Developing large-scale storage of intermittent renewable energy to meet growing energy demands is a pressing current need. Multiphase single flow batteries are a promising solution for such grid-scale energy storage, demonstrating an affordable redox flow battery design that reduces both cell and balance of plant costs. However, their major limitation is the considerable variance in electrolyte conductivity under different battery flow conditions and electrolyte properties, with no current predictive model to comprehensively understand and optimize it. Here, we develop an analytical model for such emulsion electrolytes with a continuous aqueous-based phase and dispersed reactant-rich phase, which enables electrolyte resistance prediction. We show that a key mechanism affecting electrolyte conductivity is the formation of a sedimented layer along the flow channel, revealing the critical effect of non-aqueous phase sedimentation. Experimental validation using a zinc-bromine single flow battery demonstrates excellent agreement with theoretical results during both transient and steady operations, allowing extraction of challenging-to-measure parameters, such as the in-situ size of dispersed phase droplets. This foundational model is essential in minimizing power losses, improving electrolyte and cell designs, and holds broad applicability across diverse chemistries for single-flow batteries.

The batteries that power untethered underwater vehicles (UUVs) serve a single purpose: to provide energy to electronics and motors; the more energy required, the bigger the robot must be to accommodate space for more energy storage. By choosing batteries composed primarily of liquid media [e.g., redox flow batteries (RFBs)], the increased weight can be better distributed for improved capacity with reduced inertial moment. Here, we formed an RFB into the shape of a jellyfish, using two redox chemistries and architectures: (i) a secondary ZnBr 2 battery and (ii) a hybrid primary/secondary ZnI 2 battery. A UUV was able to be powered solely by RFBs with increased volumetric ( Q ~ 11 ampere-hours per liter) and areal (108 milliampere-hours per square centimeter) energy density, resulting in a long operational lifetime ( T ~ 1.5 hours) for UUVs composed of primarily electrochemically energy-dense liquid (~90% of the robot’s weight).

Redox flow batteries (RFBs) are an emerging electrochemical technology envisioned towards storage of renewable energy. A promising sub-class of RFBs utilizes single-flow membraneless architectures in an effort to minimize system cost and complexity. To support multiple functions, including reactant separation and fast reactant transport to electrode surfaces, electrolyte flow must be carefully designed and optimized. In this work, we propose adding a secondary channel adjacent to a permeable battery electrode, solving for the flow field and analysing the effects on the reactant concentration boundary layer at the electrode. We find that an adjacent channel with gradually changing thickness leads to a desired nearly uniform flow through the electrode to the adjacent channel. Consequently, the thickness of the concentration boundary layer is significantly reduced, increasing reactant transport to the electrode surface to 140% of the rate of a battery with a constant width adjacent channel, and 350% of the rate with no adjacent channel. Overall, this theory provides insight into the important role of flow physics for this promising sub-class of flow batteries, and can pave the way to improved energy efficiency of such flow batteries.

We present experiments on rigid, nylon fiber translation, orientation, and rotation dynamics (one-way coupled) in a fully developed turbulent channel flow (Friction Reynolds number, Re-tau = 435). The experiments were performed using two-orthogonal view, digital inline Fraunhofer holographic cinematography that allowed us to track individual fibers and determine their three-dimensional (3D) position and orientation along tracks. The research focused on fiber length effects, and two fiber types having similar Stokes numbers but different mean lengths, (L) over bar (+) (=27.7 and 50.8), were investigated. Time-resolved data were acquired in the buffer layer, the log layer, and the wake region of the turbulent boundary layer. In the buffer layer irrespective of length, fibers moved faster than the fluid, presumably as a result of fiber accumulation in high-speed streaks. Beyond the buffer layer fibers lagged the fluid, more so for the longest fibers due to increased drag. Probability density functions of instantaneous components of fiber velocities showed that the longest fibers exhibit increased probabilities of "extreme" transverse and wall-normal velocities, mostly in the log layer and the wake region. This is attributed to their interaction with larger, more energetic turbulence structures. Significant fiber-wall interactions were absent, even for the longest fibers due to fiber preferential alignment with the streamwise direction resulting in limited fiber-wall interaction even when the ratio of fiber length to wall-normal distance is smaller than unity. Upon approaching the wall, fiber rotation rates strongly increased. In the wall-normal plane, in-plane fiber rotation rates as a function of wall-normal position were the same for both fiber types. However in wall-parallel planes, in-plane rotation rates of the shorter fibers were higher than those of the longer ones in the buffer layer and vice versa in the wake region. Measured mean-squared fiber tumbling rates strongly increased in the buffer layer for both fiber types, while they remained nearly constant in the log layer and the wake region. A clear length effect was apparent, and the longest fibers consistently tumbled at a higher rate than the shorter ones, surmised to be the result of their interaction with more energetic, larger turbulence structures.

While fiber-turbulence interactions are common in industrial and environmental applications, little is known about inertial fiber dynamics in isotropic turbulence. Here, rotational and translational dynamics of rigid, heavy fibers in air isotropic turbulence were measured using two-orthogonal-view, holographic cinematography. Measurements were conducted in a turbulence chamber (Re-lambda = 115). Several batches of nylon fibers with different diameters and lengths were investigated, resulting in Stokes numbers ranging between 1.0 <= St <= 32.5, and fiber length to Kolmogorov length scale ratios ranging between 3.6 <= (L) over bar/eta(k) <= 17.3. Ratios between fiber settling velocities in turbulence and quiescent conditions, (V) over bar (2)/V-s, scaled with the ratio of the rms of air fluctuating velocities, u' and V-s, similar as for spherical particles. Fiber inertia (as indicated by St) decreased the response of the fibers to the fluctuating air velocities, and ratios of the rms values of fluctuating fiber centroid velocities and air velocities dropped from 0.96 to similar to 0.77 for the highest St and were well predicted by the model of Wang and Stock [J. Atmos. Sci. 50, 1897 (1993)]. Furthermore, with increasing St, probability density functions (PDFs) of fiber centroid velocities that were well described by a normal distribution narrowed in comparison to the those of the air velocity. PDFs of in-plane fiber rotation rates could not be described by a normal distribution. In the absence of significant length effects, fiber rotation rates were governed by St. Our results indicate that the fiber "tumbling" rate peaks at around St approximate to 4, most likely as a result of reduced fiber alignment with the vorticity vector compared to fibers having lower St. At the highest investigated St, decreasing "tumbling" rates are the result of increasingly limited response to the fluctuating flow field, well predicted by the slightly modified model proposed by Bounoua et al. [Phys. Rev. Lett. 121, 124502 (2018)].