental rig. For ratios of curvature radius over the artery diameter ranging from 2 to 7, there are a minimum value for the pressure drop and, hence, a corresponding maximum value for FFR at a ratio of approximately 3. For the curved arteries with larger curvature radii, the pressure drop increases, and consequently, FFR decreases with an increase in the radius. The results showed that an accurate evaluation of the pressure drop and FFR inside a curved coronary artery can only be achieved by accounting for the effect of curvature parameters including the curvature angle and radius, such that neglecting the effect of the artery curvature results in an underestimation of the pressure drop by about 25%–35%. The developed equation is able to determine the pressure drop inside a curved coronary artery model noninvasively.

Performance evaluation of industrial large-scale cyclone separator with novel vortex finder

This paper presents an experimental and numerical study on an industrial large-scale tangential-inlet cyclone separator with a novel and easy-to-implement vortex finder. The vortex finder was designed with slots on the side wall to improve cyclone performance. The collection efficiency, pressure drop, and interior flow field were analyzed. The proposed device provides an effective gas flow pathway and a coupled swirl-inertia separation mechanism, which eliminates short circuit flows under the bottom inlet of the slotted vortex finder to reduce the swirling intensity and minimize the flow instability in the separator. The pressure drop was reduced up to 27.9% compared to the conventional separator and the maximal increase in collection efficiency was 5.45%. The results presented here may provide a workable reference regarding the effects of vortex finders on improving flow fields and corresponding performance in industrial large-scale cyclone separators.

Image-based computational fluid dynamics for estimating pressure drop and fractional flow reserve across iliac artery stenosis: A comparison with in-vivo measurements.

Computational Fluid Dynamics (CFD) and time-resolved phase-contrast magnetic resonance imaging (PC-MRI) are potential non-invasive methods for the assessment of the severity of arterial stenoses. Fractional flow reserve (FFR) is the current "gold standard" for determining stenosis severity in the coronary arteries but is an invasive method requiring insertion of a pressure wire. CFD derived FFR (vFFR) is an alternative to traditional catheter derived FFR now available commercially for coronary artery assessment, however, it can potentially be applied to a wider range of vulnerable vessels such as the iliac arteries. In this study CFD simulations are used to assess the ability of vFFR in predicting the stenosis severity in a patient with a stenosis of 77% area reduction (>50% diameter reduction) in the right iliac artery. Variations of vFFR, overall pressure drop and flow split between the vessels were observed by using different boundary conditions. Correlations between boundary condition parameters and resulting flow variables are presented. The study concludes that vFFR has good potential to characterise iliac artery stenotic disease.

The flow and cavitation characteristics of cage-type control valves

Cage-type control valves are widely used in process industries, but cavitation can occur when the valves are used in extreme high-pressure drop and large volume flow rate conditions. In this study, the cage-type control valve with improved valve cages is introduced, and its flow and cavitation characteristics are compared with other cage-type control valves with no dead zones in the regulation process. Two cage numbers and four valve cage structures are studied. Numerical simulations are conducted, and their accuracy is validated using experimental results. Results show that cage-type control valves with valve cage 1 have the maximum flow coefficient and cavitation intensity under the same cage number. Cage-type control valves with valve cage 2 have the minimum flow coefficient but medium cavitation intensity. While cage-type control valves with improved valve cages have a medium flow coefficient but minimum cavitation intensity, and water vapor volume can be reduced by 2–8 times compared with cage-type control valves with the valve cage 2. Furthermore, for cage-type control valves with improved valve cages, the cavitation intensity, and flow coefficient decrease as the cage number and groove height increase.

Optimization of Shell and Tube Condenser for Low Temperature Thermal Desalination Plant

In the current work, attempt for enhancing the heat exchanger of the shell and tube by analyzing the various parameters. The heat exchanger is a device used to transfer heat between at least two fluids. In the different kinds of heat exchangers utilized in various industries, shell and tube heat exchangers are presumably the most adaptable and widely heat exchangers utilized in most industrial areas. Based on the relationship between different parameters such as tube velocity, overall heat transfer coefficient, mass flow rate, and pumping power, analysis is carried out. Results show that the tube velocity increases the overall heat transfer coefficient, total pressure drop and mass flow rate of water, Pumping Power, up to the certain limit and starts to decrease. So that the parameters can be optimized by conducting the experiments based on different input parameters. The parameters which influence the optimal result are researched and recommended.

Effects of surface topography on low Reynolds number droplet/bubble flow through a constricted passage

This paper is an attempt to study the effects of surface topography on the flow of a droplet (or a bubble) in a low Reynolds number flow regime. Multiphase flows through a constricted passage find many interesting applications in chemistry and biology. The main parameters that determine the flow properties such as flow rate and pressure drop and govern the complex multiphase phenomena such as drop coalescence and breakup in a straight channel flow are the viscosity ratio, droplet size, and ratio of the viscous forces to the surface tension forces (denoted by the capillary number). However, in flow through a constricted passage, in addition to the above-mentioned parameters, various other geometric parameters such as constriction ratio, length, shape of the constriction, phase angle, and spacing between the constrictions also start playing an important role. Most of the studies done on the problem of drop flow through a constricted passage have aimed to understand the role of physical parameters, with some studies extending their analysis to understand the variation of one or two geometric parameters. However, no study could be found, which explicitly evaluates the role of surface topography. An attempt has been made to unify the current literature as well as analyze the effect of the geometric parameters by understanding the physics and mechanisms involved. The non-dimensional numbers that govern this problem are then identified using the scaling analysis.

Preparation of the Orange Flavoured “Boba” Ball in Milk Tea and Its Shelf-Life

Boba milk tea is very popular around the world. The “boba” balls in milk tea are usually made of tapioca. Reports on calcium alginate ball encapsulation in fruit-flavoured drinks have rarely been seen. The preparation method for this kind ball was studied. The “boba” balls were obtained by membrane formation on the interface through the addition of calcium chloride fluids into a sodium alginate solution. The operation conditions were studied, including drop height, flow velocity, sodium alginate and calcium chloride solution concentration. The diameter, mechanical strength, loading ratio and encapsulation rate of the “boba” balls are discussed. The optimized preparation conditions were as follows: the diameter of adding tube was 8 mm, the drop height was 25 cm, the drop flow rate was 60 mL/min, 1.0% sodium alginate, 1.0% calcium chloride. The prepared “boba” balls were stored at different temperatures. No microorganisms were detected in 90 days, and the sensory quality decreased with storage time. Shelf life was predicted using the Arrhenius equation; when the storage temperature was less than 10 °C, it could be stored for more than 1 year. This preparation technology of “boba” balls has potential for application by milk tea ingredient companies or relevant beverage manufacturing factories.