Flow in pounds/h versus cfm - simple question about units. 4

[acr2003]

This is a very basic question but it has been raising many doubts here, amazingly.
How do I transform a flow of lbs/h of steam in cubic feet per minute (or if you prefer cubic meters per second). Could anyone please indicate me the formula and if that would be dependent on the temperature of the steam?
Thanks a lot.

 

[fredt]

I am not a steam expert but the problem is relatively simple.

Obtain the specific volume of the steam from steam tables for the steam conditions prevailing (cu ft/lbs) and multiply by the mass flow rate (lb/hr) and divide by 60 to give cu ft per min.

 

[JStephen]

If it's superheated steam, find the specific volume from steam tables. This is one over the density, if that helps. You'll need both temperature and pressure for this.

Pressure needs to be absolute pressure. IE, "14.7 PSI" on the charts corresponds to an atmospheric tank, and would read zero on a pressure gauge.

If it's saturated steam, it's more complicated. If it is all vapor, no liquid, you should be able to find the specific volume from the steam tables. If it contains some liquid, you won't be able to determine how much based on temperature and pressure alone.

Assuming you have lbs per hour, it would be lbs/hr x 1 hr/60 min / specific volume. Specific volume is cubic feet/ lbm, and units should all cancel out to give cuft/min.

And of course, if the pressure changes down the line somewhere, the volumetric flow rate will be different there.

 

[phex]

My predecessors already gave the right answers. It is just a question of density and steam quality. The density is dependent on temperature and pressure of the steam and can be extracted from the steam tables or with any tool calculating by the IAPWS formula (as this one:

http://twt.mpei.ac.ru/orlov/watersteampro/eng/

). A tool like this would even give you the density for steam of a quality lower than 1 (free liquid water possible). A unit conversion tool will help you recalculate from SI units to the imperial units.

hth,
chris

 

[chicopee]

Flow rate(cu.ft/min)=mass rate(lbm/hr) X Specific volume(cu ft/lbm) X 1hr/60 min

 

[acr2003]

Guys,
Thanks so much for the replies. You were all very helpful and let me solve and understand this little quiz pretty fast and correctly.
I am already calculating the flow according to the conditions I have using the charts you suggested me and the right units.
Thanks a lot once again.
- acr -