Measurements and simulation of orifice flow for micropropulsion testing

Numerical and experimental results for a rarefied gas expansion through a thin circular orifice are presented. The orifice flow was used as a calibration test for a torsional thrust stand designed to measure force levels from 10(-6) to 10(-3) N. Molecular nitrogen, argon, and helium at room temperature are used as test gases. The mass flux and thrust measurements are compared with the direct simulation Monte Carlo results for Knudsen numbers from 40 to 0.01 and plenum to facility background pressure ratios of 10(3)-10(7). Factors that affect the total propulsive force, such as jet backflow and facility background gas penetrating the jet, are analyzed. The measured and calculated mass flux and total propulsive force were found to agree well for Knudsen numbers less than 1.