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Evaporation from porous media - microscale study of the dynamics and morphology of drying fronts

English title Evaporation from porous media - microscale study of the dynamics and morphology of drying fronts
Applicant Or Dani
Number 113676
Funding scheme Project funding (Div. I-III)
Research institution Institut für Terrestrische Ökosysteme ETH Zürich
Institution of higher education EPF Lausanne - EPFL
Main discipline Pedology
Start/End 01.01.2007 - 31.12.2010
Approved amount 285'396.00
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All Disciplines (2)

Discipline
Pedology
Geophysics

Keywords (6)

porous media; invasion percolation; tomography; drying front; evaporation; liquid films

Lay Summary (English)

Lead
Lay summary
Evaporation from porous media is an important process affecting many aspects of life, from water availability to plants and soil biota, to freshness of food products, curing of cement in construction, and drying of paint. The rates of drying reflect interplay between phase change from liquid to vapor, supply of liquids to the drying zone, and removal of vapor via gaseous diffusion or convection. The culmination of such processes in constrained and complex pore spaces results in formation of a drying front separating liquid filled domains from vapour phase domains.The structure and dynamics of this drying front and residual liquid connection to the surface play a critical role in the resulting evaporation behaviour hence ultimately affect the rates of exchange with the atmosphere. The spatial and temporal distributions of fluid phases are shaped by geometrical features at scales ranging from microns to millimetres involving both pore spaces and fluid distribution.Consequently, modelling the evolution of drying front dynamics requires direct observations at relatively high resolution (to elucidate the role of mass-flow through thin liquid threads maintained through the “dry”region. The ultimate goal of this project is to provide better predictive capabilities for the drying rate of realistic porous media under different boundary conditions and for different degrees of soil heterogeneities.These predictions could improve water saving strategies in agriculture and urban settings, enhance understanding of exchange processes with the atmosphere, and improve designs of waste isolation repositories based on porous earth barriers (clay liners, and subsurface tunnels).

1) We plan to measure transport properties and drying rates in laboratory experiments for various materials to distinguish between conditions where transport properties constrain evaporative demand of the atmosphere (with associated abrupt and significant changes in drying rates).
2) For simplified geometries, the effect of gravity, capillarity and viscous forces on the drying rate would be determined analytically enabling explanation and generalization of changes in drying rates measured in experiments.
3) By using new optical tools based on neutron and synchrotron light radiation the fluid phase distribution is measured in space and time. We will focus on the dynamics of the drying front (resolution of 0.1 mm) and the arrangement of the liquids in partially dry porous media (resolution0.01 mm).
4) The observational tools applied in task 3 would provide direct description of porous medium structure that enable numerical computations of transport processes within the actual pore geometry.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
135077 Evaporation from terrestrial surfaces - linking pore scale phenomena with landscape processes 01.08.2011 Project funding (Div. I-III)
172493 Evaporation suppression from water reservoirs using floating covers: scientific basis and design considerations 01.08.2017 Project funding (Div. I-III)

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