# Negative temperature

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 September 4, 2004, 16:35 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

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

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

 September 8, 2004, 14:08 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.

 September 10, 2004, 05:43 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.

 September 10, 2004, 09:28 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 ?

 September 10, 2004, 16:16 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.

 September 13, 2004, 08:39 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.

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