7.3 Gas-Phase Chemistry Solver

The mass conservation equation representing gas-phase

reactions is given as

∂ γˆ ϕ

i∂

tchem

= γˆ

Rϕi(ϕ 1,ϕ 2, ...,ϕ

N) + γˆSϕi, (36)

where

RϕiandQϕirepresent chemistry reactions andsource terms, respectively, and

Nis the total number ofspecies in the chemical mechanism. Although various units

could be used in the solution of gas-phase chemistry

problems, the use of parts per million by volume is

convenient for numerical reasons since the magnitude of the

values for trace gases is small. Because the computational

grid is constant for the duration of a synchronization time

step, the Jacobian and species density in γˆ ϕ

iof Eq. (36)can be decoupled, and the density of a trace gas species

converted to volumetric (or molar) mixing ratio units. This

leads to the following conservation equation for gas-phase

chemistry in terms of the time-rate of change of the

volumetric mixing ratio for each species:

where

m i=q i(Mair/Mi) is used as the definition of thevolumetric or molar mixing ratio, and

Rˆm i=Rϕi/ ρ and

Qˆmi=

Qϕ

i/ ρ represent chemistry reactions and sourceterms in molar mixing ratio. In the remainder of this

section, the over bars will be dropped for simplicity.

By using the kinetics laws for elementary reactions and by

applying a mass balance to each species, the equation for the

rate of change of each species concentration can be derived

for a single cell:

In Eqs. (38a-d),

Pirepresents the production of speciesi,

Limirepresents the chemical loss of speciesi, υ

i,lis thestoichiometric coefficient for species

iin reactionl, andrlisthe rate of chemical reaction

l. The suml= 1...Ii, in Eq.(38c) is over all reactions in which species

iappears as aproduct, and in Eq. (38d)

l= 1...Jiis over all reactions inwhich species

iappears as a reactant.The rate of chemical reaction

lcan be expressed as theproduct of a rate constant

kland a term that is a function ofthe concentration of the reactions. For elementary reactions,

the concentration dependent term is the product of the

reactant concentrations. In terms of mixing ratios, the rate

of reaction

l(rl) takes one of the following forms:p37

n1051 - n1052 - n1053 - n1054 - n1055 - n1056 - n1057 - n1058 - n1059 - n1060 - n1061 - n1062 - n1063 - n1064 - n1065 - n1066 - n1067 - n1068 - n1069 - n1070 - n1071 - n1072 - n1073 - n1074 - n1075 - n1076 - n1077 - n1078 - n1079 - n1080 - n1081 - n1082 - n1083 - n1084 - n1085 - n1086 - n1087 - n1088 - n1089 - n1090 - n1091 - n1092 - n1093 - n1094 - n1095 - n1096 - n1097 - n1098 - n1099 - n1100

castellano: DISPER CUSTIC DESCAR RADIA italiano:

castellano: DIS CUS DES RAD english: DIS CUS DES RAD

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