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Flash Process / Problem with thermal phase change model

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Old   July 21, 2010, 07:57
Default Flash Process / Problem with thermal phase change model
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Hey guys,

Im simulating a flash process where hot saturated water (180C) is injected into a cyclone (which is filled with hot saturated steam with 120C) and partially evaporates as the pressure in the cyclone is about 2 bar. Unfortunately I have not been able to model the fast cooling down of the water so far by using the thermal phase change model (in the real process water has about 110C at the end). Even though pressure (at the outlet) drops constantly, water temperature remains well above the saturation temperature and evaporation rate is very low (say about 1%, whereas in the real process about 20% of the water evaporates).

Im using Euler/Euler-Model with Water as continuous phase and Steam Bubbles as dispersed phase and inhomogeneous model for multiphase and turbulence. The system has an inlet where the hot water is injected and an outlet where the vapour can escape. Ive tried with Steam and Water as continous phases (evaporation rate was even lower) as well as changing heat transfer coefficients but it didnt help. Perhaps it would be more appropriate to use cavitation for phase change but its very difficult to converge and results werent very promising so far.

Maybe someone already had a similar problem and could give me a hint? Thanks a lot!
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