II مسائل سري ششم ترموديناميک
در روز ...... قابل توضيح : حتويل مترينات فقط در کالس حل مترين و
.قبول مي باشند
1. Hydrogen (H2) at 7°C is burned with 20 percent excess air that is also at 7°C during an
adiabatic steady-flow combustion process. Assuming complete combustion, determine the
exit temperature of the product gases.
2. The furnace of a particular power plant can be considered to consist of two chambers: an
adiabatic combustion chamber where the fuel is burned completely and adiabatically and a
counter flow heat exchanger where heat is transferred to a reversible heat engine. The mass
flow rate of the working fluid of the heat engine is such that the working fluid is heated
from T0 (the temperature of the environment) to Taf (the adiabatic flame temperature) while
the combustion products are cooled from Taf to T0. Treating the combustion products as
ideal gases with constant specific heats and assuming no change in their composition in the
heat exchanger, show that the work output of this reversible heat engine is
T T
W CT 0 af 1 Ln af
T0 T0
where C is a constant whose value depends on the composition of the product gases and
their specific heats. Also, show that the effective flame temperature Te of this furnace is
T T
T e af 0
T af
Ln T
0
That is, the work output of the reversible engine would be the same if the furnace above
is considered to be an isothermal furnace at a constant temperature Te.
3. One alternative to using petroleum or natural gas as fuels is ethanol (C2H5OH), which is
commonly produced from grain by fermentation. Consider a combustion process in which
liquid ethanol is burned with 120% theoretical air in an SSSF process. The reactants enter
the combustion chamber at 25°C, and the products exit at 60°C, 100 kPa. Calculate the heat
transfer per kilo mole of ethanol, using the enthalpy of formation of ethanol gas plus the
generalized charts.
4. In a new high-efficiency furnace, natural gas, assumed to be 90% methane and 10% ethane
(by volume) and 110% theoretical air each enter at 25°C, 100 kPa, and the products
(assumed to be 100% gaseous) exit the furnace at 40°C, 100 kPa. What is the heat transfer
for this process? Compare this to an older furnace where the products exit at 250°C, 100
kPa.
5. Hydrogen gas is burned with 200% theoretical air in a steady flow burner where both
reactants are supplied at the reference pressure and temperature. What is the adiabatic flame
temperature?
6. Liquid n-butane at T0, is sprayed into a gas turbine with primary air flowing at 1.0 MPa, 400
K in a stoichiometric ratio. After complete combustion, the products are at the adiabatic
flame temperature, which is too high, so secondary air at 1.0 MPa, 400 K is added, with the
resulting mixture being at 1400 K. Show that Tad > 1400 K and find the ratio of secondary to
primary air flow.
7. An Otto engine, atmospheric air with 50% humidity and 300k sucked to piston. The fuel
mixed by 150% theoretical air. In the inlet manifold pass 10% of air flow pressure dropped,
the isentropic efficiency of the compression and expansion is 90%. The compression ratio is
8. If the pressure lost in exiting manifold is 5%, calculate the maximum temperature of
cycle, the exhaust temperature and check for liquid in the exhaust. (The fuel is CH4.)
8. A gas turbine engine, atmospheric air without humidity and at Standard conditions, sucked.
The fuel mixed by 150% theoretical air. In the inlet manifold pass 10% of air flow pressure
dropped, the isentropic efficiency of the compression and expansion is 90%. The
compression ratio is 8. If the pressure lost in exiting manifold is 5%, calculate the maximum
temperature of cycle, the exhaust temperature and check for liquid in the exhaust. (The fuel
is CH4.)