I am considering the effects on volumetric and mass flow rate for two conditions: Condition 1) 1013mBar, 21C (Air density as per) Condition 2) 700mBar (10,000ft) 21C (Air density as per) Setup: A variable flow restrictor is connected to a constant source of oxygen at 50 psig. The variable flow restrictor is adjusted to give a volumetric flow rate of 10 L/min for condition 1. Question: The same setup is now in condition 2. What happens to the flowrate? Note 1: The variable restrictor is not adjusted when at condition 2. It remains as it was set for condition 1. Note 2: It appears that the flow is 'choked' as the difference between upstream pressure and downstream pressure stays within the limits required to be in the choked state (Ratio1.9±0.2) I'm unsure how the density ratio for the two conditions could affect the flow output?