Effect of liquid films on the drying of porous media (original) (raw)
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In this paper we present numerical results obtained with a pore-network model for the drying of porous media that accounts for various processes at the pore scale. These include mass transfer by advection and diffusion in the gas phase, viscous flow in the liquid and gas phases and capillary effects at the liquid-gas interface. We extend our work by studying the effect of capillarity-induced flow in macroscopic liquid films that form at the pore walls as the liquid-gas interface recedes. A mathematical model that accounts for the effect of films on the drying rates and phase distribution patterns is presented. It is shown that film flow is a major transport mechanism in the drying of porous materials, its effect being dominant when capillarity controls the process, which is the case in typical applications.
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Drying of porous media is part of our daily experience, yet this common process is central to many environmental and engineering applications ranging from soil evaporation affecting hydrological water balance and climatic processes, to the drying of food and building materials, and driving plant life through transpiration. Drying rates from porous media may exhibit complex dynamics reflecting internal transport mechanisms and motion of phase change fronts that determine rates of drying and critically affect surface energy partitioning. These interactions and resulting drying dynamics present a challenge to the prediction of drying rates and interplay among mass and energy exchange even for fixed boundary conditions. This special issue is an outcome of a symposium that was organized in the 6th International Conference of the Interpore Society held in Milwaukee, Wisconsin, USA, in 2014, that brought together researchers from various disciplines interested in drying of porous media. The contributions included in this special issue span a wide range of topics and mechanistic aspects of porous media drying and reinforcing the importance and similarity of mechanisms and parameters influencing drying processes at different settings, considering different spatial scales and representing a blend of experimental, mechanistic theoretical and numerical approaches. Although it should be clear that all aspects of drying could not be addressed, the contributions in this special issue will give the reader a wide overview of the field and will introduce several important open problems that are the subject of active research. These include the impact of second capillary effects (liquid films, liquid bridges) on drying, the coupling between internal and external transfers, the interplay between evaporation, ion transport B Nima Shokri
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I wish to acknowledge the constant support of Prof. Mukul Sharma. This dissertation would not have been possible without the support and motivation derived from Prof. Sharma. I thank Prof. Yannis Yortsos who has been very enthusiastic about my research and has devoted significant amount of time in helping me overcome many obstacles and has been a source of inspiration. I thank Prof. Larry Lake for his ever cheerful repose and his generosity in spending time with me on various scientific and engineering problems both within and outside the scope of this dissertation. I have always admired Prof. Bonnecaze's teaching of the surface phenomena class which has inspired me to like the subject.
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Invasion percolation (IP) rules under non-isothermal conditions are applied to model the pore-scale events occurring during drying of capillary porous media, namely displacement of immiscible phases and cluster formation. A saturated two-dimensional network with a bimodal pore size distribution is dried by applying two different heat transfer boundary conditions; one corresponds to convective drying and the other to less resistive contact drying. Simulated macroscopic drying behavior is presented in conjunction with freely evolved microscopic temperature fields and phase distributions for both heating modes. Convective heating exhibits similar invasion patterns as those in isothermal simulations; both are dominated by the spatial distribution of pore radii. However, in contact heating, temperature dependency of surface tension produces significantly different invasion patterns.
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Isothermal and non-isothermal drying of pore structures has been experimentally investigated using 2D square network models of interconnected etched channels with different (Gaussian) distributions of the channel width. In experiments with imposed temperature gradients, the temperatures either increase from the open side of the network with increasing network depth (referred to as the positive temperature gradient) or the temperatures decrease with increasing distance from the network opening (i.e. a negative temperature gradient). Experiments reveal that the observed phase patterns, or the distributions of liquid and gas, during drying are significantly depending on the direction of the temperature gradient; but also the presence of macro channels can have a strong effect on the phase patterns as well as on drying time.
Multiscale Modeling of Non-Isothermal Fluid Transport Involved in Drying Process of Porous Media
Porous Fluids - Advances in Fluid Flow and Transport Phenomena in Porous Media, 2021
To preserve the product quality as well as to reduce the logistics and storage cost, drying process is widely applied in the processing of porous material. In consideration of transport phenomena that involve a porous medium during drying, the complex morphology of the medium, and its influences on the distribution, flow, displacement of multiphase fluids are encountered. In this chapter, the recent advanced mass and energy transport models of drying processes are summarized. These models which were developed based on both pore- and continuum-scales, may provide a better fundamental understanding of non-isothermal liquid–vapor transport at both the continuum scale and the pore scale, and to pave the way for designing, operating, and optimizing drying and relevant industrial processes.