Background A significant quantity of aluminum-clad spent nuclear fuel (ASNF) is currently managed by the United States (U.S.) Department of Energy (DOE) at several sites in the U.S. Much of this fuel develops a corrosion layer with adsorbed water either through pre-corrosion, in-reactor, or in wet storage depending on the source. Gamma radiation from the fuel after removal from the reactor can cause evolution of hydrogen from this corrosion layer. For long-term safety it is desirable to remove the adsorbed water from the fuel surface to limit the production of hydrogen gases when the fuel is placed in road-ready sealed canisters for eventual final disposition. Methods This study presents a series of experiments showing the effectiveness of both forced helium drying and vacuum drying methods for the removal of water from surrogate fuel assemblies. A computational fluid dynamics (CFD) model is constructed to replicate the drying processes and simulate the experiments. Results The model suggests that increasing the purge gas inlet temperature is a more efficient way of improving the efficacy of a drying process. An increase in gas inlet temperature leads to a reduction in drying time 28–55% greater than the same relative increase in flow rate. One of the assemblies inside the canister consistently experiences the least amount of turbulent flow and require the longest time to dry. Therefore, the assembly with the highest decay heat should be placed in this slot in the basket in order to facilitate the drying of this assembly. Conclusions The CFD model can be used in the future as a design and analysis tool for a full-scale drying setup with actual fuel assemblies.

Background A significant quantity of aluminum-clad spent nuclear fuel (ASNF) is currently managed by the United States (U.S.) Department of Energy (DOE) at several sites in the U.S. Much of this fuel develops a corrosion layer with adsorbed water either through pre-corrosion, in-reactor, or in wet storage depending on the source. Gamma radiation from the fuel after removal from the reactor can cause evolution of hydrogen from this corrosion layer. For long-term safety it is desirable to remove the adsorbed water from the fuel surface to limit the production of hydrogen gases when the fuel is placed in road-ready sealed canisters for eventual final disposition. Methods This study presents a series of experiments showing the effectiveness of both forced helium drying and vacuum drying methods for the removal of water from surrogate fuel assemblies. A computational fluid dynamics (CFD) model is constructed to replicate the drying processes and simulate the experiments. Results The model suggests that increasing the purge gas inlet temperature is a more efficient way of improving the efficacy of a drying process. An increase in gas inlet temperature leads to a reduction in drying time 28–55% greater than the same relative increase in flow rate. One of the assemblies inside the canister consistently experiences the least amount of turbulent flow and require the longest time to dry. Therefore, the assembly with the highest decay heat should be placed in this slot in the basket in order to facilitate the drying of this assembly. Conclusions The CFD model can be used in the future as a design and analysis tool for a full-scale drying setup with actual fuel assemblies.

The one-dimensional simulation of counterflow cool flames with the plug flow assumption ignores the effects of gravity, buoyancy, and the radial velocity gradient, leading to a flow field that deviates from measurements. A two-dimensional (2D) axisymmetric multi-physics model is developed within the OpenFOAM framework, considering buoyancy and multidimensional transport to simulate the opposed flow diffusion flame of dimethyl ether operating in the cool flame regime (i.e., low-temperature combustion). Flame structures and extinction limits of diffusion-cool flames are simulated and compared with measurements and 1D simulations. While the classical 1D model (i.e., without any buoyancy effect) predicts the stagnation plane forming at the mid-plane, the 2D model with buoyancy effect predicts the formation towards the upper fuel side nozzle, deviating by similar to 23% compared to the buoyancy-free case. The extinction limit of the cool flame has been studied at atmospheric pressures of 1, 3, and 5 atm. The 2D model allows the velocity to be perturbed at the nozzle exit without imposing any radial velocity gradient, which enables the flame to sustain higher strain rates than the 1D prediction. For 1 atm cases, predictions from the 1D and 2D models deviate from the measurements at higher fuel loading conditions (i.e., > 0.48); however, the 2D model performs significantly better. For a fuel loading of = 0.525, the difference between the measurements and the 1D model is similar to 40 s(-1) (similar to 30%), while the 2D model prediction is within 14% (similar to 19 s(-1)) of the measured extinction strain rates. The models predict that an increase in pressure shifts the cool flame to higher strain rates, resulting in higher cool flame extinction strain rates. At elevated pressure, the deviation between the models decreases as buoyancy effects become less pronounced. The Richardson number is identified as a critical parameter for characterizing the counterflow cool flame configuration, where the competition between buoyancy and flow inertia determines the flame location, especially when the system deviates from the classical one-dimensional assumption.

In this study, the oxidation of methanol in a supercritical water medium has been numerically investigated. A two-dimensional axisymmetric computational model has been developed to conduct simulation over a range of fuel loading conditions using single and multi-step chemical kinetic scheme. The multi-step chemistry has been found to perform better than the single-step chemistry in predicting the flame temperature as well as its location and structure. It is found that the hydrothermal flame exhibits different flame structures depending on the fuel loading. For a higher fuel loading (X-F = 0.12), a classical non-premixed hot flame was observed with a peak temperature of similar to 2000K. Whereas, for the leanest case (X-F = 0.071), a peak temperature of similar to 1200K was observed with extremely low hydroxyl (OH) concentration (ranging to a few ppm levels). For high fuel loading, the flame forms on the jet periphery, while as the fuel loading decreases, the flame is observed to be lifted in the radial direction. At lower fuel loading, radial mixing is more prominent, and the multidimensional effect appears to be significant. Under this condition, the model predicts a peak concentration of similar to 300 ppm and similar to 1600 ppm of HO2 and H2O2, respectively, while the CO and CO2 concentrations become comparable and are distributed over a larger volume in a homogeneous fashion. This is counter to the hot flame where the CO profiles are located closer to the fuel-rich region and is dictated by the fuel-oxidizer diffusion. The CO-CO2 and the HO2-H2O2 profiles at the lowest fuel loading suggest the formation of a warm flame at supercritical conditions. Perturbation analysis was conducted to identify the impact of third-body collision efficiency of key species on the overall predictions. The predictions show that the flame formation and peak axial temperature are highly sensitive to the third body collision efficiency parameters - undergoing complete extinction or establishing a stable flame structure.

An approach is described for modeling the fuel systems components serving ship generating plants to refine the accuracy of endurance and annual fuel use calculations. Models were formulated for Operating Point analysis in a tool such as the S3D component of the Rapid Ship Design Environment but the model formulations are presented generically and can be encoded for any other suitable analysis tool. The formulations refer to a specific reference case in which ammonia is considered as a fuel, but the modeling method can be applied to other fuels by changing the fluid parameters or the combustion chemistry.

The reduction of fossil fuel resources and the ongoing surge in global energy demand have captured the interest of researchers worldwide, prompting a focus on developing renewable energy sources. For this reason, biomass conversion has emerged as a crucial pathway for renewable fuel production. Lignin, constituting 10-35% of woody biomass, represents a significant and largely untapped sustainable feedstock. Despite the potential of lignin, a substantial portion of this lignocellulosic residue remains unused, with approximately 60% considered waste. This study addresses the challenge of underutilized lignin by introducing an innovative approach to its hydrogenolysis. Despite their potential, existing hydrogenolysis methods face obstacles such as complexity, high cost, and the need for high temperatures or pressures. Herein we report a noncatalytic nonthermal hydrogen plasma method for lignin hydrogenolysis, conducted under ambient temperature and pressure conditions. Our method proves to be highly effective in breaking lignin bonds, achieving complete conversion, and generating valuable gaseous and bio-oil products including methane and aromatic dimers and monomers obtained from guaiacyl and syringyl units within the lignin structure. Our results showed an increase in gaseous products, especially methane, and aromatic monomer yields, as well as a reduction in total bio-oil and biochar yields and lignin functional groups by increasing reaction time, input power, and H2 partial pressure. This research confirms the considerable promise of utilizing noncatalytic nonthermal hydrogen plasma-assisted hydrogenolysis as an effective technique for producing gaseous and liquid fuels from lignin.

This paper summarizes the first results from isolated droplet combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial droplet droplet diameters between 1.5 and 5.0 m m , ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 a t m and ambient environments containing oxygen and nitrogen diluted with both carbon dioxide and helium. The experiments show both radiative and diffusive extinction. For both fuels, the flames exhibited pre-extinction flame oscillations during radiative extinction with a frequency of approximately 1 H z . The results revealed that as the ambient oxygen mole fraction was reduced, the diffusive-extinction droplet diameter increased and the radiative-extinction droplet diameter decreased. In between these two limiting extinction conditions, quasi-steady combustion was observed. Another important measurement that is related to spacecraft fire safety is the limiting oxygen index (LOI), the oxygen concentration below which quasi-steady combustion cannot be supported. This is also the ambient oxygen mole fraction for which the radiative and diffusive extinction diameters become equal. For oxygen/nitrogen mixtures, the LOI is 0.12 and 0.15 for methanol and heptane, respectively. The LOI increases to approximately 0.14 (0.14 O 2 /0.56 N 2 /0.30 C O 2 ) and 0.17 (0.17 O 2 /0.63 N 2 /0.20 C O 2 ) for methanol and heptane, respectively, for ambient environments that simulated dispersing an inert-gas suppressant (carbon dioxide) into a nominally air (1.0 a t m ) ambient environment. The LOI is approximately 0.14 and 0.15 for methanol and heptane, respectively, when helium is dispersed into air at 1 atm. The experiments also showed unique burning behavior for large heptane droplets. After the visible hot flame radiatively extinguished around a large heptane droplet, the droplet continued to burn with a cool flame. This phenomena was observed repeatably over a wide range of ambient conditions. These cool flames were invisible to the experiment imaging system but their behavior was inferred by the sustained quasi-steady burning after visible flame extinction. Verification of this new burning regime was established by both theoretical and numerical analysis of the experimental results. These innovative experiments have provided a wealth of new data for improving the understanding of droplet combustion and related aspects of fire safety, as well as offering important measurements that can be used to test sophisticated evolving computational models and theories of droplet combustion.

Droplet statistics of three well-studied reference jet fuels and three surrogate jet fuels with similar pre-vaporized combustion behavior are measured in a piloted spray burner using phase Doppler anemometry. The spray burner consists of a central tube of two-phase flow, resembling an open-pipe atomizer, and a surrounding hydrogen/air pilot flame to assist ignition of the liquid fuel. It is found that the droplet diameters and velocities of the reference jet fuels are quite similar, even under conditions in which their flame lift-off heights differ substantially. The droplet characteristics of the surrogate fuels are more distinct, with significant variations occurring for the droplet velocities and droplet concentrations. However, the surrogate fuel that best reproduces the droplet characteristics of the reference jet fuels is not the same as the one that best matches the average flame lift-off height. Overall, it appears that measurements of droplet characteristics are unable to answer why reference jet fuels exhibit different flame heights under various flow conditions.

A novel hybrid experimental-computational study is performed to predict the flow fields and pressure distributions on the measured three-dimensional shapes of flexible, three-tab asphalt roofing shingles undergoing increasing uplift when exposed to hurricane velocity winds for two hours. To quantify the evolution of shingle shapes, StereoDIC analysis is used to measure the transient, full-field deformed shapes of full-sized, three-tab asphalt shingles that did not separation or failure when subjected to hurricane velocity winds for two hours. Based on physical observations during wind loading, the authors performed steady state computational fluid dynamics (CFD) simulations to predict the full-field pressure distributions on as-measured, uplifted three-dimensional shingle shapes at selected time instances during wind loading.Simulation predictions clearly show flow recirculation regions on both the front and top of the shingles that remain attached throughout wind loading and control the full-field uplift pressure distribution. For low velocity flow with maximum uplift ≤ 8.4 mm,, CFD-predicted pressures are in good agreement with prior measurements. For both low and high-speed flows, the model predictions indicate that high pressures are formed at the leading-edge, upstream of the sealant layer, with maximum pressure occurring near the tab cutouts along the leading-edge of the shingle, providing a physical basis for the observed higher uplift and increased potential for shingle failure in these regions. The combined experimental-computational studies provide a contemporary way to eliminate the difficulties associated with attachment of pressure sensors to flexible materials that can alter shingle response, providing the basis for future design improvements by delineating the physical processes controlling pressure loading and shingle uplift in hurricane velocity winds.

Large carbon number n-alkanes are a notable component in all real transportation fuels, and their chemical structure fosters substantial low temperature kinetic reactivity. Normal alkanes have been studied in various canonical configurations but rarely in systems with strong coupling between low temperature chemistry and transport for pure as well as for multi-component n-alkane mixtures. The Flame Extinguishment (FLEX) experiments onboard the International Space Station provided a unique platform for investigating low temperature multi-phase n-alkane and iso-alkane combustion. Among the many interesting phenomena experimentally observed, cool flame extinction can occur, accompanied by the concurrent formation of a surrounding cloud of condensed vapor. In this work we conduct numerical simulations of high and low temperature combustion of large, initially single-component n-heptane, n-decane and n-dodecane droplets. The role of initial droplet diameter, operating pressure, and n-alkyl carbon number on the extinction of hot and low temperature flames is investigated and compared against the available experimental data. While all three fuels exhibit similar hot flame behavior, cool flame activity increases with the carbon number, resulting in an increased cool flame temperature and decreased extinction diameter. Multi-cyclic “hot/cool flame transitions” are found in air as pressure is slightly increased above one atmosphere. The cyclic behaviors correspond to continuously varying hot and cool flame transitions across the high, low, and negative temperature coefficient (NTC) kinetic regimes. Further increase in pressure results in a second stage steady “Warm flame” transition. The extinction of hot and cool flame has a strong non-linear dependence on ambient pressure but as the hot flame extinction diameter increases with pressure the extinction diameter of the cool flame decreases. The computational results are compared with a recent asymptotic analysis of FLEX n-alkane cool flames.

Pulsed dielectric barrier discharges (DBD) in He–H 2 O and He–H 2 O–O 2 mixtures are studied in near atmospheric conditions using temporally and spatially resolved quantitative 2D imaging of the hydroxyl radical (OH) and hydrogen peroxide (H 2 O 2 ). The primary goal was to detect and quantify the production of these strongly oxidative species in water-laden helium discharges in a DBD jet configuration, which is of interest for biomedical applications such as disinfection of surfaces and treatment of biological samples. Hydroxyl profiles are obtained by laser-induced fluorescence (LIF) measurements using 282 nm laser excitation. Hydrogen peroxide profiles are measured by photo-fragmentation LIF (PF-LIF), which involves photo-dissociating H 2 O 2 into OH with a 212.8 nm laser sheet and detecting the OH fragments by LIF. The H 2 O 2 profiles are calibrated by measuring PF-LIF profiles in a reference mixture of He seeded with a known amount of H 2 O 2 . OH profiles are calibrated by measuring OH-radical decay times and comparing these with predictions from a chemical kinetics model. Two different burst discharge modes with five and ten pulses per burst are studied, both with a burst repetition rate of 50 Hz. In both cases, dynamics of OH and H 2 O 2 distributions in the afterglow of the discharge are investigated. Gas temperatures determined from the OH-LIF spectra indicate that gas heating due to the plasma is insignificant. The addition of 5% O 2 in the He admixture decreases the OH densities and increases the H 2 O 2 densities. The increased coupled energy in the ten-pulse discharge increases OH and H 2 O 2 mole fractions, except for the H 2 O 2 in the He–H 2 O–O 2 mixture which is relatively insensitive to the additional pulses.

The paper reports simulation results on the influence of a direct-current driven radial electric field on the emission characteristics; especially NOx and CO of a premixed methane/air laminar jet flame. A multi-physics computational model is developed in the OpenFOAM framework to simulate electric-field-coupled premixed combustion process. The computational framework consists of coupled species, momentum and energy conservation together with a Poisson’s equation solver to resolve the electric field distribution. Electron and ion conservation equations are resolved to consider the ionic wind body force in the momentum conservation equation and the associated possible electric field distortion due to the space charge distribution. The simulations are conducted for a stochiometric and fuel rich condition and over a range of jet flow rates for a configuration representative of a test-scale experimental setup. The model predictions show that for an applied voltage of 50 kV, the flame structure changes significantly for both the stoichiometric and fuel rich conditions. The flame is stretched significantly by the electric field due to ionic wind. For the fuel rich condition, the ionic wind allows additional mixing of the fuel rich stream with the surrounding air and drastically altering the flame structure. The electric field was found to reduce the NOx emission significantly for both stoichiometric and rich conditions. Over the entire range of flowrate conditions, the stochiometric fuel-oxidizer mixture showed a decrease in maximum NOx by a factor of 1.6 in presence of electric field. For the fuel rich case, however as the flow rate is increased, the NOx reduction factor decreased from 12.0 to 1.6. For CO emissions, the presence of electric field reduces the concentration under fuel rich conditions and vice versa for the stoichiometric flame. The role of kinetics is analyzed and discussed.

Electrical discharges in humid media are of great interest in biomedical and environmental applications, such as plasma medicine, disinfection, gas treatment, and removal of volatile organic contaminants. Plasmas in high water content produce a mixture of highly reactive species, including reactive oxygen species that are strongly oxidative. We investigate two key reactive species: hydroxyl radical (OH) and hydrogen peroxide (H 2 O 2 ) using time-resolved 2D imaging in the afterglow of a dielectric barrier discharge plasma in humid helium, powered by a ns-pulser. The stagnation discharge plane is created by introducing the feed gas concentrically through the powered electrode which impinges on a grounded steel surface.

Multiphysics simulations are performed to identify the role of water pH level on liquid phase plasma discharge formation. The simulations are conducted for a needle-like powered electrode with an exponential nanosecond rise time. The simulations indicate that water pH level that denotes the available negative hydroxyl ions (OH - ) in the liquid phase has a strong influence on the discharge initiation. Electron detachment from OH - requires a much lower threshold energy and therefore provides a stream of electrons during the initial stage. A higher pH (i.e., alkaline water) allows the initial stream of electrons to be present at higher concentration and propagates further downstream from the powered electrode. The resulting electrical forces at higher pH level create larger density variation in the liquid and a significantly higher bulk fluid velocity is observed. The electron detachment from the OH - is not limited by the available electric field strength, rather the availability of negative hydroxyl ions in the system and ceases when these ions are depleted. Acidic water on the other hand was found to require higher electric field for the breakdown to take place as the system is deprived of critical initial concentration of OH - .

A global model is proposed to simulate the drying process of used nuclear fuel assemblies under vacuum drying conditions. The transient model consists of a coupled mass and energy conservation equation with appropriate source and sink terms. The classic Hertz-Knudsen expression is employed to resolve the evaporation rate and the associated water mass depletion in the system. Both latent heat of vaporization and residual decay heat are considered as sink and source in the energy conservation, respectively. The model is employed to simulate vacuum drying of spent nuclear fuel rod storage systems. Multistage stepwise vacuuming of the system is emulated, and several parametric studies are conducted to identify their role in the drying process. The predicted temporal profiles show that the proposed model is able to capture qualitative trends of the water removal rate, hence the dryness level of the system. The model prediction is also compared against experiments where the amount of residual water after a standard vacuum drying procedure is quantified. The predictions are found to compare favorably with the experimental measurements.

Plasma stratification has been studied for more than a century. Despite the many experimental studies reported on this topic, theoretical analyses and numerical modeling of this phenomenon have been mostly limited to rare gases. In this work, a one-dimensional fluid model with detailed kinetics of electrons and vibrationally excited molecules is employed to simulate moderate-pressure (i.e. a few Torrs) dc discharge in nitrogen in a 15.5 cm long tube of radius 0.55 cm. The model also considers ambipolar diffusion to account for the radial loss of ions and electrons to the wall. The proposed model predicts self-excited standing striations in nitrogen for a range of discharge currents. The impact of electron transport parameters and reaction rates obtained from a solution of local two-term and a multi-term Boltzmann equation on the predictions are assessed. In-depth kinetic analysis indicates that the striations result from the undulations in electron temperature caused due to the interaction between ionization and vibrational reactions. Furthermore, the vibrationally excited molecules associated with the lower energy levels are found to influence nitrogen plasma stratification and the striation pattern strongly. A balance between ionization processes and electron energy transport allows the formation of the observed standing striations. Simulations were conducted for a range of discharge current densities from ∼0.018 to 0.080 mA cm −2 , for an operating pressure of 0.7 Torr. Parametric studies show that the striation length decreases with increasing discharge current. The predictions from the model are compared against experimental measurements and are found to agree favorably.

Contaminants of emerging concerns such as endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal-care products (PPCPs) constitute a problem since they are not completely eliminated by traditional water and wastewater treatment methods. Non-thermal plasma (NTP) is considered as one of the most favorable treatment methods for the removal of organic contaminants in water and wastewater. The degradation of selected EDCs and PPCPs of various classes was reviewed, based on the recent literature, to (i) address the effect of the main NTP treatment parameters (water quality and NTP conditions: pH, initial concentration, temperature, background common ion, NOM, scavenger, gas type/flow rate, discharge/reactor type, input power, and energy efficiency/yield) on the degradation of contaminants and their intermediates, (ii) assess the influences of different catalysts and hybrid systems on degradation, (iii) describe EDC and PPCP degradation along with their properties, and (iv) evaluate mineralization, pathway, and degradation mechanism of selected EDCs and PPCPs for different cases studied. Furthermore, areas of potential research in NTP treatment for the degradation of EDCs and PPCPs in aqueous solutions are recommended. It could be reasonably predicted that this review is valid for developing our understanding of the fundamental scientific principles concerning the catalytic NTP of EDCs and PPCPs, providing helpful and practical references for researchers and designers on the effective removal of EDCs/PPCPs and the optimized operation of catalytic NTP systems.

View Video Presentation: https://doi.org/10.2514/6.2022-1258.vid Lift-off heights of three well-studied reference jet fuels and three surrogate jet fuels with similar pre-vaporized combustion behavior are measured in a piloted spray burner using chemiluminescence imaging. The spray burner consists of a central tube of two-phase flow, resembling an open-pipe atomizer, and a surrounding hydrogen/air pilot flame to assist ignition of the liquid fuel. It is found that the lift-off behaviors of the reference jet fuels are generally comparable, with the main differences occurring for the most transient condition. However, the surrogate fuels do not reproduce the lift-off heights of the reference fuels due to discrepancies in the spray behaviors between the two. In particular, the differences in viscosity are inferred to be the primary reason for the variations in the flame heights. This investigation confirms that the physical properties of the liquid fuel cannot be neglected in the formulation of jet fuel surrogates.