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

Natural convection in a vertical cylinder

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 14, 2007, 05:38
Default Natural convection in a vertical cylinder
  #1
Virginie
Guest
 
Posts: n/a
Hello,

I want to model heat transfer (buyoancy-induced flow, diffusion) in a vertical cylinder with a high aspect ratio (L>>r). First I choose a 2D configuration (X-Y). The boundary conditions are : X = r et X = -r (lateral edges): wall conditions, non heat flux (insulated) Y = 0 (bottom): wall condition, fixed temperatute at 55C Y = L (top): wall condition, fixed temperature at 15C The interior is filled with water, I use the boussinesq approximation for density calculation. Gravitationnal acceleration is set 0 in x direction and -9.81 in Y direction. I do a steady simulation. Initial conditions are a 0 gauge pressure and a 35 C temperature in all the domain. When I run the model, it is solving the energy equation but seems not to solve the flow equation, or not to take into account the gravity. Indeed, when I view the results, the static pressure remain 0 in the model (absolute pressure equal operating pressure), density is not modified too, only a temperature gradient is calculated by thermal diffusion. I wonder why I have not any hydrostatic pressure gradient in Y direction, and how can be the density uniform whereas there is a temperature gradient, the results make me think that gravitationnal acceleration is not working.Thanks for your help.

Virginie

  Reply With Quote

Old   September 14, 2007, 06:18
Default Re: Natural convection in a vertical cylinder
  #2
Joe
Guest
 
Posts: n/a
Gravity is not turned on as disregarding any thermal density fluctuation modeling you should still get a hydrostatic pressure distribution. Fix that and your other problems will likely be solved.
  Reply With Quote

Old   September 18, 2007, 00:40
Default Re: Natural convection in a vertical cylinder
  #3
Jun Cai
Guest
 
Posts: n/a
I think there maybe two reasons: 1. you didnot set the thermal expansion coefficient in "material" panel; 2. The property values you set resulted in a very low Ra(Rayleigh number). if Ra is very low, the buoyancy-drived flow will not take place. the heat tranfer is thermal conduction, not convective heat transfer. for details, you can see the fluent help.
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Natural convection in an infinite vertical cavity Zeppo STAR-CCM+ 3 August 31, 2013 02:29
natural convection problem with radiation jorien CFX 0 October 14, 2011 09:26
natural convection from vertical plate ghassan77 FLUENT 0 January 3, 2011 02:31
Natural convection over a vertical wall mimi FLUENT 5 February 3, 2008 21:05
natural convection in a vertical heated duct. SHANTANU CHAKRABORTY Phoenics 1 June 18, 2001 09:12


All times are GMT -4. The time now is 01:48.