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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Measurement of the Shear Lift Force on a Bubble in a Channel Flow

Two-phase flow systems play vital roles in the design of some current and anticipated space applications of two-phase systems which include: thermal management systems, transfer line flow in cryogenic storage, space nuclear power facilities, design and operation of thermal bus, life support systems, propulsion systems, In Situ Resource Utilization (ISRU), and space processes for pharmaceutical applications. The design of two-phase flow systems for space applications requires a clear knowledge of the behaviors of the dispersed phase (bubble), its interaction with the continuous phase (liquid) and its effect on heat and mass transfer processes, The need to understand the bubble generation process arises from the fact that for all space applications, the size and distribution of bubbles are extremely crucial for heat and mass transfer control. One important force in two-phase flow systems is the lift force on a bubble or particle in a liquid shear flow. The shear lift is usually overwhelmed by buoyancy in normal gravity, but it becomes an important force in reduced gravity. Since the liquid flow is usually sheared because of the confining wall, the trajectories of bubbles and particles injected into the liquid flow are affected by the shear lift in reduced gravity. A series of experiments are performed to investigate the lift force on a bubble in a liquid shear flow and its effect on the detachment of a bubble from a wall under low gravity conditions. Experiments are executed in a Poiseuille flow in a channel. An air-water system is used in these experiments that are performed in the 2.2 second drop tower. A bubble is injected into the shear flow from a small injector and the shear lift is measured while the bubble is held stationary relative to the fluid. The trajectory of the bubble prior, during and after its detachment from the injector is investigated. The measured shear lift force is calculated from the trajectory of the bubble at the detachment point. These values for the shear lift are then compared with the theoretical predictions from various published works on shear lift in the open literature, which include asymptotic solutions at low bubble Reynolds number, potential flow predictions and numerical studies that deal with intermediate bubble Reynolds numbers.

Nahra, Henry K.↗
NASA NTRS2009

Development of a Modified Vacuum Cleaner for Lunar Surface Systems

The National Aeronautics and Space Administration (NASA) mission to expand space exploration will return humans to the Moon with the goal of maintaining a long-term presence. One challenge that NASA will face returning to the Moon is managing the lunar regolith found on the Moon's surface, which will collect on extravehicular activity (EVA) suits and other equipment. Based on the Apollo experience, the issues astronauts encountered with lunar regolith included eye/lung irritation, and various hardware failures (seals, screw threads, electrical connectors and fabric contamination), which were all related to inadequate lunar regolith mitigation. A vacuum cleaner capable of detaching, transferring, and efficiently capturing lunar regolith has been proposed as a method to mitigate the lunar regolith problem in the habitable environment on lunar surface. In order to develop this vacuum, a modified "off-the-shelf" vacuum cleaner has been used to determine detachment efficiency, vacuum requirements, and optimal cleaning techniques to ensure efficient dust removal in habitable lunar surfaces, EVA spacesuits, and air exchange volume. During the initial development of the Lunar Surface System vacuum cleaner, systematic testing was performed with varying flow rates on multiple surfaces (fabrics and metallics), atmospheric (14.7 psia) and reduced pressures (10.2 and 8.3 psia), different vacuum tool attachments, and several vacuum cleaning techniques to determine the performance requirements for the vacuum cleaner. The data recorded during testing was evaluated by calculating percent removal, relative to the retained simulant on the tested surface. In addition, Scanning Electron Microscopy (SEM) imaging was used to determine particle size distribution retained on the surface. The scope of this paper is to explain the initial phase of vacuum cleaner development, including historical Apollo mission data, current state-of-the-art vacuum cleaner technology, and vacuum cleaner testing that has focused on detachment capabilities varying pressure environments.

Toon, Katherine P.↗
NASA NTRS2010

Development of a Modified Vacuum Cleaner for Lunar Surface Systems

The National Aeronautics and Space Administration (NASA) mission to expand space exploration will return humans to the Moon with the goal of maintaining a long-term presence. One challenge that NASA will face returning to the Moon is managing the lunar regolith found on the Moon's surface, which will collect on extravehicular activity (EVA) suits and other equipment. Based on the Apollo experience, the issues astronauts encountered with lunar regolith included eye/lung irritation, and various hardware failures (seals, screw threads, electrical connectors and fabric contamination), which were all related to inadequate lunar regolith mitigation. A vacuum cleaner capable of detaching, transferring, and efficiently capturing lunar regolith has been proposed as a method to mitigate the lunar regolith problem in the habitable environment on lunar surface. In order to develop this vacuum, a modified "off-the-shelf' vacuum cleaner will be used to determine detachment efficiency, vacuum requirements, and optimal cleaning techniques to ensure efficient dust removal in habitable lunar surfaces, EVA spacesuits, and air exchange volume. During the initial development of the Lunar Surface System vacuum cleaner, systematic testing was performed with varying flow rates on multiple surfaces (fabrics and metallics), atmospheric (14.7 psia) and reduced pressures (10.2 and 8.3 psia), different vacuum tool attachments, and several vacuum cleaning techniques in order to determine the performance requirements for the vacuum cleaner. The data recorded during testing was evaluated by calculating particulate removal, relative to the retained simulant on the tested surface. In addition, optical microscopy was used to determine particle size distribution retained on the surface. The scope of this paper is to explain the initial phase of vacuum cleaner development, including historical Apollo mission data, current state-of-the-art vacuum cleaner technology, and vacuum cleaner testing that has focused on detachment capabilities at varying pressure environments.

Toon, Katherine P.↗
NASA NTRS2002

Experimental Visualization of Bubble Formation from an Orifice In Microgravity in the Presence of Electric Fields

The formation of air bubbles injected into a stagnant, isothermal liquid in microgravity through an orifice was studied. The bubbles grew very large in microgravity. They attained a nearly spherical shape and showed pronounced affinity towards coalescence in the absence of electric fields and other perturbations. Under the influence of electric fields, periodic detachment was observed, with bubble sizes larger than in terrestrial conditions. The bubble shape was elongated. After detachment, the bubbles moved away from the electrode at which they formed without coalescing with other bubbles. Experimental data on bubble shape and size at detachment showed good agreement with models.

Herman, C.↗
NASA NTRS2010

The Evolution of Open Magnetic Flux Driven by Photospheric Dynamics

The coronal magnetic field is of paramount importance in solar and heliospheric physics. Two profoundly different views of the coronal magnetic field have emerged. In quasi-steady models, the predominant source of open magnetic field is in coronal holes. In contrast, in the interchange model, the open magnetic flux is conserved, and the coronal magnetic field can only respond to the photospheric evolution via interchange reconnection. In this view the open magnetic flux diffuses through the closed, streamer belt fields, and substantial open flux is present in the streamer belt during solar minimum. However, Antiochos and co-workers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet (HCS) - it will connect via narrow corridors to the polar coronal hole of the same polarity. This contradicts the requirements of the interchange model. We have performed an MHD simulation of the solar corona up to 20R solar to test both the interchange model and the Antiochos conjecture. We use a synoptic map for Carrington Rotation 1913 as the boundary condition for the model, with two small bipoles introduced into the region where a positive polarity extended coronal hole forms. We introduce flows at the photospheric boundary surface to see if open flux associated with the bipoles can be moved into the closed-field region. Interchange reconnection does occur in response to these motions. However, we find that the open magnetic flux cannot be simply injected into closed-field regions - the flux eventually closes down and disconnected flux is created. Flux either opens or closes, as required, to maintain topologically distinct open and closed field regions, with no indiscriminate mixing of the two. The early evolution conforms to the Antiochos conjecture in that a narrow corridor of open flux connects the portion of the coronal hole that is nearly detached by one of the bipoles. In the later evolution, a detached coronal hole forms, in apparent violation of the Antiochos conjecture. Further investigation reveals that this detached coronal hole is actually linked to the extended coronal hole by a separatrix footprint on the photosphere of zero width. Therefore, the essential idea of the conjecture is preserved, if we modify it to state that coronal holes in the same polarity region are always linked, either by finite width corridors or separatrix footprints. The implications of these results for interchange reconnection and the sources of the slow solar wind are briefly discussed.

Linker, Jon A.↗
NASA NTRS2014

Flow Phenomena in the Very Near Wake of a Flat Plate with a Circular Trailing Edge

The very near wake of a flat plate with a circular trailing edge, exhibiting pronounced shedding of wake vortices, is investigated with data from a direct numerical simulation. The separating boundary layers are turbulent and statistically identical thus resulting in a wake that is symmetric in the mean. The focus here is on the instability of the detached shear layers, the evolution of rib-vortex induced localized regions of reverse flow that detach from the main body of reverse flow in the trailing edge region and convect downstream, and phaseaveraged velocity statistics in the very near wake. The detached shear layers are found to exhibit unstable behavior intermittently, including the development of shear layer vortices as in earlier cylinder flow investigations with laminar separating boundary layers. Only a small fraction of the separated turbulent boundary layers undergo this instability, and form the initial shed vortices. Pressure spectra within the shear layers show a broadband peak at a multiple of shedding frequency. Phase-averaged intensity and shear stress distributions of the randomly fluctuating component of velocity are compared with those obtained in the near wake. The distributions of the production terms in the transport equations for the turbulent stresses are also provided.

Turbulence↗
NASA NTRS2012

Methods for Improving Long-Range Wireless Communication Between Extreme Terrain Vehicles

Axel is an extreme terrain, two-wheeled rover designed to traverse rocky surface and sub-surface landscapes in order to conduct remote science experiments in hard-to-reach locations. The rover's design meets many requirements for a mobile research platform capable of reaching water seeps on Martian cliff sides. Axel was developed by the Mobility and Robotic Systems section at the Caltech Jet Propulsion Laboratory. Unique design criteria associated with extreme terrain mobility led to a unique rover solution, consisting of a central module, which provides long-term energy storage and space for large-scale science payloads, and two detachable Axels that can detach and explore extreme terrain locations that are inaccessible to conventional rovers. The envisioned mission could involve a four-wheeled configuration of Axel called 'DuAxel' that is able to traverse the benign, flattened terrain of a landing site and approach the edge of the targeted crater or cave where it would deploy anchoring legs and detach one of the Axel rovers [1]. A tether provides a secure link between the Axel rover and the central module, acting as an anchor to allow Axel to descend along steep crater walls to collect data from the scientifically relevant sites along the water seeps or crater ledges. After completing its scientific mission Axel would hoist itself up to the central module and dock autonomously (using its on-board stereo cameras), allowing the once-again recombined DuAxel to travel to another location to repeat data collection.

wireless communication↗
NASA NTRS2016

Temporary Thermocouple Attachment for Thermal/Vacuum Testing at Non-Extreme Temperatures

Post-test examination and data analysis that followed a two week long vacuum test showed that numerous self-stick thermocouples became detached from the test article. The thermocouples were reattached with thermally conductive epoxy and the test was repeated to obtain the required data. Because the thermocouple detachment resulted in significant expense and rework, it was decided to investigate the temporary attachment methods used around NASA and to perform a test to assess their efficacy. The present work describes the original test and the analysis that showed that the thermocouples had become detached, temporary thermocouple attachment methods assessed in the retest and in the thermocouple attachment test, and makes a recommendation for attachment methods for future tests.

Ungar, Eugene K.↗
NASA NTRS2016

Temporary Thermocouple Attachment for Thermal/Vacuum Testing at Non-Extreme Temperatures

Post-test examination and data analysis that followed a two week long vacuum test showed that numerous self-stick thermocouples became detached from the test article. The thermocouples were reattached with thermally conductive epoxy and the test was repeated to obtain the required data. Because the thermocouple detachment resulted in significant expense and rework, it was decided to investigate the temporary attachment methods used around NASA and to perform a test to assess their efficacy. The present work describes the original test and the analysis that showed that the thermocouples had become detached, temporary thermocouple attachment methods assessed in the retest and in the thermocouple attachment test, and makes a recommendation for attachment methods for future tests.

Ungar, Eugene K.↗
NASA NTRS2016

Bridgman Growth of Germanium and Germanium-Silicon Crystals under Microgravity

Four different Bridgman growth experiments on Ge:Ga and Ge(sub x)Si(sub 1-x) were performed under microgravity during the FOTON M4 flight in fall 2014 as joint German-Russian experiments. The experiments were also part of the RDGS/ICESAGE project(s) of ESA/NASA on detached growth of Ge and Ge-Si. Three experiments on Ge:Ga investigated different heat and mass transport regimes, i.e. mostly diffusive conditions, flows driven by a rotating magnetic field, and flows driven by vibration. The fourth experiment on Ge(sub 0.98)Si(0.02) investigated detached growth. All four experiments were successful and yielded crystals. Both the Ge-Si experiment and two of the Ge:Ga experiments showed stable detachment from the ampoule wall, although this was not planned for the latter two experiments. The influence of the rotating magnetic field as well as of the vibration was pronounced in the case of the microgram experiments, but dominated by buoyancy convection under 1g.

Croell, A.↗
NASA NTRS2017

Influence of Containment on the Growth of Germanium-Silicon in Microgravity

A series of Ge(sub 1-x)Si(sub x) crystal growth experiments are planned to be conducted in the Low Gradient Furnace (LGF) onboard the International Space Station. The primary objective of the research is to determine the influence of containment on the processing-induced defects and impurity incorporation in germanium-silicon alloy crystals. A comparison will be made between crystals grown by the normal and 'detached' Bridgman methods and the ground-based float zone technique. 'Detached' or 'dewetted' Bridgman growth is similar to regular Bridgman growth in that most of the melt is in contact with the crucible wall, but the crystal is separated from the wall by a small gap, typically of the order of 10-100 microns. A meniscus bridges this gap between the top of the crystal and the crucible wall. Theoretical models indicate that an important parameter governing detachment is the pressure differential across this meniscus. An experimental method has been developed to control this pressure differential in microgravity that does not require connection of the ampoule volume to external gases or changes in the temperature profile during growth. Experiments will be conducted with positive, negative or zero pressure differential across the meniscus. Characterization results of ground-based experiments, including etch pit density, synchrotron white beam X-ray topography and double axis X-ray diffraction will also be described.

Volz, M. P.↗
NASA NTRS1972

Absorbing-sphere model for calculating ion-ion recombination total cross sections.

An 'absorbing-sphere' model based on the Landau-Zener method is set up for calculating the upper limit thermal energy (300 K) reaction rate and the energy dependence of the total cross sections. The crucial parameter needed for the calculation is the electron detachment energy for the outer electron on the anion. It is found that the cross sections increase with decreasing electron detachment energy.

Olson, R. E.↗
NASA NTRS1974

Heat transfer with nucleate boiling of liquids under weak mass force field conditions

The motion is examined of a vapor bubble growing and rising from a flat horizontal heater in the ideal fluid approximation and taking drag into account. Estimates are given of bubble lifetime, bubble radius at detachment, bubble detachment frequency, and time for the bubble to attain a constant rate of rise. The relations obtained for the microcharacteristics of the boiling process are used to determine the coefficients of heat transfer in developed nucleate boiling. A new form of the equations for describing heat transfer in nucleate boiling in dimensionless parameters is proposed.

Kirichenko, Y. A.↗
NASA NTRS1975

Ionosphere-magnetosphere coupling. I - Thermal plasma

The complex interaction of the cold plasma of the plasmasphere and ionosphere with the hot plasma of the ring current and the plasma sheet is studied. It is seen that a coupling, probably through wave particle interactions, exists which seems to have a strong influence on the temperature of the plasma of the outer plasmasphere and on the detailed dynamics of the bulge region, especially the formation of detached plasma regions or plasma tails. Also, there is evidence that the outer plasmasphere may display very high temperatures, and that detached plasma regions are closely associated with ring current injections.

Chappell, C. R.↗
NASA NTRS1975

Shock tube study of ionization rates of NaCl-contaminated argon

Electron density, electron temperature, and concentration of excited sodium atoms are measured in the weakly ionized regime behind a shock wave in impure argon in a shock tube using microwave techniques and spectrally resolved radiometry. Evidence is presented to show that an apparent increase in the rate of ionization is due to electron detachment of negative chlorine ions produced from sodium chloride vapor contained as an impurity. To be consistent with this chemical model, rate coefficients are found in the temperature range between 5500 and 8600 K for the dissociation of NaCl into an ion pair, dissociation of NaCl into a neutral pair, and electron detachment of a negative chlorine ion. Electron temperature is lower than heavy-particle temperature by roughly 1000 K. The electron-argon impact-ionization rate coefficient is a weak function of electron temperature in contradiction to expectation.

Schneider, K.-P.↗
NASA NTRS1976

Flight 1 technical report for experiment 74-36: Thermal migration of bubbles and their interaction with solidification interfaces

Specimens of gas saturated carbon tetrabromide were directionally solidified in a transparent furnace using a gradient freeze technique. The original temperature gradient was 5 C/cm and the cooling rate was 40 C/h. Progress of the experiment was monitored photographically. Gas bubbles were generated at the advancing solidification front in each of the three specimens. The gas bubbles were observed to increase in size, coalesce, and eventually be grown into the solid specimen under low gravity conditions. No bubble detachment from the interface was observed. Identical specimens processed in the laboratory showed bubble nucleation, bubble growth, and eventual bubble detachment due to buoyancy forces. Examination of the specimens showed a significantly greater void content in the low gravity processed samples. The grain size was observed to be finer in the low gravity processed samples.

Papazian, J. M.↗
NASA NTRS1977

The interaction of bubbles with solidification interfaces

The behavior of bubbles at a dendritic solidification interface was studied during the coasting phase of a sounding rocket flight. Sequential photographs of the gradient freeze experiment showed nucleation, growth and coalescence of bubbles at the moving interface during both the low-gravity and one-gravity tests. In the one-gravity test the bubbles were observed to detach from the interface and float to the top of the melt. However, in the low-gravity tests no bubble detachment from the interface or steady state bubble motion occurred and large voids were grown into the crystal. These observations are discussed in terms of the current theory of thermal migration of bubbles and in terms of their implications on the space processing of metals.

Papazian, J. M.↗
NASA NTRS1976

Natural precedents to active magnetospheric experiments

Some of the natural analogs of proposed seeding experiments in the magnetosphere are: electric charged particle injections during substorms; lightning-induced whistlers providing wave injections; 'detachment' of plasma from the plasmapause, which is equivalent to light-ion seeding in the outer magnetosphere. In the present paper, the characteristics of some natural precedents to active experiments are reviewed, and their relative advantages and drawbacks are examined. One of these precedents - wave generation in detached plasma regions - is then discussed in some detail; the discussion reveals the generation of ELF electromagnetic noise when the energetic electrons exceed the stably trapped limit, and also indicates that a critical dimension for the seeded volume exists transverse to the geomagnetic field.

Russell, C. T.↗