Research Papers: Multiphase Flows

Measurement of Velocities in Two-Phase Flow by Laser Velocimetry: Interaction Between Solid Particles’ Motion and Turbulence

[+] Author and Article Information
N. Sad Chemloul

Research Laboratory of Industrial Technologies, University Ibn Khaldoun of Tiaret, Tiaret 14000, Algeriasad_2412@yahoo.fr

O. Benrabah

Institute of Physics, University of Oran, Oran 31000, Algeria

J. Fluids Eng 130(7), 071301 (Jun 25, 2008) (10 pages) doi:10.1115/1.2948358 History: Received January 08, 2007; Revised April 01, 2008; Published June 25, 2008

In this work, an experimental method based on laser anemometry with Doppller effects is developed. This allows the measurement of velocities and their fluctuations in a flow of solid-liquid suspension in an ascendant vertical pipe. In order to distinguish between the signals coming from the continuous phase, water, and those of the glass bead particles larger than the Kolmogorov length scale, an electronic logic circuit was incorporated in the measuring equipment. This enabled the study of both the slip velocity of the solid-liquid suspension and the influence of the large particles on turbulence. The results show that a fine particle suspension, which represents a tracer, behaves as a homogeneous fluid. For large particles, we confirmed the existence of a slip velocity and the effect of particle size on the turbulence. The use of two distinct measurement volumes produces good results for the direct measurement of the turbulent length scales. The results show that the presence of solid particles modifies the turbulence characteristics.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Signal bursts and definition of visibility: Doppler component (solid line) and pedestal component (dashed line)

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Figure 2

Experimental setup of the velocity profiles and the turbulence intensity measurement: (a) flow circuit: (1) pump and tank, (2) horizontal table with micrometric displacement, (3) base, and (4) glass pipe; (b) optical measurement with acquisition and treatment system: (1) laser source, (2) beam splitter prism, (3) convergent lens, (4) flow pipe, (5) photodiode, (6) photomultiplier, (7) electronic logic, (8) bandpass filter, (9) digital storage oscilloscope, and (10) computer, (---) laser beams, (–⋅–⋅) light diffused by the particle, and (—) interfacing cable

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Figure 3

Response characteristics of (a) the bandpass filter frequency and (b) the photodiodes, wave form

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Figure 4

Electronic logic circuit and truth table: (a) electronic logic circuit: (1) impedance circuit adapter (LM 308), (2) attenuator circuit (LM 308), (3) Schmitt trigger (SN 7414), (4) inverter signal (SN 7404 TTL), (5) inverter amplifier (LM 308), (6) AND gate (SN 7408 TTL), (7) OR EXCLUSIVE gate (SN 74 LS 86 TTL), (8) AND gate, and (9) AND gate, (PHI, PHII) photodiodes, (PM) photomultiplier, (E) digital logic circuit output; (b) truth table of logical gates

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Figure 5

Output wave forms and truth table of digital logic circuit: (a) output wave forms for different logical gates; (b) truth table of logical gates output for various cases

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Figure 6

Typical signals: (a) Doppler signal of glass bead with 1mm of diameter; (b) signal obtained when the tracer and a large particle crosses the volume measurement simultaneously

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Figure 7

Calibration measurement: (a) calibration system: (–⋅–) laser beam and (---) optical axis; (b) calibration curve

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Figure 8

Optical measurement system of the turbulence length scales: (1) pump and tank, (2) horizontal table with micrometric displacement, (3) base, (4) glass pipe, (5) laser source (m: moving with 2, f: fixed near the wall), (6) photomultiplier (m: moving with 2, f: fixed), (7) bandpass filter, (8) digital storage oscilloscope and (9) computer, (---) laser beams, (—) and interfacing cable

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Figure 9

Mean velocity profiles of water for U¯=0.806m∕s

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Figure 10

Mean velocity profiles of water and glass beads at different flow mean velocities (Cv=1%); (—) theoretical profile Eq. 12; (○) water alone; (●) solid particles

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Figure 11

Comparison between the experimental results and those obtained by the model of Ohashi and Sugawara (41)

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Figure 12

Mean velocity profiles of the glass beads with various concentrations (dp=0.5mm, Re=16,200)

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Figure 13

Variation of relative viscosity versus the volumetric concentration

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Figure 14

Dimensionless velocities of the solid particles (dp=1mm)

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Figure 15

Turbulence intensity of water and solid particles (Re=16,200, dp=1mm)

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Figure 16

Reduction of turbulence intensity (Re=16,200, dp=1mm)

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Figure 17

Reduction of the lateral integral scale of turbulence, Re=16,200




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