In this thesis, PN simulations of drying are compared with experimentally obtained data fromdrying of a representative 2D microfluidic network in SiO2 under varying thermal conditions withthe aim to identify governing physical pore scale effects. Gravity and viscous effects aredisregarded in this thesis. Instead drying with slight local temperature variation and drying withimposed thermal gradients are studied. Based on this investigation, a powerful non-isothermalPNM is developed. This model incorporates i) the phenomena associated with the temperaturedependency of pore scale invasion, namely thermally affected capillary invasion and vapor flow aswell as ii) the secondary effects induced by wetting liquid films of different morphology. This studyclearly evidences that the macroscopic drying behavior is fundamentally dictated by thetemperature gradient imposed on the PN and moreover by the secondary capillary invasion aswell. In agreement with literature, invasion patterns as in invasion percolation with progressiveevaporation of single clusters are observed in drying with negligible local temperature variation;gradients with temperature decreasing from the surface (negative temperature gradient) canstabilize the drying front, evolving between the invading gas phase and the receding liquid phase,whereas temperature increasing from the surface (positive temperature gradient) leads todestabilization of the liquid phase with early breakthrough of a gas branch and initiation of asecond invasion front migrating in opposite direction to the evaporation front receding from theopen surface of the PN. Special attention is paid on the distinct drying regimes found in thesituation of a positive gradient because they are associated with different pore scale invasionprocesses. More precisely, temperature dependency of surface tension dictates the order ofinvasion as long as the liquid phase is connected in a main liquid cluster (usually found during thefirst period of drying). In contrast to this, detailed study of the vapor transfer mechanismsemphasizes that vapor diffusion through the partially saturated region can control the pore leveldistributions of liquid and gas phase during the period of drying when the liquid phase isdisconnected into small clusters. This is also related to the cluster growth induced by partialcondensation of vapor. It is shown and discussed in detail in this thesis that this effect not onlydepends on direction and height of the temperature gradient for a given pore size distribution butthat moreover the overall evaporation rate influences the cluster growth mechanism. This indicatesthat liquid migration during drying of porous media might be controlled by the interplay of thermalgradients and drying rate. In summary, the study of thermally affected drying of the 2-dimensionalPN reveals complex pore scale mechanisms, usually also expected in drying of real porous media.This leads to the development of a strong mathematical pore scale model based on experimentalfindings. It is demonstrated how this model might be applied to understand and develop moderndrying processes based on the simulation of thermally affected pore scale mass transfer
| Identifer | oai:union.ndltd.org:univ-toulouse.fr/oai:oatao.univ-toulouse.fr:23927 |
| Date | 18 September 2018 |
| Creators | Vorhauer, Nicole |
| Contributors | Institut National Polytechnique de Toulouse - INPT (FRANCE), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France) |
| Source Sets | Université de Toulouse |
| Language | English |
| Detected Language | English |
| Type | PhD Thesis, PeerReviewed, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | http://oatao.univ-toulouse.fr/23927/ |
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