heat flux/phase change
 

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

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.

heatflux
 

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

First of all, thank you for your answers...so i´ve 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 available..so 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*K...it seems to me pretty high, does anybody know what this means?

thanks in advance