Constant Electric Current Method Research Articles

Experimental study on the upward annular two-phase flow of nitrogen and ethanol aqueous solutions with different concentrations

Vertical upward annular flow experiments of nitrogen gas and ethanol aqueous solutions with volume fractions of 30 %, 60 %, and 95 % under 0.2 MPa were conducted. The characteristics of the liquid film including base, average, and maximum film thickness and height, velocity, and frequency of disturbance waves were obtained and studied based on the constant electric current method in a 5 mm inner diameter polycarbonate tube. The flow behavior was observed using a high-speed camera simultaneously. It is found that a large number of bubbles in the liquid film is critical to these characteristics. A connection between ethanol concentration and bubbles in the liquid film is found and interpreted by considering bubble stability which arises from the dynamic rise in surface tension. Our experimental investigation suggests that the effect of bubbles in the liquid film on the flow characteristics is not negligible in such annular flows under high liquid flow rates and bubble stability should be considered for annular flows employing solutions consisting of two or more components with large differences in surface tension.

On the velocity and frequency of disturbance waves in vertical annular flow with different surface tension and gas–liquid density ratio

In this study, the characteristics of disturbance waves, including velocity, longitudinal size, and frequency, are comprehensively investigated by conducting gas–liquid upward annular flow experiments in a 5 mm tube through the constant electric current method (CECM). The film thickness time trace is recorded with respect to time, and the information on disturbance waves is subsequently extracted. The effect of liquid and gas flow rate, density ratio, and surface tension on the disturbance wave is quantitatively analyzed. A predictive model of the wave velocity based on the shear stress balance of the liquid film is proposed. A physical model for wave frequency prediction is derived on the basis of the mass conservation equation. A simple empirical model with good prediction accuracy of wave frequency is also derived. Compared with existing correlations available in the literature, the newly derived models show better performance under a wide range of flow conditions.

Liquid Film Thickness for Gas-Liquid Annular Flow Across Grid Spacer with Vanes in Simple 3 × 3 Rod Bundle Channel

This study reports the effects of the grid spacer with mixing vane (MV) on gas velocity for air single-phase flow and liquid film thickness for air-water two-phase annular flow in a 3 × 3 rod bundle channel. To investigate the effects of the shape of the spacers, three kinds of spacers were installed into the channel: spacer without MV (without MV), spacer with four MVs (4-MV30), and spacer with two MVs (2-MV30). The 4-MV30 and 2-MV30 had vanes that were inclined 30 deg from the vertical axis. Gas velocity was measured with a hot-wire anemometer and liquid film thickness was measured with the constant electric current method. From the gas velocity measurement, it was found that the irregularities in the velocity distribution became smaller toward downstream of the spacer. For the 2-MV30, the flow distribution was asymmetric and the flow was biased. From the liquid film thickness measurement, it was found that the liquid film thickness became thicker downstream of the spacer.

Pengaruh Liquid Hold-Up terhadap Transisi Pola Aliran 2 Fasa Air-Udara dari Stratified Ke Slug pada Pipa 50 mm

The slug flow pattern is one of the most avoiding factors in piping systems due to its destructive characteristics. Research on the criteria of the slug formation is still the concern. The present study focused on finding out the influence of liquid hold-up toward the transition of the flow pattern from stratified to slug pattern. It was conducted on a 50 mm-diameter horizontal acrylic pipe. The visual data was obtained from a fully developed area (180-210 D) by variations of liquid superficial rate (JL) of 0,03-0,3 m/s and gas superficial rate (JG) from 0,7 to 3,77 m/s. The high-speed camera with 2000 fps recording speed was the instrument to obtain the visual data. The measurement of the liquid hold-up is made by Constant Electric Current Method (CECM). The drastic decrement of liquid hold-up value on the wave growth mechanism (JG ≤ 1,88 m/s) indicated the changes in flow patterns from the stratified to the slug pattern, while on the wave coalescence mechanism (JG > 1,88 m/s) the liquid hold-up remains increases. The pattern change from pseudo slug to the slug pattern was not decreasing on its film thickness, yet, it tends to increase the frequency and the liquid slug length.

Determination of Flow Patterns in Vertical Upward Two-Phase Flow Channel via Void Fraction Profile

Two-phase flow happens widely in the industrial plants and certain equipment. This paper attempts to study the characteristics of two-phase flow in a vertical piping system. This was achieved by comparing the void fraction, in the working fluid, by employing Constant Electric Current Method (CECM) with the actual observation using high-speed camera. The experiment requires a complete set of two-phase flow system information and was conducted based on various flow conditions. In order to carry out this experiment, the two-phase flow loop was constructed using a specific experimental apparatus and components. The flow channels were constructed using three pipes with three different inner diameters of 21.0 mm, 47.0 mm and 95.0 mm. The flow direction was vertical upward co-current flow with liquid superficial velocity range of 0.025 m/s to 3.0 m/s and gas superficial velocity range of 0.025 m/s to 3.0 m/s, depending on the size of the pipe. The flow pattern investigation focuses on experimental work, which was based on systematic observation and measurements using a high-speed camera and some measuring apparatus. The void fraction measurement using the CECM sensor was integrated into two-phase flow system with constant electric current running in the pipe and data acquisition system controlled virtually via LabVIEW software. Both result of the flow pattern and void fraction graph were then compared to determine the type of flow pattern from the void fraction graph. Information from the previous studies and experiments were collected and the assumption of any theoretical simplifications were used as a reference. According to the result, the flow pattern in pipe can be easily determined using CECM.

ANALISIS KARAKTERISTIK LIQUID HOLD-UP (FRAKSI CAIRAN) DAN KECEPATAN GELOMBANG PADA ALIRAN ANNULAR CAIR-GAS DI PIPA HORIZONTAL

The purpose of this study is to investigate characteristics of two phase flow between liquid-gas in annular two-phase flow as the application of piping in geothermal power plant. Liquid hold-up and wave velocity become the fundamental discussion in analysing flow characteristics. In this study, acrylic pipes with 16 mm ID with 9.5 length were used. Three2 Sigma-Mu Vol.8 No.2 – September 2016censors with an axial spacing 215 mm were used to record the data. The Constant Electric Current Method (CECM) was also occupied to get more liquid hold-up. The wave velocity was computed by using the cross correlation of two successive liquid hold-up sensors. As a result, it was found that the liquid hold-up signal obtained by Constant Electric Current Method (CECM) can be used to determine the liquid hold-up profile and the wave velocity. Keywords: Annular Flow, Liquid Hold-Up, Wave Velocity, Constant Electric Current Method (CECM)

Effects of Surface Tension on the Liquid Holdup and Wave Characteristics in Horizontal Annular Two-Phase Flow

The wave characteristics of horizontal annular two-phase flow in 16 mm diameter pipe were experimentally investigated using flush-mounted constant electric current method (CECM) sensors and visual observations. To examine the effect of surface tension on the wave velocity and frequency, air and three kinds of liquids with different surface tension were used, i.e., water, 2%-butanol solution, and 5%-butanol solution. The gas and liquid superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The liquid holdup was measured directly using CECM, while the wave velocity and frequency were determined using cross correlation and power spectral density functions of liquid holdup signals. Generally, combination of air and liquid with the highest surface tension gives the highest liquid holdup and wave frequency. Simple correlations for wave velocity and wave frequency were also developed.

Effects of Liquid Viscosity on the Wave Velocity and Wave Frequency in Horizontal Annular Flow

An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.

Measurement of void fraction in bubbly-slug flow with a constant electric current method

In several void fraction measurement methods, a constant electric current method which is one of conductance methods is focused in the present study. By using this method, void fraction can be measured with higher temporal resolution. However, it has been mainly applied to annular flow in previous studies. In the present study, Maxwell's estimation, Bruggemann's estimation, low void fraction approximation and new estimations which consider the bubble shape are applied in order to measure more accurately void fraction of dispersed bubbly flow and slug flow. To understand the effect of bubble shapes and flow patterns, void fraction was measured by the constant electric current method for a rising single spherical bubble and a rising single slug bubble without a forced convection. In addition, void fraction was also measured in bubbly flow and bubbly-slug flow with a forced convection. Then, effects of flow patterns on the proposed estimations of void fraction and the accuracy of their estimations were discussed with the measurement results. From the result, the new estimations which consider a bubble shape are more accurate than the previous estimation in a slug bubble and bubbly-slug flow.

Experimental Investigation on Disturbance Wave Velocity and Frequency in Air-Water Horizontal Annular Flow

The wave characteristics of horizontal air-water annular two-phase flow in 16 and 26-mm-diameter pipe were investigated experimentally using flush-mounted constant electric current method (CECM) sensors and visual observations. The air and water superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The flow morphology of annular flow such as the disturbance wave, ripple, wave coalescence, wave development, entrainment, and breakup could be observed. Using cross correlation and power spectral density functions of liquid holdup signals, the wave velocity and frequency were determined. The effect of superficial liquid velocity on the wave velocity and frequency was found to be less significant compared to that of superficial gas velocity. Simple correlations for wave velocity and frequency were also developed.

Pressure Wave Propagation with Bubble Breakup Phenomena in a Venturi Tube

A micro-bubble generator with a venturi tube generates many micro-bubbles and pressure waves with bubble breakup phenomena. However, physical characteristics of the pressure wave in the venturi tube are not clarified. In the present study, a propagation speed and a pressure value of the pressure wave in the venturi tube were measured by an observation with a high speed video camera and a pressure transducer. In addition, an effect of void fraction on the pressure wave was investigated with the observation, the pressure measurement and a void fraction measurement with a constant electric current method. From these measurements, it was confirmed that the propagation speed decreased with an increase of the void fraction. Besides, the speed followed a sonic speed of a homogeneous model for gas-liquid two-phase flow. Therefore the pressure wave propagation was affected by the gas volume of bubbly flow.

Bubble Behavior and Flow Structure on Bubble Collapse Phenomena in a Venturi Tube

A micro-bubble generator with a venturi tube generates a large number of micro-bubbles with a diameter of 10 μm ― 1 mm by bubble collapse. The bubble collapse is caused by pressure recovery in the diverging region of the venturi tube. The pressure recovery is expected to be a shock for supersonic flow in gas-liquid two-phase flow. However, a profile of Mach numbers to flow direction of the venturi tube has not been estimated experimentally. The present study reveals mechanisms of a bubble collapse. In order to achieve the objectives, we observe bubble behavior with the bubble collapse. In addition, we measure pressure and volumetric void fraction profiles in the flow direction. Pressure is measured by a differential pressure gauge. Void fraction is measured by a constant electric current method and Maxwell' s theory. From these measurements, gas-liquid mixture velocity, sonic speed and Mach number are estimated. In experimental results, bubble collapse is observed with high liquid inlet velocity. When bubble collapse is caused, bubbles expand once into a divergence region of the venturi tube. After that, they contracted rapidly and broken up into a great number of tiny bubbles. Pressure decreases sharply around the throat and increase at the bubble collapse point. On the other hand, the void fraction increase downstream from the throat and decrease around the bubble collapse point. From these results, it is confirmed that the flow is supersonic flow between the throat and the bubble collapse point, while it becomes subsonic flow downstream of the point. Therefore, it is proposed that a shock is present at the bubble collapse point.

Measurement of void fraction in dispersed bubbly flow containing micro-bubbles with the constant electric current method

Void fraction is one of the dominant parameters of gas–liquid two-phase flow in industrial equipment. An electric sensing method based on the difference in electric conductivity and permittivity between liquid and gas is one of the online measurement methods of void faction. However, the previous constant electric current method is not applicable to dispersed bubbly flow because bubbles are dispersed in three dimensions. In the present study, the new constant electric current method available to the three dimensional dispersed bubbly flow with tiny bubbles (micro-bubbles) is developed. The proposed method to estimate the void fraction is based on Maxwell’s theory and polarization of tiny bubbles. The method makes it possible to measure the void fraction of three dimensional dispersed bubbly flow. It is experimentally clarified that the present proposed method with the constant electric current method can be applicable to measure the void fraction of three dimensional bubbly flow more accurately than the previous constant electric current method. It is also clarified that Maxwell’s theory and the present proposed method with polarization are compatible with the drift flux model although void fraction estimated with the previous method is higher than the drift flux model for three dimensional dispersed bubbly flow.

Void Fraction Measurement of Dispersed Bubbly Flow with Micro-Bubbles by Constant Electric Current Method

Void fraction is one of the dominant parameter of gas-liquid two-phase flow in industrial equipment. Impedance method based on the difference of electric conductivity and permittivity between liquid and gas can act as online measurements of the void fraction. However, existed methods are not applicable to dispersed bubbly flow because bubbles are dispersed in three dimensions. In the present study, Constant Electric Current Method available to the three dimensional dispersed bubbly flow with tiny bubbles (micro-bubbles) is developed. The proposed method is based polarization to estimate the void fraction from electrical signals. The method makes possible to measure the void fraction of the three dimensional dispersed bubbly flow. It is clarified that the present proposed measurement is applicable to measure the void fraction in bubbly flow more accurately than previous methods.

219102 定電流法による微細気泡流れのボイド率計測(OS10 熱流体計測の新展開1,オーガナイズド・セッション)

219102 定電流法による微細気泡流れのボイド率計測(OS10 熱流体計測の新展開1,オーガナイズド・セッション)

S0802-2-4 定電流法による分散気泡流のボイド率計測(原子力システムおよび要素技術(2))

S0802-2-4 定電流法による分散気泡流のボイド率計測(原子力システムおよび要素技術(2))

D111 ベンチュリ管式微細気泡発生装置のボイド率特性 : 定電流法を用いたボイド率計測(OS9 混相流動),動力エネルギーシステム部門20周年,次の20年への新展開)

D111 ベンチュリ管式微細気泡発生装置のボイド率特性 : 定電流法を用いたボイド率計測(OS9 混相流動),動力エネルギーシステム部門20周年,次の20年への新展開)

Investigation of liquid film behavior at the onset of flooding during adiabatic counter-current air–water two-phase flow in an inclined pipe

The liquid film characteristics at the onset of flooding in an inclined pipe (16 mm i.d. and 2.2 m in length) have been investigated experimentally. A constant electric current method and visual observation were utilized to elucidate the flow mechanisms at the onset of flooding. Two mechanisms are clarified to control the flooding in lower flooding and upper flooding, respectively. The lower flooding occurred at lower liquid flow rate and high pipe inclination angle. In this mechanism, the liquid film does not block the pipe cross-section. On the other hand, the upper flooding occurred at higher liquid flow rate and low pipe inclination angle. In this case, blocking of the pipe cross-section by large wave and entrainment plays an important role. The experimental data indicated that there was no reversal motion of liquid film at the onset of flooding during the operation of both lower flooding and upper flooding. The effects of pipe inclination angle on the onset of flooding are also discussed.

1013 定電流法による旋回型ノズル出口付近の気柱変動に関する研究(G.S.流体工学(混相流),九州支部 第58期総会・講演会)

1013 定電流法による旋回型ノズル出口付近の気柱変動に関する研究(G.S.流体工学(混相流),九州支部 第58期総会・講演会)

Measurement of time varying thickness of liquid film flowing with high speed gas flow by a constant electric current method (CECM)

A constant-electric-current method (CECM) developed by the present author is a kind of conductance method. The characteristics of the CECM are (1) a constant-current power source is used for supplying the electric power and (2) two kinds of electrodes are installed. One is used for supplying electric power and the other is for detecting the information of hold-up or film thickness. The main merits of the CECM are (1) the output from the sensor electrode is independent of the location of gas phase, for example radial location in a tube cross-section, (2) the sensitivity of detecting the change in the hold-up is higher in the case of the thinner film thickness, and (3) the interaction among the electrodes is negligible. The basic idea, calibration and examples of the application of the CECM will be discussed in the present paper.