hi all, i am using VOF model for centrifugal contactor to simulate inner rotor zone. have a query regarding the backflow volume fraction ,since in VOF model it will ask only the volume fraction for secondary phase but not for primary phase . so i want to know if i specify backflow volume fraction for water as zero at the top what value does it take for air the primary phase. i would like to clarify that in pressure outlet condition i need to specify the volume fraction of the secondary phase which is water in my case and air is the primary phase. So ideally speaking, at the top of the cylinder water should be thrown out, hence i specified zero backflow volume fraction of the water over there,but as i have seen it doesnt ask to specify the backflow volume fraction for air, so my query is what volume fraction value will it take for air at that boundary because i dont want even air to be flowing in or out at that boundary only water should be thrown out there.

plz help me regarding this issue

Regards garima

Hi Garima,

(1) You might want to specify "water" as the primary-phase and "air" as the secondary phase.

(2) In the case of the pressure outlet condition, if you specify the back-flow fraction for one of the phases to be ZERO, the other is automatically taken as ONE.

Hope this helps.

Vimal

hi

thanx for ur guidance

ok if the backflow volume fraction for the phase which is not being asked is taken as 1-(the volume fraction specified for other phase), then can u plz tell what boundary condition shud i take if i want the following situation to model:

my system consists of a rotating cylinder(i.e. rotor of the centrifugal contactor) in which i m employiong the use of VOF model to simulate fluid flow in it. the cylinder has an inlet at the bottom thru which water enters and it goes out thru the top annular ring. this annular ring at the top is defined as pressure outlet b.c. , also there is a small opening at the centre of the top which lets the water rotating in cylinder exposed to atmosphere. so there are 2 fluids air and water. now at the top where i hav specified pressure outlet b.c. i need only water to leave out and no backflow of it and also no air shud come in or going out thru that opening then how shud i employ that .

plz guide thanks

garima