Characteristics Of Gas-liquid Two-phase Flow Research Articles

Void Fraction Characteristics of Gas-Liquid Two-Phase Flow in a Small Diameter Tube

Void fraction of nitrogen gas-water two-phase flow in a circular tube from 1 to 10 mm in diameter was measured by neutron radiography. The measured void fraction results were compared with Ishii's drift flux model based on Mishima-Ishii's flow regime criteria. The void fraction was predicted well in annular flow region except for α<0.8. Mishima-lshii flow regime map was modified by a churn to annular flow transition criterion of α=0.8. The void fraction was predicted well by Ishii's drift flux model in annular flow region in every diameter tubes.

Optical Measurement of Void Fraction and Bubble Size Distributions in a Microchannel

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μ m diameter. By using multiple optical fibers and infrared photodiodes, void fraction, gas and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase. Also, by cross-correlating the signals from two neighboring probes, the interface velocity representing gas plug velocity or ring-film propagation velocity depending on the flow pattern could be computed. Within the ranges of superficial gas and liquid velocities covered in the experiments (j L = 0.2∼0.4 m/s and j G = 0∼5 m/s), the gas plug length was found to increase with the increasing superficial gas velocity, but the liquid plug length was found to decrease sharply as the superficial gas velocity was increased; thus, the total length of the gas-liquid plug unit decreased with the superficial gas velocity.

F41 水平ミニチャンネル内気液二相流に及ぼす表面張力の影響(F4 流体工学11)

F41 水平ミニチャンネル内気液二相流に及ぼす表面張力の影響(F4 流体工学11)

G502 気液二相流におけるはく離・再付着過程に関する研究(2)(GS5 キャビテーション,剥離,一般セッション)

In Electro Chemical Machining (ECM) process, generation of air bubbles and the flow separation during processing complicate the flow behavior of electrolyte and decrease the shape accuracy of the product. It is highly important to understand the influence of air bubbles on the separated flow. In this study, the flow characteristics of vertical upward gas-liquid two-phase flow with millimeter-scale bubbles and separation in a rectangular channel were examined. Bubbles were fed to the liquid phase from stainless-steel needles with inside diameter of 0.1 mm. Flow separation is generated by a square rod. The liquid velocity was measured using the PIV and the bubble shape was detected by the shadow image technique. It was found that mean velocity profiles of the bubbly flow were steep near the wall and mainstream was flat in the main stream. Furthermore, the reattachment length was reduced by increasing the void fraction.

Flow Characteristics of Gas-Liquid Two-Phase Flow in a Plate Heat Exchanger

Adiabatic vertically downward air-water two-phase flows in a single channel commercial plate heat exchanger were visualized by a neutron radiography method to clarify the flow characteristics and the differences in liquid distribution from those of vertically upward flows. From the visualized results, it was shown that water fell down without a spreading at a lower gas volumetric flux and tended to flow in the left-side of the shortest pass between the inlet and exit. The liquid distribution was opposite to that of the upward flows in which liquid fraction was higher along the both side of the single channel. In the case of a higher gas volumetric flux above 7 m/s, liquid spread at the enlarged section and the liquid distribution in the main part of the heat exchanger seemed to be homogenous. Measured average void fractions for the air-water downward flows showed almost the same tendency as those for the upward flows, and those were well correlated based on Drift flux model. On the other hand, the frictional pressure loss of the downward flows showed lower values than those of the upward flows at the lower gas volumetric flux less than 13 m/s. The difference was might be caused by the difference in flow pattern. For the higher gas volumetric flux over 13 m/s, the difference in frictional pressure loss was a little. Frictional pressure loss was well correlated by L-M method.

Flow Characteristics and Drag Reduction of Vertical Upward Gas-Liquid Two-Phase Flow through Sudden Contraction Pipe

A gas-liquid two-phase flow through vertical sudden contraction pipe is an area that still little is known and has been studied experimentally, visually and numerically. In this study, the flow characteristics of vertical upward gas-liquid two-phase flow through a sudden contraction pipe are examined experimentally and numerically, and a new simple method of flow control to reduce the flow fluctuation and resistance is shown. When mounting a ring-shaped step before the contraction, vortex formation at the contraction was reduced. That is, the flow is suggested by mounting a ring-shaped small obstacle before the contraction to lead to stabilized flow and drag reduction. The effects of Reynolds number, volumetric flow rate ratio of air to water and the ring position were examined. Numerical analysis using an incompressible tow-fluid model was conducted in order to understand the flow pattern well.

Flow Characteristics and Control of Vertical Upward Gas-Liquid Two-Phase Flow through a Sudden Contraction Pipe

The flow characteristics of upward gas-liquid two-phase flow through a vertical sudden contraction pipe is an area that has been less studied experimentally and numerically and that is still little known (1)-(3) . The drag and its reduction for an upward bubbly two-phase flow in a sudden contraction pipe are investigated. Vortices are generated just prior to and after contraction and they significantly affect the flow characteristics. A simple and economical method to control and smoothen the flow is proposed by mounting a small obstacle (ring) upstream the contraction. The effects of ring position, Reynolds number and volumetric gas flow rate are examined and positive results were seen in all flow conditions. Moreover, the pressure fluctuation phenomenon and its control downstream the contraction was considered.

4221 マイクロチャンネル内気液二相流のボイド率と気泡寸法分布の光学的計測(G05-12 気泡・液滴(1),G05 流体工学)

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100μm diameter. By using multiple optical fibers and infrared photodiodes, void fraction and gas plug and liquid plug lengths, and their velocities were measured successfully. The probes responded to the passage of gas and liquid phases through the microchannel adequately so that the time-average void fraction could be obtained from the time fraction for each phase.

Numerical study of two-phase flow of liquid helium in a vertical converging-diverging nozzle

The fundamental characteristics of the two-dimensional gas-liquid two-phase flow of liquid helium through a vertical converging-diverging duct near the lambda point are numerically investigated to realize the further development and high performance of new multiphase superfluid cooling systems. First, the governing equations of the two-phase flow of liquid helium based on the unsteady thermal nonequilibrium multifluid model with generalized curvilinear coordinates system are presented, and several flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the gas-liquid two-phase flow of liquid helium though vertical converging-diverging nozzle is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid- to vapor-phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 432–448, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20071

Two-Phase Flow Through Square and Circular Microchannels—Effects of Channel Geometry

An adiabatic experiment was conducted to investigate the effect of channel geometry on gas-liquid two-phase flow characteristics in horizontal microchannels. A water-nitrogen gas mixture was pumped through a 96 μm square microchannel and the resulting flow pattern, void fraction and frictional pressure drop data were compared with those previously reported by the authors for a 100 μm circular microchannel. The pressure drop data were best estimated using a separated-flow model and the void fraction increased non-linearly with volumetric quality, regardless of the channel shape. However, the flow maps exhibited transition boundaries that were shifted depending on the channel shape.

04/01086 Flow characteristics of gas-liquid two-phase flow in plate heat exchanger (Visualization and void fraction measurement by neutron radiography): Asano, H. et al. Experimental Thermal and Fluid Science, 2004, 28, (2–3), 223–230

04/01086 Flow characteristics of gas-liquid two-phase flow in plate heat exchanger (Visualization and void fraction measurement by neutron radiography): Asano, H. et al. Experimental Thermal and Fluid Science, 2004, 28, (2–3), 223–230

A Study of the Flow Characteristics of Gas-Liquid Two-Phase Flow in a Plate Heat Exchanger (Visualization and Void Fraction Measurement in a Single Channel)

In order to clarify the gas-liquid two-phase flow characteristics in a plate heat exchanger, gas-liquid two-phase flows in simulated heat exchangers with a single channel placed in a vertical plane were visualized by a neutron radiography method. Adiabatic air-water two-phase flows and R 141 b boiling two-phase flows were visualized, and two-dimensional void fraction distributions were measured from visualized images via some image processing techniques. Moreover, total pressure loss of adiabatic airwater two-phase flows through the test section was measured, and the frictional pressure loss was calculated by using measured results of average void fraction. As a result, it was shown that the phase distributions in heat exchangers were strongly affected by the inlet configuration and the inlet conditions. In the case that the incoming flow was a gas-liquid two-phase flow, stagnant liquid at the test section inlet caused unsymmetrical phase distribution. For high gas volumetric flux, both phases tended to flow straight separately and liquid mixing in the channel with ribs was a little. It was also shows that the average void fractions and the frictional pressure loss of adiabatic air-water two-phase flows in the channel with ribs could be correlated by the drift-flux model and the L-M method, respectively.

Flow characteristics of gas–liquid two-phase flow in plate heat exchanger: (Visualization and void fraction measurement by neutron radiography)

In order to clarify the gas–liquid two-phase flow characteristics in a plate heat exchanger, gas–liquid two-phase flows in simulated heat exchangers with a single channel placed in a vertical plane were visualized by a neutron radiography method. Air–water adiabatic two-phase flows and chlorofluorocarbon R141b boiling two-phase flows were visualized, and two-dimensional void fraction distributions were measured from visualized images via some image processing techniques. Moreover, total pressure loss of adiabatic air–water two-phase flows through the test section was measured, and the frictional pressure loss was calculated by using measured results of average void fraction. As a result, it was shown that the phase distributions in heat exchangers were strongly affected by the inlet configuration and the inlet conditions. When the incoming flow was a gas–liquid two-phase flow, liquid stagnation at the test section inlet caused unsymmetrical phase distribution. For high gas volumetric flux, both phases tended to flow straight separately. Moreover, it was shown that the average void fractions and the frictional pressure loss of adiabatic air–water two-phase flows in the ribbed channel could be correlated by the drift-flux model and the L–M method, respectively.

Fluctuation characteristics of two-phase flow splitting at a vertical impacting T-junction

In order to investigate the fluctuation characteristics of two-phase flow splitting at a T-junction, particular attention was paid on Churn flow which had the strongest fluctuation comparing with bubble flow and annular flow. The main tube of the T-junction was vertical and the two branches were horizontal. All three pipes connecting to the junction were of 15 mm inner diameter. A statistical analysis based on Root Mean Square (RMS) was applied to temporal differential pressure signals and gas flow rate signals. The Power Spectral Density (PSD) was also employed to reveal their peculiar features in frequency domain as well. The effects of the extraction flow ratio and the gas and liquid superficial velocity upstream on fluctuation characteristics of gas-liquid two-phase flow splitting at the T-junction were investigated in detail. It is found that there is a wide fluctuation in both differential pressure and gas flow rate downstream at every extraction ratio (W 3/W 1) and the fluctuation intensity increases as W 3/W 1 increasing. It is also made clear that increasing either water superficial velocity or gas superficial velocity in inlet causes fluctuation to become more intensive.

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 1. Experimental results of flow pattern, void fraction, and pressure drop

AbstractExperiments were carried out to investigate the flow pattern, average void fraction, and pressure drop of an upward air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter, pitch, and number of coils in cross section. Five kinds of flow patterns—bubble, slug, churn, semiannular, and annular flow—were defined based on the observation of flow behavior in the experiments. At higher water flowrates, the bubble‐to‐slug transition occurred at lower air flowrates in tubes with wire coils than in smooth tubes. The average void fraction was found by using the drift flux model. Further, the experimental results of the friction pressure drop were compared with the Lockhart‐Martinelli correlation. As a result, a correlation with the constant C in Chisholm's equation was obtained as a function of the wire coil pitch‐to‐diameter ratio. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 639–651, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10066

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 2. Effect on void fraction and liquid film thickness

AbstractAn experimental study has been carried out to clarify the characteristics of the void fraction and the liquid film thickness of the air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter and pitch. The flow pattern in the experiment on the average void fraction and the local void fraction distribution in cross section was a bubble flow, and the liquid film thickness was in the region of semiannular and annular flows. It is clarified from these experiments that the average void fraction in tubes with wire coils is lower than that in a smooth tube and decreases with the wire diameter owing to the centrifugal force of the swirl flow which concentrates bubbles at the center of the tube, that the local liquid film thickness becomes more uniform with a decrease in the pitch of the wire coil, and that the liquid film becomes thicker after the passage through the wire coil with an increase in the wire diameter. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 652–664, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10067

B163 細管内気液二相流の特性を利用した液体輸送における圧力損失の検討

B163 細管内気液二相流の特性を利用した液体輸送における圧力損失の検討

415 垂直細管内気液二相流における液体物性の影響 : 第二報, 摩擦損失と界面摩擦力(O.S.4-4 混相流)(O.S.4 : 高度化に向けた流体関連解析と機器開発)

415 垂直細管内気液二相流における液体物性の影響 : 第二報, 摩擦損失と界面摩擦力(O.S.4-4 混相流)(O.S.4 : 高度化に向けた流体関連解析と機器開発)

437中性子ラジオグラフィによる液体金属-ガス二相流の液相速度計測

In a core melt accident of a fast breeder reactor, a possibility of re-criticality is anticipated in the molten fuel-steel mixture pool. One of the mechanisms to suppress the re-criticality is the boiling of steel in the molten fuel-steel mixture pool because of the negative void reactivity effect. To evaluate the reactivity change due to boiling, it is necessary to know the characteristics of gas-liquid two-phase flow in the molten fuel-steel mixture pool. For this purpose, boiling bubbles in a molten fuel-steel mixture pool were simulated by adiabatic gas bubbles in a liquid metal pool to study the basic characteristics of gas-liquid metal two-phase mixture. Visualization of the two-phase mixture and measurements of liquid phase velocity and void fraction were conducted by using neutron radiography and image processing techniques. From these measurements, the basic characteristics of gas-liquid metal two-phase mixture were clarified.

Flow Characteristics of Upward Gas-Liquid Two-Phase Flow in a Vertical Tube with a Wire Coil. 1st Report. Experimental Results of Flow Pattern, Void Fraction and Pressure Drop.

Experiments were carried out to investigate the flow pattern, average void fraction, and pressure drop of upward air-water two-phase flow in vertical tubes of 25 mm inside diameter with wire coils fo varying wire diameter, pitch and number of coil. Five kinds of flow patterns, i.e., bubble, slug, churn, semi-annular and annular flow, were defined based on the observation of flow behaviors in the experiments. At higher water flow rate, the bubble-slug transition occurred at a lower air flow rate in tubes with wire coil than in the smooth tube. The average void fraction was clarified using the drift flux model. Furthermore, the experimental results of the friction pressure drop were compared with the Lockhart-Martinelli correlation. As a result, a correlation for the constant C in Chisholm's equation was obtained as a function of wire coil pitch-to-diameter ratio.