TIME-RESOLVED MASS-FLOW MEASUREMENTS FOR A FAST GAS DELIVERY SYSTEM

A technique is demonstrated whereby the delivered mass and flow rate v ersus time of a short rise-time ps delivery system may be accurately d etermined. The gas mass M that flows past a point in a gas delivery sy stem by an arbitrary time t=t(p) may be accurately measured if that po int is sealed off with a fast closing valve within a time interval sho rt compared to the mass flow time scale. If the injected mass is allow ed to equilibrate in a known volume after being cut off from its sourc e, a conventional static pressure measurement before and after injecti on, and application of the ideal ps law suffices.-Repeating for many d ifferent values of t(p), and assuming reproducibility, the injected ma ss time history M(t) characteristic of the system without the fast clo sing valve may be determined. The flow rate versus time dM(t)/dt may t hen 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 implod ing (theta pinching) the tube using a single turn tungsten magnetic-fi eld coil. Optical measurements of the tube's internal area versus time indicate that the tube is sealed in 7 mus. Results are correlated wit h piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the theta pinch process.