Atmospheric Vapor Research Articles

Differences in respiration components and their dominant regulating factors across three alpine grasslands on the Qinghai−Tibet Plateau

Greenhouse gases (GHGs) emissions from high-cold terrestrial ecosystems underlain by permafrost on the Qinghai–Tibet Plateau (QTP) have received widespread attention. However, the dominant factors regulating ecosystem respiration (Re) and its components (soil respiration Rs and heterotrophic respiration Rh) and how the differences in carbon emissions from different ecotypes and seasons remain are still unclear. We conducted a 2-year field investigation (August 2018 to October 2020) and applied the structural equation model (SEM) to clarify the changes in the factors controlling the respiration components during different seasons. The results indicate that the Re and its controlling factors in three alpine grassland ecosystems (alpine steppe, alpine meadow, and swamp meadow) vary with seasons. Furthermore, autotrophic respiration (Ra) contributes the most to the seasonal changes in Re. The Re gradually increases in the early growing season and rapidly decreases in the late growing season. Rh remains relatively stable during the year. Under these seasonal variations in the respiration components, the dominant factors controlling Re in the nongrowing season are the temperature of the atmosphere–soil interface (heat flux, atmospheric temperature, and soil temperature at 5 cm depth) and microbial activity (microbial carbon and pH) with the variable importance projections >1.5. During the growing season, the dominant factors regulating Re, Rs, and Rh are the soil temperature with a standardized direct effect (SDE) of 0.424, soil nutrient conditions (total nitrogen and pH) with SDEs of 0.570–0.614, and microbial activity (microbial carbon) with a SDE of 0.591, respectively. In addition, meteorological conditions have an important impact on the respiration components during the growing season. Specifically, the atmospheric vapor pressure is the dominant factor regulating the three respiration components (standardized total effects = 0.44−0.53, p < 0.001). The optimal soil water contents during the growing season (water content at which Re reaches the maximum) are 10% in the alpine steppe, 13%–15% in the alpine meadow, and 40%–43% in the swamp meadow, respectively. The effect of the soil water content on Re is more important in arid ecosystems (alpine steppe and alpine meadow) than in wet ecosystem (swamp meadow). The alleviation of water limitations in arid ecosystems may potentially increase Re.

Regulation of NDVI and ET negative responses to increased atmospheric vapor pressure deficit by water availability in global drylands

Atmospheric vapor pressure deficit (VPD, indicative of atmospheric water conditions) has been identified as a major driver of global vegetation dynamics. Drylands, including deserts, temperate grasslands, savannas, and dry forests, are more sensitive to water conditions and affect carbon, nitrogen, and water cycles. However, our knowledge is limited on the way increasing VPD affects vegetation growth and evapotranspiration (ET) in global drylands. In this study, we used long-term satellite datasets combined with multiple statistical analyses to examine the relationship between the satellite-derived normalized difference vegetation index (NDVI), a proxy for vegetation growth, and ET to VPD across global drylands. We found that significant decreases in NDVI and ET predominantly influenced the NDVI (RVPD − NDVI) and ET (RVPD − ET) responses to VPD in both the savannas and dry forests of South American, African, and Australian savannas and dry forests, as well as in temperate grasslands (e.g., Eurasian steppes and American prairies). Notably, more than 60% of global drylands exhibited significantly negative RVPD − NDVI and RVPD − ET values. In contrast, the percentage of significantly negative RVPD − NDVI and RVPD − ET decreased to &amp;lt;10% in cold drylands (&amp;gt;60° N). In predominantly warm drylands (60° N~60° S), negative VPD effects were significantly and positively regulated by soil water availability, as determined by multiple linear regression models. However, these significant regulatory effects were not observed in cold drylands. Moving-window analyses further revealed that temporal changes in RVPD − NDVI and RVPD − ET were positively correlated with changes in the Standardized Precipitation Evapotranspiration Index (SPEI). In warm drylands, areas with increasing RVPD − NDVI and RVPD − ET over time showed an increasing trend in the SPEI, whereas areas with a decreasing SPEI showed a negative trend in RVPD − NDVI and RVPD − ET values over time. Given the increasing atmospheric dryness due to climate change, this study highlighted the importance of re-evaluating the representation of the role of water availability in driving the response of the carbon-water cycle to increased VPD across global drylands.

Preparation of an asymmetric membrane via vapor induced phase separation for membrane distillation

Lately, membrane with asymmetric properties of its two sides has shown promising potential in direct contact membrane distillation (DCMD) application, based on the fact that the hydrophilic side of the asymmetric membrane can effectively mitigate wetting and fouling, while the hydrophobic layer facilitate transportation of water vapor to realize separation. We here report an asymmetric membrane prepared via a facile method of vapor induced phase separation (VIPS). Namely, hydrophobic polymer of poly(styrene-block-butadiene-block-styrene) (SBS) and hydrophilic cellulose acetate (CA) were co-dissolved in tetrahydrofuran, and then cast in an ethanol vapor atmosphere to evaporate solvent. After solvent evaporation (within 10 min), the obtained membrane was observed with scanning electron microscope (SEM) to indicate even microstructure of porous network matrix with nodular morphology, and its top surface consisted of SBS only, while microspheres of CA were found to be evenly embedded in the SBS matrix at the bottom side layer. The membrane was further treated with NaOH aqueous solution for CA deacetylation, which was confirmed by attenuated total reflection Fourier transform infrared spectroscopy, SEM and water contact angle (WCA) analyses. The deacetylated CA exposes OH groups to decrease the WCA of the bottom surface greatly. As a result, an asymmetric membrane with large difference in WCA between the top surface and the bottom surface has been obtained. The asymmetric membrane was employed for DCMD to separate an oily saline emulsion containing n-hexadecane, surfactant of Tween 80, and NaCl. The stable flux and high salt rejection of the asymmetric membrane indicate excellent resistance to wetting and fouling, which is attributed to the hydration layer formed by the OH groups of the deacetylated CA at the bottom surface of the membrane. The facile strategy reported in this work implies possible large scale production of the asymmetric membrane that is suitable for membrane distillation application.

CoNi nanocrystal anchoring on MOF derived carbon skeleton autocatalytic growth N-doped carbon nanotubes for efficient bifunctional electrocatalyst towards methanol oxidation/oxygen reduction

In this paper, a novel bifunctional catalyst consisting of nitrogen doped carbon nanotubes (NCNTs) in situ grafted on CoNi-MOF derivative (named CoNi@NC/NCNTs) is controllable synthesized by simple two-steps. Characterization analysis reveal that the interconnected three-dimensional CoNi@NC-NCNTs heterostructure not only atomically dispersed CoNi nanocrystalline, but also autocatalytic grow NCNTs on its surface. The size of CoNi alloy is less than 10 nm, and the crystallization degree of coated graphene carbon layer is extraordinary high. Especially, NCNTs wrapped on CoNi@NC in dihydrodiamine vapour atmosphere form a spatial conductive network, which make the optimized CoNi@NC/NCNTs-400 deliver faster catalytic kinetics toward methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) compared with the CoNi@NC and Co@NC. The peak current density is as high as 58.37 mA cm−2 at the scanning rate is 30 mV s−1 in 0.5 M KOH + 1 M CH3OH solution. Furthermore, the CoNi@NC/NCNTs-400 hybrids display excellent ORR catalytic efficiency in terms of half-wave potential (E1/2 = 0.810 V vs RHE) and high stability. The satisfactory electrocatalytic activity is ascribed to the synergetic effect between CoNi nanoparticles embedded in nitrogen-doped carbon framework and NCNTs, which includes the high conductivity, highly dispersed active sites, optimized electronic configuration and reaction pathways.

Energy harvesting based on water evaporation-induced electrokinetic streaming potential/current in porous carbonized carrots

The use of ambient evaporation for power generation has emerged as a brand-new concept of renewable energy harvesting in recent years. However, the low output level, high cost of raw materials and complex preparation impede its development. In this work, carbonized freeze-dried carrot pieces (CFCPs), as a kind of biomass carbon materials, are proposed as a three-dimensional micro-scale porous network to generate electricity (electrokinetic streaming potential/current) via the evaporation-induced water flow. The evaporation and the capillary force induce continuous water flows within the electrically charged hydrophilic porous CFCP and then produce the streaming potential/current. A single CFCP in the ambient environment can output a stable open-circuit voltage (OCV) of up to VOC ∼0.8 V, a short-circuit current (SCC) of ISC ∼ tens of microamps, and a maximal power density of ∼1.7 μW/cm2. Moreover, a commercial calculator can be powered by a serial connection of four CFCPs (approximately one carrot). This study provides a new perspective on renewable energy harvesting, promotes the use of biomass materials as energy harvesting media, and promises the development of environment-benign power generation systems using ambient evaporation.

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Study of HDPE plastic pyrolysis characteristics using high pressure autoclave

In this study, the experiments of HDPE pyrolysis were carried out using an autoclave at the temperatures ranging from 470 °C to 550 °C. The effects of temperature, pressure and atmosphere on the production of pyrolysates were investigated. The pyrolysates were analyzed using GC, GC-MS and GC-FID. The major components of pyrolysis oil were alkanes, olefins, diolefins, mono aromatics, and cycloalkane, while the pyrolysis gas was mainly composed of hydrogen and C1–C5 hydrocarbons. As the pyrolysis temperature increased, the oil yields decreased, resulting in the increased production of gas and residual. For the composition of pyrolysis oil, the contents of alkane and olefin reduced while the yields of aromatic, diolefin and cycloalkane increased with increasing temperature. In the pyrolysis gas, increasing temperature promoted the generation of total alkanes and prohibited the production of total olefins. The increasing pressure improved the generation of diolefin, aromatics and cycloalkane to decrease the yield of pyrolysis oil and to increase the production of gas and residue. Under water vapor atmosphere, more liquid hydrocarbons with small molecules were obtained, resulting in the higher oil yields. The yields of alkane and olefin were higher in the presence of water vapor. Under the nitrogen atmosphere, the formation of diolefins, aromatics and cycloalkanes was promoted. The effects of different atmospheres on gas composition was negligible.

Moisture adsorption by porous terahertz optical materials: a case study of artificial SiO2 opals

Artificial opals fabricated by sedimentation and self-assembly of colloidal SiO2 nanoparticles and annealed at different temperatures were recently considered favorable terahertz (THz) optical materials with manageable optical properties. However, interactions between such a porous material and water vapour in a humid atmosphere can hamper their THz applications due to the related changes in the material parameters and additional power loss. To quantify such an effect, in this paper, moisture adsorption by artificial SiO2 opals is studied using THz pulsed spectroscopy. Particularly, opals of two kinds were sedimented from the colloidal suspension of 300-nm-diameter SiO2 nanoparticles with different intraglobular structures and porosity. They were annealed at temperatures of 200–800°C aimed at changing their internal structure, porosity, and THz optical properties. Opals were dehydrated in a vacuum and then exposed to a humid atmosphere with 82.0 ± 2.0% relative humidity, while their THz complex dielectric permittivity was evaluated in situ in the 0.5–2.5 THz range. The observed changes in the THz dielectric curves were analyzed using the sum rule and the adsorption kinetics models. Our findings reveal a strong dependence of the THz dielectric response, amount of adsorbed water, and adsorption time constant on the opal type and annealing conditions. This effect has a general character: it can hamper real-live applications of a variety of porous THz optical materials and, thus, should be taken into account during their synthesis.

One-Step Synthesis of a Binder-Free, Stable, and High-Performance Electrode; Cu-O|Cu3P Heterostructure for the Electrocatalytic Methanol Oxidation Reaction (MOR).

Although direct methanol fuel cells (DMFCs) have been spotlighted in the past decade, their commercialization has been hampered by the poor efficiency of the methanol oxidation reaction (MOR) due to the unsatisfactory performance of currently available electrocatalysts. Herein, we developed a binder-free, copper-based, self-supported electrode consisting of a heterostructure of Cu3P and mixed copper oxides, i.e., cuprous-cupric oxide (Cu-O), as a high-performance catalyst for the electro-oxidation of methanol. We synthesized a self-supported electrode composed of Cu-O|Cu3P using a two-furnace atmospheric pressure-chemical vapor deposition (AP-CVD) process. High-resolution transmission electron microscopy analysis revealed the formation of 3D nanocrystals with defects and pores. Cu-O|Cu3P outperformed the MOR activity of individual Cu3P and Cu-O owing to the synergistic interaction between them. Cu3P|Cu-O exhibited a highest anodic current density of 232.5 mAcm-2 at the low potential of 0.65 V vs. Hg/HgO, which is impressive and superior to the electrocatalytic activity of its individual counterparts. The formation of defects, 3D morphology, and the synergistic effect between Cu3P and Cu-O play a crucial role in facilitating the electron transport between electrode and electrolyte to obtain the optimal MOR activity. Cu-O|Cu3P shows outstanding MOR stability for about 3600 s with 100% retention of the current density, which proves its robustness alongside CO intermediate.

Effects of Solvent Vapor Atmosphere on Photovoltaic Performance of Perovskite Solar Cells

Tremendous efforts have been devoted to facilitating the commercialization of perovskite solar cells (PSCs) in the past decade. However, the influence of solvent vapor atmosphere on PSC device performance during its fabrication still lacks related investigations. Here, by using three commonly employed solvent vapors during the perovskite annealing process, i.e., isopropanol, chlorobenzene and dimethylformamide, we reveal the effects of atmosphere on related perovskite film properties and device performance. The results indicate that perovskite films prepared under these external solvent vapors exhibit distinct crystalline phases, morphologies and optical properties from films under normal conditions (nitrogen gas), resulting in a significant drop in power conversion efficiency from the initial 20.01% to the lowest of only ~15%. Our work highlights the importance of atmospheric effects in preparing efficient PSCs for scalable fabrication and commercialization.

Stand structure of Central European forests matters more than climate for transpiration sensitivity to VPD

Abstract Temperature rise and more severe and frequent droughts will alter forest transpiration, thereby affecting the global water cycle. Yet, tree responses to increased atmospheric vapour pressure deficit (VPD) and reduced soil water content (SWC) are not fully understood due to long‐term tree adjustments to local environmental conditions that modify transpiration responses to short‐term VPD and SWC changes. We analysed sap flux density (SFD) of Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus ilex from 25 sites across Europe to understand how daily variation in SWC affects the sensitivity of SFD to VPD (βVPD) and the maximum SFD (S95). Furthermore, we tested whether long‐term adjustments to site climatic conditions and stand characteristics affect βVPD and S95. The studied species showed contrasting βVPD and S95 with the largest values in F. sylvatica, followed by Q. ilex, which surpassed the two conifers that showed low βVPD and low S95. We observed that βVPD and S95 dropped during days of low SWC in F. sylvatica, P. sylvestris and Q. ilex, but not in P. abies. Both βVPD and S95 were driven by tree height, and the temperature and precipitation at the sites. However, stand basal area was the most important driver of βVPD and S95, explaining 30% of their total variance. Synthesis and applications: A future warmer and drier climate will restrict tree transpiration and thereby heavily affect the soil–plant‐atmosphere coupling. However, the effect of basal area, being the largest driver of tree transpiration sensitivity to vapour pressure deficit across a broad range of conditions, provides the opportunity to pre‐adapt European forests to future climate conditions. While stand thinning can increase the soil water availability for remaining trees, it also increases transpiration sensitivity to high air temperatures and may thereby amplify tree vulnerability to heat and drought.

Terminal Atom-Controlled Etching of 2D-TMDs.

The controlled etching of 2D transition metal dichalcogenides (2D-TMDs) is critical to understanding the growth mechanisms of 2D materials and patterning 2D materials but remains a major comprehensive challenge. Here, a rational strategy to control the terminal atoms of 2D-TMDs etched holes is reported. Using laser irradiation combined with an improved anisotropic thermal etching process under a determined atmosphere, terminal atom-controlled etched hole arrays are created on 2D-TMDs. By adjusting the gas atmosphere during the thermal etching stage, triangular etched hole arrays terminated by the tungstenzigzag(W-ZZ) edge (in an Ar/H2 atmosphere), hexagonal etched hole arrays terminated alternately by the W-ZZ edge and sulfur(selenium)zigzag(S-ZZ orSe-ZZ) edge (in a pure Ar atmosphere), and triangular etched hole arrays terminated by the S-ZZ (Se-ZZ) edge (in an Ar/sulfur [selenium] vapor atmosphere) can be obtained. Density functional theory reveals the forming energy of different edges and the different activities of metal atoms and chalcogenide atoms under different atmospheres, which determine the terminal atoms of the holes. This work may enhance the understanding of the etching and growth of 2D-TMDs. The 2D-TMDs hole arrays constructed by this work may have important applications in catalysis, nonlinear optics, spintronics, and large-scale integrated circuits.

An Urban Tree (Tabebuia argentea) Exhibits Higher Sensitivity to Environmental Conditions than an Urban Palm (Ptychosperma macarthurii) Growing in the Same Roof Garden: An Implication for Sustainable Urban Water Use

Roof gardening is popular for increasing green space in cities due to the restricted urban areas. However, when watering plants on a roof garden, one should consider loading capacity of the roof, which may limit water supply to the plants therein. To improve the efficiency in irrigating trees in a roof garden, we evaluated plant water status, represented by midday leaf water potential (ΨL), and leaf gas exchange parameters including stomatal conductance (gs) and net photosynthesis (An) of a tree (Tabebuia argentea, Ta) and a palm (Ptychosperma macarthurii, Pm) species, which dominate the garden. The ΨL mediated responses of gs and An, regulating plant water use and growth, to soil moisture. Results showed that ΨL of Ta significantly varied with changes in soil moisture, being low at low and high soil moisture. Nevertheless, gs of Ta linearly decreased when ΨL increased, suggesting a stronger response of gs to atmospheric demand. In contrast, no significant responses among the study variables were observed in Pm. For both species, An initially increased with gs and saturated after gs reached 200 mmol m-2 s-1, indicating similar stomatal regulation on atmospheric carbon dioxide absorption. The limited space for root growth and the location with surrounded building walls contributed to unconventional response patterns observed in Ta. Nonetheless, our results suggested that Ta was more sensitive to changing environments, especially the atmospheric demand, than Pm. Additionally, Ta should be irrigated during daytime and when atmospheric vapor pressure deficit is less than 2.6 kPa to allow high photosynthesis and evaporative cooling while Pm may be watered less frequently to reduce the roof’s loading and save water. This initial investigation implied that maintaining urban trees using appropriate irrigation that is specific to tree species is the key to maximize benefits from urban trees and optimize urban water use.

Formation of Large-Area Twisted Bilayer Graphene on Ni(111) Film via Ambient Pressure Chemical Vapor Deposition

Due to the destruction of the intrinsic symmetry between the layers, twisted bilayer graphene has the advantages of available interlayer coupling, tunable electronic bandgap, and diverse phonon dispersion features, which offers a unique platform for the advanced electronic devices. The segregation growth of large-area twisted bilayer graphene on Ni(111) film by ambient pressure chemical vapor deposition (APCVD) methods is presented in this paper. The growth kinetics include two main aspects of the catalytic reaction of methane on the Ni surface and the carbon segregation from the Ni bulk. The large-area twisted bilayer graphene (TBG) can be fabricated by controlling carbon segregation for the continuous second layer graphene that is rotated relative to the first layer graphene. Low energy electron diffraction (LEED) studies reveal a dominant twist angle of about 22.7°. The analysis shows that the dominant twist angle is closely related to the stable energy structure of TBG with the smallest moiré periodicity. Besides, the other twist angles of TBG are also formed in vicinity of the dominant angle, confirmed by microscopic observations with selected area electron diffraction (SAED). The work in this paper provides a convenient route for the synthesis of TBG on Ni(111) substrate, which can promote the application of twisted graphene in future photoelectric and spintronic devices.

A new colorimetric paper-based detection of furfural vapor as a fuel marker

Conventional fuel dye markers used in prevention of fuel smuggling and unauthorized mixing generally require laborious sample preparation including extraction and mixing of color developer in liquid phase which also generate high waste volume. In this work, furfural is used as an economical fuel marker which can be directly detected in vapor phase without extraction providing low waste generation. The ambient vapor pressure of furfural allows adequate amount of the marker to be captured by filter paper coated with amine color developers and detected by smartphone camera for colorimetric quantification using ImageJ processing software. The color is developed by either the Stenhouse reaction or imine condensation of amine with furfural in the presence of an appropriate acid. The dynamic quantification range of furfural marker in gasoline fuel is 5–35 ppm with the detection limit at 3.10 ppm.

Fabrication of Glutaraldehyde Vapor Treated PVA/SA/GO/ZnO Electrospun Nanofibers with High Liquid Absorbability for Antimicrobial of Staphylococcus aureus.

In this study, we aim to develop organic-inorganic hybrid nanofibers containing high moisture retention and good mechanical performance as an antimicrobial dressing platform. The main theme of this work focuses on several technical tasks including (a) the electrospinning process (ESP) to produce organic polyvinyl alcohol/sodium alginate (PVA/SA) nanofibers with an excellent diameter uniformity and fibrous orientation, (b) the fabrication of inorganic nanoparticles (NPs) as graphene oxide (GO) and ZnO NPs to be added to PVA/SA nanofibers for enhancement of the mechanical properties and an antibacterial function to Staphylococcus aureus (S. aureus), and then (c) the crosslinking process for PVA/SA/GO/ZnO hybrid nanofibers in glutaraldehyde (GA) vapor atmosphere to improve the hydrophilicity and moisture absorption of specimens. Our results clearly indicate that the uniformity nanofiber with 7 wt% PVA and 2 wt% SA condition demonstrates 199 ± 22 nm in diameter using an electrospinning precursor solution of 355 cP in viscosity by the ESP process. Moreover, the mechanical strength of nanofibers was enhanced by 17% after the handling of a 0.5 wt% GO nanoparticles addition. Significantly, the morphology and size of ZnO NPs can be affected by NaOH concentration, where 1 M NaOH was used in the synthesis of 23 nm ZnO NPs corresponding to effective inhibition of S. aureus strains. The PVA/SA/GO/ZnO mixture successfully performed an antibacterial ability with an 8 mm inhibition zone in S. aureus strains. Furthermore, the GA vapor as a crosslinking agent acting on PVA/SA/GO/ZnO nanofiber provided both swelling behavior and structural stability performance. The swelling ratio increased up to 1.406%, and the mechanical strength was 1.87 MPa after 48 h of GA vapor treatment. Finally, we successfully synthesized the hybrid nanofibers of GA-treated PVA/SA/GO/ZnO accompanied with high moisturizing, biocompatibility, and great mechanical properties, which will be a novel multi-functional candidate for wound dressing composites for patients receiving surgical operations and first aid treatments.

GALLIUM NANOPARTICLES OBTAINED ON SILICON SUBSTRATES BY THERMAL EVAPORATION METHOD

Gallium nanostructures have been obtained on silicon substrates by thermal evaporation in an argon atmosphere. The sizes, density, and shape of Ga particles have been determined by computer processing of electron SEM-images. The condensation of Ga on Si substrates for 10, 15, and 20 s ensured the formation of particles of several types: spherical, triangular, square, and in the form of rods and polyhedrons. The increase in the Ga condensation time to 20 s led to the increase in the density of spherical nanoparticles by 41%.

Determining the appropriate fin spacing for high performance and low footprint of direct contact ambient air-based vaporization systems

The continuous growth of frost over the tubes during the operation of ambient air vaporizers (AAV), which are used to re-gasify the liquefied permanent gases, eventually creates ice bridges. This phenomenon not only increases the thermal resistance but also restricts the natural convective airflow. In the present paper, the effect of fin spacing on the performance of the natural and forced draft AAV is analysed under different weather conditions. Appropriate fin spacing at different operating conditions is calculated by the three-dimensional model solved in ANSYS Fluent. A dynamic numerical model is developed to predict the frost properties in a forced draft vaporizer. A higher fin spacing not only increases the footprint but also impairs the rate of heat transfer in a forced draft AAV. At 298 K air temperature and 0.7 RH, the rate of heat transfer through a forced draft AAV can be enhanced by 8% with the appropriate fin spacing. The forced draft vaporizers are less sensitive to weather conditions compared to the natural draft vaporizers. For the identical fin specification, the number of tubes needed for vaporizing 240 Nm3hr−1 of LN2 is 16 for the forced draft, while it is 36 for a natural draft AAV. With reduced fin spacing, the footprint of the vaporizer block can be reduced by as much as 65% in a forced draft vaporizer for the identical vaporization capacity and ambient conditions.

EBM Technique Study on Microstructural Characterization of Al-Zr-N Coating

Through the implementation of the electron beam physical vapour deposition (EB-PVD) technique, an aluminium zirconium nitrate (Al-Zr-N) coating has been created in the current work on high speed steel (E19) substrates. Through the use of X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nano indentation, and scratch tests, the structural morphological and mechanical properties of the substrate are investigated. The cause of tension relaxation and vacancy concentration is explained by the fluorite phase's lattice constant decreasing with rising deposition temperature. As the temperature of the substrate rises, the coating's increased surface roughness is explained by an increase in crystallite size [1]. TBCs are frequently applied to metal substrates using the Atmospheric Plasma Spraying (APS) and Electron Beam Physical Vapour Deposition (EB-PVD) methods. For the next generation of turbine engines, the high costs and relatively high thermal conductivities of EB-PVD coatings, as well as the short thermal lifetime of APS coatings, are significant drawbacks. Suspension Plasma Spraying (SPS) was evaluated in this study to enhance the thermal properties of TBC. The SPS process enables the creation of columnar micro-structures that are easily adjustable in terms of thermal conductivity and columnar structure compaction.

About the loss of a primordial atmosphere of super-Earths by planetesimal impacts

ABSTRACT We consider planets composed of water ice and rock, located far from a central star. In an earlier study, computing the growth of planets by continuous accretion, we found that a large fraction of the ice evaporates upon accretion, creating a water vapor atmosphere. Here, we consider accretion as a discrete series of planetesimal impacts (of the order of 108), at the same time-dependent accretion rate, and investigate the fate of the vapor, as a result of its interaction with the accreting planetesimals. We find that a large fraction of the vapor escapes. The remaining fraction may form an outer layer of ice after the termination of accretion and cooling of the surface. The escaped water mass may significantly alter the ice-to-rock ratio of the planet. We investigate the effect of different choices of parameters such as the ice-to-rock ratio, the planetesimal size distribution, and the impact velocities. We find that the planetesimal size distribution has a negligible effect and explain why. By contrast, the ice-to-rock ratio and impact velocities affect the fraction of retained water masses considerably.