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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Critical point wetting drop tower experiment

Experiments with the wetting behavior of immiscible fluids against the container below the critical temperature are being performed in the MSFC Drop Tower Facility. Microgravity conditions extending up to three seconds (of the 4.5 second drop) are generated for the experiment. Specimens consist of glass cylindrical ampoules partially filled with fluid phases. How the fluids develop the meniscus geometry as well as hot the fluid interfaces respond to the microgravity induced oscillations is recorded during the experiment with on-board cameras. Drops are made at various temperatures to determine the interfacial energy variation as a function of temperature.

Kaulker, William F.↗
NASA NTRS2015

Modification Plans For The NASA 5.2 Second Drop Tower

A design study is currently underway to examine the possibility of converting the NASA Glenn Research Center 5.2 second drop-tower to include testing at partial gravity levels and to increase the test duration to approximately 10 seconds and the number of tests conducted in a day to over 30. This will be achieved by converting to a magnetic-levitation system to drive the test capsule. This conversion will require concessions in certain areas to enable the enhanced capability. In particular the quality of g or vibration attainable in the new design is currently unknown. This capability may trade against payload mass, volume, or test duration. The acceleration quality for partial-g studies and the launch and deceleration levels are also in the process of definition. The status of the redesign study is presented along with discussion of the critical design options. Input from the community is sought to enable optimization of the design for future combustion applications.

microgravity↗
NASA NTRS1994

Theoretical Basis for Estimated Test Times and Conditions for Drop Tower and Space-Based Droplet Burning Experiments With Methanol and N-Heptane

In order to develop an extensive envelope of test conditions for NASA's space-based Droplet Combustion Experiment (DCE) as well those droplet experiments which can be performed using a drop tower, the transient vaporization and combustion of methanol and n-heptane droplets were simulated using a recently developed fully time-dependent, spherically symmetric droplet combustion model. The transient vaporization of methanol and n-heptane was modeled to characterize the instantaneous gas phase composition surrounding the droplet prior to the introduction of an ignition source. The results for methanol/air showed that the entire gas phase surrounding a 2 mm methanol droplet deployed in zero-g .quickly falls outside the lean flammability limit. The gas phase surrounding an identically-sized n-heptane droplet, on the other hand, remains flammable. The combustion of methanol was then modeled considering a detailed gas phase chemical kinetic mechanism (168 steps, 26 species) and the effect of the dissolution of flame-generated water into the liquid droplet. These results were used to determine the critical ignition diameter required to achieve quasi-steady droplet combustion in a given oxidizing environment. For droplet diameters greater than the critical ignition diameter, the model predicted a finite diameter at which the flame would extinguish. These extinction diameters were found to vary significantly with initial droplet diameter. This phenomenon appears to be unique to the transient heat transfer, mass transfer and chemical kinetics of the system and thus has not been reported elsewhere to date. The extinction diameter was also shown to vary significantly with the liquid phase Lewis number since the amount of water present in the droplet at extinction is largely governed by the rate at which water is transported into the droplet via mass diffusion. Finally, the numerical results for n-heptane combustion were obtained using both 2 step and 96 step semi-emperical chemical kinetic mechanisms. Neither mechanism exhibited the variation of extinction diameter with initial diameter.

Marchese, Anthony J.↗
NASA NTRS1997

Science Support for Space-Based Droplet Combustion: Drop Tower Experiments and Detailed Numerical Modeling

This program supports the engineering design, data analysis, and data interpretation requirements for the study of initially single component, spherically symmetric, isolated droplet combustion studies. Experimental emphasis is on the study of simple alcohols (methanol, ethanol) and alkanes (n-heptane, n-decane) as fuels with time dependent measurements of drop size, flame-stand-off, liquid-phase composition, and finally, extinction. Experiments have included bench-scale studies at Princeton, studies in the 2.2 and 5.18 drop towers at NASA-LeRC, and both the Fiber Supported Droplet Combustion (FSDC-1, FSDC-2) and the free Droplet Combustion Experiment (DCE) studies aboard the shuttle. Test matrix and data interpretation are performed through spherically-symmetric, time-dependent numerical computations which embody detailed sub-models for physical and chemical processes. The computed burning rate, flame stand-off, and extinction diameter are compared with the respective measurements for each individual experiment. In particular, the data from FSDC-1 and subsequent space-based experiments provide the opportunity to compare all three types of data simultaneously with the computed parameters. Recent numerical efforts are extending the computational tools to consider time dependent, axisymmetric 2-dimensional reactive flow situations.

Marchese, Anthony J.↗
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 NTRS1987

Study of the production of some superconducting and magnetic materials by solidification in the drop tube and drop tower

A systematic study on the relationship between the microstructure and physical properties of several superconducting materials prepared by solidification in low gravity was conducted. Further study of the materials, such as the applications of hydrostatic pressure which is known to be an effective mean to vary the electronic structure of materials, in conjunction with the detailed microstructure analysis of the samples was also performed to better understand the low gravity effects on the enhancement of the electronic properties. Results of the studies on the directionally solidified AlInSn alloys processed in the KC-135 aircraft and immiscible GaBi alloy prepared during free fall in the Marshall Space Flight Center Drop Tower are presented.

Wu, M. K.↗
NASA NTRS1982

Method of forming frozen spheres in a force-free drop tower

Hollow glass spheres are shaped by the effects of surface tension acting on bubbles of glass in its molten state. A downwardly flowing stream of air accelerated at a one-G rate of acceleration is established through a drop bubbles on molten glass are introduced into the stream of air and frozen and as they are accelerated at a one-G rate of acceleration.

Kendall, J. M., Jr.↗
NASA NTRS1985

Effect of Undercooling and Modified Microstructure on the Physical Properties of Material Synthesized in the Drop Tube and Drop Tower

The effects of undercooling and modified microstructure on the physical properties of synthesized materials were investigated. The objectives of this program are: (1) to determine the possible existence of metastable phases and novel physical processes on material prepared in a microgravity environment; and (2) to investigate the feasibility of fabricating advanced electronic devices using material with microstructures obtainable in a microgravity environment. The specific alloys and compounds under study are Au-Ge and immiscible alloys Nb-Ge compounds, and Ga-Bi immiscible alloys, and Ba-Pb-Bi-O. The superconducting and normal state transport properties of the materials under different pressures and in different magnetic fields were determined. The simultaneous study on the physical properties and the microstructure of material will provide information about the potential applications of materials processed in a microgravity environment.

Chu, C. W.↗
NASA NTRS1988

Fluid oscillation in the Drop Tower

An interfluid meniscus oscillates within a cylindrical container when suddenly released from earth's gravity and taken into a microgravity environment. Oscillations damp out from energy dissipative mechanisms such as viscosity and interfacial friction. Damping out of the oscillations by the latter mechanism is affected by the nature of the interfacial junction between the fluid-fluid interface and the container wall. Perfluoromethylcyclohexane and isopropanol in glass were the materials used for the experiment. The wetting condition of the fluids against the wall changes at the critical wetting transition temperature. This change in wetting causes a change in the damping characteristics.

Kaukler, William F.↗
NASA NTRS1996

An Experimental Study of Ignition Effects and Flame Growth Over a Thin Solid Fuel in Low-Speed Concurrent Flow Using Drop-Tower Facilities

An experimental study of ignition and flame growth over a thin solid fuel in oxidizer flow speeds from 0 to 10 cm/sec concurrent flow was performed. This study examined the differences between ignition using a resistively heated wire (woven in a sawtooth pattern over the leading edge of the fuel), and a straight resistively heated wire augmented by a chemical ignitor doped onto the leading edge of the fuel. Results showed that the chemical system yielded non-uniform ignition bursts, while the system using only the hotwire gave more uniform ignition. At speeds up to 2.5 cm/sec, the chemical system yielded non-uniform pyrolysis fronts, while the hotwire system gave more uniform pyrolysis fronts. At speeds of 5 cm/sec or greater, both systems gave uniform pyrolysis fronts. The chemically-ignited flames tended to become too dim to see faster than the hotwire-ignited flames, and the flame lengths were observed to be shorter (after the initial burst subsided) for the chemical system for all speeds. Flame and pyrolysis element velocities were measured. Temperature profiles for selected tests were measured using thermocouples at the fuel surface and in the gas phase. Comparisons between the flame element velocities and peak temperatures recorded in these tests with calculated spread rates and peak temperatures from a steady-state model are presented. Agreement was found to be within 20% for most flame elements for nominal velocities of 5 cm/sec and 7.5 cm/sec.

Pettegrew, Richard Dale↗
NASA NTRS2003

Fan Beam Emission Tomography Demonstrated Successfully in the Reduced-Gravity Environment of Drop Towers

Fires onboard manned spacecraft and launch vehicles are a particularly feared hazard because one cannot jump ship while in orbit 240 nmi above the Earth at 17 000 mph! Understanding the physical properties of fires in free fall and on orbit is, therefore, a very important endeavor for NASA s Human Exploration and Development of Space (HEDS) enterprise. However, detailed information concerning the structure of microgravity fires remained elusive until recently since robustness, limited power, limited volume, and limited mass place severe constraints on diagnostic equipment for use in space and in NASA Glenn Research Center s reduced-gravity facilities. Under NASA Research Associate funding since 2001, En'Urga, Inc. (Dr. Sivathanu, principal investigator, and Dr. Lim, co-investigator) in collaboration with Glenn (Dr. Feikema, coinvestigator) have successfully demonstrated a new technology for use in microgravity combustion. A midinfrared scanning spectrometer has been developed by En'Urga and tested at Glenn to measure 30 spectra per second at different spatial locations in a flame from 1.8 to 4.8 microns.

Feikema, Douglas A.↗
NASA NTRS2001

Flame-Vortex Interactions Imaged in Microgravity - To Assess the Theory Flame Stretch

The goals of this research are to: 1) Assess the Theory of Flame Stretch by operating a unique flame-vortex experiment under microgravity conditions in the NASA Glenn 2.2 Second Drop Tower (drops to identify operating conditions have been completed); 2) Obtain high speed shadowgraph images (500-1000 frames/s) using the drop rig (images were obtained at one-g, and the NASA Kodak RO camera is being mounted on the drop rig); 3) Obtain shadowgraph and PIV images at 1-g while varying the effects of buoyancy by controlling the Froude number (completed); 4) Numerically model the inwardly-propagating spherical flame that is observed in the experiment using full chemistry and the RUN 1DL code (completed); 5) Send images of the flame shape to Dr. G. Patniak at NRL who is numerically simulating the entire flame-vortex interaction of the present experiment (data transfer completed); and 6) Assess the feasibility of obtaining PIV velocity field images in the drop rig, which would be useful (but not required) for our assessment of the Theory of Flame Stretch (PIV images were obtained at one-g using same low laser power that is available from fiber optic cable in drop tower). The motivation for the work is to obtain novel measurement needed to develop a physically accurate model of turbulent combustion that can help in the control of engine pollutants. The unique experiment allows, for the first time, the detailed study of a negatively-curved (negatively stretched) flame, which is one of the five fundamental types of premixed flames. While there have been studies of flat flames, positively-curved (outwardly-propagating) cases and positively-strained (counterflow) cases, this is the first detailed study of a negatively-curved (inwardly-propagating) flame. The first set of drops in the 2.2 Second Drop Tower showed that microgravity provides more favorable conditions for achieving inwardly-propagating flames (IPFs) than 1-g. A vortex interacts with a flame and creates a spherical pocket, which burns inwardly. Shadowgraphs at 1000 frames/sec quantify the Markstein number and flame speed. A Low-Laser Power PIV System was developed and is being added to the drop package. Numerical computations were required to explain why the Markstein numbers measured for the inwardly-propagating flames differ from those of outward propagating flames; this is an important research issue in the assessment of the Theory of Flame Stretch. The RUN-1DL code (developed by Prof. B. Rogg) was run for IPF and OPFs with complex methane and propane chemistry. Results confirmed that Ma for the IPFs are larger than for OPFs as was observed experimentally. Physical reasons for these new findings about the Theory of Flame Stretch are being determined from the experiments and the computations. Several journal papers have been published; the drop package is described in the AIAA Journal, while the one-g results appear in three other journal papers.

Driscoll, James F.↗
NASA NTRS1993

Capabilities and constraints of NASA's ground-based reduced gravity facilities

The ground-based reduced gravity facilities of NASA have been utilized to support numerous investigations addressing various processes and phenomina in several disciplines for the past 30 years. These facilities, which include drop towers, drop tubes, aircraft, and sounding rockets are able to provide a low gravity environment (gravitational levels that range from 10(exp -2)g to 10(exp -6)g) by creating a free fall or semi-free fall condition where the force of gravity on an experiment is offset by its linear acceleration during the 'fall' (drop or parabola). The low gravity condition obtained on the ground is the same as that of an orbiting spacecraft which is in a state of perpetual free fall. The gravitational levels and associated duration times associated with the full spectrum of reduced gravity facilities including spaced-based facilities are summarized. Even though ground-based facilities offer a relatively short experiment time, this available test time has been found to be sufficient to advance the scientific understanding of many phenomena and to provide meaningful hardware tests during the flight experiment development process. Also, since experiments can be quickly repeated in these facilities, multistep phenomena that have longer characteristic times associated with them can sometimes be examined in a step-by-step process. There is a large body of literature which has reported the study results achieved through using reduced-gravity data obtained from the facilities.

Lekan, Jack↗
NASA NTRS1995

Germany's five year space plan

Up to now microgravity combustion research has mainly been a powerful tool to apply on basic research items. The absence of thermal convection and thus the ability to experimentally verify simulations supposing buoyancy-free boundary conditions were ideally suited to improve knowledge about fundamental combustion processes. Beyond reasonable doubt the necessity to perform basic experiments will still be given in future in many disciplines. But the more scientists from more and more countries enter the field of microgravity combustion research and the more facilities are built for ground-based as well as suborbital and orbital research the more application-relevant items are requested to be investigated on. Thus the German microgravity combustion research program tries to enhance both fundamental as well technological aspects. The four projects described are utilizing on technologically advancing ground based facilities like drop tower drop shaft and parabolic aircrafts. Which items will be the German part of the European participation on the International Space-Station Alpha ISSA has not yet been decided.

Eigenbrod, Christian↗