Temperature jump in CFX

snpradeep · February 9, 2012, 07:02

Hi All..
I am doing a simulation on droplet evaporation.
All setting has been made according to Spray Dryer tutorial in CFX help which simulates droplet evap.
I have attached a file "setup.txt" with this post which describes about the setup used in this simulation.
I am Injecting water (0.1% of Air mdot) into the domain. During post processing I can see Jump in static temperature as shown in pic.
Can anyone please let me know why this jump happen?? Actually It should have been 573.15 K.

Thank you.

Pradeep

ghorrocks · February 9, 2012, 07:21

It could be a recirculation or it could mean rapid evaporation cooling the local air. Don't know based on what you have posted so far.

Also I note you have a reference pressure of 0. You should make this a more sensible value close to the operating pressure of the device.

snpradeep · February 9, 2012, 08:16

Thank you Mr. Horrocks for a fast reply.

I am working on evaporative cooling...I am injecting water at 25C ( on Inclined surface, NOZZLE_SIDE) to cool the hot air of 573.15 K to see how fast droplets evaporate and how much cooling can be achieved..But just a small strip above this surface shows 583K (Please refer the contour plot above) nearly 10K higher than the inlet temperature which I feel physically impossible...I did not understand that behavior of the solver...When I run simulation with dry air I have 573.15K in most of the places (as seen in Pic below).

Thanks Pradeep

ghorrocks · February 9, 2012, 17:04

What does the total temperature look like?

snpradeep · February 11, 2012, 16:37

Something similar to the 1st pic..similar to static temp plot but with 600 K or so as max temp..I think it is because of big gradients and circulation area right behind the spray..May be I have to look for better heat transfer correlation to solve my problem..By default the model uses CFX inbuilt ranz marshall correlation..Do you know any expert parameter which deals with heat transfer equations..??

ghorrocks · February 12, 2012, 06:57

Which aspect of the heat transfer equations? Wall heat flux is simulated using wall functions or integration to the wall depending on your approach.

snpradeep · February 12, 2012, 09:34

I am speaking about Interphase Heat Transfer model in "Fluid pair tab" where particle heat transfer is evaluated using Ranz marshall correlation...I read in CFX help that it is valid for particle Re in range of 0 < Re < 250...
Hugmark Corelation is valid in Ranges 0 < Re < 776 (approx.)..

So i believe, I have to write a particle user routine to calculate my own heat transfer equation.

ghorrocks · February 12, 2012, 18:03

I see. Hopefully you can define this without requiring a particle user routine, but I am not sure. You will have to see what is available.

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February 9, 2012, 07:21		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	It could be a recirculation or it could mean rapid evaporation cooling the local air. Don't know based on what you have posted so far. Also I note you have a reference pressure of 0. You should make this a more sensible value close to the operating pressure of the device.

February 9, 2012, 17:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What does the total temperature look like?

February 11, 2012, 16:37		#5
snpradeep New Member Pradeep Join Date: Nov 2009 Location: Duisburg Posts: 24 Rep Power: 17	Something similar to the 1st pic..similar to static temp plot but with 600 K or so as max temp..I think it is because of big gradients and circulation area right behind the spray..May be I have to look for better heat transfer correlation to solve my problem..By default the model uses CFX inbuilt ranz marshall correlation..Do you know any expert parameter which deals with heat transfer equations..??

February 12, 2012, 06:57		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Which aspect of the heat transfer equations? Wall heat flux is simulated using wall functions or integration to the wall depending on your approach.

February 12, 2012, 09:34		#7
snpradeep New Member Pradeep Join Date: Nov 2009 Location: Duisburg Posts: 24 Rep Power: 17	I am speaking about Interphase Heat Transfer model in "Fluid pair tab" where particle heat transfer is evaluated using Ranz marshall correlation...I read in CFX help that it is valid for particle Re in range of 0 < Re < 250... Hugmark Corelation is valid in Ranges 0 < Re < 776 (approx.).. So i believe, I have to write a particle user routine to calculate my own heat transfer equation.

February 12, 2012, 18:03		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I see. Hopefully you can define this without requiring a particle user routine, but I am not sure. You will have to see what is available.