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Rarefaction
About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.
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TL;DR: In this article, it was shown that the magnetic field near the neutral line is about one order of magnitude larger than the field of the sunspots which generates it, which is not real.
Abstract: Syrovatskii's mechanism of ‘dynamic dissipation of magnetic field’ is reinvestigated. In order to have this kind of ‘dynamic dissipation’ at a neutral line the ratio of current density to particle density must exceed a certain critical value. For conditions in the solar atmosphere near sunspots, this value can only be reached by a mechanism which produces a very large compression of the magnetic field as well as an extreme rarefaction of the density. Syrovatskii claims that his mechanism provides both these features. His enormous field compression, however, can only be obtained if one neglects the restoring Lorentz force (e.g. in Syrovatskii's model the compressed field near the neutral line is about one order of magnitude larger than the field of the sunspots which generates it). The second effect, i.e. the large plasma rarefaction around the neutral line, also is not real. This rarefaction is due to the particular flow field of Syrovatskii's model which allows for a free reconnection of the field lines across the neutral line; the magnetic field is treated like a vacuum field, the effects of the field accumulation near the neutral line being neglected. The aim of the present paper is to show how more realistic models modify Syrovatskii's results. Our numerical calculations lead to a maximum current to density ratio which is a factor of 106 smaller than the one obtained by Syrovatskii. Therefore one has to conclude that in the solar atmosphere one cannot produce in the way described by Syrovatskii the configurations which are necessary for ‘dynamic dissipation’.
11 citations
TL;DR: In this article, the interaction of a simple wave, in steady supersonic flow, with a two-dimensional mixing region is treated by applying Fourier analysis to the linearized equations of motion.
Abstract: The interaction of a simple wave, in steady supersonic flow, with a two-dimension mixing region is treated by applying Fourier analysis to the linearized equations of motion. From asymptotic forms for the Fourier transforms of physical quantities, for large wave-number, the dominant features of the resulting flow pattern are predicted; in particular it is found that a shock wave, incident on the mixing region, is reflected as a logarithmically infinite ridge of pressure. For two particular Mach-number distributions in the undisturbed flow, numerical solutions are obtained, showing greater detail than the results predicted by the asymptotic approach. A method is given whereby the linear theory may be improved to take into account some non-linear effects; and the reflected wave, for an incident shock wave, is then seen to consist of a shock wave, gradually diminishing in strength, followed by the main expansion wave.
11 citations
TL;DR: In this paper, the authors investigated the propagation of adiabatic evaporation waves arising while refrigerants R-11 rapidly transit to metastable state due to depressurization in the rarefaction wave.
Abstract: Propagation of adiabatic evaporation waves arising while refrigerants R-11 rapidly transit to metastable state due to depressurization in the rarefaction wave is experimentally investigated. New regularities of the interphase surface dynamics and the influence of interphase heat and mass transfer in propagation of adiabatic evaporation waves are obtained. It has been found that the phase transition in metastable liquid occurs in the conditions of developing multiscale turbulence in liquid and vapor phases under dynamic action of a vapor flow on the interphase surface and convective heat supply to the zone of high-intensity phase transition. The surface phase transition was visualized by a rapid video camera, its pulsating character is revealed and its properties are determined.
11 citations
TL;DR: In this paper, a one-dimensional approach for the compressible fluid flow was provided for the rarefied gas flow and the problem was solved in bounds for the constant total temperature and compared to experimental investigations by varying the pressure ratio and the circumferential speed of the clearance boundary.
Abstract: Clearance mass flows are a major loss mechanism in dry running rotatory positive displacement vacuum pumps. Therefore, a detailed knowledge of the clearance mass flow is crucial to calculate the operation of those pumps. The small clearance heights and the large pressure range of such pumps require a wide range of gas rarefaction parameters to be taken into account. The flow in the clearance can be described as a combined Couette–Poiseuille flow with variable cross section. This is typically done by solving the Stokes equation, but especially at high gas rarefaction parameters, the inertia cannot be neglected any more, which can lead to choking of the flow. A one-dimensional approach for the compressible fluid flow was provided by Shapiro. It is shown that this approach can be carried over for the rarefied gas flow. The problem is solved in bounds for the constant total temperature and compared to experimental investigations by varying the pressure ratio and the circumferential speed of the clearance boundary in a wide range of gas rarefaction parameters.
11 citations