摘要:

During the growth of a spherical vapor bubble in a superheated liquid the inertial and surface tension effects rapidly become negligible, so that most of the growth occurs in an asymptotic stage characterized by an essentially constant bubble pressure. The asymptotic bubble behavior in initially nonuniform temperature fields is studied. An explicit formula for the bubble radius relation for a general spherically symmetric initial condition is derived. Application is made to the problem of nucleate boiling on a heated surface, where two dimensionless parameters are found to be important. Bubble radius vs time curves are determined and presented graphically for typical values of these parameters. Plots of maximum bubble radius, the time at which the maximum occurs and the average growth velocity are given for the case of subcooled boiling.

ISSN:0031-9171    

DOI:10.1063/1.1711048

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Some numerical solutions are presented which describe the flow in the vicinity of a collapsing spherical bubble in water. The bubble is assumed to contain a small amount of gas and the solutions are taken beyond the point where the bubble reaches its minimum radius up to the stage where a pressure wave forms which propagates outwards into the liquid. The motion during collapse, up to the point where the minimum radius is attained, is determined by solving the equations of motion both in the Lagrangian and in the characteristic form. These are found to be in good agreement with each other and also with the approximate theory of Gilmore which is shown to be accurate over a wide range of Mach number. The liquid flow during the rebound, which occurs after the minimum radius has been attained, is determined from a solution of the Lagrangian equations. It is shown that an acoustic approximation is valid even for fairly high pressures, and this fact is used to determine the peak intensity of the pressure wave as it moves outwards at a distance from the center of collapse. It is estimated in the case of typical cavitation bubbles that such intensities are sufficient to cause cavitation damage.

ISSN:0031-9171    

DOI:10.1063/1.1711058

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The thermodynamics of He3and He4solutions is considered for temperatures and concentrations for which the solution does not show superfluidity. Calculations of the excess chemical potentials from the experimental vapor pressure data have been carried out between 1°K and 2°K by Roberts and Swartz. It is found that while the behavior of the He3component can be reasonably explained down to 1°K within the framework of the classical solution theories, no such agreement is obtainable for the He4component. The discrepancy is explained by extending some general thermodynamical considerations of Gorter regarding pure He4to the solution. Further it is found that with a suitable choice of the Gibbs free energy expression of pure He4a satisfactory quantitative agreement is also obtainable along these lines.

ISSN:0031-9171    

DOI:10.1063/1.1711047

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Two methods for solving two‐dimensional free‐surface flows in porous media are presented. Both are based on the fact that the free surface can be transformed into a straight line. The first method utilizes the principle of images, whereas in the second method the Schwarz‐Christoffel transformation is used. The solution for free‐surface flow into a sink is given to illustrate the first method. The solution of the problem of water wedging is given to illustrate the second method.

ISSN:0031-9171    

DOI:10.1063/1.1711049

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A linearized, unsteady, inviscid, compressible, relaxing gas flow over slender bodies of general cross sections is considered. Its difference from the classical nonrelaxing case is found to occur entirely because the propagation of one‐dimensional impulsive disturbances differs in the two cases. The lateral forces and moments, to the linearized approximation, are shown not to be affected by nonequilibrium relaxation, but the drag expression contains nonequilibrium terms. Thus, only the decelerated (or accelerated) motion in the direction of flight had to be investigated. General solution is obtained analytically by transform method for arbitrary speeds (subsonic, transonic, or supersonic) and accelerations (or decelerations). A special example is calculated to illustrate the relative magnitude of relaxing drags.

ISSN:0031-9171    

DOI:10.1063/1.1711050

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The version of Bogoliubov's theory of irreversible phenomena in gases, in which the coupling constant is used as an expansion parameter, is generalized to all orders.

ISSN:0031-9171    

DOI:10.1063/1.1711051

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Formal expressions are obtained for the thermodynamic behavior and many‐body functions of a one‐dimensional system of particles with an arbitrary interaction potential. These expressions are particularly simple when the potential function satisfies a linear differential equation with constant coefficients over the domain (0, ∞). Explicit, exact results are obtained for a Coulomb interaction and compared with the Kirkwood approximation.

ISSN:0031-9171    

DOI:10.1063/1.1711052

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A model is given to provide a microscopic description of plasma sheaths, using the Vlasov equation for ions and electrons coupled with Maxwell's equations for the fields. The sheaths considered connect two different constant states of a plasma in a magnetic field. In the charge‐neutral approximation a solution is obtained in closed form in terms of quadratures. The solution depends essentially on three free parameters, related to the differences in density and electric potential between the two end states, and to the value of &bgr;, the ratio of the plasma pressure to the magnetic pressure, on one side of the sheath. The scaling law changes considerably from one solution to another. Solutions are obtained which scale according to some representative electron Larmor radius, or ion Larmor radius, or piece‐wise according to both. As a limiting case, when the density is allowed to go to zero on one side of the sheath, one obtains the boundary layer between a plasma and a containing vacuum magnetic field. As a peculiar feature in this limiting situation, the curve for the electric potential appears to be very sensitive to the slightest changes in the distribution functions, in the asymptotic region where the plasma density becomes vanishingly small.

ISSN:0031-9171    

DOI:10.1063/1.1711053

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The linearized equations of a gravity driven, resistive instability of a plasma supported by a planar, sheared magnetic field are shown to be characterized by a variational principle from which an eigenvalue corresponding to a periodic growth is obtained. The effect of a finite ion Larmor radius is included through off‐diagonal terms in the pressure tensor in the momentum fluid equation.When the Larmor radius is zero a numerical solution for the growth rate is found using a one parameter trial function which indicates that the correct function maximizes this rate. When the Larmor radius becomes significant, viz., with decreasing wavelength, the instability becomes an overstability with a reduced growth rate becoming proportional to the square root of the ratio of the resistivity to the wavelength. Whilst numerical results are given beyond this transition, the Larmor radius has become comparable with the thickness of an internal resistive layer and the equations cease to be reliable.

ISSN:0031-9171    

DOI:10.1063/1.1711054

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The generation of radio noise by plasma oscillations is studied, making use of the collisionless Boltzmann equation to describe the electron component of the plasma. A second‐order perturbation calculation is performed to determine the power spectrum for radiation at the second harmonic of the plasma frequency in a hot plasma in which there is no external magnetic field and the ions are of uniform density.

ISSN:0031-9171    

DOI:10.1063/1.1711055

出版商:AIP    

年代:1964

数据来源: AIP