Performance of Critical Flow Venturis under Transient Conditions
John D. Wright
Critical flow venturis (CFVs) can be used to measure flow under transient pressure and flow conditions with uncertainties of 0.13 % or less (95 % confidence level). Blow-down tests transferred 630 g of nitrogen during a 100 s interval from an unregulated cylinder (initially at 10 MPa) through a heat exchanger and a CFV into a known collection volume. Fast pressure and temperature sensors were used to calculate the CFV flow. The integrated CFV mass flows, , averaged 0.04 % smaller than the mass V of the collected gas. The heat exchanger was essential to the excellent agreement; without it, the percentage difference between and V was 0.38 %. We conclude that even under transient conditions, a properly instrumented CFV can be used as a reference flowmeter to evaluate other flowmeter types or to test gaseous fuel dispensers in the field.