Unit conversions

[MaxPlanck]

Hi all,

Some questions, I hope someone can help me!

A: Is it possible to calculate a face velocity (units ACFM) out of the mass velocity (unit SFPM) and the density of the gas? Or what else do I need?

B: If I have a mass flux with units kg/s-m2, how can I convert it to SFPM? I received a spreadsheet and don't understand where the numbers come from.
For example:
MassVelocity (SI) = 4.5 kg/s-m2, next they convert it to MassVelocity (IP) = 738 SFPM (= 4.5 kg/s-m2 multiplied by 164.041995). Is this 164.041995 a constant?

C: This SFPM, SCFM and ACFM are they related to a certain cross-sectional area, for example 1 ft2?


Many thanks in advance.
Here in Europe we use different units (SI) and sometimes it drives me crazy.

 

[katmar]

Max, this is a real can of worms. The first problem you have to resolve is what are the Standard Conditions assumed for the SCFM. There are quite a few "standards" in common use.

You have not said what gas you are working with, but if I assume it is dry air I get close to the numbers you have given.

4,5kg/(s.m2) of air at 60 deg F and 14,7 psia (a fairly common "standard") has a density of about 1,22 kg/m3. Dividing 4,5 by this density gives you a flow of 3,69 m3/(s.m2) which is a velocity of 3,69 m/s. Dividing by 0,3048 to convert the metres to feet, and multiplying by 60 to convert the seconds to minutes gives a velocity of 726 feet per minute. Your answer was 738 SFPM.

Because I am faced with these calculations on a regular basis I created a calculator to do the mass/volume conversions. Although it is not exactly what you need here it will do 90% of it for you. It is a free download from

http://www.katmarsoftware.com

Download "Uconeer" and once it is installed click the fan icon in the toolbar to bring up the calculator. Hope this helps.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[25362]

"Standard air" in SI units, is defined as having a density of 1.2 kg/m[sup]3[/sup]. This density is the same for

dry air moist air

Pressure 101.325 kPa 101.325 kPa
Temperature 294.2K 293.2K
Humidity 0% 50%

Taken from Fan Engineering published by Buffalo Forge Company Buffalo, New York.

BTW, using katmar's procedure with this density you get the 738 SFPM figure.

 

[mbeychok]

MaxPlanck:

You might find it useful to read the article at

http://en.citizendium.org/wiki/SCFM

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[MaxPlanck]

Hi all,

Thank you very much for all of your help.