Pressure drop calculation: equivalent length

[Natje82]

Hello

Does anyone have an extended list of equivalent lengths?

I have a list (Shell Dep 31.38.01.11) which contains the usual equivalent lenghts (90° - 45° - tank inlet / exit - ball valves - check valves - gate valves ...) but for example, I also need the Leq for

* Vortex breakers
* Temporary strainer

Or does anyone know how to determine pressure drop for these items?

 

[21121956]

Hello everybody:

Natje82: visit the thread407-220184, there I hope you will find some help to your inquiry.

 

[stanier]

Suggest you use a modern approach to fluid mechanics than using equivalent lengths.

You can download Epanet for free and solve for head losses using the Colebrook White formula to determine Darcy friction factor. Use Crane Flow of Fluids, Miller or Idelchik to work out the losses of fittings.

Download AFts Fathom demo from

http://www.aft.com.

These losses are included in the demo program. Once you use the software you will invest in the full package.

There are plenty of other programs out there such as Fluid Flow 3 that enable you to model system losses.

Whenever I hear the words "equivalent length" I immediately get the feeling that the engineer does not know what he is doing and is looking for a short cut.

 

[KenA]

Must disagree with Stanier
When I hear the words "just run it through a computer programme" I immediately get the feeling that the engineer does not know what he is doing and is looking for a short cut.

AFT's Fathom programme is excellent. And so are a number of other fluid flow / pressure drop software applications.

Many of these programmes will still use the principle of equivalent length within the software, it's just that the user doesn't see what's going on within the programme. You simply select pipe diameter and pick the bends, fittings etc.

There is absolutely nothing wrong with using equivalent lengths for calculating pressure drops and I applaud an engineer who is capable of doing this type of caculation as it shows that they understand the principles behind the calculation rather than simply plugging numbers into a PC and believing the result.

Going back to Natje82's question. For items such as strainers and vortex breakers it's probably best to go to specific vendors and get charts of pressure drop versus flow or equivalent lengths. There is probably too much variety between designs for there to be a standard value.

 

[Latexman]

A lot of data is in terms of "velocity head" losses. These are usually symbolized using the letter K. To get equvalent length just use the equation:

K = fL/D to get L_e = KD/f

K = velocity head loss, dimensionless
f = Darcy/Weisbach friction factor, dimensionless
L = length, units of length
D = diameter, units of length

Good luck,
Latexman

 

[Artisi]

For the vortex breaker add a few feet of pipe to your cals., for the strainer - no guess work - ask the supplier as it depends on the area blockage etc.