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//Variable declaration:
T1 = 2000 //Hot gas temperature ( F)
T2 = 550 //Cool gas temperature ( F)
T3 = 330 //Steam temperature ( F)
T4 = 140 //Water temperature ( F)
m = 30000 //Mass flow rate of steam (lb/h)
cp = 0.279 //Average heat capacity of gas (Btu/lb. F)
N = 800 //Number of boiler tubes
//Calculation:
DT = (T1-T3)/(T2-T3) //Temperature difference ratio
Tav = (T1+T2)/2 //Average gas temperature ( F)
//From steam tables (Appendix):
hs = 1187.7 //Steam enthalpy (Btu/lb)
hw = 107.89 //Water enthalpy (Btu/lb)
Q = m*(hs-hw) //Heat duty (Btu/h)
mh = Q/cp*(T1-T2) //Mass flow rate of gas (lb/h)
x = mh/N //Gas mass flow rate per tube (lb/h)
//From figure 18.5:
L = 15 //Length of boiler tubes (ft)
//Result:
printf("The length of boiler tubes is : %f ft .",L)
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