Full exam for Energy Systems LM in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: Problem 1 Data Water mass flow, l/s 1 Adiabatic flame temperature, °C 1000 stack temperaure, °C 90 heat losses from boiler wall, % 0.5 air and fuel temperature, °C 10.00 cP air, KJ/kg-K 1.01 cP flue gases, kJ/kg-K 1.10 cP fuel, kJ/kg-K 2.30 Inlet water temperature, °C 40.00
Full exam for Energy Systems LM in the Mechanical Engineering degree programme at Politecnico di Milano. The document covers: Problem 1 Data Water mass flow, l/s 1 Adiabatic flame temperature, °C 1000 stack temperaure, °C 90 heat losses from boiler wall, % 0.5 air and fuel temperature, °C 10.00 cP air, KJ/kg-K 1.01 cP flue gases, kJ/kg-K 1.10 cP fuel, kJ/kg-K 2.30 Inlet water temperature, °C 40.00
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Problem 1 Data Water mass flow, l/s 1 Adiabatic flame temperature, °C 1000 stack temperaure, °C 90 heat losses from boiler wall, % 0.5 air and fuel temperature, °C 10.00 cP air, KJ/kg-K 1.01 cP flue gases, kJ/kg-K 1.10 cP fuel, kJ/kg-K 2.30 Inlet water temperature, °C 40.00 Outlet water temperature, °C 60.00 Fuel composition, natural gas molare MM, kg/kmol massica PCI, MJ/kg CH4 0.900 16 0.8099 50.01 C2H6 0.050 30 0.0844 47.48 CO2 0.030 44 0.0742 0.00 N2 0.020 28 0.0315 0.00 tot 1.000 17.78 1.0000 44.51 Air composition molare MM, kg/kmol N2 0.770 28 O2 0.206 32 Ar 0.009 39.944 H2O 0.015 18 tot 1.000 28.78 Results LHV of fuel 44.51 MJ/kg by passing to the mass-basis composition of fuel (Yi): LHV = sum (Yi*LHVi) where i-th dentoes the compounds of the fuel air/fuel mass ratio 39.90 from the energy balance to the adiabatic combustor used to calcuate the adiabatic flame temperture: alfa=(LHV*1000+cpfuel*(Tfuel-25)-Cpfluegases*(Tflame-25))/(-Cpair*(Tair-25)+Cpfluegases*(Tflame-25)) useful thermal power, kW 83.720 from the energy balance of the water to be heated: Qu=mwater*Cw*(Tout-Tin) fuel mass flow, kg/s 0.002056 from the energy balance of the heat exchanger: mfuel = Qu/((alfa+1)*CpFluegases*(Tflame-Tstack)-heatlosses/100*LHV*1000) air mass flow, kg/s 0.08204 as: mfuel*Alfa flue gas mass flow, jkg/s 0.08409 as mfuel*(alfa+1) boiler efficiency, % 91.49 As Qu/(mfuel*LHV) O2/fuel molar ratio stoichiometric 1.975 as 2*X_CH4+3.5*X_C2H6 Air/fuel molar ratio stoich 9.587 as (O2/fuel_ratio)/X_O2_air soichic air/fuel mass ratio 15.52 as (alfa_stoich)*MMAir/Mmfuel excess of air, % 157.1 as (alfa-alfast)/(alfast) equivalence ratio 0.389 (1/(1+excessair)) flue gas composition reaction of complete combustion: 0.9CH4+0.05C2H6+0.03CO2+0.02N2 + (O2/fuel_stoich)*(1+excess)*(O2+0.77/0.206…
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