5 replies to this topic

[Mech.Engineer]

HI EVERYBODY.

I WOULD LIKE TO KNOW WHAT SECTION OF THE PIPING NET I SHOULD TAKE FOR CALCULATING FRICTION LOSS DUE TO FLOW OF PROPANE(100%).
Should i take the complete section?(SEE ATTACHED PNG),I mean, if i`m gonna calculate NPSHa in one of the pumps, should i take the "complete" section or the "L" section..?.

Can i use the same equations than those used for water..?. any reference example?.

In advance...Many thanks...!.

Attached Files

•  T OR L.png   133.63KB   52 downloads

Edited by Mech.Engineer, 24 May 2010 - 04:57 PM.

[zdendacejka]

Hi,
you have to do complete energetical evaluation of piping (look over attached image).

• Compute velocities (or volume flows) in parts 1, 2, 3, 4 and symmetrical branch (2*, 3*, 4*) - equation of continuity for incompressible flow will be useful (v1*A1 = v2*A2). Remember that flow divides into two equal parts at part 5.
• Compute friction losses in parts 1, 2, 3, 4 - , , . L is length, D is diameter, v is velocity and lambda is cofficient of friction losses (some empirical equations for laminar or turbulent flow are mentioned). Efl is specific loss - you have to multiply it by for example mass flow to get concrete energy loss.
• Then evaluate friction loss for each pump - simply sum up one half of friction loss in part 1, with parts 2, 3, 4 (or symmetrical).

Remarks:

• In addition to friction losses there are local losses in parts 5, 6, 7, 8 - loss in elbow, piping extension / reduction...

Hope this helps...

[Mech.Engineer]

Thanks for your answer.

anyone else can help me...?. I would like to have another example, maybe an on line example...I would like to have several points of views...

In advance...many thanks for helping me.

[zdendacejka]

Several links:

• D'Arcy - Weisbach equation, head loss, pressure loss with calculator
• General problems of loss in pipings

[breizh]

HI ,
Let you try PSIM , you should be able to download it for free on Internet. PSIM : pump system improvement modeling tool
it should support your query.
Breizh

[mcgill.engineer]

Everything you need is here:
http://www.lmnoeng.c...rcyWeisbach.htm

You basically need to use Darcy Weisbach equation to get the friction losses in the pipe. H=f(L/D)(V2/2g). To get the value for the friction coefficient (f), you will have to use the Moody chart (just google it). To use the chart, you will need to calculate your Reynolds number. The other variable in the equation are V, L, and D. V=velocity=flow/crosssectional area. So you will need to split your line into sections (each of which has a constant flow and area) and calculate the velocity in each section. L will be the length of each. Finally, you will calculate H for each section and this will give you the major losses in your pipe.

You will then need to account for the minor losses for each elbow,joint,valve, etc. The equation is h=K(V2/2g) where the value of K depends on the fittings you have. You will need to sum-up all the minor losses of all the fittings. You can find the K values for fittings in the same link at the beginning of my post.

Edited by mcgill.engineer, 01 June 2010 - 07:48 AM.