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NASA NTRS2004

Droplet-Surface Impingement Dynamics for Intelligent Spray Design

Spray cooling has high potential in thermal management and life support systems by overcoming the deleterious effect of microgravity upon two-phase heat transfer. In particular spray cooling offers several advantages in heat flux removal that include the following: 1) By maintaining a wetted surface, spray droplets impinge upon a thin fluid film rather than a dry solid surface; 2. Most heat transfer surfaces will not be smooth but rough. Roughness can enhance conductive cooling, aid liquid removal by flow channeling; and 3. Spray momentum can be used to a) substitute for gravity delivering fluid to the surface, b) prevent local dryout and potential thermal runaway and c) facilitate liquid and vapor removal. Yet high momentum results in high We and Re numbers characterizing the individual spray droplets. Beyond an impingement threshold, droplets splash rather than spread. Heat flux declines and spray cooling efficiency can markedly decrease. Accordingly we are investigating droplet impingement upon a) dry solid surfaces, b) fluid films, c) rough surfaces and determining splashing thresholds and relationships for both dry surfaces and those covered by fluid films. We are presently developing engineering correlations delineating the boundary between splashing and non-splashing regions. Determining the splash/non-splash boundary is important for many practical applications. Coating and cooling processes would each benefit from near-term empirical relations and subsequent models. Such demonstrations can guide theoretical development by providing definitive testing of its predictive capabilities. Thus, empirical relations describing the boundary between splash and non-splash are given for drops impinging upon a dry solid surface and upon a thin fluid film covering a similar surface. Analytical simplification of the power laws describing the boundary between the splash and non-splash regions yields insight into the engineering parameters governing the splash and non-splash outcomes of the fluid droplets. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a dry solid surface. Splashing upon a dry surface is reasonably described by Ca greater than 0.85, reflecting the competing roles of surface tension and viscosity. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a thin fluid film covering the solid surface. Splashing upon a thin fluid film, as described by v (pd/s) greater than 63, is governed by fluid density and surface tension, but is rather independent of viscosity. Finally, the data presented here suggests that a more direct dependence upon the surface tension and viscosity, given a better understanding of their interplay, would allow accurate description of the droplet-surface impacts for more complicated situations involving non-Newtonian fluids, specifically those exhibiting viscoelastic behavior.

Wal, Randy L. Vander↗

NASA NTRS1973

A high-speed photographic system for flow visualization in a steam turbine

A photographic system was designed to visualize the moisture flow in a steam turbine. Good performance of the system was verified using dry turbine mockups in which an aerosol spray simulated, in a rough way, the moisture flow in the turbine. Borescopes and fiber-optic light tubes were selected as the general instrumentation approach. High speed motion-picture photographs of the liquid flow over the stator blade surfaces were taken using stroboscopic lighting. Good visualization of the liquid flow was obtained. Still photographs of drops in flight were made using short duration flash sources. Drops with diameters as small as 30 micrometers (0.0012 in.) could be resolved. In addition, motion pictures of a spray of water simulating the spray off the rotor blades and shrouds were taken at normal framing rates. Specially constructed light tubes containing small tungsten-halogen lamps were used. Sixteen millimeter photography was used in all cases. Two potential problems resulting from the two-phase turbine flow (attenuation and scattering of light by the fog present and liquid accumulation on the borescope mirrors) were taken into account in the photographic system design but not evaluated experimentally.

Barna, G. J.↗

NASA NTRS1988

Ejection of sodium from sodium sulfide by the sputtering of the surface of Io

The mechanism by which Na is removed from the surface of Io prior to its injection into the plasma torus is investigated experimentally. Na2S films of thickness 3-8 microns were produced by spray coating an Ni substrate in a dry N2 atmosphere and subjected to sputtering by 34-keV Ar(+), Ne(+), Kr(+), or Xe(+) ions up to total doses of about 5 x 10 to the 18th ions/sq cm. The sputtering yields and mass spectra are found to be consistent with ejection of only small amounts of atomic Na and somewhat larger amounts of Na-containing molecules. It is concluded that the amount of Na ejected by magnetospheric-ion sputtering of Na2S would be insufficient to account for the amounts observed in the Io neutral cloud. A scenario involving sputtering of larger polysulfide molecules is considered.

Chrisey, D. B.↗

NASA NTRS1987

Stimulating productivity of hydroponic lettuce in controlled environments with triacontanol

Triacontanol (1-triacontanol) applied as a foliar spray at 10(-7) M to 4-day-old, hydroponically grown leaf lettuce (Lactuca sativa L.) seedlings in a controlled environment increased leaf fresh and dry weight 13% to 20% and root fresh and dry weight 13% to 24% 6 days after application, relative to plants sprayed with water. When applied at 8 as well as 4 days after seeding, triacontanol increased plant fresh and dry weight, leaf area, and mean relative growth rate 12% to 37%. There was no benefit of repeating application of triacontanol in terms of leaf dry weight gain.

Non-NASA Center↗

NASA NTRS2006

Characterization of Space Shuttle Thermal Protection System (TPS) Materials for Return-to-Flight following the Shuttle Columbia Accident Investigation

During the Space Shuttle Columbia Accident Investigation, it was determined that a large chunk of polyurethane insulating foam (= 1.67 lbs) on the External Tank (ET) came loose during Columbia's ascent on 2-1-03. The foam piece struck some of the protective Reinforced Carbon-Carbon (RCC) panels on the leading edge of Columbia's left wing in the mid-wing area. This impact damaged Columbia to the extent that upon re-entry to Earth, superheGed air approaching 3,000 F caused the vehicle to break up, killing all seven astronauts on board. A paper after the Columbia Accident Investigation highlighted thermal analysis testing performed on External Tank TPS materials (1). These materials included BX-250 (now BX-265) rigid polyurethane foam and SLA-561 Super Lightweight Ablator (highly-filled silicone rubber). The large chunk of foam from Columbia originated fiom the left bipod ramp of the ET. The foam in this ramp area was hand-sprayed over the SLA material and various fittings, allowed to dry, and manually shaved into a ramp shape. In Return-to-Flight (RTF) efforts following Columbia, the decision was made to remove the foam in the bipod ramp areas. During RTF efforts, further thermal analysis testing was performed on BX-265 foam by DSC and DMA. Flat panels of foam about 2-in. thick were sprayed on ET tank material (aluminum alloys). The DSC testing showed that foam material very close to the metal substrate cured more slowly than bulk foam material. All of the foam used on the ET is considered fully cured about 21 days after it is sprayed. The RTF culminated in the successful launch of Space Shuttle Discovery on 7-26-05. Although the flight was a success, there was another serious incident of foam loss fiom the ET during Shuttle ascent. This time, a rather large chunk of BX-265 foam (= 0.9 lbs) came loose from the liquid hydrogen (LH2) PAL ramp, although the foam did not strike the Shuttle Orbiter containing the crew. DMA testing was performed on foam samples taken fiom a simulated PAL ramp panel. It was found that the smooth rind on the foam facing the cable tray did significantly affect the properties of foam at the PAL ramp surface. The smooth rind increased the storage modulus E' of the foam as much as 20- 40% over a temperature range of -145 to 95 C. Because of foam loss fiom the PAL ramp, future Shuttle flights were grounded indefinitely to allow further testing to better understand foam properties. The decision was also made to remove foam from the LH2 PAL, ramp. Other RTF efforts prior to the launch of Discovery included

Wingard, Doug↗

NASA NTRS1990

Natural chlorine and fluorine in the atmosphere, water and precipitation

The geochemical cycles of chlorine and fluorine are surveyed and summarized as framework for the understanding of the global natural abundances of these species in the atmosphere, water, and precipitation. In the cycles the fluxes into and out of the atmosphere can be balanced within the limits of our knowledge of the natural sources and sinks. Sea salt from the ocean surfaces represent the predominant portion of the source of chlorine. It is also an important source of atmospheric fluorine, but volcanoes are likely to be more important fluorine sources. Dry deposition of sea salt returns about 85 percent of the salt released there. Precipitation removes the remainder. Most of the sea salt materials are considered to be cyclic, moving through sea spray over the oceans and either directly back to the oceans or deposited dry and in precipitation on land, whence it runs off into rivers and streams and returns to the oceans. Most of the natural chlorine in the atmosphere is in the form of particulate chloride ion with lesser amounts as gaseous inorganic chloride and methyl chloride vapor. Fluorine is emitted from volcanoes primarily as HF. It is possible that HF may be released directly form the ocean surface but this has not been confirmed by observation. HCl and most likely HF gases are released into the atmosphere by sea salt aerosols. The mechanism for the release is likely to be the provision of protons from the so-called excess sulfate and HNO3. Sea salt aerosol contains fluorine as F(-), MgF(+), CaF(+), and NaF. The concentrations of the various species of chlorine and fluorine that characterize primarily natural, unpolluted atmospheres are summarized in tables and are discussed in relation to their fluxes through the geochemical cycle.

Friend, James P.↗

NASA NTRS1995

A design of experiments test to define critical spray cleaning parameters for Brulin 815 GD and Jettacin cleaners

Experimental design testing was conducted to identify critical parameters of an aqueous spray process intended for cleaning solid rocket motor metal components (steel and aluminum). A two-level, six-parameter, fractional factorial matrix was constructed and conducted for two cleaners, Brulin 815 GD and Diversey Jettacin. The matrix parameters included cleaner temperature and concentration, wash density, wash pressure, rinse pressure, and dishwasher type. Other spray parameters: nozzle stand-off, rinse water temperature, wash and rinse time, dry conditions, and type of rinse water (deionized) were held constant. Matrix response testing utilized discriminating bond specimens (fracture energy and tensile adhesion strength) which represent critical production bond lines. Overall, Jettacin spray cleaning was insensitive to the range of conditions tested for all parameters and exhibited bond strengths significantly above the TCA test baseline for all bond lines tested. Brulin 815 was sensitive to cleaning temperature, but produced bond strengths above the TCA test baseline even at the lower temperatures. Ultimately, the experimental design database was utilized to recommend process parameter settings for future aqueous spray cleaning characterization work.

Keen, Jill M.↗

NASA NTRS2017

Analysis of CO2 Composite Spray Cleaning System Results

In a previous study, the cleaning efficiency of a CO2 composite cleaning system for particulate removal was tested. The study covered particles from spores to fluorescent particles of different sizes as well as a variety of substrate surfaces, including aluminum, titanium, stainless steel, and nitinol. Particles were deposited using aerosol (dry) and droplet (wet) deposition. Results from the previous study show that the CO2 composite spray system is capable of cleaning to sterility for aerosol deposited spores and is capable of cleaning a minimum of a 4-log reduction for droplet deposited spores. This minimum 4-log reduction matches current Planetary Protection dry heat microbial reduction requirements. In this paper we will present new data to further correlate the cleaning efficiency with how contamination was introduced to the surface, the surface roughness, and particle size. Possible causes for such correlations will be discussed.

Chung, Shirley↗

NASA NTRS1966

Spray-on electrodes enable EKG monitoring of physically active subjects

Easily applied EKG electrodes monitor the heart signals of human subjects engaged in various physical exercises. The electrodes are formed from an air drying, electrically conductive cement mixture that can be applied to the skin by means of a modified commercially available spray gun.

Source record↗

NASA NTRS1984

Properties of simulated comet mantle

The properties of freeze-dried dilute dispersions of dust in water ice are of considerable interest in studies of comet nucleus mantles. The formation of a rind residue produced by the sublimation of water ice containing various amounts of fine clay particles may be an important process. A simulation of the development of the dry dust rind on the surface of comets is presented. This rind is the result of preferential ice sublimation. The development and disruption of this rind and its subsequent levitation by water vapor flow is studied. The most interesting rind simulant is produced by dispersing 0.1 micron particles of montmorillonite in water in concentrations of 10%, 1%, and 0.1%. These dispersions are then sprayed into liquid nitrogen in the form of 100 micron droplets. The frozen droplets are then freeze-dried in a vacuum which prevents the ice temperature from rising above -30 C. Sublimation of the nitrogen and the water produced dry rinds. The most striking result was the development of large cohesive matrices of individual clay particles, and in some cases a continuous cohesive crust. Scanning electron microscope (SEM) observations reveal that the material formed by freeze-drying the 0.1% dispersion does not retain the original spherical shape of the sprayed 100 micron droplets; instead it consists of a continuous filamentary network, as shown in the SEM stereo micrographs.

Fanale, F. P.↗

NASA NTRS1981

Development of silane-hydrolysate binder for UV-resistant thermal control coatings

Detailed characterizaton and formulation studies were performed on a methyltriakoxysilane hydrolysate as a binder for thermal control coatings. The binder was optimized by varying hydrolysis temperature, time, catalyst type, and water concentration. The candidate coating formulations, based on this binder with TiO2 pigment, were optimized via a detailed series of sprayed test panels that included the parameters of binder/pigment ratio, ethanol content, pigment particle size, coating thickness and cure conditions. A typical optimized coating was prepared by acetic acid catalyzed hydrolysis of methyltriethoxysilane with 3.25 mol-equivalents of water over a 24 hour period at room temperature. The resulting hydrolysate was directly mixed with pre-milled TiO2 (12 grams pigment/26 grams binder) to yield a sprayable consistency. Panels were sprayed to result in a nominal cure coating thickness of 2 mils. Cure was affected by air drying for 24 hr at room temperature plus 72 hr at 150 F. These coatings are typically extremely tough and abrasion-resistant, with an absorptance (alpha) of 0.20 and emittance (e) of 0.89. No significant coating damage was observed in the mandrel bend test, even after exposure to thermal cycling from -160 to 160 F. Vacuum exposure of the coatings for 930 hours at 1 equivalent UV sun resulted in no visible degradation and no significant increase in absorptance.

Patterson, W. J.↗

NASA NTRS1985

The UH-1H helicopter icing flight test program: An overview

An ongoing joint NASA/Army program to study the effects of ice accretion on unprotected helicopter rotor aerodynamic performance is discussed. This program integrates flight testing, wind tunnel testing, and analytical modeling. Results are discussed for helicopter flight testing in the Canadian NRC hover spray rig facility to measure rotor aero performance degradation and document rotor ice accretion characteristics. The results of dry wind tunnel testing of airfoil sections with artificial ice accretions and predictions of rotor performance degradation using available rotor performance codes and the wind tunnel data are presented. An alternative approach to conducting future helicopter icing flight programs is discussed.

Shaw, R. J.↗

NASA NTRS1985

The UH-1H helicopter icing flight test program - An overview

Shaw, R. J.↗

NASA NTRS1985

Heat transfer and pressure drop performance of a finned-tube heat exchanger proposed for use in the NASA Lewis Altitude Wind Tunnel

A segment of the heat exchanger proposed for use in the NASA Lewis Altitude Wind Tunnel (AWT) facility has been tested under dry and icing conditions. The heat exchanger has the largest pressure drop of any component in the AWT loop. It is therefore critical that its performance be known at all conditions before the final design of the AWT is complete. The heat exchanger segment is tested in the NASA Lewis Icing Research Tunnel (IRT) in order to provide an icing cloud environment similar to what will be encountered in the AWT. Dry heat transfer and pressure drop data are obtained and compared to correlations available in the literature. The effects of icing sprays on heat transfer and pressure drop are also investigated.

Vanfossen, G. J.↗

NASA NTRS2001

How Does a Liquid Wet a Solid? Hydrodynamics of Dynamic Contact Angles

A contact line is defined at the intersection of a solid surface with the interface between two immiscible fluids. When one fluid displaces another immiscible fluid along a solid surface, the process is called dynamic wetting and a "moving" contact line (one whose position relative to the solid changes in time) often appears. The physics of dynamic wetting controls such natural and industrial processes as spraying of paints and insecticides, dishwashing, film formation and rupture in the eye and in the alveoli, application of coatings, printing, drying and imbibition of fibrous materials, oil recovery from porous rocks, and microfluidics.

Rame, Enrique↗

NASA NTRS2011

Validation and Simulation of Ares I Scale Model Acoustic Test - 3 - Modeling and Evaluating the Effect of Rainbird Water Deluge Inclusion

The Ares I Scale Model Acoustics Test (ASMAT) is a series of live-fire tests of scaled rocket motors meant to simulate the conditions of the Ares I launch configuration. These tests have provided a well documented set of high fidelity measurements useful for validation including data taken over a range of test conditions and containing phenomena like Ignition Over-Pressure and water suppression of acoustics. Building on dry simulations of the ASMAT tests with the vehicle at 5 ft. elevation (100 ft. real vehicle elevation), wet simulations of the ASMAT test setup have been performed using the Loci/CHEM computational fluid dynamics software to explore the effect of rainbird water suppression inclusion on the launch platform deck. Two-phase water simulation has been performed using an energy and mass coupled lagrangian particle system module where liquid phase emissions are segregated into clouds of virtual particles and gas phase mass transfer is accomplished through simple Weber number controlled breakup and boiling models. Comparisons have been performed to the dry 5 ft. elevation cases, using configurations with and without launch mounts. These cases have been used to explore the interaction between rainbird spray patterns and launch mount geometry and evaluate the acoustic sound pressure level knockdown achieved through above-deck rainbird deluge inclusion. This comparison has been anchored with validation from live-fire test data which showed a reduction in rainbird effectiveness with the presence of a launch mount.

Strutzenberg, Louise L.↗

NASA NTRS1992

ASRM Process Development in Aqueous Cleaning

Viewgraphs are included on process development in aqueous cleaning which is taking place at the Aerojet Advanced Solid Rocket Motor (ASRM) Division under a NASA Marshall Space and Flight Center contract for design, development, test, and evaluation of the ASRM including new production facilities. The ASRM will utilize aqueous cleaning in several manufacturing process steps to clean case segments, nozzle metal components, and igniter closures. ASRM manufacturing process development is underway, including agent selection, agent characterization, subscale process optimization, bonding verification, and scale-up validation. Process parameters are currently being tested for optimization utilizing a Taguci Matrix, including agent concentration, cleaning solution temperature, agitation and immersion time, rinse water amount and temperature, and use/non-use of drying air. Based on results of process development testing to date, several observations are offered: aqueous cleaning appears effective for steels and SermeTel-coated metals in ASRM processing; aqueous cleaning agents may stain and/or attack bare aluminum metals to various extents; aqueous cleaning appears unsuitable for thermal sprayed aluminum-coated steel; aqueous cleaning appears to adequately remove a wide range of contaminants from flat metal surfaces, but supplementary assistance may be needed to remove clumps of tenacious contaminants embedded in holes, etc.; and hot rinse water appears to be beneficial to aid in drying of bare steel and retarding oxidation rate.

Swisher, Bill↗

NASA NTRS2008

Chamber for Aerosol Deposition of Bioparticles

Laboratory apparatus is depicted that is a chamber for aerosol deposition of bioparticles on surfaces of test coupons. It is designed for primary use in inoculating both flat and three-dimensional objects with approximately reproducible, uniform dispersions of bacterial spores of the genus Bacillus so that the objects could be used as standards for removal of the spores by quantitative surface sampling and/or cleaning processes. The apparatus is also designed for deposition of particles other than bacterial spores, including fungal spores, viruses, bacteriophages, and standard micron-sized beads. The novelty of the apparatus lies in the combination of a controllable nebulization system with a settling chamber large enough to contain a significant number of test coupons. Several companies market other nebulizer systems, but none are known to include chambers for deposition of bioparticles to mimic the natural fallout of bioparticles. The nebulization system is an expanded and improved version of commercially available aerosol generators that include nebulizers and drying columns. In comparison with a typical commercial aerosol generator, this system includes additional, higher-resolution flowmeters and an additional pressure regulator. Also, unlike a typical commercial aerosol generator, it includes stopcocks for separately controlling flows of gases to the nebulizer and drying column. To maximize the degree of uniformity of dispersion of bioaerosol, the chamber is shaped as an axisymmetrical cylinder and the aerosol generator is positioned centrally within the chamber and aimed upward like a fountain. In order to minimize electric charge associated with the aerosol particles, the drying column is made of aluminum, the drying column is in direct contact with an aluminum base plate, and three equally spaced Po-210 antistatic strips are located at the exit end of the drying column. The sides and top of the chamber are made of an acrylic polymer; to prevent accumulation of electric charge on them, they are spray-coated with an anti-static material. During use, the base plate and the sides and top of the chamber are grounded as a further measure to minimize the buildup of electric charge.

Kern, Roger↗