The radiator of a steam heating system has a volume of 20 l and is filled with superheated water vapor at 200 kpa and 150°c. at this moment both the inlet and the exit valves to the radiator are closed. after a while the temperature of the steam drops to 40°c as a result of heat transfer to the room air. determine the entropy change of the steam during this process.

Atank with constant volume contains 2.27 kg of a mixture of water phases (liquid-vapor). in the initial state the temperature and the quality are 127 °c and 0.6, respectively. the mixture is heated until the temperature of 160 oc is reached. illustrate the process in a t-v diagram. then, determine (1) the mass of the vapor in kg at the initial state, (2) the final pressure in kpa.