Species diffusivity

zhou1

I try to calculate a case. I defined a mixture which include three species (for example K, OH, H2O(last species in the species list)). Question: (1). I define each species diffusivity respectively using "dilute-appx". I know these mass diffusivities will be taken as D(i,m) where "m" is mixture, "i" is species in FLUENT. My question is whether the diffusivity of H2O does not matter if i define it as a arbitrary value because this diffusivity of H2O will not be used in FLUENT. By the way, if the diffusivty of H2O will be used in FLUENT, how is it used in FLUENT? (2). If i want to define the diffusivity of species K and OH by "DEFINE_DIFFUSIVITY" and also i want to set the diffusivity of H2O as zero, how should i do?