Temperature gradient induced double stabilization of the evaporation front within a drying porous medium

Vorhauer, Nicole; Tsotsas, Evangelos; Prat, Marc

doi:10.1103/physrevfluids.3.114201

Cited by 19 publications

(12 citation statements)

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“…There also exists a number of PNMs that additionally incorporate pore scale mechanisms, such as liquid film flow [15][16][17] or crystallization [18][19][20]. Only a few models are available that take into account coupled heat and mass transfer [21,22] or that at least consider the invasion and transport processes under non-isothermal conditions [23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

et al. 2019

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Pore network models are powerful tools to simulate invasion and transport processes in porous media. They are widely applied in the field of geology and the drying of porous media, and have recently also received attention in fuel cell applications. Here we want to describe and discuss how pore network models can be used as a prescriptive tool for future water electrolysis technologies. In detail, we suggest in a first approach a pore network model of drainage for the prediction of the oxygen and water invasion process inside the anodic porous transport layer at high current densities. We neglect wetting liquid films and show that, in this situation, numerous isolated liquid clusters develop when oxygen invades the pore network. In the simulation with narrow pore size distribution, the volumetric ratio of the liquid transporting clusters connected between the catalyst layer and the water supply channel is only around 3% of the total liquid volume contained inside the pore network at the moment when the water supply route through the pore network is interrupted; whereas around 40% of the volume is occupied by the continuous gas phase. The majority of liquid clusters are disconnected from the water supply routes through the pore network if liquid films along the walls of the porous transport layer are disregarded. Moreover, these clusters hinder the countercurrent oxygen transport. A higher ratio of liquid transporting clusters was obtained for greater pore size distribution. Based on the results of pore network drainage simulations, we sketch a new route for the extraction of transport parameters from Monte Carlo simulations, incorporating pore scale flow computations and Darcy flow.

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Section: Introductionmentioning

confidence: 99%

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

et al. 2019

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“…These authors revealed that liquid film rings can develop in systems with heterogeneous wetting properties and limited interconnection of the solid, such as in a 2D microfluidic device (as investigated in Vorhauer et al [13] ) or 3D glass bead packings. [2,15] The specific strength of the pore scale model is also revealed in face of the nonisothermal drying experiments studied in Vorhauer et al, [12] where the pore network is simultaneously invaded by the gas-phase (as a result of evaporation) and the liquid phase (as a result of condensation). This phenomenon is also expected in a wide range of other applications, such as the simultaneous drainage and imbibition in gas diffusion layers (GDL), in fuel cells usually affected by thermal gradients.…”

Section: Introductionmentioning

confidence: 89%

“…This is a completely different situation than in the isothermal simulation where the evolution of the liquid distribution in the TPM is controlled by the external vapor mass transfer structure. According to discussions in Vorhauer et al [12] it is strongly expected that thickness of the annular traveling zone (in case of a radial thermal gradient) depends on the magnitude of the temperature gradient and the overall evaporation rate as well. This is highlighted in Fig.…”

Section: Study Of the Thermal Impact Of Invasionmentioning

confidence: 99%

“…Pore network models (PNM) are discrete pore scale models well appropriate to analyze the link between the discrete phenomena taking place at the pore scale and the macroscopic behavior at the sample scale. In drying, PNM shed light on the dependency of the macroscopically observed drying rate and overall drying time on pore structure, [1][2][3] capillary number or Bond number, [4,5] wettability, [6][7][8] and thermal gradients [9][10][11][12] which naturally develop since the evaporation of liquid is basically a nonisothermal process. Exemplarily, Metzger et al [1] revealed the impact of the presence and interconnection of macropores in drying of capillary porous media.…”

Section: Introductionmentioning

confidence: 99%

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Drying of thin porous disks from pore network simulations

2017

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Thin porous media (TPM) are porous layers that are characterized by a small thickness, usually orders of magnitude smaller than the lateral dimensions. We present pore network simulation revealing that drying of TPM is substantially different from drying of thicker porous media because of the impact of the small thickness of only a few pore layers on the liquid phase structure during drying. The small thickness limits the long-distance connectivity within the liquid clusters and thus causes the formation of smaller clusters characterized by shorter residence times. As a result of this stronger and earlier liquid phase fragmentation the drying of TPM is shown to be significantly more sensitive to the distribution of the evaporation flux at the surface. It is also shown that the drying behavior transition from thin to thick porous media is progressive. Moreover, it is discussed how an imposed temperature distribution can be used to control the evolution of the liquid cluster distribution in a TPM and thereby the evolution of the evaporation rate. KEYWORDS 3D po re netwo rk model; drying; nonisothermal; temperature gradient; thin po ro us disk

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“…In contrast, when the throat size distribution becomes broader, the invasion follows the path of the least resistance, which results in a more random distribution of the phase patterns, provided that the throat sizes are randomly distributed. Following [60] and [61], the occupation probability decreases with growing ∆r.…”

Section: Bimodal Pore Size Distributionsmentioning

confidence: 99%

Steady-State Water Drainage by Oxygen in Anodic Porous Transport Layer of Electrolyzers: A 2D Pore Network Study

et al. 2020

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Recently, pore network modelling has been attracting attention in the investigation of electrolysis. This study focuses on a 2D pore network model with the purpose to study the drainage of water by oxygen in anodic porous transport layers (PTL). The oxygen gas produced at the anode catalyst layer by the oxidation of water flows counter currently to the educt through the PTL. When it invades the water-filled pores of the PTL, the liquid is drained from the porous medium. For the pore network model presented here, we assume that this process occurs in distinct steps and applies classical rules of invasion percolation with quasi-static drainage. As the invasion occurs in the capillary-dominated regime, it is dictated by the pore structure and the pore size distribution. Viscous and liquid film flows are neglected and gravity forces are disregarded. The curvature of the two-phase interface within the pores, which essentially dictates the invasion process, is computed from the Young Laplace equation. We show and discuss results from Monte Carlo pore network simulations and compare them qualitatively to microfluidic experiments from literature. The invasion patterns of different types of PTLs, i.e., felt, foam, sintered, are compared with pore network simulations. In addition to this, we study the impact of pore size distribution on the phase patterns of oxygen and water inside the pore network. Based on these results, it can be recommended that pore network modeling is a valuable tool to study the correlation between kinetic losses of water electrolysis processes and current density.

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Temperature gradient induced double stabilization of the evaporation front within a drying porous medium

Cited by 19 publications

References 50 publications

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Drying of thin porous disks from pore network simulations

Steady-State Water Drainage by Oxygen in Anodic Porous Transport Layer of Electrolyzers: A 2D Pore Network Study

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