Fluids

Fluids

Help needed with Microfluidics

    • WIZARDOUSS
      Subscriber

      Hello,


      I would like to have a little help with a simulation of gas flow in a micro-channel involving slip flow boundary condition.

    • DrAmine
      Ansys Employee

      Please elaborate more on your question and try to be more specific. Which software are you using?


      Finite Slip flow boundary condition is implemented in Fluent and CFX and PolyFlow.


       


      Fluent Theory Guide: 7.2.3. Slip Boundary Formulation for Low-Pressure Gas Systems


      CFX Modeling Guide: 2.7.1.3. Finite Slip Wall

    • WIZARDOUSS
      Subscriber

      Hello abenhadj


      thanks for your response I am using fluent 15.0


      the probleme is


      there is two chamber conected with a micro chanel


      the two chambers contain nitrogen gas the pressure in the first one is 130000 Pa and  in the second one 100000 Pa


      the flow is rarefied and steady

    • Karthik R
      Administrator

      Hello,


      I still do not quite follow why you cannot model the microchannel walls using the no-slip boundary condition. Could you please elaborate on your necessity to use a slip wall?


      Thank you.


      Best Regards,


      Karthik

    • WIZARDOUSS
      Subscriber

      hi


      comparing my result to previous work with different solver it is not the same


      what it is mentionned in literature that rareffied gas flow in micro-metric geometries involve slip conditions as


      the Maxwell based slip velocity and Smoluchowski based temperature


       


      cordially

    • Karthik R
      Administrator

      Hello,


      Thank you for this information.


      I read a little bit on the information provided by Surya. You can use the "low-pressure slip boundary formulation" for your model. Please refer to the 'Theory guide' for more information. You should be able to activate this from Models -> Viscous -> Laminar. Once you activate the 'Energy equation', you should see this under 'Options'. Please note that this option is available only for laminar flows. Here is a screenshot.



      I hope this helps.


      Best Regards,


      Karthik

    • WIZARDOUSS
      Subscriber

      thanks a lot


      I have already used it when I was searching in the theory guide but no difference I get always the same results 


      the funny thing that when I use the turbulent model (k epsilon) I approach to the wanted solution but the flow is laminar


      I searched on google for a tutorial of rarefied gaz modeling or michrochannel using fluent but there are not any


      I did the same simulation whit COMSOL and it work but with fluent I am struggling with


       


      cordialy

    • Karthik R
      Administrator

      Hello,


      You have to explain what your exact issue is with Fluent. What should be the solution and what are you getting with Fluent? We will be better equipped to help you if we understand the nature of your issue. Until now, it felt like you were unable to set-up your slip condition in Fluent. Please provide the necessary plots / screenshots so we can assist you better to resolve your issue.


      Regarding your results on COMSOL, unfortunately as ANSYS employee, I will not be able to comment on this.


      Thank you.


      Best,


      Karthik

    • WIZARDOUSS
      Subscriber

      HELLO


      sorry for taking so long to respond I ll provide you all information here



      pressure in left chamber is 130000 Pa


      pressure in right chamber is 100000 Pa


      what I get for the x-velocity in X=0



      what i shoud get



      the gaz is nitrogen


      best regard

    • Karthik R
      Administrator

      Hello,


      I have a few question regarding your problem set-up.



      • What BCs did you use to solve the model? I am especially interested in the boundary conditions along the wall of the thin 1um region. Please elaborate your inlet and outlet boundary conditions as well

      • What numerical schemes did you use to solve the problem? 

      • Could you please post an image of the grid?


      Thank you.


      Best Regards,


      Karthik

    • DrAmine
      Ansys Employee

      To add to the valuables questions of Karthik:  which material model are you using?

    • Rob
      Ansys Employee

      Can you also check the Knudsen Number and compare this against the range where continuum theory holds? 

    • zhangdongjie
      Subscriber
      Has your problem been solved? Where is the UDF loading of speed slip? Moving wall?n
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