BTEX Benzene DSMC FE analysis Fanno flow Knudsen layer Knudsen pump Micro-Electro-Mechanical Systems (MEMS) Nano-Electro-Mechanical Systems (NEMS) OpenFOAM PID detector Pitot tube UV absorption advanced measurement technologies aerodynamic effect analytical solution backward facing step bearing characteristics binary gas mixing capillary tubes compressibility computational fluid dynamics (CFD) control mixture composition direct simulation Monte Carlo (DSMC) electronic cooling ethylbenzene and xylene (BTEX) flow choking fluid damping fractal surface topography gas flows in micro scale