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At least 145 records · Page 8

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NASA NTRSDate not supplied

Low Leakage Valves for Long Duration Missions

This paper presents a status update on the low leakage cryogenic test valves currently under development at NASA’s Marshall Space Flight Center. These valves consist of a 3-inch isolation valve, a 3-inch relief valve, and an 8-inch pre-valve. Each of these valves contain a self-aligning seat and poppet design to significantly reduce the quantity of propellant flowing past the seat when the valve is in its closed state (internal leakage). This self-aligning design utilizes a metallic poppet head with five degrees of freedom and is intended to allow a valve to be more tolerant of the imperfect contacts and misalignments that are commonly found between sealing surfaces. This paper covers the test articles, facilities, objectives, and preliminary results.

Cryogenic Fluid Management↗

NASA NTRS2023

Low Leakage Valves for Long Duration Missions

Cryogenic Fluid Management↗

NASA NTRSDate not supplied

Advancements in Low Leakage Valves for Long Duration Missions

This paper reports on the advancements in the development of low-leakage valve technology for cryogenic environments, currently under development at NASA’s Marshall Space Flight Center. These valves consist of a 3-inch isolation valve, a 3-inch relief valve, and an 8-inch pre-valve. Each of these valves contain a self-aligning seat and poppet design to significantly reduce the quantity of propellant flowing past the seat when the valve is in its closed state (internal leakage). This self-aligning design utilizes a metallic poppet head with five degrees of freedom and is intended to allow a valve to be more tolerant of the imperfect contacts and misalignments that are commonly found between sealing surfaces. This paper covers the test articles, facilities, objectives, and test results.

Cryogenic Fluid Management↗

DOE OSTI2020

Improving air leakage prediction of buildings using the fan pressurization method with the Weighted Line of Organic Correlation

In many countries, the fan pressurization method is the most frequently chosen approach for measuring the air leakage of houses. The measurements are usually performed at pressures that far exceed pressures to which buildings are exposed to under normal conditions. A fit of these tests to the power-law formulation allows an extrapolation to data points outside the measured pressure range. With the Ordinary Least Square (OLS) fitting method, the pressure exponent and flow coefficient can be determined. However, the measurement results are highly sensitive to uncertainties induced by external factors like changing wind conditions during the tests, which is neglected by OLS. This may lead to errors in the prediction of flows at lower pressures. The Weighted Line of Organic Correlation (WLOC) is an alternative approach and takes measurement uncertainty into account. In this paper, a statistical analysis of an extensive data set of pressurization measurements has been performed. Both regression techniques have been compared for almost 7500 fan pressurization measurements of six houses in 109 different house leak configurations. The variability in predicting pressure exponent and flow coefficient for both WLOC and OLS regression was analyzed using probability density functions. It was found that the Weighted Line of Organic Correlation significantly decreases the uncertainty in predicting pressure exponent, flow coefficient, and other low-pressure air leakage metrics compared to the Ordinary Least Square fitting. Here, the authors highly recommend the implementation of WLOC in current measurement standards and test equipment.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2024

De-risking fault leakage risk and containment integrity for subsurface storage applications

The subsurface is pivotal in the energy transition, for the sequestration of CO 2 and energy storage. It is crucial to understand to what extent geological faults may form leakage pathways that threaten the containment integrity of these projects. Fault flow behavior has been studied in the context of hydrocarbon development, supported by observations from wells drilled through faults, but such observations are rare in geoenergy projects. Focusing on mechanical behavior as early indicator of potential leakage risks, a probabilistic Coulomb Failure Stress workflow is developed and demonstrated using data from the Decatur CO 2 sequestration project to rank faults based on their containment risk. The analysis emphasizes the importance of fault throw relative to reservoir thickness and pore pressure change in assessing reactivation risks. Integrating this mechanical assessment with geological and dynamic fault analyses contributes to derisking fault containment for geoenergy applications, providing valuable insights for the successful development of subsurface storage projects.

58 GEOSCIENCES↗

DOE OSTI2019

Modeling dislocation-related leakage currents in GaN p-n diodes

Finite element analysis software was used to model and visualize two p-n junction models: one with a single threading dislocation (TD) and a control model without a dislocation. TDs are modeled as a Gaussian distribution of trap states with an FWHM of 5 nm localized around the r=0 line in a cylindrical coordination such that the linear trap state density was 1 trap/c-translation; this model allows the cylindrical symmetry of the c-plane GaN crystal orientation to be utilized to avoid more computationally intensive 3D models. It was discovered that the interaction of the charged dislocation region with the p-n junction had many notable effects. At zero bias, it was observed that the depletion region width (using the Depletion Approximation) and the maximum electric field were markedly reduced near the dislocation line. More significantly, an asymmetric reduction in the diffusion barrier for electrons (Vbieff=3.03eV) and holes (Vbieff=0.81eV) was observed due to the asymmetric nature of the dislocation band bending related to the doping. The asymmetric reductions in diffusion barriers persisted into VA=2.4V leakage case where asymmetric current profiles for electrons and holes were also observed. Lastly, the diffusion barrier reduction resulted in an additional Shockley-Read-Hall nonradiative recombination leakage caused by a high np-product and trap state density near the intersection of the dislocation with the junction.

Robertson, C. A. (ORCID:0000000300122262)↗

DOE OSTI2022

A unified thermionic and thermionic-field emission (TE–TFE) model for ideal Schottky reverse-bias leakage current

We present a unified thermionic emission (TE) and thermionic-field emission (TFE) model for the ideal reverse-bias leakage current in Schottky junctions. The unified TE–TFE analytical model advances upon previous analytical TFE models by Murphy–Good and Padovani–Stratton, which are the two most widely adopted models by the community, in two major aspects: (i) the applicability of the TFE expression therein is extended to near-zero surface electric fields by an error-function correction, allowing for the calculation of the total current by a nontrivial sum of TE (over-the-barrier current) and TFE (below-the-barrier current) contributions; therefore, an accurate description of the TE-to-TFE transition region is captured analytically for the first time; (ii) image-force lowering is considered with much-simpler correction terms. Comparisons with the reference numerical model show that the unified TE–TFE model has excellent accuracy, as well as a 10 000× reduction in computation time. The unified model is further tested against experimental data from Schottky barrier diodes based on Si, 4H-SiC, GaN, and β-Ga 2 O 3 , revealing accurate extractions of barrier heights and correct descriptions of the ideal reverse leakage characteristics. With the extended applicable range, improved accuracy, and computational efficiency, the unified TE–TFE model is highly valuable for the design and analysis of devices based on Schottky junctions, as well as for potential integration in technology computer-aided design (TCAD) tools.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

The influence of V-defects, leakage, and random alloy fluctuations on the carrier transport in red InGaN MQW LEDs

Red InGaN-based light-emitting diodes (LEDs) exhibit lower internal quantum efficiencies than violet, blue, and green InGaN LEDs due to a reduction in radiative recombination rates relative to non-radiative recombination rates as the Indium composition increases. Additionally, the larger polarization and band offset barriers between high indium content InGaN quantum wells and GaN quantum barriers increase the forward voltage. In blue and green LEDs, random alloy fluctuations and V-defects play a key role in reducing the forward voltage. When V-defects are present, either naturally or intentionally introduced, they create an alternative path for carrier injection into the MQWs through the V-defect sidewalls. This injection mechanism explains the turn-on voltages of green LEDs. However, in InGaN red LEDs, these two phenomena do not reduce the forward voltage as effectively as in blue and green LEDs, and consequently, the computed forward voltage remains significantly higher than the measured one. Furthermore, currents are observed at low voltages before the turn-on voltage (V<ℏω/e=2.0 V) of red LEDs. To address this, we introduce dislocation-induced tail states in the modeling, suggesting that leakage current through these states may play a significant role both below and at turn-on voltages. The simulation also indicates that leakage carriers below turn-on accumulate, partially diffuse in the QWs, screen the polarization-induced barrier in the low injection regime, and further reduce the forward voltage. Despite these beneficial effects, a drawback of dislocation-induced tail states is the enhanced nonradiative recombination in the dislocation line region. This study provides a detailed analysis of device injection physics in InGaN QW red LEDs and outlines potential optimization strategies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Addition of tabulated equation of state and neutrino leakage support to illinoisgrmhd

Here we have added support for realistic, microphysical, finite-temperature equations of state (EOS) and neutrino physics via a leakage scheme to illinoisgrmhd, an open-source GRMHD code for dynamical spacetimes in the einstein toolkit. These new features are provided by two new, nrpy+-based codes: nrpyeos, which performs highly efficient EOS table lookups and interpolations, and nrpyleakage, which implements a new, adaptive mesh refinement (AMR)-capable neutrino leakage scheme in the einstein toolkit. We have performed a series of strenuous validation tests that demonstrate the robustness of these new codes, particularly on the Cartesian AMR grids provided by carpet. Furthermore, we show results from fully dynamical GRMHD simulations of single unmagnetized neutron stars, and magnetized binary neutron star mergers. This new version of illinoisgrmhd, as well as nrpyeos and nrpyleakage, is pedagogically documented in jupyter notebooks and fully open source. The codes will be proposed for inclusion in an upcoming version of the einstein toolkit.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

SWP Summary Report for Individual Legacy Well Leakage Risk Analysis at Farnsworth Unit Site: Open Well Scenario

This report summarizes results of the individual legacy well leakage risk analysis of the Farnsworth Unit site (FWU) for Open Well scenario. NRAP tools Integrated Assessment Model for Carbon Storage (NRAP-IAM-CS) and Reservoir Reduced-Order Model Generator (RROMGen) were used (Dilmore et al., 2016; Pawar et al., 2016; King, 2016). This is part one of the additional analysis addressing SWP BP4 Subtask 7.4.1.2: Extend quantitative brine and CO2 leakage calculations (Chu et al., 2020).

58 GEOSCIENCES↗

DOE OSTI2026

Advancing Building Air Leakage Measurement and Modeling: Measurement of Interior Air Leaks, Experimental Comparison to Conventional Methods, and Building Modeling Characteristics

This report, Advancing Building Air Leakage Measurement and Modeling: Measurement of Interior Air Leaks, Experimental Comparison to Conventional Methods, and Building Modeling Characteristics, developed two new building air leakage measurement methods, experimentally evaluated the performance in comparison to conventional methods, experimentally evaluated the behavior of leaks for specific crack structures, and identified testing constraints and model implications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2021

Prediction of Leakage Current and Depletion Voltage in Silicon Detectors Under Extraterrestrial Radiation Conditions

Silicon detection is a mature technology for registering the passage of charged particles. At the same time it continues to evolve toward increasing radiation tolerance as well as precision and adaptability. For these reasons it is likely to remain a critical element of detection of systems associated with extraterrestrial exploration. Silicon sensor leakage current and depletion voltage depend on the integrated fluence received by the sensor and on its thermal history during and after the irradiation process. For minimal assumptions on shielding and hence on the particle energy spectrum, and using published data on Martian ground temperature, we predict the leakage current density and the depletion voltage, as a function of time, of silicon sensors in transit to and deployed continuously on the Mars surface for a duration of up to 28 Earth-years, for several sensor geometries and a worst-case temperature scenario.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1969

Leakage tester for flat conductor cable connector

U-tube containing liquid indicates pressure differences in a leakage tester. This tube, connecting two containers, indicates that the amount of leakage over a set period of time is calculated from the pressure and gas volume.

Angele, W.↗

NASA NTRS1976

Leakage-free journal bearings

A new concept of a journal bearing is developed which prevents side leakage of the lubricant, thus eliminating the need for sealing and collecting this leakage. The cooling of the bearing is accomplished by the prevailing circumferential flow. An analysis is performed and solutions are given for the bearing geometries and inlet pressures required to achieve the above purpose.

Pinkus, O.↗

NASA NTRS1983

Calculating Static-Seal Leakage Correlation

Operational leakage rates of various working fluids predicted from test data. Method converts leakage through fixed area flow passage from one set of fluid conditions to another. Correction factor improves correlation of measured engine static seal leak rate under test conditions with rate under operating conditions. Potential applications include extrapolating from test conditions to operating condition.

Daniels, C. M.↗

NASA NTRS1983

Effects of flow separation and cove leakage on pressure and heat-transfer distributions along a wing-cove-elevon configuration at Mach 6.9

External and internal pressure and cold-wall heating-rate distributions were obtained in hypersonic flow on a full-scale heat-sink representation of the space shuttle orbiter wing-elevon-cove configuration in an effort to define effects of flow separation on cove aerothermal environment as a function of cove seal leak area, ramp angle, and free-stream unit Reynolds number. Average free-stream Mach number from all tests was 6.9; average total temperature from all tests was 3360 R; free-stream dynamic pressure ranged from about 2 to 9 psi; and wing angle of attack was 5 deg (flow compression). For transitional and turbulent flow separation, increasing cove leakage progressively increased heating rates in the cove. When ingested mass flow was sufficient to force large reductions in extent of separation, increasing cove leakage reduced heating rates in the cove to those for laminar attached flow. Cove heating-rate distributions calculated with a method that assumed laminar developing channel flow agreed with experimentally obtained distributions within root-mean-square differences that varied between 11 and 36 percent where cove walls were parallel for leak areas of 50 and 100 percent.

Deveikis, W. D.↗

NASA NTRS1984

A comparison of experimental and theoretical results for leakage, pressure distribution, and rotordynamic coefficients for annular gas seals

The importance of seal behavior in rotordynamics is discussed and current annular seal theory is reviewed. A Nelson's analytical-computational method for determining rotordynamic coefficients for this type of compressible-flow seal is outlined. Various means for the experimental identification of the dynamic coefficients are given, and the method employed at the Texas A and M University (TAMU) test facility is explained. The TAMU test apparatus is described, and the test procedures are discussed. Experimental results, including leakage, entrance-loss coefficients, pressure distributions, and rotordynamic coefficients for a smooth and a honeycomb constant-clearance seal are presented and compared to theoretical results from Nelson's analysis. The results for both seals show little sensitivity to the running speed over the test range. Agreement between test results and theory for leakage through the seal is satisfactory. Test results for direct stiffness show a greater sensitivity to fluid pre-rotation than predicted. Results also indicate that the deliberately roughened surface of the honeycomb seal provides improved stability versus the smooth seal.

Nicks, C. O.↗

NASA NTRS1984

Analysis for leakage and rotordynamic coefficients of surface-roughened tapered annular gas seals

The present analysis calculates the leakage and rotor-dynamic coefficients for tapered annular gas seals whose rotor and stator have been subjected to different surface roughness treatments. The analysis is demonstrated for the effects of changes in the Space Shuttle Main Engine High Pressure Oxygen Turbopump's turbine interstage seal length, taper, clearance, and fluid prerotation. It is noted that changes in these parameters generally resulted in major changes in leakage and rotordynamic coefficients.

Nelson, C. C.↗