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At least 55 records · Page 3

All sources NASA NTRS DOE OSTI

NASA NTRS1975

Pressure distribution in a converging-diverging nozzle during two-phase choked flow of subcooled nitrogen

Choked flow rates and axial pressure distributions were measured for subcooled nitrogen in a converging-diverging nozzle with a constant area section in the throat region. Stagnation pressures ranged from slightly above saturation to twice the thermodynamic critical pressure. Stagnation temperatures ranged from 0.75 to 1.03 times the thermodynamic critical temperature. The choking plane appears to be at the divergence end of the constant area throat section. At high stagnation pressures the fluid appears to stay liquid well into the constant area throat region; however, at near saturation stagnation pressures it appears that vaporization occurs at or before the entrance to the constant area throat region. The throat-to-stagnation pressure ratio data exhibits an anomalous flat region. This anomaly appears to be fundamentally related to the two-phase process and not merely to the present specific nozzle geometry. The fluid appears to be metastably all liquid below the saturation pressure. The data are compared to various flow models. No model adequately describes the whole range of the experiment.

Simoneau, R. J.↗

NASA NTRSDate not supplied

Gas Phase Effects on Slosh Dynamics

Gas phase effects on slosh dynamics were quantified using computational fluid dynamics (CFD) simulation for a range of propellant and ullage gas combinations. Historical slosh modeling using potential flow solutions typically neglects gas phase effects. Regardless, the results have been shown to compare well with slosh ground tests typically performed with water and air at standard temperature and pressure. CFD analysis reveals that as the liquid-to-gas density ratio decreases, slosh dynamics change due to the relative increase in gas inertia and thus influence on liquid motion. The result is a profound impact on slosh dynamics over certain parameter spaces particularly for liquid hydrogen. Gas phase effects on slosh dynamics should be considered in slosh models especially for liquid hydrogen propellant tanks.

Jacob M Brodnick↗

NASA NTRSDate not supplied

Gas Phase Effects on Slosh Dynamics

Gas phase effects on slosh dynamics were quantified using computational fluid dynamics (CFD) simulation for a range of propellant and gas combinations. Historical slosh modeling using potential flow solutions typically neglects gas phase effects. Regardless, the results have been shown to compare well with slosh ground tests typically performed with water and air at standard temperature and pressure. CFD analysis reveals that as the liquid-to-gas density ratio decreases, slosh dynamics change due to the relative increase in gas inertia and thus influence on liquid motion. The result is a profound impact on slosh dynamics over certain parameter spaces particularly for liquid hydrogen. Gas phase effects on slosh dynamics should be considered in slosh models especially for liquid hydrogen propellant tanks.

Jacob M Brodnick↗

NASA NTRSDate not supplied

Gas Phase Effects on Slosh Dynamics

Jacob M Brodnick↗

NASA NTRS1998

WSR-88D Cell Trends

This report documents the Applied Meteorology Unit's evaluation of the Cell Trends display as a tool for radar operators to use in their evaluation of storm cell strength. The objective of the evaluation is to assess the utility of the WSR-88D graphical Cell Trends display for local radar cell interpretation in support of the 45th Weather Squadron (45 WS), Spaceflight Meteorology Group (SMG), and National Weather Service (NWS) Melbourne (MLB) operational requirements. The analysis procedure was to identify each cell and track the maximum reflectivity, height of maximum reflectivity, storm top, storm base, hail and severe hail probability, cell-based Vertically Integrated Liquid (VIL) and core aspect ratio using WATADS Build 9.0 cell trends information. One problem noted in the analysis phase was that the Storm Cell Identification and Tracking (SCIT) algorithm had a difficult time tracking the small cells associated with the Florida weather regimes. The analysis indicated numerous occasions when a cell track would end or an existing cell would be give a new ID in the middle of its life cycle. This investigation has found that most cells, which produce hail or microburst events, have discernable Cell Trends signatures. Forecasters should monitor the PUP's Cell Trends display for cells that show rapid (1 scan) changes in both the heights of maximum reflectivity and cell-based VIEL. It is important to note that this a very limited data set (four case days). Fifty-two storm cells were analyzed during those four days. The above mentioned t=ds, increase in the two cell attributes for hail events and decrease in the two cell attributes for wind events were noted in most of the cells. The probability of detection was 88% for both events. The False Alarm Rate (FAR) was a 36% for hail events and a respectable 25% for microburst events. In addition the Heidke Skill Score (HSS) is 0.65 for hail events and 0.67 for microburst events. For random forecast the HSS is 0 and that a perfect score is 1.

Wheeler, Mark M.↗

NASA NTRS1999

Two-Phase Quality/Flow Meter

A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.

Moerk, J. Steven↗

NASA NTRS1986

Universal amplitude ratios and the interfacial tension near consolute points of binary liquid mixtures

The interfacial tension of the binary liquid mixtures triethylamine/heavy water, triethylamine/water, and cyclohexane/methanol near their consolute temperatures is determined experimentally by measuring the densities of the phases and the capillary lengths. The results are presented in tables and graphs and compared with published data obtained by other methods and with theoretical predictions. The findings are shown to be in good agreement with previous experiments, confirming the discrepancy between temperature-independent universal amplitude ratios calculated from such data and those predicted by renormalization-group calculations or Monte Carlo simulations of Ising models.

Moldover, M. R.↗

DOE OSTI2025

Challenges in Product Selectivity for Electrocatalytic Reduction of Amine-Captured CO 2 : Implications for Reactive Carbon Capture

CO 2 is a potential feedstock for carbon-based fuels or materials, but is only available in dilute streams. Integrated processes for CO 2 capture and conversion directly valorize the CO 2 captured by sorbent materials, skipping the energetically expensive sorbent regeneration step. Amines are the most heavily studied liquid-phase sorbent materials for CO 2 capture from dilute streams. Amines react with CO 2 in a 2:1 ratio to form the corresponding ammonium carbamate. Ammonium carbamate [NH 4 ][H 2 NCO 2 ] was tested as the substrate using the highly selective and robust CO 2 -to-formate reduction electrocatalyst [( tBu POCOP)Ir(H)(NCCH 3 ) 2 ], where ( tBu POCOP) is the tridentate pincer ligand 2,6-bis(di tert -butyl-phosphonito). When ammonium carbamate was used as the substrate instead of CO 2 , only hydrogen was produced. An equivalent electrolysis with ammonium hexafluorophosphate with CO 2 also resulted in primarily hydrogen. Methyl carbamate and urea were also tested as substrates as proxies for carbamate that do not contain an equivalent of ammonium, and there was also negligible reduction to carbon-based products. These results indicate that the loss of selectivity observed for aminecaptured CO 2 , or ammonium carbamate, is likely due to the generation of the acidic ammonium equivalent as well as the greater challenge of reducing carbamate compared to CO 2 . This study illustrates that catalysts with high selectivity for concentrated CO 2 can favor hydrogen evolution and loss of carbon-based products when amine-captured CO 2 is used instead.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1972

The Rb-Sr age of a crystalline rock from Apollo 16.

Sample 68415 is one of the few large crystalline rocks returned from Apollo 16. A meaningful age may be obtained if the sample studied represents silicate material which was isotopically homogenized at the last time it was melted. It is also assumed that the constituent phases of the sample have remained closed systems subsequent to that time. The material was crushed and separated into different fractions with the aid of heavy liquids. It was found that the mineral separates are mixtures of at least three distinct phases with intrinsically different Rb/Sr ratios. An age of 3.84 aeon was determined.

Papanastassiou, D. A.↗

NASA NTRS1980

Transverse injection of a particle-laden liquid jet in supersonic flow: A three-phase flow

The results of a two part study of the behavior of particle laden liquid jets injected into air are presented. Water was used as the liquid carrier and either 1-37 or 13-44 microns diam. spherical glass beads with a specific gravity of 2.8-3.0 as the particles. The observations were mainly photographic. The breakup of jets injected into still air was investigated as a function of particle loading, and the results were compared to the pure liquid jet case. The jets were found to be more stable with particles present. The length to breakup was increased, and the formation of satellite droplets was suppressed. The penetration and breakup of transverse jets in a Mach 3.0 air stream was studied. The general breakup mechanism of wave formation was found to be the same as for the all liquid case. Significant separation of the phases was observed, and the penetration of the liquid phase was reduced compared to all liquid cases at the same value of the jet to free stream momentum flux ratio.

Schetz, J. A.↗

NASA NTRS1999

Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity

The present investigation reports a study of bubble generation under reduced gravity conditions, using both a co-flow and a cross-flow configuration. This study may be used in the conceptual design of a space-based thermal management system. Ensuing two-phase flow void fraction can be accurately monitored using a single nozzle gas injection system within a continuous liquid flow conduit, as utilized in the present investigation. Accurate monitoring of void fraction leads to precise control of heat and mass transfer coefficients related to a thermal management system; hence providing an efficient and highly effective means of removing heat aboard spacecraft or space stations. Our experiments are performed in parabolic flight aboard the modified DC-9 Reduced Gravity Research Aircraft at NASA Lewis Research Center, using an air-water system. For the purpose of bubble dispersion in a flowing liquid, we use both a co-flow and a cross-flow configuration. In the co-flow geometry, air is introduced through a nozzle in the same direction with the liquid flow. On the other hand, in the cross-flow configuration, air is injected perpendicular to the direction of water flow, via a nozzle protruding inside the two-phase flow conduit. Three different flow conduit (pipe) diameters are used, namely, 1.27 cm, 1.9 cm and 2.54 cm. Two different ratios of nozzle to pipe diameter (D(sub N))sup * are considered, namely (D(sub N))sup * = 0.1 and 0.2, while superficial liquid velocities are varied from 8 to 70 cm/s depending on flow conduit diameter. It is experimentally observed that by holding all other flow conditions and geometry constant, generated bubbles decrease in size with increase in superficial liquid velocity. Detached bubble diameter is shown to increase with air injection nozzle diameter. Likewise, generated bubbles grow in size with increasing pipe diameter. Along the same lines, it is shown that bubble frequency of formation increases and hence the time to detachment of a forming bubble decreases, as the superficial liquid velocity is in-creased. Furthermore, it is shown that the void fraction of the resulting two-phase flow increases with volumetric gas flow rate Q(sub d), pipe diameter and gas injection nozzle diameter, while they decrease with surrounding liquid flow. The important role played by flowing liquid in detaching bubbles in a reduced gravity environment is thus emphasized. We observe that the void fraction can be accurately controlled by using single nozzle gas injection, rather than by employing multiple port injection, since the later system gives rise to unpredictable coalescence of adjacent bubbles. It is of interest to note that empirical bubble size and corresponding void fraction are somewhat smaller for the co-flow geometry than the cross-flow configuration at similar flow conditions with similar pipe and nozzle diameters. In order to supplement the empirical data, a theoretical model is employed to study single bubble generation in the dynamic (Q(sub d) = 1 - 1000 cu cm/s) and bubbly flow regime within the framework of the co-flow configuration. This theoretical model is based on an overall force balance acting on the bubble during the two stages of generation, namely the expansion and the detachment stage. Two sets of forces, one aiding and the other inhibiting bubble detachment are identified. Under conditions of reduced gravity, gas momentum flux enhances, while the surface tension force at the air injection nozzle tip inhibits bubble detachment. In parallel, liquid drag and inertia can act as both attaching and detaching forces, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with our experimental results. However, at higher superficial liquid velocities, as the bubble loses its spherical form, empirical bubble size no longer matches the theoretical predictions. In summary, we have developed a combined experimental and theoretical work, which describes the complex process of bubble generation and resulting two-phase flow in a microgravity environment. Results of the present study can be used in a wide range of space-based applications, such as thermal energy and power generation, propulsion, cryogenic storage and long duration life support systems, necessary for programs such as NASA's Human Exploration for the Development of Space (HEDS).

Pais, S. C.↗

NASA NTRS2000

Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals

Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and Kosterlitz Thouless phase transition has been observed and 2D XY quasi long range order verified. Smectic films have enabled the precise determination of smectic layer electron density and positional fluctuation profile and have been used to show that the interlayer interactions in anti-ferroelectric tilted smectics do not extend significantly beyond nearest neighbors. The interactions which are operative in liquid crystals are generally weak in comparison to those in crystalline phases, leading to the facile manipulation of the order in liquid crystals by external agents such as applied fields and surfaces. Effects arising from weak ordering are significantly enhanced in ultrathin free films and filaments wherein the intermolecular coupling is effectively reduced by loss of neighbors. Over the past four years this research, which we now detail, has produced a host of exciting new discoveries and unexpected results, maintaining the position of the study of freely suspended liquid crystal structures as one of most exciting and fruitful areas of complex fluid physics. In addition, several potentially interesting microgravity free film experiments have been identified.

Clark, Noel A.↗

DOE OSTI2025

Chromium-doped uranium dioxide fuels: A review

UO 2 doped with parts per million CR 2 O 3 powder is considered a potential near term accident tolerant fuel candidate. Here, the results of decades of industry and academic research into Cr-doped UO 2 are analyzed and their shortcomings are critiqued. Focusing on the incorporation mechanisms of Cr into the fuel matrix, we explore a mechanistic understanding of the characteristic properties of Cr-doped UO 2 , notably, enhanced fission gas retention attributed to enlarged grain sizes following sintering, along with marginal improvements in the thermophysical properties. The findings of recent X-ray Adsorption Near Edge Spectroscopy studies were compared and put into conversation with historic data regarding the incorporation of Cr in UO 2 . On the basis of defect mechanisms, the case is made for the substitutional incorporation of Cr governing the lattice solubility but not the enhanced U diffusivity. Instead, Cr/CR 2 O 3 redox chemistry in a well-defined oxygen potential explains the differences in the U diffusivity and O/M ratio. The primary mechanism of doping enhanced grain growth is found to be liquid assisted sintering due to a CRO (1) eutectic phase at the grain boundaries. The role of inhomogeneities in Cr concentration in UO 2 at various length scales across the materials microstructure is highlighted and connected to promising experimental and modeling work to fill in the gaps in the current understanding of Cr-doped UO 2 . The review considers both the open scientific questions and engineering applications to illustrate the deep connections between the practice and theory in the design of accident tolerant nuclear fuels. In conclusion, the review ends with an outline of future works that combine meticulous irradiation studies and high resolution experiments with next generation modeling and simulations techniques empowered by machine learning advances to accelerate the fabrication and adoption of Cr-doped UO 2 light water reactors.

Cleveland, Mack Wesley [Massachusetts Inst. of Tec↗

NASA NTRS1984

Recent advances in LPE GaAs-based solar cells

Several modifications were made to an infinite solution liquid phase epitaxy system that help fabricate both GaAs-based cells and thin cells that effectively reduce power-to-weight ratio for space applications. The most important development is the multiwell crucible for multilayer growth. Using a split crucible in one system, as many as five layers were grown in succession with varying Al levels and dopants. The structures grown were used to produce thin GaAs cells only 10 to 20 microns thick and also to grow cascade cell components. Results of these studies are presented and their applications to the future development of GaAs-based cells are discussed.

Kamath, G. S.↗

NASA NTRS1983

The formation of aligned spheres in miscibility gap systems

The development of regularly sized and spaced rods or spheres in a monotectic system is presently considered in terms of interface breakdown and capillary instability mechanisms between two liquid phases. The most important relationship, which governs the rod-to-aligned spheres transition, is the temperature gradient-to-growth rate ratio that determines the depth of the intercellular nodes. Rods will develop when these nodes are shallow by comparison to rod circumference, and spheres will develop when they are deep.

Schafer, C.↗

NASA NTRS1993

Thermal processing of omicron-terphenyl - A Raman study

Raman spectra from omicron-terphenyl sealed in glass capillary tubes were acquired over temperatures ranging from 233 to 343 K. Over this temperature range, omicron-terphenyl can exist in the solid-crystalline, molten, supercooled-liquid, and amorphous-glassy states. Representative structure-sensitive spectra are presented along with a qualitative description. The lattice spectral feature occurring at a Raman shift of 123/cm displays abrupt changes in profile and intensity as melting and glass transition occur. The intensity ratio of the C-C stretching 996/cm line and C-H stretching line at 1008/cm displays a change related to the transformation of the ordered-crystalline phase to the disordered-liquid or glassy state. At a Raman shift of 1162/cm the solid-crystalline state shows a splitting due to the effect of the crystal field. The possibility of using these structure-sensitive Raman characteristics for in situ diagnostics during materials processing is discussed.

Biswas, A.↗

NASA NTRS1999

Comparison of Techniques for Non-Intrusive Fuel Drop Size Measurements in a Subscale Gas Turbine Combustor

In aviation gas turbine combustors, many factors, such as the degree and extent of fuel/air mixing and fuel vaporization achieved prior to combustion, influence the formation of undesirable pollutants. To assist in analyzing the extent of fuel/air mixing, flow visualization techniques have been used to interrogate the fuel distributions during subcomponent tests of lean-burning fuel injectors. Discrimination between liquid and vapor phases of the fuel was determined by comparing planar laser-induced fluorescence (PLIF) images, elastically-scattered light images, and phase/Doppler interferometer measurements. Estimates of Sauter mean diameters are made by ratioing PLIF and Mie scattered intensities for various sprays, and factors affecting the accuracy of these estimates are discussed. Mie calculations of absorption coefficients indicate that the fluorescence intensities of individual droplets are proportional to their surface areas, instead of their volumes, due to the high absorbance of the liquid fuel for the selected excitation wavelengths.

Zaller, Michelle↗

NASA NTRS1978

Pyroxene stability and the composition of the lunar magma ocean

Data on the liquidus stability fields of pyroxene phases in lunar-like systems are used to predict the crystallization sequence and residual liquid composition of lunar magma oceans. Fractional and equilibrium crystallization of major and trace elements are modeled quantitatively through use of analytical expressions for liquidus phase boundaries. According to the model, a magma ocean that differentiated chiefly at low pressure and contained 6-8 wt% A1203 and a subchondritic Ca/Al ratio probably formed the lunar crust. The chondrite-normalized pattern of heavy REE depletion in the magma ocean could have developed by self-contamination of extensively fractionated liquids, or could have been imparted during accretion.

Longhi, J.↗