Need conversion of air supply at pressure/volume to liters/time 1

[TurboTag]

I think we have a units misunderstanding on this project. The process designer says they need 5000liters/sec. This is for a approx. 180 hand tools on an automotive assembly line. I think this number has been normalized and is not 5000liters/sec at 6 bar. Our estimate for this amount of tools was 4025 cfm(MAX) at 80 psi. The building contractor is not supplying a large enough compressor for either but I can't compare the numbers and strighten this situation out. I am far removed(Rüsselsheim, Germany) from my engineering library in MI and have been searching every where for a conversion or something to determine pressurized air to normalized air. Any help would be deeply appreciated.

Thanks

 

[RLJ]

Turbotag,

1 Liter/Sec = 2.1189 Cu-Ft/Min
1 Bar = 14.5038 Lbs/Sq-In

5000 Liter/Sec * 2.1189 = 10,594.5 Cu-Ft/Min
6 Bar * 14.5038 = 87.0228 Lbs/Sq-In

Hope this helps! RLJ s-)

 

[TurboTag]

Thanks RLJ,

The situation is very hectic and I wasn't very clear. I guess I am asking if anyone has spec't compressors and is there a comparison of a compressor suppling a volume of air at "atmosphere" versus suppling air at pressure? I realize there is an obvious load difference on the compressor. I guess I am tyring to figure out how these volume could be so different? I did get them into common units X-) (Note: I have studied compressed air but only as it relates to bodies traveling through the air at high velocity B.S. AE)

Thanks,

Tim

 

[TBP]

I've never seen a compressor manufacturer's literature that referred to anything but standard cubic feet per minute, or
SCFM (atmospheric pressure). This is also known as "free air".

The ratio of compression for 80 PSIG is (80 + 14.7)/14.7 = 6.44, so for 4025 SCFM (if I understand you correctly), the volume at 80 PSIG would be 4025/6.44 or 625 cubic feet.

Spirax Sarco in the UK used to publish a booklet called "Compressed Air Practical Study PS 12". I've only ever seen the single copy I have. Even the Spirax Sarco people around here haven't seen any for years. I'd really like to get one with North American pipe dimensions rather than British Standard, so if anyone knows where I can get one, I'd really appreciate it.

 

TurboTag,
In my experience dealing with gas compressors and fans, manufacturers will normally rate their equipment for a particular flowrate in Actual CFM (acfm) which is takes into account the pressure. If the flowrate has been "normalized", I assume you mean stated in reference to a standard state (like 60 deg F, 1 atm). THis flow would normally be stated in SCFM (standard CFM). Anyway, the common denominator of the two quantities would be the MASS flow rate which is actually constant and is related to the ACFM by the DENSITY of AIR: If you want the units in ACTUAL cfm then you should use the density of air at 80 psig. To get standard CFM (scfm), then you would use the denisty at "standard" conditions.
i.e. mass flow (lb/m) = Q (Acfm) x Density (Lb/ft)@ 80 psig

I would use a table of AIr properties to obtain the denisty.
Hope this helps.
-JK

 

[dnsalyer]

Someone please correct me if I'm wrong, but the density of air varies directly and linearly with its pressure. Since standard conditions (or "normalized" as TurboTag puts it) are roughly one bar, six bar actual flow is about 1/6 as much standard mass flow. If TurboTag's process designer is asking for 5000 L/s at standard conditions (for SI units: T=15C, P=101.325kPa), that should be the same as approx. 846 L/s at actual conditions, not adjusted for when T is not equal to 15C of course. You should be able to do a similar adjustment for T vs. P which also vary directly and linearly if I am not mistaken.

 

[dnsalyer]

Correcting my previous message,

...is about 1/6 as much standard volumetric flow.

dns