[eliastorca]

Hi everyone,

I'm trying to simulate in Fluent a concentric tube countercurrent heat exchanger and I'm experiencing some troubles.
The heat exchanger is a 10 meters length vertical tube with 10mm as internal diameter and 20mm as external diameter. The fluid which flows through the interior tube is water liquid at 298K and atmospheric pressure with a mass flow rate of 1495 kg/m^2s and through the exterior tube is air at 473K and in reverse direction with a mass flow rate of 2360kg/m^2s.
First of all I define the model without taking into account the boiling phenomenon and everything performs in a good way. But when I introduce the boiling phenomenon (because water is going to boil at 373K so I activate the Eulerian boiling RPI model and I define water vapor as secondary phase) it is not possible to match each fluid with each zone (as known, water through the interior tube and air though the exterior tube) as for each cell zone the only possibility is to play with each of the phases (mixture, liquid or vapor).
I match each fluid to each cell zone by applying 3 phases at the Eulerian boiling model (air is the 3rd phase) and doing a patch after initializing the case but, however, the model stops due to divergence problems whenever the 2nd phase volume fraction starts to appear.
I don't know how to solve this problem so I want to ask you if any of you have tried previously this type of problem and how have you make it. I also want to ask you if Fluent is the correct software to solve this problem or I have to try with CFX or any other one.

Thanks in advance for your help