Head loss at Entrance

[jacobsdl]

I'm currently working on a wastewater construction project. In our design we have asked for a flared inlet, from 48" to 42", for the suction line connection to the wet well. The contractor has submitted a concentric reducer to replace the flared inlet. Is there a significant head loss when comparing the two different inlets?

I have found that the K(flare) = .04 best case
I have found that the K(conc.) = .5 worst case if the entrance was a straight edge and not at an angle.

Do you think these values are accurate or can anyone come up with a better K(conc) value?

 

[doctorsundar]

You had better use a flared inlet if you are concerned about pressure loss.

For air ducts, conical intake has 0.25VP entry loss, plain pipe has 1.0VP entry loss. VP = velocity pressure. Sorry I don't have data on water pipes.

Sundar Narayan

 

[BobPE]

jacobsdl:

there is signicicant difference. In my opinion the concentric reducer is not even comparable in your application with the limited information you provided. The contractor seems to be tyrying to save money in the short term which will sacrifice efficiency and cost to the owner in the long run. Also, if the entrance was figured into the NPSHa calcs, the headloss may be too great for the concentric reducer.

I run into this alot due to the cost of these fittings. I have yet to allow a substitute that didnt have the entrance characteristics of the original design in suction applications.

Stick to your guns on this one, it's what the contractor bid on, and from the way it sounds, he just doesnt understand what it is for.


BobPE

 

[rbcoulter]

What is the angle of the reduction in the flared case?
There are formulas in the Crane Handbook for calculating K values but the angle is needed.