Closed Volume: Mass increases, pressure and temperature decrease...

vainilreb · December 3, 2012, 04:44

Hi there,

I'm running a case with a room without outlets which is filled with air at 20°C and an ammonia mass flow of 0.1 g/s INTO the room. The inlet gas temperature is set to 20°C, too.
I would have expected an increase in pressure and temperature, as the mass in the system increases. But now I'm observing an opposite behaviour: after 450 seconds, the average temperature has decreased by more than 10K!

I'm using sprayFoam, the thermo-model is hsPsiMixtureThermo, radiation/reactions/combustion are all set to "off". I'm afraid sprayFoam or my thermo model can't handle the mixture. I've heard about excess enthalpy for real gas mixtures, but I can't believe that mixing 45g of ammonia with 38 kg of air decreases the temperature by more than 10K !?

Has anyone ever encountered this phenomenon and is able to tell me, how to fix it?

Thank you very much!

vainilreb · December 4, 2012, 07:57

I really need help on this topic!

December 3, 2012, 04:44	Closed Volume: Mass increases, pressure and temperature decrease...	#1
vainilreb Member Robert Join Date: Aug 2012 Location: Berlin Posts: 74 Rep Power: 13	Hi there, I'm running a case with a room without outlets which is filled with air at 20°C and an ammonia mass flow of 0.1 g/s INTO the room. The inlet gas temperature is set to 20°C, too. I would have expected an increase in pressure and temperature, as the mass in the system increases. But now I'm observing an opposite behaviour: after 450 seconds, the average temperature has decreased by more than 10K! I'm using sprayFoam, the thermo-model is hsPsiMixtureThermo, radiation/reactions/combustion are all set to "off". I'm afraid sprayFoam or my thermo model can't handle the mixture. I've heard about excess enthalpy for real gas mixtures, but I can't believe that mixing 45g of ammonia with 38 kg of air decreases the temperature by more than 10K !? Has anyone ever encountered this phenomenon and is able to tell me, how to fix it? Thank you very much!

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December 4, 2012, 07:57		#2
vainilreb Member Robert Join Date: Aug 2012 Location: Berlin Posts: 74 Rep Power: 13	I really need help on this topic!