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DOE OSTI2021

The implications of future climate change on the blue water footprint of hydropower in the contiguous US

As the largest renewable energy source, hydropower is essential to the sustainability of the global energy market. However, a considerable amount of water can be lost in the form of evaporation from the associated multipurpose reservoirs, and hence enlarge the blue water footprint (BWF) of hydropower in a warming climate. To facilitate the sustainable management of both water and energy resources under the impact of climate change in the contiguous United States (CONUS), the BWF values of 143 major multipurpose reservoirs were evaluated during the historical period (1985–2014) and two future periods (2020–2049 and 2070–2099). The historical reservoir evaporation loss was calculated using the Landsat-based reservoir surface area and a new evaporation rate algorithm that considers the heat storage effect. Future projections of runoff availability, hydropower generation, and reservoir evaporation were estimated based on the downscaled climate model ensemble from phase 5 of the Coupled Model Intercomparison Project (CMIP5). It was found that the BWF for the CONUS is highly spatially heterogeneous, with an average value of 26.2 m 3 /MWh in the historical period. In the future, the BWF values are projected to increase under both Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. This is especially noticeable under RCP 8.5, which has an average BWF value of 30.2 m 3 /MWh for 2070–2099 (increasing by 15.3% from 26.2 m 3 /MWh). The uncertainty ranges increase even more, from 3.4 m 3 /MWh during 2020–2049 to 5.7 m 3 /MWh during 2070–2099. These findings can benefit water and energy resources management in identifying suitable environmental, economic, operational, and investment strategies for multipurpose reservoirs in a changing environment.

13 HYDRO ENERGY↗

DOE OSTI2025

Mineral Scaling in 3D Interfacial Solar Evaporators–A Challenge for Brine Treatment and Lithium Recovery

In this work, we analyzed the effects of mineral scaling on the performance of a 3D interfacial solar evaporator, with a focus on the cations relevant to lithium recovery from brackish water. The field has been rapidly moving toward resource recovery applications from brines with higher cation concentrations. However, the potential complications caused by common minerals in these brines other than NaCl have been largely overlooked. Therefore, in this study, we thoroughly examined the effects of two common cations (calcium and magnesium) on the long-term solar evaporation performance of a 3D graphene oxide stalk. The 3D stalk can achieve an evaporation flux as high as 17.8 kg m –2 h –1 under one-sun illumination, and accumulation of NaCl on the stalk surface has no impact. However, the presence of CaCl 2 and MgCl 2 significantly reduces the evaporative flux even in solutions lacking scale-forming anions. A close examination of scale formation during long-term evaporation experiments revealed that CaCl 2 and MgCl 2 tend to precipitate out within the stalk, thus blocking water transport through the stalk and significantly dropping the evaporation rates. These findings imply that research attention is needed to modify and optimize the internal water transport channels for 3D evaporators. Additionally, we emphasize the importance of testing realistic mixtures–including prominent divalent cations– and testing long-term operations in interfacial solar evaporation research and investigating approaches to mitigate the negative impacts of divalent cations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Journal paper

Laser technology is being widely studied for controlled energy deposition for a range of applications, including flow control, ignition, combustion, and diagnostics. The absorption and scattering of laser radiation by liquid droplets in aerosols affects propagation of the laser beam in the atmosphere, while the ignition and combustion characteristics in combustion chambers are influenced by the evaporation rate of the sprayed fuel. In this work, we present a mathematical model built on OpenFOAM for laser heating and evaporation of a single droplet in the diffusion-dominated regime taking into account absorption of the laser radiation, evaporation process, and vapor flow dynamics. The developed solver is validated against available experimental and numerical data for heating and evaporation of ethanol and water droplets. The two main regimes—continuous and pulsed laser heating—are explored. For continuous laser heating, the peak temperature is higher for larger droplets. For pulsed laser heating, when the peak irradiance is close to transition to the boiling regime, the temporal dynamics of the droplet temperature does not depend on the droplet size. With the empirical normalization of time, the dynamics of the droplet shrinkage and cooling are found to be independent of droplet sizes and peak laser intensities.

42 ENGINEERING↗

DOE OSTI2022

Numerical Modeling of Laser Heating and Evaporation of a Single Droplet

42 ENGINEERING↗

DOE OSTI2021

Cloud Top Radiative Cooling Rate Drives Non-Precipitating Stratiform Cloud Responses to Aerosol Concentration

Increases in aerosol concentration are well known to influence the microphysical processes and radiative properties of clouds. By reducing droplet size, an increase in aerosol can lessen collision efficiency and increase liquid water path (LWP) in precipitating clouds or enhance evaporation rate and decrease LWP in non-precipitating clouds. We utilize large eddy simulations to further investigate these aerosol indirect effects in Arctic mixed-phase clouds and find, in agreement with previous studies, precipitating clouds to experience an increase in LWP and non-precipitating clouds a decrease in LWP. Most importantly however, our results reveal a different explanation for why such an LWP decrease occurs in decoupled, non-precipitating clouds. We find enhanced evaporation near cloud top to be driven primarily by a strengthening of maximum radiative cooling rate with aerosol concentration which drives stronger entrainment, an effect that holds true even in clouds that are optically thick.

58 GEOSCIENCES↗

DOE OSTI2022

Transpiration-powered desalination water bottle

Inspired by mangrove trees, we present a theoretical design and analysis of a portable desalinating water bottle powered by transpiration. The bottle includes an annular fin for absorbing solar heat, which is used to boost the evaporation rate of water from the interior synthetic leaf. This synthetic leaf comprises a nanoporous film deposited atop a supporting micromesh. Water evaporating from the leaf generates a highly negative Laplace pressure, which pulls the overlying source water across an upstream reverse osmosis membrane. Evaporated water is re-condensed in the bottom of the bottle for collection. The benefit of our hybrid approach to desalination is that reverse osmosis is spontaneously enabled by transpiration, while the thermal evaporation process is enhanced by heat localization and made more durable by pre-filtering the salt. Finally, we estimate that a 9.4 cm diameter bottle, with a 10 cm wide annular fin, could harvest about a liter of fresh water per day from ocean water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Direct numerical simulation of turbulent dispersion of evaporative aerosol clouds produced by an intense expiratory event

Airborne particles are a major route for transmission of COVID-19 and many other infectious diseases. When a person talks, sings, coughs, or sneezes, nasal and throat secretions are spewed into the air. After a short initial fragmentation stage, the expelled material is mostly composed of spherical particles of different sizes. While the dynamics of the largest droplets are dominated by gravitational effects, the smaller aerosol particles, mostly transported by means of hydrodynamic drag, form clouds that can remain afloat for long times. In subsaturated air environments, the dependence of pathogen-laden particle dispersion on their size is complicated due to evaporation of the aqueous fraction. Particle dynamics can significantly change when ambient conditions favor rapid evaporation rates that result in a transition from buoyancyto-drag dominated dispersion regimes. To investigate the effect of particle size and evaporation on pathogen-laden cloud evolution, a direct numerical simulation of a mild cough was coupled with an evaporative Lagrangian particle advection model. The results suggest that while the dispersion of cough particles in the tails of the size distribution are unlikely to be disrupted by evaporative effects, preferential aerosol diameters (30-40 μm) may exhibit significant increases in the residence time and horizontal range under typical ambient conditions. Using estimations of the viral concentration in the spewed fluid and the number of ejected particles in a typical respiratory event, we obtained a map of viral load per volume of air at the end of the cough and the number of virus copies per inhalation in the emitter vicinity.

60 APPLIED LIFE SCIENCES↗

NASA NTRS2002

New Method Developed to Measure Contact Angles of a Sessile Drop

The spreading of an evaporating liquid on a solid surface occurs in many practical processes and is of importance in a number of practical situations such as painting, textile dyeing, coating, gluing, and thermal engineering. Typical processes involving heat transfer where the contact angle plays an important role are film cooling, boiling, and the heat transfer through heat pipes. The biological phenomenon of cell spreading also is analogous to a drop spreading (ref. 1). In the study of spreading, the dynamic contact angle describes the interfacial properties on solid substrates and, therefore, has been studied by physicists and fluid mechanics investigators. The dynamic contact angle of a spreading nonvolatile liquid drop provides a simple tool in the study of the free-boundary problem, but the study of the spreading of a volatile liquid drop is of more practical interest because the evaporation of common liquids is inevitable in practical processes. The most common method to measure the contact angle, the contact radius, and the height of a sessile drop on a solid surface is to view the drop from its edge through an optical microscope. However, this method gives only local information in the view direction. Zhang and Yang (ref. 2) developed a laser shadowgraphy method to investigate the evaporation of sessile drop on a glass plate. As described here, Zhang and Chao (refs. 3 and 4) improved the method and suggested a new optical arrangement to measure the dynamic contact angle and the instant evaporation rate of a sessile drop with much higher accuracy (less than 1 percent). With this method, any fluid motion in the evaporating drop can be visualized through shadowgraphy without using a tracer, which often affects the field under investigation.

Chao, David F.↗

NASA NTRS2018

Investigation of Transient Gas Phase Column Density Due to Droplet Evaporation

Analytical expressions are developed for estimating column density near a rapidly evaporating droplet along general paths. The influence for instantaneous evaporation is created first as a limiting case, where the peak value occurs at the time it takes a wave of vapor to reach the closest point along the optical path traveling at its most probable thermal speed. Next the case for finite-period evaporation is evaluated for constant conditions. Compared to the instantaneous case, peak column density occurs shortly after droplet extinction at a lower intensity. A new mathematical function is discovered that solves the integrals associated with this case. Finally, ways to account for droplet motion and changes in evaporation rate with size and temperature are discussed.

transient↗

NASA NTRS2018

Investigation of Transient Gas Phase Column Density Due to Droplet Evaporation

Column Density↗

DOE OSTI2022

Evaporation of Water Nanodroplets on Heated Surfaces: Does Nano Matter?

While experiments and continuum models have provided a relatively good understanding of the evaporation of macroscopic water droplets, elucidating how sessile nanodroplets evaporate is an open question critical for advancing nanotechnological applications where nanodroplets can play an essential role. In this study, using molecular dynamics simulations, we find that evaporating nanodroplets, in contrast to their macroscopic counterparts, are not always in thermal equilibrium with the substrate and that the vapor concentration on the nanodroplet surface does not reach a steady state. As a result, the evaporative behavior of nanodroplets is significantly different. Regardless of hydrophobicity, nanodroplets do not follow conventional evaporation modes but instead exhibit dynamic wetting behavior characterized by huge, non-equilibrium, isovolumetric fluctuations in the contact angle and contact radius. For hydrophilic nanodroplets, the evaporation rate, controlled by the vapor concentration, decays exponentially over time. Hydrophobic nanodroplets follow stretched exponential kinetics arising from the slower thermalization with the substrate. The evaporative half-lifetime of the nanodroplets is directly related to the thermalization time scale and therefore increases monotonically with the hydrophobicity of the substrate. Finally, the evaporative flux profile along the nanodroplet surface is highly nonuniform but does not diverge at the contact line as the macroscopic continuum models predict.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Monitoring Warm Wastewater and Evaporation Fans - A Brilliant Duo

The Advanced Test Reactor (ATR) generates warm wastewater which must be stored in warm wastewater ponds. The goal is to evaporate the water from the ponds and using evaporation fans may help to accomplish this. This project explores how much water has been accumulated into the ponds along with how much water has been entering and leaving the ponds over the past 5 years. Furthermore, the implementation of the evaporation fans into the ponds is evaluated to see if they are helpful for improving evaporation rates or not.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS1977

A comparative study of the effects of albedo change on drought in semi-arid regions

Numerical simulation studies of the effects of changes in albedo on rainfall involve comparisons of semiarid areas, lying at the boundary between a major desert and an adjacent monsoonal region, with areas of the same size located within the monsoonal region itself. The sensitivity of the rainfall to the ground hydrology was determined by performing the albedo simulations with two different evapotranspiration parameterizations, one giving too high evaporation over land and the other giving negligible evaporation over land. The evaporation rate is, in general, found to have as important an effect as changes in albedo. The mechanism by which an increase of albedo reduces the rainfall during conditions of high evaporation is considered.

Charney, J.↗

DOE OSTI2021

Chromium evaporation and oxidation characteristics of alumina-forming austenitic stainless steels for balance of plant applications in solid oxide fuel cells

The chromium (Cr) evaporation behavior of several different types of iron (Fe)-based AFA alloys and benchmark Cr 2 O 3 -forming Fe-based 310 and Ni-based 625 alloys was investigated for 500 h exposures at 800 °C to 900 °C in air with 10% H 2 O. The Cr evaporation rates from alumina-forming austenitic (AFA) alloys were ~5 to 35 times lower than that of the Cr 2 O 3 -forming alloys depending on alloy and temperature. The Cr evaporation behavior was correlated with extensive characterization of the chemistry and microstructure of the oxide scales, which also revealed a degree of quartz tube Si contamination during the test. As a result, long-term oxidation kinetics were also assessed at 800 to 1000 °C for up to 10,000 h in air with 10% H 2 O to provide further guidance for SOFC BOP component alloy selection.

08 HYDROGEN↗

NASA NTRS1981

Liquid spray cooling of a heated surface

The lowest surface temperature possible for the existance of spray evaporative cooling is determined experimentally to be a linear function of the impinging spray mass flux. A conduction-controlled analytical model of droplet evaporation gives fairly good agreement with experimental measurements at atmospheric pressure. At reduced pressures droplet evaporation rates are decreased significantly such that an optimum operating pressure exists for each desired surface heat flux. The initiation of the 'Leidenfrost state' provides the upper surface temperature bound for spray evaporative cooling.

Grissom, W. M.↗

DOE OSTI2024

Ensemble modeling of global lake evaporation under climate change

Global projections of lake evaporation are typically based on simulations using single mechanistic models. However, because of its complex interactions with various lake physical properties, environmental and anthropogenic drivers, lake evaporation is highly variable and sensitive to the choice of model used. In this study, we present a multi-model analysis to investigate differences across global simulations of lake evaporation during the warm-season using three different lake models driven by outputs from four general circulation models (GCM) (i.e. 12 model combinations in total) for historic and future scenarios. Our results suggest substantial differences among lake-climate model simulations of lake evaporation. These differences varied throughout the 20th and 21st century, with model driver data explaining 74% of the variance in future projections of warm- season lake evaporation. Our projections indicate that, by the end of the 21st century (2070–2099), global annual lake evaporation rates will increase by 10–27% under Representative Concentration Pathways (RCPs) 2.6–8.5. Finally, we highlight the importance of using a multi-model approach for the prediction of future global lake evaporation responses to climate change.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2002

Multilayer composite material and method for evaporative cooling

A multilayer composite material and method for evaporative cooling of a person employs an evaporative cooling liquid that changes phase from a liquid to a gaseous state to absorb thermal energy. The evaporative cooling liquid is absorbed into a superabsorbent material enclosed within the multilayer composite material. The multilayer composite material has a high percentage of the evaporative cooling liquid in the matrix. The cooling effect can be sustained for an extended period of time because of the high percentage of phase change liquid that can be absorbed into the superabsorbent. Such a composite can be used for cooling febrile patients by evaporative cooling as the evaporative cooling liquid in the matrix changes from a liquid to a gaseous state to absorb thermal energy. The composite can be made with a perforated barrier material around the outside to regulate the evaporation rate of the phase change liquid. Alternatively, the composite can be made with an imperveous barrier material or semipermeable membrane on one side to prevent the liquid from contacting the person's skin. The evaporative cooling liquid in the matrix can be recharged by soaking the material in the liquid. The multilayer composite material can be fashioned into blankets, garments and other articles.

Buckley, Theresa M.↗

NASA NTRS1988

Radiative processes in upper tropospheric mixed-phase clouds

The diffusional mass evolution of hydrometeors in upper tropospheric clouds for various radiative conditions in the cloud and for varying ambient moisture supply is simulated using a time dependent microphysical model. Radiation can play an important role in this mass evolution when only one phase is present. When both liquid droplets and ice crystals are situated in a typical upper tropospheric environment and the moisture supply is limited, radiation produces only a minor effect on the mass evolution of the hydrometeors. In these cases ice crystals grow quickly at the expense of the droplets and the droplets evaporate within several minutes, even under water supersaturation conditions. Radiation does not significantly influence the evaporation rates of the droplets in the coexisting cases. In the absence of ice crystals and under certain radiative conditions, the droplets can survive when the environment is subsaturated. For other radiative conditiions, the droplets can evaporate when the environment is supersaturated.

Wesley, Douglas A.↗