摘要:

The severe decrease of flow duration in shock tubes operating at low pressures, previously reported by Duff, is confirmed by experiment and by an analysis of the effects of the laminar‐boundary layer behind the shock wave. The latter leads to a shock tube similarity length parameterX, which depends on the tube pressure, diameter and shock Mach number, and to a flow duration parameterT. The theoretical relationT = T(X)is determined and compared with experimental results. From the theoretical resultTmax= 1, the maximum possible flow duration &tgr;min a shock tube is determined; it increases linearly with the initial pressure and the square of the tube diameter and decreases strongly with shock Mach number.

ISSN:0031-9171    

DOI:10.1063/1.1706147

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Measurements have been made of the temperature, density, and degree of ionization of plasmas produced by Mach 30 magnetically driven shock waves in helium (ambient pressure 1 mm Hg). Simultaneous photoelectric intensity measurements of the absolute spectral intensities of HeI &lgr;3889, HeI &lgr;5876, HeII &lgr;4686, and HeII &lgr;3203 indicate temperatures of 3.7 ev, electron and ion densities ∼1017cm−3, degree of ionization ∼99.9&percent;, and a density ratio of ∼4 across the shock front. The estimated error is ±2&percent; for the temperature and ±12&percent; for the electron and ion densities. The electron density was derived independently from the width of HeII &lgr;4686 and agreed with the photoelectric density measurement to within the experimental error for the line width, thus providing a proof of the ionization and excitation equilibrium assumption used in analyzing the absolute intensity data. Continuum intensity measurements also provided a check on the consistency of the results. The temperature calculated from the measured shock velocity using the usual Rankine‐Hugoniot equations is lower by a factor of about 2, and the density ratio is higher by a factor of about 3. A plausible explanation of this discrepancy is that ultraviolet radiation emitted by the hot plasma in the arc region is absorbed in front of the shock wave.

ISSN:0031-9171    

DOI:10.1063/1.1706148

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Results from a detailed experimental study of the structure of pressure‐driven incident shock waves in very pure xenon contained in a thoroughly pumped Pyrex shock tube are presented and discussed. As a result of some optical studies of the luminous structure of the shocks, the following features of the luminosity delay time were discovered: independence of the pressure in the undisturbed xenon in the range 0.75 to 4.0 mm Hg, dependence on shock velocity in a way not explainable on the basis of reasonable volume processes alone, and dependence on shock tube diameter. The visible luminosity from the shock was found to terminate well in advance of the measured position of the xenon‐driver interface. This is indicative of severe radiation cooling. The visible luminosity was also found to be profoundly altered by the addition of impurities either in the xenon itself or in the driver. The spectrum of the delayed luminosity in the region from 3000 to 10 000 A was studied with an electronic‐recording time‐resolving spectrometer and found to consist of xenon atom lines superimposed on a strong continuum. The continuum may reasonably be attributed to dissociative transitions from bound excited states of the Xe2molecule related to the xenon atom levels 7 pKJand above to unbound Xe2states related to the atomic levels 6s11and 6s12. Positive electrical signals, observed during the passage of the shock through external metal rings, are attributed to ejection of electrons from the shock tube walls by photoelectric action and/or metastable atoms. In addition, two different types of electrical precursors were observed. The first was observed under the usual conditions, namely that the shock was sufficiently strong to cause the delayed luminosity. The second was observed in some experiments in which the shock was too weak to cause the delayed luminosity. Both could be due to a photoelectric effect on the shock tube walls, but the precursor observed in the absence of the delayed luminosity may be also due to diffusion of electrons ahead of the shock front. The present experiments strongly indicate that shock tube experiments of others may need reinterpretation.

ISSN:0031-9171    

DOI:10.1063/1.1706149

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A new variational theorem is formulated which has as its Euler equations and natural boundary conditions all of the differential equations and boundary conditions of the boundary value problem under consideration. Other variational theorems, including the classical theorems of Helmholtz, follow from this fundamental theorem. Conditions under which the theorems obtained are minimum or maximum principles are discussed and application to non‐Newtonian flow in a tube is made.

ISSN:0031-9171    

DOI:10.1063/1.1706150

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Approximate solutions of the equations of motions governing laminar incompressible fluid flow through a cylindrical channel with a porous wall are derived. The invalidity of an approximation in the solution of these equations under certain circumstances is pointed out, and the results of a numerical integration in the region where the approximation is invalid are indicated. A brief description is given of an experiment to verify the calculations, and some interesting results are noted.

ISSN:0031-9171    

DOI:10.1063/1.1706151

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The behavior of a permanent gas bubble in a liquid with an oscillating pressure field is analyzed with a linearized theory. If the assumption is made that conditions within the bubble are uniform, the thermodynamic relations found are as expected; i.e., at low frequencies the bubble behaves isothermally and at high frequencies the behavior becomes adiabatic. However, a more detailed analysis, which allows the bubble interior to vary not only in time but also in space, leads to an average isothermal behavior for the bubble even in the high‐frequency limit.

ISSN:0031-9171    

DOI:10.1063/1.1706152

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Experimental evidence is presented for the ability of Sachs' complete energy scaling to account for the influence of ambient pressure and temperature at not too small distances from the charge.

ISSN:0031-9171    

DOI:10.1063/1.1706153

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The velocity of first sound has been measured in saturated liquid He3&sngbnd;He4mixtures ranging in composition from 20 to 90&percent; He3between 0.5° and 2.3°K. The velocities decrease with increasing He3concentration due to the large increase in compressibility. The temperatureTsat which a liquid mixture first begins to separate into two layers of different composition is identified by a break in the temperature derivative of the sound velocity. The values ofTsare compared with and found to agree well with all other recent direct measurements. Breaks also occur in the temperature derivatives of first sound velocity and signal amplitude at temperatures which are in good agreement with most recent determinations of lambda transition temperatures for concentrations up to 30&percent;. For higher concentrations, the values obtained are in good agreement with &lgr; points determined from second sound measurements but differ markedly from results based on the disappearance of boiling. Possible reasons for the differences are discussed. A smoothed table of &lgr; temperature as a function of concentration is given up to the intersection of the &lgr; line and the phase separation region at 68&percent; He3and 0.86°K. The vapor pressure of pure He4at its lambda point is 37.80 ± 0.01 mm Hg (at 0°C and standard gravity) based on the measured vapor pressure at the minimum sound signal and a calculated displacement of the sound minimum from the lambda point.

ISSN:0031-9171    

DOI:10.1063/1.1706154

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The rigid sphere limiting forms of the expressions for the first‐order density corrections to the transport coefficients previously derived by the authors from the modified Boltzmann equation of Green and Bogoliubov are re‐examined. It is shown that in this limit these expressions approach the classic results of Enskog.

ISSN:0031-9171    

DOI:10.1063/1.1706155

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The concentration of a gas in a chamber of Ney and Armistead type, as a function of time, has been calculated for two simple cases of concentration dependence of the diffusion coefficient viz., (i)D=D0(1 + &agr;c), and (ii)D=D0[1 + &agr;c/(1 +c)]. The correction due to the nonattainment of a quasi‐stationary state has also been calculated.

ISSN:0031-9171    

DOI:10.1063/1.1706156

出版商:AIP    

年代:1960

数据来源: AIP