I am modeling a double pipe (concentric tube) in Ansys Fluent. The center tube contains nanofluid, and the region between the pipes is a vacuum zone. The outer tube is used for reducing convection effects. A DO radiation boundary condition is applied to the outer surface of the outer tube. I am having difficulty in modeling the vacuum region since I don't know how to specify "vacuum" in Fluent.
What is the best way to model this specific region? I just want the rays to pass through the vacuum region and reach the inner tube, the vacuum itself is not important for me.
Thank you in advance.
Hi Mohammad Reza Azaddel,
By not solving the heat and flow equations in the between-the-pipes domain, you are technically considering the vacuum. However, in practice, vacuum is a relative concept: it is usually difficult to have an "absolute" vacuum. The pressure gauge may show few pascals. In this case, you may want to solve the heat/flow equations in your domain. In case it is still in continuum level (you can calculate the Knudsen number to decide), you can model the "natural convection" occurring between the two tubes. If so, you can model it in Fluent using Boussinesq model or ideal gas.
Create a model, and while giving the pressure inside , it should be given less than atmospheric pressure. CFD gives option for both Velocity and pressure at different points.
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