ME 300 Fall 2016 – Homework#7
Due Wednesday, October 19, 2016
Textbook Problem 13.6
Answers: Not attached
Textbook Problem 13.22 (NOT COLLECTED)
Answers: Not attached
SP-20
Gaseous ethane (C2H6) is burned in a combustor with dry air entering at 1 bar.
ratio is 17 kg air/kg fuel. Assume “complete” combustion.
The air-fuel
(a) Calculate the percent theoretical air (%) in the combustor.
(b) What is the equivalence ratio?
(c) Determine the molar composition of the product mixture.
(d) Find the dew point temperature (C) of the product mixture.
(e) How much water vapor (%) is condensed in the product mixture if the products are cooled to
20C?
Suppose moist air (instead of dry air) enters the combustor with an absolute humidity of 0.016 kg
water vapor/kg dry air.
(f) Find the dew point temperature (C) of the product mixture.
Answers: (d) 55C; (f) 57.2C
Textbook Problem 13.48 (NOT COLLECTED)
Answer: (b) -728,957 kJ/h, heat rejected
Textbook Problem 13.53 (NOT COLLECTED)
Answer: +439,750 kJ/kmol fuel, work output
SP-21
A mixture of 90% liquid octane (C8H18) and 10% liquid ethanol (C2H5OH) at 25C is burned
with air at the same temperature in an atmospheric pressure combustor operating at steady
conditions. Products of “complete” combustion exit the combustor at 25C.
(a) Write the balanced chemical reaction for “complete” combustion with 100% and 200%
theoretical air.
(b) Find the dew point temperature (C) of the product mixture with 100% and 200% theoretical
air.
(c) Determine the heat transfer (kJ/kg fuel) with 100% and 200% theoretical air.
Answer: (b) 52.7C, 40.2C
Textbook Problem 13.57 (NOT COLLECTED)
Answer: -1,429,059 kJ/kmol fuel, heat rejected; 1.1 atm
Textbook Problem 13.62
Answer: (a) 1,427820 kJ/kmol C2H6; 47,483 kJ/kg C2H6
SP-22
One kmol of gaseous octane (C8H18) is ignited with stoichiometric amount of dry air in a closed,
rigid vessel. The pressure of the reactants is 1 atm and the temperature is 25C; while the
temperature of the products is 727C. Assume “complete” combustion.
(a) Calculate the pressure (atm) of the products.
(b) Determine the heat transfer (kJ/kg fuel) during the reaction.
Answer: (a) 3.42 atm