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I know that in bigger pipes, Reynolds number and the dominant flow regime can be important in further decisions. Now, I have an application with tubing of about 0.5 mm in diameter and a flow rate of 70 µL / min at maximum.

When calculating Reynolds number, this would lead to values that suggest a mix of laminar and turbulent flow. But is this still relevant information for such small tubing? Or is the flow so low that this does not really apply anymore?

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Dimensionless groups like the Reynolds number are extensively used because they can be applied to any system, including yours. When the fundamental (dimensional) equations describing the fluid dynamics of a physical system are reduced to dimensionless form, the Reynolds number naturally arises a key parameter. That is the power of employing dimensionless groups. Dimensional analysis captures the essence of a physical system, while at the same time minimizing the actual number of parameters that need to be considered.

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It depends on what you want to do with the information, doesn't it? Are you interested in calculating the pressure drop thru the tubing? Trying to figure out the maximum length of tubing you can use? What?

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  • $\begingroup$ Thanks for your reply. I want to figure out the main flow regime in the tubing. I know that turbulent flow causes more internal friction, and thus, I would prefer laminar flow. My question was however, is Reynolds number in such small tubing indeed still meaningful for determining this? $\endgroup$ – Thom May 10 '16 at 10:10

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