Microfluidics - Latest Discussions - COMSOL Forums

Mesh

Wed, 16 May 2012 12:26:13 +0000

Hi. I have a problem with moving mesh too. Please help me with materials. Where I can find something about it?

finding a specified flow rate in a '3D cut plane'

Wed, 16 May 2012 02:08:55 +0000

Hello,

I'm trying to do some postprocessing in a 3D fluid channel flow over a fractured hole.
The channel is filled with water and is laminar.
Here's what I'm trying to do:

1. cut the surface at an arbitrary channel location (i used the 'cut plane')
2. within that surface, I would like to start from one edge and integrate the velocity profile in a prescribed area.
eg) if the surface slice is a 2mmx2mm rectangle, i want to make another rectangle that is 1mmx1mm within that original 'cut plane' and measure the surface integrated velocity value (flow rate).

I was able to cut the surface where I wanted it, but I cannot find a way to resolve what I said in 2.

Any ideas?

Thanks!

TJ

Determining the residence time of a massless particle in microfluidic channel

Thu, 10 May 2012 19:18:19 +0000

Hi all!

I have a question regarding determination of a residence time for a masless particle in microfluidic channel.

I have modeled steady fluid flow with 'Laminar Flow' physics in Comsol 4.2 through some channel geometry and now i would like to make an investigation on how long does a particle (masless or with really small dimensions) flow through the geometry. Thus measuring residence time for a particle.

Can anybody help me with this - maybe guide me to a tutorial on this subject?

Every help would be very much appreciated!

Thanks in advance and best regards,
Izidor

Moving membrane with FSI

Mon, 07 May 2012 19:25:07 +0000

Hi all,
I've got a problem simulating my developed sensor. In principle it is this:
A membrane covers a cell filled with liquid, for example water. On the membrane there is a kind of bumper. A force acts on this bumper in the direction of the cell. What I expect is this:
Because of the flexibility of the membrane it will bend in the water. The water should be incompressible and therefore need to move somewhere. All walls of the cell are fixed and undeformable, thus the only deformation option is again the membrane. Also the membrane gets "down" in the middle, where the force acts and goes "up" circular around this point so that the volume stays constant.
However I cannot teach COMSOL to do the right simulation. I've tried it with the solid mechanics physics. The membrane goes down where the force acts, but the volume is compressed respectively it does't go up in the same amount around the middle.

I hope you understand what I mean, and that someone is able to give me a hint on solving this problem.

Attached is the model as it is

Kind regards

Frank

Non-physic results filling microchannel model

Fri, 04 May 2012 12:23:49 +0000

I've just started working with comsol and want to simulate the effect of the contact angle on the filling of a microchannel with water.
I'm using the multiphase flow, level set method and have attached the model.
The problem is that when the contact angle of the walls change from 15 degrees to 180 degrees the waterfront should stop as there is no pressure added, however the results show that the channel keeps on filling itself.
I tried to change a lot of settings to see if that works better, but I'm pretty much stuck now.
Could anyone have a look at my model and see if they can tell me what's wrong with the model?
Thank you.

volume force field for laminar flow simulation

Thu, 03 May 2012 18:10:18 +0000

I 'm doing a laminar flow simulation and want to introduce a volume force. I found an option for a constant volume force.

However, I want to introduce a position-dependent volume force. How can I achieve this?

Thanks.

PS: I'm using comsol 4.1

Mesh query regarding open boundary FSI simulation

Thu, 03 May 2012 18:02:03 +0000

I've got a model in FSI which consists of two inlets to a central reservoir with a membrane on top.
When I use normal mesh settings, the mesh quality at the inlets is horrible.
Am I forgetting a boundary condition? Or is there something I can do regarding the mesh?
I apply simple open boundary conditions to the inlets.
See attached picture, I've filtered to show only the worst mesh quality,

any idea how to improve this mesh?

Can anyone hlep me find what's going wrong

Wed, 02 May 2012 11:08:51 +0000

Hi, all
I have attached the mph file below.Now the question is that if the Pref is 1[atm],the result can be got.However my experiment condition is low vacuum(about 1e-2Pa),that means the Pref can set 1e-2 Pa?I have tried ,but failed and Comsol shows "Can not find consist initial value and the last time step is not converged",Can anybody know what's going wrong?
Thank you for your replies

[Help]How to simulate the AC electroosmotic pumping

Mon, 30 Apr 2012 11:24:18 +0000

Dear all:

now I I study electroosmosis principle,but don’t know how to create the Model using the Comsol, I find one paper “ Poisson equation based modeling of DC and AC electroosmosis”, so I believe some one can make it easy ,if you have time ,can you tell me some details about that, or share your models ,thank you very much.
With best wishes.

Peter

How to simulate tthis filling process ,help wanted urgently

Sun, 29 Apr 2012 18:02:33 +0000

I want to simulate the gas(helium) filling a hollow fiber(about 1m long ,diameter is 200um) into a chamber(a cube,volume is 3.16e-4m^3 ).The initial condition is vacuum (about 1e-2pa) in the fiber and the chamber .The inlet is constant pressure(2000pa).Temperature is also constant.No other conditions are provided.I have tride many ways but always failed.Here I want some help uegently .Your comments or advices will be very important to me .Thank you for any help.

comsol

Sat, 28 Apr 2012 18:14:38 +0000

Dear Yang

From the comsol Discussion Forum, http://www.comsol.com/community/forums/general/thread/1414/ I known you had followed the paper " Novel systems for configurable AC electroosmotic pumping, Microfluidics and Nanofluidics"in the past as well.I am a new ,so can you tell some details for me about that.
thank you
Peter

thank you

Sat, 28 Apr 2012 18:13:02 +0000

Dear Guo

From the comsol Discussion Forum, "http://www.comsol.com/community/forums/general/thread/1414/ "I known you had followed the paper " Novel systems for configurable AC electroosmotic pumping, Microfluidics and Nanofluidics"in the past as well.I am a new ,so can you tell some details for me about that.
thank you
Peter

problem creating a model using a Matlab function from COMSOL model

Fri, 27 Apr 2012 16:08:41 +0000

Hello Sir,
I readed you answer about loading comsol code to matlab function.
I have a question about loading model from comsol to matlab function in order to simplify my equations .
Am working with windows and the software (matlab) is not installed in my PC am working with it on line (in a laboratory).
So can't found the " COMSOL with MATLAB " in the Start Menu !!!

It's my frist time working with this software am trying to read and understand the steps but i s a diffecult language so am asking you if you can give simple instructions to help me .

Sorry fo my stupid question & hope that you will help me .

Thank you very much

multiparameter model with comsol ???

Thu, 26 Apr 2012 17:08:13 +0000

hello,

Am trying to do a model with comsol but my problem is that whenever I enter a parameter value manually and it takes alot of time . I want to know how I can enter a range of values once and for all.
thank you for your answer

About optical force calculation of particles manipulated by microring resonator

Tue, 24 Apr 2012 06:49:08 +0000

Hi,everyone.

I want to simulate a structure which includes two bus waveguides and one microring resonator to form an on-chip optical tweezer. One microparticle is placed in the gap area between one waveguide and the resonator.

The structure is quite similar with:
http://pubs.acs.org/doi/abs/10.1021/nl100501d
(work from Kenneth Crozier, School of Engineering and Applied Sciences, Harvard University)

I want to use the Maxwell Stress Tensor method to calculate the optical force on it.

I tried the following:
In Results-Derived values. I added a surface integration for the whole surface of this ball-shaped particles. However, I am not sure how the expression of the force is.

If you have some ideas about optical force calculation, please feel free to discuss with me.

Thank you so much.

take concentration profile at outlet and use it for inflow boundary condition

Fri, 20 Apr 2012 07:17:50 +0000

I have a laminar flow node and two transport of diluted species physics.

how do I take the concentration profile at the outlet from the first transport of dilute species (variable c) and use it as the inlet boundary condition for my second transport of dilute species (variable c2)?

How to use periodic flow condition under single phase laminar flow

Fri, 20 Apr 2012 05:37:14 +0000

Hi,

I am confused on how to use the periodic flow condition. I have a long and repeated geometry, and I want to model just one section of it (since it is repeated anyway).

Attached is a very simple geometry. My goal is to have the flow coming out of the outlet and go back into the inlet x-number of times.

Right now, the settings I have are: Incompressible flow, and a pressure drop of 10[pa].

However, how do I specify initial conditions at the inlet, and how do I set the number of iterations (or periods) where the outlet flow goes back into inlet flow?

Alternatively, if the above doesn't work or does not make sense, how do I take the velocity at the outlet and use it as the inlet?

Error: Void equations

Thu, 19 Apr 2012 13:09:21 +0000

Hi all,

I solved for laminar flow and electric potential in a microfluidic channel, and wanted to see how charged spherical particles injected into the channel would flow.

So I compute a stationary solution for laminar flow and electric potential, then try to compute time dependent solution for particle trajectory.

However, I got this error message:

"Failed to find consistent initial values.
Singular matrix.

There are 37489 void equations (empty rows in matrix) for the variable mod1.V.

There are 37484 degrees of freedom that do not occur in any equation (empty columns in matrix) for the variable mod1.V.
Last time step is not converged."

Could anyone advise please?

I have attached the model file.

Thanks,
Jaren

Electrophoresis of spherical particles

Thu, 19 Apr 2012 03:08:42 +0000

Hi all,

I am trying to build a model for continuous free flow separation.

A hydrodynamically focused stream of spherical particles of different sizes and materials are subjected to an electric field perpendicular to its direction of flow. Particles are thus deflected perpendicularly to its flow direction due to electrophoresis and captured at the end.

The problem is how can I use Comsol to model electrophoresis of macro particles (with consideration for EDL)? The particle tracing module allows us to input a particle charge, but that is treating the particle as merely a point charge I suppose?

Thanks!

Need some help in meshing, inverted mesh elements warnings

Tue, 27 Mar 2012 13:23:37 +0000

I have an FSI problem, by moving a membrane I would like to see the fluid move.

When I setup the simulation, I've played around with the settings, looked at how other models were setup, but I can't get rid of the 'inverted mesh elements' warnings.

Does anyone have any advice on this model?