CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CD-adapco

Negative temperature

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   September 4, 2004, 16:35
Default Negative temperature
  #1
Julie
Guest
 
Posts: n/a
Hello,

I'm solving the problem with liquid fuel evaporation and combustion (on v3.150A).

For drops properties calculation I apply user subroutines written by STAR support for my case. The subroutines used to work with coarser mesh (11000 cells), but they don't work properly with finer mesh (34000 cells). The swithches 70, 71 and 199 are turned on. The problem is that temperature is too low in the drops evaporation area (93 K), which is obviously not physical value.

Can somebody help me with this?

I have only one month left to submit my work.

Regards,

Julie
  Reply With Quote

Old   September 7, 2004, 09:26
Default Re: Negative temperature
  #2
Guillaume
Guest
 
Posts: n/a
Have you checked the droplets temperature ?
  Reply With Quote

Old   September 8, 2004, 09:59
Default Re: Negative temperature
  #3
Julie
Guest
 
Posts: n/a
Yes. Tmin = 114.2K and Tmax = 301.8K (injection temperature = 293K).
  Reply With Quote

Old   September 8, 2004, 14:08
Default Re: Negative temperature
  #4
Guillaume
Guest
 
Posts: n/a
And what is the temperature in the domain (Tmin, Tmax and Taverage) ?

Is there combustion/radiation or something like that ?

I suppose that 93K is for the gas phase where the spray is.
  Reply With Quote

Old   September 10, 2004, 05:43
Default Re: Negative temperature
  #5
Julie
Guest
 
Posts: n/a
Tmin = 93 K, Tmax = 2400 K

There is combustion of n-heptane.

Yes, your guess is perfectly right. 93 K is the gas phase temperature at the area of the drops evaporation.
  Reply With Quote

Old   September 10, 2004, 09:28
Default Re: Negative temperature
  #6
Guillaume
Guest
 
Posts: n/a
Could you indicate me, please, which vaporization model do you use ?

Is the boiling model switched on ?

Are Ps(T), Hv(T) correctly defined ?

What is your configuration and where exactly in the flow do the drops evaporate ?

You are using 3.15A, is that right ?
  Reply With Quote

Old   September 10, 2004, 16:16
Default Re: Negative temperature
  #7
Julie
Guest
 
Posts: n/a
Evaporation model - Rebound (combustion can't be modelled with the Evaporate model. It just doesn't ignite).

Boiling is off.

Ps and Hv are defined in the subroutine dropro.f that was written by STAR support guy as follows:

PS = FUELFN(3, DTD, DSM, DSM)

HV = FUELFN(2, DTD, DSM, DSM)

The model consists of mushroom vaporizer and combustion chamber. Primary air inlet enters the combustion chamber and the secondary air enters to the vaporizer. The droplets are injected into the vaporizer as well. If you would give to me your e-mail I could send you a schematic description of the model.

Yes, I use 3.15A.
  Reply With Quote

Old   September 13, 2004, 08:39
Default Re: Negative temperature
  #8
Guillaume
Guest
 
Posts: n/a
What do you mean by combustion cannot be modeled with the evaporate model ? You already have combustion and evaporation, have not you.

Do you know which parameters are input in the FUELFN table ? If star does not report you numerical instabilities in the .info file, I am afraid that the data in those arrays are erroneous.
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
static temperature more than total temperature ?? mahesh FLUENT 3 June 21, 2009 17:08
Negative values of concentration while solving temperature sachin OpenFOAM Running, Solving & CFD 2 February 9, 2009 03:39
temperature going negative behind a bluff body Sourabh Phoenics 6 December 1, 2007 19:50
Negative temperature Oleg Melnik Main CFD Forum 3 October 29, 2003 12:18


All times are GMT -4. The time now is 23:57.