In the event of a nuclear power plant accident, iodine is one of the radionuclides of the greatest issue. Present in various chemical forms, the mitigation of outside releases is a crucial aspect of nuclear safety protection measures during a nuclear accident as these airborne iodine releases pose a significant radiological risk to the exposed population in the short term. Pool scrubbing device is one mean of mitigation. Tests were conducted on to study the scrubbing efficiency in a water pool of volatile iodine species: methyl iodide (CH3I) and molecular iodine (I2). This allows us to determine a Decontamination Factor (DF) for each gaseous species, characterizing its trapping capability. The influence of various physical and chemical factors on the trapping was investigated, the experimental parameters were the gas flow regime, pool’s pH, and pool’s temperature. The retention of CH3I by pool scrubbing was unaffected by the flow regime and pool chemical conditions in contrast to I2. Pool scrubbing appears to be an efficient mean to mitigate I2 releases for bubbly regime and alkaline conditions whereas for CH3I, due to its too high volatility, the retention efficiency remains quite low and cannot be considered as an effective mitigation mean.

The potential release of fission products (FPs) to the atmosphere during an hypothetical severe accidents on nuclear facilities is a main issue in nuclear safety. Accurate estimation of these releases is crucial for risk assessment and implementation of appropriate measures. To this end, IRSN studies the mitigation of FPs transported in a carrier gas injected through a liquid pool. This process, referred to 'pool scrubbing', can occur in various accident situations in Pressurized Water Reactors (PWRs), such as Filtered Containment Venting Systems (FCVS) or with the Steam Generator Tube Rupture (SGTR), as well as in nuclear-powered submarines or in new Small Modular Reactors (SMRs) with pressurized water. Experiments dealing with characterization of bubbles hydrodynamics and trapping of iodine compounds (decontamination factors measurements) are currently conducted. In this objective, a dedicated facility named TYFON (Trapping and hYdrodynamics for FissiON products behaviour in pool scrubbing) at IRSN enables to perform hydrodynamics and iodine retention tests for different carrier gas injection rates (characterized by Weber number). In this context, advanced results have been obtained on hydrodynamics in the injection zone and CsI aerosol retention. In line, a new study focused on the impact of a saline solution on these phenomena and on bubble plume modelling has been launched. In the long term, all the experimental data collected, including hydrodynamics and the decontamination factor (DF), will be used to improve the modelling of pool scrubbing phenomenon in the ASTEC code developed by IRSN.

Pool scrubbing has shown potential efficiency to reduce the release of fission products, especially in aerosol forms, into the environment. Considering the large test conditions where pool scrubbing might be encountered, there is still a lack of systematic analysis of this phenomenon, especially its dependence on different hydrodynamic regimes. Experimental work was carried out, where hydrodynamic and decontamination factor measurements were performed. Caesium iodide aerosols were injected into the TYFON facility for different flow regimes (0.08 <= We <= 15 600) by varying both injection flowrate Qinj and nozzle size D0, in which their effects were examined. The Weber number (We) has shown to be capable of characterizing the decontamination factor, when comparing this work with data from literature. Moreover, the different flow regimes induced different sensitivities of aerosol removal mechanisms, where a minimum scrubbing is observed in the transition between bubbly and jet regime. The effect of pool submergence was also investigated in case of bubbly and jet regimes, in which the contribution of residence time and inertial impaction to pool scrubbing was shown. (c) 2023 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Bubble-bubble interactions are relevant to industrial applications, for which air is injected at different flowrates from submerged orifice. These interactions provoke aperiodic bubble formation that affects their departure and size distribution, which is revealed through our experimental data. Air is injected and regulated at flow rate between 10(-4) m(3).s (-1) and10 (-3) m(3).s (-1) from a submerged orifice of inner diameter 12 mm, corresponding to a gas Weber number between 0.16 and 16. Image analysis is carried out to track the formation and departing of bubbles, as well as the formation of a globule, which is a large bubble formed after the bubbles coalescence. Upon increasing the flowrate, the different patterns of bubbling observed have been classified according to the variation of the coalescence position. In a conventional method, bubbles volumes are determined by inspecting the departure frequency and assuming single bubbling spherical pattern. Using the same assumptions and method, we find a good agreement with literature models. Owing to the phenomenological description of the flow, the frequency and volume of globules are characterized. A contrast between the conventional and phenomenological approaches is exposed, revealing a weak applicability of conventional models in estimating bubbles sizes at high flow rates. (c) 2021 Elsevier Ltd. All rights reserved.

The formation of an aqueous droplet in an organic continuous phase was studied experimentally inside a flow-focusing microchannel (190 mu m x 195 mu m: depth x width) in the presence of surfactants. A low viscosity silicone oil (0.0046 Pa s) was used as the continuous phase and a mixture of 48% w/w water and 52% w/w glycerol was the dispersed phase. Two ionic surfactants, C(12)TAB (50 mM) and C(16)TAB (5 mM) were added in the aqueous phase, at concentrations above the CMC values. Four regimes of drop formation were identified, namely squeezing, dripping, jetting and threading, whose boundaries changed when the surfactants were present. The drop formation process and the velocity profiles in both phases in the squeezing and dripping regimes were studied in more detail using a two-colour Particle Image Velocimetry technique. For all solutions studied, three distinct drop formation stages were identified, expansion, necking and pinch-off. The surfactant-laden solutions produced smaller drops. Considering the dynamic interfacial tension, rather than the equilibrium one, it was possible to explain differences in the drop formation between the two surfactant systems in the expansion stage. The forces acting on the forming drops were estimated and showed that the drag force overcomes the interfacial tension force at the transition between the expansion and necking stages. During this transition, the curvature of the neck changed while its thinning rate was increased. The transition from the necking to the pinch-off stage was signified by a flow reversal at the bottom part of the drop. (C) 2018 The Authors. Published by Elsevier Ltd.

Drop formation in a microfluidic flow-focusing device (cross-junction) was studied in absence and presence of one of two ionic surfactants. Four different flow regimes: squeezing, dripping, jetting, and threading were observed in line with existing literature. The effect of surfactant on the transition between flow regimes was shown to depend upon the value of critical micelle concentration and correlates with dynamic surface tension. Drop length in the channel increased as the ratio of flow rate of dispersed to continuous phase, φ, increased. For drops smaller than the channel width, the increase was slow, proportional to φ0.1, yet was much faster, proportional to φ, for larger drops. In contradiction to the expected stabilisation of drops by surfactant, surfactant-laden drops larger than the channel height coalesced inside the channel at a higher rate than surfactant-free drops. It is proposed that the coalescence is caused by the electrostatic attraction due to surfactant redistribution under the high shear stresses near the wall of the channel.

The plug flow of a non‐Newtonian and a Newtonian liquid was experimentally investigated in a quartz microchannel (200‐µm internal diameter). Two aqueous glycerol solutions containing xanthan gum at 1000 and 2000 ppm were the non‐Newtonian fluids and 0.0046 Pa s silicone oil was the Newtonian phase forming the dispersed plugs. Two‐color particle image velocimetry was used to obtain the hydrodynamic characteristics and the velocity profiles in both phases under different fluid flow rates. The experimental results revealed that the increase in xanthan gum concentration produced longer, bullet‐shaped plugs, and increased the thickness of the film surrounding them. From the shear rate and viscosity profiles, it was found that the polymer solution was in the shear‐thinning region while the viscosity was higher in the middle of the channel compared to the region close to the wall. Circulation times in the aqueous phase increased with the concentration of xanthan gum. © 2017 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 63: 3599–3609, 2017

The effect of a cylindrical bluff body on the interface characteristics of stratified two-phase, oil-water, pipe flows is experimentally investigated with high speed Particle Image Velocimetry (PIV). The motivation was to study the feasibility of flow pattern map actuation by using a transverse cylinder immersed in water in the stratified pattern, and particularly the transition from separated to dispersed flows. The cylinder has a diameter of 5 mm and is located at 6.75 mm from the bottom of the pipe in a 37mm ID acrylic test section. Velocity profiles were obtained in the middle plane of the pipe. For reference, single phase flows were also investigated for Reynolds numbers from 1550 to 3488. It was found that the flow behind the cylinder was similar to the two dimensional cases, while the presence of the lower pipe wall diverted the vorticity layers towards the top. In two-phase flows, the Froude number (from 1.4 to 1.8) and the depth of the cylinder submergence below the interface affected the generation of waves. For high Froude numbers and low depths of submergence the counter rotating von Karman vortices generated by the cylinder interacted with the interface. In this case, the vorticity clusters from the top of the cylinder were seen to attach at the wave crests. At high depths of submergence, a jet like flow appeared between the top of the cylinder and the interface. High speed imaging revealed that the presence of the cylinder reduced to lower mixture velocities the transition from separated to dual continuous flows where drops of one phase appear into the other. (C) 2016 The Authors. Published by Elsevier Ltd.

In this paper the effect of a transverse cylindrical rod immersed in water on the flow patterns and interfacial characteristics of an oil-water pipe flow is investigated experimentally. The cylinder is used to passively actuate the transition from stratified to non-stratified flows and to localise the formation of waves and the detachment of drops. The studies are carried out in an acrylic test section with 37 mm ID using as test fluids tap water and Exxsol D140 (density 830 kg m(-3) and viscosity 5.5 cP). The rod has 5 mm diameter and is located at 460 mm from the test section inlet. Flow patterns and interface characteristics were studied with high speed imaging. It was found that the presence of the rod generates waves shortly downstream, from which drops detach, and reduces the mixture velocity for the transition from stratified to non-stratified flows. The average interface height and wave amplitude increase with distance from the rod, while the average wave length and frequency remain almost constant. The Strouhal number is found to be equal to 0.24, while the wave velocities are slightly higher than the mixture velocities. (C) 2016 The Authors. Published by Elsevier Inc.

In this work the coalescence of an aqueous drop with a flat aqueous-organic interface was investigated in a thin gap Hele-Shaw cell. Different concentrations of a nonionic surfactant (Span 80) dissolved in the organic phase were studied. We present experimental results on the velocity field inside a coalescing droplet in the presence of surfactants. The evolution of the neck between the drop and the interface was studied with high-speed imaging. It was found that the time evolution of the neck at the initial stages of coalescence follows a linear trend, which suggests that the local surfactant concentration at the neck region for this stage of coalescence can be considered quasiconstant in time. This neck expansion can be described by the linear law developed for pure systems when the surfactant concentration at the neck is assumed higher than in the bulk solution. In addition, velocity and vorticity fields were computed inside the coalescing droplet and the bulk homophase using a high-speed shadowgraphy technique. The significant wall effects in the Hele-Shaw cell in the transverse axis cause the two vertical velocity components towards the singularity rupture point, from the drop and from the bulk homophase, to be of the same order of magnitude. This movement together with the neck expansion creates two pairs of counteracting vortices in the drop and in the bulk phase. The neck velocity is the average of the advection velocities of the two counteracting vortex pairs on each side of the neck. The presence of the surfactant slows down the dynamics of the coalescence, affects the propagation direction of the pair of vortices in the bulk phase, and reduces their size faster compared to the system without surfactant.

This paper addresses the topic of the influence of the profile of a plate on a turbulent flow. The study is based on numerical results obtained by URANS and hybrid (DDES) turbulence modeling and compared with experimental results. The flat plate has an aspect ratio of 20 (length over thickness) and the edges are not smoothed. The plate includes Shape Memory Alloys (SAM), which allows it to arch under the effect of an electric voltage. The deformation by the material corresponds to a beam deformation and is implemented in the numerical simulation according to this definition. The Reynolds number is Re = 200,000, which led to a turbulent flowwith a Von Karman vortex shedding and Kelvin Helmotz instabilities in the shear layer. The simulations are performed with several turbulence models: k-epsilon-OES, k-omega-BSL-OES, k-omega-DDES-BSL-OES, k-omega-DDES-SST-Menter. These models are used in a first step to determine the three-dimensional flow around the plate plane inclined by 10.. The behavior of the floware found similar between experiment and numerical simulations. The purpose of the curve shape by deformation is then compared to a linear form by rotation of the plate. The curved shape provides the same lift coefficient with less required deformation and thus with a lower drag coefficient and also a lower frequency. The dynamic deformation is slow compared to the freestream velocity, it weakly affects the coefficients and frequencies compared to linear shape.

Particle image velocimetry (piv) measurements are made at the trailing edge of a piezoelectric actuated aileron in order to investigate the physical effect on the flow via high-frequency low-amplitude actuation at high Reynolds numbers. The measurements at different actuation frequencies show the modification of the primary frequency components of the flow with the actuation frequency. A statistical analysis reveals the reduction of the Reynolds stress components which increases with the actuation frequency. Proper orthogonal decomposition (pod) analysis shows the modification of the spatial modes illustrating the vortex breakdown in the shear-layer and the reduction of the temporal mode spectral energy depending on the actuation. It has been shown that a specific low amplitude actuation frequency produces a significant reduction of the predominant shear-layer frequency.

Two complementary micro Particle Image Velocimetry (mu PIV) techniques have been developed in this work to study plug formation at a microchannel inlet during the flow of two immiscible liquids. Experiments were conducted for different fluid flow rate combinations in a T-junction, where all branches had internal diameters equal to 200 mu m. The dispersed phase was a water/glycerol solution and was injected from the side branch of the junction, while the continuous phase was silicon oil and was injected along the main channel axis. In the two-colour mu PIV technique two laser wavelengths are used to illuminate two different tracer particles, one in each fluid, and phase averaged velocity profiles can be obtained in both phases simultaneously. In the high speed bright field gPIV technique, a backlight illuminates the test section, where the dispersed phase plug is seeded with tracer particles. This approach allows velocity profiles of the forming dispersed plugs to be followed in time.Non-dimensional plug lengths were found to vary linearly with the aqueous to organic phase flow rate ratio, in agreement with a well-known scaling correlation. The flowrate ratio also affected the velocity profiles within the forming plugs. In particular, for a ratio equal to one, a vortex appears at the tip of the plug in the early stages of plug formation. The interface curvature at the rear of the forming plug changes sign at the later stages of plug formation and accelerates the thinning of the meniscus leading to plug breakage. The spatially resolved velocity fields obtained in both phases with the two-colour PIV show that the continuous phase resists the flow of the dispersed phase into the main channel at the rear of the plug meniscus and causes the change in the interface curvature. This change of interface curvature was accompanied by an increase in vorticity inside the dispersed phase during plug formation. (C) 2015 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.orgilicenses/by/4.0/).