Question

Thermodynamics

1. (correct answer: 0.080595 )

Initially, an insulated rigid tank contains 20 kg of water at 29.5oC and 101 kPa. The tank also contains a 4.86 kg aluminum block at 93.2oC. Using constant specific heats evaluated at 300 K, determine the total entropy production (kJ/K) after an hour assuming thermal equilibrium is achieved. 2. Correct Answer: 8.0087 ± 0.1% Steam at 1 MPa, 593.2oC, expands in a turbine to 0.01 MPa. If the process is isentropic, find the specific entropy (kJ/kg-K) at the exit of the turbine. Note: Give your answer to four decimal places. 3. (answer: 0.4914)

Initially, an insulated rigid tank contains 2.16 kg of water at 240oC and 1 MPa. A heater in the wall of the tank maintains the wall temperature at 600oC. After a period of time, the pressure in the tank rises to 1.5 MPa. Determine the final volume (m3) of the water in the tank. Assume variable specific heats (use the property tables for water). Note: Give your answer to four decimal places.

Answer 1

20 times 4.187(T - 29.5) = 4.86 times 0.91 times (93.2 - T) (1) T - 295 - 0.0528(93.2 - T) T - 29.5 = 4.92 - 0.0528 T 1.0528T - 34.42 T = 32.69 degree Celsius Then Delta S_system = 20 times 4.187 times ln 305.69/302.5 + 4.86 times 0.91 times ln 305.69/366.2 = 0.878 + (-0.7987) = 0.079 kJ/k