9 Replies Latest reply on Feb 19, 2015 11:40 AM by Jared Conway

    CO2 Gas flow analysis

    Shahar Dor Zidon

      Hi guys

      I’m new to flow simulation & would like to ask couple of questions:

      • I understood that you can’t do gas particle analysis, why is that?
      • I’m trying to simulate a co2 bubbler in an open space (just a room), don’t really know what should be my boundary condition (should I set up it as a mixture of air & co2)
      • I would like to simulate the co2 particle flow, is there any way to do that? 

      Thanks guys

      Appreciate the help

      Shahar

        • Re: CO2 Gas flow analysis
          Nathan Satter

          Flow Simulation cannot deal with mixing fluids. You can have separate fluids/gases but they must be completely separated.

           

          However you can run a particle study. This is run completely in the post processor (not part of the input data). You can inject whatever size particles (solid or liquid) you would like at a given mass flow rate. Of course the behavior is highly dependent on the particle size.

           

          Otherwise if you want to run a mixing analysis, you need to look at other CFD packages that utilize volume of fluids methods.

          • Re: CO2 Gas flow analysis
            Chris Michalski

            Shahar -

             

            Flow simulation can use multiple fluids mixing as long as they are in the same state (mixing gases or mixing liquids).  I often study the mixing of process gases to determine local concentration maxima/minima.

             

            If you want to study the bubbler as CO2 gas bubbles pass through a liquid the answer is no.  If the actual bubbling action is not important but you simply need the mixing of CO2 from a small source into the air in the room, then yes, Flow simulation will calculate the volume or mass fraction as the gases mix.

             

            If the room starts as 100% air when you first start CO2 injection then yes, set the ambient condition to 100% air.  Then when you add your boundary condition of CO2 input make sure to select 100% CO2.

             

            After the simulation is complete you can run either particle studies or trajectories and use the volume/mass fraction as your scale.  Or use contour plots of various mass fractions of CO2.

              • Re: CO2 Gas flow analysis
                Pradip Aryal

                Dear Chris,

                I am trying to simulate Co2 concentration at sleeping condition in my own room with no ventilation. The initial condition I have set is 0.0004 C02 (400 ppm, normal outdoor co2 concentration) and 0.9996 air by volume fraction. The only boundary condition I have defined is at the nose where Co2 generation is at the rate of 0.0052L/S (5.2*e-6) (source:ASHRAE) at sleeping condition. The global goal is defined as the average volume fraction of Co2, however there is absolutely no fluctuation  in Co2 concentration over several hundreds of iteration and the contour shows the same value of co2 concentration in every plane after it is converged. I believe it shouldn't be like that. What I got it wrong? Please help!!!

                Regards,

                  • Re: CO2 Gas flow analysis
                    Jared Conway

                    steady state or transient analysis?

                      • Re: CO2 Gas flow analysis
                        Pradip Aryal

                        Hello Jared,

                        Its a steady state.

                        regards,

                          • Re: CO2 Gas flow analysis
                            Jared Conway

                            what is your expected result?

                             

                            what are your other boundary conditions?

                             

                            how are you measuring the concentration? overall for the whole volume?

                             

                            what does a cut plot of the concentration look like through your c02 source?

                              • Re: CO2 Gas flow analysis
                                Pradip Aryal

                                Hello Jared,

                                There are no other boundary conditions (only Co2 generation from nose and small aperture as a environment pressure for outflow), as I am mainly interested in Co2 concentrations in room. The real room has no window or any kind of ventilation and AC usually remain off at night. So I was interested in simulating Co2 concentration of room over night. I expect the Co2 concentration over night exceeding the threshold limit (1000 ppm), 0.001 by volume fraction in major region of the room. The cut plot of Co2 concentration shows 400ppm (0.0004 by volume fraction, as initial condition) in every plane except in very small region near nose.

                                Regards

                                  • Re: CO2 Gas flow analysis
                                    Chris Michalski

                                    What goals did you apply for the convergence?  Based on your explanation I think that average and bulk average CO2 concentration are going to be crucial.  Min and max will stabilize fast and may allow it to consider the problem solved.  This is where it becomes important for the operator to understand the problem that the software has solved (which may not be the problem you wanted it to solve).  Perhaps even adding dummy fluid volumes in certain areas (from nose toward a corner of the room) to use as volume goals so that the change in regions far away are captured as relevant. 

                                    • Re: CO2 Gas flow analysis
                                      Jared Conway

                                      i'd recommend building a very simple model that you can post, along with some screenshots of what you are seeing.

                                       

                                      and like Chris mentioned (and was mentioned previously), your convergence goals may play a big part in this

                                       

                                      here is just an example that shows the software can do this: SOLIDWORKS 2012 – Carbon Monoxide Flow Tracer - YouTube

                                       

                                      And I believe there are examples in the tutorials or verification problems.