a piston–cylinder device contains 0.15 kg of air ini- tially at 2 mpa and 350°c. the air is first expanded isother- mally to 500 kpa, then compressed polytropically with a polytropic exponent of 1.2 to the initial pressure, and finally compressed at the constant pressure to the initial state. deter- mine the boundary work for each process and the net work of the cycle.