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

negative heat transfer coeffecient

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 2, 2005, 00:28
Default negative heat transfer coeffecient
  #1
sireesha
Guest
 
Posts: n/a
hello all, I am trying to simulate natural convection over a vertical plate, but i am getting a negative surface heat transfer coeffecient. why is this?
  Reply With Quote

Old   August 2, 2005, 01:26
Default Re: negative heat transfer coeffecient
  #2
rajani
Guest
 
Posts: n/a
heat transfer coefficient will be calculated by using heat flux divided by the temperature diff which is equal to (Twall - Treference). if ur Treference is greater than Twall u get a negetive h. check for the reference values and see if ur plate is g etting heated up or is it getting cooled....
  Reply With Quote

Old   August 3, 2005, 22:57
Default Re: negative heat transfer coeffecient
  #3
sireesha
Guest
 
Posts: n/a
Thanx rajani,

Inspite of having my wall temperature greater than the reference temp value the heat tranfer coefficient values are negative.

I obained negative heat transfer coeffecient for pr = 0.72 and the temperatures being below 0 degrees celcius (wall temp = 257K (-16C), air temp = 247 (-26C))

however for temperatures in the region of 900K, where pr = 0.72 (from internet), I obtained positive heat transfer coeffecients, but some how my results dont appear to correlate properly with the theoritical results.

I need to know the exact thermal properties based on prandtl number for pr = 0.69 and pr = 0.72.

Unfortunately, i browsed the internet as well as many books but founds different answers.

Can any of you give the thermal properties of air at pr=0.72.I need air temp,desity, thermal conductivity,viscosity and specific heat properties.

regards

Sireesha Pasari
  Reply With Quote

Old   August 4, 2005, 00:19
Default Re: negative heat transfer coeffecient
  #4
Swarup
Guest
 
Posts: n/a
try Perry's Chemical Engineers' Handbook. you should look at it carefully though. it is the properties that will decide Pr value and not vice versa and there are three of them involved in its definition. for all substances, you will find properties as a function of temperature.

Swarup
  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
[blockMesh] BlockMesh FOAM warning gaottino OpenFOAM Meshing & Mesh Conversion 7 July 19, 2010 15:11
Convective / Conductive Heat Transfer in Hypersonic flows enigma Main CFD Forum 2 November 1, 2009 23:53
[blockMesh] Axisymmetrical mesh Rasmus Gjesing (Gjesing) OpenFOAM Meshing & Mesh Conversion 10 April 2, 2007 15:00
negative heat transfer coefficient Sigrid Andreae CFX 1 February 26, 2005 08:13
Convective Heat Transfer - Heat Exchanger Mark CFX 6 November 15, 2004 16:55


All times are GMT -4. The time now is 16:38.