18 Replies Latest reply on Nov 2, 2016 9:43 AM by Koen Menke

Flowsimulation how to split box in to 2 fluid subdomains?

Koen Menke Oct 25, 2016 7:59 AM

Dear readers,

I'am currently working on a tile witch contains air and water and needs to absorb and conduct heat.
I had made a lid in the box to divide the water and air from each other, but flowsimulation sees the lid as a barrier between them.
There is no heatconduction between them!

How can i properly setup the model so it does ?

Thanks in advance

Greetings
Koen
The Netherlands

Re: Flowsimulation how to split box in to 2 fluid subdomains?

Siavash Khajehhasani Oct 25, 2016 11:04 AM (in response to Koen Menke)

That sounds strange! Since one of the most common application of defining fluid subdomains is for heat exchanger, which I assume that's your case. Did you turn on the heat conduction in solids option once your were setting up the problem?
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- Re: Flowsimulation how to split box in to 2 fluid subdomains?
  
  Koen Menke Oct 25, 2016 11:49 AM (in response to Siavash Khajehhasani)
  
  Yes i did.
  
  To be presice i need the air and water to exchange heat. They are both in a box divided by that lid.
  I did change lid sizes and meshing but seems to give same results.
  
  When I look in the preview window, the air is orange/red ( indication of the temperature )
  The water is still the temperature given at start. In my opinion and according to my calculations that isn't possible.
  
  It's a time depending simulation over 18000seconds.
  
  I hope somone has an idea.
  
  Thanks in advance!
  
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  - Re: Flowsimulation how to split box in to 2 fluid subdomains?
    
    Siavash Khajehhasani Oct 25, 2016 1:25 PM (in response to Koen Menke)
    
    can you upload your model/simulation or a simplified version of it?
    
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    - Re: Flowsimulation how to split box in to 2 fluid subdomains?
      
      Koen Menke Oct 26, 2016 10:09 AM (in response to Siavash Khajehhasani)
      
      Sievash I can't becouse its secret information.
      Here is an section view, simulation has runned for 33 minutes ( physical time )
      As far as I can see the lid doesn't affect heat exchange, so i belive this problem is solved.
      
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Re: Flowsimulation how to split box in to 2 fluid subdomains?

Amit Katz Oct 27, 2016 4:50 PM (in response to Koen Menke)

You cannot have a liquid-gas interface in Flow Simulation, sorry to say. This software does not have that capability. You will have to model a barrier and set a custom material with very high thermal conductivity to approximate the heat transfer.
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- Re: Flowsimulation how to split box in to 2 fluid subdomains?
  
  Koen Menke Oct 28, 2016 7:05 AM (in response to Amit Katz)
  
  According to my simulations it has exchanged heat trough the lid.
  I'am using air as the gas. Normally solidworks does calculate simulations with normal surrounding air so why should it not have a liquid-gas interface ? Solidworks is frequently used for simulating heat exchangers so why is a liquid-air interface not possible ?
  
  Thanks in advance!
  
  Koen
  
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  - Re: Flowsimulation how to split box in to 2 fluid subdomains?
    
    Amit Katz Oct 28, 2016 9:06 AM (in response to Koen Menke)
    
    I don't know why it is not possible, you'll have to ask the developers. A fluid-fluid interface would require a deformable mesh and that is a quite a luxury feature usually reserved for more expensive and complex simulation packages.
    
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    - Re: Flowsimulation how to split box in to 2 fluid subdomains?
      
      Koen Menke Oct 28, 2016 9:18 AM (in response to Amit Katz)
      
      I think you are mistaking ?
      I tought Heat exchangers are perfect to simulate in solidworks ?
      Liquid-gas / liquid-liquid / gas-gas
      
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      - Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Amit Katz Oct 28, 2016 9:56 AM (in response to Koen Menke)
        
        Heat exchangers utilize a solid barrier. You have a fluid-solid interface and then a solid-fluid interface. Flow Simulation can't hand a fluid-fluid interface, which I thought is what you were asking about originally. Just know that whatever geometry and material you pick for your solid barrier will affect your heat conduction and the steady-state temperatures of your separated fluids.
        
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  - Re: Flowsimulation how to split box in to 2 fluid subdomains?
    
    Bill McEachern Oct 28, 2016 10:22 AM (in response to Koen Menke)
    
    The physics at a multi phase interface are extremely complicated to solve in continuum mechanics. One of the oldest codes for this type of work is Flow3D. You need to think about the complexities of tracking the liquid gas interface and as it breaks up and you get bubbles and froth, surface tension effects, buoyancy effects, waves....dissolution, settling........Flow simulation can handle multi species so long as the densities do not vary by more than a factor of 10.
    
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    - Re: Flowsimulation how to split box in to 2 fluid subdomains?
      
      Koen Menke Oct 31, 2016 7:43 AM (in response to Bill McEachern)
      
      Thanks Bill,
      
      You mean the densities differences between the air-fluid. Or the density inside one fluid subdomain ?
      I recognised that if i set high differences in values inside an user defined fluid the calculation time rises with factor 1000.
      
      With air-water calculation time is about 5 hours, with air-user defined 2800 hours according to Solidworks....
      
      As far as i can see heat has exchanged between the air fluid domain and the water fluid domain..
      What is your opinion Bill ? Is the model set right ?
      
      Starting fluid temp whas 291,5 Kelvin.
      
      Thanks for the help people!
      
      With kind regards,
      Koen Menke
      The Netherlands
      
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      - Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Bill McEachern Oct 31, 2016 8:29 AM (in response to Koen Menke)
        
        The best u can do here is put in a wall/lid and divide the chamber into fluid 2 sub domains - one for the gas one for the liquid. Make the wall a thin very hi conductivity solid (Like 100.000 w/mK). Put ideal wall bc's on both sides and run your job. It should be a reasonable approximation. You will need an experiment to quantify the errors of this approach.
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Koen Menke Oct 31, 2016 8:58 AM (in response to Bill McEachern)
        
        Bill,
        I can use the create lid's function for this right ?
        Ideal walls what does that say exactly ? That it doesn't change flow of the fluidum ?
        
        I will try and compare diffrences between the model i did before and with the high conducting lid.
        
        I will keep you updated!
        
        Thanks in advance.
        
        Koen
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Koen Menke Nov 1, 2016 11:49 AM (in response to Bill McEachern)
        
        I did the simulation with the hi-conducting lid.
        
        I did measure a few points, solid and fluid with point parameters. Differences where between 0.1-0.6 Kelvin. ( on a 18000 second pshycal time frame )
        However the calculation time rised with 200% !
        
        So its better to let the software calculate with an undifined lid ( created with the create lid function )
        Than give boundry and material conditions to the lid, couses rising calculation time!
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Bill McEachern Nov 1, 2016 6:31 PM (in response to Koen Menke)
        
        Why would u think that? If you use the lid function and do nothing else it gets the properties of the default solid material.
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Koen Menke Nov 2, 2016 7:55 AM (in response to Bill McEachern)
        
        No not that, but according to some people solidworks couldn't exchange heat in a gas-fluid configuration. Seems like it does.
        
        Only problem left is that if i change water for my own user defined liquid, calculation time raises from 4 hours to 2200.
        It's pissin me of. No big differances between the value's..I'am desparate.
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Bill McEachern Nov 2, 2016 8:47 AM (in response to Koen Menke)
        
        R u referring to the predicted time in the info or log dialog? That number is like Microsoft time - almost meaningless. just watch your goals and see when they flatten out. I doubt your user defined fluid, assuming the parameters describe a real substance accurately as opposed to some form of unobtainium then it should work fine. And solve in a reasonable time. Are u using flow freezing? If not, look it up. It can dramatically reduce solve times for suitable problems.
        
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        Re: Flowsimulation how to split box in to 2 fluid subdomains?
        
        Koen Menke Nov 2, 2016 9:43 AM (in response to Bill McEachern)
        
        That makes sense, but i can't beleve it goes from to 2200 to 2 hours ? Or is t possible ? I'am really new in to flow simulation sorry.
        
        Because solidworks doesn't now any phase chaning materials I let the software calculate with values that is equivalent to a PCM.
        I tought that was the problem, but I did flatten out the value's and the time didn't reduce dramaticly.
        
        I'am familiar with flow freezing. I looked it up but then it doesn't calculate the way heat flows anymore ? Can you explain exactly ?
        
        Thanks in advance!
        
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