2-phase tank, under pressure - temperature questions

[Subystud]

Hello -

I have a 11,100 gal sealed, pressure-rated tank initially being filled with water to 10,000gal at atmosphere, creating a 1,100 gal headspace.

Chemicals are added and pressure rises to 40 psig. Temperature is measured in the liquid phase via pH probe and equals 85F.

Chemicals escape solution and collect in the headspace.

Question:

Is the temperature in the headspace approximately that of the liquid? Or is the pressurized gas in the headspace subject to Gay-Lussac relationship for temperature.

Thanks --

Rob

 

[btrueblood]

Well, at least in the lab, when we collect evolved gas over liquid, it's assumed the gas temp. is pretty much equal to the liquid temperature. This is for slow reactions, though, without much temperature rise of the liquid occurring.

If there is a gas-phase reaction occurring, the story would be different.

 

[zdas04]

At thermal equilibrium, the gas and liquid have to be at the same temperaute (by definition). If one is hotter, heat will transfer to the cooler fluid. Figuring out how ling it will take to reach effective equilibrium can be a challenge.

David

 

[MintJulep]

If the head space is initially filled with air then Gay Lussac applies.

 

[Subystud]

I did a big report for the company - here's my findings.

Nitric oxide (NO) is insoluble, is generated by chemical reaction during a sealed process, and readily escapes solution and collects in the headspace.

Pressure increase calculated by considering moles NO added to headspace at constant volume, constant temp resulted in a pressure increase comparable to observed normal processing. - That's good.

The reaction of NO and O2 (initially present in the headspace) is exothermic and using constant volume calorimetry equation dQ = CvdT resulted in a calculated temperature increase from 80F to 544F. - That's bad.

This will be empirically tested with a temperature probe in the headspace - I'll let you know how good I am thermo in a couple of days.

 

[jharris3]

Subystud

You said that the pressure increase was comparable to observed normal processing.

When you say "comparable" aren't you casting some doubt on the constant volume assumption for estimating the temperature?

How much gas can be contained in a very small change in liquid volume?

I'm really just curious to see if your constant volume estimate is maybe a worst case scenario.