Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions

Abstract

SUMMARYThis paper deals with the moisture exchanges occurring between soils and the surrounding atmosphere. Convective drying tests are performed on Awans silts at different drying temperatures and air relative humidities in order to reproduce the natural drying conditions. The experiments improve the understanding of the vapour transfers kinetics between the soil samples and the atmosphere. The experimental results are analysed assuming that the transfers take place in a boundary layer existing at the surface of the porous medium. The influence of the thermal conditions on the evaporation is also taken into account. In our model, coupled vapour and energy exchanges are controlled by mass and heat transfer coefficients characterizing the boundary layer. These coefficients are determined from the drying experiments. The modelling of the drying tests in non-isothermal conditions is performed in order to validate the formulation of the vapour and heat exchanges. The numerical results present a good agreement with the kinetic of the materials desaturation determined during the tests. The analysis of the moisture transport mechanisms into the sample and at the boundary shows that at the beginning of the test, the drying is first achieved by the transport of moisture in its liquid form and its evaporation at the sample outer boundary in contact with the atmosphere. In a second step, vapour diffusion becomes predominant into the sample and it corresponds to the most important decrease of relative humidity.

Using Local Second Gradient Model and Shear Strain Localisation to Model the Excavation Damaged Zone in Unsaturated Claystone

“…One of them is to control the vapour phase by submitting samples to a relative humidity regulated with salt solutions in a desiccator (Delage et al 1998;Romero et al 2001;Young 1967). Another technique that reproduces air circulation is the convective drying test during which air is blew at the material surface (Ta 2009;Gerard et al 2010;Léonard et al 2005). Generally, the relative humidity, the temperature and the speed of the air are controlled during the drying.…”

Study of the Drying Behavior of Resorcinol Formaldehyde Hydrogels: Experimental Investigation and Numerical Framework

“…The preheating period (I) is very short and corresponds to an increase in drying rate. The temperature at the surface of the sample also increases from its initial value to the temperature of the wet bulb [Gerard et al (2010)]. …”

“…Drying tests have been first carried out to characterize the drying kinetics of RF hydrogels. The experiments are used to calibrate the transfer parameters of a convective drying law based on the boundary layer model [Gerard et al (2010)]. Ultimately, the goal is to model the Hydromechanical behavior of the RF gels during drying and predict crack genesis.…”

Inputs from in situ experiments to the understanding of the unsaturated behaviour of Callovo-Oxfordian claystone

“…Sample are subjected to air with a control Relative Humidity and mass or/and strain changes are measured. Some devices rely on a static atmosphere with saline solution [10][11][12], other used complex system with a steam generator and a heating channel, in which air is blown through the chamber [13].…”