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Non Newtonian fluids: gravity or no gravity ?

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Old   April 1, 2018, 09:59
Default Non Newtonian fluids: gravity or no gravity ?
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MjG
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hello, I have a quick question for you. I have a square cross section (64μm^2) microfluidics channel. The fluid flow is parallel to the xz plane (with the yy' to be the vertical axis). My fluid is the blood and I used the Bird-Carreu formula for modeling it. Also my flow is pressure driven ( I have applied an inlet velocity and I set the outlet pressure to be 0 Pa). Do I have to take into account the gravity or not?
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Old   April 1, 2018, 14:04
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Uwe Pilz
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Of course you need to take into account the gravity.

BTW: A giraffe has an systolic pressure of around 400 to fight against the gravity. For not to get varices they has some kind of elastic stockings.
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Old   April 1, 2018, 14:16
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MjG
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Thank you for your answer! I was thought that the only case we can take gravity into account was when the fluid flows vertically in a pipe or when a pipe is tilted.
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Old   April 1, 2018, 14:17
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I assume Uwe is just teasing you. A giraffe ist just about the opposite of what you are trying to simulate: macro-channel with gravity pointing in stream-wise direction vs. micro-channel with gravity pointing cross-stream.
The safest/easiest way to check (i.e. without making some estimates) is by just running both simulations and comparing the results.
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Old   April 1, 2018, 14:24
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Yes I know that I have to do this eventualy ... but my laptop is not very good and it realy takes a lot to give me a result ... So I was hopping for someone to give me an answer. What parameter should I test? Is the pressure in the middle of the channel a good indicator? I am studying a FSI problem.
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Old   April 1, 2018, 14:28
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Gravity is important in a complete real circulation but if you are modelling such a small channel, the body force can be neglected compared to the pressure driven force.
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