Agas with a specific heat of y and gas constant of r in a large tank of volume v is discharged through a convergent nozzle of exit area ae. at time = 0, the gas in the tank has an initial pressure pi and an initial temperature ti. assuming the flow through the nozzle is steady, one-dimensional and isentropic with critical conditions at the exit, find the time required to "blow down" the tank isentropically from the initial pressure pi to the final pressure pf.