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zephyrus17 April 19, 2011 22:03

CFX For Heating Coils
 
What would be the best turbulence modelling/setup to analysis airflow through convection coils? Physical testing shows a drop of around 40Pa with actual coils, but the CFX analysis only shows a 1Pa drop with K-e at 5% turbulence.

seaharrier April 21, 2011 07:32

Quote:

Originally Posted by zephyrus17 (Post 304315)
What would be the best turbulence modelling/setup to analysis airflow through convection coils? Physical testing shows a drop of around 40Pa with actual coils, but the CFX analysis only shows a 1Pa drop with K-e at 5% turbulence.


Maybe you can consider the real wall roughness,

zephyrus17 April 21, 2011 07:40

I've thought about that, but it shouldn't affect it that much. All the 'walls' are smooth as they're made from sheet metal, or by extrusion.

There are fins 0.2mm thick, 2mm apart. There are only 2 rows of coils that the air has to pass through and they're arranged in a staggard manner.

My input is mass flow rate and outlet is an opening, though this should be fine.

seaharrier April 21, 2011 23:19

Quote:

Originally Posted by zephyrus17 (Post 304556)
I've thought about that, but it shouldn't affect it that much. All the 'walls' are smooth as they're made from sheet metal, or by extrusion.

There are fins 0.2mm thick, 2mm apart. There are only 2 rows of coils that the air has to pass through and they're arranged in a staggard manner.

My input is mass flow rate and outlet is an opening, though this should be fine.

The pressure loss should mainly come from the stirring of fins,
but how much does the turbulence influence the pressure loss?
maybe a little.

The inlet Re number can be estimated.
changing over to other boundary conditions of Inlet or Outlet perhaps does some effect, but the effect is unlikely so great level.

zephyrus17 April 21, 2011 23:56

Quote:

Originally Posted by seaharrier (Post 304656)
The pressure loss should mainly come from the stirring of fins

Speaking of fins, on the real thing, the fins are slightly wavy. Instead of "-------", they are "/\/\/\/\/\". Highly, highly exaggerated, of course but there's a slight kink. Could that have caused any major eddies of turbulence to impede airflow?

gullapallivijay May 15, 2011 13:50

Using RNG k-e and standard k-e an error of 40% is found in pressure drop compared to experimental results for liquid flow in plate heat exchangers. SST k-w models resulted aound 18% in a study. Up to 20% difference in pressure drop is observed using various near wall resolutions. What reference pressure is used while using air?


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