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Results for “HEAT BALANCE”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Numerical studies of the energy balance in coronal loops

A numerical method is applied to treat the energy balance of quasi-static solar coronal loops, which have been observed to persist for periods much greater than the radiative cooling time. The quasi-static loop model employed takes into account gravity, density-, temperature- or position-dependent energy input, an accurate form of the radiative losses and variable loop cross-sectional area, under assumptions of energy input by coronal heating balanced by radiative and conductive losses, an optically thin plasma, energy conduction along the field lines only and hydrostatic equilibrium. Computations of an emission measure function for various distributions of the energy input and loop geometries are then presented which show that little information on the location of the energy input may be gained from spectral line intensity measurements integrated over a single loop.

Underwood, J. H.↗
NASA NTRS1974

The differential rotation of the solar surface

The large-scale flow in the solar convection zone is discussed. The objective is to deduce from observation the principal physical balances in the governing equations. The simplest set of equations that seem potentially realistic are utilized. It is assumed that magnetic fields are negligible, that mixing-length theory gives an accurate representation of the mean structure, and that rigid-body rotation exists at the base. It is deduced that the zonal glow is geostrophic, the meridional flow is controlled by friction, and diffusive heating balances advective cooling due to vertical motion. Next, a detailed calculation of the latitude profile of surface angular velocity is performed, based on approximate equations containing only the principal balances, and agrees well with observation. Finally, it is demonstrated that the amplitude of the flow may be determined by the constraint that the net equatorward angular momentum flux vanish. The conclusions are consistent with the hypothesis that the flow is primarily a single large axisymmetric convection cell in each hemisphere.

Gierasch, P. J.↗
NASA NTRS1992

Modeling of the WSTF frictional heating apparatus in high pressure systems

In order to develop a computer program able to model the frictional heating of metals in high pressure oxygen or nitrogen a number of additions have been made to the frictional heating model originally developed for tests in low pressure helium. These additions include: (1) a physical property package for the gases to account for departures from the ideal gas state; (2) two methods for spatial discretization (finite differences with quadratic interpolation or orthogonal collocation on finite elements) which substantially reduce the computer time required to solve the transient heat balance; (3) more efficient programs for the integration of the ordinary differential equations resulting from the discretization of the partial differential equations; and (4) two methods for determining the best-fit parameters via minimization of the mean square error (either a direct search multivariable simplex method or a modified Levenburg-Marquardt algorithm). The resulting computer program has been shown to be accurate, efficient and robust for determining the heat flux or friction coefficient vs. time at the interface of the stationary and rotating samples.

Skowlund, Christopher T.↗
NASA NTRSDate not supplied

Extinction of the Stagnation Point Diffusion Flame: Effect of Conductive Heat Loss into Solid Interior

The flammability boundary of a solid is U-shaped with the ordinate as ambient oxygen percentage (or total pressure) and the abscissa represents flow velocity, gravity level, stretch rate, etc. The left side of the flammability boundary is the quenching branch, and the right side is the blow-off branch. Quenching is due to a weak flame whose heat release from combustion cannot overcome the excessive heat losses from, for example, radiation. Blow-off is due to a short gas residence time that is smaller than the chemical reaction time (traditionally referred to as the small Damköhler number effect). For thick solids, the heat conduction into the solid interior has a long transient after ignition before the solid temperature reaches the steady state. During this slow transient, there is excessive (i.e. more than that at the steady state) gas phase heat conduction into the solid interior. From the viewpoint of the quasi-static gaseous flame, this is an additional heat loss that will affect the gas flame's flammability. In this work, a previously developed one-dimensional axisymmetric stagnation-point diffusion flame model is extended to account for the excessive heat loss into the solid beyond the steady burning state. A non-dimensional excessive conductive heat loss parameter Ψ is defined in the paper to account for the transient solid effect. For each Ψ, the gas phase is considered reaching a quasi-steady state. Extensive numerical computations have been performed to determine the extinction boundary and the characteristics of near-limit flames. The U-shaped flammability boundary is now a series of boundaries with Ψ as a parameter. Flame structures under the same environment condition but with different Ψ are compared. For a given oxygen ambient, the extinction boundary Ψ vs stretch rate is an inverted U-shape. The boundary consists of a blowoff branch and a radiative quenching branch. Extensive computed data including flame and pyrolysis temperatures, burning rate, flame standoff distance, species concentration, and reaction rate are presented along the extinction boundaries. Heat balance analysis is performed for both the gas phase and the gas-solid interface. Along the extinction boundary, the relative importance of conduction, convection, radiation, and chemical reaction are analyzed in detail.

Stagnation point diffusion flame↗
NASA NTRS1988

A four-layer model for the heat budget of homogeneous land surfaces

The present model envisions the heat balance of a homogeneous land surface in terms of available energy, a set of driving potentials, and parameters for the physical state of the soil and vegetation. Two unique features of the model are: (1) the expression of the interaction of evaporation from the soil and from foliage by changes in the value of the saturation vapor pressure deficit of air in the canopy (the conclusions of this interaction being consistent with field observations); and (2) the treatment of sensible and latent heat exchange between the atmosphere and a soil consisting of two discrete layers.

Choudhury, B. J.↗
NASA NTRS1968

Electronic calorimetric computer

Electronic calorimetric computer calculates nuclear reactor thermal power output to a nominal accuracy of 1 percent. Heat balance is determined by an electronic approach. The thermal power is calculated using the inlet and outlet temperatures and the volume of cooling water and is displayed by a digital readout system.

Heckelman, J. D.↗
NASA NTRS1971

A 7.6m /25-ft/ extreme environments simulator

Stainless steel cylindrical simulation chamber permits testing equipment under extreme cold, high partial vacuums, and intense solar radiation. Applications include heat balance and temperature distribution studies, investigations of subsystem interactions, tests of attitude control equipment and sensors, and acceptance tests of complete systems.

Argoud, M. J.↗
NASA NTRS1971

Ablative heat shields for Jupiter entry probes

Jupiter atmosphere entry probes graphite ablative heat shields performance, indicating convective and radiative blockage and graphite sublimation processes in surface heat balance

Lundell, J. H.↗
NASA NTRS1972

Variable boundary II heat conduction

Computer program for solving both transient and steady-state heat transfer problems is presented. Specific applications of computer program are described. Formulation for individual nodes of solid medium for heat balance is presented. Diffusion equation is solved for all nodes simultaneously at finite increments of time.

Gramer, J.↗
NASA NTRS1972

Pioneer F mission to Jupiter

The experimental designs for the Pioneer F mission to Jupiter are described. The spacecraft is designed to make measurements of the planet's atmosphere, radiation belts, heat balance, magnetic fields, moons, and other related phenomena. The mission also characterizes the heliosphere, the interstellar gas, cosmic rays, asteroids, and meteoroids between the earth and 2.4 billion kilometers from the sun.

Allaway, H. G.↗
NASA NTRS1972

Effects of electrostatic rocket material deposited on solar cells.

If solar arrays on solar-electric spacecraft protrude into the exhaust hemisphere of the electric thrusters, they will receive fluxes (usually small) of both propellant and accelerator grid atoms. Unlike propellants, grid materials have low vapor pressures and will not reevaporate. An analysis is presented of degradation in the optical, thermal, and electrical performance of solar cells resulting from thin deposits of grid material (aluminum and molybdenum) on various array surfaces. The classical optical theory of thin films, heat balance equations, and a typical relationship for solar cell efficiency vs temperature are used to compute curves showing optical properties, temperature, and power output as functions of film thickness. The results compare favorably with available experimental data. It is shown that a few monolayers of metal deposition on the illuminated surface will seriously degrade cell performance. A means of estimating the arrival rate of these materials is provided.

Kemp, R. F.↗
NASA NTRS1972

The electron heating rate and ion chemistry in the thermosphere above Wallops Island during the solar eclipse of 7 March 1970.

Measurement of the N2 concentration and temperature, the ion composition and concentrations, and the electron temperature up to 290 km about 30 and 5 min before totality during the Mar. 7, 1970, eclipse. The rockets traveled similar trajectories, thus permitting the purely temporal changes between flights to be resolved. The neutral temperature and N2 concentration changed little, but the electron temperature decreased by as much as 20% in the lower F region. The ion concentration decreased by about 30% in the F region and about 50% in the E region, with little change in relative ion composition. The electron cooling rates decreased by a factor of 6 in the lower F region, approximately in proportion to the change in the visible solar disk. A smaller than expected decrease in the cooling rate below 150 km between the two flights indicates a hardening of the solar spectrum and suggests a significant heat contribution from the solar corona near totality. The ion composition measurements were consistent with solutions of the ion continuity equations. A proper fit required a factor-of-three enhancement of the flux below 200 A, an amount also consistent with the electron heat balance analysis. Reactions involving the minor ions N(+) and N2(+) were found to be important for the ion chemistry of the major ions O2(+) and NO(+), especially at the time of eclipse.-

Brace, L. H.↗