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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Onset of condensation effects in cryogenic wind tunnels

The onset of condensation effects in cryogenic wind tunnels which limits their minimum operating temperatures is examined. If this onset of effects occurs below saturation temperature, then the tunnels may be operated at the lower temperatures and additional benefits to cryogenic tunnel operation resulting in increased Reynolds number capability and reduced operating costs. Both homogeneous and heterogeneous nucleation processes are discussed as they pertain to continuous flow cryogenic wind tunnels. Examples from condensation experiments in the 0.3 m Transonic Cryogenic Tunnel are also reviewed.

Hall, R. M.↗
NASA NTRS1982

Venus: Halide cloud condensation and volatile element inventories

Several Venus cloud condensates, including A12C16 as well as halides, oxides and sulfides of arsenic and antimony, are assessed for their thermodynamic and geochemical plausibility. Aluminum chloride can confidently be ruled out, and condensation of arsenic sulfides on the surface will cause arsenic compounds to be too rare to produce the observed clouds. Antimony may conceivably be sufficiently volatile, but the expected molecular form is gaseous SbS, not the chloride. Arsenic and antimony compounds in the atmosphere will be regulated at very low levels by sulfide precipitation, irrespective of the planetary inventory of As and Sb. Thus the arguments for a volatile-deficient origin for Venus based on the depletion of water and mercury (relative to Earth) cannot be tested by a search for atmospheric arsenic or antimony.

Lewis, J. S.↗
NASA NTRS1982

IUS materials outgassing condensation effects on sensitive spacecraft surfaces

Four materials used on the inertial upper state (IUS) were subjected to vacuum conditions and heated to near-operational temperatures (93 to 316 C), releasing volatile materials. A fraction of the volatile materials were collected on 25 C solar cells, optical solar reflectors (OSR's) or aluminized Mylar. The contaminated surfaces were exposed to 26 equivalent sun hours of simulated solar ultraviolet (UV) radiation. Measurements of contamination deposit mass, structure, reflectance and effects on solar cell power output were made before and after UV irradiation. Standard total mass loss - volatile condensible materials (TML - VCM) tests were also performed. A 2500 A thick contaminant layer produced by EPDM rubber motor-case insulation outgassing increased the solar absorptance of the OSR's from 0.07 to 0.14, and to 0.18 after UV exposure. An 83,000 A layer caused an increase from 0.07 to 0.21, and then the 0.46 after UV exposure. The Kevlar-epoxy motor-case material outgassing condensation raised the absorptance from 0.07 to 0.13, but UV had no effect. Outgassing from multilayer insulation and carbon-carbon nozzle materials did not affect the solar absorptance of the OSR's.

Mullen, C. R.↗
NASA NTRS1982

Noble gas trapping by laboratory carbon condensates

Trapping of noble gases by carbon-rich matter was investigated by synthesizing carbon condensates in a noble gas atmosphere. Laser evaporation of a solid carbon target yielded submicron grains which proved to be efficient noble gas trappers (Xe distribution coefficients up to 13 cu cm STP/g-atm). The carbon condensates are better noble gas trappers than previously reported synthetic samples, except one, but coefficients inferred for meteoritic acid-residues are still orders of magnitude higher. The trapped noble gases are loosely bound and elementally strongly fractionated, but isotopic fractionations were not detected. Although this experiment does not simulate nebular conditions, the results support the evidence that carbon-rich phases in meteorites may be carriers of noble gases from early solar system reservoirs. The trapped elemental noble gas fractionations are remarkably similar to both those inferred for meteorites and those of planetary atmospheres for earth, Mars and Venus.

Niemeyer, S.↗
NASA NTRS1982

Stratospheric condensation nuclei variations may relate to solar activity

Observations of increases of stratospheric condensation nuclei suggest a photo-initiated sulphuric acid vapour formation process in spring in polar regions. It is proposed that the sulphuric acid rapidly forms condensation nuclei through attachment to negatively charged multi-ion complexes and that the process may be modulated through variations in solar activity.

Hofmann, D. J.↗
NASA NTRS1982

Experimental studies of the vapor phase nucleation of refractory compounds. I - The condensation of SiO

The critical partial pressure of SiO necessary to initiate avalanche nucleation in the SiO-H2 system is measured as a function of the ambient temperature in the range 750-1000 K. Results show that the condensate produced at low temperatures is Si2O3, while a mixture of Si2O3 and amorphous SiO2 is produced at high temperatures. A surface energy of approximately 500 ergs/sq cm for the particles is found by analyzing the critical partial pressure vs temperature using classical nucleation theory. It is concluded that classical nucleation theory is not applicable to this system, because several inconsistencies in the thermodynamic analysis are demonstrated, and it is suggested that a kinetic theory of nucleation may be the preferential way to describe the condensation process.

Nuth, J. A.↗
NASA NTRS1982

An estimation of the condensation rates in three severe storm systems from satellite observations of the convective mass flux

A technique was developed for estimating the condensation rates of convective storms using satellite measurements of cirrus anvil expansion rates and radiosonde measurements of environmental water vapor. Three cases of severe convection in Oklahoma were studied and a diagnostic model was developed for integrating radiosonde data with satellite data. Two methods were used to measure the anvil expansion rates - the expansion of isotherm contours on infrared images, and the divergent motions of small brightness anomalies tracked on the visible images. The differences between the two methods were large as the storms developed, but these differences became small in the latter stage of all three storms. A comparison between the three storms indicated that the available moisture in the lowest levels greatly affected the rain rates of the storms. This was evident from both the measured rain rates of the storms and the condensation rates estimated by the model. The possibility of using this diagnostic model for estimating the intensities of convective storms also is discussed.

Mack, R. A.↗
NASA NTRS1982

Refractory residues, condensates and chondrules from solar furnace experiments

Vertical access solar furnace experiments have produced refractory residues, condensates and chondrules that are similar to components of chondritic meteorites. In particular, Ca-Al-rich refractory residues similar in chemistry to inclusions in carbonaceous chondrites have been produced by partial evaporation of basaltic bulk rock samples. Fe-Mg-Si-rich condensates with distinctive microbotryoidal morphology have been collected from the same sample runs. Particle coatings and aggregates with virtually identical microbotryoidal morphology and major element chemistry have been identified in both the Allende and Murchison meteorites. Spattered drops from melt beads undergoing heating and partial evaporation resemble some meteoritic chondrules in their mineralogies, textures, grain size, and sorting. The spatter mechanism is highly efficient in the production of chondrules. If any of the refractory inclusions in chondrites are, in fact, partial evaporation residues, many meteoritic fluid drop chondrules must have been formed by this process. The hot central portion of the solar nebula, acting on a cloud of dust and gas, is the probable source of heat required to produce the fractionated chemistry and physical state of many of the components of chondritic meteorites.

King, E. A.↗
NASA NTRS1983

Techniques for avoiding discrimination errors in the dynamic sampling of condensable vapors

In the mass spectrometric sampling of dynamic systems, measurements of the relative concentrations of condensable and noncondensable vapors can be significantly distorted if some subtle, but important, instrumental factors are overlooked. Even with in situ measurements, the condensables are readily lost to the container walls, and the noncondensables can persist within the vacuum chamber and yield a disproportionately high output signal. Where single pulses of vapor are sampled this source of error is avoided by gating either the mass spectrometer ""on'' or the data acquisition instrumentation ""on'' only during the very brief time-window when the initial vapor cloud emanating directly from the vapor source passes through the ionizer. Instrumentation for these techniques is detailed and its effectiveness is demonstrated by comparing gated and nongated spectra obtained from the pulsed-laser vaporization of several materials.

Lincoln, K. A.↗
NASA NTRS1983

Stratospheric condensation nuclei and possible solar influences

Balloon-borne measurements of condensation nuclei and H2SO4 molecules in large negative ion clusters have been made in the stratosphere at around 30 km altitude. The nuclei observed were in the 0.01-0.1 micron diameter range. Consideration was given to sunspot activity as a triggering event for ionization of upper atmospheric H2SO4 species and subsequent formation of the nuclei. A numerical model was defined for a steady state between the H2SO4 association and ion recombination in order to determine a critical nucleation rate. It is concluded that condensation nuclei are produced in ion nucleation in an H2SO4 supersaturated polar cloud chamber, with the process being initiated by solar flare particle ionization.

Hofmann, D. J.↗
NASA NTRS1984

Condensation modes in magnetized cylindrical plasmas

In order to understand the formation and stability of solar prominences, attention is given to the condensation modes of the thermal instability in a cylindriical plasma whose magnetic field has both potential (longitudinal) and nonpotential (poloidal) components forming helically twisted field lines. It is noted that the field line twist has a significant effect on the stability of condensation modes which are unstable if field lines are straight, but become stable as the twist increases. The problem is treated in a fully self-consistent way, to derive a second-order ordinary differential equation for radiative MHD stability. The approximation made by neglecting inertial terms is valid for coronal loop conditions if there is no singular surface in the plasma, and a simplified differential equation is derived. Attention is given to stability for the m = zero, 1, and 2 modes numerically, for various loop parameters.

An, C.-H.↗
NASA NTRS1985

Test results from a comparative evaluation of a condensation nuclei fire detector

The fire/smoke alarm response of a condensation nuclei fire detector (CNFD) was compared with photoelectric and ionization detectors. Tests were conducted in a former control room 8.5 m by 8.9 with a 2.7 m ceiling. The room had air supplied from above the ceiling and under the floor with return air exiting from ceiling grills. The environment was varied from 278 to 305 K and relative humidities from 8 to 65%. Four detection zones were located in the room. Each zone contained a sampling head for the CNDF, a photodetector, and an ionization detector so that each detector system had four opportunities to alarm during tests. The particle level in the test room was also monitored during tests with a condensation nuclei particle counter. The CNFD responded to 90% of exposures to smoldering plastic and 84% of exposures to visible fire. The photoelectric response was 43 and 12.5% respectively for the same conditions. The ionization response was 9 and 48 respectively.

Bricker, R. W.↗
NASA NTRS1985

Condensation onto grains in the outflows from mass-losing red giants

In the outflows from red giants, grains are formed which are driven by radiation pressure. For the development of a model of the outflows, a detailed understanding of the interaction between the gas and dust is critical. The present investigation is concerned with condensation processes which occur after the grains nucleate near the stars. A physical process considered results from the cooling of the grains as they flow away from the star. Molecules which initially do not condense onto the grains can do so far from the star. It is shown that for some species this effect can be quite important in determining their gas-phase abundances in the outer circumstellar envelope. One of the major motivations of this investigation was provided by the desire to understand the physical conditions and molecular abundances in the outflows from the considered stars.

Jura, M.↗
NASA NTRS1986

Adsorption and condensation of amino acids and nucleotides with soluble mineral salts

The directed synthesis of biopolymers in an abiotic environment is presumably a cyclic sequence of steps which may be realized in a fluctuating environment such as a prebiotic pond undergoing wetting-drying cycles. Soluble mineral salts have been proposed as an essential component of this fluctuating environment. The following sequence may be considered as a most primitive mechanism of information transfer in a fluctuating environment: (1) adsorption of a biomolecule onto a soluable mineral salt surface to act as an adsorbed template; (2) specific adsorption of biomonomers onto the adsorbed template; (3) condensation of the adsorbed biomonomers; and (4) desorption of the elongated oligomer. In this investigation, the salts selected for study were CaSO4.2H2O(gypsum), SrSO4, and several other metal sulfates and chlorides. Adsorption of the monomeric species, gly, 5'AMP 5'GMP, and 5'CMP was investigated. The adsorbed template biopolymers used were Poly-A, Poly-G, Poly-C, and Poly-U. The results of studies involving these experimental participants, the first two steps of the proposed primitive information transfer mechanism, and condensation of amino acids to form oligomers in a fluctuating environment are to be reported.

Orenberg, J.↗
NASA NTRS1985

Role of minerals in the thermal alteration of organic matter. I - Generation of gases and condensates under dry condition

Pyrolysis experiments conducted at 200 and 300 C on kerogen and bitumen from the Monterey formation and on the Green River Formation kerogen with montmorillonite, illite, and calcite added are described. The pyrolysis products are identified and gas and condensate analyses are performed. A catalytic effect is detected in the pyrolysis of kerogen with montmorillonite; however, illite and calcite display no catalytic activity. The increased production of C1-C6 hydrocarbons and the dominance of branched hydrocarbons in the C4-C6 range reveals a catalytic influence. It is observed that the catalysis of montmorillonite is greater during bitumen pyrolysis than for kerogen, and catalysis with minerals affects the production of CO2. It is concluded that a mineral matrix is important in determining the type and amount of gases and condensates forming from organic matter under thermal stress.

Tannenbaum, E.↗
NASA NTRS1986

Martian dust particles as condensation nuclei - A preliminary assessment of mineralogical factors

Experiments were performed to determine the factors influencing ice nucleation detected in Viking Lander data from the Mars surface. The study focused on the relationship between mineral properties and condensate formation under Mars conditions. Pulverized particles of the primary phases of basaltic rocks and their alteration products, expandable clay minerals and a nonexpandable clay mineral, and petrologically well-characterized regolith materials ranging from 10-60 microns in size, were studied. The powders were individually or in combinations mixed with water in a flowing CO2 atmosphere while calorimetry data was taken on the ice nucleation threshold. The ice-forming characteristics of the mixes were found to be a function of the crystallographic disregistry, chemical bonding, and active-site properties of the individual minerals. The crystalline materials were better nucleators of condensates than were the cryptocrystalline mineral specimens, while nonexpandable clay materials, particularly zeolite, were the more effective nucleators among the weathering product materials.

Gooding, J. L.↗
NASA NTRS1986

A compact density condensation around L1551-IRS 5: 2.7mm continuum observations with 4" resolution

The dark cloud L1551 contains the best known examples of bipolar molecular outflow. Such outflows are assumed to be driven by winds from young stars embedded in a cloud but the mechanism for collimation of the outflows is still in doubt, though it has been much debated. Among the possibilities put forth to date are intrinsically anisotropic stellar winds, isotropic stellar winds collimated by interstellar toroidal shaped clouds on the order of 10(17) cm in size, or circumstellar disks of order 10(15) cm in size. Because the outflow in L1551 as revealed by the Very Large Array (VLA) cm continuum observations is collimated even at the arc second level it seems as though the stellar wind powering the outflow must either be initially anisotropic or be collimated by something very close to the star, such as a circumstellar disk. We have observed L1551 in the continuum at 2.7 mm with the OVRO millimeter-wave interferometer in the winter of 1983-4 and again, more extensively, in 1985-6. The resulting map shows for the first time direct evidence for a density condensation capable of collimating an initially isotropic flow from IRS 5. This map made from data taken in 1985-6 with projected baselines up to 100 m in length (37k lambda). It has been cleaned and reconstructed with a 4'' gaussian beam. It shows a nearly unresolved source with a suggestion of extension at the 3'' level (assuming a gaussian source shape). The integrated flux density in this map is 170 mJy. A composite spectrum of L1551 is presented which shows that the flux at 2.7 mm is due to the thermal radiation from dust that is also seen at shorter wavelengths. Very little of it can be due to the continuation of the nearly flat cm wavelength spectrum which is assumed to be from thermal bremsstrahlung radiation. The map and spectrum provide strong constraints on the size, temperature, and optical depth of the density condensation surrounding IRS 5.

Keene, J.↗
NASA NTRS1987

Mixing-induced fluid destratification and ullage condensation

In many applications, on-orbit storage and transfer of cryogens will require forced mixing to control tank pressure without direct venting to space. During a no-vent transfer or during operation of a thermodynamic vent system in a cryogen storage tank, pressure control is achieved by circulating cool liquid to the liquid-vapor interface to condense some of the ullage vapor. To measure the pressure and temperature response rates in mixing-induced condensation, an experiment has been developed using Freon 11 to simulate the two-phase behavior of a cryogen. A thin layer at the liquid surface is heated to raise the tank pressure, and then a jet mixer is turned on to circulate the liquid, cool the surface, and reduce the pressure. Many nozzle configurations and flow rates are used. Tank pressure and the temperature profiles in the ullage and the liquid are measured. Initial data from this ground test are shown correlated with normal-gravity and drop-tower dye-mixing data. Pressure collapse times are comparable to the dye-mixing times, whereas the times needed for complete thermal mixing are much longer than the dye-mixing times.

Meserole, Jere S.↗