Evaporation
 

I am doing evaporation analysis from a fuel tank in star ccm+, as the fluid inside the tank is static and the evaporated particles attain some velocity, I am pretty much confused what regions (wall, pressure outlet etc ) should be given for a problem like this. And I have decided to choose VOF in this case, as I am a beginner please correct me if this approach is wrong. My ultimate objective is to get evaporation rate of the gas from fuel tank. Give me some suggestions