2001 NCEES sample exam #519& #526

For the #519, the given answer is B--75710LBM/HR, however, why the turbine efficiency of 87% was not used into the calculation, which will generate the result of 87020 LBM/HR?

For the #526, the given answer used the pump efficiency of 60% into the calculation. If only the water side enthalpy was caluclated, why the pump efficiency need to be included into the calculation?

Thanks.

#519, the solution did not use the efficiency. Much like you, I used the Wt method and added in the efficiency and the enthalpies to get the 87k solution. What I did not take into account, is that equation requires that you use the "ideal" enthalpy of the steam at the outlets and then account for actual turbine efficency.

Since you are given the actual steam enthalpy at the outlets, you don't need to do this, just perform an energy balance and you get the solution of the 75k.

#526 kicked my butt, someone else will have to answer that one.

mizzoueng,I read the 519 again and agree that efficiency should not be used into calculation. Thank you.