A pistoncylinder assembly contains a twophase liquidvapor mi

A piston-cylinder assembly contains a two-phase liquid-vapor mixture of H_2O at 200 lbf/in.^2 with a quality of 80%. The mixture is heated and expands at constant pressure until a final temperature of 480 degree F is reached. Determine the work for the process, in Btu per lb of H_2O present.

Solution

Pressure of steam P = 200lbf/in²
Dryness fraction = x =0.8

Final temperature = 480⁰F

At this temperature,

Specific volume of steam = 0.817869 ft³/lb (using steam tables)
Specific volume of water = 0.0200073 ft³/lb

Hence,

Work done = P(v_g-v_f)x = 127.6578 BTU/lb