Question

Water in a piston/cylinder is at 150 lbf/in.², 900 F. There are two stops, a lower one at which V_min = 35 ft³ and an upper one at V_max = 105 ft³. The piston is loaded with a mass and outside atmosphere such that it floats when the pressure is 75 lbf/in.². This setup is now cooled to 210 F by rejecting heat to the surroundings at 70 F. Find the total entropy generated in the process. 

Answer 1

C.V. Water. State 1:  v₁ = 5.3529 ft3/lbm, u₁ = 1330.² btu/lbm,

s₁ = 1.8381 Btu/lbm 

 m = V/v₁ = 105/5.353 = 19.615 lbm

State 2: 210 F and on line in P-v diagram.

Notice the following: v_g(P_float) = 5.818 ft³/lbm, v_bot = V_min/m = 1.7843