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 co2 December 26, 2003 22:29

back flow total temperature

I have pressure outlet BC for a pipe. Let us say I specify Backflow total temperature as 300 K. I have a fluid flowing at 500 K. How does that backflow temperature affect my solution? If there is not backflow, is it true that even if I specify 400 K as the backflow temperature, that will not affect my solution?

 MN December 30, 2003 14:58

Re: back flow total temperature

As long as you have positive flow through the outlet, the backflow will not affect your solution; the backflow specifics are only there in case the solver sees reversed flow across the boundary, and thus uses that information for BC settings. Thus, you should keep the backflow conditions consistant with what you expect the output should be in temperature/composition in case there's the temporary case of reversed flow as to not cause the solver headaches, but you don't have to be exact. So specifying 300K or 400K shouldn't make a difference, but setting 5000K (5e3) may give you headaches in the iteration process.

 chauhan January 31, 2011 13:40

back flow temperature

hi,
I m still not clear with this. I am giving inlet temp as 500 K. and according to experiment outlet temp is 550 K. now in my simulation shall I give 550 K as back flow temp??? if not then my simulated outlet temp what i am getting is much lesser than that. now where is the problem???

suggestions invited.

 alekso April 24, 2012 12:23

maybe you can't "decide" your outlet temperature.
I modelling a wall heated gas solid reactor. But i have unphysical phenomenas... the colder gas in the center rise up, instead the hotter gas near the wall go down... what's the problem???

 Zigainer April 24, 2012 16:06

Quote:
 Originally Posted by chauhanji (Post 292988) hi, I m still not clear with this. I am giving inlet temp as 500 K. and according to experiment outlet temp is 550 K. now in my simulation shall I give 550 K as back flow temp??? if not then my simulated outlet temp what i am getting is much lesser than that. now where is the problem??? suggestions invited.
Hi,

so you still have backflow?
The thing is if you have a backflow temperature too high/low and you get backflow due to the simulation (I almost get backflow very time) a too wrong backflow temperature would cause some problems. If backflow later disappears it doesn´t matter, but if backflow does not disappear (that could be because of the wrong backflow temperature) you have a problem.....

 jpo April 24, 2012 17:20

Post #2 is right

Your backflow temperature setting doesn't influence your solution. The pressure setting does.

Thus, if you really have backflow, only then the backflow temperature setting will be important, because fluid with the requested backflow temperature will start entering your computational domain

 thermal energy July 17, 2014 04:02

backflow

hi all,

ı have an rectangular geometry (lenght:76, width:27 mm). heat flux is applied from one of the vertical walls. ı have velocity inlet BC at lower part and also pressure outlet BC at upper part. velocity magnitute is zero (0) (no forced convection), initial gauge pressure is also zero and temperature is 298 K at velocity inlet BC. also, for pressure outlet BC gauge pressure is 0 and backflow temperature is set 298 K. initial temperature is also 298K.

the problem is that reversed flow occured.
"reversed flow in 34 faces on pressure-outlet 17"

the solution is converged but ı am not sure it is right or not.

any suggestion. thanks for you time.

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