Optical probe for local void fraction and interface velocity measurements

1978 ◽  
Vol 49 (8) ◽  
pp. 1090-1094 ◽  
Author(s):  
N. Abuaf ◽  
O. C. Jones ◽  
G. A. Zimmer
Keyword(s):  
Void Fraction ◽  
Interface Velocity ◽  
Optical Probe ◽  
Velocity Measurements

Liquid Turbulence Spectra in Two-Phase Bubbly Flow Under Turbulence Augmentation and Suppression Conditions

2006 ◽  
Author(s):  
Mohamed E. Shawkat ◽  
Chan Y. Ching ◽  
Mamdouh Shoukri
Keyword(s):  
Void Fraction ◽  
Bubbly Flow ◽  
Bubble Diameter ◽  
Optical Probe ◽  
Wave Number ◽  
Two Phase ◽  
Number Range ◽  
Turbulence Spectra ◽  
Turbulence Suppression ◽  
Wave Number Range

An experimental investigation was performed in air-water bubbly flow to study the liquid turbulence spectra in a 200mm diameter vertical pipe. A dual optical probe was used to measure the local void fraction and bubble diameter while the liquid velocities were measured using hot-film anemometry. Experiments were performed at two liquid superficial velocities of 0.2 and 0.68m/s for gas superficial velocities in the range of 0 to 0.18m/s. Generally, as the void fraction increases there is a turbulence augmentation. However, a turbulence suppression was observed near the pipe wall at the higher liquid flow rate for low void fraction. In the augmentation case, the turbulence spectra showed a significant increase in the energy at the wave number range comparable to the bubble diameter. In the suppression case, the spectra showed that suppression initially occurs at the low wave number range and then extends to higher wave numbers as suppression increased.

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

2006 ◽  
Author(s):  
Hideo Ide ◽  
Ryuji Kimura ◽  
Masahiro Kawaji
Keyword(s):  
Void Fraction ◽  
Optical Fibers ◽  
Optical Measurement ◽  
Flow Characteristics ◽  
Interface Velocity ◽  
Gas Velocity ◽  
Two Phase ◽  
Liquid Plug ◽  
Circular Microchannel ◽  
Superficial Gas Velocity

An optical measurement system was developed to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 μm 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. 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 (jL = 0.2∼0.4 m/s and jG = 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, so that the total length of the gas-liquid plug unit decreased with the superficial gas velocity.

Optical probe for high-temperature local void fraction determination

1982 ◽  
Vol 21 (5) ◽  
pp. 886 ◽  
Author(s):  
M. A. Vince ◽  
H. Breed ◽  
G. Krycuk ◽  
R. T. Lahey
Keyword(s):  
High Temperature ◽  
Void Fraction ◽  
Optical Probe ◽  
Fraction Determination

scholarly journals Low Cost True Monofiber Optical Probe for Local Void Fraction Measurements in Minichannels

2014 ◽  
Vol 547 ◽  
pp. 012027
Author(s):  
G Guidi ◽  
P Di Marco ◽  
S Filippeschi ◽  
M Mameli
Keyword(s):  
Void Fraction ◽  
Low Cost ◽  
Optical Probe

Experimental and Numerical Study of Counter-Current Flow in a Vertical Pipe

2014 ◽  
Author(s):  
Giorgio Besagni ◽  
Gaël Guédon ◽  
Fabio Inzoli
Keyword(s):  
Void Fraction ◽  
Current Flow ◽  
Numerical Study ◽  
Bubble Diameter ◽  
Optical Probe ◽  
Numerical Results ◽  
Operating Conditions ◽  
Local Flow ◽  
Counter Current Flow ◽  
Counter Current

Counter current flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. This paper describes experimental and numerical results obtained in a circular column of 240 mm inner diameter with two inner pipes. The counter current flow studied concerns an upward flow of air and a downward flow of water at ambient temperature and pressure. The following range of operating conditions is analyzed: superficial air velocities up to 0.25 m/s and superficial water velocities up to 0.04 m/s, corresponding to global void fractions up to 27.7%. The experimental investigations concerns (i) flow visualization, (ii) local data from a double optical probe and (iii) global void fraction data. Images obtained from an optical camera are used to observe the general flow pattern and to support the boundary conditions of the numerical simulations, in terms of average bubble diameter. Data obtained from the double optical probe are used to study local flow characteristics. The gas disengagement technique is used to obtain the global void fraction over a range of superficial air velocities for the validation of the numerical method. Numerical calculations are performed with an Eulerian two-fluid model using the commercial code ANSYS Fluent Release 14.5.7 and results are compared with experimental data. The effects of bubble diameter and various interfacial drag coefficients are studied. The formulation of the drag coefficient is found to have significant effects on the global void fraction predictions. However, using merely the drag law, numerical results are inaccurate.

Non-Intrusive Unilateral Measurements of Void Incidence Within a Microchannel

2007 ◽  
Author(s):  
Douglas Heymann ◽  
Jordan Young ◽  
Ruander Cardenas
Keyword(s):  
Data Acquisition ◽  
Light Beam ◽  
Void Fraction ◽  
Vapor Bubble ◽  
Total Internal Reflection ◽  
Critical Angle ◽  
Optical Probe ◽  
Internal Reflection ◽  
Continuous Data ◽  
Two Phase

Void fraction measurements are used to characterize two-phase flow within a microchannel. Limitations of typical void fraction measurement systems include disruption of the flow (intrusive optical probe) and non-continuous data acquisition. Using the principles of total internal reflection, a Non-Intrusive Void Incidence Sensor (NIVIS) has been developed to determine the void incidence (frequency of a vapor bubble passing a known position in the channel). Continuous data can be recorded with a typical computer. A light beam is introduced through a fiber optic to the outside of a transparent channel wall at a critical angle. This critical angle is designed such that when a vapor bubble is present at the specified location, total internal reflection will occur. An output fiber is fixed in a determined position to receive light in the case of total internal reflection. Without the presence of a vapor bubble, the light beam will be reflected past the output fiber. A substantial increase in output signal is noticed when total internal reflection occurs. Characteristics of the NIVIS, proven during non-intrusive testing, include: continuous data acquisition of bubble incidences, measurements within a 100 micron wide channel, and bubble boundary differentiation.

Local Axial Relative Velocity Measurements in Bubbly, Cap-Bubbly, and Slug Flows

2013 ◽  
Author(s):  
Benjamin Doup ◽  
Xinquan Zhou ◽  
Xiaodong Sun
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Phase Velocity ◽  
Gas Phase ◽  
Void Fraction ◽  
Relative Velocity ◽  
Separation Method ◽  
Velocity Measurements ◽  
Optical Phase ◽  
Slug Flows

The local axial relative velocity between the gas and liquid phases in vertical air-water two-phase bubbly, cap-bubbly, and slug flows is investigated at axial measurement locations of z/D = 10 and 32. These measurements are performed in an acrylic vertical pipe with an inner diameter of 50 mm and a height of 3.2 m. The local gas-phase velocity and void fraction measurements are performed using a four-sensor conductivity probe at 14 radial locations. The void fraction profiles are presented to show the flow structure and are used along with visual observation to classify the flow regimes. The liquid-phase velocity measurements are performed using a particle image velocimetry (PIV) system. To separate the liquid-phase information from that of the gas phase an optical phase separation method that uses fluorescent particles and an optical filtration technique is adopted. To remove other noises, such as bubble residuals, background noise, and optically distorted particles from the images that are not removed using the optical phase separation method, an image pre-processing scheme is applied to the raw PIV images. The local axial relative velocity obtained from these local gas- and liquid-phase measurements are important for modeling the momentum transfer between the two phases.

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