Laurent Aprin

Experimental study of hydraulic ram effects on a liquid storage tank: Analysis of overpressure and cavitation induced by a high-speed projectile.

This work is part of a project for evaluating catastrophic tank failures caused by impacts with a high-speed solid body. Previous studies on shock overpressure and drag events have provided analytical predictions, but they are not sufficient to explain ejection of liquid from the tank. This study focuses on the hydrodynamic behavior of the liquid after collision to explain subsequent ejection of liquid. The study is characterized by use of high-velocity projectiles and analysis of projectile dynamics in terms of energy loss to tank contents. New tests were performed at two projectile velocities (963 and 1255 m s(-1)) and over a range of viscosities (from 1 to 23.66 mPa s) of the target liquid. Based on data obtained from a high-speed video recorder, a phenomenological description is proposed for the evolution of intense pressure waves and cavitation in the target liquids.

Investigation on cone jetting regimes of liquid droplets subjected to pyroelectric fields induced by laser blasts

Electrical conductivity and viscosity play a major role in the tip jetting behaviour of liquids subjected to electrohydrodynamic (EHD) forces, thus influencing significantly the printing performance. Recently, we developed a nozzle- and electrode-free pyro-EHD system as a versatile alternative to conventional EHD configurations and we demonstrated different applications, including inkjet printing and three-dimensional lithography. However, only dielectric fluids have been used in all of those applications. Here, we present an experimental characterization of the pyro-EHD jetting regimes, induced by laser blasts, of sessile drops in case of dielectric and conductive liquids in order to extend the applicability of the system to a wider variety of fields including biochemistry and biotechnology where conductive aqueous solutions are typically used.

Atmospheric dispersion modeling using Artificial Neural Network based cellular automata

Forecasting atmospheric dispersion in complex configurations is a current challenge in fluid dynamics in terms of calculation time and accuracy. CFD models provide good accuracy but require a great computation time. Simplified or empirical models are designed to quickly evaluate the dispersion but are not adapted to complex geometry. Cellular Automata coupled with an Artificial Neural Network (CA-ANN) are developed here to calculate the atmospheric dispersion of methane (CH4) in 2D. Efforts are made in reducing computation time while keeping an acceptable accuracy. A CFD simulations database is created and the Advection-Diffusion Equation is discretized to provide variables for the ANN. Neural network design is made thanks to best sampling selection, architecture selection and optimized initialization. The coefficient of determination is over 0.7 for most cases of the test set despite small errors accumulated through time steps. CA-ANN is faster than CFD models by a factor from 1.5 to 120. Display Omitted A new atmospheric dispersion model is developed based on combination of Cellular Automata and Artificial Neural Networks.Comparisons are made with CFD RANS standard k-ź model on 2D free field dispersion of methane.CA-ANN is faster than CFD standard k-ź by a factor from 1.5 to 120 in the modeled simulations while keeping accuracy.

Environmental Parameter Effects on the Fate of a Chemical Slick

Recent data highlights the growing trend in the transport of dangerous substances and the consequent evolution in legislation concerning such substances, whether on a European level (evolution of the Standard European Behaviour Classification, or SEBC code) or on a worldwide scale (new MARPOL-Annex II classification which entered into force on 1st January 2007, the OPRC-HNS Protocol, as well as the HNS Convention). This evolution is however based exclusively on data from the literature which all too often cannot be applied to spills, as it does not take into account the influence of factors in the marine environment on the physico-chemical characteristics of the product spilt.

An experimental investigation of evaporation rates for different volatile organic compounds

Experiments were performed in order to measure evaporation rates of four different volatile organic compounds (VOC; 2‐propanol, 1‐hexene, acetone, propanal) and water. Evaporation mass flow rates and liquid temperatures where recorded. Different correlations were tested versus the experimental. Exponents and constant were recalculated to fit the experimental data. This new correlation was tested on an additional VOC experimentation (ethanol) and the accuracy of the correlation was satisfying. The correlation robustness was investigated versus temperature and wind velocity.

Overpressure wave interaction with droplets: time resolved measurements by laser shadowscopy

Risk sciences involve increasingly optics applications to perform accurate analysis of critical behavior such as failures, explosions, fires. In this particular context, different area sizes are investigated under high temporal sampling rate up to 10000fps. With the improvement of light sources and optical sensors, it is now possible to cope with high spatial resolution even for time resolved measurement. The paper deals with the study of the interaction between overpressure waves, occurring in case of explosion for example, with a liquid droplet present in the vicinity of the overpressure wave. This is a typical scenario encountered in case of industrial breakdown including liquid leakage and explosions. We designed an experimental setup for the evaluation of the interaction between the overpressure wave and falling liquid droplets. A gas chamber is filled with nitrogen until breakage of the outlet rupture disk at about 4 bar. The droplets fall is controlled by an automatic syringe injector placed in the overpressure wave. The imaging system is based on laser shadowscopy. The laser source is a double cavity 15mJ- 1000Hz Nd YLF laser emitting double pulses of about 10ns at 527nm. To record the double pulse after crossing the falling droplets, the transmitted light is captured by a lasersynchronized double frame camera. Since these measurements are time-synchronized, it is then possible to know accurately the different parameters of the phenomenon, such as overpressure wave velocity, droplets diameter, and Reynolds number. Different experiments have been carried out at about 4000 doubleframe/s. The paper presents the whole experiment, the enhancements of the setup and the results for different liquid products from water to acetone.

Behavior of chemicals in the seawater column by shadowscopy

Ninety percent of the Global Movement of Goods transit by ship. The transportation of HNS (Hazardous and Noxious Substances) in bulk highly increases with the tanker traffic. The huge volume capacities induce a major risk of accident involving chemicals. Among the latest accidents, many have led to vessels sinking (Ievoli Sun, 2000 - ECE, 2006). In case of floating substances, liquid release in depth entails an ascending two phase flow. The visualization of that flow is complex. Indeed, liquid chemicals have mostly a refractive index close to water, causing difficulties for the assessment of the two phase medium behavior. Several physics aspects are points of interest: droplets characterization (shape evolution and velocity), dissolution kinetics and hydrodynamic vortices. Previous works, presented in the 2010 Speckle conference in Brazil, employed Dynamic Speckle Interferometry to study Methyl Ethyl Ketone (MEK) dissolution in a 15 cm high and 1 cm thick water column. This paper deals with experiments achieved with the Cedre Experimental Column (CEC - 5 m high and 0.8 m in diameter). As the water thickness has been increased, Dynamic Speckle Interferometry results are improved by shadowscopic measurements. A laser diode is used to generate parallel light while high speed imaging records the products rising. Two measurements systems are placed at the bottom and the top of the CEC. The chemical class of pollutant like floaters, dissolvers (plume, trails or droplets) has been then identified. Physics of the two phase flow is presented and shows up the dependence on chemicals properties such as interfacial tension, viscosity and density. Furthermore, parallel light propagation through this disturbed medium has revealed trailing edges vortices for some substances (e.g. butanol) presenting low refractive index changes.

Liquid blending: an investigation using dynamic speckle interferometry

The dynamics of liquid-liquid mixing is a difficult problem, encountered in many scientific and engineering branches. Experiments in this field are mandatory to help building sound mathematical models, finding out the best fit parameters, evaluating the degree of confidence of these models, or detecting traces of unwanted dangerous substances. The investigations reported here are driven by water pollution concerns. For analyzing the water-pollutant blending behavior, dynamic speckle interferometry has been preferred to more standard optical full field methods, like deflectometry, or classical and holographic interferometry. The choice of this technique is vindicated. The opto-fluidic system is described. A first series of results is presented, demonstrating the effectiveness of the technique and showing qualitatively how two liquids blend in controlled conditions. In the last part of the paper, recently appeared processing schemes, including empirical mode decomposition, Hilbert transform and piecewise treatment, give access to the numerical values of the phase maps computed for each frame of the recorded sequence. These phase maps represent the refractive index distributions integrated along the line of sight. They provide a better visualization of the dynamics of the blending behavior and therefore an improved understanding of the phenomena. These encouraging preliminary results should open the door to a full characterization of the method and to further flow investigations and diagnostics.

Recent developments in high speed imaging and applications in speckle light

High speed imagers record images at much higher speed than perceived by the human eye, but also enable to analyze it in different time bases. Recording is the keystone of sensor. It can either be embedded or remoted. The advantage of the onboard system mainly relies on the transfer speed to the in situ memory (including at the photon to charge conversion site). Its major drawback can be the onboard memory size limit. Remote storage requires the transfer of information very quickly to networks of high speed discs. If the main advantage lies in virtually infinite memory size, major drawback is the transfer speed between the camera and the external memory device. Choosing an appropriate high speed camera must be done by selecting, the maximum frame per second rate, minimum exposure time versus sensitivity and maximum recording time versus resolution and speed. Some imagers can now lead to 7kfps in relatively large resolution to 20kfps for reduced 1Mpixel images. Optics and light sources are important as continuous light require freezing the object movement by the camera exposure time, while pulsed source will remove the motion blur. For imaging, pulsed laser source in uncoherent radiation can even be used. Aperture of the optical system will determine speckle size or depth of field. Most of the imagers can be employed lensless for digital holography purposes. Small sensitive pixel will then be very attractive for this. This paper presents the recent developments and application in speckle light.

High-speed imaging optical techniques for shockwave and droplets atomization analysis

Abstract. Droplets atomization by shockwave can act as a consequence in domino effects on an industrial facility: aggression of a storage tank (projectile from previous event, for example) can cause leakage of hazardous material (toxic and flammable). As the accident goes on, a secondary event can cause blast generation, impacting the droplets and resulting in their atomization. Therefore, exchange surface increase impacts the evaporation rate. This can be an issue in case of dispersion of such a cloud. The experiments conducted in the lab generate a shockwave with an open-ended shock tube to break up liquid droplets. As the expected shockwave speed is about 400  m/s (∼Mach  1.2), the interaction with falling drops is very short. High-speed imaging is performed at about 20,000 fps. The shockwave is measured using both overpressure sensors: particle image velocimetry and pure in line shadowgraphy. The size of fragmented droplets is optically measured by direct shadowgraphy simultaneously in different directions. In these experiments, secondary breakups of a droplet into an important number of smaller droplets from the shockwave-induced flow are shown. The results of the optical characterizations are discussed in terms of shape, velocity, and size.