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Continuous Heat Transfer in a Section of Part

Posted 17 août 2020, 09:22 UTC−4 Heat Transfer & Phase Change, Heat Transfer, Microfluidics 4 Replies

Garrett Hawkins
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I am working on research where I need to model part of a microfluidic chip. The overall chip measures 6mmx6mmx1mm. The part of the chip I need to model is the center 1mmx1mmx1mm. For the heat transfer in the chip, I have the top surface as natural convection and the bottom surface as insulated. For the 4 side surfaces, I need to model as if there is still the 2.5 mm of nylon (the material of the chip) past them, but I am having a hard time in the heat transfer in solids and fluids module finding the right boundary condition to do this. Any suggestions on which one to use/which values I would need for it?

4 Replies Last Post 18 août 2020, 08:49 UTC−4
Jeff Hiller COMSOL Employee

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Posted: 4 years ago 17 août 2020, 14:34 UTC−4

Hi Garrett,

The presence of 2.5mm of nylon does not per se imply one boundary condition over another. Depending on what's happening 2.5mm away at that interface between nylon and whatever's further away there'll be a different temperature and temperature gradient where you are currently trying to set your BC.

A guess: If 2.5mm away you have an interface with air, you may well need to include that intermediary nylon region in your computational domain and set a convective cooling condition on its periphery.

Best,

Jeff

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Jeff Hiller
Hi Garrett, The presence of 2.5mm of nylon does not per se imply one boundary condition over another. Depending on what's happening 2.5mm away at that interface between nylon and whatever's further away there'll be a different temperature and temperature gradient where you are currently trying to set your BC. A guess: If 2.5mm away you have an interface with air, you may well need to include that intermediary nylon region in your computational domain and set a convective cooling condition on its periphery. Best, Jeff
Garrett Hawkins
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Posted: 4 years ago 17 août 2020, 14:44 UTC−4

Thats what i figured I might have to do. Thanks for confirming it!

Spinoff: if I decided to model the "imaginary" 2.5 mm of nylon on each side as an "imaginary" infinite distance of nylon, would there be some good way of modeling that in COMSOL or would I run into the same issue of eventually needing a boundary condition?

Thats what i figured I might have to do. Thanks for confirming it! Spinoff: if I decided to model the "imaginary" 2.5 mm of nylon on each side as an "imaginary" infinite distance of nylon, would there be some good way of modeling that in COMSOL or would I run into the same issue of eventually needing a boundary condition?
Jeff Hiller COMSOL Employee

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Posted: 4 years ago 17 août 2020, 16:42 UTC−4
Updated: 4 years ago 17 août 2020, 17:12 UTC−4

If you cut your computational domain far enough from the central region where your heat sources are, you may be able to make the engineering simplifaction that the heat flux on those side faces is small enough (compared to how much heat is lost through the top surface) that it can be neglected and therefore use an insulation condition on those far sidewalls. Whether that's true when the nylon is 2.5mm thick, I cannot tell you.

Best,

Jeff

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Jeff Hiller
If you cut your computational domain far enough from the central region where your heat sources are, you may be able to make the engineering simplifaction that the heat flux on those side faces is small enough (compared to how much heat is lost through the top surface) that it can be neglected and therefore use an insulation condition on those far sidewalls. Whether that's true when the nylon is 2.5mm thick, I cannot tell you. Best, Jeff
Garrett Hawkins
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Posted: 4 years ago 18 août 2020, 08:49 UTC−4

Thank you so much for your time and thoughts! I really appreciate it! I'll give it a go!

Thank you so much for your time and thoughts! I really appreciate it! I'll give it a go!

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