1. The problem statement, all variables and given/known data Hi there, I am trying to complete a thermodynamics assignment. I am doing fine until I get to the following question. "Hx = Specific enthalpy at dryness fraction = hf + x . hfg" - I am not quite sure where Hf came from, I guess they want a value for Saturated liquid from the Enthalpy tables but which one? 2. Relevant equations I have two Hf's I have already calculated. Hf @ Ti 63 kJ/kg Hf @ Tb 419.2 kJ/kg These are just the values for saturated water at 15°C and 100°C. Other relevant equations: X = Dryness fraction = Mev / Mw = 0.013kg / 1.805kg = 0.007 Hfg at boiling temperature = 2256.4 Hev = Hx - Hf @ Ti Qev = Mw * Hx 3. The attempt at a solution I would just like to add that I have calculated all of the above, they were not given to me. When I put the numbers I assume is supposed to be there I get. Hx = Hf + x * Hfg = 419.2 - 0.007 * 2256.4 = 435 Hev = Hx - Hf @ Ti = 435 - 63 = 372 Qev = Mw * Hx = 1805grams * 435 = 785175J Energy delivered by kettle Qk = Pk * t = 2100watt * 310.4 = 651840J Efficiency of my kettle Nev = Qev / Qk = 785175 / 651840 = 1.20 or 120% lol That can't be 120% so I have gone wrong somewhere and I think it is to do with "Hx = Specific enthalpy at dryness fraction = hf + x . hfg" If anyone could shed some light that would be great. Many Thanks. Sorry for the long post.