Learning Forum

[sinan ozbolgili]

Hi Dears,

I am trying to simulate boiling around horizontal tube to check bevaiour bubble and find heat flux and boiling heat trasfer coefficinet with different super heat temperature ( super heat = tube wall temp. - water satuation temp.) 

I selelcted Eulerian- RPI model with kepsilon model. 
Please see which corelation I put for forces, ehat-mass transfer. ( taken from a article already done by soneone for PhD thesis) 

Hovever, I am fixing time step as 10^-9 and mesh fisr layer = 10^-5 still havong floated error. 

 

 

 

 

 

 

Expectation :

 

[sinan ozbolgili]

the geometry as below picture

 

Aso I wuld lik to specify, the vapur volume fraction getting redce after some time. and it it not coverage 10^-4. alswayas remains around 1 and 10^-1

 

[Rob]

If you're setting the wall temperature like that you may be pushing the boiling too quickly: ie the near wall must boil instantly. 

Check the purpose of the wall boiling models too, and whether you have too much near wall refinement. 

[sinan ozbolgili]

Hi,

Actually vapur valume raction getting reduced after waiting a bit. So you suggest to reduce fist laye tkinckness or gowing rate ?

 

 

 

[Rob]

I'm not sure what I'm looking at but aim for an aspect ratio of nearer 1 for multiphase. You need to account for the vapour moving along the surface as well as resolving the flow normal to the wall. 

[sinan ozbolgili]

In this case, the fist layer should be much closeer to wall? Layer groving level should be less ? I mean  distance between 1stand 2nd should be considerd as much less? 

[Rob]

From the image I don't know what your near wall mesh is so can't comment. 

[sinan ozbolgili]

HI, pelase see pictures.

I am giving tempearure condtion surface of tube.  Second picture zoomed in 

 

[Rob]

You may want to read up on the boiling model, I suspect the near wall mesh is too fine. Aspect ratio is likely very high for multiphase too. 

[sinan ozbolgili]

Thanks, do I need to change first layer thinkes to increase and rescrease ratio ? 

[Rob]

If the mesh is too fine increasing the first cell height might be a good idea! Increasing the number of nodes around the pipe will also help with the aspect ratio. 

[sinan ozbolgili]

Let me try, thanks