Molecular transition and slip flows in the pumping channels of drag pumps

Abstract

Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a helical-type drag pump (HTDP) and disk-type drag pump (DTDP). The flow occuring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier–Stokes equations with slip boundary conditions, and the second one is a stochastic particle approach through the use of the direct-simulation Monte Carlo method. From the present study of a HTDP, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number Kn⩽0.01 (i.e., the slip-flow regime). But the results from the second method only agree with the experimental data for Kn>0.01 (i.e., the molecular-transition regime). From the analysis for a DTDP, we found that an actual pumping passage is strictly limited to a narrow region because of the significant backstreaming of molecules from the outlet.

Numerical and experimental investigations of channel flows in a disk-type drag pump

“…The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. As in the previous study [6], two different numerical methods are used. The first one is the continuum approach, in which the N-S equations with SBC are solved.…”

“…Heo and Hwang [6] numerically studied the molecular transition and slip flows by using both the direct simulation Monte Carlo (DSMC) method and the N-S equations with slip boundary conditions (SBC). For a helicaltype drag pump, they found that the numerical results obtained by both methods agree well with the experimental data for the Knudsen number Kn < 0.01.…”

“…The present paper is a extended report of the previous study. [6] In this study, the pumping performance of a DTDP is numerically and experimentally analyzed. First, the velocity and density fields are predicted by using the DSMC method.…”

Boundary-driven nonequilibrium gas flow in a grooved channel via kinetic theory

“…5,6 In vacuum systems, modeling of pumps operating at very low densities requires the solution of rarefied flows through grooved channels, where the grooved plate corresponds to the spiral grooved stator and the flat plate to the rotor. [7][8][9] Finally, in aeronautics, surface microgrooves have been used in several high-speed applications including near-wall exergy and flow control with applications to aircraft intake deicing. 10 In all previously mentioned work, the flow is simulated by implementing the Navier-Stokes equations subject to slip boundary conditions 2 or by the direct simulation Monte Carlo ͑DSMC͒ method.…”