Thermodynamics

where C is a constant whose value depends on the compositionof the product gases and their specific heats.Also, show that the effective flame temperature T e of thisfurnace isT e T af T 0ln 1T af >T 0 2That is, the work output of the reversible engine would be thesame if the furnace above is considered to be an isothermalfurnace at a constant temperature T e .15–108 Using EES (or other) software, determine theeffect of the amount of air on the adiabaticflame temperature of liquid octane (C 8 H 18 ). Assume both theair and the octane are initially at 25°C. Determine the adiabaticflame temperature for 75, 90, 100, 120, 150, 200, 300,500, and 800 percent theoretical air. Assume the hydrogen inthe fuel always burns H 2 O and the carbon CO 2 , except whenthere is a deficiency of air. In the latter case, assume that partof the carbon forms CO. Plot the adiabatic flame temperatureagainst the percent theoretical air, and discuss the results.15–109 Using EES (or other) software, write a generalprogram to determine the heat transferduring the complete combustion of a hydrocarbon fuel(C n H m ) at 25°C in a steady-flow combustion chamber whenthe percent of excess air and the temperatures of air and theproducts are specified. As a sample case, determine the heattransfer per unit mass of fuel as liquid propane (C 3 H 8 ) isburned steadily with 50 percent excess air at 25°C and the combustionproducts leave the combustion chamber at 1800 K.15–110 Using EES (or other) software, write a generalprogram to determine the adiabatic flametemperature during the complete combustion of a hydrocarbonfuel (C n H m ) at 25°C in a steady-flow combustion chamberwhen the percent of excess air and its temperature arespecified. As a sample case, determine the adiabatic flametemperature of liquid propane (C 3 H 8 ) as it is burned steadilywith 50 percent excess air at 25°C.15–111 Using EES (or other) software, determine theadiabatic flame temperature of the fuelsCH 4 (g), C 2 H 2 (g), CH 3 OH(g), C 3 H 8 (g), C 8 H 18 (). Assumeboth the fuel and the air enter the steady-flow combustionchamber at 25°C.15–112 Using EES (or other) software, determine theminimum percent of excess air that needs tobe used for the fuels CH 4 (g), C 2 H 2 (g), CH 3 OH(g), C 3 H 8 (g),C 8 H 18 () if the adiabatic flame temperature is not to exceed1500 K. Assume both the fuel and the air enter the steadyflowcombustion chamber at 25°C.15–113 Using EES (or other) software, repeat Prob.15–112 for adiabatic flame temperatures of(a) 1200 K, (b) 1750 K, and (c) 2000 K.Chapter 15 | 79115–114 Using EES (or other) software, determine theadiabatic flame temperature of CH 4 (g) whenboth the fuel and the air enter the combustion chamber at25°C for the cases of 0, 20, 40, 60, 80, 100, 200, 500, and1000 percent excess air.15–115 Using EES (or other) software, determine therate of heat transfer for the fuels CH 4 (g),C 2 H 2 (g), CH 3 OH(g), C 3 H 8 (g), and C 8 H 18 () when they areburned completely in a steady-flow combustion chamberwith the theoretical amount of air. Assume the reactants enterthe combustion chamber at 298 K and the products leave at1200 K.15–116 Using EES (or other) software, repeat Prob.15–115 for (a) 50, (b) 100, and (c) 200 percentexcess air.15–117 Using EES (or other) software, determine thefuel among CH 4 (g), C 2 H 2 (g), C 2 H 6 (g),C 3 H 8 (g), C 8 H 18 () that gives the highest temperature whenburned completely in an adiabatic constant-volume chamberwith the theoretical amount of air. Assume the reactants are atthe standard reference state.Fundamentals of Engineering (FE) Exam Problems15–118 A fuel is burned with 90 percent theoretical air.This is equivalent to(a) 10% excess air(b) 90% excess air(c) 10% deficiency of air (d) 90% deficiency of air(e) stoichiometric amount of air15–119 Propane (C 3 H 8 ) is burned with 150 percent theoreticalair. The air–fuel mass ratio for this combustion process is(a) 5.3 (b) 10.5 (c) 15.7(d) 23.4 (e) 39.315–120 One kmol of methane (CH 4 ) is burned with anunknown amount of air during a combustion process. If thecombustion is complete and there are 2 kmol of free O 2 in theproducts, the air–fuel mass ratio is(a) 34.3 (b) 17.2 (c) 19.0(d) 14.9 (e) 12.115–121 A fuel is burned steadily in a combustion chamber.The combustion temperature will be the highest except when(a) the fuel is preheated.(b) the fuel is burned with a deficiency of air.(c) the air is dry.(d) the combustion chamber is well insulated.(e) the combustion is complete.15–122 An equimolar mixture of carbon dioxide and watervapor at 1 atm and 60°C enter a dehumidifying section wherethe entire water vapor is condensed and removed from themixture, and the carbon dioxide leaves at 1 atm and 60°C.