# low massflow

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 November 11, 2005, 03:03 low massflow #1 Anke Hentschel Guest   Posts: n/a Hello, This is Anke from Germany. At the moment I try to simulate the force on valve between two pressure chambers. These two chambers are connected with a short pipe. In the high pressure chamber is a valve. This valve looks more or less like a thin beam. Up to now the simulation model works very well. At the moment I try to do a simulation with a small mass flow. My problem is that, if I work with a very small mass flow (0,002kg/s) and with a little pressure difference (0,02bar) between these two chambers, I assumed to have a very small force on the valve. But something went wrong. If I have zero mass flow, I still have a force one the valve and this is impossible. I had discussions with my colleagues I contacted a university professor, but nobody could answer my question. I guess it could be a problem with numerical solver algorithm, because of the small mass flow, but I am not sure. So I would be very happy if you can tell me what the problem is and maybe what's the solution for my problem. CU Anke

 November 11, 2005, 15:11 Re: low massflow #2 Mani Guest   Posts: n/a Anke, I still have trouble picturing the physical problem you are trying to simulate. Is this a 2D or 3D simulation? If 3D: How can a beam act as a valve? Is that beam deformable (i.e. are you solving a structural equation)? It sounds like you are somehow controlling mass flow and pressure difference independently, but the mass flow should be a result of the computation and not a specified parameter. It's not hard to imagine a force on a valve even at zero mass flow: You surely need some minimum force to open the valve (0.02 bar may simply not be enough to open it). But to understand your problem, I think we need to know more about that valve of yours, and about the boundary conditions and initial conditions that you are using. From your description, I suspect that your troubles are not caused by the numerical algorithm, but there could be a more fundamental issue with the way you pose the physical problem.

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