Drop Behavior Research Articles

Analyses of the effects of channel inclination and rotation on two-phase flow characteristics and pressure drop in a rectangular channel

This paper presents a broad study on gas-liquid flow in inclined channels with rectangular cross section. Experimental data are presented for flow patterns, pressure drop and bubble shape during air-water flows for channel inclinations ranging from −90° to +90° relative to the horizontal plane, and channel axial rotations of 0, 45 and 60°. The test section is 6.0 mm deep, 6.5 mm wide, and 1.2 m long. Experiments were performed for mass velocities ranging from 90 to 760 kg/m2s, corresponding to gas and liquid superficial velocities ranging from 0.09 to 19.4 m/s, and from 0.1 to 0.76 m/s, respectively. Flow patterns were identified based on flow images captured with a high-speed video camera and on the k-means clustering method based on an analysis of pressure drop and optical signals. It was found that duct inclination and channel rotation affect the flow pattern transitions. Moreover, two-phase stratification effects were enhanced by rotating the channels, and the effect of channel rotation on pressure drop was found negligible. On the other hand, the channel inclination affects significantly the pressure drop, whereas gravitational pressure drop parcel was the main parcel of the total pressure drop for most of non-horizontal conditions. The influence of flow pattern transitions on the pressure drop was inferred based on changes of the pressure drop behavior.

Behaviour of sessile drops revealed in ‘car crash’ like impact

This study reports the effect of impact forces on the behaviour of sessile drops when their rapid horizontal displacement is abruptly abrogated. The experimental setup is akin to “car crash” simulation, wherein an object is moved linearly at a predetermined speed and then brought to a complete stop by colliding with a stationary obstacle. The mechanical translator used allowed drops to attain consistent speeds prior to imposition of an impact force. In investigations on binary mixtures comprising glycerol-water (0–100% vv) and polyvinyl alcohol – water (0–10% vv), it was found that the positions as well as the contact angles of the advancing and receding contact lines could alter in tandem. The trajectories from a new phase-space representation for binary mixtures of varied compositions indicated that drop behaviour as a function of contact angle and positional displacement differed between the advancing and receding contact lines in order to dissipate the impact energy applied. The experimental results scaled well with Ohnesorge numbers but not Bond or Weber numbers, indicating a dominant effect played by viscosity. The approach here offers new vistas in viscosity determination of fluids, and in the study of drops subjected to evaporation and freezing conditions.

An experimental study on single drop rising in a low interfacial tension liquid–liquid system

Terminal velocity of liquid drops is one of the key parameters in liquid–liquid extraction column design. It is important in determining residence time, droplet lifetime, and mass transfer rate. In present paper, the rising behavior of a single drops were investigated in a low interfacial tension system by high speed camera. An n-butanol/water system was used as test system. Correlations for terminal velocity were evaluated and compared, both explicitly and implicitly. Moreover, the influence of salt addition in aqueous phase was also studied, including salt concentrations and types. A Weber–Reynolds correlation was derived on the basis of experimental data. Drag coefficient was then calculated and showed a good agreement compared to the correlations in literatures.

Airflow resistance and pressure drop behavior in different conditions of bulk‐stored onion and its dynamic modeling

AbstractThe knowledge of airflow resistance and distribution pattern in a highly porous‐bed commodity like an onion is an important consideration in designing an appropriate ventilation system and for proper selection of fans. The resistance to airflow through bulk onions was determined at the airflow rates range of 0.04–1.0 m3/s.m2, bed depth of 0–100 cm, and scaled and descaled condition of onion at vertical and horizontal position of the onion stock. Three models (Shedd, Hukill and Ives, and Ergun) were investigated to describe pressure drop data of onion bulbs. The pressure drop through bulk onion was increased with an increase in airflow rate and bed depth. Also, pressure drop was 43.5 and 33.3% higher in scaled condition over the descaled condition of bulbs at the vertical and horizontal position of the column, respectively. Shedd model was found to more reliable among three models to describe airflow resistance in bulk of onion bulbs.Practical ApplicationsOnion is perishable vegetable consumed throughout the year. Being a seasonal crop and to fulfill the demand of consumers it must be stored for off seasonal use. Storage of the onion bulbs at ambient and modified environment condition is the most commonly used methods in a tropical climate. But there were huge postharvest losses mainly in the form of physiological weight loss, sprouting, and decay and considerable loss in nutritional qualities. Properly designed aeration, ventilation, and fumigation system is the only way to reduce such losses. Therefore, the understanding of dynamic behavior of applied ventilation and fumigation with its distribution pattern in a highly porous commodity like an onion is a preliminary requirement for the proper design of storage system. Different model based approach to understand flow dynamics could be used in the dimensional design of a storage system in a tropical climate.

Liquid nitrogen flow in helically corrugated pipes with insertion of high-temperature superconducting power transmission cables

The pressure drop behavior of cryogenic flow in corrugated pipes is a critical design parameter for high-temperature superconducting (HTS) power transmission line systems. Most studies on the pressure loss and temperature increase of liquid nitrogen (LN2) flow in annularly corrugated pipes in the literature have focused on pipe geometries. However, the positioning and configuration of the HTS cables in the corrugated shell tube are also of great concern in practical applications. Moreover, helically corrugated pipes are used more frequently than annular pipes for the long-distance deployment of HTS transmission lines. This study investigates the influence of cable insertion and configuration in helically corrugated pipes on the surrounding subcooled LN2 flow, in terms of the pressure loss and temperature profiles. Triple and quadruple cables with diameters of 5 and 8 mm configured in different forms in a Φ40 mm helically corrugated pipe are comparatively studied using a three-dimensional model. Correlations among the equivalent diameter, Nusselt number, and Reynolds number are proposed for predicting the heat transfer of LN2 flow in helically corrugated pipes.

Dynamic Profile Monitoring for Flooding Prognosis in Packed Columns

AbstractIn the chemical industry, real‐time flooding prognosis is a necessity for packed‐column operation because the flooding phenomenon interferes with the performance of production systems. In this work, the profile monitoring technique is utilized to capture the dynamic behavior of pressure drop, which is an important indicator for the flooding phenomenon. In each moving window, the pressure drop signals are described by using an exponential generalized autoregressive conditional heteroskedastic model. The onset of the flooding phenomenon is then indicated by changes in model parameters. Moreover, to efficiently capture the process change, a nonparametric approach is utilized to establish a statistical control chart. Experimental and comparison results show the advantages of the proposed method.

Normal and oblique droplet impingement dynamics on moving dry walls.

Industrial applications that depend on jetting-based technology, such as painting or additive layered manufacturing, involve sequential deposition of droplets onto a moving surface. Spreading and receding dynamics of these impinging drops depend on the momentum transferred by the moving wall to the droplet liquid, which in turn governs the geometric precision and surface finish of the printed outcome. In this work, the impingement dynamics of microdroplets on a flat, smooth, and moving solid surface is computed using a phase-field-based lattice Boltzmann method. Moreover, the motion of the three-phase moving contact line is captured using a geometry-based contact angle formulation. First, we investigate the influence of various process and materials parameters such as wall velocity, droplet viscosity, surface tension, and wettability on the impact behavior of drops. The surface wettability significantly affects the droplet morphology; an elongated tail like structure forms on the rear end of the droplet which becomes sharper as the moving surface becomes more hydrophobic. Furthermore, we examine the underlying flow physics of the symmetry breaking during the spreading and recoiling phases. For a given contact angle, an increase in wall velocity is found to expedite droplet spreading. In addition, for the first time we explore the oblique droplet impingement dynamics on moving dry walls in this work. It is observed that wall momentum affects the structure of the leading edge during the inline impact situations, whereas the moving surface controls the delay in flow reversal inside the droplet for opposing impact scenarios.

Shape oscillation of a sessile drop under the effect of high frequency amplitude-modulated magnetic field

The shape oscillation behavior of a sessile mercury drop under the effect of high frequency amplitude-modulated magnetic field (AMMF) is investigated experimentally. It is an effective method to excite the shape oscillation of a liquid metal sessile drop. The high frequency AMMF is generated by a solenoid inductor fed by a specially designed alternating electric current. The surface contour of the sessile drop is observed by a digital camera. At a given modulation frequency and magnetic flux density of the high frequency AMMF, the edge deformations of the drop with azimuthal wave numbers (modes n = 2, 3, 4, 5, 6) were excited. A stability diagram of the shape oscillation of the drop is obtained by analysis of the experimental data. It turns out that when the modulation frequency and magnetic flux density reach a point in the stability diagram which can trigger shape oscillations of the drop of several modes, the shape oscillation of different modes may be seen alternatively.

On the size-dependent behavior of drop contact angle in wettability alteration of reservoir rocks to preferentially gas wetting using nanofluid

Wettability alteration of rock surfaces toward gas wetting have been recognized as a practical approach for maximizing the production from the gas condensate reservoirs. Most of the reported work in this area applied the so called sessile drop contact angle measurement technique to examine the change in wetting state of a surface. However, the size-dependent wetting behavior of drop which could affect the exact determination of wettability and wettability changes was not well discussed in the previous studies. Therefore, in this work, the size dependency of contact angle for four different liquid-solid-gas systems; i.e., water-calcite-air, water-treated calcite-air (nanofluid treated calcite), oil-calcite-air, and oil-treated calcite-air, were investigated. To provide a better understanding of the displacement of reservoir gas and liquid following the wettability alteration process, a dynamic contact angle measurement approach was designed. The effect of drop size and surface roughness on the wetting state of calcite rock samples at the initial and altered condition of wettability was then investigated through experimental and modeling approaches. The surface roughness of calcite samples and drop contact angles were determined using Atomic Force Microscopy and Low bond axisymmetric drop shape analysis method, respectively. Analysis of results demonstrated that size dependency of contact angle imposed an error as high as 22.2° on the measurement of achieved wettability alteration in the case of water-calcite/treated calcite-air system. On the basis of calculated pseudo-line tension from the modeling schemes, it was also revealed that the surface roughness had a significant impact on wettability measurements. Both low and high pseudo-line tension values of order 10−9 and 10−6 N, respectively, could dictate some level of errors in contact angle measurements. However, high values were supposed to have a considerable degree of importance in gas condensate applications. The results of this study could provide a better understanding of the contact angle measurement experiments for petroleum engineers to evaluate the wettability alteration schemes.

Pulsed Electric Current V-Bending Springback of AZ31B Magnesium Alloy Sheets

The springback of AZ31B magnesium alloy sheets subjected to pulsed electric current-assisted V-bending tests was investigated. To study the effect of pulsed electric current on the bending-dominated deformation behavior of magnesium alloy sheets, the stress–strain responses from the electric current-assisted uniaxial tension and compression tests were experimentally measured. The stress–strain curves under pulsed electric current showed an instantaneous stress drop under the application of the electric pulse. The ductility was enhanced owing to the application of electric current. The electrically assisted V-bending tests helped reduce the springback compared with conventional room-temperature V-bending tests, and the magnitude of the springback reduction increased with the increase in the electric current density. A thermo-mechanical-electrical finite element model for the electrically assisted V-bending test was developed. To consider the Joule heating effect, temperature-dependent hardening and a yield function with strength differential were implemented for simulating the AZ31B sheet. The simulations could reproduce the experimental flow stress curves of the uniaxial tension/compression tests under pulsed electric current, characterized by an instantaneous stress drop and subsequent transient hardening behavior. The simulated springback profiles were in good agreement with the measured V-bending test data, thus validating the proposed finite element modeling procedure.

Investigation of the Pressure Drop Across Packed Beds of Spherical Beads: Comparison of Empirical Models With Pore-Level Computational Fluid Dynamics Simulations

This study uses novel methods, combining discrete element method (DEM) simulations for packing and computational fluid dynamics (CFD) modeling of fluid flow, to simulate the pressure drop across rigid, randomly packed beds of spheres ranging from 1 to 3 mm in diameter, with porosities between 0.34 and 0.45. This modeling approach enables the combined effect of void fraction and particle size to be studied in more depth than that has been previously possible and is used to give insight into the ability of the well-established Ergun equation to predict the pressure drop behavior. The resulting predictions for pressure drop as a function of superficial velocity were processed to yield coefficients α and β in the Ergun equation and were found to be in keeping with equivalent data in the literature. Although the scatter in α with structural variations was very small, the scatter in β was large (±20%), leading to inaccuracies when used to predict pressure drop data at velocities beyond the Darcy regime. Evaluation of the packed particle structures showed that regions of poor packing, in samples with high porosity and large particle sizes, lead to lower β values. The findings bring strong support to the belief that a generalized model, such as that by Ergun, cannot yield a unique value for β, even for identical spheres.

Effect of inserted HTS power transmission cables on friction loss in corrugated pipes

Pressure drop behavior of cryogenic flow in corrugated pipes is one of the most important design parameters for high temperature superconducting (HTS) power transmission line systems. Most studies on pressure loss and temperature rise study the liquid nitrogen flow in annularly corrugated pipes focused on the pipe geometries. However, the positioning and configuration of the HTS cables in the corrugated shell tube are of great concern in practical application. In addition, helically corrugated pipes are more popular than annular ones for long distance deployment of HTS transmission lines. This paper focuses on the influence of inserted cable configuration in helically corrugated pipes on the surrounding subcooled liquid nitrogen flow. Triple and quadruple cables with diameters of 5 mm and 8 mm configured in different forms in a Φ40 mm helically corrugated pipe are comparatively studied with a 3D model. Results show that the Darcy friction factor is related to the pitch of the cables. The gaps and the cable size will directly influence the level of friction loss in the pipe.

Mechanical and fracture properties of concrete containing treated and untreated recycled concrete aggregates

Abstract This paper presents the results of an experimental research into concrete produced by replacing the natural aggregates with treated and untreated coarse Recycled Concrete Aggregates (RCA). The compressive and flexural strength as well as fracture energy tests were carried out. In order to determine the efficiency of treated and untreated RCA on fracture properties of concrete, single edge notched beam, semi-circular bend, and edge notched disc bend geometries were employed. The results indicated that although Treated Recycled Concrete Aggregates (TRCA) might push to more effort in production process, there are significant benefits in using TRCA in concrete mixtures. Denser microstructure and stronger interfacial transition zone in TRCA enhances crack resistance in fracture processing zone of concrete compared to RCA. In addition, the study showed that incorporating RCA and TRCA leads to a more intensive drop and brittle behavior in post-cracking extension. Furthermore, comparison of fracture toughness in different modes indicated that the RCA and TRCA are more prone to tensile opening mode compared to shear (in-plane and out-plane) modes.

Performance evaluation of a new micro gas cyclone using simulation and experimental studies to capture indoor fine particles

The aim of this study was evaluating a micro gas cyclone performance with a body diameter of 10 mm to collect indoor fine particles. The design of a cyclone requires minimizing the pressure drop and maximizing the separation efficiency. Overall and grade efficiencies, pressure drops, and cut sizes have been investigated through a theoretical model, simulation, and experimental studies. The experimental part was conducted using an Electrical Low-Pressure Impactor (ELPI) device to measure particle concentration for flow rates of 10–13.3 (l/min). In order to study the pressure drop and velocity behavior for different flow rates, COMSOL software was utilized. The obtained results from experimental work have met the theoretical and simulation outcomes adequately. It has been confirmed by all the obtained results that by increasing the flow rate and subsequently inlet velocity, the particle collection efficiency and pressure drop increase while the cut size decreases.

Presentation of frictional behavior of micro helical tubes with various geometries and related empirical correlation; an experimental study

This study provides an experimental investigation on the pressure drop and frictional behavior of air flow through helical microtubes with circle, triangle, square and pentagon geometries with different coil diameters. Pressure drop versus flow rate (1, 2, 3, 4 and 5 l/min) has been experimentally investigated for all helical coils. The effect of flow rate, coil diameter and geometry are examined on the pressure drop and friction factor. More applicable and new friction factor correlations in laminar flow regime have been developed in terms of fraction of internal diameter (din) to coil diameter (din/Dc) and the Reynolds number (Re) for all geometries. The comparison between the estimated values of new friction factor correlation and the calculated values of friction factor from general equation showed that the maximum relative errors for circle, triangle, square and pentagon geometries are respectively 9.7%, 14%, 9.47% and 6.4%. Therefore, the correlations can effectively predict the present experimental data.

Experimental investigation of oil drops behavior in dispersed oil-water two-phase flow within a centrifugal pump impeller

In oil production, one important artificial lift method involves the commonly used centrifugal pump. The use of this pump in the petroleum industry, however, is hindered by some unfavorable operational conditions. Operating centrifugal pumps with gas and viscous fluids, such as dispersions, may lead to a degradation of their performance. The objective of this paper is to analyze oil-water dispersions in a pump impeller, in order to investigate the behavior of oil drops, which may influence the pump working. Thus, experiments were carried out at different pump rotation speeds and water flow rates. Researchers used a facility with a pump prototype that enabled them to visualize the flow in all the impeller channels. Images, captured through a high-speed camera, revealed a unique flow pattern of oil drops dispersed in water. Processed with computer codes, the images indicated that the oil drops were, in general, spherical or elliptical, and only a few broke up in the impeller. The interaction with water caused the oil drops to rotate, deform, and deviate, thus moving in random paths. Size distributions suggested that the drops became smaller as the impeller rotation speed and water flow rate increased. This behavior was due to the turbulence-induced shear stress and kinetic energy. The oil drops’ equivalent diameters ranged from 0.1 to 6.0 mm; velocities took values measurable by units of m/s; accelerations reached hundreds of m/s2; and forces had magnitudes of thousandths of N. Researchers observed a clear dependence between flow conditions and drop dynamics. Carried by the water flow, the oil drops on the suction blade moved faster than those on the pressure blade of a channel. The drop dynamics were significantly influenced by the presence of adverse pressure gradients and water velocity fields.

Optimal operation of a dividing wall column using an enhanced active vapor distributor

During dividing wall column (DWC) operation, the liquid and vapor split ratios must be actively tuned to maximize the energy-saving potential for the desired separation process. However, no active vapor split control devices have been reported to be installed in existing industrial DWCs. Therefore, the enhanced active vapor distributor (EAVD®) has been developed to overcome the existing problems in controlling the vapor split ratio in DWCs. In the EAVD, the opening area for the vapor flow is tuned by altering the liquid level of a modified chimney tray. The liquid level can be adjusted by operating the control valve in each section of the DWC. In this study, a laboratory-scale EAVD was tested under a number of experimental conditions to validate its reliability for controlling the vapor flow associated with its pressure drop behavior in a DWC. The results showed that the use of an EAVD allowed the pressure drop differences in the above mass transfer section to be compensated, and the desired vapor split ratio could be achieved during operation. Furthermore, modification of the existing DWCs can be easily accomplished by substituting the current chimney tray with the EAVD, improving the operability and flexibility of DWCs.

Experimental study of the parameters for stable drop-on-demand inkjet performance

We present an experimental study of drop-on-demand inkjet behavior, with particular emphasis on the thresholds for drop generation and formation of satellite drops, using inks covering a range of fluid properties. Drop behavior can be represented as a “phase diagram” in a parameter space bound by the dimensionless number Z (the inverse of the Ohnesorge number) and the Weber number of the fluid jet prior to drop formation, Wej. Stable drop generation is found to be bounded by a parallelogram with minimum and maximum values of 2 < Wej < 25. The lower bound indicates where capillary forces prevent drop ejection, and the upper bound indicates the onset of satellite drop formation. For Z < 50, the critical Wej for drop ejection increases with decreasing Z because of the contribution of viscous dissipation during drop formation. This requires an increase in the voltage required to drive the piezoelectric actuator until at Z ≈ 0.3 no drop ejection is possible. With Z > 4, the value of Wej at which satellite drops form decreases with increasing Z until at very large values of Z single drops can no longer form at any Wej. However, despite the large range of fluid properties over which stable drops can form, the need for a large range of both Z and Wej limits the region of practical ink design to the approximate range of 2 < Z < 20. These results are shown to be compatible with current models of the drop formation process reported in the literature.

Charged Satellite Drop Avoidance in Electrohydrodynamic Dripping.

The quality of electrohydrodynamic jet (e-jet) printing is crucially influenced by the satellite drop formed when the primary drop detaches from the meniscus. If the satellite drop falls onto the substrate, the patterns on the substrate will be contaminated. The electric charge carried by the satellite drop leads to more complex satellite/meniscus interaction than that in traditional inkjet printing. Here, we numerically study the formation and flight behavior of the charged satellite drop. This paper discovered that the charge relaxation time (CRT) of the liquid determines the electric repulsion force between the satellite drop and meniscus. The satellite drop will merge with the meniscus at long CRT, and fail to merge and deteriorate the printing quality at short CRT. The simulations are adopted to discover the mechanism of generation and flight behavior of charged satellite drops. The results show that the critical CRT decreases with the dielectric constant of the liquid and the supplied flow rate. Namely, for small dielectric constant and fixed CRT, the satellite drop is less likely to merge with the meniscus, and for high flow rate, the satellite drop is prone to merge with the meniscus due to the delay of necking thread breakup. These results will help to choose appropriate parameters to avoid the satellite drop from falling onto the substrate.

Drop behaviors of a plate-type fuel assembly used in research reactor for a drop accident

The drop behaviors of a plate-type fuel assembly for a research reactor are investigated through a dropping test in water. In the test, a full-scale dummy fuel assembly and a water tank of 5 m high are utilized. Special devices are designed to minimize collisions between the equipment and test specimen and to induce a vertical drop of the fuel assembly. Falling velocities with respect to the drop heights are measured using a high-speed camera, and are determined through the image processing of the photographs. Using the analytical equation and experimental data, the drag coefficient and added mass of the plate-type fuel assembly which highly influence the falling behavior are estimated. The empirical formula with suitable drag coefficient and added mass is presented to predict the impact velocity of fuel assembly during a drop accident. The impact velocity can be utilized as an input variable in the finite element analysis of an impact.