• Sciences de l'ingénieur
  
• Sciences de l'ingénieur/Génie civil/Géotechnique
  
• Sciences de l'ingénieur/Génie civil
  
• Sciences de l'environnement/Ingénierie de l'environnement
  
• Sciences de l'ingénieur/Milieux fluides et réactifs
  
• Planète et Univers/Sciences de la Terre/Géochimie
  
• Sciences de l'environnement/Milieux et Changements globaux
  
• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Physique/Mécanique/Mécanique des matériaux
  

The aim of this communication is to analyse the influence of water activity and total pressure on water evaporation. The system is composed of liquid and gas phases, separated by a plane surface, contained in a cylinder whose volume is regulated by a piston. Water activity is regulated by saturated salt solutions and pressure by the piston. The experimental device and procedures were defined to limit the temperature variation at the interface. A transient method is used. From a steady state, a volume increment is imposed; the resulting non-equilibrium leads to an increase in the partial pressure of water vapour to the equilibrium pressure imposed by the solution. Numerical calculation shows little variation in temperature in the gas-liquid interface under the experimental conditions. An evaporation model is adopted taking into account chemical potential discontinuity at the interface. The surface flux evaporation and chemical potential jump at the interface are deducted from the total pressure recording. In the neighbourhood of equilibrium, the surface flux of phase change is shown to be proportional to the chemical potential jump. The surface coefficient of evaporation increases with the total pressure of the gas phase and water activity.

In this paper, we analyze and model the mass transfer of trichloroethylene in the surface layer of a soil. Our study essentially focuses on arid soils taking into account the phase change liquid-vapor. We have then examined the validity of the assumption of local equilibrium by comparing the values of the instantaneous pressure of the trichloroethylene vapor and the equilibrium vapor pressure during the transfer process. It appears that the assumption of local equilibrium during the transfer of trichloroethylene cannot be admitted.

This paper presents a new mechanical method to determine Henry's law constant (HLC) of a volatile organic compound (VOC). This method is an extension of the one proposed by Ouoba et al. (2010) to determine the water activity in porous media. This work focuses on TCE and aims at characterizing its liquid-vapor equilibrium in various cases in the form of a pure liquid phase or dissolved in an aqueous solution, adsorbed or not in a natural soil. A liquid phase is disposed in a closed chamber whose volume can be incrementally increased. The recording of the total gas pressure leads to evaluating the vapor partial pressure of a volatile compound even in the case of an aqueous solution. This method has been validated using various aqueous solutions of TCE and the HLC obtained is in agreement with the literature. Then, the validity of Henry's law has been asserted in the case of an aqueous solution of TCE adsorbed in a hygroscopic soil. Indeed, a linear relation between the vapor partial pressure of TCE and its concentration has been obtained while the HLC is about 16% lower. This result highlights the influence of adsorption phenomena on vapor/liquid equilibrium.

This paper presents a new method to determine the evaporation coefficient of trichloroethylene using a new experimental device called " activity-meter ". This device and the associated method have been developed in the Laboratory of Mechanical Engineering of the University of Montpellier 2 (France). The influence of diffusion on the vapor pressure of trichloroethylene and the influence of temperature at the liquid-gas interface were first determined. The results show that diffusion phenomena have no influence on the vapor pressure of trichloroethylene beyond 400 seconds of experimental time and the temperature is almost constant during experiments. Thus, in order to take into account the effects that are only due to the variation of partial pressure of trichloroethylene at the liquid-gas interface, the time interval used is between 400 seconds and the time required to reach equilibrium. The influence of pressure and temperature on the evaporation coefficient of pure trichloroethylene in an arid soil was then highlighted. The results show that the evaporation coefficient of trichloroethylene decreases with total vapor pressure but increases with temperature. A comparative study on evaporation coefficients conducted on water, heptane and trichloroethylene shows that our results are in good agreement with results on volatility.

Cette note présente une méthode mécanique pour la détermination de la porosité totale d'un sol. La méthode présentée consiste à placer un échantillon de sol dans une cellule régulée dont on peut faire varier le volume par paliers grâce à un piston. La porosité du sol se déduit de la variation de la pression totale de la phase gazeuse lors des incréments de volume. La méthode a été validée sur un sol en considérant 5 échantillons de porosités différentes. Les résultats expérimentaux sur la porosité totale sont en bon accord avec les résultats théoriques sur l'ensemble des essais réalisés.