arXiv subjects

Guillaume Castanet

Publications and source records attributed to Guillaume Castanet.

6 recordsLinked to original sources

arXiv2026

Laser-Induced Fluorescence for measuring salt mass fraction in evaporating saline solutions

A non-intrusive optical diagnostic based on Laser-Induced Fluorescence (LIF) is developed for measuring salt mass fraction in highly concentrated aqueous solutions relevant to absorption heat pump applications. The method relies on a systematic redshift of the fluorescence emission spectra of several dyes, likely induced by an increase of ionic strength with salt mass fraction. A two-color ratiometric approach, based on the ratio of fluorescence intensities in two spectral bands, enables robust mass fraction measurements. This study demonstrates that the techniques is not limited to LiBr but also NaCl, relevant for desalination applications. In parallel, fluorescence lifetime measurements using Time-Correlated Single Photon Counting (TCSPC) reveals that fluorescence lifetime is also affected by the LiBr mass fraction, allowing an alternative measurement technique. For both techniques, many dyes are tested and are compared in terms of salt mass fraction sensitivity. Both techniques are validated independently through comparison with shadowgraphbased measurements during evaporation of droplets. Good agreement is obtained in liquid-phase conditions over a wide range of salt mass fractions, confirming the reliability of the proposed diagnostics. Key sources of uncertainty including temperature, reabsorption effects and phase changes has been identified and analyzed. Finally, preliminary results demonstrate the potential extension of the approach toward planar imaging of evaporating droplets and more complex multiphase flows. The methodology provides a basis for future quantitative diagnostics of heat and mass transfer in desorption systems such as falling-films.

physics.ins-det↗

arXiv2024

Features of the Contact Angle Hysteresis at the Nanoscale: A Molecular Dynamics Insight

Understanding the physics of a three-phase contact line between gas, liquid, and solid is important for numerous applications. At the macroscale, the three-phase contact line response to an external force action is often characterized by a contact angle hysteresis, and several models are presented in the literature for its description. Yet, there is still a need for more information about such model applications at the nanoscale. In this study, a molecular dynamics approach was used to investigate the shape of a liquid droplet under an external force for different wetting regimes. In addition, an analytic model for describing the droplet shape was developed. It gives us the possibility to evaluate the receding and advancing wetting angle accurately. With our modeling, we found that the interplay between capillary forces and viscous forces is crucial to characterize the droplet shape at the nanoscale. In this frame, the importance of the rolling movement of the interface between liquid and vapor was pointed out. We also demonstrate that in the range of the external forces when capillary forces are most significant compared to others, hysteresis is well described by the macroscale Cox-Voinov model.

cond-mat.soft↗

arXiv2021

Molecular dynamics simulation of thermal transport across solid/liquid interface created by meniscus

Understandings heat transfer across a solid/liquid interface is important to develop new pathways to improve thermal management in various energy applications. One of the important questions that arises in this context is the impact of three-phase contact line between solid, liquid and gas on the perturbations of the heat fluxes at the nanoscale. Therefore, this paper is devoted to the investigations of features of thermal transport across nanosized meniscus constrained between two solid walls. Different wetting states of the meniscus were considered with molecular dynamics approach by the variation of the interactional potential between atoms of the substrate and the liquid. The effect of the size of the meniscus on the exchange of energy between two solid walls was also investigated. It was shown that the presence of a three phase contact line leads to a decrease of the interfacial boundary resistance between solid and liquid. Further, investigations with the finite element method were used to link atomistic simulations with the continuum mechanics. We demonstrate that the wetting angle and the interfacial boundary resistance are the required key-parameters to perform multiscale simulations of such engineering problems with an accurate microscale parametrization.

cond-mat.mes-hall↗

arXiv2017

Gibbs adsorption impact on a nanodroplet shape: modification of Young-Laplace equation

An efficient technique for the evaluation of the Gibbs adsorption of a liquid on a solid substrate is presented. The behavior of a water nanodroplet on a silicon surface is simulated with molecular dynamics. An external field with varying strength is applied on the system to tune the solid-liquid interfacial contact area. A linear dependence of droplet's volume on the contact area is observed. Our modified Young--Laplace equation is used to explain the influence of the Gibbs adsorption on the nanodroplet volume contraction. Fitting of the molecular dynamics results with these of an analytical approach allows us to evaluate the number of atoms per unit area adsorbed on the substrate, which quantifies the Gibbs adsorption. Thus, a threshold of a droplet size is obtained, for which the impact of the adsorption is crucial. Moreover, the presented results can be applied for the evaluation of the adsorption impact on the physical--chemical properties of systems with important surface-to-volume fraction.

cond-mat.soft↗

arXiv2010

Liquid Atomization out of a Full Cone Pressure Swirl Nozzle

A thorough numerical, theoretical and experimental investigation of the liquid atomization in a full cone pressure swirl nozzle is presented. The first part is devoted to the study of the inner flow. CAD and CFD software are used in order to determine the most important parameters of the flow at the exit of nozzle. An important conclusion is the existence of two flow regions: one in relatively slow motion (the boundary layer) and a second nearly in solid rotation at a very high angular rate (about 100 000 rad/s) with a thickness of about 4/5th of the nozzle section. Then, a theoretical and experimental analysis of the flow outside the nozzle is carried out. In the theoretical section, the size of the biggest drops is successfully compared to results stemming from linear instability theory. However, it is also shown that this theory cannot explain the occurrence of small drops observed in the stability domain whose size are close to the Kolmogorov and Taylor turbulent length scale. A Phase Doppler Particle Analyser (PDPA) is used to characterize the droplet size and velocity distribution. Due to centrifugal force, the smaller droplets tend to prevail on the spray axis and a peak close to the Taylor length scale appears progressively in the PDF when increasing the distance from the nozzle. It is then assumed that these small droplets are the results of a turbulent cascading atomization process and that in the near nozzle area, since centrifugal segregation is small, PDF can therefore be fitted with a log-stable law (Rimbert and Séro-Guillaume, 2004). The value of the stability index is found to be 1.35 very close to a previous experimental result of 1.39 (Rimbert and Delconte, 2007) but far from a known theoretical value of 1.70 (Rimbert, 2010). This let think about a slightly different underlying process due to the helical nature of the turbulence.

physics.flu-dyn↗

arXiv2010

Crossover between Rayleigh-Taylor Instability and turbulent cascading atomization mechanism in the bag-breakup regime

The question whether liquid atomization (or pulverization) resorts to instability dynamics (through refinements of Rayleigh-Plateau, Rayleigh-Taylor or Kelvin-Helmholtz mechanism) or to turbulent cascades similar to Richardson and Kolmogorov first ideas seems to be still open. In this paper, we report experimental evidences that both mechanisms are needed to explain the spray drop PDF obtained from an industrial nozzle. Instability of Rayleigh-Taylor kind governs the size of the largest droplets while the smallest ones obey a PDF given by a turbulent cascading mechanism resulting in a log-Lévy stable law of stability parameter close to 1.68. This value, very close to the inverse of the Flory exponent, can be related to a recent model for intermittency modeling stemming from self-avoiding random vortex stretching.

physics.flu-dyn↗