CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

free stream temperature

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

Like Tree3Likes
  • 1 Post By LuckyTran
  • 1 Post By LuckyTran
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 5, 2012, 11:00
Default free stream temperature
  #1
Member
 
Vaibhav Rai Khare
Join Date: Jul 2011
Location: Jaipur
Posts: 37
Rep Power: 14
vaibhavraikhare is on a distinguished road
What does Free stream temperature and external radiation temperature meant in boundary condition--> Thermal.
vaibhavraikhare is offline   Reply With Quote

Old   May 5, 2012, 15:30
Default
  #2
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Quote:
Originally Posted by vaibhavraikhare View Post
What does Free stream temperature and external radiation temperature meant in boundary condition--> Thermal.
Freestream temeprature is exactly that, freestream temperature and so is external radiation temperature, it's the temperature at which the external radiation occurs.

It should be self explanatory if you know anything about heat transfer. Did you even bother to read the Fluent help file? If you don't know those quantities perhaps you shouldn't be using Fluent?
delaneyluke likes this.
LuckyTran is offline   Reply With Quote

Old   May 15, 2012, 04:03
Default
  #3
Member
 
Vaibhav Rai Khare
Join Date: Jul 2011
Location: Jaipur
Posts: 37
Rep Power: 14
vaibhavraikhare is on a distinguished road
@LuckyTran: Ohhkkk.. That means you should have read the whole FLUENT user manual. So tell me the equation to calculate the external radiation temperature and how can we define the value of both???
And for your knowledge i would like to tell you that the free stream temp and external radiation temperature don't have any physical significance in Heat transfer..Both are defined by FLUENT itself..
vaibhavraikhare is offline   Reply With Quote

Old   May 15, 2012, 11:41
Default
  #4
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Quote:
Originally Posted by vaibhavraikhare View Post
@LuckyTran: Ohhkkk.. That means you should have read the whole FLUENT user manual. So tell me the equation to calculate the external radiation temperature and how can we define the value of both???
And for your knowledge i would like to tell you that the free stream temp and external radiation temperature don't have any physical significance in Heat transfer..Both are defined by FLUENT itself..
Both temperatures have been in use long before the first version of Fluent. Fluent did not make up these terms, they have been around and in use by heat transfer practicioners before then. And no, I don't need to read the entire Fluent help file, actually I don't need to read the Fluent help file at all to know that the the concept of free-stream velocity and free-stream temperature have been around a long time.

And for your knowledge, I would like to tell you that, for both conduction and convection, without a free-stream temperature there is no heat transfer as there is no heat. Therefore, the free-stream temperature and external radiation temperature both have a physical significance in Heat Transfer and have a direct influence on it. Heat transfer occurs via conduction, convection, and radiation. Just because it doesn't play a direct or obvious role in radiation does not mean that it has no physical significance.

I will now tell you the equation to calculate the freestream temperature and external radiation temperature as you requested. Here they are: ( ) there. They do not have any equations to them as they are just temperatures of specific configurations.
vaibhavraikhare likes this.
LuckyTran is offline   Reply With Quote

Old   May 15, 2012, 11:59
Default
  #5
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Because I am a nice guy I did spend time reading the Fluent help file just for you.

In section 7.3.13.3 Thermal Boundary Conditions at Walls (different sections occur in different versions of the manual, it is 7.3.14 in some versions but they do not differ by a whole lot)
you will find the discussion on what each term means, Fluent mentions external radiation temperature here

7.3.13.11 Fluent explains that the external radiation temperature is the temperature of the radiation source or sink on the exterior of the domain, defined by you. defined here means in the sense of applied boundary conditions, i.e. imposed. That does not mean that you get to make up a new bizarre definition of external radiation temperature, only that it is specified

There is a similar corresponding discussion for inlets in 14.3.7. For inlets, in addition to the incoming bulk temperature of the flow, you must also set the temperature of the external surface.
vaibhavraikhare likes this.
LuckyTran is offline   Reply With Quote

Old   May 16, 2012, 05:51
Default
  #6
Member
 
Vaibhav Rai Khare
Join Date: Jul 2011
Location: Jaipur
Posts: 37
Rep Power: 14
vaibhavraikhare is on a distinguished road
Hi LuckyTran.
Sorry for being so rude. Actually i got so frustrated as every person to whom i asked gave several answers and none of it helped me. If you can help me.? I am applying radiation model on a box but always getting negative heat transfer rate at absorber plate which should be positive.
vaibhavraikhare is offline   Reply With Quote

Old   April 16, 2014, 04:36
Default
  #7
New Member
 
wangyun
Join Date: Apr 2014
Posts: 2
Rep Power: 0
wangyun is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Because I am a nice guy I did spend time reading the Fluent help file just for you.

In section 7.3.13.3 Thermal Boundary Conditions at Walls (different sections occur in different versions of the manual, it is 7.3.14 in some versions but they do not differ by a whole lot)
you will find the discussion on what each term means, Fluent mentions external radiation temperature here

7.3.13.11 Fluent explains that the external radiation temperature is the temperature of the radiation source or sink on the exterior of the domain, defined by you. defined here means in the sense of applied boundary conditions, i.e. imposed. That does not mean that you get to make up a new bizarre definition of external radiation temperature, only that it is specified

There is a similar corresponding discussion for inlets in 14.3.7. For inlets, in addition to the incoming bulk temperature of the flow, you must also set the temperature of the external surface.
hi,
can you sent the fluent help to me if you have time? i don't have a clear idea for the free steam temperature and external radiation temperature.
I will be very grateful to you. thank you.
my email:1203596116@qq.com
wang yun
wangyun is offline   Reply With Quote

Old   October 17, 2014, 07:50
Default
  #8
Member
 
Join Date: Jul 2012
Posts: 48
Rep Power: 13
Abhya is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Both temperatures have been in use long before the first version of Fluent. Fluent did not make up these terms, they have been around and in use by heat transfer practicioners before then. And no, I don't need to read the entire Fluent help file, actually I don't need to read the Fluent help file at all to know that the the concept of free-stream velocity and free-stream temperature have been around a long time.

And for your knowledge, I would like to tell you that, for both conduction and convection, without a free-stream temperature there is no heat transfer as there is no heat. Therefore, the free-stream temperature and external radiation temperature both have a physical significance in Heat Transfer and have a direct influence on it. Heat transfer occurs via conduction, convection, and radiation. Just because it doesn't play a direct or obvious role in radiation does not mean that it has no physical significance.

I will now tell you the equation to calculate the freestream temperature and external radiation temperature as you requested. Here they are: ( ) there. They do not have any equations to them as they are just temperatures of specific configurations.
Hi LuckyTran
Dude I have seriously never heard such a term prior to reading it in FLUENT
I have been trying to find out how FLUENT processes the External emissivity and the external radiation temperature to calculate the heat transfer to the enviornment
I have goggled beyond my patience limit and still I don't find any reference to how fluent calculates radiation heat transfer from these inputs nor do I find any document under the name External Radiation, Even the FLUENT theory guide simply says this about it 4 lines not mentioning anything about the exact method

Although it seems obvious it uses the t^4 (Stefan-Bolztman's Law) Have u know any document which explicitly says that? So I void verifying the same thru simulations
Abhya is offline   Reply With Quote

Old   August 10, 2016, 10:54
Default
  #9
New Member
 
Alex Gtz
Join Date: Jun 2016
Location: Paris
Posts: 15
Rep Power: 9
alex_gtz is on a distinguished road
Quote:
Originally Posted by Abhya View Post
Hi LuckyTran
Dude I have seriously never heard such a term prior to reading it in FLUENT
I have been trying to find out how FLUENT processes the External emissivity and the external radiation temperature to calculate the heat transfer to the enviornment
I have goggled beyond my patience limit and still I don't find any reference to how fluent calculates radiation heat transfer from these inputs nor do I find any document under the name External Radiation, Even the FLUENT theory guide simply says this about it 4 lines not mentioning anything about the exact method

Although it seems obvious it uses the t^4 (Stefan-Bolztman's Law) Have u know any document which explicitly says that? So I void verifying the same thru simulations
Radiation heat transfer is calculated by fluent with Q_rad = epsilon*sigma*(T_inf^4-T_w^4)

where epsilon is the emissivity of the external side of the wall, sigma is the Boltzmann constant, T_inf is the external radiation temperature and T_w the temperature of the wall surface.

What do you need to understand ?
alex_gtz is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
An issue with temperature change in unsteady prob Ashok kumar FLUENT 1 January 13, 2009 05:34
Free Stream BC KP FLUENT 0 February 27, 2006 18:28
Free stream B.C. Lakshmikanth Alluru FLUENT 1 February 10, 2006 00:49
CFX 4.4 New free surface option Viatcheslav Anissimov CFX 0 April 3, 2002 07:27
Temperature in vessel during throttling process Astrid Main CFD Forum 2 January 31, 2001 03:34


All times are GMT -4. The time now is 01:18.