5 replies to this topic

[garych]

Hi,

I am confused with the term entrance loss coefficient (K value for the pipe inlet). I read that the K value differs with the pipe inlet geometry.  

 

1. What is actually the reasons that we need to take in account the "K" value for the pipe inlet?

     Is it because of the contraction of the bigger area (e.g vessel)  into a small area (e.g pipeline) and eddy           turbulence of the flow that may occur due to the transition?

 

2. In the case of the pump suction, consider that the inlet pipe which is dipped into an open air basin or we called an undefined space, do we need to consider the K value for the inlet pipe as well? Or the K value only applies to a vessel or tank?

 

Hope to hear from you all.

Thank you.

[breizh]

http://www.fao.org/d...44e09.htm#3.7.1

 

To support your work

 

Hope this helps

 

Breizh

[Mahdi1980]

Garych

 

Answer to your questions

 

1- Exactly you are right. We should consider K for changing the cross section of the pipes. for instance when a big area is reduced to a pipe or a pipe has different sizes along a distance from a source to a consumer.

 

2- For a pump, in order to calculate the friction loss throughout the suction and estimation of NPSHa, you should know the K value for the entrance of the pipe as well as other parts up to suction of the pump.

The K value for basin is meaningless because what is important might be pressure at the bottom of basin or pipe entrance.

 

Hope it is helpful

 

Mahdi

Edited by Mahdi1980, 16 April 2016 - 06:23 AM.

[katmar]

Regarding Question 2 - If you have access to the Crane TP410 Flow of Fluids manual see Pipe Entrances on page A-29.  I suggest you use the "Inward Projecting" option with a K value of 0.78 for your dip pipe.  The fact that the pipe is vertical and not horizontal will not affect the K value.

[garych]

Hi Katmar,

Yea, i did read through the Crane...mayi know why would u suggest using the "Inward Projecting (K=0.78)? Is it because it is the most severe one?

If the end of the pipe is the bell mouth type, in Ludwig it's K=0.05 but this type does not seems to be in the Crane book.

I wonder if this is a common practice?

[breizh]

Hi ,

another great resource I posted a couple of weeks ago . 

Let you review the part on page 24 .

 

The link above ( 7-3) should have answered your question .

 

Why are you so concerned ? This should not be minor in your design with little consequence on your hydraulic calculations .

 

Note : Don't duplicate the posts , it's really troublesome .

 

Good luck.

 

Breizh 

Edited by breizh, 24 April 2016 - 02:38 AM.