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Code Manual for CONTAIN 2.0 - Federation of American Scientists

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The term ~ in Equation (10-80) is the absorption coefficient at the reference wavelength. The user<br />

can specify this value directly through the ABSORB option in the RAD-HEAT input block (see ~<br />

Section 14.3.1.5). Note that in this option, the aerosol emissivity will be independent <strong>of</strong> the aerosol<br />

mass concentration in the problem. The second method models the aerosol cloud emissivity as<br />

derived by Pilat and Ensor [Pi170]<br />

%.=4000C ?.mm f<br />

(10-81)<br />

where Ch is “kmx”, a constant <strong>of</strong> proportionality specified through the KMX option <strong>of</strong> the<br />

RAD-HEAT input block, and f. is the total aerosol mass concentration (kg/m3) computed by the<br />

code. Ch in this equation is provided to allow the user to account <strong>for</strong> the effects <strong>of</strong> wavelength,<br />

index <strong>of</strong> refraction, pticle size distribution, and aerosol pficle material density. [Pi170] For Ck<br />

= 1, it corresponds to soot-like particles with a density <strong>of</strong> 2000 kg/m3. Cti is related to the<br />

coefficient P in Equation (10-78) according to C~ = ~/(4000 pP~), where pPis the aerosol material<br />

density. The aerosol absorptivity is calculated in a manner similar to the emissivity, except that the<br />

surface temperature is used in the expressions above instead <strong>of</strong> the gas temperature.<br />

10.3.3.2 Cess-Lian Radiative Property Model. The user may select the Cess-Lian model <strong>for</strong> the<br />

radiative properties. If the Cess-Lian radiative property model is chosen, CO and C02 are assumed<br />

to be transparent. Thus, this model should be used only when the effects <strong>of</strong> such gases are not<br />

significant. If this model is desired, the keyword CESS must be specified in the RAD-HEAT input<br />

block. Otherwise the default Modak model will be used.<br />

The Cess-Lian model is based on an analytic correlation developed by Cess and Lian and is used to<br />

calculate steam/air emissivity and absorptivity. [Ces76] In this model, data from Hottel emittance<br />

charts [Hot67] have been fit to an equivalent single-band exponential <strong>for</strong>m, which requires<br />

significantly less computation time than that <strong>for</strong> a wide-band exponential model. The gas mixture<br />

emissivitys~ and absorptivity am<strong>for</strong> the Cess-Lian model are defined in a similar manner to those<br />

<strong>for</strong> the Modak radiative property model, except <strong>for</strong> the fact that gas ernissivity &~and absorptivity<br />

a~ are calculated as follows.<br />

The value <strong>of</strong>&~is calculated <strong>for</strong> the steam/air mixture according to<br />

&g = aO[l -exp(-alfi)] (10-82)<br />

where % and al are coefficients determined from Table 10-3, with linear interpolation between the<br />

given temperatures.<br />

R O 10 44

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