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.

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.

Predicted performance of a two-phase underwater ramjet with a Laval nozzle

2018 ◽  
Vol 233 (3) ◽  
pp. 937-948
Author(s):  
Jiarui Zhang ◽  
Zhixun Xia ◽  
Liya Huang ◽  
Likun Ma
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Laval Nozzle ◽  
Fluid Model ◽  
Bubbly Flow ◽  
Engine Performance ◽  
Orifice Diameter ◽  
Two Phase ◽  
Convergent Nozzle

To predict engine performance and further instruct the integral engine design, a more reasonable and accurate numerical model of the two-phase underwater ramjet was introduced in this article by considering the bubble formation process. Two-fluid model was used to examine the bubbly flow in the nozzle and its mathematical model was solved by a fourth-order Runge–Kutta method. Subsequently, the influences of vessel velocity, gas mass flow rate, navigational depth, and orifice diameter of the bubble injector on the performance of the engine were discussed. Results show that, compared with convergent nozzle, Laval nozzle is proved to improve the thrust of the engine, especially at relatively high velocity and gas mass flow rate. With the other conditions fixed, there is an optimum vessel velocity for the ramjet, in which maximum thrust is generated. And a smaller orifice diameter always promotes the engine performance, while this promotion is negligible when the orifice diameter is smaller than 1 mm. Besides, increasing backpressure will cause serious performance drop, which means that the the two-phase underwater ramjet is only efficient for shallow depths.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration — (5) Measurement of Bubble Deformation Near Wall Under Structure Vibration

2012 ◽  
Author(s):  
Kousuke Mizuno ◽  
Akiko Kaneko ◽  
Hideaki Monji ◽  
Yutaka Abe ◽  
Hiroyuki Yoshida ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Flow Structure ◽  
Test Section ◽  
High Speed ◽  
Bubbly Flow ◽  
Oscillation Amplitude ◽  
Reactor Core ◽  
Two Phase ◽  
Piv Measurement ◽  
Structure Vibration

In a nuclear power plant, one of the important issues is evaluation of the safety of reactor core and its pipes when an earthquake occurs. Many researchers have conducted studies on constructions of plants. Consequently, there is some knowledge about earthquake-resisting designs. However the influence of an earthquake vibration on thermal fluid inside a nuclear reactor plant is not fully understood. Especially, there are little knowledge how coolant in a core response when large earthquake acceleration is added. Some studies about the response of fluid to the vibration were carried out. And it is supposed that the void fraction or the power of core is fluctuated with the oscillation by the experiments and numerical analysis. However detailed mechanism about a kinetic response of gas and liquid phases is not enough investigated, therefore the aim of this study is to clarify the influence of vibration of construction on bubbly flow structure. In order to investigate it, we visualize changing of bubbly flow structure in pipeline on which sine wave is applied. Bubbly flow is produced with injecting gas into liquid flow through a horizontally circular pipe. In order to vibrate the test section, the oscillating table is used. The frequency of vibration added from the table is from 1.0 Hz to 10 Hz and acceleration is from 0.4 G to 1 G (1 G = 9.8 m/s2). The test section and a high speed video camera are fixed on the table. Thus the relative velocity between the camera and the test section is ignored. In the visualization experiment, the PIV measurement is conducted. Then the motion of bubbles, for example the shape, the positions and the velocity are measured with observation. In addition, by varying added oscillation amplitude, frequency and flow rate of the fluids, the correlation between these parameters and bubble motion was evaluated. It was clarified that the behavior of liquid phase and bubble through horizontal circular pipes was affected by an oscillation. When structure vibration affects the flow, two main mechanisms are supposed. One is the addition of body force of the oscillation acceleration to liquid phase and bubble, and the other is the velocity oscillation of the test section and the effect of the boundary layer of the pipe wall. It was also found that when the added oscillation frequency and amplitude was changed, the degree of the fluctuation of liquid phase and bubble motions were changed.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (11) Bubble Motion Under the Flow Vibration

2014 ◽  
Author(s):  
Ryotaro Yokoyama ◽  
Jun-ichi Takano ◽  
Hideaki Monji ◽  
Akiko Kaneko ◽  
Yutaka Abe ◽  
...  
Keyword(s):  
Flow Rate ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubbly Flow ◽  
Plug Flow ◽  
Flow Simulation ◽  
Phase Flow ◽  
Bubble Behavior ◽  
Two Phase ◽  
Rate Fluctuation

Earthquake is one of the most serious phenomena for safety of a nuclear power plant. Therefore, nuclear reactors were contracted considering structural safety for a big earthquake. In a nuclear reactor, the gas-liquid two-phase flow is the one of primary factor of the property and bubbly or plug flow behavior is important issue to evaluate of safety. However, the influence of an earthquake vibration on the gas-liquid two-phase flow inside the nuclear power plant is not understood enough. For example, the bubbly flow behavior under the flow rate fluctuation caused by the earthquake acceleration is not clear. It is necessary to clear the two-phase flow behavior under the earthquake conditions. To develop the prediction technology of two-phase flow dynamics under the earthquake acceleration, the detailed two-phase flow simulation code with an advanced interface tracking method, TPFIT was expanded to the two-phase flow simulation under earthquake accelerating conditions. In the present study, the objective is to clarify the behavior of the gas-liquid two-phase flow under the earthquake conditions. Especially, the bubble behavior in the two-phase flow, a diameter, shape and velocity of bubbles which are expected to be influenced by the oscillation of the earthquake is investigated. In this experiment, the flow was bubbly flow and/or plug flow in a horizontal circular pipe. The working fluids were water and nitrogen gas. The nitrogen gas from gas cylinder was injected into the water through a nozzle and bubbly flow was generated at a mixer. The water was driven by a pump and the flow rate fluctuation was given by a reciprocating piston attached to the main flow loop. Main frequency of earthquakes is generally between 0.5Hz and 10Hz. Thus the frequency of the flow rate fluctuation in the experiment also was taken between 0.5Hz and 10Hz. The behavior of horizontal gas-liquid two-phase flow under the flow rate fluctuation was investigated by image processing using a high-speed video camera and PIV at test section. The pressure sensors were installed at the inlet of the mixer and the outlet of the test section. As the result, the bubble behavior mechanism under the flow rate fluctuation was obtained. In addition, the acceleration of a bubble and the pressure gradient in the pipe was synchronized under all frequency conditions. The prediction results by TPFIT were compared with the experimental results. They show good agreement on the flow field around a bubble and the bubble behavior.

Bubble Size Reduction Using Mesh Bubble Breakers in Two-Phase Vertical Co-Flow

2015 ◽  
Author(s):  
Alan Kalbfleisch ◽  
Kamran Siddiqui
Keyword(s):  
Pore Size ◽  
Bubble Size ◽  
Slug Flow ◽  
High Speed ◽  
Imaging System ◽  
Bubbly Flow ◽  
High Speed Imaging ◽  
Two Phase ◽  
Vertical Column ◽  
Experimental Apparatus

Bubble breakers have been shown to reduce the bubble size and hence increasing the bubble surface-to-volume ratio facilitating higher mass transfer. We report on an experimental study investigating the effect of mesh-type bubble breaker on two-phase co-flow in a vertical column. A range of gas-liquid flow rates ratios (GLR) has been considered that covers the two-phase regimes from bubbly flow to slug flow. A vertical glass tube was used as the experimental apparatus which provides full optical access. A high speed imaging system was used to capture the flow dynamics for bubble characterization. The results show that the bubble size generated by the mesh bubble breaker is greatly affected by the pore size. For a bubbly flow regime, the initial bubble size was reduced by approximately 60%–70% for a pore size of 1mm and by about 45%–50% for a pore size of 4mm. It is found that the transition from bubbly flow to slug flow can be affected by the mesh bubble breaker. The results show that in general, the mesh bubble breaker increases the GLR limit for the transition from bubbly to slug flow.

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.

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.

scholarly journals Atomization of Gel Fuels with Solid Particle Addition Utilizing an Air Atomizing Nozzle

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2959
Author(s):  
Yunlei Xiao ◽  
Zhixun Xia ◽  
Liya Huang ◽  
Likun Ma ◽  
Dali Yang
Keyword(s):  
Mass Flow Rate ◽  
Solid Particle ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Droplet Diameter ◽  
Aluminum Particle ◽  
Solid Particles ◽  
Particle Content ◽  
Boron Particle

Microscopic high-speed imaging is used to experimentally measure the velocity and size of droplets of gelled RP-1 based fuels with a solid particle additive. The gels are atomized using an air atomizing nozzle. The droplet diameter and velocity at a fixed position 20 cm from the nozzle on the centerline of the spray are measured at air mass flow rates of 1.5, 3 and 5 g/s. A parametric study is conducted to study the effect of gas mass flow rate, boron particle content, and species of the solid particle on the droplet characteristics. The results indicate that the droplet size decreases with the increasing of gas mass flow rate and boron particle content. Gel fuels with an aluminum particle are observed to produce smaller droplets at a low gas mass flow rate than that with a boron particle. The implication of these observations is that the atomization processes for gelled fuels with an additive of solid particles is controlled by the velocity difference between the gas and the droplets.

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.

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