NCEES 2001 - Questions 519 and 525

[Ramnares P.E.]

519. Shouldn't the calculation of the mass flow rate use the given efficiency? The equation would then look like:

P = [m(h1-h2) + 0.9m(h2-h3)] / eff which would result in 87000 lbm/hr instead of 75689.88 lbm/hr.

525. In the calculation of the fuel masses, where do the coefficients 2, 3, and 4 come from?

m(H2O) = 18[2(0.859) + 3(0.052) + 4(0.015)]

Thanks.

 

[Ramnares P.E.]

Question 525. The coefficients are the moles of water produced by each fuel reaction (duh), as seen in the Combustion section of the MERM.

Still not sure why 519 does not use the efficiency and I couldn't find the errata online.

 

[msuth22_PE]

try this for 519:

http://engineerboards.com/index.php?showtopic=20724

 

[Ramnares P.E.]

Thanks, that helped a lot!

 

[SNAPE/SMOTT PE]

Ideal would be calculated using the h values from isentropic process, correct? And in that case efficiency would be taken into account in the calculation.