Low Pressure Research Articles

Flame kinetics at scramjet-engine-relevant conditions: Role of prompt dissociation of weakly-bound radicals

Combustion in high-speed ram-based propulsion engines occurs under distinct thermodynamic conditions of high reactant temperatures (greater than 1000 K) and relatively low pressures (<5 atm). There is a lack of fundamental flame measurements at such conditions that result in adiabatic flame temperatures (Tad) exceeding 2500 K. In this work, we have measured laminar flame speeds of oxygen-enriched CH4/oxidizer mixtures at sub-atmospheric conditions to probe kinetics at high Tad using the isobaric spherically expanding flame approach. Simulations with recent kinetic models revealed increasing differences between data and model predictions with increasing Tad, reaching up to 25 %. Kinetic analyses reveal that at the thermodynamic conditions in these O2-enriched flames, i.e., lower pressures and higher Tad, the effects of HCO prompt dissociation are accentuated. In addition to HCO, the prompt dissociations of CH2OH and C2H5 are also considered. The prompt dissociations of all three radicals were evaluated and their effects considered in flame speed simulations. Reaction path analysis for the present flames revealed that approximately half of the reaction flux for HCO formation undergoes prompt dissociation to H + CO. Furthermore, these analyses also revealed that the pathways and sensitive reactions are similar between oxygen-enriched fuel/oxidizer mixtures and preheated fuel/air mixtures, if both have similar Tad. Thus, flames of oxygen-enriched mixtures could be a surrogate to probe the flame chemistry of highly preheated mixtures at relatively low pressures that are often encountered in ram-based propulsion engine combustors.

Selective Gas Adsorption in Permanently Microporous Coordination Cages with Exposed Metal Sites.

Porous coordination cages (PCCs), molecular analogs of metal-organic frameworks, offer modular platforms for studying the adsorption properties of small molecules, with coordinatively unsaturated metal centers playing a pivotal role in tuning these behaviors. In this work, we present the synthesis, activation, and detailed gas adsorption studies of second-row transition metal-based M24L24 cuboctahedral cages, specifically Mo24(bdc)24, Rh24(bdc)24, and [Ru24(bdc)24]Cl12. These materials represent rare examples of Mo-, Rh-, and Ru-based hybrid porous solids. The synthesis and activation of these cages were optimized to maximize porosity, yielding BET surface areas of up to 832 m2/g. Gas adsorption studies with CO2 and CO reveal distinctive uptake behaviors linked to the metal cations, with Mo24(bdc)24 demonstrating the highest gravimetric CO2 uptake (2.12 mmol/g at 298 K) and [Ru24(bdc)24]Cl12 exhibiting the strongest CO binding (-75 kJ/mol). Additionally, we explore the selective adsorption of unsaturated hydrocarbons, such as ethylene and propylene, revealing strong binding interactions at low pressures as a result of strong metal-hydrocarbon interactions based on pi-backbonding interactions.

Simulation study on hydrogen concentration distribution in hydrogen blended natural gas transportation pipeline.

Hydrogen is a clean energy source, and blending it with natural gas in existing pipeline networks is a key transition solution for transportation cost reduction. However, during the transportation process, a non-uniform distribution of hydrogen concentration occurs in the pipeline due to gravity. Therefore, it is necessary to study the hydrogen concentration distribution law of hydrogen-blended natural gas in pipelines. The undulation and ball valve pipelines, which are common in transport pipelines, were constructed in this study. The effects of the undulation angle, height, pipeline diameter, ball valve opening, and temperature on the distribution of the hydrogen concentration were investigated using computational fluid dynamic (CFD) methods. The results indicated that the hydrogen concentration gradient changed gently with the larger diameter of the undulating pipeline, minimizing hydrogen accumulation. Higher undulation angle and smaller height differences reduces the hydrogen accumulation risk. Increasing vertical height difference of the pipeline from 5 m to 15 m increased the hydrogen volume fraction gradient by1.3 times. In the ball valve pipeline, the velocity fluctuation decreased as the ball valve opening increased. However, the hydrogen accumulation phenomenon was obvious. The opening increased from 25% to 100% and the hydrogen volume fraction gradient increased more than two times. Selecting delivery conditions with low hydrogen blending ratios, high temperatures, low pressures, and high flow rates reduces the occurrence of hydrogen buildup in the pipeline.

Modeling Investigation on Gas Backflow Performances in Screw Vacuum Pump

Rotor structure has a great influence on the gas backflow in a screw vacuum pump. The characteristics of the gas main flow along the spiral groove of the screw rotor and the gas reverse flow along the tooth-shaped, tooth side, radial, and circumferential clearances are investigated. A new mathematical model of the pumping flow and backflow involved in a flow balance model is proposed to investigate the actions of the shearing force and pressure difference force. The calculated backflow is verified by comparing the experimental measured results. The relationships of the structural parameters of the screw rotor are established. The effects of the rotor parameters, such as pitch, diameter, and compression ratio, on backflow are revealed. The results show that the rotor diameter and compression ratio remain constant and that the influence of pitch on the backflow is slightly weak, with backflow variations of less than 3%, whereas the pitch, rotor length, and compression ratio are constant and the rotor addendum diameter is directly proportional to the backflow. The addendum diameter of rotor #4 is the largest, and its backflow is about 1.5 times larger than that of rotor #1. When the rotor radial sizes and the pitch of the suction end are constant, the compression ratio is inversely proportional to the backflow in the low-pressure region and proportional to the backflow in the high-pressure regions. Therefore, for a vacuum pump operating in low-pressure areas, the use of the compression ratio of 2.2 or higher is favorable for the reduction in backflow.

AI-Powered Weather System with Disaster Prediction

This project develops an AI-powered weather system that aims to improve disaster prediction and preparedness through advanced machine learning algorithms and real-time meteorological data. By collecting data from the OpenWeatherMap API, the system analyzes key environmental indicators, including rainfall, temperature, and wind speed, to detect risks of floods, droughts, cyclones, hailstorms, and wildfires. Through machine learning models like linear regression and threshold-based heuristics, the system achieves high predictive accuracy for natural disasters. This study demonstrates the effectiveness of AI in early warning systems, thus enhancing community preparedness and supporting timely interventions by authorities. The threshold-based heuristics method involved setting predetermined weather condition limits based on historical disaster data, where surpassing these thresholds indicates high disaster risk. Linear regression was used to forecast variables like rainfall and temperature, essential for early warning in disaster management. Both techniques were implemented in tandem, with linear regression providing probabilistic outputs that feed into the heuristic system to improve prediction accuracy

On the use of pulsed DC bias for etching high aspect ratio features

Inductively coupled plasmas (ICPs) containing Cl2 are widely used for plasma etching in the semiconductor industry. One common issue during plasma etching is aspect ratio dependent etching (ARDE), which is generally attributed to variation in the flux of etchant species to the bottom of features with different dimensions. Insufficient fluxes of neutral etchants to the bottom of high aspect ratio features can also result in sputtering, which tends to distort the feature profile. This article addresses two issues relevant to Cl2 ICP and plasma etching in these plasmas. First, a comprehensive set of diagnostics is used to validate a model for Cl2 ICP for gas pressure between 3 and 90 mTorr. The plasma diagnostics include microwave resonant hairpin probe-based measurements of electron density, photolysis-calibrated two-photon laser induced fluorescence measurement of Cl density, photo-detachment-based measurement of Cl− density, and laser diode absorption spectroscopy of argon metastable species to measure the gas temperature. Consistent with the experiments, the model shows that the electron density peaks near the center of the chamber at low gas pressure due to rapid diffusion. The electron density peak moves under the coils at higher pressures. Using the validated Cl2 model, we investigate ICPs with rectangular pulsed DC voltage for bias. It is shown that the Cl flux at the bottom of a trench decreases significantly with increasing aspect ratio of the trench. Neutral to ion flux ratio is therefore low at the bottom of higher aspect ratio trenches. The duty cycle of the pulsed bias waveform is found to be an effective means of increasing the neutral to energetic ion flux ratio, which should help with ARDE and sputter reduction.

Research on the Impact of Altitude Hypoxia on Cognitive Function and the Enhancement of Hyperbaric Oxygen Intervention

People's cognitive function is significantly influenced by the hypoxic environment at high altitudes. As elevation increases, reaching a certain threshold can exacerbate this effect. Hyperbaric oxygen therapy (HBOT) is a treatment for hypoxic conditions that involves breathing pure oxygen or high-concentration oxygen in an environment with pressure exceeding one atmosphere. Research has shown that HBOT can enhance cognitive function; however, there are limited studies focusing on individuals living in plateau regions. Compared to the low pressure and hypoxia experienced in lowland areas, HBOT offers greater therapeutic benefits in plateau regions. This paper summarizes the research on the impact of hypoxic environments on cognitive function at high altitudes and reviews the advancements in hyperbaric oxygen interventions. The aim is to explore the effectiveness of HBOT and to develop a research framework for optimizing oxygen dosage, which holds practical significance for promoting the health and well-being of people living in plateau areas.

Preservation of Microorganisms (Chroococcidiopsis sp. 029) in Salt Minerals under Low Atmospheric Pressure: Application to Life Detection on Mars

Salt minerals on Mars represent a promising target for investigating potential past surface and subsurface life. Terrestrial salt minerals have been shown to incorporate microorganisms within crystals. However, the effect of Mars’s low atmospheric pressure on the preservation of microorganisms in salt minerals during their formation remains unclear. Here we investigated the interactions between microorganisms (Chroococcidiopsis sp. 029) and crystals of halite (NaCl), epsomite (MgSO4·7H2O), and gypsum (CaSO4·2H2O) during the rapid evaporation of brines under simulated Martian atmospheric pressure. Parallel experiments were conducted under terrestrial pressure for comparison. Halite, epsomite, and gypsum formed under both terrestrial and low-pressure conditions, though crystal morphologies varied depending on the pressure. Microorganisms were identified within fluid inclusions or as solid inclusions in the crystal matrix. Halite crystals exhibited a greater propensity to incorporate cells under low pressure compared to terrestrial pressure, while the entrapment of cells in epsomite was similar under both conditions. In contrast, significantly fewer cells were trapped in gypsum crystals under low pressure. The results demonstrate the feasibility of cell entrapment in salt minerals formed by rapid evaporation under low-pressure conditions on Mars, and atmospheric pressure exerts distinct influences on different types of salts. The variation in fluid inclusion size in halite under different pressures even shows promise as a possible paleobarometer. Our findings suggest that halite is the most promising candidate for preserving potential Martian life and could be an excellent target for future Mars sample return missions.

The influence of tectonic action on the characteristics of microcrystalline and pore structure of anthracite in Qianbei Coalfield

Tectonic action strongly impacts the coal's microcrystalline and pore structural features. X-ray diffraction (XRD) was employed to analyze the impact of tectonic action on the microcrystalline structure of coal. The pore structure of anthracite was investigated through electron microscope image, mercury intrusion porosimetry and low pressure N2/CO2 adsorption, with a focus on exploring the relationship between the microcrystalline structure of coal and its micropore structure. The results show that under tectonic action, interlayer spacing of the aromatic layer d002 decreases from 0.345 to 0.342 nm, the stacking height Lc decreases from 2.73 to 2.23 nm, the average number of the effective aromatic layer Nave slightly decreases from 6.61 to 6.51, and the crystallite diameter La increases by 0.13 nm, which indicates that tectonic action changes the microcrystalline structure of anthracite. The microcrystalline structure changes from "short and thick" to "long and thin", thus schematic diagram of the anthracite basic structural unit (BSU) under tectonic action was established. The fa of tectonic coal increased by 16.92% compared with that of original coal, and the g increased from 0.85 (original) to 0.89 (tectonic), indicating that the process of aromatization and graphitization of coal was accelerated by tectonic action. Tectonic action plays an important role in promoting pore development, which makes the pore surface of anthracite more rough, the lattice fringe more dense and clear, and increases the pore volume and specific surface area of anthracite by 1.21 and 1.08 times, respectively. Tectonic action can change the BSU of coal, thus producing more nanoscale space. This study holds important implications for comprehending how tectonic action affect the microcrystalline structure of coal as well as its relationship with nanopore structures in tectonic coal.

Exploring Zeolite Potential for Hydrofluorocarbon Capture and Recycling: Insights from Molecular Simulations

The need for efficient separation of hydrofluorocarbons for recycling and environmental protection is critical due to their substantial impact on global warming. However, conventional methods such as cryogenic distillation face significant limitations due to the azeotropic behavior of many of these hydrofluorocarbons. This study evaluates the adsorption behavior of various hydrofluorocarbons in zeolite structures, specifically Linde Type A (3A, 4A, and 5A) and Faujasite Type X (13X), using molecular dynamics and grand canonical Monte Carlo simulations. The simulations were validated against experimental data, confirming the reliability of the computational models. Adsorption isotherms were fitted using the Langmuir-Freundlich model to describe the adsorption behavior across different pressures. Focusing on fluoromethane derivatives, the study highlighted key interactions and adsorption capacities in various zeolites. The isotherms of various hydrofluorocarbons in zeolite 13X were explored, revealing differential adsorption based on molecular structure. The potential for using zeolite 13X and 5A to separate refrigerant mixtures was also studied, showing distinct selectivity patterns. Additionally, the temperature dependence of adsorption isotherms and isosteric heat was studied to gain insights into the thermodynamics of the adsorption processes. Key results indicate that zeolite 13X demonstrates strong cation-fluorine interactions, particularly effective for the adsorption of large hydrofluorocarbon molecules, which preferentially occupy 12-membered ring windows. In contrast, zeolite 5A exhibited predominant hydrogen bonding interactions at low pressures, with hydrofluorocarbon molecules occupying the smaller 8-membered ring windows. These findings underscore the selective adsorption capabilities of these zeolites, highlighting their potential application in hydrofluorocarbon separation and recycling processes.

Investigation on flash boiling of superheated acetone spray under low vacuum conditions

Spray Flash Evaporation has recently demonstrated promising results in various fields of application and has more recently shown potential in the elaboration of nanoenergetic materials. This technique offers advantages in terms of morphology, size, and reactivity of the produced materials. However, specific thermodynamic conditions are required to produce these materials using acetone as a solvent: high injection temperature (typically between 80 and 160 °C) and low pressure (generally between 10 and 100 mbar) in the chamber are needed, i.e., superheat level. The study on the formation of acetone droplets in the far-field and under such conditions is lacking. Consequently, we propose here to further understand the relationship between injection temperature and back pressure in the chamber with nucleation and droplets characteristics (velocity, average size, size distribution, and concentration) in order to find optimal conditions for generating theoretically smaller particles through droplet evaporation. The tests were conducted in an unusual range of injection temperatures and pressures for flash boiling but commonly used for the production of energetic particles, from 80 to 200 °C and from 12 to 300 mbar, respectively. By using such conditions, it has been found that increasing the injection temperature and decreasing the back pressure are beneficial for generating a large concentration (up to 27.0 x 106droplets.cm−3) of smaller droplets with a narrow size distribution (down to 2.13 ± 0.13 µm) and high velocity (up to 204.2 m·s−1). It was also shown that there is an injection temperature threshold above 160 °C, beyond which the size distribution widens again by 12 % at 200 °C, and the number of droplets decreases by 64 %. This phenomenon can be observed only if we use a very high superheat level. This study demonstrates that these conditions are likely to promote and ultimately lead to the production of particles that are as fine and uniform in size as possible. Nevertheless, operating at very high injection temperatures (>160 °C) could hinder the nucleation and the formation of uniform droplets due to the high competition between the superheat level (Rp > 1188) and the surface tension of the liquid approaching near-zero values. By introducing the use of criteria related to mechanic and thermodynamics, along with droplet size and velocity, it was also observed that the droplet size is primarily influenced by the nucleation rate, while droplet velocity is influenced by both driving forces (mechanical and thermodynamic). The temperature and pressure in the chamber must therefore be carefully chosen to improve droplet formation and potentially produce smaller, homogeneous particles in size as they evaporate.

The optimum location of vapor compressor in multistage vacuum membrane distillation system

This paper investigates the performance optimization of a multistage vacuum membrane distillation (MSVMD) system integrated with a mechanical vapor compressor (MVC) for efficient water desalination. The conventional integrated MSVMD and MVC systems lack a detailed analysis regarding the optimal placement of the MVC, which can influence both productivity and energy efficiency. To address this gap, this study evaluates different compressor placements within the MSVMD setup, assessing their impact on productivity and the gained output ratio (GOR) under various operational parameters, including feed temperature, flow rate, number of stages, and vacuum pressure. The results reveal that the optimal MVC placement can increase system productivity by up to 28 % and enhance energy efficiency, achieving a GOR of about 13. Middle MVC placements maximize productivity, yielding freshwater production up to 500 L/h, while different placements, depending on the feed temperature, optimize the GOR. The parametric study demonstrates that increasing feed temperature significantly boosts productivity, particularly at lower numbers of stages, but reduces GOR due to the higher thermal losses. Additionally, higher feed flow rates improve productivity, with GOR stabilizing at the highest flow rates, and lower pressures in the permeate side increase productivity while keeping GOR consistent. The optimized MSVMD system thus offers a balanced approach, achieving substantial freshwater production with high energy efficiency

Effect of internal pressure and loading path on deformation behavior during low pressure tube hydro-pressing

To overcome the limitations of hydro-pressing process with either linear increasing pressure loading path or constant pressure loading path, a hydro-pressing process with two steps pressure loading path was proposed and an experiment was conducted on hydro-pressing process of DP590 steel tubular part with varied rectangular-section perimeters. The effects of internal pressure and loading path on cross-sectional shape and stress distribution were discussed. An analysis was conducted to give the critical punch stroke of the first step, and an optimal loading path was put forward. The pressure loading path was divided into two steps, the result indicates no buckling happens even no internal pressure adopted in the first step. The wall thickness distribution of the tubular part formed under two steps pressure loading path is more uniform than that with constant pressure loading path. Mechanical analysis proves that the flexural modulus of the tube wall in the earlier stage of deformation is high enough due to the short length of the straight side, which is no need for supporting pressure. Under a reasonable loading path, a rectangular-section tubular part with a compression ratio of 5 % was obtained with lower pressure 13.5 MPa. Its relative corner radius is only 1.5, which exceeds the limiting value of that formed by conventional tube hydroforming.

Prediction of CO2 adsorption of biochar under KOH activation via machine learning

To effectively increase the CO2 adsorption capacity of biochar, the activation process is often an indispensable link. However, the introduction of an activation process poses challenges in clarifying the relationship between the characterization parameters of biochar, adsorption parameters, and CO2 adsorption capacity. Herein, a comprehensive dataset encompassing the CO2 adsorption data of KOH-activated biochar using a “two-sep method” was compiled. Subsequently, ridge regression, multi-layer perceptron, and random forest models were employed to predict its CO2 adsorption performance. To comprehensively explore the effects of activation conditions, physicochemical properties and adsorption parameters on CO2 adsorption capacities, partial dependence via Shapley additive explanation (SHAP) values analysis was conducted. The results demonstrate that the multilayer perceptron model exhibits the highest prediction accuracy with a test R2 value of 0.961. Additionally, it was found that the CO2 adsorption capacity of activated biochar is primarily determined by micropores and nitrogen-containing groups rather than total pore volume at low adsorption pressure (< 0.3 bar). Moreover, it increases significantly with decreasing average pore size, increasing pore volume, and increasing nitrogen content at low adsorption temperatures (< 20 °C). When the ratio of KOH to biochar is in the range of 1–2 and the activation temperature is ∼ 700 °C, activated biochar with high CO2 adsorption performance can be obtained. This study may provide valuable insights for the application of activated biochar in CO2 adsorption.

Effect of tip injection on performance of highly loaded helium compressor in high-temperature gas-cooled reactor

As one of the representatives of the fourth-generation advanced nuclear reactor, the continuous development and application of high-temperature gas-cooled reactor (HTGR) technology has promoted the technical progress of the whole nuclear energy field. Helium compressor is one of the core components of HTGR. The highly loaded helium compressor effectively solves the disadvantages of the low single-stage pressure ratio and numerous stages of the traditional helium compressor. But it also brings a more complex tip-leakage flow. Tip injection, which is an active control method, can effectively control the tip clearance leakage and inhibit the development of the leakage vortex. This paper analyses the effects of axial deflection angle and injection pitch angle on the rotor performance of a highly loaded helium compressor via numerical simulation and validates them via experiment. Results show that the leakage vortex can be blown to the pressure surface of the adjacent blade by proper axial deflection angle to reduce the vorticity of the leakage vortex. The injection pitch angle directly affects the intensity of the leakage vortex during its initiation and development. When the axial deflection angle is 60° and the injection pitch angle is 20°, the adiabatic compression efficiency and total pressure ratio increase by 0.554 % and 0.160 % respectively under the design condition, and by 0.822 % and 0.162 % respectively under near-stall conditions.

Numerical investigation of combustion characteristics of hydrogen-enriched low calorific value landfill gas for energy applications

Landfill gas is regarded as a promising renewable energy resource. However, Low calorific value landfill gases with less than 40 vol% CH4 are not well suited for energy applications and therefore disposed by flaring or direct emission to atmosphere causing environmental problems. In the present work, the potential of using hydrogen-enriched low calorific value landfill gas for energy applications has been explored through numerical investigation of combustion characteristics of different blends of fuels. The ignition delay of fuel mixtures decreased with the increase of hydrogen fraction (H2 enrichment from 0 to 50 vol%) at stoichiometric conditions. At high initial pressure conditions, ignition delay showed a weak relationship with the pressure. The laminar burning velocity increased with the increment of hydrogen fraction for the range of equivalence ratios considered (φ = 0.7 – 1.4) and also with the increase of initial temperature. However, the laminar burning velocity decreased significantly with the increasing initial pressure and hydrogen enrichment has insignificant effect at high initial pressures. The sensitivity analysis shows that the main elementary reactions inhibit the laminar burning velocity more with increasing initial pressure. The combustion performance of low calorific value landfill gas with 30 vol% CH4 enriched with 30 vol% hydrogen shows comparable performance to biogas with 60 vol% CH4 for a range of operating conditions. The numerical investigation results show that hydrogen-enriched low calorific value landfill gas could be used for thermal applications with the use of suitably designed combustion systems operating at low initial pressures and relatively high initial temperatures.

Application of Laser‐Generated Au‐Ag/Al2O3 Nanoparticle Catalysts for the Selective Catalytic Oxidation of 5‐(Hydroxymethyl) Furfural to 2,5‐Furan‐Dicarboxylic Acid

AbstractConversion of lignocellulosic biomass‐derived 5‐(Hydroxymethyl) furfural (HMF) into 2,5‐Furandicarboxylic acid (FDCA) has a high potential to replace petroleum‐based feedstocks for the production of plastics. In this study, a green synthesis strategy for the selective oxidation of HMF to FDCA is reported by using laser‐generated and specifically designed bimetallic AuAg nanoparticle catalysts supported on Al2O3 using molecular oxygen as oxidant and water as a solvent. Although supported AuAg catalysts are already known as suitable catalysts for this reaction, the optimal reaction conditions (type of base, reaction temperature, oxygen pressure), Au : Ag composition, role of metal‐support effects and origin of the active site still remain under debate. Interestingly, an Au9Ag1/Al2O3 catalyst exhibited the highest activity with a FDCA yield of up to 66 % at 80 % HMF conversion. Hereby, NaHCO3 (instead of NaOH) as a smoother base in 2 : 1 base:HMF ratio, low oxygen pressures of 5 bar, and a mild temperature of 150 °C were found optimal. The yield remained fairly stable on reuse of the catalyst for 3 cycles without hints of catalyst sintering or leaching. The titration of surficial hydroxyls on the AuxAgy/Al2O3 surface showed the highest density of acidic hydroxyls for the most active Au9Ag1/Al2O3 catalyst. The respective hydroxyls potentially originate from metal‐support interactions between the AuAg nanoparticles with the alumina support and act as Lewis acidic sites that oxidize the alcohol moiety of HMF to form FDCA with high selectively. In summary, this study shows that the catalytic activity of AuAg catalysts in HMF oxidation is not just linked to an alloying effect but also to a metal‐support effect where the AuAg nanoparticles appear to directly affect the local acidity of the support.

High temperature capture of CO2 on Li4SiO4 sorbents via a simple dry ball-milling coupled with K2CO3 physical addition

The reversible CO2 absorption/desorption of lithium orthosilicate (Li4SiO4) sorbents holds potential for high temperature capture of CO2 from hot flue gases, sorption-enhanced reforming and solar thermochemical energy storage. In this study, we have prepared a series of Li4SiO4 sorbents using a combination of K2CO3 addition and dry ball-milling procedure to improve the relatively slow kinetics under low CO2 partial pressure conditions. The synergistic effects of dry ball-milling and K2CO3 addition on the intrinsic properties of Li4SiO4 sorbents were explored by thermogravimetric analysis and structural characterizations. Thermogravimetric analysis indicate that the highest CO2 uptakes were achieved with dry ball-milling combined with K2CO3 physical addition. The structural characterizations further reveal that this sorbent (P-3K-1.5 M) had the smallest crystallite/particle size, largest surface area, and highest availability of surface alkaline-sites. The kinetics analysis also demonstrates that P-3K-1.5 M exhibited the fastest sorption kinetics during a double process. Additionally, P-3K-1.5 M maintained a high capacity over 10 sorption/desorption cycles. Therefore, this synthesis technique, which is simple, cost-effective, and easily scalable, shows great promise for high-temperature CO2 capture.

Cardiac surgery-associated acute kidney injury in cardiopulmonary bypass: a focus on sex differences and preventive strategies.

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a high-risk complication with well-recognized increased morbidity and mortality after cardiac surgery attributable in large part to cardiopulmonary bypass (CPB)-associated factors contributing to AKI including hemodilution, hypothermia, hypotension, and exposure to artificial surfaces. These conditions disrupt the renal microcirculation and activate local and systemic inflammatory responses to nonpulsatile flow and low perfusion pressure. The underlying mechanisms of CSA-AKI in CPB are not fully understood, and the incidence of CSA-AKI remains high at around 30%. Furthermore, women appear to be more vulnerable than men to the renal injury associated with CPB even though the overall incidence of cardiovascular and kidney diseases is lower in premenopausal women. Nevertheless, estrogen elicits renoprotective effects in several ways including mitigating inflammation, promoting natriuresis, and endothelial protection as shown in preclinical studies. However, women have higher rates of CSA-AKI and these are exacerbated in postmenopausal women. This leads to the conundrum of whether sex, age, and hormonal status differences influence CSA-AKI. In this review, we briefly discuss the pathophysiology of CSA-AKI in CPB and sex differences in kidney functions with a focus on the possible role of estrogen-specific effects in CPB and also possible differences in CPB in women including greater hemodilution. Furthermore, we review strategies to prevent CSA-AKI in CPB with a highlight for potential sex-specific strategies. Improving our understanding of the impact of sex and sex hormones on CSA-AKI initiation and development will allow us to better manage the CPB strategies delivered to all patients.

Effects of boundary conditions on flash boiling ammonia sprays from a twin-fluid atomizer

Ammonia is a carbon-free fuel with a high hydrogen capacity (17.8 wt%) and well-established production and distribution infrastructures, making it a viable option for decarbonized and dispatchable power. In addition, ammonia combustion in its liquid phase is preferred for simplified storage, higher energy density, and compatibility with high-pressure industrial conditions. However, ammonia fuel has drawbacks that must be addressed. This work aims to investigate experimentally the effect of the boundary conditions on the dynamics of an ammonia spray injected by a commercial twin-fluid atomizer in a chamber at room pressure and temperature. A flash boiling analysis was conducted to assess the thermodynamic conditions that promote this phenomenon and the accuracy of existing correlations to predict this transition to flash boiling. The result showed that low injection pressures and preheated atomizing flow promote the formation of bubbles and the subsequent collapse inside the atomizer, creating an unstable spray. Such instabilities are significantly reduced when the injection pressure is increased. Additionally, increasing the atomizing air flow, injection pressure, and atomizing flow temperature improves the fuel breakup, widening the spray angle. However, the spray angle decreases at a certain point, indicating that atomization is more sensitive to thermodynamic conditions than a mechanical breakup.