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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Dispersing nano- and micro-sized portlandite particulates via electrosteric exclusion at short screening lengths

In spite of their high surface charge (zeta potential ζ = +34 mV), aqueous suspensions of portlandite (calcium hydroxide: Ca(OH) 2 ) exhibit a strong tendency to aggregate, and thereby present unstable suspensions. While a variety of commercial dispersants seek to modify the suspension stability and rheology (e.g., yield stress, viscosity), it remains unclear how the performance of electrostatically and/or electrosterically based additives is affected in aqueous environments having either a high ionic strength and/or a pH close to the particle's isoelectric point (IEP). We show that the high native ionic strength (pH ≈ 12.6, IEP: pH ≈ 13) of saturated portlandite suspensions strongly screens electrostatic forces (Debye length: κ -1 = 1.2 nm). As a result, coulombic repulsion alone is insufficient to mitigate particle aggregation and affect rheology. However, a longer-range geometrical particle–particle exclusion that arises from electrosteric hindrance caused by the introduction of comb polyelectrolyte dispersants is very effective at altering the rheological properties and fractal structuring of suspensions. As a result, comb-like dispersants that stretch into the solvent reduce the suspension's yield stress by 5× at similar levels of adsorption as compared to linear dispersants, thus enhancing the critical solid loading (i.e., at which jamming occurs) by 1.4×. Significantly, the behavior of diverse dispersants is found to be inherently related to the thickness of the adsorbed polymer layer on particle surfaces. These outcomes inform the design of dispersants for concentrated suspensions that present strong charge screening behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of Micro-Structural Dispersity of SiMo Ductile Iron on High Temperature Performance during Static Oxidation

High silicon and molybdenum (SiMo) ductile iron is commonly used for car exhaust systems, and its micro-structural dispersity depends on intrinsic parameters, which include alloy composition and inoculation efficiency, as well as extrinsic factors, such as casting wall thickness and molding material, which define cooling rate during solidification. Micro-structural dispersity is referred to as the degree of heterogeneity of sizes of structural constituencies within the microstructure. A variation in the micro-structural dispersity could impact the high temperature performance of SiMo ductile iron during static oxidation and transient thermo-mechanical loading conditions. In this study, static high temperature tests were performed on SiMo ductile iron solidified in a casting with varying wall thicknesses from 5 mm to 100 mm. The faster solidified specimens (taken from near chilled casting surfaces) had extremely high micro-structural dispersity as compared to the thicker section samples. After thermal exposure, each of the samples were characterized using 2D sections and 3D µCT images, and the results indicated an order of magnitude difference in graphite phase dispersity. The surface degradation was quantified after static oxidation experiments were implemented at temperature intervals between 650 °C and 800 °C. Non-destructive µCT 3D analysis and SEM/EDS were performed on cross sections and used to quantify the scale topology and structure. Carbon analysis was used to decouple the scale formation and decarburization phenomena that occurred within the samples. These methods enabled the quantification of the oxidation of the SiMo cast iron with different micro-structural dispersity levels after being exposed to high temperature static oxidation. Additionally, the complex material behavior during oxidation-assisted transient thermo-mechanical loading will be presented in a separate article.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Viscoelastic Response of Dispersed Entangled Polymer Melts

Any polymer synthesis routes result in molecular weight dispersity DAI, depending on the polymerization mechanism. The lowest dispersity polymers are those made by anionic and atom-transfer radical polymerization, which exhibit relatively narrow distributions DM=g,„1A172 — 1.02-1.04. This small divergence from monodispersity results in significant number of molecules that differ in their molecular weight from the average and their impact on the viscoelastic response remains an open question. Here the effects of low dispersity on stress relaxation and shear viscosity of entangled melts are studied using a coarse-grained model for polyethylene. Polymer melts with chain length dispersity set to follow a Schulz-Zimm distribution of Dm = 1.0 — 1.16 for an entangled polyethylene melt using molecular dynamic simulations. The systems were studied to times up to 800 ,us which is beyond the terminal time. These systems are compared to those with binary and ternary distributions. The stress relaxation functions were extracted from the Green-Kubo relation and from stress-strain relaxation following a uniaxial extension. We find on the entanglement time scale, both the mean squared displacement and the stress relaxation are independent of D m . The tube diameter and the rubbery plateau for entangled dynamics do not depend on D m . At longer times, the terminal relaxation time decreases as the faster motion of the shorter chains results in constraint release for the longer chains. Probing this low dispersity regime opens the way to evaluate the degree of dispersity that affects mechanical properties.

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

Accelerated Self-Healing and Property Recovery in Brush Particle Solids Featuring Brush Dispersity

Brush particles, hybrid materials consisting of polymer chains tethered to particle surfaces, offer tunable properties that make them promising candidates for advanced functional materials. This study investigated the role of chain dispersity in the viscoelastic self-healing of poly (methyl acrylate) (PMA)-based brush particle solids. Increasing the molecular weight dispersity of grafted chains significantly enhanced both strain-to-fracture and toughness of brush particle solids, while the elastic modulus and glass transition temperature were independent of chain dispersity. Cut-and-adhere testing revealed a significant acceleration of the rate of toughness recovery in high-dispersity systems as compared to low-dispersity analogs for which toughness recovery markedly lagged the recovery of Young’s modulus. The results suggest that structure and property recovery in brush particle solids are sensitive to the dynamical heterogeneity of brush canopies and highlight the role of molecular weight dispersity as a design parameter to enable hybrid materials with advanced self-healing ability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A new method for measuring the 3D turbulent velocity dispersion of molecular clouds

ABSTRACT The structure and star formation activity of a molecular cloud are fundamentally linked to its internal turbulence. However, accurately measuring the turbulent velocity dispersion is challenging due to projection effects and observational limitations, such as telescope resolution, particularly for clouds that include non-turbulent motions, such as large-scale rotation. Here, we develop a new method to recover the 3D turbulent velocity dispersion (σv,3D) from position–position–velocity (PPV) data. We simulate a rotating, turbulent, collapsing molecular cloud, and compare its intrinsic σv,3D with three different measures of the velocity dispersion accessible in PPV space: (1) the spatial mean of the 2nd-moment map, σi, (2) the standard deviation of the gradient/rotation-corrected 1st-moment map, σ(c − grad), and (3) a combination of (1) and (2), called the ‘gradient-corrected parent velocity dispersion’, $\sigma _{\mathrm{(p}-\mathrm{grad)}}=(\sigma _{\mathrm{i}}^2+\sigma _{(\mathrm{c}-\mathrm{grad)}}^2)^{1/2}$. We show that the gradient correction is crucial in order to recover purely turbulent motions of the cloud, independent of the orientation of the cloud with respect to the line of sight. We find that with a suitable correction factor and appropriate filters applied to the moment maps, all three statistics can be used to recover σv,3D, with method 3 being the most robust and reliable. We determine the correction factor as a function of the telescope beam size for different levels of cloud rotation, and find that for a beam full width at half-maximum f and cloud radius R, the 3D turbulent velocity dispersion can best be recovered from the gradient-corrected parent velocity dispersion via $\sigma _{v,\mathrm{3D}}= \left[(-0.29\pm 0.26)\, f/R + 1.93 \pm 0.15\right] \sigma _{\mathrm{(p}-\mathrm{grad)}}$ for f/R < 1, independent of the level of cloud rotation or LOS orientation.

Stewart, Madeleine↗
DOE OSTI2021

Dynamic properties of a polaron coupled to dispersive optical phonons

We study static and dynamic properties of an electron coupled to dispersive quantum optical phonons in the framework of the Holstein model defined on a one-dimensional lattice. Calculations are performed using the Lanczos algorithm based on a highly efficient construction of the variational Hilbert space. Even small phonon dispersion has a profound effect on the low-energy optical response. While the upward phonon dispersion broadens the optical spectra due to single-phonon excitations, the downward dispersion has the opposite effect. With increasing dispersion, a multiphonon excitation (MPE) state becomes the lowest excited state of the system at zero momentum and determines the low-frequency response of the optical conductivity where the threshold for optical absorption moves below the single-phonon frequency. Multiphonon states form a well-defined bandlike feature just above the polaron band as clearly seen in the electron spectral function. Low-energy MPEs should be observable in systems with strong optical phonon dispersion in optical as well as angle-resolved photoemission experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Impact of Catalyst Ink Dispersing Solvent on PEM Fuel Cell Performance and Durability

The dispersing solvent used for fuel cell catalyst ink preparation plays a vital role in establishing the resulting morphology of the electrode layers, which in turn will impact the performance of proton exchange membrane (PEM) fuel cells. In this study, we report the impact of various ionomer dispersion solvents on PEM fuel cell performance and durability; two aqueous (1-propanol/water and 2-propanol/water) and several non-aqueous dispersing solvents (ethylene glycol and 1,2-butanediol) are compared. The cathode catalyst layer (CCL) fabricated using inks prepared with 1-propanol/water (3:1, w/w) exhibited the best initial performance followed by the CCL prepared using ethylene glycol. The CCLs made from non-aqueous ethylene glycol and 1,2-butanediol exhibited the best durability upon accelerated stress testing. Scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy indicated that, after the stress test, the distribution of both the Nafion ionomer and Pt nanoparticles within the CCLs prepared with non-aqueous ionomer dispersions underwent less change than those prepared with aqueous dispersions, which is responsible for the improved durability

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Exploiting universal nonlocal dispersion in optically active materials for spectro-polarimetric computational imaging

Recent years have seen significant advancements in exploring novel light-matter interactions such as hyperbolic dispersion within natural crystals. However, current studies have predominantly concentrated on local optical response of materials characterized by a dielectric tensor without spatial dispersion. Here, we investigate the nonlocal response in optically-active crystals with screw symmetries, revealing their lossless, super-dispersive properties compared to traditional optical response functions. We leverage this universal nonlocal dispersion, i.e. the dispersion of optical rotatory power, to explore a novel spectral de-multiplexing scheme compared to conventional gratings, prisms and metasurfaces. We design and demonstrate an ‘Nonlocal-Cam’ - a camera that exploits nonlocal dispersion through sampling of polarized spectral states and the application of computational spectral reconstruction algorithms. The Nonlocal-Cam captures information in both laboratory and outdoor field experiments which is unavailable to traditional intensity cameras - the spectral texture of polarization. Merging the fields of nonlocal electrodynamics and computational imaging, our work paves the way for exploiting nonlocal optics of optically active materials in a variety of applications, from biological microscopy to physics-driven machine vision and remote sensing.

Wang, Xueji [Purdue Univ., West Lafayette, IN (Uni↗
DOE OSTI2021

Measurement and control of optical nonlinearities in dispersive dielectric multilayers

Dispersive dielectric multilayer mirrors, high-dispersion chirped mirrors in particular, are widely used in modern ultrafast optics to manipulate spectral chirps of ultrashort laser pulses. Dispersive mirrors are routinely designed for dispersion compensation in ultrafast lasers and are assumed to be linear optical components. In this work, we report the experimental characterization of an unexpectedly strong nonlinear response in these chirped mirrors. At modest peak intensities <2 TW/cm 2 —well below the known laser-induced damage threshold of these dielectric structures—we observed a strong reflectivity decrease, local heating, transient spectral modifications, and time-dependent absorption of the incident pulse. Through computational analysis, we found that the incident laser field can be enhanced by an order of magnitude in the dielectric layers of the structure. The field enhancement leads to a wavelength-dependent nonlinear absorption, that shows no signs of cumulative damage before catastrophic failure. The nonlinear absorption is not a simply two-photon process but instead is likely mediated by defects that facilitate two-photon absorption. To mitigate this issue, we designed and fabricated a dispersive multilayer design that strategically suppresses the field enhancement in the high-index layers, shifting the high-field regions to the larger-bandgap, low-index layers. This strategy significantly increases the maximum peak intensity that the mirror can sustain. However, our finding of an onset of nonlinear absorption even at ‘modest’ fluence and peak intensity has significant implications for numerous past published experimental works employing dispersive mirrors. Additionally, our results will guide future ultrafast experimental work and ultrafast laser design.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Flammability and dispersion of tritium in confined release scenarios

Ignition of a flammable tritium-air mixture is the most probable means to produce the water form (T 2 O or HTO), which is more easily absorbed by living tissue and is hence ~10,000 times more hazardous to human health when uptake occurs compared to the gaseous form (T 2 or HT; per Mishima and Steele, 2002). Tritium-air mixtures with T 2 concentrations below 4 mol% are considered sub-flammable and will not readily convert to the more hazardous water form. It is therefore desirable from a safety perspective to understand the dispersion behavior of tritium under different release conditions, especially since tritium is often stored in quantities and pressures much lower than is typical for normal hydrogen. The formation of a flammable layer at the ceiling is a scenario of particular concern because the rate of dispersion to nonflammable conditions is slowest in this configuration, which maximizes the time window over which the flammable tritium may encounter an ignition source. This report describes the processes of buoyant rise and dispersion of tritium. Accumulation of flammable concentrations of tritium next to the ceiling is a common safety concern for hydrogen, but this situation can only occur if dispersion rates are slow with respect to rates of release and rise. Theory and simulations demonstrate that buoyancy does not cause regions with flammable concentrations to form within buildings from sources that have previously been mixed to sub-flammable concentrations. A simulated series of tritium release events with their associated dispersion behavior are reported herein; these simulations apply computational fluid dynamics to rooms with three different ceiling heights and a variety of tritium release rates. Safety related quantities from these simulations are reported, including the mass and volume of tritium occurring in a flammable mixture, the presence or absence of a flammable layer at the ceiling, and the time required for dispersion to nonflammable conditions after the end of the tritium release event. These safety metrics are influenced by the magnitude and rate of the tritium release with respect to the air volume in the room and also the momentum of the plume or jet with respect to the ceiling height. Several screening criteria are recommended to assess whether a specific tritium release scenario is likely to form a flammable layer at the ceiling. The methods and results in this modeling study have applicability to explosion safety analysis for other buoyant flammable gases, including the lighter isotopes of hydrogen.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Controlling Factors Analyses of Sediment Dispersal From Source-to-Sink Systems of Lacustrine Rift Basin: A Case Study From Paleogene Shahejie-Dongying Formations of Nanpu Sag, Eastern China

Tectonic activity not only shapes the basic stratigraphic framework of rift basins, but also profoundly affects the sediment dispersal in rift basins. In this study, analyses of heavy mineral assemblages in different periods demonstrate that there are three obvious tectono-sedimentary evolutionary stages (E s 3 –E s 2 , E s 1 –E d 2 , and E d 1 , respectively) in the Paleogene provenance area of Nanpu Sag, and the volume of sand bodies increases from the bottom of the Paleogene Shahejie (E s ) Formation to the top of the Dongying (E d ) Formation in Nanpu Sag. Besides, this study comprehensively utilize the analyses of seismic interpretation, palynology, heavy mineral, and borehole core samples to investigate the controlling factors of sediment dispersal in the rift basin. The assemblages of heavy minerals in different periods reflect the rock composition and catchment area of different provenance areas, and their vertical differences reflect the evolution process of the provenance area and reflect the uplift-denudation process of the provenance area. The results reveal that the synergy of the evolution of tectonic activity and the adjustment of topographical evolution are the main controlling factors of sediment dispersal in Nanpu Sag, while climate change is not the main controlling factor. We conclude that an increased sediment supply rate in the long term reflects the control of tectonic activity on basin topography, rather than climate fluctuations. The differences in morphological modification result in differential sediment dispersal, which is principally related to the differential extrusion of the fault system. The catchment area and provenance distance adjustment is evidenced by the vertical changes of heavy mineral characteristics of single-well and interaction and linkage of boundary faults, and the adjustment of topography evolution. A consideration is that the interaction and linkage of boundary faults and complex subsidence history are multi-directional, and differential evolution of provenance area is universal in lacustrine rift basins, all of this highlights the adjustment of sediment pathways generated by this characteristic of rift basins and emphasizes the importance of controlling factors analyses in understanding differential sediment dispersal that presents in the rift basins. Besides, four sets of sediment dispersal patterns were delineated based on different developmental regions in the rift basin, which are fault segmental point and multi-stage fault terrace, single-stage fault terrace and axial fault valley, axial fault terrace, and paleo-terrace and axial fault valley, respectively. This study has a certain guiding significance for the prediction of the spatial distribution of sand bodies in the rift basin and the exploration of potential oil and gas targets in the rift basin.

Yu, Jifeng↗
NASA NTRS1983

Velocity dispersions of knots in Vela X and Puppis A

Very high resolution spectroscopy of optical emission lines indicates that the velocity dispersions of knots in Vela X and Puppis A result primarily from turbulence within the emitting regions. Line-of-sight velocity dispersions (half-widths at half-maximum) for the observed knots in both remnants are about 20-30 km/s. In Vela X, these include thermal velocity dispersions of roughly 16 km/s for hydrogen and 4 km/s for nitrogen. The knots themselves move randomly relative to each other, with speeds up to 30 km/s in Vela X and between 30-80 km/s in Puppis A. Occasionally, diffuse components of the filaments are observed in Puppis A. These diffuse components have velocity dispersions between 55 and 80 km/s, but the relative contributions of turbulent and thermal motions to the dispersions are unknown. The results are compared with theory and previous observations. Direct photographs may be able to show if the forbidden O III knots are less spatially dispersed than the forbidden N II, forbidden S II, forbidden O II, and H I knots.

Shull, P., Jr.↗
NASA NTRS1986

Ascent trajectory dispersion analysis for WTR heads-up space shuttle trajectory

The results of a Space Transportation System ascent trajectory dispersion analysis are discussed. The purpose is to provide critical trajectory parameter values for assessing the Space Shuttle in a heads-up configuration launched from the Western Test Range (STR). This analysis was conducted using a trajectory profile based on a launch from the WTR in December. The analysis consisted of the following steps: (1) nominal trajectories were simulated under the conditions as specified by baseline reference mission guidelines; (2) dispersion trajectories were simulated using predetermined parametric variations; (3) requirements for a system-related composite trajectory were determined by a root-sum-square (RSS) analysis of the positive deviations between values of the aerodynamic heating indicator (AHI) generated by the dispersion and nominal trajectories; (4) using the RSS assessment as a guideline, the system related composite trajectory was simulated by combinations of dispersion parameters which represented major contributors; (5) an assessment of environmental perturbations via a RSS analysis was made by the combination of plus or minus 2 sigma atmospheric density variation and 95% directional design wind dispersions; (6) maximum aerodynamic heating trajectories were simulated by variation of dispersion parameters which would emulate the summation of the system-related RSS and environmental RSS values of AHI. The maximum aerodynamic heating trajectories were simulated consistent with the directional winds used in the environmental analysis.

Source record↗
NASA NTRS1993

Prediction of three sigma maximum dispersed density for aerospace applications

Free molecular heating (FMH) is caused by the transfer of energy during collisions between the upper atmosphere molecules and a space vehicle. The dispersed free molecular heating on a surface is an important constraint for space vehicle thermal analyses since it can be a significant source of heating. To reduce FMH to a spacecraft, the parking orbit is often designed to a higher altitude at the expense of payload capability. Dispersed FMH is a function of both space vehicle velocity and atmospheric density, however, the space vehicle velocity variations are insignificant when compared to the atmospheric density variations. The density of the upper atmosphere molecules is a function of altitude, but also varies with other environmental factors, such as solar activity, geomagnetic activity, location, and time. A method has been developed to predict three sigma maximum dispersed density for up to 15 years into the future. This method uses a state-of-the-art atmospheric density code, MSIS 86, along with 50 years of solar data, NASA and NOAA solar activity predictions for the next 15 years, and an Aerospace Corporation correlation to account for density code inaccuracies to generate dispersed maximum density ratios denoted as 'K-factors'. The calculated K-factors can be used on a mission unique basis to calculate dispersed density, and hence dispersed free molecular heating rates. These more accurate K-factors can allow lower parking orbit altitudes, resulting in increased payload capability.

Charles, Terri L.↗
NASA NTRS1993

The kinematics of dense clusters of galaxies. II - The distribution of velocity dispersions

From the survey of 31 Abell R above 1 cluster fields within z of 0.02-0.05, we extract 25 dense clusters with velocity dispersions omicron above 300 km/s and with number densities exceeding the mean for the Great Wall of galaxies by one deviation. From the CfA Redshift Survey (in preparation), we obtain an approximately volume-limited catalog of 31 groups with velocity dispersions above 100 km/s and with the same number density limit. We combine these well-defined samples to obtain the distribution of cluster velocity dispersions. The group sample enables us to correct for incompleteness in the Abell catalog at low velocity dispersions. The clusters from the Abell cluster fields populate the high dispersion tail. For systems with velocity dispersions above 700 km/s, approximately the median for R = 1 clusters, the group and cluster abundances are consistent. The combined distribution is consistent with cluster X-ray temperature functions.

Zabludoff, Ann I.↗
NASA NTRS1999

Dispersion of 0.5- to 2-micron aerosol in microG and hypergravity as a probe of convective inhomogeneity in the lung

We used aerosol boluses to study convective gas mixing in the lung of four healthy subjects on the ground (1 G) and during short periods of microgravity (microG) and hypergravity ( approximately 1. 6 G). Boluses of 0.5-, 1-, and 2-micron-diameter particles were inhaled at different points in an inspiration from residual volume to 1 liter above functional residual capacity. The volume of air inhaled after the bolus [the penetration volume (Vp)] ranged from 150 to 1,500 ml. Aerosol concentration and flow rate were continuously measured at the mouth. The dispersion, deposition, and position of the bolus in the expired gas were calculated from these data. For each particle size, both bolus dispersion and deposition increased with Vp and were gravity dependent, with the largest dispersion and deposition occurring for the largest G level. Whereas intrinsic particle motions (diffusion, sedimentation, inertia) did not influence dispersion at shallow depths, we found that sedimentation significantly affected dispersion in the distal part of the lung (Vp >500 ml). For 0.5-micron-diameter particles for which sedimentation velocity is low, the differences between dispersion in microG and 1 G likely reflect the differences in gravitational convective inhomogeneity of ventilation between microG and 1 G.

NASA Discipline Cardiopulmonary↗
NASA NTRS1998

Deposition and dispersion of 1-micrometer aerosol boluses in the human lung: effect of micro- and hypergravity

We performed bolus inhalations of 1-micrometer particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (microG) and in approximately 1.6 G. Boluses of approximately 70 ml were inhaled at different points in an inspiration from residual volume to 1 liter above functional residual capacity. The volume of air inhaled after the bolus [the penetration volume (Vp)] ranged from 200 to 1,500 ml. Aerosol concentration and flow rate were continuously measured at the mouth. The deposition, dispersion, and position of the bolus in the expired gas were calculated from these data. For Vp >/=400 ml, both deposition and dispersion increased with Vp and were strongly gravity dependent, with the greatest deposition and dispersion occurring for the largest G level. At Vp = 800 ml, deposition and dispersion increased from 33.9% and 319 ml in microG to 56.9% and 573 ml at approximately 1.6 G, respectively (P < 0.05). At each G level, the bolus was expired at a smaller volume than Vp, and this volume became smaller with increasing Vp. Although dispersion was lower in microG than in 1 G and approximately 1.6 G, it still increased steadily with increasing Vp, showing that nongravitational ventilatory inhomogeneity is partly responsible for dispersion in the human lung.

Parabolic Flight↗
NASA NTRS2004

Direct Measurements of Eddy Transport and Thermal Dispersion in a High Porosity Matrix

Thermal losses from the hot end to the cold end of a Stirling cycle regenerator due to thermal dispersion through the regenerator matrix may significantly degrade the performance of the machine. Because of poor access to the void spaces within the porous medium, no direct measurements of thermal dispersion have been made and dispersion models have been derived indirectly. This is done by measuring the overall thermal performance of the regenerator and subtracting off the energy transfer caused by molecular conduction and advected enthalpy flows computed from volume-averaged fluid velocity and temperature. In the current program, a large-scale porous matrix consisting of stacked wire screens with a porosity of 90% is installed in a flow rig which is operated in a Reynolds number range that represents Stirling engine regenerator flow. Experiments are conducted to measure turbulent transport of momentum at the exit phase using hot-wires. The relationship of such turbulent transport terms to the thermal dispersion term in the volumetric-averaged energy equation for the regenerator matrix is developed and the measurements are used to determine cross-stream thermal dispersion. A dispersion model based upon the measurements is proposed and compared with models documented in the literature.

Niu, Yi↗