Hi Intel55

You are really opening a can of worms here

confused ? I am

For my purposes I have regarded NLPM (Normal litres per minute) and SLPM (Standard litres per minute) to be equivalent with conditions of 0 C (273.15 K) and 1 atm or 1.01325 bar (101.325 kPa) OR should that be 1 bar (100.000 kPa). SCFH (Standard cubic feet per hour) at conditions of 70 F and 1 atm (most of the my flow tubes are calibrated this way).

Metco or Sulzer Metco equipment appear to use either SCFH (70 F @ 1 atm) or SLPM or NLPM (both 0 C @ 1atm) I don't know what the other thermal spray equipment manufacturers use for standards of calibration, but it appears that "standard" is not so standard after all. See

Wikipedia -Standard conditions for temperature and pressure.
Problem is that many quote SCFH or SLPM or whatever without specifying the conditions of temperature and pressure. It is necessary to define the standard reference conditions of temperature and pressure when expressing a gas volume or a volumetric flow rate because the volume of a unit mass or amount of gas varies with the temperature and pressure of the gas. The available data on the various definitions of standard reference conditions clearly indicate that there is no universally accepted definition of the standard conditions of temperature and pressure. For that reason, simply stating that a gas flow rate is 10,000 cubic meters per hour at "standard conditions" or at "STP" has no meaning unless the reference conditions that were applied are clearly stated.

Using the universal gas law for ideal gases (PV=nRT) we can use the formula

V2 = V1*(P1/P2*T2/T1) or V1 = V2*(P2/P1*T1/T2) assuming same gas (n1=n2 and R1=R2)

Where:

V = volume or flow rate

P = pressure (absolute units)

T = temperature (absolute units)

1 = calibrated gas

2 = gas under new conditions of temperature and pressure

Now I have used the following formula for calculating actual flows of different gases under different conditions through the same flow meter tube:

V1 = V2*SQRT(n1/n2*P2/P1*T1/T2)

Now I'm a bit confused about the use of square root, where and why it is used. I only know that results tally closely with experimental measurement that I performed many years ago. I would appreciate any views and comments from anyone on this please.

Now to answer Intel55 question

Quote:So how do I convert the nlpm (europe) to slpm (USA) so I can compare apples to apples

You need to establish what the actual conditions of temperature and pressure calibration for your SLPM (USA) flows. To be honest I would not like to guess what they might be. Once you know, just covert them as you have done before and you should be in the right ball park at least.