Omar Emmanuel Godinez Brizuela

Floating photovoltaic (FPV) systems are an increasingly attractive route to large-scale solar deployment on water bodies, but their structural integrity and energy yield are threatened by the wave environments to which they are exposed at nearshore and offshore sites. Floating breakwaters (FBWs), and keeled geometries in particular, are a candidate protection system. Here we develop a smoothed particle hydrodynamics (SPH) model of a moored, keeled floating breakwater using the open-source solver DualSPHysics, with waves generated by a piston wavemaker with active wave absorption and, for two of the irregular sea states, by the relaxation-zone method (Altomare et al., 2017, 2018). The model is assessed against wave-basin experiments in two stages: a verification stage under regular waves spanning six height–period combinations, and an assessment stage under irregular sea states (two JONSWAP spectra and a broadband white-noise excitation). We report the wave transmission and reflection behaviour, the breakwater motions and their response amplitude operators (RAOs), and find that, once the floating body, the mooring and the incident waves are resolved consistently, the SPH model reproduces the measured heave, roll and sway to within about 20 per cent over most of the regular-wave range and follows the measured RAOs of the irregular sea states, with an accuracy comparable to a boundary-fitted finite-volume model at a fraction of its computational cost.

Liquid metal batteries have been introduced as promising option to address the needs for new energy storage technologies. Currently, batteries based on sodium and zinc are under development and a favorable option due to their high theoretical cell potential, readily abundant materials, and cost-advantages. Nevertheless, they face the problem of self-discharge, which makes it inevitable to understand fluid dynamics in the whole cell. Motivated by that, several types of fluid mechanic instabilities in Na-Zn liquid metal batteries are identified and discussed here. On the one hand they can jeopardize secure operation, but on the other hand they can also improve mixing and increase the cell efficiency. In doing so, realistic cell as well as operation parameters are included and dimensionless numbers for identifying critical conditions are presented. The phenomena with highest significance for the discussed batteries are solutal convection, swirling flow, electrocapillary Marangoni convection, and droplet formation. Still, many open research questions remain and we aim at motivating researchers to dig deeper into some of these topics to contribute to an improved cell design and performance.

Aluminum and its alloys are widely used in various applications including e-mobility applications due to their lightweight nature, high corrosion resistance, good electrical conductivity, and excellent processability such as extrusion and forming. However, aluminum and its alloys are difficult to process with a laser beam due to their high thermal conductivity and reflectivity. In this article, the two most used laser processes, i.e., laser welding and laser powder bed fusion (LPBF) additive manufacturing, for processing of aluminum have been studied. There are many common laser-material interaction mechanisms and challenges between the two processes. Deep keyhole mode is a preferred method for welding due to improved productivity, while a heat conduction mode is preferred in LPBF aiming for zero-defect parts. In LPBF, the processing maps are highly desirable to be constructed, which shows the transition zone. Presented numerical modeling provides a more in-depth understanding of porosity formation, and different laser beam movement paths have been tested including circular oscillation paths. High accuracy processing maps can be constructed for LPBF that allows us to minimize tedious and time-consuming experiments. As a result, a modeling framework is a highly viable option for the cost-efficient optimization of process parameters.

Liquid metal batteries (LMBs) are a promising alternative for large-scale stationary energy storage for renewable applications. Using high-abundance electrode materials such as Sodium and Zinc is highly desirable due to their low cost and excellent cell potential. LMBs undergo multiple complex mass transport dynamics and as a result, their operation limits and other critical parameters are not fully understood yet. In this work, a multiphase numerical model was developed to resolve electrode and electrolyte components in 1D and simulate the discharge process of a Na-Zn battery including the interfacial displacement of the molten metal electrodes. The variation in electrolyte composition was predicted throughout the process, including the species distribution and its effect on the cell conductivity and capacity. Volume change and species redistribution were found to be important in predicting the maximum theoretical capacity of the cell when neglecting convective phenomena.

Intermediate temperature molten salt batteries are a promising alternative for grid-scale energy storage with several advantages over existing solutions. The cathode of some of these batteries is composed of a porous matrix of materials containing the metal backbone of the electrode, along with electrolyte components that vary and different locations or as the state of charge of the battery changes. In this work, we aim to analyze the influence of the microstructural properties of the cathodic region at different compositions for a Na-Zn (ZnCl ₂ ) battery. Synthetic geometric models of the electrode at different compositions are generated and then the effective conductivity is estimated through numerical simulation of the current and potential distribution through the material. At a three-phase composition used by a typical electrode assembly, the effective conductivity is approximately three times larger than the electrolyte electrical conductivity.

Metal displacement batteries (MDBs), or liquid metal batteries, are an emerging technology with significant potential in providing high capacity, low-cost energy storage solutions, capable of addressing many of the challenges associated with storing energy from renewable sources. The key characteristic of metal displacement batteries is that at least one of the electrodes is in liquid state and a molten salt is used as an electrolyte. Since its original proposal in the 1960’s liquid metal batteries have re-emerged in recent years and different battery chemistries and designs have been explored, including Ca-Bi, Na-Sb, and many others [2,10]. Recently, Na-Zn liquid metal batteries have been studied as an alternative to other configurations, showing significant potential in achieving good performance for large-scale energy storage, while avoiding the high cost associated with some electrode materials such as Nickel or Lithium [7,8]. In past years, alternatives to all-liquid cells have emerged in the form of designs where the cell materials are a mixture of solids and liquids. Examples of this include the commercially available Zebra battery, where a Na-NiCl electrode pair is used [1,6]. These designs offer some of the advantages of all-liquid cells, while simultaneously mitigating many of the disadvantages of handling and operating a very high temperature system. Na-Zn have also been proposed for solid cathode designs, taking advantage of the lower cost of Zn over Ni [4,3]. The cathode in these designs is composed of a porous structure, within which multiple chemical species can co-exist. Electrolyte components share the space with metal deposits,salt crystals, and other electrochemical reaction products. As a result, the micro-porous structure of this composite system is an important factor in determining the performance of the cell, as the spatial distribution of different materials can have an impact on the effective conductivity of the electrode [5,9]. The porous structure hosts complex multi-component mass transfer phenomena as well, potentially having an impact on the mass-transfer overpotential of the cell. This work aims to study the impact of the microstructural properties of the solid electrode in a liquid displacement battery, and their importance to the effective conductivity of the system. We have developed a computational tool that enables us to create randomized microstructures in 3D, representing the electrode-electrolyte assembly. We are able to preserve the desired physical characteristics by using target pore-size distributions and volume fraction input as seed parameters. We use this tool to generate representative structures and analyze their effective bulk conductivity by solving Laplace’s equation over the resulting domain, accounting for the different local conductivity of each material. This methodology is applied to a novel Na-Zn cell in order to assess the importance of the pore-scale properties of the cathode, as well as its material components, including solid Zn metal, solid NaCl deposits, and molten salt components. It is expected that different material arrangement configurations will induce heterogeneous current distributions in this system. Furthermore, the ionic composition of the electrolyte would be different at different charge levels, leading to additional variation through its charge/discharge cycle. Using this methodology, the range of different electrode phase configurations produced during operation can be studied in the absence of microstructure imaging data. A representative elementary volume for the Zn electrode assembly is analyzed to determine the best approach for up-scaled performance predictions of the Na-Zn cell. With this method, it is possible to acquire data to elucidate desirable or undesirable electrode structure properties of this system, providing insight which can be used for improving manufacture and operation of the cell. [1] Dustmann. “Advances in ZEBRA batteries”. J. Power Sources (2004). [2] Kim et al. “Liquid metal batteries: Past, present, and future”. Chemical Reviews (2013). [3] Lu et al. “An Intermediate-Temperature High-Performance Na-ZnCl2 Bat- tery”. ACS Omega (2018). [4] Lu et al. “Liquid-metal electrode to enable ultra-low temperature sodium- beta alumina batteries for renewable energy storage”. Nature Communications (2014). [5] Qiu et al. “Pore-scale analysis of effects of electrode morphology and electrolyte flow conditions on performance of vanadium redox flow batteries”. J. Power Sources (2012). [6] Sudworth. “The sodium / nickel chloride ( ZEBRA ) battery”. J. Power Sources (2001). [7] Xu et al. “Electrode Behaviors of Na-Zn Liquid Metal Battery”. Journal of The Electrochemical Society (2017). [8] Xu et al. “Na-Zn liquid metal battery”. Journal of Power Sources (2016). [9] Zhang et al. “Progress in 3D electrode microstructure modelling for fuel cells and batteries: transport and electrochemical performance”. Progress in Energy (2019). [10] Zhang et al. “Liquid Metal Batteries for Future Energy Storage”. Energy Environmental Science (2021). Figure 1

The capillary pressure‐saturation relation is one of the key constitutive equations used for modeling multiphase (or partially saturated) flow in porous materials. It is known that this empirical relation depends strongly on dynamic conditions, but the impact of a heterogeneity interface on this relationship has been studied less. The present study employed optical imaging to visualize two‐phase drainage under different injection rates and two flow directions, in a heterogeneous micromodel. By analyzing the curvatures of the fluid‐fluid interfaces, the averaged capillary pressures for the coarse and fine sections of the micromodel, and the entire micromodel were estimated. Results show that the capillary pressure‐saturation relation in the vicinity of a heterogeneity interface does not follow the conventional models proposed in the literature. The averaged capillary pressure over the entire micromodel for the fine‐to‐coarse (FtC) direction shows decreasing capillary pressure with decreasing wetting phase saturation. However, in the coarse‐to‐fine direction, a non‐monotonic trend was observed. These initial findings highlight the gaps in the knowledge of upscaling capillary pressure in heterogeneous porous materials. Moreover, discontinuity in saturation was clearly more pronounced for the FtC direction, as a result of lower entry capillary resistance against the flow in the coarse section.

Immiscible two‐phase flow through porous materials exhibits different invasion patterns controlled by dynamic conditions, competition between the viscous and capillary forces, and the contrast between the fluids viscosities. Two distinct invasion patterns are viscous and capillary fingering. While the first one happens under unfavorable viscosity ratios at high injection rates, the second one happens when the viscous forces are very small compared to the capillary forces. Depending on whether the invasion is under the capillary fingering or viscous fingering regime, the remaining oil saturation and the effective permeability of the fluids can significantly change. The contribution of the present work has two key aspects: (a) It addresses how the remaining saturation changes at different flow rates (i.e., capillary numbers) for different unfavorable viscosity ratios in a three‐dimensional system; (b) it presents a new dynamic pore network model using the fully implicit scheme which has been enhanced by the graphic processing unit (GPU) parallel computing. Additionally, the model has been carefully validated against micromodel experiments in both time and space, which to our best knowledge has not been reported in such detail in the literature. The results of the validated 3‐D dynamic pore network model demonstrate the remaining saturation at the breakthrough time as a nonmonotonic trend with the imposed capillary number.