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Solubility Of Air In Aviation Fuel

solubility static liquid column

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#1 raju.kct

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Posted 12 December 2016 - 01:02 PM

Hello Everyone, 

 

I'm not from Chemical engineering back ground. But trying to understand the air solubility in aviation fuel. My understating is, the solubility of air in fuel, stored in a tank is keep increasing towards the bottom of the tank due to increase in absolute static pressure (due to fuel column potential head). Tank is at atm pressure.

Please correct me if i'm wrong.

I'm not getting any reference material on this variation due to liquid column.

My objective is to estimate the air evolution from the fuel as it enters the suction port of fuel pump. Since there is a drop in pressure from the Tank outlet to pump inlet, evolution of dissolved air is possible, which affects the pump operation.

 

Thanks in advance.

 

 



#2 Saml

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Posted 12 December 2016 - 09:56 PM

Check here for N2 and O2 solubility

https://srd.nist.gov...RD/jpcrd249.pdf

https://srd.nist.gov...RD/jpcrd219.pdf

 

However, in any part of the system can be more dissolved gas that what was dissolved initially at atmospheric pressure.

 

Lets think about saturated portion at the bottom of the tank (because it saturated when the tank was low). If after that, more product is added on top of it, it wont gain in dissolved gas content.

 

Unless you are coming from a process where you put your product in contact with N2 or O2 at higher than atmospheric pressure, let it saturate there, and pump it to a tank entering into the bottom you cannot have more than the equilibrium at atmospheric pressure in any part of the tank.



#3 raju.kct

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Posted 12 December 2016 - 10:47 PM

Dear Saml,

 

Thank you very much for the reply and references. These are new reference to me, surely will help me to understand better.

And i agree with your point that we can not dissolve air more than the equilibrium limit. I apologies, i missed mentioning equilibrium limit in my post.

My point was, the equilibrium limit itself is slightly (based on liquid column) higher for the layer of liquid at the bottom of the tank due to higher static pressure.

Kindly correct me.

Thank you



#4 breizh

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Posted 13 December 2016 - 01:21 AM

Hi ,

To answer to your query  consider the 2 documents attached .

 

Hope this helps .

 

Good luck.

 

Breizh


Edited by breizh, 13 December 2016 - 02:30 AM.


#5 raju.kct

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Posted 13 December 2016 - 12:37 PM

Dear Breizh and Saml,

 

Thank you very much for the valuable references. It is very helpful for me to understand the system operation with gas saturated liquid and standard solubility data available.

But the point which is not clear yet is, about the air solubility (dissolved air in liquid) along the depth of liquid in the tank. My understanding is, the air/gas solubility (saturation limit) will be keep increasing as we go down towards the bottom of tank due to increased static pressure.

Kindly correct me.

 

Thank you.



#6 Saml

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Posted 13 December 2016 - 10:49 PM

Depending on the system, you may be correct or not.

 

- If you are assuming equilibrium, then the concentration is almost the same along the depth in equilibrium with the gas on top. The fact that it is at higher pressure (almost) does not change the dissolved gas activity in the liquid. You can consider the bottom of the tank as "subcooled" that is, with some margin either in pressure or temperature to the bubble point. 

 

- If you ssume that there is no mixing (total stratification), and you feed fuel that is a equilibrium with the gas at higher pressure, and feed it  to the bottom of the tank, then in this case the pressure exerted by the liquid above would prevent bubbles and the bottom may have a higher concentration.



#7 breizh

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Posted 13 December 2016 - 11:15 PM

raju,

Can you upload a sketch of your system ( tank , pump ,piping) , location of LSL  ? It will help us and help you too .

 

Breizh  


Edited by breizh, 13 December 2016 - 11:16 PM.


#8 raju.kct

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Posted 14 December 2016 - 12:41 AM

Dear Saml and Breizh,

Thank you for the clarifications. As Mr Breizh mentioned, I've attached herewith the schematic of the system for better clarification.

I'm interested to understand about the air concentration at point 1 and 2 in the liquid side. 

Thank you for your time and valuable points.

 

Attached Files



#9 breizh

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Posted 14 December 2016 - 07:45 PM

raju ,

To be frank I don't understand the practical aspect of your question . I do believe that you have problem with NPSH . You need to understand the risk of cavitation with your existing set up and what is the minimum level of liquid you must keep in your tank to prevent the liquid to boil at the suction of the pump.

my view .

 

Breizh



#10 raju.kct

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Posted 21 December 2016 - 12:30 PM

Dear Breizh,

My apologies for the delayed reply. I could not access internet.

To brief about the objective of the work, for hydrocarbon fuels, instead of NPSH, Vapor to Liquid ratio (V/L) is specified (at pump inlet) to avoid cavitation. SAE standard AIR1326 specifies the rationale behind the V/L parameter and a equation to estimate the V/L between two points. This same can also be used to design a fuel handling system to have cavitation free pump operation (i.e. V/L=0). In this context, i was trying to understand the air solubility in fuel with various depths, because in large tanks depth is high. But from the reference "VARIATION OF SOLUBILITY WITH DEPTH IN THE OCEAN: A THERMODYNAMIC ANALYSIS,by Irving M. Klotz", i could get, the gas solubility is not function of liquid depth (for sea water). 

 

Thank you all for your valuable time and comments.






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