CFX For Heating Coils

zephyrus17 · April 19, 2011, 22:03

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

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

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

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?

April 19, 2011, 22:03	CFX For Heating Coils	#1
zephyrus17 New Member Join Date: Sep 2010 Posts: 28 Rep Power: 0	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.

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April 21, 2011, 07:40		#3
zephyrus17 New Member Join Date: Sep 2010 Posts: 28 Rep Power: 0	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.

May 15, 2011, 13:50		#6
gullapallivijay New Member Vijaya Sekhar Gullapalli Join Date: May 2011 Location: Sweden Posts: 6 Rep Power: 14	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?