Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Kinetics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Kinetic theory of current and density drift instabilities with weak charged-neutral collisions

This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.

Gary, S. P.↗
NASA NTRS1984

Chemical kinetic reaction mechanism for the combustion of propane

A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.

Jachimowski, C. J.↗
NASA NTRS1984

Buoyant production and consumption of turbulence kinetic energy in cloud-topped mixed layers

It is pointed out that studies of the entraining planetary boundary layer (PBL) have generally emphasized the role of buoyancy fluxes in driving entrainment. The buoyancy flux is proportional to the rate of conversion of the potential energy of the mean flow into the kinetic energy of the turbulence. It is not unusual for conversion to proceed in both directions simultaneously. This occurs, for instance, in both clear and cloudy convective mixed layers which are capped by inversions. A partitioning of the net conversion into positive parts, generating turbulence kinetic energy (TKE), and negative parts (TKE-consuming), would make it possible to include the positive part in the gross production rate, and closure would be achieved. Three different approaches to partitioning have been proposed. The present investigation is concerned with a comparison of the three partitioning theories. Particular attention is given to the cloud-topped mixed layer because in this case the differences between two partitioning approaches are most apparent.

Randall, D. A.↗
NASA NTRS1984

CREKID: A computer code for transient, gas-phase combustion of kinetics

A new algorithm was developed for fast, automatic integration of chemical kinetic rate equations describing homogeneous, gas-phase combustion at constant pressure. Particular attention is paid to the distinguishing physical and computational characteristics of the induction, heat-release and equilibration regimes. The two-part predictor-corrector algorithm, based on an exponentially-fitted trapezoidal rule, includes filtering of ill-posed initial conditions, automatic selection of Newton-Jacobi or Newton iteration for convergence to achieve maximum computational efficiency while observing a prescribed error tolerance. The new algorithm was found to compare favorably with LSODE on two representative test problems drawn from combustion kinetics.

Pratt, D. T.↗
NASA NTRS1985

New integration techniques for chemical kinetic rate equations. 2: Accuracy comparison

A comparison of the accuracy of several techniques recently developed for solving stiff differential equations is presented. The techniques examined include two general purpose codes EEPISODE and LSODE developed for an arbitrary system of ordinary differential equations, and three specialized codes CHEMEQ, CREKID, and GCKP84 developed specifically to solve chemical kinetic rate equations. The accuracy comparisons are made by applying these solution procedures to two practical combustion kinetics problems. Both problems describe adiabatic, homogeneous, gas phase chemical reactions at constant pressure, and include all three combustion regimes: induction, heat release, and equilibration. The comparisons show that LSODE is the most efficient code - in the sense that it requires the least computational work to attain a specified accuracy level. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for the temperature can be more accurate and efficient than computing the temperature by integrating its time derivative.

Radhakrishnan, K.↗
NASA NTRS1984

VO2 kinetics of constant-load exercise following bed-rest-induced deconditioning

Previous studies have shown that the oxygen uptake kinetics during exercise and recovery may be changed by alterations in work intensity, prior exercise, muscle group involvement, ambient conditions, posture, disease state, and level of physical conditioning. However, the effects of detraining on oxygen uptake kinetics have not been determined. The present investigation has the objective to determine the effects of deconditioning following seven days of continuous head-down bed rest on changes in steady-state oxygen uptake, O2 deficit, and recovery oxygen uptake during the performance of constant-load exercise. The obtained results may provide support for previous proposals that submaximal oxygen uptake was significantly reduced following bed rest. The major finding was that bed-rest deconditioning resulted in a reduction of total O2 transport/utilization capacity during the transient phase of upright but not supine exercise.

Convertino, V. A.↗
NASA NTRS1984

Kinetics of thermal donor generation in silicon

The generation kinetics of thermal donors at 450 C in Czochralski-grown silicon was found to be altered by high-temperature preannealing (e.g., 1100 C for 30 min). Thus, when compared with as-grown Si, high-temperature preannealed material exhibits a smaller concentration of generated thermal donors and a faster thermal donor saturation. A unified mechanism of nucleation and oxygen diffusion-controlled growth (based on solid-state plate transformation theory) is proposed to account for generation kinetics of thermal donors at 450 C, in as-grown and high-temperature preannealed Czochralski silicon crystals. This mechanism is consistent with the main features of the models which have been proposed to explain the formation of oxygen thermal donors in silicon.

Mao, B.-Y.↗
NASA NTRS1985

Study of the kinetics and mechanism of the thermal nitridation of SiO2

X-ray photoelectron spectroscopy (XPS) has been used to study the nitridation time and temperature dependence of the nitrogen distribution in thermally nitrided SiO2 films. The XPS data show that the maximum nitrogen concentration near the (SiO(x)N(y)/Si interface is initially at the interface, but moves 20-25 A away from the interface with increasing nitridation time. Computer modeling of the kinetic processes involved is carried out and reveals a mechanism in which diffusing species, initially consisting primarily of nitrogen, react with the substrate, followed by formation of the oxygen-rich oxynitride due to reaction of the diffusing oxygen displaced by the slower nitridation of the SiO2. The data are consistent with this mechanism provided the influence of the interfacial strain on the nitridation and oxidation kinetics is explicitly accounted for.

Vasquez, R. P.↗
NASA NTRS1986

A model for the kinetics of a solar-pumped long path laser experiment

A kinetic model for a solar-simulator pumped iodine laser system is developed and compared to an experiment in which the solar simulator output is dispersed over a large active volume (150 cu cm) with low simulator light intensity (approx. 200 solar constants). A trace foreign gas which quenches the upper level is introduced into the model. Furthermore, a constant representing optical absorption of the stimulated emission is introduced, in addition to a constant representing the scattering at each of the mirrors, via the optical cavity time constant. The non-uniform heating of the gas is treated as well as the pressure change as a function of time within the cavity. With these new phenomena introduced into the kinetic model, a best reasonable fit to the experimental data is found by adjusting the reaction rate coefficients within the range of known uncertainty by numerical methods giving a new bound within this range of uncertainty. The experimental parameters modeled are the lasing time, laser pulse energy, and time to laser threshold.

Stock, L. V.↗
NASA NTRS1985

Kinetics and photochemistry Golden, D. M.

The data for chemical kinetics rate constants and photochemical cross sections taken from a compilation prepared in early 1985, entitled Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, is presented.

Demore, W. B.↗
NASA NTRS1985

Finite sample size effects in transformation kinetics

The effect of finite sample size on the kinetic law of phase transformations is considered. The case where the second phase develops by a nucleation and growth mechanism is treated under the assumption of isothermal conditions and constant and uniform nucleation rate. It is demonstrated that for spherical particle growth, a thin sample transformation formula given previously is an approximate version of a more general transformation law. The thin sample approximation is shown to be reliable when a certain dimensionless thickness is small. The latter quantity, rather than the actual sample thickness, determines when the usual law of transformation kinetics valid for bulk (large dimension) samples must be modified.

Weinberg, M. C.↗
NASA NTRS1986

Kinetic theory based new upwind methods for inviscid compressible flows

Two new upwind methods called the Kinetic Numerical Method (KNM) and the Kinetic Flux Vector Splitting (KFVS) method for the solution of the Euler equations have been presented. Both of these methods can be regarded as some suitable moments of an upwind scheme for the solution of the Boltzmann equation provided the distribution function is Maxwellian. This moment-method strategy leads to a unification of the Riemann approach and the pseudo-particle approach used earlier in the development of upwind methods for the Euler equations. A very important aspect of the moment-method strategy is that the new upwind methods satisfy the entropy condition because of the Boltzmann H-Theorem and suggest a possible way of extending the Total Variation Diminishing (TVD) principle within the framework of the H-Theorem. The ability of these methods in obtaining accurate wiggle-free solution is demonstrated by applying them to two test problems.

Deshpande, S. M.↗
NASA NTRS1985

Auroral arc formation - Kinetic and MHD effects

Recent observations by the Dynamics Explorer satellites indicate that auroral field lines are not equipotentials. The field-aligned 'conductivity' is the same for up and downgoing currents and of the order of several 10 to the -8th to several 10 to the -9th/ohms sq m. This is not in agreement with models based on the resistance provided by the magnetic mirror force alone. It is suggested that the resistivity is due to damping of kinetic shear-Alfven wave packets. This damping may be nonlinear in nature or Landau damping. The properties of kinetic Alfven waves are reviewed.

Goertz, C. K.↗
NASA NTRS1986

New integration techniques for chemical kinetic rate equations. II - Accuracy comparison

A comparison of the accuracy of several techniques recently developed for solving stiff differential equations is presented. The techniques examined include two general purpose codes EEPISODE and LSODE developed for an arbitrary system of ordinary differential equations, and three specialized codes CHEMEQ, CREKID, and GCKP84 developed specifically to solve chemical kinetic rate equations. The accuracy comparisons are made by applying these solution procedures to two practical combustion kinetics problems. Both problems describe adiabatic, homogeneous, gas phase chemical reactions at constant pressure, and include all three combustion regimes: induction heat release, and equilibration. The comparisons show that LSODE is the most efficient code - in the sense that it requires the least computational work to attain a specified accuracy level. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for the temperature can be more accurate and efficient than computing the temperature by integrating its time derivative.

Radhakrishnan, K.↗
NASA NTRS1986

A kinetic model for the thermal nitridation of SiO2/Si

To explain the observed nitrogen distributions in thermally nitridated SiO2 films, a kinetic model is proposed in which the nitridation process is simulated, using the first-order chemical kinetics and Arrhenius dependence of the diffusion and reaction rates on temperature. The calculations show that initially, as the substrate reacts with diffusing nitrogen, a nitrogen-rich oxynitride forms at the SiO2-Si interface, while at nitridation temperatures above 1000 C, an oxygen-rich oxynitride subsequently forms at the interface, due to reaction of the substrate with an increasingly concentrated oxygen displaced by the slower nitridation of the SiO2. This sequence of events results in a nitrogen distribution in which the peak of the interfacial nitrogen concentration occurs away from the interface. The results are compared with the observed nitrogen distribution. The calculated results have correctly predicted the positions of the interfacial nitrogen peaks at the temperatures of 800, 1000, and 1150 C. To account for the observed width of the interfacial nitrogen distribution, it was found necessary to include in the simulations the effect of interfacial strain.

Vasquez, R. P.↗
NASA NTRS1986

Electron acceleration via kinetic Alfven waves

Kinetic effects on obliquely propagating shear Alfven waves are reviewed. The wave becomes dispersive and carries a significant parallel electric field. The polarization and dispersion of these waves are discussed, showing that electrons can be effectively accelerated along field lines by these waves. Nonlinear effects such as solitary waves, nonlinear damping due to current-driven instabilities, and anomalous resistivity are treated. Observations of electric and magnetic field perturbations on auroral field lines which seem to be related to these waves are studied. Evidence for the existence of these kinetic Alfven waves is not firm.

Goertz, C. K.↗
NASA NTRS1986

A second-order accurate kinetic-theory-based method for inviscid compressible flows

An upwind method for the numerical solution of the Euler equations is presented. This method, called the kinetic numerical method (KNM), is based on the fact that the Euler equations are moments of the Boltzmann equation of the kinetic theory of gases when the distribution function is Maxwellian. The KNM consists of two phases, the convection phase and the collision phase. The method is unconditionally stable and explicit. It is highly vectorizable and can be easily made total variation diminishing for the distribution function by a suitable choice of the interpolation strategy. The method is applied to a one-dimensional shock-propagation problem and to a two-dimensional shock-reflection problem.

Deshpande, Suresh M.↗