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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
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NASA NTRS2014

Magnetic Structure of Sites of Braiding in Hi-C Active Region

High‐resolution Coronal Imager (Hi‐C) observations of an active region (AR) corona, at a spatial resolution of 0.2 arcsec, have offered the first direct evidence of field lines braiding, which could deliver sufficient energy to heat the AR corona by current dissipation via magnetic reconnection, a proposal given by Parker three decades ago. The energy required to heat the corona must be transported from the photosphere along the field lines. The mechanism that drives the energy transport to the corona is not yet fully understood. To investigate simultaneous magnetic and intensity structure in and around the AR in detail, we use SDO/HMI+AIA data of + / ‐ 2 hours around the 5 minute Hi‐C flight. In the case of the QS, work done by convection/granulation on the inter‐granular feet of the coronal field lines probably translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. However, to the best of our knowledge, there is no observational evidence available to these processes. We investigate the changes taking place in the photospheric feet of the magnetic field involved with brightenings in the Hi‐C AR corona. Using HMI 45s magnetograms of four hours we find that, out of the two Hi‐C sub‐regions where the braiding of field lines were recently detected, flux emergence takes place in one region and flux cancellation in the other. The field in these sub‐regions are highly sheared and have apparent high speed plasma flows at their feet. Therefore, shearing flows plausibly power much of the coronal and transition region heating in these areas of the AR. In addition, the presence of large flux emergence/cancellation strongly suggests that the work done by these processes on the pre‐existing field also drives much of the observed heating.

Tiwari, S. K.↗
NASA NTRS2014

Hi-C Observations of an Active Region Corona, and Investigation of the Underlying Magnetic Structure

The solar corona is much hotter (>=10(exp 6) K) than its surface (approx 6000 K), puzzling astrophysicists for several decades. Active region (AR) corona is again hotter than the quiet Sun (QS) corona by a factor of 4-10. The most widely accepted mechanism that could heat the active region corona is the energy release by current dissipation via reconnection of braided magnetic field structure, first proposed by E. N. Parker three decades ago. The first observational evidence for this mechanism has only recently been presented by Cirtain et al. by using High-resolution Coronal Imager (Hi-C) observations of an AR corona at a spatial resolution of 0.2 arcsec, which is required to resolve the coronal loops, and was not available before the rocket flight of Hi-C in July 2012. The Hi-C project is led by NASA/MSFC. In the case of the QS, work done by convection/granulation on the inter-granular feet of the coronal field lines translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. We are currently investigating the changes taking place in photospheric feet of the magnetic field involved with brightenings in the Hi-C AR corona. For this purpose, we are also using SDO/AIA data of +/- 2 hours around the 5 minutes Hi-C flight. In the present talk, I will first summarize some of the results of the Hi-C observations and then present some results from our recent analysis on what photospheric processes feed the magnetic energy that dissipates into heat in coronal loops.

Tiwari, S. K.↗
NASA NTRS1991

Handbook of solar-terrestrial data systems, version 1

The interaction between the solar wind and the earth's magnetic field creates a large magnetic cavity which is termed the magnetosphere. Energy derived from the solar wind is ultimately dissipated by particle acceleration-precipitation and Joule heating in the magnetosphere-ionosphere. The rate of energy dissipation is highly variable, with peak levels during geomagnetic storms and substorms. The degree to which solar wind and magnetospheric conditions control the energy dissipation processes remains one of the major outstanding questions in magnetospheric physics. A conference on Solar Wind-Magnetospheric Coupling was convened to discuss these issues and this handbook is the result.

Source record↗
NASA NTRS2005

Utilizing Radioisotope Power System Waste Heat for Spacecraft Thermal Management

An advantage of using a Radioisotope Power System (RPS) for deep space or planetary surface missions is the readily available waste heat, which can be used for a number of beneficial purposes including: maintaining electronic components within a controlled temperature range, warming propulsion tanks and mobility actuators, and maintaining liquid propellants above their freezing temperature. Previous missions using Radioisotope Thermoelectric Generators (RTGs) dissipated large quantities of waste heat due to the low efficiency of the thermoelectric conversion technology. The next generation RPSs, such as the 110-Watt Stirling Radioisotope Generator (SRG110) will have higher conversion efficiencies, thereby rejecting less waste heat at a lower temperature and may require alternate approaches to transferring waste heat to the spacecraft. RTGs, with efficiencies of ~6 to 7 percent, reject their waste heat at the relatively high heat rejection temperature of 200 C. This is an advantage when rejecting heat to space; however, transferring heat to the internal spacecraft components requires a large and heavy radiator heat exchanger. At the same time, sensitive spacecraft instruments must be shielded from the thermal radiation of the RTG. The SRG110, with an efficiency around 22 percent and 50 C nominal housing surface temperature, can readily transfer the available waste heat directly via heat pipes, thermal straps, or fluid loops. The lower temperatures associated with the SRG110 avoid the chances of overheating other scientific components, eliminating the need for thermal shields. This provides the spacecraft designers more flexibility when locating the generator for a specific mission. A common misconception with high-efficiency systems is that there is not enough waste heat for spacecraft thermal management. This paper will dispel this misconception and investigate the use of a high-efficiency SRG110 for spacecraft thermal management and outline potential methods of waste heat utilization in several conceptual missions (Lunar Rover, Mars Rover, and Titan Lander). The advantages associated with the SRG110 as they relate to ease of assembly, less complex interfaces, and overall mass savings for a spacecraft will be highlighted.

Pantano, David R.↗
NASA NTRS1988

The heating of coronal loops by MHD waves

A detailed derivation of the MHD wave equation appropriate for solar coronal conditions is presented. Some general concepts are discussed regarding the propagation of MHD waves in regions where gradients in the Alfven speed exist. A solution of the ideal equation is discussed, and the ideal solution near the surface of the resonance layer is obtained. The dissipative solution is found and the matching between the ideal and dissipative solutions is demonstrated. The heating rate is calculated and the expression for the heating rate is used to estimate the wave amplitude which is necessary in the corona to explain the observed active region heating rate on the sun.

Davila, Joseph M.↗
NASA NTRS2013

Static Dissipative Cable Ties, Such as for Radiation Belt Storm Probes

Methods of cyclically heating and cooling an article formed of a static dissipative ETFE resin, such as to reduce an electrical resistivity and/or to increase a tensile strength of the article, and methods of irradiating an article formed of a static dissipative ETFE resin, such as to increase a tensile strength of the article. Also disclosed herein are articles formed of a static dissipative ETFE resin, and processed in accordance with methods disclosed herein. Such an article may include, for example and without limitation, a cable strap to wrap, support, and/or secure one or more wires or cables, such as a cable tie.

Langley, Patrick T.↗
NASA NTRS1990

Neutron viscosity in accretion disks

Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions with accreting ions. Ion temperatures are determined by balancing the heating of ions by viscous dissipation to their cooling by Coulomb collisions with the electrons, providing a self-consistent solution between neutron production and their impact on energy dissipation. The results indicate that neutrons can indeed provide the necessary dissipation to sustain the steady-state accretion of matter at rates of about 10 to the -8th solar mass/yr or less, and electron temperatures of about 100 keV-1 MeV. Neutrons thus present a promising way of modeling bright Galactic X-ray sources.

Guessoum, Nidhal↗
NASA NTRS1985

On the importance of viscous dissipation in Io

A model of Io is presented that consists of an elastic inner core, a low strength asthenosphere, and a thin elastic outer shell. The middle layer is ssumed to posses negligible shear strength and to be characterized by a Newtonian viscosity. The fluid in the viscous layer is forced to circulate mainly by the tidal distortion in the outer shell, modeled here as a variation in the distortion amplitude. As a result, heat is generated in the fluid by viscous dissipation. There are three important unconstrained parameters in the model: the fluid viscosity, the thickness of the fluid layer, and the degree to which the distortion of the outer shell is affected by the fluid viscosity. For a wide range of these model parameters viscous heating can generate just as much or even more heat than does elastic dissipation is the outer shell. The model suggests that much of Io's heat flow may be generated below the outer shell and could provide a source of energy for any silicate volcanism on the satellite.

Ross, M. N.↗
NASA NTRS1992

Energy dissipation in substorms

The energy dissipated by substorms manifested in several ways is discussed: the Joule dissipation in the ionosphere; the energization of the ring current by the injection of plasma sheet particles; auroral election and ion acceleration; plasmoid ejection; and plasma sheet ion heating during the recovery phase. For each of these energy dissipation mechanisms, a 'rule of thumb' formula is given, and a typical dissipation rate and total energy expenditure is estimated. The total energy dissipated as Joule heat (approximately) 2 x 10(exp 15) is found about twice the ring current injection term, and may be even larger if small scale effects are included. The energy expended in auroral electron precipitation, on the other hand, is smaller than the Joule heating by a factor of five. The energy expended in refilling and heating the plasma sheets is estimated to be approximately 5 x 10(exp 14)J, while the energy lost due to plasmoid ejection is between (approximately) (10 exp 13)(exp 14)J.

Weiss, Loretta A.↗
NASA NTRS2024

x Thermal Straps

Thermal straps, also known as heat straps or flexible conductive links, offer design solutions for enhancing the thermal bond of two items that may need to be mechanically decoupled. The need for mechanical decoupling can be driven by requirements for things like vibration or load isolation, or simply by packaging constraints. A few examples include thermal straps used to mechanically isolate delicate spaceborne detectors from cryocooler vibrations, or thermal straps coupling a high-dissipation electronic component to a heat sink on an adjacent surface in a volume optimized electronics unit.

thermal, heat transfer, straps↗
NASA NTRS1984

Determination of hot-spot susceptibility of multistring photovoltaic modules in a central-station application

Part of the effort of the Jet Propulsion Laboratory (JPL) Flat-Plate Solar Array Project (FSA) includes a program to improve module and array reliability. A collaborative activity with industry dealing with the problem of hot-spot heating due to the shadowing of photovoltaic cells in modules and arrays containing several paralleled cell strings is described. The use of multiparallel strings in large central-station arrays introduces the likelihood of unequal current sharing and increased heating levels. Test results that relate power dissipated, current imbalance, cross-strapping frequency, and shadow configuration to hot-spot heating levels are presented. Recommendations for circuit design configurations appropriate to central-station applications that reduce the risk of hot-spot problems are offered. Guidelines are provided for developing hot-spot tests for arrays when current imbalance is a threat.

Gonzalez, C. C.↗
NASA NTRS1977

Observations of joule and particle heating in the auroral zone

Observational data from the Chatanika, Alaska incoherent scatter radar have been used to deduce atmospheric heating rates associated with particle precipitation and joule dissipation. During periods when Chatanika is in the vicinity of the auroral oval the height-integrated heat input to the lower thermosphere can be as large as 100 ergs per sq cm per sec with joule and particle heating rates of comparable magnitude. Altitude profiles of these heat inputs are also obtained, showing that the energy liberated by joule dissipation tends to peak at a substantially higher altitude (about 130 km) than that due to particles (100-120 km). As a consequence, it follows that joule heating can be expected to provide a rapid means for creating thermospheric disturbances. It is also pointed out that joule and particle heating are permanent features of the auroral oval and polar cap. As such, expansion of the auroral oval leads to an increase in the total global heating and, hence, to the close relationship between magnetic disturbances and thermospheric perturbation.

Banks, P. M.↗
NASA NTRS1980

The polarization and directivity of solar-flare hard X-ray bremsstrahlung from a thermal source

The polarization and directivity of hard X-ray bremsstrahlung from a thermal source consisting of a region in which a thermal flux drives a pair of steel collisionless conduction fronts were evaluated. The conduction fronts are symmetrically driven from a central region, heated by the flare energy dissipation process. By comparing results with similar calculations based on a nonthermal thick-target electron beam model of the source, it was aimed to determine the degree to which the observed polarization and directivity of solar flare hard X-rays favor either model. Results which exhibit significant polarization and directivity of the hard X-ray radiation emitted by the source are produced by using Maxwellian electron-phase-space distribution functions modified to take into account a directional heat flux and a steady direct current in the X-ray source, and a fully relativistic treatment of the bremsstrahlung emission process. The results are consistent with solar hard X-ray anisotropy and polarization observations to date, although these observations are too crude to be conclusive.

Emslie, A. G.↗
NASA NTRS1988

Correlations of velocity and temperature fluctuations in the stagnation-point flow of circular cylinder in turbulent flow

Boundary layer flow and turbulence transport analyses to study the influence of the free-stream turbulence on the surface heat transfer rate and the skin friction around the stagnation point of a circular cylinder in a turbulent flow are presented. The analyses are formulated with the turbulent boundary layer equations, the Reynolds stress transport equations and the k - epsilon two-equation turbulence modeling. The analyses are used to calculate the time-averaged turbulence double correlations, the mean flow properties, the surface heat transfer rate and the skin friction with an isotropic turbulence in the freestream. The analytical results are described and compared with the existing experimental measurements. Depending on the free-stream turbulence properties, the turbulence kinetic energy can increase or decrease as the flow moves toward the surface. However, the turbulence kinetic energy induces large Reynolds normal stresses at the boundary layer edge. The Reynolds normal stresses change the boundary layer profiles of the time-averaged double correlations of the velocity and temperature fluctuations, the surface heat transfer rate and the skin friction. The free-stream turbulence dissipation rate can affect the stagnation-point heat transfer rate but the influence of the free-stream temperature fluctuation on the heat transfer rate is insignificant.

Wang, Chi R.↗
NASA NTRS2014

The Tethered Moon

A reasonable initial condition on Earth after the Moonforming impact is that it begins as a hot global magma ocean1,2. We therefore begin our study with the mantle as a liquid ocean with a surface temperature on the order of 3000- 4000 K at a time some 100-1000 years after the impact, by which point we can hope that early transients have settled down. A 2nd initial condition is a substantial atmosphere, 100-1000 bars of H2O and CO2, supplemented by smaller amounts of CO, H2, N2, various sulfur-containing gases, and a suite of geochemical volatiles evaporated from the magma. Third, we start the Moon with its current mass at the relevant Roche limit. The 4th initial condition is the angular momentum of the Earth-Moon system. Canonical models hold this constant, whilst some recent models begin with considerably more angular momentum than is present today. Here we present a ruthlessly simplified model of Earth's cooling magmasphere based on a full-featured atmosphere and including tidal heating by the newborn Moon. Thermal blanketing by H2O-CO2 atmospheres slows cooling of a magma ocean. Geochemical volatiles - chiefly S, Na, and Cl - raise the opacity of the magma ocean's atmosphere and slow cooling still more. We assume a uniform mantle with a single internal (potential) temperature and a global viscosity. The important "freezing point" is the sharp rheological transition between a fluid carrying suspended crystals and a solid matrix through which fluids percolate. Most tidal heating takes place at this "freezing point" in a gel that is both pliable and viscous. Parameterized convection links the cooling rate to the temperature and heat generation inside the Earth. Tidal heating is a major effect. Tidal dissipation in the magma ocean is described by viscosity. The Moon is entwined with Earth by the negative feedback between thermal blanketing and tidal heating that comes from the temperature-dependent viscosity of the magma ocean. Because of this feedback, the rate that the Moon's orbit evolves is limited by the modest radiative cooling rate of Earth's atmosphere, which in effect tethers the Moon to the Earth. Consequently the Moon's orbit evolves orders of magnitude more slowly than in conventional models. Slow orbital evolution promotes capture by orbital resonances that may have been important in the Earth-Moon system

Earth-Moon system↗
NASA NTRS1993

Thermal evolution of neutron stars with internal frictional heating

It has been suggested that the frictional interaction of neutron superfluids with normal matter in the inner crust of neutron stars dissipates rotational energy of superfluids and generates heat. Incorporating a general formula of internal heating into the detailed numerical codes of thermal evolution, we examine the effects of the internal heating on thermal evolution of neutron stars. We find that when a very stiff equation of state is used, it takes as long as about 2 x 10 exp 4 yr for the interior of a neutron star to reach the isothermal state, even if a strong heat source is placed in a thin layer of the inner crust. This time scale reduces to a few hundred years or less when medium to soft equations of state are used. A neutron star cools by neutrino emissions during the earlier stages referred to as the neutrino cooling era, while during the later photon cooling era it cools primarily by emission of photons from its surface. We show that heating rates expected in the current superfluid-crust interaction model can greatly increase the surface temperature in the photon cooling era, significantly changing the thermal evolution of relatively old neutron stars if a stiff equation of state is adopted.

Umeda, Hideyuki↗
NASA NTRS1978

Contribution of tidal dissipation to lunar thermal history

Possible contributions of tidal heating to the thermal history of the moon are investigated, and conditions under which such heating would have been an important factor in the evolution of the moon are defined as precisely as possible within the bounds of the uncertainties. The tidal dissipation is defined as a function of position in the moon and of the earth-moon separation for a homogeneous incompressible moon. Results for the dissipation are given for eccentricities of zero and 0.055 as well as for the lunar obliquity as determined by the equilibrium Cassini states. Possible orbital resonances which interrupt the assumed simplified expansion of the lunar orbit are considered, along with radial variations in rigidity. The dissipation in a two-layer model moon with a molten inner core and an outer mantle with the moon's present rigidity is determined, and implications of the results for the role of tidal heating in the history of the moon are discussed.

Peale, S. J.↗
NASA NTRS2008

Demonstrations that the Solar Wind Is Not Accelerated by Waves

The present work uses both observations and theoretical considerations to show that hydromagnetic waves cannot produce the acceleration of the fast solar wind and the related heating of the open solar corona. Waves do exist, and can play a role in the differential heating and acceleration of minor ions, but their amplitudes are not sufficient to power the wind, as demonstrated by extrapolation of magnetic spectra from Helios and Ulysses observations. Dissipation mechanisms invoked to circumvent this conclusion cannot be effective for a variety of reasons. In particular, turbulence does not play a strong role in the corona as shown by both observations of coronal striations and theoretical considerations of line-tying to a nonturbulent photosphere, nonlocality of interactions, and the nature of the kinetic dissipation. In the absence of wave heating and acceleration, the chromosphere and transition region become the natural source of open coronal energization. We suggest a variant of the 'velocity filtration' approach in which the emergence and complex churning of the magnetic flux in the chromosphere and transition region continuously and ubiquitously produces the nonthermal distributions required. These particles are then released by magnetic carpet reconnection at a wide range of scales and produce the wind as described in kinetic approaches. Since the carpet reconnection is not the main source of the energization of the plasma, there is no expectation of an observable release of energy in nanoflares.

Roberts, Aaron↗