DeVon W. Griffin

Phase-shifting shearing interferometer

A single-element phase-shifting interferometer has been developed based on the lateral shearing interferometer. This new interferometer requires no precise alignment, and the phase is continuously varied by changes in the voltage across a commercially available liquid-crystal phase retarder.

Detection of Smoke from Microgravity Fires

The history and current status of spacecraft smoke detection is discussed including a review of the state of understanding of the effect of gravity on the resultant smoke particle size. The results from a spacecraft experiment (Comparative Soot Diagnostics (CSD)) which measured microgravity smoke particle sizes are presented. Five different materials were tested producing smokes with different properties including solid aerosol smokes and liquid droplets aerosol smokes. The particulate size distribution for the solid particulate smokes increased substantially in microgravity and the results suggested a corresponding increase for the smokes consisting of a liquid aerosol. A planned follow on experiment that will resolve the issues raised by CSD is presented. Early results from this effort have provided the first measurements of the ambient aerosol environment on the ISS (International Space Station) and suggest that the ISS has very low ambient particle levels.

Buoyancy-induced differences in soot morphology

INTRODUCTIONReduction or elimination of buoyancy in flamesaffects the dominant mechanisms driving heattransfer, burning rates and flame shape. Theabsence of buoyancy produces longer resi-dence times for soot formation, clustering andoxidation [1]. In addition, soot pathlines arestrongly affected in microgravity [2]. We re-cently conducted the first experiments compar-ing soot morphology in normal and reduced-gravity laminar gas jet diffusion flames.Thermophoretic sampling [3-5] is a rela-tively new but well-established technique forstudying the morpho[o_ of soot primaries andaggregates. Although there have been somequestions about biasing that may be induceddue to sampling [6], recent analysis by Rosnereta[. [7] showed that the sample is not biasedwhen the system under study is operating inthe continuum limit. Furthermore, even if thesampling is preferentially biased to larger ag-gregates, the size-invariant premise of fractalanalysis should produce a correct fractal di-mension [7].EXPERIMENTAL PROCEDURESThe fuels were either propane or ethylene withflow rates of 1.0 and 1.5 cm3/s injected intoquiescent, atmospheric air from a nozzle with

Fuel Preheat Effects on Soot-Field Structure in Laminar Gas Jet Diffusion Flames Burning in 0-g and 1-g

An experimental investigation conducted at the 2.2-s drop tower of the NASA Lewis Research Center is presented to quantify the influence of moderate fuel preheat on soot-field structure within 0-g laminar gas jet diffusion flames. Parallel work in 1-g is also presented to delineate the effect of elevated fuel temperatures on soot-field structure in buoyant flames. The experimental methodology implements jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Fuel preheat of ∼100 K in the 0-g laminar jet diffusion flames is found to reduce soot loadings in the annular region, but causes an increase in soot volume fractions at the centerline. In addition, fuel preheat reduces the radial extent of the soot field in 0-g. In 1-g, the same fuel preheat levels have a more moderated influence on soot loadings in the annular region, but are also seen to enhance soot concentrations near the axis low in the flame. The increased soot loadings near the flame centerline, as caused by fuel preheat, are consistent with the hypothesis that preheat levels of ∼100 K enhance fuel pyrolysis rates. The results show that the growth stage of particles transported along the soot annulus is shortened both in 1-g and 0-g when elevated fuel temperatures are used.

Soot-field structure in laminar soot-emitting microgravity nonpremixed flames

Due to the intrinsic interest in laminar flame regimes that cannot be attained in normal gravity (1 g), the microgravity environment (0 g) offers an attractive and promising perspective to enhance our understanding of soot formation mechanisms in diffusion flames. An experimental investigation conducted at the 2.2-s drop tower of the NASA Lewis Research Center is presented to define the soot-field structure within 0-g laminar jet nonpremixed flames which operate above their smoke point. Parallel work on earthgravity flames is also presented to facilitate comparisons and define the effect of gravity on the soot fields. The experiment considers jet diffusion flames of nitrogen-diluted acetylene burning in quiescent air at atmospheric pressure. A full-field laser extinction technique is utilized to determine the transient soot spatial distributions in axisymmetric flames with fixed flow conditions corresponding to Rc=O(100). Results are presented for a nonsmoking normal-gravity flame and its nonbuoyant counterpart which releases soot from its blunt tip. Quantitative measurements on the transient postignition character of the soot field in 0 g are presented for the first time and indicate that millimeter-diameter burners result in brief soot-field transients in microgravity. At a fuel flow rate which is nearly twice that at the smoke point in 0 g, the soot field after the initial transient period sustains its annular structure throughout the luminous nonbuoyant-flamezone. The maximum soot volume fraction measured at 0 g is nearly double that at 1 g for the same flow rate, thus attesting to the higher sooting tendency of nonbuoyant flames. The results indicate that the prolonged residence times under microgravity promote soot growth more than oxidation, thus producing more soot in 0 g. Side-by-side comparisons of the soot distributions in 0-g and 1-g flames demonstrate the increased spatial resolution afforded in microgravity flames.

Soot aerosol properties in laminar soot-emitting microgravity nonpremixed flames

Abstract The spatial distributions and morphological properties of the soot aerosol are examined experimentally in a series of 0-g laminar gas-jet nonpremixed flames. The methodology deploys round jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Full-field laser-light extinction is utilized to determine transient soot spatial distributions within the flames. Thermophoretic sampling is employed in conjunction with transmission electron microscopy to define soot microstructure within the soot-emitting 0-g flames. The microgravity tests indicate that the 0-g flames attain a quasi-steady state roughly 0.7 s after ignition, and sustain their annular structure even beyond their luminous flame tip. The measured peak soot volume fractions show a complex dependence on burner exit conditions, and decrease in a nonlinear fashion with decreasing characteristic flow residence times. Fuel preheat by ∼140 K appears to accelerate the formation of soot near the flame axis via enhanced fuel pyrolysis rates. The increased soot presence caused by the elevated fuel injection temperatures triggers higher flame radiative losses, which may account for the premature suppression of soot growth observed along the annular region of preheated-fuel flames. Electron micrographs of soot aggregates collected in 0-g reveal the presence of soot precursor particles near the symmetry axis at midflame height. The observations also verify that soot primary particle sizes are nearly uniform among aggregates present at the same flame location, but vary considerably with radius at a fixed distance from the burner. The maximum primary size in 0-g is found to be by 40% larger than in 1-g, under the same burner exit conditions. Estimates of the number concentration of primary particles and surface area of soot particulate phase per unit volume of the combustion gases are also made for selected in-flame locations.

Recent advances in the development of phase-shifting liquid crystal interferometers for visible and near-IR applications

Conventional phase-shifting interferometers are extremely sensitive to mechanical shock and transmitted vibration because they utilize separate test and reference optical paths that must be aligned to within a fraction of the wavelength of the light being used. Such interferometers are difficult and time consuming to set up, align, and maintain, and are costly due to the number of optics required for the dual-path design. Common-path interferometers such as the point-diffraction type are much less sensitive to environmental disturbances but until recently have not been capable of phase-shifting. The liquid crystal point diffraction interferometer (LCPDI), first demonstrated by Mercer and Creath, employs a dye-doped, electro-optical LC device as the point-diffraction source to lend phase-shifting capability to the PDI common-path design. The advantage of this approach is that it combines the strengths of both types of interferometer to produce a phase-shifting diagnostic device that is much more compact, robust, and accurate than dual-path interferometers while at the same time using fewer optical elements. Such attributes make this device of special interest for diagnostic applications in the scientific, commercial, military, and industrial sectors where vibration insensitivity, power requirements, size, weight, and cost are critical issues. In this paper, we will describe some recent activities in the areas of materials development, device design, and fabrication techniques for the original LCPDI to improve its accuracy, extend its operation to both the visible and near-IR regions of the spectrum, and to improve its temporal data collection capabilities to near video frame rates.

The LCPDI: A Compact and Robust Phase-Shifting Point-Diffraction Interferometer Based on Dye-Doped LC Technology

Point-diffraction interferometers, by design, are much less sensitive to environmental disturbances than dual-path interferometers, but, until very recently, have not been capable of phase shifting. The liquid crystal point diffraction interferometer (LCPDI) utilizes a dye-doped, liquid crystal (LC), electro-optical device that functions as both the point-diffraction source and the phase-shifting element, yielding a phase-shifting diagnostic device that is significantly more compact and robust while also using fewer optical elements than conventional dual-path interferometers. These attributes make the LCPDI of special interest for diagnostic applications in the scientific, commercial, military, and industrial sectors, where vibration insensitivity, power requirements, size, weight, and cost are critical issues. Until very recently, LCPDI devices have used a plastic microsphere embedded in the LC fluid layer as the point-diffraction source. The process for fabricating microsphere-based LCPDI devices is low-yield, labor-intensive, very “hands-on,” and great care and skill are required to produce devices with adequate interference fringe contrast for diagnostic measurements. With the goal in mind of evolving the LCPDI beyond the level of a laboratory prototype, we have developed “second-generation” LCPDI devices in which the reference diffracting elements are an integral part of the substrates by depositing a suitable optical material (vapor-deposited thin films or photoresist) directly on the substrate surface. These “structured” substrates eliminate many of the assembly difficulties and performance limitations of previous LCPDI devices as well as open the possibility of mass-producing LCPDI devices at low cost by the same processes used to manufacture commercial LC displays.

Intravenous Solutions for Exploration Missions

*† ‡ § This paper describes the intravenous (IV) fluids requirements being developed for medical care during NASA’s future exploration class missions. Previous research on IV solution generation and mixing in space is summarized. The current exploration bas eline mission profiles are introduced, potential medical conditions described and evaluated for fluidic needs, and operational issues assessed. We briefly introduce potential methods for generating IV fluids in microgravity. Conclusions on the recommended fluid volume requirements are presented. I. Introduction The Vision for Space Exploration outlined a new direction for NASA, consisting of missions unlike those accomplished before. These missions will return astronauts to the Moon and test the technologies required for Mars missions. The International Space Station (ISS) will be used as a test bed for some of these new technologies. NASA’s Exploration Systems Architecture Study presents the Design Reference Missions (DRMs) that are being used to facilitat e the derivation of requirements for the essential technologies. These DRMs include missions to ISS, Lunar Sorties, Lunar Outposts, and Mars Exploration. 1 These longer duration missions increase the likelihood of a medical incident and thus the need for m edical fluids. The Patient Condition DataBase (PCDB) contains a list of over 400 medical conditions that may present and require treatment during ISS missions. 2 These conditions are a subset of the total possible conditions that could be encountered durin g long duration, Extra -Vehicular Activity (EVA) intensive, exploration missions. Of the 442 conditions, approximately 115 may require medical fluids during the course of treatment. Terrestrial treatment would typically include fluids such as Normal Salin e (NS) (0.9% NaCl), 5% Dextrose, Lactated Ringer’s, or whole blood. Operational constraints, such as mass limitations and lack of refrigeration, may limit the type and volume of such fluids that can be carried onboard the spacecraft. Representative condi tions that would require fluid treatment include major bone fracture, burns, and acute anemia. These conditions are described in detail later in this paper. Choosing a technology to generate sterile water for injection and produce intravenous fluids requi res balancing capabilities with mission and medical requirements. For example, the type, volume, and timeline over which IV fluids are required are key drivers in selecting an appropriate technology. Additionally, the system must operate in various gravi ty environments, such as microgravity, lunar gravity, and Martian gravity, while also functioning in earth normal gravity for testing and verification. Thrusting events also produce an effective gravitational level and could possibly occur during fluid pr oduction. Successful operation requires maintaining sterility. Some technologies might be sealed until use, requiring only seal integrity, while other systems may require internal recirculation or periodic maintenance to ensure proper operation. Diagnos tics will likely be required to verify proper operation of the system. Crew time is always an issue, and may be especially important in an emergency. Any system must be relatively simple to use, safe, and reliable.

Effects of Flow Rate on the Environment in a Microbioreactor for Bone Cells

The goal of the present paper is to report on the biophysicochemical transport processes involved in microbioreactors designed for bone cell studies. The purpose of this effort is to guide our biological testing for cell viability, growth, and morphology markers. We present a microbioreactor design that has been optimized to ensure that the flow is uniform in the direction of flow. Transport characterization results are obtained using numerical and experimental methods.© 2004 ASME