
[Sponsors] 
March 5, 2017, 00:14 
calculate friction factor & nusselt number

#1 
New Member
soheil
Join Date: Mar 2017
Posts: 7
Rep Power: 9 
Hi all
I want to simulate tube bank one of my boundary condition in flow direction is periodic wile another is symmetric. (tube temperature is cosntant) I want to calculate friction factor and local and global Nusselt number 1) for calculate friction factor I need to calculate pressure drop across a row how can I calculate this pressure drop across one single tube? 2) can I calculate local Nusselt number by calculate heat flux for each theta and then use the flow formula: Nu=q(theta)/(TbTs) where Ts is tube temperature & Tb is T inlet which is constant please help me thanks 

March 8, 2017, 15:37 

#2 
New Member
soheil
Join Date: Mar 2017
Posts: 7
Rep Power: 9 
please someone help me


March 8, 2017, 17:34 

#3 
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,683
Rep Power: 66 
For streamwise periodic, your input is either a specified pressure drop or a massflow rate. If you're using massflow rate, then Fluent calculates the pressure drop for you.
You have the wrong equation for Nusselt number. Nusselt number is dimensionless. It looks like you have the heat transfer coefficient. If your reference temperature is constant, it is simple. Go to the reference values pane and set the reference temperature to your inlet temperature. Also set the reference length to the appropriate reference length that you need to calculate the Nusselt number (it's probably your tube diameter or radius). Fluent will calculate the local Nusselt number for you. Alternatively, you can let Fluent calculate the local heat transfer coefficient and you can calculate Nusselt number yourself. However, you still need to specify the reference temperature in order to get the right heat transfer coefficient. How do you define global Nusselt number? It should be pretty straightforward to calculate. Usually it is some type of surface average. 

March 11, 2017, 09:30 

#4  
New Member
soheil
Join Date: Mar 2017
Posts: 7
Rep Power: 9 
Quote:
thanks for your response I calculate global Nusselt number by : Nu = hD/k ; where h= mdot * cp * (ToutTin) / ( A total * LMTD ) I define 2 line in inlet and outlet to calculate Tin & Tout. I do what you say and I get good result for Nusselt number but I have 30% error for friction factor how can I solve it? Fluent give me pressure drop per meter; which I should multiply it to whole domain length. Are reference values effect in calculate pressure drop? what should I set length reference value for this case? 

Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
[mesh manipulation] Mesh Refinement  Luiz Eduardo Bittencourt Sampaio (Sampaio)  OpenFOAM Meshing & Mesh Conversion  42  January 8, 2017 12:55 
Compressor Simulation using rhoPimpleDyMFoam  Jetfire  OpenFOAM Running, Solving & CFD  107  December 9, 2014 13:38 
How to calculate Nusselt number  SeRGeiSarov  Main CFD Forum  4  May 6, 2009 01:57 
how to calculate Nusselt number?  prayskyer  Main CFD Forum  0  June 17, 2006 20:57 
[Commercial meshers] Trimmed cell and embedded refinement mesh conversion issues  michele  OpenFOAM Meshing & Mesh Conversion  2  July 15, 2005 04:15 