A 0.2-m³ tank containing helium at 15 bar and 22^◦C will be used to supply 4.5 moles per minute of helium at atmospheric pressure using a controlled adiabatic throttling valve. 

a. If the tank is well insulated, what will be the pressure in the tank and the temperature of the gas stream leaving the throttling valve at any later time t? 

b. If the tank is isothermal, what will be the pressure in the tank as a function of time? You may assume helium to be an ideal gas with C^∗_P = 22 J/(mol K), and that there is no heat transfer between the tank and the gas.