The engineering of microbially induced calcium carbonate precipitation (MICP) has attracted much attention in a number of applications, such as sealing of CO2 leakage pathways, soil stabilization, and subsurface remediation of radionuclides and toxic metals. The goal of this work is to gain insight into pore‐scale processes of MICP and scale dependence of biogeochemical reaction rates. This will help us develop efficient field‐scale MICP models. In this work, we have developed a comprehensive pore‐network model for MICP, with geochemical speciation calculated by the open‐source PHREEQC module. A numerical pseudo‐3‐D micromodel as the computational domain was generated by a novel pore‐network generation method. We modeled a three‐stage process in the engineering of MICP including the growth of biofilm, the injection of calcium‐rich medium, and the precipitation of calcium carbonate. A number of test cases were conducted to illustrate how calcite precipitation was influenced by different operating conditions. In addition, we studied the possibility of reducing the computational effort by simplifying geochemical calculations. Finally, the effect of mass transfer limitation of possible carbonate ions in a pore element on calcite precipitation was explored.
For better water management in gas channels (GCs) of polymer electrolyte fuel cells (PEFCs), a profound understanding of the liquid water dynamics is needed. In this study, we propose a novel geometrical setup to conduct a series of direct simulations of the liquid water dynamics in a GC. The conducting pathways in the gas diffusion layer (GDL) are simplified by three cylindrical pipes connected to a liquid water reservoir representing the catalyst layer (CL). The droplet dynamics, corner film dynamics, and the competition between the film and droplet flows in the GC are explored in detail. The results show that the three-phase contact line plays an important role in resisting the gas drag force for a droplet movement in the GC. The gas drag force can dominate the film flow along the GC corners, and a proper selection of the contact angle of the GC sidewalls is necessary to balance two requirements: increasing the film removal ability and removing the water clogging fast. The competing mechanisms of the droplet and film flows give us the possibility to regulate liquid water flow into GCs, and maybe lead to a better water management in GCs. Finally, the results from this work also serve to provide insights into the development of a phenomenological model for the liquid water flooding in GCs.
The pore-scale modeling is a powerful tool for increasing our understanding of water transport in the fibrous gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). In this work, a new dynamic pore-network model for air-water flow in the GDL is developed. It incorporates water vapor transport coupled with liquid water by a phase change model. One important feature of our pore-network model is that a recently developed semi-implicit scheme for the update of water saturation is used. It provides good numerical stability in modeling liquid water transport in the GDL even for very small capillary number values. A number of case studies are conducted to illustrate several important mechanisms of water transport in the GDL, such as cyclic processes of local drainage and imbibition, channeling and capillary-fingering evolutions of water flow pattern, and eruptive water transport. Moreover, we show that liquid water separation in the GDL between the ribs and gas channel (GC) is formed under dry GC condition, which is qualitatively in agreement with in situ experimental results. Water management plays an important role in the durability and performance of polymer electrolyte fuel cells (PEFCs). A delicate water balance must be maintained to keep the membrane hydrated and at the same time avoid liquid water flooding in the porous components. [1][2][3] Over the past two decades, numerous studies have been conducted for improving our understanding of water transport mechanisms within the PEFC. Compared to the anode side, water transport in the cathode has usually attracted more attention. This is because the cathode is prone to being flooded first, and the oxygen reduction reaction (ORR) is very sluggish. The fibrous gas diffusion layer (GDL), as a key component, plays an important role in removing excessive water from the catalyst layer (CL) to the gas channel (GC). Up to now, much effort has been invested in gaining insights into pore-scale processes of liquid water transport in the GDL. [4][5][6][7][8][9][10] Despite the great success in in situ observations of water distribution, 8,9,[11][12][13][14] water dynamics in the GDL is still not well understood. Also, the cost of those experiments is quite high. This has stimulated many pore-scale numerical studies of the GDL over the past few years. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Several distinctive features of liquid water transport in the GDL make its pore-scale modeling extremely difficult. First, a small flow rate of liquid water, with a capillary number value of around 10 −8 , causes the modeling computationally expensive. Second, the complexity 34 of the pore structure and mixed wettability of the GDL give rise to the difficulty in developing an elegant pore-scale model. Nevertheless, many achievements still have been booked.Mukherjee et al. 4 were the first to conduct the Lattice-Boltzmann modeling of air-water flow in a stochastically reconstructed nonwoven GDL. The authors illustrated the structure-wettabili...
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