A strange problem when doing multi-phase flow

Yun Kang

Dear All, I have got a problem when doing a multi-phase simulation in CFX and I wonder if you can provide some help.

I am trying to simulate a pipe condense flow. Vapour inside a pipe is condensed by the cold air flowing around the pipe. The vapour (and the condensed water) is not contacted with the air.

I drawed the pipe with thickness. So the entired computating area includes three domain: Vapour, Pipe and Air, among which Vapour and Air are fluid domains and Pipe is a solid domain.

I chose H2ORKvl (Redlich Kwong Wet Steam) and Air Ideal Gas as fluids and Alumni as solid. Interfaces exist between Vapour and Pipe, also between Pipe and Air.

In domain Air I set volume fraction of Air Ideal Gas to 1 and H2ORKvl to 0.In domain Vapour the other way around.

I set H2ORKv as equilibrium fraction and H2ORKl as equilibrium constraint. The value of equilibrium fraction is set to be 0.95.

Static temperature of H2ORKvl is set to 400 K.

Every looks fine. But a global error appears as: "The domain, 'pipe', requires one equilibrium constraint and one equilibrium fraction set for a homogeneous binary mixture."

Does anyone know the reason and advise me how to correct it?

Many thanks.