GATE Papers >> Mechanical >> 2008 >> Question No 71

In the figure shown, the system is a pure substance kept in a piston-cylinder arrangement. The system is initially a two-phase mixture containing 1 kg of liquid and 0.03 kg of vapour at a pressure of 100 kPa. Initially, the piston rests on a set of stops, as shown in the figure. A pressure of 200kPa is required to exactly balance the weight of the piston and the outside atmospheric pressure. Heat transfer takes place into the system until its volume increases by 50%. Heat transfer to the system occurs in such a manner that the piston, when allowed to move, does so in a very slow (quasi – static / quasi – equilibrium) process. The thermal reservoir from which heat is transferred to the system has a temperature of 400^oC. Average temperature of the system boundary can be taken as 175^oC. The heat transfer to the system is 1 kJ, during which its entropy increase by 10 J/K.

Specific volume of liquid (v_f) and vapour (v_g)  phases, as well as values of saturation temperatures, are given in the below.

At the end of the process, which one of the following situations will be true?

• (A)  superheated vapour will be left in the system   
• (B)  no vapour will be left in the system   
• (C)  a liquid + vapour mixture will be left in the system   
• (D)  the mixture will exist at a dry saturate vapour state