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

laminar/turbulent internal cooling flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 14, 1999, 03:29
Default laminar/turbulent internal cooling flow
  #1
Fabien Coppens
Guest
 
Posts: n/a
Hi everybody.

I am working on CFD of an internal cooling system with mineral oil flowing inside the casing of an X-ray tube for medical imaging scanners. This is a conjuguate heat transfer problem with strong temperature gradients on the inner boundary walls. The oil is considered to be a non-participating medium as far as radiation is concerned. I am a bit confused as to whether or not I should be using turbulence models, and if so which ones. This is important since I really need to obtain heat transfer coefficients along the inner wall boundary surface (the heat source in the model). The oil's physical characteristics, and in particular kinematic viscosity, are very dependent on temperature (nu=14.2e-6 m2.s-1 at T=20C and nu=5.5e-6 m2.s-1 at T=50C). With an inlet tube diameter of 0.5 inch, I get an inlet Reynolds number between 600 and 1600 (based on tube diameter) depending on oil temperature. Inside the casing, velocity magnitudes are below 0.15 m.s-1 except in in some small-diameter areas where the velocity can reach 0.8 m.s-1. Is my assumption of laminar flow correct, and if not what turbulence model would be best suited to my problem ? I'd like to point out that my calculation mesh comes from somebody else and is definitely not refined near walls. Thanks !
  Reply With Quote

Old   April 14, 1999, 12:55
Default Re: laminar/turbulent internal cooling flow
  #2
John C. Chien
Guest
 
Posts: n/a
(1). I think it is a good idea to run a few cases starting from a lower Reynolds number case. In this way, you can get a good feeling about the mesh effect near the wall. (2). As you increase the Reynolds number, you can plot the results against the Re. In this way ,you can establish a trend. It is easier to check the accuracy and reliability of the results this way. (3). since it is not easy to cover the laminar/turbulent transitional flow region, you can then approach the calculation from the fully turbulent flow end and work backward, that is reducing the Re for the turbulent flow calculations. This will establish another trend. (4). For the turbulent flow calculations, the standard wall function appraoch is recommended, mainly because of the concern about the mesh density there. At least, wall function approach is simple and repeatable. (5). At that point, you can explore the turbulence modelling effect and the more difficult ( actually very difficult ) subject of laminar/turbulent transitional flow.
  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
Cross Flow cooling system involving multiple fluids and a solid domain ajaymenon CFX 4 March 8, 2012 18:00
Pipe flow / Internal fluid dynamics with SnappyHexMesh denner OpenFOAM Native Meshers: snappyHexMesh and Others 3 October 13, 2011 09:24
Why Re is different for external and internal flow john FLUENT 3 June 14, 2007 03:53
cooling fluid flow susan burke FLUENT 1 November 24, 2003 11:22
Internal mass flow boundary tommaso CFX 0 July 5, 2002 05:52


All times are GMT -4. The time now is 21:25.