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Sunday, August 9, 2009

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Earlier post "Heat Radiation For Pain & Blistering Threshold" and "Personnel Exposure Time For Heat Radiation" have discussed the heat radiation level lead to plant personnel pain and blistering threshold within an exposure time. Heat radiation design criteria for personnel exposure has been proposed for continuous and emergency exposure. Flare radiation run using software i.e. FLARESIM or calculation using Brzustowski and Sommer method, heat radiation level will be estimated and presented. For equipment, instrument, piping, painting, steel structure, etc expose to flare radiation will experienced increase temperature.

How shall a heat radiation level relates to temperature ?

Heat level (Et) at recepting location can be related to the sum of radiation heat (Er) plus convection heat (Ec).

Et = Er + Ec

For unit area (m2),

qt = qr + qc

where
qt = total heat flux at receptor (kW/m2)
qr = radiation heat flux at receptor (kW/m2)
qc = convection heat flux at receptor (kW/m2)

Radiation heat flux,
qr = sigma x (T4 - Ta4)

Convection heat flux
qc = (h / e) x (T - Ta)

where
sigma = stefan-Boltzman constant = 5.67 e -11 (kW/m2K)
h = convective heat transfer co-efficient = 0.007 (kW/m2K) at zero wind speed
e = Emissivity (0.8-0.9 for copper or rusted CS pipe, 0.1-0.2 for polished SS pipe)
T = Surface temperature (K)
Ta = Ambient temperature (K)

Therefore
qt = sigma x (T4 - Ta4) + (h / e) x (T - Ta)

If a heat radiation level is known at particular location, the corresponding temperature may be estimated using above equation.

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posted by Webworm, 1:40 AM

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