Topic
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 paper, a novel numerical analysis method combining the direct simulation Monte Carlo (DSMC) method with the smoothed particle hydrodynamics (SPH) method is presented for simulating the multiscale flow, which is often encountered in the application of the Knudsen pumps.
Abstract: The prediction of the multiscale flow in the Knudsen pump is important for understanding its pumping mechanism. However, there is little research on such interesting multiscale phenomenon in the Knudsen pumps. In this paper, a novel numerical analysis method combining the direct simulation Monte Carlo (DSMC) method with the smoothed particle hydrodynamics (SPH) method is presented for simulating the multiscale flow, which is often encountered in the application of the Knudsen pumps. Validity and accuracy of the new method are given by comparing its results with that of the previous research. Using the coupled multiscale approach, the rarefaction and the temperature drive are studied, which are two main factors on the performance of the Knudsen pumps. To investigate the effect of rarefaction on the performance of the Knudsen pump, various pump operation pressures are compared. The flow characteristics and pumping ability at different rarefaction are analyzed, and the phenomenon of the multiscale flow is also discussed. Several cases with different linear or nonlinear temperature gradients are set to investigate the effect of temperature gradient on the performance of the Knudsen pump. The flow characteristics of the Knudsen pump such as the velocity, pressure increase, and the mass flowrate are presented. A unique phenomenon, the reverse transpiration effect caused by the nonlinear temperature gradient is studied, and the reason of the significant pressure increase in the pump channel is also analyzed. Since the multiscale gas flow is widely encountered in the microflow systems, the above method and its results can also be greatly beneficial and provide significant insights for the design of the MEMS devices.
7 citations
TL;DR: In this paper, the authors applied the direct simulation Monte Carlo method to investigate the outflow of rarefied gas into vacuum over a forward and backward-facing step, and the non-equilibrium effects at the ends of the step channel were taken into account by considering the geometry of sufficiently large regions directly adjacent to the inlet and outlet of the channel.
7 citations
TL;DR: Five psychophysical functions for visual density are obtained with the use of the magnitude-estimation method and it is found that apparent rarefaction is barely detectable for sides longer than 10–15 cm (6–9 deg).
Abstract: Five psychophysical functions for visual density are obtained with the use of the magnitude-estimation method. Because of apparent rarefaction, a different psychophysical function ensues for each size of square used. It is found that apparent rarefaction is barely detectable for sides longer than 10–15 cm (6–9 deg). It is also found that apparent rarefaction occurs to the greatest extent when short interlinear spacings are used.
7 citations
TL;DR: In this paper, the authors examined the effects of rarefaction, dissipation, curvature, and accommodation coefficients on flow and heat transfer characteristics in rotating microdevices and found that curvature has significant effects on temperature distribution, heat transfer, and Nusselt number.
Abstract: This paper examines the effects of rarefaction, dissipation, curvature, and accommodation coefficients on flow and heat transfer characteristics in rotating microdevices. The problem is modeled as a cylindrical Couette flow with a rotating shaft and stationary housing. The housing is maintained at uniform temperature while the rotating shaft is insulated. Thus, heat transfer is due to viscous dissipation only. An analytic solution is obtained for the temperature distribution in the gas filled concentric clearance between the rotating shaft and its stationary housing. The solution is valid in the slip flow and temperature jump domain defined by the Knudsen number range of 0.001 < Kn < 0.1. The important effect of the momentum accommodation coefficient on velocity reversal and its impact on heat transfer is determined. The Nusselt number was found to depend on four parameters: the momentum accommodation coefficient of the stationary surface σ uo , Knudsen number Kn, ratio of housing to shaft radius r o /r i , and the dimensionless group [γ/(γ+1)](2σ to -1)/(σ to Pr). Results indicate that curvature, Knudsen number, and the accommodation coefficients have significant effects on temperature distribution, heat transfer, and Nusselt number.
7 citations
TL;DR: In this paper, a stationary rarefaction shock in the near wake of an electrically grounded obstacle placed in a steady state, supersonic plasma flow is found when two electron temperatures, differing by at least an order of magnitude, are present.
Abstract: Laboratory experiments and fluid theory find a stationary rarefaction shock in the near wake of an electrically grounded obstacle placed in a steady state, supersonic plasma flow The shock is only found when two electron temperatures, differing by at least an order of magnitude, are present These shocks are analogous to rarefaction shocks in plasma free expansions
7 citations