摘要:

An approximate formula for the thermal conductivity of multicomponent gas mixtures is derived from rigorous kinetic theory by well‐defined approximations. Numerical calculations with the formula are relatively simple, and the only data needed are the molecular weights, thermal conductivities, and either viscosities or heat capacities of the pure components at the same temperature as the mixture. The form of the formula is quite similar to the earlier empirical Lindsay‐Bromley equation. The formula is tested by comparison with experimental results on a number of binary and ternary mixtures involving both monatomic and polyatomic nonpolar gases. Agreement is satisfactory, and is nearly as good as obtained with the full rigorous theory.

ISSN:0031-9171    

DOI:10.1063/1.1724352

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Known intermolecular force laws are used to calculate virial coefficients of the equation of state and the transport properties at very high temperatures for the rare gases and for molecular nitrogen. The crucial force laws which enable the calculations to be carried to high temperatures are those derived from molecular beam scattering measurements, which are valid at close distances of molecular approach. The calculations cover the temperature range from 1000° to 15 000°K, but take into account only the translational degrees of freedom and neglect the effects of excitation, dissociation, and ionization. The treatment of mixtures is outlined, and illustrated by calculations for the binary system helium‐argon. The methods which are used offer an approach to the problem of obtaining reasonably accurate estimates of gas properties at temperatures so high that direct experiments would be extremely difficult, if not impossible.

ISSN:0031-9171    

DOI:10.1063/1.1724353

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

When gases flow at high velocity, the rates of internal processes may not be fast enough to maintain thermodynamic equilibrium. By defining quasi‐equilibrium in flow as the condition in which the temperature, pressure, density, and velocity deviate by less than a fixed, small percentage from what they would be if the flowing gas could actually be in thermodynamic equilibrium, criteria are derived for determining whether quasi‐equilibrium is a stable condition in the flow. By use of excitation of molecular vibration as an example, the general properties of criteria curves are discussed and interpreted. A discussion is given of how to use these results to determine definitely whether a flow is or is not in thermodynamic equilibrium. Applications to dissociating gases, to mixtures, and to the phenomenon of ``choking'' in a Laval nozzle are given special consideration. For cases when application of the criteria predict nonequilibrium, equations are provided in a form useful for numerical forward integration along streamlines.

ISSN:0031-9171    

DOI:10.1063/1.1724354

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

An x‐ray densitometer has been used to measure the density ratio across a detonation wave in a number of different gaseous mixtures involving C2H2, C2N2, or H2with O2and Kr. In a 3‐in. i.d. tube at an initial pressure of 60 cm the density ratios observed were between 1.64 and 1.67. Investigations of the influence on density ratio of tube diameter at constant initial pressure and of initial pressure at constant tube diameter both indicate an extrapolated infinite diameter density ratio of 1.70 for a 0.3 C2H2+ 0.3 O2+ 0.4 Kr mixture. This result is significantly lower than the ratio 1.79 which corresponds to the tangent point on the equilibrium Hugoniot from the initial state. At the present time these observations cannot adequately be explained by detonation theory.

ISSN:0031-9171    

DOI:10.1063/1.1724355

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

High‐speed photographic observations have been made of flame structure, flame velocity, and shock velocity during the transition from slow burning to detonation in acetylene‐oxygen mixtures contained in glass pipe at reduced pressures. During intermediate stages the dome‐shaped flame travels down the tube at about 800 m/sec and is preceded by a shock wave traveling slightly faster. During the final stages of formation of the detonation wave, the flame changes shape, accelerates, and advances along the walls in an asymmetric manner. The detonation first appears at, or slightly behind, the leading edge of the flame. The final flame acceleration occurs when the Reynolds number of the mass flow between the flame and the preceding shock, based upon the distance traveled by a mass element in the time interval between passage of the shock and the flame through it, is about 107. Under these conditions the development of turbulent regions in the boundary‐layer flow ahead of flame appears likely. Changes in flame configuration which result in the final acceleration and the formation of the detonation wave then arise from the faster flame propagation into these turbulent areas than into the free‐stream region.

ISSN:0031-9171    

DOI:10.1063/1.1724356

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

An assumption of statistical reflection symmetry is proposed for certain turbulent flows. On the basis of this assumption it is shown that some space‐time velocity correlations characterizing the flow are even functions of the time delay between the correlation measurements. In particular the second‐ and one of the fourth‐order velocity correlations are symmetric in this relative time.

ISSN:0031-9171    

DOI:10.1063/1.1724357

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The basic concepts of confinement and ohmic heating in a figure‐eight stellarator are briefly reviewed and experimental data in these areas summarized. The production of energetic x‐rays by runaway electrons, up to ten milliseconds after the disappearance of the accelerating field, has indicated effective single‐particle confinement by magnetic fields of 20 000 to 30 000 gauss. However, the plasma confinement time during ohmic heating appears to be limited by unknown processes to approximately 100 microseconds for hydrogen, more than three orders of magnitude shorter than predicted from classical collisional diffusion. The ionization level in a helium discharge, with an initial pressure of about 1 &mgr; of Hg, becomes virtually complete during the heating pulse, and the electric resistivity corresponds to a kinetic temperature of about 100 volts, or 106degrees. After the heating pulse, the electron density decays with a time constant as great as 6 milliseconds under some conditions. The hydromagnetic kink instability predicted by Kruskal has been clearly observed.

ISSN:0031-9171    

DOI:10.1063/1.1724358

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

When there is a uniform externally imposed longitudinal magnetic field much larger than the field of a discharge current in a cylindrical plasma, one should expect instabilities in the form of a lateral displacement of the plasma column into a helix of large pitch. This problem is examined under the conditions which might occur in the stellarator during ohmic heating. It is shown that the presence of external conductors is unimportant. When effects of the finite length of the machine are considered, a critical current is obtained below which the system is stable to this displacement. Consideration of current distributions other than uniform shows that instabilities which vary asei(m&thgr;+kz)can occur for values ofmgreater than one, so that instabilities can be found for any finite length machine. Experimental results are in agreement with the theory for them= 1 mode. There is no experimental indication of the highermmodes, for which several possible explanations are suggested.

ISSN:0031-9171    

DOI:10.1063/1.1724359

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Examination of the temporal distribution, relative intensity, and maximum energy of x‐rays above 30 kev emanating from the B‐1 stellarator during a pulsed discharge has revealed a number of interesting phenomena. The x‐rays are assumed to be produced by ``runaway'' electrons when they strike the wall. Spuriously large pulse heights have been observed. The x‐rays abruptly appear early in the discharge, before the Kruskal instability can occur. Depending on the operating conditions, x‐rays can be observed at any time during the discharge except when the current is at the Kruskal limiting value. If the longitudinal electric field used for ohmic heating is ``crowbarred,'' x‐rays can appear afterwards in copious quantities; furthermore, the discharge current can decay in abrupt steps correlated in time with bursts of x‐rays. The hypothesis that the current in these steps is due entirely to runaway electrons is consistent with the data. These observations are taken to be evidence for the existence of cooperative phenomena, or collective motions which can affect both the confinement and the heating of a plasma. In addition, intense nonthermal microwave noise has been detected at times correlated with x‐ray emission.

ISSN:0031-9171    

DOI:10.1063/1.1724360

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A divertor, designed to reduce the flow of impurities from the wall into a gas discharge, has been used with a small stellarator. In the divertor an outer shell of magnetic flux is bent away from the discharge channel into a large auxiliary chamber. Ions diffusing toward the wall tend to follow the lines of force of this outer shell into the divertor chamber. Impurities produced by wall bombardment in this chamber do not readily return to the discharge. The magnetic design of this device is described, and a phenomenological theory of its performance is outlined. The spectroscopic data with and without the divertor activated indicate that the divertor reduces the influx of impurities by a factor of two to three, while the impurity concentration at the core, or central region, may be diminished by an order of magnitude when the divertor is activated. Kinetic temperatures of positive ions determined from spectroscopic measurements of Doppler broadening increase from 40 ev without the divertor to 60 ev for He+and to 130 ev for O++++with use of the divertor.

ISSN:0031-9171    

DOI:10.1063/1.1724361

出版商:AIP    

年代:1958

数据来源: AIP