CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Unsteady Heat Transfer Modeling

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

LinkBack Thread Tools Search this Thread Display Modes
Old   June 5, 2003, 11:28
Default Unsteady Heat Transfer Modeling
Posts: n/a

I am having difficulties getting Fluent to accurately model the following unsteady heat transfer model:

I have a fluid-solid interface problem (i.e. a steel pressure vessel containing propane), wherein heat is applied to a small part of the exterior of one wall. The idea is that the heat transfer through the wall will cause natural convection (and thus fluid motion) of the propane within the tank.

However, after running the simulation with 100 time steps of approximately 5 seconds the fluid remains stationary, and the temperature remains the same throughout the both the fluid and the walls of the tank.

I am using the following conditions in Fluent 6.0:

Segregated Unsteady 1st Order Implicit Solver Energy equation enabled Laminar viscous flow model with visous heating Piecewise linear density with temperature Constant material properties PISO pressure-velocity coupling 20 iterations per time step

My walls are defined with a finite thickness and have a specified heat flux with a specified shell conduction.

Does anyone know if I am missing something that prevents me from getting a valid solution? Any suggestions or changes that you can think of? Could this be a pre-processing problem (i.e. some form of error in generating the mesh in Gambit?)

Thank-you very much!

  Reply With Quote

Old   June 6, 2003, 08:09
Default Re: Unsteady Heat Transfer Modeling
Posts: n/a
Hi there,

This is a wild stab in the dark because i had a similar problem.

Make sure you have scaled your mesh (grid/scale).Im assuming you created your geometry in mm and fluent reads it in meters. If this is the case as in my problem, the heat had to travel through a 2m thick wall instead of a 2mm!!!

Hope this helps.

Good luck
  Reply With Quote

Old   June 6, 2003, 10:23
Default Re: Unsteady Heat Transfer Modeling
Posts: n/a
Thanks for response, but the scale in Fluent is o.k. that is not the problem.
  Reply With Quote

Old   June 6, 2003, 17:41
Default Re: Unsteady Heat Transfer Modeling
Alex Munoz
Posts: n/a

I have never model unsteady heat transfer, however I have model unsteady flow field.

Reading your case setup, I wonder why do you choose 1er order discretization, I really suguest that you choose second order for all the equations and simple c as velocity pressure coupling.

The selection for PISO must to have certain condition that you should read before appling it to your case.

Best regards

Alex Munoz
  Reply With Quote

Old   June 6, 2003, 18:40
Default Re: Unsteady Heat Transfer Modeling
Posts: n/a
I would suggest you to perform staedy analysis first. If you have already opened gravity, you should trigger the flow in the direction you think it is going to flow by using the initial conditions panel (initial velocity in that direction -opposite to the gravity- which is very close to zero, like 0.001 m/s, may help it) What makes me think is that even if the natural conv. did not work properly, there should have been changes in the temperature. So the problem may be due to the non-matching mesh at the interface.

regards emre
  Reply With Quote

Old   June 7, 2003, 02:28
Default Re: Unsteady Heat Transfer Modeling
Posts: n/a
may i know that the properties of u's fluid is constant or not? you should define the fluid properties, specially density will change with temperature, can use some function provided in fluent.

we know that convection is due to density change, so the density of the fluid cannot be constant.

hope this help.
  Reply With Quote


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
calculate heat transfer coefficient in repeated geometry mullenc525 CFX 4 January 24, 2017 15:30
Modeling heat transfer through a porous media harimighty FLUENT 3 July 23, 2016 06:11
Modelling the heat transfer during compression and cooling of natural gas pano Main CFD Forum 0 December 10, 2010 16:53
Conjugate heat transfer and radiation modeling questions shankara.2 FLUENT 0 April 21, 2009 16:55
heat transfer modeling map FLUENT 5 December 15, 2008 13:02

All times are GMT -4. The time now is 14:17.