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To study weathering behavior under water-unsaturated conditions, flow-through dissolution experiments using a porous rhyolite were performed under both saturated and unsaturated conditions. When water was passed into a dried rock core, water saturation rapidly increased to 0.3 in 2hours, and then reached 0.4 in 6 days. The proportion of the reactive surface area under the unsaturated condition to that under the saturated condition, Auns/As, was 0.46 after 1 day and increased to 0.90 in 6 days. Because Auns/As was always greater than water saturation, the surfaces of air- filled pores seemed to be wetted with a water film and dissolved. The water film thickness was estimated to be 2–3nm. The reason for Auns/As < 1 may be that the flushing efficiency of dissolved elements in the water film was not enough to keep the concentration far from equilibrium, and thereby the dissolution rate in the water film was decreased.

When water and entrapped gas co-exist in pore spaces of a geological medium, a water film is formed on grain surfaces, which potentially influences chemical reaction and mass transport. We developed a model to estimate the film thickness in a geological medium using a concept of disjoining pressure associated with the electric double layer repulsion force and van der Waals force. The model indicates that the thickness of the water film associated with the occurrence of gas entrapment is controlled by the diameter of pore (the diameter of meniscus), and that larger pores have thicker water films. Examples of the relationship between pore size distribution and film thickness are shown.

International audience; This work is devoted to modeling the evolution of the homogenized solute diffusion coefficient within unsaturated granular materials by means of micromechanics approach. On the basis of its distinct role in solute diffusion, the liquid water within unsaturated granular materials is distinguished into four types, namely intergranular layer (interconnected capillary water), isolated capillary water, wetting layer and water film. Application on two sands shows the capability of the model to accurately reproduce the experimental results. When saturation degree is higher than the residual saturation degree Srr, the evolution of homogenized solute diffusion coefficient with respect to the saturation degree depends significantly on the connectivity of the capillary water. Below Srr, depending on the connectivity of the wetting layer, the homogenized solute diffusion coefficient within unsaturated sands decreases by 2–6 orders of magnitude with respect to that in bulk liquid water. The upper bound of the solute diffusion coefficient contributed by the water films is 4–6 orders of magnitude lower than that in bulk liquid water.

To investigate the heterogeneous uptake of SO2 by yellow sand (China loess, Kosa) particles, we used a cylindrical flow reactor to evaluate the deposition of SO2 onto yellow sand particles. The reactor, which was developed in our laboratory, permits us to vary experimental conditions (e.g., flow rate, gas concentration, relative humidity [R.H.]), and because the gas flow in the reactor was laminar, so that we could evaluate only the SO2 deposition that was due to the diffusion of SO2 molecules in the reactor.Exposure experiments of yellow sand particles to SO2 and HF were performed by the above reactor. The deposition velocities in the exposure to single component gas were compared with those in the exposure to mixed gas.It can be considered that the competitive depositions of SO2 and HF would occur in the latter exposure.The SO2 uptake coefficient depended on relative humidity. These marked changes at R.H. = 60% were probably caused by the formation of a bulk water film on the yellow sand particles; the formation of the water film substantially changed the properties of the mineral dust surface. An SO2 uptake coefficient that takes R.H. into consideration should be used in atmospheric models to predict the dynamics of the interaction between yellow sand particles and SO2.

Understanding how ozone is deposited on vegetation canopies is needed to perform tropospheric greenhouse gas budgets and evaluate the associated damage on vegetation. In this study, we propose a new multilayer scheme of ozone deposition on vegetation canopies that predicts stomatal, cuticular and soil deposition pathways separately. This mechanistic ozone deposition scheme is based on the multi-layer, multi-leaf mass and energy transfer model MuSICA. This model was chosen because it explicitly simulates the processes of rain interception, through fall and evaporation at different depths within the vegetation canopy, so that ozone deposition on wet leaf cuticles can be explicitly modelled with ozone dissolution, diffusion and chemical reaction inside the water films. The model was evaluated against a 3-year dataset of ozone, CO2 and evapotranspiration flux measurements over a winter wheat field near Paris, France (ICOS Fr-GRI). Only periods with fully developed canopies (including senescence) were considered to minimise the contribution of soil deposition to the total ozone flux. Before senescence, the model could reproduce the measured ozone deposition rates as well as the CO2 and water vapour fluxes. During senescence, large ozone deposition rates were observed under wet canopy conditions that could only be explained by first-order reaction rates in the water film of around 105 s−1. Such reaction rates are not compatible with the chemical composition of rainwater. We therefore hypothesise that, during senescence, the cell content leaks out of the leaves when they become wet, exposing anti-oxidants to ozone. These results provide for the first time a mechanistic explanation of the commonly observed increase in ozone deposition rates during rain or dew formation.

Water droplets emitted from cooling towers must be prevented for several reasons, human health hazards are the most important ones. The generation and control of these droplets are the main tasks for drift eliminators: devices installed inside mechanical draft cooling towers useful in order to prevent water droplets, originated by the crossflow between air and water inside the tower, from being released into the environment. This is the phenomenon called ‘drift’. In this paper, the operating conditions of a type of drift eliminator placed in a cooling tower are studied. This work is focused on the numerical and experimental characterization of the multiphase flow taking place when water droplets, drifted by the airstream, impact on the water film formed over the drift eliminators plates. The problem of these drop impacts has been studied throughout an experimental installation and a numerical model has been developed throughout the ANSYS software and several VOF multiphase flow simulations have been carried out showing a good agreement with experimental data

Tropospheric ozone is a greenhouse gas but also a powerful oxidant that impacts vegetation health and productivity. In order to analyse the impact of ozone on vegetation functioning it is necessary to separate stomatal ozone deposition that penetrates inside the leaf interiors from non-stomatal deposition that result from ozone chemical destruction on leaf cuticles, in the soil or in the air inside the canopy. The central objective of this PhD work is to improve our understanding and modelling of the processes involved in non-stomatal ozone deposition and more specifically in ozone deposition on water films on leaf surfaces. For that purpose I used the soil-vegetation-atmosphere transfer model of mass and energy MuSICA. The choice of this model was motivated by its ability to estimate the quantities of water on foliage at different levels inside the canopy. This allowed me to model ozone dissolution, diffusion and reaction in the water film on wet leaves. This new deposition pathway could explain observed ozone fluxes over wheat in wet conditions by adjusting the chemical reaction rate of ozone in the water film from 103 s 1 at the beginning of the growing season, up to 105 s 1 during senescence. This reaction rate seemed to vary between species (wheat, beech, maritime pine) but the trend with the senescence remained. These results were then confirmed by lab experiments using an original setup, on wheat and beech, but also white pine and pedunculate oak. Exchanges of chemical compounds between the leaf and the water film that would react with ozone could explain the order of magnitude of the reaction rate and its increase during senescence.; L'ozone troposphérique est un gaz à effet de serre et un puissant oxydant qui impacte la santé et la production végétale. Afin d'analyser son impact sur le fonctionnement de la végétation il est nécessaire d'effectuer une partition entre le dépôt stomatique, qui pénètre à l'intérieur des feuilles, et le dépôt non stomatique, qui résulte de la destruction chimique de l'ozone sur les cuticules foliaires, le sol ou dans l'air à l'intérieur du couvert. L'objectif central de ce travail de thèse est d'améliorer la compréhension et la modélisation des processus impliqués dans le dépôt non stomatique d'ozone et plus particulièrement dans le dépôt sur les films d'eau à la surface des feuilles. Le modèle de transfert de masse et d'énergie sol-végétation-atmosphère MuSICA, capable d'estimer les quantités d'eau sur le feuillage à différents niveaux dans le couvert, a permis de modéliser la solubilisation puis la diffusion et réaction de l'ozone dans l'eau sur les feuilles. Cette voie de dépôt a permis d'expliquer les flux d'ozone observés sur blé en conditions humides en ajustant les valeurs du taux de réaction chimique de l'ozone dans le film d'eau de 103 s 1 en début de saison à 105 s 1 pendant la sénescence. Ce taux semble varier entre les espèces végétales (blé, hêtre et pin maritime) mais la tendance avec la sénescence persiste. Ces résultats ont été confortés par un dispositif expérimental original en laboratoire, sur blé, hêtre, pin blanc et chêne pédonculé. Des échanges de composés chimiques entre la feuille et le film d'eau réactifs avec l'ozone pourraient expliquer les ordres de grandeur obtenus et l'augmentation du taux de réaction en période de senescence.

Water drift emitted from cooling towers is objectionable for several reasons, mainly due to human health hazards. Generation and control of drift depends mostly on the drift eliminator, a device installed in mechanical cooling towers to prevent the escape of droplets (drift). These eliminators induce a rapid alternation of direction changes, and then the droplets cannot follow the path lines of the airflow within the channels of the eliminator and impact on the plates of it, falling back to the cooling tower ground. This paper focuses on the numerical study of a type of drift eliminator, validated by experimental tests. Three main aspects are considered: the water film formed on the plates of drift eliminators, the size of water droplets detached from this film and the condition of the detachment of these droplets. Good agreement is obtained between numerical and experimental results. The study shows that the behavior of water droplets is very influenced by the air velocity inside the cooling tower. This research is sponsored by the Spanish Government (Projects ENE2010-21679-C02-01 and -02), as well as by the Seneca-Agency for Science and Technology of the Region of Murcia, Spain (Project 15184/PI/10).

Micromechanical approach is employed to investigate the transport and freezing within unsaturated porous media. In unsaturated porous media, water film as well as disjoining pressure are introduced in the transport and freezing problems. In the modeling, it is found that, capillary layer along with pore water dominate the transport at high saturation degree (Sr>10%). However, water film will play a significant role in transport at low saturation degree (Sr 10%). Cependant, le film d'eau jouera un rôle important dans le transport à degré de saturation basse (Sr

Micromechanical approach is employed to investigate the transport and freezing within unsaturated porous media. In unsaturated porous media, water film as well as disjoining pressure are introduced in the transport and freezing problems. In the modeling, it is found that, capillary layer along with pore water dominate the transport at high saturation degree (Sr>10%). However, water film will play a significant role in transport at low saturation degree (Sr 10%). Cependant, le film d'eau jouera un rôle important dans le transport à degré de saturation basse (Sr

Nanoscopic liquid-like water films were deposited onto silica mesoporous aggregates from vapour phase at 30 °C and at 0.9 P/P0 or from water–paraffin emulsions. The water layers, surround entirely the silica aggregates, reduced their specific surface area from 136 ± 5 m2/g to 80 ± 4 m2/g, and leaved substantially unchanged their meso-porosity. No formation of nano-pores smaller than 1 nm was observed. The dispersions in liquid paraffin of these powders, without applying any shear rate, result different from the correspondent suspensions obtained with dry silica meso-pores aggregates especially when the dispersions reach the gel-like status, i.e. after the percolation threshold θ*, set at 8.2% (v/v). For θ values less the θ* the water films act as insulation to reduce the stability of the dispersions, i.e. to reduce the net attractive forces between the silica surfaces and the paraffin. In the gel-like regime, the adsorbed water molecules play a new and emerging role. As the solid volume concentration is increased the silica aggregates covered with water layers come in to contact and form a “liquid menisci” between neighbouring films that allow the formation of a “pendular state” because of capillary forces. These capillary/viscous forces cause a second generation of gel agglomerates, few millimetres in dimension, that are interconnected between them and somewhat separated by thin voids. By comparison with the gel status formed by the dry silica agglomerate dispersions, it has been derive that the paraffin molecules migrate inside the void spaces created throughout the “pendular state”. Maximum static yield stress and separation energies equal to 2500 Pa and 3 × 10−18 J, respectively, were measured and compared with values of 1190 Pa and 3 × 10−19 J for dispersions without adsorbed water layers.

A study was conducted to demonstrate self-organization of perturbations in fluid films. The flow of such self-organization perturbations in the films considered in the rectangular system of coordinates OXYZ for the Reynolds numbers Re ≤ 20 by the method of multiscale expansions were analyzed to investigate the self-organization perturbations. A computing experiment was carried out for the process of self-organization of perturbations during the flow of a vertical water film to investigate the long-term nonlinear development and the interaction of perturbations on the surface of the nonisothermal fluid film.

International audience; In this paper, a numerical analysis of the coupled heat and mass transfer is proposed for a rectangular cell of form factor equal to 10. In particular, the heat and mass transfer are considered in the solid medium of the heated wall, in the liquid medium of the falling film and in the gaseous medium inside the cell. The solution of the transfer equations together with the appropriate boundary conditions allowed us to study in detail the evaporation and condensation mechanisms inside the cell. The study of the influence of the heated wall conductivity and of the heat distribution on the transfer phenomena allowed us to propose recommendations in order to improve the production of the cell.

The goal of the research was to find the relation for determining the heat transfer coefficient between a free streaming water film and metal corrugated surface. The relation between relevant parameters which determine the heat transfer coefficient has been obtained by means of Wilson-plot method using data from the measurement.

Le LIMA (Laboratoire International des Matériaux Antigivre) en collaboration avec le CIRA (Italian Aerospace Research Centre) a développé un logiciel simulant l'accrétion de la glace en régime sec et humide sur un objet bidimensionnel fixe. Le modèle thermodynamique de l'accrétion de glace est similaire aux modèles existants, LEWICE aux États Unis, TRAJICE en Grande Bretagne, ONERA en France ou CANICE au Canada, où les corrélations empiriques ont été remplacées par des analyses physiques. La hauteur des rugosités dépend de l'état de l'eau en surface qui peut exister sous forme d'un film, de gouttes ou de ruisselets et elle est calculée à partir de l'équation d'équilibre entre les forces de tension de surface, aérodynamique et gravitationnelle. Les masses d'eau liquide résiduelle, de ruissellement et d'arrachement sont calculées à partir de modèles analytiques basés sur la hauteur des rugosités, tandis que la nouvelle position de la surface est calculée à l'aide d'une méthode géométrique basée sur les bissectrices entre les panneaux définissants la surface. Le modèle d'accrétion a été validé pour les régimes sec et humide avec des formes de glace obtenues expérimentalement en soufflerie par Shin et Bond. Les formes de glace prédites numériquement sont similaires à celles mesurées expérimentalement et le modèle a été en mesure de générer les formes complexes de glace observées comme les cornes et les cannelures. Les particularités du modèle développé font qu'il pourrait être appliqué aux cas où les vitesses sont faibles ou élevées, ou encore pour les objets tournants par rapport au sol comme pour les pales d'éoliennes ou d'hélicoptères. AMIL (Anti-Icing Materials International Laboratory), in a joint project with CIRA (Italian Aerospace Research Center), developed software to simulate ice accretion in wet and dry regime on a fixed two-dimensional object. The ice accretion thermodynamic model is similar to existing models: LEWICE in the United States, TRAJICE in the United Kingdom, ONERA in France and CANICE in Canada, into which empirical correlations were replaced by physical analyses in the developed software. The roughness height depends on the surface water state, which can exist in the form of a film, bead or rivulet and is calculated from the equilibrium equation between the surface tension, aerodynamics and gravitational forces acting over the bead. Residual, runback and shedding water masses are calculated using analytical models based on the roughness height and the new surface position is calculated using a geometric method based on the bisection between the defining panel's surfaces. The accretion model was validated for dry and wet regimes with ice profiles obtained by Shin and Bond in wind tunnel experiments. The ice profiles numerically predicted are similar to those measured in wind tunnel and the model is able to generate the complex ice profiles observed in experiments, such as horns and grooves. The characteristics of the developed model are such that it can be applied to cases where speeds are slow or fast, or those involving object rotating with regard to the ground as blades of wind turbines or helicopters.