1. The problem statement, all variables and given/known data In a sample of wet steam at 11 bar, 75% of the total internal energy is contained in the vapour portion. Calculate the dryness fraction of the steam to 3 decimal places. 2. Relevant equations u(kJ/kg) = (1-x)uf + x*ug x - dryness fraction f - saturated liquid state g - saturated vapour state 3. The attempt at a solution I have done the following to no avail: At 11 bar using steam tables uf = 780 kJ/kg and ug = 2568 kj/kg Assuming u = 75% of ug. u = (1-x)uf + x*ug 0.75*ug = (1-x)uf + x*ug 0.75*2568 = (1-x)*(780) + x*(2568) x = 0.642 Therefore, dryness fraction is equal to 0.642. However this is incorrect and I'm unsure what I'm doing wrong. Possibly interpreting the 75% of total internal energy wrong. Could it be that I need to use u = 0.25*uf + 0.75*ug? Thanks for your help, it's appreciated.