Kg/hr to Cu ft/min?
by J57ltr on 08/05/03 at 14:42:13

Is there a conversion for Kilograms Per Hour to Cubic Feet Per Minute? I have a Mass airflow meter it’s output is in Kg/Hr but I need to change it to CFM. It’s supposed to be compensated for humidity, baro pressure, and temp.

Thank you

Jeff

Re: Kg/hr to Cu ft/min?
by Robert Fogt on 08/05/03 at 17:42:30

To convert weight to volume you will need to know the specific gravity of the substance.

You mentioned airflow, is it just plain air?

Re: Kg/hr to Cu ft/min?
by J57ltr on 08/06/03 at 06:33:50

Just plain old everyday air. I got a figure of 2.03 Kg/hr = 1.00 CFM @ sealevel. Sound right to you? The airflow meter is used in cars to measure airflow into the engine.

Thanks

Jeff

Re: Kg/hr to Cu ft/min?
by Robert Fogt on 08/06/03 at 07:13:15

At standard conditions, dry air at sea level at 59 ºF and 29.92"Hg, air weighs  0.0765 lb/ft³

You want kg/ft³......
0.0765 pound = 0.0346998 kilogram

That gives us the weight to volume conversion factor, but you also want "per hour" to "per minute" so multiply by 60.
0.0346998 * 60 = 2.081988

1 kg/h = 2.081988 ft³/m (at standard temperature and pressure)

Though I would imagine that there is increased pressure when dealing with automobiles, but I am not sure.

Re: Kg/hr to Cu ft/min?
by J57ltr on 08/06/03 at 07:29:33

So I guess my friend did it backwards, since his answer was 2.03 kg/hr = 1cu ft/ min?

The meter is on the suction side of the engine meaning all the air passes through the meter before it goes through the rest of the system, is mixed with fuel and makes it’s way past the intake valve into the engine. It is a supercharged car, but the meter is before the supercharger. So I’m not exactly sure what you mean by increased pressure. Basically what I am after is making a poor mans flowbench. Thanks for the info.

Jeff

Re: Kg/hr to Cu ft/min?
by Robert Fogt on 08/06/03 at 08:35:11

No that is my bad.  I used lb/ft³ instead of ft³/lb, I needed to use the recriprocal.

0.0765 lb/ft³ = 13.072 ft³/lb
13.072 ft³/lb = 28.81859 ft³/kg
28.81859 / 60 = 0.4803099

1 kg/h = 0.4803099 ft³/m
2.081989116 kg/h = 1 ft³/m

Your friend was correct. But just to make extra sure so I don't stick my foot in my mouth yet again, I will double check by working backwards.

1 ft³/m * 60 = 60 ft³/h
60 ft³/h * 0.0765 lb/ft³ = 4.59 lb/h
4.59 lb/h * 0.4535924 = 2.081989116 kg/h

Sorry about that. My bad.

Re: Kg/hr to Cu ft/min?
by J57ltr on 08/06/03 at 09:39:17

No problem thanks for the info.  This site is great I work in the scale industry and always have to convert something whether it’s Ft/Min to meters/second or just simple weight conversions I can find it here.

Thanks again

Jeff

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