Fluids and Porous Material

Research Aim | Research Methodology | Transport | Heat and mass transport at air-material interfaces | Water sorption of wood | Sustainable retrofit of historical buildings


The rich pallet of interactions are studied from nano- to macroscale and from very short to long time scales.
We focus on:

  • fluid (gas and /or liquid) transport at different pore scales and its coupling to heat transport.
  • phase change between liquid and gas at molecular, pore and macro- scales, including heat exchange.
  • coupled mechanical-sorption hysteresis behaviour, including swelling-shrinkage.
  • surface phenomena such as droplet impact on porous substrates, film forming and run-off.

More applied research covers applications such as convective drying, hygrothermal behaviour of building components, leaching of biocides.

Schematic overview of on-going research in terms of scales and investigation methods (Carmeliet et al., 2013)

Methods and Approach

Our scientific approach is based on the coupling of advanced experimental and computational methods. Advanced imaging is used to document the fluid-porous interactions in the material at different scales, providing essential insights in the undertanding of the phenomena at play. Theorethical and computational modeling provides the capability to determine material properties from experiments using inverse identification, to design optimal experiments and to explore new pathways for material development and technology innovation.

Methods and Approach

Transport in porous media (observed by neutron imaging)

Water flow | Water vapor flow | Other fluids | Neutron imaging

Water flow

Fluid transport in heterogeneous multiscale porous media is studied experimentally to elucidate the physics at play and to provide modeling validation datasets.

Porous asphalt, designed to reduce aquaplaning and noise levels in highways, displays a complex systems of very large and very small interconnected pores.

Water uptake in wood presents various wetting patterns, as imaged with neutron radiographs.

Neutron imaging of porous asphalt: dry and wet states at different saturation degree; black and white differentials, segmented at 30% saturation. Capillary uptake

Water vapor flow

Forced convective drying of fruit is analyzed non-destructively with neutron imaging to analyze the drying rate, evolution of shrinkage and moisture content distribution.

Moisture distribution in apple blocks during drying. Raw neutron radiographs of apple slices, with and without peel, before and after drying.

Other fluids

We investigate plant sap flow and transpiration with perspectives towards studying plant response to environmental conditions and plant water stress.

''Sections and front view of 3D relative moisture content in apple leaf.

Neutron imaging

We use neutron imaging to study porous materials and their interactions with fluids. Neutron imaging provides high resolution in moisture content, space and time. We aim at understanding the physics of transport processes, determining material properties and validating computer models. We have developed several experimental methods to study mass transport under different boundary conditions. Neutron images are acquired at the Neutra and Icon beamlines, SINQ, PSI

Heat and mass transport at air-material interfaces

Convective drying | Drying modeling | Evapotranspiration

Convective drying

Mass transfer from porous materials depends on the boundary conditions, i.e. air flow, velocity and turbulent kinetic energy (TKE), relative humidity and temperature. We use neutron imaging to study drying under controlled air flow conditions starting from fully wet conditions. We study the drying processes within a groove of 2 cm x 2 cm in a clay brick with neutron imaging in a small wind tunnel.

Moisture content distribution in brick during drying PIV measurements of air flow in groove

Drying modeling

The drying of porous materials involves the modeling of transport in both the air and the porous material, or conjugate modeling. With conjugate modeling, the spatial and temporal variability of convective transfer coefficients can be unveiled.
Conjugate modeling avoids the use of simplified, a-priori determined convective transfer coefficients. It is inherently more accurate and provides customized heat and mass exchange predictions at the air-material interfaces.

Drying fronts and boundary layer for a flat plate. Spatial and temporal variation of convective mass transfer coefficient from conjugate modeling.


Evapotranspiration involves transpiration via microscopic pores in the leaf surface, called stomata, and evaporation of droplets on the surface. Numerical analysis of evapotranspiration requires cross-scale numerical modelling from macro- down to the microscale.

2D isocontours in air above leaf

Water sorption of wood

Celular scale | Microscale | Nanoscale | Multiscale modeling

Celular scale

Moisture affects the stiffness of wood and leads to overall swelling. The origin lies at the cellular and sub-cellular scales, where the cell wall is a complex porous polymeric composite. High-resolution synchrotron phase- contrast X-Ray Tomography together with image registration method based on B-spline captures the micro- and nano-structure of wood, its displacement and total strains.

X-ray CTs of wood in wet and dry states Position and magnitude of local deformations in swelling from 10 to 85%RH


The anisotropy in swelling behavior of wood originates at the cell wall level. We document the hygroscopic swelling of the central and thickest secondary cell wall layer (S2) by means of phase contrast X-ray tomographic nanoscopy. It is found that the swelling/shrinkage strains are highly anisotropic in the transverse plane of the cell wall, larger in the normal than in the direction parallel to the cell walls thickness.

Xray nanoCT of wood pillars. Pillar sample.


We study the mechanisms of water interactions with wood cell S2 layer at the nanoscale, using molecular dynamics (MD) simulation, and hybrid MD-Monte Carlo to simulate water adsorption in Grand Canonical ensemble. The smallest functional part of S2 layer is a cellulose microfibril (a), surrounded by hemicellulose (b) and immersed in lignin matrix (c). In adsorption, water molecules push aside amorphous cellulose molecules, causing overall swelling and decrease of stiffness.

Visualization of MD simulation of cellulose fibrils

Multiscale modeling

The swelling behaviour of wood at cellular scale is well predicted by computational upscaling of the poromechanical behavior of honeycomb types of unit cells. A multiscale model is developed to predict the swelling behavior of wood at the growth ring level.

A multiscale modeling effort is aiming at reproducing the physics of the capacity of wood to recover its initial shape after drying in a deformed state, as imaged with tomography.

Sustainable retrofit of historical buildings

Vapor-open interior insulation | Experimental work | Simulations of insulated facades | Case studies

Vapor-open interior insulation

Interior insulation consists in a layer of aerogel plaster, a new highly insulating-vapor open render made of a lime binder with aerogel granulates.

Determination of material properties for detailed performance simulations.

Experimental work

A test wall with an interior insulation render is monitored under cyclic conditions in a weathering chamber with RH-T sensors, and newly developed sensors to measure moisture content changes based on the change of electrical conductivity of materials.

Modeled vs measured RH at the wood-masonry interface.

Simulations of insulated facades

1D and 2D numerical models are validated through measurements and used for parametric analysis of the influence of outside render and inside insulation material properties on the hygrothermal behavior of the wall.

Case studies

Schematic overview of on-going research in terms of scales and investigation methods

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