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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Wettability and capillary effects: Dynamics of pinch-off in unconstricted straight capillary tubes

We study the interfacial evolution of immiscible two-phase flow within a capillary tube in the partial wetting regime using direct numerical simulation. We investigate the flow patterns resulting from the displacement of a more viscous fluid by a less viscous one under a wide range of wettability conditions. We find that beyond a wettability dependent critical capillary number, a uniform displacement by a less viscous fluid can transition into a growing finger that eventually breaks up into discrete blobs by a series of pinch-off events for both wetting and non-wetting contact angles. This study validates previous experimental observations of pinch-off for wetting contact angles and extends those to non-wetting contact angles. We find that the blob length increases with the capillary number. We observe that the time between consecutive pinch-off events decreases with the capillary number and is greater for more wetting conditions in the displaced phase. Here, we further show that the blob separation distance as a function of the difference between the inlet velocity and the contact line speed collapses into two monotonically decreasing curves for wetting and non-wetting contact angles. For the phase separation in the form of pinch-off, this work provides a quantitative study of the emerging length and time scales and their dependence on the wettability conditions, capillary effects, and viscous forces.

42 ENGINEERING↗
DOE OSTI2022

Modeling of Supercritical CO2 Shell-and-Tube Heat Exchangers Under Extreme Conditions. Part I: Correlation Development

Abstract High-temperature supercritical CO2 Brayton cycles are promising possibilities for future stationary power generation and hybrid electric propulsion applications. Heat exchangers are critical components in supercritical CO2 thermal cycles and require accurate correlations and comprehensive performance modeling under extreme temperatures and pressures. In this paper (Part I), new Colburn and friction factor correlations are developed to quantify shell-side heat transfer and friction characteristics of flow within heat exchangers in the shell-and-tube configuration. Using experimental and computational fluid dynamics (CFD) data sets from existing literature, multivariate regression analysis is conducted to achieve correlations that capture the effect of multiple critical geometric parameters. These correlations offer superior accuracy and versatility as compared to previous studies and predict the thermohydraulic performance of about 90% of the existing experimental and CFD data within ±15%. Supplementary thermohydraulic performance data are acquired from CFD simulations with supercritical CO2 as working fluid to validate the developed correlations and demonstrate its capability to be applied to supercrtical CO2 heat exchangers.

Engineering↗
DOE OSTI2022

Modeling of Supercritical CO2 Shell-and-Tube Heat Exchangers Under Extreme Conditions: Part II: Heat Exchanger Model

Abstract Heat exchangers play a critical role in supercritical CO2 Brayton cycles by providing necessary waste heat recovery. Supercritical CO2 thermal cycles potentially achieve higher energy density and thermal efficiency operating at elevated temperatures and pressures. Accurate and computationally efficient estimation of heat exchanger performance metrics at these conditions is important for the design and optimization of sCO2 systems and thermal cycles. In this paper (Part II), a computationally efficient and accurate numerical model is developed to predict the performance of shell-and-tube heat exchangers (STHXs). Highly accurate correlations reported in Part I of this study are utilized to improve the accuracy of performance predictions, and the concept of volume averaging is used to abstract the geometry and reduce computation time. The numerical model is validated by comparison with computational fluid dynamics (CFD) simulations and provides high accuracy and significantly lower computation time compared to existing numerical models. A preliminary optimization study is conducted and the advantage of using supercritical CO2 as a working fluid for energy systems is demonstrated.

Engineering↗
DOE OSTI2022

Experimental Study of Eutectic Molten Salts NaCl/KCl/ZnCl2 Heat Transfer Inside a Smooth Tube for High-Temperature Application

Abstract Eutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are promising for being used as high-temperature heat transfer fluid (HTF) and thermal energy storage (TES) materials in a wide range of temperatures from 230 °C to 750 °C in concentrated solar thermal power systems. To conduct measurement of the heat transfer coefficient of the molten salt at high temperatures, a circulation system and instrumentation of flow and heat transfer was constructed. Experimental measurement of the convective heat transfer coefficients of NaCl-KCl-ZnCl2 (molar fraction: 13.8–41.9–44.3%) inside tubes has been accomplished to find the most suitable heat transfer correlations. Experience of salt processing and operation of the high-temperature heat transfer test system was obtained. Two correlations, Dittus-Boelter equation and Gnielinski’s correlation for Nusselt number against Reynolds number and Prandtl number, are evaluated using the test results, and the latter correlation is recommended due to its better agreement of prediction against tested data.

Energy & Fuels↗
DOE OSTI2022

Shock Tube and Flame Speed Measurements of 2,4,4-Trimethyl-1-Pentene: A Co-Optima Biofuel

Abstract The combustion of 2,4,4-trimethyl-1-pentene (diisobutylene, C8H16), which is a biofuel and a component of surrogate fuels, is examined in this work. Carbon monoxide time–histories and ignition delay times are collected behind reflected shock waves utilizing a shock tube and mid-infrared laser absorption spectroscopy. Measurements were obtained near 10 atm pressure during stoichiometric oxidation of 0.15%C8H16/O2/Ar. Simulated results from chemical kinetic models are provided, and sensitivity analyses are used to discuss differences between models for both ignition delay times and carbon monoxide formation. In addition, laminar burning speeds are obtained at 1 atm, 428 K, and equivalence ratios, phi, between 0.91 and 1.52 inside a spherical chamber facility. Measured burning speeds are found to be less than that of ethanol over the equivalence ratio span. Burning speed measurements are compared to predictions of chemical kinetic mechanisms and are in agreement for the richest conditions; however, at lean conditions, the model predicts a far slower-burning speed. The maximum burning speed occurs at an equivalence ratio of 1.08 with a magnitude of 0.70 m/s. The current work provides the crucial experimental data needed for assessing the feasibility of this biofuel and for the development of future combustion chemical kinetics models.

Energy & Fuels↗
DOE OSTI2020

Experimental investigation of the crush performance of prepreg platelet molding compound tubes

This work presents an experimental study characterizing the crush performance of hollow cylindrical tubes made with prepreg platelet molding compound (PPMC). PPMC is a composite material system that uses platelets from chopped and slit unidirectional prepreg as the basis for a molding compound. This material system has a higher fiber volume fraction and better mechanical properties than traditional short fiber systems and can be molded into complex geometries unlike continuous fiber systems. As such, this material system shows promise for use with complex structural members in vehicles. The failure morphology and specific energy absorption of the material are evaluated with different thickness-to-diameter geometries and test speeds. In addition, this work investigates how PPMC components compare to traditional continuous fiber components and finds that PPMC performs as well as continuous fiber layups with similar effective laminate stiffnesses.

Materials Science↗
DOE OSTI2021

Pulse-burst spontaneous Raman thermometry of unsteady wave phenomena in a shock tube

A high-speed temperature diagnostic based on spontaneous Raman scattering (SRS) was demonstrated using a pulse-burst laser. The technique was first benchmarked in near-adiabatic H 2 -air flames at a data-acquisition rate of 5 kHz using an integrated pulse energy of 1.0 J per realization. Both the measurement precision and accuracy in the flame were within 3% of adiabatic predictions. Furthermore, this technique was then evaluated in a challenging free-piston shock tube environment operated at a shock Mach number of 3.5. SRS thermometry resolved the temperature in post-incident and post-reflected shock flows at a repetition rate of 3 kHz and clearly showed cooling associated with driver expansion waves. Collectively, this Letter represents a major advancement for SRS in impulsive facilities, which had previously been limited to steady state regions or single-shot acquisition.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Multipacting analysis of the SNS drift tube linac (DTL) RF vacuum window using Spark3d

An ongoing study at the Spallation Neutron Source (SNS) seeks to better understand and address potential multipacting issues associated with the Drift Tube Linac (DTL) RF vacuum windows. An analysis of several failed operational windows showed indications of excessive RF heating on the TiN-coated alumina ceramics. Coupled with vacuum bursts and arcing during conditioning and/or operational periods, these problems have been attributed to electron activity likely caused by multipacting. The status of the study, 3-D electromagnetic simulation results, mitigating techniques and a future experimental plan for studying multipacting in the SNS DTL vacuum windows are presented.

Toby, George↗
DOE OSTI2020

Performance of CsI:Tl Cyrstal with a Spectrum Matching Photomultiplier Tube

This report documents an effort to improve the energy resolution for a thallium doped cesium iodide (CsI:T1) scintillator paired with a spectrum matching photomultiplier tube (PMT). A comparison of the differences in the pulse height spectra from thallium doped (CsI:T1) and sodium doped (CsI:Na) single crystals with PMTs of different spectrum responses was performed. Results show that energy resolution of the detector only improves 0.5% at room temperature when these scintillators are coupled with a spectrum matching PMT. Based on a spectrum matching PMT, the best results for energy resolution are 7.39% and 7.88% for CsI:T1 and CsI:Na scintillators, respectively. The improvement is primarily attributed to the increase of photon statistics from the increase of photons (N) being detected in the spectrum matching PMT. Other factors, such as optical quantum yield and non-proportionality of the CsI:T1 and CsI:Na crystals, that can affect the energy resolution were also studied and reported. The results indicate that although the use of a spectrum matching PMT enhances the photon statistics, it also exacerbates the nonproportionality response. Consequently, a promised improvement on energy resolution due solely to photon statistics was not fully realized.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Replacing photomultiplier tubes with silicon photomultipliers for nuclear safeguards applications

Photomultiplier tubes (PMTs) have been used for decades as the default light detection technology for scintillator-based radiation monitors. PMTs come with a handful of disadvantages, however, including large volume usage, fragility, high-voltage requirements, and susceptibility to magnetic fields. Arrays of silicon photomultipliers (SiPMs) are a possible alternative to PMTs providing similar performance while offering improvements in the areas listed. We focus on straightforward “drop-in replacement” evaluations by imposing a single channel output of the SiPM signal and a backend electronics data acquisition and analysis routine identical to that used for PMTs. In the realm of nuclear safeguards, the primary performance metric for gamma spectroscopy is detector resolution, and for neutron detection it is pulse shape discrimination (PSD) to separate neutron and gamma signals. In this work we present the results of replacing a PMT with a 2” x 2” SiPM array mounted, in turn, to the same 2” x 2” cylindrical sodium iodide (NaI) crystal. The ultimate comparison for this gamma spectrometry is confirmation of uranium enrichment standards, ranging from depleted uranium to 93% highly enriched uranium (HEU), by analyzing the resulting spectra with both a simple integral scaling in key energy regions of the spectrum, as well as with the NaIGEM software package. In addition to the gamma spectroscopy work, we will present the latest results on comparing the PSD capabilities of a 4” x 4” SiPM array to a 5” PMT. As with the gamma spectroscopy evaluations, the light detectors are mounted in turn to the same liter-scale organic scintillators. This neutron-focused work includes evaluation of prototype SiPM readout boards with a single output signal summed over 256 individual SiPM pixels, and evident tradeoffs between PSD capability and fast response.

42 ENGINEERING↗
DOE OSTI2020

Mechanical Testing of FeCrAl Tubing

The axial tensile properties of C26M tube were successful measured at Los Alamos National Laboratory. Test were conducted at a constant strain rate of 10 -3 s -1 and three different temperatures (22, 300, and 600°C). As typically expected, an increase in the testing temperature lead to a decrease in both the yield stress (YS), from 710 to 273 MPa, and ultimate tensile strength (UTS), from 730 to 290 MPa. The ultimate tensile strength was observed almost immediately post-yielding for all test conditions, and thus the uniform elongation was limited to 1.2-1.6%. The total elongation of the 600°C specimens was notably higher (~47%) than both the 22 and 300°C specimens, which exhibited a similar response (~10%).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Advanced Multi-Tube Mixer Combustion for 65% Efficiency (Final Report)

This project targeted advanced low NOx combustion for advanced gas turbines capable of 65%, or greater, efficiency in combined cycle application. This technology advancement has further potential to benefit gas turbines used in coal based IGCC applications with pre-combustion carbon capture and hydrogen as the resulting fuel. The program developed and synthesized the most advanced combustion system capable of achieving low NOX emissions up to turbine inlet temperatures of 3100F while also supporting the load-following needs of a modern grid. The combustion system contributes to the overall gas turbine efficiency goal by setting the maximum cycle temperature achievable for a given NOX level and by minimizing the through-combustor air flow pressure drop. Focus areas for this project targeted maximizing the turbine inlet temperature entitlement, as constrained by emissions considerations. The design also minimized parasitic air flow pressure drop by using advanced cooling techniques and performance materials selections and by minimizing hot surface area. These two technology objectives (maximum, emissions-compliant cycle temperature and minimum air flow pressure drop) were integrated into a prototype design. The primarily analytical project sought to identify the most promising technologies to meet these objectives. Additional critical “jugular” data were obtained from multi-tube mixer tests to realize the potential of leveraging “micro flames” for minimizing overall hot surface area. This data was used, in conjunction with an understanding of advanced material and cooling design technologies, to analytically develop multiple design concepts. Phase I focused on in-depth engineering analysis and design, with minimal supporting laboratory testing to enable a selection of the top three combustion architectures for achieving these overall objectives. Phase II of the program developed the selected design through a combination of sub-scale testing and analytical efforts. Early tests included a cold-flow cascade to establish aerodynamic performance characteristics and a sub-scale fired test at GE Global Research in Niskayuna, NY, to establish cooling and heat transfer characteristics in conjunction with combustion performance. The data from these tests validated the analytical models to ultimately design a full-scale, test article to evaluate at prototypical pressure and temperature conditions at GE Gas Power’s Gas Turbine Technology Laboratory in Greenville, SC. GE Gas Power also developed, tested, and recommended a suitable seal design to be applied to the unique features of the combustor. To assess the technology challenges from prospective future production of the combustor from a ceramic matrix composite material, screening tests of Environmental Barrier Coatings were completed.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2022

A Robotics Enabled Eddy Current Testing System for Autonomous Inspection of Heat Exchanger Tubes

The objective of the project is to develop a robotics enabled eddy current testing system (REECTS) in automatic probe deployment, inspection, and data acquisition and analysis. The main functions of the REECTS are to: 1) identify geometry and locations of heat exchange tubes with assistance of an imaging recognition system; 2) precisely control the position and motion speed of ECT probes by an adaptive control system; 3) facilitate data analysis and real-time decision making for autonomous inspection assisted by machine learning algorithms.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2022

Pressurized Tube Creep Testing of Graded Transition Joints (GTJ) for G91 and 347H Base Metals

This report briefly describes part of the research activities dedicated to a DOE FE project, graded transition joints (GTJ) development for G91 and 347H steels. The task was focused on pressurized tube creep testing on the 3D-printed GTJ materials. A specimen with reduced gage section is developed that includes G91, GTJ, and 347H subsections. A tapered GTJ subsection is introduced to address the technical challenge of mechanical testing with mismatched rupture times of the base metals. The report provides the descriptions of basic considerations, specimen preparation, testing system, and experimental results along with main findings.

36 MATERIALS SCIENCE↗
DOE OSTI2023

RF Power Estimates for LAMP Drift-Tube Linac

The LANSCE Modernization Project (LAMP) concept includes a drift-tube proton linac (DTL) from 3 MeV to 100 MeV consisting of 6 tanks. This technical note provides estimates of RF power required for the LAMP DTL tanks using DTLfish modeling.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Modeling a Miniature Voitenko-Like Explosively-Driven Shock Tube Using FLAG

Using the FLAG hydrocode, hypervelocity plasma jets observed in miniature explosively–driven shock tube experiments have been modeled with a relative error in velocity of less than 5% (a reduction from previous attempts which yielded errors of 37%). This suggests that FLAG may be well-suited to model HE systems involving the acceleration of gases through complex crack systems in HE devices: A phenomenon not accurately captured using current modeling capabilities. The Eulerian hydrocode model presented here leverages AMR to reduce computational cost and, importantly, it was found that mesh resolution and model geometry each significantly affected the average jet velocity. The model and the results are detailed here together with comments on challenges during its development and avenues for future work.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Interfacing Atmospheric Flow Tube to Ion Mobility Spectrometry: FY 2021 Final Report

An atmospheric flow tube (AFT) provides extended ion-molecule reaction times of 2-3 seconds compared to milliseconds in typical mass spectrometers. This results in several orders of magnitude enhanced sensitivity allowing for vapor detection at the parts-per-quadrillion levels when an AFT is coupled to a mass spectrometer (MS). The goal of this project was to demonstrate the feasibility of integrating an AFT ionization source to a more portable ion mobility spectrometer (IMS). This project was successful in integrating AFT to IMS, as shown in Figure ES.1. The PNNL team demonstrated measurable ion signal from an AFT-IMS with a Faraday plate detector. Reasonable ion signals were detectable at low flow rates approaching 1 m/s. This is close to the flow rates used with the AFT-MS, which has demonstrated parts-per-quadrillion vapor detection. Vapor detection enables non-contact detection of a variety of illicit substances for various applications including cargo screening, mail sorting facilities, and checkpoints. With further improvements to enhance detection, AFT-IMS has the potential to allow ultra-trace vapor detection in a more portable device.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Transfer Tube Material Properties Obtained from Test Data

A series of tension and compression tests were performed on typical transfer tubes made of 304L corrosion-resistant steel. The results were compiled and converted to true stress and true plastic strain for comparison to numerical models. The parameters of a Johnson-Cook constitutive model and fracture criterion were calibrated to mimic the test data. Comparisons were made between the converted data and the empirical formulas in the Johnson-Cook model. Simulations were performed to evaluate the implementation of the formula in finite element analysis, and the parameters were adjusted to improve the correlation.

36 MATERIALS SCIENCE↗