Velocity Oscillation and Pressure Drop in Water–Air Slug Flow

2012 ◽  
Author(s):  
Ken Yamamoto ◽  
Satoshi Ogata
Keyword(s):  
Theoretical Model ◽  
Pressure Drop ◽  
Velocity Fluctuation ◽  
Slug Flow ◽  
High Speed ◽  
Scaling Analysis ◽  
Two Phase ◽  
Semi Empirical ◽  
Measured Pressure ◽  
Circular Microchannels

Visualization and pressure drop measurements of water–air two-phase flow in circular microchannels (d = 486 μm) was conducted. In order to investigate effects of the flow rates and T-junction size on the pressure drop of the two-phase slug flow, three test channels containing various T-junctions (136, 194, and 252 μm) were prepared. The measured pressure drop was compared with the results from semi-empirical model and theoretical model, and it was found that the experimental data generally agreed with the theoretical model. However, the pressure drop increased as the T-junction size decreased. In order to detect the causes of this increase in pressure drop, effects of the velocity fluctuation on the pressure drop were investigated. The velocity fluctuations were measured from the recorded images that were obtained by a high-speed camera. Although it was found that the instantaneous velocity fluctuated in large amplitudes and its cycle was synchronized with a period of the bubble pinch-off, the effects of the velocity fluctuation were negligible on the pressure drop. Finally, from a scaling analysis, it was suggested that the bubble overpressure was the cause of the increase in pressure drop.

scholarly journals Application of RQA and SOM for identification of two-phase flow patterns during boiling in horizontal minichannel

2021 ◽  
Vol 321 ◽  
pp. 02008
Author(s):  
Hubert Grzybowski ◽  
Iwona Zaborowska ◽  
Romuald Mosdorf
Keyword(s):  
Pressure Drop ◽  
Liquid Flow ◽  
Slug Flow ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Inner Diameter

In the paper, numerical methods of data analysis recurrence quantification analysis (RQA) and self-organizing map (SOM) have been used to analyse pressure drop oscillations during the flow boiling in minichannel. The performed analysis allows us to identify flow patterns based on the character of the pressure drop oscillations. The following two-phase flow patterns have been identified: liquid flow, liquid flow with small vapour bubble, slug flow, long slug flow and confined bubble flow. In the experiment, the open-loop boiling system in a circular horizontal minichannel with an inner diameter of 1 mm was investigated. The two-phase flow patterns at the outlet of the heated section were observed through the glass tube (with an inner diameter of 1 mm) and recorded by a high-speed camera Phantom v1610.

Bubble Departure and Convection in Large Aspect Ratio Microchannels

2006 ◽  
Author(s):  
David W. Fogg ◽  
Ching-Hsiang Cheng ◽  
Ken E. Goodson
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
High Speed ◽  
Imaging System ◽  
Time History ◽  
Heat Sinks ◽  
Scaling Analysis ◽  
Two Phase ◽  
Aspect Ratios ◽  
History Of

The growth and departure of vapor bubbles governs pressure drop and thermal resistance of two-phase microchannel heat sinks. Little data is available for the growth, departure, and convection of bubbles in microchannels. The current study uses isothermal air injection to simulate the nucleation and growth of bubbles in high aspect microchannels with Dh≈48μm and aspect ratios from 20 to 40 with 1 < ReH < 10. Liquid pressure drop and flow rate are measured during bubble growth along with the time history of the bubble geometry obtained from a high speed video imaging system at rates up to 50,000 frames per second. Bubble departure is found to vary linearly with aspect ratio divided by inlet Reynolds number, while the convection velocity depends on the normalized bubble width and normalized liquid film thickness. A scaling analysis identifies the increase in axial pressure drop due to bubble confinement as the driving force for both bubble departure and convection.

Adiabatic Air-Water Two-Phase Flow in Circular Microchannels

2011 ◽  
Author(s):  
Aritra Sur ◽  
Dong Liu
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Water Mixture ◽  
Two Phase ◽  
Phase Pressure ◽  
Circular Microchannels

Gas-liquid two-phase flow in microchannels with hydraulic diameters of 100–500 μm exhibits drastically different flow behaviors from its counterpart in conventional macroscopic channels. Two particular issues are how to determine the two-phase flow patterns and how to predict the two-phase pressure drop at given flow conditions in these microchannels. This paper presents an experimental study of adiabatic two-phase flow of air-water mixture in circular microchannels with inner diameters of 100, 180 and 324 μm, respectively, to investigate the effects of channel size and phase velocity on the two-phase flow pattern and pressure drop. The air and water superficial velocities were in the range of 0.01–120 m/s and 0.005–5 m/s. Two-phase flow patterns were visualized using highspeed photographic technique. Four basic flow patterns, namely, bubbly flow, slug flow, ring flow and annular flow, were observed. The two-phase flow maps were then constructed and the transition boundaries between different flow regimes were identified. It was found that the slug flow is the dominant two-phase flow pattern in microchannels, and the transition boundaries generally shift to regions of higher gas superficial velocities as the channel dimension decreases. The experimental measurements of two-phase pressure drop were compared to the predictions from the available two-phase models in the literature. Results show that the flow pattern-based models provide the best prediction of two-phase pressure drop in microchannels.

Pressure drop and drag reduction in two-phase non-newtonian slug flow

1976 ◽  
Vol 54 (1-2) ◽  
pp. 111-114 ◽  
Author(s):  
Lambert Otten ◽  
Abdelrahman S. Fayed
Keyword(s):  
Pressure Drop ◽  
Drag Reduction ◽  
Slug Flow ◽  
Two Phase

Effect of Tube Diameter on Flow Phenomena of Gas-Liquid Two-Phase Flow in Microchannels

2015 ◽  
Author(s):  
Hideo Ide ◽  
Eiji Kinoshita ◽  
Ryo Kuroshima ◽  
Takeshi Ohtaka ◽  
Yuichi Shibata ◽  
...  
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Water Solution ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Tube Diameter ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Flow Phenomena ◽  
The Waves

Gas-liquid two-phase flows in minichannels and microchannels display a unique flow pattern called ring film flow, in which stable waves of relatively large amplitudes appear at seemingly regular intervals and propagate in the flow direction. In the present work, the velocity characteristics of gas slugs, ring films, and their features such as the gas slug length, flow phenomena and frictional pressure drop for nitrogen-distilled water and nitrogen-30 wt% ethanol water solution have been investigated experimentally. Four kinds of circular microchannels with diameters of 100 μm, 150 μm, 250 μm and 518 μm were used. The effects of tube diameter and physical properties, especially the surface tension and liquid viscosity, on the flow patterns, gas slug length and the two-phase frictional pressure drop have been investigated by using a high speed camera at 6,000 frames per second. The flow characteristics of gas slugs, liquid slugs and the waves of ring film are presented in this paper.

Study on Two-Phase Fuel Distributions in High-Speed Hot Transverse Air Stream

1986 ◽  
Vol 108 (3) ◽  
pp. 485-490
Author(s):  
Mao-lin Yang ◽  
Shan-jian Gu ◽  
Xiang-yi Li
Keyword(s):  
High Speed ◽  
Empirical Method ◽  
Mass Center ◽  
Two Phase ◽  
Fuel Distribution ◽  
Hot Air ◽  
Air Stream ◽  
Cold Stream ◽  
Fuel Evaporation ◽  
Semi Empirical

It was found that fuel distribution in a hot high-speed transverse air stream differed greatly from that in a cold stream. In a hot air stream there exist two-phase fuel distributions, and hence, two mass center lines extending downstream. Experimental results of fuel distributions are presented. By using the model of trajectory with diffusion and also considering the fuel evaporation, a semi-empirical method to predict two-phase fuel distributions has been developed.

Study on structure optimization of a bubble cap against erosion wear of an S Zorb desulfurization reactor distribution plate

2021 ◽  
pp. 095440892110424
Author(s):  
HZ Jin ◽  
SQ Gao ◽  
HL Zhao ◽  
C Wang ◽  
GF Ou
Keyword(s):  
High Speed ◽  
Effective Means ◽  
Structure Optimization ◽  
Erosion Wear ◽  
Particle Erosion ◽  
Two Phase ◽  
Wear Area ◽  
Inner Diameter ◽  
Distribution Plate ◽  
Semi Empirical

Bubble cap structures are researched for the particle erosion wear of the distribution plate (tray for short) in an S Zorb desulfurization reactor. The semi-empirical model of erosion wear prediction of gas–solid two-phase flow is revised by means of erosion wear experiments at high temperature and high speed. According to the revised erosion wear, the influence of the h0 (the distance from the bottom of the bubble cap to the tray), h1 (distance from the outlet of the lifting pipe to the top of the bubble cap interface), N (the number of cavities), d0 (the inner diameter of bubble cap) on erosion wear of trays are studied. The results show that a smaller h0 will make the erosion degree of the tray more serious; it is recommended to keep h0 = 17 mm. A larger h1 will alleviate the erosion wear degree of adsorbent particles on the tray, but considering the efficiency of the reaction, h1 = 36 mm is more appropriate. The increase of N reduces the erosion wear less but enhances the fluid disturbance and makes the erosion wear area unstable; so, N should be kept at 10. The increase of d0 reduces the velocity and density of fluid impacting the tray, thus reducing the erosion wear degree, which is an effective means.

Experimental Determination of Hydrodynamic Parameters of Air-Water Two-Phase Slug Flow in Horizontal Pipes

2012 ◽  
Author(s):  
Carlos H. Romero ◽  
María A. Márquez ◽  
Sissi D. Vergara ◽  
María T. Valecillos
Keyword(s):  
Slug Flow ◽  
High Speed ◽  
Electronic Device ◽  
Water System ◽  
Superficial Velocity ◽  
Two Phase ◽  
Horizontal Pipes ◽  
Type Pattern ◽  
Elongated Bubble

Two phase slug flow is the most common flow pattern for horizontal and near-horizontal pipelines. This study is designed to determine experimental velocities of elongated bubbles, lengths of liquid slugs and elongated bubbles, and slug frequencies for twenty flow rates combinations of a two phase air-water system that belong to a slug type pattern in horizontal pipes with a non invasive electronic device made of Photo-diodes (emitter) and photo-transistors (receiver) in a non visible length wave of 940 nanometers. The non intrusive electronic device is validated by simultaneously taking pictures with a high speed camera, (Kodak model Ektapro 4540 mx Imager, at shooting speed of 4500 frames per second, the picture resolution is 256 × 256 pixels), through a visualization cell filled with glycerin. This work is done with acrylic pipes of 0,03175 m inner diameter, to ensure complete flow development, the pictures are taken from a visualization cell located at a x/D = 249, the electronic device is located at x/D = 250. Air superficial velocity ranged between 0.156 and 0.468 m/s while water superficial velocity ranged between 0.159 and 1.264m/s. It is found that the non intrusive electronic device formed by photo diodes and photo transistors is an accurate technique that can be used in the determination of elongated bubble velocities, lengths and slug frequencies.

Compact Model of Slug Flow in Microchannels

2007 ◽  
Author(s):  
Dong Rip Kim ◽  
Jae-Mo Koo ◽  
Chen Fang ◽  
Julie E. Steinbrenner ◽  
Eon Soo Lee ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Liquid Water ◽  
Slug Flow ◽  
Flow Behavior ◽  
Contact Angles ◽  
Proton Exchange ◽  
Force Balance ◽  
Compact Model ◽  
Two Phase ◽  
Coverage Ratio

This paper presents a theoretical investigation of the movement of liquid droplets and slugs in hydrophobic microchannels and develops a compact model for this type of two-phase flow. This model is used in the prediction of pressure drop and liquid water coverage ratio, key parameters in the operation of Proton Exchange Membrane Fuel Cells (PEMFC), the primary motivation for this work. A semi-empirical, periodic-steady two-phase separated flow compact model is formulated to characterize the slug flow behavior. The momentum equation includes the effects of acceleration, friction and surface tension on the pressure drop. The model considers spatial changes in slug velocity through the use of a force balance formulation. The model uses a departure scheme that computes slug size and shape at entrainment. The steady state slug flow compact model is capable of predicting liquid water coverage ratio and pressure drop using liquid and gas flow rates and advancing/receding triple point contact angles as its only inputs. The results indicate that the pressure drop increases as the droplet formation frequency increases.

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