Constant Flow Research Articles

Experimental investigation on gas-liquid two-phase flow patterns and vibration characteristics of an inducer pump

Inducers typically enhance centrifugal pump performance in two-phase flow regimes by producing more uniform mixtures and increasing pressure before the impeller. Their impact is most pronounced under part-load conditions compared to overload situations. This study experimentally investigates air-water two-phase flow behavior within a pump inducer. Using high-speed photography and grayscale image processing, five distinct gas-liquid flow patterns were identified: bubble flow, strip bubble flow, agglomerated bubble flow, gas pocket flow, and segregated flow. The inducer's head and vibration characteristics were also measured. Results show that flow pattern transitions significantly affect performance degradation and vibration. Specifically, the head decreases as the liquid flow rate increases at a constant gas volume fraction (λ) and generally follows a downward trend as λ increases at a constant liquid flow rate. Bubble flow, representing minimal λ, has a negligible effect on performance. However, with higher λ, a sharp decline in head occurs within the agglomerated bubble flow range, followed by a gradual decrease during gas pocket flow under both optimal and overload conditions. In part-load conditions, the head decreases sharply during strip bubble and segregated flow. While bubble flow mitigates vibration fluctuations, increasing GVF leads to higher vibration amplitude, particularly in the range of 2–8 times the inducer's rotational frequency, due to flow pattern instability.

Global Sensitivity Analysis of Relative Permeability and Capillary Pressure in Unsteady-State Core-Flooding Experiment

Numerical simulation stands as a pivotal method within the petroleum industry, enabling the prediction of fluid flow in porous media. Its primary goal lies in analyzing behavior and forecasting oil production through fluid injection. However, the necessity for numerous simulations, each encompassing diverse multidimensional and compositional characteristics, presents a challenge. This leads to a significant accumulation of physical information, exacerbating the computational demands on the numerical model, particularly in terms of computational cost. To address this challenge, one potential solution is to determine the essential input parameters required for accurate oil production prediction. Global sensitivity analysis emerges as a powerful tool for this purpose, aiming to identify which input parameters exert the most significant influence on the numerical model's response, thus optimizing computation time. Unlike traditional approaches that focus on sensitivity around a single operating point, this study adopts a holistic perspective, assessing sensitivity across the entire sample space of the inputs. Specifically, this research investigates the impact of changes in parameters related to relative permeability and capillary pressure curves within a plug during unsteady-state core-flooding experiments. The key metrics under scrutiny include water saturation profiles, pressure differentials, and cumulative oil production. Sobol indices, a method for quantifying global sensitivity, are employed to assess the contribution of each input parameter's variance to the outputs' variance. The mathematical framework employed here is based on the multiphase (water/oil) Darcy equation, incorporating capillarity effects in one-dimensional longitudinal flow, incompressible flow assumptions, and constant injection flow, commonly known as the Black Oil model. The model is solved utilizing an implicit finite difference methodology with time step control, with relative permeability and capillary pressure parameterized by the LET model. The outcomes of this analysis provide valuable insights, notably in reducing the number of estimable parameters in inverse problems on a global scale. This reduction significantly diminishes computing costs, offering greater flexibility in constructing surrogate models for future simulations.

Условия для самовоспламенения при смешении продуктов горения с топливно-воздушной смесью

To date, the possibility of self-ignition of systems obtained due to mixing a cold air-fuel mixture with hot combustion products has been established. The topic of potential generation of such mixtures, however, is understudied. The article attempts to determine the conditions under which self-igniting systems are generated in the case considered. For the studies, a model of an ideal mixing reactor with increasing mass and temperature in the system under condition of constant pressure and mass flow of combustion products inflowing to the system has been applied. The cold air-fuel mixture is initially contained in the system. The mass flow and final mixing temperature are preset. The preset mixing temperature is determined without considering chemical reactions whereas the induction period considers the chemical reactions during mixing. Flaming must not be initiated in the system, otherwise mixing does not occur. This condition complies with the high-intensity turbulence requirement for an energetic cold air-fuel mixture. Less strict requirements are applied to the mixing of highly diluted or non-combustible air-fuel mixtures. The study has adopted the requirement of either the Damkeller number, Da < 1 or the Karlowitz number Ka > 100. As a result of that, requirements for the intensity and scale of turbulence, the velocity and transverse size of the jet, and mixing combustion product are derived. On the other hand, the hot flow parameters are restricted by the condition to ensure the required flow so that the temperature in the system could reach the preset value during a specific period that cannot exceed the induction period by more than 10 times. The latter requirement is the consequence of the adopted scenario of ideal mixing with monotonously increasing temperature in the system. The global quenching condition is met for highly diluted mixtures and even for non-combustible mixtures. These conditions are represented in the plane «elocity — transverse size of the jet» as areas restricted with straight lines that meet the imposed requirements.

Effect of pore plugging on transpiration cooling performance implemented with perforated flat plates

Transpiration cooling is expected to be one of the most effective cooling technologies for gas turbine blades. However, dust deposition can easily lead to pore plugging, which limits its practical application in engineering. The plugging of pores in conventional porous media models is difficult to predict, so it is essential to construct computational models with finely controllable porous structures. In this study, a transpiration cooling configuration with straight holes perforated with a diameter of 0.5 mm was adopted. The effects of plugging ratio and region on flow and heat transfer under different coolant injection ratios and pump power conditions were investigated by numerical simulation. The results showed that at constant mass flow rate, the overall cooling performance increased as the plugging ratio increased at low injection ratios. At high injection ratios, the opposite was true. With a certain pump power, as the plugging rate increased, the flow loss coefficient rose, leading to a decrease in cooling efficiency. Transpiration cooling efficiency was also highly sensitive to the distribution of plugged holes at the same plugging ratio. When the coolant flow was sufficient, the farther the plugged area was from the leading edge, the smaller the reduction in cooling efficiency.

Prescription versus over-the-counter venotonics: HPLC-DAD and static digestive model simulation comparison.

Venotonics are a class of therapeutically active molecules that have vaso-protective effects. They are used to alleviate venous diseases and disorders, particularly venous insufficiency. We compared the composition of prescription versus over-the-counter (OTC) venotonics using high-performance liquid chromatography with UV detection (HPLC-DAD) and simulating their digestion using a static digestive model. From each drug, five tablets were weighed. A homogenate was prepared, and 25 mg of crushed homogenized tablets were weighed into 25 ml volumetric flasks. Dissolved in MeOH and added two drops of saturated NaOH solution. The samples were filtered into vials (Teflon, 0.45 μm) and used for analysis. An Ultimate 3000 HPLC system (Thermo Fisher Scientific, Waltham, MA, USA) consisting of a quaternization pump, autosampler, column thermostat and DAD (UV/VIS detector) was used. The composition of the mobile phase proceeded in a linear gradient from 30% methanol and 70% phosphoric acid (0.15%) in water at time t=0 min. to 80% methanol and 20% phosphoric acid (0.15%) at time t=15 min., at a constant mobile phase flow rate of 1.2 mL/min. Detection was performed using a DAD detector in the 190-450 nm wavelength range. The content of monitored flavonoids was calculated from peaks at a wavelength of 277 nm, in which both flavonoids have their absorption maxima. The static digestive model was used to simulate the digestive phase from the oral cavity to the corresponding intestinal phase. The content of diosmin and hesperidin (mg per table) for a prescription drug: Detralex: 480 mg, 26 mg. The content of diosmin and hesperidin (mg per tablet) for OTC drugs: Venostop: 502 mg, 48 mg, Diosminol: 520 mg, 50 mg, Devenal: 496 mg, 49 mg, Diohes: 493 mg, 46 mg. Digestion did not affect the solubility of all tested drugs. The active substances could not be determined in the non-alkalized sample. After alkalization, part of the insoluble matter was visibly dissolved and converted to a yellow flavonoid complex. Neither diosmin nor hesperidin could be identified afterwards. Our experimental results show that the contents of both listed active substances, diosmin and hesperidin, met the declared amounts in all tested medicaments. Digestion simulation showed identical behaviour in prescription and OTC venotonics. The active substances could not be determined in the non-alkalized sample. Digestion did not affect the solubility of the tested drugs.

Performance study on a new solar air heater for space heating: A numerical and experimental study

The need to address energy challenges and environmental pollution has led researchers to focus on utilizing solar energy. In this study, a new solar air heater collector system was developed that incorporates arc-shaped wire roughness and external airflow recycling. The system performance was evaluated under various conditions using energy conservation equations and a semi-analytical method for modeling. The results were validated, confirming the method’s accuracy. The findings revealed that the hybrid system significantly improved energy and exergy efficiencies at lower mass flow rates. Increasing the airflow recycle ratio up to 3 in conditions of constant roughness and low mass flow rates enhanced collector performance. However, at high flow rates and recycle ratios, exergy efficiency decreased due to increased pressure drop, despite a rise in energy efficiency, making it less effective than a simple collector system. The results show that the temperature increase is not so much from a mass flow rate of more than 0.05 kg/s. The existence of considered artificial roughness has caused an increase in temperature, especially in mass flow rates of less than 0.035 kg/s.

Controlled and Safe Hydrogen Generation from Waste Aluminum and Water, a New Approach to Hydrogen Generation.

A new method is proposed to generate hydrogen in situ at low pressure from powder-pressed recycled aluminum turnings activated with small amounts of NaOH and drops of water. The contribution of this system is that the user can obtain small flows of high-purity hydrogen (>99%) to charge their portable electronic devices in remote places, in a simple, controlled, and safe way, since only water is used. Test tubes that contain tiny amounts of NaOH on their surface can be transported and used without contact. In addition to being a safer system, a smaller amount of NaOH and water is needed compared to other systems, there is no need to preheat the water, and the system can even generate heat. As the feeding is drop by drop, the hydrogen flow can be easily controlled by manual or automatic dosing. The waste obtained is solid and contains mostly aluminum hydroxide with some NaOH and impurities from the waste of origin, which are easy to sell and recycle. A study has been carried out to optimize the type of test tubes and establish critical parameters. The results show that a constant and controllable flow rate of hydrogen can be obtained depending on the drip frequency where the chemical reaction predominates over diffusion, that the optimal amount of NaOH is 20 wt%, that a finer grain size can increase the H2 yield with respect to the stoichiometric value but reduces the instantaneous flow with respect to that obtained with larger grains, and that it is very important to control the density and the impurities to increase porosity and therefore water diffusion. The estimated cost of the hydrogen produced is 3.15 EUR/kgH2 and an energy density of 1.12 kWh/kg was achieved with a test tube of 92% aluminum purity and 20 wt% NaOH.

Increased electrolyte flow resistance and blockage due to hydrogen evolution in a flow battery single cell under stack electrolyte feeding conditions

In a flow battery stack, individual cells are typically fed with electrolyte in a parallel configuration, resulting in identical pressure drops across each cell. In this parallel liquid supply system, the distribution of electrolyte flow is closely related to the flow resistance in each branch. During operation, gas bubbles generated by chemical and physical processes tend to accumulate in the electrode pores, obstructing electrolyte flow and leading to uneven electrolyte distribution. Previous studies have mainly focused on single-cell experiments using constant flow pumps, which differ significantly from the nearly constant pressure difference liquid supply within the stack electrodes. To investigate the effects of gas evolution on liquid flow under constant pressure difference conditions, we propose a gravity-driven electrolyte feeding system for testing in a single cell, which simulates the flow conditions encountered in real stack applications. Under the interaction between gas bubbles and liquid flow, hydrogen evolution reactions at the scale of “mA cm-2” significantly reduce the electrolyte flow through the porous electrode. When the pressure difference drops below a critical threshold, the electrolyte flow rate continues to decrease significantly and may even stop entirely. And a sufficient feeding pressure difference is essential for enhancing bubble removal efficiency.

Comparison of WP-2 and MOCNESS plankton samplers for measuring zooplankton biomass in the Barents Sea ecosystem.

Zooplankton in the Barents Sea has been monitored on an annual autumn survey since the late 1980s, using vertical WP-2 and oblique Multiple Opening and Closing Net and Environmental Sensing System (MOCNESS) tows over the water column. Sampling with MOCNESS is used to describe thevertical distribution and more frequent sampling with WP-2 (~3:1) to describe the horizontal distribution. We use here a large cumulative data set of 874 MOCNESS and 2850 WP-2 stations with data on size-fractioned dry-weight biomass to compare the two zooplankton sampling gears. MOCNESS is consistently collecting more biomass of the large size fraction (>2mm screen size) by ~20% and less of the small fraction (<1mm) by ~30% compared to WP-2. This is interpreted to reflect more extrusion of small plankton and less avoidance by larger plankton with the MOCNESS. The data set has been collected by three research vessels. There was a difference in vertical speed in oblique tows of MOCNESS among the ships but no clear effect on volume filtered per unit time. This demonstrates operational consistency and suggests theuse of a constant flow factor (distance per flowmeter count) when calculating results over the time series. The issue of calibration of traditional flowmeters on oblique tows needs further examination.

Knowledge and perceptions of blood donors of the Western Cape Blood Services, South Africa, toward vaginal sample donation for biobanking.

Depletion of Lactobacillus species and an overgrowth of anaerobes in the vaginal tract bacterial vaginosis (BV)], is associated with non-optimal reproductive health outcomes, and increased susceptibility to sexually transmitted infections (STIs). BV is currently treated with antibiotics, although these provide suboptimal cure levels and high recurrence rates. Vaginal microbiota transplantation (VMT), the transfer of vaginal fluid from healthy donors with an optimal vaginal microbiota to a recipient with BV, has been proposed as an alternative treatment strategy. Here, we investigated knowledge and perceptions of blood donors to the concept of an optimal vaginal microbiome and VMT via the Western Cape Blood Service (WCBS) clinics in Cape Town, South Africa, by a self-administered questionnaire. Analysis of responses from 106 eligible women showed that 86% (91/106) would consider donating samples. Responses significantly associated with willingness to donate vaginal samples included: (1) belief that helping others outweighs the inconvenience of donating vaginal sample (p = 1.093e-05) and (2) prior knowledge of the concept of a healthy vaginal microbiome (p = 0.001). Most potential donors (59/91; 65%) were willing to receive a VMT themselves if needed. Participants who were unwilling to donate vaginal samples (15/106; 14%) indicated that vaginal sample collection would be unpleasant and/or embarrassing. The benefits of a collaboration with WCBS for this project include the naturally altruistic nature of blood donors, the constant in-flow of donors to WCBS clinics, and the infrastructure and logistical aspects in place. Data from this observational study highlight factors affecting the willingness of blood donors to become vaginal sample donors.

Constant vorticity two-layer flows over variable bottom at arbitrary latitude

We investigate the three-dimensional constant vorticity stratified geophysical flows over a variable bottom at arbitrary latitude. It is proved that the geophysical flows in the two layers are necessarily irrotational, one of the horizontal component of the velocity is constant, the other two components are zero. Moreover, the free surface presents a traveling character in the horizontal direction of the nonvanishing velocity component.

Polycrystalline inclusion-free growth of thick, lattice-matched SiGeC with high substitutional Carbon concentrations up to 2%

State of the art semiconductor manufacturing seeks to expand its range of Si-based materials with novel properties, boosting performance to comply with customer demands. These materials mostly comprise of large lattice parameter materials like Ge-rich or group III/V alloys. To reduce costs, heteroepitaxy of these materials on Si substrates is desired. Buffer solutions like SiGe [1] or Ge Virtual Substrates [2] or III/V patterned Superlattices [3] usually do not result in threading dislocations densities below 106 cm-2, which affects device performance and process robustness.The incorporation of Carbon into SiGe allows to tailor SiGe’s lattice parameter, theoretically enabling to match the Si substrate’s lattice parameter. This allows the strain-free growth of a few hundred nanometers up to several micrometers thick SiGeC on a Si substrate without the formation of dislocations.The growth of SiGeC was performed in a 300 mm industrial standard Reduced Pressure-Chemical Vapor Deposition (RP-CVD) reactor. Si2H6, GeH4 and SiH3CH3 were used as precursors with constant flows at 550°C, 10 Torr. Interstitial (C Int) and substitutional Carbon (C Sub) concentrations were determined by XPS. [4]For a 50 nm SiGeC layer with C Int~0.4% and C Sub=2.0%, smooth surfaces were observed by top view Scanning Electron Microscopy (SEM) (Fig. 1 (a)) and confirmed by Atomic Force Microscopy (AFM) (Fig. 1 (b)) with a RMS of 0.23 nm. X-Ray Diffraction measurements showed the growth of SiGeC lattice matched to the Si substrate (Fig. 1 (c)). Above ~250 nm, islands are visible on the surface by top-view SEM (Fig. 2 (a)) with the island’s diameter increasing as the SiGeC layer thickness increased. Transmission Electron Microscopy showed a dislocation free growth and that the islands/clusters were polycrystalline, originating from several hundred nanometers below the surface (Fig. 2 (b)).Growing SiGeC of the same thickness range under the same growth conditions with lower SiH3CH3 flow, resulted in fully substitutional incorporated Carbon with C Sub~1.0% and C Int below the detection limit. No islands/clusters were observed by SEM and AFM (Fig. 2 (c)). The elimination of C Int allowed to suppress the formation of polycrystalline SiGeC inclusions. The starting point of these defects should be due to point defects formed by C int clusters.Even if the reduction of SiH3CH3 flow resulted in defect free growth of thick SiGeC on Si substrates, other approaches are mandatory to incorporate higher C Sub into the SiGeC layer to achieve the desired novel properties. Dhayalan et al. [5] showed in the literature the growth of SiC with 2% of Carbon (C Sub=1.6%) without the formation of islands/clusters by introducing HCl during a Cylic Deposition Etch (CDE) process. These results are based on the preferential etching of C int point defects, which are preferentially etched by HCl, reducing the amount of C Int and preventing the formation of islands/clusters. Meanwhile, the C Sub was not significantly affected by HCl etching.The impact of HCl on the growth of SiGeC was evaluated by performing co-flow (simultaneous growth and etching) and CDE (separate growth and etching steps) with various small HCl flows, preventing aggressive etching of monocrystalline SiGeC, and varying the duration of the CDE etch step. The introduction of HCl during a co-flow process changed the C and Ge incorporation. The C Sub concentration varied between 2.0% and 1.9% (Tab. 1), while the interstitial Carbon concentration varied between 0.7% and 0.3%, which is the lower detection limit of the XPS measurement. The Germanium concentration increased from 20% to 25% (Tab. 1). The growth of SiGeC without Chlorine showed the transition to a polycrystalline material at the same Carbon composition for higher Ge concentrations. XRD profiles (Fig. 3) showed a good crystalline quality, well-defined SiGeC peak, outlining a reduction of C Int thanks to the HCl etching. The CDE process did not result in significant compositional changes. To gain further understanding a wider range of HCl flows and thicker layers will be investigated in the future.The growth of dislocation free, high crystalline quality SiGeC with high C Sub was demonstrated. It was outlined that interstitial Carbon was likely to create point defects which lead to polycrystalline islands/cluster formation for thick films. HCl was shown to reduce interstitial Carbon incorporation. Other materials with large lattice parameters could benefit from the knowledge gained on defect reduction and lattice matched growth.[1] Y. Bogumilowicz et al., J. Cryst. Growth, vol. 283, no. 3, 2005.[2] J. M. Hartmann, J. Cryst. Growth, 2018.[3] J.-S. Park, M. Tang, S. Chen, and H. Liu, Crystals, vol. 10, no. 12, 2020.[4] J. Vives, J Mater Chem C, 2023.[5] S. K. Dhayalan et al., ECS J3ST, p. 6, 2017. Figure 1

Hamiltonian formulation for interfacial periodic waves propagating under an elastic sheet above stratified piecewise constant rotational flow

We present a Hamiltonian formulation of two-dimensional hydroelastic waves propagating at the free surface of a stratified rotational ideal fluid of finite depth, covered by a thin ice sheet. The flows considered exhibit a discontinuous stratification and piecewise constant vorticity, accommodating the presence of interfaces and of linearly sheared currents.

A Thermodynamic Analysis of a Proton Exchange Membrane Electrolyzer

A thermodynamic, first law analysis was conducted to understand the temperature of a proton exchange membrane electrolyzer when operated at a constant voltage and feed water flow rate. It emerged that at certain values for both voltage and flow rate, the electrolyzer could work in two operation modii: a high stoichiometry, low current modus where most of the feed water just flows through the electrolyzer unreacted and the electrolyzer itself remains cold, and the preferred low stoichiometry, high current modus that results in a much higher operating temperature. A start-up procedure has to be developed to activate the latter. Overall, the measured electrolyzer temperatures are in very good agreement with the calculated ones.

Cathode Reaction Studies in Lithium-Oxygen Battery through Operando XRD Measurements

Introduction The lithium-Oxygen (Li-O2; LOB) battery has obtained significant attention as a promising candidate for next-generation storage batteries due to its higher specific energy density compared to conventional lithium-ion batteries [1]. However, the mechanism of the cathode reaction remains unclear, and the type of Li2O2 produced during cathode discharge is still uncertain, mainly because it's challenging to directly observe the compounds generated at the cathode during LOB operations. By newly designing observation cells and improving laboratory XRD system, we clarified the discharge products and investigated the discharging process using operando XRD measurements and Rietveld refinements[2]. In this study, the cathode reaction mechanism was discussed based on the results of the operando XRD measurements. Experimental A newly designed electrochemical cell, covered with a Kapton film dome to enable constant oxygen flow to the cathode side of the LOB, was set to the diffractomator of the Rigaku Ultima IV XRD measurement system. In the XRD system, Cu Kα was utilized as the incident X-ray, and high-speed one-dimensional detector served as the detector. In the electrochemical cell, Ketjen black self-standing films were employed as cathode materials, and tetraglyme solution containing 0.5 M LiTFSI + 0.5 M LiNO3 + 0.2 M LiBr was used as the electrolyte solution. The LOB was discharged and charged at a constant current density of 0.4 mA/cm2 for 10 hours each (4.0 mAh/cm2), in which XRD profiles were recorded every 20 minutes. Rigaku's SmartLab Studio II software was utilized for Rietveld analysis of each XRD profile to determine the detailed cathode product and its crystal structure. Results and discussion Upon conducting operando XRD measurements and Rietveld analyses, the cathode reactions of the Li-O2 battery were investigated. The discharging and charging reactions at the cathode of the Li-O2 battery, as well as the x values of the major product Li2-xO2 during discharging, have been investigated and determined. In the XRD profile measured during discharging, several peaks attributed to the cathode product were observed. Detailed Rietveld analysis of these peaks revealed that LiO2 with the same P63/mmc space group structure as Li2O2 was immediately formed after discharge initiation, followed by the deposition of Li2-xO2 accompanied by an increase in lithium occupancy. As discharging progressed, the lattice constant gradually extended towards the c-axis direction, leading to the formation of Li1.5O2 at a discharge capacity of 4.0 mAh/cm2. In this presentation, we will discuss the discharge and charge reactions of the Li-O2 battery cathode in detail, and we will also discuss the charge-discharge cycle characteristics.

Cathode Reaction Analysis of Lithium-Oxygen Battery Based on Operando XRD Measurements

Introduction The lithium-air battery (LAB), which has ten times the energy density of conventional lithium-ion batteries (LIB), is one of the promising candidates for the next-generation storage batteries, and there are great expectations for its development [1]. However, the reaction mechanism of the cathode reaction is still unclear, and the type of Li2O2 that is the product of the cathode in discharging is still unknown. The main reason for this is considered to be that it was difficult to directly observe the compounds generated at the cathode during LAB operation. By improving the laboratory XRD and the observation cell, we succeeded in operando XRD measurements of the cathode reaction in the LAB. In addition, under general conditions, the cathode product was Li1.5O2 with some Li missing from the crystal lattice of Li2O2 [2]. Here, we describe the details and discuss the reaction mechanism. Experimental An electrochemical cell covered with a Kapton® dome was constructed to allow constant oxygen flow to the cathode side of the LAB, and was attached to the diffractomator of a Rigaku Ultima IV XRD measurement system. A Cu Ka was used as the incident x-ray, a high-speed one-dimensional detector was used as the detector, a Ketjen black free-standing film was used as the cathode material, and tetraglyme solution with 0.5 M LiTFSI + 0.5 M LiNO3 + 0.2 M LiBr was used as the electrolyte solution. The LAB was discharged and charged at a constant current density of 0.4 mA/cm2 for 10 hours (4.0 mAh/cm2) each, and the XRD profile was recorded every 20 minutes. Each XRD profile was subjected to Rietveld analysis using Rigaku’s SmartLab Studio II software to determine the cathode product and its crystal structure. Results and discussion In the XRD profile measured during discharging, a lot of peaks due to the cell parts were observed. But, several peaks due to the cathode product were also observed. As a result of detailed Rietveld analysis of these peaks, the cathode product at the discharging capacity of 4.0 mAh/cm2 was not Li2O2 but Li1.5O2. Instead of the normal LiO2 with a rectangular crystal structure, LiO2 with a hexagonal crystal structure, which is the same as that of Li2O2, was observed immediately after the discharge. As the discharge progressed, Li was added to it, and the lattice constant gradually extended in the c-axis direction, forming Li1.5O2 at a discharge of 4.0 mAh/cm2. In the presentation, the charging process and the charge-discharge cycle characteristics would also be discussed.

Grain Controlled Interlayer of Solid Oxide Fuel Cells Via Nitrogen Reactive Sputtering

Renewable energy conversion systems have been extensively studied and utilized due to increased environmental pollutions caused by fossil fuels. Among the various renewable energy sources, such as wind, solar, geothermal, and hydrogen, hydrogen is well known for its high energy density, non-toxicity, and easy transportation. Therefore, hydrogen production and utilization processes have been studied to enhance their efficiencies and lower costs for decades. To convert hydrogen into electricity, various types of fuel cells are frequently employed by chemical reactions between hydrogen and oxygen. Solid oxide fuel cells (SOFCs), one of the most promising energy conversion devices among the fuel cells, guarantee high conversion efficiency which is temperature dependent, thus the SOFCs are usually operate in high temperature regime (800 °C–1000 °C) to maximize their output. These high operating temperatures, however, induce thermal issues such as catalyst degradation, sealing, and cell durability which are needed to be concerned. Therefore, many researchers tried to mitigate these issues by lowering the working temperature (400 °C–600 °C). This strategy was successful, however, as abovementioned, the SOFCs are temperature dependent so that relatively low temperatures delay oxygen reduction reaction (ORR) resulted in increased polarization losses. To facilitate the SOFCs with high efficiency at this temperature regime, many studies inserted oxygen ion conducting materials between electrodes and electrolyte to promote transfer of oxygen ions. Further, researchers tried to control surface morphology of ion conductors to have large grain boundary density which is another approach to reduce polarization losses. In this study, yttria-stabilized zirconia (YSZ) was introduced between cathode and electrolyte via sputtering technique. During the sputtering processes with both argon and oxygen gases, nitrogen gas was further supplied to induce collision of YSZ atoms so that YSZ atoms with low kinetic energy will reach on substrates resulted in smaller grain sizes of YSZ interlayers.Silicon and YSZ substrates were utilized to analyze properties of YSZ interlayers and electrochemical characteristics of SOFCs, respectively. The YSZ interlayers were fabricated by sputtering of ZrY alloy target with argon, oxygen, and/ or nitrogen gases. While maintaining sputtering chamber pressure of 0.67 Pa, argon and oxygen gases were supplied with fixed amount of 40 sccm and 5 sccm, respectively. Furthermore, nitrogen gas was also introduced to sputtering chamber by 4 sccm differences from 0 to 16 sccm, hereafter, fabricated YSZ interlayers are denoted as N0, N4, N8, N12, and N16 with the meaning of applied nitrogen amount. All YSZ interlayers were deposited with RF power of 70 W and sputtering times were controlled to fabricate about 70 nm. To analyze the properties of fabricated YSZ interlayers, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted. Electrochemical characteristics of SOFCs were evaluated by linear sweep voltammetry and electrochemical impedance spectroscopy.SEM images observed all the YSZ interlayers were about 70 nm thicknesses with various surface morphologies. This phenomenon is attributed to different adatom mobility of atoms due to flow rates of nitrogen during sputtering process. Further, XRD results shown that nitrogen influenced grain development of YSZ interlayers resulted in weaker and broaden peaks compared to N0. To calculate grain sizes of the YSZ interlayers, Williamson and Hall equation was utilized. Average grain sizes of YSZ interlayers were decreased from N0 to N12, and increased at nitrogen flow rate of 16 sccm. The electrochemical performances indicated that the smallest grain sizes of YSZ interlayers had the lowest polarization losses which means the highest ORR kinetics were found at the largest grain boundary density thus, the highest peak power density was observed.All the YSZ interlayers were fabricated by sputtering technique with constant flow rates of argon, oxygen, while nitrogen flow rate was varied. The SEM images and XRD patterns revealed that nitrogen successfully modified surface morphologies in terms of various grain sizes. The EIS analysis confirmed the smallest grain sizes of N12 had the lowest polarization losses resulted in the highest peak power density. As a result, we successfully modified surface morphologies of YSZ interlayers by nitrogen reactive sputtering. We expect that this one-step novel strategy can be utilized in other thin film fabrication fields by significantly reducing process times.AcknowledgementsThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.2022R1C1C1006824) and the Basic Research Program through the National Research Foundation of Korea (NRF) funded by the MSIT (No.2022R1A4A3023960).

Multimodal Networks of Signs between Language, Body and World in Poetry, Music and Architecture in the City of Valencia (Spain)

This work will deal with the sign networks that are established between language and world in the work of semiotic different arts (poetry, music and architecture). The objective is to understand and analyze from Enaction theory and from the Semiotic sign of Peirce how the constant flow and ebb between social environment, body and language configure both language and the world. It will also be shown how the work of art constitutes an emergency in which language, body and social environment participate. To achieve these objectives, poetic texts by the Valencian author Ausiàs March and artistic works related to them will be analyzed. The work methodology includes sign analysis, the comparison of original texts with translations and the comparison of works of art of semiotic different kinds.

Frozen autocatalytic fronts in a radial flow

Autocatalytic reaction-diffusion fronts are localized reaction zones propagating at a constant speed with a constant width. We show both theoretically and experimentally that, if the reactant Y of the autocatalytic reaction is injected radially at a constant flow rate in a sea of the autocatalytic species X, a stationary front can be maintained at a fixed position that scales linearly with the flow rate. When this reaction front is about to reach a stationary state, a second outward traveling front emerges to adapt the outer concentration of the autocatalytic species to the stoichiometry ratio between X and Y. Simple analytical solutions to the reaction-diffusion-advection equations governing the dynamics are computed for both fronts. The analytical predictions for the stationary front position and moving front dynamics as a function of injection flow rate, reactant concentration, and gap of the quasi-two-dimensional reactor agree well with experimental results obtained with the autocatalytic chlorite-tetrathionate reaction. Published by the American Physical Society 2024

Experimental and machine learning insights on heat transfer and friction factor analysis of novel hybrid nanofluids subjected to constant heat flux at various mixture ratios

This study explores the combined effects of aluminum oxide (Al₂O₃)/graphene oxide (GO) hybrid nanofluids in 50:50 and 80:20 ratios, offering a notable improvement over conventional Al₂O₃ or GO nanofluids. It delivers a thorough comparison of thermophysical properties such as thermal conductivity and viscosity and heat transfer performance across water, Al₂O₃ nanofluids, and the Al₂O₃/GO hybrids. Nanofluids at 0.1–0.5 % volume concentrations were tested in a horizontal circular pipe under constant heat flux and turbulent flow with an inlet temperature of 60 °C. The maximum Nu enhancements of 64, 56 and 41 % were noted for Al₂O₃/GO (50:50), Al₂O₃/GO (80:20), and Al₂O₃ nanofluids, respectively at 0.5 vol%, compared to water. The maximum pressure drop of Al2O3/GO (50:50) nanofluid is 5.64 and 8.3 % greater than that of Al2O3/GO (80:20) and Al2O3 nanofluid, respectively at 0.5 vol%. The peak thermal performance index of 1.56, 1.48, and 1.33 is observed for Al₂O₃/GO (50:50), Al₂O₃/GO (80:20), and Al₂O₃ nanofluids. The integration of a multi-layer perceptron artificial neural network further enhances accuracy in predicting thermal performance, surpassing the precision of conventional empirical models. The adopted model showed excellent predictive accuracy, with correlation coefficients of 0.98493 in training, 0.9837 in validation, and 0.98698 in testing.