1. The problem statement, all variables and given/known data A well-insulated closed tank is of volume 70 m^3. Initially, it contains 25000 kg of water distributed between liquid and vapor phases at 30 deg C. Saturated steam at 11 bar is admitted to the tank until pressure reaches 7 bar. What mass of steam is added? 2. Relevant equations m' = m2 - m1 (where m' is mass of steam, m2 is final mass in tank and m1 is initial mass in tank, m1 = 25000 kg) m2H2 - (m1H1 + m'H') = 0 m2/m1 = (U1 - H')/(U2 - H') = (H' -U1)/(H' - U2) 3. The attempt at a solution Q = 0 if well insulated Assume W = 0 Kinetic and potential energies can be ignored V(tank) = constant and is taken to be the control volume H' = 2779.7 kJ/kg (from steam tables) I know m1 and H'. I thought if volume of tank is constant than i can calculate P1 from P1V1=P2V2 but then that just gives me that the pressure is constant too. I need to figure out the enthalpies of the contents in the tank before and after the addition of the sat. steam and then I should be okay. Can anyone help? Thanks!