Laminar smoke points of coflowing flames in microgravity

by on 9 June 2015in Physical Sciences No comment

Laminar smoke points were measured in nonbuoyant laminar jet diffusion flames in coflowing air. Microgravity was obtained on board the International Space Station. A total of 55 smoke points were found for ethylene, propane, propylene, and propylene/nitrogen mixtures. Burner diameters were 0.41, 0.76, and 1.6 mm, and coflow velocities varied from 5.4 to 65 cm/s. These flames allow extensive control over residence time via variations in dilution, burner diameter, and coflow velocity. The measured smoke-point lengths scaled with d−0.91uair0.41, where d is burner diameter and uair is coflow velocity. The measurements yielded estimates of sooting propensities of the present fuels in microgravity diffusion flames. Analytical models of residence times in gas jet flames are presented, and although residence time helps explain many of the observed trends it does not correlate the measured smoke points.

Related URLs:
http://www.sciencedirect.com/science/article/pii/S037971121100110X

Capillary channel flow experiments aboard the International Space Station

by on 9 June 2015in Physical Sciences No comment

In the near-weightless environment of orbiting spacecraft capillary forces dominate interfacial flow phenomena over unearthly large length scales. In current experiments aboard the International Space Station, partially open channels are being investigated to determine critical flow rate-limiting conditions above which the free surface collapses ingesting bubbles. Without the natural passive phase separating qualities of buoyancy, such ingested bubbles can in turn wreak havoc on the fluid transport systems of spacecraft. The flow channels under investigation represent geometric families of conduits with applications to liquid propellant acquisition, thermal fluids circulation, and water processing for life support. Present and near future experiments focus on transient phenomena and conduit asymmetries allowing capillary forces to replace the role of gravity to perform passive phase separations. Terrestrial applications are noted where enhanced transport via direct liquid-gas contact is desired.

Related URLs:
http://link.aps.org/doi/10.1103/PhysRevE.88.063009

Preliminary Results of the Fluid Merging Viscosity Measurement Space Station Experiment

by on 9 June 2015in Physical Sciences No comment

During the Space Shuttle “down period” a call was put out for low upmass payloads. One of these “low up mass” International Space Station science experiments is the “Fluid merging Viscosity Measurement”, FMVM investigation. The purpose of FMVM is to measure the rate of coalescence of two highly viscous liquid drops and correlate the results with the liquid viscosity and surface tension. The experiment take advantage of the low gravitational free floating conditions in space to permit the unconstrained coalescence of two nearly spherical drops. The merging of the drops is accomplished by deploying them from a syringe and suspending them on 2 Nomex threads followed by the astronaut’s manipulation of one of the drops towards a stationary droplet till contact is achieved. Coalescence and merging occurs due to shape relaxation and reduction of surface energy, being resisted by the viscous drag within the liquid. The coalescence was recorded on video (ISS VTR) and some of the data was downlinked near real-time. A range of drop diameters, different liquids with differing viscosity and surface tensions should yield a large range of experiment parameters used to correlate with theory and to compare with numerical experiments. The results are important for a better understanding of the coalescence process. The experiment is also relevant to liquid phase sintering and is a potential new method for measuring viscosity of viscous glass formers at low shear rates.

Related URLs:
http://dx.doi.org/10.2514/6.2006-1142

Physical and Biological Organ Dosimetry Analysis for International Space Station Astronauts

by on 9 June 2015in Physical Sciences No comment

In this study, we analyzed the biological and physical organ dose equivalents for International Space Station (ISS) astronauts. Individual physical dosimetry is difficult in space due to the complexity of the space radiation environment, which consists of protons, heavy ions and secondary neutrons, and the modification of these radiation types in tissue as well as limitations in dosimeter devices that can be worn for several months in outer space. Astronauts returning from missions to the ISS undergo biodosimetry assessment of chromosomal damage in lymphocyte cells using the multicolor fluorescence in situ hybridization (FISH) technique. Individual-based pre-flight dose responses for lymphocyte exposure in vitro to γ rays were compared to those exposed to space radiation in vivo to determine an equivalent biological dose. We compared the ISS biodosimetry results, NASA's space radiation transport models of organ dose equivalents, and results from ISS and space shuttle phantom torso experiments. Physical and biological doses for 19 ISS astronauts yielded average effective doses and individual or population-based biological doses for the approximately 6-month missions of 72 mSv and 85 or 81 mGy-Eq, respectively. Analyses showed that 80% or more of organ dose equivalents on the ISS are from galactic cosmic rays and only a small contribution is from trapped protons and that GCR doses were decreased by the high level of solar activity in recent years. Comparisons of models to data showed that space radiation effective doses can be predicted to within about a ±10% accuracy by space radiation transport models. Finally, effective dose estimates for all previous NASA missions are summarized.

Related URLs:
http://dx.doi.org/10.1667/RR1330.1

Results From the Physics of Colloids Experiment on ISS

by on 9 June 2015in Physical Sciences No comment

The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab ‘Destiny’ Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or sub-micron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

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Preparation of Highly Crystalline TiO(2) Nanostructures by Acid-assisted Hydrothermal Treatment of Hexagonal-structured Nanocrystalline Titania/Cetyltrimethyammonium Bromide Nanoskeleton

by on 9 June 2015in Physical Sciences No comment

Highly crystalline TiO(2) nanostructures were prepared through a facile inorganic acid-assisted hydrothermal treatment of hexagonal-structured assemblies of nanocrystalline titiania templated by cetyltrimethylammonium bromide (Hex-ncTiO(2)/CTAB Nanoskeleton) as starting materials. All samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of hydrochloric acid concentration on the morphology, crystalline and the formation of the nanostructures were investigated. We found that the morphology and crystalline phase strongly depended on the hydrochloric acid concentrations. More importantly, crystalline phase was closely related to the morphology of TiO(2) nanostructure. Nanoparticles were polycrystalline anatase phase, and aligned nanorods were single crystalline rutile phase. Possible formation mechanisms of TiO(2) nanostructures with various crystalline phases and morphologies were proposed.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/21124640

Spacecraft Fire Detection: Smoke Properties and Transport in Low-Gravity

by on 9 June 2015in Physical Sciences No comment

Results from a recent smoke particle size measurement experiment conducted on the International Space Station (ISS) are presented along with the results from a model of the transport of smoke in the ISS. The experimental results show that, for the materials tested, a substantial portion of the smoke particles are below 500 nm in diameter. The smoke transport model demonstrated that mixing dominates the smoke transport and that consequently detection times are longer than in normal gravity.

Related URLs:
http://dx.doi.org/10.2514/6.2008-806

MISSE 2 PEACE Polymers Atomic Oxygen Erosion Experiment on the International Space Station

by on 9 June 2015in Physical Sciences No comment

Forty-one different polymer samples, collectively called the Polymer Erosion and Contamination Experiment (PEACE) Polymers, were exposed to the low Earth orbit (LEO) environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of Materials International Space Station Experiment 2 (MISSE 2). The objective of the PEACE Polymers experiment was to determine the atomic oxygen erosion yield of a wide variety of polymeric materials after long-term exposure to the space environment. The polymers range from those commonly used for spacecraft applications, such as Teflon ® FEP, to more recently developed polymers, such as high temperature polyimide PMR (polymerization of monomer reactants). Additional polymers were included to explore erosion yield dependence upon chemical composition. The MISSE PEACE Polymers experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), tray 1, attached to the exterior of the ISS Quest Airlock. It was exposed to atomic oxygen along with solar and charged particle radiation. MISSE 2 was successfully retrieved during a space walk on July 30, 2005 during Discovery's STS-114 Return to Flight mission. Details on the specific polymers flown, flight sample fabrication, pre-flight and post-flight characterization techniques, and atomic oxygen fluence calculations are discussed along with a summary of the atomic oxygen erosion yield results. The MISSE 2 PEACE Polymers experiment is unique because it has the widest variety of polymers flown in LEO for a long duration and was exposed to an unusually clean LEO spacecraft environment. This experiment provides extremely valuable erosion yield data for spacecraft design purposes.

Related URLs:
http://hip.sagepub.com/content/20/4-5/388.abstract

Space Environment Exposure of Polymer Films on the Materials International Space Station Experiment: Results from MISSE 1 and MISSE 2

by on 9 June 2015in Physical Sciences No comment

A total of thirty-one samples were included in the National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) Polymer Film Thermal Control (PFTC) and Gossamer Materials experiments, which were exposed to the low Earth orbit environment for nearly 4 years on the exterior of the International Space Station (ISS) as part of the Materials International Space Station Experiment (MISSE 1 and MISSE 2). This paper describes objectives, materials, and characterizations for the MISSE 1 and MISSE 2 GRC PFTC and Gossamer Materials samples. Samples included films of polyimides, fluorinated polyimides, and Teflon® fluorinated ethylene propylene (FEP) with and without second-surface metalized layers and/or surface coatings. Films of polyphenylene benzobisoxazole (PBO) and a polyarylene ether benzimidazole (TOR-LM TM) were also included. Polymer film samples were examined post-flight for changes in mechanical and optical properties. The environment in which the samples were located was characterized through analysis of sapphire contamination witness samples and samples dedicated to atomic oxygen (AO) erosion measurements. Results of the analyses of the PFTC and Gossamer Materials experiments are discussed.

Related URLs:
http://hip.sagepub.com/content/20/4-5/371.abstract

Nucleate Pool Boiling Experiments (NPBX) on the International Space Station

by on 9 June 2015in Physical Sciences No comment

During the period of March–May 2011, a series of boiling experiments was carried out in the Boiling Experimental Facility (BXF) located in the Microgravity Science Glovebox (MSG) of the International Space Station (ISS). The BXF Facility was carried to ISS on Space Shuttle Mission STS–133 on February 24, 2011. Nucleate Pool Boiling Experiment (NPBX) was one of the two experiments housed in the BXF. Results of experiments on single bubble dynamics (e.g., inception and growth), multiple bubble dynamics (lateral merger and departure, if any), nucleate pool boiling heat transfer, and critical heat flux are described. In the experiments Perfluoro-n-hexane was used as the test liquid. The system pressure was varied from 51 to 243 kPa, pool temperature was varied from 30° to 59°C, and test surface temperature was varied from 40° to 80°C. The test surface was a polished aluminum disc (1 mm thick, 89.5 mm in diameter) heated from below with strain gage heaters. Five cylindrical cavities were formed on the surface with four cavities located at the corners of a square and one in the middle. During experiments the magnitude of mean gravity level normal to the heater surface varied from 1.2 × 10 − 7g e to 6 × 10 − 7g e . The results of the experiments show that a single bubble continues to grow to occupy the size of the chamber without departing from the heater surface. During lateral merger of bubbles, at high superheats a large bubble may lift off from the surface but continues to hover near the surface. Neighboring bubbles are continuously pulled into the large bubble. At low superheats bubbles at neighboring sites simply merge to yield a larger bubble. The larger bubble mostly locates in the middle of the heated surface and serves as a vapor sink. The latter mode continues to persist when boiling is occurring all over the heater surface. Heat fluxes for steady state nucleate boiling and critical heat fluxes are found to be much lower than those obtained under earth normal gravity conditions. The data are useful for calibration of results of numerical simulations. Any correlations that are developed for nucleate boiling heat transfer under microgravity condition must account for the existence of vapor escape path (sink) from the heater, size of the heater, and the size and geometry of the chamber.

Related URLs:
http://dx.doi.org/10.1007/s12217-012-9315-8