1. The problem statement, all variables and given/known data "Dry, saturated steam at 1500kPa is throttled (perhaps, expanded) to a final condition of 100kPa, dry and saturated. Calculate the change in internal energy." 2. Relevant equations Q= ΔU + W (Q, heat supplied. U, internal energy. W, work) Steam table interpolation. (I generally don't use the interpolation formula, just ratios) h= U + PV (not sure on this one as it is not a constant pressure process, h, enthalpy.) 3. The attempt at a solution Hard to get a handle on this one for me, so far I have collected that work is being removed by some means (turbine blade, stationary nozzle, piston..) seeing as it is not a constant enthalpy process. Taking the difference between the two conditions on the steam tables seems too easy and well...wrong. Made it as far as calculating the difference between the enthalpy at 100kPa D & S and what it would have been in a constant enthalpy process, to find the enthalpy rejected to the system. Also that the temperature difference between Tsat at 100kPa and what it should be superheated to is 40.33°C. This is a frustrating problem for me because it seems easy and I'm positive that I've learned it before. I'm just 3 years out of school and I think it's a simple problem. Any help would be greatly appreciated, thanks in advance.