Question

In: Chemistry

A small gas turbine uses C8H18(l) for fuel and it enters the combustion chamber at 25◦C...

A small gas turbine uses C8H18(l) for fuel and it enters the combustion
chamber at 25◦C whereas air coming from the high pressure stage is at 287◦C . The products of combustion leave the combustion chamber at 1167◦C . The fuel is injected at a rate of 0.95 kg/min where it is mixed and burned with 400 % excess air. An analysis of combustions reveals that all the hydrogen in the fuel burns to H2O but only 90% of the carbon burns to CO2, with remaining 10% forming CO. Determine:
(a) the phase of the water in the products
(b) the mass flow rate of the air
(c) the rate of heat transfer from the combustion chamber.

Solutions

Expert Solution

Solution

here

C8H18-------->CO2 +H2O+O2+N2 .......... in combustion chember

here we assume that combution gases are ideal

C8H18 +b(1+a)(O2+3.76N2) -------->xCO2 + yH2O + abO2 + zN2

(1+a) is percent theoretical air a is excess air

a =3

after putting these value we get

C ---->x =8

H----> 18=2y so y =9

O ----->22b =2xY2b b =12.5

N ----->3.76 (1+a) =188

BALANCE REACTION

C8H18 +50(O2+3.76N2) -------->8CO2 + 9H2O + 37.5O2 + 188N2

TO DETERMINE HEAT TRANSFER

Qin +Win Nr(h0f +h-h0)r =Qout +Wout Np(h0f +h-h0)p

heat transfer and work done assumed to be out of these system is zero

enthalpies of reactants will be determined

for reactants

Enthalpy of formation

for stable moleculs enthalpy is zero

h0f o2 =0

h0f N2=0

The enthalpy of formation for C8H18 (l)

,h0f = –249950 kJ/kmol


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