Rarefaction

About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.

Three dimensionality of pulsed second-sound waves in He II

Abstract: Three dimensionality of three-dimensional (3D) pulsed second-sound waves in He II emitted from a finite size heater is experimentally investigated and theoretically studied based on the two-fluid model in this study. The detailed propagation of the 3D pulsed second-sound wave is presented and reasonable agreement between the experimental and theoretical results is obtained. Heater size has a big influence on the profile of the 3D second-sound wave. The counterflow between the superfluid and normal fluid components becomes inverse in the rarefaction of the 3D second-sound wave. The amplitude of rarefaction decreases due to the interaction between second-sound wave and quantized vortices, which explains the experimental results about the second-sound wave near ${T}_{\ensuremath{\lambda}}$ [L. C. Krysac, Phys. Rev. Lett. 73, 2480 (1994)]. The accumulation of dense quantized vortices in the vicinity of heater surface leads to the formation of a thermal boundary layer, and further increase of heating duration results in the occurrence of boiling phenomena.

Influence of Langmuir adsorption and viscous fingering on transport of finite size samples in porous media

Abstract: We examine the transport in a homogeneous porous medium of a finite slice of a solute which adsorbs on the porous matrix following a Langmuir adsorption isotherm and can influence the dynamic viscosity of the solution. In the absence of any viscosity variation, the Langmuir adsorption induces the formation of a shock layer wave at the frontal interface and of a rarefaction wave at the rear interface of the sample. For a finite width sample, these waves interact after a given time that varies nonlinearly with the adsorption properties to give a triangle-like concentration profile in which the mixing efficiency of the solute is larger in comparison to the linear or no-adsorption cases. In the presence of a viscosity contrast such that a less viscous carrier fluid displaces the more viscous finite slice, viscous fingers are formed at the rear rarefaction interface. The fingers propagate through the finite sample to preempt the shock layer at the viscously stable front. In the reverse case i.e. when the shock layer front features viscous fingering, the fingers are unable to intrude through the rarefaction zone and the qualitative properties of the expanding rear wave are preserved. A non-monotonic dependence with respect to the Langmuir adsorption parameter $b$ is observed in the onset time of interaction between the nonlinear waves and viscous fingering. The coupled effect of viscous fingering at the rear interface and of Langmuir adsorption provides a powerful mechanism to enhance the mixing efficiency of the adsorbed solute.

Solution of Riemann problem for ideal polytropic dusty gas

Abstract: The Riemann problem for a quasilinear hyperbolic system of equations governing the one dimensional unsteady flow of an ideal polytropic gas with dust particles is solved analytically without any restriction on magnitude of the initial states. The elementary wave solutions of the Riemann problem, that is shock waves, rarefaction waves and contact discontinuities are derived explicitly and their properties are discussed, for a dusty gas. The existence and uniqueness of the solution for Riemann problem in dusty gas is discussed. Also the conditions leading to the existence of shock waves or simple waves for a 1-family and 3-family curves in the solution of the Riemann problem are discussed. It is observed that the presence of dust particles in an ideal polytropic gas leads to more complex expression as compared to the corresponding ideal case; however all the parallel results remain same. Also, the effect of variation of mass fraction of dust particles with fixed volume fraction (Z) and the ratio of specific heat of the solid particles and the specific heat of the gas at constant pressure on the variation of velocity and density across the shock wave, rarefaction wave and contact discontinuities are discussed.

Numerical Study of Shock Compression of Graphite and Its Conversion to Diamond in Conical Targets

Abstract: The shock compression of carbon placed into lead conical targets that are subjected to a blow from aluminum strikers moving at a velocity of 4 km/s is numerically studied. The statement of the problem includes the hydrodynamic equations for compressed media, semi-empirical wide-range equations of state, and a kinetic model of nonequilibrium graphite-to-diamond conversion that is calibrated with known experimental data. All stages of the process are analyzed, starting from the cumulative effect at the symmetry axis of the target to the release of the sample due to the rarefaction wave coming from the rear side of the striker with allowance for spalling.

Gaseous Detonations. VIII. Two‐Stage Detonations in Acetylene‐Oxygen Mixtures

Abstract: Detonation waves in acetylene‐oxygen mixtures containing slightly more than 70% acetylene were studied using a slit and a moving film camera combination. It was observed that an initially diffuse luminous region part way down the rarefaction wave gradually sharpens into a strongly luminous shock front which then overtakes the primary wave front. Thereafter, a single wave moves forward with a velocity intermediate between those of the two initial waves. The region behind the rear shock front shows strong luminous particle tracks, whereas the region between is free of them. These observations are interpreted as evidence that acetylene left over after the oxidation reaction decomposes into carbon and hydrogen only after an induction period which is a sensitive function of the temperature and concentration of acetylene. The hydrodynamic aspects of the observations are discussed and are found to be consistent with the above explanation.