Converting LPM to SLPM
07-10-2008, 03:08 PM,
 Intel55 SuperMember Posts: 156 Threads: 45 Joined: Sep 2007 Reputation: 2
Converting LPM to SLPM
Does someone have a formula to convert LPM to SLPM?

I have 279.4 LPM of O2
402 LPM of Air
66.6 LPM of C3H8

Hmmmmmmmmmmm thanks
07-10-2008, 03:33 PM,
 TurbineRepair Senior Member Posts: 75 Threads: 20 Joined: Jun 2008 Reputation: 2
RE: Converting LPM to SLPM
Hi,

There's a thread a bit further down titled "cmf to slpm" might be helpful.

Jim
07-10-2008, 03:50 PM, (This post was last modified: 07-10-2008, 04:04 PM by Intel55.)
 Intel55 SuperMember Posts: 156 Threads: 45 Joined: Sep 2007 Reputation: 2
RE: Converting LPM to SLPM
TurbineRepair Wrote:Hi,

There's a thread a bit further down titled "cmf to slpm" might be helpful.

Jim

I was actually just reading that

I read where Gordon went from lpm to slpm, but I did not know how.

So I just played with dividing the numbers by 1.077 and got the same answer as using the formulas below.

I have these reference conditions:
nlpm: 1.01325 bar (14.696 psi), 0 C (273.15 K)

scfh: 1.01325 bar (14.696 psi), 20 C (293.15 K)

1 nlpm = 2.11888 / (273.15 / 293.15) scfh

1 nlpm = 2.274 scfh

So I got 260 nlpm
62 nlpm
375 nlpm

so now I wonder how much of a difference there is between nlpm (0*C) and slpm (70*F or 21.1*C)...arggggg

ugggg I have the SCFH... maybe I can get those right into SLPM....hmmmm

buller........buller.....
07-11-2008, 01:10 AM,
RE: Converting LPM to SLPM
Hi Intel55

Quote:I have 279.4 LPM of O2
402 LPM of Air
66.6 LPM of C3H8
How were these flows measured and what were the conditions of temperature and pressure? If these are not known, conversion to SLPM or NLPM will not be possible.

Quote:I have these reference conditions:
nlpm: 1.01325 bar (14.696 psi), 0 C (273.15 K)

scfh: 1.01325 bar (14.696 psi), 20 C (293.15 K)

SCFH: 1.01325 bar (14.696 psi), 70 F (294.26 K)

1 nlpm = 2.11888 / (273.15 / 294.26) scfh

1 nlpm = 2.283 scfh

nit picking
07-11-2008, 04:53 PM,
 Intel55 SuperMember Posts: 156 Threads: 45 Joined: Sep 2007 Reputation: 2
RE: Converting LPM to SLPM

thanks for the nit pick,

OK, now what do I do to go from nlpm to slpm?

I did this:
O2 = 592 scfh @150psig ------ 260 nlpm
C3H8 = 141 scfh @ 80 psig ------- 62 nlpm
Air = 853 scfh @ 75 psig ------- 375 nlpm

I am trying to get a comparison between those nlpm numbers above and this parameter:

O2 = 280 slpm @ 160 psig
C3H8 = 76 slpm @ 85 psig
Air = 550 slpm @ 110 psig

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

thanks
07-12-2008, 05:47 PM,
RE: Converting LPM to SLPM
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.

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.
06-17-2016, 05:49 PM,
 robodave538 Newbie Posts: 1 Threads: 0 Joined: Jun 2016 Reputation: 0
RE: Converting LPM to SLPM
(07-10-2008, 03:08 PM)Intel55 Wrote: Does someone have a formula to convert LPM to SLPM?

I have 279.4 LPM of O2
402 LPM of Air
66.6 LPM of C3H8

Hmmmmmmmmmmm thanks

F[SLPM] = F[LPM] x ( 294.26/Tgas)x (Pgas/14.696)
06-21-2016, 10:51 PM,
 loriolo SuperMember Posts: 302 Threads: 1 Joined: Jan 2010 Reputation: 4
RE: Converting LPM to SLPM
Hi Intel55
Take in mind that you are working with volumetric flows, affected from temperature and pressure changes, so, in order to have a precision flow, you must work in a controlled media, or use systems with mass flow rate meter, and you must use the spray table from OEM, they did the work for you, so ask the manufacturer of your equipment for the spray tables, if you need to do conversion by yourself, you could use the following conversion formula:
F[SLPM] = F[LPM] x ( 294.26 / Tgas) x ( Pgas / 14.696)
Pgas – Absolute gas pressure in Psia
Tgas – Gas Temperature in K
Best regards
Luigi

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