resistance coefficient - T fitting 1

[kagadpencil]

in a duct system of ours, we had a T fitting to allow for gas flow in perpendicular direction to the main flow direction. Then we decided not to allow that flow and hence we blanked the opening off using a wooden plank. But since it is not 100% air-tight, there is some resistance coeff. associated with this section. Can someone please point me to the correct source to look up to calculate the resistance coefficient for this section. I was looking in ASHRAE 1992, but could not find anything relevant.

 

[kagadpencil]

actually, there is no air leakage, but the geometry is causing turbulence in the chimney stack following the T joint. Thus this turbulence is giving rise to additional flow resistance and hence pressure drop -- can some one point me in the right direction to look up some stuff to come up with a flow resistance value for whatever that is going on (turbulence) in that T joint.

 

[TD2K]

Many hydraulic handbooks have resistance coefficients.

I believe from your explanation that the flow you now have cotinues straight through the tee and the sideways branch is the one blanked off. The resistance for a tee in that flow configuration has an equivalent pipe length (L/D) of 20. If the flow has to make a 90 degree turn and flow out the branch, the L/D increases to about 60.

 

[kagadpencil]

TD2K (Chemical):

I think your tip is helpful.

I was looking into "Hand book of Hydraulic Resistance" by Idelchik. I have not found any mention of such case there. May be I am not looking carefullly.

Can you please tell me the book source where I can get the info that you provided? I will like to quote that source in my report.

Thank you very much.

 

[kagadpencil]

Also,
When calculating the pressure drop, I understand that I need to take L/D as 20, but what value of f should I use ? --- Is that the same as used for the pipe ? -- The one that was calculated from Moody chart ?

 

[sshep]

A reference of L/D=20 for a straight run can be found in Crane Technical Paper No. 410. This is based on testing of pipe in turbulent flow and may be good for you.

I recommend you consider posting this same question in the Mechanical/HVAC forum. As you are probably dealing with fractional inches of water pressure drop where velocity head is a significant component, there could be additional considerations for your system beyond the general chemical engineering experience with piping systems. Just a thought, SShep

 

[friartuck]

Unless the flow or velocity is high, you should be able to ignore the pressure drop. The "K" for a poor bend is around 1.2, for a radius bend is around 0.7 and for a good quality air turn mitre bend would be 0.35, so a minor obstruction would be under 0.30.

Friar Tuck