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

2d Heat transfer external flow

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 4, 2008, 20:47
Default 2d Heat transfer external flow
  #1
Richard belcher
Guest
 
Posts: n/a
Im doing a study on a heated cylinder in a uniform cross flow situation ,and my wish is to calculate the avg nusselt number over the surface of the cylinder for various reynolds numbers.

at the moment my results are out by by 40%ish percent from known correlations and my mesh is very refined around the cylinder (yplus 0.1-0.5)and has been checked by others.

Cylinder is defined as fixed 40C temperature, SST and thermal energy models. 100 cycles per timestep

What i dont understand is i believe all my expressions for calculating it are correct but i would appreciate if someone could cross check them for me as it is been a few days now troubleshooting this problem.

here is my list of expressions , my approach is to find heat flux using CFX and use the convection eqn to find h. and then using that to calculate Nu (my diam = 19mm ,0.019m)

It also requires i define Cp (or so it tells me) but i am unsure where i can input this , couldnt turn up anythign in help.

Ts = areaAve(T)@cylinder

q = areaAve(Wall Heat Flux)@cylinder

h = q/(Ts-Tinf) Tinf = 298K

(h*0.019[m])/(areaAve(Thermal Conductivity)@cylinder)

and for defning outlet temperature(m.cp.deltaT)

(((area()@inlet)*q)/(mdot*Specific Heat Capacity at Constant Pressure )) + Tinf

Thanks alot,

  Reply With Quote

Old   August 4, 2008, 21:42
Default Re: 2d Heat transfer external flow
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

I assume you have a fully validated model and things like timestep, mesh, physics are all OK.

If you are in the laminar flow regime then hopefully you can get the heat transfer better than that. If you are turbulent the accuracy might be inherent in the correlations and no amount of model tweaking will get it right. Also, if turbulent then consider the turbulence transition model. It will make a big difference to the heat transfer is some regimes.

Other comments: * Consider using the in-built h variable rather than calculating it yourself. * Consider using variable properties for the air (eg viscosity, k, Cp versus temperature)

Glenn Horrocks
  Reply With Quote

Old   November 23, 2020, 04:34
Default External flow over a cylinder to plot Nusselt number variation on cylinder surface at
  #3
New Member
 
Velmareddy Prudhwidhar Reddy
Join Date: Nov 2020
Posts: 1
Rep Power: 0
VELMAREDDY PRUDHWIDHAR is on a distinguished road
Hi
I am trying to validate my results.
For validation, I have considered a Cylinder in external cross flow.
Steady state problem.
Dia of cylinder = 1m
Inlet Velocity= 29.21m/sec
Flow medium is air with Re= 2e6
Outlet pressure boundary
Symmetry on either sides
I have taken constant heat flux at cylinder wall surface with no slip condition=1000..
Y+ value <1
Activated both energy and turbulence models(k-w SST).
Convergence is set to 10e-05
Plotting Surface Nusselt number is resulting in a large difference
VELMAREDDY PRUDHWIDHAR is offline   Reply With Quote

Old   November 23, 2020, 16:47
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
FAQ: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks 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
Water subcooled boiling Attesz CFX 7 January 5, 2013 03:32
heat transfer with laminar flow David_010 OpenFOAM 10 November 16, 2012 16:05
Double layer Microchannel - Flow and Heat transfer priyanka.asp FLUENT 0 September 7, 2010 20:04
pipe flow with heat transfer Fabian OpenFOAM 2 December 12, 2009 04:53
Flow and Heat transfer in a Thawing chamber B.Prabhu FLUENT 0 May 12, 2002 15:13


All times are GMT -4. The time now is 12:45.