SLPM is the unit that a gas flow meter reads, but even though it appears to be a volume flow rate, it is in fact a mass flow rate. It is nonsense to report the SLPM at equivalent standard (or STP) conditions (0°C or 273.15K and 1atm) without also noting the pressure and temperature for the reference condition. I have a conversion spreadsheet that you can also use in cases where someone gives you a gas flow rate at standard conditions. You can download the spreadsheet from here: http://bit.ly/djd5ca (5.66 KB)
The second tab of the spreadsheet has the molecular mass for different gas mixtures that you can use to populate the "Mole Mass" column on the first sheet.
On the main tab, you insert values in the white columns and the calculated values are in yellow columns. Insert the reference temperature (in °C) and pressure (in atm), and then finally put in the stated SLPM for the gas flow, and you will get the mass flow rate to be used in kg/s.
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