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NASA NTRS1950

Foaming of mixtures of pure hydrocarbons

Mixtures of pure liquid hydrocarbons are capable of foaming. Nine hydrocarbons were mixed in pairs, in all possible combinations, and four proportions of each combination. These mixtures were sealed in glass tubes, and the foaming was tested by shaking. Mixtures of aliphatic with other aliphatic hydrocarbons, or of alkyl benzenes with other alkyl benzenes, did not foam. Mixtures of aliphatic hydrocarbons with alkyl benzenes did foam. The proportions of the mixtures greatly affected the foaming, the maximum foaming of 12 of 20 pairs being at the composition 20 percent aliphatic hydrocarbon, 80 percent alkyl benzene. Six seconds was the maximum foam lifetime of any of these mixtures. Aeroshell 120 lubricating oil was fractionated into 52 fractions and a residue by extraction with acetone in a fractionating extractor. The index of refraction, foam lifetime, color, and viscosity of these fractions were measured. Low viscosity and high index fractions were extracted first. The viscosity of the fractions extracted rose and the index decreased as fractionation proceeded. Foam lifetimes and color were lowest in the middle fractions. Significance is attached to the observation that none of the foam lifetimes of the fractions or residue is as high as the foam lifetime of the original Aeroshell, indicating that the foaming is not due to a particular foaming constituent, but rather to the entire mixture.

LUBRICATING OILS - DISTILLATION↗

NASA NTRS1992

Dielectric constant of liquid alkanes and hydrocarbon mixtures

The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

NASA Program Exobiology↗

NASA NTRSDate not supplied

Demonstration of Capability to Simulate Particle Irregular Shape and Poly-Disperse Mixtures Within Lunar Lander Plume-Surface Interaction

Plume-Surface Interaction (PSI) between lander engine plumes and regolith soil creates hazards in obscuration and contamination by particle clouds, high-energy ejecta streams, and landing area cratering damage. The MSFC Fluid Dynamics Branch is developing simulation tools to offer a predictive PSI capability to NASA customers such as the Human Lander System (HLS) and Commercial Lunar Payload Services (CLPS). The Gas-Granular Flow Solver (GGFS) is the main application tool for coupled gas-particle two-phase flow simulations to predict the range of PSI effects from onset of surface erosion to deep crater formation. GGFS features an Eulerian-Eulerian modeling approach, treating both gas and granular material as interacting continuum phases. Modeling the lunar regolith granular material fluidic characteristics poses special challenges due to complex particle shapes and mixture composition. The lunar regolith is poorly sorted with broad particle size distributions and large fines content. It has significant cohesion, due to interlocking jagged particle shapes. Eulerian granular material flow modeling requires closure formulations for the granular material constitutive models (stress, friction, collisional and kinetic energy dissipation, drag, etc.). While closure models for spherical particles are available from particle kinetic theory, closure models for realistic non-spherical particles must be extracted from unit physics Discrete Element Model (DEM) particle interaction simulations and provided in the form of tabular datasets. The effects of particle irregular shape (non-spherical shape factors, angular particle surface roughness, and interlocking features) are simulated by approximating the particle features in the form of grouped elemental spheres to form composite particles in the DEM simulations. The effects of the wide range of regolith mixture particle sizes and the strong effects of the presence of the small particle sizes results in high cohesion and low porosity of the regolith mixture. The range of particle sizes is simulated by binning the particle sizes into an appropriate finite number of particle-size species and solving the problem as a species mixture. Combining these two modeling approaches enables simulations to capture both, the contributions of the irregular particle shape and the particle size distribution. The integration and maturation of the DEM-based constitutive model database generation process and poly-disperse mixture binning approach into the GGFS simulation framework are proceeding under funding by the NASA Game Changing Development program. The status of current capabilities will be presented in comparisons of crater characteristics resulting for spherical and irregular shape particles, and for mono-, bi-, and tri-disperse mixture simulations of Apollo LM plume-surface interaction. The computational results confirm the significance of including the particle shape and mixture effects. Going forward plans for the full implementation of the general poly-disperse regolith modeling capability and maturation towards NASA project application readiness under the GCD program will be presented.

Peter A Liever↗

NASA NTRSDate not supplied

Demonstration of Capability to Simulate Particle Irregular Shape and Poly-Disperse Mixtures Within Lunar Lander Plume-Surface Interaction

Peter A. Liever↗

NASA NTRS1981

Laboratory measurements of selected optical, physical, chemical, and remote-sensing properties of five water mixtures containing Calvert clay and a nonfluorescing dye

Total suspended solids concentrations ranged from 6.1 ppm to 24.3 ppm and sizes ranged between 1.5 micrometers and 10 micrometers with the most frequently occurring size less than 2 micrometers. Iron concentration was less than 1 percent of the total suspended solids. Nonfluorescing dye concentrations of the two mixtures were 20 ppm and 40 ppm. Attenuation coefficient for the five mixtures ranged from 4.8/m to 21.3/m. Variations in volume scattering function with phase angle were typical. Variations in attenuation and absorption coefficient with wavelength were similar for the mixtures without the dye. Attenuation coefficient of the mixtures with the dye increased for wavelengths less than 600 nm due to the dye's strong absorption peak near 500 nm. Reflectance increased as the concentration of Calvert clay increased and peaked near 600 nm. The nonfluorescent dye decreased the magnitude of the peak, but had practically no effect on the variation for wavelengths greater than 640 nm. At wavelengths less than 600 nm, the spectral variations of the mixtures with the dye were significantly different from those mixtures without the dye.

Usry, J. W.↗

NASA NTRS1987

RL10A-3-3B high mixture ratio qualification program

The results of the high mixture ratio qualification testing of the RL10 engine for the Shuttle/Centaur program are presented. The objective of the engine qualification test was to demonstrate the suitability of the RL10A-3-3B engine for space vehicle flight by subjecting it to the testing specified in RL10A-3-3B Model Specification Number 2295 dated February 1986. The applicable section of the specification is presented. Due to payload volume advantages which can be achieved by increasing the operating mixture ratio of the RL10, a decision was made to qualify the engine to run at a higher mixture ratio. A program was created to qualify the RL10 engine for operation at 15,000 pounds thrust and a nominal 6.0 to 1 mixture ratio. This model of the engine was designated the RL10A-3-3B. The qualification program included three test series as follows: (1) hardware durability and limits test in which the engine completed 23 firings and 4605.7 seconds with 1588.7 seconds at less than 6.6 mixture ratio; (2) preliminary qualification test in which the engine completed 26 firings and 5750 seconds; and (3) qualification test in which the engine completed 26 hot firings and 5693.4 seconds with 905.9 seconds at 6.7 mixture ratio. Several changes in engine hardware were required for operation of the RL10A-3-3B engine in the Space Shuttle which include a duel pressure switch ignition, an oxidizer flow control, and helium plumbing changes.

Vogel, T.↗

NASA NTRS1991

Experimental thermal conductivity, thermal diffusivity, and specific heat values for mixtures of nitrogen, oxygen, and argon

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Perkins, R. A.↗

NASA NTRS1991

Soot formation during combustion of unsupported methanol/toluene mixture droplets in microgravity

Results are reported of an experimental study tracing the influence of liquid composition on soot formation and the burning rate of a droplet composed of a binary miscible mixture of liquids. The mixture components represented a highly sooting fuel, toluene, and a nonsooting fuel, methanol. The toluene concentration in methanol was shown to dramatically influence flame luminosity and soot production. Neither burning rates nor a propensity for flame extinction appeared to be significantly affected by toluene mixture fractions. Five-percent toluene mixture droplets behaved like pure methanol droplets in terms of burning rate, lack of flame luminosity, and extinction. Increasing the toluene concentration in the droplets to 25 percent increased flame luminosity, yet no visible soot agglomerates were observed. The 50-percent-mixture droplets burned with highly luminous flames and large amounts of soot agglomerates collecting inside the flame. All the mixture droplets showed burning rates similar to those of pure methanol and likewise exhibited flame extinction before complete droplet vaporization.

Jackson, G. S.↗

NASA NTRS1996

Isopycnic Phases and Structures in H2O/CO2/Ethoxylated Alcohol Surfactant Mixtures

Ternary mixtures of H2O and CO2 with ethoxylated alcohol (C(i)E(j)) surfactants can form three coexisting liquid phases at conditions where two of the phases have the same density (isopycnic phases). Isopycnic phase behavior has been observed for mixtures containing the surfactants C8E5, C10E6, and C12E6, but not for those mixtures containing either C4E1 or CgE3. Pressure-temperature (PT) projections for this isopycnic three-phase equilibrium were determined for H2O/CO2/C8E5 and H2O/CO2/C10E6 mixtures at temperatures from approximately 25 to 33 C and pressures between 90 and 350 bar. As a preliminary to measuring the microstructure in isopycnic three component mixtures, phase behavior and small angle neutron scattering (SANS) experiments were performed on mixtures of D2O/CO2/ n-hexaethyleneglycol monododecyl ether (C12E6) as a function of temperature (25-31 C), pressure (63.1-90.7 bar), and CO2 composition (0-3.9 wt%). Parameters extracted from model fits of the SANS spectra indicate that, while micellar structure remains essentially unchanged, critical concentration fluctuations increase as the phase boundary and plait point are approached.

Paulaitis, Michael E.↗

NASA NTRS1999

Phase Separation Kinetics in Isopycnic Mixtures of H2O/CO2/Ethoxylated Alcohol Surfactants

Ternary mixtures of H2O and CO2 with ethoxylated alcohol (C(sub i)E(sub j)) surfactants form three coexisting liquid phases at conditions where two of the phases have equal densities (isopycnic phases). Isopycnic phase behavior has been observed for mixtures containing C8E5, C10E6, and C12E6 surfactants, but not for those mixtures containing either C4E1 or C8E3 surfactants. Pressure-temperature (PT) projections for this three-phase equilibrium were determined for H2O/CO2/C8E5 and H2O/CO2/C10E6 mixtures at temperatures from approximately 25 to 33 C and pressures between 90 and 350 bar. Measurements of the microstructure in H2O/CO2/C12E6 mixtures as a function of temperature (25-31 C), pressure (63.1-90.7 bar), and CO2 composition (0-3.9 wt%) have also been carried out to show that while micellar structure remains essentially un-changed, critical concentration fluctuations increase as the phase boundary and plait point are approached. In this report, we present our first measurements of the kinetics of isopycnic phase separation for ternary mixtures of H2O/CO2/C8E5.

Lesemann, Markus↗

NASA NTRS2000

Marangoni Effects on Near-Bubble Microscale Transport During Boiling of Binary Fluid Mixtures

In earlier investigations, Marangoni effects were observed to be the dominant mechanism of boiling transport in 2-propanol/water mixtures under reduced gravity conditions. In this investigation we have examined the mechanisms of binary mixture boiling by exploring the transport near a single bubble generated in a binary mixture between a heated surface and cold surface. The temperature field created in the liquid around the bubble produces vaporization over the portion of its interface near the heated surface and condensation over portions of its interface near the cold surface. Experiments were conducted using different mixtures of water and 2-propanol under 1g conditions and under reduced gravity conditions aboard the KC135 aircraft. Since 2-propanol is more volatile than water, there is a lower concentration of 2-propanol near the hot surface and a higher concentration of 2-propanol near the cold plate relative to the bulk quantity. This difference in interface concentration gives rise to strong Marangoni effects that move liquid toward the hot plate in the near bubble region for 2-propanol and water mixtures. In the experiments in this study, the pressure of the test system was maintained at about 5 kPa to achieve the full spectrum of boiling behavior (nucleate boiling, critical heat flux and film boiling) at low temperature and heat flux levels. Heat transfer data and visual documentation of the bubble shape were extracted from the experimental results. In the 1-g experiments at moderate to high heat flux levels, the bubble was observed to grow into a mushroom shape with a larger top portion near the cold plate due to the buoyancy effect. The shape of the bubble was somewhat affected by the cold plate subcooling and the superheat of the heated surface. At low superheat levels for the heated surface, several active nucleation sites were observed, and the vapor stems from them merged to form a larger bubble. The generation rate of vapor is moderate in this regime and the bubble shape is cylindrical in appearance. In some instances, the bubble interface appeared to oscillate. At higher applied heat flux levels, the top of the bubble became larger, apparently to provide more condensing interface area adjacent to the cold plate. Increasing the applied heat flux ultimately led to dry-out of the heated surface, with conditions just prior to dryout corresponding to the maximum heat flux (CHF). A more stable bubble was observed when the system attained the minimum heat flux (for film boiling). In this regime, most of the surface under the bottom of the bubble was dry with nucleate boiling sometimes occuring around the contact perimeter of the bubble at heated surface. Different variations (e.g. gap between two plates, molar concentration of the liquid mixture) of the experiments were examined to determine parametric effects on the boiling process and to determine the best conditions for the KC135 reduced gravity tests. Variation of the gap was found to have a minor impact on the CHF. However, reducing the gap between the hot and cold surface was observed to significantly reduce the minimum heat flux for fixed molar concentration of 2-propanol. In the reduced gravity experiments aboard the KC135 aircraft, the bubble formed in the 6.4 mm gap was generally cylindrical or barrel shaped and it increased its extent laterally as the surface superheat increased. In reduced gravity experiments, dryout of the heated surface under the bubble was observed to occur at a lower superheated temperature than for 1g conditions. Observed features of the boiling process and heat transfer data under reduced gravity will be discussed in detail. The results of the reduced gravity experiments will also be compared to those obtained in comparable 1g experiments. In tandem with the experiments we are also developing a computational model of the transport in the liquid surrounding the bubble during the boiling process. The computational model uses a level set method to model motion of the interface. It will incorporate a macroscale treatment of the transport in the liquid gap between the surfaces and a microscale treatment of transport in the regions between the bubble interface and the solid surfaces. The features of the model will be described in detail. Future research directions suggested by the results to date will also be discussed.

V. Carey↗

NASA NTRS1996

Near azeotropic mixture substitute for dichlorodifluoromethane

The present invention comprises a refrigerant mixture having two halocarbon components. The first component is present in a mole fraction of about 0.7 to less than 1.0 while the second component is present in a mole fraction of more than 0.0 to about 0.3. The first component is CH.sub.2 FCF.sub.3. The second component can be CHClFCF.sub.3, CH.sub.3 CClF.sub.2, a mixture of CHClFCF.sub.3 and CH.sub.3 CClF.sub.2, a mixture of CHF.sub.2 CH.sub.3 and CHClFCF.sub.3, a mixture of CHF.sub.2 CH.sub.3 and CH.sub.3 CClF.sub.2, or a mixture of CHClFCF.sub.3, CH.sub.3 CClF.sub.2 and CHF.sub.2 CH.sub.3. The preferred embodiment of this invention comprises about 0.7 to less than 1.0 mole fraction CH.sub.2 FCF.sub.3, and more than 0.0 to about 0.3 mole fraction of a mixture of CHClFCF.sub.3 and CH.sub.3 CClF.sub.2. The most preferred embodiment of this invention comprises about 0.7 to less than 1.0 mole fraction CH.sub.2 FCF.sub.3 and more than 0.0 to about 0.3 mole fraction CH.sub.3 CClF.sub.2. The resulting refrigerant has a vapor pressure close to-that of CF.sub.2 Cl.sub.2, a nearly constant vapor pressure with evaporation, and is substantially less damaging to the Earth's ozone layer than CF.sub.2 Cl.sub.2.

Jones, Jack A.↗

NASA NTRS2011

Exploring the Fate of Nitrogen Heterocycles in Complex Prebiotic Mixtures

A long standing question in the field of prebiotic chemistry is the origin of the genetic macromolecules DNA and RNA. DNA and RNA have very complex structures with repeating subunits of nucleotides, which are composed of nucleobases (nitrogen heterocycles) connected to sugar-phosphate. Due to the instability of some nucleobases (e.g. cytosine), difficulty of synthesis and instability of D-ribose, and the likely scarcity of polyphosphates necessary for the modern nucleotides, alternative nucleotides have been proposed for constructing the first genetic material. Thus, we have begun to investigate the chemistry of nitrogen heterocycles in plausible, complex prebiotic mixtures in an effort to identify robust reactions and potential alternative nucleotides. We have taken a complex prebiotic mixture produced by a spark discharge acting on a gas mixture of N2, CO2, CH4, and H2, and reacted it with four nitrogen heterocycles: uracil, 5-hydroxymethyluracil, guanine, and isoxanthopterin (2-amino-4,7-dihydroxypteridine). The products of the reaction between the spark mixture and each nitrogen heterocycle were characterized by liquid chromatography coupled to UV spectroscopy and Orbitrap mass spectrometry. We found that the reaction between the spark mixtUl'e and isoxanthopterin formed one major product, which was a cyanide adduct. 5-hydroxymethyluracil also reacted with the spark mixture to form a cyanide adduct, uracil-5-acetonitrile, which has been synthesized previously by reacting HCN with S-hydroxymethyluracil. Unlike isoxanthopterin, the chromatogram of the 5-hydroxymethyluracil reaction was much more complex with multiple products including spark-modified dimers. Additionally, we observed that HMU readily self-polymerizes in solution to a variety of oligomers consistent with those suggested by Cleaves. Guanine and uracil, the biological nucleobases, did not react with the spark mixture, even at high temperature (100 C). This suggests that there are alternative nucleobases which are more reactive under prebiotic conditions and may have been involved in producing precursor nucleotides.

Smith, Karen E.↗

NASA NTRS1973

A fluidic device for measuring constituent masses of a flowing binary gas mixture

A continuous reading mass flow device was developed to measure the component flow of a binary gas mixture. The basic components of the device are a fluidic humidity sensor and a specially designed flow calorimeter. These components provide readings of gas mixture ratio, mixture heat capacity, heat dissipated by the calorimeter and the gas temperature rise across the calorimeter. These parameter values, applied in the general definitions of specific heat capacity and the heat capacity of a gas mixture, produce calculated component flow rates of the mixture being metered. A test program was conducted to evaluate both the steady state and dynamic performance of the device.

Prokopius, P. R.↗

NASA NTRS1979

On matching the spectrum of Io - Variations in the photometric properties of sulfur-containing mixtures

The problem of comparing laboratory spectra of sulfur-containing binary mixtures with the spectrum of Io is discussed. For the satellite, the observable is the geometric albedo as a function of wavelength, whereas in the laboratory one often measures some other type of albedo. A previous paper demonstrated that for pure sulfur the multiplicative factor which converts the laboratory albedos to geometric albedos can be strongly wavelength dependent. The present paper demonstrates that this is also true for binary sulfur-containing mixtures. Furthermore, there is no universal conversion factor applicable to all binary mixtures, nor can the factor be interpolated for a particular mixture from the conversion factors of the two end members. The conversion factor is a function not only of the specific composition of a binary mixture but also of the relative particle size distributions of the two components, and must be measured specifically for each individual sample if a quantitative comparison between a laboratory sample and Io's surface is desired.

Veverka, J.↗

NASA NTRS1982

Mixture densities, maximum likelihood, and the EM algorithm

The problem of estimating the parameters which determine a mixture density is reviewed as well as maximum likelihood estimation for it. A particular iterative procedure for numerically approximating maximum likelihood estimates for mixture density problems is considered. This EM algorithm, is a specialization to the mixture density context of a general algorithm of the same name used to approximate maximum likelihood estimates for incomplete data problems. The formulation and theoretical and practical properties of the EM algorithm for mixture densities are discussed focussing in particular on mixtures of densities from exponential families.

Redner, R. A.↗

NASA NTRS1987

Deconvolution of spectra for intimate mixtures

Visible to near infrared reflectance spectra of macroscopic mixtures have been shown to be linear combinations of the reflections of the pure mineral components in the mixture. However, for microscopic mixtures the mixing systematics are in general nonlinear. The systematics may be linearized by conversion of reflectance to single scattering albedo (w), where the equations which relate reflectance to w depend on the method of data collection. Several proposed mixing models may be used to estimate mineral abundances from the reflectance spectra of intimate mixtures. These models are summarized and a revised model is presented. A noniterative (linear) least squares approach was used for curve fitting and the data, measured as bi-directional reflectance with incidence and emergence angles of 30 and 0 deg were converted to w by a simplified version of Hapke's equation for bi-directional reflectance. This model was tested with two mixture series composed of 45 to 75 micron particles: an anorthite-enstatite series and an olivine-magnetite series. The data indicate that the simplified Hapke's equation may be used to convolve reflectance spectra into mineral abundances if appropriate endmembers are known or derived from other techniques. For surfaces that contain a significant component of very low albedo material, a somewhat modified version of this technique will need to be developed. Since the abundances are calculated using a noniterative approach, the application of this method is especially efficient for large spectral data sets, such as those produced by mapping spectrometers.

Mustard, John F.↗

NASA NTRS1991

Combustion of unsupported methanol/dodecanol mixture droplets at low gravity

Experiments are reported on the combustion of free or unsupported methanol/dodecanol mixture droplets in a reduced gravity environment. The experiments were conducted in a drop tower. The Grashof number (based on drop diameter) in the moving frame of reference was on the order of 10 exp -5 for the period of droplet burning. Combustion of the mixture droplets was characterized by a multi-stage process indicative of diffusion controlled burning. The flame was not visible during the first stage because of the lighting used, but was visible (and spherical) in the final stage. The results suggested that the mixture droplets did not extinguish. By contrast, methanol droplets consistently extinguished. Microexplosions were not observed for mixtures with initial concentrations of equal volumes of methanol and dodecanol. However, most of the droplets containing initially 75 percent (by volume) of methanol exploded. The initiation of microexplosion, as defined by the occurrence of homogeneous nucleation within the droplet, is explained by comparing the calculated nonlinear variation of superheat limit with composition for a methanol/dodecanol mixture with the boiling point of dodecanol.

Yang, J. C.↗