I'm trying to apply a nonuniform electric field and create a dielectrophoretic force in a channel and put a particle in the middle of the channel.
I added these 2 physics, creeping flow and electrostatics.
I did choose particle tracing for fluid flow module, But the problem is that I don't want to separate the particles (i am going to have only one particle) or get the particle trajectories, I have to choose it just because only that physics has drag force and dielectric force.
I found out that I can simulate Dielectrophoresis force and drag force acting on particles in a fluid by using AC/DC module, but I don't know how?
Is it possible to help me?
your help is really appreciated.
Hi,
You should use Electric Currents (ec) to obtain electric field, Creeping Flow (spf) to obtain flow profile and finally Particle Tracing for Fluid Flow (fpt) to obtain particle trajectories. You can find a quite similar example in Application Libraries (in File menu) of your COMSOL which has example file as well as a PDF description (it is also available online https://www.comsol.com/model/dielectrophoretic-separation-of-platelets-from-red-blood-cells-17013). From your description I guess your situation is very similar to that example, perhaps you only need to change geometry, boundary conditions, particle size, etc.
Briefly what would you do is (assuming particle concentration is not that much that it affects electric field and flow): first purely solve electric field. Then solve for fluid flow also independently. Finally perform particle tracing using solutions from previous two steps. Two forces must be enabled to act on particles: Drag force (which drags particles along with the fluid). Dielectrophoresis force.
Thank you for your response.
I did choose particle tracing for fluid flow module, But the problem is that I don't want to separate the particles (i am going to have only one particle) or get the particle trajectories, I have to choose it just because only that physics has drag force and dielectric force.
I found out that I can create drag force and dielectrophoresis force in AC/DC module, but I don't know, how? I would really appreciate it if you help me.
@ Hamidreza Shirinkami
Azam Ranjbaran
It does not matter if you want to separate particle(s) or not. What happens to particle(s) (whether separation or drift ot whatever motion) is just a matter of channel design and balance of parameters. So, if your physical system involves a particle suspended in fluid, inside a channel and being subject to dielectrophoresis, then still exactly same procedure I mentioned above is needed for simulating it. Just follow the example step by step, but implement your own situation (geometry, boundary conditions, etc.) instead of the original one. There you'll see that drag and dielectrophoretic forces must be added in Particle Tracing for Fluid Flow section. Fluid Flow and AC/DC modules are just used to solve for fluid and electric field, they generally do not consider COMSOL particles (unless Fluid-Particle Interaction is enabled).
That being said, I feel I should stress a point, especially since you say you have only one particle:
COMSOL's particle tracing module treats particles as a single point, i.e. somehow a zero-dimensional thing. Any force in this module is calculated by a formula. For example when calculating dielectrophoretic force, COMSOL does NOT assume a 2D (or 3D) particle, meshing inside and around it and solving true electric field distribution locally and integrating results to calculate the net force on particle. Instead, it just plugs your input parameters (particle size, permittivity, etc) and existing electric field (obtained by solving AC/DC) into a formula and calculates the force, and uses this force together with laws of motion to estimate incremental trajectory every time-step. If this type of simulation suits your purpose then go on with it. But if you need to physically calculate dielectrophoretic force, then that's a different story. In the latter case you cannot use particle tracing module. You need to draw your particle, mesh inside and outside it with appropriate size, and solve the whole physics. In this case if you want to simulate particle motion, you'll need moving mesh. Not easy.
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