A tank with an internal volume of 1 m3 contains air at 800 kPa and 25°C. A valve on the tank is opened, allowing air to escape, and the pressure inside quickly drops to 150 kPa, at which point the valve is closed. Assume there is negligible heat transfer from the tank to the air left in the tank. Consider the same process but broken into two parts. That is, consider an intermediate state at P2 = 400 kPa, calculate the mass removed during the process from P1 = 800 kPa to P2 and then the mass removed during the process from P2 to P3 = 150 kPa.

R-134a is a refrigerant, which is used inside of refrigerators and air conditioners. You can buy canisters of this as a compressed liquid, which can be used to recharge a leaky air conditioner. The canister initially contains 0.539 kg of R-134a at room temperature (25 °C). For simplicity, let's assume that the R-134a is initially saturated liquid. You use this canister to recharge an air conditioner, until the canister has half of its original mass remaining. The canister is upright with the exit on the top of the canister, so the exit flow is saturated vapor. In order to maintain the temperature at 25 °C, how much heat must be supplied to the canister? Note that this is why compressed liquid/gas canisters feel cold when you use them – they require heat - input to maintain constant T.