Three identical steady devices, A, B, and C, operate between three thermal reservoirs, 1,2 , and 3 , as shown in Figure P21.17. Each device takes thermal energy from the warmer of its two reservoirs, and each upgrades to mechanical energy as much of that thermal energy as possible without lowering the entropy of the threedevice, three-reservoir system.

(a) Which reservoir has the highest-quality energy?

(b) Is enough information provided to determine which device can upgrade the highest percentage of its input thermal energy to mechanical energy? If so, which is the most efficient of the three devices? If not, what information is lacking?

Data from Figure P21.17

3 T = 400 K T = 800 K 1 A B 2 T = 150 K