Pressure drop calculation: equivalent length
Pressure drop calculation: equivalent length
(OP)
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?
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?





RE: Pressure drop calculation: equivalent length
Natje82: visit the thread407-220184: Pumping against a sand filter, there I hope you will find some help to your inquiry.
RE: Pressure drop calculation: equivalent length
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 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.
RE: Pressure drop calculation: equivalent length
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.
RE: Pressure drop calculation: equivalent length
K = fL/D to get Le = 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
RE: Pressure drop calculation: equivalent length