Dynamics of Droplets Impacting on Thin Heated Strips

1988 ◽  
Vol 110 (1) ◽  
pp. 214-220 ◽  
Author(s):  
S. C. Yao ◽  
L. E. Hochreiter ◽  
K. Y. Cai
Keyword(s):  
High Speed ◽  
Nuclear Reactor ◽  
Droplet Diameter ◽  
Volume Ratio ◽  
Two Phase ◽  
Steel Strips ◽  
Mean Diameter ◽  
Size Groups ◽  
Leidenfrost Temperature ◽  
The Mean

Experiments were conducted with water droplets impacting on the edge of thin steel strips that were heated to beyond the Leidenfrost temperature. High-speed movies were taken and analyzed and showed that the shattered droplets were generally bimodal in size distribution. The volume ratio of these two size groups of generated droplets, the mean diameter of droplets, and the ejection angles and velocities of shattered droplets are shown as a function of incoming droplet Weber number, the ratio of incoming droplet diameter to strip thickness, and the offset of the droplet relative to the strip. The data are presented in nondimensional form and correlations are provided for the mean diameter of the shattered droplets. The theoretical limiting conditions of a droplet impacting normally to a large plate and cutting by a strip of zero thickness are analyzed. The present results are compared with those of the limiting conditions. The application to a nuclear reactor spacer grid behavior during two-phase dispersed flow is discussed.

Atomization of Liquid by Two-Phase Gas-Liquid Flow Through a Nozzle

2000 ◽  
Author(s):  
M. Lörcher ◽  
D. Mewes
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Droplet Diameter ◽  
Critical Mass ◽  
Bubbly Flow ◽  
Plug Flow ◽  
Volumetric Flow Rate ◽  
Two Phase ◽  
Equal Distribution ◽  
The Mean

Abstract A liquid or a suspension is divided into small droplets by atomization. The mean goal is either the equal distribution of the droplets, or the generation of large surface areas of the liquid phase in order to increase heat- and mass-transfer. In two-phase atomization the spatial and time distribution of the mean droplet diameter of the spray depend on the total pressure upstream of the nozzle, the volumetric flow rate of the liquid and the gas, as well as on the flow regime in the nozzle. Thus the radial and axial profile of the void fraction inside the nozzle are measured with an electrical measurement technique. In addition, the flow in the nozzle is visualized by a high-speed camera. Three flow regimes are identified. These are bubbly flow, plug flow, and annular flow. At the smallest cross section of the nozzle critical mass flow is observed. A literature review on models to calculate the critical mass flow is given. The calculated and the measured mass flow rates are compared.

Unsteady Two-Phase Flow Analysis on Water Retarder Performance Using Sliding Mesh Technique and VOF Method

2015 ◽  
Author(s):  
Wonju Lee ◽  
Nahmkeon Hur
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Volume Ratio ◽  
Working Fluid ◽  
Water Volume ◽  
Phase Flow ◽  
Two Phase ◽  
Sliding Mesh ◽  
Mesh Technique

Hydraulic retarders are used as auxiliary brake system in heavy vehicles and high speed trains. A hydraulic retarder is composed of two parts, a rotor and a stator. When the system is activated, the working fluid is injected into the wheel and circulates between the rotor and stator vanes using the resisting torque of the stator to slow down the vehicle. The purpose of this research is to investigate a water retarder system and the details of flow characteristics of the water, and to investigate the device performance as well. The water retarder is basically composed of a rotor and a stator. In the present research, the rotor rotating speed is fixed at 2000 rpm. Since the performance characteristic of the water retarder is dependent upon the water volume ratio, different volume ratios have been investigated. In this paper water retarder simulations are carried out using CFD using sliding mesh technique. To capture the unsteady effects, the cases have been solved as transient simulations using standard k-ε turbulence model. The simulations have been solved as two phase flow, water and air. The results are compared for different water volume ratios. The result show that the air particles are accumulated in the center of the wheels forming a tube shape (doughnut shape) and water particles are at the outside, wrapping the air particles. In addition, torque values are sensitively dependent upon water volume fraction.

Behavior of Bubbles Separated by a Cross-Shaped Obstacle Placed in a Circular Flow Channel

2017 ◽  
Author(s):  
Kazuyuki Takase ◽  
Hiep H. Nguyen ◽  
Gaku Takase ◽  
Yoshihisa Hiraki
Keyword(s):  
High Speed ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Flow Direction ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Wire Mesh ◽  
Phase Flow ◽  
Two Phase ◽  
Validation Data

Clarifying two-phase flow characteristics in a nuclear reactor core is important in particular to enhance the thermo-fluid safety of nuclear reactors. Moreover, bubbly flow data in subchannels with spacers are needed as validation data for current CFD codes like a direct two-phase flow analysis code. In order to investigate the spacer effect on the bubbly flow behavior in a subchannel of the nuclear reactor, bubble dynamics around the simply simulated spacer was visually observed by a high speed camera. Furthermore, the void fraction and interfacial velocity distributions just behind the simulated spacer were measured quantitatively by using a wire-mesh sensor system with three wire-layers in the flow direction. From the present study, bubble separation behavior dependence upon the spacer shape was clarified.

Image Based Bubbly Flow Feature Identification Using Deep Learning

2021 ◽  
Author(s):  
Takashi Furuhashi ◽  
Takuro Sasaki ◽  
Shuichiro Miwa
Keyword(s):  
High Speed ◽  
Nuclear Reactor ◽  
Two Phase Flow ◽  
Fluid Model ◽  
Bubbly Flow ◽  
Interfacial Area ◽  
Liquid Interface ◽  
Phase Flow ◽  
Two Phase ◽  
Interfacial Area Concentration

Abstract Gas-liquid two-phase flow has high potential in heat transfer and mixing capabilities, and therefore it is utilized in various technologies such as nuclear reactor and chemical plants. There are several flow regimes since the gas-liquid interface transforms constantly. For the sake of safety and optimization in operating plants, it is crucial to understand the behavior of the gas-liquid interface. We have focused on extracting the bubble features in the bubbly flow by filming the bubbly flow with a high-speed camera and training convolutional neural network (CNN) for feature extraction. The assumption made was bubbles in the bubbly flow being ellipsoids. Since void fraction and interfacial area concentration are one of the geometric parameters in the two-phase flow models, like two-fluid model, it becomes possible to evaluate the flow field of the two-phase flow quickly and quantitively by calculating these parameters from the extracted features. We have compared two-phase flow parameters with the conventional object detection method using bounding boxes, and the new ellipse fitting method to identify the best region proposal shape. As a result, the conventional method showed higher accuracy in extracting bubble features under our flow conditions.

Template Polymerization of Acrylamide in Ethanol/Water Mixtures

2016 ◽  
Vol 69 (10) ◽  
pp. 1149
Author(s):  
Jie Dong ◽  
Xiang'an Yue ◽  
Jie He
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Monomer Concentration ◽  
Volume Ratio ◽  
Polyvinyl Butyral ◽  
Template Polymerization ◽  
Transmission Electron ◽  
Mean Diameter ◽  
The Mean ◽  
Concentration Threshold

Irregular hollow polyacrylamide (PAAm) particles with the mean diameter varying from 125 to 413 nm were prepared in ethanol/water mixtures by template polymerization using polyvinyl butyral (PVB) microspheres as the template and 2,2′-azobisisobutyronitrile (AIBN) as the initiator. The influence of the solvent composition, monomer concentration, and template concentration on the yield, molecular weight, and particle size of PAAm were investigated. Decreasing the volume ratio of ethanol to water or increasing the monomer concentration can increase the yield, molecular weight, and particle size of PAAm. The monomer concentration threshold for coagulum-free polymerization is 6 % (w/v). Although the PVB concentration does not show significant influence on the yield, molecular weight, and particle size of PAAm, keeping the PVB concentration between 0.1 and 0.3 % (w/v) is the key to forming PVB microspheres. The formation of PAAm particles is discussed based on transmission electron microscopy results, it is concluded that the shrinkage and dehydration on hollow PAAm particles, which is caused by the removal of templates, results in the formation of micro-sized irregular hollow PAAm particles.

scholarly journals Application of SIM, HSPIV, BTM, and BIV Techniques for Evaluations of a Two-Phase Air–Water Chute Aerator Flow

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1590
Author(s):  
James Yang ◽  
Chang Lin ◽  
Ming-Jer Kao ◽  
Penghua Teng ◽  
Rajkumar V. Raikar
Keyword(s):  
Probability Distribution ◽  
High Speed ◽  
Transverse Velocity ◽  
Image Method ◽  
Air Bubbles ◽  
Two Phase ◽  
Mean Velocity ◽  
Water Stream ◽  
Image Velocimetry ◽  
The Mean

Four image-based techniques—i.e., shadowgraphic image method (SIM), high-speed particle image velocimetry (HSPIV), bubble tracking method (BTM), and bubble image velocimetry (BIV)—are employed to investigate an aerator flow on a chute with a 17° inclination angle. The study focuses on their applications to the following issues: (1) to explore the characteristic positions of three water–air interfaces; (2) to interpret the evolution process of air bubbles shed from the wedged tip of the air cavity; (3) to identify the probabilistic means for characteristic positions near the fluctuating free surface; (4) to explore the probability distribution of intermittent appearance of air bubbles in the flow; (5) to obtain the mean streamwise and transverse velocity distributions of the water stream; (6) to acquire velocity fields, both instantaneous and mean, of air bubbles; (7) to construct a two-phase mean velocity field of both water flow and air-bubbles; and (8) to correlate the relationship among the probability distribution of air bubbles, the mean streamwise and transverse velocity profiles of air bubbles, and water stream. The combination of these techniques contributes to a better understanding of two-phase flow characteristics of the chute aerator.

An investigation into oil—gas two-phase leakage flow through micro gaps in oil-injected compressors

2010 ◽  
Vol 224 (4) ◽  
pp. 925-933
Author(s):  
D Xin ◽  
J Feng ◽  
X Jia ◽  
X Peng
Keyword(s):  
High Speed ◽  
Critical Pressure ◽  
Pressure Ratio ◽  
Volume Ratio ◽  
Flow Patterns ◽  
Leakage Flow ◽  
Two Phase ◽  
Gas Leakage ◽  
Flow Through ◽  
Oil Gas

This article presents the investigation on the oil—gas two-phase leakage flow through the micro gaps in oil-injected compressors and provides a new way of investigating the internal leakage process in the compressors. The oil—gas leakage rates were measured through the micro gaps of various gap sizes, the volume ratios of oil to gas, and pressure differences/ratios; and the flow patterns reflecting the flow characteristics were observed by using a high-speed video. The experimental results showed that the leakage flowrate was significantly related to the flow patterns in the gap, which were similar to those found in the existing literature and agreed well with the predicted ones by the Weber number. The gas leakage flowrate through the gap increased rapidly with the increased pressure ratio until the pressure ratio reached the critical pressure ratio, which ranged from 1.8 to 2.7. At the critical pressure ratio, the flow pattern transition from churn flow to annular flow occurred, resulting in gas leakage driven by a different sealing mechanism. As the volume ratio of oil to gas increased by 0.5 per cent, the gas leakage flowrate decreased by 77 per cent.

On high-speed impingement of cylindrical droplets upon solid wall considering cavitation effects

2018 ◽  
Vol 857 ◽  
pp. 851-877 ◽  
Author(s):  
Wangxia Wu ◽  
Gaoming Xiang ◽  
Bing Wang
Keyword(s):  
Phase Transition ◽  
Shock Wave ◽  
High Speed ◽  
Solid Wall ◽  
Fluid Model ◽  
Droplet Diameter ◽  
Droplet Surface ◽  
Rarefaction Waves ◽  
Two Phase ◽  
The Impact

The high-speed impingement of droplets on a wall occurs widely in nature and industry. However, there is limited research available on the physical mechanism of the complicated flow phenomena during impact. In this study, a simplified multi-component compressible two-phase fluid model, coupled with the phase-transition procedure, is employed to solve the two-phase hydrodynamics system for high-speed cylindrical droplet impaction on a solid wall. The threshold conditions of the thermodynamic parameters of the fluid are established to numerically model the initiation of phase transition. The inception of cavitation inside the high-speed cylindrical droplets impacting on the solid wall can thus be captured. The morphology and dynamic characteristics of the high-speed droplet impingement process are analysed qualitatively and quantitatively, after the mathematical models and numerical procedures are carefully verified and validated. It was found that a confined curved shock wave is generated when the high-speed cylindrical droplet impacts the wall and this shock wave is reflected by the curved droplet surface. A series of rarefaction waves focus at a position at a distance of one third of the droplet diameter away from the top pole due to the curved surface reflection. This focusing zone is identified as the cavity because the local liquid state satisfies the condition for the inception of cavitation. Moreover, the subsequent evolution of the cavitation zone is demonstrated and the effects of the impact speed, ranging from $50$ to $200~\text{m}~\text{s}^{-1}$ , on the deformation of the cylindrical droplet and the further evolution of the cavitation were studied. The focusing position, where the cavitation core is located, is independent of the initial impaction speed. However, the cavity zone is enlarged and the stronger collapsing wave is induced as the impaction speed increases.

Isolation and Purification of Aloin a and Aloin B by High-Speed Counter-Current Chromatography

2013 ◽  
Vol 634-638 ◽  
pp. 1241-1246 ◽  
Author(s):  
Shi Rong Tang ◽  
Shang Long Chen ◽  
Sang Sang Lu ◽  
Xin Yang Hu
Keyword(s):  
High Speed ◽  
High Performance ◽  
Volume Ratio ◽  
Solvent System ◽  
Two Phase ◽  
Lower Phase ◽  
Isolation And Purification ◽  
Counter Current ◽  
Chloroform Methanol ◽  
Crude Methanol Extract

High-speed counter-current chromatography(HSCCC) was successfully used for isolation and purification of Aloin A and Aloin B from the crude methanol extract of Aloe with a two-phase solvent system composed of chloroform–methanol–n-butylalcohol-water at an optimized volume ratio of 4:3:1:2 (v/v/v/v). The lower phase was used as the mobile phase in the head to tail elution mode. The preparative HSCCC separation was performed on 180 mg of the crude extract yielding pure Aloin A(18mg) and Aloin B(16mg) at purities of 95.2% and 96.8%, respectively, as determined by high performance liquid chromatography (HPLC). HSCCC is a powerful technique for isolation and separation of chemical composition from aloe.

Isolation and Purification of Ginkgo Flavonoids by High-Speed Counter-Current Chromatography

2013 ◽  
Vol 781-784 ◽  
pp. 741-745
Author(s):  
Sang Sang Lu ◽  
Hui Song ◽  
Jing Zhi Miao ◽  
Shi Rong Tang
Keyword(s):  
Mobile Phase ◽  
High Speed ◽  
High Performance ◽  
Leaf Extract ◽  
Volume Ratio ◽  
Solvent System ◽  
Two Phase ◽  
Lower Phase ◽  
Isolation And Purification ◽  
Counter Current

High-speed counter-current chromatography (HSCCC) was successfully used for isolation and purification of Ginkgo flavonoids from the Ginkgo biloba L. leaf extract (GBE) with a two-phase solvent system composed of n-hexaneethyl acetatemethanolwater at an optimized volume ratio of 4:6:5:5(v/v/v/v). The lower phase was used as the mobile phase in the head to tail elution mode. The preparative HSCCC separation was performed on 200 mg of GBE yielding pure Quercetin (22mg), Kaempferol (15mg) and Isorhamnetin (4mg) at purities of 96.6%, 92.3% and 93.6%, respectively, as determined by high performance liquid chromatography (HPLC). HSCCC is a powerful technique for isolation and separation of chemical composition from GBE.

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