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Posted Nov 10, 2011, 11:59 a.m. EST Fluid & Heat, Chemical Reaction Engineering, Geometry, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2 6 Replies

Santhosh Reddy
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Hello all,
I have a system as follows:
A small cylinder (capillary) is inside the big cylinder (channel). I want to study the effect of capillary on the flow distribution inside the channel. The flow rate in the capillary depends on the pressure maintained at the capillary outlet.
I created two cylinders but I do not know how to join them. I think I need to use contact or identity pairs. But I did not understand them clearly from the user guide.

Currently, I am using difference (big cylinder-capillary, geometry figure attached). Then I use laminar outflow condition at the capillary inlet. The results make sense. My next step is to solve the equations in capillary also. Can somebody help me to connect these two domains.

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6 Replies Last Post Nov 30, 2011, 11:05 a.m. EST
Santhosh Reddy
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Posted: 1 decade ago Nov 27, 2011, 11:33 a.m. EST
I still could not figure out. Can anybody help me?
I still could not figure out. Can anybody help me?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 27, 2011, 2:48 p.m. EST
Hi

if you make 3 cylinders one inside the next, in "Geometry Finish Union" mode you should get your capillary well defined. If you do not need the solid wall, then indeed subtract it from the rest.

In union mode you have continuity across internal boundaries, so there are no need to make "identity pairs", they are there by default

--
Good luck
Ivar
Hi if you make 3 cylinders one inside the next, in "Geometry Finish Union" mode you should get your capillary well defined. If you do not need the solid wall, then indeed subtract it from the rest. In union mode you have continuity across internal boundaries, so there are no need to make "identity pairs", they are there by default -- Good luck Ivar
Santhosh Reddy
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Posted: 1 decade ago Nov 28, 2011, 7:15 p.m. EST
Hi Ivar,

Thank you very much for your reply. At present, I do not have access to comsol. So I did not try the way you mentioned.

Does "geometry finish union" work differently than the "union" from "Boolean operations" ?

Because I used the "union" from "Boolean operations" . In this case, I could not edit internal boundaries (to specify the capillary walls).

Can you please send me a simple example if you have some time?

Thank you.
Hi Ivar, Thank you very much for your reply. At present, I do not have access to comsol. So I did not try the way you mentioned. Does "geometry finish union" work differently than the "union" from "Boolean operations" ? Because I used the "union" from "Boolean operations" . In this case, I could not edit internal boundaries (to specify the capillary walls). Can you please send me a simple example if you have some time? Thank you.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 29, 2011, 1:25 a.m. EST
Hi

indeed the finish - union is first making an union of all objects, then it analyses the objects and transform them into entities, which are numbered, identified, overlapping objects are split and duplicates removed. Common boundaries are also grouped, as by default there is a continuity of the flux over such boundaries

now in V4 COMSOL accepts certain "thin film" BC on internal boundaries, so one do not always need to use the Finish - assembly mode and define all related identity and special physics pairs by hand. Note you can do some geometry union operations before the final assembly, the the "assembly" criteria is only applied to the non united objects, which reduces the number of pairs to define

--
Good luck
Ivar
Hi indeed the finish - union is first making an union of all objects, then it analyses the objects and transform them into entities, which are numbered, identified, overlapping objects are split and duplicates removed. Common boundaries are also grouped, as by default there is a continuity of the flux over such boundaries now in V4 COMSOL accepts certain "thin film" BC on internal boundaries, so one do not always need to use the Finish - assembly mode and define all related identity and special physics pairs by hand. Note you can do some geometry union operations before the final assembly, the the "assembly" criteria is only applied to the non united objects, which reduces the number of pairs to define -- Good luck Ivar
Santhosh Reddy
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Posted: 1 decade ago Nov 30, 2011, 10:42 a.m. EST

Hi

indeed the finish - union is first making an union of all objects, then it analyses the objects and transform them into entities, which are numbered, identified, overlapping objects are split and duplicates removed. Common boundaries are also grouped, as by default there is a continuity of the flux over such boundaries


In fact, continuity of flux over interior boundaries is my problem. It should be wall bc at the interior boundaries.

May be I am not able to understand something.

Currently I subtracted capillary from the tube and in this case I am able to chose the wall bc. I use laminar outflow bc at the capillary inlet. Results make sense. But someday I may need to solve the physics in capillary also.
[QUOTE] Hi indeed the finish - union is first making an union of all objects, then it analyses the objects and transform them into entities, which are numbered, identified, overlapping objects are split and duplicates removed. Common boundaries are also grouped, as by default there is a continuity of the flux over such boundaries [/QUOTE] In fact, continuity of flux over interior boundaries is my problem. It should be wall bc at the interior boundaries. May be I am not able to understand something. Currently I subtracted capillary from the tube and in this case I am able to chose the wall bc. I use laminar outflow bc at the capillary inlet. Results make sense. But someday I may need to solve the physics in capillary also.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 30, 2011, 11:05 a.m. EST
Hi

you have the "Geometry - Finish Assembly" mode to dedouble all common boundaries, then you can link them with some how brew physics, not necesarily respecting only the continuity. This is what COMSOL does implictely for its internal "thin layer physics"

Check the help and the doc on the "Finsih Assembly" for further examples

--
Good luck
Ivar
Hi you have the "Geometry - Finish Assembly" mode to dedouble all common boundaries, then you can link them with some how brew physics, not necesarily respecting only the continuity. This is what COMSOL does implictely for its internal "thin layer physics" Check the help and the doc on the "Finsih Assembly" for further examples -- Good luck Ivar

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