Time resolved mass flow measurements for a fast gas delivery system

Abstract

A technique is demonstrated whereby the delivered mass and flow rate versus time of a short rise-time gas delivery system may be accurately determined. The gas mass M that flows past a point in a gas delivery system by an arbitrary time t=tp may be accurately measured if that point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values of tp, and assuming reproducibility, the injected mass time history M(t) characteristic of the system without the fast closing valve may be determined. The flow rate versus time dM(t)/dt may then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2-mm-i.d., 0.76-mm-thick copper tube is isolated by imploding (θ pinching) the tube using a single turn tungsten magnetic-field coil. Optical measurements of the tube’s internal area versus time indicate that the tube is sealed in 7 μs. Results are correlated with piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the θ pinch process.