Standard litre per minute explained

The standard liter per minute (SLM or SLPM) is a unit of (molar or) mass flow rate of a gas at standard conditions for temperature and pressure (STP), which is most commonly practiced in the United States, whereas European practice revolves around the normal litre per minute (NLPM).^[1] Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 101.325 kPa (1 atm). Since 1982, STP is defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 100 kPa (1 bar).

Conversions between each volume flow metric are calculated using the following formulas:

Prior to 1982,

1 LPM = (. 001 / 60 )~ m ^{3} / s = 1 NLPM ⋅ (T _{gas})/(293 . 15 K) ⋅ (14 . 696 psi)/(P _{gas}) = 1 SLPM ⋅ (T _{gas})/(273 . 15 K) ⋅ (14 . 696 psi)/(P _{gas})

Post 1982,

1 LPM = (. 001 / 60 )~ m ^{3} / s = 1 NLPM ⋅ (T _{gas})/(293 . 15 K) ⋅ (14 . 696 psi)/(P _{gas}) = 1 SLPM ⋅ (T _{gas})/(273 . 15 K) ⋅ (14 . 504 psi)/(P _{gas}) 1 SLPM = 1 NLPM ⋅ (273 . 15 K)/(293 . 15 K) ⋅ (14 . 696 psi)/(14 . 504 psi) ≈ 0 . 94411 NLPM ^[2]

assuming zero degree Celsius reference point for STP when using SLPM, which differs from the "room" temperature reference for the NLPM standard. These methods are used due to differences in environmental temperatures and pressures during data collection.

R = 8.314510 J⋅K⁻¹⋅mol⁻¹: 1 SLPM = (0 . 001 x 10 ^{5})/(60 ⋅ 8 . 314510 ⋅ 273 . 15) = 0 . 00073386 mol/s.

See also

• Flow measurement
• Gas laws
• Standard cubic foot (SCF)
• Standard cubic feet per minute (SCFM)

Notes and References

1. Picas, J. A., Punset, M., Baile, M. T., Martín, E., & Forn, A. (2011). Effect of oxygen/fuel ratio on the in-flight particle parameters and properties of HVOF WC-CoCr coatings. Surface and Coatings Technology, 205, S364–S368.
2. Web site: STP – Standard Temperature and Pressure & NTP - Normal Temperature and Pressure. www.engineeringtoolbox.com.