Rarefaction

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

Existence and uniqueness of normal shock waves in gas-particle mixtures

Abstract: A mixture of a gas and small solid particles is considered which, far upstream, is in a constant equilibrium state, and moves with a constant velocity. The existence of shock waves is investigated in the four possible cases, namely for frozen flow, for two kinds of partly frozen flow, and for equilibrium flow. It is shown that, in all these cases, compressive shocks may exist, if the upstream velocity exceeds the velocity of sound appropriate to the type of flow. Rarefaction shocks are impossible in each case. Moreover, it is shown that the downstream values of the flow parameters are determined uniquely, and the direction of their change is given. Only rather general assumptions concerning the behaviour of the gas are needed. The paper takes into account the influence of the finite particle volume fraction unlike most previous papers on the topic.

Relativistic hydrodynamics and non-equilibrium steady states

Abstract: We review recent interest in the relativistic Riemann problem as a method for generating a non-equilibrium steady state. In the version of the problem under consideration, the initial conditions consist of a planar interface between two halves of a system held at different temperatures in a hydrodynamic regime. The new double shock solutions are in contrast with older solutions that involve one shock and one rarefaction wave. We use numerical simulations to show that the older solutions are preferred. Briefly we discuss the effects of a conserved charge. Finally, we discuss deforming the relativistic equations with a nonlinear term and how that deformation affects the temperature and velocity in the region connecting the asymptotic fluids.

Single-phase gas flow in microchannels

Abstract: The role of rarefaction and its consequences on the behavior of gas flows in microchannels are discussed in this chapter. Heat transfer in microchannels and thermally driven gas microflows are particularly interesting for vacuum generation, using microsystems without moving parts. The main micro-effect that results from shrinking down the devices' size is rarefaction. In microchannels, the main effects are those of rarefaction, essentially quantified by the Knudsen number. Rarefaction affects steady microflows and modifies the behavior of unsteady microflows. The case of pulsed flows is of particular interest because such flows are encountered in many applications. Theoretical knowledge for gas flows is currently more advanced than that for liquid flows in microchannels. The regime of gas flow in a macrochannel refers to viscosity and compressibility effects quantified by the Reynolds number and the Mach number and depends on the rarefaction regime. Generating vacuum by means of microsystems concerns various applications such as the taking of biological or chemical samples, or the control of the vacuum level in the neighborhood of some specific microsystems during working. However, there is still a need for accurate experimental data, both for steady or unsteady gas microflows, with or without heat transfer.

Coherent Cavitation in the Liquid of Light

Abstract: We study the cubic- (focusing-)quintic (defocusing) nonlinear Schr\"odinger equation in two transverse dimensions. We discuss a family of stationary traveling waves, including rarefaction pulses and vortex-antivortex pairs, in a background of critical amplitude. We show that these rarefaction pulses can be generated inside a flattop soliton when a smaller bright soliton collides with it. The fate of the evolution strongly depends on the relative phase of the solitons. Among several possibilities, we find that the dark pulse can reemerge as a bright soliton.

Auditory discrimination between compressions and rarefactions by goldfish.

Abstract: 1. Goldfish were taught to discriminate between a given click and the same click inverted, that is, with the compression and rarefaction phases reversed. 2. The responses were true auditory responses involving the sacculus but not the lateral line. 3. The responses were independent of both waveform (frequency) and intensity and could be elicited with single clicks. Phase was the relevant parameter. 4. Tail flips were found to send a rarefaction wave (rarefaction is the first deflexion) forward from the fish and a compression wave backward. 5. It is proposed that phase analysis of tail-flip sounds is used to tell whether a swimming fish is approaching or receding.