Humid Air Environments Research Articles

CFD Analysis of the Effects of a Barrier in a Hydrogen Refueling Station Mock-Up Facility during a Vapor Cloud Explosion Using the radXiFoam v2.0 Code

A CFD (computational fluid dynamics) analysis to investigate the effects of the installation of a barrier in a hydrogen refueling station (HRS) mock-up facility, with a dummy vehicle and dispensers in the vapor cloud region, during a hydrogen-air explosion using a gas mixture volume of 70.16 m3 was conducted to determine whether the radXiFoam v2.0 code with the established analysis methodology to predict the peak overpressure can be utilized to evaluate the safety of a HRS with such a barrier installed in a large city in the Republic of Korea. The radXiFoam v2.0 code was developed on the basis of the XiFoam solver in the open-source CFD software OpenFOAM-v2112 by modifying C++ source codes in several libraries and governing equations so as to ensure effective calculations of the hydrogen-air chemical reaction and radiative heat transfer through water vapor in a humid air environment and to remove unnecessary warning messages that arise when using the radXiFoam v1.0 code. First, we conducted a validation analysis on the basis of measured overpressure datasets from a near field to a far field of a vapor cloud explosion (VCE) site in the HRS mock-up facility to evaluate the uncertainty in prediction datasets by radXiFoam v2.0. After this validation analysis, we undertook CFD sensitivity calculations by installing barriers with heights of 2.1 m and 4.2 m at a horizontal distance of 2.3 m from the VCE region in the grid model used for the validation analysis to assess the effects of these barriers on reducing the peak overpressure of the blast wave. From these calculations, we judged that the radXiFoam v2.0 code can accurately simulate the effects of the barrier during a VCE, as the calculated overpressure reduction values according to the barrier height are reasonable on the basis of previous validation results from Stanford Research Institute’s explosion test with such a barrier. The results herein imply that the radXiFoam v2.0 code is feasible for use in HRS safety when barrier installation must meet the technical regulations of the Korea Gas Safety Corporation in a large city.

A Janus WSi2P2As2 monolayer: A promising material for detecting NO2 with excellent sensitivity, selectivity, reversibility, and humidity resistance

Realizing highly sensitive, selective, humidity-resistant, and reversible detection of hazardous gas molecules with low detection limit in the air environment at room temperature is essential. Herein, we predict a novel two-dimensional Janus WSi2P2As2 material and propose a NO2 gas sensor with excellent response, selectivity, humidity resistance, and reversibility based on WSi2P2As2, by employing density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green’s function approach. The Janus WSi2P2As2 monolayer is a stable semiconductor with a direct band gap of 0.85 eV and an intrinsic out-of-plane dipole moment. We study the sensing properties of the Janus WSi2P2As2 monolayer towards several typical toxic gases (NO, NO2, NH3, SO2, and H2S). All the gas molecules are physically adsorbed on the surface. Different adsorption energies and electronic structures are found for the top- and bottom-surface adsorptions due to the intrinsic dipole of the Janus WSi2P2As2. The experimental viability is characterized by the adsorption density and the recovery time. The statistical estimation of the adsorption density shows that the oxide gases can be adsorbed practically even at ultra-low concentration of part per billion (ppb) at room temperature. The rapid natural desorption of these toxic gases at 300 K indicates the recyclability of the WSi2P2As2 material. Furthermore, we evaluate the sensing performance of the WSi2P2As2-based gas sensor by the conductance change. The sensor exhibits ultra-response of 374 % and excellent selectivity towards NO2 molecules. Importantly, the sensor remains operating with high performance in the humid environment and air environment. These results demonstrate that the Janus WSi2P2As2 is a promising gas-sensing material for the NO2 detection.

A Database Extension for a Safety Evaluation of a Hydrogen Refueling Station with a Barrier Using a CFD Analysis and a Machine Learning Method

A methodology is proposed to extend datasets in a database suitable for use as a reference tool to support an evaluation of damage mitigation by a barrier wall in a hydrogen refueling station (HRS) during a vapor cloud explosion (VCE) accident. This is realized with a computational fluid dynamic (CFD) analysis and machine learning (ML) technology because measured data from hydrogen explosion tests with various installed barrier models usually require considerable amounts of time, a secured space, and precise measurements. A CFD sensitivity calculation was conducted using the radXiFoam v1.0 code and the established analysis methodology with an error range of approximately ±30% while changing the barrier height from that was used in an experiment conducted by the Stanford Research Institute (SRI) to investigate the effect of the barrier height on the reduction in peak overpressures from an explosion site to far fields in an open space. The radXiFoam code was developed based on the open-source CFD software OpenFOAM-v2112 to simulate a VCE accident in a humid air environment at a compressed gaseous or liquefied HRS. We attempted to extend the number of datasets in the VCE database through the use of the ML method on the basis of pressure data predicted by a CFD sensitivity calculation, also uncovering the possibility of utilizing the ML method to extend the VCE database. The data produced by the CFD sensitivity calculation and the ML method will be examined to confirm their validity and applicability to hypothetical VCE accident simulations if the related test data can be produced during experimental research. The database constructed using core data from the experiment and extended data from the CFD analysis and the ML method will be used to increase the credibility of radXiFoam analysis results for VCE accident scenarios at HRSs, ultimately contributing to safety assurances of HRSs in Republic of Korea.

Mechanisms of Environmentally Induced Crack Initiation in Humid Air for New-Generation Al-Zn-Mg-Cu Alloys

Recent experience has shown that new-generation 7xxx-series alloys, that have a high Zn content and Zn/Mg ratios, have a greater susceptibility to hydrogen-environmental induced cracking (H-EIC) on exposure to humid air than more established materials, like AA7050. In this study, we report new evidence of the EIC initiation and crack growth behavior of two new-generation alloys, AA7085 and AA7449, when exposed to 50% humidity. In situ, time-lapse, optical imaging over large areas has enabled the exact initiation sites to be identified and investigated with high-resolution fractographic studies, providing evidence for the sequence and mechanisms of initiation and transition to sustained cracking. A consistent behavior was observed for both alloys. This has revealed that minute-scale corrosion reactions, involving highly localized condensed water, are necessary for initiation. The preferred initiation sites are metal ligaments between surface-connected pore clusters and/or intermetallic particles that are subjected to high-stress concentration and undergo mechanical damage with associated higher levels of local oxidation. The growth of short protocracks from these sites is a distinct stage and displays intermittent arrest markings evidenced by localized corrosion. In contrast, in humid air environments, long cracks in these alloys exhibited relatively constant, higher velocity, with extremely limited corrosion commensurate with oxidation of a free surface in this environment resulting in approximately 5 nm oxide layer.

Realizing long-cycling all-solid-state Li-In||TiS2 batteries using Li6+xMxAs1-xS5I (M=Si, Sn) sulfide solid electrolytes

Inorganic sulfide solid-state electrolytes, especially Li6PS5X (X = Cl, Br, I), are considered viable materials for developing all-solid-state batteries because of their high ionic conductivity and low cost. However, this class of solid-state electrolytes suffers from structural and chemical instability in humid air environments and a lack of compatibility with layered oxide positive electrode active materials. To circumvent these issues, here, we propose Li6+xMxAs1-xS5I (M=Si, Sn) as sulfide solid electrolytes. When the Li6+xSixAs1-xS5I (x = 0.8) is tested in combination with a Li-In negative electrode and Ti2S-based positive electrode at 30 °C and 30 MPa, the Li-ion lab-scale Swagelok cells demonstrate long cycle life of almost 62500 cycles at 2.44 mA cm−2, decent power performance (up to 24.45 mA cm−2) and areal capacity of 9.26 mAh cm−2 at 0.53 mA cm−2.

Preferred Mode of Atmospheric Water Vapor Condensation on Nanoengineered Surfaces: Dropwise or Filmwise?

Condensing atmospheric water vapor on surfaces is a sustainable approach to addressing the potable water crisis. However, despite extensive research, a key question remains: what is the optimal combination of the mode and mechanism of condensation as well as the surface wettability for the best possible water harvesting efficacy? Here, we show how various modes of condensation fare differently in a humid air environment. During condensation from humid air, it is important to note that the thermal resistance across the condensate is nondominant, and the energy transfer is controlled by vapor diffusion across the boundary layer and condensate drainage from the condenser surface. This implies that, unlike condensation from pure steam, filmwise condensation from humid air would exhibit the highest water collection efficiency on superhydrophilic surfaces. To demonstrate this, we measured the condensation rates on different sets of superhydrophilic and superhydrophobic surfaces that were cooled below the dew points using a Peltier cooler. Experiments were performed over a wide range of degrees of subcooling (10-26 °C) and humidity-ratio differences (5-45 g/kg of dry air). Depending upon the thermodynamic parameters, the condensation rate is found to be 57-333% higher on the superhydrophilic surfaces compared to the superhydrophobic ones. The findings of the study dispel ambiguity about the preferred mode of vapor condensation from humid air on wettability-engineered surfaces and lead to the design of efficient atmospheric water harvesting systems.

Robust high-performance self-lubrication of nanostructured Mo-S-Cu-B film

Molybdenum disulfide (MoS2) has long been used as a superb lubricant in aerospace applications, but attempts to extend its use in more diverse environments have met great challenges of deteriorating performances caused by oxidation effects in terrestrial air and short service lifetime due to weak mechanical strength. Here, we present a new pathway for developing MoS2-based robust high-performance self-lubrication with concurrent ultralow friction and wear in both nitrogen and humid air environments achieved in nanostructured Mo-S-Cu-B film. In this tailor-designed nanostructure, boron passivates oxidation sites and strengthens film via densification, while copper induces the formation of curved MoS2 (002) nanosheets to provide an abundant lubricant source. The present method of optimizing tribological properties via rational multicomponent nanostructure design may help develop a distinct class of superb self-lubricating films.

An amorphous SiAlN barrier coating against NaCl attack in humid air at elevated temperature

Amorphous magnetron sputtered SiAlN films have been designed to prevent NaCl attack of Ti alloy substrates in high temperature humid air environments. Uncoated Ti alloys suffer severe degradation after exposure to NaCl deposits in humid air at 700 °C for 100 h, whereas SiAlN coating forms protective scale mainly consisting of sodium silicate in identical conditions. Amorphous sodium silicate exhibits fast Na+ diffusion rate and extremely slow O2- diffusion rate, but degradation of SiAlN takes place in presence of both O2- and Na+ species. Sodium silicate scale provides good protection for SiAlN due to slow diffusion of O2- through sodium silicate.

The second law analysis of a humidification-dehumidification desalination system using M-cycle

Humidification-dehumidification desalination (HDD) systems offer a feasible approach for the production of fresh water in inaccessible areas as they can be operational using renewable energy and require little maintenance. Various studies are being carried out to boost the system performance. In this paper, an open air open water HDD system is proposed that exploits the enhanced evaporation and condensation processes by implementing with the Maisotsenko cycle (M-cycle). The system utilizes solar energy as the energy input to heat the saline water. A thermodynamic model is formulated under steady-state conditions, considering the first and second law of thermodynamics. The energetic and exergetic performance of the system is studied. The model is first validated with the experimental data and a good agreement is found where the maximum discrepancy is about 6.0 %. Effects of different operating conditions on key performance parameters such as the Gain Output Ratio (GOR), specific energy consumption (SEC), exergy destruction, and exergy efficiency are analyzed. An improvement is observed in the GOR when the inlet air temperature is raised at constant humidity ratio. The system exhibits better performance in dry air environment when compared with humid air environment. The analysis shows a maximum mass flow rate of desalinated water of 22.3 kg/h, recovery ratio (RR) of 0.223, GOR of 3, SEC of 0.23 kWh/kg and an exergy efficiency of 43.21 %.

Corrosion Monitoring of Carbon Steels under Humid Air Environment with Ozone Simulating Irradiation

Corrosion Monitoring of Carbon Steels under Humid Air Environment with Ozone Simulating Irradiation

Theoretical Investigation of Organohalide Perovskite Degradation in Water

Methylammonium lead iodide (CH3NH3PbI3) is an extensively used organic-inorganic perovskite material with a remarkable potential for solar energy conversion. Despite its high photovoltaic efficiency, it suffers from fast degradation in humid air atmospheric working environments. Low stability of CH3NH3PbI3 solar cells in humid air environments is a serious drawback, severely limiting their practical application. Protecting organohalide perovskite thin films from water and ambient humidity represents a paramount challenge, in which the interfacial interactions between CH3NH3PbI3 surface and water molecules need to be understood thoroughly. Here, we present ab initio molecular dynamics simulations aimed at investigating interfacial interactions between the CH3NH3PbI3 perovskite of different surfaces and water molecules. We harness enhanced free-energy sampling techniques to simulate CH3NH3PbI3 degradation with explicit treatment of water molecules to examine the degradation kinetics. The degradation energetics from different CH3NH3PbI3 surfaces along with the effect of various type of defects in the material are also explored. Our findings add a comprehensive mechanistic understanding to the state of knowledge of CH3NH3PbI3 degradation mechanisms in humid air. The presentation will close with a discussion of similar stability predictions on other organohalide perovskite materials.

Environmentally-adaptive epoxy lubricating coating using self-assembled pMXene@polytetrafluoroethylene core-shell hybrid as novel additive

In this work, a novel lubricating additive was designed and synthesized via self-assembling of wrapped PTFE nanoparticles by exfoliated MXene nanosheets. Then the pMXene@polytetrafluoroethylene (pMXene@PTFE) hybrid was introduced into epoxy coating and painted to substrate. The composite with PTFE would effectively alleviate the oxidation of MXene sheets. The research results show that the epoxy-based composite coating has excellent friction-reduction and wear-resistance properties in dry air, humid air (RH = 80%), and vacuum (3 × 10−5 Mbar) environments, achieving multi-environmental stability binary composite coating. The performance improvement of composite coating mainly depends on the following points: (a) the lubricating synergistic effect of MXene sheets and PTFE hybrid additive with core-shell structure; (b) the good dispersibility and adhesion of composite additive in the epoxy matrix; (c) the formation of protective film on the upper counterpart. The obtained friction results demonstrate that self-assembled pMXene@PTFE epoxy coatings greatly enhance the lubricating and anti-wear properties in multiple environments, establishing a promising platform for the design and application of novel high-performance additive with environmental insensitivity.

Deliquescence of Eutectic LiCl-KCl Diluted with NaCl for Interim Waste Salt Storage

Molten eutectic LiCl-KCl salt is a widely used electrolyte for electrorefining uranium from spent nuclear fuel. Due to the hygroscopic nature of this salt, such operations must be performed under controlled atmospheric conditions, and waste salts require careful storage to avoid deliquescence and corrosion of container materials. This study investigated a potential processing path for reducing the degree of deliquescence through dilution to varying extents with NaCl. The hydration behavior of LiCl-KCl salts diluted with NaCl was evaluated in terms of mass gain due to water absorption, degree of deliquescence (including first appearances of standing water), and evidence of corrosion to stainless steel containers in a humid air environment (40°C, 20% relative humidity). In this humid air environment, pure eutectic LiCl-KCl exhibited a 50 mass % increase due to water absorption and showed evidence of standing water after 24 h. Waste salt diluted with NaCl required loadings of 89 mass % NaCl in order to prevent deliquescence and exhibited a 3 mass % increase due to water absorption. After periodic observation for 48 h, standing water was observed near all ingots with the exception of the 89 mass % NaCl samples. Dilution with 89% NaCl was also found to reduce evidence of corrosion when stored in stainless steel crucibles. While dilution with NaCl greatly decreases steady-state hydration, the storage volume is increased ~10× through this procedure.

Experimental Analysis of Friction and Wear of Self-Lubricating Composites Used for Dry Lubrication of Ball Bearing for Space Applications

Lubricating space mechanisms are a challenge. Lubrication must be sustained in different environments, for a very long period of time, and without any maintenance possible. This study focuses on the self-lubricating composite used in the double transfer lubrication of ball bearing. Ball/races contacts are lubricated via the transfer of materials from the cage that is made of the composite. A dedicated tribometer has been designed for the study. A specificity of the tribometer is to not fully constrain the composite sample but to let it move, as the cage would do in the bearing. Four composites (PTFE, MoS2, glass or mineral fibers) where tested in ultrahigh vacuum and humid air environments. Transfer was achieved with morphologies and composition similar to what is observed on real bearings. Adhesion measurements performed on composite materials before and after friction allowed one to explain the differences in tribological behaviors observed (transfer quality and contact instabilities). Beyond strengthening the composites, fibers are shown to be critical in trapping mechanically and chemically the transferred material to lubricate and prevent instabilities. Equilibrium between internal cohesion of transferred material, and adhesion to counterparts must be satisfied. Mass spectrometry showed that water appears also critical in the establishment of stable transfer film, even in vacuum.

Oxidized Carbon Nanohorns as Novel Sensing Layer for Resistive Humidity Sensor

The paper reports the relative humidity (RH) sensing response of a resistive sensor employing oxidized carbon nanohorns - based sensing layer. The sensing layer is deposited on an interdigitated (IDT) structure, comprising a Si substrate, a SiO2 layer, and IDT electrodes. The structure exhibits good RH sensitivity when varying RH from 0% up to 90%, either in humid nitrogen or in a humid air environment. The conductivity of the sensing layer decreases, while the RH level increases. During the interaction with the water molecules (acting as electron donors), the number of holes will decrease and oxidized single-walled carbon nanohorns (SWCNHs), considered normally p-type semiconductor, will become more resistive. The sensing mechanism is explained in terms of the Hard Soft Acid Base (HSAB) paradigm, building on the fact that water molecules are hard bases, while oxidized carbon nanohorns can be virtually assimilated with hard acids.

Фазовые превращения в оксидах железа под действием микроволнового излучения

It is shown that microwave radiation induces structure changes and, consequently, magnetic phase transitions in iron oxide alpha-Fe2O3. We subjected finely dispersed partially amorphized particles of iron oxide Fe2O3 to 10-minute-long microwave field treatment in a humid air environment. This resulted in a reduction of the hematite crystalline phase by 40%. At the same time the total fraction of crystalline components increased due to the creation of a new ferromagnetic modification which is maghemite alpha-Fe2O3. The original antiferromagnetic samples and the finial ferrimagnetic batches were powders composed of spherical particles with similar values of the area of a coherent X-ray scattering area (40-60 nm).

Monitoring Atmospheric, Soil, and Dissolved CO2 Using a Low-Cost, Arduino Monitoring Platform (CO2-LAMP): Theory, Fabrication, and Operation

Variability of CO2 concentrations within the Earth system occurs over a wide range of time and spatial scales. Resolving this variability and its drivers in terrestrial and aquatic environments ultimately requires high-resolution spatial and temporal monitoring; however, relatively high-cost gas analyzers and data loggers can present barriers in terms of cost and functionality. To overcome these barriers, we developed a low-cost Arduino monitoring platform (CO2-LAMP) for recording CO2 variability in electronically harsh conditions: humid air, soil, and aquatic environments. A relatively inexpensive CO2 gas analyzer was waterproofed using a semi-permeable, expanded polytetrafluoroethylene membrane. Using first principles, we derived a formulation of the theoretical operation and measurement of PCO2(aq) by infrared gas analyzers submerged in aquatic environments. This analysis revealed that an IRGA should be able to measure PCO2(aq) independent of corrections for hydrostatic pressure. CO2-LAMP theoretical operation and measurement were also verified by accompanying laboratory assessment measuring PCO2(aq) at multiple water depths. The monitoring platform was also deployed at two sites within the Springfield Plateau province in northwest Arkansas, USA: Blowing Springs Cave and the Savoy Experimental Watershed. At Blowing Springs Cave, the CO2-LAMP operated alongside a relatively greater-cost CO2 monitoring platform. Over the monitoring period, measured values between the two systems covaried linearly (r2 = 0.97 and 0.99 for cave air and cave stream dissolved CO2, respectively). At the Savoy Experimental Watershed, measured soil CO2 variability capturing sub-daily variation was consistent with previously documented studies in humid, temperate soils. Daily median values varied linearly with soil moisture content (r2 = 0.84). Overall, the CO2-LAMP captured sub-daily variability of CO2 in humid air, soil, and aquatic environments that, while out of the scope of the study, highlight both cyclical and complex CO2 behavior. At present, long-term assessment of platform design is ongoing. Considering cost-savings, CO2-LAMP presents a working base design for continuous, accurate, low-power, and low-cost CO2 monitoring for remote locations.

Microstructure and tribological properties of GLC/MoS2 composite films deposited by magnetron sputtering

Graphite-like carbon (denoted as GLC)/MoS2 composite films were deposited by closed field unbalanced magnetron sputtering system under different MoS2 target currents. The microstructure of the films was investigated by means of X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The tribological behavior of GLC/MoS2 composite films was evaluated using a ball-on-disk tribometer. The results revealed that with the increasing of MoS2 target currents, the existing state of Cr from nanocrystallite to amorphous, leading to the lower of hardness. The film deposited at 0.4A MoS2 target current exhibits the highest hardness (14.6 GPa) and elastic modulus (163.4 GPa) due to the structure of nanocrystallites embedded in amorphous matrix. Additionally, the film showed the lowest friction coefficient (about 0.1) and wear rate of 1.3 × 10−1633correct display 10-16 m3/N·m under 30% RH as the MoS2 target current increased to 1.6A. By contrast, the values of friction coefficient of other films were more than 0.2. On the other hand, the value of the friction coefficient of GLC/MoS2 film decreased to 0.15 as MoS2 target currents increased to 1.6A in the environment of much greater humidity (80% RH). These findings corroborate a thesis that the incorporation of GLC can improve the tribological properties of MoS2 films in humid air environment.

Self-adaptive terahertz spectroscopy from atmospheric vapor based on Hilbert-Huang transform.

Absorption lines of atmospheric vapor commonly appear in terahertz (THz) spectra measured in a humid air environment. However, these effects are generally undesirable because they may mask critical spectroscopic information. Here, a self-adaptive method is demonstrated for effectively identifying and eliminating atmospheric vapor noise from THz spectra of an all-fiber THz system with the Hilbert-Huang transform. The THz signal was decomposed into eight components in different time scales called the intrinsic mode functions and the interference of atmospheric vapor was accurately isolated. A series of experiments confirmed the effectiveness and strong self-adaptiveness of the proposed system in vapor noise elimination.

Mechanism of Yellowing: Carbonyl Formation during Hygrothermal Aging in a Common Amine Epoxy.

Epoxies are often exposed to water due to rain and humid air environments. Epoxy yellows during its service time under these conditions, even when protected from UV radiation. The material’s color is not regained upon redrying, indicating irreversible aging mechanisms. Understanding what causes a discoloration is of importance for applications where the visual aspect of the material is significant. In this work, irreversible aging mechanisms and the cause of yellowing were identified. Experiments were performed using a combination of FT-NIR, ATR-FT-IR, EDX, HR-ICP-MS, pH measurements, optical microscopy, SEM, and DMTA. Such extensive material characterization and structured logic of investigation, provided the necessary evidence to investigate the long-term changes. No chain scission (hydrolysis or oxidation-induced) was present in the studied common DGEBA/HDDGE/IPDA/POPA epoxy, whilst it was found that thermo-oxidation and leaching occurred. Thermo-oxidation involved evolution of carbonyl groups in the polymeric carbon–carbon backbone, via nucleophilic radical attack and minor crosslinking of the HDDGE segments. Four probable reactive sites were identified, and respective reactions were proposed. Compounds involved in leaching were identified to be epichlorohydrin and inorganic impurities but were found to be unrelated to yellowing. Carbonyl formation in the epoxy backbone due to thermo-oxidation was the cause for the yellowing of the material.