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

Why Fluent give me wrong heat transfer coefficient?

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 21, 2015, 09:13
Default Why Fluent give me wrong heat transfer coefficient?
  #1
Senior Member
 
Join Date: Jan 2011
Posts: 338
Rep Power: 16
mariam.sara is on a distinguished road
Hello I did simple heat transfer case represented by water flowing in a tube with uniform heat flux at tube wall I run the case in Fluent but it gives me incorrect values for heat transfer coefficient from reports>surface integrals>wall fluxes>surface heat transfer coefficient with unknown reason? I fixed all reference values but the heat transfer coefficient values still incorrect??

Mariam
mariam.sara is offline   Reply With Quote

Old   July 23, 2015, 04:27
Default
  #2
Senior Member
 
Join Date: Jan 2011
Posts: 338
Rep Power: 16
mariam.sara is on a distinguished road
No one know to answer my question?
mariam.sara is offline   Reply With Quote

Old   July 23, 2015, 09:04
Default
  #3
Member
 
Shaheer
Join Date: Jul 2015
Posts: 37
Rep Power: 10
Shaheer is on a distinguished road
I want to add if i have a fluid flowing over a surface with high temperature and i dont know the heat flux of the system rather i want to find out from the flow. Is it possible ? because most of the ANSYS tutorials on heat transfer assumes a heat flux then it just shows how the heat is being distributed. I know the temperature difference and my main interest is how the flow will occur and when its occuring how much will be the the heat flux.
Shaheer is offline   Reply With Quote

Old   July 24, 2015, 02:53
Default
  #4
Senior Member
 
Join Date: May 2012
Location: Melbourne
Posts: 161
Rep Power: 13
Steffen595 is on a distinguished road
how can you solve that equation? If you don't have a temperature and a flow rate you only got the heat coefficent. You cannot solve that equation manually.
The FAQ for boundaries for a stable/soluable simulation say give boundary conditions you can reproduce in a lab.
Steffen595 is offline   Reply With Quote

Old   July 24, 2015, 18:04
Default
  #5
Senior Member
 
Join Date: Jan 2011
Posts: 338
Rep Power: 16
mariam.sara is on a distinguished road
Steffen595 I have known heat flux on the pipe wall but fluent give me incorrect heat transfer coefficient when I compare with experiment may you tell me the reason why this happen with me?

mariam
mariam.sara is offline   Reply With Quote

Old   July 24, 2015, 19:40
Default
  #6
Senior Member
 
Join Date: May 2012
Location: Melbourne
Posts: 161
Rep Power: 13
Steffen595 is on a distinguished road
sorry, cannot help you on that
Steffen595 is offline   Reply With Quote

Old   July 26, 2015, 04:39
Default
  #7
Senior Member
 
Join Date: Jan 2011
Posts: 338
Rep Power: 16
mariam.sara is on a distinguished road
I asked general question?? really no one know to answer it??
mariam.sara is offline   Reply With Quote

Old   July 26, 2015, 19:28
Default
  #8
Senior Member
 
Join Date: May 2012
Location: Melbourne
Posts: 161
Rep Power: 13
Steffen595 is on a distinguished road
Don’t you have to define a HTC in the 1st place if you calculate heat transfer? So then there will be problems with what you defined and what is happening?
The heat flow is not evenly distributed I guess, so there may be problems? I.e. constant wall thickness, but different flow, how to average the HTC?
Did you check anything else, heat and mass coming in and out?
Is your simulation fully converged?
Steffen595 is offline   Reply With Quote

Old   July 28, 2015, 05:50
Default
  #9
Senior Member
 
Join Date: Jan 2011
Posts: 338
Rep Power: 16
mariam.sara is on a distinguished road
My geometry is so simple its just 2D tube the mesh quality is good the solution is converge and the prove for the solution is correct I get correct temperature distribution. I mentioned in my first post HTC predicted from surface integral (see my first post above) but its values seems incorrect when compared to experiments??
mariam.sara is offline   Reply With Quote

Old   July 28, 2015, 08:01
Default
  #10
Senior Member
 
Join Date: May 2012
Location: Melbourne
Posts: 161
Rep Power: 13
Steffen595 is on a distinguished road
that sound like a recent post. In 2d and the velocity was way off. It had to do with, in 2d the depth is set as 1m. So if you calculate with surface integral, maybe assume the surface with 1m deep?
There are way less people doing CFD than CAD, so this forum is less busy. And some problems I guess are pretty rare.
Steffen595 is offline   Reply With Quote

Old   July 28, 2015, 12:28
Default
  #11
Senior Member
 
ghost82's Avatar
 
Rick
Join Date: Oct 2010
Posts: 1,016
Rep Power: 26
ghost82 will become famous soon enough
My 10 minutes test shows no problem in calculating Nusselt/h values in 2d axisymmetric pipe.

Once you have finished your simulation if you want an avarage value of Nusselt or h just go to reports and perform area-weight surface integral of surface heat transfer coefficient on the surface of interest.
This will give you an average h, if you want Nusselt number just multiply this h by Diameter/(thermal conductivity).

In my test:
Nusselt calculated with:
0.023*Re^0.8*Pr^0.4 = 83.32 (Re=13000, smooth wall)

Nusselt from Fluent = 85.40

Daniele
__________________
Google is your friend and the same for the search button!
ghost82 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
Heat Transfer Problem in FLUENT eng_yasser_2020 FLUENT 3 February 19, 2019 03:13
UDF to change heat transfer coefficient with wall temperature emmkell Fluent UDF and Scheme Programming 18 August 7, 2018 04:44
Heat trasfer coefficient in a pipe - Fluent elios FLUENT 1 February 6, 2015 15:18
Wall y+, heat transfer coefficient crevoise STAR-CCM+ 0 January 29, 2014 10:44
Convective Heat Transfer - Heat Exchanger Mark CFX 6 November 15, 2004 16:55


All times are GMT -4. The time now is 02:36.