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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Numerical Evaluation of Effective Thermal Conductivity of PCM with Metal Foam Incorporating Buoyancy Effects for Thermal Energy Storage

The thermal energy storage (TES) system has the capability to efficiently preserve thermal energy directly derived from the energy source, minimizing any conversion losses. Especially latent heat storage offers distinct advantages, including a substantial increase in energy storage density and minimization of temperature fluctuations within the plants. However, the phase change material (PCM) employed in latent heat storage has low thermal conductivity. Consequently, various studies are being conducted to enhance heat transfer. One approach to enhance heat transfer involves utilizing metal foam to maximize the heat transfer area. However, modeling metal foam with its intricate structure is a challenging task in numerical analysis. For this reason, ongoing research focuses on simplifying the modeling of metal foam. Nevertheless, fully encompassing all the characteristics of actual metal foam proves to be a challenging task for the simplified analytical model. The objective of this paper is to interpret the simple lattice metal foam analysis model from the perspective of behavior induced by buoyancy. When comparing the analysis results of solid PCM and liquid PCM with the same thermal conductivity under changes in porosity and gravity direction, we conducted an analysis to discern the trends in effective thermal conductivity that are overestimated due to convection. In the analysis, a constant heat flux of 10 kW and a constant surface boundary condition of 350 K were applied, and a sensitivity study regarding the mesh was conducted. The results indicate that, from the perspective of gravity in the simple lattice model, the solid analysis yields an effective thermal conductivity 29-47% higher compared to the liquid analysis. Additionally, as porosity increases, there is an observed increase of 24-33% in effective thermal conductivity.

25 ENERGY STORAGE↗
DOE OSTI2021

Protective effects of non–catalytic proteins on endoglucanase activity at air and lignin interfaces

The manner in which added non-catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated that a reduction in the non-specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air–liquid interface provide rationale. This work investigated root causes including effects of the air–liquid interface on non-catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air–liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non-enzymatic protein (bovine serum albumin [BSA] or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%–50% of its activity due to an air–liquid interface in the presence of lignin while addition of non-enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. Finally, these results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Hydrodynamics of countercurrent flows in a structured packed column: effects of initial wetting and dynamic contact angle

The structured packed column has gained considerable attention as a prospective technology to mitigate carbon dioxide emissions from thermal power plants. The computational flow investigation of such systems is a multiscale problem, and local hydrodynamics plays a key role in overall column efficiency. Accordingly, multiphase flow studies in the representative elementary unit (REU) of a packed column can offer insights into the local flow behavior such as flow pattern, interfacial area, etc. The interfacial area plays a key role in the overall interphase mass transfer and thereby in separation efficiency. The predicted effective area matches well with corresponding ones in experiments for Mellapak 250.Y packings. The contact angle (i.e., solid substrate behavior) is one of the critical factors that dictates wettings, and thereby the interfacial area. The dynamic contact angle (DCA) was considered in order to explore the effects of contact angle hysteresis on the interfacial area. DCA has more pronounced impact on the interfacial area for a solvent possessing a higher value of surface tension and equilibrium contact angle. The interfacial area shows temporal undulation and does not achieve a pseudo steady state due to the capillary force. In contrary, the interfacial area gets a net value for a solvent having low surface tension value. Further, specification of the static contact angle at the solid substrate shows the least value of the interfacial area. We also extensively studied the effect of the initial sheet condition (dry vs wet) on the interfacial area. The initially wetted sheets show slightly higher value of the interfacial area as compared to the initially dry sheets at a fixed flow rate for a solvent having high surface tension value. Wetting hysteresis decreases with increasing liquid loads. On the other hand, wetting hysteresis does not occur for a solvent having value of low surface tension and equilibrium contact angle.

structured packings, dynamic contact angle, interf↗
DOE OSTI2021

Irradiation effects in tungsten—From surface effects to bulk mechanical properties

Advanced materials such as tungsten fibre-reinforced composites allow to overcome severe weaknesses of the baseline materials for plasma-facing components — copper and tungsten. The effect of the fusion environment on the mechanical properties of these materials, e.g. the embrittlement by neutron irradiation, plays a key role for the development of future fusion reactors. To simulate this effect, high-energy ions are used as a substitute for the displacement damage by neutrons. We propose the use of very fine tungsten wire as a possibility of studying the influence of irradiation damage on the mechanical properties. This is possible as they allow full-depth irradiation of almost the entire volume despite the limited penetration depth of ions. Geometrical size effects are mitigated due to the nanoscale microstructure of the wire. In addition, similar wire is used in tungsten fibre-reinforced composites. Thus, the investigation of irradiated wire can directly be used for the prediction of the bulk composite properties. For the proof of this concept tungsten wire with a diameter of 16 μm was electrochemically thinned to 5 μm and irradiated with 20.5 MeV W 6+ ions. The mechanical properties were subsequently determined by macroscopic tensile testing. Irradiation to 0.3, 1 and 9 dpa did not lead to a change of the mechanical behaviour. Both strength and ductility, the latter indicated by the reduction of area, were similar to the as-fabricated state.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ab-Initio Investigation of Finite Size Effects in Rutile Titania Nanoparticles with Semilocal and Nonlocal Density Functionals

In this work, we employ hybrid and generalized gradient approximation (GGA) level density functional theory (DFT) calculations to investigate the convergence of surface properties and electronic gap of rutile titania nanoparticles with particle size. The surface energies and electronic gaps are calculated for cuboidal particles with minimum dimension ranging from 3.7 Angstrom (24 atoms) to 10.3 Angstrom (384 atoms) using a highly-parallel real-space DFT code to enable hybrid level DFT calculations of larger nanoparticles than are typically practical. We deconvolute the geometric and electronic finite size effects in surface energy, and evaluate the influence of defects on electronic gap and density of states (DOS). The electronic finite size effects in surface energy vanish when the minimum length scale of the nanoparticles becomes greater than 10 Angstrom. We show that this length scale is consistent with a computationally efficient numerical analysis of the characteristic length scale of electronic interactions. The surface energy of nanoparticles having minimum dimension beyond this characteristic length can be approximated using slab calculations that account for the geometric defects. In contrast, the finite size effects on the electronic gap and DOS is highly dependent on the shape and size of these particles. Furthermore, the DOS for cuboidal particles and more realistic particles constructed using the Wulff algorithm reveal that defect states within the electronic gap play a key role in determining the eigen value distribution of nanoparticles and the electronic gap does not converge to the bulk limit for the particle sizes investigated.

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

Understanding the Effect of Single Atom Cationic Defect Sites in an Al 2 O 3 (012) Surface on Altering Selenate and Sulfate Adsorption: An Ab Initio Study

Adsorption is a promising under-the-sink selenate remediation technique for distributed water systems. Recently it was shown that adsorption induced water network rearrangement control adsorption energetics on the α-Al 2 O 3 (012) surface. Here, we aim to elucidate the relative importance of the water network effects and surface cation identity on controlling selenate and sulfate adsorption energy using density functional theory calculations. Density functional theory (DFT) calculations predicted the adsorption energies of selenate and sulfate on nine transition metal cations (Sc–Cu) and two alkali metal cations (Ga and In) in the α-Al 2 O 3 (012) surface under simulated acidic and neutral pH conditions. We find that the water network effects had a larger impact on the adsorption energy than the cationic identity. However, cation identity secondarily controlled adsorption. Most cations decreased the adsorption energy, weakening the overall performance, the larger Sc and In cations enabled inner-sphere adsorption in acidic conditions because they relaxed outward from the surface, providing more space for adsorption. Additionally, only Ti induced Se selectivity over S by reducing the adsorbing selenate to selenite but not reducing the sulfate. Altogether, this study indicates that tuning water network structure will likely have a larger impact than tuning cation–selenate interactions for increasing adsorbate effectiveness.

Adsorption↗
DOE OSTI2021

Effect of Dilute Acetic Acid Hydrolysis on Xylooligosaccharide Production and the Inhibitory Effect of Cellulolytic Enzyme Lignin from Poplar

Acetic acid (AC) hydrolysis has been reported to prepare xylooligosaccharides (XOS) from poplar. However, the influence of AC hydrolysis on the lignin structure changes is not clear, which is important for the following enzymatic hydrolysis of poplar. Herein, AC was used to produce XOS, and cellulase adsorption on cellulolytic enzyme lignin (CEL) from AC-hydrolyzed poplar and its inhibitory effect on two commercial cellulase preparations were investigated. AC hydrolysis gave a XOS yield of 39.8% from poplar. After AC hydrolysis at 170 °C, the hydrophobicity and ζ-potential of CEL decreased to 2.3 L/g and 14.8 mV, respectively. The adsorption strength of CTec2 on CEL samples did not increase by AC hydrolysis, and the inhibitory effect of CEL on Celluclast 1.5L and β-glucosidase was observed, but not on CTec2. CEL samples improved the lytic polysaccharide monooxygenase (LPMO) activity of the enzymatic hydrolysis by CTec2. After CEL samples were added in enzymatic hydrolysis, the free filter paper activity of Celluclast 1.5L and β-G retained in the enzymatic hydrolysate decreased from 60.5 to 29.3–42.9%. The addition of CEL samples in enzymatic hydrolysis could not decrease the free filter paper activity of CTec2 retained in the enzymatic hydrolysate. In the enzymatic hydrolysis with CEL samples, higher glucose yields were obtained by CTec2 than those by Celluclast 1.5L and β-glucosidase. This work will help to understand the structure and inhibitory effects of AC-CELs and guide the development of AC hydrolysis for the production of XOS and monosaccharides from poplar.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Heavy boron doping effects on biaxially tensile strained germanium (>1.5%) investigated via structural characterization, effective lifetime assessment and atomistic modeling

Highly tensile strained germanium (ε-Ge) represents an essential material system for emerging electronic and photonics applications. Moreover, adjusting the doping levels to moderate or high concentrations can effectively tailor the properties of ε-Ge for specific applications. This article combines experimental characterization with a theoretical framework to examine the effects of heavy elemental boron (B) doping on pseudomorphic sub-50 nm ε-Ge. High resolution X-ray diffractometry is used to validate tensile strain levels of 1.53% and 1.68% in Ge epilayers, surpassing the indirect-to-direct band gap crossover point at ∼1.5% biaxial tensile strain. Cross-sectional transmission electron microscopy revealed visual evidence of stacking faults and surface roughening in 1.68% ε-Ge, although a coherent and abrupt Ge/III–V heterointerface is observed, devoid of interfacial misfit dislocations. Effective lifetime measurements demonstrated approximately twofold enhancement in 1.53% B-doped ε-Ge (N B ∼7 × 10 19 cm −3 ) compared to its unstrained B-doped counterpart, while no such improvement was observed in 1.68% B-doped ε-Ge. This lack of enhancement is attributed to the presence of stacking faults and surface roughness within the ε-Ge epilayer. Through density functional theory calculations, we independently demonstrate that substitutional B atoms induce local deformation of Ge–Ge bonds in both unstrained Ge and ε-Ge epilayers, resulting in an additive tensile strain. This phenomenon could potentially lead to dynamic reduction and overcoming of the critical layer thickness for the system, facilitating the nucleation and subsequent glide of 90° leading Shockley partial dislocations, thereby generating stacking faults. In essence, these findings establish an upper limit on the B-doping concentration that can be achieved in highly ε-Ge epilayers, and collectively, offer valuable insights into the significance of heavy doping in Ge-based heterostructures. As such, this study delineates a fundamental constraint for integrating heavily doped ε-Ge in high-performance optoelectronic systems, necessitating precise strain-doping co-optimization to avoid performance degradation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Current polarity effects on laboratory plasma jets

Plasma jets produced by a pulsed power machine were investigated using Thomson scattering and other diagnostics in order to make detailed comparisons to simulations. These jets were produced from a 15 μm thick disc of Al foil on a 1.2 MA, 100 ns rise time, pulsed power machine. Experiments were performed with both a radially inward and a radially outward current ow in the Al foil to investigate the effects of voltage polarity in the experiments and determine how extended magnetohydrodynamic (XMHD) effects, such as the Hall effect, change the formation of the jet. We recorded Thomson scattering spectra with a low enough laser energy to not perturb the plasma, while providing a high enough signal to noise ratio to resolve the scattered features. This enabled the measurement of the electron temperature in the jet region of the plasma, 15.5±4 eV for both current polarities. Jets with a radially outward current ow were heated more from inverse bremsstrahlung when 10 J of laser energy was used, implying that these jets are denser than the ones with a radially inward current. This higher density was con rmed by interferometry measurements. Experimental results were compared with XMHD computer simulations, which predicted electron temperatures 1.5 to 3 σ above those measured, and significantly higher density than experiments in both polarities. In this paper, possible sources of this discrepancy are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Effects of polymer grain boundary passivation on organic–inorganic hybrid perovskite field-effect transistors

Despite successful applications of solution-processed organic–inorganic hybrid perovskites (OIHPs) such as archetypical methylammonium lead iodide (MAPI) in high-performance optoelectronic devices including solar cells and light emitting diodes, their application in field-effect transistors (FETs) remains relatively limited due to the unresolved issues caused by ion migration in OIHPs, such as screening of gate electric fields, lowered device on-off ratios and field-effect mobility, and large hysteresis in the FET transfer characteristics. Here, we report improved performances of the MAPI-based FET via a polymer-additive-based grain boundary (GB) passivation approach that suppresses the ion migration. Polycaprolactone (PCL) was incorporated into the MAPI FET as a GB-passivation additive as confirmed by scanning electron and atomic force microscopies. Unlike the typical n-type behavior and large transfer hysteresis in the starting, pristine MAPI FETs, the GB passivation by PCL led to a drastically reduced hysteresis in FET transfer characteristics, while hinting at an ambipolar transport and slight improvement in mobility, indicating a reduced ion migration in the PCL-incorporated MAPI FET. The effect of PCL GB passivation in suppressing ion migration was directly confirmed by the measured, increased activation energy for ion migration in the PCL-incorporated MAPI. Here, the results not only represent the first report of the polymer-additive-based mitigation of the ion migration in the MAPI FET but also suggest potential utilities of the approach for enabling high-performance OIHP FETs and electronic devices in general.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Baryonic effects in the Effective Field Theory of Large-Scale Structure and an analytic recipe for lensing in CMB-S4

Upcoming Large-Scale Structure surveys will likely become the next leading sources of cosmological information, making it crucial to have a precise understanding of the influence of baryons on cosmological observables. The Effective Field Theory of Large-Scale Structure (EFTofLSS) provides a consistent way to predict the clustering of dark matter and baryons on large scales, where their leading corrections in perturbation theory are given by a simple and calculable functional form even after the onset of baryonic processes. In this paper, we extend the two-fluid-like system up to two-loop order in perturbation theory. Along the way, we show that a new linear counterterm proportional to the relative velocity of the fluids could generically be present, but we show that its effects are expected to be small in our universe. Regardless, we show how to consistently perform perturbation theory in the presence of this new term. We find that the EFTofLSS at two-loop order can accurately account for the details of baryonic processes on large scales. Additionally, we compare our results to a hydrodynamical N-body simulation at many redshifts and find that the counterterms associated with the leading corrections to dark matter and baryons start to differ between redshifts z ≈ 3 and z ≈ 2, signaling the onset of star-formation physics. We then use these fits to compute the lensing power spectrum, show that the understanding of baryonic processes will be important for analyzing CMB-S4 data, and show that the two-loop EFTofLSS accurately captures these effects for ℓ ≲ 2000. Our results are also potentially of interest for current and future weak lensing surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Large anomalous Nernst effect and topological Nernst effect in the noncollinear antiferromagnet NdMn 2⁢ Ge 2

ThCr 2 Si 2 -type NdMn 2 Ge 2 was recently proposed to be a magnetic skyrmion candidate exhibiting the topological Hall effect. In this work, we report magnetic, electronic, and thermoelectric measurements for NdMn 2 Ge 2 single crystals. We show that, in the canted antiferromagnetic phase and the conical magnetic phase with a large out-of-plane ferromagnetic component, this system exhibits both an anomalous Nernst effect and a topological Nernst effect. Here we argue that NdMn 2 Ge 2 is a unique magnetic material, with its topological characteristics associated with the Berry phases in both real space and momentum space.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Effects on Structure’s Electromagnetic Shielding Effectiveness Considering Penetrating Cables Coupling Energy from HEMP Event

The threat of weaponized electromagnetic pulse (EMP) is a serious factor in defining power system resilience. Without adequate knowledge regarding the interaction between EMP and power system infrastructure, system personnel may be unable to plan for and operate during an EMP event and major blackouts could occur. This work studies the interaction between EMP and structures, specifically analyzing the shielding effectiveness of buildings emulating power generation facilities. The main focus is to determine how penetrating cables affect the structure’s shielding effectiveness. Several cable parameters including height above ground, radius, termination configuration, and length are analyzed via computational electromagnetic simulations. Results demonstrated penetrating cables can significantly diminish a structure’s shielding effectiveness, especially the electric field. Length of cable is the most influential parameter.

Mignardot, David↗