Soot emission from flames and fires is a primary source of unwanted pollution. But it is also a product from some manufacturing industries and is necessary to enhance performance efficiency in furnaces. A fundamental understanding of the processes leading to soot particle formation, growth, and oxidation is needed to develop methods for predicting and controlling these combustion processes. Laser-induced incandescence (LII), a new, two-dimensional imaging diagnostic for the measurement of soot volume fraction, provides unparalleled temporal and spatial resolution and insight into soot formation and oxidation processes.
Laser-induced incandescence uses pulsed laser excitation to heat soot to far greater temperatures than the flame and exploits the resultant emission. The laser light is directed through the flame in a line or sheet. The LII signal is then collected and sent to a monochromator or camera for detection and analysis. LII achieves high temporal resolution by obtaining a signal induced by a single laser pulse. The temperature of a soot particle rapidly rises to its vaporization temperature, roughly 4000 K, for high laser intensities. The particle thermal emission at these elevated temperatures increases and shifts to the blue, in contrast to the non-laser-heated soot and flame gases.
The LII signal is linearly proportional to, and may be interpreted as a relative measure of, soot volume fraction. The technique can be absolutely calibrated by in-situ comparison of the LII signal to a system with a known soot volume fraction. Point measurements are easily made by using a photomultiplier tube. One- and two-dimensional imaging measurements can be made with a gated, intensified array camera.
Knowledge of the soot volume fraction and its spatial distribution is central to understanding several types of combustion phenomena. Formation of a soot shell around isolated burning droplets controls the radiative heat transfer from the flame back to the droplet and controls the burning rate. The small spatial scale and transient nature of droplet combustion impede measurement of soot volume fraction by traditional techniques. Although gas-jet diffusion flames may be steady state, LII measures soot volume fraction independently of contributions from scattering by soot aggregates and absorption by polycyclic aromatic hydrocarbons. LII can measure soot in turbulent combustion, as measurements can be collected with a single laser pulse. LII possesses geometric versatility not available in traditional line-of-sight techniques.
Since its initiation in 1994 we have characterized the spectral and temporal nature of the LII signal and excitation wavelength dependencies and demonstrated linearity between the LII signal and soot volume fraction. The next effort is to complete the technique verification by examining photochemical interferences and the effects of soot aggregate composition and size on the LII signal and by establishing the technique on a quantitative basis. Future work includes laboratory and reduced-gravity demonstrations.
Lewis contact: Karen J. Weiland, (216) 433-3623
Headquarters program office: OLMSA
Interestingly, the patterns formed by these flames are similar to those that occur in the formation of galaxies, the electrical patterns formed around the heart when it beats, the solitary pulses that travel along nerve fibers, and the patterns and spots on animals. It is thought that such a system may even give a hint to the origin of life. This similarity came as quite a surprise since, at first glance, these systems are remarkably different, yet after careful consideration we realized that they all involve some sort of diffusional process (thermal, molecular, and/or electrical) and a chemical reaction.
This premixed gas system-a lean mixture of butane and oxygen diluted with helium-is characterized by a high Lewis (Le) number, where Le is a relative measure of the rate at which heat liberated by the flame preheats the reactants versus the rate at which the stoichiometrically deficient component in the mixture diffuses into the flame by its own molecular Brownian motion.
In this mixture the flame propagates in one of two possible intrinsically unstable modes: it pulsates or it pulsates and spins. The first mode, termed radial pulsation, consists of a single, centrally located pacemaker site (bright spot in the middle), which propagates radially outward as its luminosity monotonically decreases. When the flame approaches the tube wall, it extinguishes, another pacemaker site appears at (or near) the center of the tube, and the cycle repeats. In contrast, the spinning (traveling wave) instability assumes the form of a rotating spiral wave that winds its way through the tube as the flame consumes the reactants.
Researchers believe that these instabilities are caused by a sufficiently large imbalance between the rate at which the flame can heat (energize) the reactants and begin their chemical conversion to products versus the rate at which the stoichiometrically deficient component (governing the reaction rate) can diffuse into the flame. Presently, experimental studies are attempting to isolate the role of chemical kinetics from diffusive transport (i.e., Le-number effects). This is inherently fundamental to our understanding of transport phenomena in the presence of chemical reaction and the stability of premixed flames.
Lewis contact: Dr. Howard Ross, (216) 433-2562
Headquarters program office: OLMSA
Dr. Subramanian's experiment, Thermocapillary Migrations and Interactions of Bubbles and Drops, studies the bubble's (or droplet's) velocities and shapes as it travels (or migrates) through another fluid medium having a linear temperature distribution. Local temperature gradients around the bubble impose a surface tension gradient on the bubble interface and produce motion in the film. This motion is typically from the bubble's hot side to its cold side, causing a jetting action that propels the bubble toward the relatively hotter areas of the surrounding fluid.
This type of science can only be done in low gravity, which can isolate the thermocapillary effects from the dominant effects of buoyancy and natural convection always present in normal gravity (1 g). The results have applications in ceramic and glass formation, as well as in metal and alloy solidification, on Earth. Better understanding of these thermocapillary effects can lead to superior bubble management techniques for crew life support processes required in the exploration of space.
This facility was designed and constructed under ESA Technology Center management by various Italian, German, and Belgian contractors (among others). NASA Lewis' function was to assist with the two U.S. BDPU experiments-of Dr. Subramanian (described above) and Dr. J.N. Koster of the University of Colorado, Boulder, in design and ground testing and during conduct of the flight experiment. The facility comprises various modules. The service and power modules provide computer and power control, respectively. But the backbone of the experiment is contained in the basic experiment module, an optics bench surrounding the specific test container. Only the test container is changed out between experiments.
The facility and test container hardware for this experiment performed very well. Overall, the total number of bubble and droplet migrations for the Subramanian experiments performed in separate test containers exceeded his expectations, and the video data were also considered excellent.
Lewis contact: Myron E. Hill, (216) 433-5279 Headquarters program office: OLMSA
Although both CM-1 principal investigators are studying combustion processes, their investigations are quite different. Professor Paul D. Ronney of the University of Southern California will examine structures of flame balls at low Lewis numbers (SOFBALL) in which a variety of fuel-lean gaseous mixtures fill the combustion chamber and are ignited. Professor Gerard M. Faeth of the University of Michigan will investigate laminar soot processes (LSP) by studying the key properties of burning gas jets of fuel, employing different fuels and nozzle sizes. CM-1 was challenged to meet the needs of these broadly different investigations and to plan ahead to the space station era, where the same concept will be employed for a multitude of investigations.
A chamber mockup and two experiment mounting structure mockups were fabricated in-house. The chamber mockup was constructed of clear Plexiglass to enable visualization. Other components, such as the power, fuel, and data connectors, were chosen to give realistic flight-like operation. Of critical importance for mission success and safety considerations, each make/break connection and seal has to be tight when reassembled.
The completed mockups illustrated both nominal and off-nominal operations and design feasibility. The engineers who designed the hardware were able to check out the form, fit, and function of many components. Several changes were made to improve the design, which was then critiqued by personnel knowledgeable in crew operations, including NASA Marshall Space Flight Center Spacelab Integration, leading to more design refinement. Next, the operational feasibility and timing requirements were tested by subjects who spanned the full size range of astronauts (5% female, 95% male). The final checkout was performed by three crew members with flight experience, who offered relatively minor criticism and gave the concept a "thumbs up" for operability in space.
At this time the flight chamber and experiment mounting structure are being fabricated in-house, and the entire CM-1 experiment will be assembled, qualified, and functionally tested beginning in early 1995, supporting a launch date of April 1997.
The CM-1 chamber mockup has served its primary purpose, but it continues to be an asset to the CM-1 project for crew training and the demonstration of CM-1 for several audiences, including shuttle safety personnel and Lewis visitors.
Lewis contact: Ann P. Over, (216) 433-6535
Headquarters program office: OLMSA
By studying this phenomenon we expect to also advance our basic understanding of combustion in space. Fuel spills in the form of liquid droplets can occur anywhere. Methods of detecting fires that result from liquid droplet combustion in space will need to be modified because of the absence of buoyancy.
The experiment was conceived by Prof. Forman A. Williams of the University of California at San Diego, with the help of his co-investigator, Prof. Frederick L. Dryer of Princeton University, and developed by NASA Lewis.
Before flight hardware could be developed for this experiment, it was essential to develop and test in microgravity a system for dispensing, deploying, and igniting single droplets. The science of this experiment requires precisely sized droplets (1 to 5 mm in diameter) free from all physical support, moving at very low (millimeters per second) velocities, and rapidly ignited. To be avoided are overdriving the flame with too hot an igniter or the ignition system causing the hot gas surrounding the heating source to push on and move the droplet.
The droplet is dispensed by using a precision fuel syringe precisely controlled by a stepper motor. The fuel, once it passes shutoff valves, flows to two opposed needles. These needles, each mounted on a servodisk motor, are precisely aligned to flow fuel to the gap between them. The correct amount of fuel is fed to the dispensing site, and then the gap between needles is adjusted so that the tips of the needles are on the surface of the droplet. The droplet is deployed when the two needles simultaneously retract at very high speed. In microgravity the droplet is then floating in the gas. Ignition takes place immediately after deployment when two prepositioned, opposed hot-wire igniters are quickly turned on, igniting the droplet. The hot-wire igniters, after being switched off, are quickly removed from the area near the droplet combustion site. The droplet combustion process can occur over the next 10 to 20 sec.
Testing in the Lewis 5-sec Zero-Gravity Facility has demonstrated the feasibility of this technique for a wide range of test conditions. The testing showed that the hardware, when the correct operational timing was used, performed virtually 100% of the time. The feasibility demonstration in this facility has allowed flight hardware development to be started. Testing will continue to improve understanding of the correct operating parameters for each point in the spaceflight test matrix. DCE is expected to fly in April 1997.
Lewis contacts: John B. Haggard, Jr., (216) 433-2832; Beth A. Parent, (216) 433-5284
Headquarters program office: OLMSA
STDCE was designed and built at NASA Lewis for a Spacelab rack on the 14-day United States Microgravity Laboratory 1 (USML-1) mission launched in June 1992. A test cell, 10 cm in diameter and 5 cm deep, was filled with 10-cSt silicone oil centrally heated with a submerged cartridge or with laser radiation. Flows were measured by using a laser light sheet and a video camera to record light from particles in the oil. Oil surface temperatures were measured with an infrared scanning imager. Analysis of the 38 tests conducted (12.5 hr of data recorded) showed good agreement with the CWRU model, which predicted that, even though the critical Marangoni number was exceeded, oscillations would not occur because the test cell was too large and the oil too viscous.
STDCE was rebuilt at Lewis for a second experiment using 2-cSt silicone oil and smaller test cells (diameters of 1.2, 2.0, and 3.0 cm) in six test modules: three using laser heating (constant flux) and three using submerged heaters (constant temperature). New optics include the free-surface-deformation measurement system, a single-channel Ronchi method for determining surface slopes of 5 to 30 mm/mm; the three-dimensional flow visualization system; an infrared telescope for the infrared imager; and changes to the laser focus to produce smaller heating zones (0.5 to 6 mm).
Other modifications will allow the crew to change out test modules and to optimize the measurements. Electrical and software systems were upgraded on the basis of lessons learned from USML-1 and to allow more crew interaction (73 hr of operation) and add a three-deck video cassette recorder. Three video pictures (infrared imager, flow visualization, and free-surface deformation) will be recorded and also downlinked to the payload operations control center at NASA Marshall Space Flight Center and to the user operations facility at Lewis. The STDCE-2 payload operations team was chosen to assist Ostrach and Kamotani in conducting the experiment during the 16-day USML-2 mission that will occur in autumn 1995. Three shifts will operate around the clock at Marshall, and one shift will operate at Lewis.
During fiscal 1994 the STDCE team completed the design and fabrication of flight hardware and entered the final stages of testing. Many serious challenges were met during the STDCE development, especially with optical systems alignment and the completion of the test modules. The STDCE rack simulator was used for astronaut crew training in July and then sent, along with a tabletop simulator of the optical systems, to Marshall and installed in their Spacelab mockup. Crew training on the flight hardware was completed at Lewis in September.
Bibliography
Light-scattering spectroscopy and correlation analysis was used to study the density fluctuations in xenon at temperatures very near the liquid-vapor critical point of this ideal fluid. The density fluctuations observed near the critical point reflect the underlying heat modes of the fluid and decay by thermal diffusion. The ultimate impact of this careful test can be far reaching because the theories to be compared with these measurements provide "universal" descriptions of many critical-point phase transitions, such as ferromagnetization, superconductivity, superfluidity, and binary fluid miscibility limits.
The principal investigator, Prof. Robert W. Gammon of the Institute for Physical Science and Technology at the University of Maryland, led a team of 15 scientists and engineers during nearly 14 days of continuous operations to make unprecedented measurements of a critical fluid in the low gravity of the space shuttle during the March 1994 STS-62 mission of the space shuttle Columbia . The instrument, built by Ball Aerospace Corp. and the University of Maryland, operated with no failures or problems for the duration of the mission, a total of 326 hr on orbit.
During the mission both autonomous and commanded operations were conducted. Approximately 480 commands were sent to the instrument to accomplish:
Preliminary analyses show that the measured decay rates exhibit the required precision within .300 mK of the critical temperature. Additional high-quality measurements were made within a few microkelvins of the critical temperature, and the density fluctuation correlation data exhibit, as predicted, an ever slower rate of decay. Measurements below the critical temperature, in the two-phase region, were also made. All measurements closer than 10 mK from Tc reflect data unattainable on Earth at the required accuracy of 1%.
Lewis contact: Dr. Richard W. Lauver, (216) 433-2860
Headquarters program office: OLMSA
IDGE used an apparatus designed, built, tested, and operated by NASA Lewis personnel at less than half the normal cost. It flew aboard the space shuttle Columbia (STS-62) from March 4 to 17, 1994. This IDGE mission was the first of three planned as part of the United States Microgravity Payload (USMP) series. It was suggested by the principal investigator, Professor Martin E. Glicksman from Rensselaer Polytechnic Institute in Troy, New York.
The IDGE mission was an unqualified success. In fact, by one important measure, it was 370% successful. This extraordinary success was possible because IDGE was fully operable by remote control from Earth (scientists on the ground monitored progress and sent up commands to alter IDGE programming). During the flight, dendritic solidification behaved differently than the scientists had expected-experiments could be completed more quickly. Remote operation (and some heroics from the Lewis operations team in sending a near record 8000 discrete commands over nine days) permitted IDGE to take advantage of the situation and operate far outside its programmed limits.
Fifty-eight dendrites were solidified at more than 20 different supercoolings, ranging from about 0.05 to 1.93 K (supercooling is the condition in which a dendrite solidifies at a temperature below its normal freezing point). The data consisted of more than 400 photographs and 800 television images of dendrites solidifying in space, along with associated supercooling, pressure, and acceleration data. Similar data, more than 1200 photographs, were taken on Earth before and after the flight. Photographs were possible because the test material was transparent succinonitrile, which mimics the behavior of iron when it solidifies.
Dendrite tip radii, tip solidification speed, and volumetric solidification rates have been determined from the space and Earth data. These rates were compared with predictions made by theorists over the last 50 years and used for metal production here on Earth. IDGE results indicate that the theories, although sound in some respects, are flawed. Consequently, corrected theories based on IDGE data should result in improved industrial metal production here on Earth.
The IDGE STS-62 data will provide a benchmark for testing theoretical developments for decades to come. Additional flights in 1996 and 1997 will provide data to test advanced solidification theories and the universality of their applicability.
Lewis contact: Edward A. Winsa, (216) 433-2861
Headquarters program office: OLMSA
The SSCE was the first combustion experiment to fly on the space shuttle-and the first such experiment in the NASA spaceflight program since Skylab. It was conceived by Professor Robert A. Altenkirch, Dean of Engineering at Mississippi State University. NASA Lewis designed the SSCE and built the flight payload in-house, providing all engineering, testing, flight qualification, scientific, and flight operations support functions. The SSCE project was supported in some way by nearly every major element of the Lewis organizational structure.
In the first five flights (conducted in 1990-92) thin-fuel samples made of ashless filter paper were burned in a sealed chamber filled with mixtures of 50% or 35% oxygen in nitrogen at pressures of 1.0, 1.5, or 2.0 atm. In the other three flights thick-fuel samples of PMMA (polymethylmethacrylate) were burned in 50% or 70% oxygen in nitrogen at 1.0 or 2.0 atm. The second of the thick-fuel flights was conducted onboard the space shuttle Discovery as part of the STS-64 mission, completing the seventh successful flight of eight planned spaceflights. During this mission two fuel samples were burned in a quiescent mixture of 50% oxygen and 50% nitrogen. The flight hardware performed without incident and provided all the required science data.
In orbit the fuel samples are ignited by the astronauts using an incandescent wire. Two 16-mm motion picture cameras photograph the flame from perpendicular perspectives while the fuel and flame temperatures and the chamber pressure are recorded by a digital data acquisition and control system. The fuels, the atmospheric conditions, and the measurement systems were chosen to provide benchmark data for comparison with evolving theory.
The principal investigator, Professor Altenkirch, has developed a time-dependent numerical simulation of the flame-spreading process from first principles (of fluid mechanics, heat transfer, and reaction kinetics). The spread rates, flame shape, and thermodynamic data from the completed SSCE flights have been compared directly with the results of the computational model, confirming the prediction that radiation heat transfer mechanisms must be included to accurately predict the behavior observed in the flight experiments. Without the radiation mechanisms the effects of pressure observed in the flight experiments are not captured by the model. The flight temperature data are being used to develop an improved numerical model of gas-phase radiative heat loss from the flame, which has been identified as a rate-limiting mechanism in many low-gravity flames. As the fundamental understanding of the flame-spreading process is enhanced by the results of the SSCE, the engineering of fire safety in spacecraft and on Earth can be improved with better knowledge of safety margins and fire prevention techniques.
Bibliography
Lewis contacts: John M. Koudelka, (216) 433-2852;
Kurt R. Sacksteder, (216) 433-2857
Headquarters program office: OLMSA
Pool Boiling Experiment Has Third Successful Shuttle Flight
The Pool Boiling Experiment (PBE) is designed to improve understanding of the
fundamental mechanisms that constitute nucleate pool boiling. Nucleate pool
boiling occurs when a stagnant pool of liquid is in contact with a surface that
can supply heat to the liquid--as when a pot of water boils. If the liquid
absorbs enough heat, a vapor bubble can be formed. Nucleate boiling has many
Earth-bound applications, such as steam-generated powerplants and petroleum and other chemical plants. Also, by studying the test fluid R-113, some basic understanding of the boiling behavior of cryogenic fluids could be obtained without the large cost of an experiment using an actual cryogen.
The Pool Boiling Experiment was conceived by Dr. Herman Merte of the University of Michigan and developed by NASA Lewis. The experiment was conducted on three space shuttle missions. The prototype system, first flown on STS-47 in September 1992, acquired a considerable amount of scientific data at different heat flux levels. Some minor modifications were made in the timing sequences in the test matrix for the STS-57 flight (June 1993). The prototype system was reflown on STS-60 in February 1994 as essentially a repeat of the STS-47 mission. The following general observations and conclusions are based on the data from all three flights:
Lewis contact: Angel M. Otero, (216) 433-3878
Headquarters program office: OLMSA
In this experiment molten bismuth-tin material within a furnace is cooled at one end and begins to solidify as the temperature of the liquid falls below the freezing point. It is important to know the position of the boundary between the solid and liquid material as well as how fast it moves during crystal growth. Hence, the data being sought are the rate at which the crystal grows, the mechanism by which it grows, and the structure and chemical composition of the crystal produced.
The In-Situ Monitoring of Bismuth-Tin Crystal Growth Experiment is a collaborative United States and French investigation of crystal growth fundamentals. The United States experimenters are studying bismuth doped with tin, and the French are studying tin doped with bismuth. The results of these two sets of experiments will be of fundamental importance to the semiconductor industry, which supplies the solid-state components, such as integrated circuits, for the manufacture of electronic equipment.
This experiment was conceived, designed, and developed by Professor Reza Abbaschian of the University of Florida and managed by NASA Lewis. It was conducted in the MEPHISTO furnace facility, a French-designed and -built materials processing furnace, on United States Microgravity Payload 2 (USMP-2).
The experiment flew aboard Columbia (STS-62) in March 1994. The MEPHISTO furnace carried three bismuth-tin samples, each approximately
1 m long and 6 mm in diameter. The middle portion of each sample was melted by the two heating elements in MEPHISTO, thus creating two solid-liquid interfaces. One of the heaters was kept stationary while the other was moved back and forth at specified rates to melt or solidify at that side of each sample. More than 55 melting and solidification cycles with different thermal and velocity conditions were performed during the mission, and more than 45 "interface temperature histories" were obtained during these cycles. Other data obtained were the continuous monitoring of the sample resistance, the heater translation histories, and the thermal measurements.
Lewis contact: Richard L. DeWitt, (216) 433-2601
Headquarters program office: OLMSA
In this investigation mixed powders of tungsten, nickel, and iron were initially cold compacted under pressure in the shape desired for the final product. The compacts were then heated to just below the nickel-iron alloy melting temperature to provide handling strength, a process called presintering. In the experiment they were heated above 1465 °ree;C to form a liquid-solid mixture. The tungsten, with its very high melting point
(3370 °ree;C), remained a solid while the nickel and iron, with much lower melting points, became liquid. The liquid permitted more rapid transport of material for faster sintering than would be possible if all the material were solid. After sintering, the microstructure of the samples (i.e., the structure when viewed under very high magnification), consisted of connected tungsten grains surrounded by the solidified liquid.
This experiment was conceived, designed, and developed by Professor Randall M. German of Pennsylvania State University. It flew as part of International Microgravity Laboratory 2 (IML-2) in July 1994 aboard the space shuttle Columbia . The experiment was conducted in an apparatus called the large isothermal furnace (LIF), which can operate at the high temperatures required. The LIF was developed by Ishikawajima-Harima Heavy Industries Co., Ltd., for the National Space Development Agency of Japan. This project was managed by NASA Lewis.
The LIF test specimens consisted of three different cartridges, each containing seven samples 10 mm in diameter by 10 mm high. One cartridge was tested at each of the three critical sintering periods identified in earlier ground-based experiments: 1, 15, and 120 min. In 1 min liquid penetrates along existing solid-solid boundaries; 15 min is needed for full densification; 120 min is needed to observe grain rotation and coalescence events.
In summary, a nominal temperature of 1506 deg.C (+/-4 deg C) was achieved for each test time. Free drift of Columbia during the appropriate times was confirmed. All functional objectives were achieved. The samples will be analyzed at the laboratories of Pennsylvania State University.
Lewis contact: Richard L. DeWitt, (216) 433-2601
Headquarters program office: OLMSA
The experiment plate included solar cell samples of standard silicon cells, International Space Station Alpha (ISSA) cells, Advanced Photovoltaic Solar Array (APSA) cells, and solar cells modified to suppress arcing effects. Various other samples of power system materials were also tested to investigate snapover effects, pinhole effects in insulators, and metal-to-metal variations in arcing effects.
During the 16-day mission of the space shuttle Columbia in March 1994, SAMPIE operated for more than 70 hr in space. The primary set of required measurements were taken with the Columbia payload bay oriented in the "ram" direction (coincident with the velocity vector). In this orientation all planned current collection data at direct-current voltages to 300 V were collected, all low-voltage arcing data (at voltages down to -300 V dc) were collected, and 90% of the high-voltage data (at voltages down to -600 V dc) were collected.
In the other required attitude orientation, known as the "wake" direction (with the payload bay oriented 180deg. away from the velocity vector), the planned low-voltage (to 300 V dc) current collection measurements were not taken owing to on-orbit problems with the high-voltage bias line of one power supply. The other high-voltage power supply was used to collect high-voltage arcing data in the wake. This step was not in the original plan because it had been assumed that there would be no arcing in the wake owing to the low plasma density. In fact, arcing was seen on several samples in the wake, providing unexpected information to the SAMPIE team. During both orbiter attitudes the plasma diagnostic instruments collected high-fidelity data on plasma temperature, plasma turbulence, and orbiter vehicle potential. These data will be used to "normalize" the arcing and current collection data, removing variations due only to plasma variations.
The flight data are now being analyzed by the SAMPIE principal investigator, Dr. Dale Ferguson. He has already used the flight data to validate the design of the ISSA plasma contactor program. The flight data will also be used to help validate computer modeling codes developed at Lewis in support of space power system design. The SAMPIE flight hardware is presently awaiting another flight opportunity.
Lewis contacts: Lawrence W. Wald, (216) 433-5219;
Dr. Dale C. Ferguson, (216) 433-2298; Dr. G. Barry Hillard, (216) 433-2220
Headquarters program office: OSAT
Upon return from flight STS-62 the annular test section was examined nondestructively. By a technique called tomography, computer-assisted radiographic images were developed of the phase-change material inside the annular volume. Cross sections of the lithium fluoride were examined axially and at 10 equidistant points perpendicular to the axis.
The predominance of the frozen fluoride at the radiator end of the canister indicated the sensitivity of the surface tension at the liquid/vapor interface to temperature. The void (bubble) was designed to be at 0deg. orientation during the melt phase (by the higher flux heater strip) but was allowed to seek its own position when the heat input was shut off and heat was allowed to pass to the radiator. The temperature gradient drove the bubble to the hotter end of the annulus, where it remained while the fluoride was gradually being frozen.
A temperature history was obtained from more than 40 thermocouples on and about the test canister. These readings are being analyzed in conjunction with the analytical program, which is being developed to predict the two-phase behavior of materials under microgravity.
Comparing the temperature history of any sets of thermocouples indicated that the results were repeatable well within the four melt/freeze cycles conducted. The temperature history of the first cycle differed noticeably from the subsequent cycles because of the phase-change material's location. When installed, the lithium fluoride was frozen with the canister axis horizontal, with the void at 0deg. orientation. The void under microgravity was at a very different location. The first temperature cycle reflects the transition.
Although most temperatures continually increased during the heating phase of the cycle, some decreased for a short period before increasing again. Earlier ground experiments showed the same phenomenon, the changes in inflection of temperature occurring at the 90°ree;. and 270°ree;. points. Because the melt line would pass these points during heating, and recognizing the large change in density as lithium fluoride changes phase, it is reasonable to expect that abrupt temperature changes may occur.
The TES-1 flight results have produced reliable data and information on materials melting and freezing under microgravity. Development of the computer analysis is under way and will enable predictions of such behavior. NASA Lewis provided the funding, project management, and scientific oversight for the design and development of the flight experiment, as well as safety, quality assurance, specialized hardware development, and unique skills required for experiment assembly. Work was accomplished by an in-house dedicated project team of engineers and technicians from NASA and NYMA.
Bibliography
NASA Lewis has combined the activities for several different projects into a single project to serve the microgravity environment needs of the scientists participating in the NASA microgravity science program. The Space Acceleration Measurement System (SAMS) Project, the SAMS-II Project, the Orbital Acceleration Research Experiment (OARE), and the Acceleration Characterization and Analysis Project (ACAP) were combined into the Microgravity Measurement and Analysis Project (MMAP) in April 1993.
SAMS measures the microgravity environment on the orbiter to support science experiments mounted in the middeck, the cargo bay, and the Spacelab and Spacehab modules. The eighth SAMS flight supported the Spacehab-01 payload on STS-60 in February 1994. The ninth flight supported four experiments of United States Microgravity Payload 2 (USMP-2) on STS-62 in February 1994. This mission provided near-real-time acceleration data to the scientists in the payload operations center. The tenth flight supported multiple science experiments in the Spacelab module of the International Microgravity Laboratory 2 (IML-2) payload on STS-65 in July 1994.
SAMS also delivered one flight unit to Moscow early in the year for launch to the Russian space station, Mir . In August 1994 the SAMS unit, along with the other American and Russian equipment, was successfully launched and docked with Mir . Operations are planned to begin during October 1994 and will extend for several years.
The OARE instrument was originally prepared for aerodynamic investigations of the orbiter at orbital altitudes. When that program finished, the OARE device, a sensitive accelerometer, was acquired by the microgravity science program to support microgravity characterization for science experiments. The OARE instrument flew on STS-62 and STS-65 in support of the USMP-2 and IML-2 payloads on those missions. An OARE data downlink from the orbiter to the payload operations center was developed to relay low-frequency acceleration data to the scientists in a timely fashion.
SAMS-II has continued developing an advanced SAMS-type system for the International Space Station Alpha (ISSA). The SAMS-II flight unit and its associated data and control equipment will take advantage of the unique ISSA operating environment to provide more dynamic and useful information to scientists conducting experiments on ISSA.
The Principal Investigators Microgravity Services Project was formed to acquire the functions of ACAP to provide microgravity information to the microgravity science investigators.
Mission summary reports were prepared for SAMS and OARE operations on STS-57, STS-60, and STS-62. These reports summarize mission activities and map the microgravity environment for the mission. Consultation was also provided on ISSA microgravity requirements and vibration isolation technology.
Lewis contact: Pete A. Vrotsos, (216) 433-3560
Headquarters program office: OLMSA
The goal of this project is to provide a means to measure three-dimensional fluid velocities quantitatively and qualitatively in space at many points. The method would apply to any system with an optically transparent fluid that can be seeded with tracer particles. Except for the tracer particles this measurement technique is nonintrusive. Velocity accuracies should be 1% to 5% of full field for flows in the 1-mm/sec range over a field of view of 3 to 4 cm.
Although stereoscopic imaging velocimetry can now be performed in a few research laboratories using two-camera systems, the technology is neither commercially available nor mature enough to be used in microgravity flight experiments. This Advanced Technology Development Project is drawing on the work of earlier researchers to produce a system more standardized in nature, more precise in performance, and easier to use. The velocimeter will be fully automatic and usable on any flow pattern within its specified speed regime, and it will track at least 500 tracer particles. The tracer particles will be chosen on the basis of neutral buoyancy, chemical compatibility, and optical reflectance.
Image data are recorded by two independent digital charge-coupled device cameras. These two cameras, oriented at 90°ree;. with respect to each other, provide a stereo pair of two-dimensional images. These images are stored on an optical disk in real time (30 frames/sec), and four types of off-line data processing are performed using the stored images.
Lewis contacts: Mark D. Bethea, (216) 433-8161;
Thomas K. Glasgow, (216) 433-5013
Headquarters program office: OLMSA
In general, a fluid can receive or release energy or transfer energy from one part of the fluid to another in two ways: heat diffusion and imposed work (e.g., pressure-volume work). Very close to the critical point these two energy transfer mechanisms become quite different-with very different time scales. Studying quantitatively the competition and the interaction of these mechanisms is the goal of this experiment, which consists of two parts, each with its own separate thermostat. One part, called Thermal Equilibration Bis (TEQB), studies heat diffusion. The other part, called Thermal Adiabatic Fast Equilibration (AFEQ), studies how pressure-volume work transports energy. Each thermostat has one interferometer and one visualization cell. Each cell will contain a layer 1 or 2 mm thick of the fluid sulfur hexafluoride (SF6) confined between parallel transparent windows and at the proper critical density.
The response of the fluid in the TEQB cells was monitored by video camera, light attenuation, and interferometry. Because fluid opalescence (light attenuation) becomes more intense near the critical point, it is a sensitive measure of temperature changes. Interferometry gives information on the local fluid density changes in various parts of the cells. An analysis of the time evolution of the interferograms determines the rate of relaxation of the fluid toward equilibrium, as a function of how far it is away from the critical temperature.
In AFEQ the temperature of the fluid is changed in the normal way by changing the temperature of the confining cell. More attention was directed to the rapid changes in the fluid that are induced internally, by heat from a current pulse through a resistance wire inside the cell. The wire was also used as a high-voltage electrode. When the wire was charged to a static potential of 500 V, the resulting pull of the SF6 molecules into the electric field surrounding the wire causes a local and global density change that can be observed interferometrically. Hence, there are two ways to induce nonequilibrium, one with heat and one without.
AFEQ and TEQB flew on International Microgravity Laboratory 2 (IML-2) in July 1994. They are sequel experiments to TEQ, which flew in January 1992 on IML-1. The principal investigator for the AFEQ and TEQB experiments was Professor Richard Ferrell from the University of Maryland. The AFEQ-TEQ team, based at NASA Lewis, designed and built the test cells.
The AFEQ-TEQB experiment team is now developing the necessary software to store and access the digital images acquired during the experiment and converting the high-rate-multiplexer videotapes from the European video standard (PAL) to the National Television System Committee (NTSC) configuration. Moreover, the team, the principal investigator, and the co-investigators are analyzing the data from AFEQ and TEQB events performed by the critical-point facility on IML-2. For instance, analyses of the fringe-shift data induced by a heat pulse and electric field in the AFEQ cell and of the relaxation time constant of SF6 fluid in the TEQB cell are under way.
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