Mass Transport Coefficient Research Articles

Quantifying Lithium-Ion Battery Rate Capacity, Electrode Structuring, and Transport Phenomena Using E-I Measurements

The specific energy of lithium-ion batteries (LIBs) can be enhanced through various approaches, one of which is increasing the proportion of active materials by thickening the electrodes. However, this typically leads to the battery having lower performance at a high cycling rate, a phenomenon commonly known as rate capacity retention. One solution to this is perforating the electrode, by creating channels or corrugations in the active electrode material, either as holes or as channels. This is known to reduce the rate capacity retention effect, but in order to engineer this better, a simplified transport process analysis needs to be established. In this paper, we propose a classic electrochemical analysis based on voltage–charge cycling measurements in order to obtain a classical mass transport coefficient, hm, that is further used as a main indicator for electrode design quality assessment. We also demonstrate theoretically and experimentally how the mass transfer coefficient, hm, can be determined and how it changes as the electrode layer thickness increases, with and without electrode corrugations.

Hydrodynamics and mass transport in an anodic oxidation reactor: Influence of gas evolution and flow path through mesh electrodes

Removal of organic compounds by anodic oxidation requires a sufficiently high rate of mass transport of target compounds to the electrode surface. Since anodic oxidation is often accelerated by the formation of hydroxyl radicals from water oxidation at high anodic potential, the role of oxygen/hydrogen evolution reactions was investigated. Residence time distributions showed that formation of bubbles in zones where fluid velocity was minimal, allowed for strongly improving global hydrodynamics in the reactor. The role of bubbles was also discussed by comparing mass transport coefficients obtained from the limiting current technique to values obtained from kinetics of COD removal during treatment of a model pollutant (phenol). The use of mesh electrodes (with liquid flowing through the electrode) further promoted convection and mass transport of organic compounds compared to plates. However, large bubbles generated at plate electrodes also allowed for convection enhancement in the vicinity of surface of plate electrodes. In both cases, an adverse effect from bubble adhesion was observed because of the decrease in the active surface of electrodes. The mass transport coefficient obtained with the limiting current technique using mesh electrodes was 0.69 10−3 cm/s at 10.8 L/h with a mean velocity of electrolyte past the mesh surface (u¯mesh) of 0.37 cm/s. It decreased to 0.58 10−3 cm/s during the treatment of phenol at the same flow and reached 0.75 10−3 cm/s when increasing the flow to 32.4 L/h. By taking into consideration gas evolution at the surface of electrodes, this study allowed for accurate calibration of an advective – dispersive model with reaction that could be used for sizing such reactors according to the intended application.Abbreviations: Ae, the volumetric surface area (ratio between the geometric volume and the active surface area of the mesh electrodes) (cm−1); CA, aeration by a floor diffuser of fine bubbles and no current at the electrodes; CEP, polarization of the electrodes with a current intensity and no aeration; CW, no electrode polarization and no aeration; COD, chemical oxygen demand (mgO2 L−1);Di, diffusion coefficient of specie i (m2/s); D, dispersion coefficient (cm2 min−1); E(θ), residence time distribution function; EC, electrical energy consumption (kWh gCOD−1);F, Faraday constant (96485C mol−1); HER, hydrogen evolution reaction; IOA, index of agreement;km, mass transport coefficient (m/s); MCE, mineralization current efficiency; ME, model efficiency; OER, oxygen evolution reaction; OH, hydroxyl radical;Ql, liquid flow rate (L/h); rAO: anodic oxidation rate (mol/m−3 s−1); RTD: residence time distribution; ts¯: mean residence time or first moment order; u¯: mean flow velocity (m/s); VT: total volume (L); σ2: variance or second moment order; γ: skewness factor or third moment order; τ: residence time; μ: order moment.

Elucidating Degradation of Aqueous Organic Redox Flow Batteries by Electrochemical Impedance Spectroscopy

Redox flow batteries, facilitating the dissociation of energy and power, emerge as a promising avenue for electrochemical electricity storage. A shift from vanadium flow batteries to those employing aqueous organic electroactive species is evident due to the latter's advantageous features, such as diverse design possibilities through functionalization, reduced cost, non-toxicity, and improved availability. Despite expectations that organic redox flow batteries can surpass a lifespan of 10 years or 2000 cycles, their practical long-term performance faces challenges arising from electrode, membrane, and organic species degradation. The intricate interplay of various degradation factors during full cell cycling results in observable capacity decay over cycles. Effectively mitigating degradation necessitates the dissection of these factors to identify the limiting component. Electrochemical impedance spectroscopy (EIS) emerges as a potent diagnostic tool capable of pinpointing and disentangling the sources of resistance within an electrochemical device. Through deconvolution of different factors, EIS allows for the quantitative measurement of resistance evolution throughout full cell cycling, reflecting degradation through changes in resistance. Consequently, by monitoring resistance evolution with EIS, the degradation rates of individual factors can be calculated.This study employs an alkaline aqueous organic redox flow battery with 2,5-di-tert-butyl-1,4-dihydroxybenzene sulfate (DHPS) as anolyte and ferrocyanide as catholyte for demonstration. EIS measurements are conducted at various cycles, and three distinct resistance components (charge transfer, ohmic, and mass transport) are identified as functions of cycle numbers. Subsequently, the degradation rates of crucial electrochemical parameters, such as reaction rate and mass transport coefficient, are quantified, providing essential inputs for subsequent modeling endeavors.

Control of paleoclimate and paleoweathering on chromium contents in a non-ultramafic aquifer hosting high chromium groundwater.

Cr(VI) is a carcinogen with proven mutagenic and genotoxic effects. The effects of the depositional environment (e.g., paleoweathering, paleoclimate, and paleoredox condition) on Crenrichment in non-ultramafic aquifer solids are unclear. In this study, we presented the sedimentary characteristics of a borehole from a typical non-ultramafic aquifer with high Cr groundwater in Jingbian, central Ordos Basin, China. Chromium was enriched in the K1h sandstone aquifer, especially at depths of 400-500m, with the highest value of mass transport coefficient (τAl,Cr) up to 92.13% and τAl,Fe up to 33.5%. The provenance of aquifer Cr was predominantly intermediate and felsic igneous rocks with a mafic rock mixture. This mafic source was inferred from Cr-rich granodiorite and mafic/ultramafic rocks in the Yinshan (Daqingshan-Wulashan) Block, northern Ordos Basin. The Cr-rich aquifer in K1h was developed due to a moderate chemical index of alteration (CIA) (mean, 56.7) under relatively warm and humid paleoclimate, as evidenced by high CIA-temperature (CIA-Temp) (mean, 6.79°C) and paleoclimatic index values (mean, 0.40). Fe-Mn redox cycling in the oxic to suboxic environments contributed to aquifer Cr accumulation. Using path analysis, we identified that paleoclimate created favorable weathering conditions and enrichment of Fe contributed to the formation of high-Cr aquifers. The study reveals the formation of positive Cr anomalies in non-ultramafic aquifers, which is the potential source of groundwater Cr, and highlights the effects of depositional factors on Cr accumulation during aquifer deposition or early diagenesis. It can provide new insights into the natural processes of high-Cr sediments occurring in non-ultramafic aquifers.

Asymptotic analysis of fluid thermodynamic behaviors in the near-critical region under highly variable physical properties

Asymptotic analysis based on the fluids governing equations with the exponential model of thermophysical properties is introduced to quantify the influence of each property on the heat and mass transfer behavior of the near-critical fluid. The one-dimensional asymptotic model finds the different behavior in boundary layers and bulk regions controlled by the diffusion and wave mode, respectively. From the asymptotic model, three characteristic parameters are found: nondimensional wave velocity for wave mode, nondimensional diffusion coefficient for diffusion mode, and nondimensional mass transport coefficient for the coupling in between. Larger thermal conductivity, fluid compressibility, and lower specific heat are found to enhance the thermal wave. However, the efficiency of heat transfer by thermal waves is irrelevant to the thermal diffusivity but related to the fluid compressibility. From the calculation of the asymptotic model for supercritical carbon dioxide (sCO2), such efficiency is 0.150, which indicates that most of the thermal energy is accumulated in the boundary layers.

Hydrogen and Oxygen Permeability through PEFC Membrane and Membrane Electrode Assembly

IntroductionThe permeation of feed gas through a proton exchange membrane (PEM) affects a PEFC performance [1, 2]. The temperature and relative humidity (RH) dependences of the hydrogen and oxygen permeability through the perfluorinated sulfonic-acid (PFSA) membrane were investigated. A membrane is considered to consist of a bulk layer sandwiched between skin layers [3]. In this study, by measuring the hydrogen and oxygen permeation flux through a membrane and plotting the permeation resistance against the membrane thickness, the bulk layer effective diffusion coefficients and the skin layer mass transport coefficients of PEM and membrane electrode assembly (MEA) were examined.ExperimentalNafion™ NR-211, NR-212, and N115 (Chemours) with different thickness (at RH of 50 %), 25.8, 51, and 127 μm, respectively, were used as PEM. Catalyst layers made of Pt-loaded carbon (Pt 50 wt%) and Nafion ionomer (I/C = 1.0) with a thickness of 8.5-10 μm on both sides of PEMs were prepared as MEA. They were installed separately in a Japan Automobile Research Institute (JARI) standard cell whose active area was 5.0 cm×5.0 cm. The cell was placed in the constant temperature and humidity oven (ESPEC, LHL-113) and the relative humidity of the supplied gas was controlled by the bubbler temperature. The hydrogen and oxygen fluxes through a membrane were measured at cell temperatures of 60-90 °C and RH of 0.2-1.0 (moisture content λ = 1.7-10.5) with different partial pressures of nitrogen diluent gas. Permeate gas was quantified by a gas chromatograph (Agilent 990 micro GC, column: MSieve5A, detector: TCD). The schematic drawing of the measurement system is shown in Fig. 1.Results and discussionThe permeate gas flux through a membrane, Nj (j = H, O), is expressed asNj = k pj Δpj , where k pj is the gas permeance and Δpj is the partial pressure difference between the supply side and the permeate side.Fig. 2 shows the temperature and RH dependences of O2 permeance through PEM and Fig. 3 shows the permeation resistance against the membrane thickness. k pO increases with increasing RH and 1/k pj becomes lower at higher temperature. The permeation resistance through MEA tends to be lower than PEM. By assuming that Nafion has a bulk layer and skin layers [3], the bulk layer and skin layer resistances were separated from a slope and an intercept of trend lines in Fig. 3. The permeation resistances through MEA do not have y-axis intercept. The fused layer can be created by hot press process in manufacturing MEA and an x-axis intercept might be a fused layer thickness. It is easier to permeate gas through the fused layer than the skin layer of PEM. The temperature dependences of the bulk layer effective diffusion coefficient, D ej (B), are shown in Fig. 4. D eH (B) and D eO (B) of PEM and MEA are on the same line, with activation energies, E a, of 23.9 and 20.6 kJ/mol, respectively at λ = 6. D ej (B) can be formulated as follows: D eH (B) = (4.26×10-11 + 6.50×10-11RH) exp(-E aH/R (1/T-1/T ref)) m2/s D eO (B) = (8.16×10-12 + 3.39×10-11RH) exp(-E aO/R (1/T-1/T ref)) m2/s T ref = 353.15 K, E aH = 0.65 λ + 20.0 kJ/mol, E aO = 21.2 kJ/mol,Reproduced D eH (B) and D eO (B) are shown in Fig. 5. The skin layer mass transport coefficient, k pj (S), can be obtained from the y-axis intercept of a trend line in Fig. 4 and it shows that only PEM has skin layers. It is necessary to consider the gas permeation through MEA not through PEM in designing PEFCs because using the transport properties through PEM may lead to overestimate the performance.ConclusionsBy measuring the hydrogen and oxygen permeation flux through PEM and MEA in PEFC, the bulk layer effective diffusion coefficients and the skin layer mass transport coefficients of hydrogen and oxygen were obtained. The bulk layer effective diffusion coefficients of PEM and MEA were found to be the same and the temperature and RH dependences of D ej (B) were formulated as a function of temperature and RH. The skin layer mass transport coefficient appears only in PEM.AcknowledgementThis work was supported by the FC Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high-performance project (FY 2020–FY 2023) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Physical and reactive absorption of CO2 in capillaries: Mass transfer, modelling and produced chemical species

In a circular economy and sustainability context, CO2 utilization is key. For photochemical or electrochemical transformations, CO2 absorption in liquids has become crucial and even a limiting step. This work aimed to establish an average mass transport coefficient (k̅La) characteristic of the CO2 absorption in water and in alkaline solutions in capillary absorbers (2–4 mm) under Taylor flow and recirculation mode. A correlation among prevailing dimensionless numbers (Sh, Re, Ca and Sc) was also established. To achieve so, the absorption of CO2 was conducted in both, water and NaOH solutions (0.5 mol/dm3), and its concentration was monitored by measuring total inorganic carbon and pH. The gas and liquid flowrates used for the tests were 1.66×10−4 L/s and 2.5×10−4 L/s, respectively. The effect of temperature was investigated in the range of 283 and 308 K. The highest k̅La was found to be 12 × 10−2 and 2.1 × 10−2 s−1, for water and NaOH solutions, respectively. The modelling and simulation of the carbon species formation and production was also conducted and a determination coefficient (R2) of 0.99 was found.

(Invited) Charge Propagation in Highly Concentrated Iodine/Iodide Solutions as Potential Redox Electrolytes and Mediators for Redox Flow Batteries and Solar Cells

The technology of Redox Flow Batteries is an important option to store energy from the operating irregularly renewable energy sources. The perspectives concern stationary energy storage, including grid-scale energy storage, thanks to their high power performance, flexible design, and ease of scaling-up. The flow-based electrochemical energy storage systems utilize the appropriate electroactive species dissolved in externally flowing electrolytes which are ready to accumulate all (or part) of the charge. Among important issues is the search for highly efficient (i.e., capable of fast electron transfers) electroactive systems that would yield high power and energy densities during the systems’ operation. Highly concentrated iodine/iodide system can act as redox conducting electrolyte. Furthermore its charge mediating capabilities has been recognized in the Dye Sensitized Solar Cell technology due to the feasibilioty of fast charge propagation accompanied by efficient electron self-exchange or diffusional-type electron hopping.In the present work, we concentrate on utilization of highly concentrated iodine/iodide redox systems and their possibility to exhibit high rates of charge propagation. In practical terms, it can be combined with ZnI2, or other zinc salt, containing electrolyte. Reactions in the zinc/iodine (polyiodide) redox flow battery are as follows: Zn → Zn2+ + 2e- (E = −0.76 V vs SHE) at the negative electrode (anode), and 3I- → I3 − + 2e− (E = 0.54 V vs SHE) at the positive electrode (cathode) thus yielding a total theoretical potential output as high as ∼1.3 V. The increase of current density could be achieved not only by reducing the viscosity of the electrolyte, thus accelerating charge-carrier transport, but also – by referencing to my experience with the iodine/iodide couple as charge relay for dye-sensitized solar cells – through improvement of the dynamics of charge propagation in highly concentrated iodine/iodide solution via the catalyzed enhancement of rates of electron self-exchange (hopping) between iodine/iodide (polyiodide) redox species as well as by accelerating the interfacial kinetics at electrodes. This can be realized by choosing appropriate electrode materials and through their activation or modification. The electrochemical activities of the redox couples are usually significantly increased through application of nanostructured functionalized carbons. While dispersed in solutions they can improve electron transfers to the redox sites. The proposed chemistry has been first tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation, heterogeneous and homogeneous (electron self-exchange) rates of electron transfers. Unless catalyzed, both interfacial and bulk (self-exchange) electron transfers involving the iodine/iodide redox system are somewhat complicated; there is a need to break the I-I bond in the I3 -or I2 molecule; it has also been well-established that platinum (e.g. when deposited on the counter electrode) induces electron transfers within the iodine/iodide redox system [1]. In the presentation, we are going to explore the respective interfacial (electrocatalytic) phenomena on nanostructured metal oxides (e.g. zirconia), in addition to traces of expensive platinum or palladium nanoparticles (provided that catalytic centers are three-dimensionally distributed in the electrolyte phase), and we will utilize them to enhance iodine/iodide electron transfers to develop a new generation of redox mediators or ultra-fast components of redox electrolytes. Our results show that the catalyzed iodine/iodide system can reach extremely high electron self-exchange rates, namely on the level of109 – 1010 mol-1 dm3 s-1 . [1] I.A. Rutkowska I.A., M. Marszalek, J. Orlowska, W. Ozimek, S.M. Zakeeruddin, P.J. Kulesza, M. Grätzel, ChemSusChem 8 (2015) 2560-2568.

Single-Flow Batteries Leveraging Multiphase Electrolytes

The share of electricity generated from renewable sources is growing rapidly, and thus grid-scale battery storage is becoming more prevalent. Aqueous redox flow batteries have the potential to provide safe and scalable energy storage, but the high cost of storage, particularly the membrane and balance of plant costs, has inhibited commercialization. The recently developed single-flow battery leveraging a multiphase electrolyte promises a low-cost system [1], as it is membraneless and uses only one tank and flow loop, but suffers from low Coulombic efficiency [1]. To unlock the potential of such a system, the interplay between interphase mass transport, multiphase flow phenomena, and battery performance must be unraveled. Here, we will compare our previously developed theoretical battery model derived from a boundary layer analysis [2,3] to results from a dedicated experimental program [4]. This led to several key findings, including that our battery operates in a regime characterized by a high Stanton number, and that our analytical solutions led to excellent predictions in various operational regimes when using the interphase mass transport coefficient as a single-valued fitting parameter [4]. In other regimes, such as at low electrolyte velocity, results indicate that gravity acting on the denser polybromide phase played a significant role, and progress towards incorporating gravitational effects into models will be discussed [4]. Figure 1: Schematic of a discharging single-flow battery leveraging a multiphase flow electrolyte. The flow consists of a continuous, bromine-poor aqueous phase and dispersed, bromine-rich polybromide phase. Bromine in the polybromide phase is largely electrochemically inactive, thus such an electrolyte enables membraneless operation by limiting the crossover of bromine to the zinc anode.

Comparison study of fluid thermal boundary-bulk behaviors in the close-to-critical region under different property trends

The high-efficiency energy system based on the utilization of supercritical CO2 has been widely developed in recent years to meet the growing demands of clean energy and the elimination of CO2 emissions. Within this field, the design of the corresponding equipment requires an understanding of the thermodynamic behavior of supercritical fluid affected by the singular thermophysical properties. The analysis of this study is based on the asymptotic expansion of hydrodynamic equations and the thermophysical properties characterized by the exponential trends. The asymptotic model finds the wave and diffusion modes valid within the bulk region in second-order and within the boundary layer region (BLR) in first-order, respectively. Main findings include: (1) The wave mode is found in the bulk region with the wave celerity Γ. When the critical point is approached, Γ decreases from (γ0Mac0/κT0)0.5 = 1 to [(γ0–1)Mac0/κT0]0.5, which; (2) The diffusion mode found in BLR is characterized by non-dimensional diffusion coefficient ζ. This coefficient has the same behavior as thermal diffusivity, which is enlarged by thermal conductivity but weakened by isobaric specific heat. (3) Mass transport from BLR to bulk leads to the generation of the thermal wave, which can be measured by mass transport coefficient Mb=ζβp. Mb also characterizes the magnitude of the thermal wave as u2=Mb(Tb1)z|z=0 (that is, 0.17 mm/s when ϕ=10−4). The behavior of Mb is similar to one of ζ. However, the effect of cp is limited; (4) Two different modes of viscosity are identified. The increase in viscosity leads to the change of viscous stress mode from the second order to the first order, which also leads to a decrease in mass transport.

Enhancing of transport parameters and antifouling properties of PVDF membranes modified with Fe3O4 nanoparticles in the process of proteins fractionation

Polyvinylidene fluoride (PVDF) possesses a broad range of applications, including membrane separation used for water and wastewater treatment. However, the natural hydrophobic character of PVDF causes fouling problems which limit the applicability of this material. For that reason, various experimental protocols focused on the PVDF modification are in the spotlight of the recent research.This work focuses on PVDF membranes, modified with iron (II, III) oxide nanoparticles (NPs). The structural and morphological properties of membrane materials have been evaluated using FTIR, SEM, SEM-EDX, AFM, and contact angle (CA) measurements. The modified membrane demonstrated improved hydrophilicity as the contact angle value decreased from 68°± 2° to 51°± 2°. Transport parameters of the obtained membranes were investigated during the dead-end ultrafiltration (UF) process. Compared to the pristine PVDF membrane, the mass transport coefficient of the modified membrane increased twice owing to the ability of Fe3O4 to move in a magnetic field, which allowed to enhance transport parameters and reduce the fouling and concentration polarization phenomena. The modification process improved pure water permeability from 45 L·m−2·h−1·bar−1 for a pristine PVDF membrane to 72 L·m−2·h−1·bar−1 for PVDF with immobilized Fe3O4 NPs. The appropriateness of magnetically active membrane materials in UF of various proteins was also discussed in terms of protein separation and fractionation. The developed magnetoactive PVDF membrane can be used in the process of proteins fractionation owing to its property to prevent the accumulation of lysozyme on the membrane surface at the alkaline medium: the rejection of lysozyme was only 5.3 % at the pH equal to 12.

Outstanding productions of peroxymonosulfuric acid combining tailored electrode coating and 3D printing

In this work, the combination of a tailored design of electrode and electrochemical cell to produce peroxymonosulfuric acid (PMSA), also known as Caro's acid, is evaluated. For the electrode, a customized coating of BDD was deposited onto a niobium substrate. This electrode exhibited a good reproducibility and efficiency in the production of PMSA, thus promoting direct oxidation of sulfuric acid into Caro's acid and preventing the action of scavengers. The electrochemical cell was manufactured after the application of computer-aided design (CAD) combined with computational fluid-dynamics (CFD) simulation and 3D printing. The prototype, with an area of 25sqcm and a designed flowrate of 48 L/h, has been characterized with the evaluation of mass transfer coefficients and RDT curves, which demonstrate an outstanding performance with mass transport coefficients over 3·10−5 m s−1 without turbulence promoter. The cell equipped with the electrodes was tested in the production of Caro's acid enabling a remarkable production of 200 mM of peroxymonosulfuric acid in discontinuous operation mode with a coulombic efficiency (57.2 %) and energy Efficiency (10.67 mmolA−1 h−1). These values outperform the previous state-of-the-art works done in the field for undivided cells operated in discontinuous mode. The results obtained were successfully fitted to a phenomenological model for the generation of Caro's acid.

Evaluation of drying kinetics of carrot and thermal characteristics of natural and forced convection indirect solar dryer

The thermal characteristics of natural (setup-A) and forced (setup-B) convection indirect solar dryers were evaluated and compared by drying carrot slices. Several modifications were made to setup-A to promote setup-B, including a trapezoidal tunnel, and central processing unit fans which were powered by photovoltaic panels. From the experimental solution, the performance terminologies and the drying characteristics of the carrot were examined. The actual rate of heat supplied to setup-A was 705.64 W and setup-B was 789.55 W. In the respective tests, collectors had an average efficiency of 56.84% and 68.74%. Accordingly, the drying efficiencies for the same were 7.5% and 9.55%, respectively. As a result of the aforementioned calculations, activation energy, effective diffusion coefficient, mass and heat transfer coefficients for setup-A and setup-B were 42.71 kJ/mol and 37.85 kJ/mol, 6.32 × 10−9 m2/s and 7.25 × 10−9 m2/s, 0.0055 m/s and 0.0065 m/s, and 6.32 W/m2 K and 7.25 W/m2 K, respectively. The setup-B showed a better effective moisture extraction rate and energy consumption. Characteristic relationships between moisture content vs diffusion, heat and mass transport coefficients were derived. Uncertainty estimations were performed to verify the precision of the findings.

Utilization of Electrodeionization for Lithium Removal.

In this work, usage of a hybrid polymeric ion exchange resin and a polymeric ion exchange membrane in the same unit to remove Li+ from aqueous solutions was reported. The effects of the applied potential difference to the electrodes, the flow rate of the Li-containing solution, the presence of coexisting ions (Na+, K+, Ca2+, Ba2+, and Mg2+), and the influence of the electrolyte concentration in the anode and cathode chambers on Li+ removal were investigated. At 20 V, 99% of Li+ was removed from the Li-containing solution. In addition, a decrease in the flow rate of the Li-containing solution from 2 to 1 L/h resulted in a decrease in the removal rate from 99 to 94%. Similar results were obtained when the concentration of Na2SO4 was decreased from 0.01 to 0.005 M. The selectivity test showed that the simultaneous presence of monovalent ions such as Na+ and K+ did not change the removal rate of Li+. However, the presence of divalent ions, Ca2+, Mg2+, and Ba2+, reduced the removal rate of Li+. Under optimal conditions, the mass transport coefficient of Li+ was found as 5.39 × 10-4 m/s, and the specific energy consumption was found as 106.2 W h/g LiCl. Electrodeionization provided stable performance in terms of the removal rate and transport of Li+ from the central compartment to the cathode compartment.

Imaging concentration fields in microfluidic fuel cells as a mass transfer characterization platform

Microfluidic fuel cells (MFCs) are microfluidic electrochemical conversion devices that are used to power electrical equipment. Their performance relies on improving reactant mass transfer at the electrode interface. In this work, a MFC is developed to implement a novel imaging technique that allows the measurement of reactant concentration fields, featuring formic acid as the fuel and potassium permanganate as the oxidant. The concentration fields were imaged based on transmitted visible spectroscopy, which links the light intensity passing through the MFC to its local reactant concentration. An analytical model was developed to estimate the mass diffusivity and kinetic reaction rate coefficient. For the first time, mass transport and transfer coefficient were simultaneously measured during operation. These parameters estimated using the proposed technique can be implemented in a numerical model to predict the MFC performance and concentration distribution. This work paves the way towards advanced imaging tools for operando mass transfer characterizations in microfluidics and Tafel kinetic characterization in many electrochemical devices.

Local structures and undercooling ability of Zr–Ti melts

We developed an accurate model of Zr–Ti melts for classical molecular-dynamics simulations via regauging the existing embedded-atom method (EAM) potential, using particularly the diffusion coefficient data obtained from quasielastic neutron scattering. This EAM potential well reproduces the properties of the melts observed in experiments, including mass density, transport coefficients, melting temperatures, and static structure factors. The latter are also obtained from ab initio simulations. Using the developed EAM potentials, we analyzed the short-range order of the liquids and found a chemically preferred formation of Zr–Zr and Zr–Ti nearest neighbor pairs. When decreasing the temperature the number of icosahedral-like aggregates increases on the expense of more crystal-like structures. This is most pronounced at intermediate alloy compositions. At intermediate compositions also the lowest thermodynamic driving force for crystallization is found, resulting in the largest undercooling ability of the alloys.

Mechanistic Study of Arsenate Adsorption onto Different Amorphous Grades of Titanium (Hydr)Oxides Impregnated into a Point-of-Use Activated Carbon Block.

Millions of households still rely on drinking water from private wells or municipal systems with arsenic levels approaching or exceeding regulatory limits. Arsenic is a potent carcinogen, and there is no safe level of it in drinking water. Point-of-use (POU) treatment systems are a promising option to mitigate arsenic exposure. However, the most commonly used POU technology, an activated carbon block filter, is ineffective at removing arsenic. Our study aimed to explore the potential of impregnating carbon blocks with amorphous titanium (hydr)oxide (THO) to improve arsenic removal without introducing titanium (Ti) into the treated water. Four synthesis methods achieved 8-16 wt.% Ti loading within the carbon block with 58-97% amorphous THO content. The THO-modified carbon block could adsorb both oxidation states of arsenic (arsenate and arsenite) in batch or column tests. Modified carbon block with higher Ti and amorphous content always led to better arsenate removal, achieving arsenic loadings up to 31 mg As/mg Ti after 70,000 bed volumes in continuous flow tests. Impregnating carbon block with amorphous THO consistently outperformed impregnation using crystalline TiO2. The best-performing system (TTIP-EtOH carbon block) was an amorphous THO derived using titanium isopropoxide, ethanol, and acetic acid via sol-gel technique, aged at 80° for 18 hours and dried overnight at 60°. Comparable pore size distribution and surface area of the impregnated carbon blocks suggested that chemical properties play a more crucial role than physical and textural properties in removing arsenate via amorphous Ti-impregnated carbon block. Freundlich isotherms indicated energetically favorable adsorption for amorphous chemically synthesized adsorbents. The mass transport coefficients for the amorphous TTIP-EtOH carbon block were fitted using a pore surface diffusion model, resulting in Dsurface = 3.1×10-12 cm2/s and Dpore = 3.2×10-6 cm2/s. Impregnating the carbon block with THO enabled effective arsenic removal from water without adversely affecting the pressure drop across the unit or the carbon block's ability to remove polar organic chemical pollutants efficiently.

Study of drying parameters of pineapple and performance of indirect solar dryer supported with thermal energy storage: Comparing passive and active modes

In this study, passive and active indirect solar dryers (PISD and AISD) with an energy storage system (paraffin wax) and the drying kinetics of pineapple were investigated. To form AISD, the PISD was restructured by providing solar-powered central processing unit fans. The mass variation and temperature data recorded during the experiments were used to evaluate drying characteristics and parameters. As a result, AISD showed an improvement of 0.089 kW, 4.34 kJ/mol, and 3.5 kWh/kg of actual heat supply, activation energy, and specific energy consumption, respectively, compared to PISD. Similarly, the dryer and collector efficiencies of AISD improved by 25.77 % and 16.52 %, respectively, compared to PISD. For PISD and AISD, the mean specific moisture extraction rate, moisture diffusivity, heat and mass transport coefficients were 3.10 and 3.67 kg/kWh, 5.23 and 5.97 × 10−9 m2/s, 0.00489 and 0.00576 m/s, and 5.6 and 6.47 W/m2K, respectively. After 16 h in PISD and 14 h in AISD, moisture content decreased from 7.91 to 0.417 (db) with an average drying rate of 0.408 and 0.45 kg/h, respectively. Based on the evaluated parameters, AISD performed better than PISD. Uncertainty analysis was performed to check the validity of the results.

Neuroendocrine pancreatic tumors: about 13 cases

This article intends to revisit the electro-diffusional theory for the wall shear stress measurement from mass transfer probes of rectangular shape by considering the existence of two components of the wall shear rate (i.e., axial and transversal). General analytical formulas for the effective transfer length and the dimensionless mass transport coefficient were derived as a function of two parameters: a dimensionless angle of the flow direction, relative to the leading edge of the probe, and the aspect ratio between the width and the length of the strip probe. The correctness of the analytical relations for arbitrary flow direction and the aspect ratio was confirmed by numerical solutions of the transport equation in the convective-diffusive regime. It has also been proved that the differences between the Lévêque solution and the general analytical formula exhibit a significant deviation for a specific range of parameters. In the case of the three-dimensional boundary layers, in addition to the magnitude of the wall shear stress, the direction of the fluid flow in the vicinity of the probe’s surface is of paramount importance. Accordingly, a measurement methodology is proposed using two strip probes with different aspect ratios. The resulting equations required to quantify the magnitude of the wall shear rate vector and the dimensionless angle are also derived.

Comparative Analysis of Lead Removal from Liquid Copper by ICF and CCF Refining Technologies.

Innovative technologies require the use of materials that meet increasingly high requirements; one such requirement is the purity of metals. In the case of copper, this translates into a parameter related to electrical conductivity. Traditional metal refining technologies have some limitations that can be eliminated through the use of modern melting aggregates. Such solutions include vacuum induction furnaces, comprising an induction furnace with a cold crucible. As part of this work, the possibilities of refining copper and lead alloys were investigated. In addition, the research was carried out with the use of two induction vacuum aggregates, allowing us to compare their effectiveness. The tests were carried out in a pressure range of 10–1000 Pa and at temperatures of 1273–1473 K. The results obtained made it possible to determine the mass transport coefficient of lead from an alloy with copper, and to determine the share of resistance in individual stages of the process. For experiments conducted inside an induction crucible furnace, lowering the working pressure inside the furnace chamber from 1000 to 10 Pa while increasing the temperature from 1323 to 1473 K was accompanied by a drop in the lead concentration inside the alloy of 69 to 96%, compared to its initial mass. For experiments conducted inside a cold crucible furnace, approximate values of lead removal appeared for lower temperatures (1273 to 1323 K), confirming that the analyzed process happens faster in this aggregate.