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  • 1
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    Equilibrium Climate Sensitivity Estimated by Equilibrating Climate Models (2021)
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    Publication Date: 2021-10-12
    Description: The methods to quantify equilibrium climate sensitivity are still debated. We collect millennial-length simulations of coupled climate models and show that the global mean equilibrium warming is higher than those obtained using extrapolation methods from shorter simulations. Specifically, 27 simulations with 15 climate models forced with a range of CO2 concentrations show a median 17% larger equilibrium warming than estimated from the first 150 years of the simulations. The spatial patterns of radiative feedbacks change continuously, in most regions reducing their tendency to stabilizing the climate. In the equatorial Pacific, however, feedbacks become more stabilizing with time. The global feedback evolution is initially dominated by the tropics, with eventual substantial contributions from the mid-latitudes. Time-dependent feedbacks underscore the need of a measure of climate sensitivity that accounts for the degree of equilibration, so that models, observations, and paleo proxies can be adequately compared and aggregated to estimate future warming.
    Keywords: 551.6 ; equilibrium climate sensitivity ; climate models
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 2
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    Structural Fluctuations and Thermophysical Properties of Molten II-VI Compounds (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-12
    Description: The objectives of the project are to conduct ground-based experimental and theoretical research on the structural fluctuations and thermophysical properties of molten II-VI compounds to enhance the basic understanding of the existing flight experiments in microgravity materials science programs as well as to study the fundamental heterophase fluctuation phenomena in these melts by: 1) conducting neutron scattering analysis and measuring quantitatively the relevant thermophysical properties of the II-VI melts (such as viscosity, electrical conductivity, thermal diffusivity and density) as well as the relaxation characteristics of these properties to advance the understanding of the structural properties and the relaxation phenomena in these melts and 2) performing theoretical analyses on the melt systems to interpret the experimental results. All the facilities required for the experimental measurements have been procured, installed and tested. It has long been recognized that liquid Te presents a unique case having properties between those of metals and semiconductors. The electrical conductivity for Te melt increases rapidly at melting point, indicating a semiconductor-metal transition. Te melts comprise two features, which are usually considered to be incompatible with each other: covalently bound atoms and metallic-like behavior. Why do Te liquids show metallic behavior? is one of the long-standing issues in liquid metal physics. Since thermophysical properties are very sensitive to the structural variations of a melt, we have conducted extensive thermophysical measurements on Te melt.
    Keywords: Metals and Metallic Materials
    Type: 2002 Microgravity Materials Science Conference; 604-611; NASA/CP-2003-212339
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    NASA TECHNICAL REPORTS
  • 3
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    Theory and Simulation of A Novel Viscosity Measurement Method for High Temperature Semiconductor (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The properties of molten semiconductors are good indicators for material structure transformation and hysteresis under temperature variations. Viscosity, as one of the most important properties, is difficult to measure because of high temperature, high pressure, and vapor toxicity of melts. Recently, a novel method was developed by applying a rotating magnetic field to the melt sealed in a suspended quartz ampoule, and measuring the transient torque exerted by rotating melt flow on the ampoule wall. The method was designed to measure viscosity in short time period, which is essential for evaluating temperature hysteresis. This paper compares the theoretical prediction of melt flow and ampoule oscillation with the experimental data. A theoretical model was established and the coupled fluid flow and ampoule torsional vibration equations were solved numerically. The simulation results showed a good agreement with experimental data. The results also showed that both electrical conductivity and viscosity could be calculated by fitting the theoretical results to the experimental data. The transient velocity of the melt caused by the rotating magnetic field was found reach equilibrium in about half a minute, and the viscosity of melt could be calculated from the altitude of oscillation. This would allow the measurement of viscosity in a minute or so, in contrast to the existing oscillation cup method, which requires about an hour for one measurement.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: 2002 ASME International Mechanical Engineering Congress and Exposition; Nov 17, 2002 - Nov 22, 2002; New Orleans, LA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Modified Laser Flash Method for Thermal Properties Measurements and the Influence of Heat Convection (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The study examined the effect of natural convection in applying the modified laser flash method to measure thermal properties of semiconductor melts. Common laser flash method uses a laser pulse to heat one side of a thin circular sample and measures the temperature response of the other side. Thermal diffusivity can be calculations based on a heat conduction analysis. For semiconductor melt, the sample is contained in a specially designed quartz cell with optical windows on both sides. When laser heats the vertical melt surface, the resulting natural convection can introduce errors in calculation based on heat conduction model alone. The effect of natural convection was studied by CFD simulations with experimental verification by temperature measurement. The CFD results indicated that natural convection would decrease the time needed for the rear side to reach its peak temperature, and also decrease the peak temperature slightly in our experimental configuration. Using the experimental data, the calculation using only heat conduction model resulted in a thermal diffusivity value is about 7.7% lower than that from the model with natural convection. Specific heat capacity was about the same, and the difference is within 1.6%, regardless of heat transfer models.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: Proceedings of IMECE2003: 2003 ASME International Mechanical Engineering Congress and R&D EXPO; Nov 15, 2003 - Nov 21, 2003; Washington, DC; United States
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    NASA TECHNICAL REPORTS
  • 5
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    Thermal Conductivity Based on Modified Laser Flash Measurement (2005)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The laser flash method is a standard method for thermal diffusivity measurement. It employs single-pulse heating of one side of a thin specimen and measures the temperature response of the other side. The thermal diffusivity of the specimen can be obtained based on a one-dimensional transient heat transfer analysis. This paper reports the development of a theory that includes a transparent reference layer with known thermal property attached to the back of sample. With the inclusion of heat conduction from the sample to the reference layer in the theoretical analysis, the thermal conductivity and thermal diffusivity of sample can be extracted from the temperature response data. Furthermore, a procedure is established to select two points from the data to calculate these properties. The uncertainty analysis indicates that this method can be used with acceptable levels of uncertainty.
    Keywords: Lasers and Masers
    Type: 28th International Thermal Conductivity Confrence (ITCC-28); Jun 26, 2005 - Jun 29, 2005; New Brunswick; Canada|16th International Thermal Expansion Symposium; Jun 26, 2005 - Jun 29, 2005; New Brunswick; Canada
    Format: text
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  • 6
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    Viscosity Measurement for Tellurium Melt (2006)
    In:  Other Sources
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    Publication Date: 2019-07-18
    Description: The viscosity of high temperature Te melt was measured using a new technique in which a rotating magnetic field was applied to the melt sealed in a suspended ampoule, and the torque exerted by rotating melt flow on the ampoule wall was measured. Governing equations for the coupled melt flow and ampoule torsional oscillation were solved, and the viscosity was extracted from the experimental data by numerical fitting. The computational result showed good agreement with experimental data. The melt velocity transient initiated by the rotating magnetic field reached a stable condition quickly, allowing the viscosity and electrical conductivity of the melt to be determined in a short period.
    Keywords: Fluid Mechanics and Thermodynamics
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  • 7
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    Thermal Property Measurement of Semiconductor Melt using Modified Laser Flash Method (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This study further developed standard laser flash method to measure multiple thermal properties of semiconductor melts. The modified method can determine thermal diffusivity, thermal conductivity, and specific heat capacity of the melt simultaneously. The transient heat transfer process in the melt and its quartz container was numerically studied in detail. A fitting procedure based on numerical simulation results and the least root-mean-square error fitting to the experimental data was used to extract the values of specific heat capacity, thermal conductivity and thermal diffusivity. This modified method is a step forward from the standard laser flash method, which is usually used to measure thermal diffusivity of solids. The result for tellurium (Te) at 873 K: specific heat capacity 300.2 Joules per kilogram K, thermal conductivity 3.50 Watts per meter K, thermal diffusivity 2.04 x 10(exp -6) square meters per second, are within the range reported in literature. The uncertainty analysis showed the quantitative effect of sample geometry, transient temperature measured, and the energy of the laser pulse.
    Keywords: Lasers and Masers
    Type: HT2003-40448 , American Society of Mechanical Engineers Heat Transfer Conference; Jul 21, 2003 - Jul 23, 2003; Las Vegas, NV; United States
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    NASA TECHNICAL REPORTS
  • 8
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    Thermophysical and Optical Properties of Semiconducting Ga2Te3 Melt (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The majority of bulk semiconductor single crystals are presently grown from their melts. The thermophysical and optical properties of the melts provide a fundamental understanding of the melt structure and can be used to optimize the growth conditions to obtain higher quality crystals. In this paper, we report several thermophysical and optical properties for Ga2Te3 melts, such as electrical conductivity, viscosity, and optical transmission for temperatures ranging from the melting point up to approximately 990 C. The conductivity and viscosity of the melts are determined using the transient torque technique. The optical transmission of the melts is measured between the wavelengths of 300 and 2000 nm by an dual beam reversed-optics spectrophotometer. The measured properties are in good agreement with the published data. The conductivities indicate that the Ga2Te3 melt is semiconductor-like. The anomalous behavior in the measured properties are used as an indication of a structural transformation in the Ga2Te3 melt and discussed in terms of Eyring's and Bachinskii's predicted behaviors for homogeneous melts.
    Keywords: Mechanical Engineering
    Type: 16th American Conference on Crystal Growth and Epitaxy (ACCGE); Jul 10, 2005 - Jul 15, 2005; Big Sky Resort, MT; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Torque Transient of Magnetically Drive Flow for Viscosity Measurement (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Viscosity is a good indicator of structural changes for complex liquids, such as semiconductor melts with chain or ring structures. This paper discusses the theoretical and experimental results of the transient torque technique for non-intrusive viscosity measurement. Such a technique is essential for the high temperature viscosity measurement of high pressure and toxic semiconductor melts. In this paper, our previous work on oscillating cup technique was expanded to the transient process of a magnetically driven melt flow in a damped oscillation system. Based on the analytical solution for the fluid flow and cup oscillation, a semi-empirical model was established to extract the fluid viscosity. The analytical and experimental results indicated that such a technique has the advantage of short measurement time and straight forward data analysis procedures
    Keywords: Fluid Mechanics and Thermodynamics
    Type: 2004 Heat Transfer/Fluids Engineering Summer Conference; Jul 11, 2004 - Jul 15, 2004; Charlotte, NC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    PETI-298 Prepared by Microwave Synthesis: Neat Resin and Composite Properties (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: PETI-298 is a high temperature/high performance matrix resin that is processable into composites by resin transfer molding (RTM), resin infusion and vacuum assisted RTM techniques. It is typically synthesized in a polar aprotic solvent from the reaction of an aromatic anhydride and a combination of diamines and endcapped with phenylethynylphthalic anhydride. Microwave synthesis of PETI-298 was investigated as a means to eliminate solvent and decrease reaction time. The monomers were manually mixed and placed in a microwave oven for various times to determine optimum reaction conditions. The synthetic process was subsequently scaled-up to 330g. Three batches were synthesized and combined to give 1 kg of material that was characterized for thermal and rheological properties and compared to PETI-298 prepared by the classic solution based synthetic method. The microwave synthesized PETI-298 was subsequently used to fabricate flat laminates on T650 carbon fabric by RTM. The composite panels were analyzed and mechanical properties determined and compared with those fabricated from PETI-298 prepared by the classic solution method. The microwave synthesis process and characterization of neat resin and carbon fiber reinforced composites fabricated by RTM will be presented. KEY WORDS: Resin Transfer Molding, High Temperature Polymers, Phenylethynyl Terminated Imides, Microwave Synthesis
    Keywords: Composite Materials
    Type: 36th International SAMPE Technical Conference; Nov 15, 2004 - Nov 18, 2004; San Diego, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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