Lattice Boltzmann modeling of transport phenomena in fuel cells and flow batteries

Abstract

Fuel cells and flow batteries are promising renewable energy technologies to address climate change and air pollution problems. Understanding the complex multiscale and multiphysics transport phenomena in these electrochemical systems requires effective numerical approaches. Among various numerical methods, the lattice Boltzmann (LB) method stands out as a powerful tool to simulate fluid flows and associated transport phenomena. This thesis focuses on LB modeling of transport phenomena in fuel cells and flow batteries. It starts with accelerating LB simulation using the combined Open Accelerator programming standard and graphics processing unit (GPU) accelerator. By optimizing the data layout, minimizing the memory access frequency, and adjusting the number of gangs and vector length, a speed up around 50-60 times for multiphysics LB simulation can be achieved comparing with the serial implementations. The enhanced computational performance highlights the potential of LB method to utilize the emerging GPU accelerator for applications in large-scale engineering problems. Subsequently, efforts are devoted to gas-liquid two-phase flows in polymer electrolyte membrane fuel cells, coupled fluid flows and mass transport in aqueous redox flow batteries, and particulate flows in suspension redox flow batteries. In a polymer electrolyte membrane fuel cell system, the transport phenomena involve gas-liquid two-phase flows in the flow channels and in the porous gas diffusion layers on both the anode and cathode. Previous LB models to simulate gas-liquid two-phase flows are applicable to low-density-ratio interfacial problems only, whereas the density ratio is large in practical fuel cell systems. To address this issue, a three-dimensional pseudo-potential-based LB model is developed to simulate gas-liquid two-phase flows with large density ratio. It is demonstrated that this three-dimensional model enables the density ratio to be as large as 700 in static and quasi-static cases while maintaining variable surface tension. In an aqueous redox flow battery system, the transport phenomena involve coupled fluid flows, mass transport, and electrochemical reactions in both the positive and negative porous electrodes. Mass transfer coefficient, which quantifies mass transfer from the bulk flows to pore surfaces and represented by the dimensionless Sherwood number (Sh), is predicted via LB simulations of chemically reactive flows through porous media. It is found that Sh increases linearly with Reynolds number (Re) at the creeping flow regime; Sh and Re exhibit a one-half power law dependence at the inertial flow regime. Meanwhile, for Shmidt number (Sc) between 1 and 10, Sh is proportional to Sc^0.8; for Sc between 10 and 100, Sh is proportional to Sc^0.3. In a suspension redox flow battery system, the transport phenomena in the suspension electrodes involve the particulate flows of both charge storing active materials and conductive additives. To simulate a suspension that contains both micro- and nanoparticles, the microparticle dynamics are explicitly resolved and the nanoparticles with base fluid are implicitly described as continua. Couette flows are simulated to obtain the viscous dissipation of the particles, and a mathematical correlation for viscosity as a function of micro- and nanoparticle volume fraction is proposed for the dilute suspension system. In addition to solid particles that are impermeable to fluids, porous particles that are permeable to fluids are also frequently encountered in real-world applications, such as core-shell like particles. To simulate a suspension of porous particles, the fluid flows around and inside the porous particle is described by the volume-averaged macroscopic equations in terms of intrinsic phase average. Results show that for a dilute suspension of porous spherical particles, the relative viscosity increases linearly with the particle volume fraction. A correlation equation is obtained for the intrinsic viscosity as a function of Darcy number (Da). It is found that when the suspension is at the inertial flow regime, its intrinsic viscosity increases linearly with Re, and the increasing rate depends on Da. Keywords: Lattice Boltzmann method; Transport phenomena; Multiphase flow; Fuel cells; Flow batteries.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology