CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Energy balance

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 6, 2014, 13:13
Default Energy balance
  #1
New Member
 
Join Date: Jul 2014
Posts: 15
Rep Power: 4
atlan is on a distinguished road
Hi all,
Can anyone advise me please how to check the energy balance in a simple straight tube?
I have tube with one inlet and one outlet and one wall. At the inlet I impose constant temperature and at the wall a heat flux.
When I use wallHeatFlux utility to calculate the power it shows at the inlet and outlet values in order lower than the heat loss at the wall.
However, if I roughly estimate the power from the mass flow rate and the temperature difference between inlet and outlet (cp*m*dt) it looks similar to the heat loss trough the wall. But the problem is that there is already temperature profile at the inlet and I cannot set the outlet temperature exactly.
The solver is buoyantSimpleFoam.
Thanks
Atlan
atlan is offline   Reply With Quote

Old   August 7, 2014, 04:59
Default
  #2
Senior Member
 
RodriguezFatz's Avatar
 
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,296
Rep Power: 19
RodriguezFatz will become famous soon enough
I have no experience with "wallHeatFlux" utility, but just from the wording: Maybe it just calculates the heat flux as a spatial derivative of temperature times the heat conductivity, because that is how you would calculate the heat flux at a wall:
q=lambda*dT/dy.
At the inlet and outlet you don't have a wall but the moving fluid. Thus, "q" gets an additional component by the heat that is transported by the moving fluid rho * u * E0.
This could be the reason the balance doesn't work how you do it, because heat conduction at inlet and outlet ist just way less than convective heat transport.
__________________
The skeleton ran out of shampoo in the shower.
RodriguezFatz is offline   Reply With Quote

Old   August 7, 2014, 09:54
Default Energy balance
  #3
New Member
 
Join Date: Jul 2014
Posts: 15
Rep Power: 4
atlan is on a distinguished road
You are right. I have realized, it is not possible to use the wallHeatFlux utility for inlet and outlet. It is applicable only for walls.
atlan 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
Natural convection, problems with total energy balance MdoNascimento STAR-CCM+ 0 March 13, 2014 13:15
volumetric reaction and energy balance? m.beh FLUENT 1 October 17, 2011 17:21
Energy balance error with high prandtl numbers. David_010 OpenFOAM Running, Solving & CFD 0 January 20, 2011 06:21
energy balance zdz198728 Main CFD Forum 1 November 19, 2009 01:07
HELP needed: Energy balance in gaseous combustion James Willie FLUENT 11 August 10, 2005 04:58


All times are GMT -4. The time now is 02:07.