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

UDF for heat transfer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 15, 2007, 01:56
Default UDF for heat transfer
  #1
ranjit
Guest
 
Posts: n/a
Can anyone help me with creating a udf for heat transfer between ice and air...Since this is the first time i am going to attempt writing a udf, even a basics help is welcome..
  Reply With Quote

Old   January 15, 2007, 03:42
Default Re: UDF for heat transfer
  #2
ranjit
Guest
 
Posts: n/a
please someone atleast suggest the macros that can be used , the logic, etc , i just need something to build upon..
  Reply With Quote

Old   January 15, 2007, 15:15
Default Re: UDF for heat transfer
  #3
Sujith S Nair
Guest
 
Posts: n/a
Are you simulating air flow over ice with ice as wall boundary condition. Then you can use a constant heat flux or a heat flux profile using DEFINE_PROFILE macro.May i know what is the exact physics in your model?
  Reply With Quote

Old   January 16, 2007, 08:57
Default Re: UDF for heat transfer
  #4
ranjit
Guest
 
Posts: n/a
thanks for the response

yeah basically my aim is to find the amount of chilling caused by airflow over ice. Actually an ice-water mixture is to flow inside a tube , and the air flows over the tube.. I need to find the amount of heat that the ice-water mixture can absorb.

Can such a problem be done in multiphase flows in fluent without UDF?. As of now i am treating it as a convection problem between air and ice, bur dont know how to bring the latent heat of "melting of ice" into picture..

Thanks for the suggestion to use Heat flux macros, i ll look into it.. Do you have any idea how to formulate a governing equation for this.. Any help besides that is also welcome.

Thanks!
  Reply With Quote

Old   January 16, 2007, 10:26
Default Re: UDF for heat transfer
  #5
Venkatesh V
Guest
 
Posts: n/a
What is the size of ice particles interms of tube dia or volume fraction.
  Reply With Quote

Old   January 16, 2007, 10:37
Default Re: UDF for heat transfer
  #6
ranjit
Guest
 
Posts: n/a
the volume fraction will be around 0.4 how is that going to help?
  Reply With Quote

Old   January 16, 2007, 12:22
Default Re: UDF for heat transfer
  #7
Venkatesh V
Guest
 
Posts: n/a
I thought if volume fraction is low you can consider using DPM (Multiphase) and you can control the melting using UDF is needed.
  Reply With Quote

Old   January 16, 2007, 21:18
Default Re: UDF for heat transfer
  #8
ranjit
Guest
 
Posts: n/a
@venkatesh

but how to specify three different materials in fluent, ice , water and air. Also i thought multiphase in fluent is only for immiscible fluids, water and ice are miscible. What approach do you suggest
  Reply With Quote

Old   January 17, 2007, 08:25
Default Re: UDF for heat transfer
  #9
ranjit
Guest
 
Posts: n/a
any further help please..
  Reply With Quote

Old   January 17, 2007, 09:53
Default Re: UDF for heat transfer
  #10
Hugo
Guest
 
Posts: n/a
Hi. Is this a steady state problem? is the ice/water mixture flowing down the tube? Is the amaount of heat exchanged actually melting the ice? Options: - a domain of only air and a solid tube. Define specific heat of tube to be temperature dependant, with very very high value (2.27 MJ/kg/K) in the range 272.5<T<273.5. see example 1 in 4.3.14 DEFINE_PROPERTY section of UDF guide for format. Can't find syntax for specific heat capacity there. Anyone? - hand calculate it, using heat transfer correlation from eg. Bejan, 2004. Convecton Heat Transfer. Wiley&Son. p.363. Hugo.
  Reply With Quote

Old   January 17, 2007, 11:40
Default Re: UDF for heat transfer
  #11
ranjit
Guest
 
Posts: n/a
Thanks, will give it a try surely... is it sufficient to give the define_property macros alone? i am new to writing UDF's
  Reply With Quote

Old   January 18, 2007, 05:34
Default Re: UDF for heat transfer
  #12
Hugo
Guest
 
Posts: n/a
Sorry, me last message was truncated - I was going to say have variable heat capacity, with a value of 2.27 MJ/kg/K in the range 272.5 < T < 273.5, following the format in example 1 in 4.3.14 of UDF manual, using DEFINE_PROPERTY macro:

DEFINE_PROPERTY(cell_viscosity,c,t) { real mu_lam; real temp = C_T(c,t);

if (temp > 288.)

mu_lam = 5.5e-3; else if (temp > 286.)

mu_lam = 143.2135 - 0.49725 * temp; else

mu_lam = 1.;

return mu_lam; }

obviously you'll have to change it to specific heat capacity.

Not sure I understood you question " is it sufficient to give the define_property macros alone?" - could you give more details?

Hugo.

  Reply With Quote

Old   January 18, 2007, 10:43
Default Re: UDF for heat transfer
  #13
ranjit
Guest
 
Posts: n/a
thanks for the reply, but in the same documentation, if you scroll up its given that "specific heat values can only be read and not assigned in fluent"..

does that make this method ineffective?

  Reply With Quote

Old   January 18, 2007, 11:36
Default Re: UDF for heat transfer
  #14
Sujith
Guest
 
Posts: n/a
ya... in Fluent specific heat cannot be specfied through a UDF, But you can give a temperature dependant polynonial/piecewise polynomial using the options availble in the Materials panel.

--sujith
  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
How to add a UDF to a compiled UDF library kim FLUENT 3 October 26, 2011 21:38
UDF programming fullmonty FLUENT 5 June 30, 2011 02:40
Mass Transfer UDF using Fluent VOF Anirudh_Deodhar FLUENT 0 February 7, 2011 16:10
I need UDF help. S.Whitney FLUENT 0 October 15, 2007 11:29
Convective Heat Transfer - Heat Exchanger Mark CFX 6 November 15, 2004 16:55


All times are GMT -4. The time now is 11:10.