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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Intensity Biased PSP Measurement

The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Volmer Equation) between intensity ratio (I(sub 0)/I) and pressure ratio (P/P(sub 0)) over a wide range of pressures (vacuum to ambient or higher). Although this may be valid for some PSPs, in most PSPs the relationship is nonlinear, particularly at low pressures (less than 0.2 psia when the oxygen level is low). This non-linearity can be attributed to variations in the oxygen quenching (de-activation) rates (which otherwise is assumed constant) at these pressures. Other studies suggest that some paints also have non-linear calibrations at high pressures; because of heterogeneous (non-uniform) oxygen diffusion and c quenching. Moreover, pressure sensitive paints require correction for the output intensity due to light intensity variation, paint coating variation, model dynamics, wind-off reference pressure variation, and temperature sensitivity. Therefore to minimize the measurement uncertainties due to these causes, an in- situ intensity correction method was developed. A non-oxygen quenched paint (which provides a constant intensity at all pressures, called non-pressure sensitive paint, NPSP) was used for the reference intensity (I(sub NPSP)) with respect to which all the PSP intensities (I) were measured. The results of this study show that in order to fully reap the benefits of this technique, a totally oxygen impermeable NPSP must be available.

Subramanian, Chelakara S.↗
NASA NTRS2000

Intensity Biased PSP Measurement

The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Volmer Equation) between intensity ratio (I(sub o)/I) and pressure ratio (P/P(sub o)) over a wide range of pressures (vacuum to ambient or higher). Although this may be valid for some PSPs, in most PSPs the relationship is nonlinear, particularly at low pressures (less than 0.2 psia when the oxygen level is low). This non-linearity can be attributed to variations in the oxygen quenching (de-activation) rates (which otherwise is assumed constant) at these pressures. Other studies suggest that some paints also have non-linear calibrations at high pressures; because of heterogeneous (non-uniform) oxygen diffusion and quenching. Moreover, pressure sensitive paints require correction for the output intensity due to light intensity variation, paint coating variation, model dynamics, wind-off reference pressure variation, and temperature sensitivity. Therefore to minimize the measurement uncertainties due to these causes, an insitu intensity correction method was developed. A non-oxygen quenched paint (which provides a constant intensity at all pressures, called non-pressure sensitive paint, NPSP) was used for the reference intensity (I(sub NPSP) with respect to which all the PSP intensities (I) were measured. The results of this study show that in order to fully reap the benefits of this technique, a totally oxygen impermeable NPSP must be available.

Subramanian, Chelakara S.↗
NASA NTRS2007

Nanorod-Based Fast-Response Pressure-Sensitive Paints

A proposed program of research and development would be devoted to exploitation of nanomaterials in pressuresensitive paints (PSPs), which are used on wind-tunnel models for mapping surface pressures associated with flow fields. Heretofore, some success has been achieved in measuring steady-state pressures by use of PSPs, but success in measuring temporally varying pressures has been elusive because of the inherent slowness of the optical responses of these materials. A PSP contains a dye that luminesces in a suitable wavelength range in response to photoexcitation in a shorter wavelength range. The luminescence is quenched by oxygen at a rate proportional to the partial pressure of oxygen and thus proportional to the pressure of air. As a result, the intensity of luminescence varies inversely with the pressure of air. The major problem in developing a PSP that could be easily applied to a wind-tunnel model and could be useful for measuring rapidly varying pressure is to provide very high gas diffusivity for rapid, easy transport of oxygen to and from active dye molecules. Most PSPs include polymer-base binders, which limit the penetration of oxygen to dye molecules, thereby reducing responses to pressure fluctuations. The proposed incorporation of nanomaterials (somewhat more specifically, nanorods) would result in paints having nanostructured surfaces that, relative to conventional PSP surfaces, would afford easier and more nearly complete access of oxygen molecules to dye molecules. One measure of greater access is effective surface area: For a typical PSP as proposed applied to a given solid surface, the nanometer-scale structural features would result in an exposed surface area more than 100 times that of a conventional PSP, and the mass of proposed PSP needed to cover the surface would be less than tenth of the mass of the conventional PSP. One aspect of the proposed development would be to synthesize nanorods of Si/SiO2, in both tangle-mat and regular- array forms, by use of chemical vapor deposition (CVD) and wet chemical processes, respectively. The rods would be coated with a PSP dye, and the resulting PSP signals would be compared with those obtained from PSP dye coats on conventional support materials. Another aspect of the proposed development would be to seek to exploit the quantum properties of nanorods of a suitable semiconductor (possibly GaN), which would be synthesized by CVD. These quantum properties of semiconductor nanorods include narrow-wavelength-band optical absorption and emission characteristics that vary with temperature. The temperature sensitivity might enable simultaneous measurement of fluctuating temperature and pressure and to provide a temperature correction for the PSP response.

Bencic, Timothy↗
NASA NTRS1998

Low-Speed Pressure Sensitive Paint Studies

A series of low speed (M less than 0.2) experiments using University of Washington Fib-07 Pressure Sensitive Paint (PSP) have been conducted at NASA Ames on a NACA 0012 airfoil. Significant improvements in results have been shown: PSP calibration errors of the improved data (with pressure taps as a reference) now agree with theoretical error limits. Additional measurements on the 0012 airfoil using Temperature Sensitive Paint have been made. These TSP measurements now fully quantify the impact of temporal temperature changes on model surfaces on PSP measurements. Finally, simultaneous PSP - TSP measurements have been performed, allowing in-situ temperature correction of PSP data with good results.

Owen, Brown↗
NASA NTRS2000

Viscous and Thermal Effects on Hydrodynamic Instability in Liquid-Propellant Combustion

A pulsating form of hydrodynamic instability has recently been shown to arise during the deflagration of liquid propellants in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau, form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that when the burning rate is realistically allowed to depend on temperature as well as pressure, that sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes the pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wavenumbers are sufficiently small. In the present work, this analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wavenumber perturbations, the intrinsic pulsating instability for small wavenumbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.

Margolis, Stephen B.↗
NASA NTRS2000

Viscous Analysis of Pulsating Hydrodynamic Instability and Thermal Coupling Liquid-Propellant Combustion

A pulsating form of hydrodynamic instability has recently been shown to arise during liquid-propellant deflagration in those parameter regimes where the pressure-dependent burning rate is characterized by a negative pressure sensitivity. This type of instability can coexist with the classical cellular, or Landau form of hydrodynamic instability, with the occurrence of either dependent on whether the pressure sensitivity is sufficiently large or small in magnitude. For the inviscid problem, it has been shown that, when the burning rate is realistically allowed to depend on temperature as well as pressure, sufficiently large values of the temperature sensitivity relative to the pressure sensitivity causes like pulsating form of hydrodynamic instability to become dominant. In that regime, steady, planar burning becomes intrinsically unstable to pulsating disturbances whose wave numbers are sufficiently small. This analysis is extended to the fully viscous case, where it is shown that although viscosity is stabilizing for intermediate and larger wave number perturbations, the intrinsic pulsating instability for small wave numbers remains. Under these conditions, liquid-propellant combustion is predicted to be characterized by large unsteady cells along the liquid/gas interface.

Margolis, Stephen B.↗
NASA NTRS1991

The mid-Cretaceous super plume, carbon dioxide, and global warming

Carbon-dioxide releases associated with a mid-Cretaceous super plume and the emplacement of the Ontong-Java Plateau have been suggested as a principal cause of the mid-Cretaceous global warming. A carbonate-silicate cycle model is developed to quantify the possible climatic effects of these CO2 releases, utilizing four different formulations for the rate of silicate-rock weathering as a function of atmospheric CO2. CO2 emissions resulting from super-plume tectonics could have produced atmospheric CO2 levels from 3.7 to 14.7 times the modern preindustrial value of 285 ppm. Based on the temperature sensitivity to CO2 increases used in the weathering-rate formulations, this would cause a global warming of from 2.8 to 7.7 C over today's glogal mean temperature. Altered continental positions and higher sea level may have been contributed about 4.8 C to mid-Cretaceous warming. Thus, the combined effects of paleogeographic changes and super-plume related CO2 emissions could be in the range of 7.6 to 12.5 C, within the 6 to 14 C range previously estimated for mid-Cretaceous warming. CO2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20 percent of the mid-Cretaceous increase in atmospheric CO2.

Caldeira, Ken↗
NASA NTRS1993

Ionization effects in three-dimensional solar granulation simulations

These numerical studies show that ionization influences both the transport and dynamical properties of compressible convection near the surface of the Sun. About two-thirds of the enthalpy transported by convective motions in the region of partial hydrogen ionization is carried as latent heat. The role of fast downflow plumes in total convective transport is substantially elevated by this contribution. Instability of the thermal boundary layer is strongly enhanced by temperature sensitive variations in the radiative properties of the fluid, and this provides a mechanism for plume initiation and cell fragmentation in the surface layers. As the plumes descend, temperature fluctuations and associated buoyancy forces are maintained because of the increased specific heat of the partially ionized material. This can result is supersonic vertical flows. At greater depths, ionization effects diminish, and the plumes are decelerated by significant entrainment of surrounding fluid.

Rast, Mark P.↗
NASA NTRS1994

Method development for compensating temperature effects in pressure sensitive paint measurements

Pressure sensitive luminescent paints (PSP) have recently emerged as a viable technique for aerodynamic pressure measurements. The technique uses a surface coating which contains probe molecules that luminesce when excited by light of an appropriate wavelength. The photoluminescence of these materials is known to be quenched by the presence of molecular oxygen. Since oxygen is a fixed mole fraction of the air, the coating's luminescence intensity varies inversely with air pressure. Digital imaging of the luminescence varying across a coated surface produces a pressure distribution map over that surface. One difficulty encountered with this technique is the temperature effect on the luminescence intensity. Present PSP formulations have significant sensitivity to temperature. At the moment, the most practical way of correcting for temperature effects is to calibrate the paint in place at the operating temperatures by using a few well-placed pressure taps. This study is looking at development of temperature indicating coatings that can be applied and measured concurrently with PSP, and use the temperature measurement to compute the correct pressure. Two methods for this dual paint formulation are proposed. One method will use a coating that consists of temperature sensitive phosphors in a polymer matrix. This is similar in construction to PSP, except that the probe molecules used are selected primarily for their temperature sensitivity. Both organic phosphors (e.g., europium thenoyltrifluoroacetonate, bioprobes) and inorganic phosphors (e.g., Mg4(F)GeO6:Mn, La2O2S:Eu, Radelin Type phosphors, Sylvania Type phosphors) will be evaluated for their temperature sensing potential. The next method will involve a novel coating composing of five membered heterocyclic conducting polymers which are known to show temperature dependent luminescence (e.g., poly(3-alkylthiopene), poly(3-alkylselenophene), poly(3-alkylfuran)). Both methods will involve applying a bottom layer of temperature sensitive coating followed by a top coating of PSP. An oxygen-impermeable polymer can be used as the temperature sensitive coating matrix, or it can be layered in between the coatings to prevent oxygen quenching of the bottom coating's luminescence. The probe molecules of the coatings will be excited by a broad band of light, with the different emissions detected and measured at their distinct wavelengths. Developmental research of these coatings is still in progress; however, preliminary results look very promising.

Demandante, Carlo Greg N.↗
NASA NTRS1996

Testing of 100 mK bolometers for space applications

Electrical and optical performance data are presented for a prototype 100 mK spider-web bolometer operating under very low photon backgrounds. These data are compared with the bolometer theory and are used to estimate the expected sensitivity of such a detector used for low background space astronomy. The results demonstrate that the sensitivity and speed of response requirements of the bolometer instruments proposed for these missions can be met by 100 mK spider-web bolometers using neutron transmutation doped germanium as the temperature sensitive element.

Murray, A. G.↗
NASA NTRS2017

Steady State Thermal Analyses of SCEPTOR X-57 Wingtip Propulsion

Electric aircraft concepts enable advanced propulsion airframe integration approaches that promise increased efficiency as well as reduced emissions and noise. NASA's fully electric Maxwell X-57, developed under the SCEPTOR program, features distributed propulsion across a high aspect ratio wing. There are 14 propulsors in all: 12 high lift motor that are only active during take off and climb, and 2 larger motors positioned on the wingtips that operate over the entire mission. The power electronics involved in the wingtip propulsion are temperature sensitive and therefore require thermal management. This work focuses on the high and low fidelity heat transfer analysis methods performed to ensure that the wingtip motor inverters do not reach their temperature limits. It also explores different geometry configurations involved in the X-57 development and any thermal concerns. All analyses presented are performed at steady state under stressful operating conditions, therefore predicting temperatures which are considered the worst-case scenario to remain conservative.

Thermal↗
NASA NTRS1998

Rotating Pressure and Temperature Measurements on Scale Model Fans Using Luminescent Paints

Pressure and temperature sensitive paint (PSP, TSP) technology is a rapidly developing measurement technique that is widely accepted in external aerodynamic wind tunnel measurements. Almost all quantitative full field measurements have been on stationary surfaces. Rotating pressure and temperature measurements were successfully acquired during scale-model fan tests in the NASA Lewis Research Center 9 foot by 15 foot low speed wind tunnel at speeds as high as 9500 RPM. The use of PSP and TSP on rotating surfaces presents additional challenges to data acquisition. This paper describes in detail the techniques used to acquire global rotating pressure and temperature measurements and overcome the problems associated with this type of measurement. These include illumination and detection problems associated with moving surfaces, temperature dependence of PSP and limited emitted light available from short duration illumination sources. Solutions to these problems as well as pressure and temperature results will be discussed.

Bencic, Timothy J.↗
NASA NTRS1990

Thermal design and verification of an instrument cooling system for infrared detectors utilizing the Oxford Stirling cycle refrigerator

A detailed nodal computer model was developed to thermally represent the hardware, and sensitivity studies were performed to evaluate design parameters and orbital environmental effects of an instrument cooling system for IR detectors. Thermal-vacuum testing showed excellent performance of the system and a correspondence with math model predictions to within 3 K. Results show cold stage temperature sensitivity to cold patch backload, outer stage external surface emittance degradation, and cold stage emittance degradation, respectively. The increase in backload on the cold patch over the mission lifetime is anticipated to be less than 3.0 watts, which translates to less than a 3-degree increase in detector temperatures.

Werrett, Stephen↗
NASA NTRS2010

Report on Lithium Ion Battery Trade Studies to Support the Exploration Technology Development Program (ETDP) Energy Storage Project

This report documents the results of two system related analyses to support the Exploration Technology Development Program (ETDP) Energy Storage Project. The first study documents a trade study to determine the optimum Li-ion battery cell capacity for the ascent stage battery for the Altair lunar lander being developed under the Constellation Systems program. The battery cell capacity for the Ultra High Energy (UHE) Li-ion battery initially chosen as the target for development was 35 A-hr; this study concludes that a 19.4 A-hr cell capacity would be more optimum from a minimum battery mass perspective. The second study in this report is an assessment of available low temperature Li-ion battery cell performance data to determine whether lowering the operating temperature range of the Li-ion battery, in a rover application, could save overall system mass by eliminating thermal control system mass normally needed to maintain battery temperature within a tighter temperature limit than electronics or other less temperature sensitive components. The preliminary assessment for this second study indicates that the reduction in the thermal control system mass is negated by an increase in battery mass to compensate for the loss in battery capacity due to lower temperature operating conditions.

Green, Robert D.↗
NASA NTRS1984

Atomic hydrogen maser active oscillator cavity and bulb design optimization

The performance characteristics and reliability of the active oscillator atomic hydrogen maser depend upon oscillation parameters which characterize the interaction region of the maser, the resonant cavity and atom storage bulb assembly. With particular attention to use of the cavity frequency switching servo (1) to reduce cavity pulling, it is important to maintain high oscillation level, high atomic beam flux utilization efficiency, small spin exchange parameter and high cavity quality factor. It is also desirable to have a small and rigid cavity and bulb structure and to minimize the cavity temperature sensitivity. Curves for a novel hydrogen maser cavity configuration which is partially loaded with a quartz dielectric cylinder and show the relationships between cavity length, cavity diameter, bulb size, dielectric thickness, cavity quality factor, filling factor and cavity frequency temperature coefficient are presented. The results are discussed in terms of improvement in maser performance resulting from particular design choices.

Peters, H. E.↗
NASA NTRS1992

Ultra-high temperature stability Joule-Thomson cooler with capability to accomodate pressure variations

A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to a cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature in the refrigerating system, independent of the changes in atmospheric pressure.

Bard, Steven↗
NASA NTRS2003

Observed and Modeled Trends in Southern Ocean Sea Ice

Conceptual models and global climate model (GCM) simulations have both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by the polar abundance of snow and ice surfaces. Some models further indicate that the changes in the polar regions can have a significant impact globally. For instance, 37% of the temperature sensitivity to a doubling of atmospheric CO2 in simulations with the GCM of the Goddard Institute for Space Studies (GISS) is attributable exclusively to inclusion of sea ice variations in the model calculations. Both sea ice thickness and sea ice extent decrease markedly in the doubled CO, case, thereby allowing the ice feedbacks to occur. Stand-alone sea ice models have shown Southern Ocean hemispherically averaged winter ice-edge retreats of 1.4 deg latitude for each 1 K increase in atmospheric temperatures. Observations, however, show a much more varied Southern Ocean ice cover, both spatially and temporally, than many of the modeled expectations. In fact, the satellite passive-microwave record of Southern Ocean sea ice since late 1978 has revealed overall increases rather than decreases in ice extents, with ice extent trends on the order of 11,000 sq km/year. When broken down spatially, the positive trends are strongest in the Ross Sea, while the trends are negative in the Bellingshausen/Amundsen Seas. Greater spatial detail can be obtained by examining trends in the length of the sea ice season, and those trends show a coherent picture of shortening sea ice seasons throughout almost the entire Bellingshausen and Amundsen Seas to the west of the Antarctic Peninsula and in the far western Weddell Sea immediately to the east of the Peninsula, with lengthening sea ice seasons around much of the rest of the continent. This pattern corresponds well with the spatial pattern of temperature trends, as the Peninsula region is the one region in the Antarctic with a strong record of temperature increases. Still, although the patterns of the temperature and ice changes match fairly well, there is a substantial ways to go before these patterns are understood (and can be modeled) in the full context of global change.

Parkinson, Claire L.↗
NASA NTRS2011

NASA Tech Briefs, November 2011

The topics include: 1) Flight Test Results from the Rake Airflow Gage Experiment on the F-15B; 2) Telemetry and Science Data Software System; 3) CropEx Web-Based Agricultural Monitoring and Decision Support; 4) High-Performance Data Analysis Tools for Sun-Earth Connection Missions; 5) Experiment in Onboard Synthetic Aperture Radar Data Processing; 6) Microfabrication of a High-Throughput Nanochannel Delivery/Filtration System; 7) Improved Design and Fabrication of Hydrated-Salt Pills; 8) Monolithic Flexure Pre-Stressed Ultrasonic Horns; 9) Cryogenic Quenching Process for Electronic Part Screening; 10) Broadband Via-Less Microwave Crossover Using Microstrip-CPW Transitions; 11) Wheel-Based Ice Sensors for Road Vehicles; 12) G-DYN Multibody Dynamics Engine; 13) Multibody Simulation Software Testbed for Small-Body Exploration and Sampling; 14) Propulsive Reaction Control System Model; 15) Licklider Transmission Protocol Implementation; 16) Core Recursive Hierarchical Image Segmentation; 17) Two-Stage Centrifugal Fan; 18) Combined Structural and Trajectory Control of Variable-Geometry Planetary Entry Systems; 19) Pressure Regulator With Internal Ejector Circulation Pump, Flow and Pressure Measurement Porting, and Fuel Cell System Integration Options; 20) Temperature-Sensitive Coating Sensor Based on Hematite; 21) Standardization of a Volumetric Displacement Measurement for Two-Body Abrasion Scratch Test Data Analysis; 22) Detection of Carbon Monoxide Using Polymer-Carbon Composite Films; 23) Substituted Quaternary Ammonium Salts Improve Low-Temperature Performance of Double-Layer Capacitors; 24) Sustainably Sourced, Thermally Resistant, Radiation Hard Biopolymer; 25) Integrated Lens Antennas for Multi-Pixel Receivers; 26) 180-GHz Interferometric Imager; 27) Maturation of Structural Health Management Systems for Solid Rocket Motors; 28) Validating Phasing and Geometry of Large Focal Plane Arrays; 29) Transverse Pupil Shifts for Adaptive Optics Non-Common Path Calibration; 30) Qualification of Fiber Optic Cables for Martian Extreme Temperature Environments; 31) Solid-State Spectral Light Source System; 32) Multiple-Event, Single-Photon Counting Imaging Sensor; 33) Surface Modeling to Support Small-Body Spacecraft Exploration and Proximity Operations; and 34) Achieving Exact and Constant Turnaround Ratio in a DDS-Based Coherent Transponder.

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