Flue gas mixture volume flow calc 1

[ProcessJim]

I think I am just having a mind blank here so apologies if this is simple!

I have two gas streams mixing (flue gas and air). I know the flow rate of the combined stream, I also know the temperature of all three streams and can calculate the combined Cp.

I need to know the flow rates of the flue gas and air streams. I am thinking that I need to go and measure one of them.

So far I have:

m3 = m1 + m2
Q3 = Q1 + Q2
Q3 = (m3-m2)(Cp1T1) + (m3-m1)(Cp2T2)

Unknowns are m1 and m2.

Can someone please put me out of my misery? Is my thinking right that I just need to go and measure one?

Cheers,
James

 

[PaoloPemi]

if you need just an estimate based on a mass & energy balance you can guess the flows for the two (entering) streams, of course if you need accurate values a volumetric sensor will give better result.
You can start for example from
(tmix-t1)*cp1*w1-(tmix-t2)*cp2*w2 = 0
w2 = wtot-w1
etc.

 

[25362]

If you know Q3, m3, T1, T2, Cp2 and Cp1, then, from your last equation:

Q3 = (m3-m2)(Cp1T1) + (m3-m1)(Cp2T2)​

put (m3-m1) = m2

and having just one unknown, m2, proceed to

m2 = (Q3-m3Cp1T1)[÷](Cp2T2-Cp1T1)

 

[ProcessJim]

thank you that has cleared my blank mind which was clearly the problem.