NCEES 2008 Thermal Fluids 515

[kfrazie1]

Does anyone have errata for NCEES Thermal Fluids 2008 exam?

Question 515 gives a stoiciometric equation and asks for air fuel ratio with 12 percent excess air but there solution assumes that air consists of only N2 and O2. Shouldnt we be using the std that for every volume of O2 you need X volumes of air? I think it's 3.773 volumes of air but I don't have MERM in front of me.

 

[salsill]

I don't know if you still need an answer but here it goes.

I think it should be for every volume of O2 you need 3.773 volumes of N2.

From composition of air: O2 is 20.95 and N2 78.09. 78.09/20.95=3.727

If you look at the equation given: you have 13.5 O2 and 50.8 N2. 50.8/13.5=3.76 which is very close to the ratio obtained from composition of air.

 

[kfrazie1]

Thx. I also thought they were giving me the equation with excess air included because in MERM they generally give the stoic equations without the Nitrogen listed and add it in after excess air is included.