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The dynamic viscosity of air is $1.78\cdot 10^{-5}Pas = 1.78\cdot 10^{-5}\frac{kg}{ms}$. How do I convert this to the minute scale? I see a reason for multiplying the value with 60 (because of the $\frac{kg}{ms}$) or dividing it by 60 (because of the $Pa s$).

Background: I need the value in a numerical CFD simulation, where I have all my timesteps in the minute scale.

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If you just want to do a straight up unit conversion, do the proper steps for dimensional analysis:

$$ 1.78\times 10^{-5}\frac{kg}{m\dot\ sec} * \frac{60\ sec}{1\ min} = (1.78 \times 10^{-5}) * 60 \frac{kg}{m\dot\ min} $$

Then the seconds cancel and you're left with the term on the "minute scale", if this is what you mean.

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  • $\begingroup$ Yes, this is what I mean. But if you do the same thing with the Pascal second unit, you get another value. Which way is the one to choose? And why? $\endgroup$
    – Till B
    Jun 29, 2011 at 17:47
  • $\begingroup$ I don't understand - the Pascal-second unit is completely equivalent to kg/ms, so you shouldn't have to choose anything to do the conversion. $\endgroup$
    – Jen
    Jun 29, 2011 at 18:11
  • $\begingroup$ yes. But when I change the Pascal-second into Pascal-minute, I get another value. Or am I wrong here? $\endgroup$
    – Till B
    Jun 29, 2011 at 18:15

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