Example 8.13: Firetube Flux


Fire Tube Heat Duty(Q, MMBtu/hr):
Pipe Outside Temperature (To, oF)
Fluid Temperature(Tf, oF)
Excess Air(%):
Flue Gas Rate(r,lb/MMBtu):
Pipe ID(ID, ft):
Flue Gas Specific Heat(Cp, Btu/(lb.oF)
Flue Gas Thermal Conductivity (k, Btu/[(hr. sq ft.oF)/ft])
Flue Gas Bulk Viscosity (μb, cp)
Flue Gas Viscosity at Pipe Wall (μw, cp)
Convective Heat Flux(Hfc, Btu/(hr.ft2)) Refer Example 8-6
Result
Flue Gas Mass Flow(Ma, lb/hr)
ΔT(oF)
Reynolds Number(Re)
Prandtl Number(Pr)
C per Fig 8-5
m per Fig 8-5
Result
Heat Transfer Coefficient (hi, Btu/(hr.ft2.oF))
Convective Heat Flux(Hfc, Btu/(hr.ft2))
Total Heat Flux(Hf, Btu/(hr.ft2))


Example 8-3; Heat transfer coefficient for forced convection

Step 1: Calculate Re, Pr, select C and M for Fig 8-5

Re =
1488*D*V*ρ / μ
=
0.5263 * M / D * μ
         Eq8-9a
Pr =
2.419*Cp*μ / k
         Eq 8-7

Fig 8-5 from GPSA Section 8



Step 2: Calculate ho

Nu = C * Rem * Pr0.33 * (μbw)0.14 =
hi * di / 12 * k
         Eq8-5b

Convective Heat Flux = Q / Ac = hi * ΔT

Total Heat Flux = Convective Heat Flux + Radiant Heat Flux




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