ideal gas mixing volumetric flowrate calculation

[450sxf]

Two ideal gas mixture inlet flowstreams are joined to form an exiting third ideal gas flowstream mixture, no reactions involved. The pressures and temperatures of the three streams are different. The mass flowrates of the two inlet streams added together equals the mass flowrate of the exiting stream. The actual volumetric flowrate of each inlet stream is measured. The actual volumetric flowrate of each inlet stream can be converted to a volumetric flowrate at standard temperature and pressure using the corresponding actual pressure and temperature measurements of each inlet stream. If I add the standard T&P volumetric flowrates of the inlet streams, will this sum be equal to standard T&P volumetric flowrate of the exiting stream ??.

 

[zdas04]

I frequently refer to volume flow rates at STP as a "surrogate" for mass flow rate. The reason I can say that is the conversion from mass flow rate to STP flow rate is to multiply mass flow rate times density. Density at standard conditions is always the same value for the same gas. This means that you can add a gas stream at 30 barg to another stream of the same gas at 3 barg--this only works in mass flow units or in STP volumes.

If you add the volume flow rate at standard conditions of your two streams they should be acceptably close to the single stream.

David

 

[450sxf]

Thank you David. Could I trouble you to prove it by equations, showing that the sum of inlet STP volumetric flowrates equals the exit STP volumetric flowrate, step-by-step, starting with conservation of mass equation mdotA + mdotB = mdotC ?.

 

[dcasto]

beside sounding like homework, what is the process that can take two streams at different pressures and come out with another pressure (actually there is, but in homework problems they don't tell you that).

Anyway, zdas is correct except for including zfactor on all streams, which must be applied.

 

[zdas04]

Yeah, yeah, yeah, but I bet his prof doesn't know that. The conversion from ACF to SCF that I use has compressibility in it.

450sxf,
I provide proof of my statements for paying clients when they ask (and they never do). For free you just get the opinion.

David