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FrankLucas February 3, 2010 13:27

heat flux/phase change
1 Attachment(s)
hi friends,

i'm a student from spain, and i have this following problem:

i have water-bearing pipe (100m) which gets an external heat flux (50000W*m-2), so after some meters the water inside the pipe is going to vaporize

i dont know much neither about cfd nor about star-ccm+, so i tried
solving using the user-guide and came to this solution:

the models i use are
- three dim.
- stationary
- steady
- liquid
- segregated flow
- segregated fluid temp.
- constant density
- turbulent
- reynolds-averaged navier-stokes
- k-e-turbulence
- realizable k-e two-layer
- two-layer all y+ wall treatment
- boiling

the result i get is in the attachment

so my questions are:

- why is all the line linear?
- why the line does not change after boiling (373K)?
- or is there a general problem with my models?
- and if so, could anybody help me? :-)

thank you in advance
saludos, frank

seang February 4, 2010 03:12

you need to model/define two phases. otherwise, in a single phase, this is what you would expect to get. There is nothing to define phase change from water to vapor etc.

karthickeyan February 4, 2010 04:13

you should specify multiphase mixture option instead of liquid option in starCCM+

FrankLucas February 12, 2010 10:46

First of all, thank you for your ive been reading the user guide again and there really is a capital about boiling and multiphase, so the new models i chose (due to the user guide) are:

- three dimensional
- stationary
- multiphase mixture
- eulerian multiphase
- water (liquid,h2O,constant density)
- vapor (gas, h20, constant density)
- volume of fluid
- segregated flow
- multiphase equation of state
- implicit unsteady
- turbulent
- reynolds-averaged navier-stokes
- k-e turbulence
- realizable k-e two-layer
- two-layer all y+ wall treatment
- segregated multi-phase temperature
- gravity
- surface tension
- boiling

Gravity and surface tension i had to choose, because without them boiling was not far so good, but now i have temperatures up to 5000 K...
almost all of the properties are by default, only thing i changed is the volume fraction in the inlet to [1.0,0.0], to have only water in the inlet...

i know it is hard to understand without seeing it, but anybody has an idea for me?

by the way, there is a nod called "HTCxArea" within boiling under the models, it has by default a value of 5000000 W/m^3* seems to me pretty high, does anybody know what this means?

thanks in advance

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