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

Model for a profile temperature inside a digester

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 7, 2011, 13:12
Default Model for a profile temperature inside a digester
  #1
New Member
 
vincenzo
Join Date: Nov 2011
Posts: 3
Rep Power: 5
enzome is on a distinguished road
Hi to everyone. I am not able to solve this problem.
I'm working on a digester which has 2 velocity inlets at the top and 2 pressure outlet at the bottom. The sludge is entering from the top, it is moving in the digester and it is going out from the pipes at the bottom. I already have the solution that shows the movement of the fluid, streamlines, velocity vectors etc. Now I have to look for the correct model (always in monophase) that let me find the profile of temperature when the sludge enter with a temperature inside the digester and goes out with another a bit lower. That is because the microorganisms which are inside could die if there is a change of + or - 1 C.
Questions:
Should I create 2 regions, solid (Concrete) and liquid (sludge)?
Should I create 2 Physics continuum? (solid and liquid)?
Does anyone have a tutorial whit a similar problem?!
Please help me, and don't hesitate to ask for additional data. Thank you
enzome is offline   Reply With Quote

Old   November 7, 2011, 18:52
Default
  #2
Member
 
Join Date: Feb 2011
Location: DE-PB
Posts: 56
Rep Power: 6
willimanili is on a distinguished road
Yes, you need two regions and two physics continua. Set the concrete region to solid with constant density and segregated temperature, the sludge should be modeled as a liqiud region also with segregated temperature. Important is that you have the right material values for the sludge as dyn. viscosity, heat capacity, density and heat conductivity. Because you said that the bacteria will die if there is a change of temperature more than +/- 1 degree is think you dont need to take temperature depended material values so you can set them all to constant. You can change the values under the physics continuum child.
Also very important is how the digester get in contact to the environment?! You need to specify the thermal specification of the outer boundaries of your digester as close to reality as possible because they will have a main influence to the solution.
willimanili is offline   Reply With Quote

Old   November 8, 2011, 04:41
Default
  #3
Senior Member
 
Ping
Join Date: Mar 2009
Posts: 223
Rep Power: 9
ping is on a distinguished road
this is good advice but can i add that a quicker and possibly less accurate method is to use your current model and apply a convection thermal specification on the outer wall, then you also need the the heat transfer coef which includes the conduction through the contrete and the external transfer to the air, and an external air temp.. a good first step method which is much easier to get going and if the tank is pretty constant in thickness then probably just as accurate. and if even greater accuracy is required then you might need to model the outside air flow too to get more accurate tank external heat transfer coefs.
ping is offline   Reply With Quote

Old   November 9, 2011, 06:28
Default
  #4
New Member
 
vincenzo
Join Date: Nov 2011
Posts: 3
Rep Power: 5
enzome is on a distinguished road
Quote:
Originally Posted by ping View Post
this is good advice but can i add that a quicker and possibly less accurate method is to use your current model and apply a convection thermal specification on the outer wall, then you also need the the heat transfer coef which includes the conduction through the contrete and the external transfer to the air, and an external air temp.. a good first step method which is much easier to get going and if the tank is pretty constant in thickness then probably just as accurate. and if even greater accuracy is required then you might need to model the outside air flow too to get more accurate tank external heat transfer coefs.
Thank you to both of them. Without reading you I was trying to work with the advice of Ping cos the thickness is constant. I've calculated the heat transfer coef of the conduction through the concrete ( i supposed a plane surfaces cos the diameter is quite big), K=thermal conductivity concrete/ thickness= 7,5 W/m^2K. how can i evaluate the conduction through the external transfer to the air? I can suppose an air temperature in the worst conditions in summer and winter (35 Celsius and 5 Celsius, we are in Spain )And after it, should I sum to the one calculated above? Thank you for the useful suggestions
enzome is offline   Reply With Quote

Old   November 11, 2011, 15:44
Default
  #5
Senior Member
 
Join Date: Oct 2009
Location: Germany
Posts: 637
Rep Power: 12
abdul099 is on a distinguished road
You could calculate a heat transfer resistance from a heat conductivity through the wall and the heat transfer to the outer air. BUT:

Heat transfer to the outside air depens on:
- wall temperature
- air temperature
- heat transfer coefficient, which depens on the geometry, wind speed, surrounding objects etc.

So it's too complicated to invent a single value. I advice to follow ping's suggestions: Either live with the inaccuracy or model the outer air flow.
abdul099 is offline   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
Use of k-epsilon and k-omega Models Jade M Main CFD Forum 12 June 2, 2015 13:16
Superlinear speedup in OpenFOAM 13 msrinath80 OpenFOAM Running, Solving & CFD 18 March 3, 2015 06:36
Please Help! Temperature profile UDF for 3D geometry subhankar_bhandari FLUENT 0 August 16, 2010 08:40
Linear Temperature Profile Ferdous Rana FLUENT 1 April 24, 2006 16:51
Boundary Profile computed with different model Gerd FLUENT 0 November 17, 2005 06:23


All times are GMT -4. The time now is 04:51.