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[FAQ]

Species volume fraction can be evaluated from its mass fraction value using the following expression via custom-field-functions:
volume-fraction of species “i” = (mass-fraction of species “i”)*(mixture-density)/(density of species “i”)
Note that the mixture-density is directly available under the field-function “Density…” Species “i” density is not directly available as a field variable and can be provided as a constant value/state function/ideal gas law using a custom-field-function. Sample journal command to create a custom-field-function to evaluate water-vapor (h2o) volume fraction are as below. Here, h2o_density is also a custom-field-function assigning it a constant value of 1.3 [kg/m3] and is used in the volume-fraction expression.
define custom-field-functions
define “h2o_density” “1.3” define custom-field-functions define “vol-frac-h2o” “h2o*density/h2o_density”