Flow visualization of two-phase flows using photochromic dye activation method

Kawaji, Masahiro; Ahmad, W.; DeJesus, J.M.; Sutharshan, B.; Lorencez, C.; Ojha, Matadial

doi:10.1016/0029-5493(93)90111-l

Cited by 28 publications

(5 citation statements)

References 32 publications

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“…Upon illumination by a light source, for example an ultraviolet (UV) laser, thin fluorescing traces arranged perpendicular to the direction of the flow are generated, serving as local markers of the fluid motion and allowing for direct velocity profile measurements. Typically applied alongside back-illuminated high-speed photography, PDA-based turbulent flow visualization experiments have been carried out by Karimi and Kawaji with the ultimate goal of characterizing a wide range of two-phase flows, including counter-current annular flows (Karimi and Kawaji [36]), slug and stratified flows (Kawaji et al [37]), freely falling films down a vertical tube (Karimi and Kawaji [38]) and falling films with counter-current shear gas flow (Karimi and Kawaji [39]). More recently, Moran et al [40] investigated the flow dynamics of laminar films flowing down a 45° incline (Re = 11 -220), and noted significant over-predictions of the time-averaged mean and maximum velocities by the Nusselt theory (gravity-viscosity equilibrium).…”

Section: Review Of Experimental Methodsmentioning

confidence: 99%

A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

Charogiannis

Markides

2015

Experimental Thermal and Fluid Science

113

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A simultaneous measurement technique based on planar laser-induced fluorescence imaging (PLIF) and particle image/tracking velocimetry (PIV/PTV) is described for the investigation of the hydrodynamic characteristics of harmonically excited liquid thin-film flows. The technique is applied as part of an extensive experimental campaign that covers four different Kapitza (Ka) number liquids, Reynolds (Re) numbers spanning the range 2.3 -320, and inlet-forced/wave frequencies in the range 1 -10 Hz. Film thicknesses (from PLIF) for flat (viscous and unforced) films are compared to micrometer stage measurements and analytical predictions (Nusselt solution), with a resulting mean deviation being lower than the nominal resolution of the imaging setup (around 20 μm). Relative deviations are calculated between PTV-derived interfacial and bulk velocities and analytical results, with mean values amounting to no more than 3.2% for both test cases. In addition, flow rates recovered using LIF/PTV (film thickness and velocity profile) data are compared to direct flowmeter readings. The mean relative deviation is found to be 1.6% for a total of six flat and nine wavy flows. The practice of wave/phase locked flow-field averaging is also implemented, allowing the generation of highly localized velocity profile, bulk velocity and flow rate data along the wave topology. Based on this data, velocity profiles are extracted from 20 locations along the wave topology and compared to analytically derived ones based on local film thickness measurements and the Nusselt solution. Increasing the waviness by modulating the forcing frequency is found to result in lower absolute deviations between experiments and theoretical predictions ahead of the wave crests, and higher deviations behind the wave crests. At the wave crests, experimentally derived interfacial velocities are overestimated by nearly 100%. Finally, locally non-parabolic velocity profiles are identified ahead of the wave crests; a phenomenon potentially linked to the cross-stream velocity field.

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Section: Review Of Experimental Methodsmentioning

confidence: 99%

A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

Charogiannis

Markides

2015

Experimental Thermal and Fluid Science

113

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“…The photochromic dye activation (PDA) technique is a prime example of the latter; thin fluorescing traces are generated perpendicular to the direction of the flow and imaged at different time delays using a high-speed visualization setup yielding direct velocity-profile measurements. The PDA technique has been implemented in a plethora of two-phase flow visualization experiments, including countercurrent annular flows [52], slug and stratified flows [53], free-falling films down a vertical tube [54], laminar films flowing down an incline [55], and falling films with countercurrent shear-gas flow [56].…”

Section: Experimental Methodsmentioning

confidence: 99%

Detailed hydrodynamic characterization of harmonically excited falling-film flows: A combined experimental and computational study

et al. 2017

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We present results from the simultaneous application of planar laser-induced fluorescence (PLIF), particle image velocimetry (PIV) and particle tracking velocimetry (PTV), complemented by direct numerical simulations, aimed at the detailed hydrodynamic characterization of harmonically excited liquid-film flows falling under the action of gravity. The experimental campaign comprises four different aqueous-glycerol solutions corresponding to four Kapitza numbers (Ka = 14, 85, 350, 1800), spanning the Reynolds number range Re = 2.3-320, and with forcing frequencies f w = 7 and 10 Hz. PLIF was employed to generate spatiotemporally resolved film-height measurements, and PIV and PTV to generate two-dimensional velocity-vector maps of the flow field underneath the wavy film interface. The latter allows for instantaneous, highly localized velocity-profile, bulk-velocity, and flow-rate data to be retrieved, based on which the effect of local film topology on the flow field underneath the waves is studied in detail. Temporal sequences of instantaneous and local film height and bulk velocity are generated and combined into bulk flow-rate time series. The time-mean flow rates are then decomposed into steady and unsteady components, the former represented by the product of the mean film height and mean bulk velocity and the latter by the covariance of the film-height and bulk-velocity fluctuations. The steady terms are found to vary linearly with the flow Re, with the best-fit gradients approximated closely by the kinematic viscosities of the three examined liquids. The unsteady terms, typically amounting to 5%-10% of the mean and peaking at approximately 20%, are found to scale linearly with the film-height variance. And, interestingly, the instantaneous flow rate is found to vary linearly with the instantaneous film height. Both experimental and numerical flow-rate data are closely approximated by a simple analytical relationship with only minor deviations. This relationship includes terms such as the wave speed c and mean flow rate Q, which can be obtained by relatively simple and inexpensive methods, thus allowing for spatiotemporally resolved flow-rate predictions to be made without requiring explicit knowledge of the full flow-field information underneath the wavy interface.

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“…Also, from the standpoint of system operation and flow rate control, real-time void fraction sensing can be used to anticipate and avoid conditions of dryout or departure from nucleate boiling [13]. For development of correlations, void fraction is typically measured by image analysis of high-speed flow visualizations performed under conditions where optical access is artificially made available [13][14][15][16]. A variety of alternative radiation-, optical-fiber-, ultrasound-and electrical…”

Section: Introductionmentioning

confidence: 99%

Design of a non-intrusive electrical impedance-based void fraction sensor for microchannel two-phase flows

Valiorgue

Ritchey

Weibel

et al. 2014

Meas. Sci. Technol.

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Flow visualization of two-phase flows using photochromic dye activation method

Cited by 28 publications

References 32 publications

A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

Detailed hydrodynamic characterization of harmonically excited falling-film flows: A combined experimental and computational study

Design of a non-intrusive electrical impedance-based void fraction sensor for microchannel two-phase flows

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