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I'm really confused about these three units commonly used for measuring airflow:

  • cubic meters per second (m3/s)
  • normal liters per minute (NLPM)
  • standard liters per minute (SLPM)

I would appreciate if you could help me know how to convert them to each other. For example, is

$$1 \, m^3/s = 1 \, NLPM / \left( 1000 . 60 \right) $$

correct?

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The conversions can be found at this wikipedia page

$$ 1 \frac{m^3}{s} = 1000 [NLPM] \frac{T_{gas}}{293.15}\cdot\frac{14.696 [psi]}{P_{gas}} = 1000 [SLPM] \frac{T{gas}}{273.15}\cdot\frac{14.504 [psi]}{P_{gas} [psi]} $$

where:

  • $T_{gas}$: is the temperature that the gas is flowing
  • $P_{gas}$: is the pressure that the gas is flowing
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  • $\begingroup$ yeah I saw that Wikipedia page and that's why I'm confused. It seem like that NLPM and SLPM are mass flow rates not volumetric flow rates. Is that correct? $\endgroup$
    – Foad
    Sep 7 '20 at 8:42
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    $\begingroup$ In a way, they are. Because indirectly when comparing NLPM and SLPM flow rates, you are comparing the mass that flows. The mass of the gas that flows cannot be directly measured, (while the volume can), so it can be used to estimate the mass rate. $\endgroup$
    – NMech
    Sep 7 '20 at 9:15

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