Pressure drop and thrust predictions for transonic micronozzle flows

Abstract

In this paper, the expansion of xenon, argon, krypton, and neon gases through a Laval nozzle is studied experimentally and numerically. The pressurized gases are accelerated through the nozzle into a vacuum chamber in an attempt to simulate the operating conditions of a cold-gas thruster for attitude control of a micro-satellite. The gases are evaluated at several mass flow rates ranging between 0.178 mg/s and 3.568 mg/s. The Re numbers are low (8–256) and the estimated values of Kn number lie between 0.33 and 0.02 (transition and slip-flow regime). Direct Simulation Monte Carlo (DSMC) and continuum-based simulations with a no-slip boundary condition are performed. The DSMC and the experimental results show good agreement in the range Kn > 0.1, while the Navier-Stokes results describe the experimental data more accurately for Kn < 0.05. Comparison between the experimental and Navier-Stokes results shows high deviations at the lower mass flow rates and higher Kn numbers. A relation describing the deviation of the pressure drop through the nozzle as a function of Kn is obtained. For gases with small collision cross sections, the experimental pressure results deviate more strongly from the no-slip assumption. From the analysis of the developed function, it is possible to correct the pressure results for the studied gases, both in the slip-flow and transition regimes, with four gas-independent accommodation coefficients. The thrust delivered by the cold-gas thruster and the specific impulse is determined based on the numerical results. Furthermore, an increase of the thickness of the viscous boundary layer through the diffuser of the micronozzle is observed. This results in a shock-less decrease of the Mach number and the flow velocity, which penalizes thrust efficiency. The negative effect of the viscous boundary layer on thrust efficiency can be lowered through higher values of Re and a reduction of the diffuser length.

Molecular tagging velocimetry by direct phosphorescence in gas microflows: Correction of Taylor dispersion

“…The last two decades have witnessed a rapid development of micro-electromechanical systems (MEMS) leading to the emergence of a number of new microfluidic applications involving gas microflows in various technical fields. Gas microflows are notably involved in micro heat exchangers [1] designed for chemical applications or for cooling electronic components, in fluidic micro-actuators developed for active flow control purposes [2], in micronozzles used for the micropropulsion of nano and picosats [3], in micro gas chromatographs [4], gas analyzers [5] or gas separators [6], in vacuum generators and in Knudsen micropumps [7] as well as in some microfluidic-based in vitro devices such as artificial lungs [8]. Similar flows are also observed in porous media with applications relative to the extraction of shale gas [9].…”

Gas density structure of supersonic flows impinged on by thin blades for laser–plasma accelerator targets

“…These simulations, like the interferogram images, principally capture the plasma, leaving neutral density and the rest of the plume out. Detailed flow simulations have been performed for conical gas targets [50][51][52] , however, neutral flow studies showing the dynamics of the gas plume as a function of blade positions have not, up until now, been published.…”

Velocity Measurements in Channel Gas Flows in the Slip Regime by means of Molecular Tagging Velocimetry

“…The development of new microfabrication techniques has made the design of novel MEMS possible, highly increasing the range of possible practical applications. There are many examples of MEMS that found a commercial application and that are present in many of our daily life utilities, such as microaccelerometers for smartphones, micronozzles [1] for space applications, microactuators [2] for aeronautical applications, micro heat exchangers [3], and Knudsen pumps [4], to name just a few.…”