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

Computing Nusselt number

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 15, 2016, 14:16
Lightbulb Computing Nusselt number
  #1
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
http://www.cfd-online.com/Forums/ima.../icon3.gifDear Fellows,

I have modeled a quarter pipe with its solid thickness modeled too. I have applied the flux over wall as 3500 W/m2. I have the formula for havg= flux/(Tavg,fluid-Tinside). The T inside is the temperature at the lower end of wall, the region that touches fluid.
In experiment Tinside is measured via thermocouples that are installed across the tube length wherever the flux is applied. These TC however measures the inner temperature of the wall.
Nusselt number is Nu=havg*Di/k. Di=inned dia, and k=thermal conductivity of fluid.
My computed Nu is very low from experiment. I am using Fluent, and applied flux on top wall. and specify coupled BC on interface. This creates wall shadow.I do not use any heat value (flux or temp) except on top wall. I saw as well "via System coupling" written in these BC. do I need to turn it on too? In fluent I take Area weighted average for inlet and outlet (Ttotal) while for Thermocouples I made Isolines at TC positions and took Temp (total) with Area weighted average.

The error is more than 10 % from experiment. http://www.cfd-online.com/Forums/images/icons/icon3.gif
Shamoon Jamshed is offline   Reply With Quote

Old   February 18, 2016, 10:52
Default
  #2
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Please help, anyone here?
Shamoon Jamshed is offline   Reply With Quote

Old   February 22, 2016, 04:11
Default
  #3
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Please help me guys, no heat transfer expert here?
Shamoon Jamshed is offline   Reply With Quote

Old   February 25, 2016, 13:51
Default
  #4
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Quote:
Originally Posted by Shamoon Jamshed View Post
Please help me guys, no heat transfer expert here?
?????????????????????????
Shamoon Jamshed is offline   Reply With Quote

Old   March 3, 2016, 01:08
Default
  #5
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Please reply, anyone expert in heat transfer?
Shamoon Jamshed is offline   Reply With Quote

Old   March 3, 2016, 01:13
Default
  #6
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
Ok, I figured out one way, For inner wall temperature I used the relation with some proprer understanding of it (that previously was not ) and managed to get results close to experiment. But here are two comments:

1. If for Tavg, fluid I take only pressure outlet massweighted temperature, I come close to experiment. If I take the mean of inlet and outlet , My error remains as low as 7 % and as high as 18%.

2. Turbulence modelling
=================
The results of k-omega SST matches (somewhat cloase max error 11%) at low Re, while k-epsilon Standard matches at high Reynolds number. Whats the point?
Shamoon Jamshed is offline   Reply With Quote

Old   October 28, 2016, 08:44
Default Nusselt and friction factor with two turbulence models
  #7
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 270
Rep Power: 14
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
This is of much surprise that no one is replying. Let me qutoe my problem again:

I am comparing heat transfer and friction factor results for a pipe with grooves in it. I am comparing Nusselt and friction factor in the two cases. The results are very surprising. The nusselt is comparable to experiment with k epsilon while friction is good in case of k omega. Could you please tell me the discrepancy? Please help me as I am not getting why two models are behaving differently.
Shamoon Jamshed is offline   Reply With Quote

Reply

Tags
havg, nusselt, thermocouples, tinside

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
[snappyHexMesh] snappyHexMesh sticking point natty_king OpenFOAM Meshing & Mesh Conversion 10 August 5, 2019 19:18
[mesh manipulation] Mesh Refinement Luiz Eduardo Bittencourt Sampaio (Sampaio) OpenFOAM Meshing & Mesh Conversion 42 January 8, 2017 12:55
decomposePar -allRegions stru OpenFOAM Pre-Processing 2 August 25, 2015 03:58
AMI interDyMFoam for mixer danny123 OpenFOAM Running, Solving & CFD 4 June 19, 2013 04:49
[Commercial meshers] Trimmed cell and embedded refinement mesh conversion issues michele OpenFOAM Meshing & Mesh Conversion 2 July 15, 2005 04:15


All times are GMT -4. The time now is 07:16.