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rosaria.mosciatti
Posts: 5
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 Posted: Wed Jun 01, 2011 1:17 pm Post subject: Heat transfer coefficents |
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Hello,
I'm doing simulation about radiant heating system and radiator with CFD. I must have a thermal balance = 0. I must set the surface tempearature of the radiator and of the floor to obtain a mean internal tempearture = 20°C. To this end i should know how the CFD calculates the heat trasfer coefficents between hot/cold surface and the ambient.
Is there a matematical reference manual?
Thank you!
Rosaria |
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Steve Potter
Posts: 615
Location: newcastle |
| Posted: Thu Jun 02, 2011 3:58 pm Post subject: |
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Hi Rosaria,
DB CFD uses a logarithmic law of the wall function to calculate heat transfer between solid surfaces and adjacent air volumes and consequently the effective heat transfer coefficient can vary from cell to cell.
If the specification of surface heat transfer coefficients is important for your project, you could consider defining the coefficients yourself. You can do this by selecting the "User-defined" option from the "Surface heat transfer" drop list that you will find on the CFD Calculation Options dialog.
Regards,
Steve |
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andfranz
Posts: 104
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| Posted: Wed Dec 28, 2011 11:29 am Post subject: |
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| Steve Potter wrote: | DB CFD uses a logarithmic law of the wall function to calculate heat transfer between solid surfaces and adjacent air volumes and consequently the effective heat transfer coefficient can vary from cell to cell.
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Hi, Steve.
What does "wall function" mean? Are the convective heat transfer coefficients calculated as
h = funct(Dt°)
where Dt° is the difference between the surface temperature and the air temperature and funct is a logarithmic function?
Does a similar inside convection algorithm exist for EnergyPlus simulation? More in general, what is the best solution to integrate the CFD simulation with the EnergyPlus simulation from the point of view of the internal convective heat transfer, in your opinion?
With Regards |
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Steve Potter
Posts: 615
Location: newcastle |
| Posted: Mon Jan 09, 2012 3:22 pm Post subject: |
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Yes, wall functions are a conventional method used by certain CFD turbulence models for calculating surface heat transfer across the fluid layer adjacent to solid boundaries and they assume a logarithmic velocity profile in the vicinity of the wall.
Bear in mind that only radiant heat exchange is accounted for when you import the results of an E+ calculation into DB CFD as boundary conditions. In order to ensure a correspondence between casual gains, you will need to include all of the convective heat gains explicitly in the CFD calculation that you have specified for the E+ calculation.
Regards,
Steve |
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