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[mqdias]

Hi to everyone!

I've searched a lot in Cheresources Forum about this issue and i found some interesting posts.
Yet, i still not see anyone refering and talking about more specificly about the flue gas dewpoint pressure.

We know that the dewpoint is calculated from the H2O partial pressure. This partial pressure comes from a "Total pressure". This "Total pressure" is the sum of "Static pressure" and "Dynamic pressure". Some times both this parts are negleted and treated as unic one. For example, i've seen many people using "Air Pressure" or "Ambient pressure", taken as 101kPa as the "Total Pressure".

Other times i see people mentioning pressures in mmH2O wich i supose to be gauge pressures and not absolute ones.

THE BIG QUESTION: What pressure must be used as the "Total Pressue"? Absolute or gauge pressure?

[djack77494]

Let me start with a warning - be careful about that which "we know". Often dewpoint when refering to fluegases means the Acid (or SO2) Dewpoint, and not the water dewpoint.

You enter into a very confusing realm by talking about static and dynamic pressures. There is no need to think in these terms in ordinary chemical/process engineering calculations. If you're not at very high velocity (and you definitely should not be in a flue gas application), then the dynamic pressure is negligable, and we can talk about just pressure.

Finally, at given a temperature your condensible fluid will have a certain vapor pressure. In a gaseous mixture, we often refer to that as its partial pressure. Both the partial and the total pressures are absolute pressures.