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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Prehydration of calcium sulfoaluminate (CSA) clinker at different relative humidities

The use of CSA cement in practice has been hindered by its unstable performance and short shelf-life caused by the prehydration of CSA clinker. In this study, the effect of ambient humidity on the prehydration rate and process of CSA clinker was investigated. The prehydration degree, ageing progress, and the dynamic change of mineral composition of CSA clinker exposed to five different relative humidities (ranging from 23% to 98%) for up to 180 days were studied. Experiments revealed that the ambient humidity of 60% RH can be considered a threshold value for storage of CSA clinker. Exposure of CSA clinker to RH higher than 60% will not only result in a significant decrease of hydraulic reactivity, but also in agglomeration of the clinker. Although the exposure of CSA clinker to RH lower than 60% has little effect on the hydraulic reactivity, the main hydration peak was found to be slightly delayed with the increase of RH.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of relative humidity on the interlayer spacing of phosphate intercalated Mg, Al layered double hydroxide (hydrotalcite‐like) crystals

Abstract The availability of water and the type of interlayer anions present affect the arrangement and interlayer spacing of layered double hydroxide (LDH). A systematic study of the effect of relative humidity (RH) on the basal spacing of phosphate intercalated, magnesium aluminum LDHs (MgAl–PO 4 LDH) was conducted, confirming that MgAl‐PO 4 LDH exhibit distinct interlayer spacing corresponding to separate low‐ and high‐hydration states produced when exposed to low and high humidity conditions. The transition from the low‐ to high‐hydration form begins when RH exceeds 33% and is accompanied by the transition from one to two interlayers of water. An improved understanding of the effect of RH on MgAl–PO 4 LDHs will enable more accurate atomistic modeling and experimental characterization of MgAl–PO 4 LDHs and may lead to improvements in the tunability of MgAl‐PO 4 LDHs for commercial applications such as slow‐release fertilizer.

Reed, Titus↗
NASA NTRS1940

An Approximate Method of Calculation of Relative Humidity Required to Prevent Frosting on Inside of Aircraft Pressure Cabin Windows, Special Report

This report has been prepare in response to a request for information from an aircraft company. A typical example was selected for the presentation of an approximate method of calculation of the relative humidity required to prevent frosting on the inside of a plastic window in a pressure type cabin on a high speed airplane. The results of the study are reviewed.

Jones, Alun R.↗
DOE OSTI2026

The effect of relative humidity and temperature on the response of stomatal conductance to vapor pressure deficit in tropical trees

Understanding how leaf gas exchange responds to changes in vapor pressure deficit (VPD) is key to predicting tropical forest resilience to climate change. Stomata regulate leaf water and CO2 diffusion, and respond to changes in temperature and relative humidity (RH), two drivers of VPD. At high temperatures, the cuticular pathway may also become significant and participate in the overall leaf conductance. Here, we measured gas exchange under light and dark conditions to investigate the stomatal and cuticular responses to temperature and RH on detached branches in five tropical tree species. Leaf conductance in the dark, when stomata are essentially closed, was not markedly impacted by temperature and RH, suggesting a minimal response of the cuticular pathway to these conditions. We compared six steady-state conductance models incorporating different effects of photosynthesis and evaporative demand on stomatal control. All models performed well (residual standard deviation, σ, < 0.025 mol m-2 s-1), but the best-fitting model (σ = 0.017 mol m-2 s-1) used a nonlinear relationship between photosynthesis and stomatal conductance and incorporated RH rather than vapor pressure difference. All models overestimated the steady-state conductance at high RH. Furthermore, leaf conductance immediately increased after a decrease in RH (wrong-way response), but not after an increase in leaf temperature. This suggests that the mechanisms underlying stomatal response to VPD need further investigation. The non-linear coupling between photosynthetic rate and stomatal conductance indicates a sharper physiological response than previously acknowledged.

Lamour, Julien↗
DOE OSTI2023

The effect of relative humidity on eddy covariance latent heat flux measurements and its implication for partitioning into transpiration and evaporation

While the eddy covariance (EC) technique is a well-established method for measuring water fluxes (i.e., evaporation or 'evapotranspiration’, ET), the measurement is susceptible to many uncertainties. One such issue is the potential underestimation of ET when relative humidity (RH) is high (> 70%), due to low-pass filtering with some EC systems. Yet, this underestimation for different types of EC systems (e.g. open-path or closed-path sensors) has not been characterized for synthesis datasets such as the widely used FLUXNET2015 dataset. Here, we assess the RH-associated underestimation of latent heat fluxes (LE, or ET) from different EC systems for 163 sites in the FLUXNET2015 dataset. We found that the LE underestimation is most apparent during hours when RH is higher than 70%, predominantly observed at sites using closed-path EC systems, but the extent of the LE underestimation is highly site-specific. We then propose a machine learning based method to correct for this underestimation, and compare it to two energy balance closure based LE correction approaches (Bowen ratio correction, BRC, and attributing all errors to LE). Our correction increases LE by 189% for closed-path sites at high RH (> 90%), while BRC increases LE by around 30% for all RH conditions. Additionally, we assess the influence of these corrections on ET-based transpiration (T) estimates using two different ET partitioning methods. Results show opposite responses (increasing vs. slightly decreasing T-to-ET ratios, T/ET) between the two methods when comparing T based on corrected and uncorrected LE. Overall, our results demonstrate the existence of a high RH bias in water fluxes in the FLUXNET2015 dataset and suggest that this bias is a pronounced source of uncertainty in ET measurements to be considered when estimating ecosystem T/ET and WUE.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1985

The (RH+t) aging correlation. Electrical resistivity of PVB at various temperatures and relative humidities

Electrical products having organic materials functioning as pottants, encapsulants, and insulation coatings are commonly exposed to elevated conditions of temperature and humidity. In order to assess service life potential from this method of accelerated aging, it was empirically observed that service life seems proportional to an aging correlation which is the sum of temperature in degrees Celsius (t), and the relative humidity (RH) expressed in percent. Specifically, the correlation involves a plot of time-to-failure on a log scale versus the variable RH + T plotted on a linear scale. A theoretical foundation is provided for this empirically observed correlation by pointing out that the correlation actually involves a relationship between the electrical resistivity (or conductivity) of the organic material, and the variable RH + t. If time-to-failure is a result of total number of coulombs conducted through the organic material, then the correlation of resistivity versus RH + t is synonymous with the empirical correlation of time-to-failure versus RH + t.

Cuddihy, E. F.↗
DOE OSTI2023

The physics of desiccation cracks 1: Ductile fracturing and dependence on relative humidity

Ductile deformation is ubiquitously found in the shrinkage of geomaterials. The existence of ductility requires elastoplastic mechanics when analyzing the structure deformation under external stress. Here, in this work, we explore the physics of ductile fracturing based on the results from desiccation experiments and triaxial tests. By using the digital image correlation (DIC) method to generate the strain maps of samples undergoing desiccation cracking under different relative humidities, we obtain results showing the previously postulated Cnoidal Wave ductile failure patterns propagating under atmospheric condition-controlled crack velocities. We then correlate these observations with rate-dependent plasticity models calibrated through triaxial tests undergoing several unloading–reloading cycles and velocity stepping. This work demonstrates the necessity to consider ductility in soil cracking, indicating that the formation of crack patterns in soil desiccation is a slow and predictable process.

58 GEOSCIENCES↗
DOE OSTI2025

What is the Role of Relative Humidity on Conductivity in Polymer Electrolytes?

Ion transport properties in polymer electrolytes have been widely studied under rigorously dry and highly water-swollen conditions. However, the transition between these extremes, i.e., the low hydration regime, is still poorly understood at the molecular level and relevant to applications ranging from battery electrolytes to electrophoretic separations. Here, in this study, we apply atomistic molecular dynamics simulations to probe the role of hydration on ion mobilities and conductivities in LiTFSI-doped polyethers at low water content (less than 10% water by volume), which corresponds to 0−80% relative humidity conditions. With increasing water content, Li + ions exhibit two distinct regimes in their mobilities. At low water content, the majority of the Li + ions are weakly hydrated (two or fewer water molecules per Li + ion), maintaining strong interactions with their polymer solvation cage, and therefore exhibit only a weak increase in mobility relative to dry conditions. As water content increases, Li + ions form complete hydration shells, residing within water-rich domains that promote faster mobilities. Further, Li + mobilities increase more significantly in polymer electrolytes composed of more hydrophilic polymers and higher salt concentrations due to the formation of larger water-rich domains. In contrast, TFSI − has comparatively weak interactions with both the polymer and water, exhibiting a monotonic increase in mobility as a function of water content. Overall, these results help clarify the molecular mechanisms underlying ionic mobilities and conductivities in polymer electrolytes at low water content.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mitigation of PtCo/C Cathode Catalyst Degradation via Control of Relative Humidity

Maintaining the high performance of proton-exchange membrane fuel cells (PEMFC) over the course of its lifetime is a key enabling factor for its successful commercialization as a primary power source in zero-emission transportation applications. In this context, it is important to mitigate the degradation of PtCo-alloy based cathode catalysts used for oxygen reduction reaction (ORR). PtCo-alloy catalysts exhibit high activity at beginning-of-life (BOL) which tends to decrease during operation due to loss of electrochemical surface area (ECSA) and dissolution-contamination related effects of the Co-alloying component. Here, we demonstrate the use of relative humidity (RH) of the inlet gases as a controllable parameter to mitigate the degradation of PtCo-alloy catalyst degradation. We employ a catalyst-specific voltage cycling accelerated stress test (AST) durability protocol as a function of inlet RH to degrade PtCo catalysts. A series of in situ electrochemical diagnostics and ex situ characterizations have been carried out to investigate the catalyst layer characteristics at end-of-test (EOT). Our results show that at sub-saturated conditions of durability protocol operation, PtCo catalyst sustains higher EOT H 2 /air performance due to better retention of ECSA and smaller impact of Co 2+ dissolution/contamination.

25 ENERGY STORAGE↗
DOE OSTI2024

Capturing the Relative‐Humidity‐Sensitive Gas–Particle Partitioning of Organic Aerosols in a 2D Volatility Basis Set

Abstract Aerosol water affects the physicochemical properties and mass concentration of organic aerosols (OA), but it is typically omitted by air quality, weather, and climate models. We compare two classes of simplified models to estimate the OA water uptake and gas–particle partitioning of organic compounds. One class uses a single‐hygroscopicity‐parameter (κ) approach while the other is based on the reduced‐complexity Binary Activity Thermodynamics (BAT) model. We show that a BAT‐based two‐dimensional volatility basis set (VBS) model always predicts a higher OA mass concentration at elevated relative humidity (RH), for example, ∼16% at 80% RH, than any variation of theκ‐based method considered—even when BAT‐VBS predicts a lower water uptake. The main reason being that the BAT‐VBS model captures variations in effective saturation mass concentration of organics (C*) with RH, a feature that other VBS methods lack. The BAT‐VBS framework offers an efficient, RH‐sensitive treatment for reduced‐complexity OA modeling.

Geology↗
DOE OSTI2023

Relative-Humidity Dependence of Electrochemically Active Surface Area in Porous Carbon Catalyst Layers

Polymer-electrolyte fuel cells (PEFCs) utilize porous catalyst layers (CLs) formed of carbon supports on which Pt particles are deposited and ionomer films are distributed. Carbon supports themselves have varying degrees of porosity, where high-surface-area carbon (HSC) supports possess nanometer-sized interior pores that are suitable for Pt nanoparticle deposition but prevent deleterious ionomer penetration. However, this requires protons to transport through water pathways inside the pores. To understand the generation of such pathways, we examine the various mechanisms of water uptake by PEFC CLs, and the subsequent impact of water uptake on Pt utilization through developing a multiphysics model of the water wetting phenomena as a function of relative humidity. The model details water uptake via ionomer absorption, capillary condensation in the hydrophilic pores, and surface adsorption using molecular potential that account for various water and surface dipole interactions. The results quantify how mesoporous carbons with highly hydrophilic pores increase Pt utilization through the development of wetted layers, which at the same time enable optimized gas-transport pathways. It also demonstrates the impact of pore-size distribution (PSD) and physical and chemical parameters on the water uptake phenomena, allowing for future CL particle and structure optimization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1998

LASE validation experiment: preliminary processing of relative humidity from LASE derived water vapor in the middle to upper troposphere

Lidar Atmospheric Sensing Experiment (LASE) is the first fully engineered, autonomous airborne DIAL (Differentials Absorption Lidar) system to measure water vapor, aerosols, and clouds throughout the troposphere. This system uses a double-pulsed Ti:sapphire laser, which is pumped by a frequency-doubled flashlamp-pumped Nd: YAG laser, to transmit light in the 815 mn absorption band of water vapor. LASE operates by locking to a strong water vapor line and electronically tuning to any spectral position on the absorption line to choose the suitable absorption cross-section for optimum measurements over a range of concentrations in the atmosphere. During the LASE Validation Experiment, which was conducted over Wallops Island during September, 1995, LASE operated on either the strong water line for measurements in middle to upper troposphere, or on the weak water line for measurements made in the middle to lower troposphere including the boundary layer. Comparisons with water vapor measurements made by airborne dew point and frost point hygrometers, NASA/GSFC (Goddard Space Flight Center) Raman Lidar, and radiosondes showed the LASE water vapor mixing ratio measurements to have an accuracy of better than 6% or 0.01 g/kg, whichever is larger, throughout the troposphere. In addition to measuring water vapor mixing ratio profiles, LASE simultaneously measures aerosol backscattering profiles at the off-line wavelength near 815 nm from which atmospheric scattering ratio (ASR) profiles are calculated. ASR is defined as the ratio of total (aerosol + molecular) atmospheric scattering to molecular scattering. Assuming a region with very low aerosol loading can be identified, such as that typically found just below the tropopause, then the ASR can be determined. The ASR profiles are calculated by normalizing the scattering in the region containing enhanced aerosols to the expected scattering by the "clean" atmosphere at that altitude. Images of the total ASR clearly depict cloud regions, including multiple cloud layers, thin upper level cirrus, etc., throughout the troposphere. New data products that are being derived from the LASE aerosol and water measurements include: 1) aerosol extinction coefficient, 2) aerosol optical thickness, 3) precipitable water vapor, and 4) relative humidity (RH). These products can be compared with airborne in-situ, and ground and satellite remote sensing measurements,. This paper presents a preliminary examination of RH profiles in the middle to upper troposphere that are generated from LASE measured water vapor mixing ratio profiles coupled with rawinsonde profiles of temperature and pressure.

Brackett, Vincent G.↗
DOE OSTI2023

Observationally Constrained Modeling of the Reactive Uptake of Isoprene-Derived Epoxydiols under Elevated Relative Humidity and Varying Acidity of Seed Aerosol Conditions

Isoprene is the non-methane volatile organic compound (VOC) emitted in largest amounts to the atmosphere, and it is a significant source of secondary organic aerosol (SOA) mass. The uptake of isoprene oxidation products followed by multiphase chemistry in fine particles is the key pathway to form isoprene epoxydiol-derived SOA (IEPOX-SOA). However, many parameters that relate to diffusion and reaction of IEPOX in the particle phase remain uncertain, since reaction kinetics previously measured in bulk aqueous phase solutions might be different from atmospheric aerosols. Here, we use simultaneous environmental chamber measurements of multiple parameters governing IEPOX-SOA formation at timescales of ~hours: particle size distribution, composition, and volatility of IEPOX-SOA to constrain the key parameters governing IE-POX-SOA formation under humid (i.e., 50% relative humidity, RH) and varying seed aerosol acidity conditions. Reducing the 2-methyltetrol (tetrol) reaction rate constants by a factor of 4 brings the model predictions in agreement with the IEPOX-SOA measurements with acidified ammonium bisulfate seed aerosols. For less acidic ammonium sulfate aerosols both the organo-sulfate (OS) and tetrol reaction rate constants need to be reduced to bring model predictions closer to chamber observations. Using the measured non-volatile content of IEPOX-SOA we constrain the oligomerization timescale of 2-methyltetrols. We find that the oligomerization timescale is 4 hours with acidified seed aerosols, but a much longer time scale of 24 hours is needed for non-acidified seed aerosols, indicating that the aerosol acidity greatly affects the oligomerization rate of tetrols. Here we show that the actual kinetics of IEPOX-SOA formation rate on aerosol seeds consisting of both ammonium bisulfate and ammonium sulfate are a factor of 4~5 slower under 50-60% RH conditions compared to their application in previous models, which were based on bulk aqueous solution measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Air temperature and relative humidity for the SALVO 2022 Campaign

The springtime, surface-albedo transition in the Alaskan Arctic and the forcings that determine the duration and nature of that transition are the focus of our Snow ALbedo eVOlution (SALVO I & II) campaign. The SALVO team are assessing the “whys” and “how longs” of the stages of the spring melt during which albedo values drop from 0.8 to 0.1, the largest and most significant change of the year. The near-shore location of the ARM NSA observatory makes this an ideal place to investigate these melt stages.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

The 65 Elevated Risk Container Status Relative Humidity Measurements RFID RH/T Sensors in Containers [Slides]

In March of 2023, a memo was issued, drafted by the Container Management, Safety, and Engineering Team, identifying 65 elevated risk legacy containers for priority disposition at TA-55. These 65 were identified separately from the “typical” prioritization decision-making method used at TA-55 to disposition legacy items. This new technique gave important feedback and revealed improvement opportunities for the selection process of legacy containers for disposition. The DOE complex and TA-55 have a long history of nuclear operations and therefore the disposition of these legacy materials is vital.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1985

Sensitivity of a mesoscale model to initial specification of relative humidity, liquid water and vertical motion

The influence of synoptic scale initial conditions on the accuracy of mesoscale precipitation modeling is investigated. Attention is focused on the relative importance of the water vapor, cloud water, rain water, and vertical motion, with the analysis carried out using the Limited Area Mesoscale Prediction System (LAMPS). The fully moist primitive equation model has 15 levels and a terrain-following sigma coordinate system. A K-theory approach was implemented to model the planetary boundary layer. A total of 15 sensitivity simulations were run to investigate the effects of the synoptic initial conditions of the four atmospheric variables. The absence of synoptic cloud and rain water amounts in the initialization caused a 2 hr delay in the onset of precipitation. The delay was increased if synoptic-scale vertical motion was used instead of mesoscale values. Both the delays and a choice of a smoothed moisture field resulted in underestimations of the total rainfall.

Kalb, M. W.↗
DOE OSTI2023

Pit growth kinetics in aluminum: effects of salt loading and relative humidity

Abstract The growth kinetics of localized corrosion, e.g. pits, in corrosive environments often controls the service life of metallic components. Yet, our understanding of these kinetics is largely based on coupon-level, e.g. mass-loss, studies which provide limited insights into the evolution of individual damage events. It is critical to relate observed cumulative loss trends, such as links between changing humidity and mass loss rates, to the growth kinetics of individual pits. Towards this goal, we leverage in-situ X-ray computed tomography to measure the growth rates of over sixty pits in aluminum in four different humid, chloride environments over ≈3 days of exposure. Pit growth rates and final volumes increased with increasing droplet volume, which was observed to increase with increasing humidity and salt loading. Two factors, droplet spreading and oxide jacking, dramatically increased pit growth rates and final volumes.

Noell, Philip J. (ORCID:0000000346998999)↗