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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Viscosity Measurement Using Drop Coalescence in Microgravity

We present in here validation studies of a new method for application in microgravity environment which measures the viscosity of highly viscous undercooled liquids using drop coalescence. The method has the advantage of avoiding heterogeneous nucleation at container walls caused by crystallization of undercooled liquids during processing. Homogeneous nucleation can also be avoided due to the rapidity of the measurement using this method. The technique relies on measurements from experiments conducted in near zero gravity environment as well as highly accurate analytical formulation for the coalescence process. The viscosity of the liquid is determined by allowing the computed free surface shape relaxation time to be adjusted in response to the measured free surface velocity for two coalescing drops. Results are presented from two sets of validation experiments for the method which were conducted on board aircraft flying parabolic trajectories. In these tests the viscosity of a highly viscous liquid, namely glycerin, was determined at different temperatures using the drop coalescence method described in here. The experiments measured the free surface velocity of two glycerin drops coalescing under the action of surface tension alone in low gravity environment using high speed photography. The liquid viscosity was determined by adjusting the computed free surface velocity values to the measured experimental data. The results of these experiments were found to agree reasonably well with the known viscosity for the test liquid used.

Antar, Basil N.↗
NASA NTRS1990

Preliminary drop-tower experiments on liquid-interface geometry in partially filled containers at zero gravity

Plexiglass containers with rounded trapezoidal cross sections were designed and built to test the validity of Concus and Finn's existence theorem (1974, 1983) for a bounded free liquid surface at zero gravity. Experiments were carried out at the NASA Lewis two-second drop tower. Dyed ethanol-water solutions and three immiscible liquid pairs, with one liquid dyed, were tested. High-speed movies were used to record the liquid motion. Liquid rose to the top of the smaller end of the containers when the contact angle was small enough, in agreement with the theory. Liquid interface motion demonstrated a strong dependence on physical properties, including surface roughness and contamination.

Smedley, G.↗
NASA NTRS1996

Bubble formation in microgravity

An extensive experimental program was initiated for the purpose of understanding the mechanisms leading to bubble generation during fluid handling procedures in a microgravity environment. Several key fluid handling procedures typical for PCG experiments were identified for analysis in that program. Experiments were designed to specifically understand how such procedures can lead to bubble formation. The experiments were then conducted aboard the NASA KC-135 aircraft which is capable of simulating a low gravity environment by executing a parabolic flight attitude. However, such a flight attitude can only provide a low gravity environment of approximately 10-2go for a maximum period of 30 seconds. Thus all of the tests conducted for these experiments were designed to last no longer than 20 seconds. Several experiments were designed to simulate some of the more relevant fluid handling procedures during protein crystal growth experiments. These include submerged liquid jet cavitation, filling of a cubical vessel, submerged surface scratch, attached drop growth, liquid jet impingement, and geysering experiments. To date, four separate KC-135 flight campaigns were undertaken specifically for performing these experiments. However, different experiments were performed on different flights.

Antar, Basil N.↗
NASA NTRS1990

More About Evaporation In Clusters Of Drops

Report presents theoretical study of evaporation in clusters of spray drops in liquid fuel. Related to reports described in "Turbulence and Evaporation in Clusters of Drops" (NPO-17323) and "Effects of Turbulence on Ignition" (NPO-17335). Purpose of study to improve theoretical description of transport of molecular species, mass, and heat between cluster and its surroundings.

Bellan, Josette↗
NASA NTRS2003

Caustics and Caustic-Diffraction in Laser Shadowgraphy of a Sessile Drop and Identification of Profile Near Contact Line

This paper presents an optical method based on the caustics and caustic-difraction in laser shadowgaphy of a sessile drop to identify and estimate the drop profile near the contact line. A parallel laser beam passes through a liquid sessile drop placed on a transparent substrate to produce a shadowgraphic image of the drop on the screen far from the substrate. Along the inflection line of the drop the Gaussian curvature of the wavefront deformed by the drop vanishes, and therefore the inflection line gives caustics in the far field of the wave, which can be seen on the screen. The neighboring light rays at both sides of the inflection line interfere with each other to form interference fringes at the inner side of the caustics. According to the pattern of the caustics, the drop-profile shape can be identified and estimated.

Zhang, Neng-Li↗
NASA NTRS1988

Liquid-Seeding Atomizer

Particles sprayed in drops of evaporating liquid. Placed near wind-tunnel inlet, atomizer sprays evaporating liquid containing solid particles into wind-tunnel airflow. Particles entrained in flow and scatter light, enabling flow to be observed optically. One end of atomizer slides on stationary pin to accommodate thermal expansion and contraction.

Seegmiller, Henry L. B.↗
NASA NTRS1990

Electrostatic Dispersion Of Drops In Clusters

Electrical charging speeds evaporation. Report presents theoretical study of evaporation and dispersion of electrostatically charged clusters of drops in liquid fuel sprays. Represents extension of studies described in article, "More About Evaporation of Drops in Clusters" (NPO-17594). Undertaken in effort to learn how electrostatic atomization used to disperse fuel better in order to reduce formation of soot in diesel engines and other power and combustion systems.

Bellan, Josette↗
NASA NTRS1992

Pressure drop in fully developed, turbulent, liquid-vapor annular flows in zero gravity

The prediction of frictional pressure drop in fully developed, turbulent, annular liquid-vapor flows in zero gravity using simulation experiments conducted on earth is described. The scheme extends the authors' earlier work on dispersed flows. The simulation experiments used two immiscible liquids of identical density, namely, water and n-butyl benzoate. Because of the lack of rigorous analytical models for turbulent, annular flows, the proposed scheme resorts to existing semiempirical correlations. Results based on two different correlations are presented and compared. Others may be used. It was shown that, for both dispersed and annular flow regimes, the predicted frictional pressure gradients in 0-g are lower than those in 1-g under otherwise identical conditions. The physical basis for this finding is given.

Sridhar, K. R.↗
NASA NTRSDate not supplied

Exploring Cryogenic Propellant Behavior in Low-Gravity Environments, Insights from the Saturn AS-203 Vent Experiments and CFD Analysis

In the 1960s, NASA embarked on a series of groundbreaking flight tests on the Saturn AS-203, aiming to understand the complex dynamics of propellants in the distinctive low-gravity lunar environment. These tests centered on venting experiments, subjecting cryogenic liquid hydrogen to conditions beneath its saturation pressure while accelerating the vehicle to manage the propellant's positioning. During these experiments, NASA meticulously scrutinized the propellant tank using a suite of instruments, including temperature and pressure sensors, as well as a camera placed internal to the liquid hydrogen tank. The outcomes provided anecdotal evidence revealing the phenomenon of boiling along the tank's walls and the intriguing formation of liquid globules and droplets in the ullage during the venting process. Notably, the substantial drop in liquid temperature during these tests suggests adiabatic cooling as liquid hydrogen evaporates. This evaporation leads to a cooling of the remaining hydrogen due to the heat it releases. This paper presents the outcomes of our initial analysis, wherein CFD models were used to simulate the observed boiling phenomena and the bulk movement of the liquid hydrogen propellant, both qualitatively and quantitatively. The implications of these findings may extend to mission and vehicle designers, providing invaluable insights for crafting more efficient and effective in-space propulsion systems utilizing cryogenic propellant including impacts to vehicle control systems. Understanding propellant behavior under these conditions may better inform GNC teams, ensuring more stable vehicle operations when utilizing cryogenic propellants. This includes essential considerations for cryogenic propellant transfer and storage systems, integral to NASA's forthcoming Artemis missions. While we recognize the challenges tied to CFD models, this study represents a step forward, highlighting current progress and signaling the potential for refining our predictive understanding in the future.

Computational Fluid Dynamics↗
NASA NTRSDate not supplied

Exploring Cryogenic Propellant Behavior in Low-Gravity Environments, Insights from the Saturn AS-203 Vent Experiments and CFD Analysis

In the 1960s, NASA embarked on a series of groundbreaking flight tests on the Saturn AS-203, aiming to understand the complex dynamics of propellants in the distinctive low-gravity lunar environment. These tests centered on venting experiments, subjecting cryogenic liquid hydrogen to conditions beneath its saturation pressure while accelerating the vehicle to manage the propellant's positioning. During these experiments, NASA meticulously scrutinized the propellant tank using a suite of instruments, including temperature and pressure sensors, as well as a camera placed internal to the liquid hydrogen tank. The outcomes provided anecdotal evidence revealing the phenomenon of boiling along the tank's walls and the intriguing formation of liquid globules and droplets in the ullage during the venting process. Notably, the substantial drop in liquid temperature during these tests suggests adiabatic cooling as liquid hydrogen evaporates. This evaporation leads to a cooling of the remaining hydrogen due to the heat it releases. This paper presents the outcomes of our initial analysis, wherein CFD models were used to simulate the observed boiling phenomena and the bulk movement of the liquid hydrogen propellant, both qualitatively and quantitatively. The implications of these findings may extend to mission and vehicle designers, providing invaluable insights for crafting more efficient and effective in-space propulsion systems utilizing cryogenic propellant including impacts to vehicle control systems. Understanding propellant behavior under these conditions may better inform GNC teams, ensuring more stable vehicle operations when utilizing cryogenic propellants. This includes essential considerations for cryogenic propellant transfer and storage systems, integral to NASA's forthcoming Artemis missions. While we recognize the challenges tied to CFD models, this study represents a step forward, highlighting current progress and signaling the potential for refining our predictive understanding in the future.

Computational Fluid Dynamics↗
NASA NTRS2008

Raindrop Size Distribution Measurements in Tropical Cyclones

Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004-06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometercalculated reflectivity of 40 dBZ, the number concentration was 700 plus or minus 100 drops m(sup -3), while the liquid water content and rain rate were 0.90 plus or minus 0.05 g m(sup -3) and 18.5 plus or minus 0.5 mm h(sup -1), respectively. The mean mass diameter, on the other hand, was 1.67 plus or minus 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized intercept parameter had an increasing trend with reflectivity. The shape parameter, on the other hand, decreased in a reflectivity range from 10 to 20 dBZ and remained steady at higher reflectivities. Considering the repeatability of the characteristics of the raindrop size distribution, a second impact disdrometer that was located 5.3 km away from the primary site in Wallops Island, Virginia, had similar size spectra in selected tropical cyclones.

Tokay, Ali↗
NASA NTRS1987

Atmospheric science

The following types of experiments for a proposed Space Station Microgravity Particle Research Facility are described: (1) growth of liquid water drop populations; (2) coalescence; (3) drop breakup; (4) breakup of freezing drops; (5) ice nucleation for large aerosols or bacteria; (6) scavenging of gases, for example, SO2 oxidation; (7) phoretic forces, i.e., thermophoresis versus diffusiophoresis; (8) Rayleigh bursting of drops; (9) charge separation due to collisions of rimed and unrimed ice; (10) charged drop dynamics; (11) growth of particles in other planetary atmospheres; and (12) freezing and liquid-liquid evaporation. The required capabilities and desired hardware for the facility are detailed.

Hamill, Patrick↗
NASA NTRS2004

Small-Scale Variability of Large Cloud Drops

Cloud droplet size distribution is one of the most fundamental subjects in cloud physics. Understanding of spatial distribution and small-scale fluctuations of cloud droplets is essential for both cloud physics and atmospheric radiation. For cloud physics, it relates to the coalescence growth of raindrops while for radiation, it has a strong impact on a cloud's radiative properties. Most of the existing cloud radiation and precipitation formation models assume that the mean number of drops with a given radius varies proportionally to volume. The analysis of microphysical data on liquid water drop sizes shows that, for sufficiently small volumes, the number is proportional to the drop size dependent power of the volume. For abundant small drops present, the exponent is 1 as assumed in the conventional approach. However, for rarer large drops, the exponents fall below unity. At small scales, therefore, the mean number of large drops decreases with volume at a slower rate than the conventional approach assumes, suggesting more large drops at these scales than conventional models account for; their impact is consequently underestimated. Size dependent models of spatial distribution of cloud drops that simulate the observed power laws show strong drop clustering, the more so the larger the drops. The degree of clustering is determined by the observed exponents. The strong clustering of large drops arises naturally from the observed power-law statistics. Current theories of photon-cloud interaction and warm rain formation will need radical revision in order to produce these statistics; their underlying equations are unable to yield the observed power law.

Marshak, Alexander↗
NASA NTRS2005

Small-Scale Drop Size Variability: Impact on Estimation of Cloud Optical Properties

Most cloud radiation models and conventional data processing techniques assume that the mean number of drops of a given radius is proportional to volume. The analysis of microphysical data on liquid water drop sizes shows that, for sufficiently small volumes, this proportionality breaks down; the number of cloud drops of a given radius is instead proportional to the volume raised to a drop size-dependent nonunit power. The coefficient of proportionality, a generalized drop concentration, is a function of the drop size. For abundant small drops the power is unity as assumed in the conventional approach. However, for rarer large drops, it falls increasingly below unity. This empirical fact leads to drop clustering, with the larger drops exhibiting a greater degree of clustering. The generalized drop concentration shows the mean number of drops per cluster, while the power characterizes the occurrence frequency of clusters. With a fixed total number of drops in a cloud, a decrease in frequency of clusters is accompanied by a corresponding increase in the generalized concentration. This initiates a competing process missed in the conventional models: an increase in the number of drops per cluster enhances the impact of rarer large drops on cloud radiation while a decrease in the frequency suppresses it. Because of the nonlinear relationship between the number of clustered drops and the volume, these two opposite tendencies do not necessarily compensate each other. The data analysis suggests that clustered drops likely have a stronger radiative impact compared to their unclustered counterpart; ignoring it results in underestimation of the contribution from large drops to cloud horizontal optical path.

Knyazikhin, Y.↗
NASA NTRS1982

The motion of a drop in a rigid surface

The assumptions of a region of slip near a moving contact line (to remove the force singularity) and a constant contact angle are used to obtain the equation for the shape of a thin drop of liquid resting on a rigid plane. Three asymptotic expansions are matched together to obtain an expression for the rate at which the drop spreads. Some cases of sliding motion are also examined. Although the technique is presented here for thin drops only, it can also be applied to drops of arbitrary size.

Hocking, L. M.↗
NASA NTRS1971

Transfer of thermal microwaves in the atmosphere, volume 2

Figures and tabular information that are supplemental to a study on transfer of thermal microwaves in the atmosphere are presented. The numerical values for the absorption and scattering cross sections of a pure, liquid, water drop are given for drop diameters ranging up to 6 mm, and for various drop temperatures. These values were obtained through the Mie theory. For a Marshall-Palmer distribution of drop sizes, the volume absorption and scattering coefficients of rain are given for the same temperatures and microwave frequencies shown above and for contents of liquid water in the rain mass. Also, scattergrams are given of the katabatic and upwelling brightness temperatures of up to 582 model atmospheres over a calm ocean versus the equivalent depths of liquid water in cloud form, rain form, or combined cloud and rain form.

Paris, J. F.↗