Steam at 20 bars is in the saturated vapor state (call this state 1) and contain
ID: 1848628 • Letter: S
Question
Steam at 20 bars is in the saturated vapor state (call this state 1) and contained in a pistoncylinder device with a volume of 0.03 m 3 . Assume the steam is cooled at constant volume (i.e. the piston is held fixed in place) until the temperature reaches 200 C (call this state 2). Then the steam is expanded isothermally until its volume is twice the initial value (state 3). (a) Determine the pressures at state 2 and 3. ans. 15.5 bar, ~10 bar (b) Determine the change in specific internal energy, u, for each of the two processes. ans. - 389 kJ/kg, ~21.6 kJ/kg.Explanation / Answer
PV = nr T considering 1 mole of gas so , 20/T1 = p2 / T2 473 * 20 = T1*P2 T1 = 610k so p2 = 15.5 bar... p1 v1 =p3 v3 20 *0.03 = 2 *0.03 p3 p3 = 10 bar...