Re: Correct Flow Conversion

[acfm]

I deal mostly with liquid ring vacuum pumps and commpressors. I have an gas application in which the following conditions were supplied:
suction Pressure: 50 Torr
discharge pressure: 900 Torr
mw:50 (50% water)
inlet temp: 33 deg. C
volume: 3 MMACFH (I'm assuming this is actual cubic feet per hour?)

Here are the problems that I'm having and looking for assistance on:
1. (3 MMACFH?) Normally MSCFD is given and this form references the volume of gas under standard conditions. How do you convert this from MMACFH to SCFM? I now MSCFD is approximately 1000 SCFM.

Based on the pressure requirements I know That I could possibly use a liquid ring vacuum pump however, determining the actual capacity is proving rather difficult. I'm trying to determine the actual cubic feet per miniute (ACFM) required.

Any assistance would be greatly appreciated.

 

[zdas04]

Is this post for real? Anyone who "works with liquid-ring compressors" must know the conversion from ACF to SCF and back again.

At the pressures you're talking about, an ACF is so close to an SCF that it just doesn't matter what you call it (900 torr absolute is 3 psig at sea level).

Most of the time the prefix "MM" should be read as "millions" (or "thousand thousands&quot. 1 MSCFD is "one thousand standard cubic fee per day" or 694 SCFM.

David Simpson, PE
MuleShoe Engineering

 

[acfm]

zdas04,
Thank you much for your quick response and yes this post is for real. My problem is the "3 million actual cubic feet per hour? Normally this volume would be stated as MCFD and (it is understood to be "standard" conditions). Based on your post, I calculate the following:

Assuming seal level and based upon your post, would you agree with the following:
694x3 = 2082 SCFM x (760/50)X(551/520)=33,533 ACFM ?

Can you confirm?

 

[zdas04]

If the 50 Torr is absolute, then you can't disregard pressure differences and 3 MMACFH at 50 torr is:
3*10^6 ACF/hr * (hr/60 min) *(50 torr/762 torr)* (273/(33+273)) = 2,547 SCF/minute

If the 50 Torr is gauge, then your 3 MMACF/h becomes 50 MACF/min and 47.5 MSCF/min which is probably close enough for design purposes.

The numbers work out differently if you do them in U.S. standard units since standard temp in Celsius is 0C and in U.S. it is 60F. The 50 Torr absolute value becomes 3,094 SCF/minute or 21% higher. Any time you're mixing apples and Volkswagons (i.e., temp in C and flow in cubic feet) you are asking for problems. Pick a consistent set of units and convert everything to that set of units FIRST.

If someone asks me for an engineering analysis that is in units that I'm not familiar with, I ask them to clarify. After getting the definitions, it is an easy thing to put all the units into a consistent system, do the analysis, and then convert the results back into the format the client is comfortable with. If someone gives you data in MMACFM and you don't know what this means (and you don't ask), you have failed in a duty to that client.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[acfm]

zdas04,

Thanks for your assistance.