# Energy balance

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

 August 6, 2014, 13:13 Energy balance #1 New Member   Join Date: Jul 2014 Posts: 15 Rep Power: 4 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

 August 7, 2014, 04:59 #2 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,296 Rep Power: 19 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.

 August 7, 2014, 09:54 Energy balance #3 New Member   Join Date: Jul 2014 Posts: 15 Rep Power: 4 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.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post MdoNascimento STAR-CCM+ 0 March 13, 2014 13:15 m.beh FLUENT 1 October 17, 2011 17:21 David_010 OpenFOAM Running, Solving & CFD 0 January 20, 2011 06:21 zdz198728 Main CFD Forum 1 November 19, 2009 01:07 James Willie FLUENT 11 August 10, 2005 04:58

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