An old abandoned saltmine, 3.5 x 106 ft3 in volume, contains air at 520 R, 14.7 lbf/in.2. The mine is used for energy storage so the local power plant pumps it up to 310 lbf/in.2 using outside air at 520 R, 14.7 lbf/in.2. Assume the pump is ideal and the process is adiabatic. Find the final mass and temperature of the air and the required pump work. Overnight, the air in the mine cools down to 720 R. Find the final pressure and heat transfer.
