The volume of a particular gas that moves across a specific surface in a fixed amount of time is its flow rate. Similar to how the output of water moves from a faucet head, for example, in liters per minute or pints per second. The amount of gas leaving a tank may be in similar units.
One issue with this, however, is that the amount of space a given number of molecules of a gas occupies is often strongly dependent on physical properties such as temperature and pressure. This occurs to some extent with liquids, but you can usually neglect it in everyday calculations. As a result, it is usually necessary to give gas flow rates in units such as standard cubic feet per minute, or SCFM. Another common measure is normal cubic meters per hour or Nm3/hr.
The "standard" and "normal" indicate that these units are not strict volumes of gas that are flowing but quantities of gas. A SCF corresponds to 1 cubic foot of gas at 60 °F (15.6 °C) and 14.73 PSIA, while a Nm3 corresponds to 1 cubic meter of gas at 15°C at 101.325 kPa.
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That said, the difference between converting ft3 to m3 (a simple volume conversion) and the difference between SCF to Nm3 (a standard quantity conversion) can be ignored out to four decimal places. As a result, the following steps allow you to convert SCFM to Nm3/hr.
Step 1: Convert Cubic Feet to Cubic Meters
Say you have a gas flowing at a rate of 15 ft3 per minute through a pipe.
1 ft = 0.3048 m, so (1 ft)3 = (0.3048)3 m3 = 0.0265 m3
15 × 0.0265 = 0.40275 Nm3/min
Step 2: Convert Cubic Meters Per Minute to Cubic Meters Per Hour
An hour includes 60 minutes, so simply multiply the result from Step 1 by 60 to get the desired answer.
(0.40275 Nm3/min)(60 min/hr) = 24.165 Nm3/hr